A comparative study on the model of PM_2.5 direct or indirect interaction with bronchial epithelial cells

The impact of PM_2.5 on epithelial cells is a pivotal process leading to many lung pathological changes and pulmonary diseases. In addition to PM_2.5 direct interaction with epithelia, macrophages that engulf PM_2.5 may also influence the function of epithelial cells. However, among the toxic researches of PM_2.5, there is a lack of evaluation of direct or indirect exposure model on human bronchial epithelial cell against PM_2.5. In this present research, PM_2.5-exposed human bronchial epithelial cell line (BEAS-2B) serves as the direct interaction model. By contrast, a PM_2.5-stimulated co-culture model of macrophages and epithelial cells based on the transwell system was adopted as indirect stimulation model. By comparing these two models of interaction, we examined the viability of BEAS-2B and mRNA/protein expression profile of oxidative stress and inflammatory response-related transcription factors Nrf2, NF-kB, and according inflammatory indicators such as IL-1, IL-6, and IL-8, with a view to evaluating the effects of different interaction models of PM_2.5 on epithelial cell damage in vitro. Our results indicated that under the same doses, the direct stimulation model of PM_2.5 could inhibit the viability of BEAS-2B. Furthermore, the indirect stimulation model strengthen inflammation response of epithelia under the higher concentration of PM_2.5 and induce epithelia to undergo EMT under the lower concentration of PM_2.5. Overall, we have found that macrophage involvement may protect epithelia from PM_2.5 cytotoxic effect, while it strengthens the inflammation response and induce epithelia to undergo EMT.