Adipose tissue expression of the glycerol channel aquaporin-7 gene is altered in severe obesity but not in type 2 diabetes

Context: Aquaporin-7 is required for efflux of glycerol from adipocytes and influences whole-body glucose homeostasis in animal studies. Objective: Our objective was to test the hypothesis that AQP7 gene expression levels may be affected by presence of obesity and type 2 diabetes in humans. Design: The obesity study cohort consisted of 12 lean, 22 nonseverely obese, and 13 severely obese subjects. The type 2 diabetes study cohort consisted of 17 lean and 39 obese type 2 diabetic patients. Circulating levels of plasma soluble proteins monocyte chemoattractant protein-1, TNF receptors 1 and 2, and IL-6 and glycerol were measured. The sc adipose tissue gene expression of AQP7, MCP-1, IL-6, TNF alpha, PPAR gamma, and SREBP1c genes was measured by real-time PCR. AQP7 gene mutation analysis was performed. Results: Severely obese women showed lower AQP7 expression levels compared with lean and nonseverely obese ( P < 0.001). Moreover, circulating glycerol concentration was lower in severely obese subjects, but no correlation with AQP7 adipose tissue expression was observed. AQP7 expression was negatively related with proinflammatory genes ( for monocyte chemoattractant protein-1, r = -0.203 and P = 0.044; for TNF alpha, r = -0.209 and P = 0.036). Concerning adipogenic factors, AQP7 expression levels were found to be positively determined by PPAR gamma mRNAexpression levels ( r = 0.265; P = 0.012). AQP7 expression did not show differences regarding the presence of type 2 diabetes. Conclusion: Expression of AQP7 is down-regulated in women with severe obesity. The expression of this glycerol channel is not affected by type 2 diabetes.