Peripherally derived macrophages infiltrate the brain after bone marrow transplantation and during central nervous system (CNS) inflammation. It was initially suggested that these engrafting cells ...were newly derived microglia and that irradiation was essential for engraftment to occur. However, it remains unclear whether brain-engrafting macrophages (beMφs) acquire a unique phenotype in the brain, whether long-term engraftment may occur without irradiation, and whether brain function is affected by the engrafted cells. In this study, we demonstrate that chronic, partial microglia depletion is sufficient for beMφs to populate the niche and that the presence of beMφs does not alter behavior. Furthermore, beMφs maintain a unique functional and transcriptional identity as compared with microglia. Overall, this study establishes beMφs as a unique CNS cell type and demonstrates that therapeutic engraftment of beMφs may be possible with irradiation-free conditioning regimens.
Mutations in MECP2, encoding the epigenetic regulator methyl-CpG-binding protein 2, are the predominant cause of Rett syndrome, a disease characterized by both neurological symptoms and systemic ...abnormalities. Microglial dysfunction is thought to contribute to disease pathogenesis, and here we found microglia become activated and subsequently lost with disease progression in Mecp2-null mice. Mecp2 was found to be expressed in peripheral macrophage and monocyte populations, several of which also became depleted in Mecp2-null mice. RNA-seq revealed increased expression of glucocorticoid- and hypoxia-induced transcripts in Mecp2-deficient microglia and peritoneal macrophages. Furthermore, Mecp2 was found to regulate inflammatory gene transcription in response to TNF stimulation. Postnatal re-expression of Mecp2 using Cx3cr1creER increased the lifespan of otherwise Mecp2-null mice. These data suggest that Mecp2 regulates microglia and macrophage responsiveness to environmental stimuli to promote homeostasis. Dysfunction of tissue-resident macrophages might contribute to the systemic pathologies observed in Rett syndrome.
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•Mecp2 is broadly expressed in macrophages and resident monocytes•Mecp2-null mice exhibit monocyte and resident macrophage deficiencies•Mecp2 expression under Cx3cr1creER extends survival of Mecp2Lox-Stop/y mice•Mecp2 regulates transcriptional responses to inflammatory stimuli
Mutations in the gene encoding Methyl-CpG binding protein 2 (MeCP2) are the primary cause of the neurodevelopmental disease Rett syndrome. Kipnis and colleagues demonstrate that Mecp2 regulates macrophage transcriptional responses to glucocorticoid and inflammatory stimuli, raising the possibility that abnormal macrophage responses contribute to systemic impairments in Rett syndrome.
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