Extracellular vesicles and their miRNA contents counterbalance the pro-inflammatory effect of air pollution during physiological pregnancy: a focus on Syncytin-1 positive vesicles

The impact of exposure to respirable particulate matter (PM) during pregnancy is a growing concern, as several studies have associated increased risks of adverse pregnancy and birth outcomes, and impaired intrauterine growth with air pollution. The molecular mechanisms responsible for such effects are still under debate. Extracellular vesicles (EVs), which travel in body fluids and transfer microRNAs (miRNAs) between tissues (e.g., pulmonary environment and placenta), might play an important role in PM-induced risk. We sought to determine whether the levels of PM with aerodynamic diameters of ≤10 μm (PM10) and ≤2.5 μm (PM2.5) are associated with changes in plasmatic EV release and EV-miRNA content by investigating 518 women enrolled in the INSIDE study during the first trimester of pregnancy. In all models, we included both the 90-day averages of PM (long-term effects) and the differences between the daily estimate of PM and the 90-day average (short-term effects). Short-term PM10 and PM2.5 were associated with increased concentrations of all seven EV types that we assayed (positive for human antigen leukocyte G (HLA-G), Syncytin-1 (Sync-1), CD14, CD105, CD62e, CD61, or CD25 determinants), while long-term PM10 showed a trend towards decreased EV concentrations. Increased Sync-1 + EV levels were associated with the plasmatic decrease of sVCAM-1, but not of sICAM-1, which are circulating biomarkers of endothelial dysfunction. Thirteen EV-miRNAs were downregulated in response to long-term PM10 and PM2.5 variations, while seven were upregulated (p-value < 0.05, false discovery rate p-value (qFDR) < 0.1). Only one EV-miRNA (hsa-miR-221-3p) was downregulated after short-term variations. The identified PM-modulated EV-miRNAs exhibited putative roles in inflammation, gestational hypertension, and pre-eclampsia, as highlighted by miRNA target analysis. Our findings strongly support the hypothesis that EVs have an important role in modulating PM exposure effects during pregnancy, possibly through their miRNA cargo.