Sex-specific APOE4-dependent innate immunity regulates meningeal lymphatics, brain lipids, neuroinflammation, and cognition.

Sex and apolipoprotein E ε4 (APOE4) interact to alter the risk for Alzheimer's disease and other neurodegenerative disorders. Herein, we show sex-specific differences in immune activation and lymphatic function in the meningeal dura of humanized female and male mice expressing two alleles of APOE4 (E4/E4), when compared with their respective sex-matched E3/E3 controls. We also describe distinct effects of APOE4 on brain lipid composition and inflammation in females and males that were partially reverted upon colony-stimulating factor 1 receptor (CSF1R) inhibition. Suppressing innate immunity reduced neuroinflammation and restored cognitive function in E4/E4 females, while exacerbating neuroinflammation and accelerating cognitive decline in E4/E4 males. Finally, in line with the E4/E4 humanized mouse model data, we show that APOE4 expression is linked to sexually dimorphic leukocyte activation profiles in the human brain. This study highlights the need for personalized therapies when targeting APOE, brain immunity, and meningeal lymphatics to promote cognitive resilience in both females and males.