RNA-seq to investigate sex-dependent changes in microglia in Cst7 knockout mice crossed with a mouse model of amyloid-driven Alzheimer's Disease
Ontology highlight
ABSTRACT: Microglial endolysosomal dysfunction is strongly implicated in neurodegeneration. Transcriptomic studies show that a microglial state characterised by a set of genes involved in endolysosomal function is induced in both mouse Alzheimer’s Disease (AD) models and in human AD brain, and that the onset of this state is emphasised in females. Cst7 (Cystatin F) is among the most highly unregulated genes in these microglia. However, the sex-specific function of Cst7 in neurodegenerative disease is not understood. Here, we crossed Cst7 -/- mice with the App NL-G-F mouse to test the role of Cst7 in a model of amyloid-driven AD.
Project description:Background: The p38 alpha mitogen-activated protein kinase (p38a) pathway is linked to both innate and adaptive immune responses, and as such, is currently under active investigation as a target for drug development in the context of Alzheimer’s disease (AD) and other conditions with neuroinflammatory dysfunction. While preclinical data has shown that p38a inhibition can protect against AD-associated neuropathology, the underlying mechanisms are only partially elucidated. Inhibitors of p38a may provide benefit via modulation of microglial-associated neuroinflammatory responses that contribute to the development of AD pathology. The present study tests this hypothesis by knocking out microglial p38a and assessing early-stage pathological changes. Materials and methods: Conditional knockout of microglial p38a was accomplished in 5-month-old C57BL/6J wild-type and amyloidogenic AD model (APPswe/PS1dE9) mice using a tamoxifen-inducible Cre/loxP system. Beginning at 7.5 months of age, animals underwent behavioral assessment on the open field and radial arm water maze tests, followed by collection of cortical and hippocampal tissues at 11 months. Additional endpoint measures included microglial RNA-seq analysis, quantification of pro-inflammatory cytokines, assessment of amyloid burden and plaque deposition, and characterization of microglia-plaque dynamics using a combination of ELISA, immunohistochemical, and immunofluorescent techniques. Results: Loss of microglial p38a did not alter behavioral outcomes, pro-inflammatory cytokine levels, or overall amyloid plaque burden. However, this manipulation did significantly increase hippocampal levels of soluble Abeta42 and reduce colocalization of Iba1 and 6E10 in a subset microglia in close proximity to plaques, indicating that p38a suppression may alter microglial phagocytosis. Conclusion: The data presented here suggest that rather than reducing inflammation per se, the net effect of microglial p38a inhibition in the context of AD-type amyloid pathology could be an alteration of phagocytosis and/or plaque deposition. Additionally, these results support future investigations of microglial p38a signaling at different stages of disease, as well as its relationship to phagocytic processes in this particular cell-type.
Project description:Microglia are essential to maintain brain homeostasis, but when dysregulated, exert pathogenic functions in Alzheimer’s disease (AD). Recent evidence has implicated senescent/dystrophic microglia in the pathological process of AD. Whether microglial senescence is a cause or consequence of AD pathogenesis however is unclear. Here we report that autophagy, a lysosomal degradation pathway, restricts cellular senescence of microglia and confer neuroprotection in AD mouse model. Autophagy-deficient microglia show hallmarks of cellular senescence evidenced by reduced proliferation, increased Cdkn1a/p21Cip, dystrophy, and typical secretory phenotype. While disease-associated microglia (DAM) surrounding amyloid plaques exhibit heightened autophagy, autophagy deficient, senescent microglia (SAM) disengage from and thus fail to limit the diffusive amyloid plaques, causing enhanced tau phosphorylation and neurotoxicity in AD model. Treatment of senolytic drugs removes senescent microglia and alleviates neuropathology. Our study demonstrates a causal role of autophagy impairment in microglial senescence and neurotoxicity and suggests therapeutic potential of senolytic treatment for AD.
Project description:Alzheimer’s disease (AD) is an age-associated neurodegenerative disease characterized by amyloidosis, tauopathy, and activation of microglia, the brain resident innate immune cells. We show that a RiboTag translational profiling approach can bypass biases due to cellular enrichment/cell sorting. In our recent study entitled “Microglial translational profiling reveals a convergent APOE pathway from aging, amyloid, and tau”, we utilized data acquired using this approach in models of amyloidosis, tauopathy, and aging, to reveal a common set of alterations and identified a central APOE-driven network that converged on CCL3 and CCL4 across all conditions. Notably, examination of the aged female dataset demonstrated a significant exacerbation of many of these shared transcripts in this APOE network, revealing a potential mechanism for increased AD susceptibility in females. This study has broad implications for microglial transcriptomic approaches and provides new insights into microglial pathways associated with different pathological aspects of aging and AD.
Project description:Alzheimer’s disease (AD) therapies utilizing amyloid-β (Aβ) immunization have shown potential in clinical trials. Yet, the mechanisms driving Aβ clearance in the immunized AD brain remain unclear. Here, we use spatial transcriptomics to explore the effects of both active and passive Aβ immunization in the AD brain. We compare actively immunized AD patients with nonimmunized AD patients and neurologically healthy controls, identifying distinct microglial states associated with Aβ clearance. Using high-resolution spatial transcriptomics alongside single-cell RNA sequencing, we delve deeper into the transcriptional pathways involved in Aβ removal after lecanemab treatment. We uncover spatially distinct microglial responses that vary by brain region. Our analysis reveals upregulation of the triggering receptor expressed on myeloid cells 2 (TREM2) and apolipoprotein E (APOE) in microglia across immunization approaches, which correlate positively with antibody responses and Aβ removal. Furthermore, we show that complement signaling in brain myeloid cells contributes to Aβ clearance after immunization. These findings provide new insights into the transcriptional mechanisms orchestrating Aβ removal and shed light on the role of microglia in immune-mediated Aβ clearance. Importantly, our work uncovers potential molecular targets that could enhance Aβ-targeted immunotherapies, offering new avenues for developing more effective therapeutic strategies to combat AD.
Project description:Alzheimer’s disease (AD) therapies utilizing amyloid-β (Aβ) immunization have shown potential in clinical trials. Yet, the mechanisms driving Aβ clearance in the immunized AD brain remain unclear. Here, we use spatial transcriptomics to explore the effects of both active and passive Aβ immunization in the AD brain. We compare actively immunized AD patients with nonimmunized AD patients and neurologically healthy controls, identifying distinct microglial states associated with Aβ clearance. Using high-resolution spatial transcriptomics alongside single-cell RNA sequencing, we delve deeper into the transcriptional pathways involved in Aβ removal after lecanemab treatment. We uncover spatially distinct microglial responses that vary by brain region. Our analysis reveals upregulation of the triggering receptor expressed on myeloid cells 2 (TREM2) and apolipoprotein E (APOE) in microglia across immunization approaches, which correlate positively with antibody responses and Aβ removal. Furthermore, we show that complement signaling in brain myeloid cells contributes to Aβ clearance after immunization. These findings provide new insights into the transcriptional mechanisms orchestrating Aβ removal and shed light on the role of microglia in immune-mediated Aβ clearance. Importantly, our work uncovers potential molecular targets that could enhance Aβ-targeted immunotherapies, offering new avenues for developing more effective therapeutic strategies to combat AD.
Project description:Alzheimer’s disease (AD) therapies utilizing amyloid-β (Aβ) immunization have shown potential in clinical trials. Yet, the mechanisms driving Aβ clearance in the immunized AD brain remain unclear. Here, we use spatial transcriptomics to explore the effects of both active and passive Aβ immunization in the AD brain. We compare actively immunized AD patients with nonimmunized AD patients and neurologically healthy controls, identifying distinct microglial states associated with Aβ clearance. Using high-resolution spatial transcriptomics alongside single-cell RNA sequencing, we delve deeper into the transcriptional pathways involved in Aβ removal after lecanemab treatment. We uncover spatially distinct microglial responses that vary by brain region. Our analysis reveals upregulation of the triggering receptor expressed on myeloid cells 2 (TREM2) and apolipoprotein E (APOE) in microglia across immunization approaches, which correlate positively with antibody responses and Aβ removal. Furthermore, we show that complement signaling in brain myeloid cells contributes to Aβ clearance after immunization. These findings provide new insights into the transcriptional mechanisms orchestrating Aβ removal and shed light on the role of microglia in immune-mediated Aβ clearance. Importantly, our work uncovers potential molecular targets that could enhance Aβ-targeted immunotherapies, offering new avenues for developing more effective therapeutic strategies to combat AD.
Project description:Alzheimer’s disease (AD) therapies utilizing amyloid-β (Aβ) immunization have shown potential in clinical trials. Yet, the mechanisms driving Aβ clearance in the immunized AD brain remain unclear. Here, we use spatial transcriptomics to explore the effects of both active and passive Aβ immunization in the AD brain. We compare actively immunized AD patients with nonimmunized AD patients and neurologically healthy controls, identifying distinct microglial states associated with Aβ clearance. Using high-resolution spatial transcriptomics alongside single-cell RNA sequencing, we delve deeper into the transcriptional pathways involved in Aβ removal after lecanemab treatment. We uncover spatially distinct microglial responses that vary by brain region. Our analysis reveals upregulation of the triggering receptor expressed on myeloid cells 2 (TREM2) and apolipoprotein E (APOE) in microglia across immunization approaches, which correlate positively with antibody responses and Aβ removal. Furthermore, we show that complement signaling in brain myeloid cells contributes to Aβ clearance after immunization. These findings provide new insights into the transcriptional mechanisms orchestrating Aβ removal and shed light on the role of microglia in immune-mediated Aβ clearance. Importantly, our work uncovers potential molecular targets that could enhance Aβ-targeted immunotherapies, offering new avenues for developing more effective therapeutic strategies to combat AD.
Project description:Two microglial TAM receptor tyrosine kinases - Axl and Mer - have been linked to Alzheimer’s disease, but their roles in disease have not been tested experimentally. We find that in Alzheimer’s disease and its mouse models, induced expression of Axl and Mer in amyloid plaque-associated microglia is coupled to induced plaque decoration by the TAM ligand Gas6 and its co-ligand phosphatidylserine. In the APP/PS1 mouse model of Alzheimer’s disease, sIngle cell RNAseq analysis comparing wild type microglia with those with Axl and Mer deficiency reveals a similar disease state transitional program of microglia but a dampened differential expression of numerous AD siganture genes in microglia lacking TAM receptors. In line with the transcriptomic data, using two-photon microscopy, we show that genetic ablation of Axl and Mer results in microglia that are unable to normally detect, respond to, organize, or phagocytose amyloid beta plaques. These major deficits notwithstanding, and contrary to expectation, TAM-deficient APP/PS1 mice develop fewer dense-core plaques than APP/PS1 mice with normal microglia. Our findings reveal that the TAM system is an essential mediator of microglial recognition and engulfment of amyloid plaques, and that TAM-driven microglial phagocytosis does not constrain, but rather promotes, plaque development.
Project description:Impairment of microglial clearance activity contributes to beta-amyloid (Aβ) pathology in Alzheimer disease (AD). While the transcriptome profile of microglia directs microglial functions, how the microglial transcriptome can be regulated to alleviate AD pathology is largely unknown. Here, we show that injection of interleukin (IL)-33 in an AD transgenic mouse model ameliorates Aβ pathology by reprogramming microglial epigenetic and transcriptomic profiles to induce a microglial subpopulation with enhanced phagocytic activity. These IL-33–responsive microglia (IL-33RM) express distinct transcriptome signature, highlighted by major histocompatibility complex class II genes, and restored homeostatic signature genes. IL-33–induced remodeling of chromatin accessibility and PU.1 transcription factor binding at the signature genes of IL-33RM control their transcriptome reprogramming. Specifically, disrupting PU.1–DNA interaction abolishes the microglial state transition and Aβ clearance induced by IL-33. Thus, we define a PU.1-dependent transcriptional pathway that drives the IL-33–induced functional state transition of microglia, resulting in enhanced Aβ clearance.
Project description:In Alzheimer’s disease (AD), sensome receptor dysfunction impairs microglial danger-associated molecular pattern (DAMP) clearance and exacerbates disease pathology. While extrinsic signals including interleukin-33 (IL-33) can restore microglial DAMP clearance, it remains largely unclear how the sensome receptor(s) is regulated and interacts with DAMP during phagocytic clearance. Here, we show that IL-33 induces VCAM1 in microglia, which promotes microglial chemotaxis toward amyloid-beta (Aβ) plaque-associated ApoE, and leads to Aβ clearance. We show that IL-33 stimulates a chemotactic state in microglia, characterized by Aβ-directed migration. Functional screening identified that VCAM1 directs microglial Aβ chemotaxis by sensing Aβ plaque-associated ApoE. Moreover, we found that disrupting VCAM1–ApoE interaction abolishes microglial Aβ chemotaxis, resulting in decreased microglial clearance of Aβ. In patients with AD, higher cerebrospinal fluid levels of soluble VCAM1 were correlated with impaired microglial Aβ chemotaxis. Together, our findings demonstrate that promoting VCAM1–ApoE-dependent microglial functions ameliorates AD pathology.