Circular RNA hsa_circ_0008726 Targets the hsa-miR-206-3p/KLF4 Axis to Modulate 4,4’-Methylene Diphenyl Diisocyanate-Glutathione Conjugate-Induced Chemokine Transcription in 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 plays important roles during asthma pathogenesis. Our prior studies identified MDI/MDI-GSH-exposure downregulates endogenous human/murine(hsa/mmu)-microRNA(miR)-206-3p, resulting in the activation of mmu/hsa-miR-206-3p-regulated signaling including KLF4-mediated signaling in MØs. The hsa-miR-206-3p-regulated signaling activation leading to induction of chemokines and chemotaxis activities of immune cells. However, the underlying molecular mechanism(s) by which MDI/ MDI in the form of MDI-GSH conjugate exposure downregulated endogenous hsa-miR-206-3p expression is unclear. Circular RNAs (circRNAs) play important roles in many different biological processes by targeting endogenous miRs, affecting protein translation and gene transcription in different cell types. The circRNA expression can be regulated via outside stimuli exposures; however, whether MDI-exposure influence circRNAs expression is unknown. Several circRNAs have been identified to regulate hsa-miR-206-3p levels through miR binding/targeting. We hypothesize that MDI-exposure induces endogenous circRNA(s) to regulate hsa-miR-206-3p in MØs. The first aim of this study was to identified candidate hsa-miR-206-3p-binding circRNA(s) that can be regulated by MDI/MDI-GSH regulated. The second aim of this study was to examine whether MDI/MDI-GSH regulated hsa-miR-206-3p-binding circRNA(s) can indeed regulate the endogenous hsa-miR-206-3p in MØs. After identified the roles of endogenous circRNA(s) in regulation of endogenous hsa-miR-206-3p after MDI/MDI-GSH-exposure, we investigated the roles of circRNAs in regulation of hsa-miR-206-3p-mediated M2 macrophage-associated markers and chemokines’ expressions in relation to the exposure to MDI.