Hormonal control of subcutaneous adipose tissue aquaglyceroporins

Glycerol metabolism in normal condition and in metabolic disorders like type-2 diabetes and obesity could depend at least in part on the transmembrane transport mechanisms of glycerol. Aquaglyceroporins (AQPs) are integral membrane protein belonging to the water channel proteins family (aquaporins) that are permeable to glycerol as well as water. Adipose tissue, the main source of plasma glycerol, expresses high levels of AQP7 but also AQP3, 9, 10. Recently, in adipose tissue was also found AQP11, whose permeability to glycerol is uncertain. However, the hormonal regulation of AQPs in the adipose tissue is not completely characterized. To this purpose we evaluated the effect of insulin, isoproterenol, thyroxin, dexamethasone in human isolated adipose tissue by real time RT-PCR. Immunocytochemistry was also performed to define the localization of the AQPs. Results showed that all the AQPs investigated are expressed in the human subcutaneous adipose tissue with a localization of AQP3,7 and 10 in both plasma membranes and in lipid droplets membranes, AQP9 mainly in the plasma membrane and AQP11 in the lipid droplets membrane. Generally, lipolytic and lipogenic stimuli differently affected the AQPs expression which depicts a complex situation involving, probably, different signaling pathway. These results and other recently described by the literature seem support the existence of different AQPs that under hormonal control and in pathological conditions can modify their expression levels and cellular localization, suggesting them as potential therapeutic targets in obesity and metabolic syndrome.