Alterations in proteoglycan metabolism in the nephrotic syndrome induced by the aminonucleoside of puromycin.

The synthesis of intact proteoglycans and their glycosaminoglycan (GAG) side chains by isolated rat glomeruli in vitro were studied both at the onset (5 days) and at the point of maximal proteinuria (7 days) of the nephrotic syndrome induced with the aminonucleoside of puromycin. Glomeruli from nephrotic animals incorporated 1.5-fold and 3.0-fold more 35SO4 label into GAG than glomeruli from control animals at 5 and 7 days, respectively, with heparan-35SO4 GAG being responsible for the majority of the increment. Both nephrotic and control incubations contained 60% of the label in the incubation medium, 40% in the glomerular fractions, and less than 1% in the glomerular basement membrane. Glomerular basement membrane from nephrotic rats had no change in their total heparan-35SO4 GAG content. The majority of intact proteoglycan(s) from the glomerular matrix and from the incubation medium of nephrotic and control animals was found in the most buoyantly dense fraction of CsCl gradients (fraction 1). 35S-labeled material isolated from glomeruli of nephrotic animals showed a consistent shift toward lower density gradient fractions, indicating a decrease in their overall carbohydrate to protein ratio. Diethylaminoethyl chromatography of fraction 1 proteoglycan showed a single biphasic peak with the nephrotic rat having an increase in the proportion contributed by the earlier component of the peak. Fraction 1 proteoglycan(s) from the nephrotic experiment was found to have a smaller average hydrodynamic size by Sepharose CL-2B chromatography without a significant change in the corresponding 35S-GAG chain sizes (molecular weight 14,000) by Sepharose CL-6B chromatography. 35S-macromolecules from glomeruli of nephrotic and control rats that appeared in the middle of the CsCl gradients (fraction 3) had similar Sepharose CL-2B elution volumes, whereas the corresponding 35S-GAG chains from incubations of glomeruli from nephrotic animals were smaller. Increased synthesis of heparan sulfate proteoglycan by glomeruli from puromycin aminonucleoside-induced nephrotic rats may be compensatory to loss of another component of the glomerular filtration barrier or may result from abnormal interaction of proteoglycan(s) from nephrotic animals with other glomerular matrix constituents.