Background. The present study tested the hypothesis that disruption of Smad7 function may accelerate renal fibrosis and inflammation.

Methods. This was investigated in a unilateral ureteral obstruction (UUO) model induced in wild-type (WT) and Smad7ΔE1 mice in which functional Smad7 is disrupted by deleting exon I in the Smad7 gene. Renal fibrosis and inflammation after UUO were examined by histology, real-time PCR, western blot analyses and immunohistochemistry.

Results. Seven days after UUO, severe tubulointerstitial fibrosis developed in WT mice as evidenced by a marked increase in α-SMA, collagen I and III extracellular matrix. This was associated with a significant upregulation of renal TGF-β1 and CTGF and activation of Smad2/3. Interestingly, compared to WT UUO mice, Smad7ΔE1 mice with UUO exhibited a further increase in TGF-β/Smad2/3-dependent renal fibrosis. Moreover, compared to WT UUO mice, deletion of the Smad7 gene also sustained NF-κB activation and thus enhanced further renal inflammation such as macrophage infiltration and upregulation of TNF-α, MCP-1, OPN and ICAM-1.

Conclusion. Smad7 is a critical negative regulator of TGF-β/Smad2/3 and NF-κB signalling and plays a negative regulating role in both renal fibrosis and inflammation after UUO. Results from this study further support the notion that Smad7 may be a therapeutic agent for kidney diseases.