Iguratimod inhibits skin fibrosis by regulating TGF‐β1/Smad signalling pathway in systemic sclerosis

Iguratimod (T-614), exerting a powerful anti-inflammatory ability, has therapeutic efficacy in multiple autoimmune diseases. However, the effect of T-614 on systemic sclerosis (SSc) is unclear. Here, we investigate the effect and molecular mechanism of T-614 in experimental SSc models.In vitro, cultured dermal fibroblasts from four SSc patients were subjected to different doses of T-614 in the presence or absence of TGF-β1 stimulation. Cell proliferation, apoptosis and migration were determined by CCK-8, flow cytometry and transwell assay, respectively. Fibrosis markers and smad signalling pathway-related proteins were detected by immunoblotting and immunofluorescence. In vivo, a bleomycin-induced SSc mouse model was used to evaluate the effect of T-614 on skin fibrosis. Pathological changes in skin tissues were evaluated by HE, Masson staining and immunohistochemistry.In the study, we found T-614 inhibited TGF-β1-induced cell proliferation, migration and promoted apoptosis in a dose-dependent manner (all p < 0.01). T-614 partially reversed TGF-β1-induced upregulation of fibrosis markers and phosphorylation of smad2 and smad3 and blocked p-Smad3 nuclear translocation (all p < 0.05), suggesting T-614 may inhibit dermal fibroblasts activation by regulating TGF-β1/smad pathway. In vivo experiments, T-614 alleviated skin thickness in bleomycin-induced SSc mice (all p < 0.05). The expression of fibrosis markers and the infiltration of macrophages in skin tissue were significantly decreased after T-614 treatment (all p < 0.05).Our preliminary data indicated T-614 inhibited dermal fibroblasts activation and skin fibrosis at least partly by regulating TGF-β1/smad pathway in experimental SSc models and may be a promising therapeutic agent for SSc.