Retention of glomerular basement membrane-proteoglycans accompanying loss of anionic site staining in experimental diabetes.

The occurrence of heparan sulfate proteoglycan anionic site staining in the glomerular basement membranes of healthy and streptozotocin-induced diabetic rats was investigated. After 12 weeks diabetes, a marked loss of staining by ruthenium red was observed, compared with the age-matched controls. However, extraction and quantitation of total proteoglycan from the glomerular basement membrane revealed no significant differences between the two groups, in terms of absolute yield of glycosaminoglycan, when the latter is expressed per glomerulus. Glomerular basement membranes from both groups become thicker in an age-dependent manner, although they do so at a faster rate in the diabetic group, and a higher collagen content is found in the diabetic membrane at 12 weeks. Thus when proteoglycan content is expressed per mass protein, relative decreases are observed in diabetes. Similarly, a relative but not absolute decrease in proteoglycan content was observed in glomerular basement membranes from spontaneously diabetic BB rats with diabetes of 12 weeks duration. Glycosaminoglycans isolated from control and diabetic glomerular basement membrane have similar characteristics on ion exchange chromatography, to each other, and to newly sulfated, intact glomerular proteoglycans labelled in vitro. We conclude that loss of anionic site staining with ruthenium red in early diabetes is not a consequence of absolute loss or undersulfation of heparan sulfate proteoglycan but reflects structural or biochemical changes in the diabetic matrix.