The role ofglycosaminoglycan N-sulfation in glomerular biology/pathobiology

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The incidence of chronic kidney disease (CKD) in adults 60 and older increased from 18.8 to 24.5 percent between 1988-1994; currently this has risen to 26 percent. The mortality rate resulting from end stage renal disease (ESRD) is 150/1000 individuals in the population. In light of this information, it becomes important to identify key pathways that contribute to the development and the progression of CKD/ESRD. Over the past decade it has become recognized in the renal field that the glomerular podocyte is a key and critical determinant in the regulation of glomerular homeostasis. Recent studies have shown that the β1 integrins, primarily the α3β1 integrin heterodimer, mediate podocyte/glomerular basement membrane (GBM) interactions. It is also well known that integrin affinity for its respective ligand can be modified by the activity of intracellular signaling pathways (inside-out signaling or affinity modulation) and/or by the activity of cell surface co-receptors. Previous studies in other cell systems have shown that several members of the syndecan (Sdc) family of cell surface proteoglycans serve as cell adhesion co-receptors, which function alongside integrins in the formation of focal adhesions in most cells. Unlike integrins, the binding of Sdcs to their respective ligands is mediated primarily by the heparan sulfate glycosaminoglycan chains (HS) that are covalently attached to Sdc core proteins. Because the HS chains are capable of engaging/binding multiple ligands along the length of their chains, the interactions mediated by Sdc are promiscuous (many different ligand targets) and multiplexed (many ligand binding sites per HS chain). There is a degree of specificity in the HS-ligand interactions that is derived from the post-assembly modifications to HS, one key modification is the modification of the nascent carbohydrate chain during its assembly by the enzyme NDST1 (N- deacetylase-N-Sulfotransferase). The overarching Hypothesis for this current proposal is that decreased N- sulfation of heparan sulfate proteoglycans and/or modification of the HS binding sites on matrix protein ligands accelerates the development of diabetic nephropathy in individuals afflicted with either type I or type II diabetes mellitus. To test this hypothesis we propose the following Specific Aims: 1.) To conduct in vivo studies on potential changes in either the rate of development or the degree of progression of diabetic nephropathy in the kidneys of animal models in which NDST1 has been deleted in glomerular podocytes; 2.)To explore the effects of hyperglycemia on podocyte-matrix interactions in vitro in cells deficient for the enzyme NDST1.