Abstract
Although, a number of pathogenic mutations have been found for Alzheimer’s disease (AD), only one protective mutation has been identified so far in humans. Here we identify possible protective deletion mutations in the 3′-UTR of the amyloid precursor protein (App) gene in mice. We use an App knock-in mouse model carrying a humanized Aβ sequence and three AD mutations in the endogenous App gene. Genome editing of the model zygotes using multiple combinations of CRISPR/Cas9 tools produces genetically mosaic animals with various App 3′-UTR deletions. Depending on the editing efficiency, the 3′-UTR disruption mitigates the Aβ pathology development through transcriptional and translational regulation of APP expression. Notably, an App knock-in mouse with a 34-bp deletion in a 52-bp regulatory element adjacent to the stop codon shows a substantial reduction in Aβ pathology. Further functional characterization of the identified element should provide deeper understanding of the pathogenic mechanisms of AD.
Highlights
A number of pathogenic mutations have been found for Alzheimer’s disease (AD), only one protective mutation has been identified so far in humans
A previous human genomic study with a set of whole-genome sequence data from 1,795 Icelanders revealed that a missense mutation (p.A673T) on the amyloid precursor protein (App) gene has a protective effect against the onset of AD, possibly via reducing the levels of amyloidogenic peptides[3,4]
We explored whether disruption of the endogenous App 3′-UTR prevents Aβ accumulation in our AD mouse model
Summary
A number of pathogenic mutations have been found for Alzheimer’s disease (AD), only one protective mutation has been identified so far in humans. We recently established single-App knock-in model mice carrying a humanized Aβ sequence, as well as two or three clinically causative mutations in the endogenous murine App gene[7,8] Generating these mice, we unexpectedly found that App knock-in mice lacking the last two introns (intron 16, 17) and 3′-UTR did not display Aβ deposition or deleterious effects at any ages due to a substantial reduction in APP expression at both the transcriptional and translational levels (Supplementary Fig. 1). Subsequent quantitative Aβ measurements, as well as APP expression analyses in the 6-month-old edited model mice provided that deletion of the App 3′-UTR mitigated Aβ accumulation in the brain through the reduction of APP expression levels Further experiments using another combination of genome editing tools enabled us to narrow down a possible responsible element in the App 3′-UTR. Our results suggest that targeted screening strategy based on relevant AD models would be useful for the identification of novel protective AD mutations
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