REGULATION OF RAT GLOMERULAR EPITHELIAL-CELL PROTEOGLYCANS BY HIGH-GLUCOSE MEDIUM

In diabetic nephropathy the heparan sulfate proteoglycan (HSPG) conten t of the glomerular basement membrane (GBM) is reduced but the cellula r mechanisms involved have not been studied. Glomerular epithelial cel ls (GEC) are thought to be the source of HSPG present in the GBM. In t his study we examined if proteoglycan metabolism of the rat GEC in cul ture is dysregulated in a metabolic environment simulating diabetes. F ollowing incubation for 8 days with a serum-supplemented medium contai ning 30 mM glucose and no added insulin, a significant increase in the overall synthesis of (SO4)-S-35-labeled molecules by the GEC was seen compared to control monolayers incubated with medium containing 5 mM glucose and insulin. Ion exchange chromatography revealed that 30 mM g lucose did not alter the anionic charge density of proteoglycans, but significantly increased the amount of S-35-labeled low-anionic macromo lecules in the medium; mannitol induced similar changes. Sepharose CL- 4B chromatography, glycosaminoglycan analysis and immunoprecipitation of control cell layer proteoglycans demonstrated the presence of HSPG of hydrodynamic size, K-av 0.4, resembling rat GBM HSPG in size and an tigenic nature. Incubation of GEC with 30 mM glucose resulted in a sig nificant reduction (58%) in this HSPG species, an effect not seen with equimolar mannitol. Additionally, 30 mM glucose induced a significant increment in synthesis of a small HS species (K-av 0.71 on Sepharose CL-4B column) present in the cell layer. Our findings suggest that bot h osmotic and nonosmotic mechanisms are operative in dysregulation of glycopeptide metabolism by high-glucose medium and that reduced synthe sis by the GEC may contribute to decreased content of GBM HSPG in diab etic nephropathy. (C) 1994 Academic Press, Inc.