Localization of Smad 2, 3, 6, 7 and their changes of expression in experimental interstitial fibrosis model in rats

Objective To investigate the localization of Smad protein 2, 3, 6, 7 and their changes of expression in experimental interstitial fibrosis model in rats. Methods Thirty-six rats were divided into normal control, sham operation, and unilateral ureteral obstruction(UUO) groups, and were sacrificed at postoperative day 3, 7, 14, 21. The level of TGF-β1 mRNA was examined by RT-PCR. The sites and levels of expression of Smad protein 2, 3, 6, 7 were examined by immunohistochemistry staining and Western blot . Renal fibrosis was assessed by measuring tissue hydroxyproline. Results Compared to sham operation group, TGF-β1 mRNA was significantly increased in UUO rats, and this trend was positively correlated to increased hydroxyproline content. Immunohistochemistry staining studies indicated that Smad protein 2, 3 mainly expressed in renal tubular cells, rarely in glomeruli, and Smad protein 6, 7 were presented in both the glomeruli and proximal renal tubular cells. Expression of the Smad protein 2, 3 were significantly increased from day 3 to 21 after UUO, while the Smad protein 6, 7 were significantly reduced in the obstructive kidney. Conclusions TGF-β1/Smad signaling is involved in the progression of renal tubulointerstitial fibrosis. The absence of up-regulation of these anti-Smads proteins may be the major cause of the interstitial fibrosis in this model.