Human umbilical cord mesenchymal stem cells ameliorate liver fibrosis in vitro and in vivo: From biological characteristics to therapeutic mechanisms

Figure 3 TGF-β1 receptors and intracellular signal transmission. TβR type I, type II and type III have high affinity with TGF-β1. The TβR-III recruits TGF-β1 and submits it to TβR-II, activating TβR-II phosphorylation kinase when it combines to type II receptors. Then, they are recognized and combined by TβR-I, forming a tetramer ligand receptor complex and initiating downstream signaling pathways. TβR: TGF-β receptor; TGF: Transforming growth factor.