SMAD2 and idiopathic pulmonary fibrosis: Some examples of in vivo studies regarding altered roles of miRs in IPF are summarized as follows (72): (1) miR-21 expression level is significantly elevated in the lungs of mice treated with bleomycin or TGF-β and implicated in the pro-fibrogenic activities of TGF-β through suppressing the transcription of inhibitory Smad7 in the TGF-β/Smad signaling pathway-Smad7, as an inhibitory factor negatively regulates the activity of Smad2 and Smad3 by preventing the binding of Smad2/3 to the TGF-β receptors (69, 73, 74), (2) the expression of miR-155 was also up-regulated in a mouse model of PF.