Abstract

Progressive renal fibrosis is considered to be the final common pathway leading to chronic renal insufficiency, however, the mechanism regarding renal fibrosis in renal injury is not well understood. Recently, several kinds of cytokines have been known to be related to fibrosis after renal injury. The interaction between elements regulating fibrogenesis would be better understood by looking at the effect of TGF-beta1 on the synthesis and accumulation of extracellular matrix, especially collagenous proteins. Crescentic glomerulonephritis (CGN) was induced in New Zealand White rabbits by administration of guinea pig anti-GBM IgG after sensitization with guinea pig IgG; and their kidneys were analyzed for the development of crescents and fibrosis through sequential renal biopsies. Serum creatinine levels in a time course progressively increased until day 15. We semi-quantitatively assayed the levels of the expression of alpha1(I) collagen mRNA and TGF-beta1 mRNA factored for GAPDH mRNA using RT-PCR. We observed a progressive interstitial fibrosis and the expression of collagen I both in the cortex and medulla. The effect of repeated renal biopsy itself on pathology and on the expression of alpha1(I) collagen mRNA and TGF-beta1 mRNA in a time course were not significant, but a very mild increase of the expression of alpha1(I) collagen mRNA was noted at day 15. Histology showed a progressive crescent formation and interstitial fibrosis in a time course that roughly paralleled the expression of alpha1(I) collagen mRNA in both cortex and medulla. TGF-beta1 mRNA was hardly expressed at day 0 in cortex as well as in medulla. It was elevated from day 1, peaked at day 7, and then decreased. In medulla, TGF-beta1 mRNA was noticeably expressed at day 1, peaked at day 4, and then decreased. The expression of alpha1(I) collagen mRNA was seen even before inducing CGN. It was gradually and continuously increased until day 15 both in cortex and medulla. These results suggest that the expression of TGF-beta1 mRNA precedes that of alpha1(I) collagen mRNA in the early stage of CGN and has a central role for provoking the accumulation the collagen I, the most representative interstitial extracellular matrix, in the rabbit model CGN induced by anti-GBM antibody. We conclude that the measurement of the expression of TGF-beta1 mRNA and/or alpha1(I) collagen mRNA in a biopsy sample can be a useful predictor for renal outcome.

• Keywords: Anti-GBM disease;Fibrosis;Extracellular matrix mRNA;Collagen I;TGF-beta