Project description:iPSC-derived brain organoids with microglial cells (assembloids) were used for this study. We used single cell RNA sequencing (scRNA-seq) to analyze the difference between APOE3 and APOE4 genotypes
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: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:TREM2 is a receptor for lipids expressed in microglia. The R47H variant of human TREM2 impairs ligand binding and increases Alzheimer’s Disease (AD) risk. In mouse models of amyloid b (Ab) accumulation, defective TREM2 function affects microglial response to Ab plaques exacerbating tissue damage, whereas TREM2 overexpression attenuates pathology. Thus, AD may benefit from TREM2 activation. Here, we examined the impact of an anti-human TREM2 agonistic mAb, AL002c, in a mouse AD model expressing either the common variant (CV) or the R47H variant of TREM2. Single cell RNA-seq of microglia after acute systemic administration of AL002c showed induction of proliferation in both CV- and R47H-transgenic mice. Prolonged administration of AL002c reduced filamentous plaques and neurite dystrophy, impacted behavior and tempered glial inflammatory response. We further showed that a variant of AL002c has been given safely in a first-in-human phase I clinical trial and engages TREM2 based on CSF biomarkers. We conclude that AL002c is a promising candidate for AD therapy.
Project description:We induced TREM2 expression at 2 months of age in our 5xFAD/TREM2 mouse models and harvested the animals at 5 months of age. The single cells from the cortex were isolated and subjected to the single-cell RNA seq to investigate the effects of TREM2 on microglia transcriptomic profiles in the middle stage of amyloid development. Our data showed that TREM2-WT induced the mTOR/EIF2 signaling pathways and restricted the disease associated microglia (DAM) signature. In contrast TREM2-R47H variant significantly upregulated the MHC class II molecules, enriched the antigen presentation pathway, and exacerbated a signature of antigen presentation contributing to enhanced amyloid pathology.
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:We aim to investigate the interaction between two of the major genetic risk factors for AD: inheritance of APOEε4 and deficiency of Triggering Receptor Expressed on Myeloid cells 2 (TREM2). Trem2 deletion worsened memory in AD model mice but not in their WT littermates. Interestingly, the lack Trem2 resulted in a significantly less microglia around amyloid plaques in APP mice expressing both APOE isoforms but had no impact on amyloid load. Gene expression analysis identified as Trem2 signature a cluster of highly connected immune response genes, commonly downregulated as a result of Trem2 deletion in all experimental groups, such as Clec7a, Itgax, Cts7, Mpeg1, Csf1r, Cx3cr1, Pik3cg and Spi1/PU.1. In vitro experiments with primary microglia demonstrated a decrease of Aβ phagocytosis in APOE4 versus APOE3 microglia a difference that was augmented by the absence of Trem2. Our data demonstrate that the lack of Trem2 differentially impact the phenotype and brain transcriptome of APP mice expressing human APOE isoforms probably reflecting the difference between APOE isoforms to transport lipids that can affect APOE receptor-binding properties.
Project description:We induced TREM2 expression at birth in our 5xFAD/TREM2 mouse models and harvested the animals at 3.5 months of age. The single cells from the cortex were isolated and subjected to the single-cell RNA seq to investigate the effects of TREM2 on microglia transcriptomic profiles in the early stage of amyloid development. Our data showed that TREM2-WT, to a lesser extent of TREM2-R47H, restricted the disease associated microglia (DAM) signature at this stage.
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.