Studies on Macromolecular Components of Human Glomerular Basement Membrane and Alterations in Diabetes: Decreased Levels of Heparan Sulfate Proteoglycan and Laminin

Abstract

Treatment of human glomerular basement membrane (GBM) with 4 M guanidine HCI resulted in a preferential extraction of noncollagenous components including laminin, fibronectin, entactin, and heparan sulfate proteoglycan, whereas effective solubilization of type IV collagen required exposure to denaturing solvents in the presence of reducing agents. The guanidine HCI–solubilized constituents were identified by immunochemical procedures after resolution by polyacrylamide gel electrophoresis, CL-6B filtration, and DEAE-cellulose chromatography. Two immunologically related heparan sulfate proteoglycans (Mr ∼350,000 and 210,000) were observed by electrophoresis, with the higher-molecular-weight form being predominant. An examination of the two proteoglycans after heparitinase digestion or chemical deglycosylation indicated that heparan sulfate chains and other carbohydrate units are attached to core proteins with Mr ∼140,000 and 110,000, respectively. Radioimmunoassays indicated that human diabetic GBM contained significantly lower (P < .005) amounts of heparan sulfate proteoglycan and laminin with average values that were 30 and 60%, respectively, of nondiabetic controls; the fibronectin content of the diabetic GBM, however, was not significantly different from the normal. These findings, together with previous studies showing increases in GBM collagen, indicate that an alteration in the macromolecular architecture of this basement membrane occurs in diabetes that may be responsible for the filtration defect and the ultimate glomerular occlusion.