Regulation of type IV collagen alpha chains of glomerular epithelial cells in diabetic conditions.

An early feature of diabetic nephropathy is the alteration of the glomerular basement membrane (GBM), which may result in microalbuminuria, subsequent macroproteinuria, and eventual chronic renal failure. Although type IV collagen is the main component of thickened GBM in diabetic nephropathy, cellular metabolism of each alpha chains of type IV collagen has not been well studied. To investigate the regulation of alpha(IV) chains in diabetic conditions, we examined whether glucose and advanced glycosylation endproduct (AGE) regulate the metabolism of each alpha(IV) chains in the diabetic tissue and glomerular epithelial cells (GEpC). Glomerular collagen alpha3(IV) and alpha5(IV) chains protein were higher and more intense in immunofluorescence staining according to diabetic durations compared to controls. In vitro, mainly high glucose and partly AGE usually increased total collagen protein of GEpC by [(3)H]-proline incorporation assay and each alpha(IV) chain proteins including alpha1(IV), alpha3(IV), and alpha5(IV) in time-dependent and subchain-specific manners. However, the changes of each alpha(IV) chains mRNA expression was not well correlated to the those of each chain proteins. The present findings suggest that the metabolism of individual alpha(IV) chains of GBM is differentially regulated in diabetic conditions and those changes might be induced not only by transcriptional level but also by post-translational modifications.