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CD8+ T-cells infiltrate Alzheimer’s disease brains and regulate neuronal- and synapse-related gene expression in APP-PS1 transgenic mice

ABSTRACT: Neuroinflammation is a major contributor to disease progression in Alzheimer´s disease (AD) and is characterized by the activity of brain resident glial cells, in particular microglia cells. However, there is increasing evidence that peripheral immune cells infiltrate the brain at certain stages of AD progression and shape disease pathology. We recently identified CD8+ T-cells in the brain parenchyma of APP-PS1 transgenic mice being tightly associated with microglia as well as with neuronal structures. The functional role of CD8+ T-cells in the AD brain is however completely unexplored. Here, we demonstrate increased numbers of intra-parenchymal CD8+ T-cells in human AD post-mortem hippocampus, which was replicated in APP-PS1 mice. Also, aged WT mice show a remarkable infiltration of CD8+ T-cells, which was more pronounced and had an earlier onset in APP-PS1 mice. To address their functional relevance in AD, we successfully ablated the pool of CD8+ T-cells in the blood, spleen and brain from 12 months-old APP-PS1 and WT mice for a total of 4 weeks using an anti-CD8 antibody treatment. While the treatment at this time of disease stage did neither affect the cognitive outcome nor plaque pathology, RNAseq analysis of the hippocampal transcriptome from APP-PS1 mice lacking CD8+ T-cells revealed highly altered neuronal- and synapse-related gene expression including an up-regulation for neuronal immediate early genes (IEGs) such as the Activity Regulated Cytoskeleton Associated Protein (Arc) and the Neuronal PAS Domain Protein 4 (Npas4). Gene ontology enrichment analysis illustrated that the biological processes “regulation of neuronal synaptic plasticity” and the cellular components “postsynapses” were over-represented upon CD8+ T-cell ablation. Additionally, Kegg pathway analysis showed up-regulated pathways for “calcium signaling”, “long-term potentiation”, “glutamatergic synapse” and “axon guidance”. Therefore, we conclude that CD8+ T-cells infiltrate the aged and AD brain and that brain CD8+ T-cells might directly contribute to neuronal dysfunction in modulating synaptic plasticity. Further analysis will be essential to uncover the exact mechanism of how CD8+ T-cells modulate the neuronal landscape and thereby contribute to AD pathology.

ORGANISM(S): Mus musculus

PROVIDER: GSE149661 | GEO | 2020/06/22

REPOSITORIES: GEO

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Project description:Immune cell infiltration to the brain is a prominent feature in aging and in various neurodegenerative diseases such as Alzheimer´s disease (AD). For example, a specific subpopulation of CD8+ T-cells clonally expands in the CSF of AD patients. Also, with AD progression that typically includes amyloid-beta plaque formation, neuronal damage and microglia-associated neuroinflammation, CD8+ T-cells infiltrate into the AD brain parenchyma and tightly associate with neuronal and microglia structures. The functional properties of CD8+ T-cells in the brain are largely unknown, besides the fact that experimental ablation in a transgenic AD animal model (APP-PS1) leads to changes in the expression of neuronal- and synapse-related genes. To gain further insights into the putative functional role of CD8+ T-cells in the brain, we explored and compared the transcriptomic profile of these cells in blood and brain of aged and transgenic AD mice. Surprisingly, CD8+ T-cells isolated from brains of aged APP-PS1 and WT animals had a similar transcriptomic profile, but they substantially differed from blood circulating CD8+ T-cells. The gene expression signature of brain CD8+ T-cells from APP-PS1 mice identified these cells as tissue-resident memory T-cells (Trm) indicated by specific regulation of genes such as Klf2/3, Ccr7, Sell, and Cxcr6. Immunohistochemical analysis confirmed the Trm identity of CD8+ T-cells at sites of amyloid-plaques. Gene ontology enrichment analysis on the significantly up-regulated genes showed an overrepresentation of biological processes as “response to virus”, “T-cell mediated immunity” and “response to interferon-beta” suggesting similarities to virus-responding T-cells. This is also supported by KEGG analysis, which highlighted upregulation of several pathways for “virus infections”, “cellular senescence” and “antigen processing and presentation”. In addition, the transcriptome of APP-PS1 brain CD8+ T-cells overlapped with gene microarray data of brain Trm CD8+ T-cells derived from an acute virus infection mouse model, suggesting similar functions of CD8+ T-cells in the brain either after viral infections or in AD. In conclusion, our herein presented data give new insights on the transcriptome of brain CD8+ T-cells and demonstrate adaptive immune responses in transgenic AD mice. This might open the door for immunotherapy as potential treatment option for AD.

Project description:Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by a progressive cognitive decline. Epidemiological studies have suggested a protective role of caffeine consumption against age-related cognitive impairments and the risk of developing AD. Effects of caffeine have been particularly ascribed to its ability to block adenosine A2A receptors (A2ARs). Early pathological upregulation of these receptors by neurons is thought to be involved in the development of synaptic and memory deficits in AD but this remains ill-defined. To tackle this question, we employed a novel transgenic mouse model allowing to promote a neuronal upregulation of A2AR in the hippocampus of APP/PS1 mice, developing AD-like amyloidogenesis. This new model was used to determine the impact of an early upregulation of A2AR on the progression of neuropathological lesions, associated behavior and underlying mechanisms in APP/PS1 mice. Our findings revealed that the early upregulation of A2AR in the presence of an ongoing amyloid pathology exacerbates memory impairments of APP/PS1 mice. These behavioral changes were not linked to major change in the development of amyloid pathology but rather associate with an increased p-tau at neuritic plaques. Moreover, proteomic and transcriptomic analysis coupled to quantitative immunofluorescence studies indicated that neuronal impairment of the receptor promoted both neuronal- and non-neuronal autonomous alterations i.e. loss of excitatory synapses and neuroinflammatory response, respectively, both presumably accounting for the detrimental effect on memory. Overall, our results provide compelling evidence that neuronal A2AR dysfunction as seen in the brain of patients contributes to AD pathogenesis, favoring synaptic deficits promoted by both amyloid (this study) and tau lesions (our previous study). In addition to provide new insights into the complex pathophysiology of AD, the present findings underscore the potential of A2AR as a relevant therapeutic target for mitigating early synaptic loss in this neurodegenerative disorder.

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CD8+ T-cells infiltrate Alzheimer’s disease brains and regulate neuronal- and synapse-related gene expression in APP-PS1 transgenic mice

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