Adipose tissue hypoxia induces inflammatory M1 polarity of macrophages in an HIF-1α-dependent and HIF-1α-independent manner in obese mice.

AIMS/HYPOTHESIS: As obesity progresses, adipose tissue exhibits a hypoxic and inflammatory phenotype characterised by the infiltration of adipose tissue macrophages (ATMs). In this study, we examined how adipose tissue hypoxia is involved in the induction of the inflammatory M1 and anti-inflammatory M2 polarities of ATMs. METHODS: The hypoxic characteristics of ATMs were evaluated using flow cytometry after the injection of pimonidazole, a hypoxia probe, in normal-chow-fed or high-fat-fed mice. The expression of hypoxia-related and inflammation-related genes was then examined in M1/M2 ATMs and cultured macrophages. RESULTS: Pimonidazole uptake was greater in M1 ATMs than in M2 ATMs. This uptake was paralleled by the levels of inflammatory cytokines, such as TNF-α, IL-6 and IL-1ß. The expression level of hypoxia-related genes, as well as inflammation-related genes, was also higher in M1 ATMs than in M2 ATMs. The expression of Il6, Il1ß and Nos2 in cultured macrophages was increased by exposure to hypoxia in vitro but was markedly decreased by the gene deletion of Hif1a. In contrast, the expression of Tnf, another inflammatory cytokine gene, was neither increased by exposure to hypoxia nor affected by Hif1a deficiency. These results suggest that hypoxia induces the inflammatory phenotypes of macrophages via Hif1a-dependent and -independent mechanisms. On the other hand, the expression of inflammatory genes in cultured M2 macrophages treated with IL-4 responded poorly to hypoxia. CONCLUSIONS/INTERPRETATION: Adipose tissue hypoxia induces an inflammatory phenotype via Hif1a-dependent and Hif1a-independent mechanisms in M1 ATMs but not in M2 ATMs.

Deletion of platelet-derived growth factor receptor-ß improves diabetic nephropathy in Ca²âº/calmodulin-dependent protein kinase IIα (Thr286Asp) transgenic mice.

AIMS/HYPOTHESIS: The activation of platelet-derived growth factor receptor-ß (PDGFR-ß) signalling is increased in the glomeruli and tubules of diabetic animals. In this study, we examined the role of PDGFR-ß signalling during the development of diabetic nephropathy. METHODS: We recently generated pancreatic beta cell-specific Ca(2+)/calmodulin-dependent protein kinase IIα (Thr286Asp) transgenic mice (CaMKIIα mice), which show very high plasma glucose levels up to 55.5 mmol/l and exhibit the features of diabetic nephropathy. These mice were crossed with conditional knockout mice in which Pdgfr-ß (also known as Pdgfrb) was deleted postnatally. The effect of the deletion of the Pdgfr-ß gene on diabetic nephropathy in CaMKIIα mice was evaluated at 10 and 16 weeks of age. RESULTS: The plasma glucose concentrations and HbA(1c) levels were elevated in the CaMKIIα mice from 4 weeks of age. Variables indicative of diabetic nephropathy, such as an increased urinary albumin/creatinine ratio, kidney weight/body weight ratio and mesangial area/glomerular area ratio, were observed at 16 weeks of age. The postnatal deletion of the Pdgfr-ß gene significantly decreased the urinary albumin/creatinine ratio and mesangial area/glomerular area ratio without affecting the plasma glucose concentration. Furthermore, the increased oxidative stress in the kidneys of the CaMKIIα mice as shown by the increased urinary 8-hydroxydeoxyguanosine (8-OHdG) excretion and the increased expression of NAD(P)H oxidase 4 (NOX4), glutathione peroxidase 1 (GPX1) and manganese superoxide dismutase (MnSOD) was decreased by Pdgfr-ß gene deletion. CONCLUSIONS/INTERPRETATION: The activation of PDGFR-ß signalling contributes to the progress of diabetic nephropathy, with an increase in oxidative stress and mesangial expansion in CaMKIIα mice.

Long-term interleukin-1alpha treatment inhibits insulin signaling via IL-6 production and SOCS3 expression in 3T3-L1 adipocytes.

Proinflammatory cytokines are well-known to inhibit insulin signaling to result in insulin resistance. IL-1alpha is also one of the proinflammatory cytokines, but the mechanism of how IL-1alpha induces insulin resistance remains unclear. We have now examined the effects of IL-1alpha on insulin signaling in 3T3-L1 adipocytes. Prolonged IL-1alpha treatment for 12 to 24 hours partially decreased the protein levels as well as the insulin-stimulated tyrosine phosphorylation of IRS-1 and Akt phosphorylation. mRNA for SOCS3, an endogenous inhibitor of insulin signaling, was dramatically augmented 4 hours after IL-1alpha treatment. Concomitantly, the level of IL-6 in the medium and STAT3 phosphorylation were increased by the prolonged IL-1alpha treatment. Addition of anti-IL-6 neutralizing antibody to the medium or overexpression of dominant-negative STAT3 decreased the IL-1alpha-stimulated STAT3 activation and SOCS3 induction, and ameliorated insulin signaling. These results suggest that the IL-1alpha-mediated deterioration of insulin signaling is largely due to the IL-6 production and SOCS3 induction in 3T3-L1 adipocytes.