Molecular biological approach to the abnormalities of extracelluar matrix of the diabetic nephropathy.

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Extracellular matrix has been shown to be consisted of collagens, laminins and proteoglycans. In diabetic nephropathy, the altertions of biochemical properties of type IV collagen and the decreased expression of proteoglycans are considered to be major pathological changes of the disease and related to the phenotypic changes of glomerular cells. Immunoelectron microscopic studies of diabetic nepropathy patients with nephrotic syndrome showed the thicking of glomerular basement membranes (GBM), increased amount of type IV collagens with decreased density, and decreased heparan sulfate proteoglycan. These alterations of extracellular matrix components seems to contribute to the the impairment of size and charge barrier of the GBM and proteinuria. Furthermore, we cloned a novel chain of type IV collagen, i.e.alpha4 chain, which cDNA (NK4) included NC-1 domain and expands 1.9 Kb. Northern blot analyzes showed -9.5 Kb transcript. Immunofluorescence studies of alpha1, alpha2, alpha3, alpha4, and basement membrane associated-collagen (BAC) showed alpha1 and alpha2 localized to the glomerular mesangial area and glomerular capillary, while alpha3 and alpha4 localized mainly along the capillary wall. BAC immunoreactivity was observed in the mesangial area. In the kidney of diabetic patients, expanded mesangial matrix and thickened GBM showed increased expression of alpha1-alpha4 chains and BAC.Furthermore, we analyzed the expression of the interstitial collagens, such as III,V,VI collagens. Type III collagen exclusively expressed in the interstinum of the kidney and type V and VI collagens had mesangial expressions. In diabetic kidney, these collagens were increased in the mesangial area.