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Systemic infections alter cortical transcriptional signatures in Alzheimer′s disease

ABSTRACT: Alzheimer′s disease (AD) is characterized by neuroinflammation, yet the impact of concurrent systemic infections on the AD brain remains poorly understood. We investigated the molecular mechanisms underlying the central nervous system response to systemic infections in AD by analyzing RNA sequencing data generated in the prefrontal cortex from 202 post-mortem donors (113 AD, 89 controls), where we stratified by the presence of a respiratory infection at the time of death. We identified 763 significantly differentially expressed genes (DEGs) between AD and controls without infection, which were enriched for oxidative phosphorylation and neurodegenerative pathways. In contrast, 122 DEGs distinguished AD from controls during infection, with 57 genes uniquely altered in AD in the presence of infection, including MAPK4 , VAV3 , and POU3F4 , implicating infection-dependent mechanisms of vascular and immune regulation. Pathway activity analysis revealed that infection in AD suppresses some immune and vascular pathways, while enhancing transcriptional and developmental programs. Weighted gene co-expression network analysis uncovered three key modules: one module strongly associated with AD, enriched for aging and signal transduction; one module linked to both AD and infection, highlighting cytoskeletal remodelling and host–pathogen interactions; and one module specific to infection, enriched in astrocytes, pericytes, and endothelial cells, implicating blood–brain–barrier dysfunction. These findings suggest that systemic respiratory infections reshape transcriptional programs in the AD brain, dampening immune effector pathways and engaging vascular and host–pathogen processes in blood–brain–barrier–associated cell types. Our results highlight the complex interplay between systemic infection, neuroinflammation, and vascular responses in AD.

ORGANISM(S): Homo sapiens

PROVIDER: GSE313307 | GEO | 2025/12/16

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.

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Systemic infections alter cortical transcriptional signatures in Alzheimer′s disease

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