MicroRNA-124 promotes microglia quiescence and suppresses EAE by deactivating macrophages via the C/EBP-α–PU.1 pathway

Abstract

MicroRNAs are a family of regulatory molecules involved in many physiological processes, including differentiation and activation of cells of the immune system. We found that brainspecific miR-124 is expressed in microglia but not in peripheral monocytes or macrophages. When overexpressed in macrophages, miR-124 directly inhibited the transcription factor CCAAT/ enhancer-binding protein-α (C/EBP-α) and its downstream target PU.1, resulting in transformation of these cells from an activated phenotype into a quiescent CD45 low , major histocompatibility complex (MHC) class II low phenotype resembling resting microglia. During experimental autoimmune encephalomyelitis (EAE), miR-124 was downregulated in activated microglia. Peripheral administration of miR-124 in EAE caused systemic deactivation of macrophages, reduced activation of myelin-specific T cells and marked suppression of disease. Conversely, knockdown of miR-124 in microglia and macrophages resulted in activation of these cells in vitro and in vivo. These findings identify miR-124 both as a key regulator of microglia quiescence in the central nervous system and as a previously unknown modulator of monocyte and macrophage activation.MicroRNAs (miRNAs) belong to a family of small non-protein-coding RNAs that regulate expression of multiple target genes and are involved in many fundamental biological processes, such as embryonic development, cell proliferation, differentiation and apoptosis [1][2][3][4][5] . miRNAs promote degradation of mRNA or prevent translation of the target genes, and they can be viewed as endogenous mediators of RNA interference (RNAi) 1 . miRNAs have been identified as crucial regulators of differentiation of various cell types, © 2011 Nature America, Inc. All rights reserved. Correspondence should be addressed to H.L.W. (hweiner@rics.bwh.harvard.edu) and A.M.K. (akrichevsky@rics.bwh.harvard.edu).. 3 These authors contributed equally to this work. AUTHOR CONTRIBUTIONS E.D.P. performed all flow-cytometry assays, EAE experiments, experiments with chimeric, knockout and transgenic mice, in vivo injections of oligonucleotides, cell isolations, cell cultures, coculture assays and immunohistochemistry; collected and analyzed the data; and wrote the manuscript. T.V. performed in vitro transfections, miRNA and mRNA expression assays and data analysis, western blots, luciferase target validation assay, immunohistochemistry and in silico target prediction analysis and helped to write the manuscript. N.B. performed imaging cytometry. E.D.P. and A.M.K. conceived the project. E.D.P., T.V. and A.M.K. developed the hypothesis and designed the experiments. A.M.K. and H.L.W. discussed the hypothesis, helped with data interpretation, coordinated and directed the project and wrote the manuscript.Note: Supplementary information is available on the Nature Medicine website. COMPETING FINANCIAL INTERESTSThe authors declare no competing financial interests. 2,6 . Furthermore, deregulated expression of specific miRNAs is associated with many patholo...

Taming of macrophage and microglial cell activation by microRNA-124

“…Utilizing a mouse model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE), they found that at the onset of disease the activated microglial cell population had significantly downregulated microRNA-124 expression [3]. In concordance with this finding, highly activated peripheral macrophages expressed very low levels of microRNA-124.…”

“…In concordance with this finding, highly activated peripheral macrophages expressed very low levels of microRNA-124. Moreover, microRNA-124 expression was found to be low in prenatal and postnatal microglial cells, which exhibit a quasi-activated state compared to adult microglial cells [3]. Thus, microRNA-124 expression in microglial cells is correlated with microglial cell development and activation status.…”

“…Forced expression of microRNA-124 in bone marrow-derived macrophages resulted in the downregulation of activation markers and inhibition of TNF-α and inducible nitric oxide synthase expression. Concurrently, there was an upregulation of both the anti-inflammatory cytokine TGF-β1 and markers of alternatively activated macrophages, Arg1 and FIZZ1 [3]. MicroRNA-124 was shown to directly inhibit the production of the transcription factor C/ EBP-α, resulting in the downregulation of PU.1 [3,8].…”

“…Since activated microglial cells have been implicated in a number of neurological disorders, knowing how they are maintained in the quiescent state is of great interest. A recent paper by Ponomarev et al in Nature Medicine [3] unravels this mystery implicating the brain-specific microRNA-124 in regulating the activation state of microglial cells and macrophages.…”

“…At least seven brain-specific microRNAs have been described, including microRNA-124, which is thought to play a prominent role in brain development by downregulating hundreds of nonneuronal transcripts and by regulating nervous system-specific alternative splicing [5][6][7]. The study by Ponomarev and colleagues, now demonstrates the expression of high levels of microR-NA-124 in the CNS-resident microglial cell population and presents evidence supporting its role in maintaining their quiescent state [3].…”