Distribution of alpha-chains of type IV collagen in glomerular basement membranes with ultrastructural alterations suggestive of Alport syndrome.

Abstract

In Alport syndrome (AS) impaired production and/or assembly of col IV alpha-chain isoforms results in abnormal structure of glomerular basement membrane (GBM), haematuria and, frequently, progressive renal disease. We investigated the relationship between col IV alpha-chains expression and morphology of GBM, as a possible key to the better understanding of the pathogenesis of renal disease in AS. GBM distribution of col IV alpha1-, alpha3-, and alpha5-chain was investigated by immunohistochemistry in 32 patients (21 males and 11 females, mean age at biopsy of 11.5 years) with ultrastructural findings suggestive of AS. Ten patients had a proven COL4A5 mutation. Based on the severity of ultrastructural findings, the biopsies were grouped in three (I-III) electron microscopy (EM) classes. Significant EM changes of GBM (thinning, thickening, splitting, basket weaving of the lamina densa) were singularly evaluated using a semiquantitative scale (0-3). Col IV alpha1-chain was demonstrated in GBM of all patients. Three patterns of staining for col IValpha3- and alpha5-chains were observed: positive, negative, and alpha3(IV)-positive/alpha5(IV)-negative. By chi(2)-test, EM class III lesions and complete loss of alpha3(IV)- and alpha5(IV)-antigen were significantly more frequent (P<0.05 and P<0.01) in male patients, but no significant relation was observed between EM classes and immunohistochemical patterns. GBM alterations did not correlate with staining for alpha5(IV)-chain. Intensity of alpha3(IV)-chain staining, however, had a negative correlation (P<0.05) with the severity of GBM basket weaving. Our results suggest that the alpha3(IV)-chain-containing col IV-network plays a fundamental role in structural and, possibly, functional organization of GBM. Absence of alpha3(IV)-chain in GBM could indicate a more severe renal disease in AS.