α-Asarone attenuates synaptic loss in APP/PS1 mice by restoring microglial phagocytic-lysosomal balance via the SPP1-mTOR-TFEB axis.

BACKGROUND

Synaptic loss in Alzheimer disease (AD) is closely linked to aberrant microglial phagocytosis. Complement-dependent synaptic pruning and microglial lysosomal dysfunction drive this process, yet effective pharmacological strategies targeting this axis are lacking. α-Asarone (ASA) is neuroprotective, but its effects on SPP1-centered microglial synaptic pathology remain unclear.

PURPOSE: To determine whether ASA protects against AD-related synaptic injury by modulating SPP1-associated microglial phagocytic-lysosomal dysfunction and define the underlying mechanism.

STUDY

DESIGN

An integrated in vivo and in vitro pharmacological study was performed using APP/PS1 mice and BV2 microglia.

METHODS

Six-month-old APP/PS1 mice were treated with ASA for 100 days and evaluated behaviorally. ASA effects on microglial complement activation, complement-tagged synapses, lysosomal dysfunction, and hippocampal synaptic injury were assessed by transcriptomic analysis, qPCR, western blotting, immunofluorescence, Golgi staining, and transmission electron microscopy. In Aβ-stimulated BV2 cells, the role of SPP1 in phagocytic-lysosomal dysfunction was evaluated using SPP1 knockdown and recombinant SPP1, together with assays of lysosomal acidification, DQ-BSA degradation, and TFEB subcellular localization. Potential ASA-SPP1 engagement was further assessed by molecular docking, molecular dynamics simulation, and cellular thermal shift assay.

RESULTS

ASA improved behavioral performance and preserved hippocampal synaptic integrity in APP/PS1 mice. It reduced complement-associated microglial activation, CR3 signal, and complement deposition on PSD95-positive synapses, while restoring lysosomal acidification and proteolysis. SPP1 was upregulated in APP/PS1 mice and suppressed by ASA. ASA also inhibited SPP1-associated mTOR activation, reduced TFEB Ser211 phosphorylation and cytoplasmic retention, and improved lysosomal function. SPP1 silencing or mTOR inhibition mimicked ASA, whereas rSPP1 or mTOR activation attenuated these effects.

CONCLUSION

ASA attenuated AD-related synaptic injury by restoring microglial phagocytic-lysosomal balance through the SPP1-mTOR-TFEB pathway, supporting its potential as a phytomedicine candidate for AD intervention.