Particulate matter 2.5 induces autophagy via inhibition of the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin kinase signaling pathway in human bronchial epithelial cells

Particulate matter 2.5 (PM2.5) is a significant risk factor for asthma. A recent study revealed that autophagy was associated with asthma pathogenesis. However, the specific mechanisms underlying PM2.5-induced autophagy in asthma have remained elusive. In the present study, PM2.5-induced autophagy was evaluated in Beas-2B human bronchial epithelial cells and the potential molecular mechanisms were investigated. Using electron microscopy, immunofluorescence staining and immunoblot studies, it was confirmed that PM2.5 induced autophagy in Beas-2B cells as a result of PM2.5-mediated inhibition of the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway in Beas-2B cells. LY294002, a PI3K inhibitor, reduced the accumulation of microtubule-associated protein 1 light chain 3 II and attenuated the effect of PM2.5. Phosphorylated (p-)p38, p-extracellular signal-regulated kinase and p-c-Jun N-terminal kinase were dephosphorylated following exposure to PM2.5. The roles of p53, reactive oxygen species scavenger tetramethylthiourea and autophagy inhibitor 3-methyladenine in PM2.5-induced autophagy in Beas-2B cells were also investigated. The results suggested that the PI3K/Akt/mTOR signaling pathway may be a key contributor to PM2.5-induced autophagy in Beas-2B cells. The results of the present study therefore provided an a insight into potential future clinical applications targeting these signaling pathways, for the prevention and/or treatment of PM2.5-induced lung diseases.