SR9009 attenuates TGF-β1-induced renal fibrotic responses by inhibiting the NOX4/p38 signaling pathway in NRK-49F cells.

The circadian clock protein reverse erythroblastosis virus (REV)-ERBα is implicated in the pathogenesis of various diseases, including cancer and myocardial infarction. Emerging evidence suggests that SR9009, an agonist of REV-ERBα, regulates multiple signaling molecules independent or dependent of REV-ERBα. However, the impact of SR9009 on renal fibrosis remains largely unevaluated. In this study, we investigated the effects of SR9009 on transforming growth factor (TGF)-β1-induced fibrotic responses and elucidated the mechanisms involved. Masson's trichome staining revealed that in the unilateral ureteral obstruction groups, there was a decrease in REV-ERBα expression, accompanied by increased levels of the profibrotic factor TGF-β1 and the fibrosis marker α-smooth muscle actin (α-SMA). REV-ERBα knockdown significantly increased α-SMA expression in NRK-49F cells. SR9009 significantly attenuated unilateral ureteral obstruction-induced fibrosis and TGF-β1-induced fibrotic responses in normal rat kidney fibroblasts (NRK-49F cells). Conversely, the REV-ERBα antagonist SR8278 did not affect TGF-β1-induced fibrotic responses. Mechanistic studies revealed that SR9009 significantly inhibited the phosphorylation of ERK and p38, concomitant with reduced α-SMA levels, suppressing TGF-β1-induced NADPH oxidase 4 (NOX4) mRNA expression in NRK-49F cells. Notably, SR9009 did not influence the expression of dual specificity phosphatase 4, which dephosphorylates MAPKs, including p38. Furthermore, REV-ERBα knockdown did not affect the ability of SR9009 to inhibit TGF-β1-induced fibrotic responses and NOX4 expression in NRK-49F cells. In conclusion, SR9009 exerts a protective role against renal fibrosis independent of REV-ERBα. Therefore, SR9009 is a promising therapeutic agent for the prevention and treatment of renal fibrosis associated with renal failure.