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OBJECTIVE-Based on rodent studies, we examined the hypothesis that increased adipose tissue (AT) mass in obesity without an adequate support of vascularization might lead to hypoxia, macrophage infiltration, and inflammation.RESEARCH DESIGN AND METHODS-Oxygen partial pressure (AT pO 2 ) and AT temperature in abdominal AT (9 lean and 12 overweight/obese men and women) was measured by direct insertion of a polarographic Clark electrode. Body composition was measured by dual-energy X-ray absorptiometry, and insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp. Abdominal subcutaneous tissue was used for staining, quantitative RT-PCR, and chemokine secretion assay.RESULTS-AT pO 2 was lower in overweight/obese subjects than lean subjects (47 Ϯ 10.6 vs. 55 Ϯ 9.1 mmHg); however, this level of pO 2 did not activate the classic hypoxia targets (pyruvate dehydrogenase kinase and vascular endothelial growth factor [VEGF]). AT pO 2 was negatively correlated with percent body fat (R ϭ Ϫ0.50, P Ͻ 0.05). Compared with lean subjects, overweight/ obese subjects had 44% lower capillary density and 58% lower VEGF, suggesting AT rarefaction (capillary drop out). This might be due to lower peroxisome proliferator-activated receptor ␥1 and higher collagen VI mRNA expression, which correlated with AT pO 2 (P Ͻ 0.05). Of clinical importance, AT pO 2 negatively correlated with CD68 mRNA and macrophage inflammatory protein 1␣ secretion (R ϭ Ϫ0.58, R ϭ Ϫ0.79, P Ͻ 0.05), suggesting that lower AT pO 2 could drive AT inflammation in obesity.CONCLUSIONS-Adipose tissue rarefaction might lie upstream of both low AT pO 2 and inflammation in obesity. These results suggest novel approaches to treat the dysfunctional AT found in obesity. Diabetes 58:718-725, 2009 B oth insulin resistance and ␤-cell failure are present in individuals with type 2 diabetes. Insulin resistance is closely linked to adiposity with a central or visceral pattern, providing a greater risk of insulin resistance and metabolic dysfunction. Adipose tissue (AT) serves as an endocrine organ secreting a variety of autocrine, paracrine, and endocrine factors that can produce or prevent insulin resistance (1). The failure of AT to adequately proliferate and/or differentiate to sequester lipids away from liver, skeletal muscle, and the pancreatic ␤-cell has been proposed as a precursor to type 2 diabetes, broadening the number of potential mechanisms linking obesity to insulin resistance (2).The increase in body fat in obesity should be accompanied by an increase in vascularization, in order to provide adequate oxygen and nutrients (3). In contrast to expectations, obese mice have lower AT capillary density (rarefaction, also known as capillary drop out) and decreased vascular endothelial growth factor (VEGF), the most potent angiogenic factor (4,5). Consistent with this model, preclinical studies suggest that obese AT is hypoxic (6); however, the hypothesis that AT rarefaction might lead to hypoxia remains untested.In humans, short-term whole-body hypoxia decreases i...

SUMMARY Despite a wealth of clinical data showing an association between inflammation and degenerative disorders in elderly, the immune sensors that causally link systemic inflammation to aging remain unclear. Here we detail a mechanism that the Nlrp3 inflammasome controls systemic low grade age-related ‘sterile’ inflammation in both periphery and brain independently of the non-canonical caspase-11 inflammasome. Ablation of Nlrp3 inflammasome protected mice from age-related increases in the innate immune activation, alterations in CNS transcriptome and astrogliosis. Consistent with the hypothesis that systemic low grade inflammation promotes age-related degenerative changes, the deficient Nlrp3 inflammasome mediated caspase-1 activity improved glycemic control and attenuated bone loss and thymic demise. Notably, IL-1 mediated only Nlrp3 inflammasome dependent improvement in cognitive function and motor performance in aged mice. These studies reveal Nlrp3 inflammasome as an upstream target that controls age-related inflammation and offer innovative therapeutic strategy to lower Nlrp3 activity to delay multiple age-related chronic diseases.

Summary FGF21 contributes to the metabolic response to dietary protein restriction, and prior data implicate GCN2 as the amino acid sensor linking protein restriction to FGF21 induction. Here we demonstrate the persistent and essential role of FGF21 in the metabolic response to protein restriction. We show that FGF21-KO mice are fully resistant to low protein (LP)-induced changes in food intake, energy expenditure (EE), body weight gain and metabolic gene expression for 6 months. GCN2-KO mice recapitulate this phenotype, but LP-induced effects on food intake, EE, and body weight subsequently begin to appear after 14 days on diet. We show that this delayed emergence of LP-induced metabolic effects in GCN2-KO mice coincides with a delayed but progressive increase of hepatic FGF21 expression and blood FGF21 concentrations over time. These data indicate that FGF21 is essential for the metabolic response to protein restriction, but that GCN2 is only transiently required for LP-induced FGF21.