BACKGROUND: Accumulating evidence implicates both the brain-spleen axis and the gut microbiota-brain axis in Alzheimer's disease (AD) pathogenesis. While our previous work demonstrated heterophyllin B (HB) rectifies splenic Th1/Th2 imbalance and ameliorates cognitive deficits in Aβ1-42-induced AD mice, its potential modulation of the vagus nerve-spleen circuit remains unexplored.
METHODS: Using 8-month-old male APP/PS1 mice with/without splenic denervation (SD), we systematically investigated HB's therapeutic mechanisms via the spleen-gut microbiota-brain axis. Cognitive function was assessed through novel object recognition (ORT) and object location memory (OLT) tests. Immunofluorescence (IF) and enzyme-linked immunosorbent assay (ELISA) were employed to analyze Aβ plaques, phosphorylated tau (p-Tau) levels, and associated neuroinflammatory responses. Flow cytometry was utilized to examine the subtypes of splenic lymphocytes. Hematoxylin and eosin (H&E) staining, along with immunohistochemical (IHC) experiments, was conducted to evaluate the protective effects of HB on the intestinal barrier. Gut microbiota composition was analyzed using 16S rRNA sequencing.
RESULTS: HB administration significantly improved cognitive performance (ORT discrimination index: +28.7 %; OLT discrimination index: +26.6 %), reduced brain and serum Aβ1-42 and p-Tau levels, downregulated the Th1/Th2 ratio in the spleen, and alleviated intestinal permeability and neuroinflammation, which were abolished in SD APP/PS1 mice. Gut microbiota shifts showed HB-induced enrichment of cognition-associated Dubosiella and Muribaculaceae, with concurrent suppression of pathogenic Lachnospiraceae_NK4A136 and ASF356.
CONCLUSION: This study provides first evidence that HB ameliorates AD pathology through vagus nerve-dependent regulation of the spleen-gut microbiota-brain axis, establishing its multimodal therapeutic potential for neural-immune-gut circuit modulation in neurodegenerative diseases.
