Aquaporins in adipocytes:insights into the pathophysiology of human obesity

Tese de doutoramento, Farmácia (Bioquímica), Universidade de Lisboa, Faculdade de Farmácia, 2014

Adipocyte glycerol permeability has been appointed as a novel regulator of adipocyte metabolism and whole body fat mass. Up to now, Aquaporin-7 (AQP7) has been the mainly characterized protein in adipocytes with known ability to transport glycerol. However, the glycerol pathways in adipocytes are not yet fully understood. For these reasons AQP7 activity was further characterized in adipocytes, and its water and glycerol permeabilities were determined. The regulatory mechanisms of water and glycerol permeability in adipocytes were also investigated, being given special emphasis to the regulation of AQP7. Within the search for alternative glycerol channels in mice and human adipocytes, it was also investigated the presence of unexpected aquaporins in these cells. Our studies led us to conclude that both human and mouse AQP7 are functional water and glycerol channels when expressed in adipocytes. Regarding the mechanisms of AQP7 modulation it was detected the inhibition of both mice and human AQP7 activity by a gold (III) coordination compound. Methionine residues have been identified as possible binding sites for gold ions. It was also tested the effect of dietary conjugated linoleic acid (CLA) on adipose cells membrane permeability to water and glycerol. It was observed that CLA supplementation in obese Zucker rats reduces the fluidity and permeability of adipose membranes, whereas in 3T3-L1, CLA supplementation during adipocytes differentiation increases glycerol permeability. The search for novel aquaporins in adipose tissue led us to detect AQP11 in both subcutaneous and visceral human mature adipocytes. Moreover, it was observed that AQP11 is primarily located intracellularly in human adipocytes and that it partially colocalizes with perilipin, pointing towards AQP11 preferential location in the vicinity of lipid droplets. Very importantly, it was described for the first time the specificity of human AQP11 for both water and glycerol when expressed in adipocytes.

Fundação para a Ciência e a Tecnologia (FCT, SFRH/BD/45930/2008)