Synthesis of Type VI Collagen by Cultured Glomerular Cells and Comparison of Its Regulation by Glucose and Other Factors With That of Type IV Collagen

Homogeneous cultures of calf glomerular mesangial and endothelial cells were found to be active in the synthesis of type VI as well as type IV collagen in contrast to the epithelial cells that were devoted primarily to the production of the latter collagen. Studies with rat mesangial cells indicated that they responded to high glucose (20 mM) in the medium by a significant (P < 0.001) increase in type VI collagen synthesis as measured by the production of the protein and its mRNA level, both of which were closely correlated to each other and to glucose consumption. Similar observations were made with type IV collagen, but the enhanced formation of this protein was not as rapidly apparent as that of type VI and, moreover, could not be as readily reversed on restoration of the glucose to a physiological level (5 mM). Evaluation of a number of other agents indicated that although mannitol had no effect, L-glucose and NaCI significantly stimulated synthesis of both type VI and IV collagens and glucose consumption. Insulin-like growth factor I and aldosterone, on the other hand, also increased glucose consumption but brought about an enhancement of only type IV collagen production, suggesting that the two collagens are independently regulated. This possibility was supported by our observation that pyruvate, which was actively taken up by the cells, selectively stimulated type IV collagen production. Although the details of the regulation of these two major glomerular extracellular matrix components have not yet been defined, it is apparent that mesangial cells in culture reflect the enhanced formation of type VI and type IV collagen, which is evident in the diabetic glomerular lesions.