Rationale: While there are dozens of anti-seizure medications available for patients with epilepsy, as many as one third of patients experience seizures refractory to treatment. Identifying treatments that prevent epileptogenesis is an unmet need with clear translational applications. Epileptogenesis involves DNA damage, apoptosis, and inflammation, three features also relevant to the cellular senescence program. Senescent cells (SCs) arise in response to extreme stress or injury, leading to a decline in normal functioning and increased inflammation mediated by the senescence associated secretory phenotype. Critically, the role of SCs in epileptogenesis or as an antiepileptogenic target is understudied. Ongoing studies from our group show that genetic ablation of SCs and pharmacological ablation (a combination of Dasatinib and Quercetin) normalizes spatial memory and reduces seizure burden in the status epilepticus (SE) mouse model. However, no studies have looked at newer senolytic therapies, such as senescence-specific killing compound 1 (SSK1), a prodrug which requires β-galactosidase action to activate its gemcitibine core.
1 Here, we investigate the effects of SSK1 on seizure burden and behavioral comorbidities in the SE mouse model.
Methods: A 4 month old wild type C57Bl/6 mice were injected with pilocarpine to induce SE and monitored for two hours. Seizures were terminated with diazepam. Following SE termination, mice were randomly assigned to receive either SSK1 (0.5mg/kg, IP) or a vehicle injection twice a week for the duration of the study. Two months after SE, mice were tested in a battery of behavioral tests (open field test, novel object recognition test, novel location test, object context mismatch test, elevated plus maze, Barnes maze) in order to assay object and spatial memory and anxiety. After behavioral testing, telemeters were implanted in the mice, and video EEG was recorded continuously for two weeks. Mice were then euthanized, and their brains were fixed for histology to confirm SC ablation.
Results: Treatment with SSK1 following SE eliminates ~25% of SCs in the hippocampus. SSK1 also appears to reduce a subset of spatial memory deficits seen following SE (object-location memory, but not navigational memory). Finally, SSK1 treatment also leads to a reduction of frequency, average duration, and total seizure burden.
Conclusions: These results demonstrate that SSK1 replicates a majority of the findings of earlier SC ablation methods. Interestingly, SSK1 does not rescue deficits in navigational memory, which may suggest that a higher threshold of SC ablation is necessary to rescue this phenotype. Further work may explore different dosing regimens, the incidence of off-target effects compared to other senolytic therapies, and mechanisms affected by SSK1 (inflammation, synaptic plasticity). Overall, this study furthers our understanding of how SCs may be targeted to prevent or slow epileptogenesis.
References:
1 Cai, Y., Zhou, H., Zhu, Y. et al. Elimination of senescent cells by β-galactosidase-targeted prodrug attenuates inflammation and restores physical function in aged mice. Cell Res 30, 574–589 (2020). https://doi.org/10.1038/s41422-020-0314-9
Funding: 1R21NS125552-01