Abstracts

Rationale: Clinical and experimental data suggest a potential interaction between epilepsy and Alzheimer’s disease (AD), as seizures are occurring in 20% or more of AD patients, often prior to the onset of memory impairment. Additionally, chronic epilepsy syndromes such as temporal lobe epilepsy exhibit AD-like neuropathology. We hypothesize that chronic hyperexcitability promotes neurodegeneration and cognitive decline and can therefore further exacerbate AD neuropathology. Methods: For these experiments, we used the 5XFAD (5 times Familial Alzheimer’s disease) mouse model of AD. 5XFAD mice exhibit β-amyloid (Aβ42) accumulation starting from 2 months (mo) old and major behavioral deficits and neurodegeneration at 8-9 mo of age. At the pre-symptomatic stage of 3 mo, 5XFAD and wild type (WT) littermates were subjected to a standard pentylenetetrazol (PTZ) kindling protocol to induce chronic hyperexcitability: 35 mg/kg i.p., every other day for 14 days (8 injections in total). Control mice, WT and 5XFAD, received saline injections. Seizure behavior (latency and severity) was recorded for 1h after each injection and classified following a modified Racine scale: 0, normal behavior; 1, freezing; 2, hunching with facial automatism; 3, rearing and forelimb clonus; 4, rearing with forelimb clonus and fall; 5, tonic-clonic seizure; 6, death. Three months after the last PTZ injection, cognitive testing (contextual fear conditioning) and AD neuropathology, including Aβ42 accumulation (by ELISA), neuronal death (by Fluorojade B staining), neuroinflammation (glial cells activation by quantitative immunohistochemistry and cytokines expression by Multiplex assay), were assessed when mice were then 6.5-7 mo of age (n=12-19/group). Results: During the PTZ kindling protocol, the 5XFAD mice exhibited an increased seizure severity versus age-matched WT (163% of WT, p<0.001) and a decreased latency to seizure (-1.050.21 min vs WT, p<0.0001). Three months later, the PTZ kindled 5XFAD mice showed significantly decreased remote memory compared to 5XFAD saline-injected mice (70% of 5XFAD-saline, p<0.05), increased soluble Aβ42 accumulation (166% of 5XFAD-saline, p<0.05) and increased neuronal death (204% of 5XFAD-saline, p<0.05). Both markers were positively correlated with seizure severity (r=0.52, p<0.05 and r=0.61, p<0.01, respectively). Further analyses revealed that the PTZ kindled 5XFAD mice exhibited an increased labeling of the astrocyte marker GFAP (411% of 5XFAD-saline, p<0.0001), microglial marker Iba1 (298% of 5XFAD-saline, p<0.0001), and an increased expression of pro-inflammatory cytokines IL-1 and TNF (119% and 122% of 5XFAD-saline, respectively; p<0.05). Conclusions: These results demonstrate that AD mice are more susceptible to seizure induction, and that seizures in the pre-symptomatic stage appear to enhance AD neuropathology. As AD patients experience more epileptic seizures than the control population, epilepsy-associated factors could represent a therapeutic target in the prodromal stages to attenuate AD progression. Funding: NIH NINDS R21NS105437