The anti-fibrotic drug pirfenidone inhibits liver fibrosis by targeting the small oxidoreductase glutaredoxin-1.

Activation of the hepatic stellate cells (HSCs) is a key pathogenic event in liver fibrosis. Protein S-glutathionylation (PSSG) of cysteine residues is a distinct form of oxidative response that modifies protein structures and functions. Glutaredoxin-1 (GLRX) reverses PSSG by liberating glutathione (GSH). In this study, we showed that pirfenidone (PFD), an anti-lung fibrosis drug, inhibited HSC activation and liver fibrosis in a GLRX-dependent manner. Glrx depletion exacerbated liver fibrosis, and decreased GLRX and increased PSSG were observed in fibrotic mouse and human livers. In contrast, overexpression of GLRX inhibited PSSG and liver fibrosis. Mechanistically, the inhibition of HSC activation by GLRX may have been accounted for by deglutathionylation of Smad3, which inhibits Smad3 phosphorylation, leading to the suppression of fibrogenic gene expression. Our results have established GLRX as the therapeutic target of PFD and uncovered an important role of PSSG in liver fibrosis. GLRX/PSSG can be both a biomarker and a therapeutic target for liver fibrosis.