Proteomic investigation of pathogenesis mechanisms and the role of ITIH4 in PM2.5-induced lung injury

Exposure to fine particulate matter (PM2.5) air pollution has detrimental effects on human health with increased risk of mortality and progression of pre-existing illnesses. Our previous studies have reported that the expression level of inter-alpha-trypsin inhibitor heavy chain H4 (ITIH4) was negatively correlated to PM2.5 exposure and emphysema severity and may have a role in inflammation. However, how the PM2.5 causes damages in lung at molecular level and the detailed role of ITIH4 in this pathogenesis remain largely unknown. Thus, we aim to elucidate the underlying mechanisms of PM2.5-caused lung injury and examine the molecular interactions of ITIH4 in BEAS-2B, a lung epithelial cell, by using quantitative proteomic analyses. Two doses (high and low doses) of PM2.5 were selected to treat BEAS-2B in comparison with untreated control. In the results, we observed dysregulation of idiopathic pulmonary fibrosis (IPF) and the macroautophagy signaling pathway which is mediated by misfolded collagens. Activation of ferroptosis, acute phase response signaling, pulmonary fibrosis idiopathic signaling pathway, and hepatic fibrosis as well as suppression of NAD and sirtuin signaling pathways were observed at both low- and high-dose treatments. The protection mechanisms such as NRF2-mediated oxidative stress response and wound healing signaling pathways were triggered only under high-dose PM2.5 treatment. In BEAS-2B cells, we explored the ITIH4-interacting network by using the optimized affinity purification mass spectrometry workflow and detected 49 proteins confidently interacted with ITIH4, including ITIH1, ITIH2, and ITIH3 as well as proteins involved in complement activation, coagulation, and intermediate filament cytoskeleton organization. Based on these findings, we are able to construct the detailed molecular mechanisms underlying PM2.5-induced lung injury and clarify the ITIH4-mediated cellular functions. Potential targets could be proposed to seek possible therapeutic strategies to restore the cell repair or protection ability against PM2.5.