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.