INDUCTION OF NODULAR SCLEROSIS BY INSULIN IN RAT MESANGIAL CELLS IN-VITRO - STUDIES OF COLLAGEN

These studies evaluated the contribution of insulin to the development of the abnormal mesangial matrix that characterizes diabetic nephropa thy and is common to mesangial cells in culture. Glomeruli were isolat ed from a single rat and divided into two aliquots. In one set (SI(-)M C), the insulin contained in the medium was only that contributed by t he fetal calf serum (20%). For the other set, the tissue culture mediu m was supplemented with 1 mu M insulin (SI(+)MC). Mesangial cell outgr owths from each condition were isolated, cloned, and propagated. At pa ssage 4, mesangial cells were characterized by morphology and cell mar kers, and compared in terms of composition and appearance of the secre ted extracellular matrix. SI(-)MC grew in nests of cells surrounded by a thin layer of matrix that was rich in collagen IV. In contrast, mes angial cells supplemented with insulin aggregated into macroscopic ''h illocks'' rich in collagens I and III as described previously. Insulin (1 mu M) Or IGF-I (0.1 mu M) was subsequently added to the medium of SI(-)MC. Insulin, but not IGF-I, induced a change in culture morpholog y and collagen accumulation characteristic of SI(+)MC. In contrast to SI(+)MC, SI-MC express insulin receptors and at physiologic concentrat ions insulin is a more potent stimulator of MC proliferation than is I GF-I. Insulin-induced changes in the collagenous composition of the ac cumulated ECM were directionally correlated with the rate of collagen I synthesis measured by biosynthetic labeling experiments and collagen s III and IV as determined by ELISA. These data demonstrate that insul in alters the phenotype of mesangial cells in culture and their expres sion of interstitial and basement membrane collagens. These observatio ns implicate insulin as a factor in the pathogenesis of mesangial matr ix accumulation in diabetic nephropathy. Furthermore, a method for cul turing mesangial cells that accumulate an extracellular matrix that is similar in composition to normal mesangial matrix provides a new mode l system for future studies of mesangial cell biology.