Background: Glycerol production and its efflux from adipocytes to the liver are key to modulate lipid and glucose homeostasis. Aquaporin 7 (AQP7) is an aquaglyceroporin that acts as the adipose glycerol channel, whereas aquaporin 9 (AQP9) is the specific channel operating in the liver. The aim of the present work was to evaluate the effect of obesity and type 2 diabetes mellitus (T2DM) on gene expression levels of AQP7 in visceral adipose tissue (VAT) and AQP9 in liver.
Methods: VAT and liver biopsies obtained from 20 women were used in the study. Patients were classified as lean or obese with the last group being further subclassified as normoglycemic (NG), patients with impaired glucose tolerance (IGT), or with T2DM. Anthropometric measurements as well as circulating metabolites, hormones, and adipokines were determined. Real-time polymerase chain reaction analyses were performed to quantify transcript levels of AQP7 in VAT and AQP9 in the liver.
Results: Gene expression levels of AQP7 in VAT showed a tendency toward an increase (P = 0.065) in obese patients (both NG and T2DM) compared to lean subjects. AQP9 showed a significant downregulation in the hepatic biopsies obtained from obese T2DM patients compared to obese NG and IGT patients (P = 0.028).
Conclusion: The tendency toward an elevation of mRNA expression of VAT AQP7 in obesity together with the decreased hepatic AQP9 expression observed in obese T2DM subjects suggests a potential role in facilitating glycerol release from adipose tissue and reducing glycerol entry into hepatocytes in obesity and T2DM, respectively.