MicroRNA-206 relieves irradiation-induced neuroinflammation by regulating connexin 43

Radiation therapy has been widely used for the treatment of various types of cancer; however, it may cause neuroinflammation during the pathological process of the disease. Astrocytes, the most abundant cell type in the central nervous system, have been confirmed to play vital roles in various diseases. Connexin (Cx)43, the main Cx type in astrocytes, which has been identified as a direct target gene of microRNA (miR)-206, was found to be involved in diseases pathologies in regions with astrocytes. The aim of the present study was to investigate the mechanism through which gamma-radiation may cause astrocyte neuroinflammation and determine the specific mechanism underlying the effects of miR-206 in irradiation-induced HA-1800 cells. A dual-luciferase reporter system was used to predict and verify the target binding site between Cx43 and miR-206. HA-1800 cell viability and apoptosis were determined using a MTT assay and flow cytometry, respectively. In addition, the HA-1800 cells were induced by gamma-radiation, then the protein and mRNA expression levels of Cx43, miR-206 and cleaved-caspase-3 were determined using western blot and reverse transcription-quantitative PCR analyses, respectively. ELISA was also performed to evaluate the concentrations of different inflammatory cytokines (TNF-alpha, IL-beta, IL-6 and IFN-gamma). The dual-luciferase reporter system indicated that Cx43 was a direct target of miR-206. miR-206 mimics increased the expression level of miR-206 in the astrocytes. Irradiation suppressed cell proliferation, increased apoptotic cells and enhanced cleaved-caspase-3 expression and inflammatory cytokines secretion in astrocytes. Furthermore, miR-206 was found to be downregulated and its expression was inversely associated with that of Cx43 in gamma-radiation-induced astrocytes. Overexpression of miR-206 enhanced miR-206 and suppressed Cx43 expression, while Cx43 was upregulated in HA-1800 cells transfected with miR-206 mimic + Cx43-plasmid. However, the expression level of miR-206 was not significantly different in the Cx43-plasmid transfected group. In addition, it was found that miR-206 mimics relieved irradiation-induced neuroinflammation, which was confirmed by increased cell viability, and reduced cell apoptosis and cleaved caspase-3 protein expression, as well as decreased inflammatory cytokine secretion. Furthermore, all the effects of miR-206 mimics on gamma-radiation-induced astrocytes were reversed by Cx43-plasmid. In summary, the results of the present study indicated that miR-206 may relieve irradiation-induced neural damage by regulating Cx43, which may provide a novel research direction and a potential therapeutic target for the clinical treatment of inflammation-associated neuronal injury following irradiation.