TGF‐β1 mediated Smad signaling pathway and EMT in hepatic fibrosis induced by Nano NiO in vivo and in vitro

Nickel oxide nanoparticles (Nano NiO) bears hepatotoxicity, while whether it leads to liver fibrosis remains unclear. The aim of this study was to establish the Nano NiO‐induced hepatic fibrosis model in vivo and investigate the roles of transforming growth factor β1 (TGF‐β1) in Smad pathway activation, epithelial‐mesenchymal transition (EMT) occurrence, and extracellular matrix (ECM) deposition in vitro. Male Wistar rats were exposed to 0.015, 0.06, and 0.24 mg/kg Nano NiO by intratracheal instilling twice a week for 9 weeks. HepG2 cells were treated with 100 μg/mL Nano NiO and TGF‐β1 inhibitor (SB431542) to explore the mechanism of collagen formation. Results of Masson staining as well as the elevated levels of type I collagen (Col‐I) and Col‐III suggested that Nano NiO resulted in hepatic fibrosis in rats. Furthermore, Nano NiO increased the protein expression of TGF‐β1, p‐Smad2, p‐Smad3, alpha‐smooth muscle actin (α‐SMA), matrix metalloproteinase9 (MMP9), and tissue inhibitors of metalloproteinase1 (TIMP1), while decreased the protein content of E‐cadherin and Smad7 in rat liver and HepG2 cells. Most importantly, Nano NiO‐triggered the abnormal expression of the abovementioned proteins were all alleviated by co‐treatment with SB431542, implying that TGF‐β1‐mediated Smad pathway, EMT and MMP9/TIMP1 imbalance were involved in overproduction of collagen in HepG2 cells. In conclusion, these findings indicated that Nano NiO induced hepatic fibrosis via TGF‐β1‐mediated Smad pathway activation, EMT occurrence, and ECM deposition.