Jedi-1/MEGF12-mediated phagocytosis controls the pro-neurogenic properties of microglia in the ventricular-subventricular zone

Abstract

Microglia are the primary phagocytes in the central nervous system and are responsible for clearing dead cells generated during development or disease. The phagocytic process shapes the phenotype of the microglia, which affects the local environment. A unique population of microglia reside in the ventricular-subventricular zone (V-SVZ) of neonatal mice, but how they influence this neurogenic niche is not well-understood. Here, we demonstrate that phagocytosis creates a pro-neurogenic microglial phenotype in the V-SVZ and that these microglia phagocytose apoptotic cells via the engulfment receptor Jedi-1. Deletion of Jedi-1 decreases apoptotic cell clearance, triggering the development of a neuroinflammatory phenotype, reminiscent of neurodegenerative and-age-associated microglia, that reduces neural precursor proliferation via elevated interleukin (IL)-1{beta} signaling; inhibition of IL-1 receptor rescues precursor proliferation in vivo. Together, these results reveal a critical role for Jedi-1 in connecting microglial phagocytic activity to a phenotype that promotes neurogenesis in the developing V-SVZ. Graphical Abstract. Jedi-1-dependent phagocytosis supports neurogenesis via suppression of microglial inflammatory pathway activationTop: Wild-type Proliferative-zone-Associated Microglia (PAMs) (cyan) use the engulfment receptor Jedi-1 ( Jedi) to engulf apoptotic cells (yellow) in the neurogenic ventricular-subventricular zone (V-SVZ) of the early postnatal brain. Jedi activation supports neural precursor cell (NPC) proliferation and the generation of new neurons. Bottom: Deletion of Jedi reduces microglial phagocytosis and transforms PAMs into Disease-associated Inflammatory Microglia (DIMs) characterized by the upregulation of canonical inflammatory genes and core DIM markers iden ified in the aging and neurodegenerative brain (Nlrp3, NLR family pyrin domain-containing 3; Tnf, tumor necrosis factor; Ccl4, C-C chemokine ligand 4 (also called macrophage inflammatory protein 1{beta}); Ccr5, C-C chemokine receptor type 5). Increased interleukin-1{beta} (IL-1{beta}) synthesis, release, and signaling in the Jedi-null V-SVZ reduces NPC proliferation and newborn neuron number. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC="FIGDIR/small/531012v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@16b9785org.highwire.dtl.DTLVardef@a8be50org.highwire.dtl.DTLVardef@66b726org.highwire.dtl.DTLVardef@1825d8b_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIThe engulfment receptor Jedi-1 is expressed by microglia in the neonatal ventricular-subventricular zone (V-SVZ) neurogenic niche. C_LIO_LIJedi-1 knockout microglia have decreased engulfment ability, resulting in accumulation of dead cells in the V-SVZ. C_LIO_LILoss of Jedi-1 leads to a neuroinflammatory phenotype in microglia that is characteristic of neurodegenerative and age-associated microglia. C_LIO_LIMicroglial-specific loss of Jedi-1 reduces neurogenesis, which is rescued in vivo by inhibition of interleukin-1{beta} signaling. C_LI