Effects of IGF-I and glucose on protein and proteoglycan synthesis by human fetal mesangial cells in culture.
Abnormalities in proteoglycan metabolism have been implicated in the pathogenesis of diabetic nephropathy. Whether hyperglycemia plays a direct role in these events is unknown. To evaluate the effects of high glucose concentrations and insulinlike growth factor I (IGF-I) on kidney proteoglycan and protein metabolism, we incubated quiescent, subconfluent human fetal mesangial cells for 24 h in serum-free media containing either physiological (5.6-mM) or elevated (25-mM) glucose concentrations with or without 1.3 x 10(-9) M IGF-I. In the presence of physiological glucose concentrations, IGF-I stimulated incorporation of [3H]leucine into protein and [35S]sulfate or [3H]glucosamine into proteoglycans. High glucose concentrations significantly amplified IGF-I-mediated stimulation of protein synthesis but totally abolished IGF-I-induced proteoglycan synthesis. The hydrodynamic size and proportions of heparan-35SO4 and chondroitin/dermatan-35SO4 proteoglycans in all experimental media were the same. However, high glucose concentrations decreased the iduronic acid content of dermatan-35SO4. In separate experiments, quiescent cells were cultured for 7 days in media supplemented with 2% fetal calf serum. IGF-I had no effect on mesangial cell proliferation, but as cells reached confluence, high glucose concentrations significantly inhibited cell proliferation. This inhibition was not mimicked by isosmolar concentrations of mannitol. After 7 days, uptake of radioactive precursors into proteoglycans and proteins over 24 h was similar under all culture conditions. However, IGF-I decreased the ratio of [35S]sulfate to [3H]glucosamine in proteoglycans and their glycosaminoglycan side chains. This difference persisted in disaccharides derived by chondroitin ABC lyase digestion of dermatan-35SO4.(ABSTRACT TRUNCATED AT 250 WORDS)
Moran
A
A
Department of Pediatrics and Laboratory Medicine, Medical School, University of Minnesota, Minneapolis.
Brown
D M
DM
Kim
Y
Y
Klein
D J
DJ
D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005333:Fetus; D005920:Glomerular Mesangium / Q000187:drug effects* / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D006023:Glycoproteins / Q000096:biosynthesis; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D014176:Protein Biosynthesis; D011509:Proteoglycans / Q000096:biosynthesis*
D006023:Glycoproteins; D011509:Proteoglycans; D007334:Insulin-Like Growth Factor I; D005947:Glucose