Interleukin-9 promotes EMT-mediated PM2.5-induced pulmonary fibrosis by activating the STAT3 pathway

This study investigated the impact of PM 2.5 on promoting EMT in PM 2.5 -induced pulmonary fibrosis (PF) development and explored molecular mechanisms of the IL-9/STAT3/Snail/TWIST1 signaling pathway in PF owing to PM 2.5 . Four groups of male SD rats were formed: control (0 mg/kg.bw), low (1 mg/kg.bw), medium (5 mg/kg.bw), and high-dose (25 mg/kg.bw) PM 2.5 groups. Experimental rats were subjected to PM 2.5 exposure via intratracheal instillation, given once weekly for 16 weeks. 24 h after the final exposure, blood, BALF, and lung tissues were collected. Pulmonary epithelial cells underwent cultivation and exposure to varying PM 2.5 concentrations with/without inhibitors for 24 h, after which total protein was extracted for relevant protein assays. The findings demonstrated that PM 2.5 damaged lung tissue to different degrees and led to PF in rats. Rats subjected to PM 2.5 exposure exhibited elevated concentrations of IL-9 protein in both serum and BALF, and elevated levels of IL-9 and its receptor, IL-9R, in lung tissues, compared to control counterparts. Furthermore, PM 2.5 -exposed groups demonstrated significantly augmented protein levels of p-STAT3, Snail, TWIST1, Vimentin, COL-I, and α-SMA, while displaying notably diminished levels of E-Cadherin compared to control group. The same findings were observed in PM 2.5 -treated cells. In BEAS-2B cells co-treated with Stattic (STAT3 inhibitor) and PM 2.5 , the opposite results occurred. Similar results were obtained for cells co-treated with IL-9-neutralizing antibody and PM 2.5 . Our findings suggest PM 2.5 mediates PF development by promoting IL-9 expression, leading to STAT3 phosphorylation and upregulation of Snail and TWIST1 expression, triggering EMT occurrence and progression in lung epithelial cells. Highlights Chronic exposure to PM 2.5 can cause pulmonary fibrosis in rats. PM 2.5 -induced IL-9 can lead to the development of EMT in lung epithelial cells. PM 2.5 may cause pulmonary fibrosis through the IL-9-STAT3-EMT signalling pathway.