SMAD2 and pulmonary fibrosis: PPS significantly improved bleomycin-induced lung fibrosis in mice through ameliorating pathological damages of lung tissues; it exerted antifibrotic effects in vitro via inhibiting fibroblast-to-myofibroblast transition, suppressing ECM deposition, repressing lung fibroblast proliferation and migration, suppressing TGF-1β-induced Smad2/3 activating