Specification of CNS macrophage subsets occurs postnatally in defined anatomical niches
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ABSTRACT: All tissue resident macrophages of the central nervous system (CNS), including parenchymal microglia as well as CNS-associated macrophages (CAMs) such as meningeal (mMF) and perivascular macrophages (pvMF) are part of the CNS endogenous innate immune system that acts as the first line of defense during infections or trauma. It has been suggested that microglia and all CAM subsets are derived from prenatal cellular sources in the yolk sac that were defined as early erythromyeloid progenitors. However, the precise ontogenetic relationships, the underlying transcriptional programs and the molecular signals that drive the development of distinct CAMs subsets in situ are poorly understood. Using novel fate mapping systems, single-cell profiling and cell-specific mutants, we show that only mMF and microglia share a common prenatal progenitor. In contrast, pvMF originate from perinatal mMF only after birth in an integrin-dependent manner. Furthermore, the establishment of pvMF critically requires the presence of vascular smooth muscle cells. In summary, our data reveal a novel precisely timed process in distinct anatomical niches for the establishment of CNS macrophage subsets.
Project description:All tissue resident macrophages of the central nervous system (CNS), including parenchymal microglia as well as CNS-associated macrophages (CAMs) such as meningeal (mMF) and perivascular macrophages (pvMF) are part of the CNS endogenous innate immune system that acts as the first line of defense during infections or trauma. It has been suggested that microglia and all CAM subsets are derived from prenatal cellular sources in the yolk sac that were defined as early erythromyeloid progenitors. However, the precise ontogenetic relationships, the underlying transcriptional programs and the molecular signals that drive the development of distinct CAMs subsets in situ are poorly understood. Using novel fate mapping systems, single-cell profiling and cell-specific mutants, we show that only mMF and microglia share a common prenatal progenitor. In contrast, pvMF originate from perinatal mMF only after birth in an integrin-dependent manner. Furthermore, the establishment of pvMF critically requires the presence of vascular smooth muscle cells. In summary, our data reveal a novel precisely timed process in distinct anatomical niches for the establishment of CNS macrophage subsets.
Project description:All tissue resident macrophages of the central nervous system (CNS), including parenchymal microglia as well as CNS-associated macrophages (CAMs) such as meningeal (mMF) and perivascular macrophages (pvMF) are part of the CNS endogenous innate immune system that acts as the first line of defense during infections or trauma. It has been suggested that microglia and all CAM subsets are derived from prenatal cellular sources in the yolk sac that were defined as early erythromyeloid progenitors. However, the precise ontogenetic relationships, the underlying transcriptional programs and the molecular signals that drive the development of distinct CAMs subsets in situ are poorly understood. Using novel fate mapping systems, single-cell profiling and cell-specific mutants, we show that only mMF and microglia share a common prenatal progenitor. In contrast, pvMF originate from perinatal mMF only after birth in an integrin-dependent manner. Furthermore, the establishment of pvMFcritically requires the presence of vascular smooth muscle cells. In summary, our data reveal a novel precisely timed process in distinct anatomical niches for the establishment of CNS macrophage subsets.
Project description:The central nervous system (CNS) includes anatomically distinct macrophage populations including parenchyma microglia and CNS-associated macrophages (CAMs). The stepwise development and specification of macrophage populations in the CNS rely on several key transcription factors, such as IRF8 and MAFB. In order to better understand the roles of IRF8 and MAFB for phenotypic determination of homeostatic microglia and CAMs, we performed quantitative bulk RNA sequencing of microglia and CAMs isolated from mouse models with myeloid cell-specific deletion of IRF8 or MAFB transcription factors. We found the distinct transcriptional machinery, mediated by IRF8 and MAFB, which underlies the diversity of macrophages in the CNS.
Project description:The immune cells of the central nervous system (CNS) comprise parenchymal microglia and at the CNS border regions meningeal, perivascular and choroid plexus macrophages (summarized as CNS-associated macrophages, CAMs). Previous work has uncovered that microglial properties are strongly dependent on environmental signals from the commensal microbiota while its effect on CAMs remained unknown. By combining several microbiota manipulation approaches, genetic mouse models and single-cell RNA-sequencing, we comprehensively characterized CNS myeloid cell composition and function. Under steady-state, the transcriptional profile and numbers of choroid plexus macrophages were found to be tightly steered by complex microbiota. Divergently, perivascular and meningeal macrophages were affected to a lesser extent. An acute perturbation through viral infection evoked an attenuated immune response of all CAMs in germ-free mice. Additionally, we assessed CAMs in a more chronic pathological state in 5xFAD mice as a model for Alzheimer’s disease whereby exclusively perivascular macrophages displayed enhanced amyloid beta uptake in GF 5xFAD mice. Our results provide novel insights for understanding distinct microbiota-CNS macrophage interactions during health and perturbation that could potentially be targeted therapeutically.
Project description:Cells in the cortex of mice expressing apoE3 or apoE4 in the microglia were isolated and subjected to the single-cell RNA seq to investigate the effects of microglia/CNS-associated macrophages (CAMs) apoE on the brain transcriptomic profiles. Our data revealed that microglia/CAM-expressed apoE3 promotes antigen presentation and immune patnways, whereas apoE4 down-regulates complement and promotes stress-related responses.
Project description:Gene profiling of CNS-derived microglia vs splenic CD11b+Ly6C+ monocyte subsets deom adult mice Gene array identified 1572 genes that were enriched in microglia vs. 611 monocyte enriched genes with a greater than 5-fold difference (P<0.001). Gene profiling of CD11b+CD45Low microglia isolated from the CNS and CD11b+Ly6C+ monocyte subsets isolated from the spleen of naM-CM-/ve adult mice.
Project description:The innate immune system of the human central nervous system (CNS) is highly diverse already during homeostasis. Several immune cell populations such as macrophages that are frequent in the brain parenchyma (microglia) and less numerous at the brain interfaces as CNS-associated macrophages (CAMs) constitute the local immune compartment. Due to their scantiness and particular location, little is known about the presence of temporally and spatially restricted CAM subclasses during development, health and perturbation. Here, we combined several high-dimensional technologies, such as single-cell RNA-sequencing, time-of-flight mass cytometry and single-cell spatial transcriptomics with fate mapping and advanced immunohistochemistry to comprehensively characterize the immune system at human CNS interfaces. We also provide a comprehensive analysis of resident and engrafted myeloid cells in the brains of individuals with peripheral blood stem cell transplantation, revealing remarkable dynamics. These approaches enabled us to identify a previously unappreciated spectrum of transcriptional classes of human CAMs and to decipher their turnover with circulating cells. CAM signatures profoundly changed during ontogeny and pathology. Our results highlight myeloid diversity at the interfaces of the human CNS with the periphery and provide new insights into the human brain’s immune system.
Project description:Microglia are the resident macrophages of the central nervous system (CNS). Gene profiling identified the transcriptional regulator Sall1 as a microglia signature gene. Given the high expression of Sall1 in microglia, we sought to identify its function in vivo. The Sall1CreER allele has been targeted into the Sall1 locus, therefore Sall1CreER/fl mice (heterozygous for both alleles) allow inducible ablation of Sall1 expression in microglia after tamoxifen treatment. We performed RNA-seq to examine gene expression profiles of microglia sorted from tamoxifen treated adult Sall1CreER/fl mice and Sall1fl/fl control littermates. Microglia were obtained with > 98% purity and the absence of Sall1 was confirmed in Sall1CreER/fl microglia. We could show that deletion of Sall1 in microglia in vivo resulted in the conversion of these cells from resting tissue macrophages into inflammatory phagocytes leading to altered neurogenesis and disturbed tissue homeostasis. Similar changes in gene expression profiles were found in Sall1-deficient microglia isolated from tamoxifen-treated Cx3cr1CreERSall1fl/fl mice. In these mice, deletion of Sall1 is targeted to CX3CR1+ myeloid cells including microglia and CNS-associated macrophages but not to any other CNS-resident cells. This indicated that Sall1 transcriptional regulation maintains microglia identity and physiological properties in the CNS.
Project description:Microglia as tissue macrophages of the central nervous system (CNS) provide immunological defense and contribute to the establishment and maintenance of CNS homeostasis. Several transcription factors have been described that regulate microglia development and its steady state form, however little is known about the epigenetic signals that control microglia function in vivo. Here, we employed constitutive and inducible mutagenesis in microglia to delete two class I histone deacetylases (HDACs), Hdac1 and 2. Prenatal ablation of Hdac1 and 2 from microglia drastically impaired microglial development with reduced cell number, altered morphology and induction of apoptosis. Comparative transcriptomic profiling revealed an essential role of Hdac1/2 in the regulation of microglia survival and expansion. Mechanistically, hyperacetylation at H3K9 and H3K27 was found at the promoters of pro-apoptotic and cell cycle genes in the absence of Hdac1/2. In contrast, Hdac1/2 were not required in adult microglia during homeostasis. In a mouse model of Alzheimer’s disease, suppression of Hdac1/2 in microglia, but not in neuroectodermal cells, remarkably displayed substantial decrease in amyloid load and improved cognitive impairment by enhancing microglial amyloid phagocytosis. Collectively, we report a previously unknown role of epigenetic factors that differentially affect microglia development, homeostasis and disease that could potentially be utilized therapeutically.
Project description:Microglia as tissue macrophages of the central nervous system (CNS) provide immunological defense and contribute to the establishment and maintenance of CNS homeostasis. Several transcription factors have been described that regulate microglia development and its steady state form, however little is known about the epigenetic signals that control microglia function in vivo. Here, we employed constitutive and inducible mutagenesis in microglia to delete two class I histone deacetylases (HDACs), Hdac1 and 2. Prenatal ablation of Hdac1 and 2 from microglia drastically impaired microglial development with reduced cell number, altered morphology and induction of apoptosis. Comparative transcriptomic profiling revealed an essential role of Hdac1/2 in the regulation of microglia survival and expansion. Mechanistically, hyperacetylation at H3K9 and H3K27 was found at the promoters of pro-apoptotic and cell cycle genes in the absence of Hdac1/2. In contrast, Hdac1/2 were not required in adult microglia during homeostasis. In a mouse model of Alzheimer’s disease, suppression of Hdac1/2 in microglia, but not in neuroectodermal cells, remarkably displayed substantial decrease in amyloid load and improved cognitive impairment by enhancing microglial amyloid phagocytosis. Collectively, we report a previously unknown role of epigenetic factors that differentially affect microglia development, homeostasis and disease that could potentially be utilized therapeutically.