PM2.5 regulates TGF-β1/Smads-mediated pulmonary fibrosis via ROS/SnoN in vitro and in vivo

Abstract

PM2.5 can result in a chronic lung disease, such as pulmonary fibrosis (PF), but the precise mechanism is unclear. In vivo, 40 male C57BL/6 mice were exposed to three concentrations of PM2.5 (0.5 mg/kg·Wt, 5 mg/kg·Wt and 8 mg/kg·Wt) and PM2.5 was administered by tracheal drip every three days for a total of 15 times. Then all mice were euthanized, blood and lung tissue were collected for testing of various indicators. In vitro, rat alveolar type II epithelial cells (RLE-6TN) were pretreated with different concentrations of PM2.5, ROS inhibitor (Vitamin C) and ubiquitin proteasome inhibitor (MG132) separately. Our results indicated that PM2.5 resulted in inflammation and oxidative stress, which in turn caused pathological damage and collagen deposition of lung tissue. In addition, exposure to PM2.5 increased TGF-β1 protein expression and Smad3 phosphorylation both in cells and in lung tissue, which involved collapse of antioxidant reduction system and degradation of SnoN. Additionally, in order to explored potential mechanisms, we used MG132 and VC pretreated cells and found that MG132 and VC pretreatment both inhibited ROS production, and increased SnoN protein expression levels. Further testing of EMT related indicators revealed that MG132 and VC pretreatment reversed the changes under PM2.5 exposure. Moreover, MG132 pretreatment reversed the increase of TGF-β1 protein expression and the Smad3 phosphorylation induced by PM2.5, but the effects were not as strong as those of VC pretreatment, which was related to the fact that VC inhibited both ROS production and SnoN degradation, which further clarifies the key role of ROS and SnoN in PM2.5-induced EMT. Therefore, this study conjectured that ROS/SnoN functioned as a key regulating factor in PM2.5-induced PF and EMT.