Rapamycin Reduces Amyloid‐β Plaques and Improves Behavioral Performance in a Sex‐Dependent Manner in Mouse Models of Amyloidosis

ABSTRACT Background Alzheimer's disease (AD), the most common form of dementia, lacks effective disease‐modifying treatments. Rapamycin, an mTOR inhibitor with immunomodulatory properties, may mitigate AD pathology by restoring microglial functions. Methods Rapamycin was orally administered to 2‐month‐old 5xFAD and hAPP NL ‐G‐F mice (amyloid plaque‐dominant AD models). At 5 months of age, these mice were subjected to behavioral, histopathological, and molecular analyses. To assess microglial function, primary microglia were treated with rapamycin and evaluated for their ability to phagocytose and degrade fluorescently labeled amyloid‐β (Aβ) via the IncuCyte real‐time imaging system. Furthermore, the effects of rapamycin and autophagy inhibitors on lipid droplet content were analyzed in oleic acid‐treated BV2 microglial cells using flow cytometry and confocal microscopy. Results Rapamycin treatment reduced the cerebral Aβ plaque burden, alleviated dystrophic neurites, suppressed glial hyperactivation, and increased plaque‐associated microglial density in both mouse models, with more pronounced effects in female mice. These pathological improvements were associated with attenuated deficits in hippocampal‐dependent memory tasks (spontaneous alternation in the Y‐maze and contextual fear conditioning tasks). Mechanistically, rapamycin enhances microglial lysosomal degradation, promotes lipid droplet clearance in BV2 cells, and increases Aβ phagocytic clearance in primary microglial cells. Conclusions Our findings suggest that rapamycin reduces amyloid pathology and associated behavioral deficits in AD mice, an effect associated with enhanced microglial lysosomal activity and Aβ clearance, highlighting its therapeutic potential in AD treatment.