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, TNFalpha, PPARgamma, 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 TNFalpha, r = -0.209 and P = 0.036). Concerning adipogenic factors, AQP7 expression levels were found to be positively determined by PPARgamma mRNA expression 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.