Madeline Grucci

Abstract Background APOE4 is the strongest genetic risk factor for late‐onset Alzheimer’s disease (AD). The role of human APOE variants in AD has been studied extensively in the regulation of brain cells but not in peripheral immunity. APOE is also expressed in neutrophils and controls their activation. Moreover, neutrophils have been shown to play a negative role in AD mice via the induction of neutrophil extracellular traps (NETs) Method Here we aimed to dissect the impact of APOE4‐neutrophils on AD pathology, using Ly6g‐CRE mice crossed to APOE‐KI(E3 and E4) fl/fl :APP/PS1. Result We identified a cell intrinsic role of APOE3 in controlling neutrophil maturation and degranulation, which is exacerbated in APOE4‐KI neutrophils and reduced in APOE4‐KO neutrophils. Moreover, APOE4 neutrophils accumulated in the brains of AD mice and in AD patients, associated with microglia at sites of plaque pathology. Here we show that genetic deletion of APOE4 in neutrophils suppressed their activation and reduced their recruitment to the brains of APP/PS1 mice. RNAseq analysis showed increased proportion of disease associated microglia (DAM/MGnD) in APP/PS1: Ly6g‐CRE:APOE4 fl/fl mice, associated with reduced plaque pathology. Furthermore, we show impaired induction of MGnD signature in AD brains of APOE4 carriers. Our findings show that APOE4‐induced inflammatory neutrophils are recruited to the diseased brain and impair MGnD response leading to accelerated AD pathology. Conclusion Taken together, these findings identify a cell‐intrinsic role of APOE4 in the induction of hyperactivated neutrophils recruited to the brain, which may provide new molecular targets to modulate and restore functional microglia in AD.