Type 2 diabetes (T2D) is one of the fasting growing chronic diseases, caused by insulin resistance and pancreatic β-cell dysfunction. While over thirty medications were approved to treat T2D in the United States, less than one in four patients treated with anti-diabetic drugs achieved the glycemic target. Thus, identifying more effective anti-diabetic drugs is still needed for improving glycemic control in T2D patients. Incretins are gut hormones that possess potent insulinotropic action, which have drawn considerable attention in research and developing treatment strategy for T2D. Specifically, glucagon like peptide 1 (GLP-1), the most important incretin that is secreted from enteroendocrine L-cells in response to food ingestion, plays a vital role in maintaining glycemic homeostasis via potentiating glucose stimulated insulin secretion (GSIS) and promoting pancreatic β-cell proliferation and survival. Therefore, targeting L-cells to induce GLP-1 secretion would be an alternative strategy for treating T2D. The goal of this research was to identify low-cost and safe naturally occurring agents as a primary or adjuvant treatment for T2D. Here, I found that a small molecule, elenolic acid (EA), which was generated in our lab but is also present in mature olive and extra virgin olive oil, dose-dependently stimulated GLP-1 secretion in mouse clonal L-cells and isolated mouse ileum crypts. EA induced a rapid increase in intracellular [Ca2+]i and the production of inositol trisphosphate in L-cells, indicating that EA activates phospholipase C (PLC)-mediated signaling. Consistently, inhibition of (PLC) ablated EA-stimulated increase of [Ca2+]i and GLP-1 secretion in L-cells. In addition, EA-triggered GLP-1 secretion from L-cells was blocked by YM-254890, a Gαq inhibitor. Consistent with our in vitro study, a single dose of EA acutely stimulated GLP-1 secretion in mice, accompanied with an improved oral glucose tolerance. Chronic administration of EA restored the impaired glucose and lipid homeostasis in DIO mice, which may be partially due to promoting GLP-1 secretion and reduced hepatic gluconeogenesis. In addition, EA suppressed appetite, reduced food intake and gastric emptying rate, as well as promoted weight loss in obese mice, demonstrating that it is also an anti-obesity agent. Further, EA treatment reduced lipid absorption, and promoted hepatic fatty acid oxidation, and reversed abnormal plasma lipid profiles in DIO mice. Consistently, EA exerted potent anti-diabetic action in db/db mice, and its blood glucose-lowering effect is comparable with that of liraglutide in blood glycemic control but is better than that of metformin in this overt diabetic model. Collectively, I have identified for the first time, as to the best of our knowledge, that EA could be a dual-action compound that exerts anti-diabetic effects via activation of the GLP-1 mediated metabolic pathway and suppression of hepatic gluconeogenesis, leading to effective control on food intake, body weight gain, and glycemia in T2D mice. / Doctor of Philosophy / Type 2 diabetes (T2D) is one of the fasting growing chronic diseases, which results from insulin resistance and pancreatic β-cell dysfunction. Even though there have been over thirty drugs approved to treat T2D in the United States, less than 25% of patients treated with anti-diabetic drugs achieved the glycemic target. Thus, more effective anti-diabetic drugs are still needed for improving glycemic control in patients with T2D. Incretins are a group of gut hormones and responsible for over 50% postprandial insulin secretion in humans, which have drawn considerable attention in research and developing a treatment strategy for T2D. Specifically, glucagon-like peptide 1 (GLP-1), the most important incretin that is secreted from enteroendocrine L-cells in response to food ingestion, plays a vital role in controlling blood glucose via potentiating glucose-stimulated insulin secretion (GSIS) and promoting pancreatic β-cell proliferation and survival. Therefore, targeting L-cells to induce GLP-1 secretion would be an alternative strategy for treating T2D. The goal of this research was to identify low-cost and safe naturally occurring agents as a primary or adjuvant treatment for T2D. Here, I found that a small molecule, elenolic acid (EA), which was synthesized in our lab but is also present in mature olive and extra virgin olive oil, dose-dependently stimulated GLP-1 secretion in mouse clonal L-cells and isolated mouse ileum crypts (containing L-cells). Further experiments showed that EA induced a rapid increase in intracellular [Ca2+]i and the production of inositol trisphosphate (IP3) in L-cells, indicating that EA activates phospholipase C (PLC)-mediated signaling, as IP3 is a direct product of PLC. Consistently, inhibition of PLC ablated EA-stimulated increase of [Ca2+]i and GLP-1 secretion in L-cells. In addition, EA-triggered GLP-1 secretion from L-cells was blocked by YM-254890, a Gαq inhibitor. In line with the in vitro study, a single dose of EA acutely elevated plasma GLP-1 concentration in mice, accompanied by improved oral glucose tolerance. Chronic administration of EA restored the impaired glucose and lipid homeostasis in diet-induced obese (DIO) mice, which may be partially due to promoting GLP-1 secretion and reduced hepatic gluconeogenesis. In addition, EA suppressed appetite, reduced food intake, and gastric emptying rate, as well as promoted weight loss in the DIO mice, demonstrating that it is also an anti-obesity agent. Further, EA treatment reduced lipid absorption and promoted hepatic fatty acid oxidation, as well as reversed abnormal plasma lipid profiles in the DIO mice. Consistently, EA exerted potent anti-diabetic action in predisposed diabetic mice (db/db), and its blood glucose-lowering effect is comparable with that of liraglutide, a commercial GLP-1 receptor agonist, in blood glycemic control but is better than that of metformin, a widely used first-line anti-diabetic drug, in this overt diabetic model. Collectively, I have identified for the first time, as to the best of our knowledge, that EA could be a dual-action compound that exerts anti-diabetic effects via activation of the GLP-1 mediated metabolic pathway and suppression of hepatic gluconeogenesis, leading to effective control on food intake, body weight gain, and glycemia in T2D mice.

Submitted by Eunice Novais (enovais@uepg.br) on 2018-06-05T17:25:05Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Daiane Didek.pdf: 2147992 bytes, checksum: fb8c4ca29516a68c37c8dc766dc39e8f (MD5) / Made available in DSpace on 2018-06-05T17:25:05Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Daiane Didek.pdf: 2147992 bytes, checksum: fb8c4ca29516a68c37c8dc766dc39e8f (MD5) Previous issue date: 2018-03-23 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / A liraglutida é um análogo do peptídeo semelhante ao glucagon-1 (GLP-1), já utilizada comercialmente para o tratamento da Diabetes mellitus tipo 2, que também mostra resultados na redução da ingestão alimentar e consequente redução do peso corporal. A associação do exercício físico com a liraglutida pode ser um importante meio de controle do metabolismo lipídico e ocasionalmente tratamento de alterações metabólicas como a obesidade. O objetivo do nosso trabalho foi avaliar o efeito da liraglutida, análogo do GLP-1 associado ao exercício físico nos parâmetros metabólicos, bioquímicos e antropométricos de ratos normais e obesos, induzidos por dieta de cafeteria. O experimento iniciou-se aos 21 dias de vida dos animais, estes foram divididos em oito grupos: Quatro controles (CON) recebendo ração padrão e agua ad libitum; quatro obesos (OBESO) recebendo a dieta de cafeteria ad libitum, adicionada a dieta padrão; subdivididos em (CON LIRA e OBESO LIRA) recebendo injeções subcutâneas de liraglutida dos 80 aos 90 dias de vida; (CON EXE LIRA e OBESO EXE LIRA) com intervenção da liraglutida e submetidos a natação por 15 minutos, três dias por semana e (CON EXE e OBESO EXE) somente com intervenção do exercício físico. Os resultados dos animais obesos demonstraram que a liraglutida reduziu, somente o consumo alimentar no final do experimento. O exercício físico mostrou melhores resultados na redução da gordura mesentérica, epididimal, retroperitoneal, níveis circulantes de glicose, índice de Lee, ganho de peso dos 80-90 dias de vida e aumentou o peso da glândula adrenal nos animais obesos, nos animais controle reduziu o peso do pâncreas, índice de Lee e colesterol total. A associação do exercício físico com a liraglutida apresentou melhores resultados na redução do peso corporal no final do experimento, redução do consumo dos 80-90 dias de vida, peso do fígado, níveis circulantes de triglicerídeos e insulina, índice HOMA-IR, nos animais obesos, porém aumentou o TNF-α nos animais obesos e controles. Concluímos que a intervenção com o exercício físico foi eficaz na redução de alguns parâmetros relacionados ao desenvolvimento da obesidade, porém a sua associação com a liraglutida por 10 dias mostra melhores resultados na redução do peso corporal, consumo alimentar e parâmetros bioquímicos, em animais obesos obtidos por dieta de cafeteria. / Liraglutide is an analog of the Glucagon-like peptide-1 (GLP-1), already commercially used for the treatment of Type 2 Diabetes Mellitus, which also shows results in the reduction of food intake and consequent reduction of body weight. The association of physical exercise with liraglutide may be an important means of controlling lipid metabolism and, occasionally, the treatment of metabolic disorders such as obesity. The objective of our study was to evaluate the effect of liraglutide, GLP-1 analog associated with physical exercise on metabolic, biochemical and anthropometric parameters of normal and obese rats, induced by the cafeteria diet. The experiment started at the 21 days of life of the animals, which these divided into eight groups: Four controls (CON) receiving standard chow and water ad libitum; four obese (OBESO) receiving the cafeteria diet ad libitum, added to the standard diet. The animals were further subdivided into (CON LIRA and OBESO LIRA) receiving subcutaneous injections of liraglutide from 80 to 90 days of life; (CON EXE LIRA and OBESO EXE LIRA) with intervention of liraglutide and submitted to swimming for 15 minutes, three days a week and (CON EXE and OBESO EXE) only with physical exercise intervention. The results of obese animals show that liraglutide reduced only food intake at the end of experiment. The physical exercise show better results in the reduction of the mesenteric, epididymal, retroperitoneal fat pad, circulating levels of glucose, Lee index, weight gain from 80-90 days of life and increased adrenal gland weight in obese animals, in control animals reduced the weight of the pancreas, Lee index and total cholesterol. The association of exercise with liraglutide show better results in reducing body weight at the end of the experiment, food intake of the 80-90 days of life, liver weight, circulating levels of triglycerides and insulin, HOMA-IR index, in obese animals, but increased the TNF-α in obese and control animals. We conclude that the intervention with physical exercise was effective in reducing some parameters related to the development of obesity, but its association with liraglutide for 10 days show that better results in reducing body weight, food intake and biochemical parameters in obese animals obtained by cafeteria diet.

Chez les eucaryotes, l’expression des gènes dépend en partie du degré de compaction de la chromatine. La structure chromatinienne est régulée par des marques dites épigénétiques,telles que les modifications post-traductionnelles des protéines structurelles de la chromatine, les histones. Ainsi, la méthylation de la lysine 9 de l’histone H3 (H3K9) sur le promoteur des gènes est essentiellement associée à la répression de la transcription. H3K9 est méthylée par différentes enzymes appelées lysine méthyltransférases (KMTs). L’objectif principal de mon projet de thèse a été de mieux comprendre le rôle de principales KMTs de H3K9, que sontG9a, GLP, Suv39h1 et SETDB1, dans la régulation de l’équilibre entre prolifération et différenciation terminale. Pour cela, j’ai utilisé le modèle de différenciation terminale de cellules du muscle squelettique. En effet, durant la différenciation terminale, les myoblastes arrêtent de proliférer et fusionnent entre eux pour former de longues cellules multi nucléées que sont les myotubes. Ce processus implique, d’une part, l’expression des gènes de différenciation musculaire et, d’autre part, la répression irréversible des gènes associés à la prolifération cellulaire. L’introduction bibliographique de ce travail de thèse est séparée en trois chapitres. Le premier chapitre porte sur la chromatine et ses modifications post-traductionnelles. Le second s’attache à décrire les rôles de la méthylation de H3K9 et, en particulier, des quatre KMTs sur lesquelles j’ai travaillé durant ma thèse : G9a, GLP, SETDB1 et Suv39h1. Dans le troisième chapitre, je présente le modèle de la différenciation terminale du muscle squelettique. Dans la partie "Résultats", je décris deux des principales études que j’ai menées durant ma thèse. La première porte sur les rôles antagonistes de G9a et GLP. La seconde porte sur le rôle de SETDB1 durant la différenciation musculaire. Les résultats que j’ai obtenus sont discutés dans cette partie. Je conclus ce manuscrit en discutant mes résultats de manière plus générale et en proposant des perspectives à long terme. Enfin, une annexe présentera les autres articles de recherche auxquels j’ai participé pendant ma thèse. / In eukaryotes, gene expression partly relies on chromatin compaction degree. Chromatin status is controlled by epigenetic marks, such as histones (chromatin structural proteins) posttranslational modifications. As an example, histone H3 lysine 9 (H3K9) methylation on gene promoters is mainly associated with transcriptional repression. H3K9 is methylated by several enzymes called lysine methyltransferases (KMTs). The aim of my thesis project was to understand the role of the H3K9 KMTs, G9a, GLP, Suv39h1 and SETDB1 in regulating the balance between proliferation and terminal differentiation. For this purpose, I used skeletal muscle terminal differentiation as model. Upon muscle terminal differentiation, myoblasts exit, in an irreversible way, from the cell cycle and under go differentiation where cells fusion and form myotubes. During this process, cell cycle genes are permanently silenced and muscle specific genes are activated. Thesis introduction is divided into three chapters. The first chapter focuses on chromatin and post-translational modifications. The second chapter describes H3K9 methylation characteristics and the role of the four KMTs that I studied during my thesis project: G9a,GLP, Suv39h1 and SETDB1. In the third chapter, the skeletal muscle terminal differentiation model is described in details. Results section reports my two major studies outcomes and their discussion. The first concerns the antagonistic roles of G9a and GLP regarding the muscle terminal differentiation and the second focuses on the role of SETDB1 during muscle differentiation. Finally, I conclude this manuscript by a plainer discussion followed by long term perspectives and an appendix presents other research articles, in which I collaborated during my PhD.

G-protein coupled receptors (GPCRs) have been shown to act as part of GPCR associated protein complexes (GAPCs) which are required to appropriately transduce downstream signaling pathways leading to specific cellular actions. I hypothesize that there are distinct molecular effectors that couple to the glucagon superfamily of B-class GPCRs (glucagon, GLP-1, GLP-2, GIP receptors) to effect the myriad of reported actions in numerous target cells including regulation of insulin secretion, intestinal growth and appetite suppression. GLP-1R, GIPR, GLP-2R and GCGR were screened using a newly developed membrane-based split-ubiquitin yeast two-hybrid (MYTH) system to reveal 181 novel candidate protein interactors associated with signal transduction, transport, metabolism and cell survival. Each candidate was validated using yeast two-hybrid prey retransformation tests and by co-purification to confirm coupling to each receptors. The present work is the first demonstration of a split-ubiquitin interaction screen using in situ membrane expressed GPCRs of the secretin-like B class.

G-protein coupled receptors (GPCRs) have been shown to act as part of GPCR associated protein complexes (GAPCs) which are required to appropriately transduce downstream signaling pathways leading to specific cellular actions. I hypothesize that there are distinct molecular effectors that couple to the glucagon superfamily of B-class GPCRs (glucagon, GLP-1, GLP-2, GIP receptors) to effect the myriad of reported actions in numerous target cells including regulation of insulin secretion, intestinal growth and appetite suppression. GLP-1R, GIPR, GLP-2R and GCGR were screened using a newly developed membrane-based split-ubiquitin yeast two-hybrid (MYTH) system to reveal 181 novel candidate protein interactors associated with signal transduction, transport, metabolism and cell survival. Each candidate was validated using yeast two-hybrid prey retransformation tests and by co-purification to confirm coupling to each receptors. The present work is the first demonstration of a split-ubiquitin interaction screen using in situ membrane expressed GPCRs of the secretin-like B class.

Selon l'organisation mondiale de la santé, le diabète de type II (DT2), caractérisé par un défaut de contrôle de la glycémie, est une des causes principales de décès dans le monde. Le GLP-1, sécrété par l'intestin après un repas, contribue au contrôle de la glycémie en stimulant la sécrétion d'insuline par le pancréas et en inhibant la vidange gastrique et la prise alimentaire. Ces actions sont principalement médiées par le nerf vague selon un axe intestin-cerveau-organes périphériques, bien que l'hormone puisse aussi agir de manière endocrine directement sur ses organes cibles via son récepteur (GLP-1r). Des stratégies thérapeutiques basées sur le GLP-1 sont donc utilisées pour traiter les patients diabétiques, mais les réponses sont hétérogènes voire inefficaces pour le contrôle glycémique. Les mécanismes moléculaires responsables sont inconnus mais pourraient être en lien avec la modification du microbiote intestinal, élément déterminant dans le développement des maladies métaboliques. Nous avons d'abord montré que des souris rendues diabétiques (régimes riches en graisse) perdent leur sensibilité aux actions hypoglycémiantes du GLP-1 et présentent une neuropathie entérique, une baisse de l'expression du GLP-1r intestinal et vagal et une altération de l'axe intestin-cerveau. De plus, dans les neurones entériques en culture primaire issus de ces souris diabétiques, la production de NO induite par le GLP-1, est diminuée. Tous ces effets sont retrouvés chez des souris axéniques ou traitées aux antibiotiques sous régime normal démontrant l'implication du microbiote. À l'inverse, des souris sous régime gras traitées aux antibiotiques ont une amélioration de l'action du GLP-1. Cette action hormonale intestinale pourrait aussi dépendre du cycle nycthéméral pour lequel nous avons observé une oscillation de la sécrétion d'insuline, de l'expression du GLP-1r et des bactéries intestinales. De plus, les souris contrôles répondent moins bien à l'hormone au cours du jour que de la nuit et les souris diabétiques, axéniques et antibiotiques - modèles résistants au GLP-1 - ont des variations très marquées et communes de l'expression des "clock genes". L'ensemble de ces résultats montre qu'au cours diabète, l'action du GLP-1 est diminuée. Cette diminution peut s'expliquer par une baisse de l'expression neuronale du GLP-1r et une diminution de la voie de signalisation dépendant du NO capable de réguler la sécrétion d'insuline induite par le GLP-1. Le microbiote et/ou la régulation circadienne semblent déterminants dans la sensibilité au GLP-1. / According to the World Health Organisation, Type II Diabetes, characterized by an alteration of glycemic control, causes numerous death around the world. After a meal, gut secretes Glucagon-Like Peptide one (GLP-1) which regulates glycemia by stimulation of insulin secretion and inhibition of gastric emptying and food intake. Although GLP-1 acts as an endocrine hormone on its target organs through the GLP1 receptor, its action is mainly mediated by nervous pathway involving vagus nerve and gut-brain-periphery axis. Thus, GLP-1 based therapies are used to control glycaemia in type 2 diabetic patients, but, efficiency of the treatment is heterogeneous defining a state of GLP-1 unresponsiveness. Molecular mechanisms involved in this unresponsiveness are not known but could be linked to the changes in gut microbiota (dysbiosis), key element in the development of metabolic diseases. We first found that diabetic mice (high fat diet) are unresponsive to hypoglycemic action of GLP-1 and present enteric neuropathy, impaired gut-brain axis and reduction of GLP-1r and neuronal NO synthase expression in the ileum. In addition, GLP-1-induced nitric oxide production in primary neuron culture is decreased. These effects were also found in germ-free or antibiotic-treated mice under normal chow diet, indicating the involvement of gut microbiota. By contrast, high fat diet mice treated with antibiotics show an improvement of GLP-1 action. This gut incretin action could also depend on the circadian cycle for which we observed a wavering of insulin secretion, GLP-1r expression and gut microbiota. Moreover, the GLP-1 response of control mice is better in the day than in the night and the different mice model resistant to GLP-1 (HFD, axenic or antibiotics) present the same marked variations in the expression of major clock genes. Overall our results show that in type 2 diabetes GLP-1 action is lowered and can be explained by decreased neuronal expression of GLP-1r as well as the NO-dependent signaling pathway regulating insulin secretion induced by GLP-1. Microbiota or the circadian clock seems essential in this GLP-1 sensitivity.

Certains mammifères, dont l’Homme, ont une forte attraction pour les lipides alimentaires. Pendant longtemps, il était admis que ces nutriments étaient détectés uniquement via leurs propriétés olfactives, texturales et post-ingestives. Cependant, l’existence d’une dimension gustative a été suggérée depuis. Dans ce contexte, notre Laboratoire a démontré que la glycoprotéine CD36 exerçait une fonction de lipido-récepteur gustatif impliquée à la fois dans la préférence spontanée pour les lipides alimentaires et la phase céphalique de la digestion induite par la présence de lipides au niveau oral chez la souris. Une autre protéine, GPR120, semble également jouer un rôle dans la détection gustative des lipides alimentaires. Ces travaux de thèse avaient donc pour objectif de comprendre les rôles respectifs de ces deux protéines au sein des bourgeons du goût chez la souris. En utilisant une combinaison d'approches biochimiques, physiologiques et comportementales, nous avons pu montrer que le CD36 lingual était régulé négativement par les lipides alimentaires lors d'une exposition court terme, contrairement au GPR120. Cette régulation pourrait se traduire par une désensibilisation au cours du repas du système de lipido-réception gustatif et donc jouer un rôle dans le rassasiement sensoriel spécifique. Nos résultats suggèrent également que l'activation de GPR120 par les acides gras à longues chaînes peut jouer un rôle dans la modulation de la sensibilité gustative aux saveurs sucrées, voire aux lipides eux-mêmes. Ce phénomène est dépendant de la sécrétion de l'hormone glucagon-like peptide-1 par la papille caliciforme, indépendamment du CD36 lingual. Nous avons également mis en évidence que l'exposition des souris à un régime obésogène chronique perturbe la détection oro-sensorielle des lipides, suggérant une hyposensibilité chez la souris obèse. On peut donc penser qu'une perturbation du système de perception gustative des graisses alimentaires pourrait induire des changements de préférence alimentaire, propice à l’installation d'une obésité. De plus amples investigations sont requises pour explorer le rôle du CD36 et/ou du GPR120 dans ce phénomène. L'aboutissement de telles recherches serait l'émergence de nouvelles voies de traitement de l’obésité et des maladies associées, par des approches pharmacologiques et/ou nutritionnelles ciblées. / Some mammals including humans display a spontaneous attraction for dietary fat. For a long time, it was thought that these nutrients were detected only by olfactory, textural and post-oral cues. However, recent data have indicated that the sense of taste could also contribute to this perception in laboratory rodents. In this context, it was demonstrated by our Laboratory that the glycoprotein CD36 is likely a lingual lipid sensor, involved both in preference for long-chain fatty acids and cephalic phase of digestion secondary to an oral lipid stimulation in mice. Another protein, GPR120, seems also to play a role in the gustatory detection of lipids. The aim of this Thesis was to understand the respective roles of these putative gustatory lipid sensors in mice. Using a combination of biochemical, physiological and behavioral approaches, we showed that the lingual CD36 is negatively regulated by dietary fat during a short term exposure (i.e. during a meal), in contrast to GPR120. This regulation is reminiscent of the receptor desensitization and might play a role in the sensory-specific satiety phenomenon. Our data also suggest that GPR120 activation by long-chain fatty acids plays a role in the modulation of sweet taste sensitivity, and likely of fat taste itself. This phenomenon is dependent from the secretion of the glucagon-like peptide-1 hormone by the circumvallate papillae, independently of lingual CD36. Finally, we showed that chronic exposure of mice to an obesogenic diet disturbs the oro-sensory perception of dietary lipids, suggesting that obese mice become hyposensitive to lipids. This alteration might induce changes in feeding preferences which could lead to obesity. More investigations are required to better understand the role of CD36 and/or GPR120 in this phenomenon. This new field of research might lead to new ways of investigations for the treatment of obesity and related diseases, by using novel pharmacological and/or nutritional approaches.

No description available.

Les cellules β pancréatiques synthétisent et sécrètent l'insuline, seule hormone hypoglycémiante de l'organisme. Dans le cas du diabète de type 2, du diabète de type 1 et suite à une greffe d'îlots de Langherans, on observe une diminution drastique de cette masse fonctionnelle β. L'hyperglycémie chronique et la libération de cytokines proinflammatoires jouent un rôle cytotoxique prépondérant dans ces phénomènes. Dans le but de préserver ou de restaurer cette masse fonctionnelle β chez les patients diabétiques, notre objectif était d'identifier des outils permettant de protéger des effets délétères de l'hyperglycémie chronique et des cytokines proinflammatoires, en s'intéressant à 3 cibles potentielles. Nous montrons tout d'abord que les activités du système ubiquitine protéasome (UPS), impliqué dans la dégradation de protéines, sont altérées en condition d'hyperglycémie chronique. Ces altérations sont corrélées à l'émergence d'un programme apoptotique au sein des cellules β. L'activation du récepteur du GLP-1 (Glucagon-Like Peptide-1), stratégie thérapeutique majeure dans le diabète de type 2, protège l'UPS des effets délétères de l'hyperglycémie chronique. Le facteur de transcription CREB (cAMP Response Element Binding Protein), essentiel pour la survie et la fonction des cellules β, est dégradé par l'hyperglycémie chronique et l'inflammation. Nous montrons que la prévention de sa dégradation prévient les effets de l'hyperglycémie chronique, mais pas de l'inflammation. Ces observations nous ont amenés à étudier la MAP3 kinase Tpl2 (Tumor progression locus 2), impliquée, notamment via l'activation de ERK1/2 (Extra-cellular Regulated Kinases 1/2), dans les processus inflammatoires d'autres types cellulaires. Nous montrons que Tpl2 est exprimé dans la lignée cellulaire β INS-1E, et dans les îlots murins et humains, et qu'elle gouverne spécifiquement l'activation des kinases ERK1/2 induite par les cytokines proinflammatoires IL-1β, TNFα et IFNγ. Cette protéine est surexprimée dans des conditions d'inflammation (in vitro et modèle de diabète murin). L'inhibition de Tpl2 protège contre l'apoptose induite par les cytokines, dans les INS-1E et les îlots de souris et restaure la capacité sécrétrice d'insuline des ilots de souris altérée suite à une exposition aux cytokines. En combinaison avec un analogue du GLP-1, l'inhibition pharmacologique de cette kinase protège totalement contre les effets délétères des cytokines sur la fonction et la survie des îlots humains. Ces données suggèrent que l'inhibition pharmacologique de la kinase Tpl2, seule ou en combinaison avec un analogue du GLP-1, pourrait constituer de nouvelles stratégies thérapeutiques pour protéger contre l'altération de la masse fonctionnelle β pouvant survenir chez des patients diabétiques de type 2 ou après la transplantation d'îlots. / Pancreatic β cells synthesize and secrete insulin, the sole hormone of the organism able to reduce glycemia. In the course of type 2 and type 1 diabetes, and after islet transplantation, there is a drastic loss of function and mass of these cells. Among the common origins of this decrease, chronic hyperglycemia and the release of proinflammatory cytokines play major roles. With the aim to preserve or to restore this functional β cell mass in diabetic patients, our objective was to identify tools able to protect against deleterious effects of these two phenomenons, interesting in three potential targets. We first demonstrated that the ubiquitin-proteasome system (UPS) activities, that degrade proteins, are altered in β cells exposed to chronic hyperglycemia, and correlated with apoptosis. Activation of the GLP-1 (Glucagon-Like Peptide-1) receptor, a key therapeutic strategy in type 2 diabetes, protects UPS from deleterious effects of chronic hyperglycemia. The transcription factor CREB (cAMP Response Element Binding Protein), crucial for β cell survival and function, is involved in deleterious effects of chronic hyperglycemia and inflammation. We demonstrated that prevention of CREB degradation protects β cells from chronic hyperglycemia, but not from the deleterious effects of the proinflammatory cytokines. These observations prompted us to study the MAP3 kinase Tpl2 (Tumor progression locus 2), known to be implicated in inflammatory process in other cell types, through the activation of the kinases ERK1/2 (Extra-cellular Regulated Kinases 1/2). We showed that Tpl2 is expressed in INS-1E clonal β cells and in mouse and human islets, and that it governs specifically the activation of ERK1/2 in response to proinflammatory cytokines IL-1β, TNFα and IFNγ. This protein is overexpressed by inflammatory conditions and in a rat type 2 diabetes model. Inhibition of Tpl2 protects against cytokine-induced apoptosis in INS-1E and in mouse islets. Furthermore, the capacity of mouse islets to secrete insulin in response to glucose, that is altered by a chronic exposure to cytokines, is restored by Tpl2 inhibitor. Finally, we showed that in combination with GLP-1 analog (Exendin-4), Tpl2 inhibitor can entirely restore the survival and function in human islets cultured in pro-inflammatory conditions. These results suggest that pharmacological inhibition of Tpl2, alone or in combination with Exendin-4, may be novel therapeutic strategies to alleviate β-cell failure observed in Type 2 diabetes and islets transplantation.

Made available in DSpace on 2017-07-21T19:59:56Z (GMT). No. of bitstreams: 1 Priscila Costa Estabile.pdf: 1735178 bytes, checksum: b258b31793d5d5954531a50cbe4206cc (MD5) Previous issue date: 2012-02-13 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / The Type 2 Diabetes Mellitus, as well as the metabolic syndrome (MS), is a multifactorial and metabolic disorder that now presents itself as a worldwide pandemic with effects on morbidity and mortality, possibly as a result of the mismatch between biological and cultural evolution of man. Was the object of research of this study to analyze the tissue expression of incretin hormones glucagon Pepitide Like-1 (GLP1) and Pepitide YY (PYY3-36), to identify and quantify L cells along the gastrointestinal tract in patients with DM2 subjected to adaptative gastroenteromentectomia with intestinal bipartition (Partial Duodenal Switch - DSP). The study was approved by the Ethics Committee of UEPG and patients informed and educated about the research objectives. The volunteer group consisted of 7 patients aged between 35 and 65 years, body mass index> 25 kg/m2 with T2DM on dietary treatment and medication for a minimum of 2 years and with difficulty on glycemic control and hypertriglyceridemia associated. Samples were obtained from the intestinal mucosa (jejunum and ileum) of DSP in patients undergoing preoperative and postoperative condition of fasting for 12 hours (three and twelve months respectively), through incisional biopsy. These biopsies were designed to test immunohistochemistry, qRT-PCR (Quantitative Real Time PCR) and Western Blott. The results were consistent and indicate a very significant differential expression between the state of pre-and postoperative tests for qRT-PCR (p = 0.1669) and Western Blot (p = 0.1569). Immunohistochemistry also showed low significance (p = 0.0043) of immune marked L cells for the same patients under the same conditions. These data can be interpreted in light of the fast imposed on patients. In addition the results are unprecedented for the immunostaining of L-cells of the human gastrointestinal tract, the data indicate that these cells have basal secretion for GLP-1, even after 12 hours without feed stimulation. In addition, the patients showed normalization of blood glucose levels in the post-surgery, suggesting metabolic improvement. It was also found that the number of L cells marked increases in density along the gastrointestinal tract toward the distal portion of the ileum (p = 0.0409). With these results it was possible to identify, locate and investigate different levels of expression and secretion from intestinal L cells in patients with DM2 and subjected to surgical control. / Diabetes mellitus do tipo 2 (DM2), assim como a Síndrome Metabólica (SM), é uma desordem metabólica e multifatorial que atualmente se apresenta como pandemia mundial com reflexos na morbimortalidade, possivelmente em decorrência do descompasso entre a evolução biológica e cultural do homem. Foi objeto de investigação do presente estudo analisar a expressão tecidual dos hormônios incretínicos Glucagon Like Pepitide-1 (GLP1) e Pepitide YY (PYY3-36), visando identificar e quantificar células L ao longo do trato gastrointestinal, de pacientes portadores de DM2 submetidos a gastroenteromentectomia adaptativa com bipartição intestinal (Duodenal Switch Parcial - DSP). O trabalho foi aprovado pelo Comitê de Ética da UEPG e os pacientes informados e esclarecidos sobre os objetivos da pesquisa. O grupo de voluntários foi composto de 7 pacientes com idade entre 35 e 65 anos, Índice de Massa Corporal > 25 Kg/m2, com DM2 em tratamento dietético e medicamentoso por um período mínimo de 2 anos e com dificuldade de controle glicêmico e hipertrigliceridemia associada. Foram obtidas amostras da mucosa intestinal (jejuno e íleo) dos pacientes submetidos à DSP no pré-operatório e no pós-operatório em condição de jejum de 12 horas (três e doze meses, respectivamente), através de biópsia incisional. Estas biópsias foram destinadas aos ensaios de Imunohistoquímica, qRT-PCR (Quantitative Real Time PCR) e Western Blott. Os resultados obtidos foram congruentes e apontam uma expressão diferencial pouco significativa entre o estado de pré- e pós-operatório para os ensaios de qRT-PCR (p=0,1669) e Western Blott (p=0,1569). A imunohistoquímica mostrou também baixa significância (p=0,0043) de células L imuno marcadas para os mesmos pacientes, nas mesmas condições. Estes dados podem ser interpretados a luz do jejum imposto aos pacientes. Além dos resultados serem inéditos para a imunomarcação de células L do trato gastrointestinal humano, os dados obtidos indicam que estas células apresentam secreção basal para GLP-1, mesmo após 12 horas sem estímulo alimentar. Em adição, os pacientes apresentaram normalização dos níveis de glicemia no estado pós-operado, sugerindo melhora metabólica. Foi ainda constatado que o número de células L marcadas aumenta em densidade ao longo do trato gastrointestinal em direção à porção mais distal do íleo (p=0,0409). Com estes resultados foi possível identificar, localizar e investigar diferentes níveis de expressão e secreção das células L intestinais em pacientes portadores de DM2 e submetidos a controle cirúrgico.