APOE Allele Switching in a Novel Transgenic Mouse Model as a Therapeutic Approach for Alzheimer’s Disease

Abstract

AbstractBackgroundIndividuals homozygous for the ε4 allele of Apolipoprotein E (APOE) face up to a 15‐fold increase in Alzheimer’s Disease (AD) risk. In comparison, those carrying two ε2 alleles have nearly a 99.6% reduction in risk. Given APOE’s strong risk profile and multitude of effects, APOE itself has emerged as a promising therapeutic target. CRISPR‐Cas9 technology has been used to successfully edit APOE in vitro, where iPSC‐derived glia and neurons edited from ε4 to ε3 show pronounced transcriptional and phenotypic changes. However, whether the putatively beneficial effects of switching to APOE2 holds true in in vivo models has yet to be fully determined.MethodsWe developed a novel transgenic mouse model, the APOE “switch mouse” (4S2) which allows for an inducible (CreERT2) transition from expression of ApoE4 to ApoE2. Gene expression, western blotting, ELISA, and mass spectrometry based proteomic analysis were used to confirm that 4S2 mice synthesize full‐length human ApoE4 at baseline (pre‐switch) and full‐length human ApoE2 after tamoxifen administration (post‐switch). Analysis of plasma lipids, metabolomics, and transcriptomic analyses were used to identify downstream, physiological effects of replacing ApoE4 with ApoE2.ResultsPhysiological phenotyping, gene expression measures, and proteomic analyses further show that following tamoxifen injection, the inducible switch successfully results in efficient (>98%) recombination and expression of human ApoE2. Global genetic replacement of ApoE4 with ApoE2 results in changes to plasma lipids. Mass spec imaging revealed changes in multiple classes of lipids, while single‐cell and spatial RNAseq analyses shows distinct alterations in glial cell transcriptomes. Together these data suggest a successful transition from ApoE4 to ApoE2 that has broad impact on the glial transcriptome as well as on peripheral and cerebral metabolism.ConclusionsOur exciting preliminary studies have leveraged this new mouse as a promising model to assess the feasibility and therapeutic window of replacing APOE4 with APOE2, along with any potential off‐target effects. Ongoing studies aim to determine whether cell‐specific replacement of ApoE4 with APOE2 will rescue E4 associated metabolic dysfunction, disease associated gene signatures, and AD pathology. We hope that this new model will be a valuable resource for the AD/APOE research community.