Regulation of Glucose Homeostasis by GLP-1

PubMed Central

Nadkarni, Prashant; Chepurny, Oleg G.; Holz, George G.

2014-01-01

Glucagon-like peptide-1(7–36)amide (GLP-1) is a secreted peptide that acts as a key determinant of blood glucose homeostasis by virtue of its abilities to slow gastric emptying, to enhance pancreatic insulin secretion, and to suppress pancreatic glucagon secretion. GLP-1 is secreted from L cells of the gastrointestinal mucosa in response to a meal, and the blood glucose-lowering action of GLP-1 is terminated due to its enzymatic degradation by dipeptidyl-peptidase-IV (DPP-IV). Released GLP-1 activates enteric and autonomic reflexes while also circulating as an incretin hormone to control endocrine pancreas function. The GLP-1 receptor (GLP-1R) is a G protein-coupled receptor that is activated directly or indirectly by blood glucose-lowering agents currently in use for the treatment of type 2 diabetes mellitus (T2DM). These therapeutic agents include GLP-1R agonists (exenatide, liraglutide, lixisenatide, albiglutide, dulaglutide, and langlenatide) and DPP-IV inhibitors (sitagliptin, vildagliptin, saxagliptin, linagliptin, and alogliptin). Investigational agents for use in the treatment of T2DM include GPR119 and GPR40 receptor agonists that stimulate the release of GLP-1 from L cells. Summarized here is the role of GLP-1 to control blood glucose homeo-stasis, with special emphasis on the advantages and limitations of GLP-1-based therapeutics. PMID:24373234

Glucose Tolerance, Lipids, and GLP-1 Secretion in JCR:LA-cp Rats Fed a High Protein Fiber Diet

PubMed Central

Reimer, Raylene A.; Russell, James C.

2013-01-01

Background We have shown that individually, dietary fiber and protein increase secretion of the anorexigenic and insulinotropic hormone, glucagon-like peptide-1 (GLP-1). Objective Our objective was to combine, in one diet, high levels of fiber and protein to maximize GLP-1 secretion, improve glucose tolerance, and reduce weight gain. Methods and Procedures Lean (+/?) and obese (cp/cp) male James C Russell corpulent (JCR:LA-cp) rats lacking a functional leptin receptor were fed one of four experimental diets (control, high protein (HP), high fiber (HF, prebiotic fiber inulin), or combination (CB)) for 3 weeks. An oral glucose tolerance test (OGTT) was performed to evaluate plasma GLP-1, insulin and glucose. Plasma lipids and intestinal proglucagon mRNA expression were determined. Results Energy intake was lower with the HF diet in lean and obese rats. Weight gain did not differ between diets. Higher colonic proglucagon mRNA in lean rats fed a CB diet was associated with higher GLP-1 secretion during OGTT. The HP diet significantly reduced plasma glucose area under the curve (AUC) during OGTT in obese rats, which reflected both an increased GLP-1 AUC and higher fasting insulin. Diets containing inulin resulted in the lowest plasma triglyceride and total cholesterol levels. Discussion Overall, combining HP with HF in the diet increased GLP-1 secretion in response to oral glucose, but did not improve glucose tolerance or lipid profiles more than the HF diet alone did. We also suggest that glycemic and insulinemic response to prebiotics differ among rat models and future research work should examine their role in improving glucose tolerance in diet-induced vs. genetic obesity with overt hyperleptinemia. PMID:18223610

The glucagon-like peptide-2 receptor C terminus modulates beta-arrestin-2 association but is dispensable for ligand-induced desensitization, endocytosis, and G-protein-dependent effector activation.

PubMed

Estall, Jennifer L; Koehler, Jacqueline A; Yusta, Bernardo; Drucker, Daniel J

2005-06-10

Classic models of receptor desensitization and internalization have been largely based on the behavior of Family A G-protein-coupled receptors (GPCRs). The glucagon-like peptide-2 receptor (GLP-2R) is a member of the Family B glucagon-secretin GPCR family, which exhibit significant sequence and structural differences from the Family A receptors in their intracellular and extracellular domains. To identify structural motifs that regulate GLP-2R signaling and cell surface receptor expression, we analyzed the functional properties of a series of mutant GLP-2Rs. The majority of the C-terminal receptor tail was dispensable for GLP-2-induced cAMP accumulation, ERK1/2 activation, and endocytosis in transfected cells. However, progressive truncation of the C terminus reduced cell surface receptor expression, altered agonist-induced GLP-2R trafficking, and abrogated protein kinase A-mediated heterologous receptor desensitization. Elimination of the distal 21 amino acids of the receptor was sufficient to promote constitutive receptor internalization and prevent agonist-induced recruitment of beta-arrestin-2. Site-directed mutagenesis identified specific amino acid residues within the distal GLP-2R C terminus that mediate the stable association with beta-arrestin-2. Surprisingly, although the truncated mutant receptors failed to interact with beta-arrestin-2, they underwent homologous desensitization and subsequent resensitization with kinetics similar to that observed with the wild-type GLP-2R. Our data suggest that, although the GLP-2R C terminus is not required for coupling to cellular machinery regulating signaling or desensitization, it may serve as a sorting signal for intracellular trafficking. Taken together with the previously demonstrated clathrin and dynamin-independent, lipid-raft-dependent pathways for internalization, our data suggest that GLP-2 receptor signaling has evolved unique structural and functional mechanisms for control of receptor trafficking

GLP-1 nanomedicine alleviates gut inflammation

PubMed Central

Anbazhagan, Arivarasu N.; Thaqi, Mentor; Priyamvada, Shubha; Jayawardena, Dulari; Kumar, Anoop; Gujral, Tarunmeet; Chatterjee, Ishita; Mugarza, Edurne; Saksena, Seema; Onyuksel, Hayat; Dudeja, Pradeep K.

2017-01-01

The gut hormone, glucagon like peptide-1 (GLP-1) exerts anti-inflammatory effects. However, its clinical use is limited by its short half-life. Previously, we have shown that GLP-1 as a nanomedicine (GLP-1 in sterically stabilized phospholipid micelles, GLP-1-SSM) has increased in vivo stability. The current study was aimed at testing the efficacy of this GLP-1 nanomedicine in alleviating colonic inflammation and associated diarrhea in dextran sodium sulfate (DSS) induced mouse colitis model. Our results show that GLP-1-SSM treatment markedly alleviated the colitis phenotype by reducing the expression of pro-inflammatory cytokine IL-1β, increasing goblet cells and preserving intestinal epithelial architecture in colitis model. Further, GLP-1-SSM alleviated diarrhea (as assessed by luminal fluid) by increasing protein expression of intestinal chloride transporter DRA (down regulated in adenoma). Our results indicate thatGLP-1 nanomedicine may act as a novel therapeutic tool in alleviating gut inflammation and associated diarrhea in inflammatory bowel disease (IBD). PMID:27553076

Glucagon Like Peptide-1 (GLP-1) Modulates OVA-Induced Airway Inflammation and Mucus Secretion Involving a Protein Kinase A (PKA)-Dependent Nuclear Factor-κB (NF-κB) Signaling Pathway in Mice.

PubMed

Zhu, Tao; Wu, Xiao-Ling; Zhang, Wei; Xiao, Min

2015-08-26

Asthma is a common chronic pulmonary inflammatory disease, featured with mucus hyper-secretion in the airway. Recent studies found that glucagon like peptide-1 (GLP-1) analogs, including liraglutide and exenatide, possessed a potent anti-inflammatory property through a protein kinase A (PKA)-dependent signaling pathway. Therefore, the aim of current study was to investigate the value of GLP-1 analog therapy liraglutide in airway inflammation and mucus secretion in a murine model of ovalbumin (OVA)-induced asthma, and its underlying molecular mechanism. In our study, BALB/c mice were sensitized and challenged by OVA to induce chronic asthma. Pathological alterations, the number of cells and the content of inflammatory mediators in bronchoalveolar lavage fluid (BALF), and mucus secretion were observed and measured. In addition, the mRNA and protein expression of E-selectin and MUC5AC were analyzed by qPCR and Western blotting. Then, the phosphorylation of PKA and nuclear factor-κB (NF-κB) p65 were also measured by Western blotting. Further, NF-κB p65 DNA binding activity was detected by ELISA. OVA-induced airway inflammation, airway mucus hyper-secretion, the up-regulation of E-selectin and MUC5AC were remarkably inhibited by GLP-1 in mice (all p < 0.01). Then, we also found that OVA-reduced phosphorylation of PKA, and OVA-enhanced NF-κB p65 activation and NF-κB p65 DNA binding activity were markedly improved by GLP-1 (all p < 0.01). Furthermore, our data also figured out that these effects of GLP-1 were largely abrogated by the PKA inhibitor H-89 (all p < 0.01). Taken together, our results suggest that OVA-induced asthma were potently ameliorated by GLP-1 possibly through a PKA-dependent inactivation of NF-κB in mice, indicating that GLP-1 analogs may be considered an effective and safe drug for the potential treatment of asthma in the future.

A Novel GLP1 Receptor Interacting Protein ATP6ap2 Regulates Insulin Secretion in Pancreatic Beta Cells*

PubMed Central

Dai, Feihan F.; Bhattacharjee, Alpana; Liu, Ying; Batchuluun, Battsetseg; Zhang, Ming; Wang, Xinye Serena; Huang, Xinyi; Luu, Lemieux; Zhu, Dan; Gaisano, Herbert; Wheeler, Michael B.

2015-01-01

GLP1 activates its receptor, GLP1R, to enhance insulin secretion. The activation and transduction of GLP1R requires complex interactions with a host of accessory proteins, most of which remain largely unknown. In this study, we used membrane-based split ubiquitin yeast two-hybrid assays to identify novel GLP1R interactors in both mouse and human islets. Among these, ATP6ap2 (ATPase H+-transporting lysosomal accessory protein 2) was identified in both mouse and human islet screens. ATP6ap2 was shown to be abundant in islets including both alpha and beta cells. When GLP1R and ATP6ap2 were co-expressed in beta cells, GLP1R was shown to directly interact with ATP6ap2, as assessed by co-immunoprecipitation. In INS-1 cells, overexpression of ATP6ap2 did not affect insulin secretion; however, siRNA knockdown decreased both glucose-stimulated and GLP1-induced insulin secretion. Decreases in GLP1-induced insulin secretion were accompanied by attenuated GLP1 stimulated cAMP accumulation. Because ATP6ap2 is a subunit required for V-ATPase assembly of insulin granules, it has been reported to be involved in granule acidification. In accordance with this, we observed impaired insulin granule acidification upon ATP6ap2 knockdown but paradoxically increased proinsulin secretion. Importantly, as a GLP1R interactor, ATP6ap2 was required for GLP1-induced Ca2+ influx, in part explaining decreased insulin secretion in ATP6ap2 knockdown cells. Taken together, our findings identify a group of proteins that interact with the GLP1R. We further show that one interactor, ATP6ap2, plays a novel dual role in beta cells, modulating both GLP1R signaling and insulin processing to affect insulin secretion. PMID:26272612

Carboxy-terminal truncation activates glp-1 protein to specify vulval fates in Caenorhabditis elegans.

PubMed

Mango, S E; Maine, E M; Kimble, J

1991-08-29

The glp-1 and lin-12 genes encode homologous transmembrane proteins that may act as receptors for cell interactions during development. The glp-1 product is required for induction of germ-line proliferation and for embryogenesis. By contrast, lin-12 mediates somatic cell interactions, including those between the precursor cells that form the vulval hypodermis (VPCs). Here we analyse an unusual allele of glp-1, glp-1(q35), which displays a semidominant multivulva phenotype (Muv), as well as the typical recessive, loss-of-function Glp phenotypes (sterility and embryonic lethality). We find that the effects of glp-1(q35) on VPC development mimic those of dominant lin-12 mutations, even in the absence of lin-12 activity. The glp-1(q35) gene bears a nonsense mutation predicted to eliminate the 122 C-terminal amino acids, including a ProGluSerThr (PEST) sequence thought to destabilize proteins. We suggest that the carboxy terminus bears a negative regulatory domain which normally inactivates glp-1 in the VPCs. We propose that inappropriate glp-1(q35) activity can substitute for lin-12 to determine vulval fate, perhaps by driving the VPCs to proliferate.

Targeting GLP-1 receptor trafficking to improve agonist efficacy.

PubMed

Jones, Ben; Buenaventura, Teresa; Kanda, Nisha; Chabosseau, Pauline; Owen, Bryn M; Scott, Rebecca; Goldin, Robert; Angkathunyakul, Napat; Corrêa, Ivan R; Bosco, Domenico; Johnson, Paul R; Piemonti, Lorenzo; Marchetti, Piero; Shapiro, A M James; Cochran, Blake J; Hanyaloglu, Aylin C; Inoue, Asuka; Tan, Tricia; Rutter, Guy A; Tomas, Alejandra; Bloom, Stephen R

2018-04-23

Glucagon-like peptide-1 receptor (GLP-1R) activation promotes insulin secretion from pancreatic beta cells, causes weight loss, and is an important pharmacological target in type 2 diabetes (T2D). Like other G protein-coupled receptors, the GLP-1R undergoes agonist-mediated endocytosis, but the functional and therapeutic consequences of modulating GLP-1R endocytic trafficking have not been clearly defined. Here, we investigate a series of biased GLP-1R agonists with variable propensities for GLP-1R internalization and recycling. Compared to a panel of FDA-approved GLP-1 mimetics, compounds that retain GLP-1R at the plasma membrane produce greater long-term insulin release, which is dependent on a reduction in β-arrestin recruitment and faster agonist dissociation rates. Such molecules elicit glycemic benefits in mice without concomitant increases in signs of nausea, a common side effect of GLP-1 therapies. Our study identifies a set of agents with specific GLP-1R trafficking profiles and the potential for greater efficacy and tolerability as T2D treatments.

Evolutionary hierarchy of vertebrate-like heterotrimeric G protein families.

PubMed

Krishnan, Arunkumar; Mustafa, Arshi; Almén, Markus Sällman; Fredriksson, Robert; Williams, Michael J; Schiöth, Helgi B

2015-10-01

Heterotrimeric G proteins perform a crucial role as molecular switches controlling various cellular responses mediated by G protein-coupled receptor (GPCR) signaling pathway. Recent data have shown that the vertebrate-like G protein families are found across metazoans and their closest unicellular relatives. However, an overall evolutionary hierarchy of vertebrate-like G proteins, including gene family annotations and in particular mapping individual gene gain/loss events across diverse holozoan lineages is still incomplete. Here, with more expanded invertebrate taxon sampling, we have reconstructed phylogenetic trees for each of the G protein classes/families and provide a robust classification and hierarchy of vertebrate-like heterotrimeric G proteins. Our results further extend the evidence that the common ancestor (CA) of holozoans had at least five ancestral Gα genes corresponding to all major vertebrate Gα classes and contain a total of eight genes including two Gβ and one Gγ. Our results also indicate that the GNAI/O-like gene likely duplicated in the last CA of metazoans to give rise to GNAI- and GNAO-like genes, which are conserved across invertebrates. Moreover, homologs of GNB1-4 paralogon- and GNB5 family-like genes are found in most metazoans and that the unicellular holozoans encode two ancestral Gβ genes. Similarly, most bilaterian invertebrates encode two Gγ genes which include a representative of the GNG gene cluster and a putative homolog of GNG13. Interestingly, our results also revealed key evolutionary events such as the Drosophila melanogaster eye specific Gβ subunit that is found conserved in most arthropods and several previously unidentified species specific expansions within Gαi/o, Gαs, Gαq, Gα12/13 classes and the GNB1-4 paralogon. Also, we provide an overall proposed evolutionary scenario on the expansions of all G protein families in vertebrate tetraploidizations. Our robust classification/hierarchy is essential to further

A high carbohydrate, but not fat or protein meal attenuates postprandial ghrelin, PYY and GLP-1 responses in Chinese men

PubMed Central

Parvaresh Rizi, Ehsan; Loh, Tze Ping; Baig, Sonia; Chhay, Vanna; Huang, Shiqi; Caleb Quek, Jonathan; Tai, E. Shyong; Toh, Sue-Anne

2018-01-01

It is known that the macronutrient content of a meal has different impacts on the postprandial satiety and appetite hormonal responses. Whether obesity interacts with such nutrient-dependent responses is not well characterized. We examined the postprandial appetite and satiety hormonal responses after a high-protein (HP), high-carbohydrate (HC), or high-fat (HF) mixed meal. This was a randomized cross-over study of 9 lean insulin-sensitive (mean±SEM HOMA-IR 0.83±0.10) and 9 obese insulin-resistant (HOMA-IR 4.34±0.41) young (age 21–40 years), normoglycaemic Chinese men. We measured fasting and postprandial plasma concentration of glucose, insulin, active glucagon-like peptide-1 (GLP-1), total peptide-YY (PYY), and acyl-ghrelin in response to HP, HF, or HC meals. Overall postprandial plasma insulin response was more robust in the lean compared to obese subjects. The postprandial GLP-1 response after HF or HP meal was higher than HC meal in both lean and obese subjects. In obese subjects, HF meal induced higher response in postprandial PYY compared to HC meal. HP and HF meals also suppressed ghrelin greater compared to HC meal in the obese than lean subjects. In conclusion, a high-protein or high-fat meal induces a more favorable postprandial satiety and appetite hormonal response than a high-carbohydrate meal in obese insulin-resistant subjects. PMID:29385178

Mechanisms of Action of GLP-1 in the Pancreas

PubMed Central

Doyle, Máire E.; Egan, Josephine M.

2007-01-01

Glucagon-like peptide-1 is a hormone that is encoded in the proglucagon gene. It is mainly produced in enteroendocrine L cells of the gut and is secreted into the blood stream when food containing fat, protein hydrolysate and/or glucose enters the duodenum. Its particular effects on insulin and glucagon secretion have generated a flurry of research activity over the past twenty years culminating in a naturally occurring GLP-1 receptor agonist, exendin-4, now being used to treat type 2 diabetes. GLP-1 engages a specific G-protein coupled receptor that is present in tissues other than the pancreas (brain, kidney, lung, heart, major blood vessels). The most widely studied cell activated by GLP-1 is the insulin-secreting beta cell where its defining action is augmentation of glucose-induced insulin secretion. Upon GLP-1 receptor activation, adenylyl cyclase is activated and cAMP generated, leading, in turn, to cAMP-dependent activation of second messenger pathways, such as the PKA and Epac pathways. As well as short-term effects of enhancing glucose-induced insulin secretion, continuous GLP-1 receptor activation also increases insulin synthesis, and beta cell proliferation and neogenesis. Although these latter effects cannot be currently monitored in humans, there are substantial improvements in glucose tolerance and increases in both first phase and plateau phase insulin secretory responses in type 2 diabetic patients treated with exendin-4. This review we will focus on the effects resulting from GLP-1 receptor activation in islets of Langerhans PMID:17306374

Differential structural properties of GLP-1 and exendin-4 determine their relative affinity for the GLP-1 receptor N-terminal extracellular domain.

PubMed

Runge, Steffen; Schimmer, Susann; Oschmann, Jan; Schiødt, Christine Bruun; Knudsen, Sanne Möller; Jeppesen, Claus Bekker; Madsen, Kjeld; Lau, Jesper; Thøgersen, Henning; Rudolph, Rainer

2007-05-15

Glucagon-like peptide-1 (GLP-1) and exendin-4 (Ex4) are homologous peptides with established potential for treatment of type 2 diabetes. They bind and activate the pancreatic GLP-1 receptor (GLP-1R) with similar affinity and potency and thereby promote insulin secretion in a glucose-dependent manner. GLP-1R belongs to family B of the seven transmembrane G-protein coupled receptors. The N-terminal extracellular domain (nGLP-1R) is a ligand binding domain with differential affinity for Ex4 and GLP-1: low affinity for GLP-1 and high affinity for exendin-4. The superior affinity of nGLP-1R for Ex4 was previously explained by an additional interaction between nGLP-1R and the C-terminal Trp-cage of Ex4. In this study we have combined biophysical and pharmacological approaches thus relating structural properties of the ligands in solution to their relative binding affinity for nGLP-1R. We used both a tracer competition assay and ligand-induced thermal stabilization of nGLP-1R to measure the relative affinity of full length, truncated, and chimeric ligands for soluble refolded nGLP-1R. The ligands in solution and the conformational consequences of ligand binding to nGLP-1R were characterized by circular dichroism and fluorescence spectroscopy. We found a correlation between the helical content of the free ligands and their relative binding affinity for nGLP-1R, supporting the hypothesis that the ligands are helical at least in the segment that binds to nGLP-1R. The Trp-cage of Ex4 was not necessary to maintain a superior helicity of Ex4 compared to GLP-1. The results suggest that the differential affinity of nGLP-1R is explained almost entirely by divergent residues in the central part of the ligands: Leu10-Gly30 of Ex4 and Val16-Arg36 of GLP-1. In view of our results it appears that the Trp-cage plays only a minor role for the interaction between Ex4 and nGLP-1R and for the differential affinity of nGLP-1R for GLP-1 and Ex4.

A Targeted RNAi Screen Identifies Endocytic Trafficking Factors That Control GLP-1 Receptor Signaling in Pancreatic β-Cells.

PubMed

Buenaventura, Teresa; Kanda, Nisha; Douzenis, Phoebe C; Jones, Ben; Bloom, Stephen R; Chabosseau, Pauline; Corrêa, Ivan R; Bosco, Domenico; Piemonti, Lorenzo; Marchetti, Piero; Johnson, Paul R; Shapiro, A M James; Rutter, Guy A; Tomas, Alejandra

2018-03-01

The glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) is a key target for type 2 diabetes (T2D) treatment. Because endocytic trafficking of agonist-bound receptors is one of the most important routes for regulation of receptor signaling, a better understanding of this process may facilitate the development of new T2D therapeutic strategies. Here, we screened 29 proteins with known functions in G protein-coupled receptor trafficking for their role in GLP-1R potentiation of insulin secretion in pancreatic β-cells. We identify five (clathrin, dynamin1, AP2, sorting nexins [SNX] SNX27, and SNX1) that increase and four (huntingtin-interacting protein 1 [HIP1], HIP14, GASP-1, and Nedd4) that decrease insulin secretion from murine insulinoma MIN6B1 cells in response to the GLP-1 analog exendin-4. The roles of HIP1 and the endosomal SNX1 and SNX27 were further characterized in mouse and human β-cell lines and human islets. While HIP1 was required for the coupling of cell surface GLP-1R activation with clathrin-dependent endocytosis, the SNXs were found to control the balance between GLP-1R plasma membrane recycling and lysosomal degradation and, in doing so, determine the overall β-cell incretin responses. We thus identify key modulators of GLP-1R trafficking and signaling that might provide novel targets to enhance insulin secretion in T2D. © 2017 by the American Diabetes Association.

Ghrelin suppresses cholecystokinin (CCK), peptide YY (PYY) and glucagon-like peptide-1 (GLP-1) in the intestine, and attenuates the anorectic effects of CCK, PYY and GLP-1 in goldfish (Carassius auratus).

PubMed

Blanco, Ayelén Melisa; Bertucci, Juan Ignacio; Valenciano, Ana Isabel; Delgado, María Jesús; Unniappan, Suraj

2017-07-01

Ghrelin is an important gut-derived hormone with an appetite stimulatory role, while most of the intestinal hormones, including cholecystokinin (CCK), peptide YY (PYY) and glucagon-like peptide-1 (GLP-1), are appetite-inhibitors. Whether these important peptides with opposing roles on food intake interact to regulate energy balance in fish is currently unknown. The aim of this study was to characterize the putative crosstalk between ghrelin and CCK, PYY and GLP-1 in goldfish (Carassius auratus). We first determined the localization of CCK, PYY and GLP-1 in relation to ghrelin and its main receptor GHS-R1a (growth hormone secretagogue 1a) in the goldfish intestine by immunohistochemistry. Colocalization of ghrelin/GHS-R1a and CCK/PYY/GLP-1 was found primarily in the luminal border of the intestinal mucosa. In an intestinal explant culture, a significant decrease in prepro-cck, prepro-pyy and proglucagon transcript levels was observed after 60min of incubation with ghrelin, which was abolished by preincubation with the GHS-R1a ghrelin receptor antagonist [D-Lys3]-GHRP-6 (except for proglucagon). The protein expression of PYY and GLP-1 was also downregulated by ghrelin. Finally, intraperitoneal co-administration of CCK, PYY or GLP-1 with ghrelin results in no modification of food intake in goldfish. Overall, results of the present study show for the first time in fish that ghrelin exerts repressive effects on enteric anorexigens. It is likely that these interactions mediate the stimulatory effects of ghrelin on feeding and metabolism in fish. Copyright © 2017 Elsevier Inc. All rights reserved.

The glpD gene is a novel reporter gene for E. coli that is superior to established reporter genes like lacZ and gusA.

PubMed

Wegener, Marius; Vogtmann, Kristina; Huber, Madeleine; Laass, Sebastian; Soppa, Jörg

2016-12-01

Reporter genes facilitate the characterization of promoter activities, transcript stabilities, translational efficiencies, or intracellular localization. Various reporter genes for Escherichia coli have been established, however, most of them have drawbacks like transcript instability or the inability to be used in genetic selections. Therefore, the glpD gene encoding glycerol-3-phosphate dehydrogenase was introduced as a novel reporter gene for E. coli. The enzymatic assay was optimized, and it was verified that growth on glycerol strictly depends on the presence of GlpD. The 5'-UTRs of three E. coli genes were chosen and cloned upstream of the new reporter gene glpD as well as the established reporter genes lacZ and gusA. Protein and transcript levels were quantified and translational efficiencies were calculated. The lacZ transcript was very unstable and its level highly depended on its translation, compromising its use as a reporter. The results obtained with gusA and glpD were similar, however, only glpD can be used for genetic selections. Therefore, glpD was found to be a superior novel reporter gene compared to the established reporter genes lacZ and gusA. Copyright © 2016 Elsevier B.V. All rights reserved.

A role of PLC/PKC-dependent pathway in GLP-1-stimulated insulin secretion.

PubMed

Shigeto, Makoto; Cha, Chae Young; Rorsman, Patrik; Kaku, Kohei

2017-04-01

Glucagon-like peptide-1 (GLP-1) is an endogenous glucose-lowering hormone and GLP-1 receptor agonists are currently being used as antidiabetic drugs clinically. The canonical signalling pathway (including cAMP, Epac2, protein kinase A (PKA) and K ATP channels) is almost universally accepted as the main mechanism of GLP-1-stimulated insulin secretion. This belief is based on in vitro studies that used nanomolar (1-100 nM) concentrations of GLP-1. Recently, it was found that the physiological concentrations (1-10 pM) of GLP-1 also stimulate insulin secretion from isolated islets, induce membrane depolarization and increase of intracellular [Ca 2+ ] in isolated β cells/pancreatic islets. These responses were unaffected by PKA inhibitors and occurred without detectable increases in intracellular cAMP and PKA activity. These PKA-independent actions of GLP-1 depend on protein kinase C (PKC), involve activation of the standard GLP-1 receptor (GLP1R) and culminate in activation of phospholipase C (PLC), leading to an elevation of diacylglycerol (DAG), increased L-type Ca 2+ and TRPM4/TRPM5 channel activities. Here, we review these recent data and contrast them against the effects of nanomolar concentrations of GLP-1. The differential intracellular signalling activated by low and high concentrations of GLP-1 could provide a clue to explain how GLP-1 exerts different function in the central nervous system and peripheral organs.

Genetically encoded photocross-linkers determine the biological binding site of exendin-4 peptide in the N-terminal domain of the intact human glucagon-like peptide-1 receptor (GLP-1R)

PubMed Central

Koole, Cassandra; Reynolds, Christopher A.; Mobarec, Juan C.; Hick, Caroline; Sexton, Patrick M.; Sakmar, Thomas P.

2017-01-01

The glucagon-like peptide-1 receptor (GLP-1R) is a key therapeutic target in the management of type II diabetes mellitus, with actions including regulation of insulin biosynthesis and secretion, promotion of satiety, and preservation of β-cell mass. Like most class B G protein-coupled receptors (GPCRs), there is limited knowledge linking biological activity of the GLP-1R with the molecular structure of an intact, full-length, and functional receptor·ligand complex. In this study, we have utilized genetic code expansion to site-specifically incorporate the photoactive amino acid p-azido-l-phenylalanine (azF) into N-terminal residues of a full-length functional human GLP-1R in mammalian cells. UV-mediated photolysis of azF was then carried out to induce targeted photocross-linking to determine the proximity of the azido group in the mutant receptor with the peptide exendin-4. Cross-linking data were compared directly with the crystal structure of the isolated N-terminal extracellular domain of the GLP-1R in complex with exendin(9–39), revealing both similarities as well as distinct differences in the mode of interaction. Generation of a molecular model to accommodate the photocross-linking constraints highlights the potential influence of environmental conditions on the conformation of the receptor·peptide complex, including folding dynamics of the peptide and formation of dimeric and higher order oligomeric receptor multimers. These data demonstrate that crystal structures of isolated receptor regions may not give a complete reflection of peptide/receptor interactions and should be combined with additional experimental constraints to reveal peptide/receptor interactions occurring in the dynamic, native, and full-length receptor state. PMID:28283573

Induction of miR-132 and miR-212 Expression by Glucagon-Like Peptide 1 (GLP-1) in Rodent and Human Pancreatic β-Cells

PubMed Central

Li, Jing; Keller, Mark P.; Hohmeier, Hans E.; Wang, Yong; Feng, Yue; Zhou, Heather H.; Shen, Xiaolan; Rabaglia, Mary; Soni, Mufaddal; Attie, Alan D.; Newgard, Christopher B.; Thornberry, Nancy A.; Howard, Andrew D.; Zhou, Yun-Ping

2015-01-01

Better understanding how glucagon-like peptide 1 (GLP-1) promotes pancreatic β-cell function and/or mass may uncover new treatment for type 2 diabetes. In this study, we investigated the potential involvement of microRNAs (miRNAs) in the effect of GLP-1 on glucose-stimulated insulin secretion. miRNA levels in INS-1 cells and isolated rodent and human islets treated with GLP-1 in vitro and in vivo (with osmotic pumps) were measured by real-time quantitative PCR. The role of miRNAs on insulin secretion was studied by transfecting INS-1 cells with either precursors or antisense inhibitors of miRNAs. Among the 250 miRNAs surveyed, miR-132 and miR-212 were significantly up-regulated by GLP-1 by greater than 2-fold in INS-1 832/3 cells, which were subsequently reproduced in freshly isolated rat, mouse, and human islets, as well as the islets from GLP-1 infusion in vivo in mice. The inductions of miR-132 and miR-212 by GLP-1 were correlated with cAMP production and were blocked by the protein kinase A inhibitor H-89 but not affected by the exchange protein activated by cAMP activator 8-pCPT-2′-O-Me-cAMP-AM. GLP-1 failed to increase miR-132 or miR-212 expression levels in the 832/13 line of INS-1 cells, which lacks robust cAMP and insulin responses to GLP-1 treatment. Overexpression of miR-132 or miR-212 significantly enhanced glucose-stimulated insulin secretion in both 832/3 and 832/13 cells, and restored insulin responses to GLP-1 in INS-1 832/13 cells. GLP-1 increases the expression of miRNAs 132 and 212 via a cAMP/protein kinase A-dependent pathway in pancreatic β-cells. Overexpression of miR-132 or miR-212 enhances glucose and GLP-1-stimulated insulin secretion. PMID:26218441

Induction of miR-132 and miR-212 Expression by Glucagon-Like Peptide 1 (GLP-1) in Rodent and Human Pancreatic β-Cells.

PubMed

Shang, Jin; Li, Jing; Keller, Mark P; Hohmeier, Hans E; Wang, Yong; Feng, Yue; Zhou, Heather H; Shen, Xiaolan; Rabaglia, Mary; Soni, Mufaddal; Attie, Alan D; Newgard, Christopher B; Thornberry, Nancy A; Howard, Andrew D; Zhou, Yun-Ping

2015-09-01

Better understanding how glucagon-like peptide 1 (GLP-1) promotes pancreatic β-cell function and/or mass may uncover new treatment for type 2 diabetes. In this study, we investigated the potential involvement of microRNAs (miRNAs) in the effect of GLP-1 on glucose-stimulated insulin secretion. miRNA levels in INS-1 cells and isolated rodent and human islets treated with GLP-1 in vitro and in vivo (with osmotic pumps) were measured by real-time quantitative PCR. The role of miRNAs on insulin secretion was studied by transfecting INS-1 cells with either precursors or antisense inhibitors of miRNAs. Among the 250 miRNAs surveyed, miR-132 and miR-212 were significantly up-regulated by GLP-1 by greater than 2-fold in INS-1 832/3 cells, which were subsequently reproduced in freshly isolated rat, mouse, and human islets, as well as the islets from GLP-1 infusion in vivo in mice. The inductions of miR-132 and miR-212 by GLP-1 were correlated with cAMP production and were blocked by the protein kinase A inhibitor H-89 but not affected by the exchange protein activated by cAMP activator 8-pCPT-2'-O-Me-cAMP-AM. GLP-1 failed to increase miR-132 or miR-212 expression levels in the 832/13 line of INS-1 cells, which lacks robust cAMP and insulin responses to GLP-1 treatment. Overexpression of miR-132 or miR-212 significantly enhanced glucose-stimulated insulin secretion in both 832/3 and 832/13 cells, and restored insulin responses to GLP-1 in INS-1 832/13 cells. GLP-1 increases the expression of miRNAs 132 and 212 via a cAMP/protein kinase A-dependent pathway in pancreatic β-cells. Overexpression of miR-132 or miR-212 enhances glucose and GLP-1-stimulated insulin secretion.

Crystal structure of the ligand-bound glucagon-like peptide-1 receptor extracellular domain.

PubMed

Runge, Steffen; Thøgersen, Henning; Madsen, Kjeld; Lau, Jesper; Rudolph, Rainer

2008-04-25

The glucagon-like peptide-1 receptor (GLP-1R) belongs to Family B1 of the seven-transmembrane G protein-coupled receptors, and its natural agonist ligand is the peptide hormone glucagon-like peptide-1 (GLP-1). GLP-1 is involved in glucose homeostasis, and activation of GLP-1R in the plasma membrane of pancreatic beta-cells potentiates glucose-dependent insulin secretion. The N-terminal extracellular domain (nGLP-1R) is an important ligand binding domain that binds GLP-1 and the homologous peptide Exendin-4 with differential affinity. Exendin-4 has a C-terminal extension of nine amino acid residues known as the "Trp cage", which is absent in GLP-1. The Trp cage was believed to interact with nGLP-1R and thereby explain the superior affinity of Exendin-4. However, the molecular details that govern ligand binding and specificity of nGLP-1R remain undefined. Here we report the crystal structure of human nGLP-1R in complex with the antagonist Exendin-4(9-39) solved by the multiwavelength anomalous dispersion method to 2.2A resolution. The structure reveals that Exendin-4(9-39) is an amphipathic alpha-helix forming both hydrophobic and hydrophilic interactions with nGLP-1R. The Trp cage of Exendin-4 is not involved in binding to nGLP-1R. The hydrophobic binding site of nGLP-1R is defined by discontinuous segments including primarily a well defined alpha-helix in the N terminus of nGLP-1R and a loop between two antiparallel beta-strands. The structure provides for the first time detailed molecular insight into ligand binding of the human GLP-1 receptor, an established target for treatment of type 2 diabetes.

Glucagon-Like Peptide-1 Receptor Ligand Interactions: Structural Cross Talk between Ligands and the Extracellular Domain

PubMed Central

West, Graham M.; Willard, Francis S.; Sloop, Kyle W.; Showalter, Aaron D.; Pascal, Bruce D.; Griffin, Patrick R.

2014-01-01

Activation of the glucagon-like peptide-1 receptor (GLP-1R) in pancreatic β-cells potentiates insulin production and is a current therapeutic target for the treatment of type 2 diabetes mellitus (T2DM). Like other class B G protein-coupled receptors (GPCRs), the GLP-1R contains an N-terminal extracellular ligand binding domain. N-terminal truncations on the peptide agonist generate antagonists capable of binding to the extracellular domain, but not capable of activating full length receptor. The main objective of this study was to use Hydrogen/deuterium exchange (HDX) to identify how the amide hydrogen bonding network of peptide ligands and the extracellular domain of GLP-1R (nGLP-1R) were altered by binding interactions and to then use this platform to validate direct binding events for putative GLP-1R small molecule ligands. The HDX studies presented here for two glucagon-like peptide-1 receptor (GLP-1R) peptide ligands indicates that the antagonist exendin-4[9-39] is significantly destabilized in the presence of nonionic detergents as compared to the agonist exendin-4. Furthermore, HDX can detect stabilization of exendin-4 and exendin-4[9-39] hydrogen bonding networks at the N-terminal helix [Val19 to Lys27] upon binding to the N-terminal extracellular domain of GLP-1R (nGLP-1R). In addition we show hydrogen bonding network stabilization on nGLP-1R in response to ligand binding, and validate direct binding events with the extracellular domain of the receptor for putative GLP-1R small molecule ligands. PMID:25180755

CORRELATION BETWEEN PRE AND POSTOPERATIVE LEVELS OF GLP-1/GLP-2 AND WEIGHT LOSS AFTER ROUX-EN-Y GASTRIC BYPASS: A PROSPECTIVE STUDY.

PubMed

Cazzo, Everton; Gestic, Martinho Antonio; Utrini, Murillo Pimentel; Pareja, José Carlos; Chaim, Elinton Adami; Geloneze, Bruno; Barreto, Maria Rita Lazzarini; Magro, Daniéla Oliveira

2016-01-01

The role of gut hormones in glucose homeostasis and weight loss achievement and maintenance after bariatric surgery appears to be a key point in the understanding of the beneficial effects observed following these procedures. To determine whether there is a correlation between the pre and postoperative levels of both GLP-1 and GLP-2 and the excess weight loss after Roux-en-Y gastric bypass (RYGB). An exploratory prospective study which enrolled 11 individuals who underwent RYGB and were followed-up for 12 months. GLP-1 and GLP-2 after standard meal tolerance test (MTT) were determined before and after surgery and then correlated with the percentage of excess loss (%EWL). GLP-2 AUC presented a significant postoperative increase (945.3±449.1 vs.1787.9±602.7; p=0.0037); GLP-1 AUC presented a non-significant trend towards increase after RYGB (709.6±320.4 vs. 1026.5±714.3; p=0.3808). Mean %EWL was 66.7±12.2%. There was not any significant correlation between both the pre and postoperative GLP-1 AUCs and GLP-2 AUCs and the %EWL achieved after one year. There was no significant correlation between the pre and postoperative levels of the areas under the GLP-1 and GLP-2 curves with the percentage of weight loss reached after one year. O papel de hormônios gastrointestinais sobre a homeostase glicêmica e a obtenção e manutenção da perda de peso após a cirurgia bariátrica parece ser elemento fundamental na compreensão dos benefícios observados após estes procedimentos. Determinar se há correlação entre os níveis pré e pós-operatórios de GLP-1 e GLP-2 com a perda do excesso de peso após o bypass gástrico em Y-de-Roux. Estudo prospectivo exploratório que envolveu 11 indivíduos submetidos ao bypass gástrico, acompanhados por 12 meses. Os níveis GLP-1 e GLP-2 após um teste de refeição padrão foram determinados antes e 12 meses após a operação e então foram correlacionados com o percentual de perda do excesso de peso. Houve aumento

Molecular evolution of GPCRs: GLP1/GLP1 receptors.

PubMed

Hwang, Jong-Ik; Yun, Seongsik; Moon, Mi Jin; Park, Cho Rong; Seong, Jae Young

2014-06-01

Glucagon-like peptide 1 (GLP1) is an intestinal incretin that regulates glucose homeostasis through stimulation of insulin secretion from pancreatic β-cells and inhibits appetite by acting on the brain. Thus, it is a promising therapeutic agent for the treatment of type 2 diabetes mellitus and obesity. Studies using synteny and reconstructed ancestral chromosomes suggest that families for GLP1 and its receptor (GLP1R) have emerged through two rounds (2R) of whole genome duplication and local gene duplications before and after 2R. Exon duplications have also contributed to the expansion of the peptide family members. Specific changes in the amino acid sequence following exon/gene/genome duplications have established distinct yet related peptide and receptor families. These specific changes also confer selective interactions between GLP1 and GLP1R. In this review, we present a possible macro (genome level)- and micro (gene/exon level)-evolution mechanisms of GLP1 and GLP1R, which allows them to acquire selective interactions between this ligand-receptor pair. This information may provide critical insight for the development of potent therapeutic agents targeting GLP1R. © 2014 Society for Endocrinology.

Astrocytes Regulate GLP-1 Receptor-Mediated Effects on Energy Balance

PubMed Central

Reiner, David J.; Mietlicki-Baase, Elizabeth G.; McGrath, Lauren E.; Zimmer, Derek J.; Bence, Kendra K.; Sousa, Gregory L.; Konanur, Vaibhav R.; Krawczyk, Joanna; Burk, David H.; Kanoski, Scott E.; Hermann, Gerlinda E.; Rogers, Richard C.

2016-01-01

Astrocytes are well established modulators of extracellular glutamate, but their direct influence on energy balance-relevant behaviors is largely understudied. As the anorectic effects of glucagon-like peptide-1 receptor (GLP-1R) agonists are partly mediated by central modulation of glutamatergic signaling, we tested the hypothesis that astrocytic GLP-1R signaling regulates energy balance in rats. Central or peripheral administration of a fluorophore-labeled GLP-1R agonist, exendin-4, localizes within astrocytes and neurons in the nucleus tractus solitarius (NTS), a hindbrain nucleus critical for energy balance control. This effect is mediated by GLP-1R, as the uptake of systemically administered fluorophore-tagged exendin-4 was blocked by central pretreatment with the competitive GLP-1R antagonist exendin-(9–39). Ex vivo analyses show prolonged exendin-4-induced activation (live cell calcium signaling) of NTS astrocytes and neurons; these effects are also attenuated by exendin-(9–39), indicating mediation by the GLP-1R. In vitro analyses show that the application of GLP-1R agonists increases cAMP levels in astrocytes. Immunohistochemical analyses reveal that endogenous GLP-1 axons form close synaptic apposition with NTS astrocytes. Finally, pharmacological inhibition of NTS astrocytes attenuates the anorectic and body weight-suppressive effects of intra-NTS GLP-1R activation. Collectively, data demonstrate a role for NTS astrocytic GLP-1R signaling in energy balance control. SIGNIFICANCE STATEMENT Glucagon-like peptide-1 receptor (GLP-1R) agonists reduce food intake and are approved by the Food and Drug Administration for the treatment of obesity, but the cellular mechanisms underlying the anorectic effects of GLP-1 require further investigation. Astrocytes represent a major cellular population in the CNS that regulates neurotransmission, yet the role of astrocytes in mediating energy balance is largely unstudied. The current data provide novel evidence that

The truncated metabolite GLP-2 (3-33) interacts with the GLP-2 receptor as a partial agonist.

PubMed

Thulesen, Jesper; Knudsen, Lotte Bjerre; Hartmann, Bolette; Hastrup, Sven; Kissow, Hannelouise; Jeppesen, Palle Bekker; Ørskov, Cathrine; Holst, Jens Juul; Poulsen, Steen Seier

2002-01-15

The therapeutic potential of the intestinotrophic mediator glucagon-like peptide-2 (1-33) [GLP-2 (1-33)] has increased interest in the pharmacokinetics of the peptide. This study was undertaken to investigate whether the primary degradation product GLP-2 (3-33) interacts with the GLP-2 receptor. Functional (cAMP) and binding in vitro studies were carried out in cells expressing the transfected human GLP-2 receptor. Furthermore, a biologic response of GLP-2 (3-33) was tested in vivo. Mice were allocated to groups treated for 10 days (twice daily) with: (1) 5 microg GLP-2 (1-33), (2) 25 microg GLP-2 (3-33), (3) 5 microg GLP-2 (1-33)+100 microg GLP-2 (3-33), or (4) 5 microg GLP-2 (1-33)+500 microg GLP-2 (3-33). The intestine was investigated for growth changes. GLP-2 (3-33) bound to the GLP-2 receptor with a binding affinity of 7.5% of that of GLP-2 (1-33). cAMP accumulation was stimulated with an efficacy of 15% and a potency more than two orders of magnitude lower than that of GLP-2 (1-33). Increasing doses of GLP-2 (3-33) (10(-7)-10(-5) M) caused a shift to the right in the dose-response curve of GLP-2 (1-33). Treatment of mice with either GLP-2 (1-33) or (3-33) induced significant growth responses in both the small and large intestines, but the response induced by GLP-2 (3-33) was much smaller. Co-administration of 500 microg of GLP-2 (3-33) and 5 microg GLP-2 (1-33) resulted in a growth response that was smaller than that of 5 microg GLP-2 (1-33) alone. Consistent with the observed in vivo activities, our functional studies and binding data indicate that GLP-2 (3-33) acts as a partial agonist with potential competitive antagonistic properties on the GLP-2 receptor.

Use of CRISPR/Cas9-engineered INS-1 pancreatic β cells to define the pharmacology of dual GIPR/GLP-1R agonists.

PubMed

Naylor, Jacqueline; Suckow, Arthur T; Seth, Asha; Baker, David J; Sermadiras, Isabelle; Ravn, Peter; Howes, Rob; Li, Jianliang; Snaith, Mike R; Coghlan, Matthew P; Hornigold, David C

2016-09-15

Dual-agonist molecules combining glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) activity represent an exciting therapeutic strategy for diabetes treatment. Although challenging due to shared downstream signalling pathways, determining the relative activity of dual agonists at each receptor is essential when developing potential novel therapeutics. The challenge is exacerbated in physiologically relevant cell systems expressing both receptors. To this end, either GIP receptors (GIPR) or GLP-1 receptors (GLP-1R) were ablated via RNA-guided clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 endonucleases in the INS-1 pancreatic β-cell line. Multiple clonal cell lines harbouring gene disruptions for each receptor were isolated and assayed for receptor activity to identify functional knockouts (KOs). cAMP production in response to GIPR or GLP-1R activation was abolished and GIP- or GLP-1-induced potentiation of glucose-stimulated insulin secretion (GSIS) was attenuated in the cognate KO cell lines. The contributions of individual receptors derived from cAMP and GSIS assays were confirmed in vivo using GLP-1R KO mice in combination with a monoclonal antibody antagonist of GIPR. We have successfully applied CRISPR/Cas9-engineered cell lines to determining selectivity and relative potency contributions of dual-agonist molecules targeting receptors with overlapping native expression profiles and downstream signalling pathways. Specifically, we have characterised molecules as biased towards GIPR or GLP-1R, or with relatively balanced potency in a physiologically relevant β-cell system. This demonstrates the broad utility of CRISPR/Cas9 when applied to native expression systems for the development of drugs that target multiple receptors, particularly where the balance of receptor activity is critical. © 2016 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

Crystal structure of glucagon-like peptide-1 in complex with the extracellular domain of the glucagon-like peptide-1 receptor.

PubMed

Underwood, Christina Rye; Garibay, Patrick; Knudsen, Lotte Bjerre; Hastrup, Sven; Peters, Günther H; Rudolph, Rainer; Reedtz-Runge, Steffen

2010-01-01

GLP-1 (glucagon-like peptide-1) is an incretin released from intestinal L-cells in response to food intake. Activation of the GLP-1 receptor potentiates the synthesis and release of insulin from pancreatic beta-cells in a glucose-dependent manner. The GLP-1 receptor belongs to class B of the G-protein-coupled receptors, a subfamily characterized by a large N-terminal extracellular ligand binding domain. Exendin-4 and GLP-1 are 50% identical, and exendin-4 is a full agonist with similar affinity and potency for the GLP-1 receptor. We recently solved the crystal structure of the GLP-1 receptor extracellular domain in complex with the competitive antagonist exendin-4(9-39). Interestingly, the isolated extracellular domain binds exendin-4 with much higher affinity than the endogenous agonist GLP-1. Here, we have solved the crystal structure of the extracellular domain in complex with GLP-1 to 2.1 Aresolution. The structure shows that important hydrophobic ligand-receptor interactions are conserved in agonist- and antagonist-bound forms of the extracellular domain, but certain residues in the ligand-binding site adopt a GLP-1-specific conformation. GLP-1 is a kinked but continuous alpha-helix from Thr(13) to Val(33) when bound to the extracellular domain. We supplemented the crystal structure with site-directed mutagenesis to link the structural information of the isolated extracellular domain with the binding properties of the full-length receptor. The data support the existence of differences in the binding modes of GLP-1 and exendin-4 on the full-length GLP-1 receptor.

Novel role of GLP-1 receptor signaling in energy expenditure during chronic high fat diet feeding in rats.

PubMed

Krieger, Jean-Philippe; Langhans, Wolfgang; Lee, Shin J

2018-04-11

Glucagon-like peptide-1 (GLP-1) secreted from intestinal L-cells plays a major role in meal termination and glucose-dependent insulin secretion. Several lines of evidence indicate, however, that the acute satiating and incretin effects of GLP-1 are attenuated with high fat diet (HFD) exposure. Here we tested the hypothesis that endogenous GLP-1 differentially affects energy balance and glucose homeostasis dependent on whether rats are fed chow or HFD (60% energy from fat). We blocked GLP-1 receptor (GLP-1R) signaling by daily intraperitoneal (IP) injection of the GLP-1R antagonist exendin (9-39) (Ex9, 10 μg/kg) or vehicle for 5 weeks in male Sprague-Dawley rats fed either chow or HFD, recorded body weight (BW) and food intake throughout, and assessed energy expenditure (3rd week) and glucose tolerance (4th week). Five week daily Ex9 injections reduced BW gain in HFD-fed rats, but did not affect BW in chow-fed rats. On the other hand, chronic Ex9 treatment did not affect daily food intake in either chow or HFD-fed rats during the entire study. The reduced BW gain in HFD-fed rats was associated with an increase in energy expenditure. Interestingly, chronic Ex9 treatment induced glucose intolerance in chow-fed rats, but not in HFD-fed rats, suggesting a differential role of GLP-1R signaling in glucose metabolism during chow and HFD feeding. Our findings reveal a novel role of GLP-1R signaling, modulating energy expenditure rather than eating behavior during HFD feeding. Furthermore, these results suggest a previously unrecognized contribution of GLP-1R signaling to the pathophysiology of obesity. Copyright © 2018 Elsevier Inc. All rights reserved.

IL-6-Type Cytokine Signaling in Adipocytes Induces Intestinal GLP-1 Secretion.

PubMed

Wueest, Stephan; Laesser, Céline I; Böni-Schnetzler, Marianne; Item, Flurin; Lucchini, Fabrizio C; Borsigova, Marcela; Müller, Werner; Donath, Marc Y; Konrad, Daniel

2018-01-01

We recently showed that interleukin (IL)-6-type cytokine signaling in adipocytes induces free fatty acid release from visceral adipocytes, thereby promoting obesity-induced hepatic insulin resistance and steatosis. In addition, IL-6-type cytokines may increase the release of leptin from adipocytes and by those means induce glucagon-like peptide 1 (GLP-1) secretion. We thus hypothesized that IL-6-type cytokine signaling in adipocytes may regulate insulin secretion. To this end, mice with adipocyte-specific knockout of gp130, the signal transducer protein of IL-6, were fed a high-fat diet for 12 weeks. Compared with control littermates, knockout mice showed impaired glucose tolerance and circulating leptin, GLP-1, and insulin levels were reduced. In line, leptin release from isolated adipocytes was reduced, and intestinal proprotein convertase subtilisin/kexin type 1 ( Pcsk1 ) expression, the gene encoding PC1/3, which controls GLP-1 production, was decreased in knockout mice. Importantly, treatment with the GLP-1 receptor antagonist exendin 9-39 abolished the observed difference in glucose tolerance between control and knockout mice. Ex vivo, supernatant collected from isolated adipocytes of gp130 knockout mice blunted Pcsk1 expression and GLP-1 release from GLUTag cells. In contrast, glucose- and GLP-1-stimulated insulin secretion was not affected in islets of knockout mice. In conclusion, adipocyte-specific IL-6 signaling induces intestinal GLP-1 release to enhance insulin secretion, thereby counteracting insulin resistance in obesity. © 2017 by the American Diabetes Association.

Duodenal GLP-1 signaling regulates hepatic glucose production through a PKC-δ-dependent neurocircuitry

PubMed Central

Yang, Mengliu; Wang, Jinzhi; Wu, Shaobo; Yuan, Lei; Zhao, Xiaodong; Liu, Chaohong; Xie, Jing; Jia, Yanjun; Lai, Yerui; Zhao, Allan Zijian; Boden, Guenther; Li, Ling; Yang, Gangyi

2017-01-01

Intestinal glucagon-like peptide-1 (GLP-1) is a hormone that stimulates insulin secretion and acts as a neuropeptide to control glucose homeostasis, but little is known whether intestinal GLP-1 has any effect in the control of hepatic glucose production (HGP). Here we found that intraduodenal infusion of GLP-1 activated duodenal PKC-δ, lowered HGP and was accompanied by a decrease in hepatic expression of gluconeogenic enzymes and an increase in hepatic insulin signaling in rats. However, gut co-infusion of either the GLP-1 receptor antagonist Ex-9, or the PKC-δ inhibitor rottlerin with GLP-1, negated the ability of gut GLP-1 to lower HGP and to increase hepatic insulin signaling during clamps. The metabolic and molecular signal effects of duodenal GLP-1 were also negated by co-infusion with tetracaine, pharmacologic inhibition of N-methyl-d-aspartate receptors within the dorsalvagal complex, or hepatic vagotomy in rats. In summary, we identified a neural glucoregulatory function of gut GLP-1 signaling. PMID:28182013

Influence of hydrophobic mismatch on the catalytic activity of Escherichia coli GlpG rhomboid protease

PubMed Central

Foo, Alexander C Y; Harvey, Brandon G R; Metz, Jeff J; Goto, Natalie K

2015-01-01

Rhomboids comprise a broad family of intramembrane serine proteases that are found in a wide range of organisms and participate in a diverse array of biological processes. High-resolution structures of the catalytic transmembrane domain of the Escherichia coli GlpG rhomboid have provided numerous insights that help explain how hydrolytic cleavage can be achieved below the membrane surface. Key to this are observations that GlpG hydrophobic domain dimensions may not be sufficient to completely span the native lipid bilayer. This formed the basis for a model where hydrophobic mismatch Induces thinning of the local membrane environment to promote access to transmembrane substrates. However, hydrophobic mismatch also has the potential to alter the functional properties of the rhomboid, a possibility we explore in the current work. For this purpose, we purified the catalytic transmembrane domain of GlpG into phosphocholine or maltoside detergent micelles of varying alkyl chain lengths, and assessed proteolytic function with a model water-soluble substrate. Catalytic turnover numbers were found to depend on detergent alkyl chain length, with saturated chains containing 10–12 carbon atoms supporting maximal activity. Similar results were obtained in phospholipid bicelles, with no proteolytic activity being detected in longer-chain lipids. Although differences in thermal stability and GlpG oligomerization could not explain these activity differences, circular dichroism spectra suggest that mismatch gives rise to a small change in structure. Overall, these results demonstrate that hydrophobic mismatch can exert an inhibitory effect on rhomboid activity, with the potential for changes in local membrane environment to regulate activity in vivo. PMID:25307614

GLP-1 is both anxiogenic and antidepressant; divergent effects of acute and chronic GLP-1 on emotionality.

PubMed

Anderberg, Rozita H; Richard, Jennifer E; Hansson, Caroline; Nissbrandt, Hans; Bergquist, Filip; Skibicka, Karolina P

2016-03-01

Glucagon-like peptide 1 (GLP-1), produced in the intestine and hindbrain, is known for its glucoregulatory and appetite suppressing effects. GLP-1 agonists are in clinical use for treatment of type 2 diabetes and obesity. GLP-1, however, may also affect brain areas associated with emotionality regulation. Here we aimed to characterize acute and chronic impact of GLP-1 on anxiety and depression-like behavior. Rats were subjected to anxiety and depression behavior tests following acute or chronic intracerebroventricular or intra-dorsal raphe (DR) application of GLP-1 receptor agonists. Serotonin or serotonin-related genes were also measured in the amygdala, DR and the hippocampus. We demonstrate that both GLP-1 and its long lasting analog, Exendin-4, induce anxiety-like behavior in three rodent tests of this behavior: black and white box, elevated plus maze and open field test when acutely administered intraperitoneally, into the lateral ventricle, or directly into the DR. Acute central GLP-1 receptor stimulation also altered serotonin signaling in the amygdala. In contrast, chronic central administration of Exendin-4 did not alter anxiety-like behavior but significantly reduced depression-like behavior in the forced swim test. Importantly, this positive effect of Exendin-4 was not due to significant body weight loss and reduced food intake, since rats pair-fed to Exendin-4 rats did not show altered mood. Collectively we show a striking impact of central GLP-1 on emotionality and the amygdala serotonin signaling that is divergent under acute versus chronic GLP-1 activation conditions. We also find a novel role for the DR GLP-1 receptors in regulation of behavior. These results may have direct relevance to the clinic, and indicate that Exendin-4 may be especially useful for obese patients manifesting with comorbid depression. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

Glucagon-Like Peptide-1 and Its Class B G Protein–Coupled Receptors: A Long March to Therapeutic Successes

PubMed Central

de Graaf, Chris; Donnelly, Dan; Wootten, Denise; Lau, Jesper; Sexton, Patrick M.; Miller, Laurence J.; Ahn, Jung-Mo; Liao, Jiayu; Fletcher, Madeleine M.; Brown, Alastair J. H.; Zhou, Caihong; Deng, Jiejie; Wang, Ming-Wei

2016-01-01

The glucagon-like peptide (GLP)-1 receptor (GLP-1R) is a class B G protein–coupled receptor (GPCR) that mediates the action of GLP-1, a peptide hormone secreted from three major tissues in humans, enteroendocrine L cells in the distal intestine, α cells in the pancreas, and the central nervous system, which exerts important actions useful in the management of type 2 diabetes mellitus and obesity, including glucose homeostasis and regulation of gastric motility and food intake. Peptidic analogs of GLP-1 have been successfully developed with enhanced bioavailability and pharmacological activity. Physiologic and biochemical studies with truncated, chimeric, and mutated peptides and GLP-1R variants, together with ligand-bound crystal structures of the extracellular domain and the first three-dimensional structures of the 7-helical transmembrane domain of class B GPCRs, have provided the basis for a two-domain–binding mechanism of GLP-1 with its cognate receptor. Although efforts in discovering therapeutically viable nonpeptidic GLP-1R agonists have been hampered, small-molecule modulators offer complementary chemical tools to peptide analogs to investigate ligand-directed biased cellular signaling of GLP-1R. The integrated pharmacological and structural information of different GLP-1 analogs and homologous receptors give new insights into the molecular determinants of GLP-1R ligand selectivity and functional activity, thereby providing novel opportunities in the design and development of more efficacious agents to treat metabolic disorders. PMID:27630114

Crystal Structure of Glucagon-like Peptide-1 in Complex with the Extracellular Domain of the Glucagon-like Peptide-1 Receptor*

PubMed Central

Underwood, Christina Rye; Garibay, Patrick; Knudsen, Lotte Bjerre; Hastrup, Sven; Peters, Günther H.; Rudolph, Rainer; Reedtz-Runge, Steffen

2010-01-01

GLP-1 (glucagon-like peptide-1) is an incretin released from intestinal L-cells in response to food intake. Activation of the GLP-1 receptor potentiates the synthesis and release of insulin from pancreatic β-cells in a glucose-dependent manner. The GLP-1 receptor belongs to class B of the G-protein-coupled receptors, a subfamily characterized by a large N-terminal extracellular ligand binding domain. Exendin-4 and GLP-1 are 50% identical, and exendin-4 is a full agonist with similar affinity and potency for the GLP-1 receptor. We recently solved the crystal structure of the GLP-1 receptor extracellular domain in complex with the competitive antagonist exendin-4(9–39). Interestingly, the isolated extracellular domain binds exendin-4 with much higher affinity than the endogenous agonist GLP-1. Here, we have solved the crystal structure of the extracellular domain in complex with GLP-1 to 2.1 Åresolution. The structure shows that important hydrophobic ligand-receptor interactions are conserved in agonist- and antagonist-bound forms of the extracellular domain, but certain residues in the ligand-binding site adopt a GLP-1-specific conformation. GLP-1 is a kinked but continuous α-helix from Thr13 to Val33 when bound to the extracellular domain. We supplemented the crystal structure with site-directed mutagenesis to link the structural information of the isolated extracellular domain with the binding properties of the full-length receptor. The data support the existence of differences in the binding modes of GLP-1 and exendin-4 on the full-length GLP-1 receptor. PMID:19861722

Effects of Substitution, and Adding of Carbohydrate and Fat to Whey-Protein on Energy Intake, Appetite, Gastric Emptying, Glucose, Insulin, Ghrelin, CCK and GLP-1 in Healthy Older Men—A Randomized Controlled Trial

PubMed Central

Lange, Kylie; Hatzinikolas, Seva; Hausken, Trygve; Jones, Karen L.; Horowitz, Michael; Chapman, Ian; Soenen, Stijn

2018-01-01

Protein-rich supplements are used widely for the management of malnutrition in the elderly. We reported previously that the suppression of energy intake by whey protein is less in older than younger adults. The aim was to determine the effects of substitution, and adding of carbohydrate and fat to whey protein, on ad libitum energy intake from a buffet meal (180–210 min), gastric emptying (3D-ultrasonography), plasma gut hormone concentrations (0–180 min) and appetite (visual analogue scales), in healthy older men. In a randomized, double-blind order, 13 older men (75 ± 2 years) ingested drinks (~450 mL) containing: (i) 70 g whey protein (280 kcal; ‘P280’); (ii) 14 g protein, 28 g carbohydrate, 12.4 g fat (280 kcal; ‘M280’); (iii) 70 g protein, 28 g carbohydrate, 12.4 g fat (504 kcal; ‘M504’); or (iv) control (~2 kcal). The caloric drinks, compared to a control, did not suppress appetite or energy intake; there was an increase in total energy intake (drink + meal, p < 0.05), which was increased most by the M504-drink. P280- and M504-drink ingestion were associated with slower a gastric-emptying time (n = 9), lower ghrelin, and higher cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) than M280 (p < 0.05). Glucose and insulin were increased most by the mixed-macronutrient drinks (p < 0.05). In conclusion, energy intake was not suppressed, compared to a control, and particularly whey protein, affected gastric emptying and gut hormone responses. PMID:29360778

Brain GLP-1 and insulin sensitivity

USDA-ARS?s Scientific Manuscript database

Type 2 diabetes is often treated with a class of drugs referred to as glucagon-like peptide-1 (GLP-1) analogs. GLP-1 is a peptide secreted by the gut that acts through only one known receptor, the GLP-1 receptor. The primary function of GLP-1 is thought to be lowering of postprandial glucose levels....

Endogenous GLP-1 in lateral septum contributes to stress-induced hypophagia.

PubMed

Terrill, Sarah J; Maske, Calyn B; Williams, Diana L

2018-03-03

Glucagon-like peptide 1 (GLP-1) neurons of the caudal brainstem project to many brain areas, including the lateral septum (LS), which has a known role in stress responses. Previously, we showed that endogenous GLP-1 in the LS plays a physiologic role in the control of feeding under non-stressed conditions, however, central GLP-1 is also involved in behavioral and endocrine responses to stress. Here, we asked whether LS GLP-1 receptors (GLP-1R) contribute to stress-induced hypophagia. Male rats were implanted with bilateral cannulas targeting the dorsal subregion of the LS (dLS). In a within-subjects design, shortly before the onset of the dark phase, rats received dLS injections of saline or the GLP-1R antagonist Exendin (9-39) (Ex9) prior to 30 min restraint stress. Food intake was measured continuously for the next 20 h. The stress-induced hypophagia observed within the first 30 min of dark was not influenced by Ex9 pretreatment, but Ex9 tended to blunt the effect of stress as early as 1 and 2 h into the dark phase. By 4-6 h, there were significant stress X drug interactions, and Ex9 pretreatment blocked the stress-induced suppression of feeding. These effects were mediated entirely through changes in average meal size; stress suppressed meal size while dLS Ex9 attenuated this effect. Using a similar design, we examined the role of dLS GLP-1R in the neuroendocrine response to acute restraint stress. As expected, stress potently increased serum corticosterone, but blockade of dLS GLP-1Rs did not affect this response. Together, these data show that endogenous GLP-1 action in the dLS plays a role in some but not all of the physiologic responses to acute stress. Copyright © 2018 Elsevier Inc. All rights reserved.

Glucagon-like peptide-1 acutely affects renal blood flow and urinary flow rate in spontaneously hypertensive rats despite significantly reduced renal expression of GLP-1 receptors.

PubMed

Ronn, Jonas; Jensen, Elisa P; Wewer Albrechtsen, Nicolai J; Holst, Jens Juul; Sorensen, Charlotte M

2017-12-01

Glucagon-like peptide-1 (GLP-1) is an incretin hormone increasing postprandial insulin release. GLP-1 also induces diuresis and natriuresis in humans and rodents. The GLP-1 receptor is extensively expressed in the renal vascular tree in normotensive rats where acute GLP-1 treatment leads to increased mean arterial pressure (MAP) and increased renal blood flow (RBF). In hypertensive animal models, GLP-1 has been reported both to increase and decrease MAP. The aim of this study was to examine expression of renal GLP-1 receptors in spontaneously hypertensive rats (SHR) and to assess the effect of acute intrarenal infusion of GLP-1. We hypothesized that GLP-1 would increase diuresis and natriuresis and reduce MAP in SHR. Immunohistochemical staining and in situ hybridization for the GLP-1 receptor were used to localize GLP-1 receptors in the kidney. Sevoflurane-anesthetized normotensive Sprague-Dawley rats and SHR received a 20 min intrarenal infusion of GLP-1 and changes in MAP, RBF, heart rate, dieresis, and natriuresis were measured. The vasodilatory effect of GLP-1 was assessed in isolated interlobar arteries from normo- and hypertensive rats. We found no expression of GLP-1 receptors in the kidney from SHR. However, acute intrarenal infusion of GLP-1 increased MAP, RBF, dieresis, and natriuresis without affecting heart rate in both rat strains. These results suggest that the acute renal effects of GLP-1 in SHR are caused either by extrarenal GLP-1 receptors activating other mechanisms (e.g., insulin) to induce the renal changes observed or possibly by an alternative renal GLP-1 receptor. © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

Glucagon-like peptide 1 receptor (GLP-1R) expression by nerve fibres in inflammatory bowel disease and functional effects in cultured neurons.

PubMed

Anand, Uma; Yiangou, Yiangos; Akbar, Ayesha; Quick, Tom; MacQuillan, Anthony; Fox, Mike; Sinisi, Marco; Korchev, Yuri E; Jones, Ben; Bloom, Steve R; Anand, Praveen

2018-01-01

Glucagon like-peptide 1 receptor (GLP-1R) agonists diminish appetite and may contribute to the weight loss in inflammatory bowel disease (IBD). The aim of this study was to determine, for the first time, the expression of GLP-1R by colon nerve fibres in patients with IBD, and functional effects of its agonists in cultured rat and human sensory neurons. GLP-1R and other nerve markers were studied by immunohistochemistry in colon biopsies from patients with IBD (n = 16) and controls (n = 8), human dorsal root ganglia (DRG) tissue, and in GLP-1R transfected HEK293 cells. The morphological effects of incretin hormones oxyntomodulin, exendin-4 and glucagon were studied on neurite extension in cultured DRG neurons, and their functional effects on capsaicin and ATP signalling, using calcium imaging. Significantly increased numbers of colonic mucosal nerve fibres were observed in IBD biopsies expressing GLP-1R (p = 0.0013), the pan-neuronal marker PGP9.5 (p = 0.0008), and sensory neuropeptide CGRP (p = 0.0014). An increase of GLP-1R positive nerve fibres in IBD colon was confirmed with a different antibody to GLP-1R (p = 0.016). GLP-1R immunostaining was intensely positive in small and medium-sized neurons in human DRG, and in human and rat DRG cultured neurons. Co-localization of GLP-1R expression with neuronal markers in colon and DRG confirmed the neural expression of GLP-1R, and antibody specificity was confirmed in HEK293 cells transfected with the GLP-1R. Treatment with oxyntomodulin, exendin-4 and GLP-1 increased neurite length in cultured neurons compared with controls, but did not stimulate calcium influx directly, or affect capsaicin responses. However, exendin-4 significantly enhanced ATP responses in human DRG neurons. Our results show that increased GLP-1R innervation in IBD bowel could mediate enhanced visceral afferent signalling, and provide a peripheral target for therapeutic intervention. The differential effect of GLP-1R agonists on capsaicin and ATP

Glucagon-like peptide 1 receptor (GLP-1R) expression by nerve fibres in inflammatory bowel disease and functional effects in cultured neurons

PubMed Central

Yiangou, Yiangos; Akbar, Ayesha; Quick, Tom; MacQuillan, Anthony; Fox, Mike; Sinisi, Marco; Korchev, Yuri E.; Jones, Ben; Bloom, Steve R.; Anand, Praveen

2018-01-01

Introduction Glucagon like-peptide 1 receptor (GLP-1R) agonists diminish appetite and may contribute to the weight loss in inflammatory bowel disease (IBD). Objectives The aim of this study was to determine, for the first time, the expression of GLP-1R by colon nerve fibres in patients with IBD, and functional effects of its agonists in cultured rat and human sensory neurons. Methods GLP-1R and other nerve markers were studied by immunohistochemistry in colon biopsies from patients with IBD (n = 16) and controls (n = 8), human dorsal root ganglia (DRG) tissue, and in GLP-1R transfected HEK293 cells. The morphological effects of incretin hormones oxyntomodulin, exendin-4 and glucagon were studied on neurite extension in cultured DRG neurons, and their functional effects on capsaicin and ATP signalling, using calcium imaging. Results Significantly increased numbers of colonic mucosal nerve fibres were observed in IBD biopsies expressing GLP-1R (p = 0.0013), the pan-neuronal marker PGP9.5 (p = 0.0008), and sensory neuropeptide CGRP (p = 0.0014). An increase of GLP-1R positive nerve fibres in IBD colon was confirmed with a different antibody to GLP-1R (p = 0.016). GLP-1R immunostaining was intensely positive in small and medium-sized neurons in human DRG, and in human and rat DRG cultured neurons. Co-localization of GLP-1R expression with neuronal markers in colon and DRG confirmed the neural expression of GLP-1R, and antibody specificity was confirmed in HEK293 cells transfected with the GLP-1R. Treatment with oxyntomodulin, exendin-4 and GLP-1 increased neurite length in cultured neurons compared with controls, but did not stimulate calcium influx directly, or affect capsaicin responses. However, exendin-4 significantly enhanced ATP responses in human DRG neurons. Conclusion Our results show that increased GLP-1R innervation in IBD bowel could mediate enhanced visceral afferent signalling, and provide a peripheral target for therapeutic intervention. The differential

In vivo dual-delivery of glucagon like peptide-1 (GLP-1) and dipeptidyl peptidase-4 (DPP4) inhibitor through composites prepared by microfluidics for diabetes therapy

NASA Astrophysics Data System (ADS)

Araújo, F.; Shrestha, N.; Gomes, M. J.; Herranz-Blanco, B.; Liu, D.; Hirvonen, J. J.; Granja, P. L.; Santos, H. A.; Sarmento, B.

2016-05-01

Oral delivery of proteins is still a challenge in the pharmaceutical field. Nanoparticles are among the most promising carrier systems for the oral delivery of proteins by increasing their oral bioavailability. However, most of the existent data regarding nanosystems for oral protein delivery is from in vitro studies, lacking in vivo experiments to evaluate the efficacy of these systems. Herein, a multifunctional composite system, tailored by droplet microfluidics, was used for dual delivery of glucagon like peptide-1 (GLP-1) and dipeptidyl peptidase-4 inhibitor (iDPP4) in vivo. Oral delivery of GLP-1 with nano- or micro-systems has been studied before, but the simultaneous nanodelivery of GLP-1 with iDPP4 is a novel strategy presented here. The type 2 diabetes mellitus (T2DM) rat model, induced through the combined administration of streptozotocin and nicotinamide, a non-obese model of T2DM, was used. The combination of both drugs resulted in an increase in the hypoglycemic effects in a sustained, but prolonged manner, where the iDPP4 improved the therapeutic efficacy of GLP-1. Four hours after the oral administration of the system, blood glucose levels were decreased by 44%, and were constant for another 4 h, representing half of the glucose area under the curve when compared to the control. An enhancement of the plasmatic insulin levels was also observed 6 h after the oral administration of the dual-drug composite system and, although no statistically significant differences existed, the amount of pancreatic insulin was also higher. These are promising results for the oral delivery of GLP-1 to be pursued further in a chronic diabetic model study.

Lipid Raft-dependent Glucagon-like Peptide-2 Receptor Trafficking Occurs Independently of Agonist-induced Desensitization

PubMed Central

Estall, Jennifer L.; Yusta, Bernardo; Drucker, Daniel J.

2004-01-01

The intestinotrophic and cytoprotective actions of glucagon-like peptide-2 (GLP-2) are mediated by the GLP-2 receptor (GLP-2R), a member of the class II glucagon-secretin G protein-coupled receptor superfamily. Although native GLP-2 exhibits a short circulating half-life, long-acting degradation-resistant GLP-2 analogues are being evaluated for therapeutic use in human subjects. Accordingly, we examined the mechanisms regulating signaling, internalization, and trafficking of the GLP-2R to identify determinants of receptor activation and desensitization. Heterologous cells expressing the transfected rat or human GLP-2R exhibited a rapid, dose-dependent, and prolonged desensitization of the GLP-2–stimulated cAMP response and a sustained GLP-2–induced decrease in levels of cell surface receptor. Surprisingly, inhibitors of clathrin-dependent endocytosis failed to significantly decrease GLP-2R internalization, whereas cholesterol sequestration inhibited ligand-induced receptor internalization and potentiated homologous desensitization. The hGLP-2R localized to both Triton X-100–soluble and –insoluble (lipid raft) cellular fractions and colocalized transiently with the lipid raft marker caveolin-1. Although GLP-2R endocytosis was dependent on lipid raft integrity, the receptor transiently associated with green fluorescent protein tagged-early endosome antigen 1–positive vesicles and inhibitors of endosomal acidification attenuated the reappearance of the GLP-2R on the cell surface. Our data demonstrate that GLP-2R desensitization and raft-dependent trafficking represent distinct and independent cellular mechanisms and provide new evidence implicating the importance of a clathrin- and dynamin-independent, lipid raft-dependent pathway for homologous G protein-coupled receptor internalization. PMID:15169869

Critical role for GLP-1 in symptomatic post-bariatric hypoglycaemia.

PubMed

Craig, Colleen M; Liu, Li-Fen; Deacon, Carolyn F; Holst, Jens J; McLaughlin, Tracey L

2017-03-01

Post-bariatric hypoglycaemia (PBH) is a rare, but severe, metabolic disorder arising months to years after bariatric surgery. It is characterised by symptomatic postprandial hypoglycaemia, with inappropriately elevated insulin concentrations. The relative contribution of exaggerated incretin hormone signalling to dysregulated insulin secretion and symptomatic hypoglycaemia is a subject of ongoing inquiry. This study was designed to test the hypothesis that PBH and associated symptoms are primarily mediated by glucagon-like peptide-1 (GLP-1). We conducted a double-blinded crossover study wherein eight participants with confirmed PBH were assigned in random order to intravenous infusion of the GLP-1 receptor (GLP-1r) antagonist. Exendin (9-39) (Ex-9), or placebo during an OGTT on two separate days at the Stanford University Clinical and Translational Research Unit. Metabolic, symptomatic and pharmacokinetic variables were evaluated. Results were compared with a cohort of BMI- and glucose-matched non-surgical controls (NSCs). Infusion of Ex-9 decreased the time to peak glucose and rate of glucose decline during OGTT, and raised the postprandial nadir by over 70%, normalising it relative to NSCs and preventing hypoglycaemia in all PBH participants. Insulin AUC and secretion rate decreased by 57% and 71% respectively, and peak postprandial insulin was normalised relative to NSCs. Autonomic and neuroglycopenic symptoms were significantly reduced during Ex-9 infusion. GLP-1r blockade prevented hypoglycaemia in 100% of individuals, normalised beta cell function and reversed neuroglycopenic symptoms, supporting the conclusion that GLP-1 plays a primary role in mediating hyperinsulinaemic hypoglycaemia in PBH. Competitive antagonism at the GLP-1r merits consideration as a therapeutic strategy. ClinicalTrials.gov NCT02550145.

Crystal structure of the protein At3g01520, a eukaryotic universal stress protein-like protein from Arabidopsis thaliana in complex with AMP.

PubMed

Kim, Do Jin; Bitto, Eduard; Bingman, Craig A; Kim, Hyun-Jung; Han, Byung Woo; Phillips, George N

2015-07-01

Members of the universal stress protein (USP) family are conserved in a phylogenetically diverse range of prokaryotes, fungi, protists, and plants and confer abilities to respond to a wide range of environmental stresses. Arabidopsis thaliana contains 44 USP domain-containing proteins, and USP domain is found either in a small protein with unknown physiological function or in an N-terminal portion of a multi-domain protein, usually a protein kinase. Here, we report the first crystal structure of a eukaryotic USP-like protein encoded from the gene At3g01520. The crystal structure of the protein At3g01520 was determined by the single-wavelength anomalous dispersion method and refined to an R factor of 21.8% (Rfree = 26.1%) at 2.5 Å resolution. The crystal structure includes three At3g01520 protein dimers with one AMP molecule bound to each protomer, comprising a Rossmann-like α/β overall fold. The bound AMP and conservation of residues in the ATP-binding loop suggest that the protein At3g01520 also belongs to the ATP-binding USP subfamily members. © 2015 The Authors. Proteins: Structure, Function, and Bioinformatics Published by Wiley Periodicals, Inc.

Polycomb-like proteins link the PRC2 complex to CpG islands

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Haojie; Liefke, Robert; Jiang, Junyi

The Polycomb repressive complex 2 (PRC2) mainly mediates transcriptional repression1,2 and has essential roles in various biological processes including the maintenance of cell identity and proper differentiation. Polycomb-like (PCL) proteins, such as PHF1, MTF2 and PHF19, are PRC2-associated factors that form sub-complexes with PRC2 core components3, and have been proposed to modulate the enzymatic activity of PRC2 or the recruitment of PRC2 to specific genomic loci4,5,6,7,8,9,10,11,12,13. Mammalian PRC2-binding sites are enriched in CG content, which correlates with CpG islands that display a low level of DNA methylation14. However, the mechanism of PRC2 recruitment to CpG islands is not fully understood.more » Here we solve the crystal structures of the N-terminal domains of PHF1 and MTF2 with bound CpG-containing DNAs in the presence of H3K36me3-containing histone peptides. We show that the extended homologous regions of both proteins fold into a winged-helix structure, which specifically binds to the unmethylated CpG motif but in a completely different manner from the canonical winged-helix DNA recognition motif. We also show that the PCL extended homologous domains are required for efficient recruitment of PRC2 to CpG island-containing promoters in mouse embryonic stem cells. Our research provides the first, to our knowledge, direct evidence to demonstrate that PCL proteins are crucial for PRC2 recruitment to CpG islands, and further clarifies the roles of these proteins in transcriptional regulation in vivo.« less

Multiple regulatory elements for the glpA operon encoding anaerobic glycerol-3-phosphate dehydrogenase and the glpD operon encoding aerobic glycerol-3-phosphate dehydrogenase in Escherichia coli: further characterization of respiratory control.

PubMed

Iuchi, S; Cole, S T; Lin, E C

1990-01-01

In Escherichia coli, sn-glycerol-3-phosphate can be oxidized by two different flavo-dehydrogenases, an anaerobic enzyme encoded by the glpACB operon and an aerobic enzyme encoded by the glpD operon. These two operons belong to the glp regulon specifying the utilization of glycerol, sn-glycerol-3-phosphate, and glycerophosphodiesters. In glpR mutant cells grown under conditions of low catabolite repression, the glpA operon is best expressed anaerobically with fumarate as the exogenous electron acceptor, whereas the glpD operon is best expressed aerobically. Increased anaerobic expression of glpA is dependent on the fnr product, a pleiotropic activator of genes involved in anaerobic respiration. In this study we found that the expression of a glpA1(Oxr) (oxygen-resistant) mutant operon, selected for increased aerobic expression, became less dependent on the FNR protein but more dependent on the cyclic AMP-catabolite gene activator protein complex mediating catabolite repression. Despite the increased aerobic expression of glpA1(Oxr), a twofold aerobic repressibility persisted. Moreover, anaerobic repression by nitrate respiration remained normal. Thus, there seems to exist a redox control apart from the FNR-mediated one. We also showed that the anaerobic repression of the glpD operon was fully relieved by mutations in either arcA (encoding a presumptive DNA recognition protein) or arcB (encoding a presumptive redox sensor protein). The arc system is known to mediate pleiotropic control of genes of aerobic function.

Feedback suppression of meal-induced glucagon-like peptide-1 (GLP-1) secretion mediated through elevations in intact GLP-1 caused by dipeptidyl peptidase-4 inhibition: a randomized, prospective comparison of sitagliptin and vildagliptin treatment.

PubMed

Baranov, Oleg; Kahle, Melanie; Deacon, Carolyn F; Holst, Jens J; Nauck, Michael A

2016-11-01

To compare directly the clinical effects of vildagliptin and sitagliptin in patients with type 2 diabetes, with a special emphasis on incretin hormones and L-cell feedback inhibition induced by dipeptidyl peptidase (DPP-4) inhibition. A total of 24 patients (12 on a diet/exercise regimen, 12 on metformin) were treated, in randomized order, for 7-9 days, with either vildagliptin (50 mg twice daily = 100 mg/d), sitagliptin (100 mg once daily in those on diet, 50 mg twice daily in those on metformin treatment = 100 mg/d) or placebo (twice daily). A mixed-meal test was performed. Intact glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide concentrations were doubled by both DPP-4 inhibitors. Meal-related total GLP-1 responses were reduced by vildagliptin and sitagliptin treatment alike in the majority of patients (vildagliptin: p = 0.0005; sitagliptin: p = 0.019), but with substantial inter-individual variation. L-cell feedback appeared to be more pronounced in those whose intact GLP-1 relative to total GLP-1 increased more, and who had greater reductions in fasting plasma glucose after DPP-4 inhibition. K-cell feedback inhibition overall was not significant. There were no differences in any of the clinical variables (glycaemia, insulin and glucagon secretory responses) between vildagliptin and sitagliptin treatment. Vildagliptin and sitagliptin affected incretin hormones, glucose concentrations, insulin and glucagon secretion in a similar manner. Inter-individual variations in L-cell feedback inhibition may indicate heterogeneity in the clinical response to DPP-4 inhibition. © 2016 John Wiley & Sons Ltd.

Effects of the glucagon-like polypeptide-1 analogue (Val8)GLP-1 on learning, progenitor cell proliferation and neurogenesis in the C57B/16 mouse brain.

PubMed

McGovern, Stephen F J; Hunter, Kerry; Hölscher, Christian

2012-09-14

Type 2 diabetes (T2DM) has been identified as a risk factor for Alzheimer's disease. Here, we tested the properties of the glucagon-like polypetide-1 (GLP-1) analogue (Val8)GLP-1, a drug originally developed as a treatment for T2DM at a range of doses (2.5 nmol; 25 nmol; 100 nmol; or 250 nmol/kg bw ip.) in an acute memory study in wild type C57B/l6 mice. We also tested (Val8)GLP-1 and the GLP-1 receptor antagonist exendin (9-39) in a chronic study (3 weeks at 25 nmol/kg bw ip. once-daily). We found that (Val8)GLP-1 crossed the blood brain barrier readily and that peripheral injection increased levels in the brain 30 min post-injection ip. but not 2h post-injection in rats. In the acute study, the low dose of 2.5 nmol/kg ip. enhanced motor activity in the open field task, while total distance travelled, exploratory behaviour and anxiety was not affected at any dose. Learning an object recognition task was not affected either. In the chronic study, no effect was observed in the open field assessment. The antagonist exendin (9-39) impaired object recognition learning and spatial learning in a water maze task, demonstrating the importance of GLP-1 signalling in memory formation. Locomotor activity was also affected in some cases. Blood sugar levels and insulin sensitivity was not affected in chronically treated mice. Neuronal stem cells and neurogenesis was enhanced by (Val8)GLP-1 in the dentate gyrus of wild type mice. The results demonstrate that (Val8)GLP-1 is safe in a range of doses, crosses the BBB and has potentially beneficial effects in the CNS by enhancing neurogenesis. Copyright © 2012 Elsevier B.V. All rights reserved.

Functional importance of GLP-1 receptor species and expression levels in cell lines.

PubMed

Knudsen, Lotte Bjerre; Hastrup, Sven; Underwood, Christina Rye; Wulff, Birgitte Schjellerup; Fleckner, Jan

2012-04-10

Of the mammalian species, only the GLP-1 receptors of rat and human origin have been described and characterized. Here, we report the cloning of the homologous GLP-1 receptors from mouse, rabbit, pig, cynomolgus monkey and chimp. The GLP-1 receptor is highly conserved across species, thus underlining the physiological importance of the peptide hormone and its receptor across a wide range of mammals. We expressed the receptors by stable transfection of BHK cells, both in cell lines with high expression levels of the cloned receptors, as well as in cell lines with lower expression levels, more comparable to endogenous expression of these receptors. High expression levels of cloned GLP-1 receptors markedly increased the potency of GLP-1 and other high affinity ligands, whereas the K(d) values were not affected. For a low affinity ligand like the ago-allosteric modulator Compound 2, expression levels of the human GLP-1 receptor were important for maximal efficacy as well as potency. The two natural metabolites of GLP-1, GLP-1(9-37) and GLP-1(9-36)amide were agonists when tested on a cell line with high expression of the recombinant human GLP-1 receptor, whereas they behaved as (low potent) antagonists on a cell line that expressed the receptor endogenously, as well as cells expressing a moderate level of the recombinant human GLP-1 receptor. The amide form was a more potent agonist than the free acid from. In conclusion, receptor expression level is an important parametre for selecting cell lines with cloned GLP-1 receptors for functional characterization of physiological and pharmaceutical ligands. Copyright © 2011 Elsevier B.V. All rights reserved.

Involvement of gut microbiota in association between GLP-1/GLP-1 receptor expression and gastrointestinal motility.

PubMed

Yang, Mo; Fukui, Hirokazu; Eda, Hirotsugu; Xu, Xin; Kitayama, Yoshitaka; Hara, Ken; Kodani, Mio; Tomita, Toshihiko; Oshima, Tadayuki; Watari, Jiro; Miwa, Hiroto

2017-04-01

The microbiota in the gut is known to play a pivotal role in host physiology by interacting with the immune and neuroendocrine systems in gastrointestinal (GI) tissues. Glucagon-like peptide 1 (GLP-1), a gut hormone, is involved in metabolism as well as GI motility. We examined how gut microbiota affects the link between GLP-1/GLP-1 receptor (GLP-1R) expression and motility of the GI tract. Germ-free (GF) mice (6 wk old) were orally administered a fecal bacterial suspension prepared from specific pathogen-free (SPF) mice, and then after fecal transplantation (FT) GI tissues were obtained from the GF mice at various time points. The expression of GLP-1 and its receptor was examined by immunohistochemistry, and gastrointestinal transit time (GITT) was measured by administration of carmine red solution. GLP-1 was expressed in endocrine cells in the colonic mucosa, and GLP-1R was expressed in myenteric neural cells throughout the GI wall. GLP-1R-positive cells throughout the GI wall were significantly fewer in GF mice with FT than in GF mice without gut microbiota reconstitution. GITT was significantly shorter in GF mice with FT than in control GF mice without FT and correlated with the number of GLP-1R-positive cells throughout the GI wall. GITT was significantly longer in GF control mice than in SPF mice. When those mice were treated with GLP-1 agonist extendin4, GITT was significantly longer in the GF mice. The gut microbiota may accelerate or at least modify GI motility while suppressing GLP-1R expression in myenteric neural cells throughout the GI tract. NEW & NOTEWORTHY The gut microbiota has been intensively studied, because it plays a pivotal role in various aspects of host physiology. On the other hand, glucagon-like peptide 1 (GLP-1) plays important roles in metabolism as well as gastrointestinal motility. In the present study, we have suggested that the gut microbiota accelerates gastrointestinal motility while suppressing the expression of GLP-1 receptor in

Gαs regulates Glucagon-Like Peptide 1 Receptor-mediated cyclic AMP generation at Rab5 endosomal compartment.

PubMed

Girada, Shravan Babu; Kuna, Ramya S; Bele, Shilpak; Zhu, Zhimeng; Chakravarthi, N R; DiMarchi, Richard D; Mitra, Prasenjit

2017-10-01

Upon activation, G protein coupled receptors (GPCRs) associate with heterotrimeric G proteins at the plasma membrane to initiate second messenger signaling. Subsequently, the activated receptor experiences desensitization, internalization, and recycling back to the plasma membrane, or it undergoes lysosomal degradation. Recent reports highlight specific cases of persistent cyclic AMP generation by internalized GPCRs, although the functional significance and mechanistic details remain to be defined. Cyclic AMP generation from internalized Glucagon-Like Peptide-1 Receptor (GLP-1R) has previously been reported from our laboratory. This study aimed at deciphering the molecular mechanism by which internalized GLP-R supports sustained cyclic AMP generation upon receptor activation in pancreatic beta cells. We studied the time course of cyclic AMP generation following GLP-1R activation with particular emphasis on defining the location where cyclic AMP is generated. Detection involved a novel GLP-1 conjugate coupled with immunofluorescence using specific endosomal markers. Finally, we employed co-immunoprecipitation as well as immunofluorescence to assess the protein-protein interactions that regulate GLP-1R mediated cyclic AMP generation at endosomes. Our data reveal that prolonged association of G protein α subunit Gαs with activated GLP-1R contributed to sustained cyclic AMP generation at Rab 5 endosomal compartment. The findings provide the mechanism of endosomal cyclic AMP generation following GLP-1R activation. We identified the specific compartment that serves as an organizing center to generate endosomal cyclic AMP by internalized activated receptor complex. Copyright © 2017 The Authors. Published by Elsevier GmbH.. All rights reserved.

Small-molecule agonists for the glucagon-like peptide 1 receptor

PubMed Central

Knudsen, Lotte Bjerre; Kiel, Dan; Teng, Min; Behrens, Carsten; Bhumralkar, Dilip; Kodra, János T.; Holst, Jens J.; Jeppesen, Claus B.; Johnson, Michael D.; de Jong, Johannes Cornelis; Jorgensen, Anker Steen; Kercher, Tim; Kostrowicki, Jarek; Madsen, Peter; Olesen, Preben H.; Petersen, Jacob S.; Poulsen, Fritz; Sidelmann, Ulla G.; Sturis, Jeppe; Truesdale, Larry; May, John; Lau, Jesper

2007-01-01

The peptide hormone glucagon-like peptide (GLP)-1 has important actions resulting in glucose lowering along with weight loss in patients with type 2 diabetes. As a peptide hormone, GLP-1 has to be administered by injection. Only a few small-molecule agonists to peptide hormone receptors have been described and none in the B family of the G protein coupled receptors to which the GLP-1 receptor belongs. We have discovered a series of small molecules known as ago-allosteric modulators selective for the human GLP-1 receptor. These compounds act as both allosteric activators of the receptor and independent agonists. Potency of GLP-1 was not changed by the allosteric agonists, but affinity of GLP-1 for the receptor was increased. The most potent compound identified stimulates glucose-dependent insulin release from normal mouse islets but, importantly, not from GLP-1 receptor knockout mice. Also, the compound stimulates insulin release from perfused rat pancreas in a manner additive with GLP-1 itself. These compounds may lead to the identification or design of orally active GLP-1 agonists. PMID:17213325

Flavonoid-rich extract of Chromolaena odorata modulate circulating GLP-1 in Wistar rats: computational evaluation of TGR5 involvement.

PubMed

Omotuyi, Olaposi Idowu; Nash, Oyekanmi; Inyang, Olumide Kayode; Ogidigo, Joyce; Enejoh, Ojochenemi; Okpalefe, Okiemute; Hamada, Tsuyoshi

2018-02-01

Chromolaena odorata is a major bio-resource in folkloric treatment of diabetes. In the present study, its anti-diabetic component and underlying mechanism were investigated. A library containing 140 phytocompounds previously characterized from C. odorata was generated and docked (Autodock Vina) into homology models of dipeptidyl peptidase (DPP)-4, Takeda-G-protein-receptor-5 (TGR5), glucagon-like peptide 1 (GLP1) receptor, renal sodium dependent glucose transporter (SGLUT)-1/2 and nucleotide-binding oligomerization domain (NOD) proteins 1&2. GLP-1 gene (RT-PCR) modulation and its release (EIA) by C. odorata were confirmed in vivo. From the docking result above, TGR5 was identified as a major target for two key C. odorata flavonoids (5,7-dihydroxy-6-4-dimethoxyflavanone and homoesperetin-7-rutinoside); sodium taurocholate and C. odorata powder included into the diet of the animals both raised the intestinal GLP-1 expression versus control ( p  < 0.05); When treated with flavonoid-rich extract of C. odorata (CoF) or malvidin, circulating GLP-1 increased by 130.7% in malvidin-treated subjects (0 vs. 45 min). CoF treatment also resulted in 128.5 and 275% increase for 10 and 30 mg/kg b.w., respectively. The results of this study support that C. odorata flavonoids may modulate the expression of GLP-1 and its release via TGR5. This finding may underscore its anti-diabetic potency.

LARETH-25 and β-CD improve central transitivity and central pharmacological effect of the GLP-2 peptide.

PubMed

Nakao, Yusuke; Horiguchi, Michiko; Nakamura, Ryuji; Sasaki-Hamada, Sachie; Ozawa, Chihiro; Funane, Taichi; Ozawa, Ryo; Oka, Jun-Ichiro; Yamashita, Chikamasa

2016-12-30

Depression is a common mental disorder. More than 350 million people of all ages suffer from depression worldwide. Although a number of antidepressants are available, >20% of patients with major depressive disorder suffer from treatment-resistant depression. Therefore, development of novel therapeutics to overcome this condition is required. We reported that intracerebroventricular administration of glucagon-like peptide-2 (GLP-2) exerts antidepressant-like effects treated with or without adrenocorticotropic hormone. In the present study, we developed a nasal formulation of GLP-2 containing 5% polyoxyethylene (25) lauryl ether and 1% β-cyclodextrin that enhanced the resistance of GLP-2 to inactivation by dipeptidyl peptidase-4. Intranasal administration of this formulation (60μg/kg) increased the delivery of GLP-2 to the brain and had antidepressant-like effects on rats. These results suggest the potential of the GLP-2 nasal formulation for use as a novel antidepressant. Copyright © 2016 Elsevier B.V. All rights reserved.

Active metabolite of GLP-1 mediates myocardial glucose uptake and improves left ventricular performance in conscious dogs with dilated cardiomyopathy.

PubMed

Nikolaidis, Lazaros A; Elahi, Dariush; Shen, You-Tang; Shannon, Richard P

2005-12-01

We have shown previously that the glucagon-like peptide-1 (GLP-1)-(7-36) amide increases myocardial glucose uptake and improves left ventricular (LV) and systemic hemodynamics in both conscious dogs with pacing-induced dilated cardiomyopathy (DCM) and humans with LV systolic dysfunction after acute myocardial infarction. However, GLP-1-(7-36) is rapidly degraded in the plasma to GLP-1-(9-36) by dipeptidyl peptidase IV (DPP IV), raising the issue of which peptide is the active moiety. By way of methodology, we compared the efficacy of a 48-h continuous intravenous infusion of GLP-1-(7-36) (1.5 pmol.kg(-1).min(-1)) to GLP-1-(9-36) (1.5 pmol.kg(-1).min(-1)) in 28 conscious, chronically instrumented dogs with pacing-induced DCM by measuring LV function and transmyocardial substrate uptake under basal and insulin-stimulated conditions using hyperinsulinemic-euglycemic clamps. As a result, dogs with DCM demonstrated myocardial insulin resistance under basal and insulin-stimulated conditions. Both GLP-1-(7-36) and GLP-1-(9-36) significantly reduced (P < 0.01) LV end-diastolic pressure [GLP-1-(7-36), 28 +/- 1 to 15 +/- 2 mmHg; GLP-1-(9-36), 29 +/- 2 to 16 +/- 1 mmHg] and significantly increased (P < 0.01) the first derivative of LV pressure [GLP-1-(7-36), 1,315 +/- 81 to 2,195 +/- 102 mmHg/s; GLP-1-(9-36), 1,336 +/- 77 to 2,208 +/- 68 mmHg] and cardiac output [GLP-1-(7-36), 1.5 +/- 0.1 to 1.9 +/- 0.1 l/min; GLP-1-(9-36), 2.0 +/- 0.1 to 2.4 +/- 0.05 l/min], whereas an equivolume infusion of saline had no effect. Both peptides increased myocardial glucose uptake but without a significant increase in plasma insulin. During the GLP-1-(9-36) infusion, negligible active (NH2-terminal) peptide was measured in the plasma. In conclusion, in DCM, GLP-1-(9-36) mimics the effects of GLP-1-(7-36) in stimulating myocardial glucose uptake and improving LV and systemic hemodynamics through insulinomimetic as opposed to insulinotropic effects. These data suggest that GLP-1-(9-36) amide is

Class II G Protein-Coupled Receptors and Their Ligands in Neuronal Function and Protection

PubMed Central

Martin, Bronwen; de Maturana, Rakel Lopez; Brenneman, Randall; Walent, Tom; Mattson, Mark P.; Maudsley, Stuart

2008-01-01

G protein-coupled receptors (GPCRs) play pivotal roles in regulating the function and plasticity of neuronal circuits in the nervous system. Among the myriad of GPCRs expressed in neural cells, class II GPCRs which couples predominantly to the Gs–adenylate cyclase–cAMP signaling pathway, have recently received considerable attention for their involvement in regulating neuronal survival. Neuropeptides that activate class II GPCRs include secretin, glucagon-like peptides (GLP-1 and GLP-2), growth hormone-releasing hormone (GHRH), pituitary adenylate cyclase activating peptide (PACAP), corticotropin-releasing hormone (CRH), vasoactive intestinal peptide (VIP), parathyroid hormone (PTH), and calcitonin-related peptides. Studies of patients and animal and cell culture models, have revealed possible roles for class II GPCRs signaling in the pathogenesis of several prominent neurodegenerative conditions including stroke, Alzheimer's, Parkinson's, and Huntington's diseases. Many of the peptides that activate class II GPCRs promote neuron survival by increasing the resistance of the cells to oxidative, metabolic, and excitotoxic injury. A better understanding of the cellular and molecular mechanisms by which class II GPCRs signaling modulates neuronal survival and plasticity will likely lead to novel therapeutic interventions for neurodegenerative disorders. PMID:16052036

Loss of dorsomedial hypothalamic GLP-1 signaling reduces BAT thermogenesis and increases adiposity.

PubMed

Lee, Shin J; Sanchez-Watts, Graciela; Krieger, Jean-Philippe; Pignalosa, Angelica; Norell, Puck N; Cortella, Alyssa; Pettersen, Klaus G; Vrdoljak, Dubravka; Hayes, Matthew R; Kanoski, Scott; Langhans, Wolfgang; Watts, Alan G

2018-05-01

Glucagon-like peptide-1 (GLP-1) neurons in the hindbrain densely innervate the dorsomedial hypothalamus (DMH), a nucleus strongly implicated in body weight regulation and the sympathetic control of brown adipose tissue (BAT) thermogenesis. Therefore, DMH GLP-1 receptors (GLP-1R) are well placed to regulate energy balance by controlling sympathetic outflow and BAT function. We investigate this possibility in adult male rats by using direct administration of GLP-1 (0.5 ug) into the DMH, knocking down DMH GLP-1R mRNA with viral-mediated RNA interference, and by examining the neurochemical phenotype of GLP-1R expressing cells in the DMH using in situ hybridization. GLP-1 administered into the DMH increased BAT thermogenesis and hepatic triglyceride (TG) mobilization. On the other hand, Glp1r knockdown (KD) in the DMH increased body weight gain and adiposity, with a concomitant reduction in energy expenditure (EE), BAT temperature, and uncoupling protein 1 (UCP1) expression. Moreover, DMH Glp1r KD induced hepatic steatosis, increased plasma TG, and elevated liver specific de-novo lipogenesis, effects that collectively contributed to insulin resistance. Interestingly, DMH Glp1r KD increased neuropeptide Y (NPY) mRNA expression in the DMH. GLP-1R mRNA in the DMH, however, was found in GABAergic not NPY neurons, consistent with a GLP-1R-dependent inhibition of NPY neurons that is mediated by local GABAergic neurons. Finally, DMH Glp1r KD attenuated the anorexigenic effects of the GLP-1R agonist exendin-4, highlighting an important role of DMH GLP-1R signaling in GLP-1-based therapies. Collectively, our data show that DMH GLP-1R signaling plays a key role for BAT thermogenesis and adiposity. Copyright © 2018 The Authors. Published by Elsevier GmbH.. All rights reserved.

Exenatide exerts a PKA-dependent positive inotropic effect in human atrial myocardium: GLP-1R mediated effects in human myocardium.

PubMed

Wallner, Markus; Kolesnik, Ewald; Ablasser, Klemens; Khafaga, Mounir; Wakula, Paulina; Ljubojevic, Senka; Thon-Gutschi, Eva Maria; Sourij, Harald; Kapl, Martin; Edmunds, Nicholas J; Kuzmiski, J Brent; Griffith, David A; Knez, Igor; Pieske, Burkert; von Lewinski, Dirk

2015-12-01

Glucagon-like peptide-1 receptor (GLP-1R) agonists are a rapidly growing class of drugs developed for treating type-2 diabetes mellitus. Patients with diabetes carry an up to 5-fold greater mortality risk compared to non-diabetic patients, mainly as a result of cardiovascular diseases. Although beneficial cardiovascular effects have been reported, exact mechanisms of GLP-1R-agonist action in the heart, especially in human myocardium, are poorly understood. The effects of GLP-1R-agonists (exenatide, GLP-1(7-36)NH2, PF-06446009, PF-06446667) on cardiac contractility were tested in non-failing atrial and ventricular trabeculae from 72 patients. The GLP-1(7-36)NH2 metabolite, GLP-1(9-36)NH2, was also examined. In electrically stimulated trabeculae, the effects of compounds on isometric force were measured in the absence and presence of pharmacological inhibitors of signal transduction pathways. The role of β-arrestin signaling was examined using a β-arrestin partial agonist, PF-06446667. Expression levels were tested by immunoblots. Translocation of GLP-1R downstream molecular targets, Epac2, GLUT-1 and GLUT-4, were assessed by fluorescence microscopy. All tested GLP-1R-agonists significantly increased developed force in human atrial trabeculae, whereas GLP-1(9-36)NH2 had no effect. Exendin(9-39)NH2, a GLP-1R-antagonist, and H-89 blunted the inotropic effect of exenatide. In addition, exenatide increased PKA-dependent phosphorylation of phospholamban (PLB), GLUT-1 and Epac2 translocation, but not GLUT-4 translocation. Exenatide failed to enhance contractility in ventricular myocardium. Quantitative real-time PCR (qRT-PCR) revealed a significant higher GLP-1R expression in the atrium compared to ventricle. Exenatide increased contractility in a dose-dependent manner via GLP-1R/cAMP/PKA pathway and induced GLUT-1 and Epac2 translocation in human atrial myocardium, but had no effect in ventricular myocardium. Therapeutic use of GLP-1R-agonists may therefore impart

Glucagon-Like Peptide-1 (GLP-1) Receptor Agonists in the Treatment of Obese Women with Polycystic Ovary Syndrome.

PubMed

Tzotzas, Themistoklis; Karras, Spyridon N; Katsiki, Niki

2017-01-01

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in females and is often associated with a number of cardiometabolic disorders such as central obesity, dyslipidaemia, hypertension, insulin resistance, hyperinsulinaemia, glucose intolerance and type 2 diabetes mellitus (T2DM). Glucagon-like peptide-1 (GLP-1), a gut hormone secreted after a meal, enhances glucosestimulated insulin secretion and additionally suppresses appetite and gastric motility. Most studies found impaired GLP-1 kinetics in obese individuals, whereas small studies in PCOS reported reduced, normal or even elevated GLP-1 levels. Apart from their efficacy in patients with T2DM, some GLP-1 receptor agonists (GLP-1 RAs) have been successfully tested in terms of both efficiency and safety in obese individuals without diabetes and liraglutide 3 mg once daily has been approved as an antiobesity drug in the USA and the European Union. Recently, some small trials of short duration using GLP-1 RAs as monotherapy or combined with metformin in obese PCOS women showed positive results regarding weight reduction and a decrease in testosterone levels but without significant effects on insulin levels, insulin sensitivity and menstrual patterns. Longer term studies with more patients and higher doses of liraglutide (as this drug is already approved for obese individuals) are required to determine the precise indications of GLP-1 RAs in PCOS and to evaluate safety issues. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Glucagon-like peptide-1 binding to rat skeletal muscle.

PubMed

Delgado, E; Luque, M A; Alcántara, A; Trapote, M A; Clemente, F; Galera, C; Valverde, I; Villanueva-Peñacarrillo, M L

1995-01-01

We have found [125I]glucagon-like peptide-1(7-36)-amide-specific binding activity in rat skeletal muscle plasma membranes, with an estimated M(r) of 63,000 by cross-linking and SDS-PAGE. The specific binding was time and membrane protein concentration dependent, and displaceable by unlabeled GLP-1(7-36)-amide with an ID50 of 3 x 10(-9) M of the peptide; GLP-1(1-36)-amide also competed, whereas glucagon and insulin did not. GLP-1(7-36)-amide did not modify the basal adenylate cyclase activity in skeletal muscle plasma membranes. These data, together with our previous finding of a potent glycogenic effect of GLP-1(7-36)-amide in rat soleus muscle, and also in isolated hepatocytes, which was not accompanied by a rise in the cell cyclic AMP content, lead use to believe that the insulin-like effects of this peptide on glucose metabolism in the muscle could be mediated by a type of receptor somehow different to that described for GLP-1 in pancreatic B cells, where GLP-1 action is mediated by the cyclic AMP-adenylate cyclase system.

The pepper GNA-related lectin and PAN domain protein gene, CaGLP1, is required for plant cell death and defense signaling during bacterial infection.

PubMed

Kim, Nak Hyun; Lee, Dong Hyuk; Choi, Du Seok; Hwang, Byung Kook

2015-12-01

Carbohydrate-binding proteins, commonly referred to as lectins or agglutinins, function in defense responses to microbial pathogens. Pepper (Capsicum annuum) GNA-related lectin and PAN-domain protein gene CaGLP1 was isolated and functionally characterized from pepper leaves infected with Xanthomonas campestris pv. vesicatoria (Xcv). CaGLP1 contained an amine-terminus prokaryotic membrane lipoprotein lipid attachment site, a Galanthus nivalis agglutinin (GNA)-related lectin domain responsible for the recognition of high-mannose N-glycans, and a carboxyl-terminus PAN/apple domain. RNA gel blot and immunoblot analyses determined that CaGLP1 was strongly induced in pepper by compatible and incompatible Xcv infection. CaGLP1 protein localized primarily to the plasma membrane and exhibited mannose-binding specificity. CaGLP1-silenced pepper plants were more susceptible to compatible or incompatible Xcv infection compared with that of non-silenced control plants. CaGLP1 silencing in pepper leaves did not accumulate H2O2 and induce cell death during incompatible Xcv infection. Defense-related CaDEF1 (defensin) gene expression was significantly reduced in CaGLP1-silenced pepper plants. CaGLP1-overexpression in Arabidopsis thaliana enhanced resistance to Pseudomonas syringae pv. tomato. Defense-related AtPDF1.2 expression was elevated in CaGLP1-overexpression lines. Together, these results suggest that CaGLP1 is required for plant cell death and defense responses through the reactive oxygen species burst and downstream defense-related gene expression in response to bacterial pathogen challenge. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Effects of a high-protein/low-carbohydrate versus a standard hypocaloric diet on adipocytokine levels and cardiovascular risk factors during 9 months, role of rs6923761 gene variant of glucagon-like peptide 1 receptor.

PubMed

de Luis, D A; Aller, R; Izaola, O; Romero, E

2015-11-01

The role of GLP-1 R variants on body weight response after dietary intervention is unclear. The aim was to investigate the role of this polymorphism on cardiovascular risk factors, adipokine levels and weight loss secondary to a high-protein/low-carbohydrate vs. standard hypocaloric diets during 9 months. 211 obese subjects were randomly allocated to one of these two diets for a period of 9 months; diet HP (high protein/low carbohydrate) and diet S (standard). Ninety-four patients (44.5%) had the genotype GG (wild group) and 117 (55.5%) patients had the next genotypes; GA (89 patients, 42.2%) or AA (28 patients, 13.3%) (mutant group). With both diets and in both genotype groups, body mass index, weight, fat mass, waist circumference and systolic blood pressure decreased. Anthropometric parameters were higher in non-A allele carriers than A allele carriers. With diet HP in both genotypes, LDL cholesterol, total cholesterol, leptin, insulin levels and HOMA-R decreased. With the diet S and only in wild genotype, the same parameters decreased, too. Our data showed a lack of association of rs6923761 GLP-1 R polymorphism with weight loss. Better anthropometric parameters in obese subjects with the mutant allele (A) of rs6923761 GLP-1 R polymorphism were observed. Total cholesterol, LDL cholesterol, insulin levels and HOMA-R decreased in all patients with both diets, although A allele carriers treated with standard diet did not show these changes.

Enteroendocrine-derived glucagon-like peptide-2 controls intestinal amino acid transport.

PubMed

Lee, Jennifer; Koehler, Jacqueline; Yusta, Bernardo; Bahrami, Jasmine; Matthews, Dianne; Rafii, Mahroukh; Pencharz, Paul B; Drucker, Daniel J

2017-03-01

Glucagon-like peptide-2 (GLP-2) is co-secreted with GLP-1 from gut endocrine cells, and both peptides act as growth factors to expand the surface area of the mucosal epithelium. Notably, GLP-2 also enhances glucose and lipid transport in enterocytes; however, its actions on control of amino acid (AA) transport remain unclear. Here we examined the mechanisms linking gain and loss of GLP-2 receptor (GLP-2R) signaling to control of intestinal amino acid absorption in mice. Absorption, transport, and clearance of essential AAs, specifically lysine, were measured in vivo by Liquid Chromatography triple quadrupole Mass Spectrometry (LC-MS/MS) and ex vivo with Ussing chambers using intestinal preparations from Glp2 r +/+ and Glp2r - / - mice. Immunoblotting determined jejunal levels of protein components of signaling pathways (PI3K-AKT, and mTORC1-pS6-p4E-BP1) following administration of GLP-2, protein gavage, and rapamycin to fasted Glp2 r +/+ and Glp2r - / - mice. Expression of AA transporters from full thickness jejunum and 4F2hc from brush border membrane vesicles (BBMVs) was measured by real-time PCR and immunoblotting, respectively. Acute administration of GLP-2 increased basal AA absorption in vivo and augmented basal lysine transport ex vivo . GLP-2-stimulated lysine transport was attenuated by co-incubation with wortmannin, rapamycin, or tetrodotoxin ex vivo . Phosphorylation of mTORC1 effector proteins S6 and 4E-BP1 was significantly increased in wild-type mice in response to GLP-2 alone, or when co-administered with protein gavage, and abolished following oral gavage of rapamycin. In contrast, activation of GLP-1R signaling did not enhance S6 phosphorylation. Disruption of GLP-2 action in Glp2r -/- mice reduced lysine transport ex vivo and attenuated the phosphorylation of S6 and 4E-BP1 in response to oral protein. Moreover, the expression of cationic AA transporter slc7a9 in response to refeeding, and the abundance of 4F2hc in BBMVs following protein

Residues within the Transmembrane Domain of the Glucagon-Like Peptide-1 Receptor Involved in Ligand Binding and Receptor Activation: Modelling the Ligand-Bound Receptor

PubMed Central

Coopman, K.; Wallis, R.; Robb, G.; Brown, A. J. H.; Wilkinson, G. F.; Timms, D.

2011-01-01

The C-terminal regions of glucagon-like peptide-1 (GLP-1) bind to the N terminus of the GLP-1 receptor (GLP-1R), facilitating interaction of the ligand N terminus with the receptor transmembrane domain. In contrast, the agonist exendin-4 relies less on the transmembrane domain, and truncated antagonist analogs (e.g. exendin 9–39) may interact solely with the receptor N terminus. Here we used mutagenesis to explore the role of residues highly conserved in the predicted transmembrane helices of mammalian GLP-1Rs and conserved in family B G protein coupled receptors in ligand binding and GLP-1R activation. By iteration using information from the mutagenesis, along with the available crystal structure of the receptor N terminus and a model of the active opsin transmembrane domain, we developed a structural receptor model with GLP-1 bound and used this to better understand consequences of mutations. Mutation at Y152 [transmembrane helix (TM) 1], R190 (TM2), Y235 (TM3), H363 (TM6), and E364 (TM6) produced similar reductions in affinity for GLP-1 and exendin 9–39. In contrast, other mutations either preferentially [K197 (TM2), Q234 (TM3), and W284 (extracellular loop 2)] or solely [D198 (TM2) and R310 (TM5)] reduced GLP-1 affinity. Reduced agonist affinity was always associated with reduced potency. However, reductions in potency exceeded reductions in agonist affinity for K197A, W284A, and R310A, while H363A was uncoupled from cAMP generation, highlighting critical roles of these residues in translating binding to activation. Data show important roles in ligand binding and receptor activation of conserved residues within the transmembrane domain of the GLP-1R. The receptor structural model provides insight into the roles of these residues. PMID:21868452

Islet-selectivity of G-protein coupled receptor ligands evaluated for PET imaging of pancreatic {beta}-cell mass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cline, Gary W., E-mail: gary.cline@yale.edu; Zhao, Xiaojian; Jakowski, Amy B.

2011-09-02

Highlights: {yields} We screened G-protein coupled receptors for imaging pancreatic. {yields} Database mining and immunohistochemistry identified GPCRs enriched in {beta}-cells. {yields} In vitro and in vivo assays were used to determine exocrine vs endocrine specificity. {yields} GPCR candidates for imaging of {beta}-cell mass are Prokineticin-1R, mGluR5, and GLP-1R. -- Abstract: A critical unmet need exists for methods to quantitatively measure endogenous pancreatic {beta}-cell mass (BCM) for the clinical evaluation of therapies to prevent or reverse loss of BCM and diabetes progression. Our objective was to identify G-protein coupled receptors (GPCRs) that are expressed with a high degree of specificity tomore » islet {beta}-cells for receptor-targeted imaging of BCM. GPCRs enriched in pancreatic islets relative to pancreas acinar and hepatic tissue were identified using a database screen. Islet-specific expression was confirmed by human pancreas immunohistochemistry (IHC). In vitro selectivity assessment was determined from the binding and uptake of radiolabeled ligands to the rat insulinoma INS-1 832/13 cell line and isolated rat islets relative to the exocrine pancreas cell-type, PANC-1. Tail-vein injections of radioligands into rats were used to determine favorable image criteria of in vivo biodistribution to the pancreas relative to other internal organs (i.e., liver, spleen, stomach, and lungs). Database and IHC screening identified four candidate receptors for further in vitro and in vivo evaluation for PET imaging of BCM: prokineticin-1 receptor (PK-1R), metabotropic glutamate receptor type-5 (mGluR5), neuropeptide Y-2 receptor (NPY-2R), and glucagon-like peptide 1 receptor (GLP-1R). In vitro specificity ratios gave the following receptor rank order: PK-1R > GLP-1R > NPY-2R > mGluR5. The biodistribution rank order of selectivity to the pancreas was found to be PK-1R > VMAT2 {approx} GLP-1R > mGluR5. Favorable islet selectivity and biodistribution

Insulin and GLP-1 infusions demonstrate the onset of adipose-specific insulin resistance in a large fasting mammal: potential glucogenic role for GLP-1.

PubMed

Viscarra, Jose A; Rodriguez, Ruben; Vazquez-Medina, Jose Pablo; Lee, Andrew; Tift, Michael S; Tavoni, Stephen K; Crocker, Daniel E; Ortiz, Rudy M

2013-08-01

Prolonged food deprivation increases lipid oxidation and utilization, which may contribute to the onset of the insulin resistance associated with fasting. Because insulin resistance promotes the preservation of glucose and oxidation of fat, it has been suggested to be an adaptive response to food deprivation. However, fasting mammals exhibit hypoinsulinemia, suggesting that the insulin resistance-like conditions they experience may actually result from reduced pancreatic sensitivity to glucose/capacity to secrete insulin. To determine whether fasting results in insulin resistance or in pancreatic dysfunction, we infused early- and late-fasted seals (naturally adapted to prolonged fasting) with insulin (0.065 U/kg), and a separate group of late-fasted seals with low (10 pM/kg) or high (100 pM/kg) dosages of glucagon-like peptide-1 (GLP-1) immediately following a glucose bolus (0.5g/kg), and measured the systemic and cellular responses. Because GLP-1 facilitates glucose-stimulated insulin secretion, these infusions provide a method to assess pancreatic insulin-secreting capacity. Insulin infusions increased the phosphorylation of insulin receptor and Akt in adipose and muscle of early and late fasted seals; however the timing of the signaling response was blunted in adipose of late fasted seals. Despite the dose-dependent increases in insulin and increased glucose clearance (high dose), both GLP-1 dosages produced increases in plasma cortisol and glucagon, which may have contributed to the glucogenic role of GLP-1. Results suggest that fasting induces adipose-specific insulin resistance in elephant seal pups, while maintaining skeletal muscle insulin sensitivity, and therefore suggests that the onset of insulin resistance in fasting mammals is an evolved response to cope with prolonged food deprivation.

GLP-2: A POORLY UNDERSTOOD MEDIATOR ENROLLED IN VARIOUS BARIATRIC/METABOLIC SURGERY-RELATED PATHOPHYSIOLOGIC MECHANISMS.

PubMed

Cazzo, Everton; Gestic, Martinho Antonio; Utrini, Murillo Pimentel; Chaim, Felipe David Mendonça; Geloneze, Bruno; Pareja, José Carlos; Chaim, Elinton Adami; Magro, Daniéla Oliveira

2016-01-01

Glucagon-like peptide-2 (GLP-2) is a gastrointestinal hormone whose effects are predominantly trophic on the intestinal mucosa. Critically evaluate the current literature on the influence of bariatric/metabolic surgery on the levels of GLP-2 and its potential clinical implications. s: Narrative review through online research on the databases Medline and Lilacs. There were six prospective human studies, two cross-sectional human studies, and three experimental animal studies selected. There is evidence demonstrating significant increase in the levels of GLP-2 following gastric bypass, Scopinaro operation, and sleeve gastrectomy. There are no differences between gastric bypass and sleeve gastrectomy in regards to the increase in the GLP-2 levels. There is no correlation between the postoperative levels of GLP-2 and the occurrence of adequate or insufficient postoperative weight loss. GLP-2 plays significant roles on the regulation of nutrient absorption, permeability of gut mucosa, control of bone resorption, and regulation of satiety. The overall impact of these effects potentially exerts a significant adaptive or compensatory effect within the context of varied bariatric surgical techniques. O peptídeo semelhante ao glucagon-2 (GLP-2) é hormônio gastrointestinal com efeitos predominantemente tróficos sobre a mucosa intestinal. Avaliar criticamente a literatura atual a respeito da cirurgia bariátrica/metabólica sobre os níveis de GLP-2 e suas potenciais implicações clínicas. Revisão narrativa realizada através de pesquisa on-line nas bases de dados Medline e LILACS. Foram selecionados seis estudos prospectivos em humanos, dois transversais em humanos e três experimentais em animais. Existem evidências demonstrando aumento significativo nos níveis de GLP-2 após o bypass gástrico, a operação de Scopinaro e a gastrectomia vertical. Não foram observadas diferenças entre o bypass gástrico e a gastrectomia vertical em relação ao aumento do GLP-2

Hindbrain GLP-1 receptor mediation of cisplatin-induced anorexia and nausea.

PubMed

De Jonghe, Bart C; Holland, Ruby A; Olivos, Diana R; Rupprecht, Laura E; Kanoski, Scott E; Hayes, Matthew R

2016-01-01

While chemotherapy-induced nausea and vomiting are clinically controlled in the acute (<24 h) phase following treatment, the anorexia, nausea, fatigue, and other illness-type behaviors during the delayed phase (>24 h) of chemotherapy are largely uncontrolled. As the hindbrain glucagon-like peptide-1 (GLP-1) system contributes to energy balance and mediates aversive and stressful stimuli, here we examine the hypothesis that hindbrain GLP-1 signaling mediates aspects of chemotherapy-induced nausea and reductions in feeding behavior in rats. Specifically, hindbrain GLP-1 receptor (GLP-1R) blockade, via 4th intracerebroventricular (ICV) exendin-(9-39) injections, attenuates the anorexia, body weight reduction, and pica (nausea-induced ingestion of kaolin clay) elicited by cisplatin chemotherapy during the delayed phase (48 h) of chemotherapy-induced nausea. Additionally, the present data provide evidence that the central GLP-1-producing preproglucagon neurons in the nucleus tractus solitarius (NTS) of the caudal brainstem are activated by cisplatin during the delayed phase of chemotherapy-induced nausea, as cisplatin led to a significant increase in c-Fos immunoreactivity in NTS GLP-1-immunoreactive neurons. These data support a growing body of literature suggesting that the central GLP-1 system may be a potential pharmaceutical target for adjunct anti-emetics used to treat the delayed-phase of nausea and emesis, anorexia, and body weight loss that accompany chemotherapy treatments. Copyright © 2015 Elsevier Inc. All rights reserved.

Endogenous GLP-1 as a key self-defense molecule against lipotoxicity in pancreatic islets.

PubMed

Huang, Chenghu; Yuan, Li; Cao, Shuyi

2015-07-01

The number of pro-α cells is known to increase in response to β cell injury and these cells then generate glucagon-like peptide-1 (GLP-1), thus attenuating the development of diabetes. The aim of the present study was to further examine the role and the mechanisms responsible for intra-islet GLP-1 production as a self-protective response against lipotoxicity. The levels of the key enzyme, prohormone convertase 1/3 (PC1/3), as well as the synthesis and release of GLP-1 in models of lipotoxicity were measured. Furthermore, islet viability, apoptosis, oxidative stress and inflammation, as well as islet structure were assessed after altering GLP-1 receptor signaling. Both prolonged exposure to palmitate and a high-fat diet facilitated PC1/3 expression, as well as the synthesis and release of GLP-1 induced by β cell injury and the generation of pro-α cells. Prolonged exposure to palmitate increased reactive oxygen species (ROS) production, and the antioxidant, N-acetylcysteine (NAC), partially prevented the detrimental effects induced by palmitate on β cells, resulting in decreased GLP-1 levels. Furthermore, the inhibition of GLP-1 receptor (GLP-1R) signaling by treatment with exendin‑(9-39) further decreased cell viability, increased cell apoptosis and caused a stronger inhibition of the β cell-specific transcription factor, pancreatic duodenal homeobox 1 (PDX1). Moreover, treatment with the GLP-1R agonist, liraglutide, normalized islet structure and function, resulting in a decrease in cell death and in the amelioration of β cell marker expression. Importantly, liraglutide maintained the oxidative balance and decreased inflammatory factor and p65 expression. Overall, our data demonstrate that an increase in the number of pro-α cells and the activation of the intra-islet GLP-1 system comprise a self-defense mechanism for enhancing β cell survival to combat lipid overload, which is in part mediated by oxidative stress and inflammation.

The GIP receptor displays higher basal activity than the GLP-1 receptor but does not recruit GRK2 or arrestin3 effectively.

PubMed

Al-Sabah, Suleiman; Al-Fulaij, Munya; Shaaban, Ghina; Ahmed, Hanadi A; Mann, Rosalind J; Donnelly, Dan; Bünemann, Moritz; Krasel, Cornelius

2014-01-01

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are important regulators of insulin secretion, and their functional loss is an early characteristic of type 2 diabetes mellitus (T2DM). Pharmacological levels of GLP-1, but not GIP, can overcome this loss. GLP-1 and GIP exert their insulinotropic effects through their respective receptors expressed on pancreatic β-cells. Both the GLP-1 receptor (GLP-1R) and the GIP receptor (GIPR) are members of the secretin family of G protein-coupled receptors (GPCRs) and couple positively to adenylate cyclase. We compared the signalling properties of these two receptors to gain further insight into why GLP-1, but not GIP, remains insulinotropic in T2DM patients. GLP-1R and GIPR were transiently expressed in HEK-293 cells, and basal and ligand-induced cAMP production were investigated using a cAMP-responsive luciferase reporter gene assay. Arrestin3 (Arr3) recruitment to the two receptors was investigated using enzyme fragment complementation, confocal microscopy and fluorescence resonance energy transfer (FRET). GIPR displayed significantly higher (P<0.05) ligand-independent activity than GLP-1R. Arr3 displayed a robust translocation to agonist-stimulated GLP-1R but not to GIPR. These observations were confirmed in FRET experiments, in which GLP-1 stimulated the recruitment of both GPCR kinase 2 (GRK2) and Arr3 to GLP-1R. These interactions were not reversed upon agonist washout. In contrast, GIP did not stimulate recruitment of either GRK2 or Arr3 to its receptor. Interestingly, arrestin remained at the plasma membrane even after prolonged (30 min) stimulation with GLP-1. Although the GLP-1R/arrestin interaction could not be reversed by agonist washout, GLP-1R and arrestin did not co-internalise, suggesting that GLP-1R is a class A receptor with regard to arrestin binding. GIPR displays higher basal activity than GLP-1R but does not effectively recruit GRK2 or Arr3.

Protein kinase G confers survival advantage to Mycobacterium tuberculosis during latency-like conditions.

PubMed

Khan, Mehak Zahoor; Bhaskar, Ashima; Upadhyay, Sandeep; Kumari, Pooja; Rajmani, Raju S; Jain, Preeti; Singh, Amit; Kumar, Dhiraj; Bhavesh, Neel Sarovar; Nandicoori, Vinay Kumar

2017-09-29

Protein kinase G (PknG), a thioredoxin-fold-containing eukaryotic-like serine/threonine protein kinase, is a virulence factor in Mycobacterium tuberculosis , required for inhibition of phagolysosomal fusion. Here, we unraveled novel functional facets of PknG during latency-like conditions. We found that PknG mediates persistence under stressful conditions like hypoxia and abets drug tolerance. PknG mutant displayed minimal growth in nutrient-limited conditions, suggesting its role in modulating cellular metabolism. Intracellular metabolic profiling revealed that PknG is necessary for efficient metabolic adaptation during hypoxia. Notably, the PknG mutant exhibited a reductive shift in mycothiol redox potential and compromised stress response. Exposure to antibiotics and hypoxic environment resulted in higher oxidative shift in mycothiol redox potential of PknG mutant compared with the wild type. Persistence during latency-like conditions required kinase activity and thioredoxin motifs of PknG and is mediated through phosphorylation of a central metabolic regulator GarA. Finally, using a guinea pig model of infection, we assessed the in vivo role of PknG in manifestation of disease pathology and established a role for PknG in the formation of stable granuloma, hallmark structures of latent tuberculosis. Taken together, PknG-mediated GarA phosphorylation is important for maintenance of both mycobacterial physiology and redox poise, an axis that is dispensable for survival under normoxic conditions but is critical for non-replicating persistence of mycobacteria. In conclusion, we propose that PknG probably acts as a modulator of latency-associated signals. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Birth of Archaeal Cells: Molecular Phylogenetic Analyses of G1P Dehydrogenase, G3P Dehydrogenases, and Glycerol Kinase Suggest Derived Features of Archaeal Membranes Having G1P Polar Lipids

PubMed Central

2016-01-01

Bacteria and Eukarya have cell membranes with sn-glycerol-3-phosphate (G3P), whereas archaeal membranes contain sn-glycerol-1-phosphate (G1P). Determining the time at which cells with either G3P-lipid membranes or G1P-lipid membranes appeared is important for understanding the early evolution of terrestrial life. To clarify this issue, we reconstructed molecular phylogenetic trees of G1PDH (G1P dehydrogenase; EgsA/AraM) which is responsible for G1P synthesis and G3PDHs (G3P dehydrogenase; GpsA and GlpA/GlpD) and glycerol kinase (GlpK) which is responsible for G3P synthesis. Together with the distribution of these protein-encoding genes among archaeal and bacterial groups, our phylogenetic analyses suggested that GlpA/GlpD in the Commonote (the last universal common ancestor of all extant life with a cellular form, Commonote commonote) acquired EgsA (G1PDH) from the archaeal common ancestor (Commonote archaea) and acquired GpsA and GlpK from a bacterial common ancestor (Commonote bacteria). In our scenario based on this study, the Commonote probably possessed a G3P-lipid membrane synthesized enzymatically, after which the archaeal lineage acquired G1PDH followed by the replacement of a G3P-lipid membrane with a G1P-lipid membrane. PMID:27774041

GlpR is a direct transcriptional repressor of fructose metabolic genes in Haloferax volcanii.

PubMed

Martin, Jonathan H; Rawls, Katie Sherwood; Chan, Jou Chin; Hwang, Sungmin; Martinez-Pastor, Mar; McMillan, Lana J; Prunetti, Laurence; Schmid, Amy K; Maupin-Furlow, Julie A

2018-06-18

DeoR-type helix-turn-helix (HTH) domain proteins are transcriptional regulators of sugar and nucleoside metabolism in diverse bacteria and occur in select archaea. In the model archaeon Haloferax volcanii , previous work implicated GlpR, a DeoR-type transcriptional regulator, in transcriptional repression of glpR and the gene encoding the fructose-specific phosphofructokinase ( pfkB ) during growth on glycerol. However, the global regulon governed by GlpR remained unclear. Here we compared transcriptomes of wild type and Δ glpR mutant strains grown on glycerol and glucose to detect significant transcript level differences for nearly 50 new genes regulated by GlpR. By coupling computational prediction of GlpR binding sequences with in vivo and in vitro DNA binding experiments, we determined that GlpR directly controls genes encoding enzymes in fructose degradation, including fructose bisphosphate aldolase, a central control point in glycolysis. GlpR also directly controls other transcription factors. In contrast, other metabolic pathways appear to be under indirect influence of GlpR. In vitro experiments demonstrated that GlpR purifies as a tetramer that binds the effector molecule fructose-1-phosphate (F1P). These results suggest that Hfx. volcanii GlpR functions as a direct negative regulator of fructose degradation during growth on carbon sources other than fructose, such as glucose and glycerol, and that GlpR bears striking functional similarity to bacterial DeoR-type regulators. IMPORTANCE Many archaea are extremophiles, able to thrive in habitats of extreme salinity, pH and temperature. These biological properties are ideal for applications in biotechnology. However, limited knowledge of archaeal metabolism is a bottleneck that prevents broad use of archaea as microbial factories for industrial products. Here we characterize how sugar uptake and use is regulated in a species that lives in high salinity. We demonstrate that a key sugar regulatory protein in

Oxyntomodulin differentially affects glucagon-like peptide-1 receptor beta-arrestin recruitment and signaling through Galpha(s).

PubMed

Jorgensen, Rasmus; Kubale, Valentina; Vrecl, Milka; Schwartz, Thue W; Elling, Christian E

2007-07-01

The glucagon-like peptide (GLP)-1 receptor is a promising target for the treatment of type 2 diabetes and obesity, and there is great interest in characterizing the pharmacology of the GLP-1 receptor and its ligands. In the present report, we have applied bioluminescence resonance energy transfer assays to measure agonist-induced recruitment of betaarrestins and G-protein-coupled receptor kinase (GRK) 2 to the GLP-1 receptor in addition to traditional measurements of second messenger generation. The peptide hormone oxyntomodulin is described in the literature as a full agonist on the glucagon and GLP-1 receptors. Surprisingly, despite being full agonists in GLP-1 receptor-mediated cAMP accumulation, oxyntomodulin and glucagon were observed to be partial agonists in recruiting betaarrestins and GRK2 to the GLP-1 receptor. We suggest that oxyntomodulin and glucagon are biased ligands on the GLP-1 receptor.

cAMP-secretion coupling is impaired in diabetic GK/Par rat β-cells: a defect counteracted by GLP-1.

PubMed

Dolz, Manuel; Movassat, Jamileh; Bailbé, Danielle; Le Stunff, Hervé; Giroix, Marie-Hélène; Fradet, Magali; Kergoat, Micheline; Portha, Bernard

2011-11-01

cAMP-raising agents with glucagon-like peptide-1 (GLP-1) as the first in class, exhibit multiple actions that are beneficial for the treatment of type 2 diabetic (T2D) patients, including improvement of glucose-induced insulin secretion (GIIS). To gain additional insight into the role of cAMP in the disturbed stimulus-secretion coupling within the diabetic β-cell, we examined more thoroughly the relationship between changes in islet cAMP concentration and insulin release in the GK/Par rat model of T2D. Basal cAMP content in GK/Par islets was significantly higher, whereas their basal insulin release was not significantly different from that of Wistar (W) islets. Even in the presence of IBMX or GLP-1, their insulin release did not significantly change despite further enhanced cAMP accumulation in both cases. The high basal cAMP level most likely reflects an increased cAMP generation in GK/Par compared with W islets since 1) forskolin dose-dependently induced an exaggerated cAMP accumulation; 2) adenylyl cyclase (AC)2, AC3, and G(s)α proteins were overexpressed; 3) IBMX-activated cAMP accumulation was less efficient and PDE-3B and PDE-1C mRNA were decreased. Moreover, the GK/Par insulin release apparatus appears less sensitive to cAMP, since GK/Par islets released less insulin at submaximal cAMP levels and required five times more cAMP to reach a maximal secretion rate no longer different from W. GLP-1 was able to reactivate GK/Par insulin secretion so that GIIS became indistinguishable from that of W. The exaggerated cAMP production is instrumental, since GLP-1-induced GIIS reactivation was lost in the presence the AC blocker 2',5'-dideoxyadenosine. This GLP-1 effect takes place in the absence of any improvement of the [Ca(2+)](i) response and correlates with activation of the cAMP-dependent PKA-dependent pathway.

The Aversive Agent Lithium Chloride Suppresses Phasic Dopamine Release Through Central GLP-1 Receptors.

PubMed

Fortin, Samantha M; Chartoff, Elena H; Roitman, Mitchell F

2016-02-01

Unconditioned rewarding stimuli evoke phasic increases in dopamine concentration in the nucleus accumbens (NAc) while discrete aversive stimuli elicit pauses in dopamine neuron firing and reductions in NAc dopamine concentration. The unconditioned effects of more prolonged aversive states on dopamine release dynamics are not well understood and are investigated here using the malaise-inducing agent lithium chloride (LiCl). We used fast-scan cyclic voltammetry to measure phasic increases in NAc dopamine resulting from electrical stimulation of dopamine cell bodies in the ventral tegmental area (VTA). Systemic LiCl injection reduced electrically evoked dopamine release in the NAc of both anesthetized and awake rats. As some behavioral effects of LiCl appear to be mediated through glucagon-like peptide-1 receptor (GLP-1R) activation, we hypothesized that the suppression of phasic dopamine by LiCl is GLP-1R dependent. Indeed, peripheral pretreatment with the GLP-1R antagonist exendin-9 (Ex-9) potently attenuated the LiCl-induced suppression of dopamine. Pretreatment with Ex-9 did not, however, affect the suppression of phasic dopamine release by the kappa-opioid receptor agonist, salvinorin A, supporting a selective effect of GLP-1R stimulation in LiCl-induced dopamine suppression. By delivering Ex-9 to either the lateral or fourth ventricle, we highlight a population of central GLP-1 receptors rostral to the hindbrain that are involved in the LiCl-mediated suppression of NAc dopamine release.

Effect of oral contraceptives and/or metformin on GLP-1 secretion and reactive hypoglycaemia in polycystic ovary syndrome.

PubMed

Glintborg, Dorte; Mumm, Hanne; Holst, Jens Juul; Andersen, Marianne

2017-05-01

Insulin resistance in polycystic ovary syndrome (PCOS) may increase the risk of reactive hypoglycaemia (RH) and decrease glucagon-like peptide-1 (GLP-1) secretion. The possible effects of treatment with oral contraceptives (OCP) and/or metformin on GLP-1 secretion and risk of RH in PCOS is undetermined. Outpatient clinic. Randomized, controlled clinical trial. Ninety women with PCOS were randomized to 12-month treatment with OCP (150 mg desogestrel + 30 mg ethinylestradiol), metformin (2 g/day) or metformin + OCP. Five-hour oral glucose tolerance tests (5-h OGTT) measuring fasting and area under the curve (AUC) for GLP-1, glucose, insulin and C-peptide were performed before and after the intervention period. Sixty-five women completed the study and 34 weight-matched healthy women were included as controls. Changes in GLP-1, glucose, insulin and C-peptide during 5-h OGTT. Fasting GLP-1 levels increased during metformin + OCP vs OCP treatment, whereas AUC GLP-1 levels were unchanged during medical treatment. The prevalence of reactive hypoglycemia increased from 9/65 to 14/65 after intervention ( P  < 0.01) and was more common after treatment with metformin + OCP (increase from 3/23 to 6/23, P  = 0.01). Reactive hypoglycaemia was associated with higher insulin and C-peptide levels during 5-h OGTT, but was unassociated with BMI and AUC GLP-1. GLP-1 levels were comparable in PCOS vs controls. AUC GLP-1 levels were significantly lower in obese vs lean patients and were inversely associated with BMI. AUC GLP-1 levels were unchanged during treatment. Increased risk of hypoglycemia during metformin + OCP could be associated with increased insulin secretion. © 2017 The authors.

Improvement of L-phenylalanine production from glycerol by recombinant Escherichia coli strains: the role of extra copies of glpK, glpX, and tktA genes.

PubMed

Gottlieb, Katrin; Albermann, Christoph; Sprenger, Georg A

2014-07-11

For the production of L-phenylalanine (L-Phe), two molecules of phosphoenolpyruvate (PEP) and one molecule erythrose-4-phosphate (E4P) are necessary. PEP stems from glycolysis whereas E4P is formed in the pentose phosphate pathway (PPP). Glucose, commonly used for L-Phe production with recombinant E. coli, is taken up via the PEP-dependent phosphotransferase system which delivers glucose-6-phosphate (G6P). G6P enters either glycolysis or the PPP. In contrast, glycerol is phosphorylated by an ATP-dependent glycerol kinase (GlpK) thus saving one PEP. However, two gluconeogenic reactions (fructose-1,6-bisphosphate aldolase, fructose-1,6-bisphosphatase, FBPase) are necessary for growth and provision of E4P. Glycerol has become an important carbon source for biotechnology and reports on production of L-Phe from glycerol are available. However, the influence of FBPase and transketolase reactions on L-Phe production has not been reported. L-Phe productivity of parent strain FUS4/pF81 (plasmid-encoded genes for aroF, aroB, aroL, pheA) was compared on glucose and glycerol as C sources. On glucose, a maximal carbon recovery of 0.19 mM C(Phe)/C(Glucose) and a maximal space-time-yield (STY) of 0.13 g l(-1) h(-1) was found. With glycerol, the maximal carbon recovery was nearly the same (0.18 mM C(Phe)/C(Glycerol)), but the maximal STY was higher (0.21 g l(-1) h(-1)). We raised the chromosomal gene copy number of the genes glpK (encoding glycerol kinase), tktA (encoding transketolase), and glpX (encoding fructose-1,6-bisphosphatase) individually. Overexpression of glpK (or its feedback-resistant variant, glpK(G232D)) had little effect on growth rate; L-Phe production was about 30% lower than in FUS4/pF81. Whereas the overexpression of either glpX or tktA had minor effects on productivity (0.20 mM C(Phe)/C(Glycerol); 0.25 g l(-1) h(-1) and 0.21 mM C(Phe)/C(Glycerol); 0.23 g l(-1) h(-1), respectively), the combination of extra genes of glpX and tktA together led to an increase in

A Human Glucagon-Like Peptide-1-albumin Recombinant Protein with Prolonged Hypoglycemic Effect Provides Efficient and Beneficial Control of Glucose Metabolism in Diabetic Mice.

PubMed

Li, Caina; Yang, Miaomiao; Hou, Guojiang; Liu, Shuainan; Huan, Yi; Yu, Dongan; Sun, Sujuan; Liu, Quan; Yan, Shousheng; Shen, Zhufang

2017-09-01

GW002 is a recombinant protein engineered by fusing the C-terminal region of human glucagon-like peptide-1 (GLP-1) to the N-terminal region of human serum albumin (HSA) with a peptide linker. This study aims to evaluate its anti-diabetic effects both in vitro and in vivo. The GLP-1 receptor-dependent luciferase reporter plasmid was transiently transfected in NIT-1 cells to calculate the half-maximal concentration (EC 50 ) for GLP-1 receptor activation, and normal ICR mice and diabetic KKAy mice were acutely injected with GW002 (1, 3, 9 mg/kg) subcutaneously to evaluate the hypoglycemic action, while the diabetic KKAy and db/db mice were treated with GW002 once daily for 7 weeks to evaluate the effects on glucose metabolism. The results showed that GW002 activated GLP-1 receptor in NIT-1 cells with higher EC 50 versus exendin-4 (46.7 vs. 7.89 nM), and single subcutaneous injection of GW002 at doses of 1, 3 and 9 mg/kg efficiently restrained the glycemia variation after oral glucose loading in ICR mice for at least 4 d, as well as reducing the non-fasting blood glucose in KKAy mice for about 2 d, while repeated injections of GW002 significantly improved abnormal glycaemia, hemoglobin (Hb)A1c levels, oral glucose intolerance and β-cell function in diabetic db/db mice. These results suggested that GW002 showed prolonged hypoglycemic action by activating its cognate receptor and provided efficient control of glucose metabolism. Thus GW002 may be a potential treatment for the management of type 2 diabetes.

GLP-1 response to a mixed meal: what happens 10 years after Roux-en-Y gastric bypass (RYGB)?

PubMed

Dar, Moahad S; Chapman, William H; Pender, John R; Drake, Almond J; O'Brien, Kevin; Tanenberg, Robert J; Dohm, G Lynis; Pories, Walter J

2012-07-01

Oral meal consumption increases glucagon-like peptide 1 (GLP-1) release which maintains euglycemia by increasing insulin secretion. This effect is exaggerated during short-term follow-up of Roux-en-y gastric bypass (RYGB). We examined the durability of this effect in patient with type 2 diabetes (T2DM) >10 years after RYGB. GLP-1 response to a mixed meal in the 10-year post-RYGB group (n = 5) was compared to lean (n = 9), obese (n = 6), and type 2 diabetic (n = 10) controls using a cross-sectional study design. Analysis of variance (ANOVA) was used to evaluate GLP-1 response to mixed meal consumption from 0 to 300 min, 0-20 min, 20-60 min, and 60-300 min, respectively. Weight, insulin resistance, and T2DM were also assessed. GLP-1 response 0-300 min in the 10-year post-RYGB showed a statistically significant overall difference (p =  0.01) compared to controls. Furthermore, GLP-1 response 0-20 min in the 10-year post-RYGB group showed a very rapid statistically significant rise (p = 0.035) to a peak of 40 pM. GLP-1 response between 20 and 60 min showed a rapid statistically significant (p = 0.041) decline in GLP-1 response from ~40 pM to 10 pM. GLP-1 response in the 10-year post-RYGB group from 60 to 300 min showed no statistically significant difference from controls. BMI, HOMA, and fasting serum glucose before and >10 years after RYGB changed from 59.9 → 40.4, 8.7 → 0.88, and 155.2 → 87.6 mg/dl, respectively, and were statistically significant (p < 0.05). An exaggerated GLP-1 response was noted 10 years after RYGB, strongly suggesting a durability of this effect. This phenomenon may play a key role in maintaining type 2 diabetes remission and weight loss after RYGB.

[Glucagon-like peptide 2, a neurotransmitter with a newly discovered role in the regulation of food ingestion].

PubMed

Tang-Christensen, M; Larsen, P J; Thulesen, J; Nielsen, J R; Vrang, N

2001-01-15

We report here that glucagon-like peptide 2(GLP-2) and its receptor constitute a distinct projection system connecting the nucleus of the solitary tract with the dorsomedial hypothalamic nucleus (DMH). The DMH contains a dense plexus of GLP-2 immunoreactive fibres and is the only hypothalamic nucleus expressing GLP-2 receptor mRNA. Consistent with this, central application of GLP-2 activates the expression of neurones solely in the DMH. Furthermore, central administration of GLP-2 causes a dose-related, a pharmacologically and behaviourally specific inhibition of food intake in rats. Surprisingly, the alleged GLP-1 receptor antagonist, Exending (9-39), proved a functional antagonist of centrally applied GLP-2. These data implicate GLP-2 as an important neurotransmitter in the regulation of food intake and likely bodyweight. Our data therefore point to the DMH as a crossroad for endocrine and visceral information affecting feeding behaviour.

Characterization of glucagon-like peptide-1 receptor-binding determinants.

PubMed

Xiao, Q; Jeng, W; Wheeler, M B

2000-12-01

Glucagon-like peptide 1 (GLP-1) is a potent insulinotropic hormone currently under study as a therapeutic agent for type 2 diabetes. Since an understanding of the molecular mechanisms leading to high-affinity receptor (R) binding and activation may facilitate the development of more potent GLP-1R agonists, we have localized specific regions of GLP-1R required for binding. The purified N-terminal fragment (hereafter referred to as NT) of the GLP-1R produced in either insect (Sf9) or mammalian (COS-7) cells was shown to bind GLP-1. The physical interaction of NT with GLP-1 was first demonstrated by cross-linking ((125)I-GLP-1/NT complex band at approximately 28 kDa) and secondly by attachment to Ni(2+)-NTA beads. The GLP-1R NT protein attached to beads bound GLP-1, but with lower affinity (inhibitory concentration (IC(50)): 4.5 x 10(-7) M) than wild-type (WT) GLP-1R (IC(50): 5.2 x 10(-9)M). The low affinity of GLP-1R NT suggested that other receptor domains may contribute to GLP-1 binding. This was supported by studies using chimeric glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptors. GIP(1-151)/GLP-1R, but not GIP(1-222)/GLP-1R, exhibited specific GLP-1 binding and GLP-1-induced cAMP production, suggesting that the region encompassing transmembrane (TM) domain 1 through to TM3 was required for binding. Since it was hypothesized that certain charged or polar amino acids in this region might be involved in binding, these residues (TM2-TM3) were analyzed by substitution mutagenesis. Five mutants (K197A, D198A, K202A, D215A, R227A) displayed remarkably reduced binding affinity. These studies indicate that the NT domain of the GLP-1R is able to bind GLP-1, but charged residues concentrated at the distal TM2/extracellular loop-1 (EC1) interface (K197, D198, K202) and in EC1 (D215 and R227) probably contribute to the binding determinants of the GLP-1R.

β cell membrane remodelling and procoagulant events occur in inflammation-driven insulin impairment: a GLP-1 receptor dependent and independent control.

PubMed

Gleizes, Céline; Kreutter, Guillaume; Abbas, Malak; Kassem, Mohamad; Constantinescu, Andrei Alexandru; Boisramé-Helms, Julie; Yver, Blandine; Toti, Florence; Kessler, Laurence

2016-02-01

Inflammation and hyperglycaemia are associated with a prothrombotic state. Cell-derived microparticles (MPs) are the conveyors of active procoagulant tissue factor (TF) and circulate at high concentration in diabetic patients. Liraglutide, a glucagon-like peptide (GLP)-1 analogue, is known to promote insulin secretion and β-cell preservation. In this in vitro study, we examined the link between insulin impairment, procoagulant activity and plasma membrane remodelling, under inflammatory conditions. Rin-m5f β-cell function, TF activity mediated by MPs and their modulation by 1 μM liraglutide were examined in a cell cross-talk model. Methyl-β-cyclodextrine (MCD), a cholesterol depletor, was used to evaluate the involvement of raft on TF activity, MP shedding and insulin secretion as well as Soluble N-éthylmaleimide-sensitive-factor Attachment protein Receptor (SNARE)-dependent exocytosis. Cytokines induced a two-fold increase in TF activity at MP surface that was counteracted by liraglutide. Microparticles prompted TF activity on the target cells and a two-fold decrease in insulin secretion via protein kinase A (PKA) and p38 signalling, that was also abolished by liraglutide. Large lipid raft clusters were formed in response to cytokines and liraglutide or MCD-treated cells showed similar patterns. Cells pre-treated by saturating concentration of the GLP-1r antagonist exendin (9-39), showed a partial abolishment of the liraglutide-driven insulin secretion and liraglutide-decreased TF activity. Measurement of caspase 3 cleavage and MP shedding confirmed the contribution of GLP-1r-dependent and -independent pathways. Our results confirm an integrative β-cell response to GLP-1 that targets receptor-mediated signalling and membrane remodelling pointing at the coupling of insulin secretion and inflammation-driven procoagulant events. © 2015 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and

Individually timing high-protein preloads has no effect on daily energy intake, peptide YY and glucagon-like peptide-1.

PubMed

Willbond, S M; Doucet, É

2011-01-01

Gut hormones have been shown to influence energy intake (EI). To our knowledge, no study has investigated the effects of dietary patterns aimed at optimizing fullness on EI, appetite and gut hormones. To determine whether individually timing high-protein preloads would impact EI, appetite, and peptide YY and glucagon-like peptide-1 (GLP-1) levels. Ten men (body mass index = 25.5 ± 2.6 kg/m(2)) participated in a randomized crossover trial. The three conditions consisted of the self-selection of snacks (condition 1), or the consumption of a preload (300 kcal: 40% protein, 40% carbohydrates and 20% fat) at either 15 min (condition 2) or ∼ 50 min (individually set) (condition 3) before lunch and dinner. During each condition, a standardized breakfast was served, whereas lunch and dinner were self-selected from a five-item menu, and eaten ad libitum. Mealtime and daily EI were measured. Appetite, peptide YY and GLP-1 were sampled over 9 h. No differences in daily EI were noted across conditions (1 = 3078 ± 720 kcal; 2 = 2929 ± 264 kcal; 3 = 2998 ± 437 kcal; not significant). For the most part, daily profiles as well as premeal levels of peptide YY and GLP-1 were not different between conditions. Desire to eat, hunger and prospective food consumption were found to be lowest during condition 1 (P < 0.05). According to these results, it would seem that individually timing high-protein preloads does not reduce daily EI in healthy human subjects.

Recent Advances in GLP-1 Receptor Agonists for Use in Diabetes Mellitus.

PubMed

McBrayer, Dominic N; Tal-Gan, Yftah

2017-09-01

Preclinical Research Mimetics of Glucagon-like peptide 1 (GLP-1) represent a useful alternative or complementary treatment choice to insulin in the treatment of diabetes mellitus. The lack of hypoglycemia as a side effect when GLP-1 receptor agonists are used along with the tendency of these therapeutic agents to prevent or even reduce weight gain makes them valuable targets in therapy development. However, native GLP-1 and many of its early analogues have very short half-lives, requiring repeated treatment to maintain therapeutic levels. As all current treatments are injected subcutaneously, a large focus has been made on trying to extend the half-lives of GLP-1 analogues while retaining bioactivity. Most success in this regard has been achieved with the use of peptide-protein fusions, which are not as well suited for oral administration. However, recent work focused on the development of non-fusion peptides with increased half-lives that may be more appropriate for oral administration. This minireview discusses the structural characteristics of past and present analogues as well as the recent work conducted toward developing novel GLP-1 receptor agonists. Drug Dev Res 78 : 292-299, 2017. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Improvement of L-phenylalanine production from glycerol by recombinant Escherichia coli strains: The role of extra copies of glpK, glpX, and tktA genes

PubMed Central

2014-01-01

Background For the production of L-phenylalanine (L-Phe), two molecules of phosphoenolpyruvate (PEP) and one molecule erythrose-4-phosphate (E4P) are necessary. PEP stems from glycolysis whereas E4P is formed in the pentose phosphate pathway (PPP). Glucose, commonly used for L-Phe production with recombinant E. coli, is taken up via the PEP-dependent phosphotransferase system which delivers glucose-6-phosphate (G6P). G6P enters either glycolysis or the PPP. In contrast, glycerol is phosphorylated by an ATP-dependent glycerol kinase (GlpK) thus saving one PEP. However, two gluconeogenic reactions (fructose-1,6-bisphosphate aldolase, fructose-1,6-bisphosphatase, FBPase) are necessary for growth and provision of E4P. Glycerol has become an important carbon source for biotechnology and reports on production of L-Phe from glycerol are available. However, the influence of FBPase and transketolase reactions on L-Phe production has not been reported. Results L-Phe productivity of parent strain FUS4/pF81 (plasmid-encoded genes for aroF, aroB, aroL, pheA) was compared on glucose and glycerol as C sources. On glucose, a maximal carbon recovery of 0.19 mM CPhe/CGlucose and a maximal space-time-yield (STY) of 0.13 g l−1 h−1 was found. With glycerol, the maximal carbon recovery was nearly the same (0.18 mM CPhe/CGlycerol), but the maximal STY was higher (0.21 g l−1 h−1). We raised the chromosomal gene copy number of the genes glpK (encoding glycerol kinase), tktA (encoding transketolase), and glpX (encoding fructose-1,6-bisphosphatase) individually. Overexpression of glpK (or its feedback-resistant variant, glpKG232D) had little effect on growth rate; L-Phe production was about 30% lower than in FUS4/pF81. Whereas the overexpression of either glpX or tktA had minor effects on productivity (0.20 mM CPhe/CGlycerol; 0.25 g l−1 h−1 and 0.21 mM CPhe/CGlycerol; 0.23 g l−1 h−1, respectively), the combination of extra genes of glpX and tktA together led

Eukaryotic major facilitator superfamily transporter modeling based on the prokaryotic GlpT crystal structure.

PubMed

Lemieux, M Joanne

2007-01-01

The major facilitator superfamily (MFS) of transporters represents the largest family of secondary active transporters and has a diverse range of substrates. With structural information for four MFS transporters, we can see a strong structural commonality suggesting, as predicted, a common architecture for MFS transporters. The rate for crystal structure determination of MFS transporters is slow, making modeling of both prokaryotic and eukaryotic transporters more enticing. In this review, models of eukaryotic transporters Glut1, G6PT, OCT1, OCT2 and Pho84, based on the crystal structures of the prokaryotic GlpT, based on the crystal structure of LacY are discussed. The techniques used to generate the different models are compared. In addition, the validity of these models and the strategy of using prokaryotic crystal structures to model eukaryotic proteins are discussed. For comparison, E. coli GlpT was modeled based on the E. coli LacY structure and compared to the crystal structure of GlpT demonstrating that experimental evidence is essential for accurate modeling of membrane proteins.

Ingestion of diet soda before a glucose load augments glucagon-like peptide-1 secretion.

PubMed

Brown, Rebecca J; Walter, Mary; Rother, Kristina I

2009-12-01

The goal of this study was to determine the effect of artificial sweeteners on glucose, insulin, and glucagon-like peptide (GLP)-1 in humans. For this study, 22 healthy volunteers (mean age 18.5 +/- 4.2 years) underwent two 75-g oral glucose tolerance tests with frequent measurements of glucose, insulin, and GLP-1 for 180 min. Subjects drank 240 ml of diet soda or carbonated water, in randomized order, 10 min prior to the glucose load. Glucose excursions were similar after ingestion of carbonated water and diet soda. Serum insulin levels tended to be higher after diet soda, without statistical significance. GLP-1 peak and area under the curve (AUC) were significantly higher with diet soda (AUC 24.0 +/- 15.2 pmol/l per 180 min) versus carbonated water (AUC 16.2 +/- 9.0 pmol/l per 180 min; P = 0.003). Artificial sweeteners synergize with glucose to enhance GLP-1 release in humans. This increase in GLP-1 secretion may be mediated via stimulation of sweet-taste receptors on L-cells by artificial sweetener.

First cytoplasmic loop of glucagon-like peptide-1 receptor can function at the third cytoplasmic loop position of rhodopsin.

PubMed

Yamashita, Takahiro; Tose, Koji; Shichida, Yoshinori

2008-01-01

G protein-coupled receptors (GPCRs) are classified into several families based on their amino acid sequences. In family 1, GPCRs such as rhodopsin and adrenergic receptor, the structure-function relationship has been extensively investigated to demonstrate that exposure of the third cytoplasmic loop is essential for selective G protein activation. In contrast, much less is known about other families. Here we prepared chimeric mutants between Gt-coupled rhodopsin and Gi/Go- and Gs-coupled glucagon-like peptide-1 (GLP-1) receptor of family 2 and tried to identify the loop region that functions at the third cytoplasmic loop position of rhodopsin. We succeeded in expressing a mutant having the first cytoplasmic loop of GLP-1 receptor and found that this mutant activated Gi and Go efficiently but did not activate Gt. Moreover, the rhodopsin mutant having the first loop of Gs-coupled secretin receptor of family 2 decreased the Gi and Go activation efficiencies. Therefore, the first loop of GLP-1 receptor would share a similar role to the third loop of rhodopsin in G protein activation. This result strongly suggested that different families of GPCRs have maintained molecular architectures of their ancestral types to generate a common mechanism, namely exposure of the cytoplasmic loop, to activate peripheral G protein.

Quantification of the Contribution of GLP-1 to Mediating Insulinotropic Effects of DPP-4 Inhibition With Vildagliptin in Healthy Subjects and Patients With Type 2 Diabetes Using Exendin [9-39] as a GLP-1 Receptor Antagonist.

PubMed

Nauck, Michael A; Kind, Joachim; Köthe, Lars D; Holst, Jens J; Deacon, Carolyn F; Broschag, Matthias; He, Yan Ling; Kjems, Lise; Foley, James

2016-08-01

We quantified the contribution of GLP-1 as a mediator of the therapeutic effects of dipeptidyl peptidase 4 (DPP-4) inhibition (vildagliptin) by using the GLP-1 receptor antagonist exendin [9-39] in patients with type 2 diabetes and in healthy subjects. Thirty-two patients with type 2 diabetes and 29 age- and weight-matched healthy control subjects were treated in randomized order with 100 mg once daily vildagliptin or placebo for 10 days. Meal tests were performed (days 9 and 10) without and with a high-dose intravenous infusion of exendin [9-39]. The main end point was the ratio of the areas under the curve (AUCs) of integrated insulin secretion rates (total AUCISR) and glucose (total AUCglucose) over 4 h after the meal. Vildagliptin treatment more than doubled responses of intact GLP-1 and glucose-dependent insulinotropic polypeptide and lowered glucose responses without changing AUCISR/AUCglucose in healthy subjects. Vildagliptin significantly increased this ratio by 10.5% in patients with type 2 diabetes, and exendin [9-39] reduced it (both P < 0.0001). The percentage reduction in the AUCISR/AUCglucose ratio achieved with exendin [9-39] was significantly smaller after vildagliptin treatment than after placebo treatment (P = 0.026) and was equivalent to 47 ± 5% of the increments due to vildagliptin. Thus, other mediators appear to contribute significantly to the therapeutic effects of DPP-4 inhibition. © 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.

Trichoderma G protein-coupled receptors: functional characterisation of a cAMP receptor-like protein from Trichoderma atroviride.

PubMed

Brunner, Kurt; Omann, Markus; Pucher, Marion E; Delic, Marizela; Lehner, Sylvia M; Domnanich, Patrick; Kratochwill, Klaus; Druzhinina, Irina; Denk, Dagmar; Zeilinger, Susanne

2008-12-01

Galpha subunits act to regulate vegetative growth, conidiation, and the mycoparasitic response in Trichoderma atroviride. To extend our knowledge on G protein signalling, we analysed G protein-coupled receptors (GPCRs). As the genome sequence of T. atroviride is not publicly available yet, we carried out an in silico exploration of the genome database of the close relative T. reesei. Twenty genes encoding putative GPCRs distributed over eight classes and additional 35 proteins similar to the Magnaporthe grisea PTH11 receptor were identified. Subsequently, four T. atroviride GPCR-encoding genes were isolated and affiliated to the cAMP receptor-like family by phylogenetic and topological analyses. All four genes showed lowest expression on glycerol and highest mRNA levels upon carbon starvation. Transcription of gpr3 and gpr4 responded to exogenously added cAMP and the shift from liquid to solid media. gpr3 mRNA levels also responded to the presence of fungal hyphae or cellulose membranes. Further characterisation of mutants bearing a gpr1-silencing construct revealed that Gpr1 is essential for vegetative growth, conidiation and conidial germination. Four genes encoding the first GPCRs described in Trichoderma were isolated and their expression characterized. At least one of these GPCRs is important for several cellular processes, supporting the fundamental role of G protein signalling in this fungus.

GLP-1 secretion is stimulated by 1,10-phenanthroline via colocalized T2R5 signal transduction in human enteroendocrine L cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jiyoung; Kim, Ki-Suk; Kim, Kang-Hoon

Glucagon-like peptide-1 (GLP-1) hormone is known to regulate blood glucose by an insulinotropic effect and increases proliferation as and also prevents apoptosis of pancreatic β cells. We know that GLP-1 is secreted by nutrients such as fatty acids and sweet compounds but also bitter compounds via stimulation of G-protein coupled receptors (GPCRs) in the gut. Among these, bitter compounds are multiply-contained in phytochemicals or artificial materials and perceived as ligands of various bitter taste receptors. We hypothesized that GLP-1 hormone is secreted through stimulation of a single bitter taste receptor by 1,10-phenanthroline which is known agonist of taste receptor typemore » 2 member 5 (T2R5). To prove this hypothesis, we used the representatively well-known 1,10-phenanthroline as ligand of single receptor and evaluated the existence of T2R5 by double-labeling immunofluorescence and then 1,10-phenanthroline is able to secrete GLP-1 hormone through stimulation of T2R5 in human enteroendocrine cells. Consequently, we verify that GLP-1 hormone is colocalized with T2R5 in the human duodenum and ileum tissue and is secreted by 1,10-phenanthroline via T2R5 signal transduction in differentiated human enteroendocrine L cells. - Highlights: • Taste receptor type 2 member 5 (T2R5) is colocalized with GLP-1 hormone in human enteroendocrine cells. • GLP-1 secretion is stimulated by 1,10-phenanthroline via stimulation of T2R5. • Inhibition of the bitter taste pathway reduce GLP-1 secretion.« less

Activation of GLP-1 receptors on vascular smooth muscle cells reduces the autoregulatory response in afferent arterioles and increases renal blood flow.

PubMed

Jensen, Elisa P; Poulsen, Steen S; Kissow, Hannelouise; Holstein-Rathlou, Niels-Henrik; Deacon, Carolyn F; Jensen, Boye L; Holst, Jens J; Sorensen, Charlotte M

2015-04-15

Glucagon-like peptide (GLP)-1 has a range of extrapancreatic effects, including renal effects. The mechanisms are poorly understood, but GLP-1 receptors have been identified in the kidney. However, the exact cellular localization of the renal receptors is poorly described. The aim of the present study was to localize renal GLP-1 receptors and describe GLP-1-mediated effects on the renal vasculature. We hypothesized that renal GLP-1 receptors are located in the renal microcirculation and that activation of these affects renal autoregulation and increases renal blood flow. In vivo autoradiography using (125)I-labeled GLP-1, (125)I-labeled exendin-4 (GLP-1 analog), and (125)I-labeled exendin 9-39 (GLP-1 receptor antagonist) was performed in rodents to localize specific GLP-1 receptor binding. GLP-1-mediated effects on blood pressure, renal blood flow (RBF), heart rate, renin secretion, urinary flow rate, and Na(+) and K(+) excretion were investigated in anesthetized rats. Effects of GLP-1 on afferent arterioles were investigated in isolated mouse kidneys. Specific binding of (125)I-labeled GLP-1, (125)I-labeled exendin-4, and (125)I-labeled exendin 9-39 was observed in the renal vasculature, including afferent arterioles. Infusion of GLP-1 increased blood pressure, RBF, and urinary flow rate significantly in rats. Heart rate and plasma renin concentrations were unchanged. Exendin 9-39 inhibited the increase in RBF. In isolated murine kidneys, GLP-1 and exendin-4 significantly reduced the autoregulatory response of afferent arterioles in response to stepwise increases in pressure. We conclude that GLP-1 receptors are located in the renal vasculature, including afferent arterioles. Activation of these receptors reduces the autoregulatory response of afferent arterioles to acute pressure increases and increases RBF in normotensive rats. Copyright © 2015 the American Physiological Society.

Enteral nutrients potentiate glucagon-like peptide-2 action and reduce dependence on parenteral nutrition in a rat model of human intestinal failure

PubMed Central

Brinkman, Adam S.; Murali, Sangita G.; Hitt, Stacy; Solverson, Patrick M.; Holst, Jens J.

2012-01-01

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, proglucagon-derived gut hormone that shows promise for the treatment of short bowel syndrome (SBS). Our objective was to investigate how combination GLP-2 + enteral nutrients (EN) affects intestinal adaption in a rat model that mimics severe human SBS and requires parenteral nutrition (PN). Male Sprague-Dawley rats were assigned to one of five groups and maintained with PN for 18 days: total parenteral nutrition (TPN) alone, TPN + GLP-2 (100 μg·kg−1·day−1), PN + EN + GLP-2(7 days), PN + EN + GLP-2(18 days), and a nonsurgical oral reference group. Animals underwent massive distal bowel resection followed by jejunocolic anastomosis and placement of jugular catheters. Starting on postoperative day 4, rats in the EN groups were allowed ad libitum access to EN. Groups provided PN + EN + GLP-2 had their rate of PN reduced by 0.25 ml/day starting on postoperative day 6. Groups provided PN + EN + GLP-2 demonstrated significantly greater body weight gain with similar energy intake and a safe 80% reduction in PN compared with TPN ± GLP-2. Groups provided PN + EN + GLP-2 for 7 or 18 days showed similar body weight gain, residual jejunal length, and digestive capacity. Groups provided PN + EN + GLP-2 showed increased jejunal GLP-2 receptor (GLP-2R), insulin-like growth factor-I (IGF-I), and IGF-binding protein-5 (IGFBP-5) expression. Treatment with TPN + GLP-2 demonstrated increased jejunal expression of epidermal growth factor. Cessation of GLP-2 after 7 days with continued EN sustained the majority of intestinal adaption and significantly increased expression of colonic proglucagon compared with PN + EN + GLP-2 for 18 days, and increased plasma GLP-2 concentrations compared with TPN alone. In summary, EN potentiate the intestinotrophic actions of GLP-2 by improving body weight gain allowing for a safe 80% reduction in PN with increased jejunal expression of GLP-2R, IGF-I, and IGFBP-5 following distal bowel

Differential Requirement of the Extracellular Domain in Activation of Class B G Protein-coupled Receptors.

PubMed

Zhao, Li-Hua; Yin, Yanting; Yang, Dehua; Liu, Bo; Hou, Li; Wang, Xiaoxi; Pal, Kuntal; Jiang, Yi; Feng, Yang; Cai, Xiaoqing; Dai, Antao; Liu, Mingyao; Wang, Ming-Wei; Melcher, Karsten; Xu, H Eric

2016-07-15

G protein-coupled receptors (GPCRs) from the secretin-like (class B) family are key players in hormonal homeostasis and are important drug targets for the treatment of metabolic disorders and neuronal diseases. They consist of a large N-terminal extracellular domain (ECD) and a transmembrane domain (TMD) with the GPCR signature of seven transmembrane helices. Class B GPCRs are activated by peptide hormones with their C termini bound to the receptor ECD and their N termini bound to the TMD. It is thought that the ECD functions as an affinity trap to bind and localize the hormone to the receptor. This in turn would allow the hormone N terminus to insert into the TMD and induce conformational changes of the TMD to activate downstream signaling. In contrast to this prevailing model, we demonstrate that human class B GPCRs vary widely in their requirement of the ECD for activation. In one group, represented by corticotrophin-releasing factor receptor 1 (CRF1R), parathyroid hormone receptor (PTH1R), and pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1R), the ECD requirement for high affinity hormone binding can be bypassed by induced proximity and mass action effects, whereas in the other group, represented by glucagon receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R), the ECD is required for signaling even when the hormone is covalently linked to the TMD. Furthermore, the activation of GLP-1R by small molecules that interact with the intracellular side of the receptor is dependent on the presence of its ECD, suggesting a direct role of the ECD in GLP-1R activation. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Effects of exendin-4 and selenium on the expression of GLP-1R, IRS-1, and preproinsulin in the pancreas of diabetic rats.

PubMed

Barakat, Ghinwa; Moustafa, Mohamed E; Khalifeh, Ibrahim; Hodroj, Mohammad H; Bikhazi, Anwar; Rizk, Sandra

2016-08-01

The mechanisms by which exendin-4 and selenium exert their antidiabetic actions are still unclear. Here, we investigated the effects of exendin-4 or selenium administration on the expression of glucagon-like peptide-1 receptor (GLP-1R), insulin receptor substrate-1 (IRS-1), and preproinsulin in the pancreas of diabetic rats. Diabetes was induced by streptozotocin administration. Diabetic rats were injected intraperitoneally with 0.03 μg exendin-4/kg body weight/daily or treated with 5 ppm selenium in drinking water for a period of 4 weeks. GLP-1R and IRS-1 levels were decreased while the level of preproinsulin messenger RNA (mRNA) was increased in the pancreas of diabetic untreated rats, as compared to that in control rats. Treatment of diabetic rats with exendin-4 increased protein and mRNA levels of GLP-1R, and IRS-1, and the mRNA level of preproinsulin in the pancreas, as compared to their levels in diabetic untreated rats. Selenium treatment of diabetic rats increased the pancreatic mRNA levels of GLP-1R, IRS-1, and preproinsulin. Exendin-4 or selenium treatment of diabetic rats also increased the numbers of pancreatic islets and GLP-1R molecules in the pancreas. Therefore, exendin-4 and selenium may exert their antidiabetic effects by increasing GLP-1R, IRS-1, and preproinsulin expression in the pancreas and by increasing the number of pancreatic islets.

Characterization of glucagon-like peptide 2 pathway member expression in bovine gastrointestinal tract.

PubMed

Connor, E E; Baldwin, R L; Capuco, A V; Evock-Clover, C M; Ellis, S E; Sciabica, K S

2010-11-01

Glucagon-like peptide 2 (GLP-2), secreted by enteroendocrine cells, has several physiological effects on the intestine of monogastric species, including promotion of growth of intestinal epithelium, reduction of epithelial cell apoptosis, and enhancement of intestinal blood flow, nutrient absorption, and epithelial barrier function. The regulatory functions of GLP-2 in the ruminant gastrointestinal tract (GIT) have not been well studied. The objectives of this investigation were to characterize the mRNA expression of 4 members of the GLP-2 pathway throughout the bovine GIT, including (1) proglucagon (GCG), the parent peptide from which GLP-2 is derived through cleavage by prohormone convertase; (2) prohormone convertase (PCSK1); (3) GLP-2 receptor (GLP2R); and (4) dipeptidyl peptidase IV (DPP4), the enzyme that inactivates GLP-2. Gene expression was evaluated in rumen, reticulum, omasum, abomasum, duodenum, jejunum, ileum, cecum, and rectum collected at slaughter from prepubertal heifers, mature cows in early, mid, and late lactation, and nonlactating cows (n=3 per stage) by a gene expression profiling assay. In addition, mRNA expression of 14 genes involved in nutrient transport, enzyme activity, blood flow, apoptosis, and proliferation were evaluated in the 9 GIT tissues for their association with GCG and GLP2R mRNA expression. Immunohistochemistry was used to localize GLP2R protein in tissues of the lower GIT. Results indicated that mRNA expression of GCG, PCSK1, GLP2R, and DPP4 varies across the 9 GIT tissues, with greatest expression in small and large intestines, and generally nondetectable levels in forestomachs. Expression of DPP4 and GLP2R mRNA varied by developmental stage or lactational state in intestinal tissues. Expression of GCG or GLP2R mRNA was correlated with molecular markers of proliferation, apoptosis, blood flow, enzyme activity, and urea transport, depending on the tissue examined, which suggests a potential for involvement of GLP-2 in these

Blockade of Central GLP-1 Receptors Deteriorates the Improvement of Diabetes after Ileal Transposition.

PubMed

Chen, Weijie; Xu, Qianqian; Xiao, Yiding; Zhou, Jiaolin; Zhang, Weimin; Lin, Guole; Gong, Fengying

2016-01-01

Background: The mechanism of improvement of type 2 diabetes mellitus induced by ileal transposition (IT) is undefined. Our aim was to investigate the possible role of central glucagon-like peptide 1 (GLP-1) after IT. Methods: Ninety male diabetic rats were randomly divided into the IT, sham IT (S-IT) and control group. The food intake, glucose metabolism and GLP-1 level were measured. Subsequently, we administered GLP-1 antagonist via lateral brain ventricle cannula to block central GLP-1 receptor, and verified whether the food intake, glucose metabolism changed. And the activated pro-opiomelanocortin (POMC) neurons in different groups were compared after sacrifice. Results: IT induced significant diabetic improvement with decreased maximum food intake and higher postprandial GLP-1 level. The GLP-1 level in cerebrospinal fluid increased in correlation with the plasma GLP-1 level. When the central GLP-1 receptor antagonist was given to the IT group rats, the improvement of the glucose level declined. The glucose level surged (169.9 ± 14.2) % during the oral glucose tolerance test, the range was larger than that before central blockade ((67.1 ± 14.2) %, P < 0.001). Moreover, the POMC neuron number in the arcuate nucleus of the hypothalamus were reduced (12.7 ± 6.1 at a magnification of 100×). The relative content level of POMC-derived peptides in the pituitary was lower (0.1 ± 0.05). Conclusions: The central GLP-1 might play an important role in the remission of diabetes after IT. POMC neurons in the hypothalamus may be activated by the enhanced level of GLP-1 after IT.

Vibrational resonance, allostery, and activation in rhodopsin-like G protein-coupled receptors

PubMed Central

Woods, Kristina N.; Pfeffer, Jürgen; Dutta, Arpana; Klein-Seetharaman, Judith

2016-01-01

G protein-coupled receptors are a large family of membrane proteins activated by a variety of structurally diverse ligands making them highly adaptable signaling molecules. Despite recent advances in the structural biology of this protein family, the mechanism by which ligands induce allosteric changes in protein structure and dynamics for its signaling function remains a mystery. Here, we propose the use of terahertz spectroscopy combined with molecular dynamics simulation and protein evolutionary network modeling to address the mechanism of activation by directly probing the concerted fluctuations of retinal ligand and transmembrane helices in rhodopsin. This approach allows us to examine the role of conformational heterogeneity in the selection and stabilization of specific signaling pathways in the photo-activation of the receptor. We demonstrate that ligand-induced shifts in the conformational equilibrium prompt vibrational resonances in the protein structure that link the dynamics of conserved interactions with fluctuations of the active-state ligand. The connection of vibrational modes creates an allosteric association of coupled fluctuations that forms a coherent signaling pathway from the receptor ligand-binding pocket to the G-protein activation region. Our evolutionary analysis of rhodopsin-like GPCRs suggest that specific allosteric sites play a pivotal role in activating structural fluctuations that allosterically modulate functional signals. PMID:27849063

GLP-1 Treatment Improves Diabetic Retinopathy by Alleviating Autophagy through GLP-1R-ERK1/2-HDAC6 Signaling Pathway.

PubMed

Cai, Xiangsheng; Li, Jingjing; Wang, Mingzhu; She, Miaoqin; Tang, Yongming; Li, Jinlong; Li, Hongwei; Hui, Hongxiang

2017-01-01

Objective: Apoptosis and autophagy of retinal cells, which may be induced by oxidative stress, are tightly associated with the pathogenesis of diabetic retinopathy (DR). The autophagy induced by oxidative stress is considered as excessively stimulated autophagy, which accelerates the progression of DR. This study aims to investigate the protective effect of GLP-1 treatment on alleviating apoptosis and autophagy of retinal cells in type 2 diabetic rats and reveals its possible mechanism. Methods: Type 2 diabetic rats were induced by fed with high sugar, high fat diet and followed with streptozotocin injection. GLP-1 was applied to treat the diabetic rats for one week after the onset of diabetes. The expressions of oxidative stress-related enzymes, retinal GLP-1R, mitochondria-dependent apoptosis- related genes, autophagy markers, and autophagy-associated pathway genes were studied by Western blotting or immunohistochemistry analysis. Results: GLP-1treatment reduced the levels of NOX3 and SOD2 in DR. The expression of BCL2 was increased, while the levels of caspase3 and LC3B were reduced through GLP-1 treatment in DR . GLP-1 treatment restored the GLP-1R expression and decreased the levels of phosphorylated AKT and phosphorylated ERK1/2, which was accompanied with the reduction of the HDAC6 levels in DR. Conclusions: GLP-1 treatment can alleviate autophagy which may be induced by oxidative stress; this protective effect is likely through GLP-1R-ERK1/2-HDAC6 signaling pathway.

Ingestion of Diet Soda Before a Glucose Load Augments Glucagon-Like Peptide-1 Secretion

PubMed Central

Brown, Rebecca J.; Walter, Mary; Rother, Kristina I.

2009-01-01

OBJECTIVE The goal of this study was to determine the effect of artificial sweeteners on glucose, insulin, and glucagon-like peptide (GLP)-1 in humans. RESEARCH DESIGN AND METHODS For this study, 22 healthy volunteers (mean age 18.5 ± 4.2 years) underwent two 75-g oral glucose tolerance tests with frequent measurements of glucose, insulin, and GLP-1 for 180 min. Subjects drank 240 ml of diet soda or carbonated water, in randomized order, 10 min prior to the glucose load. RESULTS Glucose excursions were similar after ingestion of carbonated water and diet soda. Serum insulin levels tended to be higher after diet soda, without statistical significance. GLP-1 peak and area under the curve (AUC) were significantly higher with diet soda (AUC 24.0 ± 15.2 pmol/l per 180 min) versus carbonated water (AUC 16.2 ± 9.0 pmol/l per 180 min; P = 0.003). CONCLUSIONS Artificial sweeteners synergize with glucose to enhance GLP-1 release in humans. This increase in GLP-1 secretion may be mediated via stimulation of sweet-taste receptors on L-cells by artificial sweetener. PMID:19808921

Adverse Effects of GLP-1 Receptor Agonists

PubMed Central

Filippatos, Theodosios D.; Panagiotopoulou, Thalia V.; Elisaf, Moses S.

2014-01-01

Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of injective anti-diabetic drugs that improve glycemic control and many other atherosclerosis-related parameters in patients with type 2 diabetes (T2D). However, the use of this relatively new class of drugs may be associated with certain adverse effects. Concerns have been expressed regarding the effects of these drugs on pancreatic and thyroid tissue, since animal studies and analyses of drug databases indicate an association of GLP-1 receptor agonists with pancreatitis, pancreatic cancer, and thyroid cancer. However, several meta-analyses failed to confirm a cause-effect relation between GLP-1 receptor agonists and the development of these adverse effects. One benefit of GLP-1 receptor agonists is that they do not cause hypoglycemia when combined with metformin or thiazolidinediones, but the dose of concomitant sulphonylurea or insulin may have to be decreased to reduce the risk of hypoglycemic episodes. On the other hand, several case reports have linked the use of these drugs, mainly exenatide, with the occurrence of acute kidney injury, primarily through hemodynamic derangement due to nausea, vomiting, and diarrhea. The most common symptoms associated with the use of GLP-1 receptor agonists are gastrointestinal symptoms, mainly nausea. Other common adverse effects include injection site reactions, headache, and nasopharyngitis, but these effects do not usually result in discontinuation of the drug. Current evidence shows that GLP-1 receptor agonists have no negative effects on the cardiovascular risk of patients with T2D. Thus, GLP-1 receptor agonists appear to have a favorable safety profile, but ongoing trials will further assess their cardiovascular effects. The aim of this review is to analyze critically the available data regarding adverse events of GLP-1 receptor agonists in different anatomic systems published in Pubmed and Scopus. Whenever possible, certain differences between GLP-1

GLP-1 mediates antiapoptotic effect by phosphorylating Bad through a beta-arrestin 1-mediated ERK1/2 activation in pancreatic beta-cells.

PubMed

Quoyer, Julie; Longuet, Christine; Broca, Christophe; Linck, Nathalie; Costes, Safia; Varin, Elodie; Bockaert, Joël; Bertrand, Gyslaine; Dalle, Stéphane

2010-01-15

Strategies based on activating GLP-1 receptor (GLP-1R) are intensively developed for the treatment of type 2 diabetes. The exhaustive knowledge of the signaling pathways linked to activated GLP-1R within the beta-cells is of major importance. In beta-cells, GLP-1 activates the ERK1/2 cascade by diverse pathways dependent on either Galpha(s)/cAMP/cAMP-dependent protein kinase (PKA) or beta-arrestin 1, a scaffold protein. Using pharmacological inhibitors, beta-arrestin 1 small interfering RNA, and islets isolated from beta-arrestin 1 knock-out mice, we demonstrate that GLP-1 stimulates ERK1/2 by two temporally distinct pathways. The PKA-dependent pathway mediates rapid and transient ERK1/2 phosphorylation that leads to nuclear translocation of the activated kinases. In contrast, the beta-arrestin 1-dependent pathway produces a late ERK1/2 activity that is restricted to the beta-cell cytoplasm. We further observe that GLP-1 phosphorylates the cytoplasmic proapoptotic protein Bad at Ser-112 but not at Ser-155. We find that the beta-arrestin 1-dependent ERK1/2 activation engaged by GLP-1 mediates the Ser-112 phosphorylation of Bad, through p90RSK activation, allowing the association of Bad with the scaffold protein 14-3-3, leading to its inactivation. beta-Arrestin 1 is further found to mediate the antiapoptotic effect of GLP-1 in beta-cells through the ERK1/2-p90RSK-phosphorylation of Bad. This new regulatory mechanism engaged by activated GLP-1R involving a beta-arrestin 1-dependent spatiotemporal regulation of the ERK1/2-p90RSK activity is now suspected to participate in the protection of beta-cells against apoptosis. Such signaling mechanism may serve as a prototype to generate new therapeutic GLP-1R ligands.

Synergism by individual macronutrients explains the marked early GLP-1 and islet hormone responses to mixed meal challenge in mice.

PubMed

Ahlkvist, L; Vikman, J; Pacini, G; Ahrén, B

2012-10-10

Apart from glucose, proteins and lipids also stimulate incretin and islet hormone secretion. However, the glucoregulatory effect of macronutrients in combination is poorly understood. We therefore developed an oral mixed meal model in mice to 1) explore the glucagon-like peptide-1 (GLP-1) and islet hormone responses to mixed meal versus isocaloric glucose, and 2) characterize the relative contribution of individual macronutrients to these responses. Anesthetized C57BL/6J female mice were orally gavaged with 1) a mixed meal (0.285 kcal; glucose, whey protein and peanut oil; 60/20/20% kcal) versus an isocaloric glucose load (0.285 kcal), and 2) a mixed meal (0.285 kcal) versus glucose, whey protein or peanut oil administered individually in their mixed meal caloric quantity, i.e., 0.171, 0.055 and 0.055 kcal, respectively. Plasma was analyzed for glucose, insulin and intact GLP-1 before and during oral challenges. Plasma glucose was lower after mixed meal versus after isocaloric glucose ingestion. In spite of this, the peak insulin response (P=0.02), the peak intact GLP-1 levels (P=0.006) and the estimated β-cell function (P=0.005) were higher. Furthermore, the peak insulin (P=0.004) and intact GLP-1 (P=0.006) levels were higher after mixed meal ingestion than the sum of responses to individual macronutrients. Compared to glucose alone, we conclude that there is a marked early insulin response to mixed meal ingestion, which emanates from a synergistic, rather than an additive, effect of the individual macronutrients in the mixed meal and is in part likely caused by increased levels of GLP-1. Copyright © 2012 Elsevier B.V. All rights reserved.

The 2-monoacylglycerol moiety of dietary fat appears to be responsible for the fat-induced release of GLP-1 in humans.

PubMed

Mandøe, Mette J; Hansen, Katrine B; Hartmann, Bolette; Rehfeld, Jens F; Holst, Jens J; Hansen, Harald S

2015-09-01

Dietary triglycerides can, after digestion, stimulate the intestinal release of incretin hormones through activation of G protein-coupled receptor (GPR) 119 by 2-monoacylglycerol and by the activation of fatty acid receptors for long- and short-chain fatty acids. Medium-chain fatty acids do not stimulate the release of intestinal hormones. To dissect the mechanism of fat-induced glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) release in humans, we compared the effects of tributyrin (containing short-chain fatty acids; i.e., butyric acid), olive oil [containing long-chain fatty acids; e.g., oleic acid plus 2-oleoyl glycerol (2-OG)], and 1,3-dioctanoyl-2-oleoyl glycerol (C8-dietary oil), which is digested to form medium-chain fatty acids : i.e., octanoic acid : and 2-OG. In a randomized, single-blinded crossover study, 12 healthy white men [mean age: 24 y; BMI (in kg/m(2)): 22] were given the following 4 meals on 4 different days: 200 g carrots + 6.53 g tributyrin, 200 g carrots + 13.15 g C8-dietary oil, 200 g carrots + 19 g olive oil, or 200 g carrots. All of the lipids totaled 0.0216 mol. Main outcome measures were incremental areas under the curve for total GLP-1, GIP, and cholecystokinin (CCK) in plasma. C8-dietary oil and olive oil showed the same GLP-1 response [583 ± 101 and 538 ± 71 (pmol/L) × 120 min; P = 0.733], whereas the GIP response was higher for olive oil than for C8-dietary oil [3293 ± 404 and 1674 ± 270 (pmol/L) × 120 min; P = 0.002]. Tributyrin and carrots alone resulted in no increase in any of the measured hormones. Peptide YY (PYY) and neurotensin responses resembled those of GLP-1. Only olive oil stimulated CCK release. Under our study conditions, 2-OG and GPR119 activation can fully explain the olive oil-induced secretion of GLP-1, PYY, and neurotensin. In contrast, both oleic acid and 2-OG contributed to the GIP response. Dietary butyrate did not stimulate gut hormone secretion. Olive oil

Prediction of thyroid C-cell carcinogenicity after chronic administration of GLP1-R agonists in rodents.

PubMed

van den Brink, Willem; Emerenciana, Annette; Bellanti, Francesco; Della Pasqua, Oscar; van der Laan, Jan Willem

2017-04-01

Increased incidence of C-cell carcinogenicity has been observed for glucagon-like-protein-1 receptor (GLP-1r) agonists in rodents. It is suggested that the duration of exposure is an indicator of carcinogenic potential in rodents of the different products on the market. Furthermore, the role of GLP-1-related mechanisms in the induction of C-cell carcinogenicity has gained increased attention by regulatory agencies. This study proposes an integrative pharmacokinetic/pharmacodynamic (PKPD) framework to identify explanatory factors and characterize differences in carcinogenic potential of the GLP-1r agonist products. PK models for four products (exenatide QW (once weekly), exenatide BID (twice daily), liraglutide and lixisenatide) were developed using nonlinear mixed effects modelling. Predicted exposure was subsequently linked to GLP-1r stimulation using in vitro GLP-1r potency data. A logistic regression model was then applied to exenatide QW and liraglutide data to assess the relationship between GLP-1r stimulation and thyroid C-cell hyperplasia incidence as pre-neoplastic predictor of a carcinogenic response. The model showed a significant association between predicted GLP-1r stimulation and C-cell hyperplasia after 2years of treatment. The predictive performance of the model was evaluated using lixisenatide, for which hyperplasia data were accurately described during the validation step. The use of a model-based approach provided insight into the relationship between C-cell hyperplasia and GLP-1r stimulation for all four products, which is not possible with traditional data analysis methods. It can be concluded that both pharmacokinetics (exposure) and pharmacodynamics (potency for GLP-1r) factors determine C-cell hyperplasia incidence in rodents. Our work highlights the pharmacological basis for GLP-1r agonist-induced C-cell carcinogenicity. The concept is promising for application to other drug classes. Copyright © 2017 Elsevier Inc. All rights reserved.

Changes in gut microbiota control inflammation in obese mice through a mechanism involving GLP-2-driven improvement of gut permeability.

PubMed

Cani, P D; Possemiers, S; Van de Wiele, T; Guiot, Y; Everard, A; Rottier, O; Geurts, L; Naslain, D; Neyrinck, A; Lambert, D M; Muccioli, G G; Delzenne, N M

2009-08-01

Obese and diabetic mice display enhanced intestinal permeability and metabolic endotoxaemia that participate in the occurrence of metabolic disorders. Our recent data support the idea that a selective increase of Bifidobacterium spp. reduces the impact of high-fat diet-induced metabolic endotoxaemia and inflammatory disorders. Here, we hypothesised that prebiotic modulation of gut microbiota lowers intestinal permeability, by a mechanism involving glucagon-like peptide-2 (GLP-2) thereby improving inflammation and metabolic disorders during obesity and diabetes. Study 1: ob/ob mice (Ob-CT) were treated with either prebiotic (Ob-Pre) or non-prebiotic carbohydrates as control (Ob-Cell). Study 2: Ob-CT and Ob-Pre mice were treated with GLP-2 antagonist or saline. Study 3: Ob-CT mice were treated with a GLP-2 agonist or saline. We assessed changes in the gut microbiota, intestinal permeability, gut peptides, intestinal epithelial tight-junction proteins ZO-1 and occludin (qPCR and immunohistochemistry), hepatic and systemic inflammation. Prebiotic-treated mice exhibited a lower plasma lipopolysaccharide (LPS) and cytokines, and a decreased hepatic expression of inflammatory and oxidative stress markers. This decreased inflammatory tone was associated with a lower intestinal permeability and improved tight-junction integrity compared to controls. Prebiotic increased the endogenous intestinotrophic proglucagon-derived peptide (GLP-2) production whereas the GLP-2 antagonist abolished most of the prebiotic effects. Finally, pharmacological GLP-2 treatment decreased gut permeability, systemic and hepatic inflammatory phenotype associated with obesity to a similar extent as that observed following prebiotic-induced changes in gut microbiota. We found that a selective gut microbiota change controls and increases endogenous GLP-2 production, and consequently improves gut barrier functions by a GLP-2-dependent mechanism, contributing to the improvement of gut barrier functions

Role of lateral septum glucagon-like peptide 1 receptors in food intake

PubMed Central

Jackson, Christine M.; Greene, Hayden E.; Lilly, Nicole; Maske, Calyn B.; Vallejo, Samantha

2016-01-01

Hindbrain glucagon-like peptide 1 (GLP-1) neurons project to numerous forebrain areas, including the lateral septum (LS). Using a fluorescently labeled GLP-1 receptor (GLP-1R) agonist, Exendin 4 (Ex4), we demonstrated GLP-1 receptor binding throughout the rat LS. We examined the feeding effects of Ex4 and the GLP-1R antagonist Exendin (9–39) (Ex9) at doses subthreshold for effect when delivered to the lateral ventricle. Intra-LS Ex4 suppressed overnight chow and high-fat diet (HFD) intake, and Ex9 increased chow and HFD intake relative to vehicle. During 2-h tests, intra-LS Ex9 significantly increased 0.25 M sucrose and 4% corn oil. Ex4 can cause nausea, but intra-LS administration of Ex4 did not induce pica. Furthermore, intra-LS Ex4 had no effect on anxiety-like behavior in the elevated plus maze. We investigated the role of LS GLP-1R in motivation for food by examining operant responding for sucrose on a progressive ratio (PR) schedule, with and without a nutrient preload to maximize GLP-1 neuron activation. The preload strongly suppressed PR responding, but blockade of GLP-1R in the intermediate subdivision of the LS did not affect motivation for sucrose under either load condition. The ability of the nutrient load to suppress subsequent chow intake was significantly attenuated by intermediate LS Ex9 treatment. By contrast, blockade of GLP-1R in the dorsal subdivision of the LS increased both PR responding and overnight chow intake. Together, these studies suggest that endogenous activity of GLP-1R in the LS influence feeding, and dLS GLP-1Rs, in particular, play a role in motivation. PMID:27194565

Role of lateral septum glucagon-like peptide 1 receptors in food intake.

PubMed

Terrill, Sarah J; Jackson, Christine M; Greene, Hayden E; Lilly, Nicole; Maske, Calyn B; Vallejo, Samantha; Williams, Diana L

2016-07-01

Hindbrain glucagon-like peptide 1 (GLP-1) neurons project to numerous forebrain areas, including the lateral septum (LS). Using a fluorescently labeled GLP-1 receptor (GLP-1R) agonist, Exendin 4 (Ex4), we demonstrated GLP-1 receptor binding throughout the rat LS. We examined the feeding effects of Ex4 and the GLP-1R antagonist Exendin (9-39) (Ex9) at doses subthreshold for effect when delivered to the lateral ventricle. Intra-LS Ex4 suppressed overnight chow and high-fat diet (HFD) intake, and Ex9 increased chow and HFD intake relative to vehicle. During 2-h tests, intra-LS Ex9 significantly increased 0.25 M sucrose and 4% corn oil. Ex4 can cause nausea, but intra-LS administration of Ex4 did not induce pica. Furthermore, intra-LS Ex4 had no effect on anxiety-like behavior in the elevated plus maze. We investigated the role of LS GLP-1R in motivation for food by examining operant responding for sucrose on a progressive ratio (PR) schedule, with and without a nutrient preload to maximize GLP-1 neuron activation. The preload strongly suppressed PR responding, but blockade of GLP-1R in the intermediate subdivision of the LS did not affect motivation for sucrose under either load condition. The ability of the nutrient load to suppress subsequent chow intake was significantly attenuated by intermediate LS Ex9 treatment. By contrast, blockade of GLP-1R in the dorsal subdivision of the LS increased both PR responding and overnight chow intake. Together, these studies suggest that endogenous activity of GLP-1R in the LS influence feeding, and dLS GLP-1Rs, in particular, play a role in motivation. Copyright © 2016 the American Physiological Society.

Characteristics of patients with type 2 diabetes mellitus newly treated with GLP-1 receptor agonists (CHADIG Study): a cross-sectional multicentre study in Spain

PubMed Central

Conget, Ignacio; Mauricio, Dídac; Ortega, Rafael; Detournay, Bruno

2016-01-01

Objective Several glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1Ra) have been made recently available in Spain for type 2 diabetes mellitus (DM2) treatment. There are no published data on the clinical and sociodemographic profile of patients initiating treatment with GLP-1Ra in Spain. Our objective was to understand these patients' characteristics in a real-world clinical practice setting. Design Cross-sectional observational study. Setting Spanish specialist outpatient clinics. Participants 403 adults with DM2 initiating GLP-1Ra treatment were included. Primary and secondary outcome measures Sociodemographic and DM2-related clinical data, including treatment at and after GLP-1Ra initiation and comorbidities, were collected. Results Evaluable patients (n=403; 50.9% female) were included (July 2013 to March 2014) at 24 centres by 53 specialists (47 endocrinology, 6 internal medicine), with the following profile (value±SD): age (58.3±10.4 years), diabetes duration (9.9±7 years), body mass index (BMI; 36.2±5.5) and glycated haemoglobin (HbA1c; 8.4±1.4%); 14% had HbA1c≤7%. Previous antidiabetic treatment: 53.8% only oral antidiabetic drugs (OADs), 5.2% insulin and 40% insulin and OAD; of those receiving OAD, 35% single drug, 38.2% 2 drugs and 24% 3 drugs. Concomitant to GLP-1Ra, 55.3% were only on OAD, 36.2% on insulin and OAD, and 7.2% only on insulin. Of those receiving OAD, the GLP-1Ra was mainly associated with 1 drug (65%) or 2 drugs (31.8%). GLP-1Ra are frequently added to existing antidiabetic drugs, with dipeptidyl peptidase-4 inhibitors being the OAD most frequently switched (45% receiving 1 before starting GLP-1Ra, only 2.7% receiving it concomitantly). Conclusions In Spain, GLP-1Ra therapy is usually started in combination with OADs or OADs and insulin. These drugs are used in relatively young patients often not reaching therapeutic goals with other treatment combinations, roughly a decade after diagnosis and with a relatively high BMI

PPG neurons of the lower brain stem and their role in brain GLP-1 receptor activation

PubMed Central

Cork, Simon C.

2015-01-01

Within the brain, glucagon-like peptide-1 (GLP-1) affects central autonomic neurons, including those controlling the cardiovascular system, thermogenesis, and energy balance. Additionally, GLP-1 influences the mesolimbic reward system to modulate the rewarding properties of palatable food. GLP-1 is produced in the gut and by hindbrain preproglucagon (PPG) neurons, located mainly in the nucleus tractus solitarii (NTS) and medullary intermediate reticular nucleus. Transgenic mice expressing glucagon promoter-driven yellow fluorescent protein revealed that PPG neurons not only project to central autonomic control regions and mesolimbic reward centers, but also strongly innervate spinal autonomic neurons. Therefore, these brain stem PPG neurons could directly modulate sympathetic outflow through their spinal inputs to sympathetic preganglionic neurons. Electrical recordings from PPG neurons in vitro have revealed that they receive synaptic inputs from vagal afferents entering via the solitary tract. Vagal afferents convey satiation to the brain from signals like postprandial gastric distention or activation of peripheral GLP-1 receptors. CCK and leptin, short- and long-term satiety peptides, respectively, increased the electrical activity of PPG neurons, while ghrelin, an orexigenic peptide, had no effect. These findings indicate that satiation is a main driver of PPG neuronal activation. They also show that PPG neurons are in a prime position to respond to both immediate and long-term indicators of energy and feeding status, enabling regulation of both energy balance and general autonomic homeostasis. This review discusses the question of whether PPG neurons, rather than gut-derived GLP-1, are providing the physiological substrate for the effects elicited by central nervous system GLP-1 receptor activation. PMID:26290108

PPG neurons of the lower brain stem and their role in brain GLP-1 receptor activation.

PubMed

Trapp, Stefan; Cork, Simon C

2015-10-15

Within the brain, glucagon-like peptide-1 (GLP-1) affects central autonomic neurons, including those controlling the cardiovascular system, thermogenesis, and energy balance. Additionally, GLP-1 influences the mesolimbic reward system to modulate the rewarding properties of palatable food. GLP-1 is produced in the gut and by hindbrain preproglucagon (PPG) neurons, located mainly in the nucleus tractus solitarii (NTS) and medullary intermediate reticular nucleus. Transgenic mice expressing glucagon promoter-driven yellow fluorescent protein revealed that PPG neurons not only project to central autonomic control regions and mesolimbic reward centers, but also strongly innervate spinal autonomic neurons. Therefore, these brain stem PPG neurons could directly modulate sympathetic outflow through their spinal inputs to sympathetic preganglionic neurons. Electrical recordings from PPG neurons in vitro have revealed that they receive synaptic inputs from vagal afferents entering via the solitary tract. Vagal afferents convey satiation to the brain from signals like postprandial gastric distention or activation of peripheral GLP-1 receptors. CCK and leptin, short- and long-term satiety peptides, respectively, increased the electrical activity of PPG neurons, while ghrelin, an orexigenic peptide, had no effect. These findings indicate that satiation is a main driver of PPG neuronal activation. They also show that PPG neurons are in a prime position to respond to both immediate and long-term indicators of energy and feeding status, enabling regulation of both energy balance and general autonomic homeostasis. This review discusses the question of whether PPG neurons, rather than gut-derived GLP-1, are providing the physiological substrate for the effects elicited by central nervous system GLP-1 receptor activation. Copyright © 2015 the American Physiological Society.

Properly Substituted Analogues of BIX-01294 Lose Inhibition of G9a Histone Methyltransferase and Gain Selective Anti-DNA Methyltransferase 3A Activity

PubMed Central

Rotili, Dante; Tarantino, Domenico; Marrocco, Biagina; Gros, Christina; Masson, Véronique; Poughon, Valérie; Ausseil, Fréderic; Chang, Yanqi; Labella, Donatella; Cosconati, Sandro; Di Maro, Salvatore; Novellino, Ettore; Schnekenburger, Michael; Grandjenette, Cindy; Bouvy, Celine; Diederich, Marc; Cheng, Xiaodong; Arimondo, Paola B.; Mai, Antonello

2014-01-01

Chemical manipulations performed on the histone H3 lysine 9 methyltransferases (G9a/GLP) inhibitor BIX-01294 afforded novel desmethoxyquinazolines able to inhibit the DNA methyltransferase DNMT3A at low micromolar levels without any significant inhibition of DNMT1 and G9a. In KG-1 cells such compounds, when tested at sub-toxic doses, induced the luciferase re-expression in a stable construct controlled by a cytomegalovirus (CMV) promoter silenced by methylation (CMV-luc assay). Finally, in human lymphoma U-937 and RAJI cells, the N-(1-benzylpiperidin-4-yl)-2-(4-phenylpiperazin-1-yl)quinazolin-4-amine induced the highest proliferation arrest and cell death induction starting from 10 µM, in agreement with its DNMT3A inhibitory potency. PMID:24810902

Differences in acute anorectic effects of long-acting GLP-1 receptor agonists in rats.

PubMed

Sisley, Stephanie; Smith, Kathleen; Sandoval, Darleen A; Seeley, Randy J

2014-08-01

Long-acting glucagon-like peptide-1 receptor (GLP-1R) agonists have both glucose- and weight-lowering effects. The brain is poised to mediate both of these actions since GLP-1Rs are present in key areas known to control weight and glucose. Although some research has been performed on the effects of exendin-4 in the brain, little data exists on the central effects of liraglutide, a long-acting GLP-1R agonist with much closer structural homology to native GLP-1. In lean, Long-Evans rats, we found that direct intra-third cerebroventricular (i3vt) administration of 0.26 nmol liraglutide caused a 50% reduction in food intake. However, exendin-4 produced the same reduction in food intake with 10-fold greater potency (0.02 nmol). These data are supported by similar c-Fos immunoreactivity in the hypothalamic paraventricular nuclei by exendin-4 as compared to liraglutide despite differing doses. The anorectic effects of both drugs were blocked with i3vt pre-treatment of a GLP-1R competitive antagonist, exendin(9-39), indicating that both drugs required the GLP-1R for their effects. Exendin-4, and not liraglutide, caused hyperglycemia when given i3vt prior to an oral glucose tolerance test, although liraglutide did not lower glucose. Thus, these data show that GLP-1R agonists have differing anorectic potencies in the CNS, which may account for some of their clinical differences. Additionally, we show here that the glucose lowering properties of acute administration of GLP-1R agonists are not accounted for by their central effects. Copyright © 2014 Elsevier Inc. All rights reserved.

GLP-1 Receptor Stimulation of the Lateral Parabrachial Nucleus Reduces Food Intake: Neuroanatomical, Electrophysiological, and Behavioral Evidence

PubMed Central

Richard, Jennifer E.; Farkas, Imre; Anesten, Fredrik; Anderberg, Rozita H.; Dickson, Suzanne L.; Gribble, Fiona M.; Reimann, Frank; Jansson, John-Olov; Liposits, Zsolt

2014-01-01

The parabrachial nucleus (PBN) is a key nucleus for the regulation of feeding behavior. Inhibitory inputs from the hypothalamus to the PBN play a crucial role in the normal maintenance of feeding behavior, because their loss leads to starvation. Viscerosensory stimuli result in neuronal activation of the PBN. However, the origin and neurochemical identity of the excitatory neuronal input to the PBN remain largely unexplored. Here, we hypothesize that hindbrain glucagon-like peptide 1 (GLP-1) neurons provide excitatory inputs to the PBN, activation of which may lead to a reduction in feeding behavior. Our data, obtained from mice expressing the yellow fluorescent protein in GLP-1-producing neurons, revealed that hindbrain GLP-1-producing neurons project to the lateral PBN (lPBN). Stimulation of lPBN GLP-1 receptors (GLP-1Rs) reduced the intake of chow and palatable food and decreased body weight in rats. It also activated lPBN neurons, reflected by an increase in the number of c-Fos-positive cells in this region. Further support for an excitatory role of GLP-1 in the PBN is provided by electrophysiological studies showing a remarkable increase in firing of lPBN neurons after Exendin-4 application. We show that within the PBN, GLP-1R activation increased gene expression of 2 energy balance regulating peptides, calcitonin gene-related peptide (CGRP) and IL-6. Moreover, nearly 70% of the lPBN GLP-1 fibers innervated lPBN CGRP neurons. Direct intra-lPBN CGRP application resulted in anorexia. Collectively, our molecular, anatomical, electrophysiological, pharmacological, and behavioral data provide evidence for a functional role of the GLP-1R for feeding control in the PBN. PMID:25116706

Glucagon-like peptide-2 induces rapid digestive adaptation following intestinal resection in preterm neonates

PubMed Central

Vegge, Andreas; Thymann, Thomas; Lund, Pernille; Stoll, Barbara; Bering, Stine B.; Hartmann, Bolette; Jelsing, Jacob; Qvist, Niels; Burrin, Douglas G.; Jeppesen, Palle B.; Holst, Jens J.

2013-01-01

Short bowel syndrome (SBS) is a frequent complication after intestinal resection in infants suffering from intestinal disease. We tested whether treatment with the intestinotrophic hormone glucagon-like peptide-2 (GLP-2) increases intestinal volume and function in the period immediately following intestinal resection in preterm pigs. Preterm pigs were fed enterally for 48 h before undergoing resection of 50% of the small intestine and establishment of a jejunostomy. Following resection, pigs were maintained on total parenteral nutrition (TPN) without (SBS, n = 8) or with GLP-2 treatment (3.5 μg/kg body wt per h, SBS+GLP-2, n = 7) and compared with a group of unresected preterm pigs (control, n = 5). After 5 days of TPN, all piglets were fed enterally for 24 h, and a nutrient balance study was performed. Intestinal resection was associated with markedly reduced endogenous GLP-2 levels. GLP-2 increased the relative absorption of wet weight (46 vs. 22%), energy (79 vs. 64%), and all macronutrients (all parameters P < 0.05). These findings were supported by a 200% increase in sucrase and maltase activities, a 50% increase in small intestinal epithelial volume (P < 0.05), as well as increased DNA and protein contents and increased total protein synthesis rate in SBS+GLP-2 vs. SBS pigs (+100%, P < 0.05). Following intestinal resection in preterm pigs, GLP-2 induced structural and functional adaptation, resulting in a higher relative absorption of fluid and macronutrients. GLP-2 treatment may be a promising therapy to enhance intestinal adaptation and improve digestive function in preterm infants with jejunostomy following intestinal resection. PMID:23764891

Role of fatty acid transport protein 4 in oleic acid-induced glucagon-like peptide-1 secretion from murine intestinal L cells

PubMed Central

Poreba, M. A.; Dong, C. X.; Li, S. K.; Stahl, A.; Miner, J. H.

2012-01-01

The antidiabetic intestinal L cell hormone glucagon-like peptide-1 (GLP-1) enhances glucose-dependent insulin secretion and inhibits gastric emptying. GLP-1 secretion is stimulated by luminal oleic acid (OA), which crosses the cell membrane by an unknown mechanism. We hypothesized that L cell fatty acid transport proteins (FATPs) are essential for OA-induced GLP-1 release. Therefore, the murine GLUTag L cell model was used for immunoblotting, [3H]OA uptake assay, and GLP-1 secretion assay as determined by radioimmunoassay following treatment with OA ± phloretin, sulfo-N-succinimidyl oleate, or siRNA against FATP4. FATP4−/− and cluster-of-differentiation 36 (CD36)−/− mice received intraileal OA, and plasma GLP-1 was measured by sandwich immunoassay. GLUTag cells were found to express CD36, FATP1, FATP3, and FATP4. The cells demonstrated specific 3H[OA] uptake that was dose-dependently inhibited by 500 and 1,000 μM unlabeled OA (P < 0.001). Cell viability was not altered by treatment with OA. Phloretin and sulfo-N-succinimidyl oleate, inhibitors of protein-mediated transport and CD36, respectively, also decreased [3H]OA uptake, as did knockdown of FATP4 by siRNA transfection (P < 0.05–0.001). OA dose-dependently increased GLP-1 secretion at 500 and 1,000 μM (P < 0.001), whereas phloretin, sulfo-N-succinimidyl oleate, and FATP4 knockdown decreased this response (P < 0.05–0.01). FATP4−/− mice displayed lower plasma GLP-1 at 60 min in response to intraileal OA (P < 0.05), whereas, unexpectedly, CD36−/− mice displayed higher basal GLP-1 levels (P < 0.01) but a normal response to intraileal OA. Together, these findings demonstrate a key role for FATP4 in OA-induced GLP-1 secretion from the murine L cell in vitro and in vivo, whereas the precise role of CD36 remains unclear. PMID:22871340

Purine inhibitors of protein kinases, G proteins and polymerases

DOEpatents

Gray, Nathanael S.; Schultz, Peter; Kim, Sung-Hou; Meijer, Laurent

2004-10-12

The present invention relates to 2-N-substituted 6-(4-methoxybenzylamino)-9-isopropylpurines that inhibit, inter alia, protein kinases, G-proteins and polymerases. In addition, the present invention relates to methods of using such 2-N-substituted 6-(4-methoxybenzylamino)-9-isopropylpurines to inhibit protein kinases, G-proteins, polymerases and other cellular processes and to treat cellular proliferative diseases.

GLP-1 acts on habenular avoidance circuits to control nicotine intake.

PubMed

Tuesta, Luis M; Chen, Zuxin; Duncan, Alexander; Fowler, Christie D; Ishikawa, Masago; Lee, Brian R; Liu, Xin-An; Lu, Qun; Cameron, Michael; Hayes, Matthew R; Kamenecka, Theodore M; Pletcher, Matthew; Kenny, Paul J

2017-05-01

Tobacco smokers titrate their nicotine intake to avoid its noxious effects, sensitivity to which may influence vulnerability to tobacco dependence, yet mechanisms of nicotine avoidance are poorly understood. Here we show that nicotine activates glucagon-like peptide-1 (GLP-1) neurons in the nucleus tractus solitarius (NTS). The antidiabetic drugs sitagliptin and exenatide, which inhibit GLP-1 breakdown and stimulate GLP-1 receptors, respectively, decreased nicotine intake in mice. Chemogenetic activation of GLP-1 neurons in NTS similarly decreased nicotine intake. Conversely, Glp1r knockout mice consumed greater quantities of nicotine than wild-type mice. Using optogenetic stimulation, we show that GLP-1 excites medial habenular (MHb) projections to the interpeduncular nucleus (IPN). Activation of GLP-1 receptors in the MHb-IPN circuit abolished nicotine reward and decreased nicotine intake, whereas their knockdown or pharmacological blockade increased intake. GLP-1 neurons may therefore serve as 'satiety sensors' for nicotine that stimulate habenular systems to promote nicotine avoidance before its aversive effects are encountered.

Inhibiting receptor for advanced glycation end product (AGE) and oxidative stress involved in the protective effect mediated by glucagon-like peptide-1 receptor on AGE induced neuronal apoptosis.

PubMed

Chen, Song; Yin, Lei; Xu, Zheng; An, Feng-Mao; Liu, Ai-Ran; Wang, Ying; Yao, Wen-Bing; Gao, Xiang-Dong

2016-01-26

Our previous study has demonstrated that glucagon-like peptide-1 (GLP-1) receptor agonist could protect neurons from advanced glycation end products (AGEs) toxicity in vitro. However, further studies are still needed to clarify the molecular mechanism of this GLP-1 receptor -dependent action. The present study mainly focused on the effect of GLP-1 receptor agonists against the receptor for advanced glycation end products (RAGE) signal pathway and the mechanism underlying this effect of GLP-1. Firstly the data based on the SH-GLP-1R(+) and SH-SY5Y cells confirmed our previous finding that GLP-1 receptor could mediate the protective effect against AGEs. The assays of the protein activity and of the mRNA level revealed that apoptosis-related proteins such as caspase-3, caspase-9, Bax and Bcl-2 were involved. Additionally, we found that both GLP-1 and exendin-4 could reduce AGEs-induced reactive oxygen species (ROS) accumulation by suppressing the activity of nicotinamide adenine dinucleotide phosphate-oxidase. Interestingly, we also found that GLP-1 receptor activation could attenuate the abnormal expression of the RAGE in vitro and in vivo. Furthermore, based on the analysis of the protein expression and translocation level of transcription factor nuclear factor-κB (NF-κB), and the use of GLP-1 receptor antagonist exendin(9-39) and NF-κB inhibitor pyrrolidine dithiocarbamate, we found that the effect mediated by GLP-1 receptor could alleviate the over expression of RAGE induced by ligand via the suppression of NF-κB. In summary, the results indicated that inhibiting RAGE/oxidative stress was involved in the protective effect of GLP-1 on neuron cells against AGEs induced apoptosis. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Helixconstraints and amino acid substitution in GLP-1 increase cAMP and insulin secretion but not beta-arrestin 2 signaling.

PubMed

Plisson, Fabien; Hill, Timothy A; Mitchell, Justin M; Hoang, Huy N; de Araujo, Aline D; Xu, Weijun; Cotterell, Adam; Edmonds, David J; Stanton, Robert V; Derksen, David R; Loria, Paula M; Griffith, David A; Price, David A; Liras, Spiros; Fairlie, David P

2017-02-15

Glucagon-like peptide (GLP-1) is an endogenous hormone that induces insulin secretion from pancreatic islets and modified forms are used to treat diabetes mellitus type 2. Understanding how GLP-1 interacts with its receptor (GLP-1R) can potentially lead to more effective drugs. Modeling and NMR studies of the N-terminus of GLP-1 suggest a β-turn between residues Glu9-Phe12 and a kinked alpha helix between Val16-Gly37. N-terminal turn constraints attenuated binding affinity and activity (compounds 1-8). Lys-Asp (i, i+4) crosslinks in the middle and at the C-terminus increased alpha helicity and cAMP stimulation without much effect on binding affinity or beta-arrestin 2 recruitment (compounds 9-18). Strategic positioning of helix-inducing constraints and amino acid substitutions (Tyr16, Ala22) increased peptide helicity and produced ten-fold higher cAMP potency (compounds 19-28) over GLP-1(7-37)-NH 2 . The most potent cAMP activator (compound 23) was also the most potent inducer of insulin secretion. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

The Impacts of Gastroileostomy Rat Model on Glucagon-like Peptide-1: a Promising Model to Control Type 2 Diabetes Mellitus.

PubMed

Keleidari, Behrouz; Mohammadi Mofrad, Rastin; Shahabi Shahmiri, Shahab; Sanei, Mohammad Hossein; Kolahdouzan, Mohsen; Sheikhbahaei, Erfan

2018-05-21

One of the new current treatment options for Diabetes Mellitus is about increasing glucagon-like peptide-1 (GLP-1) activity. GLP-1 with its incretin effect showed major role in glucose homeostasis. Gastroileostomy can increase GLP-1 secretion by rapid delivery of undigested food to the terminal ileum. We studied the early effects of a gastroileostomy on serum levels of GLP-1, glucose, and insulin in rats. Gastroileostomies with side-to-side anastomosis were performed on 15 male New Zealand rats. Blood samples were obtained before and 1 week after the gastroileostomy. Our results showed that the rats lost a lot of weight from start (330 ± 15 g) to the end (240 ± 25 g) of the experiment (p = 0.048). The data analysis showed that the gastroileostomy surgery elevates the level of GLP-1in plasma significantly (89.1852 vs. 177.440 respectively; p < 0.001) and caused a significant decrease in plasma glucose as well (92.00 and 66.29 mg/dL respectively; p < 0.001). However, the insulin state elevated after the surgery significantly (8.03 vs. 9.89; p < 0.001). In this study, we showed the effectiveness of gastroileostomy treatment to decrease body weight and plasma glucose with increased GLP-1 in rats. This small rat model suggests the potential of this surgery to treat type 2 diabetes mellitus.

Elevated Postoperative Endogenous GLP-1 Levels Mediate Effects of Roux-en-Y Gastric Bypass on Neural Responsivity to Food Cues.

PubMed

Ten Kulve, Jennifer S; Veltman, Dick J; Gerdes, Victor E A; van Bloemendaal, Liselotte; Barkhof, Frederik; Deacon, Carolyn F; Holst, Jens J; Drent, Madeleine L; Diamant, Michaela; IJzerman, Richard G

2017-11-01

It has been suggested that weight reduction and improvements in satiety after Roux-en-Y gastric bypass (RYGB) are partly mediated via postoperative neuroendocrine changes. Glucagon-like peptide-1 (GLP-1) is a gut hormone secreted after food ingestion and is associated with appetite and weight reduction, mediated via effects on the central nervous system (CNS). Secretion of GLP-1 is greatly enhanced after RYGB. We hypothesized that postoperative elevated GLP-1 levels contribute to the improved satiety regulation after RYGB via effects on the CNS. Effects of the GLP-1 receptor antagonist exendin 9-39 (Ex9-39) and placebo were assessed in 10 women before and after RYGB. We used functional MRI to investigate CNS activation in response to visual food cues (pictures) and gustatory food cues (consumption of chocolate milk), comparing results with Ex9-39 versus placebo before and after RYGB. After RYGB, CNS activation was reduced in the rolandic operculum and caudate nucleus in response to viewing food pictures ( P = 0.03) and in the insula in response to consumption of palatable food ( P = 0.003). GLP-1 levels were significantly elevated postoperatively ( P < 0.001). After RYGB, GLP-1 receptor blockade resulted in a larger increase in activation in the caudate nucleus in response to food pictures ( P = 0.02) and in the insula in response to palatable food consumption ( P = 0.002). We conclude that the effects of RYGB on CNS activation in response to visual and gustatory food cues may be mediated by central effects of GLP-1. Our findings provide further insights into the mechanisms underlying the weight-lowering effects of RYGB. © 2017 by the American Diabetes Association.

Tyrosine phosphorylation switching of a G protein.

PubMed

Li, Bo; Tunc-Ozdemir, Meral; Urano, Daisuke; Jia, Haiyan; Werth, Emily G; Mowrey, David D; Hicks, Leslie M; Dokholyan, Nikolay V; Torres, Matthew P; Jones, Alan M

2018-03-30

Heterotrimeric G protein complexes are molecular switches relaying extracellular signals sensed by G protein-coupled receptors (GPCRs) to downstream targets in the cytoplasm, which effect cellular responses. In the plant heterotrimeric GTPase cycle, GTP hydrolysis, rather than nucleotide exchange, is the rate-limiting reaction and is accelerated by a receptor-like regulator of G signaling (RGS) protein. We hypothesized that posttranslational modification of the Gα subunit in the G protein complex regulates the RGS-dependent GTPase cycle. Our structural analyses identified an invariant phosphorylated tyrosine residue (Tyr 166 in the Arabidopsis Gα subunit AtGPA1) located in the intramolecular domain interface where nucleotide binding and hydrolysis occur. We also identified a receptor-like kinase that phosphorylates AtGPA1 in a Tyr 166 -dependent manner. Discrete molecular dynamics simulations predicted that phosphorylated Tyr 166 forms a salt bridge in this interface and potentially affects the RGS protein-accelerated GTPase cycle. Using a Tyr 166 phosphomimetic substitution, we found that the cognate RGS protein binds more tightly to the GDP-bound Gα substrate, consequently reducing its ability to accelerate GTPase activity. In conclusion, we propose that phosphorylation of Tyr 166 in AtGPA1 changes the binding pattern with AtRGS1 and thereby attenuates the steady-state rate of the GTPase cycle. We coin this newly identified mechanism "substrate phosphoswitching." © 2018 by The American Society for Biochemistry and Molecular Biology, Inc.

Characteristics of patients with type 2 diabetes mellitus newly treated with GLP-1 receptor agonists (CHADIG Study): a cross-sectional multicentre study in Spain.

PubMed

Conget, Ignacio; Mauricio, Dídac; Ortega, Rafael; Detournay, Bruno

2016-07-26

Several glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1Ra) have been made recently available in Spain for type 2 diabetes mellitus (DM2) treatment. There are no published data on the clinical and sociodemographic profile of patients initiating treatment with GLP-1Ra in Spain. Our objective was to understand these patients' characteristics in a real-world clinical practice setting. Cross-sectional observational study. Spanish specialist outpatient clinics. 403 adults with DM2 initiating GLP-1Ra treatment were included. Sociodemographic and DM2-related clinical data, including treatment at and after GLP-1Ra initiation and comorbidities, were collected. Evaluable patients (n=403; 50.9% female) were included (July 2013 to March 2014) at 24 centres by 53 specialists (47 endocrinology, 6 internal medicine), with the following profile (value±SD): age (58.3±10.4 years), diabetes duration (9.9±7 years), body mass index (BMI; 36.2±5.5) and glycated haemoglobin (HbA1c; 8.4±1.4%); 14% had HbA1c≤7%. Previous antidiabetic treatment: 53.8% only oral antidiabetic drugs (OADs), 5.2% insulin and 40% insulin and OAD; of those receiving OAD, 35% single drug, 38.2% 2 drugs and 24% 3 drugs. Concomitant to GLP-1Ra, 55.3% were only on OAD, 36.2% on insulin and OAD, and 7.2% only on insulin. Of those receiving OAD, the GLP-1Ra was mainly associated with 1 drug (65%) or 2 drugs (31.8%). GLP-1Ra are frequently added to existing antidiabetic drugs, with dipeptidyl peptidase-4 inhibitors being the OAD most frequently switched (45% receiving 1 before starting GLP-1Ra, only 2.7% receiving it concomitantly). In Spain, GLP-1Ra therapy is usually started in combination with OADs or OADs and insulin. These drugs are used in relatively young patients often not reaching therapeutic goals with other treatment combinations, roughly a decade after diagnosis and with a relatively high BMI. The latter could be explained by Spanish regional payers limiting reimbursed prescription to

99mTc Labeled Glucagon-Like Peptide-1-Analogue (99mTc-GLP1) Scintigraphy in the Management of Patients with Occult Insulinoma

PubMed Central

Sowa-Staszczak, Anna; Trofimiuk-Müldner, Małgorzata; Stefańska, Agnieszka; Tomaszuk, Monika; Buziak-Bereza, Monika; Gilis-Januszewska, Aleksandra; Jabrocka-Hybel, Agata; Głowa, Bogusław; Małecki, Maciej; Bednarczuk, Tomasz; Kamiński, Grzegorz; Kowalska, Aldona; Mikołajczak, Renata; Janota, Barbara; Hubalewska-Dydejczyk, Alicja

2016-01-01

Introduction The aim of this study was to assess the utility of [Lys40(Ahx-HYNIC-99mTc/EDDA)NH2]-exendin-4 scintigraphy in the management of patients with hypoglycemia, particularly in the detection of occult insulinoma. Materials and Methods Forty patients with hypoglycemia and increased/confusing results of serum insulin and C-peptide concentration and negative/inconclusive results of other imaging examinations were enrolled in the study. In all patients GLP-1 receptor imaging was performed to localise potential pancreatic lesions. Results Positive results of GLP-1 scintigraphy were observed in 28 patients. In 18 patients postsurgical histopathological examination confirmed diagnosis of insulinoma. Two patients had contraindications to the surgery, one patient did not want to be operated. One patient, who presented with postprandial hypoglycemia, with positive result of GLP-1 imaging was not qualified for surgery and is in the observational group. Eight patients were lost for follow up, among them 6 patients with positive GLP-1 scintigraphy result. One patient with negative scintigraphy was diagnosed with malignant insulinoma. In two patients with negative scintigraphy Munchausen syndrome was diagnosed (patients were taking insulin). Other seven patients with negative results of 99mTcGLP-1 scintigraphy and postprandial hypoglycemia with C-peptide and insulin levels within the limits of normal ranges are in the observational group. We would like to mention that 99mTc-GLP1-SPECT/CT was also performed in 3 pts with nesidioblastosis (revealing diffuse tracer uptake in two and a focal lesion in one case) and in two patients with malignant insulinoma (with the a focal uptake in the localization of a removed pancreatic headin one case and negative GLP-1 1 scintigraphy in the other patient). Conclusions 99mTc-GLP1-SPECT/CT could be helpful examination in the management of patients with hypoglycemia enabling proper localization of the pancreatic lesion and effective

Prediction of thyroid C-cell carcinogenicity after chronic administration of GLP1-R agonists in rodents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brink, Willem van den; Emerenciana, Annette

Increased incidence of C-cell carcinogenicity has been observed for glucagon-like-protein-1 receptor (GLP-1r) agonists in rodents. It is suggested that the duration of exposure is an indicator of carcinogenic potential in rodents of the different products on the market. Furthermore, the role of GLP-1-related mechanisms in the induction of C-cell carcinogenicity has gained increased attention by regulatory agencies. This study proposes an integrative pharmacokinetic/pharmacodynamic (PKPD) framework to identify explanatory factors and characterize differences in carcinogenic potential of the GLP-1r agonist products. PK models for four products (exenatide QW (once weekly), exenatide BID (twice daily), liraglutide and lixisenatide) were developed using nonlinearmore » mixed effects modelling. Predicted exposure was subsequently linked to GLP-1r stimulation using in vitro GLP-1r potency data. A logistic regression model was then applied to exenatide QW and liraglutide data to assess the relationship between GLP-1r stimulation and thyroid C-cell hyperplasia incidence as pre-neoplastic predictor of a carcinogenic response. The model showed a significant association between predicted GLP-1r stimulation and C-cell hyperplasia after 2 years of treatment. The predictive performance of the model was evaluated using lixisenatide, for which hyperplasia data were accurately described during the validation step. The use of a model-based approach provided insight into the relationship between C-cell hyperplasia and GLP-1r stimulation for all four products, which is not possible with traditional data analysis methods. It can be concluded that both pharmacokinetics (exposure) and pharmacodynamics (potency for GLP-1r) factors determine C-cell hyperplasia incidence in rodents. Our work highlights the pharmacological basis for GLP-1r agonist-induced C-cell carcinogenicity. The concept is promising for application to other drug classes. - Highlights: • An integrative PKPD model is

Acarbose improves hypoglycaemia following gastric bypass surgery without increasing glucagon-like peptide 1 levels.

PubMed

Valderas, Juan Patricio; Ahuad, Jessica; Rubio, Lorena; Escalona, Manuel; Pollak, Felipe; Maiz, Alberto

2012-04-01

Postprandial hypoglycaemia is a severe complication of Roux-en-Y gastric bypass (RYGBP). Acarbose, an α-glucosidase inhibitor (AGI), is employed in its treatment. Several studies have shown that AGIs increase the postprandial levels of glucagon-like peptide 1 (GLP-1). However, an excessive level of GLP-1 is one of the factors involved in the physiopathology of this condition. We analysed the effect of acarbose oral administration in eight RYBGP patients with clinically significant hypoglycaemia or dumping syndrome. Glucose, insulin and GLP-1 plasma levels in fasting and after ingestion of a standard meal (Ensure Plus®; 13 g protein, 50 g carbohydrate, 11 g fat) were measured. The test was repeated the following week with the oral administration of 100 mg of acarbose 15 min prior to the meal. Five patients developed asymptomatic hypoglycaemia during the test (glucose level <50 mg/dl) with inappropriately high insulin levels and exaggerated GLP-1 response. Acarbose ingestion avoided hypoglycaemia in all of the patients and increased the lowest plasma glucose level (46.4 ± 4.8 vs. 59.0 ± 2.6 mg/dl, p < 0.01). Acarbose ingestion decreased the area under the curve for serum insulin and GLP-1 levels at 15 min after the meal. Acarbose avoided postprandial hypoglycaemia following RYGBP by decreasing the hyperinsulinemic response. This was associated with a decrease in early GLP-1 secretion, in contrast to that observed in non-surgical subjects. This finding could be explained by the reduction of glucose load in the jejunum produced by the α-glucosidase inhibition, which is the main stimulus for GLP-1 secretion.

Recombinant human GLP-1(rhGLP-1) alleviating renal tubulointestitial injury in diabetic STZ-induced rats.

PubMed

Yin, Weiqin; Xu, Shiqing; Wang, Zai; Liu, Honglin; Peng, Liang; Fang, Qing; Deng, Tingting; Zhang, Wenjian; Lou, Jinning

2018-01-01

GLP-1-based treatment improves glycemia through stimulation of insulin secretion and inhibition of glucagon secretion. Recently, more and more findings showed that GLP-1 could also protect kidney from diabetic nephropathy. Most of these studies focused on glomeruli, but the effect of GLP-1 on tubulointerstitial and tubule is not clear yet. In this study, we examined the renoprotective effect of recombinant human GLP-1 (rhGLP-1), and investigated the influence of GLP-1 on inflammation and tubulointerstitial injury using diabetic nephropathy rats model of STZ-induced. The results showed that rhGLP-1 reduced urinary albumin without influencing the body weight and food intake. rhGLP-1 could increased the serum C-peptide slightly but not lower fasting blood glucose significantly. In diabetic nephropathy rats, beside glomerular sclerosis, tubulointerstitial fibrosis was very serious. These lesions could be alleviated by rhGLP-1. rhGLP-1 decreased the expression of profibrotic factors collagen I, α-SMA, fibronectin, and inflammation factors MCP-1 and TNFα in tubular tissue and human proximal tubular cells (HK-2 cells). Furthermore, rhGLP-1 significantly inhibited the phosphorylation of NF-κB, MAPK in both diabetic tubular tissue and HK-2 cells. The inhibition of the expression of TNFα, MCP-1, collagen I and α-SMA in HK-2 cells by GLP-1 could be mimicked by blocking NF-κB or MAPK. These results indicate that rhGLP-1 exhibit renoprotective effect by alleviation of tubulointerstitial injury via inhibiting phosphorylation of MAPK and NF-κB. Therefore, rhGLP-1 may be a potential drug for treatment of diabetic nephropathy. Copyright © 2017 Elsevier Inc. All rights reserved.

Modulation of taste sensitivity by GLP-1 signaling in taste buds.

PubMed

Martin, Bronwen; Dotson, Cedrick D; Shin, Yu-Kyong; Ji, Sunggoan; Drucker, Daniel J; Maudsley, Stuart; Munger, Steven D

2009-07-01

Modulation of sensory function can help animals adjust to a changing external and internal environment. Even so, mechanisms for modulating taste sensitivity are poorly understood. Using immunohistochemical, biochemical, and behavioral approaches, we found that the peptide hormone glucagon-like peptide-1 (GLP-1) and its receptor (GLP-1R) are expressed in mammalian taste buds. Furthermore, we found that GLP-1 signaling plays an important role in the modulation of taste sensitivity: GLP-1R knockout mice exhibit a dramatic reduction in sweet taste sensitivity as well as an enhanced sensitivity to umami-tasting stimuli. Together, these findings suggest a novel paracrine mechanism for the hormonal modulation of taste function in mammals.

Farnesoid X receptor induces Takeda G-protein receptor 5 cross-talk to regulate bile acid synthesis and hepatic metabolism.

PubMed

Pathak, Preeti; Liu, Hailiang; Boehme, Shannon; Xie, Cen; Krausz, Kristopher W; Gonzalez, Frank; Chiang, John Y L

2017-06-30

The bile acid-activated receptors, nuclear farnesoid X receptor (FXR) and the membrane Takeda G-protein receptor 5 (TGR5), are known to improve glucose and insulin sensitivity in obese and diabetic mice. However, the metabolic roles of these two receptors and the underlying mechanisms are incompletely understood. Here, we studied the effects of the dual FXR and TGR5 agonist INT-767 on hepatic bile acid synthesis and intestinal secretion of glucagon-like peptide-1 (GLP-1) in wild-type, Fxr -/- , and Tgr5 -/- mice. INT-767 efficaciously stimulated intracellular Ca 2+ levels, cAMP activity, and GLP-1 secretion and improved glucose and lipid metabolism more than did the FXR-selective obeticholic acid and TGR5-selective INT-777 agonists. Interestingly, INT-767 reduced expression of the genes in the classic bile acid synthesis pathway but induced those in the alternative pathway, which is consistent with decreased taurocholic acid and increased tauromuricholic acids in bile. Furthermore, FXR activation induced expression of FXR target genes, including fibroblast growth factor 15, and unexpectedly Tgr5 and prohormone convertase 1/3 gene expression in the ileum. We identified an FXR-responsive element on the Tgr5 gene promoter. Fxr -/- and Tgr5 -/- mice exhibited reduced GLP-1 secretion, which was stimulated by INT-767 in the Tgr5 -/- mice but not in the Fxr -/- mice. Our findings uncovered a novel mechanism in which INT-767 activation of FXR induces Tgr5 gene expression and increases Ca 2+ levels and cAMP activity to stimulate GLP-1 secretion and improve hepatic glucose and lipid metabolism in high-fat diet-induced obese mice. Activation of both FXR and TGR5 may therefore represent an effective therapy for managing hepatic steatosis, obesity, and diabetes. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

COMPARATIVE GUT PHYSIOLOGY SYMPOSIUM: Comparative physiology of glucagon-like peptide-2: Implications and applications for production and health of ruminants.

PubMed

Connor, E E; Evock-Clover, C M; Walker, M P; Elsasser, T H; Kahl, S

2015-02-01

Glucagon-like peptide-2 (GLP-2) is a 33-amino acid peptide derived from proteolytic cleavage of proglucagon by prohormone convertase 1/3 in enteroendocrine L cells. Studies conducted in humans, in rodent models, and in vitro indicate that GLP-2 is secreted in response to the presence of molecules in the intestinal lumen, including fatty acids, carbohydrates, amino acids, and bile acids, which are detected by luminal chemosensors. The physiological actions of GLP-2 are mediated by its G protein-coupled receptor expressed primarily in the intestinal tract on enteric neurons, enteroendocrine cells, and myofibroblasts. The biological activity of GLP-2 is further regulated by dipeptidyl peptidase IV, which rapidly cleaves the N-terminus of GLP-2 that is responsible for GLP-2 receptor activation. Within the gut, GLP-2 increases nutrient absorption, crypt cell proliferation, and mesenteric blood flow and decreases gut permeability and motility, epithelial cell apoptosis, and inflammation. Outside the gut, GLP-2 reduces bone resorption, can suppress appetite, and is cytoprotective in the lung. Thus, GLP-2 has been studied intensively as a therapeutic to improve intestinal function of humans during parenteral nutrition and following small bowel resection and, more recently, as a treatment for osteoporosis and obesity-related disorders and to reduce cellular damage associated with inflammation of the gut and lungs. Recent studies demonstrate that many biological actions and properties of GLP-2 in ruminants are similar to those in nonruminants, including the potential to reduce intestinal nitro-oxidative stress in calves caused by parasitic diseases such as coccidiosis. Because of its beneficial impacts on nutrient absorption, gut healing, and normal gut development, GLP-2 therapy offers significant opportunities to improve calf health and production efficiency. However, GLP-2 therapies require an extended time course to achieve desired physiological responses, as well as

Minireview: Signal Bias, Allosterism, and Polymorphic Variation at the GLP-1R: Implications for Drug Discovery

PubMed Central

Koole, Cassandra; Savage, Emilia E.; Christopoulos, Arthur; Miller, Laurence J.

2013-01-01

The glucagon-like peptide-1 receptor (GLP-1R) controls the physiological responses to the incretin hormone glucagon-like peptide-1 and is a major therapeutic target for the treatment of type 2 diabetes, owing to the broad range of effects that are mediated upon its activation. These include the promotion of glucose-dependent insulin secretion, increased insulin biosynthesis, preservation of β-cell mass, improved peripheral insulin action, and promotion of weight loss. Regulation of GLP-1R function is complex, with multiple endogenous and exogenous peptides that interact with the receptor that result in the activation of numerous downstream signaling cascades. The current understanding of GLP-1R signaling and regulation is limited, with the desired spectrum of signaling required for the ideal therapeutic outcome still to be determined. In addition, there are several single-nucleotide polymorphisms (used in this review as defining a natural change of single nucleotide in the receptor sequence; clinically, this is viewed as a single-nucleotide polymorphism only if the frequency of the mutation occurs in 1% or more of the population) distributed within the coding sequence of the receptor protein that have the potential to produce differential responses for distinct ligands. In this review, we discuss the current understanding of GLP-1R function, in particular highlighting recent advances in the field on ligand-directed signal bias, allosteric modulation, and probe dependence and the implications of these behaviors for drug discovery and development. PMID:23864649

Nutrient-induced glucagon like peptide-1 release is modulated by serotonin.

PubMed

Ripken, Dina; van der Wielen, Nikkie; Wortelboer, Heleen M; Meijerink, Jocelijn; Witkamp, Renger F; Hendriks, Henk F J

2016-06-01

Glucagon like peptide-1 (GLP-1) and serotonin are both involved in food intake regulation. GLP-1 release is stimulated upon nutrient interaction with G-protein coupled receptors by enteroendocrine cells (EEC), whereas serotonin is released from enterochromaffin cells (ECC). The central hypothesis for the current study was that nutrient-induced GLP-1 release from EECs is modulated by serotonin through a process involving serotonin receptor interaction. This was studied by assessing the effects of serotonin reuptake inhibition by fluoxetine on nutrient-induced GLP-1, PYY and CCK release from isolated pig intestinal segments. Next, serotonin-induced GLP-1 release was studied in enteroendocrine STC-1 cells, where effects of serotonin receptor inhibition were studied using specific and non-specific antagonists. Casein (1% w/v), safflower oil (3.35% w/v), sucrose (50mM) and rebaudioside A (12.5mM) stimulated GLP-1 release from intestinal segments, whereas casein only stimulated PYY and CCK release. Combining nutrients with fluoxetine further increased nutrient-induced GLP-1, PYY and CCK release. Serotonin release from intestinal tissue segments was stimulated by casein and safflower oil while sucrose and rebaudioside A had no effect. The combination with fluoxetine (0.155μM) further enhanced casein and safflower oil induced-serotonin release. Exposure of ileal tissue segments to serotonin (30μM) stimulated GLP-1 release whereas it did not induce PYY and CCK release. Serotonin (30 and 100μM) also stimulated GLP-1 release from STC-1 cells, which was inhibited by the non-specific 5HT receptor antagonist asenapine (1 and 10μM). These data suggest that nutrient-induced GLP-1 release is modulated by serotonin through a receptor mediated process. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Ligand-induced dynamics of heterotrimeric G protein-coupled receptor-like kinase complexes.

PubMed

Tunc-Ozdemir, Meral; Jones, Alan M

2017-01-01

Arabidopsis, 7-transmembrane Regulator of G signaling protein 1 (AtRGS1) modulates canonical G protein signaling by promoting the inactive state of heterotrimeric G protein complex on the plasma membrane. It is known that plant leucine-rich repeat receptor-like kinases (LRR RLKs) phosphorylate AtRGS1 in vitro but little is known about the in vivo interaction, molecular dynamics, or the cellular consequences of this interaction. Therefore, a subset of the known RLKs that phosphorylate AtRGS1 were selected for elucidation, namely, BAK1, BIR1, FLS2. Several microscopies for both static and dynamic protein-protein interactions were used to follow in vivo interactions between the RLKs and AtRGS1 after the presentation of the Pathogen-associated Molecular Pattern, Flagellin 22 (Flg22). These microscopies included Förster Resonance Energy Transfer, Bimolecular Fluoresence Complementation, and Cross Number and Brightness Fluorescence Correlation Spectroscopy. In addition, reactive oxygen species and calcium changes in living cells were quantitated using luminometry and R-GECO1 microscopy. The LRR RLKs BAK1 and BIR1, interact with AtRGS1 at the plasma membrane. The RLK ligand flg22 sets BAK1 in motion toward AtRGS1 and BIR1 away, both returning to the baseline orientations by 10 minutes. The C-terminal tail of AtRGS1 is important for the interaction with BAK1 and for the tempo of the AtRGS1/BIR1 dynamics. This window of time corresponds to the flg22-induced transient production of reactive oxygen species and calcium release which are both attenuated in the rgs1 and the bak1 null mutants. A temporal model of these interactions is proposed. flg22 binding induces nearly instantaneous dimerization between FLS2 and BAK1. Phosphorylated BAK1 interacts with and enables AtRGS1 to move away from BIR1 and AtRGS1 becomes phosphorylated leading to its endocytosis thus leading to de-repression by permitting AtGPA1 to exchange GDP for GTP. Finally, the G protein complex becomes

Ligand-induced dynamics of heterotrimeric G protein-coupled receptor-like kinase complexes

DOE PAGES

Tunc-Ozdemir, Meral; Jones, Alan M.

2017-02-10

Background Arabidopsis, 7-transmembrane Regulator of G signaling protein 1 (AtRGS1) modulates canonical G protein signaling by promoting the inactive state of heterotrimeric G protein complex on the plasma membrane. It is known that plant leucine-rich repeat receptor-like kinases (LRR RLKs) phosphorylate AtRGS1 in vitro but little is known about the in vivo interaction, molecular dynamics, or the cellular consequences of this interaction. Methods Therefore, a subset of the known RLKs that phosphorylate AtRGS1 were selected for elucidation, namely, BAK1, BIR1, FLS2. Several microscopies for both static and dynamic protein-protein interactions were used to follow in vivo interactions between the RLKsmore » and AtRGS1 after the presentation of the Pathogen-associated Molecular Pattern, Flagellin 22 (Flg22). These microscopies included FoÈrster Resonance Energy Transfer, Bimolecular Fluoresence Complementation, and Cross Number and Brightness fluorescence Correlation Spectroscopy. In addition, reactive oxygen species and calcium changes in living cells were quantitated using luminometry and R-GECO1 microscopy. Results The LRR RLKs BAK1 and BIR1, interact with AtRGS1 at the plasma membrane. The RLK ligand flg22 sets BAK1 in motion toward AtRGS1 and BIR1 away, both returning to the baseline orientations by 10 minutes. The C-terminal tail of AtRGS1 is important for the interaction with BAK1 and for the tempo of the AtRGS1/BIR1 dynamics. This window of time corresponds to the flg22-induced transient production of reactive oxygen species and calcium release which are both attenuated in the rgs1 and the bak1 null mutants. Conclusions A temporal model of these interactions is proposed. flg22 binding induces nearly instantaneous dimerization between FLS2 and BAK1. Phosphorylated BAK1 interacts with and enables AtRGS1 to move away from BIR1 and AtRGS1 becomes phosphorylated leading to its endocytosis thus leading to de-repression by permitting AtGPA1 to exchange GDP for GTP

Ligand-induced dynamics of heterotrimeric G protein-coupled receptor-like kinase complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tunc-Ozdemir, Meral; Jones, Alan M.

Background Arabidopsis, 7-transmembrane Regulator of G signaling protein 1 (AtRGS1) modulates canonical G protein signaling by promoting the inactive state of heterotrimeric G protein complex on the plasma membrane. It is known that plant leucine-rich repeat receptor-like kinases (LRR RLKs) phosphorylate AtRGS1 in vitro but little is known about the in vivo interaction, molecular dynamics, or the cellular consequences of this interaction. Methods Therefore, a subset of the known RLKs that phosphorylate AtRGS1 were selected for elucidation, namely, BAK1, BIR1, FLS2. Several microscopies for both static and dynamic protein-protein interactions were used to follow in vivo interactions between the RLKsmore » and AtRGS1 after the presentation of the Pathogen-associated Molecular Pattern, Flagellin 22 (Flg22). These microscopies included FoÈrster Resonance Energy Transfer, Bimolecular Fluoresence Complementation, and Cross Number and Brightness fluorescence Correlation Spectroscopy. In addition, reactive oxygen species and calcium changes in living cells were quantitated using luminometry and R-GECO1 microscopy. Results The LRR RLKs BAK1 and BIR1, interact with AtRGS1 at the plasma membrane. The RLK ligand flg22 sets BAK1 in motion toward AtRGS1 and BIR1 away, both returning to the baseline orientations by 10 minutes. The C-terminal tail of AtRGS1 is important for the interaction with BAK1 and for the tempo of the AtRGS1/BIR1 dynamics. This window of time corresponds to the flg22-induced transient production of reactive oxygen species and calcium release which are both attenuated in the rgs1 and the bak1 null mutants. Conclusions A temporal model of these interactions is proposed. flg22 binding induces nearly instantaneous dimerization between FLS2 and BAK1. Phosphorylated BAK1 interacts with and enables AtRGS1 to move away from BIR1 and AtRGS1 becomes phosphorylated leading to its endocytosis thus leading to de-repression by permitting AtGPA1 to exchange GDP for GTP

Effect of apolipoprotein B mRNA-editing catalytic polypeptide-like protein-3G in cervical cancer

PubMed Central

Xu, Yanhua; Leng, Junhong; Xue, Fang; Dong, Ruiqian

2015-01-01

Cervical cancer is one of the most common gynecologic cancers. The role of apolipoprotein B mRNA-editing catalytic polypeptide-like protein-3G (APCBEC-3G) in cervical cancer has yet to be elucidated. This study intends to explore the effect ofAPCBEC-3G on cervical cancer cell proliferation and invasion. In vitro, the cervical cancer cell line Hela was transfected by APCBEC-3G plasmid. The mRNA and protein expression levels of APCBEC-3G were detected by Real-time PCR and Western blot, respectively. Cervical cancer cell proliferation was determined by MTT. Transwell assay was applied to measure the effect of APCBEC-3G on cell invasion. APCBEC-3G mRNA and protein increased significantly after transfection (P<0.05) and cervical cancer cell proliferation and invasive ability were decreased significantly (P<0.05). APOBEC-3G serves as a suppressor of cervical cancer cell proliferation and invasion. Our research provides theoretical basis for further investigationAPOBEC-3G effect in cervical cancer occurrence and development. PMID:26722417

Effect of apolipoprotein B mRNA-editing catalytic polypeptide-like protein-3G in cervical cancer.

PubMed

Xu, Yanhua; Leng, Junhong; Xue, Fang; Dong, Ruiqian

2015-01-01

Cervical cancer is one of the most common gynecologic cancers. The role of apolipoprotein B mRNA-editing catalytic polypeptide-like protein-3G (APCBEC-3G) in cervical cancer has yet to be elucidated. This study intends to explore the effect of APCBEC-3G on cervical cancer cell proliferation and invasion. In vitro, the cervical cancer cell line Hela was transfected by APCBEC-3G plasmid. The mRNA and protein expression levels of APCBEC-3G were detected by Real-time PCR and Western blot, respectively. Cervical cancer cell proliferation was determined by MTT. Transwell assay was applied to measure the effect of APCBEC-3G on cell invasion. APCBEC-3G mRNA and protein increased significantly after transfection (P<0.05) and cervical cancer cell proliferation and invasive ability were decreased significantly (P<0.05). APOBEC-3G serves as a suppressor of cervical cancer cell proliferation and invasion. Our research provides theoretical basis for further investigation APOBEC-3G effect in cervical cancer occurrence and development.

Dulaglutide, a long-acting GLP-1 analog fused with an Fc antibody fragment for the potential treatment of type 2 diabetes.

PubMed

Jimenez-Solem, Espen; Rasmussen, Mette H; Christensen, Mikkel; Knop, Filip K

2010-12-01

Dulaglutide (LY-2189265) is a novel, long-acting glucagon-like peptide 1 (GLP-1) analog being developed by Eli Lilly for the treatment of type 2 diabetes mellitus (T2DM). Dulaglutide consists of GLP-1(7-37) covalently linked to an Fc fragment of human IgG4, thereby protecting the GLP-1 moiety from inactivation by dipeptidyl peptidase 4. In vitro and in vivo studies on T2DM models demonstrated glucose-dependent insulin secretion stimulation. Pharmacokinetic studies demonstrated a t1/2 in humans of up to 90 h, making dulaglutide an ideal candidate for once-weekly dosing. Clinical trials suggest that dulaglutide reduces plasma glucose, and has an insulinotropic effect increasing insulin and C-peptide levels. Two phase II clinical trials demonstrated a dose-dependent reduction in glycated hemoglobin (HbA1c) of up to 1.52% compared with placebo. Side effects associated with dulaglutide administration were mainly gastrointestinal. To date, there have been no reports on the formation of antibodies against dulaglutide, but, clearly, long-term data will be needed to asses this and other possible side effects. The results of several phase III clinical trials are awaited for clarification of the expected effects on HbA1c and body weight. If dulaglutide possesses similar efficacy to other GLP-1 analogs, the once-weekly treatment will most likely be welcomed by patients with T2DM.

Rate of Homologous Desensitization and Internalization of the GLP-1 Receptor.

PubMed

Shaaban, Ghina; Oriowo, Mabayoje; Al-Sabah, Suleiman

2016-12-26

The glucagon-like peptide-1 receptor (GLP-1R) is an important target in the treatment of type 2 diabetes mellitus. The aim of this study was to compare the rate of agonist stimulated desensitization and internalization of GLP-1R. To this end, an N-terminally myc-tagged GLP-1R was stably expressed in HEK-293 cells. Homologous desensitization was assessed by measuring the cAMP response to agonist stimulation following pre-incubation with agonist for up to 120 min. Receptor internalization was monitored using an indirect ELISA-based method and confocal microscopy. Pre-incubation with GLP-1 resulted in a time-dependent loss of response to a second stimulation. Washing cells following pre-incubation failed to bring cAMP levels back to basal. Taking this into account, two desensitization rates were calculated: "apparent" (t 1/2 = 19.27 min) and "net" (t 1/2 = 2.99 min). Incubation of cells with GLP-1 also resulted in a time-dependent loss of receptor cell surface expression (t 1/2 = 2.05 min). Rapid agonist-stimulated internalization of GLP-1R was confirmed using confocal microscopy. Stimulation of GLP-1R with GLP-1 results in rapid desensitization and internalization of the receptor. Interestingly, the rate of "net" desensitization closely matches the rate of internalization. Our results suggest that agonist-bound GLP-1R continues to generate cAMP after it has been internalized.

Gut-expressed gustducin and taste receptors regulate secretion of glucagon-like peptide-1

PubMed Central

Jang, Hyeung-Jin; Kokrashvili, Zaza; Theodorakis, Michael J.; Carlson, Olga D.; Kim, Byung-Joon; Zhou, Jie; Kim, Hyeon Ho; Xu, Xiangru; Chan, Sic L.; Juhaszova, Magdalena; Bernier, Michel; Mosinger, Bedrich; Margolskee, Robert F.; Egan, Josephine M.

2007-01-01

Glucagon-like peptide-1 (GLP-1), released from gut endocrine L cells in response to glucose, regulates appetite, insulin secretion, and gut motility. How glucose given orally, but not systemically, induces GLP-1 secretion is unknown. We show that human duodenal L cells express sweet taste receptors, the taste G protein gustducin, and several other taste transduction elements. Mouse intestinal L cells also express α-gustducin. Ingestion of glucose by α-gustducin null mice revealed deficiencies in secretion of GLP-1 and the regulation of plasma insulin and glucose. Isolated small bowel and intestinal villi from α-gustducin null mice showed markedly defective GLP-1 secretion in response to glucose. The human L cell line NCI-H716 expresses α-gustducin, taste receptors, and several other taste signaling elements. GLP-1 release from NCI-H716 cells was promoted by sugars and the noncaloric sweetener sucralose, and blocked by the sweet receptor antagonist lactisole or siRNA for α-gustducin. We conclude that L cells of the gut “taste” glucose through the same mechanisms used by taste cells of the tongue. Modulating GLP-1 secretion in gut “taste cells” may provide an important treatment for obesity, diabetes and abnormal gut motility. PMID:17724330

Novel coumarin modified GLP-1 derivatives with enhanced plasma stability and prolonged in vivo glucose-lowering ability.

PubMed

Han, Jing; Sun, Lidan; Huang, Xun; Li, Zheng; Zhang, Chenyu; Qian, Hai; Huang, Wenlong

2014-12-01

The short biological half-life limits the therapeutic use of glucagon-like peptide-1 (GLP-1) and chemical modification to improve the interaction of peptides with serum albumin represents an effective strategy to develop long-acting peptide analogues. Coumarin, a natural product, is known to bind tightly to plasma proteins and possesses many biological activities. Therefore, we designed and synthesized a series of coumarin-modified GLP-1 derivatives, hypothesizing that conjugation with coumarin would retain the therapeutic effects and prolong the biological half-life of the conjugates. Four cysteine-modified GLP-1 analogues (1-4) were prepared using Gly8 -GLP-1(7-36)-NH2 peptide as a starting point. These analogues were conjugated with two coumarin maleimides to yield eight compounds (conjugates 6-13) for testing. Activation of human GLP-1 receptors, stability to enzymic inactivation in plasma and binding to human albumin were assessed in vitro. In vivo, effects on oral glucose tolerance tests (OGTT) in rats and on blood glucose levels in db/db mice were studied. Most conjugates showed well preserved receptor activation efficacy, enhanced albumin-binding properties and improved in vitro plasma stability and conjugate 7 was selected to undergo further assessment. In rats, conjugate 7 had a longer circulating t1/2 than exendin-4 or liraglutide. A prolonged antidiabetic effect of conjugate 7 was observed after OGTT in rats and a prolonged hypoglycaemic effect in db/db mice. Cysteine-specific coumarin conjugation with GLP-1 offers a useful approach to the development of long-acting incretin-based antidiabetic agents. Conjugate 7 is a promising long-lasting GLP-1 derivative deserving further investigation. © 2014 The British Pharmacological Society.

Dietary resistant starch upregulates total GLP-1 and PYY in a sustained day-long manner through fermentation in rodents.

PubMed

Zhou, June; Martin, Roy J; Tulley, Richard T; Raggio, Anne M; McCutcheon, Kathleen L; Shen, Li; Danna, Samuel Colby; Tripathy, Sasmita; Hegsted, Maren; Keenan, Michael J

2008-11-01

Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are anti-diabetes/obesity hormones secreted from the gut after meal ingestion. We have shown that dietary-resistant starch (RS) increased GLP-1 and PYY secretion, but the mechanism remains unknown. RS is a fermentable fiber that lowers the glycemic index of the diet and liberates short-chain fatty acids (SCFAs) through fermentation in the gut. This study investigates the two possible mechanisms by which RS stimulates GLP-1 and PYY secretion: the effect of a meal or glycemic index, and the effect of fermentation. Because GLP-1 and PYY secretions are stimulated by nutrient availability in the gut, the timing of blood sample collections could influence the outcome when two diets with different glycemic indexes are compared. Thus we examined GLP-1 and PYY plasma levels at various time points over a 24-h period in RS-fed rats. In addition, we tested proglucagon (a precursor to GLP-1) and PYY gene expression patterns in specific areas of the gut of RS-fed rats and in an enteroendocrine cell line following exposure to SCFAs in vitro. Our findings are as follows. 1) RS stimulates GLP-1 and PYY secretion in a substantial day-long manner, independent of meal effect or changes in dietary glycemia. 2) Fermentation and the liberation of SCFAs in the lower gut are associated with increased proglucagon and PYY gene expression. 3) Glucose tolerance, an indicator of increased active forms of GLP-1 and PYY, was improved in RS-fed diabetic mice. We conclude that fermentation of RS is most likely the primary mechanism for increased endogenous secretions of total GLP-1 and PYY in rodents. Thus any factor that affects fermentation should be considered when dietary fermentable fiber is used to stimulate GLP-1 and PYY secretion.

Venous blood provides lower GLP-1 concentrations than arterialised blood in the postprandial, but not fasted state: Consequences of sampling methods.

PubMed

Chen, Yung-Chih; Edinburgh, Robert M; Hengist, Aaron; Smith, Harry A; Walhin, Jean-Philippe; Betts, James A; Thompson, Dylan; Gonzalez, Javier T

2018-06-27

What is the central question of this study? Glucagon-like peptide-1 (GLP-1) is an important obesity/diabetes target, with effects dependent on circulating GLP-1 concentrations. Peripheral tissues extract GLP-1, therefore sampling venous versus arterialised blood may provide different GLP-1 concentrations. This study examined whether arterialisation alters GLP-1 concentrations during fasting and feeding. What is the main finding and its importance? This study demonstrates that venous blood provides lower postprandial, but not fasting, GLP-1 concentrations versus arterialised blood. Therefore, when accurate assessment of postprandial peripheral availability of GLP-1 is required, blood sampling methods should be carefully considered, clearly reported, and arterialisation is recommended. Glucagon-like peptide-1 (GLP-1) displays concentration-dependent effects on metabolism, appetite and angiogenesis, so accurate determination of circulating GLP-1 concentrations is important. This study compared GLP-1 concentrations in venous versus arterialised blood under both fasted and fed conditions. Venous and arterialised blood samples were simultaneously drawn from ten, young, healthy men before, and 30, 60 and 120 min after, ingestion of 75 g glucose. Plasma GLP-1 concentrations increased in response to glucose ingestion (time effect: p < 0.01) and to a lesser extend in venous versus arterialised plasma (time x arterialisation interaction: p < 0.01). Accordingly, the plasma incremental area under the curve was lower in venous versus arterialised plasma (974 ± 88 versus 1214 ± 115 pmol·L x 120 min -1 , respectively, p = 0.049). In the postprandial state, there was a positive relationship between arterialised GLP-1 concentrations and the venous-arterialised difference in GLP-1 concentrations (r 2  = 0.51; p < 0.01). Both arterialised and venous peak GLP-1 concentrations showed positive relationships with peak arterialised insulin concentrations (both r 2 �

Mechanisms underlying metformin-induced secretion of glucagon-like peptide-1 from the intestinal L cell.

PubMed

Mulherin, Andrew J; Oh, Amy H; Kim, Helena; Grieco, Anthony; Lauffer, Lina M; Brubaker, Patricia L

2011-12-01

Glucagon-like peptide-1(7-36NH2) (GLP-1) is secreted by the intestinal L cell in response to both nutrient and neural stimulation, resulting in enhanced glucose-dependent insulin secretion. GLP-1 is therefore an attractive therapeutic for the treatment of type 2 diabetes. The antidiabetic drug, metformin, is known to increase circulating GLP-1 levels, although its mechanism of action is unknown. Direct effects of metformin (5-2000 μm) or another AMP kinase activator, aminoimidazole carboxamide ribonucleotide (100-1000 μm) on GLP-1 secretion were assessed in murine human NCI-H716, and rat FRIC L cells. Neither agent stimulated GLP-1 secretion in any model, despite increasing AMP kinase phosphorylation (P < 0.05-0.01). Treatment of rats with metformin (300 mg/kg, per os) or aminoimidazole carboxamide ribonucleotide (250 mg/kg, sc) increased plasma total GLP-1 over 2 h, reaching 37 ± 9 and 29 ± 9 pg/ml (P < 0.001), respectively, compared with basal (7 ± 1 pg/ml). Plasma activity of the GLP-1-degrading enzyme, dipeptidylpeptidase-IV, was not affected by metformin treatment. Pretreatment with the nonspecific muscarinic antagonist, atropine (1 mg/kg, iv), decreased metformin-induced GLP-1 secretion by 55 ± 11% (P < 0.05). Pretreatment with the muscarinic (M) 3 receptor antagonist, 1-1-dimethyl-4-diphenylacetoxypiperidinium iodide (500 μg/kg, iv), also decreased the GLP-1 area under curve, by 48 ± 8% (P < 0.05), whereas the antagonists pirenzepine (M1) and gallamine (M2) had no effect. Furthermore, chronic bilateral subdiaphragmatic vagotomy decreased basal secretion compared with sham-operated animals (7 ± 1 vs. 13 ± 1 pg/ml, P < 0.001) but did not alter the GLP-1 response to metformin. In contrast, pretreatment with the gastrin-releasing peptide antagonist, RC-3095 (100 μg/kg, sc), reduced the GLP-1 response to metformin, by 55 ± 6% (P < 0.01) at 30 min. These studies elucidate the mechanism underlying metformin-induced GLP-1 secretion and highlight the

The type 2 dengue virus envelope protein interacts with small ubiquitin-like modifier-1 (SUMO-1) conjugating enzyme 9 (Ubc9).

PubMed

Chiu, Mei-Wui; Shih, Hsiu-Ming; Yang, Tsung-Han; Yang, Yun-Liang

2007-05-01

Dengue viruses are mosquito-borne flaviviruses and may cause the life-threatening dengue hemorrhagic fever and dengue shock syndrome. Its envelope protein is responsible mainly for the virus attachment and entry to host cells. To identify the human cellular proteins interacting with the envelope protein of dengue virus serotype 2 inside host cells, we have performed a screening with the yeast-two-hybrid-based "Functional Yeast Array". Interestingly, the small ubiquitin-like modifier-1 conjugating enzyme 9 protein, modulating cellular processes such as those regulating signal transduction and cell growth, was one of the candidates interacting with the dengue virus envelope protein. With co-precipitation assay, we have demonstrated that it indeed could interact directly with the Ubc9 protein. Site-directed mutagenesis has demonstrated that Ubc9 might interact with the E protein via amino acid residues K51 and K241. Furthermore, immunofluorescence microscopy has shown that the DV2E-EGFP proteins tended to progress toward the nuclear membrane and co-localized with Flag-Ubc9 proteins around the nuclear membrane in the cytoplasmic side, and DV2E-EGFP also shifted the distribution of Flag-Ubc9 from evenly in the nucleus toward concentrating around the nuclear membrane in the nucleic side. In addition, over-expression of Ubc9 could reduce the plaque formation of the dengue virus in mammalian cells. This is the first report that DV envelope proteins can interact with the protein of sumoylation system and Ubc9 may involve in the host defense system to prevent virus propagation.

Liraglutide Modulates Appetite and Body Weight Via GLP-1R-Expressing Glutamatergic Neurons.

PubMed

Adams, Jessica M; Pei, Hongjuan; Sandoval, Darleen A; Seeley, Randy J; Chang, Rui B; Liberles, Stephen D; Olson, David P

2018-05-18

Glucagon-like peptide-1 receptor (GLP-1R) agonists are FDA-approved weight loss drugs. Despite their widespread use, the sites of action through which GLP-1R agonists (GLP1RAs) impact appetite and body weight are still not fully understood. Here, we determined whether GLP-1Rs in either GABAergic or glutamatergic neurons are necessary for the acute and chronic effects of the GLP1RA liraglutide on food intake, visceral illness, body weight and neural network activation. We found that mice lacking GLP-1Rs in vGAT -expressing GABAergic neurons responded identically to controls in all parameters measured, whereas deletion of GLP-1Rs in vGlut2 -expressing glutamatergic neurons eliminated liraglutide-induced weight loss and visceral illness and severely attenuated its effects on feeding. Concomitantly, deletion of GLP-1Rs from glutamatergic neurons completely abolished the neural network activation observed after liraglutide administration. We conclude that liraglutide activates a dispersed but discrete neural network to mediate its physiological effects, and that these effects require GLP-1R expression on glutamatergic but not GABAergic neurons. © 2018 by the American Diabetes Association.

Central GLP-1 receptor signalling accelerates plasma clearance of triacylglycerol and glucose by activating brown adipose tissue in mice.

PubMed

Kooijman, Sander; Wang, Yanan; Parlevliet, Edwin T; Boon, Mariëtte R; Edelschaap, David; Snaterse, Gido; Pijl, Hanno; Romijn, Johannes A; Rensen, Patrick C N

2015-11-01

Glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) agonism, used in the treatment of type 2 diabetes, has recently been shown to increase thermogenesis via the brain. As brown adipose tissue (BAT) produces heat by burning triacylglycerol (TG) and takes up glucose for de novo lipogenesis, the aim of this study was to evaluate the potential of chronic central GLP-1R activation by exendin-4 to facilitate clearance of lipids and glucose from the circulation by activating BAT. Lean and diet-induced obese (DIO) C57Bl/6J mice were used to explore the effect of a 5 day intracerebroventricular infusion of the GLP-1 analogue exendin-4 or vehicle on lipid and glucose uptake by BAT in both insulin-sensitive and insulin-resistant conditions. Central administration of exendin-4 in lean mice increased sympathetic outflow towards BAT and white adipose tissue (WAT), resulting in increased thermogenesis as evidenced by increased uncoupling protein 1 (UCP-1) protein levels and decreased lipid content, while the uptake of TG-derived fatty acids was increased in both BAT and WAT. Interestingly, in DIO mice, the effects on WAT were blunted, while exendin-4 still increased sympathetic outflow towards BAT and increased the uptake of plasma TG-derived fatty acids and glucose by BAT. These effects were accompanied by increased fat oxidation, lower plasma TG and glucose concentrations, and reduced body weight. Collectively, our results suggest that BAT activation may be a major contributor to the glucose- and TG-lowering effects of GLP-1R agonism.

The histone methyltransferase G9a: a new therapeutic target in biliary tract cancer.

PubMed

Mayr, Christian; Helm, Katharina; Jakab, Martin; Ritter, Markus; Shrestha, Rajeev; Makaju, Ramesh; Wagner, Andrej; Pichler, Martin; Beyreis, Marlena; Staettner, Stefan; Jaeger, Tarkan; Klieser, Eckhard; Kiesslich, Tobias; Neureiter, Daniel

2018-02-01

The histone methyltransferase G9a (EHMT2) is a key enzyme for dimethylation of lysine 9 at histone 3 (H3K9me2), a suppressive epigenetic mark. G9a is over-expressed in tumor cells and contributes to cancer aggressiveness. Biliary tract cancer (BTC) is a rare cancer with dismal prognosis due to a lack of effective therapies. Currently, there are no data on the role of G9a in BTC carcinogenesis. We analyzed G9a expression in n=68 BTC patient specimens and correlated the data with clinicopathological and survival data. Moreover, we measured G9a expression in a panel of BTC cell lines and evaluated the cytotoxic effect of G9a inhibition in BTC cells using established small-molecule G9a inhibitors. G9a was considerably expressed in about half of BTC cases and was significantly associated with grading and tumor size. Additionally, we observed significant differences of G9a expression between growth type and tumor localization groups. G9a expression diametrically correlated with Vimentin (positive) and E-Cadherin (negative) expression. Importantly, survival analysis revealed G9a as a significant prognostic factor of poor survival in patients with BTC. In BTC cells, G9a and H3K9me2 were detectable in a cell line-dependent manner on mRNA and/or protein level, respectively. Treatment of BTC cells with established small-molecule G9a inhibitors resulted in reduction of cell viability as well as reduced G9a and H3K9me2 protein levels. The present study strongly suggests that G9a contributes to BTC carcinogenesis and may represent a potential prognostic factor as well as a therapeutic target. Copyright © 2017 Elsevier Inc. All rights reserved.

A novel human-based receptor antagonist of sustained action reveals body weight control by endogenous GLP-1.

PubMed

Patterson, James T; Ottaway, Nickki; Gelfanov, Vasily M; Smiley, David L; Perez-Tilve, Diego; Pfluger, Paul T; Tschöp, Matthias H; Dimarchi, Richard D

2011-02-18

Ex-4 (9-39)a is a well characterized GLP-1 receptor antagonist that suffers from two notable limitations, its nonhuman amino acid sequence and its relatively short in vivo duration of action. Comparable N-terminal shortening of human GLP-1 lessens agonism but does not provide a high potency antagonist. Through a series of GLP-1/Ex-4 hybrid peptides, the minimal structural changes required to generate a pure GLP-1-based antagonist were identified as Glu16, Val19, and Arg20, yielding an antagonist of approximately 3-fold greater in vitro potency compared with Ex-4 (9-39)a. The structural basis of antagonism appears to result from stabilization of the α helix combined with enhanced electrostatic and hydrophobic interactions with the extracellular domain of the receptor. Site-specific acylation of the human-based antagonist yielded a peptide of increased potency as a GLP-1 receptor antagonist and 10-fold greater selectivity relative to the GIP receptor. The acylated antagonist demonstrated sufficient duration of action to maintain inhibitory activity when administered as a daily subcutaneous injection. The sustained pharmacokinetics and enhanced human sequence combine to form an antagonist optimized for clinical study. Daily administration of this antagonist by subcutaneous injection to diet-induced obese mice for 1 week caused a significant increase in food intake, body weight, and glucose intolerance, demonstrating endogenous GLP-1 as a relevant hormone in mammalian energy balance in the obese state.

Immunogenicity and efficacy of immunodeficiency virus-like particles pseudotyped with the G protein of vesicular stomatitis virus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuate, Seraphin; Stahl-Hennig, Christiane; Stoiber, Heribert

2006-07-20

Vaccination with exogenous antigens such as recombinant viral proteins, immunodeficiency virus-derived whole inactivated virus particles, or virus-like particles (VLP) has generally failed to provide sufficient protection in animal models for AIDS. Pseudotyping VLPs with the vesicular stomatitis virus G protein (VSV-G), which is known to mediate entry into dendritic cells, might allow more efficient stimulation of immune responses. Therefore, we pseudotyped noninfectious immunodeficiency virus-like particles with VSV-G and carried out a preliminary screen of their immunogenicity and vaccination efficacy. Incorporation of VSV-G into HIV-1 VLPs led to hundred-fold higher antibody titers to HIV-1 Gag and enhancement of T cell responsesmore » in mice. Repeated vaccination of rhesus monkeys for 65 weeks with VSV-G pseudotyped simian immunodeficiency virus (SIV)-like particles (VLP[G]) provided initial evidence for efficient suppression of viral load after mucosal challenge with the SIVmac239 virus. Challenge of monkeys after a 28 week vaccination regimen with VLP[G] led to a reduction in peak viremia, but persistent suppression of viral load was not achieved. Due to limitations in the number of animals available for this study, improved efficacy of VSV-G pseudotyped VLPs in nonhuman primates could not be demonstrated. However, mouse experiments revealed that pseudotyping of VLPs with fusion-competent VSV-G clearly improves their immunogenicity. Additional strategies, particularly adjuvants, should be considered to provide greater protection against a challenge with pathogenic immunodeficiency virus.« less

GLP-2 receptor in POMC neurons suppresses feeding behavior and gastric motility

USDA-ARS?s Scientific Manuscript database

Glucagon-like peptides (GLP-1/2) are cosecreted from endocrine L cells in the gut and preproglucagonergic neurons in the brain. Peripheral GLP-2 action is essential for maintaining intestinal homeostasis, improving absorption efficiency and blood flow, promoting immune defense, and producing efficac...

Expression, purification, and C-terminal site-specific PEGylation of cysteine-mutated glucagon-like peptide-1.

PubMed

Gao, Mingming; Tian, Hong; Ma, Chen; Gao, Xiangdong; Guo, Wei; Yao, Wenbing

2010-09-01

Glucagon-like peptide-1 (GLP-1) is attracting increasing interest on account of its prominent benefits in type 2 diabetes. However, its clinical application is limited because of short biological half-life. This study was designed to produce a C-terminal site-specific PEGylated analog of cysteine-mutated GLP-1 (cGLP-1) to prolong its action. The gene of cGLP-1 was inserted into pET32a to construct a thioredoxinA fusion protein. After expression in BL21 (DE3) strain, the fusion protein was purified with Ni-affinity chromatography and then was PEGylated with methoxy-polyethylene glycol-maleimide (mPEG(10K)-MAL). The PEGylated fusion protein was purified with anion exchange chromatography and then was cleaved by enterokinase. The digested product was further purified with reverse-phase chromatography. Finally, 8.7 mg mPEG(10K)-cGLP-1 with a purity of up to 98% was obtained from the original 500 ml culture. The circular dichroism spectra indicated that mPEG(10K)-cGLP-1 maintained the secondary structure of native GLP-1. As compared with that of native GLP-1, the plasma glucose lowering activity of mPEG(10K)-cGLP-1 was significantly extended. These results suggest that our method will be useful in obtaining a large quantity of mPEG(10K)-cGLP-1 for further study and mPEG(10K)-cGLP-1 might find a role in the therapy of type 2 diabetes through C-terminal site-specific PEGylation.

A chromatin activity based chemoproteomic approach reveals a transcriptional repressome for gene-specific silencing

PubMed Central

Liu, Cui; Yu, Yanbao; Liu, Feng; Wei, Xin; Wrobel, John A.; Gunawardena, Harsha P.; Zhou, Li; Jin, Jian; Chen, Xian

2015-01-01

Immune cells develop endotoxin tolerance (ET) after prolonged stimulation. ET increases the level of a repression mark H3K9me2 in the transcriptional-silent chromatin specifically associated with pro-inflammatory genes. However, it is not clear what proteins are functionally involved in this process. Here we show that a novel chromatin activity based chemoproteomic (ChaC) approach can dissect the functional chromatin protein complexes that regulate ET-associated inflammation. Using UNC0638 that binds the enzymatically active H3K9-specific methyltransferase G9a/GLP, ChaC reveals that G9a is constitutively active at a G9a-dependent mega-dalton repressome in primary endotoxin-tolerant macrophages. G9a/GLP broadly impacts the ET-specific reprogramming of the histone code landscape, chromatin remodeling, and the activities of select transcription factors. We discover that the G9a-dependent epigenetic environment promotes the transcriptional repression activity of c-Myc for gene-specific co-regulation of chronic inflammation. ChaC may be also applicable to dissect other functional protein complexes in the context of phenotypic chromatin architectures. PMID:25502336

Acting on Hormone Receptors with Minimal Side Effect on Cell Proliferation: A Timely Challenge Illustrated with GLP-1R and GPER.

PubMed

Gigoux, Véronique; Fourmy, Daniel

2013-01-01

G protein-coupled receptors (GPCRs) constitute a large family of receptors that sense molecules outside the cell and activate inside signal transduction pathways and cellular responses. GPCR are involved in a wide variety of physiological processes, including in the neuroendocrine system. GPCR are also involved in many diseases and are the target of 30% of marketed medicinal drugs. Whereas the majority of the GPCR-targeting drugs have proved their therapeutic benefit, some of them were associated with undesired effects. We develop two examples of used drugs whose therapeutic benefits are tarnished by carcinogenesis risks. The chronic administration of glucagon-like peptide-1 (GLP-1) analogs widely used to treat type-2 diabetes was associated with an increased risk of pancreatic or thyroid cancers. The long-term treatment with the estrogen antagonist tamoxifen, developed to target breast cancer overexpressing estrogen receptors ER, presents agonist activity on the G protein-coupled estrogen receptor which is associated with an increased incidence of endometrial cancer and breast cancer resistance to hormonotherapy. We point out and discuss the need of pharmacological studies to understand and overcome the undesired effects associated with the chronic administration of GPCR ligands. In fact, biological effects triggered by GPCR often result from the activation of multiple intracellular signaling pathways. Deciphering which signaling networks are engaged following GPCR activation appears to be primordial to unveil their contribution in the physiological and physiopathological processes. The development of biased agonists to elucidate the role of the different signaling mechanisms mediated by GPCR activation will allow the generation of new therapeutic agents with improved efficacy and reduced side effects. In this regard, the identification of GLP-1R biased ligands promoting insulin secretion without inducing pro-tumoral effects would offer therapeutic benefit.

Glucagon-like peptide-1 increases myocardial glucose uptake via p38alpha MAP kinase-mediated, nitric oxide-dependent mechanisms in conscious dogs with dilated cardiomyopathy.

PubMed

Bhashyam, Siva; Fields, Anjali V; Patterson, Brandy; Testani, Jeffrey M; Chen, Li; Shen, You-Tang; Shannon, Richard P

2010-07-01

We have shown that glucagon-like peptide-1 (GLP-1[7-36] amide) stimulates myocardial glucose uptake in dilated cardiomyopathy (DCM) independent of an insulinotropic effect. The cellular mechanisms of GLP-1-induced myocardial glucose uptake are unknown. Myocardial substrates and glucoregulatory hormones were measured in conscious, chronically instrumented dogs at control (n=6), DCM (n=9) and DCM after treatment with a 48-hour infusion of GLP-1 (7-36) amide (n=9) or vehicle (n=6). GLP-1 receptors and cellular pathways implicated in myocardial glucose uptake were measured in sarcolemmal membranes harvested from the 4 groups. GLP-1 stimulated myocardial glucose uptake (DCM: 20+/-7 nmol/min/g; DCM+GLP-1: 61+/-12 nmol/min/g; P=0.001) independent of increased plasma insulin levels. The GLP-1 receptors were upregulated in the sarcolemmal membranes (control: 98+/-2 density units; DCM: 256+/-58 density units; P=0.046) and were expressed in their activated (65 kDa) form in DCM. The GLP-1-induced increases in myocardial glucose uptake did not involve adenylyl cyclase or Akt activation but was associated with marked increases in p38alpha MAP kinase activity (DCM+vehicle: 97+/-22 pmol ATP/mg/min; DCM+GLP-1: 170+/-36 pmol ATP/mg/min; P=0.051), induction of nitric oxide synthase 2 (DCM+vehicle: 151+/-13 density units; DCM+GLP-1: 306+/-12 density units; P=0.001), and GLUT-1 translocation (DCM+vehicle: 21+/-3% membrane bound; DCM+GLP-1: 39+/-3% membrane bound; P=0.005). The effects of GLP-1 on myocardial glucose uptake were blocked by pretreatment with the p38alpha MAP kinase inhibitor or the nonspecific nitric oxide synthase inhibitor nitro-l-arginine. GLP-1 stimulates myocardial glucose uptake through a non-Akt-1-dependent mechanism by activating cellular pathways that have been identified in mediating chronic hibernation and the late phase of ischemic preconditioning.

Novel coumarin modified GLP-1 derivatives with enhanced plasma stability and prolonged in vivo glucose-lowering ability

PubMed Central

Han, Jing; Sun, Lidan; Huang, Xun; Li, Zheng; Zhang, Chenyu; Qian, Hai; Huang, Wenlong

2014-01-01

Background and Purpose The short biological half-life limits the therapeutic use of glucagon-like peptide-1 (GLP-1) and chemical modification to improve the interaction of peptides with serum albumin represents an effective strategy to develop long-acting peptide analogues. Coumarin, a natural product, is known to bind tightly to plasma proteins and possesses many biological activities. Therefore, we designed and synthesized a series of coumarin-modified GLP-1 derivatives, hypothesizing that conjugation with coumarin would retain the therapeutic effects and prolong the biological half-life of the conjugates. Experimental Approach Four cysteine-modified GLP-1 analogues (1–4) were prepared using Gly8-GLP-1(7–36)-NH2 peptide as a starting point. These analogues were conjugated with two coumarin maleimides to yield eight compounds (conjugates 6–13) for testing. Activation of human GLP-1 receptors, stability to enzymic inactivation in plasma and binding to human albumin were assessed in vitro. In vivo, effects on oral glucose tolerance tests (OGTT) in rats and on blood glucose levels in db/db mice were studied. Key Results Most conjugates showed well preserved receptor activation efficacy, enhanced albumin-binding properties and improved in vitro plasma stability and conjugate 7 was selected to undergo further assessment. In rats, conjugate 7 had a longer circulating t1/2 than exendin-4 or liraglutide. A prolonged antidiabetic effect of conjugate 7 was observed after OGTT in rats and a prolonged hypoglycaemic effect in db/db mice. Conclusions and Implications Cysteine-specific coumarin conjugation with GLP-1 offers a useful approach to the development of long-acting incretin-based antidiabetic agents. Conjugate 7 is a promising long-lasting GLP-1 derivative deserving further investigation. PMID:25039358

Targeted Elimination of G Proteins and Arrestins Defines Their Specific Contributions to Both Intensity and Duration of G Protein-coupled Receptor Signaling.

PubMed

Alvarez-Curto, Elisa; Inoue, Asuka; Jenkins, Laura; Raihan, Sheikh Zahir; Prihandoko, Rudi; Tobin, Andrew B; Milligan, Graeme

2016-12-30

G protein-coupled receptors (GPCRs) can initiate intracellular signaling cascades by coupling to an array of heterotrimeric G proteins and arrestin adaptor proteins. Understanding the contribution of each of these coupling options to GPCR signaling has been hampered by a paucity of tools to selectively perturb receptor function. Here we employ CRISPR/Cas9 genome editing to eliminate selected G proteins (Gα q and Gα 11 ) or arrestin2 and arrestin3 from HEK293 cells together with the elimination of receptor phosphorylation sites to define the relative contribution of G proteins, arrestins, and receptor phosphorylation to the signaling outcomes of the free fatty acid receptor 4 (FFA4). A lack of FFA4-mediated elevation of intracellular Ca 2+ in Gα q /Gα 11 -null cells and agonist-mediated receptor internalization in arrestin2/3-null cells confirmed previously reported canonical signaling features of this receptor, thereby validating the genome-edited HEK293 cells. FFA4-mediated ERK1/2 activation was totally dependent on G q / 11 but intriguingly was substantially enhanced for FFA4 receptors lacking sites of regulated phosphorylation. This was not due to a simple lack of desensitization of G q / 11 signaling because the G q / 11 -dependent calcium response was desensitized by both receptor phosphorylation and arrestin-dependent mechanisms, whereas a substantially enhanced ERK1/2 response was only observed for receptors lacking phosphorylation sites and not in arrestin2/3-null cells. In conclusion, we validate CRISPR/Cas9 engineered HEK293 cells lacking G q / 11 or arrestin2/3 as systems for GPCR signaling research and employ these cells to reveal a previously unappreciated interplay of signaling pathways where receptor phosphorylation can impact on ERK1/2 signaling through a mechanism that is likely independent of arrestins. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Activation of GLP-1 Receptor Promotes Bone Marrow Stromal Cell Osteogenic Differentiation through β-Catenin

PubMed Central

Meng, Jingru; Ma, Xue; Wang, Ning; Jia, Min; Bi, Long; Wang, Yunying; Li, Mingkai; Zhang, Huinan; Xue, Xiaoyan; Hou, Zheng; Zhou, Ying; Yu, Zhibin; He, Gonghao; Luo, Xiaoxing

2016-01-01

Summary Glucagon-like peptide 1 (GLP-1) plays an important role in regulating bone remodeling, and GLP-1 receptor agonist shows a positive relationship with osteoblast activity. However, GLP-1 receptor is not found in osteoblast, and the mechanism of GLP-1 receptor agonist on regulating bone remodeling is unclear. Here, we show that the GLP-1 receptor agonist exendin-4 (Ex-4) promoted bone formation and increased bone mass and quality in a rat unloading-induced bone loss model. These functions were accompanied by an increase in osteoblast number and serum bone formation markers, while the adipocyte number was decreased. Furthermore, GLP-1 receptor was detected in bone marrow stromal cells (BMSCs), but not in osteoblast. Activation of GLP-1 receptor by Ex-4 promoted the osteogenic differentiation and inhibited BMSC adipogenic differentiation through regulating PKA/β-catenin and PKA/PI3K/AKT/GSK3β signaling. These findings reveal that GLP-1 receptor regulates BMSC osteogenic differentiation and provide a molecular basis for therapeutic potential of GLP-1 against osteoporosis. PMID:26947974

Refinement of glucagon-like peptide 1 docking to its intact receptor using mid-region photolabile probes and molecular modeling.

PubMed

Miller, Laurence J; Chen, Quan; Lam, Polo C-H; Pinon, Delia I; Sexton, Patrick M; Abagyan, Ruben; Dong, Maoqing

2011-05-06

The glucagon-like peptide 1 (GLP1) receptor is an important drug target within the B family of G protein-coupled receptors. Its natural agonist ligand, GLP1, has incretin-like actions and the receptor is a recognized target for management of type 2 diabetes mellitus. Despite recent solution of the structure of the amino terminus of the GLP1 receptor and several close family members, the molecular basis for GLP1 binding to and activation of the intact receptor remains unclear. We previously demonstrated molecular approximations between amino- and carboxyl-terminal residues of GLP1 and its receptor. In this work, we study spatial approximations with the mid-region of this peptide to gain insights into the orientation of the intact receptor and the ligand-receptor complex. We have prepared two new photolabile probes incorporating a p-benzoyl-l-phenylalanine into positions 16 and 20 of GLP1(7-36). Both probes bound to the GLP1 receptor specifically and with high affinity. These were each fully efficacious agonists, stimulating cAMP accumulation in receptor-bearing CHO cells in a concentration-dependent manner. Each probe specifically labeled a single receptor site. Protease cleavage and radiochemical sequencing identified receptor residue Leu(141) above transmembrane segment one as its site of labeling for the position 16 probe, whereas the position 20 probe labeled receptor residue Trp(297) within the second extracellular loop. Establishing ligand residue approximation with this loop region is unique among family members and may help to orient the receptor amino-terminal domain relative to its helical bundle region.

Central GLP-2 enhances hepatic insulin sensitivity via activating PI3K signaling in POMC neurons.

PubMed

Shi, Xuemei; Zhou, Fuguo; Li, Xiaojie; Chang, Benny; Li, Depei; Wang, Yi; Tong, Qingchun; Xu, Yong; Fukuda, Makoto; Zhao, Jean J; Li, Defa; Burrin, Douglas G; Chan, Lawrence; Guan, Xinfu

2013-07-02

Glucagon-like peptides (GLP-1/GLP-2) are coproduced and highlighted as key modulators to improve glucose homeostasis and insulin sensitivity after bariatric surgery. However, it is unknown if CNS GLP-2 plays any physiological role in the control of glucose homeostasis and insulin sensitivity. We show that mice lacking GLP-2 receptor (GLP-2R) in POMC neurons display glucose intolerance and hepatic insulin resistance. GLP-2R activation in POMC neurons is required for GLP-2 to enhance insulin-mediated suppression of hepatic glucose production (HGP) and gluconeogenesis. GLP-2 directly modulates excitability of POMC neurons in GLP-2R- and PI3K-dependent manners. GLP-2 initiates GLP-2R-p85α interaction and facilitates PI3K-Akt-dependent FoxO1 nuclear exclusion in POMC neurons. Central GLP-2 suppresses basal HGP and enhances insulin sensitivity, which are abolished in POMC-p110α KO mice. Thus, CNS GLP-2 plays a key physiological role in the control of HGP through activating PI3K-dependent modulation of membrane excitability and nuclear transcription of POMC neurons in the brain. Copyright © 2013 Elsevier Inc. All rights reserved.

Lysophosphatidylinositol-induced activation of the cation channel TRPV2 triggers glucagon-like peptide-1 secretion in enteroendocrine L cells.

PubMed

Harada, Kazuki; Kitaguchi, Tetsuya; Kamiya, Taichi; Aung, Kyaw Htet; Nakamura, Kazuaki; Ohta, Kunihiro; Tsuboi, Takashi

2017-06-30

The lysophosphatidylinositol (LPI) has crucial roles in multiple physiological processes, including insulin exocytosis from pancreatic islets. However, the role of LPI in secretion of glucagon-like peptide-1 (GLP-1), a hormone that enhances glucose-induced insulin secretion, is unclear. Here, we used the murine enteroendocrine L cell line GLUTag and primary murine small intestinal cells to elucidate the mechanism of LPI-induced GLP-1 secretion. Exogenous LPI addition increased intracellular Ca 2+ concentrations ([Ca 2+ ] i ) in GLUTag cells and induced GLP-1 secretion from both GLUTag and acutely prepared primary intestinal cells. The [Ca 2+ ] i increase was suppressed by an antagonist for G protein-coupled receptor 55 (GPR55) and by silencing of GPR55 expression, indicating involvement of G q and G 12/13 signaling pathways in the LPI-induced increased [Ca 2+ ] i levels and GLP-1 secretion. However, GPR55 agonists did not mimic many of the effects of LPI. We also found that phospholipase C inhibitor and Rho-associated kinase inhibitor suppressed the [Ca 2+ ] i increase and that LPI increased the number of focal adhesions, indicating actin reorganization. Of note, blockage or silencing of transient receptor potential cation channel subfamily V member 2 (TRPV2) channels suppressed both the LPI-induced [Ca 2+ ] i increase and GLP-1 secretion. Furthermore, LPI accelerated TRPV2 translocation to the plasma membrane, which was significantly suppressed by a GPR55 antagonist. These findings suggest that TRPV2 activation via actin reorganization induced by G q and G 12/13 signaling is involved in LPI-stimulated GLP-1 secretion in enteroendocrine L cells. Because GPR55 agonists largely failed to mimic the effects of LPI, its actions on L cells are at least partially independent of GPR55 activation. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Effects of the GLP-1 Agonist Exendin-4 on Intravenous Ethanol Self-Administration in Mice.

PubMed

Sørensen, Gunnar; Caine, S Barak; Thomsen, Morgane

2016-10-01

Glucagon-like peptide 1 (GLP-1) receptor agonists have been shown to decrease ethanol (EtOH) drinking in rodent assays. The GLP-1 system also powerfully modulates food and fluid intake, gastrointestinal functions, and metabolism. To begin to understand the neurobiological mechanisms by which GLP-1 receptor ligands may be able to control EtOH intake, it is important to ascertain whether they can modulate the direct reinforcing effects of EtOH, without the confound of effects on ingestive behaviors generally. We trained experimentally naïve, free-fed C57BL/6J mice to self-administer EtOH intravenously. Once stable EtOH intake was acquired, we tested the effect of acute pretreatment with the GLP-1 receptor agonist Exendin-4. Effect of Exendin-4 on operant behavior reinforced by a palatable liquid food was similarly evaluated as a control. Intravenous EtOH functioned as a positive reinforcer in over half the mice tested. In mice that acquired self-administration, EtOH intake was high, indeed, reaching toxic doses; 3.2 μg/kg Exendin-4 decreased intravenous EtOH intake by at least 70%, but had no significant effect on food-maintained operant responding. This experiment produced 2 main conclusions. First, although technically challenging and yielding only moderate throughput, the intravenous self-administration procedure in mice is feasible, and sensitive to pharmacological manipulations. Second, GLP-1 receptor agonists can powerfully attenuate voluntary EtOH intake by directly modulating the reinforcing effects of EtOH. These findings support the potential usefulness of GLP-1 receptor ligands in the treatment of alcohol use disorder. Copyright © 2016 by the Research Society on Alcoholism.

[Effects of GLP-1 receptor agonists on carbohydrate metabolism control].

PubMed

Fernández-García, José Carlos; Colomo, Natalia; Tinahones, Francisco José

2014-01-01

Glucagon-like peptide-1 (GLP-1) receptor agonists are a new group of drugs for the treatment of type 2 diabetes mellitus (DM2). In the present article, we review the available evidence on the efficacy of GLP-1 receptor agonists as glucose-lowering agents, their place in therapeutic algorithms, and the clinical factors associated with a favorable treatment response. Finally, we describe the clinical characteristics of patients who may benefit from these drugs.

GLP-2 potentiates L-type CA2+ channel activity associated with stimulated glucose uptake in hippocampal neurons

USDA-ARS?s Scientific Manuscript database

Glucagon-like peptide-2 (GLP-2) is a neuropeptide secreted from endocrine cells in the gut and neurons in the brain. GLP-2 stimulates intestinal crypt cell proliferation and mucosal blood flow while decreasing gastric emptying and gut motility. However, a GLP-2-mediated signaling network has not bee...

Presence and dynamics of leptin, GLP-1, and PYY in human breast milk at early postpartum.

PubMed

Schueler, Jessica; Alexander, Brenda; Hart, Ann Marie; Austin, Kathleen; Larson-Meyer, D Enette

2013-07-01

The presence of appetite hormones, namely glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and leptin in breast milk may be important in infant feeding regulation and infant growth. This study evaluated whether concentrations of GLP-1, PYY, and leptin change across a single feeding (from fore- to hindmilk), and are associated with maternal and infant anthropometrics. Thirteen postpartum women (mean ± SD: 25.6 ± 4.5 years, 72.0 ± 11.9 kg) provided fore- and hindmilk samples 4-5 weeks after delivery and underwent measurements of body weight and composition by Dual X-ray Absorptiometry. GLP-1, PYY, and leptin concentrations were measured using radioimmunoassay, and milk fat content was determined by creamatocrit. Concentration of GLP-1 and content of milk fat was higher in hindmilk than foremilk (P ≤ 0.05). PYY and leptin concentrations did not change between fore- and hindmilk. Both leptin concentration and milk fat content were correlated with indices of maternal adiposity, including body mass index (r = 0.65-0.85, P < 0.02), and fat mass (r = 0.65-0.84, P < 0.02). Hindmilk GLP-1 was correlated with infant weight gain from birth to 6 months (r = -0.67, P = 0.034). The presence of appetite hormones in breast milk may be important in infant appetite and growth regulation. Copyright © 2013 The Obesity Society.

The effects of fiber enrichment of pasta and fat content on gastric emptying, GLP-1, glucose, and insulin responses to a meal.

PubMed

Frost, G S; Brynes, A E; Dhillo, W S; Bloom, S R; McBurney, M I

2003-02-01

To assess whether the addition of viscous fiber at an amount recommended by the US FDA to allow a 'low saturated fat, cholesterol, soluble fiber and coronary heart disease', health claim label on a food package (1.7 g psyllium) and/or fat (30 g sunflower oil and 3 g sodium propionate) to a pasta meal would affect gastric emptying, postprandial glucose, insulin and GLP-1 concentrations. Ten subjects participated in a two-by-two single blind randomized crossover study. Four meals containing 50 g of available carbohydrate were consumed: pasta with or without psyllium enrichment served with a tomato sauce with (520 kcal per meal) and without (240 kcal per meal) fat. Blood samples were taken for 240 min following the meal and all subjects consumed a buffet meal at the end of the study. Gastric emptying was measured using the paracetamol absorption test. Blood was analysed for glucose, insulin, GLP-1. Visual analog scales were used to record feelings of hunger, pleasantness and nausea. The psyllium-enriched pasta had no significant effect on gastric emptying or the incremental area under the curve (IAUC) for GLP-1, insulin or glucose compared with the control pasta. The addition of polyunsaturated fat and sodium propionate significantly increased the IAUC for GLP-1 (P<0.001), delaying gastric emptying (P<0.002), and decreasing glucose (P<0.002). A dose of 1.7 g psyllium did not evoke measurable effects on gastric emptying, postprandial GLP-1, insulin or glucose metabolism. However the addition of 30 g of oil and 3 g of sodium propionate to the pasta did reduce gastric emptying, increase GLP-1 and reduce glucose and insulin concentrations. While this short-term study may have implications in terms of reducing the risk of diabetes and improving coronary risk factor profiles the long term effects of these nutrients need to be studied.

Central GLP-2 enhances hepatic insulin sensitivity via activating PI3K signaling in POMC neurons

PubMed Central

Shi, Xuemei; Zhou, Fuguo; Li, Xiaojie; Chang, Benny; Li, Depei; Wang, Yi; Tong, Qingchun; Xu, Yong; Fukuda, Makoto; Zhao, Jean J.; Li, Defa; Burrin, Douglas G.; Chan, Lawrence; Guan, Xinfu

2013-01-01

Glucagon-like peptides (GLP-1/2) are co-produced and highlighted as key modulators to improve glucose homeostasis and insulin sensitivity after bariatric surgery. However, it is unknown if CNS GLP-2 plays any physiological role in the control of glucose homeostasis and insulin sensitivity. We show that mice lacking GLP-2 receptor (GLP-2R) in POMC neurons display glucose intolerance and hepatic insulin resistance. GLP-2R activation in POMC neurons is required for GLP-2 to enhance insulin-mediated suppression of hepatic glucose production (HGP) and gluconeogenesis. GLP-2 directly modulates excitability of POMC neurons in GLP-2R- and PI3K-dependent manners. GLP-2 initiates GLP-2R-p85α interaction and facilitates PI3K-Akt-dependent FoxO1 nuclear exclusion in POMC neurons. Central GLP-2 suppresses basal HGP and enhances insulin sensitivity, which are abolished in POMC-p110α KO mice. Thus, CNS GLP-2 plays a key physiological role in the control of hepatic glucose production through activating PI3K-dependent modulation of membrane excitability and nuclear transcription of POMC neurons in the brain. PMID:23823479

Central GLP-2 enhances hepatic insulin sensitivity via activating PI3K signaling in POMC neurons

USDA-ARS?s Scientific Manuscript database

Glucagon-like peptides (GLP-1/GLP-2) are coproduced and highlighted as key modulators to improve glucose homeostasis and insulin sensitivity after bariatric surgery. However, it is unknown if CNS GLP-2 plays any physiological role in the control of glucose homeostasis and insulin sensitivity. We sho...

PSCs and GLP-1R: occurrence in normal pancreas, acute/chronic pancreatitis and effect of their activation by a GLP-1R agonist

PubMed Central

Nakamura, Taichi; Ito, Tetsuhide; Uchida, Masahiko; Hijioka, Masayuki; Igarashi, Hisato; Oono, Takamasa; Kato, Masaki; Nakamura, Kazuhiko; Suzuki, Koichi; Jensen, Robert T.; Takayanagi, Ryoichi

2013-01-01

Background and Aims There is increasing concern about the development of pancreatitis in patients with diabetes mellitus who received long-term GLP-1 analog treatment. Its pathogenesis is unknown. The effects of GLP-1 agonists on pancreatic endocrine cells is well studied, however there is little information on effects on other pancreatic tissues that might be involved in inflammatory processes. Pancreatic stellate cells (PSCs) can play an important role in pancreatitis, secreting various inflammatory cytokines/chemokines, as well as collagen. In this study, we investigated GLP-1R occurrence in normal pancreas, acute/chronic pancreatitis, and the effects of GLP-1 analog on normal PSCs, their ability to stimulate inflammatory mediator secretion or proliferation. Methods GLP-1R expression/localization in normal pancreas and pancreatitis (acute/chronic) tissues were evaluated with histological/immunohistochemical analysis. PSCs were isolated from male Wistar rats. GLP1R expression and effects of GLP-1 analog on activated PSCs was examined with realtime PCR, MTS assays and Western Blotting. Results In normal pancreas, pancreatic β cells expressed GLP-1R, with only low expression in acinar cells, whereas in acute or chronic pancreatitis, acinar cells, ductal cells and activated PSCs expressed GLP-1R. With activation of normal PSCs, GLP-1R is markedly increased, as is multiple other incretin-related receptors. The GLP-1 analog, liraglutide, did not induce inflammatory genes expression in activated PSCs, but induced proliferation. Liraglutide activated multiple signaling cascades in PSCs, and the ERK pathway mediated the PSCs proliferation. Conclusions GLP-1Rs are expressed in normal pancreas and there is marked enhanced expression in acute/chronic pancreatitis. GLP-1-agonist induced cell proliferation of activated PSCs without increasing release of inflammatory mediators. These results suggest chronic treatment with GLP-1R agonists could lead to proliferation

Extension of in vivo half-life of biologically active peptides via chemical conjugation to XTEN protein polymer.

PubMed

Podust, Vladimir N; Sim, Bee-Cheng; Kothari, Dharti; Henthorn, Lana; Gu, Chen; Wang, Chia-wei; McLaughlin, Bryant; Schellenberger, Volker

2013-11-01

XTEN, unstructured biodegradable proteins, have been used to extend the in vivo half-life of genetically fused therapeutic proteins and peptides. To expand the applications of XTEN technology to half-life extension of other classes of molecules, XTEN protein polymers and methods for chemical XTENylation were developed. Two XTEN precursors were engineered to contain enzymatically removable purification tags. The proteins were readily expressed in bacteria and purified to homogeneity by chromatography techniques. As proof-of-principle, GLP2-2G peptide was chemically conjugated to each of the two XTEN protein polymers using maleimide-thiol chemistry. The monodisperse nature of XTEN protein polymer enabled reaction monitoring as well as the detection of peptide modifications in the conjugated state using reverse phase-high performance liquid chromatography (RP-HPLC) and electrospray ionization mass spectrometry. The resulting GLP2-2G-XTEN conjugates were purified by preparative RP-HPLC to homogeneity. In comparison with recombinantly fused GLP2-2G-XTEN, chemically conjugated GLP2-2G-XTEN molecules exhibited comparable in vitro activity, in vitro plasma stability and pharmacokinetics in rats. These data suggest that chemical XTENylation could effectively extend the half-life of a wide spectrum of biologically active molecules, therefore broadening its applicability.

The glucagon-like peptides: a new genre in therapeutic targets for intervention in Alzheimer's disease.

PubMed

Perry, TracyAnn; Greig, Nigel H

2002-12-01

Glucagon-like peptide-1 (7-36)-amide (GLP-1) is an insulinotropic hormone, secreted from the enteroendocrine L cells of the intestinal tract in response to nutrient ingestion. It enhances pancreatic islet beta-cell proliferation and glucose-dependent insulin secretion, and lowers blood glucose in patients with type 2 diabetes mellitus. GLP-1 receptors, which are coupled to the cyclic AMP second messenger pathway, are expressed throughout the brains of rodents and humans. The chemoarchitecture of receptor distribution in the brain correlates well with a central role for GLP-1 in the regulation of food intake and response to aversive stress. We have recently reported that GLP-1 and several longer acting analogs that bind at the GLP-1 receptor, possess neurotrophic properties, and offer protection against glutamate-induced apoptosis and oxidative injury in cultured neuronal cells. Furthermore, GLP-1 can modify processing of the amyloid beta- protein precursor in cell culture and dose-dependently reduces amyloid beta-peptide levels in the brain in vivo. As such, this review discusses the known role of GLP-1 within the central nervous system, and considers the potential of GLP-1 and analogs as novel therapeutic targets for intervention in Alzheimer's disease (AD) and potentially other central and peripheral neurodegenerative conditions.

Herpes Simplex Virus Membrane Proteins gE/gI and US9 Act Cooperatively To Promote Transport of Capsids and Glycoproteins from Neuron Cell Bodies into Initial Axon Segments

PubMed Central

Howard, Paul W.; Howard, Tiffani L.

2013-01-01

Herpes simplex virus (HSV) and other alphaherpesviruses must move from sites of latency in ganglia to peripheral epithelial cells. How HSV navigates in neuronal axons is not well understood. Two HSV membrane proteins, gE/gI and US9, are key to understanding the processes by which viral glycoproteins, unenveloped capsids, and enveloped virions are transported toward axon tips. Whether gE/gI and US9 function to promote the loading of viral proteins onto microtubule motors in neuron cell bodies or to tether viral proteins onto microtubule motors within axons is not clear. One impediment to understanding how HSV gE/gI and US9 function in axonal transport relates to observations that gE−, gI−, or US9− mutants are not absolutely blocked in axonal transport. Mutants are significantly reduced in numbers of capsids and glycoproteins in distal axons, but there are less extensive effects in proximal axons. We constructed HSV recombinants lacking both gE and US9 that transported no detectable capsids and glycoproteins to distal axons and failed to spread from axon tips to adjacent cells. Live-cell imaging of a gE−/US9− double mutant that expressed fluorescent capsids and gB demonstrated >90% diminished capsids and gB in medial axons and no evidence for decreased rates of transport, stalling, or increased retrograde transport. Instead, capsids, gB, and enveloped virions failed to enter proximal axons. We concluded that gE/gI and US9 function in neuron cell bodies, in a cooperative fashion, to promote the loading of HSV capsids and vesicles containing glycoproteins and enveloped virions onto microtubule motors or their transport into proximal axons. PMID:23077321

GLP2: an underestimated signal for improving glycaemic control and insulin sensitivity.

PubMed

Amato, Antonella; Baldassano, Sara; Mulè, Flavia

2016-05-01

Glucagon-like peptide 2 (GLP2) is a proglucagon-derived peptide produced by intestinal enteroendocrine L-cells and by a discrete population of neurons in the brainstem, which projects mainly to the hypothalamus. The main biological actions of GLP2 are related to the regulation of energy absorption and maintenance of mucosal morphology, function and integrity of the intestine; however, recent experimental data suggest that GLP2 exerts beneficial effects on glucose metabolism, especially in conditions related to increased uptake of energy, such as obesity, at least in the animal model. Indeed, mice lacking GLP2 receptor selectively in hypothalamic neurons that express proopiomelanocortin show impaired postprandial glucose tolerance and hepatic insulin resistance (by increased gluconeogenesis). Moreover, GLP2 acts as a beneficial factor for glucose metabolism in mice with high-fat diet-induced obesity. Thus, the aim of this review is to update and summarize current knowledge about the role of GLP2 in the control of glucose homeostasis and to discuss how this molecule could exert protective effects against the onset of related obesity type 2 diabetes. © 2016 Society for Endocrinology.

A surface plasmon resonance assay for characterisation and epitope mapping of anti-GLP-1 antibodies.

PubMed

Thomsen, Lasse; Gurevich, Leonid

2018-04-19

The incretin hormone glucagon-like peptide-1 (GLP-1) has been subject to substantial pharmaceutical research regarding the treatment of type 2 diabetes mellitus. However, quantification of GLP-1 levels remains complicated due to the low circulation concentration and concurrent existence of numerous metabolites, homologous peptides, and potentially introduced GLP-1 receptor agonists. Surface plasmon resonance (SPR) facilitates real-time monitoring allowing a more detailed characterisation of the interaction compared with conventional enzyme-linked immunosorbent assays (ELISA). In this paper, we describe the development of the first SPR assays for characterisation of anti-GLP-1 antibodies for ELISA purposes. Binding responses were obtained on covalently immobilised anti-GLP-1 antibodies at 12°C, 25°C, and 40°C and fitted to a biomolecular (1:1) interaction model showing association rates of 1.01 × 10 3 to 4.54 × 10 3  M -1  s -1 and dissociation rates of 3.56 × 10 -5 to 1.56 × 10 -3  s -1 leading to affinities of 35.2 to 344 nM, depending on the temperature. Determination of thermodynamic properties revealed an enthalpy driven interaction (ΔH < ΔS < 0) with higher affinities at lower temperatures due to the formation and stabilisation of hydrogen bonds within the binding site primarily composed of polar amino acids (ΔC p  < 0). Pair-wise epitope mapping was performed on captured anti-GLP-1 antibodies followed by subsequent interaction with GLP-1 (7-36) and other anti-GLP-1 antibodies. A global evaluation of every binding response led to an epitope map elucidating the potential of various anti-GLP-1 antibody pairs for sandwich ELISA and hence pinpointing the optimal antibody combinations. The SPR assays proved capable of providing vital information for ELISA development endorsing it as a useful optimisation tool. Copyright © 2018 John Wiley & Sons, Ltd.

Acute but not chronic activation of brain glucagon-like peptide-1 receptors enhances glucose-stimulated insulin secretion in mice.

PubMed

Tudurí, E; Beiroa, D; Porteiro, B; López, M; Diéguez, C; Nogueiras, R

2015-08-01

To investigate the role of brain glucagon-like peptide-1 (GLP-1) in pancreatic β-cell function. To determine the role of brain GLP-1 receptor (GLP-1R) on β-cell function, we administered intracerebroventricular (i.c.v.) infusions of GLP-1 or the specific GLP-1 antagonist exendin-9 (Ex-9), in both an acute and a chronic setting. We observed that acute i.c.v. GLP-1 infusion potentiates glucose-stimulated insulin secretion (GSIS) and improves glucose tolerance, whereas central GLP-1R blockade with Ex-9 impaired glucose excursion after a glucose load. Sustained activation of central nervous system GLP-1R, however, did not produce any effect on either GSIS or glucose tolerance. Similarly, ex vivo GSIS performed in islets from mice chronically infused with i.c.v. GLP-1 resulted in no differences compared with controls. In addition, in mice fed a high-fat diet we observed that acute i.c.v. GLP-1 infusion improved glucose tolerance without changes in GSIS, while chronic GLP-1R activation had no effect on glucose homeostasis. Our results indicate that, under non-clamped conditions, brain GLP-1 plays a functional neuroendocrine role in the acute regulation of glucose homeostasis in both lean and obese rodents. © 2015 John Wiley & Sons Ltd.

Linear {GLP}-algebras and their elementary theories

NASA Astrophysics Data System (ADS)

Pakhomov, F. N.

2016-12-01

The polymodal provability logic {GLP} was introduced by Japaridze in 1986. It is the provability logic of certain chains of provability predicates of increasing strength. Every polymodal logic corresponds to a variety of polymodal algebras. Beklemishev and Visser asked whether the elementary theory of the free {GLP}-algebra generated by the constants \\mathbf{0}, \\mathbf{1} is decidable [1]. For every positive integer n we solve the corresponding question for the logics {GLP}_n that are the fragments of {GLP} with n modalities. We prove that the elementary theory of the free {GLP}_n-algebra generated by the constants \\mathbf{0}, \\mathbf{1} is decidable for all n. We introduce the notion of a linear {GLP}_n-algebra and prove that all free {GLP}_n-algebras generated by the constants \\mathbf{0}, \\mathbf{1} are linear. We also consider the more general case of the logics {GLP}_α whose modalities are indexed by the elements of a linearly ordered set α: we define the notion of a linear algebra and prove the latter result in this case.

Noribogaine is a G-protein biased κ-opioid receptor agonist.

PubMed

Maillet, Emeline L; Milon, Nicolas; Heghinian, Mari D; Fishback, James; Schürer, Stephan C; Garamszegi, Nandor; Mash, Deborah C

2015-12-01

Noribogaine is the long-lived human metabolite of the anti-addictive substance ibogaine. Noribogaine efficaciously reaches the brain with concentrations up to 20 μM after acute therapeutic dose of 40 mg/kg ibogaine in animals. Noribogaine displays atypical opioid-like components in vivo, anti-addictive effects and potent modulatory properties of the tolerance to opiates for which the mode of action remained uncharacterized thus far. Our binding experiments and computational simulations indicate that noribogaine may bind to the orthosteric morphinan binding site of the opioid receptors. Functional activities of noribogaine at G-protein and non G-protein pathways of the mu and kappa opioid receptors were characterized. Noribogaine was a weak mu antagonist with a functional inhibition constants (Ke) of 20 μM at the G-protein and β-arrestin signaling pathways. Conversely, noribogaine was a G-protein biased kappa agonist 75% as efficacious as dynorphin A at stimulating GDP-GTP exchange (EC50=9 μM) but only 12% as efficacious at recruiting β-arrestin, which could contribute to the lack of dysphoric effects of noribogaine. In turn, noribogaine functionally inhibited dynorphin-induced kappa β-arrestin recruitment and was more potent than its G-protein agonistic activity with an IC50 of 1 μM. This biased agonist/antagonist pharmacology is unique to noribogaine in comparison to various other ligands including ibogaine, 18-MC, nalmefene, and 6'-GNTI. We predict noribogaine to promote certain analgesic effects as well as anti-addictive effects at effective concentrations>1 μM in the brain. Because elevated levels of dynorphins are commonly observed and correlated with anxiety, dysphoric effects, and decreased dopaminergic tone, a therapeutically relevant functional inhibition bias to endogenously released dynorphins by noribogaine might be worthy of consideration for treating anxiety and substance related disorders. Copyright © 2015 The Authors. Published by Elsevier

The autonomic nervous system and cardiac GLP-1 receptors control heart rate in mice.

PubMed

Baggio, Laurie L; Ussher, John R; McLean, Brent A; Cao, Xiemin; Kabir, M Golam; Mulvihill, Erin E; Mighiu, Alexandra S; Zhang, Hangjun; Ludwig, Andreas; Seeley, Randy J; Heximer, Scott P; Drucker, Daniel J

2017-11-01

Glucagon-like peptide-1 (GLP-1) is secreted from enteroendocrine cells and exerts a broad number of metabolic actions through activation of a single GLP-1 receptor (GLP-1R). The cardiovascular actions of GLP-1 have garnered increasing attention as GLP-1R agonists are used to treat human subjects with diabetes and obesity that may be at increased risk for development of heart disease. Here we studied mechanisms linking GLP-1R activation to control of heart rate (HR) in mice. The actions of GLP-1R agonists were examined on the control of HR in wild type mice (WT) and in mice with cardiomyocyte-selective disruption of the GLP-1R (Glp1r CM-/- ). Complimentary studies examined the effects of GLP-1R agonists in mice co-administered propranolol or atropine. The direct effects of GLP-1R agonism on HR and ventricular developed pressure were examined in isolated perfused mouse hearts ex vivo, and atrial depolarization was quantified in mouse hearts following direct application of liraglutide to perfused atrial preparations ex vivo. Doses of liraglutide and lixisenatide that were equipotent for acute glucose control rapidly increased HR in WT and Glp1r CM-/- mice in vivo. The actions of liraglutide to increase HR were more sustained relative to lixisenatide, and diminished in Glp1r CM-/- mice. The acute chronotropic actions of GLP-1R agonists were attenuated by propranolol but not atropine. Neither native GLP-1 nor lixisenatide increased HR or developed pressure in perfused hearts ex vivo. Moreover, liraglutide had no direct effect on sinoatrial node firing rate in mouse atrial preparations ex vivo. Despite co-localization of HCN4 and GLP-1R in primate hearts, HCN4-directed Cre expression did not attenuate levels of Glp1r mRNA transcripts, but did reduce atrial Gcgr expression in the mouse heart. GLP-1R agonists increase HR through multiple mechanisms, including regulation of autonomic nervous system function, and activation of the atrial GLP-1R. Surprisingly, the

Influenza virus-like particles harboring H9N2 HA and NA proteins induce a protective immune response in chicken.

PubMed

Li, Xin; Ju, Houbin; Liu, Jian; Yang, Dequan; Qi, Xinyong; Yang, Xianchao; Qiu, Yafeng; Zheng, Jie; Ge, Feifei; Zhou, Jinping

2017-11-01

Avian influenza viruses represent a growing threat of an influenza pandemic. The co-circulation of multiple H9N2 genotypes over the past decade has been replaced by one predominant genotype-G57 genotype, which displays a changed antigenicity and improved adaptability in chickens. Effective H9N2 subtype avian influenza virus vaccines for poultry are urgently needed. In this study, we constructed H9N2 subtype avian influenza virus-like particle (VLP) and evaluated its protective efficacy in specific pathogen-free (SPF) chickens to lay the foundation for developing an effective vaccine against influenza viruses. Expression of influenza proteins in VLPs was confirmed by Western blot, hemagglutination inhibition (HI), and neuraminidase inhibition (NI). The morphology was observed by electron microscopy. A group of 15 three-week-old SPF chickens was divided into three subgroups of five chickens immunized with VLP, commercial vaccine, and PBS. Challenge study was performed to evaluate efficacy of VLP vaccine. The hemagglutinin (HA) and neuraminidase (NA) proteins were co-expressed in the infected cells, self-assembled, and were released into the culture medium in the form of VLPs of diameter ~80 nm. The VLPs exhibited some functional characteristics of a full influenza virus, including hemagglutination and neuraminidase activity. In SPF chickens, the VLPs elicited serum antibodies specific for H9N2 and induced a higher HI titer (as detected by a homologous antigen) than did a commercial H9N2 vaccine (A/chicken/Shanghai/F/1998). Viral shedding from VLP vaccine subgroup was reduced compared with commercial vaccine subgroup and control subgroup. © 2017 The Authors. Influenza and Other Respiratory Viruses Published by John Wiley & Sons Ltd.

Lupin Peptides Modulate the Protein-Protein Interaction of PCSK9 with the Low Density Lipoprotein Receptor in HepG2 Cells

NASA Astrophysics Data System (ADS)

Lammi, Carmen; Zanoni, Chiara; Aiello, Gilda; Arnoldi, Anna; Grazioso, Giovanni

2016-07-01

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has been recently identified as a new useful target for hypercholesterolemia treatment. This work demonstrates that natural peptides, deriving from the hydrolysis of lupin protein and absorbable at intestinal level, are able to inhibit the protein-protein interaction between PCSK9 and the low density lipoprotein receptor (LDLR). In order to sort out the best potential inhibitors among these peptides, a refined in silico model of the PCSK9/LDLR interaction was developed. Docking, molecular dynamics (MD) simulations and peptide binding energy estimations, by MM-GBSA approach, permitted to select the two best candidates among tested peptides that were synthesized and evaluated for their inhibitory activity. The most active was P5 that induced a concentration dependent inhibition of the PCSK9-LDLR binding, with an IC50 value equal to 1.6 ± 0.33 μM. Tested at a 10 μM concentration, this peptide increased by 66 ± 21.4% the ability of HepG2 cells to take up LDL from the extracellular environment.

Active G protein-coupled receptors (GPCR), matrix metalloproteinases 2/9 (MMP2/9), heparin-binding epidermal growth factor (hbEGF), epidermal growth factor receptor (EGFR), erbB2, and insulin-like growth factor 1 receptor (IGF-1R) are necessary for trenbolone acetate-induced alterations in protein turnover rate of fused bovine satellite cell cultures.

PubMed

Thornton, K J; Kamanga-Sollo, E; White, M E; Dayton, W R

2016-06-01

Trenbolone acetate (TBA), a testosterone analog, increases protein synthesis and decreases protein degradation in fused bovine satellite cell (BSC) cultures. However, the mechanism through which TBA alters these processes remains unknown. Recent studies indicate that androgens improve rate and extent of muscle growth through a nongenomic mechanism involving G protein-coupled receptors (GPCR), matrix metalloproteinases (MMP), heparin-binding epidermal growth factor (hbEGF), the epidermal growth factor receptor (EGFR), erbB2, and the insulin-like growth factor-1 receptor (IGF-1R). We hypothesized that TBA activates GPCR, resulting in activation of MMP2/9 that releases hbEGF, which activates the EGFR and/or erbB2. To determine whether the proposed nongenomic pathway is involved in TBA-mediated alterations in protein turnover, fused BSC cultures were treated with TBA in the presence or absence of inhibitors for GPCR, MMP2/9, hbEGF, EGFR, erbB2, or IGF-1R, and resultant protein synthesis and degradation rates were analyzed. Assays were replicated at least 9 times for each inhibitor experiment utilizing BSC cultures obtained from at least 3 different steers that had no previous exposure to steroid compounds. As expected, fused BSC cultures treated with 10 n TBA exhibited increased ( < 0.05) protein synthesis rates and decreased ( < 0.05) protein degradation rates when compared to control cultures. Treatment of fused BSC cultures with 10 n TBA in the presence of inhibitors for GPCR, MMP2/9, hbEGF, EGFR, erbB2, or IGF-1R suppressed ( < 0.05) TBA-mediated increases in protein synthesis rate. Alternatively, inhibition of GPCR, MMP2/9, hbEGF, EGFR, erbB2, or IGF-1R in the presence of 10 n TBA each had no ( > 0.05) effect on TBA-mediated decreases in protein degradation. However, inhibition of both EGFR and erbB2 in the presence of 10 n TBA resulted in decreased ( < 0.05) ability of TBA to decrease protein degradation rate. Additionally, fused BSC cultures treated with 10 n

GLP-1 agonists for type 2 diabetes: pharmacokinetic and toxicological considerations.

PubMed

Jespersen, Maria J; Knop, Filip K; Christensen, Mikkel

2013-01-01

Within recent years, glucagon-like peptide 1 receptor agonists (GLP-1-RA) have emerged as a new treatment option for type 2 diabetes. The GLP-1-RA are administered subcutaneously and differ substantially in pharmacokinetic profiles. This review describes the pharmacokinetics and safety aspects of the currently available GLP-1 receptor agonists, liraglutide (based on the structure of native GLP-1), exenatide twice daily and exenatide once weekly (based on exendin-4) in relation to the kinetics and toxicology of native GLP-1. The review is based on electronic literature searches and legal documents in the form of assessment reports from the European Medicines Agency and the United States Food and Drug Administration. GLP-1-based therapy combines several unique mechanisms of action and have the potential to gain widespread use in the fight against diabetes and obesity. The difference in chemical structure have strong implications for key pharmacokinetic parameters such as absorption and clearance, and eventually the safety and efficacy of the individual GLP-1-RA. The main safety concerns are pancreatitis and neoplasms, for which there are no identifiable differences in risk between the available agents. Antibody formation and injection site reactions are more frequent with the exendin-4-based compounds. The efficacy with regard to Hb(A1c) reduction is superior with the longer-acting agonists, whereas the shorter-acting GLP-1-RA seems to provide greater postprandial glucose control and lower tolerability as a possible consequence of less induction of tachyphylaxis. The future place of these agents will depend on the added safety and efficacy data in the several ongoing cardiovascular outcome trials.

Cloning and characterization of the rat free fatty acid receptor GPR120: in vivo effect of the natural ligand on GLP-1 secretion and proliferation of pancreatic beta cells.

PubMed

Tanaka, Toshiki; Yano, Takeaki; Adachi, Tetsuya; Koshimizu, Taka-aki; Hirasawa, Akira; Tsujimoto, Gozoh

2008-06-01

We have recently found that GPR120, which is abundantly expressed in intestine, functions as a receptor for unsaturated long-chain free fatty acids (FFAs) and that GPR120 stimulation promotes the secretion of glucagons-like peptide-1 (GLP-1) in the mouse (Hirasawa et al., Nat Med 11:90-94, 2005). In this study, we cloned and characterized rat GPR120 (rGPR120), and then we examined the in vivo effects of acute and long-term administration of the natural ligand alpha-linolenic acid (alpha-LA). The cloned rat GPR120 complimentary DNA had a seven transmembrane structure, and a homology comparison of human, mouse, and rat GPR120 revealed that the rat GPR120 (rGPR120) shares 85 and 98% sequence identity with the human and mouse GPR120 proteins, respectively. The tissue distribution and ligand properties of rGPR120 were similar to those of mouse GPR120. In addition, alpha-LA provoked a transient increase in [Ca2+]i levels in HEK293 cells expressing rGPR120. Furthermore, administration of alpha-LA to the rat increased plasma GLP-1 levels, and long-term administration of alpha-LA led to proliferation of pancreatic beta cells, probably because of the enhanced GLP-1 secretion. These results show that rat GPR120 is a G-protein-coupled receptor whose ligand is a free fatty acid, and it may play an important role in the FFA-associated physiological responses.

Choosing between GLP-1 Receptor Agonists and DPP-4 Inhibitors: A Pharmacological Perspective

PubMed Central

Brown, Dominique Xavier; Evans, Marc

2012-01-01

In recent years the incretin therapies have provided a new treatment option for patients with type 2 diabetes mellitus (T2DM). The incretin therapies focus on the increasing levels of the two incretin hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). This results in increased glucose dependent insulin synthesis and release. GLP-1 receptor agonists such as liraglutide and exenatide exert an intrinsic biological effect on GLP-1 receptors directly stimulating the release of insulin from pancreatic beta cells. DPP-4 inhibitors such as sitagliptin and linagliptin prevent the inactivation of endogenous GLP-1 and GIP through competitive inhibition of the DPP-4 enzyme. Both incretin therapies have good safety and tolerability profiles and interact minimally with a number of medications commonly prescribed in T2DM. This paper focuses on the pharmacological basis by which the incretin therapies function and how this knowledge can inform and benefit clinical decisions. Each individual incretin agent has benefits and pitfalls relating to aspects such as glycaemic and nonglycaemic efficacy, safety and tolerability, ease of administration, and cost. Overall, a personalized medicine approach has been found to be favourable, tailoring the incretin agent to benefit and suit patient's needs such as renal impairment (RI) or hepatic impairment (HI). PMID:23125920

SR proteins SRp20 and 9G8 contribute to efficient export of herpes simplex virus 1 mRNAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Escudero-Paunetto, Laurimar; Li Ling; Hernandez, Felicia P.

2010-06-05

Herpes simplex virus 1 (HSV-1) mRNAs are exported to the cytoplasm through the export receptor TAP/NFX1. HSV-1 multifunctional protein ICP27 interacts with TAP/NXF1, binds viral RNAs, and is required for efficient viral RNA export. In ICP27 mutant infections, viral RNA export is reduced but not ablated, indicating that other export adaptors can aid in viral RNA export. Export adaptor protein Aly/REF is recruited to viral replication compartments, however, Aly/REF knockdown has little effect on viral RNA export. SR proteins SRp20 and 9G8 interact with TAP/NXF1 and mediate export of some cellular RNAs. We report that siRNA knockdown of SRp20 ormore » 9G8 resulted in about a 10 fold decrease in virus yields and in nuclear accumulation of poly(A+) RNA. In infected cells depleted of SRp20, newly transcribed Bromouridine-labeled RNA also accumulated in the nucleus. We conclude that SRp20 and 9G8 contribute to HSV-1 RNA export.« less

Glucagon-like peptide 1 receptor expression in primary porcine proximal tubular cells.

PubMed

Schlatter, P; Beglinger, C; Drewe, J; Gutmann, H

2007-06-07

GLP-1 is secreted into the circulation after food intake. The main biological effects of GLP-1 include stimulation of glucose dependent insulin secretion and induction of satiety feelings. Recently, it was demonstrated in rats and humans that GLP-1 can stimulate renal excretion of sodium. Based on these data, the existence of a renal GLP-1 receptor (GLP-1R) was postulated. However, the exact localization of the GLP-1R and the mechanism of this GLP-1 action have not yet been investigated. Primary porcine proximal tubular cells were isolated from porcine kidneys. Expression of GLP-1R was measured at the mRNA level by quantitative RT-PCR. Protein expression of GLP-1R was verified with immunocytochemistry, immunohistochemistry and Western blot analysis. Functional studies included transport assessments of sodium and glucose using three different GLP-1 concentrations (200 pM, 2 nM and 20 nM), 200 pM exendin-4 (GLP-1 analogue) and an inhibitor of the dipeptidylpeptidase IV (DPPIV) enzyme (P32/98 at 10 microM). Finally, the expression of NHE3, the predominant Na(+)/H(+) exchanger in proximal tubular cells, was also investigated. GLP-1R, NHE3 and DPPIV were expressed at the mRNA level in porcine proximal tubular kidney cells. GLP-1R expression was confirmed at the protein level. Staining of human and pig kidney cortex revealed that GLP-1R was predominantly expressed in proximal tubular cells. Functional assays demonstrated an inhibition of sodium re-absorption with GLP-1 after 3 h of incubation. Exendin-4 and GLP-1 in combination with P32/98 co-administration had no clear influence on glucose and sodium uptake and transport. GLP-1R is functionally expressed in porcine proximal tubular kidney cells. Addition of GLP-1 to these cells resulted in a reduced sodium re-absorption. GLP-1 had no effect on glucose re-absorption. We conclude that GLP-1 modulates sodium homeostasis in the kidney most likely through a direct action via its GLP-1R in proximal tubular cells.

Derepression of microRNA-mediated protein translation inhibition by apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G (APOBEC3G) and its family members.

PubMed

Huang, Jialing; Liang, Zhihui; Yang, Bin; Tian, Heng; Ma, Jin; Zhang, Hui

2007-11-16

The apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G (APOBEC3G or A3G) and its fellow cytidine deaminase family members are potent restrictive factors for human immunodeficiency virus type 1 (HIV-1) and many other retroviruses. A3G interacts with a vast spectrum of RNA-binding proteins and is located in processing bodies and stress granules. However, its cellular function remains to be further clarified. Using a luciferase reporter gene and green fluorescent protein reporter gene, we demonstrate that A3G and other APOBEC family members can counteract the inhibition of protein synthesis by various microRNAs (miRNAs) such as mir-10b, mir-16, mir-25, and let-7a. A3G could also enhance the expression level of miRNA-targeted mRNA. Further, A3G facilitated the association of microRNA-targeted mRNA with polysomes rather than with processing bodies. Intriguingly, experiments with a C288A/C291A A3G mutant indicated that this function of A3G is separable from its cytidine deaminase activity. Our findings suggest that the major cellular function of A3G, in addition to inhibiting the mobility of retrotransposons and replication of endogenous retroviruses, is most likely to prevent the decay of miRNA-targeted mRNA in processing bodies.

Serodiagnosis of Louse-Borne Relapsing Fever with Glycerophosphodiester Phosphodiesterase (GlpQ) from Borrelia recurrentis

PubMed Central

Porcella, Stephen F.; Raffel, Sandra J.; Schrumpf, Merry E.; Schriefer, Martin E.; Dennis, David T.; Schwan, Tom G.

2000-01-01

Human louse-borne relapsing fever occurs in sporadic outbreaks in central and eastern Africa that are characterized by significant morbidity and mortality. Isolates of the causative agent, Borrelia recurrentis, were obtained from the blood of four patients during a recent epidemic of the disease in southern Sudan. The glpQ gene, encoding glycerophosphodiester phosphodiesterase, from these isolates was sequenced and compared with the glpQ sequences obtained from other relapsing-fever spirochetes. Previously we showed that GlpQ of Borrelia hermsii is an immunogenic protein with utility as a serological test antigen for discriminating tick-borne relapsing fever from Lyme disease. In the present work, we cloned and expressed the glpQ gene from B. recurrentis and used recombinant GlpQ in serological tests. Acute- and convalescent-phase serum samples obtained from 42 patients with louse-borne relapsing fever were tested with an indirect immunofluorescence assay (IFA) and an enzyme-linked immunosorbent assay (ELISA) that used whole cells of B. recurrentis and with immunoblotting to whole-cell lysates of the spirochete and Escherichia coli producing recombinant GlpQ. The geometric mean titers of the acute- and convalescent-phase serum samples measured by IFA were 1:83 and 1:575, respectively. The immunoblot analysis identified a high level of reactivity and seroconversion to GlpQ, and the assay was more sensitive than the whole-cell IFA and ELISA using purified, recombinant histidine-tagged GlpQ. Serum antibodies to GlpQ and other antigens persisted for 27 years in one patient. We conclude that assessment of anti-GlpQ antibodies will allow serological confirmation of louse-borne relapsing fever and determination of disease prevalence. PMID:11015364

[Effects of GLP-1 receptor agonists on carbohydrate metabolism control].

PubMed

Fernández-García, José Carlos; Colomo, Natalia; Tinahones, Francisco José

2014-09-01

Glucagon-like peptide-1 (GLP-1) receptor agonists are a new group of drugs for the treatment of type 2 diabetes mellitus (DM2). In the present article, we review the available evidence on the efficacy of GLP-1 receptor agonists as glucose-lowering agents, their place in therapeutic algorithms, and the clinical factors associated with a favorable treatment response. Finally, we describe the clinical characteristics of patients who may benefit from these drugs. Copyright © 2014 Elsevier España, S.L.U. All rights reserved.

Aspergillus glaucus Aquaglyceroporin Gene glpF Confers High Osmosis Tolerance in Heterologous Organisms.

PubMed

Liu, Xiao-Dan; Wei, Yi; Zhou, Xiao-Yang; Pei, Xue; Zhang, Shi-Hong

2015-10-01

Aquaglyceroporins (GlpFs) that transport glycerol along with water and other uncharged solutes are involved in osmoregulation in myriad species. Fungal species form a large group of eukaryotic organisms, and their GlpFs may be diverse, exhibiting various activities. However, few filamentous fungal GlpFs have been biologically investigated. Here, a glpF gene from the halophilic fungus Aspergillus glaucus (AgglpF) was verified to be a channel of water or glycerol in Xenopus laevis oocytes and was further functionally analyzed in three heterologous systems. In Saccharomyces cerevisiae, cells overexpressing AgglpF possessed significant tolerance of drought, salt, and certain metal ions. AgglpF was then characterized in the filamentous fungus of Neurospora crassa. Based on the N. crassa aquaporin gene (NcAQP) disruption mutant (the Δaqp mutant), a series of complementary strains carrying NcAQP and AgglpF and three asparagine-proline-alanine-gene (NPA)-deleted AgglpF fragments were created. As revealed by salt resistance analysis, the AgglpF complementary strain possessed the highest salt resistance among the tested strains. In addition, the intracellular glycerol content in the AgglpF complementary strain was markedly higher than that in the other strains. The AgGlpF-green fluorescent protein (GFP) fusion protein was subcellularly localized in the plasma membrane of onion epidermal cells, suggesting that AgglpF functions in plants. Indeed, when AgglpF was expressed in Arabidopsis thaliana, transgenic lines survived under conditions of high osmotic stress and under conditions of drought stress in particular. Overall, our results revealed that AgGlpF as a water/glycerol transporter is required for survival of both fungi and plants under conditions of high osmotic stress and may have value in applications in genetic engineering for generating high salt and drought resistance. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Aspergillus glaucus Aquaglyceroporin Gene glpF Confers High Osmosis Tolerance in Heterologous Organisms

PubMed Central

Liu, Xiao-Dan; Wei, Yi; Zhou, Xiao-Yang; Pei, Xue

2015-01-01

Aquaglyceroporins (GlpFs) that transport glycerol along with water and other uncharged solutes are involved in osmoregulation in myriad species. Fungal species form a large group of eukaryotic organisms, and their GlpFs may be diverse, exhibiting various activities. However, few filamentous fungal GlpFs have been biologically investigated. Here, a glpF gene from the halophilic fungus Aspergillus glaucus (AgglpF) was verified to be a channel of water or glycerol in Xenopus laevis oocytes and was further functionally analyzed in three heterologous systems. In Saccharomyces cerevisiae, cells overexpressing AgglpF possessed significant tolerance of drought, salt, and certain metal ions. AgglpF was then characterized in the filamentous fungus of Neurospora crassa. Based on the N. crassa aquaporin gene (NcAQP) disruption mutant (the Δaqp mutant), a series of complementary strains carrying NcAQP and AgglpF and three asparagine-proline-alanine-gene (NPA)-deleted AgglpF fragments were created. As revealed by salt resistance analysis, the AgglpF complementary strain possessed the highest salt resistance among the tested strains. In addition, the intracellular glycerol content in the AgglpF complementary strain was markedly higher than that in the other strains. The AgGlpF-green fluorescent protein (GFP) fusion protein was subcellularly localized in the plasma membrane of onion epidermal cells, suggesting that AgglpF functions in plants. Indeed, when AgglpF was expressed in Arabidopsis thaliana, transgenic lines survived under conditions of high osmotic stress and under conditions of drought stress in particular. Overall, our results revealed that AgGlpF as a water/glycerol transporter is required for survival of both fungi and plants under conditions of high osmotic stress and may have value in applications in genetic engineering for generating high salt and drought resistance. PMID:26209670

Coagonist of GLP-1 and glucagon decreases liver inflammation and atherosclerosis in dyslipidemic condition.

PubMed

Patel, Vishal; Joharapurkar, Amit; Kshirsagar, Samadhan; Sutariya, Brijesh; Patel, Maulik; Pandey, Dheerendra; Patel, Hiren; Ranvir, Ramchandra; Kadam, Shekhar; Patel, Dipam; Bahekar, Rajesh; Jain, Mukul

2018-02-25

Dyslipidemia enhances progression of atherosclerosis. Coagonist of GLP-1 and glucagon are under clinical investigation for the treatment of obesity and diabetes. Earlier, we have observed that coagonist reduced circulating and hepatic lipids, independent of its anorexic effects. Here, we investigated the role of coagonist of GLP-1 and glucagon receptors in complications of diet-induced dyslipidemia in hamsters and humanized double transgenic mice. Hamsters fed on high fat high cholesterol diet were treated for 8 weeks with coagonist of GLP-1 and glucagon receptors (75 and 150 μg/kg). Pair-fed control was maintained. Cholesterol fed transgenic mice overexpressing hApoB100 and hCETP with coagonist (300 μg/kg) for 4 weeks. After the completion of treatment, biochemical estimations were done. Coagonist treatment reduced triglycerides in plasma, liver and aorta, plasma cholesterol and hepatic triglyceride secretion rate. Expressions of HMG-CoA reductase and SBREBP-1C were reduced and expressions of LDLR, CYP7A1, ABCA1 and ABCB11 were increased in liver, due to coagonist treatment. Coagonist treatment increased bile flow rate and biliary cholesterol excretion. IL-6 and TNF-α were reduced in plasma and expression of TNF-α, MCP-1, MMP-9 and TIMP-1 decreased in liver. Treatment with coagonist reduced oxidative stress in liver and aorta. Energy expenditure was increased and respiratory quotient was reduced by coagonist treatment. These changes were correlated with reduced hepatic inflammation and lipids in liver and aorta in coagonist treated hamsters. Coagonist treatment also reduced lipids in cholesterol-fed transgenic mice. These changes were independent of glycaemia and anorexia observed after coagonist treatment. Long term treatment with coagonist of GLP-1 and glucagon receptor ameliorated diet-induced dyslipidemia and atherosclerosis by regulating bile homeostasis, liver inflammation and energy expenditure. Copyright © 2018 Elsevier B.V. All rights reserved.

Fructose stimulates GLP-1 but not GIP secretion in mice, rats, and humans

PubMed Central

Kuhre, Rune E.; Gribble, Fiona M.; Hartmann, Bolette; Reimann, Frank; Windeløv, Johanne A.; Rehfeld, Jens F.

2014-01-01

Nutrients often stimulate gut hormone secretion, but the effects of fructose are incompletely understood. We studied the effects of fructose on a number of gut hormones with particular focus on glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). In healthy humans, fructose intake caused a rise in blood glucose and plasma insulin and GLP-1, albeit to a lower degree than isocaloric glucose. Cholecystokinin secretion was stimulated similarly by both carbohydrates, but neither peptide YY3–36 nor glucagon secretion was affected by either treatment. Remarkably, while glucose potently stimulated GIP release, fructose was without effect. Similar patterns were found in the mouse and rat, with both fructose and glucose stimulating GLP-1 secretion, whereas only glucose caused GIP secretion. In GLUTag cells, a murine cell line used as model for L cells, fructose was metabolized and stimulated GLP-1 secretion dose-dependently (EC50 = 0.155 mM) by ATP-sensitive potassium channel closure and cell depolarization. Because fructose elicits GLP-1 secretion without simultaneous release of glucagonotropic GIP, the pathways underlying fructose-stimulated GLP-1 release might be useful targets for type 2 diabetes mellitus and obesity drug development. PMID:24525020

Cloning and expression analysis of Zmglp1, a new germin-like protein gene in maize.

PubMed

Fan, Zhanmin; Gu, Hongya; Chen, Xiaowei; Song, Hui; Wang, Qian; Liu, Meihua; Qu, Li-Jia; Chen, Zhangliang

2005-06-17

The cDNA and genomic DNA of a green tissue-specific gene were cloned from maize (Zea mays L.) using cDNA-amplified fragment length polymorphism (cDNA-AFLP) and library screening. The deduced protein was highly similar to Hordeum vulgare germin-like protein 1 (HvGLP1), and the maize gene was therefore designated Zmglp1. Northern blot specifically detected the mRNA of Zmglp1 in young whorl leaves at the early-whorl stage. However, at the late-whorl, tassel, and silk stages, Zmglp1 transcripts were highly abundant in young whorl leaves; less abundant in mature leaves, young tassels, and cobs; and not detectable in roots, immature kernels, and stalks. RNA in situ hybridization revealed that Zmglp1 expressed only in mesophyllous, phloem, and guard cells in the young whorl leaves. Deletion analysis of the promoter in transgenic Arabidopsis resulted in the identification of several regions containing important regulatory cis-elements controlling the expression levels and circadian rhythm-oscillated patterns of Zmglp1.

A review of the new GLP-1 receptor agonist/basal insulin fixed-ratio combination products.

PubMed

Nuffer, Wesley; Guesnier, Ashley; Trujillo, Jennifer M

2018-03-01

There have been several new treatment approaches established for the management of hyperglycemia in type 2 diabetes (T2D), with treatment guidelines listing both glucagon-like peptide 1 receptor agonists (GLP-1 RAs) and basal insulin therapies as considerations for patients who have failed to control their blood glucose with oral antidiabetic agents. New studies have highlighted the importance of initiating combination therapy earlier in the T2D disease process to avoid clinical inertia and prevent the long-term complications arising from uncontrolled diabetes. Until recently, both GLP-1 RAs and basal insulin therapies were only available as single agents, but there are now two combination pen devices that deliver both a GLP-1 RA and basal insulin simultaneously. This article reviews the current clinical evidence evaluating the use of these combination GLP-1 RA/basal insulin preparations to treat T2D, presents both potential benefits as well as possible downsides with the use of these agents, and discusses the current place in therapy these products represent in the management of T2D.

[Role of p38MAPK/eNOS signaling pathway in the inhibition of AGEs-induced apoptosis of human umbilical vein endothelial cells by glucagon-like peptide-1].

PubMed

Zeng, Hailong; Huang, Zhiqiu; Zhang, Yineng; Sun, Huilin

2016-01-01

To investigate the role of p38MAPK signaling pathway in the mechanism by which glucagon-like peptide-1 (GLP-1) inhibits endothelial cell damage induced by AGEs. Human umbilical vein endothelial cells were divided into control group, AGEs group, GLP-1 group, AGEs+GLP-1 group, AGEs+inhibitor group, and AGEs+GLP-1+inhibitor group. The expressions of p-p38MAPK/p38MAPK and p-eNOS/eNOS protein were examined by Western blotting, and the cell apoptosis rates were tested by flow cytometry. Compared with the control group, AGEs significantly enhanced the expression of p-p38 MAPK protein (P=0.001) while GLP-1 significantly inhibited its expression (P<0.001). AGEs significantly inhibited the expression of p-eNOS protein (P=0.007), which was enhanced by GLP-1 and p38 MAPK inhibitor (SB203580) (P=0.004). Both SB203580 and GLP-1 treatment decreased the apoptosis rate of AGEs-treated cells (P<0.001). GLP-1 can protect human umbilical vein endothelial cells against AGEs-induced apoptosis partially by inhibiting the phosphorylation of p38MAPK protein and promoting the expression of p-eNOS protein.

Glucagon-like peptide 1 interacts with ghrelin and leptin to regulate glucose metabolism and food intake through vagal afferent neuron signaling.

PubMed

Ronveaux, Charlotte C; Tomé, Daniel; Raybould, Helen E

2015-04-01

Emerging evidence has suggested a possible physiologic role for peripheral glucagon-like peptide 1 (GLP-1) in regulating glucose metabolism and food intake. The likely site of action of GLP-1 is on vagal afferent neurons (VANs). The vagal afferent pathway is the major neural pathway by which information about ingested nutrients reaches the central nervous system and influences feeding behavior. Peripheral GLP-1 acts on VANs to inhibit food intake. The mechanism of the GLP-1 receptor (GLP-1R) is unlike other gut-derived receptors; GLP-1Rs change their cellular localization according to feeding status rather than their protein concentrations. It is possible that several gut peptides are involved in mediating GLP-1R translocation. The mechanism of peripheral GLP-1R translocation still needs to be elucidated. We review data supporting the role of peripheral GLP-1 acting on VANs in influencing glucose homeostasis and feeding behavior. We highlight evidence demonstrating that GLP-1 interacts with ghrelin and leptin to induce satiation. Our aim was to understand the mechanism of peripheral GLP-1 in the development of noninvasive antiobesity treatments. © 2015 American Society for Nutrition.

Estradiol modulates the anorexic response to central glucagon-like peptide 1.

PubMed

Maske, Calyn B; Jackson, Christine M; Terrill, Sarah J; Eckel, Lisa A; Williams, Diana L

2017-07-01

Estrogens suppress feeding in part by enhancing the response to satiation signals. Glucagon-like peptide 1 (GLP-1) acts on receptor populations both peripherally and centrally to affect food intake. We hypothesized that modulation of the central GLP-1 system is one of the mechanisms underlying the effects of estrogens on feeding. We assessed the anorexic effect of 0, 1, and 10μg doses of GLP-1 administered into the lateral ventricle of bilaterally ovariectomized (OVX) female rats on a cyclic regimen of either 2μg β-estradiol-3-benzoate (EB) or oil vehicle 30min prior to dark onset on the day following hormone treatment. Central GLP-1 treatment significantly suppressed food intake in EB-treated rats at both doses compared to vehicle, whereas only the 10μg GLP-1 dose was effective in oil-treated rats. To follow up, we examined whether physiologic-dose cyclic estradiol treatment influences GLP-1-induced c-Fos in feeding-relevant brain areas of OVX females. GLP-1 significantly increased c-Fos expression in the area postrema (AP) and nucleus of the solitary tract (NTS), and the presence of estrogens may be required for this effect in the paraventricular nucleus of the hypothalamus (PVN). Together, these data suggest that modulation of the central GLP-1 system may be one of the mechanisms by which estrogens suppress food intake, and highlight the PVN as a region of interest for future investigation. Copyright © 2017 Elsevier Inc. All rights reserved.

A comparative safety review between GLP-1 receptor agonists and SGLT2 inhibitors for diabetes treatment.

PubMed

Consoli, Agostino; Formoso, Gloria; Baldassarre, Maria Pompea Antonia; Febo, Fabrizio

2018-03-01

Glucagon-like peptide-1 receptor agonists (GLP-1RA) and sodium glucose cotransporter 2 inhibitors (SGLT2i) are of particular interest in type 2 diabetes treatment strategies, due to their efficacy in reducing HbA1c with a low risk of hypoglycaemia, to their positive effects on body weight and blood pressure and in light of their effects on cardiovascular risk and on nephroprotection emerged from the most recent cardiovascular outcome trials. Since it is therefore very likely that GLP-1RA and SGLT2i use will become more and more common, it is more and more important to gather and discuss information about their safety profile. Area Covered: adverse events and the safety concerns most often emerged in trials with GLP-1RA namely, exenatide long acting release (LAR), dulaglutide, liraglutide, semaglutide, lixisenatide or SGLT2i, namely empagliflozin, dapagliflozin, canagliflozin and SGLT2i with an attempt at comparing the safety profiles of molecules of these two classes. Expert opinion: GLP-1RA and SGLT2i, although each associated with different specific side effects, share a 'similar' safety profile and are both drugs relatively easy to handle. The potentially complementary mechanisms of action, the cardio and nephroprotective effects demonstrated by molecules of both classes, make these drugs potentially useful even in add on to each other.

Topical CpG Adjuvantation of a Protein-Based Vaccine Induces Protective Immunity to Listeria monocytogenes

PubMed Central

Cheng, Wing Ki; Wee, Kathleen; Kollmann, Tobias R.

2014-01-01

Robust CD8+ T cell responses are essential for immune protection against intracellular pathogens. Using parenteral administration of ovalbumin (OVA) protein as a model antigen, the effect of the Toll-like receptor 9 (TLR9) agonist, CpG oligodeoxynucleotide (ODN) 1826, as an adjuvant delivered either topically, subcutaneously, or intramuscularly on antigen-specific CD8+ T cell responses in a mouse model was evaluated. Topical CpG adjuvant increased the frequency of OVA-specific CD8+ T cells in the peripheral blood and in the spleen. The more effective strategy to administer topical CpG adjuvant to enhance CD8+ T cell responses was single-dose administration at the time of antigen injection with a prime-boost regimen. Topical CpG adjuvant conferred both rapid and long-lasting protection against systemic challenge with recombinant Listeria monocytogenes expressing the cytotoxic T lymphocyte (CTL) epitope of OVA257–264 (strain Lm-OVA) in a TLR9-dependent manner. Topical CpG adjuvant induced a higher proportion of CD8+ effector memory T cells than parenteral administration of the adjuvant. Although traditional vaccination strategies involve coformulation of antigen and adjuvant, split administration using topical adjuvant is effective and has advantages of safety and flexibility. Split administration of topical CpG ODN 1826 with parenteral protein antigen is superior to other administration strategies in enhancing both acute and memory protective CD8+ T cell immune responses to subcutaneous protein vaccines. This vaccination strategy induces rapid and persistent protective immune responses against the intracellular organism L. monocytogenes. PMID:24391136

Framework for the quality assurance of 'omics technologies considering GLP requirements.

PubMed

Kauffmann, Hans-Martin; Kamp, Hennicke; Fuchs, Regine; Chorley, Brian N; Deferme, Lize; Ebbels, Timothy; Hackermüller, Jörg; Perdichizzi, Stefania; Poole, Alan; Sauer, Ursula G; Tollefsen, Knut E; Tralau, Tewes; Yauk, Carole; van Ravenzwaay, Ben

2017-12-01

'Omics technologies are gaining importance to support regulatory toxicity studies. Prerequisites for performing 'omics studies considering GLP principles were discussed at the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) Workshop Applying 'omics technologies in Chemical Risk Assessment. A GLP environment comprises a standard operating procedure system, proper pre-planning and documentation, and inspections of independent quality assurance staff. To prevent uncontrolled data changes, the raw data obtained in the respective 'omics data recording systems have to be specifically defined. Further requirements include transparent and reproducible data processing steps, and safe data storage and archiving procedures. The software for data recording and processing should be validated, and data changes should be traceable or disabled. GLP-compliant quality assurance of 'omics technologies appears feasible for many GLP requirements. However, challenges include (i) defining, storing, and archiving the raw data; (ii) transparent descriptions of data processing steps; (iii) software validation; and (iv) ensuring complete reproducibility of final results with respect to raw data. Nevertheless, 'omics studies can be supported by quality measures (e.g., GLP principles) to ensure quality control, reproducibility and traceability of experiments. This enables regulators to use 'omics data in a fit-for-purpose context, which enhances their applicability for risk assessment. Copyright © 2017 Elsevier Inc. All rights reserved.

The glycerol-dependent metabolic persistence of Pseudomonas putida KT2440 reflects the regulatory logic of the GlpR repressor.

PubMed

Nikel, Pablo I; Romero-Campero, Francisco J; Zeidman, Joshua A; Goñi-Moreno, Ángel; de Lorenzo, Víctor

2015-03-31

The growth of the soil bacterium Pseudomonas putida KT2440 on glycerol as the sole carbon source is characterized by a prolonged lag phase, not observed with other carbon substrates. We examined the bacterial growth in glycerol cultures while monitoring the metabolic activity of individual cells. Fluorescence microscopy and flow cytometry, as well as the analysis of the temporal start of growth in single-cell cultures, revealed that adoption of a glycerol-metabolizing regime was not the result of a gradual change in the whole population but rather reflected a time-dependent bimodal switch between metabolically inactive (i.e., nongrowing) and fully active (i.e., growing) bacteria. A transcriptional Φ(glpD-gfp) fusion (a proxy of the glycerol-3-phosphate [G3P] dehydrogenase activity) linked the macroscopic phenotype to the expression of the glp genes. Either deleting glpR (encoding the G3P-responsive transcriptional repressor that controls the expression of the glpFKRD gene cluster) or altering G3P formation (by overexpressing glpK, encoding glycerol kinase) abolished the bimodal glpD expression. These manipulations eliminated the stochastic growth start by shortening the otherwise long lag phase. Provision of glpR in trans restored the phenotypes lost in the ΔglpR mutant. The prolonged nongrowth regime of P. putida on glycerol could thus be traced to the regulatory device controlling the transcription of the glp genes. Since the physiological agonist of GlpR is G3P, the arrangement of metabolic and regulatory components at this checkpoint merges a positive feedback loop with a nonlinear transcriptional response, a layout fostering the observed time-dependent shift between two alternative physiological states. Phenotypic variation is a widespread attribute of prokaryotes that leads, inter alia, to the emergence of persistent bacteria, i.e., live but nongrowing members within a genetically clonal population. Persistence allows a fraction of cells to avoid the

Hyperphagia and Increased Fat Accumulation in Two Models of Chronic CNS Glucagon-Like Peptide-1 Loss of Function

PubMed Central

Jones, Kenneth R.; Herman, James P.; D'Alessio, David A.; Woods, Stephen C.; Seeley, Randy J.

2011-01-01

Central administration of glucagon-like peptide-1 (GLP-1) causes a dose-dependent reduction in food intake, but the role of endogenous CNS GLP-1 in the regulation of energy balance remains unclear. Here, we tested the hypothesis that CNS GLP-1 activity is required for normal energy balance by using two independent methods to achieve chronic CNS GLP-1 loss of function in rats. Specifically, lentiviral-mediated expression of RNA interference was used to knock down nucleus of the solitary tract (NTS) preproglucagon (PPG), and chronic intracerebroventricular (ICV) infusion of the GLP-1 receptor (GLP-1r) antagonist exendin (9-39) (Ex9) was used to block CNS GLP-1r. NTS PPG knockdown caused hyperphagia and exacerbated high-fat diet (HFD)-induced fat accumulation and glucose intolerance. Moreover, in control virus-treated rats fed the HFD, NTS PPG expression levels correlated positively with fat mass. Chronic ICV Ex9 also caused hyperphagia; however, increased fat accumulation and glucose intolerance occurred regardless of diet. Collectively, these data provide the strongest evidence to date that CNS GLP-1 plays a physiologic role in the long-term regulation of energy balance. Moreover, they suggest that this role is distinct from that of circulating GLP-1 as a short-term satiation signal. Therefore, it may be possible to tailor GLP-1-based therapies for the prevention and/or treatment of obesity. PMID:21389245

Hyperphagia and increased fat accumulation in two models of chronic CNS glucagon-like peptide-1 loss of function.

PubMed

Barrera, Jason G; Jones, Kenneth R; Herman, James P; D'Alessio, David A; Woods, Stephen C; Seeley, Randy J

2011-03-09

Central administration of glucagon-like peptide-1 (GLP-1) causes a dose-dependent reduction in food intake, but the role of endogenous CNS GLP-1 in the regulation of energy balance remains unclear. Here, we tested the hypothesis that CNS GLP-1 activity is required for normal energy balance by using two independent methods to achieve chronic CNS GLP-1 loss of function in rats. Specifically, lentiviral-mediated expression of RNA interference was used to knock down nucleus of the solitary tract (NTS) preproglucagon (PPG), and chronic intracerebroventricular (ICV) infusion of the GLP-1 receptor (GLP-1r) antagonist exendin (9-39) (Ex9) was used to block CNS GLP-1r. NTS PPG knockdown caused hyperphagia and exacerbated high-fat diet (HFD)-induced fat accumulation and glucose intolerance. Moreover, in control virus-treated rats fed the HFD, NTS PPG expression levels correlated positively with fat mass. Chronic ICV Ex9 also caused hyperphagia; however, increased fat accumulation and glucose intolerance occurred regardless of diet. Collectively, these data provide the strongest evidence to date that CNS GLP-1 plays a physiologic role in the long-term regulation of energy balance. Moreover, they suggest that this role is distinct from that of circulating GLP-1 as a short-term satiation signal. Therefore, it may be possible to tailor GLP-1-based therapies for the prevention and/or treatment of obesity.

Molecular mechanisms redirecting the GLP-1 receptor signalling profile in pancreatic β-cells during type 2 diabetes.

PubMed

Roussel, Morgane; Mathieu, Julia; Dalle, Stéphane

2016-05-01

Treatments with β-cell preserving properties are essential for the management of type 2 diabetes (T2D), and the new therapeutic avenues, developed over the last years, rely on the physiological role of glucagon-like peptide-1 (GLP-1). Sustained pharmacological levels of GLP-1 are achieved by subcutaneous administration of GLP-1 analogues, while transient and lower physiological levels of GLP-1 are attained following treatment with inhibitors of dipeptidylpeptidase 4 (DPP4), an endoprotease which degrades the peptide. Both therapeutic classes display a sustained and durable hypoglycaemic action in patients with T2D. However, the GLP-1 incretin effect is known to be reduced in patients with T2D, and GLP-1 analogues and DPP4 inhibitors were shown to lose their effectiveness over time in some patients. The pathological mechanisms behind these observations can be either a decrease in GLP-1 secretion from intestinal L-cells and, as a consequence, a reduction in GLP-1 plasma concentrations, combined or not with a reduced action of GLP-1 in the β-cell, the so-called GLP-1 resistance. Much evidence for a GLP-1 resistance of the β-cell in subjects with T2D have emerged. Here, we review the potential roles of the genetic background, the hyperglycaemia, the hyperlipidaemia, the prostaglandin E receptor 3, the nuclear glucocorticoid receptor, the GLP-1R desensitization and internalisation processes, and the β-arrestin-1 expression levels on GLP-1 resistance in β-cells during T2D.

GLP-1 promotes mitochondrial metabolism in vascular smooth muscle cells by enhancing endoplasmic reticulum-mitochondria coupling.

PubMed

Morales, Pablo E; Torres, Gloria; Sotomayor-Flores, Cristian; Peña-Oyarzún, Daniel; Rivera-Mejías, Pablo; Paredes, Felipe; Chiong, Mario

2014-03-28

Incretin GLP-1 has important metabolic effects on several tissues, mainly through the regulation of glucose uptake and usage. One mechanism for increasing cell metabolism is modulating endoplasmic reticulum (ER)-mitochondria communication, as it allows for a more efficient transfer of Ca(2+) into the mitochondria, thereby increasing activity. Control of glucose metabolism is essential for proper vascular smooth muscle cell (VSMC) function. GLP-1 has been shown to produce varied metabolic actions, but whether it regulates glucose metabolism in VSMC remains unknown. In this report, we show that GLP-1 increases mitochondrial activity in the aortic cell line A7r5 by increasing ER-mitochondria coupling. GLP-1 increases intracellular glucose and diminishes glucose uptake without altering glycogen content. ATP, mitochondrial potential and oxygen consumption increase at 3h of GLP-1 treatment, paralleled by increased Ca(2+) transfer from the ER to the mitochondria. Furthermore, GLP-1 increases levels of Mitofusin-2 (Mfn2), an ER-mitochondria tethering protein, via a PKA-dependent mechanism. Accordingly, PKA inhibition and Mfn2 down-regulation prevented mitochondrial Ca(2+) increases in GLP-1 treated cells. Inhibiting both Ca(2+) release from the ER and Ca(2+) entry into mitochondria as well as diminishing Mfn2 levels blunted the increase in mitochondrial activity in response to GLP-1. Altogether, these results strongly suggest that GLP-1 increases ER-mitochondria communication in VSMC, resulting in higher mitochondrial activity. Copyright © 2014 Elsevier Inc. All rights reserved.

Combination therapy with GLP-1 receptor agonists and basal insulin: a systematic review of the literature

PubMed Central

Balena, R; Hensley, I E; Miller, S; Barnett, A H

2013-01-01

Treatment algorithms for type 2 diabetes call for intensification of therapy over time as the disease progresses and glycaemic control worsens. If diet, exercise and oral antihyperglycaemic medications (OAMs) fail to maintain glycaemic control then basal insulin is added and ultimately prandial insulin may be required. However, such an intensification strategy carries risk of increased hypoglycaemia and weight gain, both of which are associated with worse long-term outcomes. An alternative strategy is to intensify therapy by the addition of a short-acting glucagon-like peptide-1 receptor agonist (GLP-1 RA) rather than prandial insulin. Short-acting GLP-1 RAs such as exenatide twice daily are particularly effective at reducing postprandial glucose while basal insulin has a greater effect on fasting glucose, providing a physiological rationale for this complementary approach. This review analyzes the latest randomized controlled clinical trials of insulin/GLP-1 RA combination therapy and examines results from ‘real-world’ use of the combinations as reported through observational and clinical practice studies. The most common finding across all types of studies was that combination therapy improved glycaemic control without weight gain or an increased risk of hypoglycaemia. Many studies reported weight loss and a reduction in insulin use when a GLP-1 RA was added to existing insulin therapy. Overall, the relative degree of benefit to glycaemic control and weight was influenced by the insulin titration employed in conjunction with the GLP-1 RA. The greatest glycaemic benefits were observed in studies with structured titration of insulin to glycaemic targets while the greatest weight benefits were observed in studies with a protocol-specified focus on insulin sparing. The adverse event profile of GLP-1 RAs in the reviewed trials was similar to that reported with GLP-1 RAs as monotherapy or in combination with OAMs with gastrointestinal events being the most commonly

Roles of increased glycaemic variability, GLP-1 and glucagon in hypoglycaemia after Roux-en-Y gastric bypass

PubMed Central

Tharakan, George; Behary, Preeshila; Wewer Albrechtsen, Nicolai J; Chahal, Harvinder; Kenkre, Julia; Miras, Alexander D; Ahmed, Ahmed R; Holst, Jens J; Bloom, Stephen R

2017-01-01

Objective Roux-en-Y gastric bypass (RYGB) surgery is currently the most effective treatment for diabetes and obesity. An increasingly recognized and highly disabling complication of RYGB is postprandial hypoglycaemia (PPH). The pathophysiology of PPH remains unclear with multiple mechanisms suggested including nesidioblastosis, altered insulin clearance and increased glucagon-like peptide-1 (GLP-1) secretion. Whilst many PPH patients respond to dietary modification, some have severely disabling symptoms. Multiple treatments are proposed, including dietary modification, GLP-1 antagonism, GLP-1 analogues and even surgical reversal, with none showing a more decided advantage over the others. A greater understanding of the pathophysiology of PPH could guide the development of new therapeutic strategies. Methods We studied a cohort of PPH patients at the Imperial Weight Center. We performed continuous glucose monitoring to characterize their altered glycaemic variability. We also performed a mixed meal test (MMT) and measured gut hormone concentrations. Results We found increased glycaemic variability in our cohort of PPH patients, specifically a higher mean amplitude glucose excursion (MAGE) score of 4.9. We observed significantly greater and earlier increases in insulin, GLP-1 and glucagon in patients who had hypoglycaemia in response to an MMT (MMT Hypo) relative to those that did not (MMT Non-Hypo). No significant differences in oxyntomodulin, GIP or peptide YY secretion were seen between these two groups. Conclusion An early peak in GLP-1 and glucagon may together trigger an exaggerated insulinotropic response to eating and consequent hypoglycaemia in patients with PPH. PMID:28855269

Identification of herpesvirus proteins that contribute to G1/S arrest.

PubMed

Paladino, Patrick; Marcon, Edyta; Greenblatt, Jack; Frappier, Lori

2014-04-01

Lytic infection by herpesviruses induces cell cycle arrest at the G1/S transition. This appears to be a function of multiple herpesvirus proteins, but only a minority of herpesvirus proteins have been examined for cell cycle effects. To gain a more comprehensive understanding of the viral proteins that contribute to G1/S arrest, we screened a library of over 200 proteins from herpes simplex virus type 1, human cytomegalovirus, and Epstein-Barr virus (EBV) for effects on the G1/S interface, using HeLa fluorescent, ubiquitination-based cell cycle indicator (Fucci) cells in which G1/S can be detected colorimetrically. Proteins from each virus were identified that induce accumulation of G1/S cells, predominantly tegument, early, and capsid proteins. The identification of several capsid proteins in this screen suggests that incoming viral capsids may function to modulate cellular processes. The cell cycle effects of selected EBV proteins were further verified and examined for effects on p53 and p21 as regulators of the G1/S transition. Two EBV replication proteins (BORF2 and BMRF1) were found to induce p53 but not p21, while a previously uncharacterized tegument protein (BGLF2) was found to induce p21 protein levels in a p53-independent manner. Proteomic analyses of BGLF2-interacting proteins identified interactions with the NIMA-related protein kinase (NEK9) and GEM-interacting protein (GMIP). Silencing of either NEK9 or GMIP induced p21 without affecting p53 and abrogated the ability of BGLF2 to further induce p21. Collectively, these results suggest multiple viral proteins contribute to G1/S arrest, including BGLF2, which induces p21 levels likely by interfering with the functions of NEK9 and GMIP. Most people are infected with multiple herpesviruses, whose proteins alter the infected cells in several ways. During lytic infection, the viral proteins block cell proliferation just before the cellular DNA replicates. We used a novel screening method to identify proteins

Sepsis-induced activation of endogenous GLP-1 system is enhanced in type 2 diabetes.

PubMed

Perl, Sivan H; Bloch, Olga; Zelnic-Yuval, Dana; Love, Itamar; Mendel-Cohen, Lior; Flor, Hadar; Rapoport, Micha J

2018-05-01

High levels of circulating GLP-1 are associated with severity of sepsis in critically ill nondiabetic patients. Whether patients with type 2 diabetes (T2D) display different activation of the endogenous GLP-1 system during sepsis and whether it is affected by diabetes-related metabolic parameters are not known. Serum levels of GLP-1 (total and active forms) and its inhibitor enzyme sDPP-4 were determined by ELISA on admission and after 2 to 4 days in 37 sepsis patients with (n = 13) and without T2D (n = 24) and compared to normal healthy controls (n = 25). Correlations between GLP-1 system activation and clinical, inflammatory, and diabetes-related metabolic parameters were performed. A 5-fold (P < .001) and 2-fold (P < .05) increase in active and total GLP-1 levels, respectively, were found on admission as compared to controls. At 2 to 4 days from admission, the level of active GLP-1 forms in surviving patients were decreased significantly (P < .005), and positively correlated with inflammatory marker CRP (r = 0.33, P = .05). T2D survivors displayed a similar but more enhanced pattern of GLP-1 response than nondiabetic survivors. Nonsurvivors demonstrate an early extreme increase of both total and active GLP-1 forms, 9.5-fold and 5-fold, respectively (P < .05). The initial and late levels of circulating GLP-1 inhibitory enzyme sDPP-4 were twice lower in all studied groups (P < .001), compared with healthy controls. Taken together, these data indicate that endogenous GLP-1 system is activated during sepsis. Patients with T2D display an enhanced and prolonged activation as compared to nondiabetic patients. Extreme early increased GLP-1 levels during sepsis indicate poor prognosis. Copyright © 2018 John Wiley & Sons, Ltd.

Characterization of a gene coding for a type IIo bacterial IgG-binding protein.

PubMed

Boyle, M D; Weber-Heynemann, J; Raeder, R; Podbielski, A

1995-06-01

Two antigenic classes of non-immune IgG-binding proteins can be expressed by group A streptococci. One antigenic group of proteins is recognized by an antibody prepared against the product of a cloned fcrA gene (anti-FcRA). In this study, the immunogen used to prepare the antibody that defines the second antigenic class was shown to be the product of the emm-like (emmL) gene of M serotype 55 group A isolate, A928. The emmL55 gene expressed in E. coli produced an M(r) approximately 58,000 molecule which bound human IgG1, IgG2, IgG3 and IgG4, as well as horse, rabbit and pig IgG in a non-immune fashion. These properties are characteristic of the previously described type IIo IgG-binding protein isolated from this strain. In addition, the recombinant protein was reactive with human serum albumin and fibrinogen. The emmL 55 gene sequence was analysed and found to have the organization and sequence characteristics of a typical class I emm-like gene.

Uncoupling protein-2 mediates DPP-4 inhibitor-induced restoration of endothelial function in hypertension through reducing oxidative stress.

PubMed

Liu, Limei; Liu, Jian; Tian, Xiao Yu; Wong, Wing Tak; Lau, Chi Wai; Xu, Aimin; Xu, Gang; Ng, Chi Fai; Yao, Xiaoqiang; Gao, Yuansheng; Huang, Yu

2014-10-10

Although uncoupling protein 2 (UCP2) negatively regulates intracellular reactive oxygen species (ROS) production and protects vascular function, its participation in vascular benefits of drugs used to treat cardiometabolic diseases is largely unknown. This study investigated whether UCP2 and associated oxidative stress reduction contribute to the improvement of endothelial function by a dipeptidyl peptidase-4 inhibitor, sitagliptin, in hypertension. Pharmacological inhibition of cyclooxygenase-2 (COX-2) but not COX-1 prevented endothelial dysfunction, and ROS scavengers reduced COX-2 mRNA and protein expression in spontaneously hypertensive rats (SHR) renal arteries. Angiotensin II (Ang II) evoked endothelium-dependent contractions (EDCs) in C57BL/6 and UCP2 knockout (UCP2KO) mouse aortae. Chronic sitagliptin administration attenuated EDCs in SHR arteries and Ang II-infused C57BL/6 mouse aortae and eliminated ROS overproduction in SHR arteries, which were reversed by glucagon-like peptide 1 receptor (GLP-1R) antagonist exendin 9-39, AMP-activated protein kinase (AMPK)α inhibitor compound C, and UCP2 inhibitor genipin. By contrast, sitagliptin unaffected EDCs in Ang II-infused UCP2KO mice. Sitagliptin increased AMPKα phosphorylation, upregulated UCP2, and downregulated COX-2 expression in arteries from SHR and Ang II-infused C57BL/6 mice. Importantly, exendin 9-39, compound C, and genipin reversed the inhibitory effect of GLP-1R agonist exendin-4 on Ang II-stimulated mitochondrial ROS rises in SHR endothelial cells. Moreover, exendin-4 improved the endothelial function of renal arteries from SHR and hypertensive patients. We elucidate for the first time that UCP2 serves as an important signal molecule in endothelial protection conferred by GLP-1-related agents. UCP2 could be a useful target in treating hypertension-related vascular events. UCP2 inhibits oxidative stress and downregulates COX-2 expression through GLP-1/GLP-1R/AMPKα cascade.

Complex reassortment events of unusual G9P[4] rotavirus strains in India between 2011 and 2013.

PubMed

Doan, Yen Hai; Suzuki, Yoshiyuki; Fujii, Yoshiki; Haga, Kei; Fujimoto, Akira; Takai-Todaka, Reiko; Someya, Yuichi; Nayak, Mukti K; Mukherjee, Anupam; Imamura, Daisuke; Shinoda, Sumio; Chawla-Sarkar, Mamta; Katayama, Kazuhiko

2017-10-01

Rotavirus A (RVA) is the predominant etiological agent of acute gastroenteritis in young children worldwide. Recently, unusual G9P[4] rotavirus strains emerged with high prevalence in many countries. Such intergenogroup reassortant strains highlight the ongoing spread of unusual rotavirus strains throughout Asia. This study was undertaken to determine the whole genome of eleven unusual G9P[4] strains detected in India during 2011-2013, and to compare them with other human and animal global RVAs to understand the exact origin of unusual G9P[4] circulating in India and other countries worldwide. Of these 11 RVAs, four G9P[4] strains were double-reassortants with the G9-VP7 and E6-NSP4 genes on a DS-1-like genetic backbone (G9-P[4]-I2-R2-C2-M2-A2-N2-T2-E6-H2). The other strains showed a complex genetic constellation, likely derived from triple reassortment event with the G9-VP7, N1-NSP2 and E6-NSP4 on a DS-1-like genetic backbone (G9-P[4]-I2-R2-C2-M2-A2-N1-T2-E6-H2). Presumably, these unusual G9P[4] strains were generated after several reassortment events between the contemporary co-circulating human rotavirus strains. Moreover, the point mutation S291L at the interaction site between inner and outer capsid proteins of VP6 gene may be important in the rapid spread of this unusual strain. The complex reassortment events within the G9[4] strains may be related to the high prevalence of mixed infections in India as reported in this study and other previous studies. Copyright © 2017. Published by Elsevier B.V.

Differences in acute anorectic effects of long-acting GLP-1 receptor agonists in rats

USDA-ARS?s Scientific Manuscript database

Long-acting glucagon-like peptide-1 receptor (GLP-1R) agonists have both glucose- and weight-lowering effects. The brain is poised to mediate both of these actions since GLP-1Rs are present in key areas known to control weight and glucose. Although some research has been performed on the effects of ...

Sucralose enhances GLP-1 release and lowers blood glucose in the presence of carbohydrate in healthy subjects but not in patients with type 2 diabetes.

PubMed

Temizkan, S; Deyneli, O; Yasar, M; Arpa, M; Gunes, M; Yazici, D; Sirikci, O; Haklar, G; Imeryuz, N; Yavuz, D G

2015-02-01

Artificial sweeteners were thought to be metabolically inactive, but after demonstrating that the gustatory mechanism was also localized in the small intestine, suspicions about the metabolic effects of artificial sweeteners have emerged. The objective of this study was to determine the effect of artificial sweeteners (aspartame and sucralose) on blood glucose, insulin, c-peptide and glucagon-like peptide-1 (GLP-1) levels. Eight newly diagnosed drug-naive type 2 diabetic patients (mean age 51.5±9.2 years; F/M: 4/4) and eight healthy subjects (mean age 45.0±4.1 years; F/M: 4/4) underwent 75 g oral glucose tolerance test (OGTT). During OGTT, glucose, insulin, c-peptide and GLP-1 were measured at 15- min intervals for 120 min. The OGTTs were performed at three settings on different days, where subjects were given 72 mg of aspartame and 24 mg of sucralose in 200 ml of water or 200 ml of water alone 15 min before OGTT in a single-blinded randomized order. In healthy subjects, the total area under the curve (AUC) of glucose was statistically significantly lower in the sucralose setting than in the water setting (P=0.002). There was no difference between the aspartame setting and the water setting (P=0.53). Total AUC of insulin and c-peptide was similar in aspartame, sucralose and water settings. Total AUC of GLP-1 was significantly higher in the sucralose setting than in the water setting (P=0.04). Total AUC values of glucose, insulin, c-peptide and GLP-1 were not statistically different in three settings in type 2 diabetic patients. Sucralose enhances GLP-1 release and lowers blood glucose in the presence of carbohydrate in healthy subjects but not in newly diagnosed type 2 diabetic patients.

Surface Density of the Hendra G Protein Modulates Hendra F Protein-Promoted Membrane Fusion: Role for Hendra G Protein Trafficking and Degradation

PubMed Central

Whitman, Shannon D.; Dutch, Rebecca Ellis

2007-01-01

Hendra virus, like most paramyxoviruses, requires both a fusion (F) and attachment (G) protein for promotion of cell-cell fusion. Recent studies determined that Hendra F is proteolytically processed by the cellular protease cathepsin L after endocytosis. This unique cathepsin L processing results in a small percentage of Hendra F on the cell surface. To determine how the surface densities of the two Hendra glycoproteins affect fusion promotion, we performed experiments that varied the levels of glycoproteins expressed in transfected cells. Using two different fusion assays, we found a marked increase in fusion when expression of the Hendra G protein was increased, with a 1:1 molar ratio of Hendra F:G on the cell surface resulting in optimal membrane fusion. Our results also showed that Hendra G protein levels are modulated by both more rapid protein turnover and slower protein trafficking than is seen for Hendra F. PMID:17328935

Sustained expression of GLP-1 receptor differentially modulates β-cell functions in diabetic and nondiabetic mice

PubMed Central

Kubo, Fumiyo; Miyatsuka, Takeshi; Sasaki, Shugo; Takahara, Mitsuyoshi; Yamamoto, Yuichi; Shimo, Naoki; Watada, Hirotaka; Kaneto, Hideaki; Gannon, Maureen; Matsuoka, Taka-aki; Shimomura, Iichiro

2017-01-01

Glucagon-like peptide 1 (GLP-1) has been shown to play important roles in maintaining β-cell functions, such as insulin secretion and proliferation. While expression levels of GLP-1 receptor (Glp1r) are compromised in the islets of diabetic rodents, it remains unclear when and to what degree Glp1r mRNA levels are decreased during the progression of diabetes. In this study, we performed real-time PCR with the islets of db/db diabetic mice at different ages, and found that the expression levels of Glp1r were comparable to those of the islets of nondiabetic db/misty controls at the age of four weeks, and were significantly decreased at the age of eight and 12 weeks. To investigate whether restored expression of Glp1r affects the diabetic phenotypes, we generated the transgenic mouse model Pdx1PB-CreER™; CAG-CAT-Glp1r (βGlp1r) that allows for induction of Glp1r expression specifically in β cells. Whereas the expression of exogenous Glp1r had no measurable effect on glucose tolerance in nondiabetic βGlp1r;db/misty mice, βGlp1r;db/db mice exhibited higher glucose and lower insulin levels in blood on glucose challenge test than control db/db littermates. In contrast, four weeks of treatment with exendin-4 improved the glucose profiles and increased serum insulin levels in βGlp1r;db/db mice, to significantly higher levels than those in control db/db mice. These differential effects of exogenous Glp1r in nondiabetic and diabetic mice suggest that downregulation of Glp1r might be required to slow the progression of β-cell failure under diabetic conditions. PMID:26854076

Definition of IgG- and albumin-binding regions of streptococcal protein G.

PubMed

Akerström, B; Nielsen, E; Björck, L

1987-10-05

Protein G, the immunoglobin G-binding surface protein of group C and G streptococci, also binds serum albumin. The albumin-binding site on protein G is distinct from the immunoglobulin G-binding site. By mild acid hydrolysis of the papain-liberated protein G fragment (35 kDa), a 28-kDa fragment was produced which retained full immunoglobulin G-binding activity (determined by Scatchard plotting) but had lost all albumin-binding capacity. A protein G (65 kDa), isolated after cloning and expression of the protein G gene in Escherichia coli, had comparable affinity to immunoglobulin G (5-10 X 10(10)M-1), but much higher affinity to albumin than the 35- and 28-kDa protein G fragments (31, 2.6, and 0 X 10(9)M-1, respectively). The amino-terminal amino acid sequences of the 65-, 35-, and 28-kDa fragments allowed us to exactly locate the three fragments in an overall sequence map of protein G, based on the partial gene sequences published by Guss et al. (Guss, B., Eliasson, M., Olsson, A., Uhlen, M., Frej, A.-K., Jörnvall, H., Flock, J.-I., and Lindberg, M. (1986) EMBO J. 5, 1567-1575) and Fahnestock et al. (Fahnestock, S. R., Alexander, P., Nagle, J., and Filpula, D. (1986) J. Bacteriol. 167, 870-880). In this map could then be deduced the location of three homologous albumin-binding regions and three homologous immunoglobulin G-binding regions.

Reconstitution and functional comparison of purified GlpF and AqpZ, the glycerol and water channels from Escherichia coli.

PubMed

Borgnia, M J; Agre, P

2001-02-27

A large family of membrane channel proteins selective for transport of water (aquaporins) or water plus glycerol (aquaglyceroporins) has been found in diverse life forms. Escherichia coli has two members of this family-a water channel, AqpZ, and a glycerol facilitator, GlpF. Despite having similar primary amino acid sequences and predicted structures, the oligomeric state and solute selectivity of AqpZ and GlpF are disputed. Here we report biochemical and functional characterizations of affinity-purified GlpF and compare it to AqpZ. Histidine-tagged (His-GlpF) and hemagglutinin-tagged (HA-GlpF) polypeptides encoded by a bicistronic construct were expressed in bacteria. HA-GlpF and His-GlpF appear to form oligomers during Ni-nitrilotriacetate affinity purification. Sucrose gradient sedimentation analyses showed that the oligomeric state of octyl glucoside-solubilized GlpF varies: low ionic strength favors subunit dissociation, whereas Mg(2+) stabilizes tetrameric assembly. Reconstitution of affinity-purified GlpF into proteoliposomes increases glycerol permeability more than 100-fold and water permeability up to 10-fold compared with control liposomes. Glycerol and water permeability of GlpF both occur with low Arrhenius activation energies and are reversibly inhibited by HgCl(2). Our studies demonstrate that, unlike AqpZ, a water-selective stable tetramer, purified GlpF exists in multiple oligomeric forms under nondenaturing conditions and is highly permeable to glycerol but less well permeated by water.

The Dynamics and Regulatory Mechanism of Pronuclear H3k9me2 Asymmetry in Mouse Zygotes

PubMed Central

Ma, Xue-Shan; Chao, Shi-Bin; Huang, Xian-Ju; Lin, Fei; Qin, Ling; Wang, Xu-Guang; Meng, Tie-Gang; Zhu, Cheng-Cheng; Schatten, Heide; Liu, Hong-Lin; Sun, Qing-Yuan

2015-01-01

H3K9 methylation is an important histone modification that is correlated with gene transcription repression. The asymmetric H3K9 dimethylation (H3K9me2) pattern between paternal and maternal genomes is generated soon after fertilization. In the present study, we carefully determined the dynamics of H3K9me2 changes in mouse zygotes, and investigated the regulatory mechanisms. The results indicated that histone methyltransferase G9a, but not GLP, was involved in the regulation of asymmetric H3K9me2, and G9a was the methyltransferase that induced the appearance of H3K9me2 in the male pronucleus of the zygote treated with cycloheximide. We found that there were two distinct mechanisms that regulate H3K9me2 in the male pronucleus. Before 8 h of in vitro fertilization (IVF), a mechanism exists that inhibits the association of G9a with the H3K9 sites. After 10 h of IVF the inhibition of G9a activity depends on yet unknown novel protein(s) synthesis. The two mechanisms of transfer take place between 8–10 h of IVF, and the novel protein failed to inhibit G9a activity in time, resulting in the appearance of a low level de novo H3K9me2 in the male pronucleus. PMID:26639638

Role of G protein-coupled estrogen receptor-1, matrix metalloproteinases 2 and 9, and heparin binding epidermal growth factor-like growth factor in estradiol-17β-stimulated bovine satellite cell proliferation.

PubMed

Kamanga-Sollo, E; Thornton, K J; White, M E; Dayton, W R

2014-10-01

In feedlot steers, estradiol-17β (E2) and combined E2 and trenbolone acetate (a testosterone analog) implants enhance rate and efficiency of muscle growth; and, consequently, these compounds are widely used as growth promoters. Although the positive effects of E2 on rate and efficiency of bovine muscle growth are well established, the mechanisms involved in these effects are not well understood. Combined E2 and trenbolone acetate implants result in significantly increased muscle satellite cell number in feedlot steers. Additionally, E2 treatment stimulates proliferation of cultured bovine satellite cells (BSC). Studies in nonmuscle cells have shown that binding of E2 to G protein-coupled estrogen receptor (GPER)-1 results in activation of matrix metalloproteinases 2 and 9 (MMP2/9) resulting in proteolytic release of heparin binding epidermal growth factor-like growth factor (hbEGF) from the cell surface. Released hbEGF binds to and activates the epidermal growth factor receptor resulting in increased proliferation. To assess if GPER-1, MMP2/9, and/or hbEGF are involved in the mechanism of E2-stimulated BSC proliferation, we have examined the effects of G36 (a specific inhibitor of GPER-1), CRM197 (a specific inhibitor of hbEGF), and MMP-2/MMP-9 Inhibitor II (an inhibitor of MMP2/9 activity) on E2-stimulated BSC proliferation. Inhibition of GPER-1, MMP2/9, or hbEGF suppresses E2-stimulated BSC proliferation (P < 0.001) suggesting that all these are required in order for E2 to stimulate BSC proliferation. These results strongly suggest that E2 may stimulate BSC proliferation by binding to GPER-1 resulting in MMP2/9-catalyzed release of cell membrane-bound hbEGF and subsequent activation of epidermal growth factor receptor by binding of released hbEGF. Copyright © 2014 Elsevier Inc. All rights reserved.

Role of central nervous system glucagon-like Peptide-1 receptors in enteric glucose sensing.

PubMed

Knauf, Claude; Cani, Patrice D; Kim, Dong-Hoon; Iglesias, Miguel A; Chabo, Chantal; Waget, Aurélie; Colom, André; Rastrelli, Sophie; Delzenne, Nathalie M; Drucker, Daniel J; Seeley, Randy J; Burcelin, Remy

2008-10-01

Ingested glucose is detected by specialized sensors in the enteric/hepatoportal vein, which send neural signals to the brain, which in turn regulates key peripheral tissues. Hence, impairment in the control of enteric-neural glucose sensing could contribute to disordered glucose homeostasis. The aim of this study was to determine the cells in the brain targeted by the activation of the enteric glucose-sensing system. We selectively activated the axis in mice using a low-rate intragastric glucose infusion in wild-type and glucagon-like peptide-1 (GLP-1) receptor knockout mice, neuropeptide Y-and proopiomelanocortin-green fluorescent protein-expressing mice, and high-fat diet diabetic mice. We quantified the whole-body glucose utilization rate and the pattern of c-Fos positive in the brain. Enteric glucose increased muscle glycogen synthesis by 30% and regulates c-Fos expression in the brainstem and the hypothalamus. Moreover, the synthesis of muscle glycogen was diminished after central infusion of the GLP-1 receptor (GLP-1Rc) antagonist Exendin 9-39 and abolished in GLP-1Rc knockout mice. Gut-glucose-sensitive c-Fos-positive cells of the arcuate nucleus colocalized with neuropeptide Y-positive neurons but not with proopiomelanocortin-positive neurons. Furthermore, high-fat feeding prevented the enteric activation of c-Fos expression. We conclude that the gut-glucose sensor modulates peripheral glucose metabolism through a nutrient-sensitive mechanism, which requires brain GLP-1Rc signaling and is impaired during diabetes.

Neuroprotective effects of (Val8)GLP-1-Glu-PAL in the MPTP Parkinson's disease mouse model.

PubMed

Zhang, YanFang; Chen, YiMei; Li, Lin; Hölscher, Christian

2015-10-15

Glucagon-like peptide 1 (GLP-1) is a hormone and a growth factor. GLP-1 mimetics are currently on the market as treatments for type 2 diabetes. They also have shown neuroprotective properties in animal models of neurodegenerative disorders. In addition, the GLP-1 mimetic exendin-4 has shown protective effects in animal models of Parkinson's disease (PD), and a first clinical trial in PD patients showed promising results. (Val8)GLP-1-glu-PAL is a new GLP-1 analogue which has a longer biological half-life than exendin-4. We previously showed that (Val8)GLP-1-glu-PAL has neuroprotective properties. Here we tested the drug in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. MPTP was injected (30mg/kg i.p.) along with (Val8)GLP-1-glu-PAL (25nmol/kg i.p.) once-daily for 8 days. (Val8)GLP-1-glu-PAL showed good effects in preventing the MPTP-induced motor impairment (Rotarod, open field locomotion, swim test), reduction in tyrosine hydroxylase levels (dopamine synthesis) in the substantia nigra, a reduction of activated caspase 3 levels, of TUNEL positive cell numbers, of the pro-apoptotic signaling molecule BAX and an increase in the growth signaling molecule Bcl-2. The results demonstrate that (Val8)GLP-1-glu-PAL shows promise as a novel treatment of PD. Copyright © 2015 Elsevier B.V. All rights reserved.

Glucagon-like peptide-1 ameliorates cardiac lipotoxicity in diabetic cardiomyopathy via the PPARα pathway.

PubMed

Wu, Lujin; Wang, Ke; Wang, Wei; Wen, Zheng; Wang, Peihua; Liu, Lei; Wang, Dao Wen

2018-04-16

Lipotoxicity cardiomyopathy is the result of excessive accumulation and oxidation of toxic lipids in the heart. It is a major threat to patients with diabetes. Glucagon-like peptide-1 (GLP-1) has aroused considerable interest as a novel therapeutic target for diabetes mellitus because it stimulates insulin secretion. Here, we investigated the effects and mechanisms of the GLP-1 analog exendin-4 and the dipeptidyl peptidase-4 inhibitor saxagliptin on cardiac lipid metabolism in diabetic mice (DM). The increased myocardial lipid accumulation, oxidative stress, apoptosis, and cardiac remodeling and dysfunction induced in DM by low streptozotocin doses and high-fat diets were significantly reversed by exendin-4 and saxagliptin treatments for 8 weeks. We found that exendin-4 inhibited abnormal activation of the (PPARα)-CD36 pathway by stimulating protein kinase A (PKA) but suppressing the Rho-associated protein kinase (ROCK) pathway in DM hearts, palmitic acid (PA)-treated rat h9c2 cardiomyocytes (CMs), and isolated adult mouse CMs. Cardioprotection in DM mediated by exendin-4 was abolished by combination therapy with the PPARα agonist wy-14643 but mimicked by PPARα gene deficiency. Therefore, the PPARα pathway accounted for the effects of exendin-4. This conclusion was confirmed in cardiac-restricted overexpression of PPARα mediated by adeno-associated virus serotype-9 containing a cardiac troponin T promoter. Our results provide the first direct evidence that GLP-1 protects cardiac function by inhibiting the ROCK/PPARα pathway, thereby ameliorating lipotoxicity in diabetic cardiomyopathy. © 2018 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.

Effects of 1 and 3 g cinnamon on gastric emptying, satiety, and postprandial blood glucose, insulin, glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1, and ghrelin concentrations in healthy subjects.

PubMed

Hlebowicz, Joanna; Hlebowicz, Anna; Lindstedt, Sandra; Björgell, Ola; Höglund, Peter; Holst, Jens J; Darwiche, Gassan; Almér, Lars-Olof

2009-03-01

A previous study of healthy subjects showed that intake of 6 g cinnamon with rice pudding reduced postprandial blood glucose and the gastric emptying rate (GER) without affecting satiety. The objective was to study the effect of 1 and 3 g cinnamon on GER, postprandial blood glucose, plasma concentrations of insulin and incretin hormones [glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1)], the ghrelin response, and satiety in healthy subjects. GER was measured by using real-time ultrasonography after ingestion of rice pudding with and without 1 or 3 g cinnamon. Fifteen healthy subjects were assessed in a crossover trial. The addition of 1 or 3 g cinnamon had no significant effect on GER, satiety, glucose, GIP, or the ghrelin response. The insulin response at 60 min and the area under the curve (AUC) at 120 min were significantly lower after ingestion of rice pudding with 3 g cinnamon (P = 0.05 and P = 0.036, respectively, after Bonferroni correction). The change in GLP-1 response (DeltaAUC) and the change in the maximum concentration (DeltaC(max)) were both significantly higher after ingestion of rice pudding with 3 g cinnamon (P = 0.0082 and P = 0.0138, respectively, after Bonferroni correction). Ingestion of 3 g cinnamon reduced postprandial serum insulin and increased GLP-1 concentrations without significantly affecting blood glucose, GIP, the ghrelin concentration, satiety, or GER in healthy subjects. The results indicate a relation between the amount of cinnamon consumed and the decrease in insulin concentration.

GLP-1 receptor signaling is not required for reduced body weight after RYGB in rodents

PubMed Central

Ye, Jianping; Hao, Zheng; Mumphrey, Michael B.; Townsend, R. Leigh; Patterson, Laurel M.; Stylopoulos, Nicholas; Münzberg, Heike; Morrison, Christopher D.; Drucker, Daniel J.

2014-01-01

Exaggerated GLP-1 and PYY secretion is thought to be a major mechanism in the reduced food intake and body weight after Roux-en-Y gastric bypass surgery. Here, we use complementary pharmacological and genetic loss-of-function approaches to test the role of increased signaling by these gut hormones in high-fat diet-induced obese rodents. Chronic brain infusion of a supramaximal dose of the selective GLP-1 receptor antagonist exendin-9–39 into the lateral cerebral ventricle significantly increased food intake and body weight in both RYGB and sham-operated rats, suggesting that, while contributing to the physiological control of food intake and body weight, central GLP-1 receptor signaling tone is not the critical mechanism uniquely responsible for the body weight-lowering effects of RYGB. Central infusion of the selective Y2R-antagonist BIIE0246 had no effect in either group, suggesting that it is not critical for the effects of RYGB on body weight under the conditions tested. In a recently established mouse model of RYGB that closely mimics surgery and weight loss dynamics in humans, obese GLP-1R-deficient mice lost the same amount of body weight and fat mass and maintained similarly lower body weight compared with wild-type mice. Together, the results surprisingly provide no support for important individual roles of either gut hormone in the specific mechanisms by which RYGB rats settle at a lower body weight. It is likely that the beneficial effects of bariatric surgeries are expressed through complex mechanisms that require combination approaches for their identification. PMID:24430883

GLP-1 receptor signaling is not required for reduced body weight after RYGB in rodents.

PubMed

Ye, Jianping; Hao, Zheng; Mumphrey, Michael B; Townsend, R Leigh; Patterson, Laurel M; Stylopoulos, Nicholas; Münzberg, Heike; Morrison, Christopher D; Drucker, Daniel J; Berthoud, Hans-Rudolf

2014-03-01

Exaggerated GLP-1 and PYY secretion is thought to be a major mechanism in the reduced food intake and body weight after Roux-en-Y gastric bypass surgery. Here, we use complementary pharmacological and genetic loss-of-function approaches to test the role of increased signaling by these gut hormones in high-fat diet-induced obese rodents. Chronic brain infusion of a supramaximal dose of the selective GLP-1 receptor antagonist exendin-9-39 into the lateral cerebral ventricle significantly increased food intake and body weight in both RYGB and sham-operated rats, suggesting that, while contributing to the physiological control of food intake and body weight, central GLP-1 receptor signaling tone is not the critical mechanism uniquely responsible for the body weight-lowering effects of RYGB. Central infusion of the selective Y2R-antagonist BIIE0246 had no effect in either group, suggesting that it is not critical for the effects of RYGB on body weight under the conditions tested. In a recently established mouse model of RYGB that closely mimics surgery and weight loss dynamics in humans, obese GLP-1R-deficient mice lost the same amount of body weight and fat mass and maintained similarly lower body weight compared with wild-type mice. Together, the results surprisingly provide no support for important individual roles of either gut hormone in the specific mechanisms by which RYGB rats settle at a lower body weight. It is likely that the beneficial effects of bariatric surgeries are expressed through complex mechanisms that require combination approaches for their identification.

Protein A-like activity and streptococcal cross-reactions.

PubMed Central

Kingston, D

1981-01-01

Recognition of the protein A-like activity of some strains of group A streptococci has thrown doubt on much previous work suggesting antigenic cross-reactions between these streptococci and mammalian tissues. The strains used in our previous studies have now been examined by the mixed reverse passive antiglobulin reaction (MRPAH) for the 'non-specific' absorption of purified Fc portion of human IgG. They were found to have only traces of activity. The strain of Staphylococcus aureus used to control 'non-specific' absorption by bacterial cell walls was strongly positive. Protein A-like material as detected in this way was not therefore responsible for our earlier results. PMID:7039880

Sustained expression of GLP-1 receptor differentially modulates β-cell functions in diabetic and nondiabetic mice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kubo, Fumiyo; Miyatsuka, Takeshi, E-mail: miyatsuka-takeshi@umin.net; Department of Medicine, Metabolism and Endocrinology, Juntendo University Graduate School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421

2016-02-26

Glucagon-like peptide 1 (GLP-1) has been shown to play important roles in maintaining β-cell functions, such as insulin secretion and proliferation. While expression levels of GLP-1 receptor (Glp1r) are compromised in the islets of diabetic rodents, it remains unclear when and to what degree Glp1r mRNA levels are decreased during the progression of diabetes. In this study, we performed real-time PCR with the islets of db/db diabetic mice at different ages, and found that the expression levels of Glp1r were comparable to those of the islets of nondiabetic db/misty controls at the age of four weeks, and were significantly decreasedmore » at the age of eight and 12 weeks. To investigate whether restored expression of Glp1r affects the diabetic phenotypes, we generated the transgenic mouse model Pdx1{sup PB}-CreER{sup TM}; CAG-CAT-Glp1r (βGlp1r) that allows for induction of Glp1r expression specifically in β cells. Whereas the expression of exogenous Glp1r had no measurable effect on glucose tolerance in nondiabetic βGlp1r;db/misty mice, βGlp1r;db/db mice exhibited higher glucose and lower insulin levels in blood on glucose challenge test than control db/db littermates. In contrast, four weeks of treatment with exendin-4 improved the glucose profiles and increased serum insulin levels in βGlp1r;db/db mice, to significantly higher levels than those in control db/db mice. These differential effects of exogenous Glp1r in nondiabetic and diabetic mice suggest that downregulation of Glp1r might be required to slow the progression of β-cell failure under diabetic conditions. - Highlights: • Expression levels of incretin receptors were significantly decreased in diabetic db/db islets after the age of eight weeks. • A transgenic mouse model expressing Glp1r specifically in β cells was generated. • Exogenous expression of Glp1r in β cells did not affect metabolic profiles in nondiabetic mice. • Sustained expression of Glp1r in diabetic db/db β cells

Direct Modulation of Heterotrimeric G Protein-coupled Signaling by a Receptor Kinase Complex.

PubMed

Tunc-Ozdemir, Meral; Urano, Daisuke; Jaiswal, Dinesh Kumar; Clouse, Steven D; Jones, Alan M

2016-07-01

Plants and some protists have heterotrimeric G protein complexes that activate spontaneously without canonical G protein-coupled receptors (GPCRs). In Arabidopsis, the sole 7-transmembrane regulator of G protein signaling 1 (AtRGS1) modulates the G protein complex by keeping it in the resting state (GDP-bound). However, it remains unknown how a myriad of biological responses is achieved with a single G protein modulator. We propose that in complete contrast to G protein activation in animals, plant leucine-rich repeat receptor-like kinases (LRR RLKs), not GPCRs, provide this discrimination through phosphorylation of AtRGS1 in a ligand-dependent manner. G protein signaling is directly activated by the pathogen-associated molecular pattern flagellin peptide 22 through its LRR RLK, FLS2, and co-receptor BAK1. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Characterization of a Fasciola gigantica protein carrying two DM9 domains reveals cellular relocalization property.

PubMed

Phadungsil, Wansika; Smooker, Peter M; Vichasri-Grams, Suksiri; Grams, Rudi

2016-01-01

Even at the present age of whole-organism analysis, e.g., genomics, transcriptomics, and proteomics, the biological roles of many proteins remain unresolved. Classified among the proteins of unknown function is a family of proteins harboring repeats of the DM9 domain, a 60-75 amino acids motif first described in a small number of Drosophila melanogaster proteins. Proteins may carry two or more DM9 domains either in combination with other domains or as their sole constituent. Here we have characterized a 16.8 kDa Fasciola gigantica protein comprising two tandem repeated DM9 domains (FgDM9-1). The protein was located in the parenchyma of the immature and mature parasite and consequently it was not detected in the ES product of the parasite but only in the whole worm extract. Interestingly, extraction with SDS yielded a substantially higher amount of the protein suggesting association with insoluble cell components. In Sf9 insect cells a heterologously expressed EGFP-FgDM9-1 chimera showed cell-wide distribution but relocated to vesicle-like structures in the cytoplasm after stimulating cellular stress by bacteria, heat shock or chloroquine. These structures did not colocalize with the markers of endocytosis/phagocytosis ubiquitin, RAB7, GABARAP. The same behavior was noted for Aedes aegypti PRS1, a homologous mosquito DM9 protein as a positive control while EGFP did not exhibit such relocation in the insect cells. Cross-linking experiments on soluble recombinant FgDM9-1 indicated that the protein can undergo specific oligomerization. It is speculated that proteins carrying the DM9 domain have a role in vesicular transport in flatworms and insects. Copyright © 2016 Elsevier B.V. All rights reserved.

The bioactive effects of casein proteins on enteroendocrine cell health, proliferation and incretin hormone secretion.

PubMed

Gillespie, Anna L; Green, Brian D

2016-11-15

Previous studies suggest that casein exerts various anti-diabetic effects. However, it is not known which casein proteins are bioactive, nor their effects on enteroendocrine cells. This study evaluated the effects of intact whole casein, intact individual proteins (alpha, beta and kappa casein) and hydrolysates on an enteroendocrine cell line. High content analysis accurately monitored changes in cell health and intracellular glucagon-like peptide-1 (GLP-1) content. Cheese ripening duration and GLP-1 secretory responses were also considered. Beta casein significantly stimulated enteroendocrine cell proliferation and all caseins were potent GLP-1 secretagogues (except kappa casein). Interestingly the GLP-1 secretory activity was almost always lost or significantly reduced upon hydrolysis with proteolytic enzymes. Only pepsin-derived beta casein hydrolysates had significantly increased potency compared with the intact protein, but this was diminished with prolonged hydrolysis. In conclusion casein proteins are not detrimental to enteroendocrine cells, and alpha and beta casein are particularly beneficial stimulating proliferation and GLP-1 secretion. Copyright © 2016 Elsevier Ltd. All rights reserved.

Enhanced AMPA Receptor Trafficking Mediates the Anorexigenic Effect of Endogenous Glucagon-like Peptide-1 in the Paraventricular Hypothalamus.

PubMed

Liu, Ji; Conde, Kristie; Zhang, Peng; Lilascharoen, Varoth; Xu, Zihui; Lim, Byung Kook; Seeley, Randy J; Zhu, J Julius; Scott, Michael M; Pang, Zhiping P

2017-11-15

Glucagon-like Peptide 1 (GLP-1)-expressing neurons in the hindbrain send robust projections to the paraventricular nucleus of the hypothalamus (PVN), which is involved in the regulation of food intake. Here, we describe that stimulation of GLP-1 afferent fibers within the PVN is sufficient to suppress food intake independent of glutamate release. We also show that GLP-1 receptor (GLP-1R) activation augments excitatory synaptic strength in PVN corticotropin-releasing hormone (CRH) neurons, with GLP-1R activation promoting a protein kinase A (PKA)-dependent signaling cascade leading to phosphorylation of serine S845 on GluA1 AMPA receptors and their trafficking to the plasma membrane. Finally, we show that postnatal depletion of GLP-1R in the PVN increases food intake and causes obesity. This study provides a comprehensive multi-level (circuit, synaptic, and molecular) explanation of how food intake behavior and body weight are regulated by endogenous central GLP-1. VIDEO ABSTRACT. Copyright © 2017 Elsevier Inc. All rights reserved.

Enhanced AMPA receptor trafficking mediates the anorexigenic effect of endogenous glucagon like peptide-1 in the paraventricular hypothalamus

PubMed Central

Liu, Ji; Conde, Kristie; Zhang, Peng; Lilascharoen, Varoth; Xu, Zihui; Lim, Byung Kook; Seeley, Randy J.; Zhu, Julius J.; Scott, Michael M.; Pang, Zhiping P.

2017-01-01

SUMMARY Glucagon Like Peptide 1 (GLP-1)-expressing neurons in the hindbrain send robust projections to the paraventricular nucleus of the hypothalamus (PVN), which is involved in the regulation of food intake. Here, we describe that stimulation of GLP-1 afferent fibers within the PVN is sufficient to suppress food intake independent of glutamate release. We also show that GLP-1 receptor (GLP-1R) activation augments excitatory synaptic strength in PVN corticotropin-releasing hormone (CRH) neurons, with GLP-1R activation promoting a protein kinase A (PKA) dependent signaling cascade leading to phosphorylation of serine S845 on GluA1 AMPA receptors and their trafficking to the plasma membrane. Finally, we show that postnatal depletion of GLP-1R in the PVN increases food intake and causes obesity. This study provides a comprehensive multi-level (circuit, synaptic, and molecular) explanation of how food intake behavior and body weight are regulated by endogenous central GLP-1. PMID:29056294

High fat diet and GLP-1 drugs induce pancreatic injury in mice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rouse, Rodney, E-mail: rodney.rouse@fda.hhs.gov; Xu, Lin; Stewart, Sharron

Glucagon Like Peptide-1 (GLP-1) drugs are currently used to treat type-2 diabetes. Safety concerns for increased risk of pancreatitis and pancreatic ductal metaplasia have accompanied these drugs. High fat diet (HFD) is a type-2 diabetes risk factor that may affect the response to GLP-1 drug treatment. The objective of the present study was to investigate the effects of diet and GLP-1 based drugs on the exocrine pancreas in mice. Experiments were designed in a mouse model of insulin resistance created by feeding a HFD or standard diet (STD) for 6 weeks. The GLP-1 drugs, sitagliptin (SIT) and exenatide (EXE) weremore » administered once daily for additional 6 weeks in both mice fed HFD or STD. The results showed that body weight, blood glucose levels, and serum levels of pro-inflammatory cytokines (TNFα, IL-1β, and KC) were significantly greater in HFD mice than in STD mice regardless of GLP-1 drug treatment. The semi-quantitative grading showed that pancreatic changes were significantly greater in EXE and SIT-treated mice compared to control and that HFD exacerbated spontaneous exocrine pancreatic changes seen in saline-treated mice on a standard diet. Exocrine pancreatic changes identified in this study included acinar cell injury (hypertrophy, autophagy, apoptosis, necrosis, and atrophy), vascular injury, interstitial edema and inflammation, fat necrosis, and duct changes. These findings support HFD as a risk factor to increased susceptibility/severity for acute pancreatitis and indicate that GLP-1 drugs cause pancreatic injury that can be exacerbated in a HFD environment.« less

Inhibition of H3K9 Methyltransferase G9a Repressed Cell Proliferation and Induced Autophagy in Neuroblastoma Cells

PubMed Central

Ke, Xiao-Xue; Zhang, Dunke; Zhu, Shunqin; Xia, Qingyou; Xiang, Zhonghuai; Cui, Hongjuan

2014-01-01

Histone methylation plays an important role in gene transcription and chromatin organization and is linked to the silencing of a number of critical tumor suppressor genes in tumorigenesis. G9a is a histone methyltransferase (HMTase) for histone H3 lysine 9. In this study, we investigated the role of G9a in neuroblastoma tumor growth together with the G9a inhibitor BIX01294. The exposure of neuroblastoma cells to BIX01294 resulted in the inhibition of cell growth and proliferation, and BIX01294 treatment resulted in the inhibition of the tumorigenicity of neuroblastoma cells in NOD/SCID mice. Therefore, G9a may be a potential therapeutic target in neuroblastoma. Moreover, we found several specific characteristics of autophagy after BIX01294 treatment, including the appearance of membranous vacuoles and microtubule-associated protein light chain 3 (LC3B). Similar results were observed in G9a-knockdown cells. In conclusion, our results demonstrated that G9a is a prognostic marker in neuroblastoma, and revealed a potential role of G9a in regulating the autophagy signaling pathway in neuroblastoma. PMID:25198515

S100A8/A9 (Calprotectin) Negatively Regulates G2/M Cell Cycle Progression and Growth of Squamous Cell Carcinoma

PubMed Central

Khammanivong, Ali; Wang, Chengxing; Sorenson, Brent S.; Ross, Karen F.; Herzberg, Mark C.

2013-01-01

Malignant transformation results in abnormal cell cycle regulation and uncontrolled growth in head and neck squamous cell carcinoma (HNSCC) and other cancers. S100A8/A9 (calprotectin) is a calcium-binding heterodimeric protein complex implicated in cell cycle regulation, but the specific mechanism and role in cell cycle control and carcinoma growth are not well understood. In HNSCC, S100A8/A9 is downregulated at both mRNA and protein levels. We now report that downregulation of S100A8/A9 correlates strongly with a loss of cell cycle control and increased growth of carcinoma cells. To show its role in carcinogenesis in an in vitro model, S100A8/A9 was stably expressed in an S100A8/A9-negative human carcinoma cell line (KB cells, HeLa-like). S100A8/A9 expression increases PP2A phosphatase activity and p-Chk1 (Ser345) phosphorylation, which appears to signal inhibitory phosphorylation of mitotic p-Cdc25C (Ser216) and p-Cdc2 (Thr14/Tyr15) to inactivate the G2/M Cdc2/cyclin B1 complex. Cyclin B1 expression then downregulates and the cell cycle arrests at the G2/M checkpoint, reducing cell division. As expected, S100A8/A9-expressing cells show both decreased anchorage-dependent and -independent growth and mitotic progression. Using shRNA, silencing of S100A8/A9 expression in the TR146 human HNSCC cell line increases growth and survival and reduces Cdc2 inhibitory phosphorylation at Thr14/Tyr15. The level of S100A8/A9 endogenous expression correlates strongly with the reduced p-Cdc2 (Thr14/Tyr14) level in HNSCC cell lines, SCC-58, OSCC-3 and UMSCC-17B. S100A8/A9-mediated control of the G2/M cell cycle checkpoint is, therefore, a likely suppressive mechanism in human squamous cell carcinomas and may suggest new therapeutic approaches. PMID:23874958

Mapping the energy landscape for second-stage folding of a single membrane protein

PubMed Central

Min, Duyoung; Jefferson, Robert E; Bowie, James U; Yoon, Tae-Young

2016-01-01

Membrane proteins are designed to fold and function in a lipid membrane, yet folding experiments within a native membrane environment are challenging to design. Here we show that single-molecule forced unfolding experiments can be adapted to study helical membrane protein folding under native-like bicelle conditions. Applying force using magnetic tweezers, we find that a transmembrane helix protein, Escherichia coli rhomboid protease GlpG, unfolds in a highly cooperative manner, largely unraveling as one physical unit in response to mechanical tension above 25 pN. Considerable hysteresis is observed, with refolding occurring only at forces below 5 pN. Characterizing the energy landscape reveals only modest thermodynamic stability (ΔG = 6.5 kBT) but a large unfolding barrier (21.3 kBT) that can maintain the protein in a folded state for long periods of time (t1/2 ~3.5 h). The observed energy landscape may have evolved to limit the existence of troublesome partially unfolded states and impart rigidity to the structure. PMID:26479439

G9a histone methyltransferase plays a dominant role in euchromatic histone H3 lysine 9 methylation and is essential for early embryogenesis

PubMed Central

Tachibana, Makoto; Sugimoto, Kenji; Nozaki, Masami; Ueda, Jun; Ohta, Tsutomu; Ohki, Misao; Fukuda, Mikiko; Takeda, Naoki; Niida, Hiroyuki; Kato, Hiroyuki; Shinkai, Yoichi

2002-01-01

Covalent modification of histone tails is crucial for transcriptional regulation, mitotic chromosomal condensation, and heterochromatin formation. Histone H3 lysine 9 (H3-K9) methylation catalyzed by the Suv39h family proteins is essential for establishing the architecture of pericentric heterochromatin. We recently identified a mammalian histone methyltransferase (HMTase), G9a, which has strong HMTase activity towards H3-K9 in vitro. To investigate the in vivo functions of G9a, we generated G9a-deficient mice and embryonic stem (ES) cells. We found that H3-K9 methylation was drastically decreased in G9a-deficient embryos, which displayed severe growth retardation and early lethality. G9a-deficient ES cells also exhibited reduced H3-K9 methylation compared to wild-type cells, indicating that G9a is a dominant H3-K9 HMTase in vivo. Importantly, the loss of G9a abolished methylated H3-K9 mostly in euchromatic regions. Finally, G9a exerted a transcriptionally suppressive function that depended on its HMTase activity. Our results indicate that euchromatic H3-K9 methylation regulated by G9a is essential for early embryogenesis and is involved in the transcriptional repression of developmental genes. PMID:12130538

Effects of different starch source of starter on small intestinal growth and endogenous GLP-2 secretion in preweaned lambs.

PubMed

Sun, Daming; Li, Hongwei; Mao, Shengyong; Zhu, Weiyun; Liu, Junhua

2018-02-15

The objective of this study was to investigate the effects of different sources of starch in starter feed on small intestinal growth and endogenous glucagon-like peptide 2 (GLP-2) secretion in preweaned lambs. Twenty-four 10-d-old lambs were divided into three groups that were treated with different iso-starch diets containing purified cassava starch (CS, n = 8), maize starch (MS, n = 8), and pea starch (PS, n = 8). At 56 d old, there was no significant difference in final body weight (BW) of lambs among the three groups. However, different starch source in starter significantly affected the average daily feed intake (ADFI) and average daily gain (ADG) of lambs among three groups. Compared with the CS and MS diets, the PS diet significantly increased the GLP-2 concentration in blood plasma (P < 0.001), the crypt depth of the jejunum (P = 0.006), and the villus height of the ileum (P = 0.039). Meanwhile, PS diet significantly increased the mRNA expression of proglucagon and the glucagon-like peptide 2 receptor (GLP-2R) in the jejunum and ileum (P < 0.001). Furthermore, the PS diet significantly upregulated the mRNA expression of cyclin D1 (P < 0.001), cyclin E (P = 0.006), and cyclin-dependent kinases 6 (CDK6) (P = 0.048) in the jejunum and cyclin A (P < 0.001), cyclin D1 (P < 0.001), and CDK6 (P = 0.002) in the ileum. Correlation analysis showed that endogenous GLP-2 secretion was positively related to the mRNA levels of cell cycle proteins in small intestinal mucosa. In summary, all results showed that PS in starter feed promoted small intestinal growth that may, in part, be related to cell cycle acceleration and endogenous GLP-2 secretion in preweaned lambs. These findings provide new insights into nutritional interventions that promote the development of small intestines in young ruminants.

Modulation of GLP-1 Levels by a Genetic Variant That Regulates the Cardiovascular Effects of Intensive Glycemic Control in ACCORD.

PubMed

Shah, Hetal S; Morieri, Mario Luca; Marcovina, Santica M; Sigal, Ronald J; Gerstein, Hertzel C; Wagner, Michael J; Motsinger-Reif, Alison A; Buse, John B; Kraft, Peter; Mychaleckyj, Josyf C; Doria, Alessandro

2018-02-01

A genome-wide association study in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial identified two markers (rs57922 and rs9299870) that were significantly associated with cardiovascular mortality during intensive glycemic control and could potentially be used, when combined into a genetic risk score (GRS), to identify patients with diabetes likely to derive benefit from intensive control rather than harm. The aim of this study was to gain insights into the pathways involved in the modulatory effect of these variants. Fasting levels of 65 biomarkers were measured at baseline and at 12 months of follow-up in the ACCORD-Memory in Diabetes (ACCORD-MIND) MRI substudy ( n = 562). Using linear regression models, we tested the association of the GRS with baseline and 12-month biomarker levels, and with their difference (Δ), among white subjects, with genotype data ( n = 351) stratified by intervention arm. A significant association was observed between GRS and ΔGLP-1 (glucagon-like peptide 1, active) in the intensive arm ( P = 3 × 10 -4 ). This effect was driven by rs57922 ( P = 5 × 10 -4 ). C/C homozygotes, who had been found to derive cardiovascular benefits from intensive treatment, showed a 22% increase in GLP-1 levels during follow-up. By contrast, T/T homozygotes, who had been found to experience increased cardiac mortality with intensive treatment, showed a 28% reduction in GLP-1 levels. No association between ΔGLP-1 and GRS or rs57922 was observed in the standard treatment arm. Differences in GLP-1 axis activation may mediate the modulatory effect of variant rs57922 on the cardiovascular response to intensive glycemic control. These findings highlight the importance of GLP-1 as a cardioprotective factor. © 2017 by the American Diabetes Association.

Brain GLP-1/IGF-1 Signaling and Autophagy Mediate Exendin-4 Protection Against Apoptosis in Type 2 Diabetic Rats.

PubMed

Candeias, Emanuel; Sebastião, Inês; Cardoso, Susana; Carvalho, Cristina; Santos, Maria Sancha; Oliveira, Catarina Resende; Moreira, Paula I; Duarte, Ana I

2018-05-01

Type 2 diabetes (T2D) is a modern socioeconomic burden, mostly due to its long-term complications affecting nearly all tissues. One of them is the brain, whose dysfunctional intracellular quality control mechanisms (namely autophagy) may upregulate apoptosis, leading to cognitive dysfunction and Alzheimer disease (AD). Since impaired brain insulin signaling may constitute the crosslink between T2D and AD, its restoration may be potentially therapeutic herein. Accordingly, the insulinotropic anti-T2D drugs from glucagon-like peptide-1 (GLP-1) mimetics, namely, exendin-4 (Ex-4), could be a promising therapy. In line with this, we hypothesized that peripherally administered Ex-4 rescues brain intracellular signaling pathways, promoting autophagy and ultimately protecting against chronic T2D-induced apoptosis. Thus, we aimed to explore the effects of chronic, continuous, subcutaneous (s.c.) exposure to Ex-4 in brain cortical GLP-1/insulin/insulin-like growth factor-1 (IGF-1) signaling, and in autophagic and cell death mechanisms in middle-aged (8 months old), male T2D Goto-Kakizaki (GK) rats. We used brain cortical homogenates obtained from middle-aged (8 months old) male Wistar (control) and T2D GK rats. Ex-4 was continuously administered for 28 days, via s.c. implanted micro-osmotic pumps (5 μg/kg/day; infusion rate 2.5 μL/h). Peripheral characterization of the animal models was given by the standard biochemical analyses of blood or plasma, the intraperitoneal glucose tolerance test, and the heart rate. GLP-1, insulin, and IGF-1, their downstream signaling and autophagic markers were evaluated by specific ELISA kits and Western blotting. Caspase-like activities and other apoptotic markers were given by colorimetric methods and Western blotting. Chronic Ex-4 treatment attenuated peripheral features of T2D in GK rats, including hyperglycemia and insulin resistance. Furthermore, s.c. Ex-4 enhanced their brain cortical GLP-1 and IGF-1 levels, and subsequent

Cas9 gRNA engineering for genome editing, activation and repression

DOE PAGES

Kiani, Samira; Chavez, Alejandro; Tuttle, Marcelle; ...

2015-09-07

Here we demonstrate that by altering the length of Cas9-associated guide RNA(gRNA) we were able to control Cas9 nuclease activity and simultaneously perform genome editing and transcriptional regulation with a single Cas9 protein. We exploited these principles to engineer mammalian synthetic circuits with combined transcriptional regulation and kill functions governed by a single multifunctional Cas9 protein.

Rice G-protein subunits qPE9-1 and RGB1 play distinct roles in abscisic acid responses and drought adaptation.

PubMed

Zhang, Dong-Ping; Zhou, Yong; Yin, Jian-Feng; Yan, Xue-Jiao; Lin, Sheng; Xu, Wei-Feng; Baluška, František; Wang, Yi-Ping; Xia, Yi-Ji; Liang, Guo-hua; Liang, Jian-Sheng

2015-10-01

Heterotrimeric GTP-binding protein (G-protein)-mediated abscisic acid (ABA) and drought-stress responses have been documented in numerous plant species. However, our understanding of the function of rice G-protein subunits in ABA signalling and drought tolerance is limited. In this study, the function of G-protein subunits in ABA response and drought resistance in rice plants was explored. It was found that the transcription level of qPE9-1 (rice Gγ subunit) gradually decreased with increasing ABA concentration and the lack of qPE9-1 showed an enhanced drought tolerance in rice plants. In contrast, mRNA levels of RGB1 (rice Gβ subunit) were significantly upregulated by ABA treatment and the lack of RGB1 led to reduced drought tolerance. Furthermore, the results suggested that qPE9-1 negatively regulates the ABA response by suppressing the expression of key transcription factors involved in ABA and stress responses, while RGB1 positively regulates ABA biosynthesis by upregulating NCED gene expression under both normal and drought stress conditions. Taken together, it is proposed that RGB1 is a positive regulator of the ABA response and drought adaption in rice plants, whereas qPE9-1 is modulated by RGB1 and functions as a negative regulator in the ABA-dependent drought-stress responses. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

A G Protein-biased Designer G Protein-coupled Receptor Useful for Studying the Physiological Relevance of Gq/11-dependent Signaling Pathways.

PubMed

Hu, Jianxin; Stern, Matthew; Gimenez, Luis E; Wanka, Lizzy; Zhu, Lu; Rossi, Mario; Meister, Jaroslawna; Inoue, Asuka; Beck-Sickinger, Annette G; Gurevich, Vsevolod V; Wess, Jürgen

2016-04-08

Designerreceptorsexclusivelyactivated by adesignerdrug (DREADDs) are clozapine-N-oxide-sensitive designer G protein-coupled receptors (GPCRs) that have emerged as powerful novel chemogenetic tools to study the physiological relevance of GPCR signaling pathways in specific cell types or tissues. Like endogenous GPCRs, clozapine-N-oxide-activated DREADDs do not only activate heterotrimeric G proteins but can also trigger β-arrestin-dependent (G protein-independent) signaling. To dissect the relative physiological relevance of G protein-mediatedversusβ-arrestin-mediated signaling in different cell types or physiological processes, the availability of G protein- and β-arrestin-biased DREADDs would be highly desirable. In this study, we report the development of a mutationally modified version of a non-biased DREADD derived from the M3muscarinic receptor that can activate Gq/11with high efficacy but lacks the ability to interact with β-arrestins. We also demonstrate that this novel DREADD is activein vivoand that cell type-selective expression of this new designer receptor can provide novel insights into the physiological roles of G protein (Gq/11)-dependentversusβ-arrestin-dependent signaling in hepatocytes. Thus, this novel Gq/11-biased DREADD represents a powerful new tool to study the physiological relevance of Gq/11-dependent signaling in distinct tissues and cell types, in the absence of β-arrestin-mediated cellular effects. Such studies should guide the development of novel classes of functionally biased ligands that show high efficacy in various pathophysiological conditions but display a reduced incidence of side effects. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Encapsulated Glucagon-Like Peptide-1-Producing Mesenchymal Stem Cells Have a Beneficial Effect on Failing Pig Hearts

PubMed Central

Wright, Elizabeth J.; Farrell, Kelly A.; Malik, Nadim; Kassem, Moustapha; Lewis, Andrew L.; Wallrapp, Christine

2012-01-01

Stem cell therapy is an exciting and emerging treatment option to promote post-myocardial infarction (post-MI) healing; however, cell retention and efficacy in the heart remain problematic. Glucagon-like peptide-1 (GLP-1) is an incretin hormone with cardioprotective properties but a short half-life in vivo. The effects of prolonged GLP-1 delivery from stromal cells post-MI were evaluated in a porcine model. Human mesenchymal stem cells immortalized and engineered to produce a GLP-1 fusion protein were encapsulated in alginate (bead-GLP-1 MSC) and delivered to coronary artery branches. Control groups were cell-free beads and beads containing unmodified MSCs (bead-MSC), n = 4–5 per group. Echocardiography confirmed left ventricular (LV) dysfunction at time of delivery in all groups. Four weeks after intervention, only the bead-GLP-1 MSC group demonstrated LV function improvement toward baseline and showed decreased infarction area compared with controls. Histological analysis showed reduced inflammation and a trend toward reduced apoptosis in the infarct zone. Increased collagen but fewer myofibroblasts were observed in infarcts of the bead-GLP-1 MSC and bead-MSC groups, and significantly more vessels per mm2 were noted in the infarct of the bead-GLP-1 MSC group. No differences were observed in myocyte cross-sectional area between groups. Post-MI delivery of GLP-1 encapsulated genetically modified MSCs provided a prolonged supply of GLP-1 and paracrine stem cell factors, which improved LV function and reduced epicardial infarct size. This was associated with increased angiogenesis and an altered remodeling response. Combined benefits of paracrine stem cell factors and GLP-1 were superior to those of stem cells alone. These results suggest that encapsulated genetically modified MSCs would be beneficial for recovery following MI. PMID:23197668

Arsenic silences hepatic PDK4 expression through activation of histone H3K9 methylatransferase G9a

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xi; Wu, Jianguo; Choiniere, Jonathan

It is well established that increased liver cancer incidence is strongly associated with epigenetic silencing of tumor suppressor genes; the latter is contributed by the environmental exposure to arsenic. Pyruvate dehydrogenase kinase 4 (PDK4) is a mitochondrial protein that regulates the TCA cycle. However, the epigenetic mechanisms mediated by arsenic to control PDK4 expression remain elusive. In the present study, we showed that histone methyltransferase G9a- and Suv39H-mediated histone H3 lysine 9 (H3K9) methylations contributed to PDK4 silencing in hepatic cells. The PDK4 expression was induced by G9a inhibitor BRD4770 (BRD) and Suv39H inhibitor Chaetocin (CHA). In contrast, arsenic exposuremore » decreased PDK4 expression by inducing G9a and increasing H3K9 di- and tri-methylations levels (H3K9me2/3). In addition, arsenic exposure antagonizes the effect of BRD by enhancing the enrichment of H3K9me2/3 in the PKD4 promoter. Moreover, knockdown of G9a using siRNA induced PDK4 expression in HCC cells. Furthermore, arsenic decreased hepatic PDK4 expression as well as diminished the induction of PDK4 by BRD in mouse liver and hepatocytes. Overall, the results suggest that arsenic causes aberrant repressive histone modification to silence PDK4 in both HCC cells and in mouse liver. - Graphical abstract: Schematic showing arsenic-mediated epigenetic pathway that inhibits PDK4 expression. (A) BRD induces PDK4 expression by decreasing G9a protein and histone H3K9me2 and H3K9me3 levels as well as diminishing their recruitment to the PDK4 promoter. (B) Arsenic counteracts the effect of BRD by increasing histone H3K9me2 and H3K9me3 levels as well as enhancing their enrichment to the PDK4 promoter. Display Omitted - Highlights: • Histone methyltrasferase G9a inhibitor BRD induces PDK4 expression. • Arsenic decreases PDK4 expression and increases H3K9me2 and me3 levels. • Arsenic enhances H3K9me2/me3 enrichment in the PDK4 promoter. • Arsenic antagonizes the

GLP-1 receptor agonists in the treatment of polycystic ovary syndrome.

PubMed

Lamos, Elizabeth Mary; Malek, Rana; Davis, Stephen N

2017-04-01

Polycystic ovarian syndrome (PCOS) affects many women of child-bearing age and is characterized by hyperandrogenism, ovulatory and metabolic dysfunction. A primary treatment goal is weight reduction. The weight loss effects of glucagon-like peptide-1 receptor agonists (GLP-1RA), previously demonstrated in diabetic and obese non-diabetic patients, offer a unique opportunity to expand the medical options available to PCOS patients. Areas covered: Available clinical trials of glucagon-like peptide-1 receptor agonist therapy in PCOS were reviewed. Literature was searched from PubMed using appropriate search terms up to November 2016. Expert commentary: The available studies of GLP-1 RA therapy in the treatment of excess body weight in women with PCOS demonstrate that exenatide and liraglutide are effective in weight reduction either as monotherapy or in combination with metformin. A few studies showed that androgens may be modestly decreased and menstrual frequency may be increased. Eating behavior may be improved with liraglutide therapy. Glucose parameters are generally improved. GLP-1RAs were well-tolerated, with nausea being the most significant adverse side effect. Barriers to utilization may be the short duration studies, lack of familiarity of the medication, the route of administration (injection) and the variable outcomes on ovulation and hyperandrogenism.

Quantitative Impact of Plasma Clearance and Down-regulation on GLP-1 Receptor Molecular Imaging.

PubMed

Zhang, Liang; Thurber, Greg M

2016-02-01

Quantitative molecular imaging of beta cell mass (BCM) would enable early detection and treatment monitoring of type 1 diabetes. The glucagon-like peptide-1 (GLP-1) receptor is an attractive target due to its beta cell specificity and cell surface location. We quantitatively investigated the impact of plasma clearance and receptor internalization on targeting efficiency in healthy B6 mice. Four exenatide-based probes were synthesized that varied in molecular weight, binding affinity, and plasma clearance. The GLP-1 receptor internalization rate and in vivo receptor expression were quantified. Receptor internalization (54,000 receptors/cell in vivo) decreased significantly within minutes, reducing the benefit of a slower-clearing agent. The multimers and albumin binding probes had higher kidney and liver uptake, respectively. Slow plasma clearance is beneficial for GLP-1 receptor peptide therapeutics. However, for exendin-based imaging of islets, down-regulation of the GLP-1 receptor and non-specific background uptake result in a higher target-to-background ratio for fast-clearing agents.

Quantitative Impact of Plasma Clearance and Down-regulation on GLP-1 Receptor Molecular Imaging

PubMed Central

Zhang, Liang; Thurber, Greg M.

2016-01-01

Purpose Quantitative molecular imaging of beta cell mass (BCM) would enable early detection and treatment monitoring of type-1 diabetes. The glucagon like peptide-1 (GLP-1) receptor is an attractive target due to its beta cell specificity and cell surface location. We quantitatively investigated the impact of plasma clearance and receptor internalization on targeting efficiency in healthy B6 mice. Procedures Four exenatide-based probes were synthesized that varied in molecular weight, binding affinity, and plasma clearance. The GLP-1 receptor internalization rate and in vivo receptor expression were quantified. Results Receptor internalization (54,000 receptors/cell in vivo) decreased significantly within minutes, reducing the benefit of a slower clearing agent. The multimers and albumin binding probes had higher kidney and liver uptake, respectively. Conclusions Slow plasma clearance is beneficial for GLP-1 receptor peptide therapeutics. However, for exendin-based imaging of islets, downregulation of the GLP-1 receptor and non-specific background uptake result in a higher TBR for fast-clearing agents. PMID:26194012

The GLP-1 response to glucose does not mediate beta and alpha cell dysfunction in Hispanics with abnormal glucose metabolism.

PubMed

Adams, Elizabeth; Genter, Pauline; Keefe, Emma; Sandow, Kevin; Gray, Virginia; Rotter, Jerome I; Chen, Yii-Der Ida; Ipp, Eli

2018-01-01

Glucagon-like peptide-1 (GLP-1) contributes to insulin secretion after meals. Though Hispanics have increased risk for type 2 diabetes mellitus, it is unknown if impaired GLP-1 secretion contributes to this risk. We therefore studied plasma GLP-1 secretion and action in Hispanic adults. Hispanic (H; n = 31) and non-Hispanic (nH; n = 15) participants underwent an oral glucose tolerance test (OGTT). All participants were categorized by glucose tolerance into four groups: normal glucose tolerant non-Hispanic (NGT-nH; n = 15), normal glucose tolerant Hispanic (NGT-H; n = 12), impaired glucose tolerant Hispanic (IGT-H; n = 11), or newly diagnosed type 2 diabetes mellitus, Hispanic (T2D-H; n = 8). Glucose-induced increments in plasma GLP-1 (Δ-GLP-1) were not different in NGT-H and NGT-nH (p = .38), nor amongst Hispanic subgroups with varying degrees of glucose homeostasis (p = .6). In contrast, the insulinogenic index in T2D-H group was lower than the other groups (p = .016). Subjects with abnormal glucose homeostasis (AGH), i.e., T2D-H plus IGT-H, had a diminished glucagon suppression index compared to patients with normal glucose homeostasis (NGT-H plus NGT-nH) (p = .035). GLP-1 responses to glucose were similar in Hispanic and Non-Hispanic NGT. Despite similar glucose-induced Δ-GLP-1, insulin and glucagon responses were abnormal in T2D-H and AGH, respectively. Thus, impaired GLP-1 secretion is unlikely to play a role in islet dysfunction in T2D. Although GLP-1 therapeutics enhance insulin secretion and glucagon suppression, it is likely due to pharmacological amplification of the GLP-1 pathways rather than treatment of hormonal deficiency. Copyright © 2017 Elsevier B.V. All rights reserved.

Quality goal attainment and maintenance in patients with type II diabetes mellitus initiated on canagliflozin or a glucagon-like peptide-1 receptor agonist in an actual practice setting.

PubMed

Wysham, Carol H; Pilon, Dominic; Ingham, Mike; Lafeuille, Marie-Hélène; Emond, Bruno; Kamstra, Rhiannon; Pfeifer, Michael; Lefebvre, Patrick

2018-06-01

To compare achievement of quality goals (HbA1c, weight loss/body mass index [BMI], systolic blood pressure [SBP]), including maintaining HbA1c, between patients with type 2 diabetes mellitus (T2DM) treated with canagliflozin 300 mg (CANA) or a GLP-1 in an actual practice setting. Adults with T2DM newly initiated on CANA or a GLP-1 were identified from the IQVIA TM Real-World Data Electronic Medical Records-US database (2012Q2-2016Q1). To account for differences in baseline characteristics, inverse probability of treatment weighting was used. Outcomes were compared using Cox models (hazard ratios [HRs] and 95% confidence intervals [CIs]) and Kaplan-Meier analyses. CANA (n = 11,435) and GLP-1 (n = 11,582) cohorts had similar attainment of HbA1c < 8.0% (64 mmol/mol) and HbA1c < 9.0% (75 mmol/mol; HbA1c < 8.0%: HR [CI] = 0.98 [0.91-1.06]; HbA1c < 9.0%: HR [CI] = 1.02 [0.93-1.12]), while GLP-1 patients were 10% more likely to achieve HbA1c < 7.0% (53 mmol/mol). CANA and GLP-1 patients were similar in maintaining HbA1c < 7.0%, < 8.0%, or <9.0%, achieving weight loss ≥5% (HR [CI] = 1.05 [0.99-1.12]), achieving BMI <30 kg/m 2 (HR [CI] = 1.11 [0.98-1.27]), and achieving SBP <140 mmHg (HR [CI] = 1.07 [0.98-1.17]). CANA patients were 30% less likely to discontinue treatment, 28% less likely to have a prescription for a new anti-hyperglycemic, and 17-21% less likely to fail to maintain HbA1c < 8.0% or 9.0% or have a prescription for a new anti-hyperglycemic (composite outcome) vs GLP-1. No significant difference was observed for the composite outcome using the HbA1c < 7.0% threshold. This retrospective study in an actual practice setting showed that CANA patients were generally as likely as GLP-1 patients to achieve HbA1c, weight, and blood pressure thresholds, and to maintain glycemic control while being less likely to discontinue treatment and/or have a new anti-hyperglycemic prescribed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Yanqi; Levy, Dan; Horton, John R.

SET domain containing 6 (SETD6) monomethylates the RelA subunit of nuclear factor kappa B (NF-{kappa}B). The ankyrin repeats of G9a-like protein (GLP) recognizes RelA monomethylated at Lys310. Adjacent to Lys310 is Ser311, a known phosphorylation site of RelA. Ser311 phosphorylation inhibits Lys310 methylation by SETD6 as well as binding of Lys310me1 by GLP. The structure of SETD6 in complex with RelA peptide containing the methylation site, in the presence of S-adenosyl-l-methionine, reveals a V-like protein structure and suggests a model for NF-{kappa}B binding to SETD6. In addition, structural modeling of the GLP ankyrin repeats bound to Lys310me1 peptide provides insightmore » into the molecular basis for inhibition of Lys310me1 binding by Ser311 phosphorylation. Together, these findings provide a structural explanation for a key cellular signaling pathway centered on RelA Lys310 methylation, which is generated by SETD6 and recognized by GLP, and incorporate a methylation-phosphorylation switch of adjacent lysine and serine residues. Finally, SETD6 is structurally similar to the Rubisco large subunit methyltransferase. Given the restriction of Rubisco to plant species, this particular appearance of the protein lysine methyltransferase has been evolutionarily well conserved.« less

Posttranslational Modifications of Baculovirus Protamine-Like Protein P6.9 and the Significance of Its Hyperphosphorylation for Viral Very Late Gene Hyperexpression

PubMed Central

Li, Ao; Zhao, Haizhou; Lai, Qingying; Huang, Zhihong; Yuan, Meijin

2015-01-01

ABSTRACT Many viruses utilize viral or cellular chromatin machinery for efficient infection. Baculoviruses encode a conserved protamine-like protein, P6.9. This protein plays essential roles in various viral physiological processes during infection. However, the mechanism by which P6.9 regulates transcription remains unknown. In this study, 7 phosphorylated species of P6.9 were resolved in Sf9 cells infected with the baculovirus type species Autographa californica multiple nucleopolyhedrovirus (AcMNPV). Mass spectrometry identified 22 phosphorylation and 10 methylation sites but no acetylation sites in P6.9. Immunofluorescence demonstrated that the P6.9 and virus-encoded serine/threonine kinase PK1 exhibited similar distribution patterns in infected cells, and coimmunoprecipitation confirmed the interaction between them. Upon pk1 deletion, nucleocapsid assembly and polyhedron formation were interrupted and the transcription of viral very late genes was downregulated. Interestingly, we found that the 3 most phosphorylated P6.9 species vanished from Sf9 cells transfected with the pk1 deletion mutant, suggesting that PK1 is involved in the hyperphosphorylation of P6.9. Mass spectrometry suggested that the phosphorylation of the 7 Ser/Thr and 5 Arg residues in P6.9 was PK1 dependent. Replacement of the 7 Ser/Thr residues with Ala resulted in a P6.9 phosphorylation pattern similar to that of the pk1 deletion mutant. Importantly, the decreases in the transcription level of viral very late genes and viral infectivity were consistent. Our findings reveal that P6.9 hyperphosphorylation is a precondition for the maximal hyperexpression of baculovirus very late genes and provide the first experimental insights into the function of the baculovirus protamine-like protein and the related protein kinase in epigenetics. IMPORTANCE Diverse posttranslational modifications (PTMs) of histones constitute a code that creates binding platforms that recruit transcription factors to

Adding prandial GLP-1 receptor agonists to basal insulin: a promising option for type 2 diabetes therapy.