Regulation of IFN-Is by MEF2D Promotes Inflammatory Homeostasis in Microglia

Abstract Background Microglia play an essential role in the host defense of central nervous system. Transcription factor MEF2D is known to participate in stress regulation of various cells and is tightly triggered in microglia in vivo and in vitro. MEF2D is shown to bind at the promoter region of several cytokine genes in immune cells, and directly regulates inflammatory response, suggesting that MEF2D may act as a key stimulus response regulator of microglia and is involved in the regulation of brain micro-homeostasis. In order to uncover the molecular mechanism of MEF2D in inflammatory system, in the present study, we investigated the global effect of MEF2D in activated microglia, and explored its potential regulatory network. Methods Experiments of recombinant lentivirus vector of shRNA and specific MEF2D over-expression were performed in BV2 cells. Transcriptome sequencing and the global gene expression patterns were analyzed in lipopolysaccharide-stimulated shMEF2D BV2 cells. The pro- and anti-inflammatory factors were assessed by western blot, qPCR or ELISA, and microglia activity by phagocytosis and morphologic analysis. The directly binding of MEF2D to the promoter regions of IRF7 were tested by ChIP-qPCR and PCR. The ISGs were tested by qPCR. Results MEF2D was shown to actively participate in the inflammatory response of BV2 microglial cells. RNAi induced stable silence of MEF2D broke the immune balance of microglia, in two ways: (1) promoted the expression of pro-inflammatory factors, such as NLRP3, IL-1β, iNOS; and (2) markedly inhibited the type-I interferon signaling pathway by directly modulating the transcription of IRF7. On the contrary, overexpression of MEF2D significantly reduced the expression of NLRP3 and iNOS under LPS stimulation, and alleviated the level of immune stress in microglia. Conclusions These findings demonstrate that MEF2D plays an important role in the regulation of inflammatory homeostasis partly through transcriptional regulation of the IFN-Is response signaling pathway.