Functional Interaction between APOE4 and mutant APP promotes cerebrovascular changes in young animals
The Apolipoprotein E4 (ApoE4) allele is one of the strongest risk factors for late-onset Alzheimer's disease (AD) and is associated with a breakdown of the blood-brain barrier and vascular dysfunction (Nation et al 2019; Liu and Bu 2022). Importantly, these vascular pathologies are exacerbated when APOE4 is coexpressed with familial mutations in APP or components of the ?-secretase complex (Montagne and Zlokovic 2021), suggesting that the interactions between APOE4 and AD mutations can drive progression of the disease. However, most studies have been done in aging animals and few look at the impact of APOE4 expression in young animals and how that potentially contributes toward late-stage disease susceptibility. Here, we examined the potential functional interaction between APP mutations and ApoE4 in the progression of AD pathophysiology by comparing the hippocampal transcriptomes of 3-month-old female mice of 4 different genotypes: AppNL-G-F/NL-G-F , which harbours three knock-in mutations in the humanised Aß region of APP  (APP-TKI; Saito et al., 2014), mice with a single allele of human ApoE4 knocked-in, ApoE4+/wt (ApoE4), crosses of these two mouse lines, to create AppNL-G-F/NL-G-F;Apoe4+/wt (double-mutant or DM) mice, and wild-type (WT) mice that served as controls. RNAseq revealed nascent microglial activation signatures in both APP-TKI and double mutant datasets, as well as subtle but significant differences between APP-TKI and double mutant in expression of a subset of vascular remodeling genes. Overall design: Hippocampal transcriptomes of 3-month-old female wild-type, APP knock-in, ApoE4 and double mutant mice