Expression of aquaporin-1 in human peritoneal mesothelial cells and its upregulation by glucose in vitro

Aquaporin (AQP) is a family of water channels that are highly selective for the passage of water and occasionally glycerol. In previous studies, only AQP1 was found in human peritoneal endothelial cells in both control subjec ts and patients on peritoneal dialysis. As human peritoneal mesothelial cel ls (HPMC) play an important role in dialysis adequacy and fluid balance in continuous ambulatory peritoneal dialysis patients, this study examined whe ther AQP1 is present in HPMC, It was found that AQP1 mRNA and protein are p resent in HPMC constitutively. The localization of AQP1 protein in peritone al mesothelial cells was confirmed by double immunohistochemical staining o f the mesothelial lining of human peritoneal membrane. More important, the expression of AQP1 in HPMC is not constitutive and the transcription and bi osynthesis of AQP1 in HPMC is inducible by osmotic agents such as glucose a nd mannitol, There was significant enhancement of AQP1 biosynthesis upon ex posure to glucose in a time- and dose-dependent manner (P < 0.0001). Simila r findings were observed in the AQP1 biosynthesis by an endothelial cell li ne, EA.hy 926. Of particular interest, the upregulation in AQP1 mRNA or bio synthesis in mesothelial cells was always significantly higher than that of endothelial cells when the experiments were conducted under identical sett ings (P < 0.001). AQP1 expression in HPMC was demonstrated for the first ti me. Osmotic agents upregulate both mRNA and protein expression of this aqua porin, The role of AQP1 in HPMC in maintaining the ultrafiltration of the p eritoneal membrane is potentially of clinical interest.