Dust Fall Microplastics from a Megacity of China Inhibit Autophagy via the PI3K/Akt/mTOR Pathway

The problem of microplastics (MPs) pollution has caused many health risks to residents of Chinese cities. In this study, nine kinds of MPs or microrubbers (MRs) from dust fall (DF) in Xi'an, a megacity in northwestern China, were measured by pyrolysis-gas chromatography-mass spectroscopy, namely, polyethylene, polypropylene, nylon 88, polybutylene, polytetrafluorethylene, polyisoprene, polyvinyl chloride, natural rubber, and synthesis rubber. Here, 51.20% of MPs were extracted from the original DF (samples denoted DF-O). After the subtracting procedure, MPs and their residual (DF-S samples) were divided into two parts. Our results indicated that the DF-O and MPs samples exhibited higher cytotoxicity, inflammatory, and oxidative stress levels than the DF-S samples did. The DF-O and MPs samples suppressed autophagy by decreasing expression levels of microtubule-associated protein light chain 3 (LC3B), p-phosphatidylinositol 3-kinase (p-PI3K), phosphorylated AKT protein (p-Akt), and p-mammalian target of rapamycin (p-mTOR) while increasing the level of p62. Meanwhile, DF-O and MPs samples induced apoptosis through increasing levels of Bax/Bcl-2 and Cleaved Caspase-3/Caspase-3 in Raw264.7 cells. These trends could be reversed through removing half of the MPs in DF-O. Therefore, dust fall microplastics inhibited autophagy and induced apoptosis via activating the PI3K/Akt/mTOR pathway, increasing the Bax/Bcl-2 and Cleaved Caspase-3/Caspase-3 ratios. Here we provide a comprehensive perspective into the studies of atmospheric MPs pollution status and mechanisms of inhalation toxicity for health risk assessment of MPs in DF.