Gut microbiota dysbiosis is associated with hippocampal neuronal damage and behavioral alterations in APP/PS1 mice with high-salt diet.

INTRODUCTION: High-salt diet (HSD) has been shown to influence cognition and emotional behavior in mice via gut microbiota modulation, yet its chronic effects in Alzheimer's disease (AD) pathology remain poorly understood. This study aimed to investigate whether long-term HSD exacerbates cognitive and emotional deficits in APP/PS1 transgenic mice and to explore the underlying gut-brain axis mechanisms involving microbiota dysbiosis, peripheral and central inflammation, hippocampal neuronal integrity, and metabolic alterations. METHODS: Six-month-old male APP/PS1 mice were randomly assigned to a normal diet (ND, 0.4% NaCl, n = 43) or high-salt diet (HSD, 8% NaCl, n = 41) for 6 months. Body weight, water intake, and blood pressure were monitored regularly (n = 10 per group). Behavioral phenotypes were assessed via open field, elevated plus maze, marble burying, light-dark box, and novel object recognition tests (n = 10). Hippocampal neuronal density was quantified by Nissl staining in CA1 and CA2, and dendritic complexity was evaluated by Golgi staining with Sholl analysis (n = 4). Gut microbiota composition was profiled by 16S rRNA sequencing (ND: n=13; HSD: n = 12), and inflammatory cytokine expression (TNF-α, IL-6, and IL-1β) in brain and liver was measured by RT-PCR and ELISA (n = 4). Hippocampal metabolomics was performed using LC-MS (ND: n = 8; HSD: n = 7). Correlation analyses integrated microbial, inflammatory, metabolic, and neuropathological data. RESULTS: HSD significantly altered gut microbiota structure, as shown by reduced α-diversity, distinct β-diversity (PCoA), and differential abundance of taxa including Prevotellaceae, Rikenellaceae, and Ruminococcaceae (LEfSe). Concurrently, HSD elevated pro-inflammatory cytokine expression in both brain and liver, reduced neuronal density in hippocampal CA1/CA2, and impaired dendritic arborization. Behaviorally, HSD-treated mice exhibited aggravated emotional disorders (anxiety- and compulsive-like behaviors) and worsened cognitive impairment in novelty recognition. Hippocampal metabolomics revealed substantial shifts in amino acid, energy, and neurotransmitter metabolic pathways. Spearman correlation analyses demonstrated significant interconnections among specific gut microbial genera, inflammatory markers, neuronal damage indices, and differential metabolites. DISCUSSION AND CONCLUSION: Long-term high-salt intake exacerbates cognitive decline and emotional disturbances in APP/PS1 mice, likely through a cascading gut-brain axis pathway: HSD-induced microbiota dysbiosis promotes peripheral and central inflammation, which in turn drives hippocampal neuronal damage and metabolic reprogramming. The strong correlations among microbial shifts, metabolic alterations, and neuropathological changes suggest that gut microbiota may serve as a critical mediator of HSD's deleterious effects on AD-related brain functions. These findings provide new mechanistic insights into dietary risk factors in AD and highlight potential microbiota-metabolite targets for therapeutic intervention.