Senescence-associated ß-galactosidase in subcutaneous adipose tissue associates with altered glycaemic status and truncal fat in severe obesity.

AIM/HYPOTHESIS: Altered adipose tissue secretory profile contributes to insulin resistance and type 2 diabetes in obesity. Preclinical studies have identified senescent cells as a cellular source of proinflammatory factors in adipose tissue of obese mice. In humans, potential links with obesity comorbidities are poorly defined. Here, we investigated adipose tissue senescent status and relationships with metabolic complications in human obesity. METHODS: The study includes a prospective cohort of 227 individuals with severe obesity. A photometric method was used to quantify senescence-associated ß-galactosidase (SA-ß-gal) activity in paired subcutaneous and omental adipose tissue biopsies obtained during gastric surgery. Gene and secretory profiling was performed in adipose tissue biopsies and in human primary pre-adipocytes in the presence or absence of senolytic drugs targeting senescent cells. Participants were phenotyped for anthropometric and bioclinical variables, metabolic complications and gastric surgery-induced improvement to address relationships with adipose tissue SA-ß-gal. RESULTS: SA-ß-gal activity was sevenfold higher in subcutaneous than in omental adipose tissue and not associated with BMI or chronological age. Several factors, including insulin-like growth factor binding protein 3 (IGFBP3), plasminogen activator inhibitor 1 (PAI1), C-C motif chemokine ligand 2 (CCL2) and IL-6, were upregulated in subcutaneous adipose tissue in relation with SA-ß-gal (p for linear trend across tertiles <0.05) and in pre-adipocytes cultured with inflammatory macrophage conditioned media. Senolytic treatment reduced SA-ß-gal staining and normalised these alterations. In the whole population, subcutaneous adipose tissue SA-ß-gal activity was positively associated with serum leptin, markers of insulin resistance and increased trunk fat mass. Metabolic complications, including type 2 diabetes and dyslipidaemia, were more prevalent in patients with high levels of SA-ß-gal, but improved with bariatric surgery whatever the initial adipose tissue senescent status. CONCLUSIONS/INTERPRETATION: This study highlights a phenotype of senescence in adipose tissue of severely obese individuals, which characterises prominently subcutaneous fat depots. Subcutaneous adipose tissue senescence is significantly linked to altered glucose metabolism and body fat distribution. Elimination of senescent cells through senolytic treatment could alleviate metabolic complications in severely obese people. Graphical abstract.

Adipose tissue adaptive response to trans-10,cis-12-conjugated linoleic acid engages alternatively activated M2 macrophages.

In mice, nutritional supplementation with the trans-10,cis-12 isomer of linoleic acid (t10,c12-CLA) promotes lipoatrophy, hyperinsulinemia, and macrophage infiltration in white adipose tissue (WAT). We explored the dynamics of these interrelated responses over 2 consecutive 7 d periods of t10,c12-CLA administration and withdrawal. t10,c12-CLA down-regulated lipogenic and lipolytic gene expression and increased collagen deposition, but with no evidence of cross-linking. An abundant CD45(+) cell infiltrate, comprising prominently CD206(+)CD11c(-) macrophages, was found in WAT in association with an anti-inflammatory gene signature. Infiltration of natural killer (NK) and dendritic cells contributed to WAT's innate immune response to t10,c12-CLA. Less abundant adaptive immune cells colonized WAT, including B, NK T, γδ T, and αß T cells. By contrast, T-regulatory cell abundance was not affected. Interruption of treatment allowed recovery of WAT mass and normalization of insulinemia, coincident with regain of WAT homeostasis owing to a coordinated reversion of genic, structural, and immune deregulations. These data revealed a striking resilience of WAT after a short-term metabolic injury induced by t10,c12-CLA, which relies on alternatively activated M2 macrophage engagement. In addition, the temporal links between variations in WAT alterations and insulinemia upon t10,c12-CLA manipulation strengthen the view that WAT dysfunctional status is critically involved in altered glucose homeostasis.

Cathepsin S inhibition lowers blood glucose levels in mice.

AIMS/HYPOTHESIS: Cathepsin S (CatS) belongs to a family of proteases that have been implicated in several disease processes. We previously identified CatS as a protein that is markedly overexpressed in adipose tissue of obese individuals and downregulated after weight loss and amelioration of glycaemic status induced by gastric bypass surgery. This prompted us to test whether the protease contributes to the pathogenesis of type 2 diabetes using mouse models with CatS inactivation. METHODS: CatS knockout mice and wild-type mice treated with orally active small-molecule CatS inhibitors were fed chow or high-fat diets and explored for change in glycaemic status. RESULTS: CatS deletion induced a robust reduction in blood glucose, which was preserved in diet-induced obesity and with ageing and was recapitulated with CatS inhibition in obese mice. In vivo testing of glucose tolerance, insulin sensitivity and glycaemic response to gluconeogenic substrates revealed that CatS suppression reduced hepatic glucose production despite there being no improvement in insulin sensitivity. This phenotype relied on downregulation of gluconeogenic gene expression in liver and a lower rate of hepatocellular respiration. Mechanistically, we found that the protein 'regulated in development and DNA damage response 1' (REDD1), a factor potentially implicated in reduction of respiratory chain activity, was overexpressed in the liver of mice with CatS deficiency. CONCLUSIONS/INTERPRETATION: Our results revealed an unexpected metabolic effect of CatS in promoting pro-diabetic alterations in the liver. CatS inhibitors currently proposed for treatment of autoimmune diseases could help to lower hepatic glucose output in obese individuals at risk for type 2 diabetes.

Defining macrophage phenotype and function in adipose tissue.

In obesity, chronic low-grade inflammation is thought to mediate the effects of increased adipose tissue mass on metabolic comorbidity. Of the different cell types that contribute to obesity-induced inflammation in adipose tissue, this review focuses on macrophages and their monocytes precursors. Mechanisms for monocyte recruitment to adipose tissue, and how both monocytes and macrophages are phenotypically modified in this environment in response to increasing fat mass, are considered. The versatile phenotype of adipose tissue macrophages might contribute not only to inflammatory and metabolic alterations, but could also help to maintain adipose tissue homeostasis in the setting of obesity.

Cathepsin L activity controls adipogenesis and glucose tolerance.

Cysteine proteases play an important part in human pathobiology. This report shows the participation of cathepsin L (CatL) in adipogenesis and glucose intolerance. In vitro studies demonstrate the role of CatL in the degradation of the matrix protein fibronectin, insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF-1R), essential molecules for adipogenesis and glucose metabolism. CatL inhibition leads to the reduction of human and murine pre-adipocyte adipogenesis or lipid accumulation, protection of fibronectin from degradation, accumulation of IR and IGF-1R beta-subunits, and an increase in glucose uptake. CatL-deficient mice are lean and have reduced levels of serum glucose and insulin but increased levels of muscle IR beta-subunits, fibronectin and glucose transporter (Glut)-4, although food/water intake and energy expenditure of these mice are no less than their wild-type littermates. Importantly, the pharmacological inhibition of CatL also demonstrates reduced body weight gain and serum insulin levels, and increased glucose tolerance, probably due to increased levels of muscle IR beta-subunits, fibronectin and Glut-4 in both diet-induced obese mice and ob/ob mice. Increased levels of CatL in obese and diabetic patients suggest that this protease is a novel target for these metabolic disorders.

Structural and inflammatory heterogeneity in subcutaneous adipose tissue: relation with liver histopathology in morbid obesity.

BACKGROUND & AIMS: In addition to total body fat, the regional distribution and inflammatory status of enlarged adipose tissue are strongly associated with metabolic co-morbidities of obesity. We recently showed that the severity of histological liver lesions related to obesity increases with the amount of macrophage accumulation in visceral adipose tissue (VAT), while no association was found with the subcutaneous adipose tissue (SAT). In the abdominal region, SAT is anatomically divided into two layers, i.e. superficial (sSAT) and deep (dSAT). The aim of the present study was to test the hypothesis that these distinct compartments differentially contribute to hepatic alterations in obesity. METHODS: Biopsies of the liver, sSAT, dSAT, and VAT were collected in 45 subjects with morbid obesity (age 43.7±1.6 years; BMI 48.5±1.2kg/m(2)) during bariatric surgery. Large scale gene expression analysis was performed to identify the pathways that discriminate sSAT from dSAT. Adipose tissue macrophages were quantified by immunohistochemistry using HAM56 antibody in subjects scored for liver histopathology. RESULTS: An inflammatory gene pattern discriminates between sSAT and dSAT. dSAT displayed an intermediate level of macrophage accumulation between sSAT and VAT. The abundance of macrophages in dSAT, but not in sSAT, was significantly increased in patients with non-alcoholic steatohepatitis (NASH) and/or fibroinflammatory hepatic lesions. CONCLUSIONS: These data show distinct gene signature and macrophage abundance in the two compartments of SAT, with dSAT more closely related to VAT than to sSAT in terms of inflammation and relation with the severity of liver diseases in morbid obesity.

[Adipose tissue, a new playground for immune cells]. / Le tissu adipeux - Un nouveau terrain de jeu pour les cellules immunitaires.

Adipose tissue has been under focus in the last decade and pivotal concepts have emerged from the studies of its complex biology. Low-grade inflammation both at the systemic level and in adipose tissue itself characterizes obesity. Among the different cell types contributing to inflammation, this review focuses on the mechanisms and consequences of macrophage accumulation in obese adipose tissue. Mechanisms for monocyte recruitment to adipose tissue, and how macrophages' phenotypes are modified in this environment in response to increasing fat mass, are considered. We review recent studies addressing the complex and versatile phenotype of adipose tissue macrophages that contribute to inflammatory and metabolic alterations, but could also help to maintain adipose tissue homeostasis in the setting of obesity both in mouse and human situations. A newly discovered consequence of adipose tissue inflammation is fibrosis. Whether macrophages and/or other immune cells exert a pro-fibrotic effect in adipose tissue is still unclear. This wealth of new information will hopefully help to design new ways to control adipose tissue inflammation and its deleterious sequels.

Association between omental adipose tissue macrophages and liver histopathology in morbid obesity: influence of glycemic status.

BACKGROUND/AIMS: Recently we showed that macrophage accumulation in omental adipose tissue is associated with liver fibro-inflammation in morbidly obese subjects. Here, we evaluated the influence of glycemic status and extended the analysis to the spectrum of obesity-linked liver damage. METHODS: Liver biopsies, subcutaneous and omental adipose tissue were collected in 132 obese subjects during gastric bypass surgery. HAM56+ adipose tissue macrophages were counted in subjects classified by liver histopathology and by their degree of insulin resistance. RESULTS: In the whole population, the number of omental macrophages increased with the score of steatosis, the non-alcoholic fatty liver disease activity score, the stage of fibrosis and with fibro-inflammation index. None of these relationships were significant with subcutaneous macrophage count. In insulin-sensitive participants, omental macrophages accumulation was higher in subjects with high indexes of fibro-inflammation (p=0.012 vs. low indexes). In insulin-resistant including type 2 diabetic participants, omental macrophage count was higher both in subjects with high scores of steatosis and in subjects with high indexes of fibro-inflammation (p<0.05 vs. low scores). CONCLUSIONS: Macrophage accumulation in omental adipose tissue is associated with aggravated steatosis and fibro-inflammation in insulin-resistant obese subjects independently of altered glycemic status.

Deficiency and inhibition of cathepsin K reduce body weight gain and increase glucose metabolism in mice.

OBJECTIVE: Previous studies demonstrated increased levels of cysteine proteases cathepsins in serum and adipose tissues from obese patients. We now provide evidence from a mouse model of obesity to suggest a direct participation of cathepsin K (CatK) in mouse body weight gain and glucose metabolism. METHODS AND RESULTS: Using real-time polymerase chain reaction, we detected 12-fold increase in CatK transcripts after adipogenesis of human preadipocytes. Using an immunohistology analysis, we consistently observed high levels of CatK expression in adipose tissues from obese humans and mice. Selective inhibition of CatK activity blocked the lipid accumulation in human and mouse preadipocytes. In mice, CatK deficiency reduced significantly diet-induced body weight gain and serum glucose and insulin levels. Similar results were obtained in diet-induced and genetically created (ob/ob) obese mice after animals were treated with a CatK-selective inhibitor. Mechanistic study demonstrated a role for CatK in degrading fibronectin, a matrix protein that controls adipogenesis. Deficiency or inhibition of CatK leads to fibronectin accumulation in muscle and adipose tissues. CONCLUSIONS: This study demonstrates an essential role of CatK in adipogenesis and mouse body weight gain, possibly via degradation of fibronectin, thus suggesting a novel therapeutic strategy for the control of obesity by regulating CatK activity.

Comparative Evaluation of Microbiota Engraftment Following Fecal Microbiota Transfer in Mice Models: Age, Kinetic and Microbial Status Matter.

The intestinal microbiota and its functions are intricately interwoven with host physiology. Colonizing rodents with donor microbiota provides insights into host-microbiota interactions characterization and the understanding of disease physiopathology. However, a better assessment of inoculation methods and recipient mouse models is needed. Here, we compare the engraftment at short and long term of genetically obese mice microbiota in germ-free (GF) mice and juvenile and adult specific pathogen free (SPF) mice. We also tested the effects of initial microbiota depletion before microbiota transfer. In the present work, donor microbiota engraftment was better in juvenile SPF mice than in adult SPF mice. In juvenile mice, initial microbiota depletion using laxatives or antibiotics improved donor microbiota engraftment 9 weeks but not 3 weeks after microbiota transfer. Microbiota-depleted juvenile mice performed better than GF mice 3 weeks after the microbiota transfer. However, 9 weeks after transfer, colonized GF mice microbiota had the lowest Unifrac distance to the donor microbiota. Colonized GF mice were also characterized by a chronic alteration in intestinal absorptive function. With these collective results, we show that the use of juvenile mice subjected to initial microbiota depletion constitutes a valid alternative to GF mice in microbiota transfer studies.

Increased infiltration of macrophages in omental adipose tissue is associated with marked hepatic lesions in morbid human obesity.

In human obesity, white adipose tissue (WAT) is enriched in macrophages. How macrophage infiltration in WAT contributes to the complications of obesity is unknown. This study tested the hypothesis that recruitment of macrophages in omental WAT is associated with hepatic damage in obese patients. Paired biopsies of subcutaneous and omental WAT and a liver biopsy were collected during gastric surgery in 46 obese women and 9 obese men (BMI 47.9 +/- 0.93 kg/m(2)). The number of HAM56+ macrophages in WAT was quantified microscopically, and correlations with clinical and biological parameters and histological liver pathology were investigated. There were twice as many macrophages in omental as in subcutaneous WAT (P<0.0001). After adjustment for age, omental WAT macrophage infiltration was correlated to fasting glucose and insulin, quantitative insulin sensitivity check index, triglycerides, aspartate aminotransferase (AST), and gamma-glutamyltranspeptidase. We propose an easy equation to estimate the amount of macrophages in omental WAT. Increased macrophage accumulation specifically in omental WAT was associated with hepatic fibroinflammatory lesions (P=0.01). The best predictive model for the severity of hepatic damage includes adiponectinemia, AST, and omental WAT macrophages. These data suggest that the presence of macrophages in omental WAT participates in the cellular mechanisms favoring hepatic fibroinflammatory lesions in obese patients.

Treatment for 2 mo with n 3 polyunsaturated fatty acids reduces adiposity and some atherogenic factors but does not improve insulin sensitivity in women with type 2 diabetes: a randomized controlled study.

BACKGROUND: Information is lacking on the potential effect of n-3 polyunsaturated fatty acids (PUFAs) on the adipose tissue of patients with type 2 diabetes. OBJECTIVE: We evaluated whether n-3 PUFAs have additional effects on adiposity, insulin sensitivity, adipose tissue function (production of adipokines and inflammatory and atherogenic factors), and gene expression in type 2 diabetes. DESIGN: Twenty-seven women with type 2 diabetes without hypertriglyceridemia were randomly allocated in a double-blind parallel design to 2 mo of 3 g/d of either fish oil (1.8 g n-3 PUFAs) or placebo (paraffin oil). RESULTS: Although body weight and energy intake measured by use of a food diary were unchanged, total fat mass (P < 0.019) and subcutaneous adipocyte diameter (P < 0.0018) were lower in the fish oil group than in the placebo group. Insulin sensitivity was not significantly different between the 2 groups (measured by homeostasis model assessment in all patients and by euglycemic-hyperinsulinemic clamp in a subgroup of 5 patients per group). By contrast, atherogenic risk factors, including plasma triacylglycerol (P < 0.03), the ratio of triacylglycerol to HDL cholesterol (atherogenic index, P < 0.03), and plasma plasminogen activator inhibitor-1 (P < 0.01), were lower in the fish oil group than in the placebo group. In addition, a subset of inflammation-related genes was reduced in subcutaneous adipose tissue after the fish oil, but not the placebo, treatment. CONCLUSIONS: A moderate dose of n-3 PUFAs for 2 mo reduced adiposity and atherogenic markers without deterioration of insulin sensitivity in subjects with type 2 diabetes. Some adipose tissue inflammation-related genes were also reduced. These beneficial effects could be linked to morphologic and inflammatory changes in adipose tissue. This trial was registered at clinicaltrials.gov as NCT0037.

Chronic Exposure to Low Doses of Dioxin Promotes Liver Fibrosis Development in the C57BL/6J Diet-Induced Obesity Mouse Model.

BACKGROUND: Exposure to persistent organic pollutants (POPs) has been associated with the progression of chronic liver diseases, yet the contribution of POPs to the development of fibrosis in non-alcoholic fatty liver disease (NAFLD), a condition closely linked to obesity, remains poorly documented. OBJECTIVES: We investigated the effects of subchronic exposure to low doses of the POP 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an aryl hydrocarbon receptor ligand, on NAFLD progression in diet-induced obese C57BL/6J mice. METHODS: Male C57BL/6J mice were fed either a 10% low-fat (LFD) or a 45% high-fat (HFD) purified diet for 14 weeks and TCDD-exposed groups were injected once a week with 5 µg/kg TCDD or the vehicle for the last 6 weeks of the diet. RESULTS: Liver histology and triglyceride levels showed that exposure of HFD fed mice to TCDD worsened hepatic steatosis, as compared to either HFD alone or LFD plus TCDD and the mRNA levels of key genes of hepatic lipid metabolism were strongly altered in co-treated mice. Further, increased liver collagen staining and serum transaminase levels showed that TCDD induced liver fibrosis in the HFD fed mice. TCDD in LFD fed mice increased the expression of several inflammation and fibrosis marker genes with no additional effect from a HFD. CONCLUSIONS: Exposure to TCDD amplifies the impairment of liver functions observed in mice fed an enriched fat diet as compared to a low fat diet. The results provide new evidence that environmental pollutants promote the development of liver fibrosis in obesity-related NAFLD in C57BL/6J mice. Citation: Duval C, Teixeira-Clerc F, Leblanc AF, Touch S, Emond C, Guerre-Millo M, Lotersztajn S, Barouki R, Aggerbeck M, Coumoul X. 2017. Chronic exposure to low doses of dioxin promotes liver fibrosis development in the C57BL/6J diet-induced obesity mouse model. Environ Health Perspect 125:428-436; http://dx.doi.org/10.1289/EHP316.

Immune cell-derived cytokines contribute to obesity-related inflammation, fibrogenesis and metabolic deregulation in human adipose tissue.

Adipose tissue contains a variety of immune cells, which vary in abundance and phenotype with obesity. The contribution of immune cell-derived factors to inflammatory, fibrotic and metabolic alterations in adipose tissue is not well established in human obesity. Human primary adipose tissue cells, including pre-adipocytes, endothelial cells and mature adipocytes, were used to investigate deregulation of cell- and pathway-specific gene profiles. Among factors known to alter adipose tissue biology, we focus on inflammatory (IL-1ß and IL-17) and pro-fibrotic (TGF-ß1) factors. rIL-1ß and rIL-17 induced concordant pro-inflammatory transcriptional programs in pre-adipocytes and endothelial cells, with a markedly more potent effect of IL-1ß than IL-17. None of these cytokines had significant effect on fibrogenesis-related gene expression, contrasting with rTGF-ß1-induced up-regulation of extracellular matrix components and pro-fibrotic factors. In mature adipocytes, all three factors promoted down-regulation of genes functionally involved in lipid storage and release. IL-1ß and IL-17 impacted adipocyte metabolic genes in relation with their respective pro-inflammatory capacity, while the effect of TGF-ß1 occurred in face of an anti-inflammatory signature. These data revealed that IL-1ß and IL-17 had virtually no effect on pro-fibrotic alterations but promote inflammation and metabolic dysfunction in human adipose tissue, with a prominent role for IL-1ß.

Insulin and leptin induce Glut4 plasma membrane translocation and glucose uptake in a human neuronal cell line by a phosphatidylinositol 3-kinase- dependent mechanism.

The insulin-sensitive glucose transporter Glut4 is expressed in brain areas that regulate energy homeostasis and body adiposity. In contrast with peripheral tissues, however, the impact of insulin on Glut4 plasma membrane (PM) translocation in neurons is not known. In this study, we examined the role of two anorexic hormones (leptin and insulin) on Glut4 translocation in a human neuronal cell line that express endogenous insulin and leptin receptors. We show that insulin and leptin both induce Glut4 translocation to the PM of neuronal cells and activate glucose uptake. Wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase, totally abolished insulin- and leptin-dependent Glut4 translocation and stimulation of glucose uptake. Thus, Glut4 translocation is a phosphatidylinositol 3-kinase-dependent mechanism in neuronal cells. Next, we investigated the impact of chronic insulin and leptin treatments on Glut4 expression and translocation. Chronic exposure of neuronal cells to insulin or leptin down-regulates Glut4 proteins and mRNA levels and abolishes the acute stimulation of glucose uptake in response to acute insulin or leptin. In addition, chronic treatment with either insulin or leptin impaired Glut4 translocation. A cross-desensitization between insulin and leptin was apparent, where exposure to insulin affects leptin-dependent Glut4 translocation and vice versa. This cross-desensitization could be attributed to the increase in suppressor of cytokine signaling-3 expression, which was demonstrated in response to each hormone. These results provide evidence to suggest that Glut4 translocation to neuronal PM is regulated by both insulin and leptin signaling pathways. These pathways might contribute to an in vivo glucoregulatory reflex involving a neuronal network and to the anorectic effect of insulin and leptin.

Weight loss reduces adipose tissue cathepsin S and its circulating levels in morbidly obese women.

CONTEXT: Human adipose tissue produces several adipokines, including the newly identified protein cathepsin S (CTSS), a cysteine protease involved in the pathogenesis of atherosclerosis. Obesity is characterized by high levels of CTSS in the circulation and in sc white adipose tissue (scWAT). OBJECTIVE: We investigated the effect of surgery-induced weight loss on circulating CTSS and its protein expression in scWAT. DESIGN: Fifty morbidly obese women before and 3 months after surgery and 10 healthy lean women were studied. We analyzed the relationships between circulating CTSS and clinical and biological parameters. Immunohistochemistry of the CTSS protein variations in scWAT was performed. RESULTS: Weight loss decreased by 42% (P < 0.0001) the circulating CTSS levels, which correlated with changes in body weight (P = 0.03). We observed a significant decrease in CTSS enzymatic activity by 25% after weight loss (P = 0.001). Adipose tissue CTSS content was reduced by 30% (P = 0.002) after surgery. The variations in CTSS expression in scWAT after surgery correlated with changes in circulating CTSS serum levels (P = 0.03). Most of the correlations between CTSS and clinical and biological parameters disappeared after adjustment for body mass index, emphasizing the strong link between CTSS and corpulence in humans. CONCLUSIONS: Changes in CTSS scWAT might contribute to serum variations in CTSS during weight loss. The decrease in CTSS concentrations in the circulation may contribute to vascular improvement in obese subjects after weight loss.

Deletion of the angiotensin type 2 receptor (AT2R) reduces adipose cell size and protects from diet-induced obesity and insulin resistance.

The renin-angiotensin system with its active metabolite angiotensin (Ang) II has been related not only to hypertension but also to obesity and insulin resistance. Recent evidence obtained in vitro suggests that the type 2 Ang II receptor (AT2R) mediates the trophic action of Ang II on adipocyte differentiation and lipogenesis. We used AT2R(y/-) mice to delineate a potential role of AT2R in adipose tissue development and metabolism. AT2R(y/-) mice had a normal adiposity but displayed a striking adipose tissue phenotype characterized by small adipocytes and an increase in cell number. In muscle, the expression of several genes involved in lipid metabolism, including fatty acid translocase, uncoupling protein-3, peroxisome proliferator-activated receptors (alpha, delta), and carnitine palmitoyl transferase-1, was increased in AT2R-deficient mice. In response to high-fat feeding, these mice were protected against obesity and obesity-related glucose intolerance, as assessed by glucose tolerance tests. Moreover, lipid oxidation assessed by indirect calorimetry was higher in AT2R-deficient mice than in wild-type mice, irrespective of the diet. This suggests that AT2R-dependent signaling exerts a direct or indirect negative control on lipid utilization in muscles. These data support the idea that AT2R-dependent Ang II signaling increases adipose cell mass and glucose intolerance and thus could participate to the deleterious effects of a high-fat diet.

Leptin receptor-deficient obese Zucker rats reduce their food intake in response to a systemic supply of calories from glucose.

It has been established that leptin exerts a negative control on food intake, allowing one to maintain stable caloric intake over time. The aim of the present study was to investigate whether leptin regulates food intake when a supply of calories is provided by the systemic route. Experiments were carried out in leptin receptor-deficient obese fa/fa rats and lean Fa/fa controls. In both groups, 48 h of glucose infusion reduced food intake in proportion to caloric supply, resulting in virtually no change in total caloric intake as compared to before the infusion. This hypophagic response was reproduced without adding systemic calories, but by increasing glucose and insulin concentrations specifically in the brain through carotid artery infusion. Concomitant intracerebroventricular administration of 5-(tetradecyloxy)-2-furoic acid, an acetyl CoA carboxylase inhibitor that precludes malonyl-CoA synthesis, abolished the restriction of feeding in carotid-infused lean and obese rats. These data indicate that a supply of calories via glucose infusion induces a hypophagic response independent of leptin signaling in the rat, and support the hypothesis that a rise in central malonyl-CoA, triggered by increased glucose and insulin concentrations, participates in this adaptation. This process could contribute to the limiting of hyperphagia, primarily when leptin signaling is altered, as in the obese state.

Pancreatic islet response to hyperglycemia is dependent on peroxisome proliferator-activated receptor alpha (PPARalpha).

This study tests the hypothesis that islet peroxisome proliferator-activated receptor alpha (PPARalpha) influences insulin secretion. Freshly isolated islets of normoglycemic PPARalpha-null mice display no major alteration of glucose-stimulated insulin release. However, after 24 h of culture in high glucose, PPARalpha-null islets exhibit elevated basal insulin secretion and fail to increase insulin mRNA. 24-h culture with palmitate replicates this phenotype in wild-type islets. The data suggest that PPARalpha is needed to ensure appropriate insulin secretory response in situation of short-term hyperglycemia, likely by maintaining islet lipid homeostasis. As such, islet PPARalpha could contribute to delay the progression of type 2 diabetes.

Embryonic expression of the leptin receptor gene in mesoderm-derived tissues.

Leptin acts on the hypothalamus to reduce food intake and on a number of non-neuronal tissues via specific receptors (Lepr). The use of in situ hybridisation to map the Lepr gene in pre-natal mice revealed transcripts in the yolk sac in various structures of the central nervous system and in mesoderm-derived tissues, such as cartilage/bone primordia and musculoaponeurotic laminae. At later stages, significant amounts of Lepr were expressed in the region surrounding the developing eye of the embryo. Lepr was also found to be expressed in the choroid, sclera and connective tissues of the limbus in the adult eye. In conclusion, we have identified new targets for leptin action during embryogenesis and adulthood.