Species: Rat
Genes: App
Mutations: APP A673T (Icelandic)
Modification: App: Knock-In
Disease Relevance: Alzheimer's Disease
Strain Name: N/A
Genetic Background: Long-Evans
Availability: Available through Luciano D'Adamio.

Summary

The A673T (“Icelandic”) mutation in APP is associated with protection against Alzheimer's disease and age-related cognitive decline. This knock-in rat model carries the Icelandic mutation and a humanized Aβ sequence within the endogenous rat App gene (Tambini et al., 2020). The initial characterization of these animals showed a gene-dose-dependent decrease in levels of Aβ40 and Aβ42.

Rats homozygous for the humanized Aβ sequence, without the Icelandic mutation, were also generated to serve as controls; these animals are referred to as App^h/h. Animals that carry the Icelandic mutation on an App^h/h background are referred to as App^p/p ("p" for "protective") and App^p/h, when homozygous or heterozygous for the Icelandic mutation, respectively.

For the initial characterization of these animals, mRNA and protein levels were measured in the brains of 21-day-old animals.

Expression of mutant App in these knock-in rats is under the control of natural regulatory elements. Levels of App mRNA were similar in rats homozygous for the Icelandic mutation and control rats with the humanized App gene (App^h/h). It was previously shown that levels of App mRNA in the brains of App^h/h rats were the same as the levels in wild-type animals (App^w/w) (Tambini et al., 2019).

Levels of APP protein were similar in App^p/p, App^p/h, and App^h/h rats.

Levels of sAPPβ were lower and levels of sAPPα were elevated in the brains of rats homozygous for the Icelandic mutation, compared with control (App^h/h) rats, while heterozygous carriers of the mutation did not consistently differ from controls. Levels of CTFβ were also lower in the brains of App^p/p rats compared with App^h/h rats, although levels of CTFα did not differ between the genotypes.

Levels of Aβ40 and Aβ42 were decreased in a gene-dose-dependent manner. In females, but not males, the Aβ42/Aβ40 ratio was also reduced by the Icelandic mutation.

Modification Details

CRISPR/Cas9 was used to edit the endogenous rat App gene, generating a humanized Aβ sequence through the following mutations (amino acid positions numbered as in Aβ1-40): G5R (GGA > CGA), F10Y (TTC > TAC), R13H (CGC > CAT).

The Icelandic mutation, A673T (numbered as in the 770-amino acid isoform of human APP), located at the second amino acid in Aβ1-40, was also introduced: GCG > ACG.

APP mutation carriers were crossed five times to wild-type Long-Evans rats to reduce the probability of off-target mutations, then male and female F5-App^p/w rats (animals heterozygous for the humanized Aβ sequence and the protective Icelandic mutation) were bred to generate rats homozygous for humanized Aβ and the Icelandic mutation.

Related Strains

App^h knock‐in. This knock-in rat model carries a humanized Aβ sequence within the endogenous rat App gene.

App^s knock‐in. This knock-in rat model carries the Swedish double mutation and a humanized Aβ sequence within the endogenous rat App gene.

Phenotype Characterization

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References

Mutations Citations

1. APP A673T (Icelandic)
2. APP K670_M671delinsNL (Swedish)

Research Models Citations

1. App knock-in (humanized Aβ)
2. App knock‐in (Swedish mutation and humanized Aβ)

Paper Citations

1. Tambini MD, Norris KA, D'Adamio L. Opposite changes in APP processing and human Aβ levels in rats carrying either a protective or a pathogenic APP mutation. Elife. 2020 Feb 5;9 PubMed.
2. Tambini MD, Yao W, D'Adamio L. Facilitation of glutamate, but not GABA, release in Familial Alzheimer's APP mutant Knock-in rats with increased β-cleavage of APP. Aging Cell. 2019 Dec;18(6):e13033. Epub 2019 Sep 9 PubMed.

Other Citations

1. Luciano D'Adamio

Further Reading

No Available Further Reading