Elevated expression of miR-146, miR-139 and miR-340 involved in regulating Th1/Th2 balance with acute exposure of fine particulate matter in mice

Airborne fine particulate matter (PM2.5) is detrimental to human health, and frequently leads to a variety of lung diseases. Recently, IARC conclude that particulate matter is carcinogenic to humans (level one). However, the pulmonary toxicological mechanism induced by PM2.5 remains obscure. Our previous studies confirmed that PM2.5 hurt the human immune system by means of causing the imbalance of Th1/Th2 lymphocytes. MicroRNAs (miRNAs) are post-transcriptional gene suppressors and potential mediators of environmental effects, which play an important role in the regulation of CD4(+) T lymphocyte differentiation. In order to further understand the roles of microRNAs in regulating the imbalance of Th1/Th2 differentiation triggered by PM2.5, mice were subjected to intratracheal instillation of 2.5, 10, or 20 mg/kg PM2.5 in this study. Mice were euthanized on the 1st, 7th and 14th day to screen out differential miRNAs in lung tissue by employing the miRNA microarray. The expression levels of IL-4 and IFN-gamma in bronchoalveolar lavage fluid (BALF) were quantified by ELISA and their mRNA expressions in lung tissue were detected by qRT-PCR. The experiment demonstrated that 10 differential miRNAs (miR-146a, -146b, -139, -129, -340, -691, -181a, -155, -21-3p, and -21-5p) were up-regulated. IL-4 levels were found decreased, nevertheless, IFN-gamma levels were increased, and the IL-4/IFN-gamma ratio was inclined to Th1 shifting. Besides that, we also found that miRNA-691, -181a, -146a, -146b, -21a-3p, -21a-5p, and -340 had a positive linear correlation with BALF IFN-gamma, while a negative linear correlation between microRNAs (miR-146, -139, -340, -21, and -181a) and the IL-4/IFN-gamma level of BALF was observed. In conclusion, elevated microRNAs profiles correlated with T lymphocyte immune imbalance, driving a Th1-biased immune response after acute PM2.5 exposure. These findings improve our understanding of the toxicological pathways of PM2.5 exposure.