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Fate-mapping via Spp1-expression history revealed innate immune memory of microglia imprinted by neonatal injury [Spp1Tdt]

ABSTRACT: Microglial reactivity to injury and disease is emerging as a heterogeneous, dynamic, and crucial determinant in neurological disorders. However, the plasticity and ultimate fate of disease-associated microglia (DAM) remains largely unknown. We established a lineage tracing system, leveraging the expression dynamics of Spp1, which allows for genetic labeling of DAM-like microglia and tracking their behavior during brain injury and recovery. Fate-mapping of Spp1+ microglia in juvenile stroke revealed an irreversible state of reactive microglia that are ultimately eliminated from the injured brain. In contrast, DAM-like microglia in the neonatal context exhibit high plasticity, capable of regaining a homeostatic signature and integrating into the global microglial network after recovery. Furthermore, neonatal injury has a lasting impact on microglia, rendering them intrinsically sensitized to subsequent immune challenges. Therefore, by unraveling the fate of DAM-like microglia in various neuropathological conditions, our work highlights the exceptional plasticity and innate immune memory of neonatal microglia.

ORGANISM(S): Mus musculus

PROVIDER: GSE247391 | GEO | 2024/01/24

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).