miRNA-6515-5p regulates particulate matter-induced inflammatory responses by targeting CSF3 in human bronchial epithelial cells

Particulate matter (PM) is associated with the incidence, exacerbation, and mortality of variable respiratory diseases. However, the molecular mechanisms of PM10-mediated inflammation are unclear. We identified microRNAs (miRNAs) and messenger RNAs (mRNAs) related to the inflammatory response in PM10-exposed bronchial epithelial cells using next-generation sequencing. Of the miRNAs, miR-6515-5p was significantly downregulated in PM10-exposed human bronchial epithelial BEAS-2B cells. miR-6515-5p regulated the production of pro-inflammatory cytokines (IL-6 and IL-8) and the expression of inflammatory genes (IL-1β, IL-6, IL-8, TNF-α, CXCL-1, and MCP-1) via MAPK/ERK signaling; overexpression of miR-6515-5p using a mimic inhibited PM10-induced inflammatory responses via inactivation of the ERK pathway, whereas downregulation of miR-6515-5p via an inhibitor significantly increased inflammation in PM10-exposed cells via activation of ERK. Furthermore, we identified colony stimulating factor 3 (CSF3) as a target gene of miR-6515-5p using TargetScanHuman, and confirmed the association between miR-6515-5p and CSF3 using a luciferase reporter assay. Furthermore, we found that mRNA and protein levels of CSF3 were negatively regulated by miR-6515-5p. Inhibition of CSF3 by small interfering RNA significantly reduced the expression and production of inflammatory markers in PM10-exposed cells by inactivating the MAPK/ERK signaling pathway. Therefore, we suggest that miR-6515-5p regulates PM10-induced inflammatory responses by targeting CSF3 via MAPK/ERK signaling in bronchial epithelial cells.