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Ethanol increases diffuse amyloid plaque load and impairs memory in the 5xFAD mouse model of Alzheimer’s disease

ABSTRACT: Alzheimer’s disease (AD) is the most common age-related dementia. Lifestyle factors, including alcohol use, can increase the risk of AD. While human studies demonstrate that alcohol use can negatively impact AD risk and disease progression, the underlying alcohol-dependent mechanisms that increase Aβ burden and impair cognition remain elusive. We have recently shown that alcohol (ethanol) can acutely affect microglial dynamics, which are critical to microglial function, and many other studies have reported inflammatory activation of microglia after long-term alcohol exposure in both humans and animal models. Here, we administered 4 weeks of ethanol at dosages that mimic human binge drinking to 2.5-month-old male 5xFAD mice, a common mouse model of AD. After a two-week abstinence period, we performed behavior assays and analyzed amyloid pathology and microglial transcriptome in the hippocampus and morphology in the subiculum where amyloid pathology develops earlier than in other brain regions. We found that ethanol exposure facilitated amyloid pathology and worsened cognitive function in 5xFAD mice, while microglial transcriptomic landscape, arborization and phagocytosis appeared unchanged. Overall, our results suggest that pronounced ethanol exposure, when started early in the disease before amyloid pathology is established, can worsen AD progression in an amyloidosis model.

ORGANISM(S): Mus musculus

PROVIDER: GSE301393 | GEO | 2025/07/07

REPOSITORIES: GEO

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Project description:Alzheimer’s disease (AD) is a progressive neurodegenerative disorder marked by the buildup of amyloid-β and tau protein tangles. Alcohol use has been identified as a risk factor for AD; however, the molecular mechanisms underlying this potential causal link remain elusive. An emerging area of research focuses on the role of microglia, the brain's innate immune cells, in AD pathogenesis, with evidence suggesting that alcohol exposure may prime microglia to exhibit an exaggerated immune response when they are subsequently exposed to proinflammatory stimuli. We used a single 10-day chronic-plus-binge alcohol exposure model in male and female C57BL/J mice aged 8- to 10-weeks old. One month later, tauopathy was induced via adenoviral vector (AAV)-mediated overexpression of h-p301L tau. After 2.5 months, the mice underwent behavioral and cognitive testing. Two weeks later, microglia were collected using fluorescence-activated cell sorting (FACS) and processed for unbiased mass spectrometry and deep proteomic analysis to determine the molecular pathways related to microglial reactivity. Microglia from mice exposed to alcohol in young adulthood exhibited a blunted immune response when challenged with AAV-mediated delivery and accumulation of human tau later in life. This was characterized by decreased expression of MHC II- and interferon-associated proteins and bioinformatic prediction of inhibited inflammation-related pathways in the absence of gross histological, behavioral, or cognitive deficits. These results demonstrate unique, temporally specific microglial reactivity to tau that is modulated by early life alcohol exposure, implicating a microglial response that could negatively affect the mechanisms necessary for tau clearance and potentially exacerbate tau pathogenesis. This study provides novel insights into the long-term effects of early alcohol exposure on microglial function and the complexity of context-dependent microglial involvement in tau pathology. Consideration of early life environmental factors is critical for understanding and potentially mitigating the risk of neurodegenerative diseases, such as AD.

Project description:Microglia are innate immune cells of the brain that perform phagocytic and inflammatory functions in disease conditions. Transcriptomic studies of acutely-isolated microglia have provided novel insights into their molecular and functional diversity in homeostatic and neurodegenerative disease states. State-of-the-art mass spectrometric methods can comprehensively characterize proteomic alterations in microglia in neurodegenerative disorders, potentially providing novel functionally-relevant molecular insights that are not provided by transcriptomics. However, proteomic profiling of adult primary microglia in neurodegenerative disease conditions has not been performed. We performed quantitative proteomic analyses of purified CD11b+ acutely-isolated microglia adult mice in normal, acute neuroinflammatory (LPS-treatment) and chronic neurodegenerative states (5xFAD model of Alzheimer’s disease [AD]) using tandem mass tag mass spectrometry. Differential expression analyses were performed to characterize specific microglial proteomic changes in 5xFAD mice and identify overlap with LPS-induced pro-inflammatory changes. Our results were also contrasted with existing proteomic data from wild-type mouse microglia and from existing microglial transcriptomic data from wild-type and 5xFAD mice. Neuropathological validation studies of select proteins were performed in human AD and 5xFAD brains. Of 4,133 proteins identified, 187 microglial proteins were differentially expressed in the 5xFAD mouse model of AD pathology, including proteins with previously known (Apoe, Clu and Htra1) as well as previously unreported relevance to AD biology (Cotl1 and Hexb). Proteins upregulated in 5xFAD microglia shared significant overlap with pro-inflammatory changes observed in LPS-treated mice. Several proteins increased in human AD brain were also upregulated by 5xFAD microglia (Aβ peptide, Apoe, Htra1, Cotl1 and Clu). Cotl1 was identified as a novel microglia-specific marker with increased expression and strong association with AD neuropathology. Apoe protein was also detected within plaque-associated microglia in which Apoe and Aβ were highly co-localized suggesting a role for Apoe in phagocytic clearance of Aβ. We report the first comprehensive comparative proteomic study of adult mouse microglia derived from acute neuroinflammatory and AD models, representing a valuable resource to the neuroscience research community. We highlight shared and unique microglial proteomic changes in acute neuroinflammatory, aging and AD mouse models in addition to identifying novel roles for microglial proteins in human neurodegeneration.

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Ethanol increases diffuse amyloid plaque load and impairs memory in the 5xFAD mouse model of Alzheimer’s disease

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