The relationship between peritoneal transport characteristics and messenger RNA expression of aquaporin in the peritoneal dialysis effluent of CAPD patients

Abstract: Background: Cell culture experiments show that peritoneal mesothelial cells express aquaporin-1 (AQP1) and aquaporin-3 (AQP3), which can be important for peritoneal transport. However, the functional relevance of aquaporin in mesothelial cells remains uncertain because endothelial cells are generally regarded as the major barrier of peritoneal transport. Methods: We studied 74 prevalent peritoneal dialysis (PD) patients. Peritoneal permeability was determined by the standard peritoneal equilibration test (PET). Messenger RNA (mRNA) was extracted from the peritoneal dialysis effluent (PDE) after PET, and the aquaporin gene expression was determined by quantitative polymerase chain reaction (PCR). Results: AQP3 mRNA expression in PDE correlated closely with peritoneal transport characteristics, including dialysate-to-plasma creatinine (Cr) ratio at 4 hr (D/P4) (r = 0.42, p = 0.007), mass transfer area coefficient (MTAC) of Cr (r = 0.60, p<0.0001), and net ultrafiltration (UF) (r = 0.34, p = 0.03). On the other hand, AQP1 mRNA expression did not correlate with D/P4 (r = 0.21, p = 0.2), MTAC of Cr (r = 0.05, p = 0.7), or with net UF (r = 0.17, p = 0.3). There was a modest correlation between AQP3 and connective tissue growth factor (CTGF) mRNA expression in PDE (r = 0.30, p = 0.06), while AQP1 expression correlated closely with CTGF expression (r = 0.56, p = 0.0002) and vascular endothelial growth factor (VEGF) expression (r = 0.37, p = 0.02). AQP3 expression was unaffected by dialysis duration or peritonitis history. The expression of neither AQP1 nor AQP3 correlated with that of transforming growth factor. Conclusions: Since mesothelial cells are the major source of aquaporin mRNA found in PDE, our findings support a functional role for mesothelial AQP3 in peritoneal transport. Our findings also suggest that AQP3 expression in vivo is regulated by mechanisms other than glucose exposure, peritonitis and traditional growth factors.