SMAD3 and pulmonary fibrosis: Figure 7 shows that OST could inhibit TGF-β1-induced Smad3 activation, lung fibroblast differentiation, and collagen synthesis in vitro, and overexpression of NOX4 could eliminate this effect. Hence, OST blocks TGF-β1-induced pulmonary fibrosis by inhibiting NOX4-mediated oxidative stress and Smad3 activation.