Regulation of Glomerular Endothelial Cell Proteoglycans by Glucose

The presence of heparan sulfate proteoglycan (HSPG) in anionic sites in the lamina rara interna of glomerular basement membrane suggests that the proteoglycan may be deposited by the glomerular endothelial cells (GEndo). We have previously demonstrated that bovine GEndo in vitro synthesize perlecan, a species of glomerular basement membrane HSPG. In this study we examined whether high glucose medium regulates the GEndo metabolism of glycopeptides including perlecan. Metabolic labeling of glycoconjugates with 35S-SO4, sequential ion exchange and Sepharose CL-4B chromatography of labeled glycoconjugates, and northern analysis were performed. Incubation of GEndo for 8 to 14 weeks (but not for 1-2 weeks) in medium containing 30 mM glucose resulted in nearly 50% reduction in the synthesis of cell layer and medium 35SO4-labeled low anionic glycoproteins and proteoglycans, including that of basement membrane HSPG (Kav 0.42) compared to GEndo grown in 5 mM glucose medium; no changes in anionic charge density or hydrodynamic size of proteoglycans were noted. Northern analysis demonstrated that the mRNA abundance of perlecan was reduced by 47% in cells incubated with 30 mM glucose. Our data suggest that high glucose medium reduces the GEndo synthesis of perlecan by regulating its gene expression. Reduced synthesis of perlecan by GEndo may contribute to proteinuria seen in diabetic nephropathy.

Effects of Eligh Glucose and Advance Gilycosylation Endproducts(AGE) on the Heparan Sulfate Proteoglycan(HSPG) Produced by Cultured Rat Clomerular Epithelial Cells(GEC) / 대한신장학회잡지

HSPG, a component of size-and charge-selective barrier of glomerular basement membrane, is one of important matrix proteins which has been known to be reduced in the kidney of diabetic patients or animals. To examine the effects of glucose and AGE on the HSPG production by cultured GEC, we cultured rat GEC on the AGE- or BSA-coated plate under normal(5mM) and high glucose.(30mM) conditions and measured the change of HSPG production by sandwich-ELISA assay and northern blot analysis at 2 days and one week incubation periods. There was no difference in proliferation between 2 different conditions of culture plate surface. We measured the relative amount of the extracted HSPC and observed significant decreases in high glucose condition at one week incubation, and particularly on the AGE-coated surface as compared to the results of BSA-coated condition, by 22% and 5%, respectively. The expression of mRNA for perlecan promoter was decreased in condition of high glucose and AGE-coated surface by 20Yo at 2 days and 61i at one week. Even in normal glucose condition, the expression of mRNA was reduced by 30Yo at one week if the plate was coated with AGE. In conclusion, both high glucose and AGE have reducing effects on the production of HSPG by GEC in vitro. Their effects seem to be additive, however, the role of AGE is greater than that of glucose, This means that the effort to inhibit AGE formation is more important than short-term glucose control for the prevention of diabetic proteinuria.