Seizures exacerbate tau spread in the 5XFAD mouse model

Abstract

AbstractBackgroundCentral to the progression of Alzheimer’s disease (AD) is the spread of pathological tau along neuronal connections. This aspect of pathological progression can be recapitulated in WT mice by intracerebral injection of human AD brain derived tau lysate (AD‐tau). AD‐tau spread is enhanced in the amyloidosis mouse model, five times familial AD (5XFAD), suggesting that tau propagation is facilitated by β‐amyloid (Aβ) plaques. Once assumed to simply be a biproduct of Aβ‐induced hyperexcitability, a bidirectional relationship between seizures and AD progression has been established. Our lab has demonstrated worsened tau and Aβ pathology and cognitive deficits in AD patients with seizure history and in seizure‐kindled 5XFAD mice. Thus, we hypothesized that seizures would exacerbate the spread of AD‐tau in the 5XFAD mouse model and that 5XFAD mice would show increased seizure susceptibility and related neuronal activity.MethodTo investigate seizure‐pathology interactions, we crossed the 5XFAD mouse model with targeted recombination in active populations (TRAP; 5X‐TRAP) mice to permanently label seizure‐activated neurons. We injected AD‐tau unilaterally into the hippocampus and overlying cortex (1 µg/site) at 3 months of age in 5X‐TRAP and WT‐TRAP littermates. Seizures were induced with pentylenetetrazol (PTZ) kindling 2‐3 weeks following surgery and seizure‐activated neurons were labeled (tdTomato) on the final day of kindling via 4‐hydroxytamoxifen administration (50 mg/kg). Mice were euthanized three months post AD‐tau injection and immunohistochemistry for phospho‐tau (AT8) was performed.ResultWe found that kindled 5X‐TRAP mice show increased pathological tau (% AT8 coverage) in the dentate gyrus (DG) and CA1 contralateral to injection site compared to non‐kindled mice (p<0.05). We also found a trend towards elevated AT8 in the ipsilateral DG across seizure kindled groups (p = 0.083) and that 5X‐TRAP mice showed increased AT8 in the ipsilateral CA1 compared to WT‐TRAP (p<0.05). Further, we found a trend towards increased seizure susceptibility (0.059) in 5X‐TRAP mice and significantly increased seizure activated neurons (tdTomato+) in the DG of kindled 5X‐TRAP mice compared to WT‐TRAP (p<0.05).ConclusionOverall, our data further indicate a bidirectional relationship between seizures and AD. We also demonstrate that seizures facilitate the spread of pathological tau, thus suggesting that targeting seizure activity may slow AD progression.