Diabetic nephropathy with renal failure is a major complication of diabetes mellitus which occurs in 35 to 45% of diabetic patients. Characteristic lesions of diabetic glomerulopathy include thickening of the glomerular basement membrane and a progressive expansion of the mesangial matrix which surrounds the mesangial cells. A number of studies have correlated the expansion of the mesangium with loss of renal function, in part due to a restriction of the filtering area. An interesting observation is that following pancreatic transplantation, when glucose levels become normalized, the renal function is restored and the mesangial expansion recesses whereas GBM thickening persists. These findings indicate the utmost importance of the mesangial space in the development of diabetic glomerulopathy and provide evidence that the mesangial expansion is directly related to hyperglycemia. Because mesangial cells secrete at least several components of the mesangial matrix (MM), one of which is type IV collagen, we propose to study interactions between the mesangial matrix, type IV collagen (tIV) and mesangial cells under control conditions and following exposure to high glucose levels. A major modification of long- lived proteins (like matrix proteins, i.e., type IV collagen) which occurs in the presence of high glucose is the process of non-enzymatic glucosylation which alters the proteins structurally and functionally. It is known that type IV collagen extracted from kidneys of diabetic animals and patients is non-enzymatically glucosylated. Our goal therefore is to test whether non-enzymatic glucosylation of type IV collagen and MM relate to the expansion of MM by causing altered interactions with the mesangial cells. Three questions will be asked: first, whether the adhesion and spreading of mesangial cells is different when these cells interact with unmodified versus non-enzymatically glucosylated tIV and intact, isolated GBM which also contains the mesangial matrix (GBM/MM); second, whether the growth rate of mesangial cells changes in response to non-enzymatic glucosylation of tIV and GBM/MM, when compared to their unmodified counterparts; and third, whether the biosynthesis of the (a1) and (a2) chains of tIV based on mRNA levels is increased in response to diabetic modifications of tIV and GBM/MM, when compared to their unmodified counterparts. These studies will seek to address a fundamental question, whether the abnormal expansion of the mesangium may be in part causally related to altered interactions between mesangial cells and their surrounding matrix and in particular tIV, as a consequence of non-enzymatic glucosylation of tIV and the MM in general. Therefore, these studies will contribute to a better understanding of the causes of diabetic mesangial expansion at a molecular level and will lead to seek means which may subsequently be used to prevent or minimize the process of non-enzymatic glucosylation.
