SMAD2 and pulmonary fibrosis: TGF-β will induce lung epithelial cells and fibroblasts differentiated into myofibroblasts, upregulate the mesenchymal marker protein α-SMA expression, accelerate collagen deposition in the lung interstitial, and ultimately cause pulmonary fibrosis after binding to its receptors (TβRI and TβRII) and then activating Smad2/3 phosphorylation (45).