Disturbances in Glomerular Basement Membrane Glycosaminoglycans in Experimental Diabetes

Abstract

Glycosaminoglycans (GAGs) were purified from basement membranes isolated from glomeruli of control and streptozocin-induced diabetic rats and were quantitatively analyzed with a recently described competitive binding assay that is specific for and sensitive to microgram amounts of chondroitin and heparan sulfate. Total GAG content in glomeruli from diabetic rats and in the basement membranes prepared from these samples (17.22 ± 1.45 and 6.56 ± 0.49 μg/105 glomeruli, respectively) was significantly less than that found in comparable control preparations (43.71 ± 3.35 and 16.05 ± 1.41 μg/105 glomeruli, respectively). The portion of total GAG in the water-soluble fraction recovered after osmotic lysis of isolated glomeruli was also markedly decreased in diabetic samples (26.11 ± 4.55 vs. 3.30 ± 0.32 μg/105 glomeruli, control vs. diabetic). Treatment of lysed glomeruli with the ionic detergent deoxycholate, required for liberation of the extracellular matrix from plasma membrane lipoproteins and purification of the insoluble glomerular basement membrane (GBM), resulted in solubilization of ∼10% of the waterinsoluble GAG in control samples but >50% in diabetic membranes. Heparan sulfate comprised >90% of the GAGs in both control and diabetic GBM, defined as the water- and detergent-insoluble matrix. The findings clearly demonstrate that the GAG content of GBM is diminished in experimental diabetes and provide evidence that the reduction in GBM anionic sites associated with diabetes derives from a decrease in the constituent GAGs of this extracellular matrix. The results further suggest that the interaction between GBM and populations of GAG associated with the surface of plasma membranes of adjacent cells is disturbed in diabetes.