AS-IV attenuates nigral NLRP3 inflammasome in a Parkinson’s disease mouse model via gut microbiota

Astragaloside IV (AS-IV) neuroprotection against rotenone (ROT)-induced Parkinson's pathology was examined via microbiota-gut-brain axis mechanisms. Methods included intraperitoneal AS-IV, fecal microbiota transplantation (FMT) from AS-IV-treated mice, and AS-IV-modulated microbiota transplantation. Substantia nigra dopaminergic neurons/microglia were evaluated by confocal imaging, while NLRP3, caspase-1, IL-1β, and α-synuclein (α-syn) levels were quantified via Western blot. Gut microbiota (16S rRNA sequencing) and striatal metabolites (LC-MS/MS) were analyzed. AS-IV attenuated ROT-induced motor deficits, dopaminergic neuron loss, α-syn overexpression, and NLRP3/caspase-1 activation, while elevating fecal SCFAs and increasing Bacteroidetes/Porphyromonadaceae with reduced Firmicutes. FMT from AS-IV-treated to ROT mice improved motor function, suppressed TH⁺ neuron loss, and inhibited microglial/NLRP3 activation. AS-IV-modulated microbiota transplantation upregulated Bacteroidetes, Porphyromonadaceae, Barnesiella, and downregulated Firmicutes, Lactobacillaceae, Lactobacillus, and Desulfovibrio. Crucially, FMT from AS-IV-treated to naïve mice alleviated ROT-induced damage, whereas ROT microbiota transplantation induced rotations and decreased Bacteroidetes, Actinobacteria, Porphyromonadaceae, Sutterellaceae, and Parasutterella. AS-IV reversed these microbial changes. Genus-level microbiota alterations correlated with motor severity. ROT microbiota reduced 5-HIAA, indole-3-carboxaldehyde, thyroxine, and glutathione; AS-IV restored indole-3-carboxaldehyde and thyroxine. AS-IV exerts neuroprotection by suppressing NLRP3 inflammasome activation via gut microbiota remodeling and metabolic regulation through the microbiota-gut-brain axis.