No description available.

<p>The endoplasmic reticulum (ER) is a specialized organelle that facilitates correct protein folding and maturation. Disruptions in ER homeostasis lead to ER stress and activation of a series of signal transduction cascades known as the unfolded protein response (UPR), which acts to restore ER homeostasis. In recent years, ER stress and UPR dysfunction have been linked to obesity, fatty liver and insulin resistance. Lipid-laden adipocytes, the main cellular component of white adipose tissue (WAT), play a critical role in whole body energy homeostasis as well as lipid and carbohydrate metabolism. Mature adipocytes, which are metabolically active endocrine cells, differentiate from precursor fibroblast-like preadipocytes, through a process called adipogenesis, leading to formation of cells capable of secreting numerous proteins, cytokines and hormones. ER homeostasis and UPR activation are essential to the function/differentiation of highly secretory cells, however, the role of ER stress/UPR activation in adipogenesis had previously not been examined. We hypothesized that<em> adipogenesis may rely on physiological UPR activation to accommodate the demand on the ER for increased folding and secretion of proteins.</em></p> <p>Initial experiments examining UPR activation during 3T3-L1 adipogenesis identified that expression of ER stress/UPR markers was modulated during adipocyte differentiation. Furthermore, inhibition of ER stress/UPR activation by the chemical chaperone, 4-phenyl butyric acid (4-PBA), inhibited adipogenesis and blunted high fat-diet induced weight gain in 4-PBA supplemented mice. These findings suggested that UPR activation modulates adipogenesis and adipose tissue metabolism.</p> <p>Subsequently, we sought to identify novel candidate ER stress/UPR responsive genes that may be involved in adipogenesis and WAT metabolism. The expression of a recently recognized ER stress-responsive gene, T-cell death associated gene 51 (TDAG51) was identified to be differentially regulated during adipogenesis. However, the function of TDAG51 in adipogenesis or energy regulation was not known. Studies from this thesis showed that TDAG51 protein expression is attenuated by ER stress/UPR activation in preadipocytes and declines during adipogenesis. Based on these results, and given the importance of adipogenesis in WAT function and whole body energy metabolism, it was<em> </em>hypothesized that<em> TDAG51 may be a novel regulator of adipogenesis and energy homeostasis.</em> Indeed, as reported here, knock-down or absence of TDAG51 (<em>TDAG51^-/-</em>) in pre-adipocytes increased lipogenesis and lead to earlier and more potent expression of adipogenic markers.</p> <p>Finally, we investigated whether absence of TDAG51 in mice affected adiposity and metabolic outcomes. Consistent with the <em>in vitro </em>results, we found that <em>TDAG51^-/-</em>mice fed a standard chow diet, exhibited an age-associated increase in WAT, developed fatty liver, and exhibited insulin resistance as compared to wild-type mice.</p> <p>Taken together, the findings in this thesis indicate that physiological UPR activation and the UPR-responsive gene TDAG51 play important roles in regulating adipogenesis, lipogenesis and whole-body energy metabolism. Thus, therapeutic approaches aimed at modulating ER folding capacity, UPR activation and/or TDAG51 expression may have great potential in the treatment of obesity and its co-morbidities.</p> / Doctor of Philosophy (PhD)

Un régime alimentaire déséquilibré et/ou la présence de composés contaminantsexogènes peuvent modifier la signalisation endocrine et l’homéostasie des lipides et induirel’obésité. Les travaux réalisés dans le cadre de cette thèse ont permis, dans un premier temps,de développer une méthode simple et rapide, dénommée "zebrafish obesogenic (ZO) test",pour identifier in vivo, par utilisation de la larve de poisson zèbre, des facteurs qui peuventaugmenter ou diminuer la taille de l’adipocyte blanc et ainsi moduler le niveau de l’adiposité(Tingaud-Sequeira, Ouadah, Babin, J. Lipid Res. 52, 1765-1772, 2011). Ce test permetd’identifier des composés et des mélanges de molécules obésogènes et anti-obésogènes etfournit des informations pertinentes pour l'évaluation des risques liés leur présence maiségalement pour élucider les mécanismes impliqués. Les travaux ont, dans un second temps,permis d’apporter des réponses quant aux modalités d’action d’un obésogène puissant, lechlorure de tributylétain, contaminant retrouvé très largement dans notre environnement.Cette molécule agit sur l’adipocyte blanc à une concentration de l’ordre du nano molaire viales récepteurs nucléaires RXR et LXR, et non pas via les isoformes PPARgamma/delta(Ouadah et Babin, manuscrit en préparation). / An unbalanced diet and / or the presence of exogenous compounds contaminants mayalter endocrine signaling and lipid homeostasis and induce obesity. The work done in thisthesis have, at first, developed a simple and rapid method, called "zebrafish obesogenic (ZO)test" to identify in vivo by using the zebrafish larva, the factors that may increase or decreasethe size of the white adipocyte and therefore modulate the level of adiposity (Tingaud-Sequeira, Ouadah, Babin, J. Lipid Res. 52, 1765-1772, 2011). This test helps to identifycompounds and mixtures of obesogenic and anti-obesogenic molecules and providesinformation relevant to the risk assessment of their presence but also to elucidate themechanisms involved. Work in a second time allowed to answer as to how the action oftributyltin chloride, a powerful obesogenic contaminant found widely in the environment.This molecule acts in vivo on white adipocytes in a concentration of the order of nano molarvia nuclear receptors LXR and RXR, and not via the PPARgamma isoforms / delta (Ouadahand Babin, manuscript in preparation).

Le diabète de type 2 constitue un enjeu majeur de santé publique et la mise au point de stratégies insulino-sensibilisantes est un défi permanent pour les scientifiques. Cette étude montre qu’un traitement chronique au myo-inositol améliore la sensibilité à l’insuline, réduit l’accrétion adipeuse et augmente la capacité de survie des souris au paraquat. L’effet insulino-sensibilisant semble passer, au moins en partie, par un effet direct sur la voie de signalisation insuline (éventuelle implication de médiateurs de type inositol glycanes). La diminution de l’accrétion adipeuse semble, quant à elle, liée à une réduction de l’activité de lipogenèse de novo et doit probablement aussi contribuer à l’effet insulino-sensibilisant sur le long terme. Une supplémentation en myo-inositol a également amélioré la sensibilité à l’insuline et réduit l’accrétion adipeuse chez la souris sous régime riche en graisses, mais n’a pu prévenir le dévelopement d’une obésité et d’une insulino-résistance associée à une lipotoxicité. Par ailleurs, chez des souris âgées obèses et au contrôle glycémique altéré, la supplémentation en myo-inositol fut inefficace. Cette réduction ou perte d’effet insulino-sensibilisant dans ces deux modèles murins pourrait être liée à la perte d’efficacité du myo-inositol sur la réduction de la masse adipeuse dans un contexte d’obésité déjà installée (souris âgées) et d’activité de lipogenèse de novo réduite (régime gras). De plus, la génération de messagers secondaires putatifs de l’insuline de type inositol glycanes est probablement réduite en cas d’insulino-résistance et pourrait aussi expliquer la perte d’efficacité du myo-inositol dans ces deux cas. Finalement, le myo-inositol seul et/ou utilisé dans le contexte d’une suralimentation chronique n’est pas une stratégie viable de prévention ou de traitement de la résistance à l’insuline. Par contre, son association avec d’autres stratégies insulino-sensibilisantes pourrait potentialiser son/leurs action(s) et éventuellement aider à réduire l’utilisation de stratégies médicamenteuses. / Insulin resistance is the first step in the development of type 2 diabetes so finding insulin-sensitizing strategies is challenging for scientists. Some inositol isomers or derivatives have been reported to exert insulin-mimetic activity. myo-Inositol being the most abundant stereoisomeric form of inositol in foodstuffs, we tested its insulin-mimetic potential in the long term and as a nutritional strategy for insulin resistance prevention and/or treatment. This study demonstrates that chronic myo-inositol treatment improves insulin sensitivity, reduces white adipose tissue accretion and improves mice survival mice to paraquat challenge. The insulin-sensitizing effect seems to be related to a direct effect on insulin signaling pathway. Reduction in adipose tissue mass also probably contribute to the long term effect of myo-inositol on insulin sensitivity. Myo-Inositol supplementation also improved insulin sensitivity and reduced white adipose tissue deposition in mice fed a high fat diet, but did not prevent insulin-resistance or obesity development. On one year-old mice with established obesity and altered glycemic control, myo-inositol supplementation showed no beneficial effect. myo-Inositol apparently acts on adipose tissue through reduction of de novo lipogenesis rather than stimulation of lipolysis. This may explain the lack or loss of myo-inositol efficiency in reducing adipose tissue mass in contexts of already well-established obesity (old mice) or reduced de novo lipogenesis (high fat diet feeding). Generation of inositol glycan putative insulin second messengers is probably reduced in context of insulin resistance which may explain the reduced effect of myo-inositol in both obese mice models. Moreover, myo-Inositol did not prevent lipotoxicity and so the associated insulin-resistance in high fat diet fed mice. In conclusion, myo-inositol alone and/or in a context of overnutrition is not a suitable strategy for the prevention or treatment of insulin resistance. Combining it with other insulin sentitizing strategies may however potentiate their action and help reducing insulin-sensitizing drugs use.

Previous investigators demonstrated that epididymal white adipose tissue (EWAT) lipectomy suppressed spermatogenesis and caused atrophy of the seminiferous tubules. EWAT lipectomy, however, may disrupt testicular innervation, which reportedly compromises testicular function. To resolve this confound and better clarify the role of EWAT in spermatogenesis, three experimental groups of hamsters were created in which: i.) the superior and inferior spermatic nerves were transected (SSNx) at the testicular level, ii.) EWAT was extirpated (EWATx), and iii.) testicular nerves and EWAT were left intact (SHAM controls). It was hypothesized that transection of the superior and inferior spermatic nerves would disrupt normal spermatogenesis. The findings indicate a significant reduction in spermatogenic activity and marked seminal tubule atrophy within the EWATx testis, as compared to the SSNx and controls testes, which did not differ significantly from each other. From these data, it is concluded that EWAT, and not testicular innervation, is central to normal spermatogenesis.

L’obésité et le diabète sont associés à des complications, notamment une fragilité cutanée. Celle-ci pourrait être associée à une altération du métabolisme du glucose et à une augmentation du tissu adipeux sous-cutané. Il a été montré que l’hypoderme pourrait avoir une fonction spécifique pour la peau. Notre travail a consisté d’une part à caractériser l’adiposité hypodermique et à étudier son influence dans la réactivité du tissu cutané en réponse à des pressions faibles ou fortes chez des souris obèses et d’autre part à étudier le processus de cicatrisation. Les fortes pressions augmentent la fragilité cutanée ce qui peut aboutir à des lésions, notamment des ulcères de pression. Les études ont été réalisées chez des souris C57BL/6J développant une obésité induite par une alimentation riche en lipides et en sucres pendant 4 et 12 semaines. La taille des adipocytes de l’hypoderme a été mesurée ainsi que leur réponse lipolytique en présence ou non d’insuline. La réactivité tissulaire a été évaluée en mesurant les variations du flux sanguin en réponse : 1) à l’application d’une pression locale faible afin de déterminer la vasodilatation induite par la pression (PIV), 2) par iontophorèse d’acétylcholine ou de nitroprussiate de sodium. Afin d’explorer le processus spécifique d’ulcère de pression chez les souris obèses diabétiques, une compression par cycles d’ischémie-reperfusion a été réalisée. Ces études ont été complétées par des explorations métaboliques, histologiques et biochimiques. Par ailleurs nous avons déterminé l’impact de l’augmentation de l’adiposité sur des fibroblastes dermiques in vitro afin de mieux comprendre le processus de cicatrisation.Dans ce travail de thèse, nous avons mis en évidence une augmentation de l’adiposité hypodermique associée à une insulinorésistance tissulaire et systémique. Nous avons également montré un retard de cicatrisation en fonction de l’évolution de l’obésité et des réponses micro vasculaires diminuées post cicatrisation par rapport à une peau non lésée / Obesity and diabetes led to complications, including skin fragility. Skin fragility could be associated to a glucose metabolism alteration and a subcutaneous adipose tissue increase. It has been shown that hypodermis could have a specific function for the skin. Our work consisted on the one hand in characterizing the dermal adiposity and studying its involvement in the skin tissue reactivity in response to low or high pressures in obese mice and, on the other hand, in studying the healing process. High pressures increase cutaneous fragility which can lead to skin wounds, in particular pressure ulcers. This study was realized using C57BL/6J male mice with a diet-induced obesity. C57BL/6J mice were fed a high fat and high sugar diet during 4 or 12 weeks. Hypodermis adipocytes size was measured as well as their lipolytic response in presence or absence of insulin. The skin tissue reactivity was assessed measuring the skin blood flow variations in response to 1) a local pressure application in order to determine the pressure-induced vasodilation (PIV), 2) an acetylcholine or sodium nitroprusside iontophoresis. To examine the specific mechanism of the pressure ulcer in obese diabetic mice, a compression with ischemia-reperfusion cycles was realized. Metabolic assessment, histological and molecular biological studies were carried out to characterize each stage of healing through obesity. Furthermore, we determined the adiposity increase on dermal fibroblasts in vitro to better understand the healing process. In this thesis work, we have highlighted a hypodermis adiposity linked to a tissue and a systemic insulin resistance. We have also showed a delayed healing depending on the evolution of the obesity. The microvascular responses were decreased post healing compared to a non-wounded skin

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A modulação do tecido adiposo marrom (TAM) e do tecido adiposo branco (TAB) está associada à prevenção ou redução do ganho de massa corporal. O óleo de peixe possui diversos efeitos benéficos que podem estar relacionados a esses tecidos. Dessa forma, objetivou-se avaliar os efeitos antiobesogênicos de diferentes dietas hiperlipídicas com óleo de peixe na termogênese do TAM e na lipogênese e beta-oxidação do TAB. Para isso, foram utilizados camundongos machos C57BL/6, com três meses de idade, que foram divididos em quatro grupos experimentais: um que recebeu dieta standard-chow (SC, 10% kcal de lipídios) e outros três que receberam dieta hiperlipídica (HL, 50% kcal de lipídios). Obtivemos os grupos HL com banha de porco (HL-B), HL com banha de porco mais óleo de peixe (HL-B+Px) e HL com óleo de peixe (HL-Px). As dietas foram administradas por um período de oito semanas, sendo que a ingestão alimentar foi avaliada diariamente e a massa corporal, semanalmente. Na última semana de experimento, realizou-se a calorimetria indireta e o teste oral de tolerância à glicose. No sacrifício, a glicemia foi aferida, o sangue foi puncionado para obtenção do plasma e o TAM interescapular e o TAB epididimário foram dissecados e armazenados. A leptina, os triglicerídeos e a insulina foram mensurados no plasma. O índice de adiposidade e o HOMA-IR foram calculados. O TAM e o TAB foram avaliados por microscopia confocal e de luz. Realizou-se RT-qPCR e Western blot para avaliação de marcadores termogênicos, da captação e oxidação de ácidos graxos e glicose e de PPAR no TAM, e para a avaliação da lipogênese e beta-oxidação e de PPAR no TAB. Com relação aos resultados, o grupo HL-B apresentou ganho de massa corporal e elevação da adiposidade, associado com hipertrofia dos adipócitos, hiperleptinemia, hipertrigliceridemia, intolerância à glicose e resistência à insulina, reproduzindo um quadro de obesidade e síndrome metabólica. Por outro lado, a ingestão de óleo de peixe nos dois grupos (HL-B+Px e HL-Px) foi capaz de reduzir o ganho de massa corporal e a adiposidade, sem alterar a ingestão alimentar. Essa ingestão também aumentou o gasto energético dos animais, regularizou a leptina e os triglicerídeos plasmáticos, bem como a tolerância à glicose e a resistência à insulina. Esses efeitos foram associados ao aumento de marcadores termogênicos no TAM, bem como da captação e oxidação de ácidos graxos e glicose e da expressão de PPAR nesse tecido. No TAB, houve redução de marcadores da lipogênese e aumento de marcadores da beta-oxidação, juntamente com elevação na expressão de PPAR. Em conclusão, nossos resultados mostram que a ingestão de óleo de peixe tem efeitos antiobesogênicos em camundongos através da modulação benéfica do TAM e do TAB e pode, portanto, representar uma terapia auxiliar alternativa contra a obesidade e suas comorbidades. / Brown adipose tissue (BAT) and white adipose tissue (WAT) modulation is associated with prevention or reduction of body mass gain. Fish oil has several beneficial effects which can be related to these tissues. Thus, we aimed to evaluate the anti-obesity effects of different high-fat diets with fish oil on BAT thermogenesis and WAT lipogenesis and beta-oxidation. For this, we used 3-mo-old C57BL/6 male mice that were divided into four groups: one that received a standard-chow diet (SC, 10% kcal of lipids) and three that received a high-fat diet (HF, 50% kcal of lipids). We obtained the HF with lard group (HF-L), the HF with lard plus fish oil group (HF-L+FO), and the HF with fish oil group (HF-FO). Diets were administrated for eight weeks, and food intake was evaluated daily and the body mass, weekly. At the end of the experiment, we performed indirect calorimetry and an oral glucose tolerance test. At sacrifice, glycemia was assessed, the blood was punctured to obtain plasma and interscapular BAT and epididymal WAT were dissected and stored. Plasmatic leptin, triglycerides and insulin were analyzed. Adiposity index and HOMA-IR were calculated. BAT and WAT were evaluated through confocal and light microscopy. RT-qPCR and Western blot were performed for analyses of thermogenic markers, fatty acids and glucose uptake and oxidation, and PPAR in BAT, and lipogenesis, beta-oxidation and PPAR in WAT. In relation to the results, the HF-L group presented elevated body mass gain and adiposity, associated with adipocyte hypertrophy, hyperleptinemia, hypertriglyceridemia, glucose intolerance and insulin resistance, displaying a condition that simulates obesity and metabolic syndrome. On the contrary, fish oil intake in both groups (HF-L+FO and HF-FO) was able to reduce body mass gain and adiposity, without affecting food intake. It also increased energy expenditure, normalized plasmatic leptin and triglycerides as well as glucose tolerance and insulin resistance. These effects were associated with increases in thermogenic markers, in uptake and oxidation of fatty acids and glucose and in PPAR expression in BAT. In WAT, lipogenesis was reduced and beta-oxidation and PPAR expression were increased. In conclusion, our results demonstrated that fish oil intake has anti-obesity effects in mice through beneficial modulation of BAT and WAT and can, therefore, represent an auxiliary alternative therapy against obesity and its comorbidities.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A modulação do tecido adiposo marrom (TAM) e do tecido adiposo branco (TAB) está associada à prevenção ou redução do ganho de massa corporal. O óleo de peixe possui diversos efeitos benéficos que podem estar relacionados a esses tecidos. Dessa forma, objetivou-se avaliar os efeitos antiobesogênicos de diferentes dietas hiperlipídicas com óleo de peixe na termogênese do TAM e na lipogênese e beta-oxidação do TAB. Para isso, foram utilizados camundongos machos C57BL/6, com três meses de idade, que foram divididos em quatro grupos experimentais: um que recebeu dieta standard-chow (SC, 10% kcal de lipídios) e outros três que receberam dieta hiperlipídica (HL, 50% kcal de lipídios). Obtivemos os grupos HL com banha de porco (HL-B), HL com banha de porco mais óleo de peixe (HL-B+Px) e HL com óleo de peixe (HL-Px). As dietas foram administradas por um período de oito semanas, sendo que a ingestão alimentar foi avaliada diariamente e a massa corporal, semanalmente. Na última semana de experimento, realizou-se a calorimetria indireta e o teste oral de tolerância à glicose. No sacrifício, a glicemia foi aferida, o sangue foi puncionado para obtenção do plasma e o TAM interescapular e o TAB epididimário foram dissecados e armazenados. A leptina, os triglicerídeos e a insulina foram mensurados no plasma. O índice de adiposidade e o HOMA-IR foram calculados. O TAM e o TAB foram avaliados por microscopia confocal e de luz. Realizou-se RT-qPCR e Western blot para avaliação de marcadores termogênicos, da captação e oxidação de ácidos graxos e glicose e de PPAR no TAM, e para a avaliação da lipogênese e beta-oxidação e de PPAR no TAB. Com relação aos resultados, o grupo HL-B apresentou ganho de massa corporal e elevação da adiposidade, associado com hipertrofia dos adipócitos, hiperleptinemia, hipertrigliceridemia, intolerância à glicose e resistência à insulina, reproduzindo um quadro de obesidade e síndrome metabólica. Por outro lado, a ingestão de óleo de peixe nos dois grupos (HL-B+Px e HL-Px) foi capaz de reduzir o ganho de massa corporal e a adiposidade, sem alterar a ingestão alimentar. Essa ingestão também aumentou o gasto energético dos animais, regularizou a leptina e os triglicerídeos plasmáticos, bem como a tolerância à glicose e a resistência à insulina. Esses efeitos foram associados ao aumento de marcadores termogênicos no TAM, bem como da captação e oxidação de ácidos graxos e glicose e da expressão de PPAR nesse tecido. No TAB, houve redução de marcadores da lipogênese e aumento de marcadores da beta-oxidação, juntamente com elevação na expressão de PPAR. Em conclusão, nossos resultados mostram que a ingestão de óleo de peixe tem efeitos antiobesogênicos em camundongos através da modulação benéfica do TAM e do TAB e pode, portanto, representar uma terapia auxiliar alternativa contra a obesidade e suas comorbidades. / Brown adipose tissue (BAT) and white adipose tissue (WAT) modulation is associated with prevention or reduction of body mass gain. Fish oil has several beneficial effects which can be related to these tissues. Thus, we aimed to evaluate the anti-obesity effects of different high-fat diets with fish oil on BAT thermogenesis and WAT lipogenesis and beta-oxidation. For this, we used 3-mo-old C57BL/6 male mice that were divided into four groups: one that received a standard-chow diet (SC, 10% kcal of lipids) and three that received a high-fat diet (HF, 50% kcal of lipids). We obtained the HF with lard group (HF-L), the HF with lard plus fish oil group (HF-L+FO), and the HF with fish oil group (HF-FO). Diets were administrated for eight weeks, and food intake was evaluated daily and the body mass, weekly. At the end of the experiment, we performed indirect calorimetry and an oral glucose tolerance test. At sacrifice, glycemia was assessed, the blood was punctured to obtain plasma and interscapular BAT and epididymal WAT were dissected and stored. Plasmatic leptin, triglycerides and insulin were analyzed. Adiposity index and HOMA-IR were calculated. BAT and WAT were evaluated through confocal and light microscopy. RT-qPCR and Western blot were performed for analyses of thermogenic markers, fatty acids and glucose uptake and oxidation, and PPAR in BAT, and lipogenesis, beta-oxidation and PPAR in WAT. In relation to the results, the HF-L group presented elevated body mass gain and adiposity, associated with adipocyte hypertrophy, hyperleptinemia, hypertriglyceridemia, glucose intolerance and insulin resistance, displaying a condition that simulates obesity and metabolic syndrome. On the contrary, fish oil intake in both groups (HF-L+FO and HF-FO) was able to reduce body mass gain and adiposity, without affecting food intake. It also increased energy expenditure, normalized plasmatic leptin and triglycerides as well as glucose tolerance and insulin resistance. These effects were associated with increases in thermogenic markers, in uptake and oxidation of fatty acids and glucose and in PPAR expression in BAT. In WAT, lipogenesis was reduced and beta-oxidation and PPAR expression were increased. In conclusion, our results demonstrated that fish oil intake has anti-obesity effects in mice through beneficial modulation of BAT and WAT and can, therefore, represent an auxiliary alternative therapy against obesity and its comorbidities.

No description available.

No description available.