Signaling mechanism of renal fibrosis in unilateral ureteral obstructive kidney disease in ROCK1 knockout mice

It has been shown that blockade of Rho kinase with pharmacologic inhibitors inhibits renal fibrosis. This study examined the role of Rho kinase in renal fibrosis in the unilateral ureteral obstruction (UUO) model in mice that do not express the ROCK1 gene, a critical downstream mediator of Rho GTPase. Unexpected, real-time PCR, Western blot, and immunohistochemistry demonstrated that, compared with the wild-type mice, mice with ROCK1 knockout (KO) were not protected against renal fibrosis at both the early (day 5) and late (day 10) UUO, as determined by histology and expression of both mRNA and protein levels of α-smooth muscle actin, collagen types I and III, and fibronectin within the diseased kidney. Then the mechanisms of loss of protective effect on renal fibrosis in ROCK1 KO mice were investigated. It is interesting that mice that lacked ROCK1 did not have altered expression of ROCK2 but significantly increased TGF-β expression and Smad2/3 activation (phosphorylation and nuclear translocation) in the diseased kidney at day 5, which remained high at day 10 of UUO. Similarly, primary cultures of kidney fibroblasts that were obtained from both ROCK1 wild-type and KO mice showed that deletion of ROCK1 did not prevent TGF-β-induced activation of Smad2/3 and collagen I expression. This also was observed in the presence of Rho kinase inhibitor Y-27632. Taken together, results from this study suggest that Rho/Rho kinase may not be a necessary or a central pathway for renal fibrosis in the UUO model. The interplay between the Rho/Rho kinase pathway and the Smad signaling pathway may be a key mechanism by which loss of ROCK1 does not prevent renal fibrosis in the UUO model.