SEX-DEPENDENT APOE4 NEUTROPHIL-MICROGLIA INTERACTIONS DRIVE COGNITIVE IMPAIRMENT IN ALZHEIMER'S DISEASE [Mouse_Microglia_APOE3_4]

APOE4 is the strongest genetic risk factor for Alzheimer's disease (AD) with increased odds ratios in females. Targeting amyloid plaques show modest improvement in male non-APOE4 carriers. Leveraging transcriptomics across APOE variants in both sexes, multiplex flow cytometry and validation in two independent cohorts of APOE4 female AD patients, we identify a new subset of neutrophils associated with cognitive impairment. This phenotype is defined by increased IL-17 and IL-1 co-expressed gene modules in blood neutrophils of cognitively impaired female APOE e4 carriers, showing increased infiltration to the AD brain. APOE4 female IL-17+ neutrophils upregulated the immunosuppressive cytokines IL-10 and TGFb, and immune checkpoints including LAG-3 and PD-1, associated with accelerated immune aging. Deletion of APOE4 in neutrophils reduced this immunosuppressive phenotype and restored microglial response to neurodegeneration (MGnD), limiting plaque pathology in AD mice. Mechanistically, IL-17Fupregulated in APOE4 neutrophils interacts with microglial IL-17RA to suppress the induction of MGnD phenotype, and blocking this axis supported cognitive improvement in AD mice. These findings provide a translational basis to target IL-17F in APOE e4 female carriers with cognitive impairment. Overall design: Microglia from 12-month-old female APP/PS1 mice expressing human APOE3 or APOE4 globally or either heterozygous APOE3 or APOE4 deletion in neutrophils via Ly6g Cre mediated deletion.