Network Dysfunction Precedes Neurodegeneration in a dox-Regulatable TDP-43 Mouse Model of ALS-FTD

Neuronal hyperexcitability is a hallmark of amyotrophic lateral sclerosis (ALS), but its relationship with the TDP-43 aggregates that comprise the predominant pathology in over 90% of ALS cases remains unclear. Emerging evidence indicates that TDP-43 pathology induces neuronal hyperexcitability, which may contribute to excitotoxic neuronal death. To characterize TDP-43 mediated network excitability changes in a disease-relevant model, we performed in vivo continuous electroencephalography monitoring and ex vivo acute hippocampal slice electrophysiology in rNLS8 mice (males and females), which express human TDP-43 with a defective nuclear localization signal (hTDP-43ΔNLS). Surprisingly, we identified the presence of seizures in ∼64% of rNLS8 mice beginning ∼2.5 weeks after transgene induction (off-DOX). More broadly, we observed longitudinal changes in cortical EEG patterns and circuit hyperexcitability preceding neurodegeneration of vulnerable hippocampal subfields. Consistent with previous reports, we have observed broad dysregulation of AMPA subunit expression in mice expressing hTDP-43ΔNLS. These changes were most pronounced in the hippocampus, where we hypothesized they promote hyperexcitability and ultimately, excitotoxic cell death. Interestingly, hippocampal injection of AAV encoding inhibitory DREADDs (hM4Di) and daily activation with CNO ligand rescued anxiety deficits on the elevated zero maze but did not reduce neurodegeneration. Moreover, therapeutic doses of the antiseizure medications, valproic acid and levetiracetam, did not improve behavior or prevent neurodegeneration. These results highlight the complex relationship between TDP-43-mediated neuronal hyperexcitability and neurodegeneration. Although targeting hyperexcitability may ameliorate some behavioral deficits, our study suggests it may not be sufficient to halt or slow neurodegeneration in TDP-43-related proteinopathies.