SMAD4 and pulmonary fibrosis: The protective role of baicalein against BLM-induced pulmonary fibrosis was partly independent in inhibiting TGF-β/Smad signalling, as shown by the improved lung architecture, decreased collagen deposition and amounts of hydroxyproline and type I collagen, as well as TGF-β1 production and phosphorylation of Smad2, Smad3 and Smad4 expression in the lung.