Le diabète de type 2 (DT2) est une maladie qui affecte de plus en plus de personnes à travers le monde et comporte plusieurs complications. Les moyens thérapeutiques actuels sont assez limités, car même s'ils sont efficaces, ils sont associés à d'importants effets secondaires. Ainsi, il est important de trouver de nouvelles cibles thérapeutiques pour améliorer la sensibilité à l'insuline en situation d'obésité ou de diabète. Nous nous intéressons ici à une nouvelle cible potentielle, appelée SHP2, qui est une protéine tyrosine phosphatase impliquée dans la transduction du signal en régulant plusieurs voies canoniques (MAPK, PI3K). Cette protéine est connue pour ses rôles cruciaux dans le développement ainsi que son implication dans le métabolisme glucidique. Cependant, cette dernière fonction est encore assez peu comprise, car l'effet d'une délétion de SHP2 sur la sensibilité à l'insuline est différent suivant les tissus et son rôle global n'est pas connu. Nous utilisons ici un modèle original pour étudier l'impact de SHP2 sur le métabolisme glucidique au niveau du corps entier, en travaillant sur le syndrome de Noonan (SN). En effet, cette maladie génétique est principalement causée par une mutation hyperactivatrice du gène PTPN11 codant la protéine SHP2. L'étude du métabolisme glucidique dans le contexte du SN a permis de mettre en évidence une intolérance au glucose, qui est dissociée de l'adiposité réduite, à la fois chez les patients et dans le modèle murin de la maladie (SHP2D61G/+). Nous montrons que les souris SN présentent une inflammation caractérisée par une surexpression de marqueurs pro-inflammatoires, ainsi qu'une augmentation de macrophages pro-inflammatoires dans les tissus métaboliques. [...] / Type 2 diabetes (T2D) is a disease that affects more and more people worldwide and has many severe, lifethreatening complications. The current therapies are rather limited, because even if they are effective, they are associated with significant side effects. Thus, it is important to find new therapeutic targets to improve insulin sensitivity in obesity or diabetes. We are interested here in a new potential target called SHP2, a protein tyrosine phosphatase involved in signal transduction by regulating several canonical pathways (MAPK, PI3K). This protein is known for its crucial roles in development as well as its involvement in glucidic metabolism. However, this latter function is still poorly understood because the effect of a deletion of SHP2 on insulin sensitivity is different between tissues and its overall role is not known. Here, to study the impact of SHP2 on whole body glucidic metabolism we used Noonan Syndrome (NS) as an original model system. Indeed, this genetic disease is mainly caused by a hyperactivating mutation of the gene PTPN11 encoding the protein SHP2. The study of glucidic metabolism in the context of SN has revealed glucose intolerance, which is dissociated from reduced adiposity, both in patients and in the murine model of the disease (SHP2D61G/+). We show that NS mice exhibit inflammation characterized by overexpression of pro-inflammatory markers, as well as an increase of pro-inflammatory macrophages in metabolic tissues. Thanks to bone marrow transplantation and clodronate treatment, we show this inflammation comes from macrophage and is the cause of the insulin resistance in SN.[...]

La prévalence de l’obésité est en net progrès et constitue un problème majeur de santé publique. Cette pathologie est d’autant plus dangereuse qu’elle s’accompagne d’un cluster de désordres métaboliques dont l’inflammation chronique de bas grade et la résistance à l’insuline, principal facteur de risque du diabète de type 2. Les études montrent que la consommation d’un régime hyper lipidique (HFD) représente la cause majeure qui expose à l’obésité et aux pathologies qui lui sont associées. L’obésité induite par un régime HFD s’associe en effet à une inflammation hypothalamique ainsi qu’une altération des circuits neuronaux régissant le contrôle de la balance énergétique, ces altérations sont propices aux développements de résistances à l’insuline et à la leptine. De récentes études montrent que la consommation d’un régime HFD de quelques jours seulement s’accompagne d’une inflammation hypothalamique transitoire, antérieure à l’installation de l’obésité et à l’inflammation périphérique. Ces résultats suggèrent que l’inflammation hypothalamique précoce représente une étape critique dans le développement de l’obésité et de ses altérations. Les médiateurs et les voies de signalisations impliqués dans l’installation de l’inflammation hypothalamique ne sont pas totalement élucidées. Chez les rongeurs, la résistine est associée à l’inflammation et l’insulino-résistance au cours de l’obésité. Bien que majoritairement produite par le tissu adipeux, les études montrent que la résistine est également exprimée par l’hypothalamus ; toutefois, peu d’études renseignent sur son action au niveau central. Notre équipe a démontré chez le rat, qu’une perfusion centrale de résistine altère fortement la sensibilité à l’insuline via l’activation du récepteur TLR4 et l’induction des principales voies de l’inflammation. Dans ce contexte, l’objectif de cette étude a été d’investiguer le rôle de la voie résistine/TLR4 dans l’installation de l’inflammation hypothalamique associée au régime HFD. Nous montrons pour la première fois que, chez la souris, la consommation d’un régime HFD provoque une augmentation de l’expression génique de la résistine dans l’hypothalamus dès 3 jours de régime HFD. L’expression de la résistine est diminuée jusqu’au niveau basal après 8 jours et est de nouveau fortement augmentée après 8 semaines de régime HFD. Nous montrons que l’augmentation de l’expression de la résistine est concomitante avec la gliose réactionnelle associée au régime HFD de court terme, connue pour précocement altérer l’équilibre de la balance énergétique. De façon intéressante, nous montrons quel’augmentation de l’expression de la résistine est observée dans les neurones anorexigènes POMC, critiques pour le maintien de l’homéostasie énergétique ainsi que dans les tanycytes dont les prolongements contactent les capillaires fenêtrés du sang porte hypothalamohypophysaire et dont l’importance pour l’équilibre de la balance énergétique a été démontrée. De façon intéressante, nous montrons que la résistine active l’inflammation dans les tanycytes via TLR4 suggérant que la résistine pourrait promouvoir l’inflammation au sein des tanycytes en réponse au régime HFD, et ce même à court terme. De plus, nous montrons qu’une ICV de 3 jours de résistine chez la souris provoque une inflammation hypothalamique ainsi qu’une gliose réactionnelle au sein de l’ARC qui rappellent les effets du régime HFD. De façon intéressante, nos résultats montrent que l’invalidation du récepteur TLR4 aboli l’inflammation et la gliose réactionnelle hypothalamiques induites par l’ICV de résistine. L’ensemble nos données démontrent que la voie résistine/TLR4 pourrait jouer un rôle critique dansl’inflammation hypothalamique associée au régime HFD de court et long terme, quiprédispose à l’obésité. / Obesity is closely linked to a cluster of metabolic disorders including chronic low-grade inflammation and insulin resistance, which constitutes a principal risk factor for type 2 diabetes. In rodents, cumulative evidence support that the consumption of high fat diet (HFD) is among the most important nutritional factors predisposing to obesity associated insulin resistance and low-grade inflammation. Indeed, HFD induces hypothalamic inflammation and deregulates energy homeostasis control through the alteration of hypothalamic insulin and leptin responsiveness, considered as the main anorexigenic hormones. In addition, it has been shown that unlike peripheral inflammation, which occurs as a consequence of obesity, hypothalamic inflammation develops selectively in the hypothalamic arcuate nucleus (ARC) within the first days of HFD exposure. These data suggest that hypothalamic inflammation is a critical step in the early onset of the deregulation of energy homeostasis by HFD. The cellular and molecular mechanisms underlying obesity-induced hypothalamic inflammation are still not fully characterized. In rodents, resistin is described as a causal factor in obesitymediated insulin resistance and type 2 diabetes. Resistin is mainly secreted by adipose tissue in rodents but an endogenous expression of resistin was also reported in the hypothalamus. However, its action at the central level is not fully understood. Our group recently demonstrated that central resistin, via hypothalamic TLR4, promotes overall insulin resistance through the promotion of inflammatory pathway. In this context, we aimed to investigate the role of resistin/TLR4 pathway in HFD-induced hypothalamic inflammation and insulin resistance. In the present study we report for the first time that both short and long term HFD are associated with a significant increase of resistin expression throughout the MBH. Our results revealed a transient increase in resistin mRNA expression in the ARC after 3 days of HFD, followed by a decline to baseline at day 8 and an expression that increases again after 8 weeks of HFD. We showed that the increase of resistin expression is concomitant with short term HFD-induced ARC reactive gliosis, known to early disrupt energy balance and to predispose to obesity. Interestingly, our results revealed that resistin is expressed by POMC neurons which are critical for energy balance and tanycytes that have the specificity to contact both cerebro-spinal fluid and fenestrated capillary in the mediane eminence. Interestingly, we show that resistin induces tanycytes inflammation through TLR4 suggesting that resistin could promote inflammation in tanycytes in response to short term HFD. Additionally, we show that ICV resistin markedly increases inflammatory markers in the hypothalamic arcuate nucleus in association with reactive gliosis involving recruitment of both microglia and astrocytes. Interestingly, we report that the knockdown of TLR4 almost completely abolished resistin-dependent both hypothalamic inflammation and reactive gliosis. Our data demonstrate that restitin/TLR4 pathway could play a critical role in HFD-diet induced hypothalamic inflammation in response to short and long term HFD which predispose to obesity, a hallmark of metabolic syndrome.

L'inflammation du tissu adipeux, le stress oxydatif ou encore les modifications du microbiote intestinal semblent constituer des facteurs essentiels dans l'initiation, l'aggravation, voire même la "chronicisation" du syndrome métabolique et de l'insulinorésistance. La lectine Reg3a (également appelée HIP/PAP) est un composant de l'immunité innée qui déploie des activités anti-bactérienne, anti-oxydante et anti-inflammatoire. Dans ces conditions, Reg3a pourrait jouer un rôle clé en tant que modulateur du dialogue moléculaire entre le foie, le tissu adipeux et le tube digestif. Via son expression dans le foie de souris transgéniques, ou bien son administration par voie sous-cutanée, nous montrons que la protéine humaine Reg3a présente des effets bénéfiques sur le phénotype des animaux, en contribuant à leur capacité à mieux gérer les troubles du métabolisme d’origine à la fois glucidique et lipidique liés au vieillissement, à un régime alimentaire hyperlipidique ou une obésité et une insulinorésistance génétiquement acquises. Elle permet une diminution de la proportion de masse grasse et une meilleure régulation de la glycémie. Les mécanismes moléculaires sous-jacents restent à déterminer mais pourraient d’une part impliquer le régulateur énergétique AMPK, d’autre part être en lien avec le phénomène de brunissement du tissu adipeux. / Inflammation of adipose tissue, oxidative stress or modifications of intestinal microbiota seem to stand among crucial factors contributing to the initiation, worsening or even "chronification" of metabolic syndrome and insulin resistance. The lectin Reg3a (also called HIP/PAP) is a component of innate immunity with antibacterial, antioxidant and anti-inflammatory activities. In these conditions, Reg3a could play a key role as a modulator of the molecular dialogue between the liver, the adipose tissue and the gut. Through its expression in the liver of transgenic mice or its subcutaneous administration, we show that the human protein Reg3a has a positive impact on animals’ phenotype and contribute to their capacity to better manage both glucose and lipid metabolic disorders related to ageing, a high fat diet or genetically acquired obesity and insulin resistance. Notably it leads to a decrease in the proportion of fat and allows a better control of glycaemia. The associated molecular mechanisms remain to be determined but they could involve the energy sensor AMPK and the phenomenon of adipose tissue browning.

Orientador: Amanda Martins Baviera / Resumo: A obesidade é considerada um problema de saúde pública devido a sua alta prevalência e incidência mundial, e está entre os principais fatores de risco para o desenvolvimento de resistência à insulina e diabetes mellitus tipo 2, ambos levando à hiperglicemia. A manutenção da hiperglicemia por longos períodos é responsável pelo desenvolvimento de complicações microvasculares e macrovasculares, desencadeadas principalmente pelo estresse glico-oxidativo, caracterizado pelo aumento na formação de produtos finais de glicação avançada (AGE). A pentoxifilina, um derivado de metilxantina que atua como um inibidor não-seletivo de fosfodiesterases, tem sido utilizada para o tratamento da claudicação intermitente. No entanto, estudos pré-clínicos indicam que a pentoxifilina é eficaz na promoção de melhorias na resistência à insulina e complicações associadas à obesidade. O objetivo deste estudo foi avaliar os efeitos do tratamento com pentoxifilina em camundongos submetidos ao modelo de obesidade e resistência à insulina, com ênfase nas alterações de parâmetros fisiometabólicos, biomarcadores do estresse glico-oxidativo e da inflamação. Camundongos machos C57BL-6J foram alimentados durante 14 semanas com dieta padrão (P; 3,85 kcal/g, 4% lipídeos) ou com dieta hiperlípidica/hipercalórica (HL; 5,40 kcal/g; 35% de lipídeos). A partir da 7ª semana foram iniciados os tratamentos diários (i.p.) com veículo (salina 0,85%; grupos P e HL) ou com pentoxifilina (50 mg/kg; grupo HPTX), durante as pr... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Obesity is considered a public health problem due to its increased prevalence and incidence worldwide, and is one main risk factor for the development of insulin resistance and type 2 diabetes mellitus, both leading to hyperglycemia. The maintenance of hyperglycemia for long periods is responsible for the onset of microvascular and macrovascular complications, mainly triggered by glycoxidative stress, characterized by the increased generation of advanced glycation end products (AGEs). Pentoxifylline, a methylxanthine derivative that acts as a non-selective inhibitor of phosphodiesterases, has been used for the treatment of intermittent claudication. However, preclinical studies indicate that pentoxifylline is effective in promoting improvements in insulin resistance and complications associated with obesity. The objective of this study was to investigate with emphasis in the changes in physiometabolic parameters, biomarkers of glyco-oxidative stress and inflammation of mice under an experimental model of high-fat diet-induced obesity and treated with pentoxifylline. C57BL-6J male mice were fed a standard diet (P; 3.85 kcal/g, 4% lipids) or a high-fat/hypercaloric diet (HFD, 5.40 kcal/g, 35% lipid) for 14 weeks. Daily treatments (i.p.) were performed with vehicle (0.85% saline, P and HL groups) or with pentoxifylline (50 mg/kg, HPTX group) from the 7th week, during the next 7 weeks. Body weight and food intake were monitored weekly. At 12th and 13th weeks, the oral glucose tol... (Complete abstract click electronic access below) / Doutor

Galactopoietic effects of somatotropin are the result of IGF-I and require high-quality nutrient intake. This study investigated short-term partitioning effects during recombinant bovine somatotropin (bST) administration in high yielding early lactation dairy cows. Administration of recombinant bST has been shown generally to alter results of metabolic tests in the face of unchanged basal glucose and insulin concentrations. Ten multiparous Holstein cows were subjected to rbST (Lactotropin®) and/or feed intake restriction to 80% of predicted ME requirement (80% ME). Responses to insulin challenge (0.1 IU porcine insulin/kg BW. 210 min) and hyperglycaemic clamp (+50 mg/dL whole blood, 120 min) were tested during weeks 8 (control), 9 (rbST ), 11 (80% ME) and 12 (rbST + 80% ME) postpartum. Plasma and whole blood samples were assayed for glucose concentrations. The rbST treatment decreased fasting whole-blood glucose concentration by 9.4% (P<0.0001), which was likely a remnant of control hyperglycaemia. Maximum glucose response was 4.0 mg/dL (21.7%) lower (P<0.0038) and took 6.5 minutes longer to attain (P<0.0037). Steady-state glucose infusion rate (SSGIR) decreased by 8.1 % (P<0.0001). The 80% ME treatment decreased glucose availability by 5 to 6% (P<0.0100), while no glucose responses were affected. Restricted energy intake during treatment with rbST resulted in plasma glucose increase by 5.5% (P<0.0001). Peripheral uptake and utilization of glucose increased by 5.1 % (P<0.0005). Compared to energy restriction, 80%ME + rbST did not alter effects of nutrient restriction on responses to exogenous insulin challenge. Effects were small and inconsistent. SSGIR decreased by 5.0% in the 80% ME + rbST compared to the 80% ME period (P<0.0004) and the change in the hyperglycaemic clamp in the absence of an effect in the insulin challenge may be due to differences in endogenous insulin secretion. The conclusion was that rbST treatment resulted in altered glucose metabolic responses, even with restricted energy intake. / Dissertation (MSc(Agric))--University of Pretoria, 2008. / Animal and Wildlife Sciences / unrestricted

Apelin ist ein Adipokin, das Einfluß auf die Glukosehomöostase hat und vermutlich eine wichtige Rolle in der Regulation von Adipositas und den damit assoziierten Erkrankungen einnimmt. Die Effekte von Apelin scheinen metabolisch günstig zu sein. In dieser Arbeit wurden zunächst Apelin-Serumkonzentrationen und metabolische Parameter bei 740 Studienteilnehmern bestimmt und in einer Querschnittsstudie (n=629) sowie in drei Interventionsstudien (n=111) dargestellt. In einer Subgruppe (n=161) wurde die mRNA-Expression von Apelin und dessen Rezeptor APJ im viszeralen und subkutanen Fettgewebe bei Patienten mit Typ-2-Diabetes genauer untersucht. Im Rahmen der Interventionsstuden wurde der Einfluß von 12 Wochen körperlichem Training (n=60), 6 Monaten hypokalorischer Mischkost (n=19) und bariatrischer Chirurgie (n=32) auf den Serum-Apelinspiegel sowie Zusammenhänge mit Gewichtsreduktion, verbesserter Insulinsensitivität und subklinischer Inflammation analysiert. Die höchsten Apelin-Serumkonzentrationen fanden sich beim adipösen Typ-2-Diabetiker. Die Apelin-Serumkonzentration korrelierte aber auch unabhängig vom Bodymassindex signifikant mit Parametern für Insulinresistenz und subklinischer Inflammation. Die Apelin-Expression war in den unterschiedlichen Fettgewebsdepots bei normal glukosetoleranten Patienten gleich, beim Typ-2-Diabetiker mit insgesamt höherer Expression überwog sie im viszeralen Fettgewebe. Nach allen Interventionsstudien kam es zur Abnahme der Apelin-Serumkonzentration und korrelierte auch dann signifikant mit einer verbesserten Insulinsensitivität, wenn es zu keiner Gewichtsreduktion kam. Die Apelinkonzentration im Serum sowie die Expression im Fettgewebe ist nicht nur vom Bodymassindex abhängig, sondern steht im direkten Zusammenhang mit Insulinsensitivität und inflammatorischen Prozessen. Die unterschiedliche fettdepotspezifische Regulation unterstreicht die pathogenetische Bedeutung eines „kranken“ viszeralen Fettgewebes in der Entwicklung von Typ-2-Diabetes, wobei Apelin als metabolisch günstiges Adipokin vermutlich eine kompensatorische Rolle einnimmt.

Obesity leads to many severe metabolic disorders, e.g. dyslipidemia, insulin resistance, ectopic fat accumulation in the liver and skeletal muscles, non-alcoholic fatty liver disease and finally diabetes mellitus type 2. Metformin (1,1-dimethylbiguanide) is the most favored medicament for the treatment and prevention of these disorders. It stimulates cellular glucose uptake and normalizes blood levels of lipid metabolites without triggering insulin secretion. Research on insulin resistance and diabetes is often realized through developing diet- induced obesity in laboratory animals. The aim of this project is to compare metabolic effects of two different high-fat diets named HFD and HSD. The HFD diet consists chiefly of n-6 polyunsaturated fatty acids (corn oil) and starch (100% glucose). The HSD diet contains mainly saturated fatty acids (lard) and sucrose (50% glucose and 50% fructose). I also studied metabolic effects of metformin by adding it continuously to the drinking water given to obese mice fed with the HFD or the HSD diet. Methods: Intraperitoneal glucose tolerance test (IPGTT), blood and tissue levels of lipid metabolites assessment, radio-immunological assessment of blood levels of insulin, assessment of AMPK activity in liver by western blotting. Results: Increased consumption of the...

Magister Artium (Sport, Recreation and Exercise Science) - MA(SRES) / Obesity is recognised as a risk factor for non-communicable diseases which has reached epidemic proportions globally. South Africa is one of the developing countries with significant statistical representation reported for these conditions. Obesity is associated with other conditions such as type 2 diabetes, hypertension and dyslipidaemia which are all part of what is called metabolic syndrome. As a strategy to reduce the levels of obesity, physical activity has been introduced to compliment clients who are on medication for diabetes.

Vaspin is an adipokine which improves glucose metabolism and insulin sensitivity in obesity. Kallikrein 7 (KLK7) is the first known protease target inhibited by vaspin and a potential target for the treatment of metabolic disorders. Here, we tested the hypothesis that inhibition of KLK7 in adipose tissue may beneficially affect glucose metabolism and adipose tissue function. Therefore, we have inactivated the Klk7 gene in adipose tissue using conditional gene-targeting strategies in mice. Klk7-deficient mice (ATKlk7 −/−) exhibited less weight gain, predominant expansion of subcutaneous adipose tissue and improved whole body insulin sensitivity under a high fat diet (HFD). ATKlk7 −/− mice displayed higher energy expenditure and food intake, most likely due to altered adipokine secretion including lower circulating leptin. Pro-inflammatory cytokine expression was significantly reduced in combination with an increased percentage of alternatively activated (anti-inflammatory) M2 macrophages in epigonadal adipose tissue of ATKlk7 −/−. Taken together, by attenuating adipose tissue inflammation, altering adipokine secretion and epigonadal adipose tissue expansion, Klk7 deficiency in adipose tissue partially ameliorates the adverse effects of HFD-induced obesity. In summary, we provide first evidence for a previously unrecognized role of KLK7 in adipose tissue with effects on whole body energy expenditure and insulin sensitivity.

AMP-activated protein kinase (AMPK) is an energy-sensing enzyme that is activated when cellular energy is low and causes muscle and other cells to increase glucose uptake and fat oxidation, diminish lipid synthesis, and alter expression of various genes. AMPK activity is diminished in animals with the metabolic syndrome, though the mechanisms causing this reduction are unknown. To examine nutrient-induced changes in AMPK activity over time and factors that may regulate it, we compared rat muscle incubated with high glucose (HG) (30min-2h) and muscle of glucose-infused rats (3-8h) with appropriate controls. In addition to diminished AMPK activity (measured by the SAMS peptide assay) and phosphorylation of its activation loop at Thr172, we observed increased muscle glycogen, phosphorylation of AMPK’s α1/α2 subunit at Ser485/491, and PP2A activity, and decreased SIRT1 expression, all of which have been shown to diminish AMPK activity. Dysregulation of one or more of these factors could contribute to pathophysiological changes leading to metabolic syndrome associated disorders. Since recent studies suggest phosphorylation at Ser485/491 may play an important role in AMPK inhibition, we sought to determine how phosphorylation of this site is regulated. We investigated whether insulin or diacylglycerol (DAG) signaling pathways may be involved, since both are increased in at least one of the HG models. Akt and Protein Kinase (PK)D1 phosphorylated AMPK at Ser485/491 and diminished its activity in C2C12 myotubes, downstream of insulin and the DAG-mimetic PMA, respectively. Additionally, p-AMPK Ser485/491 was increased in muscle and liver of fed versus fasted mice and liver of diabetic mice. Our results suggest that Akt- and PKD1-mediated inhibition of AMPK via Ser485/491 phosphorylation may inhibit energy-metabolizing processes, while favoring energy-storing processes. Our results highlight the fact that phosphorylation of Ser485/491 can inhibit AMPK activity independent of changes in p-AMPK Thr172, a measure which is often used as a readout of AMPK activity. We hypothesize that Akt-mediated inhibition of AMPK is an acute, physiological response to insulin, whereas PKD1-mediated inhibition may be associated with more chronic pathophysiological changes. Thus, PKD1 inhibition or prevention of Ser485/491 phosphorylation may represent new strategies for therapeutic AMPK activation as treatment for the metabolic syndrome.