Effects of advanced glycosylation endproducts on perlecan core protein of glomerular epithelium

Perlecan is one of major heparan sulfate proteoglycans in the glomerular basement membrane and is reduced in the renal parenchyma of diabetic patients and animals with proteinuria. To examine the effects of glucose and advanced glycosylated end-products (AGE) on perlecan, we cultured rat glomerular epithelial cells (GEpC) on AGE- or bovine serum albumin (BSA)-coated plates under normal (NG, 5 mM) and high-glucose (HG, 30 mM) conditions and measured the change in perlecan core protein production by a sandwich ELISA and northern blot analysis. We observed significant decreases of perlecan core protein under HG conditions at 1 week incubation, specifically on the AGE-coated compared with the BSA-coated surface, by 22.2% and 4.7%, respectively. The expression of mRNA for perlecan promoter was decreased under HG conditions on AGE-coated surfaces by 19.7% at 2 days and 61.1% at 1 week. Even under NG condition, the expression of mRNA was reduced by 30% at 1 week if GEpC were grown on an AGE-coated surface. In conclusion, HG and AGE have an additive effect in reducing the production of perlecan core protein by GEpC in vitro. AGE had a greater effect than HG, implying that the inhibition of AGE formation may be more effective than short-term glucose control in the prevention of diabetic proteinuria.