The adipocyte-specific hormone leptin, the product of the obese (ob) gene, regulates adipose-tissue mass through hypothalamic effects on satiety and energy expenditure. Leptin acts through the leptin receptor, a single-transmembrane-domain receptor of the cytokine-receptor family. In rodents, homozygous mutations in genes encoding leptin or the leptin receptor cause early-onset morbid obesity, hyperphagia and reduced energy expenditure. These rodents also show hypercortisolaemia, alterations in glucose homeostasis, dyslipidaemia, and infertility due to hypogonadotropic hypogonadisms. In humans, leptin deficiency due to a mutation in the leptin gene is associated with early-onset obesity. Here we describe a homozygous mutation in the human leptin receptor gene that results in a truncated leptin receptor lacking both the transmembrane and the intracellular domains. In addition to their early-onset morbid obesity, patients homozygous for this mutation have no pubertal development and their secretion of growth hormone and thyrotropin is reduced. These results indicate that leptin is an important physiological regulator of several endocrine functions in humans.

In human obesity, the stroma vascular fraction (SVF) of white adipose tissue (WAT) is enriched in macrophages. These cells may contribute to low-grade inflammation and to its metabolic complications. Little is known about the effect of weight loss on macrophages and genes involved in macrophage attraction. We examined subcutaneous WAT (scWAT) of 7 lean and 17 morbidly obese subjects before and 3 months after bypass surgery. Immunomorphological changes of the number of scWAT-infiltrating macrophages were evaluated, along with concomitant changes in expression of SVF-overexpressed genes. The number of sc-WAT-infiltrating macrophages before surgery was higher in obese than in lean subjects (HAM56؉/CD68؉; 22.6 ؎ 4.3 vs. 1.4 ؎ 0.6%, P < 0.001). Typical "crowns" of macrophages were observed around adipocytes. Drastic weight loss resulted in a significant decrease in macrophage number (؊11.63 ؎ 2.3%, P < 0.

Adipose tissue produces inflammation and immunity molecules suspected to be involved in obesity-related complications. The pattern of expression and the nutritional regulation of these molecules in humans are poorly understood. We analyzed the gene expression profiles of subcutaneous white adipose tissue from 29 obese subjects during very low calorie diet (VLCD) using cDNA microarray and reverse transcription quantitative PCR. The patterns of expression were compared with that of 17 non-obese subjects. We determined whether the regulated genes were expressed in adipocytes or stromavascular fraction cells. Gene expression profiling identified 100 inflammation-related transcripts that are regulated in obese individuals when eating a 28 day VLCD but not a 2 day VLCD. Cluster analysis showed that the pattern of gene expression in obese subjects after 28 day VLCD was closer to the profile of lean subjects than to the pattern of obese subjects before VLCD. Weight loss improves the inflammatory profile of obese subjects through a decrease of proinflammatory factors and an increase of anti-inflammatory molecules. The genes are expressed mostly in the stromavascular fraction of adipose tissue, which is shown to contain numerous macrophages. The beneficial effect of weight loss on obesity-related complications may be associated with the modification of the inflammatory profile in adipose tissue.

OBJECTIVE Nonalcoholic fatty liver disease (i.e., increased intrahepatic triglyceride [IHTG] content), predisposes to type 2 diabetes and cardiovascular disease. Adipose tissue lipolysis and hepatic de novo lipogenesis (DNL) are the main pathways contributing to IHTG. We hypothesized that dietary macronutrient composition influences the pathways, mediators, and magnitude of weight gain-induced changes in IHTG. RESEARCH DESIGN AND METHODS We overfed 38 overweight subjects (age 48 ± 2 years, BMI 31 ± 1 kg/m2, liver fat 4.7 ± 0.9%) 1,000 extra kcal/day of saturated (SAT) or unsaturated (UNSAT) fat or simple sugars (CARB) for 3 weeks. We measured IHTG (1H-MRS), pathways contributing to IHTG (lipolysis ([2H5]glycerol) and DNL (2H2O) basally and during euglycemic hyperinsulinemia), insulin resistance, endotoxemia, plasma ceramides, and adipose tissue gene expression at 0 and 3 weeks. RESULTS Overfeeding SAT increased IHTG more (+55%) than UNSAT (+15%, P &lt; 0.05). CARB increased IHTG (+33%) by stimulating DNL (+98%). SAT significantly increased while UNSAT decreased lipolysis. SAT induced insulin resistance and endotoxemia and significantly increased multiple plasma ceramides. The diets had distinct effects on adipose tissue gene expression. CONCLUSIONS Macronutrient composition of excess energy influences pathways of IHTG: CARB increases DNL, while SAT increases and UNSAT decreases lipolysis. SAT induced the greatest increase in IHTG, insulin resistance, and harmful ceramides. Decreased intakes of SAT could be beneficial in reducing IHTG and the associated risk of diabetes.

Obesity-induced white adipose tissue (WAT) fibrosis is believed to accelerate WAT dysfunction. However, the cellular origin of WAT fibrosis remains unclear. Here, we show that adipocyte platelet-derived growth factor receptor-α-positive (PDGFRα) progenitors adopt a fibrogenic phenotype in obese mice prone to visceral WAT fibrosis. More specifically, a subset of PDGFRα cells with high CD9 expression (CD9) originates pro-fibrotic cells whereas their CD9 counterparts, committed to adipogenesis, are almost completely lost in the fibrotic WAT. PDGFRα pathway activation promotes a phenotypic shift toward PDGFRαCD9 fibrogenic cells, driving pathological remodeling and altering WAT function in obesity. These findings translated to human obesity as the frequency of CD9 progenitors in omental WAT (oWAT) correlates with oWAT fibrosis level, insulin-resistance severity, and type 2 diabetes. Collectively, our data demonstrate that in addition to representing a WAT adipogenic niche, different PDGFRα cell subsets modulate obesity-induced WAT fibrogenesis and are associated with loss of metabolic fitness.

Background: Roux-en-Y gastric bypass (RYGB) surgery is one of the most efficient procedures for treating morbid obesity and results in weight-loss and improvements in metabolism and inflammation. Objective: We examined the impact of RYGB on modifications of gut microbiota and its potential associations with changes in gene expression in white adipose tissue (WAT). Design: Gut microbiota were profiled from fecal samples by using pyrosequencing in morbidly obese individuals, explored before (0 mo), 3 mo after, and 6 mo after RYGB. WAT gene expression was studied at 0 and 3 mo. We explored associations between microbial genera and differentially expressed genes in WAT and clinical markers. Results: The richness of gut microbiota increased after RYGB; 37% of increased bacteria belonged to Proteobacteria. The associations between gut microbiota composition and WAT gene expression increased after RYGB. Fourteen discriminant bacterial genera (7 were dominant and 7 were subdominant) and 202 WAT genes changed after RYGB. Variations in bacterial genera correlated with changes in both clinical phenotype and adipose tissue gene expression. Some genes encode metabolic and inflammatory genes. Almost half of the correlations were independent of the change in calorie intake. Conclusion: These results show an increase in gut microbiota richness and in the number of associations between gut microbiota and WAT genes after RYGB in obesity. Variations of gut microbiota were associated with changes in WAT gene expression. These findings stimulate deeper explorations of the mechanisms linking gut microbiome and WAT pathological alterations in human obesity and its changes after weight loss.Am J Clin Nutr 2013;98:16-24.

El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido facilitado todavía por el investigador a cargo del archivo del mismo.

This study opens new perspectives in understanding the physiology of human EAT and its local interaction with neighbouring structures.