Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and -independent cellular responses in Alzheimer’s disease [15 months]
Ontology highlight
ABSTRACT: Glia have been implicated in Alzheimer’s disease (AD) pathogenesis. Variants of the microglia receptor TREM2 increase AD risk and activation of “disease-associated microglia” (DAM) is dependent on TREM2 in mouse models of AD. We surveyed gene expression changes associated with AD pathology and TREM2 in 5XFAD mice and human AD by snRNA-seq. We confirmed the presence of Trem2-dependent DAM and identified a novel Serpina3n+C4b+ reactive oligodendrocyte population in mice. Interestingly, remarkably different glial phenotypes were evident in human AD. Microglia signature was reminiscent of IRF8-driven reactive microglia in peripheral nerve injury. Oligodendrocyte signatures suggested impaired axonal myelination and metabolic adaptation to neuronal degeneration. Astrocyte profiles indicated weakened metabolic coordination with neurons. Notably, the reactive phenotype of microglia was less palpable in TREM2 R47H and R62H carriers than in non-carriers, demonstrating a TREM2 requirement in both mouse and human AD, despite the marked species-specific differences.
Project description:Glia have been implicated in Alzheimer’s disease (AD) pathogenesis. Variants of the microglia receptor TREM2 increase AD risk and activation of “disease-associated microglia” (DAM) is dependent on TREM2 in mouse models of AD. We surveyed gene expression changes associated with AD pathology and TREM2 in 5XFAD mice and human AD by snRNA-seq. We confirmed the presence of Trem2-dependent DAM and identified a novel Serpina3n+C4b+ reactive oligodendrocyte population in mice. Interestingly, remarkably different glial phenotypes were evident in human AD. Microglia signature was reminiscent of IRF8-driven reactive microglia in peripheral nerve injury. Oligodendrocyte signatures suggested impaired axonal myelination and metabolic adaptation to neuronal degeneration. Astrocyte profiles indicated weakened metabolic coordination with neurons. Notably, the reactive phenotype of microglia was less palpable in TREM2 R47H and R62H carriers than in non-carriers, demonstrating a TREM2 requirement in both mouse and human AD, despite the marked species-specific differences.
Project description:Alzheimer's disease (AD) is a detrimental neurodegenerative disease with no effective treatments. Due to cellular heterogeneity, the roles of immune cell subsets in AD onset and progression are poorly understood. By transcriptional single cell sorting, we comprehensively map all immune populations in wild type and AD–transgenic (Tg-AD) mouse brains. We describe a novel microglia type associated with neurodegenerative diseases (DAM) and identify the markers, spatial-location, and pathways associated with these cells. Immunohistochemical staining of mice and human brain slices showed DAM with intracellular/phagocytic Aβ particles. Single cell analysis of DAM in Tg-AD and Trem2-/- Tg-AD revealed that the DAM program is activated in a two-step process. Activation is initiated in a Trem2 independent manner which involves down-regulation of microglia checkpoints, followed by activation of a Trem2-dependent program. These data identify a unique microglia-type, which may have important implications for future treatment of AD and other neurodegenerative diseases.
Project description:Alzheimer's disease (AD) is a detrimental neurodegenerative disease with no effective treatments. Due to cellular heterogeneity, the roles of immune cell subsets in AD onset and progression are poorly understood. By transcriptional single cell sorting, we comprehensively map all immune populations in wild type and AD–transgenic (Tg-AD) mouse brains. We describe a novel microglia type associated with neurodegenerative diseases (DAM) and identify the markers, spatial-location, and pathways associated with these cells. Immunohistochemical staining of mice and human brain slices showed DAM with intracellular/phagocytic Aβ particles. Single cell analysis of DAM in Tg-AD and Trem2-/- Tg-AD revealed that the DAM program is activated in a two-step process. Activation is initiated in a Trem2 independent manner which involves down-regulation of microglia checkpoints, followed by activation of a Trem2-dependent program. These data identify a unique microglia-type, which may have important implications for future treatment of AD and other neurodegenerative diseases.
Project description:Genetic studies have highlighted microglia as pivotal in orchestrating Alzheimer’s disease (AD). Microglia that adhere to Aβ plaques acquire a transcriptional signature, “diseaseassociated microglia” (DAM), which largely emanates from the TREM2-DAP12 receptor complex that transmits intracellular signals through the protein tyrosine kinase SYK. The human TREM2R47H variant associated with high AD risk fails to activate microglia via SYK. We found that SYK-deficient microglia cannot encase Aβ plaques, accelerating brain pathology and behavioral deficits. SYK deficiency impaired the PI3K-AKT-GSK3β-mTOR pathway, incapacitating anabolic support required for attaining the DAM profile. However, SYK-deficient microglia proliferated and advanced to an Apoe-expressing prodromal stage of DAM; this pathway relied on the adaptor DAP10, which also binds TREM2. Thus, microglial responses to Aβ involve non-redundant SYK- and DAP10-pathways. Systemic administration of an antibody against CLEC7A, a receptor that directly activates SYK, rescued microglia activation in mice expressing the TREM2R47H allele, unveiling new options for AD immunotherapy.
Project description:Genetic studies have highlighted microglia as pivotal in orchestrating Alzheimer’s disease (AD). Microglia that adhere to Aβ plaques acquire a transcriptional signature, “diseaseassociated microglia” (DAM), which largely emanates from the TREM2-DAP12 receptor complex that transmits intracellular signals through the protein tyrosine kinase SYK. The human TREM2R47H variant associated with high AD risk fails to activate microglia via SYK. We found that SYK-deficient microglia cannot encase Aβ plaques, accelerating brain pathology and behavioral deficits. SYK deficiency impaired the PI3K-AKT-GSK3β-mTOR pathway, incapacitating anabolic support required for attaining the DAM profile. However, SYK-deficient microglia proliferated and advanced to an Apoe-expressing prodromal stage of DAM; this pathway relied on the adaptor DAP10, which also binds TREM2. Thus, microglial responses to Aβ involve non-redundant SYK- and DAP10-pathways. Systemic administration of an antibody against CLEC7A, a receptor that directly activates SYK, rescued microglia activation in mice expressing the TREM2R47H allele, unveiling new options for AD immunotherapy.
Project description:TREM2, a microglia-specific receptor, is strongly associated with Alzheimer’s disease (AD) risk and modulates microglial responses critical to AD pathogenesis. However, its role in tauopathy and neurodegeneration remains unclear. Here, by using a PS19 tauopathy mouse model with inducible overexpression of human wild-type TREM2 (TREM2-WT) or the R47H variant (TREM2-R47H), we show that TREM2-WT overexpression modestly reduces soluble phosphorylated tau (p-tau) levels and mildly preserves neuronal integrity, whereas TREM2-R47H fails to impact p-tau levels or neurodegeneration. Single-cell RNA sequencing revealed that TREM2-WT enhances disease-associated microglia (DAM) signatures, while TREM2-R47H drives the MHCII+ microglial phenotypes. These findings demonstrate that TREM2-WT confers modest benefits in tauopathy models, whereas TREM2-R47H exhibits reduced functionality. Our study underscores the therapeutic potential of enhancing TREM2 activity to modulate microglial responses and mitigate neurodegeneration in AD.
Project description:Microglia-mediated neuroinflammation has been implicated in the pathogenesis of Alzheimer's disease (AD). Although microglia in aging and neurodegenerative disease model mice show a loss of homeostatic phenotype and activation of disease-associated microglia (DAM), a correlation between those phenotypes and the degree of neuronal cell loss has not been clarified. In this study, we performed RNA sequencing of microglia isolated from three representative neurodegenerative mouse models, AppNL-G-F/NL-G-F with amyloid pathology, rTg4510 with tauopathy, and SOD1G93A with motor neuron disease by magnetic activated cell sorting. In parallel, gene expression patterns of the human precuneus with early Alzheimer's change (n=11) and control brain (n=14) were also analyzed by RNA sequencing. We found that a substantial reduction of homeostatic microglial genes in rTg4510 and SOD1G93A microglia, whereas DAM genes were uniformly upregulated in all mouse models. The reduction of homeostatic microglial genes was correlated with the degree of neuronal cell loss. In human precuneus with early AD pathology, reduced expression of genes related to microglia- and oligodendrocyte-specific markers was observed, although the expression of DAM genes was not upregulated. Our results implicate a loss of homeostatic microglial function in the progression of AD and other neurodegenerative diseases. Moreover, analyses of human precuneus also suggest loss of microglia and oligodendrocyte functions induced by early amyloid pathology in human.
Project description:The hemizygous R47H variant of TREM2, a microglia-specific gene in the brain, increases risk for late-onset Alzheimer’s disease (AD). Using transcriptomic analysis at the single-nuclei level from brain tissue of AD patients with the R47H mutation or the common variant (CV)-TREM2, we found that R47H-associated microglial subpopulations had enhanced inflammatory signatures reminiscent of previously-identified disease-associated microglia (DAM) and hyperactivation of AKT, one of the signaling pathways downstream of TREM2. We established a tauopathy mouse model with heterozygous knock-in of the human TREM2 with R47H mutation or CV, and found that R47H induced and exacerbated tau-mediated spatial memory deficits in female mice. Single-cell transcriptomic analysis of microglia from these mice also revealed transcriptomic changes induced by R47H that had significant overlaps with R47H microglia in human AD brains, including robust increases in proinflammatory cytokines, activation of Akt signaling, and elevation of a subset of disease-associated microglial signatures. Pharmacological Akt inhibition with MK-2206 largely reversed the enhanced inflammatory signatures in primary R47H microglia treated with tau fibrils. Strikingly, in R47H heterozygous tauopathy mice, MK-2206 treatment abolished a tauopathy-dependent microglial subcluster, and rescued tauopathy-induced synapse loss. By uncovering disease-enhancing mechanisms of the R47H mutation conserved in human and mouse, our study supports inhibitors of AKT signaling as a novel microglial modulating strategy to treat AD.
Project description:The hemizygous R47H variant of TREM2, a microglia-specific gene in the brain, increases risk for late-onset Alzheimer’s disease (AD). Using transcriptomic analysis at the single-nuclei level from brain tissue of AD patients with the R47H mutation or the common variant (CV)-TREM2, we found that R47H-associated microglial subpopulations had enhanced inflammatory signatures reminiscent of previously-identified disease-associated microglia (DAM) and hyperactivation of AKT, one of the signaling pathways downstream of TREM2. We established a tauopathy mouse model with heterozygous knock-in of the human TREM2 with R47H mutation or CV, and found that R47H induced and exacerbated tau-mediated spatial memory deficits in female mice. Single-cell transcriptomic analysis of microglia from these mice also revealed transcriptomic changes induced by R47H that had significant overlaps with R47H microglia in human AD brains, including robust increases in proinflammatory cytokines, activation of Akt signaling, and elevation of a subset of disease-associated microglial signatures. Pharmacological Akt inhibition with MK-2206 largely reversed the enhanced inflammatory signatures in primary R47H microglia treated with tau fibrils. Strikingly, in R47H heterozygous tauopathy mice, MK-2206 treatment abolished a tauopathy-dependent microglial subcluster, and rescued tauopathy-induced synapse loss. By uncovering disease-enhancing mechanisms of the R47H mutation conserved in human and mouse, our study supports inhibitors of AKT signaling as a novel microglial modulating strategy to treat AD.
Project description:Loss-of-function mutations in TREM2 (triggering receptor expressed on myeloid cells 2) strongly increase Alzheimer’s disease (AD) risk. Preclinical models using Trem2 deletion or overexpression have revealed a protective Trem2 function related to β-amyloid accumulation, a process that is most prominent during the pre-diagnosis stages of AD. The role of TREM2 in later AD stages characterized by tau-mediated neurodegeneration is less clear. To understand Trem2 function in the context of both β-amyloid and tau pathologies, we examined Trem2-deficient mice expressing mutant tau alone (pR5-183 model) or in the TauPS2APP model, in which β-amyloid pathology exacerbates tau pathology and neurodegeneration. Single-cell RNA-sequencing in these models revealed robust disease-associated microglia (DAM) activation in TauPS2APP mice that was both amyloid-dependent and Trem2-dependent. In the presence of β-amyloid pathology, Trem2 deletion further exacerbated tau accumulation and spreading and promoted brain atrophy. Without β-amyloid pathology, Trem2 deletion did not affect these processes. Therefore, TREM2 may slow AD progression and reduce tau-driven neurodegeneration by restricting the degree to which β-amyloid facilitates the spreading of pathogenic tau