Nanoplastics are tiny plastic particles that can easily enter human lungs through breathing contaminated air. By damaging alveolar epithelial cells, nanoplastic particles can enter the blood system and may cause a wide range of toxic effects and pulmonary disorders. 

In order to determine the bio-molecular mechanisms by which nanoplastics damage human respiratory system, a research team led by Prof. Xu Mingkai from the Institute of Applied Ecology of the Chinese Academy of Sciences recently investigated the toxic effects of polystyrene nanoplastics (PS-NPs) on epithelial-to-mesenchymal transition (EMT) using human alveolar type II epithelial A549 cell line as an in vitro model of respiratory epithelial system. 

The researchers found that PS-NPs could induce epithelial-to-mesenchymal transition (EMT, the prelude to lung fibrosis) in A549 cells regardless of the particle size and surface charge of PS-NPs. EMT, the "prelude to lung fibrosis," is a complex cellular reprogramming process involving various bio-molecular mechanisms. In the study by Prof. XU and their colleagues, PS-NPs caused up-regulation of EMT protein markers, matrix metallopeptidase 2 (MMP2) and E-cadherin, and enhanced cell migration. PS-NPs also induced up-regulation of reactive oxygen species (ROS), NADPH oxidase 4 (NOX4), immunoglobulin heavy chain binding protein in pre-B cells (Bip) and activating transcriptional factor 4 (ATF4), which can all directly or indirectly affect the mitochondria and endoplasmic reticulum (ER) in A549 cells, resulting in mitochondria dysfunction and ER stress. On the contrary, however, gene silencing of NOX4 could inhibit the PS-NP-induced up-regulation of BiP and ATF4, according to the research. 

In addition, the researchers found that the toxic effects and related mechanisms of PS-NPs on A549 cells varied with the concentration, particle size and surface charge type of PS-NPs. For example, smaller PS-NPs with positive surface charge (cationic type) had stronger toxic effects. 

These findings may benefit future research concerning nanoplastic air pollution and risk prevention. 

The study titled "Toxic effects of nanoplastics with different sizes and surface charges on epithelial-to-mesenchymal transition in A549 cells and the potential toxicological mechanism" has been published in JOURNAL OF HAZARDOUS MATERIALS, and it was supported by the National Natural Science Foundation of China, the People's Livelihood, Science and Technology Program of Liaoning Province, the Liaoning Revitalization Talents Program, and the Young and Middle-aged S&T Innovative Talent Program of Shenyang Science and Technology Bureau.