Antibiotic-Induced Gut Dysbiosis Modulates Alzheimer's Disease-Associated Gene Expression and Protein Aggregation in 3xTg-AD Mice via the Gut–Brain Axis

Introduction: Alzheimer's disease (AD) is a progressive neurodegenerative disorder that poses a major global health challenge due to its increasing prevalence and lack of effective treatments. Emerging evidence suggests the gut–brain axis may play a pivotal role in AD pathogenesis. However, causal links between dysbiosis and late-stage AD pathology remain unclear. Methods: This study evaluated the effects of antibiotic-induced gut dysbiosis in aged 3xTg-AD mice (46–48 weeks). Female mice were randomly assigned to control or treatment groups and administered a broad-spectrum antibiotic cocktail (ampicillin, vancomycin, and neomycin) for 14 days. Behavioral tests (Y-maze, elevated plus maze) were performed to assess cognitive and anxiety-like behaviors. Gut microbiota composition was assessed via 16S rRNA qPCR. Gene expression of Acetylcholinesterase (AChE), Butyrylcholinesterase (BChE), and Tumor Necrosis Factor-Alpha (TNF-α) was analyzed via qRT-PCR, and cerebral amyloid-β_1–42 and tau protein levels were quantified by ELISA. Results: Antibiotic treatment induced significant dysbiosis, with > 90% reduction in Firmicutes and Bacteroidetes. Dysbiotic mice displayed impaired spatial working memory, heightened anxiety-like behavior, and reduced locomotor activity. Molecular analyses revealed region-specific dysregulation of cholinergic genes: AChE was upregulated in the hippocampus but downregulated in the cortex, while BChE showed the opposite trend. TNF-α was significantly elevated in both regions, indicating neuroinflammation. Dysbiosis also led to increased brain levels of amyloid-β_1–42 and tau. Conclusion: Gut microbiome disruption exacerbates late-stage AD pathology, driving cognitive deficits, neuroinflammation, and hallmark protein aggregation. These findings support the gut–brain axis as a critical modulator of AD and highlight the microbiome as a potential therapeutic target.