Age-related changes in the plasma membrane proteoglycans of rat kidney glomerular cells

In a previous in vivo study, we showed that the glomerular cells of rat kidney synthesize both peripheral and integral plasma membrane proteoglycans. The present work focuses on the age-related changes in these cell membrane proteoglycans. The peripheral proteoglycans in "adult control" rats aged 3 months were found to be heparan sulfate, dermatan sulfate, and chondroitin sulfate, with heparan sulfate being the main glycosaminoglycan. The integral membrane proteoglycans contained mainly dermatan sulfate plus less amounts of heparan sulfate. The relative proportions of the glycosaminoglycans in the integral membrane proteoglycans changed between 1 and 3 months. In addition, the degree of sulfation increased in both families of proteoglycans, and this was associated with an increase in glycosaminoglycan synthesis in the peripheral proteoglycans. The nature and relative proportions of the glycosaminoglycans forming the proteoglycans, did not change with age, after 10 months, and neither did the amount of glycosaminoglycans. But, the degree of sulfation of both peripheral and integral membrane proteoglycans decreased. De novo synthesized proteoglycans from 24-month-old rats had a higher overall charge than did those at other ages, owing to the presence of sulfate and carboxylic groups. We conclude that, as for glomerular basement membrane proteoglycans, biochemical alterations affect the glomerular cell membrane proteoglycans with aging.