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:Alzheimer’s disease (AD) is the most prevalent form of dementia and is characterized by abnormal extracellular aggregates of amyloid-b and intraneuronal hyperphosphorylated, tau tangles and neuropil threads. Microglia, the tissue-resident macrophages of the central nervous system (CNS), are important for CNS homeostasis and implicated in AD pathology. In amyloid mouse models, a phagocytic/activated microglia phenotype has been identified. How increasing levels of amyloid-b and tau pathology affect human microglia transcriptional profiles is unknown. Here, we performed snRNAseq on 482,472 nuclei from non-demented control brains and AD brains containing only amyloid-b plaques or both amyloid-b plaques and tau pathology. Within the microglia population, distinct expression profiles were identified of which two were AD pathology-associated. The phagocytic/activated AD1-microglia population abundance strongly correlated with tissue amyloid-b load and localized to amyloid-b plaques. The AD2-microglia abundance strongly correlated with tissue phospho-tau load and these microglia were more abundant in samples with over tau pathology. This full characterization of human disease associated microglia phenotypes provides new insights in the pathophysiological role of microglia in AD and offers new targets for microglia-state-specific therapeutic strategies.
Project description:Alzheimer’s disease (AD) is a progressive neurodegenerative disease and the most common cause of dementia, characterized by deposition of extracellular amyloid-beta (Aβ) aggregates and intraneuronal hyperphosphorylated Tau. Many AD risk genes, identified in genome-wide association studies (GWAS), are expressed in microglia, the innate immune cells of the central nervous system. Specific subtypes of microglia emerged in relation to AD pathology, such as disease-associated microglia (DAMs), which increased in number with age in amyloid mouse models and in human AD cases. However, the initial transcriptional changes in these microglia in response to amyloid are still unknown. Here, to determine early changes in microglia gene expression, hippocampal microglia from APPswe/PS1dE9 (APP/PS1) mice and wildtype littermates were isolated and analyzed by RNA sequencing (RNA-seq). By bulk RNA-seq, transcriptomic changes were detected in hippocampal microglia from 6-months-old APP/PS1 mice. By performing single cell RNA-seq of CD11c-positive and negative microglia from 6-months-old APP/PS1 mice and analysis of the transcriptional trajectory from homeostatic to CD11c-positive microglia, we identified a set of genes that potentally reflect the initial response of microglia to Aβ.
Project description:We examined the role of TREM2 on microglia responses to amyloid-beta deposition in a mouse model of Alzheimer's disease Microglia were FACS-purified from 8.5 month old WT, Trem2-/-, 5XFAD, and Trem2-/- 5XFAD mice
Project description:Alzheimer’s disease (AD) is a progressive neurodegenerative disease and the most common cause of dementia, characterized by deposition of extracellular amyloid-beta (Aβ) aggregates and intraneuronal hyperphosphorylated Tau. Many AD risk genes, identified in genome-wide association studies (GWAS), are expressed in microglia, the innate immune cells of the central nervous system. Specific subtypes of microglia emerged in relation to AD pathology, such as disease-associated microglia (DAMs), which increased in number with age in amyloid mouse models and in human AD cases. However, the initial transcriptional changes in these microglia in response to amyloid are still unknown. Here, to determine early changes in microglia gene expression, hippocampal microglia from APPswe/PS1dE9 (APP/PS1) mice and wildtype littermates were isolated and analyzed by RNA sequencing (RNA-seq). By bulk RNA-seq, transcriptomic changes were detected in hippocampal microglia from 6-months-old APP/PS1 mice. By performing single cell RNA-seq of CD11c-positive and negative microglia from 6-months-old APP/PS1 mice and analysis of the transcriptional trajectory from homeostatic to CD11c-positive microglia, we identified a set of genes that potentally reflect the initial response of microglia to Aβ.
Project description:Polygenic risk scores have identified that genetic variants without genome-wide significance still add to the genetic risk of developing Alzheimer’s disease (AD). Whether and how subthreshold risk loci translate into relevant disease pathways, is unknown. We investigate here the involvement of AD risk variants in the transcriptional responses of two mouse models: APPswe/PS1L166P and Thy-TAU22. A unique gene expression module, highly enriched for AD risk genes, is specifically responsive to Aβ but not TAU pathology. We identify in this module 7 established AD risk genes (APOE, CLU, INPP5D, CD33, PLCG2, SPI1 and FCER1G) and 11 AD GWAS genes below the genome-wide significance threshold (GPC2, TREML2, SYK, GRN, SLC2A5, SAMSN1, PYDC1, HEXB, RRBP1, LYN and BLNK), that become significantly upregulated when exposed to Aβ. Single microglia sequencing confirms that Aβ, not TAU, pathology induces marked transcriptional changes in microglia, including increased proportions of activated microglia. We conclude that genetic risk of AD functionally translates into different microglia pathway responses to Aβ pathology, placing AD genetic risk downstream of the amyloid pathway but upstream of TAU pathology.
Project description:Polygenic risk scores have identified that genetic variants without genome-wide significance still add to the genetic risk of developing Alzheimer’s disease (AD). Whether and how subthreshold risk loci translate into relevant disease pathways, is unknown. We investigate here the involvement of AD risk variants in the transcriptional responses of two mouse models: APPswe/PS1L166P and Thy-TAU22. A unique gene expression module, highly enriched for AD risk genes, is specifically responsive to Aβ but not TAU pathology. We identify in this module 7 established AD risk genes (APOE, CLU, INPP5D, CD33, PLCG2, SPI1 and FCER1G) and 11 AD GWAS genes below the genome-wide significance threshold (GPC2, TREML2, SYK, GRN, SLC2A5, SAMSN1, PYDC1, HEXB, RRBP1, LYN and BLNK), that become significantly upregulated when exposed to Aβ. Single microglia sequencing confirms that Aβ, not TAU, pathology induces marked transcriptional changes in microglia, including increased proportions of activated microglia. We conclude that genetic risk of AD functionally translates into different microglia pathway responses to Aβ pathology, placing AD genetic risk downstream of the amyloid pathway but upstream of TAU pathology.
Project description:Complement protein C1q is induced after injury in the brain and during Alzheimer's disease and has been shown to protect against amyloid-beta induced neuronal death. In this study, we used microarray approach to identify the pathways modulated by C1q that are associated with neuroprotection. Immature rat cortical primary neurons are treated with fibrillar amyloid-beta peptides and/or C1q for 3h before RNA extraction and hybridization on rat Affymetrix microarrays. Supplementary file: Processed/normalized, probe-level signal intensities from neurons treated with amyloid-beta or C1q. Median signal intensity used as global normalization method, done with JMP genomics (v5.0) software.