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Microglial SHIP1 controls synaptic pruning in the developing hippocampus via the complement system

ABSTRACT: INPP5D, which encodes the lipid phosphatase SHIP1, is one of the most common genes associated with the risk of Alzheimer’s disease and is enriched in microglia in the central nervous system. SHIP1 has been found to be highly expressed in plaque-associated microglia. However, how it regulates microglial function and influences brain physiology has been poorly investigated. Here we show that SHIP1 is not only enriched in microglia associated with amyloid beta plaques, but also in early stages of healthy brain development. By combining in vivo loss-of-function approaches and proteomics, we discovered that conditional knockout mice lacking microglial SHIP1 (cKO) display increased complement and synapse loss in the early postnatal brain. Additionally, SHIP1 KO microglia show reduced morphological complexity, altered transcriptional signatures, and abnormal synaptic pruning, which is dependent on the complement system. Single nucleus RNA-sequencing analysis of the entire hippocampus confirmed decreased interaction for synaptic structure-related pathways in both excitatory and inhibitory neurons. Importantly, cKO mice show cognitive defects in adulthood only when microglial SHIP1 is depleted at early postnatal days, but not when depleted at later stages. Finally, using CRISPR/Cas9 we generated human iPSC-derived microglia lacking SHIP1, and validated the increased engulfment of synaptic structures. Altogether, these findings suggest that SHIP1 is essential for proper microglia-mediated synapse remodeling through the complement system in the early postnatal brain. Disrupting this process has lasting behavioral effects and may provide a link to vulnerability to neurodegeneration.

ORGANISM(S): Homo sapiens

PROVIDER: GSE279176 | GEO | 2024/12/09

REPOSITORIES: GEO

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Project description:Microglia colonize the brain parenchyma at early stages of development and accumulate in specific regions where they actively participate in cell death, angiogenesis, neurogenesis and synapse elimination. A recurring feature of embryonic microglial distribution is their association with developing axon tracts which, together with in vitro data, supports the idea of a physiological role for microglia in neurite development. Yet the demonstration of this role of microglia is still lacking. Here, we have studied the consequences of microglial dysfunction on the formation of the corpus callosum, the largest connective structure in the mammalian brain, which shows consistent microglial accumulation during development. We studied two models of microglial dysfunction: the loss-of-function of DAP12, a key microglial-specific signaling molecule, and a model of maternal inflammation by peritoneal injection of LPS at E15.5. We performed transcriptional profiling of maternally inflamed and Dap12-mutant microglia at E17.5. We found that both treatments principally down-regulated genes involved in nervous system development and function, particularly in neurite formation. We then analyzed the functional consequences of these microglial dysfunctions on the formation of the corpus callosum. We also took advantage of the Pu.1-/- mouse line, which is devoid of microglia. We now show that all three models of altered microglial activity resulted in the same defasciculation phenotype. Our study demonstrates that microglia are actively involved in the fasciculation of corpus callosum axons. To investigate possible roles for microglial during brain development, we challenged microglial function by two complementary approaches. First, we induced maternal inflammation by peritoneal injection of LPS into pregnant dams. Next, we analyzed the consequences of a loss of function of DAP12, a signaling molecule specifically expressed in microglia that is crucial for several aspects of microglia biology (references in Wakselman et al., 2008). We compared the gene expression profiles of microglia from control, maternally-inflamed by LPS (MI), and Dap12-mutated embryos. We isolated RNA from FACS sorted maternally inflamed (by LPS) and Dap12-mutant microglia at E17.5 pooled per pregnant dam; as a control we included PBS treated and untreated (UT) microglia. We compared gene expression between maternally inflamed microlgia (PBSvsLPS) and DAP12-mutant microglia (UTvsDAP12KO).

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Microglial SHIP1 controls synaptic pruning in the developing hippocampus via the complement system

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