Project description:Microglia activation is a hallmark in Alzheimer Disease. Non-active and Active microglia were isolated from young and aged WT mice and before- and after- pathology mouse models of Alzheimer Disease. Microarray analysis was used to determine the global gene expression programe in microglia during pathological (Abeta or TAU pathology) versus control state.
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: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:Extracellular senile plaques of amyloid beta (Abeta) are a pathological hallmark in brain of patients with Alzheimer`s Disease (AD). Abeta is generated by the amyloidogenic processing of the amyloid precursor protein (APP). Concomitant to Abeta load, AD brain is characterized by an increase in protein level and activity of the angiotensin-converting enzyme (ACE). ACE inhibitors are a widely used class of drugs with established benefits for patients with cardiovascular disease. However, the role of ACE and ACE inhibition in the development of Abeta plaques and the process of AD-related neurodegeneration is not clear since ACE was reported to degrade Abeta. To investigate the effect of ACE inhibition on AD-related pathomechanisms, we used Tg2576 mice with neuron-specific expression of APPSwe as AD model. From 12 months of age, substantial Abeta plaque load accumulates in the hippocampus of Tg2576 mice as a brain region, which is highly vulnerable to AD-related neurodegeneration. The effect of central ACE inhibition was studied by treatment of 12 month-old Tg2576 mice for six months with the brain penetrating ACE inhibitor captopril. At an age of 18 months, hippocampal gene expression profiling was performed of captopril-treated Tg2576 mice relative to untreated 18 month-old Tg2576 controls with high Abeta plaque load. As an additional control, we used 12 month-old Tg2576 mice with low Abeta plaque load. Whole genome microarray gene expression profiling revealed gene expression changes induced by the brain-penetrating ACE inhibitor captopril, which could reflect the neuro-regenerative potential of central ACE inhibition.
Project description:Extracellular senile plaques of amyloid beta (Abeta) are a pathological hallmark in brain of patients with Alzheimer`s Disease (AD). Abeta is generated by the amyloidogenic processing of the amyloid precursor protein (APP). Concomitant to Abeta load, AD brain is characterized by an increase in protein level and activity of the angiotensin-converting enzyme (ACE). ACE inhibitors are a widely used class of drugs with established benefits for patients with cardiovascular disease. However, the role of ACE and ACE inhibition in the development of Abeta plaques and the process of AD-related neurodegeneration is not clear since ACE was reported to degrade Abeta. To investigate the effect of ACE inhibition on AD-related pathomechanisms, we used Tg2576 mice with neuron-specific expression of APPSwe as AD model. From 12 months of age, substantial Abeta plaque load accumulates in the hippocampus of Tg2576 mice as a brain region, which is highly vulnerable to AD-related neurodegeneration. The effect of central ACE inhibition was studied by treatment of 12 month-old Tg2576 mice for six months with the brain penetrating ACE inhibitor captopril. At an age of 18 months, hippocampal gene expression profiling was performed of captopril-treated Tg2576 mice relative to untreated 18 month-old Tg2576 controls with high Abeta plaque load. As an additional control, we used 12 month-old Tg2576 mice with low Abeta plaque load. Whole genome microarray gene expression profiling revealed gene expression changes induced by the brain-penetrating ACE inhibitor captopril, which could reflect the neuro-regenerative potential of central ACE inhibition. Microarray gene expression profiling was performed of hippocampi isolated from aged, 18 month-old Tg2576 (APPSwe-transgenic) AD mice with high Abeta plaque load relative to age-matched Tg2576 mice, which were treated for 6 months with the centrally active ACE inhibitor captopril. Another study group consisted of 12 month-old Tg2576 mice with low Abeta plaque load. In total, three study groups were analyzed, i.e. (i) 18 month-old untreated Tg2576 mice with high Abeta plaque load, (ii) age-matched Tg2576 mice treated for 6 months with the brain-penetrating ACE inhibitor captopril (20 mg/kg body weight/day in drinking water), and (iii) untreated 12 month-old Tg2576 mice with low Abeta plaque load reflecting the time point when captopril treatment was initiated. Two biological replicates were made of each group, and total hippocampal RNA of four mice was pooled for one gene chip.
Project description:Alzheimer's disease (AD) is characterized by a sequential progression of amyloid plaques (A), neurofibrillary tangles (T) and neurodegeneration (N), constituting ATN pathology. While microglia are considered key contributors to AD pathogenesis, their contribution in the combined presence of ATN pathologies remains incompletely understood. As sensors of the brain microenvironment, microglial phenotypes and contributions are importantly defined by the pathologies in the brain, indicating the need for their analysis in preclinical models that recapitulate combined ATN pathologies, besides their role in A and T models only. Here, we report a new tau-seed model in which amyloid pathology facilitates bilateral tau propagation associated with brain atrophy, thereby recapitulating robust ATN pathology. Single-cell RNA sequencing revealed that ATN pathology exacerbated microglial activation towards disease-associated microglia (DAM) states, with a significant upregulation of Apoe as compared to amyloid-only models (A). Importantly, Colony-Stimulating Factor 1 Receptor inhibition preferentially eliminated non-plaque-associated versus plaque associated microglia. The preferential depletion of non-plaque-associated microglia significantly attenuated tau pathology and neuronal atrophy, indicating their detrimental role during ATN progression. Together, our data reveal the intricacies of microglial activation and their contributions to pathology in a model that recapitulates the combined ATN pathologies of Alzheimer's disease. Our data may provide a basis for microglia-targeting therapies selectively targeting detrimental microglial populations, while conserving protective populations.
Project description:Background: Activation of microglia, the resident immune cells of the central nervous system, is a prominent pathological hallmark of Alzheimer’s disease (AD). However, the gene expression changes underlying microglia activation in response to tau pathology remain elusive. Furthermore, it is not clear how murine gene expression changes relate to human gene expression networks. Methods: Microglia cells were isolated from rTg4510 tau transgenic mice and gene expression was profiled using RNA sequencing. Four age groups of mice (2-, 4-, 6-, and 8-months) were analyzed to capture longitudinal gene expression changes that correspond to varying levels of pathology, from minimal tau accumulation to massive neuronal loss. Statistical and system biology approaches were used to analyze the genes and pathways that underlie microglia activation. Differentially expressed genes were compared to human brain co-expression networks. Results:Statistical analysis of RNAseq data indicated that more than 4000 genes were differentially expressed in rTg4510 microglia compared to wild type microglia, with the majority of gene expression changes occurring between 2- and 4-months of age. These genes belong to four major clusters based on their temporal expression pattern. Genes involved in innate immunity were continuously up-regulated, whereas genes involved in the glutamatergic synapse were down-regulated. Up-regulated innate inflammatory pathways included NF-κB signaling, cytokine-cytokine receptor interaction, lysosome, oxidative phosphorylation, and phagosome. NF-κB and cytokine signaling were among the earliest pathways activated, likely driven by the RELA, STAT1 and STAT6 transcription factors. The expression of many AD associated genes such as APOE and TREM2 was also altered in rTg4510 microglia cells. Differentially expressed genes in rTg4510 microglia were enriched in human neurodegenerative disease associated pathways, including Alzheimer’s, Parkinson’s, and Huntington’s diseases, and highly overlapped with the microglia and endothelial modules of human brain transcriptional co-expression networks. Conclusion: This study revealed temporal transcriptome alterations in microglia cells in response to pathological tau perturbation and provides insights into the molecular changes underlying microglia activation during tau mediated neurodegeneration.