Enhanced collagen synthesis in cultured skin fibroblasts from insulin-dependent diabetic patients with nephropathy

Abstract

Excessive production and deposition of extracellular matrix proteins are characteristic features of diabetic nephropathy. This study tests the hypothesis that cells from diabetic patients who develop nephropathy have a disturbance in collagen metabolism compared with cells from diabetic patients without complications. Kinetics of overall collagen metabolism and total protein synthesis were examined in serially passaged, subconfluent, quiescent skin fibroblasts cultured in either normal (5 mM) or high (25 mM) glucose concentrations from 14 insulin-dependent diabetic (IDDM) patients with nephropathy; 14 IDDM patients without nephropathy matched for age, diabetes duration, and body mass index; and 14 healthy subjects. Fibroblasts were incubated in the presence of 2 μCi/ml [3H]proline, and after labeling the incorporation of [3H]proline into total protein, collagen (collagenase-sensitive material), and noncollagen proteins (collagenase-resistant material) was determined at different time points. Collagen degradation was determined in pulse-chase experiments by following the residual collagen-bound radioactivity after incubation for 8 h with 10 μCi/ml [3H]proline. In high glucose concentrations (25 mM), overall collagen synthesis (measured as [3H]proline incorporation into extracellular and intracellular collagenase-sensitive material) was significantly greater in the patients with nephropathy (mean ± SEM after a 24-h labeling period: 7189 ± 671 dpm/106 cells) than in the patients without (4341 ± 267 dpm/106 cells; P < 0.01) or healthy control subjects (3836 ± 234 dpm/106 cells; P < 0.01). No significant differences were observed in noncollagen protein production or in collagen degradation rates among the three groups of subjects. In the presence of normal glucose concentrations (5 mM), collagen synthesis was lower in all groups studied, but the differences between IDDM patients with nephropathy and those without remained unaltered. These results suggest that long-term cultured fibroblast derived from diabetic patients with nephropathy exhibit an abnormality in collagen metabolism. Cells from long-standing diabetic patients without nephropathy have normal collagen metabolism. The increased collagen synthesis is likely to be intrinsic to those diabetic patients susceptible to nephropathy and may play an important role in the sclerotic processes that occur in the kidneys, arteries, and heart.