Background: Transforming growth factor-beta (TGF-beta) has been implicated in the development of renal fibrosis induced by unilateral ureteral obstruction (UUO). However, there is little information on signaling pathways mediating TGF-beta activity involved in molecular and cellular events leading to renal fibrosis induced by UUO. In this study, we sought to determine whether Smad3, a major signaling component of TGF-beta, mediated renal fibrosis induced by UUO.
Methods: Renal fibrosis, inflammation, and apoptosis induced by UUO were macroscopically and histologically compared between wild-type mice and Smad3 null mice.
Results: Gross appearance of the kidney after UUO showed relatively intact kidney in Smad3 null mice [Smad3(-/-) mice] when compared with that of wild-type mice [Smad3(+/+) mice]. Renal interstitial fibrosis based on the interstitial area stained with Aniline-blue or Sirius red solution was significantly attenuated in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Deposition of type I and type III collagens were also significantly reduced in the obstructed kidney of Smad3(-/-) mice. In addition, the numbers of myofibroblasts, macrophages, and CD4/CD8 T cells infiltrated into the kidney after UUO were significantly attenuated in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Furthermore, terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) staining after UUO showed significantly reduced number of tubular apoptotic cells in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Endogenous Smad pathway was activated in the obstructed kidney after UUO in wild-type mice as judged by the increase of phosphorylated Smad2 or phosphorylated Smad2/3-positive cells in renal interstitial area.
Conclusion: Smad3 deficiency attenuated renal fibrosis, inflammation, and apoptosis after UUO, suggesting that Smad3 was a key molecule mediating TGF-beta activity leading to real fibrosis after UUO.