During the course of their disease approximately 45% of IDDM patients manifest some degree of renal dysfunction and some will continue to progress over time toward renal failure, evidenced histopathologically as glomerulosclerosis. The histoarchitectural changes that occur during the progression toward glomerulosclerosis. The histoarchitectural changes that occur during the progression toward glomerulosclerosis have been well described and include glomerular hypertrophy, glomerular capillary basement membrane (GBM) thickening, and mesangial expansion. These changes are thought to be mediated in part by the overproduction of and/or the presence of biosynthetic defects in the molecules that contribute to the extracellular matrices of the GBM and mesangium. Although increases in the relative amounts of glycoprotein and collagenous components have been reported in the literature, some of the most profound effects of IDDM are on the proteoglycan component of the respective extracellular matrices. Two distinct basement membrane proteoglycan populations are known to exist: heparan sulfate (BM-HSPG) and chondroitin sulfate (BM-HSPG) and chondroitin sulfate (BM-CSPG) proteoglycans. In animal models of IDDM it has been shown that important posttranslational modifications to BM- HSPG's are altered, i.e. the synthesis of an undersulfated form that in turn affects molecular function. The principal investigator now shows that BM-CSPG, normally exclusive to the mesangial matrix, is found abnormally in the GBM of diabetic animals. Ongoing studies by the principal investigator suggest that the deposition of BM-CSPG in the subendothelial region of the GBM leads to disruption of the normal capillary histoarchitecture and eventual occlusion of affected capillaries. The results strongly suggest that the overproduction of BM- CSPG may be directly contributory to the sclerotic lesions seen in the latter stages of diabetic nephropathy. Because of these findings it now becomes important to understand the function and regulation of BM-CSPG at the molecular level.
The specific aim of the proposal is initiate studies to understand the cell and molecular biology of BM-CSPG as it relates to the progression of diabetic glomerulosclerosis. The project will address this specific aim through the following series of studies. 1. To determine the amino acid sequence of the core protein of BM-CSPG by cDNA sequence analysis 2. determine the effects of diabetes on BM-CSPG mRNA levels by northern blotting and in-situ hybridization. It is anticipated that the proposed studies will in part answer these questions and, at the same time, allow development the tools necessary for future studies which will examine the regulation of BM-CSPG mRNA transcription at the gene level.
