MicroRNA-Mediated Krüppel-Like Factor 4 upregulation Induces Alternatively Activated Macrophage-Associated Markers and Chemokines Transcription in 4,4’-Methylene Diphenyl Diisocyanate Exposed Macrophages

Occupational exposure to 4,4’-methylene diphenyl diisocyanate (MDI), the most widely used monomeric diisocyanate (dNCO), is associated with occupational asthma (OA) development. Recruitment of immune cells to the lung microenvironment via secreted chemokines by alveolar macrophages may play a role during asthma pathogenesis. Our prior study identified that alternatively activated (M2) macrophage-associated markers and chemokines were induced by MDI/MDI-Glutathione (GSH)-mediated Krüppel-Like Factor 4 (KLF4) upregulation in macrophages and induced chemotaxis abilities to naïve T-cells and eosinophils; however, the underlying molecular mechanism(s) by which MDI upregulated KLF4 expression is unclear. Previously, we identified that two microRNAs (miRs) including hsa-miR-206-3p and hsa-miR-381-3p were significantly downregulated in MDI-GSH-exposed THP-1 macrophages. In silico analysis revealed that one hsa-miR-206-3p and two hsa-miR-381-3p predicted binding sites exist on the 3’ untranslated region (UTR) of KLF4 transcripts. We hypothesize that MDI/MDI-GSH exposure induces M2 macrophage-associated markers and chemokines through hsa-miR-206-3p/hsa-miR-381-3p mediated KLF4 upregulation in macrophages. The first aim of this study was to examine whether hsa-miR-206-3p/hsa-miR-381-3p regulates KLF4 expression in THP-1 macrophages through a posttranscriptional regulation mechanism. Our second aim was to determine whether hsa-miR-206-3p/hsa-miR-381-3p participates in KLF4-regulated M2 macrophage-associated markers and chemokines after MDI-exposure. After identifying the role of endogenous hsa-miR-206-3p/hsa-miR-381-3p in regulation of KLF4 transcription factor after MDI-exposure, we investigated the role of hsa-miR-206-3p/hsa-miR-381-3p in regulation of M2 macrophage-associated markers and chemokines’ expressions in relation to the exposure to MDI.