SMAD2 and renal fibrosis: TGF-β1 triggers the trans-differentiation of the intrinsic cells not only via the downstream Smad2/3-dependent pathways, but also stimulates the Smad2/3-independent signaling, including MAPKs, Wnt/β-catenin, RhoA, and PI3K/Akt, which are implicated in renal fibrosis [75–78].