Novel neuroprotective and neurogenic phenotype of microglia

Background: Tissue macrophages contribute to development and protection, both requiring appropriately timed and located source(s) of factors controlling growth, cell differentiation and migration. Goal: To understand the role of microglia (tissue macrophages of the central nervous system), in promoting neurodevelopment and controlling neuroinflammation. Summary of findings: We show that microglia fulfill both these roles. In contrast to adult cells, neonatal microglia show a unique neurogenic phenotype with stem cell-like potential. Neonatal microglia are protective against neuroinflammation, and their transplantation ameliorates experimental autoimmune encephalomyelitis. A CD11c+ microglial subset predominates in primary myelinating areas of the developing brain and expresses genes for neuronal and glial survival, migration and differentiation. CD11c+ microglia are also found in clusters of repopulating microglia after experimental ablation and in neuroinflammation in adult mice, but despite some similarities, they do not recapitulate neurogenic neonatal microglia characteristics. Conclusions: We therefore identify a unique phenotype of neonatal microglia that deliver signals necessary for neurogenesis and myelination and suppress neuroinflammation. Overall design: The overall design was to compare transcriptomes of subsets of microglia isolated from neonatal mice, healthy adults, and adult mice with a neuroinflammatory disease (Experimental autoimmune encephalomyelitis, EAE), and to compare anti-inflammatory function of adult and neonatal microglia. Microglia were isolated by cell-sorting based on surface phenotype, and RNAseq data was analyzed using WGCNA, GO and DAVID approaches. Expression of selected genes and pathways was confirmed by histology and flow cytometry. Functional analysis involved transfer of isolated microglia to the central nervous system of animals with EAE and evaluation of outcome. EAE = Experimental autoimmune encephalomyelitis

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Wlodarczyk A, Holtman IR, Krueger M, Yogev N, Bruttger J, Khorooshi R, Benmamar-Badel A, de Boer-Bergsma JJ, Martin NA, Karram K, Kramer I, Boddeke EW, Waisman A, Eggen BJ, Owens T