PATHOBIOLOGY OF FIBRONECTIN IN DIABETES MELLITUS

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Fibronectin is a high molecular weight glycoprotein present in plasma, cell matrices, basement membranes, and basal lamina. Major complications of diabetes mellitus (DM) are microvascular abnormalities and a nephropathy which parallels the development of glomerular basement membrane (GBM) thickening and enlarged mesangial volume detected by morphometry. A major component of the mesangial matrix and GBM is fibronectin (FN), and studies have shown increased amounts of fibronectin in the mesangium in diabetes. Studies will quantitate serum levels of fibronectin, level of nonenzymatic glycosylation of plasma fibronectin, plasma glucose levels, and non-enzymatic glycosylation of FN in renal tissue. Morphometric analysis of mesangial volume and GMB thickness will be correlated with fibronectin non-enzymatic glycosylation. Fibronectin is present at sites of the apparent pathology of the diabetic kidney and interacts with various other constitutents of the GBM or cell matrix such as proteoglycans and collagen. We next will define whether there are perturbations of any molecular interactions of FN in diabetes. Many of the interactions of FN with other ligands may be related to charge interactions which could be effected by excessive nonenzymatic glucosylation. This nonenzymatic glucosylation would also be at sites other than those seen with enzymatic glycosylation which occurs at restricted domains on the FN molecule. Monoclonal antibodies and other ligands will be used to isolate FN peptides which will be characterized by 2-D gels and for affinity of binding to heparin, collagen, etc., after excess nonenzymatic glycosylation. The next studies would determine why there is excess FN in diabetic kidneys. Studies will examine turnover and distribution of normal and non-enzymatically glycosylated FN in diabetic and nondiabetic animals. Radiolabelled or human FN, both normal or non-enzymatically glycosylated, will be transfused and counted or assayed at varying times by ELISA with species specific monoclonal antibodies. Next we will study the synthetic rate, turnover, and accumulation of fibronectin in glomerular cultures established from diabetic and non-diabetic animals. It will be very fruitful if an evaluation of a plasma constituent, fibronectin may give us a direct monitor of the microvascular and renal pathology which are so profound in insulin dependent diabetes mellitus.