Distinct immune signatures associated with sex and genotype in the 15m novel hAPP+hAPOE mouse risk model of Alzheimer’s disease

Abstract

AbstractBackgroundAlzheimer’s disease research continues to struggle with the translatability of animal models to human patients. Exploring whole systems is integral to early AD biomarker discovery in the pursuit of therapeutics to delay or prevent AD. Previous finds in our lab indicate sex differences in immune transcription levels in human AD brain and in the humanized apolipoprotein E (APOE) mouse model. Herein we investigated the impact of the APOE genotype in a novel mouse model, humanized amyloid precursor protein (APP), and humanized APOE transgenes (Jackson Laboratory).MethodsTo identify immunophenotypes at late‐midlife (15 months: late 40s – early 50s human correlative) a novel hAPP+hAPOE mouse model was utilized: hAPP (5M:5F), hAPP+hAPOE ε3/3 (16M:16F), & hAPP+hAPOE ε4/4 (16M:16F). The brain was hemisected. The left side was processed for multi‐color flow cytometry analysis. Peripheral blood was taken via cardiac puncture. The plasma was isolated and ELISA was used to detect levels of Aβ 40‐42 and pro‐inflammatory cytokines. PBMCs were isolated from the peripheral blood for multi‐color flow cytometry analysis. Microglia (CD45, CD11b), microglia reactivity (MHCII, CD68), phagocytosis (pHrodo), and oxidative stress (CellRox) levels were determined in the brain. Lymphocytes (CD3, CD4, CD8, CD19), lymphocyte activity (CD69), and oxidative stress (CellRox) levels were determined in both the brain and peripheral blood. Midlife endocrine status was determined for the female mice by daily lavage.ResultshAPP+hAPOE ε4/4 animals exhibited accelerated endocrine aging evidence by increased proportion of irregular cycling mice, compared to hAPP hAPOE ε3/3 animals. Microglial activation marker by MHCII was significantly impacted by sex (p<0.0001) and less so by genotype (p = 0.0551). Microglial function measured by pHrodo was impacted by sex (p<0.0001) with hAPP+hAPOE ε3/3 males exhibiting greater phagocytosis in MHCII+ microglia relative to their female counterpart.ConclusionThe interaction between the genotypes APP and APOE in combination with sex has a significant impact on immune phenotypes in the late‐midlife brain. These indications offer unique insights for future targeted therapeutics. Our findings support further investigation into neuroimmune activation in mid‐life to delay or prevent AD.