A novel conditional knock-in mouse model for APOE4-to-APOE3 switching

Area of Science:

• Genetics
• Neuroscience
• Molecular Biology

Background:

• Apolipoprotein E4 (APOE4) is a significant genetic risk factor for Alzheimer's disease (AD), with the APOE4/E4 genotype increasing risk over 14-fold compared to APOE3/E3.
• Targeting APOE genotype conversion from risk-associated APOE4 to the neutral APOE3 allele is a potential therapeutic strategy for AD.

Purpose of the Study:

• To develop and validate a mouse model enabling postnatal Cre-mediated switching of the APOE4 isoform to APOE3.
• To assess the feasibility of in vivo APOE genotype switching using a Flip-Excision (FLEx) construct.

Main Methods:

• Generation of APOE4-FLEx 4-to-3 knock-in mice with a switchable APOE3 exon.
• In vitro validation using HEK293T cells transfected with the APOE4-FLEx construct and AAV8-mediated iCre delivery.
• In vivo studies involving Cre: APOE4-FLEx 4-to-3 double-knock-in mice crossed with Rosa26-CreERT2 mice and tamoxifen induction for Cre recombination.

Main Results:

• Successful Cre-mediated APOE4-to-APOE3 switching was confirmed in vitro.
• Postnatal APOE isoform switching was demonstrated in the liver of induced mice.
• Aberrant intron 3 retention in APOE transcripts led to reduced mature mRNA and protein levels in the brain, hindering functional assessment.

Conclusions:

• Cre-mediated FLEx switching is a viable strategy for inducing postnatal APOE genotype switching in vivo.
• Further optimization is required to enhance APOE expression in the brain for therapeutic applications in Alzheimer's disease.
• The developed mouse model provides a platform for studying the effects of APOE isoform switching on AD pathologies.