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

Exposure to 4,4'-methylene diphenyl diisocyanate (MDI) in the workplace may lead to the development of occupational asthma (OA). However, the specific mechanism(s) by which MDI induces OA are poorly understood. Previous reports have demonstrated that MDI and MDI-glutathione (GSH) conjugate exposure downregulates endogenous human/murine (<i>hsa/mmu</i>)-microRNA<i>(miR)-206-3p</i>, resulting in the activation of <i>mmu/hsa-miR-206-3p</i>-regulated signaling pathways in macrophages. Circular RNAs (circRNAs) regulate many important biological processes by targeting endogenous miRs; however, whether MDI/MDI-GSH exposure may influence circRNA expressions is unknown. Several circRNAs have been identified that regulate <i>hsa-miR-206-3p</i>. We hypothesize that MDI-GSH conjugate exposure induces endogenous circRNA(s) to regulate <i>hsa-miR-206-3p</i> in macrophages. The expression of candidate <i>hsa-miR-206-3p</i>-binding circRNAs was determined from MDI-GSH conjugate-treated differentiated THP-1 macrophages using RT-qPCR. MDI-GSH exposures induced <i>hsa_circ_0008726</i> and its host gene transcript <i>DNAJB6</i>, whereas other circRNA(s) examined were either not detected or unchanged. RNA-induced silencing complex-immunoprecipitation (RISC-IP) experiments confirm that <i>hsa-miR-206-3p</i> can bind to <i>hsa_circ_0008726</i>. The expressions of endogenous <i>hsa-miR-206-3p</i>, <i>hsa-miR-206-3p</i>-regulated <i>KLF4</i>, and KLF4-activated M2 macrophage-associated markers and chemokines were up-/down-regulated by transfection of <i>hsa_circ_0008726</i> siRNAs or <i>hsa_circ_0008726</i> overexpression plasmid in macrophages, respectively. These results suggest MDI-GSH exposure downregulates <i>hsa-miR-206-3p</i> via induction of endogenous <i>hsa_circ_0008726/DNAJB6</i>, resulting in the upregulation of <i>hsa-miR-206-3p</i>-mediated regulations in macrophages.