BackgroundEmerging evidence indicates that the neuroprotective effects of Astragalus polysaccharides (APS), an extract compound and bioactive constituent derived from traditional Chinese herbs, may be relevant to an effective prescription for delaying progression of Alzheimer’s disease (AD), yet the underlying mechanisms remain to be fully elucidated. This study aimed to investigate the therapeutic efficacy of APS in alleviating cognitive impairment and neuropathology in 5×FAD transgenic mice, with a specific focus on the regulatory role of the gut-brain axis.MethodsMale 5×FAD mice were orally administered APS (200 mg/kg/day) for 60 days. General observations were conducted to assess the in vivo tolerance of APS. Cognitive function was evaluated using the Morris water maze (MWM). Neuropathological assessments included immunofluorescence and Western blotting for amyloid-β (Aβ) deposition, synaptic proteins, and neuroinflammatory markers. Gut microbiota composition and metabolic profiles were analyzed via 16S rRNA gene sequencing and targeted metabolomics. Furthermore, fecal microbiota transplantation (FMT) was performed to verify the causal contribution of gut microbiota to the observed therapeutic effects.ResultsAPS administration was well-tolerated throughout the study period, with no overt toxic effects observed. Moreover, APS administration significantly ameliorated spatial learning and memory deficits in 5×FAD mice. Mechanistically, APS treatment reduced Aβ plaque burden, restored synaptic protein expression (PSD-95 and Syntaxin), and attenuated microglia-mediated neuroinflammation by suppressing pro-inflammatory cytokines (IL-6, TNF-α) and upregulating TREM2. Microbiome analysis revealed that APS reshaped gut microbial diversity and composition, enriching beneficial taxa such as Lactobacillus. Metabolomics indicated a partial restoration of amino acid metabolism. Notably, FMT from APS-treated donors successfully reproduced the cognitive improvements and anti-inflammatory effects in recipient mice.ConclusionThese findings demonstrate that APS alleviates cognitive deficits and AD-like pathology, partially through remodeling gut microbiota and modulating the gut-brain axis. APS represents a promising natural compound-based therapeutic candidate for managing cognitive decline associated with Alzheimer’s disease.