Dual orexin receptor antagonism with lemborexant enhances microglial clearance of β-amyloid in mice

Background: Sleep disturbances elevate brain amyloid-beta (Aβ) levels and represent a modifiable risk factor for Alzheimer's disease (AD). The orexin/hypocretin system regulates sleep-wake behavior and has emerged as a therapeutic target in AD; however, the effects of FDA-approved dual orexin receptor antagonists (DORAs) on amyloid pathology remain unclear. We compared lemborexant, an FDA-approved DORA, to doxepin, an antihistaminergic sleep medication, on amyloid pathology and microglial responses in PSAPP mice. Methods: PSAPP mice received lemborexant (10 or 30 mg/kg/day), doxepin (35 mg/kg/day), or vehicle for 6 weeks beginning prior to plaque onset or 4 weeks after established pathology. Sleep was assessed by piezoelectric monitoring and EEG/EMG polysomnography. Amyloid pathology and microglial responses were quantified by immunohistochemistry, confocal microscopy, and single-cell RNA sequencing. Microglial depletion was induced with the CSF1R inhibitor PLX3397. Results: Lemborexant enhanced sleep quality with less active-phase sedation than doxepin. Both drugs reduced initial diffuse plaque deposition, but only lemborexant prevented fibrillar plaque accumulation in young mice and slowed plaque growth in older mice. Lemborexant increased peri-plaque microglial CD68 expression and enhanced Aβ phagocytosis in vivo. Single-cell transcriptomics revealed a shift toward activated, DAM-like microglial states with upregulation of phagocytic genes without broad inflammatory induction. Microglial depletion abolished lemborexant's anti-amyloid effects. Conclusions: Lemborexant mitigates amyloid pathology by augmenting microglial phagocytic function, positioning DORAs as promising therapeutics that couple sleep promotion with beneficial microglial modulation.