Cell-associated proteoglycans of retinal pericytes and endothelial cells: modulation by glucose and ascorbic acid

Abnormalities of retinal pericytes and endothelial cells are prominent features of diabetic retinopathy. In this study, we used cultures of bovine retinal cells to examine the regulation of cell-associated proteoglycans, a class of highly sulfated macromolecules important in the regulation of cell growth. Bovine retinal pericytes and endothelial cells were radiolabeled with 35SO4 and cell-associated proteoglycans were removed from the cell surface, quantified, and characterized. The effects of high glucose concentration (25 mM), phorbol 12,13-dibutyrate (PDBu, 0.1 microM), and ascorbic acid (0.1 mM) on cell-associated proteoglycans and growth of these cells were studied. Our results showed that both the ionically bound and the membrane-intercalated forms of cell-associated proteoglycans are present on retinal cells. The predominant cell-associated proteoglycan of pericytes is chondroitin sulfate and for endothelial cells it is heparan sulfate. High glucose concentration and ascorbic acid increased the cell-associated proteoglycans on pericytes but reduced them on endothelial cells. In contrast to this divergent trend, high glucose concentration and ascorbic acid inhibited the growth of both pericytes and endothelial cells. The effects of high glucose on retinal cell-associated proteoglycans were mimicked by PDBu added in a manner to stimulate protein kinase C activity. We conclude that cell-associated proteoglycans are present on retinal pericytes and endothelial cells. High glucose concentration and ascorbic acid affect cell-associated proteoglycans of these two cell types in opposite directions, whereas both suppress the growth of the two cell types. Therefore, it is not likely that high glucose concentration and ascorbic acid change the rate of retinal cell growth directly by affecting cell-associated proteoglycan levels.