The chronic hyperglycemia of diabetes leads to serious complications that include diabetic nephropathy, the leading cause of end-stage renal disease. It is largely unknown how the elevated levels of glucose in plasma and tissues are translated into renal pathology, which is characterized by the expansion of mesangial matrix and thickening of glomerular basement membrane (GBM). Clearly, the effects of hyperglycemia on glomerular cells that interact with mesangial matrix and GBM in kidney are at the heart of pathogenic mechanisms of diabetic nephropathy. One of the major consequences of hyperglycemic conditions is the acceleration of glycation reactions, i.e., modifications of proteins by glucose forming advanced glycation endproducts or AGEs. Thus, the elevated glucose levels through glucose modification of proteins could bring about changes in glomerular cell behavior. These cellular changes result in modulation of expression of vascular adhesion molecules and growth factors, increased excretion of extracellular matrix proteins, and induction of pro-inflammatory responses. To understand such a complex pathogenic mechanism, global changes that occur in the cell proteins require identification at the molecular level. With this knowledge, new protein targets could be identified to address pathogenic mechanisms and develop new therapies. An earlier work in our laboratory has discovered that pyridoxamine (PM) is an in vitro inhibitor of protein-AGE formation. In vivo, PM prevented development of early renal disease in animal models of diabetes and is currently in Phase II clinical trials for treatment of diabetic nephropathy. Mechanism of PM action is unknown but it is likely that PM interferes with pathogenic cellular effects of glycated proteins. New proteomic technologies that allow characterizing cellular proteome offer a powerful tool for determining molecular mechanisms of diabetic nephropathy. This proposal will employ such technologies to study cellular changes brought about by hyperglycemia and glucose-modified proteins. We hypothesize that glucose and glucose-modified proteins induce complex changes in the proteome of glomerular cells altering their interaction with extracellular matrix and leading to development of diabetic nephropathy. This central hypothesis will be addressed in four specific aims designed to determine 1) the changes in the proteome of glomerular cells cultured under normal and diabetic levels of glucose; 2) the effects of glycated proteins on cellular proteome; 3) the identities of glomerular cellular receptors that interact with glycated proteins; and 4) the effect of a prospective drug pyridoxamine on changes in the proteome of glomerular cells induced by glucose and glucose-modified proteins. The unbiased proteomic approach that interrogates a totality of cellular proteins for pathogenic changes is likely to result in a new knowledge about the mechanisms of diabetic nephropathy and to identify possible cellular protein targets for novel therapeutic treatments.
