Genes: APP, PSEN1
Mutations: APP KM670/671NL (Swedish), APP V717I (London), PSEN1 M146L (A>C)
Modification: APP: Virus; PSEN1: Virus
Disease Relevance: Alzheimer's Disease
Strain Name: N/A
Genetic Background: Wistar
Availability: Viral vectors are available through AgenT SAS under collaboration or partnership agreements.
Adeno-associated viral (AAV) vectors separately encoding human APP with the Swedish and London mutations and human PSEN1 with the M146L mutation were injected bilaterally into the hippocampi of young adult (8-week-old) rats. AAV-AD rats develop amyloid plaques and cerebral amyloid angiopathy, accrue hyperphosphorylated tau, and exhibit progressive behavioral impairments.
Only male rats were used in the study reported here. Controls rats were injected with only with AAV carrying M146L PSEN1.
Full-length human PSEN1 and full-length human APP did not accumulate in the hippocampi of AAV-AD rats. However, levels of a 30-kDa N-terminal fragment of PSEN1—a component of the active γ–secretase complex—were elevated, as were levels of APP cleavage products. Measured one month after virus injection, the levels of CTFβ—the APP C-terminal fragment generated by BACE cleavage—were approximately double those measured in the hippocampi of controls, and levels of soluble Aβ40 and Aβ42 were elevated approximately 10- and 27- fold, respectively. While steady-state levels of CTFβ and Aβ40 in the hippocampus remained stable over time, levels of Aβ42 progressively increased from one to 30 months post-injection, reaching concentrations similar to those measured in hippocampal samples from AD patients.
Levels of Aβ were also measured in cerebrospinal fluid (CSF) collected from the cisterna magna, and both Aβ40 and Aβ42 were found to be elevated in AAV-AD animals. At one month post-injection, levels of Aβ40 were approximately sixfold higher in CSF from AAV-AD rats (6.00 ± 1.03 pg/mL) compared with controls (0.94 ± 0.34 pg/mL), while levels of Aβ42 were approximately 15-fold higher (control: 0.35 ± 0.09 pg/mL; AAV-AD: 5.46 ± 0.97 pg/mL). Levels of CSF Aβ40 and Aβ42 increased from one to eight months post-injection, but there was a trend toward a decline in the levels of both peptides when measured at 30 months post-injection.
There was a progressive increase in the amount of hyperphosphorylated endogenous rat tau. (In the descriptions that follow, the amino acid numbers refer to the 752-amino-acid isoform of rat tau (Uniprot P19332-1); for reference, the corresponding amino acids in the 441-amino-acid isoform of human tau (Uniprot P10636-8) are given in brackets.) Phosphorylation at Ser733 [Ser422] and Thr492 [Thr181] was apparent by eight months post-injection. At 30 months, there were further increases in the levels of tau phosphorylated at these two sites, and hyperphosphorylation was observed at additional sites (Ser513 [Ser202], Thr523 [Thr212], Thr528 [Thr217], Thr542 [Thr231], and Thr542/Ser546 [Thr231/Ser235]).
At 30 months post-injection, amyloid plaques were observed in the hippocampi of AAV-AD rats, primarily in the subiculum. Cerebral amyloid angiopathy was also present at this time. Scattered neurons in the hippocampus displayed immunoreactivity for human APP. The appearance of hippocampal neurons immunostained with antibodies AT8 (recognizes tau phosphorylated at Ser513/Thr516 [Ser202/Thr205]) and AT100 (recognizes tau phosphorylated at Thr523/Ser525 [Thr212/Ser214]) at 30 months post-injection suggests the presence of (pre)tangle-like structures, but silver staining is required to confirm the presence of actual neurofibrillary tangles. No astrogliosis was seen up to 30 months post-injection.
At three months post-injection, AAV-AD and control rats performed similarly in a battery of behavioral tests. At eight months post-injection, AAV-AD rats spent less time in the center of the open field than did controls, although both groups traveled similar total distances. The groups did not differ in their performances in the Y-maze or novel-object-recognition tests. In the Morris water maze, AAV-AD rats learned the location of the hidden platform as well as did controls. In a probe trial (memory test) conducted four hours after the last training session, both groups also performed similarly, but the AAV-AD rats did not perform as well as controls in probe tests administered three and five days after training.
Synaptic plasticity at Schaffer collateral-CA1 synapses was assessed in hippocampal slices obtained from rats three or eight months after virus injection. At three months post-injection, long-term potentiation (LTP) and long-term depression (LTD) were similar in AAV-AD and control rats. However, there appeared to be an increase in tonic glutamate currents in CA1 pyramidal neurons, believed to reflect the activation of extrasynaptic NMDA receptors, in AAV-AD animals. At eight months post-injection, LTP was impaired in hippocampal slices obtained from AAV-AD rats, but LTD and the amplitude of the tonic glutamate current did not differ from controls.
Human APP751 cDNA containing the Swedish and London mutations and human PSEN1 cDNA containing the M146L mutation were cloned separately into AAV2 plasmids with CAG promoters to generate AAV2-CAG-APPSL or AAV2-CAG-PS1M146L. The AAV packaging plasmid was replaced with a plasmid construct containing the rep gene of AAV2 and the cap gene of AAV9. Viral vectors were injected bilaterally into the hippocampi of eight-week male Wistar rats.
Viral vectors are available through AgenT SAS under collaboration or partnership agreements. Contact Jérôme Braudeau: firstname.lastname@example.org.
When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.
- Neuronal Loss
- Synaptic Loss
Amyloid plaques and cerebral amyloid angiopathy observed 30 months post-injection.
Immunostaining with monoclonal antibodies AT8 and AT100 suggests the presence of (pre)tangle-like structures 30 months post-injection.
No astrogliosis observed up to 30 months post-injection.
Changes in LTP/LTD
Deficits in LTP as Schaffer collateral-CA1 synapse at 10 months (8 months post-injection). LTD similar to controls.
AAV-AD spent less time in the target quadrant of the Morris water maze in probe tests administered 3 and 5 days after training.
Last Updated: 22 Feb 2019
- Souchet B, Audrain M, Billoir B, Lecanu L, Tada S, Braudeau J. Is it time to rethink the Alzheimer's disease drug development strategy by targeting its silent phase?. Neural Regen Res. 2018 Feb;13(2):224-225. PubMed.