Tau accumulation induces microglial state alterations in Alzheimer’s disease model mice (snRNA-seq, part 1)
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ABSTRACT: Unique microglial states have been identified in Alzheimer’s disease (AD) model mice and postmortem AD brains. Although it has been well documented that amyloid-β accumulation induces the alteration of microglial states, the relationship between tau pathology and microglial states remains incompletely understood because of a lack of suitable AD models. In the present study, we generated a novel AD model mouse by the intracerebral administration of tau purified from human brains with primary age-related tauopathy into AppNL-G-F/MAPT double knock-in (dKI) mice.
Project description:Unique microglial states have been identified in Alzheimer’s disease (AD) model mice and postmortem AD brains. Although it has been well documented that amyloid-β accumulation induces the alteration of microglial states, the relationship between tau pathology and microglial states remains incompletely understood because of a lack of suitable AD models. In the present study, we generated a novel AD model mouse by the intracerebral administration of tau purified from human brains with primary age-related tauopathy into AppNL-G-F/MAPT double knock-in (dKI) mice.
Project description:Unique microglial states have been identified in Alzheimer’s disease (AD) model mice and postmortem AD brains. Although it has been well documented that amyloid-β accumulation induces the alteration of microglial states, the relationship between tau pathology and microglial states remains incompletely understood because of a lack of suitable AD models. In the present study, we generated a novel AD model mouse by the intracerebral administration of tau purified from human brains with primary age-related tauopathy into AppNL-G-F/MAPT double knock-in (dKI) mice.
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:Tauopathies are age-associated neurodegenerative diseases whose mechanistic underpinnings remain elusive, partially due to lack of appropriate human models. Here, we engineered new human induced pluripotent stem cell (hiPSC)-derived neuronal lines to express 4R Tau and 4R Tau carrying the P301S MAPT mutation when differentiated into neurons. 4R-P301S neurons display progressive Tau inclusions upon seeding with Tau fibrils and recapitulate features of tauopathy phenotypes including shared transcriptomic signatures, autophagic body accumulation, and reduced neuronal activity. A CRISPRi screen of genes associated with Tau pathobiology identified over 500 genetic modifiers of seeding-induced Tau propagation, including retromer VPS29 and genes in the UFMylation cascade. In progressive supranuclear palsy (PSP) and Alzheimer’s Disease (AD) brains, the UFMylation cascade is altered in neurofibrillary-tangle-bearing neurons. Inhibiting the UFMylation cascade in vitro and in vivo suppressed seeding-induced Tau propagation. This model provides a robust platform to identify novel therapeutic strategies for 4R tauopathy.
Project description:Tauopathies are age-associated neurodegenerative diseases whose mechanistic underpinnings remain elusive, partially due to lack of appropriate human models. Here, we engineered new human induced pluripotent stem cell (hiPSC)-derived neuronal lines to express 4R Tau and 4R Tau carrying the P301S MAPT mutation when differentiated into neurons. 4R-P301S neurons display progressive Tau inclusions upon seeding with Tau fibrils and recapitulate features of tauopathy phenotypes including shared transcriptomic signatures, autophagic body accumulation, and reduced neuronal activity. A CRISPRi screen of genes associated with Tau pathobiology identified over 500 genetic modifiers of seeding-induced Tau propagation, including retromer VPS29 and genes in the UFMylation cascade. In progressive supranuclear palsy (PSP) and Alzheimer’s Disease (AD) brains, the UFMylation cascade is altered in neurofibrillary-tangle-bearing neurons. Inhibiting the UFMylation cascade in vitro and in vivo suppressed seeding-induced Tau propagation. This model provides a robust platform to identify novel therapeutic strategies for 4R tauopathy.
Project description:The hemizygous R47H variant of TREM2, a microglia-specific gene in the brain, increases risk for late-onset Alzheimer’s disease (AD). In this study, we identified a subpopulation of microglia with disease-enhancing proinflammatory signatures associated with the R47H mutation in human AD brains and tauopathy mouse brains. Using transcriptomic analysis at the single-nuclei level from AD patients with the R47H or the common variant (CV)-TREM2 with matched sex, pathology and clinical dementia status, we found that the R47H mutation was associated with cell type- and sex-specific transcriptional changes in human AD brains. Further characterization of microglia revealed 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. In a newly-generated tauopathy knock-in mouse model expressing one allele of human TREM2 (hTREM2) with either the R47H mutation or CV, 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. Strikingly, pharmacological Akt inhibition largely reversed the enhanced inflammatory signatures induced by R47H in primary microglia treated with tau fibrils as well as rescued the tauopathy-induced synapse loss in R47H heterozygous mice. By unraveling the disease-enhancing properties of the R47H mutation in mouse and human, our findings shed light on an immune-linked AD subtype and provide new directions for modulating microglial immune responses to treat AD.
Project description:APOE is the strongest genetic risk factor for late-onset Alzheimer’s disease. ApoE exacerbates tau-associated neurodegeneration by driving microglial activation. However, how apoE regulates microglial activation and whether targeting apoE is therapeutically beneficial in tauopathy is unclear. Here we show that overexpressing a low-density lipoprotein receptor (LDLR) transgene in P301S tau transgenic mice markedly reduces brain apoE and ameliorates tau pathology and neurodegeneration. ApoE specifically interacts with a high-molecular-weight tau species, and highly correlates with phospho-tau and insoluble tau levels. Microglial expression of the LDLR transgene reduces intracellular apoE and is associated with less microglial activation. snRNA-seq analysis of apoE-deficient or LDLR-overexpressing brains reveals that apoE deficiency drives microglial catabolism and increases the oligodendrocyte progenitor cell population. LDLR overexpression shares overlapping mechanisms, but uniquely upregulates microglial expression of specific ion channels and neurotransmitter receptors in tauopathy. A subset of disease-associated astrocytes with both neuroprotective and neurotoxic gene signatures is also identified.
Project description:Alzheimer’s disease is known to alter astrocytes, but the effect of Aß and Tau pathology on these cells remains poorly understood. We investigated the transcriptomic behaviour of astrocytes (via translating ribosome affinity purification (TRAP)), and bulk brain tissue, in mouse models of APP/PS1 ß-amyloidopathy and MAPT-P301S tauopathy, in a mouse model overexpressing cytoprotective Nrf2 specifically in astrocytes (GFAP-Nrf2 model), and in crosses between the amyloidopathy and tauopathy models with the GFAP-Nrf2 mouse.
Project description:The strongest risk factors for Alzheimer’s disease (AD) include the 4 allele of apolipoprotein E (APOE), the R47H variant of triggering receptor expressed on myeloid cells 2 (TREM2), and female sex. Here, we combine APOE4 and TREM2R47H (R47H) in female P301S tauopathy mice to identify the pathways activated when AD risk is the strongest, thereby highlighting detrimental disease mechanisms. We find that the R47H variant induces neurodegeneration in 9- to- 10-month-old female APOE4 tauopathy mice. The combination of APOE4 and R47H (APOE4-R47H) worsened hyperphosphorylated tau pathology in the frontal cortex and amplified tauopathy-induced cell-autonomous microglial cGAS-STING signaling and downstream interferon response. APOE4-R47H microglia displayed cGAS- and BAX-dependent upregulation of senescence, showing association between neurotoxic signatures and implicating mitochondrial permeabilization in pathogenesis. By uncovering pathways enhanced by the strongest AD risk factors, our study points to cGAS-STING signaling and associated microglial senescence as potential drivers of AD risk.