ABSTRACT
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
ABSTRACT
Microglia and central nervous system (CNS)-associated macrophages (CAMs), such as perivascular and meningeal macrophages, are implicated in virtually all diseases of the CNS. However, little is known about their cell-type-specific roles in the absence of suitable tools that would allow for functional discrimination between the ontogenetically closely related microglia and CAMs. To develop a new microglia gene targeting model, we first applied massively parallel single-cell analyses to compare microglia and CAM signatures during homeostasis and disease and identified hexosaminidase subunit beta (Hexb) as a stably expressed microglia core gene, whereas other microglia core genes were substantially downregulated during pathologies. Next, we generated HexbtdTomato mice to stably monitor microglia behavior in vivo. Finally, the Hexb locus was employed for tamoxifen-inducible Cre-mediated gene manipulation in microglia and for fate mapping of microglia but not CAMs. In sum, we provide valuable new genetic tools to specifically study microglia functions in the CNS.
Subject(s)
Brain/pathology , Encephalomyelitis, Autoimmune, Experimental/pathology , Facial Nerve Injuries/pathology , Microglia/metabolism , beta-Hexosaminidase beta Chain/metabolism , Animals , Brain/cytology , Brain/immunology , CRISPR-Cas Systems/genetics , Encephalomyelitis, Autoimmune, Experimental/immunology , Facial Nerve Injuries/immunology , Gene Knock-In Techniques , Genes, Reporter/genetics , Genetic Loci/genetics , Humans , Intravital Microscopy , Luminescent Agents/chemistry , Luminescent Proteins/chemistry , Luminescent Proteins/genetics , Macrophages/immunology , Macrophages/metabolism , Mice , Microglia/immunology , NIH 3T3 Cells , RNA-Seq , Single-Cell Analysis , Transfection , beta-Hexosaminidase beta Chain/genetics , Red Fluorescent ProteinABSTRACT
Inflammatory disorders of the CNS are frequently accompanied by synaptic loss, which is thought to involve phagocytic microglia and complement components. However, the mechanisms accounting for aberrant synaptic connectivity in the context of CD8+ T cell-driven neuronal damage are poorly understood. Here, we profiled the neuronal translatome in a murine model of encephalitis caused by CD8+ T cells targeting antigenic neurons. Neuronal STAT1 signaling and downstream CCL2 expression were essential for apposition of phagocytes, ensuing synaptic loss and neurological disease. Analogous observations were made in the brains of Rasmussen's encephalitis patients. In this devastating CD8+ T cell-driven autoimmune disease, neuronal STAT1 phosphorylation and CCL2 expression co-clustered with infiltrating CD8+ T cells as well as phagocytes. Taken together, our findings uncover an active role of neurons in coordinating phagocyte-mediated synaptic loss and highlight neuronal STAT1 and CCL2 as critical steps in this process that are amenable to pharmacological interventions.
Subject(s)
Neurons/metabolism , Phagocytosis/physiology , Synapses/physiology , Animals , Brain/pathology , CD8-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/metabolism , Chemokine CCL2/genetics , Chemokine CCL2/physiology , Disease Models, Animal , Encephalitis/genetics , Encephalitis/immunology , Encephalitis/physiopathology , Female , Humans , Inflammation/immunology , Inflammation/physiopathology , Male , Mice , Mice, Inbred C57BL , Microglia/metabolism , Nervous System Diseases/metabolism , Neurons/physiology , Phagocytes/immunology , Phagocytes/metabolism , Phagocytosis/immunology , Phosphorylation , STAT1 Transcription Factor/physiology , Transcriptome/geneticsABSTRACT
Recent studies have shown that tissue macrophages (MΦ) arise from embryonic progenitors of the yolk sac (YS) and fetal liver and colonize tissues before birth. Further studies have proposed that developmentally distinct tissue MΦ can be identified based on the differential expression of F4/80 and CD11b, but whether a characteristic transcriptional profile exists is largely unknown. Here, we took advantage of an inducible fate-mapping system that facilitated the identification of CD45(+)c-kit(-)CX3CR1(+)F4/80(+) (A2) progenitors of the YS as the source of F4/80(hi) but not CD11b(hi) MΦ. Large-scale transcriptional profiling of MΦ precursors from the YS stage to adulthood allowed for building computational models for F4/80(hi) tissue macrophages being direct descendants of A2 progenitors. We further identified a distinct molecular signature of F4/80(hi) and CD11b(hi) MΦ and found that Irf8 was vital for MΦ maturation. Our data provide new cellular and molecular insights into the origin and developmental pathways of tissue MΦ.
