Le récepteur membranaire TGR5 (Takeda G Protein-coupled Receptor 5), est un récepteur ubiquitaire sensible aux acides biliaires. Il est exprimé dans de nombreux tissus et organes dont l’intestin (dans les cellules entéroendocrines L), la vésicule biliaire, les muscles lisses et squelettiques, le tissu adipeux brun et dans certaines cellules immunitaires. Des études menées in vitro et in vivo chez l’animal ont montré des effets bénéfiques de l’activation de TGR5 sur l’homéostasie énergétique et glucidique. Il est maintenant communément admis que les effets bénéfiques de TGR5 sur l'homéostasie du glucose sont, au moins en partie, médiés par sa capacité à promouvoir la sécrétion de l'incrétine intestinale glucagon-like peptide-1 (GLP-1) au niveau des cellules entéroendocrines L.Cependant, de récentes expériences ont montré que l’activation de TGR5 par des agonistes systémiques dans des modèles animaux peut induire des effets non souhaités tels qu’une augmentation du volume de la vésicule biliaire, des démangeaisons et des effets cardiovasculaires. Afin de s’affranchir des effets non désirés d’agonistes systémiques de TGR5, le projet s’est orienté vers le développement d’agonistes de TGR5 présentant une distribution tissulaire ciblée et limitée à l’intestin et dont la biodisponibilité orale serait très faible, voire nulle. Nous avons alors émis l’hypothèse qu’une activation de TGR5 limitée à l’épithélium intestinal sans exposition systémique permettrait d’obtenir des effets bénéfiques sur l’homéostasie du glucose via l’effet GLP-1 sécrétagogue, tout en minimisant les effets non souhaités sur d’autres tissus ou organes exprimant TGR5.A partir des études de relations structure-activités obtenues au laboratoire sur une série d’agonistes de TGR5, nous avons conçu des composés chimériques de la façon suivante : le pharmacophore responsable de l’activité sur le récepteur TGR5 est lié via un bras espaceur à des éléments structuraux appelés kinétophores qui ajustent les propriétés physicochimiques et pharmacocinétiques de nos agonistes pour limiter leur absorption intestinale. Ainsi, l’objectif de ce travail était d’obtenir des agonistes non systémiques de TGR5, puissants et originaux, exerçant leur action dans l’intestin afin de générer la preuve de concept in vivo de l’intérêt d’utiliser de tels agonistes dans le traitement du diabète de type 2.Une étude systématique de l’effet de kinétophores variés a été réalisée. Une trentaine de composés ont été synthétisés en 8 à 12 étapes permettant l’identification d’agonistes puissants et présentant des propriétés pharmacocinétiques en accord avec notre stratégie de composés topiques intestinaux. Des études in vivo ont ensuite permis de valider l’effet GLP-1 sécrétagogue de tels composés. Enfin, l’évaluation d’un des meilleurs composés dans un modèle murin de diabète nous a permis de valider l’hypothèse qu’un agoniste topique intestinal de TGR5 peut avoir un effet bénéfique sur l’homéostasie énergétique et glucidique. / The membrane receptor TGR5 (Takeda G Protein-coupled Receptor 5) is an ubiquitous receptor sensitive to bile acids. It is expressed in many tissues and organs including the intestine (in enteroendocrine L cells), the gallbladder, smooth and skeletal muscles, brown adipose tissue and in some immune cells. In vitro and in vivo studies in animals have shown beneficial effects of TGR5 activation on energy and glucose homeostasis. It is now commonly accepted that the beneficial effects of TGR5 on glucose homeostasis are, at least in part, mediated by its ability to promote the secretion of the intestinal incretin glucagon-like peptide-1 (GLP-1) in enteroendocrine L cells.However, recent experiments have shown that the activation of TGR5 by systemic agonists in animal models can induce unwanted effects such as increased gallbladder volume, itching and cardiovascular issues. In order to avoid the undesired effects of systemic agonists of TGR5, the project focused on the development of TGR5 agonists with an intestine targeted distribution and a very low oral bioavailability. Then, we hypothesized that the activation of TGR5 limited to the intestinal epithelium without systemic exposure would promote the beneficial effects on glucose homeostasis via the GLP-1 secretagogue effect, while minimizing systemic effects on other tissues or organs expressing TGR5.On the basis of structure-activity relationships on a series of TGR5 agonists developed in the laboratory, we have designed chimeric compounds as follows: the pharmacophore responsible for activity on the TGR5 receptor is bound, via a linker, at structural elements called kinetophores that fine-tune the physicochemical and pharmacokinetic properties of our agonists to limit their intestinal absorption. Thus, the aim of this work was to obtain powerful and original non-systemic TGR5 agonists acting in the intestine to generate the in vivo proof of concept of the therapeutic potential of such agonists in the treatment of type 2 diabetes.A systematic study of the effect of various kinetophores was performed. About thirty compounds have been synthesized in 8 to 12 steps allowing the identification of powerful agonists with pharmacokinetic properties in accordance with our strategy of topical intestinal compounds. In vivo studies were then used to validate the GLP-1 secretagogue effect of such compounds. Finally, evaluation of one of the best compounds in a murine model of diabetes allowed us to validate the hypothesis that a topical intestinal agonist of TGR5 can have a beneficial effect on energy and glucose homeostasis.

Le TD2 est caractérisé par un état inflammatoire de bas grade qui compromet la sécrétion et l‘action de l‘insuline. L‘installation de cette inflammation semble être la conséquence de l‘intoxication aux polluants environnementaux tels que les POP (Polluants Organiques Persistants) et/ou le changement de la flore intestinale, induit par un régime riche en graisse (HFD). L‘intestin est l‘un des premiers tissus exposés aux bactéries pathogènes et à certains POP. Cet organe est aussi le premier impliqué dans la régulation de l‘homéostasie glucidique. Il est donc raisonnable de supposer qu‘une inflammation chronique de l‘intestin puisse avoir des conséquences sur le développement du TD2. Nos objectifs généraux étaient donc : d‘évaluer le rôle de l‘inflammation entérocytaire dans le développement du diabète TD2 et de clarifier l‘effet du Resvératrol (RSV) sur cette maladie. Nos résultats suggèrent que l'inflammation intestinale est impliquée dans l‘établissement d‘un TD2. Cette inflammation pourrait intervenir en libérant des cytokines inflammatoires, en diminuant le taux de GLP-1 et en favorisant le passage des facteurs diabétogènes, de l‘intestin vers les tissus cibles de l‘insuline. L‘induction ou la diminution de l‘inflammation intestinale par des facteurs inflammatogènes (BaP) ou anti-inflammatoires (RSV) sont respectivement associées à l‘aggravation ou à l‘amélioration de l‘état diabétique.Nous avons également montré que le RSV pourrait améliorer l‘état diabétique en normalisant la flore intestinale modifiée par un régime HFD et en augmentant la concentration de GLP-1.. De plus, une co-administration du RSV avec le sitagliptine, un inhibiteur de l‘enzyme DPP4, dégradant le GLP-1, montre une potentialisation de l‘effet du RSV par le sitagliptine: Ces résultats ouvrent la porte pour l‘utilisation de RSV dans la prévention et le traitement du TD2. / The TD2 is characterized by a low-grade inflammatory state that impairs the secretion and action of insulin. Environmental pollutants such as POP (Persistent Organic Pollutants) and the change in gut flora induced by a high fat diet (HFD), are suspected to play an important role in the installation of this inflammation.The intestine is one of the first tissues exposed to pathogenic bacteria and some POP. This organ is also the first take part in the regulation of glucose homeostasis. So, it is reasonable to assume that chronic inflammation of the bowel may affect the development of TD2. Our objectives were: to assess the role of inflammation in the enterocyte development of diabetes TD2 and clarify the effect of Resveratrol (RSV) on the disease.Our results suggest that intestinal inflammation is involved in the establishment of a TD2. This inflammation could affect TD2 through releasing inflammatory cytokines, reducing the concentration of GLP-1 and promoting the passage of diabetogenic factors from the intestine to target tissues of insulin. The induction or reduction of intestinal inflammation by factor inflammatory (BaP) or anti-inflammatory (RSV) are respectively associated with worsening or improvement of the diabetic state.We also showed that the RSV could improve the diabetic state by normalizing the intestinal flora modified by diet and HFD, by increasing the concentration of GLP-1. In addition, co-administration of sitagliptin with RSV, an inhibitor of the enzyme DPP4,which degrade GLP-1, shows a potentiation of the effect of RSV in the sitagliptin: These results open the door for the use of RSV in the prevention and treatment of TD2.Keywords: Resveratrol, type 2 diabetes

Enteroendocrine hormones released from the intestine following food intake have several roles in the control of metabolism, some of which are exploited therapeutically for the treatment of type 2 diabetes. Within this thesis, focus has been on the receptors of the gut hormones glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-2 (GLP-2). In recent years there has been a surge of interest in the enteroendocrine hormones particularly due to the success of GLP-1 mimetics in the treatment of type 2 diabetes. GLP-1 is an incretin hormone, which enhances glucose induced insulin secretion by binding GLP-1 receptors (GLP1R) on pancreatic β-cells. Despite the therapeutic success, several extra-pancreatic clinical effects of GLP-1 remain unexplained. Here, a GLP1R monoclonal antagonistic antibody that can block GLP1R signalling in vivo has been developed and characterised, providing a new tool for the study of GLP1R physiology. GIP is the second incretin hormone, initially referred to as the 'ugly duckling' incretin hormone due to it's ineffectiveness in inducing insulin secretion in type 2 diabetic patients. Aside from the incretin actions, GIP is thought to be involved in the regulation of high-fat diet (HFD) induced obesity. A new transgenic mouse model expressing a fluorescent reporter under the control of the Gipr promoter has been used here to identify GIPR expressing cells. This model showed GIPR expression in the pancreas, adipose tissue, duodenum and nodose ganglia. Surprisingly GIPR expressing cells were found centrally, in areas of the hypothalamus involved in the regulation of food intake and energy expenditure. We consequently sought to investigate the function of GIPR expressing hypothalamic cells. GLP-2, unlike GLP-1 and GIP, is not an incretin hormone. Rather, GLP-2 has been implicated in the regulation of epithelial cell proliferation and apoptosis within the intestine. Therapeutically, an analogue of GLP-2 is used for the treatment of short bowel syndrome. A common missense mutation in the GLP-2 receptor (GLP2R), D470N, has been found to be associated with type 2 diabetes, and here we sought to understand the mechanism underlying this association. The D470N mutant has decreased β-arrestin recruitment, though the significance of this finding will need further research. Overall; the new monoclonal antagonistic GLP1R antibody will help to further understand GLP1R physiology, the new transgenic GIPR mouse model has contributed to the understanding of GIPR localisation, and cell based assays have identified functional implications of a polymorphism in the GLP2R associated with an increased risk of diabetes. It is hoped that further understanding of the physiology of these gut hormone receptors will be critical in the development of new therapeutics for diabetes and obesity.

Glucagon-like peptide-1 (GLP-1) synthetic analog therapies are prescribed for type 2 diabetes due to their effects on insulin and glucagon secretion, and glycemic control. Recent studies also suggest that they may have cardiovascular benefits; however, the mechanism responsible for this is unknown. To examine this question, we evaluated the effects of GLP-1 and the GLP-1 synthetic analog, liraglutide on cell signaling and function in human aortic endothelial cells (HAECs). The results indicate that both agents inhibit TNFα and LPS induced cellular adhesion molecule expression and monocyte adhesion. They also show that incubation with 30pM GLP-1 and 100nM liraglutide stimulates an immediate increase in intracellular calcium, which activates calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ). This in turn led to a 2.5 fold increase in the phosphorylation of both AMP-activated protein kinase (AMPK) and calcium/calmodulin-dependent protein kinase 1 (CaMK1) within 5 minutes. In addition both GLP-1 and liraglutide caused a 2-fold increase in the phosphorylation of the downstream AMPK/CaMK1 targets: endothelial nitric oxide synthase (eNOS) and cAMP response element-binding protein (CREB). Inhibition of CaMKKβ with STO-609 (0.5ug/mL) blocked the phosphorylation of both AMPK and CaMK1, confirming its pivotal role. Incubation of the HAECs for three hours with lipopolysaccharide (LPS, 2ug/mL) and TNFα (10ng/mL) increased the expression of vascular cell adhesion molecule-1 (VCAM-1) and E-selectin by 5 and 2 fold, respectively. Comparable increases in THP-1 monocyte adhesion to the HAECs, a putative initiating event in atherogenesis, also occurred. Pre-incubation for one hour with either GLP-1 or liraglutide inhibited these events. Likewise, pre-incubation with the CaMKK inhibitor STO-609, or use of lentivirus shRNA to knock down AMPK, blocked the inhibitory effects of both GLP-1 and liraglutide on monocyte adhesion. These results suggest that the recently observed cardiovascular benefits of GLP-1 and liraglutide could be mediated by their effects on CaMKKβ, AMPK and CaMK1 activation, which lead to decreased adhesion molecule expression and monocyte adhesion in endothelial cells. The finding that these effects occur at concentrations of GLP-1 (30pM) and liraglutide (100nM) observed in vivo also suggests they are physiologically relevant.

Mechanisms to augment the cellular function and mass of beta-cells may be effective means of treating type 2 diabetes. Important in the physiological control of beta-cell function and nutrient disposal are factors released from gut enteroendocrine cells during nutrient digestion. In enteroendocrine L-cells, post-translational processing of proglucagon gives rise to a number of proglucagon-derived peptides. One such peptide, glucagon-like peptide-1 (GLP-1), acts via its own receptor (GLP-1R) to stimulate beta-cell insulin secretion, proliferation and survival. Another, oxyntomodulin (OXM), weakly activates the GLP-1R and inhibits food intake in a GLP-1R-dependent manner in rodents, which led us to hypothesize that OXM modulates GLP-1R-dependent glucoregulation. While OXM did not mimic the inhibitory effect of GLP-1 on gastric emptying in mice, OXM stimulated insulin secretion, beta-cell survival and improved glucose tolerance in a GLP-1R-dependent manner. In a similar manner to GLP-1, glucose-dependent insulinotropic polypeptide (GIP), secreted from enteroendocrine K-cells, physiologically stimulates insulin secretion via a distinct GIP receptor (GIPR) in beta-cells. Beyond the beta-cell, GIP and GLP-1 appear to exert divergent actions for the control of glucose homeostasis. Moreover, I illustrate that physiological and pharmacological GLP-1R signalling may be comparatively more important for the preservation of beta-cell mass and glucose homeostasis in murine streptozotocin-induced diabetes. Lastly, studies in rodents and humans have showed that metformin increases circulating levels of GLP-1, leading us to hypothesize that GIP and GLP-1 may be involved in the glucoregulatory effects of metformin. Interestingly, transcripts for the Glp1r and Gipr were significantly increased within islets of metformin-treated mice, and metformin treatment enhanced the sensitivity of cultured beta-cells to GIP and GLP-1. In summary, these studies illustrate mechanisms by which enteroendocrine peptides compare and contrast with respect to beta-cell survival and function and the control of glucose homeostasis.

Cardiovascular disease is the most common cause of morbidity and mortality in type 2 diabetes. Short-term studies of glucagon-like peptide-1 (GLP-1)-targeted therapies suggest potential beneficial effects on cardiovascular outcomes. The mechanism behind this unexpectedly rapid effect is not known. In this study, full-length human GLP-1 receptor (GLP-1R) mRNA was cloned and sequenced from a human megakaryocyte cell line. Quantitative RT-PCR results showed that expression levels were comparable to other GLP-1R expressing tissues. Furthermore, incubation with GLP-1 and the GLP-1R agonist exenatide elicited a cAMP response in these cells. As megakaryocytes are the cellular precursors of platelets, the effect of GLP-1 and exenatide were studied in gel-filtered human platelet aggregation, where they were both shown to have an inhibitory effect on thrombin-stimulated platelet aggregation. Platelet inhibition by GLP-1 and GLP-1R agonists presents a potential mechanism for the reduced incidence of atherothrombotic events thought to be associated with GLP-1-targeted therapies.

Cardiovascular disease is the most common cause of morbidity and mortality in type 2 diabetes. Short-term studies of glucagon-like peptide-1 (GLP-1)-targeted therapies suggest potential beneficial effects on cardiovascular outcomes. The mechanism behind this unexpectedly rapid effect is not known. In this study, full-length human GLP-1 receptor (GLP-1R) mRNA was cloned and sequenced from a human megakaryocyte cell line. Quantitative RT-PCR results showed that expression levels were comparable to other GLP-1R expressing tissues. Furthermore, incubation with GLP-1 and the GLP-1R agonist exenatide elicited a cAMP response in these cells. As megakaryocytes are the cellular precursors of platelets, the effect of GLP-1 and exenatide were studied in gel-filtered human platelet aggregation, where they were both shown to have an inhibitory effect on thrombin-stimulated platelet aggregation. Platelet inhibition by GLP-1 and GLP-1R agonists presents a potential mechanism for the reduced incidence of atherothrombotic events thought to be associated with GLP-1-targeted therapies.

Mechanisms to augment the cellular function and mass of beta-cells may be effective means of treating type 2 diabetes. Important in the physiological control of beta-cell function and nutrient disposal are factors released from gut enteroendocrine cells during nutrient digestion. In enteroendocrine L-cells, post-translational processing of proglucagon gives rise to a number of proglucagon-derived peptides. One such peptide, glucagon-like peptide-1 (GLP-1), acts via its own receptor (GLP-1R) to stimulate beta-cell insulin secretion, proliferation and survival. Another, oxyntomodulin (OXM), weakly activates the GLP-1R and inhibits food intake in a GLP-1R-dependent manner in rodents, which led us to hypothesize that OXM modulates GLP-1R-dependent glucoregulation. While OXM did not mimic the inhibitory effect of GLP-1 on gastric emptying in mice, OXM stimulated insulin secretion, beta-cell survival and improved glucose tolerance in a GLP-1R-dependent manner. In a similar manner to GLP-1, glucose-dependent insulinotropic polypeptide (GIP), secreted from enteroendocrine K-cells, physiologically stimulates insulin secretion via a distinct GIP receptor (GIPR) in beta-cells. Beyond the beta-cell, GIP and GLP-1 appear to exert divergent actions for the control of glucose homeostasis. Moreover, I illustrate that physiological and pharmacological GLP-1R signalling may be comparatively more important for the preservation of beta-cell mass and glucose homeostasis in murine streptozotocin-induced diabetes. Lastly, studies in rodents and humans have showed that metformin increases circulating levels of GLP-1, leading us to hypothesize that GIP and GLP-1 may be involved in the glucoregulatory effects of metformin. Interestingly, transcripts for the Glp1r and Gipr were significantly increased within islets of metformin-treated mice, and metformin treatment enhanced the sensitivity of cultured beta-cells to GIP and GLP-1. In summary, these studies illustrate mechanisms by which enteroendocrine peptides compare and contrast with respect to beta-cell survival and function and the control of glucose homeostasis.

The incidence of obesity is on the rise globally and is associated with many comorbidities, especially type 2 diabetes mellitus (T2DM). Bariatric surgery is the most effective intervention for weight loss and reducing obesity-associated morbidity. The most common bariatric surgeries are roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). RYGB and SG are equally efficacious at long-term reduction of weight in obese individuals and amelioriation of T2DM. Interestingly, the improvement of glucose regulation is noted before weight loss is observed. The most likely mechanism underlying glucose homeostasis after bariatric surgery is hormonal changes in the intestine. Enteroendrocrine changes favorable of an anti-diabetic profile are noted after only a few days of receiving either RYGB or SG surgery. Most consistently, elevated postprandial GLP-1, a potent regulator of appetite and glucose control, is observed in post-bariatric surgery patients. However, data is limited regarding post-prandial GLP-1 levels beyond two years after surgery. This study will address the gap in literature by assessing postprandial elevations of GLP-1 following RYGB or SG for up to five years. We will recruit obese type-2 diabetics from an outpatient bariatric surgery clinic at Boston Medical Center scheduled to receive RYGB or SG and periodically assess postprandial GLP-1 levels to determine if they remain elevated after 5 years. Additionally, we will provide evidence if there is a correlation among changes in postprandial GLP-1, weight loss, and hemoglobin A1c at five years. Our proposed study will help direct researchers to develop safer and more efficacious interventions for obesity and T2DM.

Les cellules béta pancréatiques synthétisent et sécrètent l’insuline, unique hormone hypoglycémiante de l’organisme. Ces cellules jouent un rôle central dans l’apparition du diabète, préserver leurs masses fonctionnelles est donc essentiel. Le récepteur GLP-1, appartenant à la classe B de la super famille des récepteurs couplés aux protéines G (RCPGs), est considéré comme une cible thérapeutique majeure dans le traitement du diabète de type 2. Via son récepteur, le GLP-1 potentialise la sécrétion d’insuline en réponse au glucose et favorise la survie des cellules beta. Les glucocorticoïdes sont des hormones du stress impliquées dans la régulation énergétique, largement utilisés en thérapeutique pour leur propriétés anti-inflammatoire, immunosuppresseur et antiallergique. Néanmoins, les glucocorticoïdes administrés en chronique sont diabétogènes en exerçant notamment des effets délétères sur les cellules beta. Nous avons caractérisé l’impact d’une exposition prolongée des cellules beta à un glucocorticoïde de synthèse (la dexaméthasone) sur les actions biologiques du glucose et du GLP-1.Nous montrons qu’une exposition prolongée des cellules beta à la dexaméthasone exerce des effets délétères en inhibant la sécrétion d’insuline en réponse au glucose et l’activation des kinases de survie ERK1/2 (Extracellular Regulated Kinases 1/2). A l’inverse, nous démontrons que l’exposition prolongée des cellules bêta à la dexaméthasone favorise le maintien du récepteur GLP-1 à la membrane plasmique, augmente le couplage du récepteur à la protéine Galpha s, ce qui se traduit par une production de second messager (AMPc) intracellulaire doublée. Malgré une diminution des effets du glucose, la sécrétion d’insuline et l’activation des kinases ERK1/2 en réponse au GLP-1 ne sont pas affectées. Cette étude révèle qu’une exposition chronique des cellules beta aux glucocorticoïdes 1) régule le trafficking du récepteur GLP-1 et favorise son maintien à la surface cellulaire, 2) hypersensibilise la signalisation du récepteur GLP-1 dépendante de la protéine Gαs , et 3) pourrait impacter les effets thérapeutiques des molécules ciblant l’activation du récepteur GLP-1. / Pancreatic beta cells synthesize and secrete insulin, the only hypoglycemic hormone in the body. These cells play a central role in the onset of diabetes. To protect the functional beta-cell mass is essential. The GLP-1 receptor, which belongs to the class B of the G protein-coupled receptor (GPCR) family, is a major therapeutic target in type 2 diabetes. Through its receptor, GLP-1 potentiates glucose-induced insulin secretion and improves the survival of pancreatic beta cells. Glucocorticoids are stress hormones implied in energetic metabolism and are widely used in therapeutics for their anti-inflammatory, immunosupressive and anti-allergic properties. Neverless, on chronic administration, glucocorticoids can induce metabolic syndrome especially due beta cell functional mass impairement. Here, we characterized the impact of a prolonged exposure of pancreatic beta cells to a synthetic glucocorticoid (dexamethasone) on biological actions of glucose and GLP-1.We show that a chronic exposure of beta cells to dexamethasone exerted deleterious effects on glucose-induced insulin secretion and ERK1/2 (Extracelllular Regulated Kinases 1/2) activation. In contrast, we observed that the glucocorticoid treatment increased GLP-1 receptor expression at the plasma membrane and improved the Galpha s protein coupling leading to an enhancement of cAMP production (2 fold increase). Despite the negative impact on glucose effects, glucocorticoids did not impair neither GLP-1-induced insulin secretion nor ERK1/2 activation. This study reveals that a glucocorticoid chronic exposure 1) regulates GLP-1 receptor trafficking and increases its expression to the plasma membrane, 2) causes supersensitization of Gαs-associated signaling, and 3) could impact on therapeutic effects of GLP-1 receptor-based drugs.