Diabetic nephropathy is a major cause of end-stage renal disease. In the present proposal we shall consider the potential contribution of non-enzymatic glycosylation to the pathogenesis of diabetic glomerulosclerosis, of which expansion of the mesangium is a hallmark. The study of cultured mesangial cells have already contributed considerably to our understanding of glomerular function. The mesangial cell not only responds to vasoactive agents but also generates prostaglandins, PAF, cytokines and matrix components. Mesangial cells are also capable of specific endocytosis of macromolecules. Our present knowledge on nonenzymatic glycosylation of proteins in DM and of the multiple functions of glomerular mesangial cells provide a clear rationale for the proposed studies. the use of the cultured mesangial cells and defined proteins allows experimental dissection of individual factors, an approach that could not be taken in vivo. The central hypothesis to be tested is: Formation of advanced nonenzymatic glycosylation products of mesangial matrix proteins and excessive glycosylatin of circulating plasma proteins effect mesangial cell function resulting in pathological expansion of the mesangium in the diabetic kidney. In order to test this hypothesis, we will examine the following specific questions on cultured rat mesangial cells: 1) Does non-enzymatic glycosylation alter the binding and uptake of proteins such as albumin, IgG, and low density lipoprotein by mesangial cells? 2) Does nonenzymatic glycosylation (as per question 1) alter the expression of autacoids and cytokines by mesangial cells and influence the generation of matrix? 3) Does advanced glycosylation of mesangial matrix alter its digestion by mesangial proteases? 4) Does advanced glycosylation of mesangial matrix influence cell proliferation, expression of cytokines and matrix components? The answer to these questions should provide insight into the consequences of nonenzymatic glycosylation of proteins on their mesangial accumulation, on generation of mesangial matrix and collagen, and thus eventually on diabetic glomerulosclerosis. This should allow identification of potentially pathogenetic steps, that may eventually help to design well targeted therapeutic intervention.
