The TREM2-APOE pathway drives the transcriptional phenotype of dysfunctional microglia in neurodegenerative diseases VI

Microglia play a pivotal role in the maintenance of brain homeostasis, but lose their homeostatic function during the course of neurodegenerative disorders. We identified a specific APOE-dependent molecular signature in microglia isolated from mouse models of amyotrophic lateral sclerosis, multiple sclerosis and Alzheimer’s disease (SOD1, EAE and APP-PS1) and in microglia surrounding neuritic A?-plaques in human Alzheimer’s disease brain. This is mediated by a switch from a (M0)-homeostatic to (MGnD)-neurodegenerative phenotype following phagocytosis of apoptotic neurons via the TREM2-APOE pathway. TREM2 induces APOE signaling which is a negative regulator of the transcription program in M0-homeostatic microglia. Targeting the TREM2-APOE pathway restores the M0-homeostatic signature of microglia in APP-PS1 and SOD1 mice and prevents from neuronal loss in an acute model of neurodegeneration. In SOD1 mice, TREM2 regulates MGnD in a gender-dependent manner. APOE-mediated MGnD microglia lose their tolerogenic function. Taken together, our work identifies the TREM2-APOE pathway as a major regulator of microglial functional phenotype in neurodegenerative diseases and serves as a novel target to restore homeostatic microglia. Overall design: Illumina NextSeq500 was used to identify disease-associated vs. homeostatic molecular microglia signature in microglia in different disease models and transgenic models. Bulk microglia (1,000 cells/sample) FCRLS+ sorted microglia.

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Krasemann S, Madore C, Cialic R, Baufeld C, Calcagno N, El Fatimy R, Beckers L, O'Loughlin E, Xu Y, Fanek Z, Greco DJ, Smith ST, Tweet G, Humulock Z, Zrzavy T, Conde-Sanroman P, Gacias M, Weng Z, Chen H, Tjon E, Mazaheri F, Hartmann K, Madi A, Ulrich JD, Glatzel M, Worthmann A, Heeren J, Budnik B, Lemere C, Ikezu T, Heppner FL, Litvak V, Holtzman DM, Lassmann H, Weiner HL, Ochando J, Haass C, Butovsky O