Reduction of perlecan synthesis and induction of TGF-beta1 in human peritoneal mesothelial cells due to high dialysate glucose concentration: implication in peritoneal dialysis

Prolonged exposure of the peritoneal mesothelium to high dialysate glucose concentrations reduces anionic sites that are critical to its selective permeability, thereby impairing the peritoneal transport properties in patients on long-term peritoneal dialysis (PD). Perlecan, an anionic heparan sulfate proteoglycan, is pivotal to the selective permeability of basement membranes, and high glucose concentrations modulate its synthesis in mesangial cells. The effect of glucose on perlecan expression in the peritoneal mesothelium has not been established. We investigated perlecan expression in peritoneal biopsies from patients on PD, and the effect of high glucose concentrations on perlecan synthesis in cultured human peritoneal mesothelial cells (HPMC). Peritoneal biopsies from PD patients showed reduced perlecan expression compared with controls. Exposure of HPMC to high glucose concentrations resulted in a dose-dependent reduction in the synthesis of perlecan polypeptide and its deposition into the extracellular matrix. These effects were mediated in part through the induction of TGF-beta1. Characterization studies showed that perlecan synthesized by HPMC contained solely heparan sulfate glycosaminoglycan (HS GAG) chains, and [(35)S]-incorporation studies demonstrated progressive reduction of their de novo synthesis with increasing glucose concentrations (68142 +/- 3658, 48147 +/- 2517, 31468 +/- 5781, and 25575 +/- 3621 cpm/ micro g cellular protein for 5 mM, 30 mM, 75 mM, and 120 mM D-glucose, respectively; P < 0.001 for 5 mM versus 30 mM D-glucose, and P < 0.0001 for 5 mM versus 75 mM or 120 mM D-glucose). Both the length and the charge density of the HS GAG chains remained unchanged. Reduction of peritoneal perlecan expression in long-term PD was attributed to high dialysate glucose concentrations, which induced TGF-beta1 and reduced perlecan synthesis in HPMC. Since perlecan can sequester growth factors, thereby modulating cell migration and differentiation perturbation of peritoneal perlecan expression contributes to the structural and functional changes of the peritoneum in long-term PD.