Sirtuin 6 inhibits myofibroblast differentiation via inactivating transforming growth factor‐β1/Smad2 and nuclear factor‐κB signaling pathways in human fetal lung fibroblasts

Fibroblast‐to‐myofibroblast differentiation, which is characterized by increased expression of α‐smooth muscle actin, is known to be involved in the pathogenesis of idiopathic pulmonary fibrosis. Sirtuin 6 (SIRT6), a member of the sirtuin family, has been proved to inhibit epithelial‐to‐mesenchymal transition during idiopathic pulmonary fibrosis. However, the function of SIRT6 in lung myofibroblast differentiation is still obscure. Transforming growth factor‐β1 (TGF‐β1) is one of the main factors that can powerfully promote myofibroblast differentiation. In the current study, we aimed to explore the role of SIRT6 in the cellular model of fibroblast‐to‐myofibroblast differentiation induced by TGF‐β1 using human fetal lung fibroblasts (HFL1). We demonstrated that the SIRT6 protein level is upregulated by TGF‐β1 in HFL1 cells. Overexpression of SIRT6 significantly suppresses TGF‐β1‐induced myofibroblast differentiation in HFL1 cells. Mechanistically, SIRT6 decreases phosphorylation and nuclear translocation of Smad2 under TGF‐β1 stimulation. Nevertheless, mutant SIRT6 (H133Y) without histone deacetylase activity fails to inhibit phosphorylation and nuclear translocation of Smad2. Meanwhile, SIRT6 interacts with the nuclear factor‐κB (NF‐κB) subunit p65 and represses TGF‐β1‐induced NF‐κB‐dependent transcriptional activity, which is also dependent on its deacetylase activity. Overexpression of wild‐type SIRT6 but not the H133Y mutant inhibits the expression of NF‐κB‐dependent genes including interleukin (IL)‐1β, IL‐6 and matrix metalloproteinase‐9 (MMP‐9) induced by TGF‐β1, all of which have been demonstrated to promote myofibroblast differentiation. Collectively, our study reveals that SIRT6 prevents TGF‐β1‐induced lung myofibroblast differentiation through inhibiting TGF‐β1/Smad2 and NF‐κB signaling pathways. Sirtuin 6 (SIRT6) overexpression attenuates fibroblast‐to‐myofibroblast differentiation induced by transforming growth factor‐β1 (TGF‐β1) in human fetal lung fibroblasts. Mechanistically, wild‐type SIRT6, but not the H133Y mutant without deacetylase activity, decreases phosphorylation and nuclear translocation of Smad2 under TGF‐β1 stimulation. Meanwhile, SIRT6 interacted with the nuclear factor‐κB (NF‐κB) subunit p65 and repressed TGF‐β1‐induced NF‐κB‐dependent transcriptional activity and the expression of NF‐κB‐dependent genes including interleukin (IL)‐1β, IL‐6 and matrix metalloproteinase‐9 (MMP‐9), which is also dependent on its deacetylase activit