Cryptotanshinone protects against pulmonary fibrosis through inhibiting Smad and STAT3 signaling pathways

Cryptotanshinone (CTS), a lipophilic compound extracted from root of Salvia miltiorrhiza (Danshen), has demonstrated multiple pharmacological activities, including anti-inflammation, anti-proliferation and anti-infection. However, the effect of CTS on pulmonary fibrosis is unknown. This study aims to investigate the effects of CTS treatment on pulmonary fibrosis and its underlying mechanism. The pulmonary fibrosis model was established by intratracheal instillation of bleomycin (5 mg/kg) in Sprague-Dawley rats (in vivo) and stimulating human fetal lung fibroblasts (HLFs) with transforming growth factor-beta 1 (TGF-β1) (in vitro). CTS (7.5, 15, 30, 60 mg/kg/day) and pirfenidone (150 mg/kg/day, positive control) were administered by oral gavage for 28 days. In this study, we found CTS treatment improved pulmonary function, relieved pathological changes and attenuated the accumulation of extracellular matrix in pulmonary fibrosis rat model induced by bleomycin. Mechanistically, CTS suppressed phosphorylation of Smad2/3 and STAT3 induced by TGF-β1 in HLFs. Stattic, a 1-benzothiophene based small-molecule STAT3 inhibitor, resulted in a significant down-regulation of fibrosis biomarkers including fibronectin, collagen type I and alpha smooth muscle actin (α-SMA). Overexpression of STAT3 promoted expression of fibrosis biomarkers in HLFs cell model induced by TGF-β1 and partially blocked the inhibitory effect of CTS on TGF-β1-induced fibrosis response. Taken together, these results suggested that CTS protects against pulmonary fibrosis via inhibition of Smad and STAT3 signaling pathways. Thus, CTS may represent a promising drug candidate for treating pulmonary fibrosis.