Species: Rat
Genes: Psen1, App
Mutations: PSEN1 L435F
Modification: Psen1: Knock-In; App: Knock-In
Disease Relevance: Alzheimer's Disease
Strain Name: N/A
Genetic Background: Long-Evans
Availability: Available through Luciano D’Adamio.

Summary

The L435F mutation in PSEN1 was found in affected individuals in a family with early onset AD (Heilig et al., 2010). This knock-in rat model carries the homologous mutation in the rat Psen1 gene and a humanized Aβ sequence within the rat App gene (Tambini and D’Adamio, 2020). (This mutation is actually at amino acid 436 in the rat protein, but it is called “L435F” here and in the original description of the model in reference to the corresponding AD-linked mutation in human PSEN1.) The model should be particularly useful for studies of the effects of the Psen1 L435F mutation in the context of human Aβ.

In the following description, Psen1^w/w, Psen1^LF/w, and Psen1^{LF /LF} refer to rats homozygous for wild-type Psen1, heterozygous for the L435F mutation in Psen1, and homozygous for the L435F mutation, respectively. All animals are on a background of a humanized Aβ sequence within App.

Levels of Psen1 expression in the brains of newborn mice were similar between the three genotypes. Psen2 expression was also unaffected by the presence of the L435F mutation in Psen1.

The L435F mutation did not appear to affect embryonic survival, as Psen1^w/w, Psen1^LF/w, and Psen1^LF/LF pups were born in the expected Mendelian ratios. However, homozygous carriers of the mutation grew more slowly and exhibited increased mortality during the first month, with only 65 percent of Psen1^LF/LF pups surviving to 28 days of age (most heterozygotes and wild-type mice survived during this period). Homozygous rats that survived their first month tended to live into adulthood.

Levels of APP and its metabolites were measured in the brains of 4-day-old rats. While the amounts of full-length APP did not differ between mutation carriers and wild-type animals, Psen1^LF/LF brains unexpectedly contained more sAPPα and less sAPPβ than did Psen1^w/w or Psen1^LF/w brains. Elevated levels of Aβ43 were found in the brains of homozygous and heterozygous L435F mutation carriers, compared with wild-type rats, and carriers also had increased Aβ43/Aβ42 and Aβ43/Aβ40 ratios. Psen1^LF/LF brains contained less Aβ38, Aβ40, and Aβ42 relative to the other two genotypes, but had a higher Aβ42/Aβ40 ratio. Levels of APP C-terminal fragments, CTF-α and CTF-β, and were elevated in Psen1^LF/LF brains, as were levels of another γ-secretase substrate, the N-cadherin C-terminal fragment. These results point toward a gene-dose-dependent decrease in γ-secretase activity in Psen1 L435F mutation carriers. Notably, autocatalysis of presenilin-1, necessary for its γ-secretase function, also decreased gene-dose-dependently in mutation carriers.

Knock-in mice homozygous for the Psen1 L435F mutation show deficits in Notch signaling, accompanied by impaired neurogenesis (Xia et al., 2015). Unlike mice, Notch signaling appeared to be normal in the brains of neonatal Psen1^LF/LF rats.

Neuropathology

The brains of 15-day-old Psen1 L435F knock-in rats did not show any obvious developmental abnormalities. There were no qualitative differences in neuron density in mutation carriers compared with wild-type rats, although quantitative analysis revealed a small but statistically significant increase in neuron density in the hippocampus in male homozygotes.

Not surprisingly, no Alzheimer’s-like pathology—amyloid plaques, astrogliosis, or microgliosis—was seen at this young age.

Modification Details

CRISPR/Cas9 was used to introduce the L435F mutation into the endogenous rat Psen1 gene. Psen1-mutation carriers were crossed five times to wild-type Long-Evans rats to reduce the probability of off-target mutations.

Animals carrying the Psen1 L435F mutation were then crossed with App^h rats (Tambini et al., 2019), in which App was mutated to carry a humanized Aβ sequence. The progeny of this cross were then bred to generate animals in which the Psen1 L435F mutation was on a background homozygous for the humanized App allele.

Related Strains

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

Phenotype Characterization

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References

Research Models Citations

1. App knock-in (humanized Aβ)

Paper Citations

1. Heilig EA, Xia W, Shen J, Kelleher RJ. A presenilin-1 mutation identified in familial Alzheimer disease with cotton wool plaques causes a nearly complete loss of gamma-secretase activity. J Biol Chem. 2010 Jul 16;285(29):22350-9. PubMed.
2. Tambini MD, D'Adamio L. Knock-in rats with homozygous PSEN1L435F Alzheimer mutation are viable and show selective γ-secretase activity loss causing low Aβ40/42 and high Aβ43. J Biol Chem. 2020 May 22;295(21):7442-7451. Epub 2020 Apr 7 PubMed.
3. Xia D, Watanabe H, Wu B, Lee SH, Li Y, Tsvetkov E, Bolshakov VY, Shen J, Kelleher RJ 3rd. Presenilin-1 knockin mice reveal loss-of-function mechanism for familial Alzheimer's disease. Neuron. 2015 Mar 4;85(5):967-81. PubMed.
4. 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