Authors :
Presenting Author: David Scott, PhD – BridgeBio Gene Therapy
Mackenzie Catron, PhD – PsychoGenics; Kristi Viles, PhD – BridgeBio Gene Therapy; Zoe Fuchs, PhD – TSC Alliance; Dean Aguiar, PhD – TSC Alliance; Stephen Morairty, PhD – PsychoGenics; Xandra Breakefield, PhD – Massachusetts General Hospital; Clayton Beard, PhD – BridgeBio Gene Therapy
Rationale:
Tuberous sclerosis complex (TSC) is a rare genetic disorder characterized by the growth of benign hamartoma tumors in various organs of the body, including the brain. Neurological manifestations including seizures, autism, anxiety, and depression represent the greatest clinical unmet need. Animal models of TSC associated epilepsy involve genetically modified mice with cell-specific deletion of TSC1 or TSC2. These models rely on floxed alleles of the TSC1 or TSC2 genes and homologous recombination mediated by Cre recombinase expressed by a cell-type specific promoter such as Syn1 (neurons) or GFAP (glial cells). Loss of TSC function leads to hyperactivation of mTOR. In contrast, a model of TSC1 has previously been described which is generated by intracerebroventricular (ICV) injection of AAV1-Cre into Tsc1tm1Djk/J mice that leads to “stochastic” knockout of the TSC1 gene in multiple cell types. Deleting TSC1 in multiple cell types may better reflect the genetics of clinical disease. While this model has been shown to recapitulate many of the features of other TSC models including activation of the mTOR pathway and decreased survival (early death), the presence and characterization of seizures in the model is unknown.
Methods:
To understand if TSC1 stochastic mice develop seizures, we conducted a dose range finding study of ICV administered AAV1-Cre into Tsc1tm1Djk/J and used survival to help define the window that would support seizure analysis. In a dose-dependent manner AAV1-Cre reduced survival and identified a regimen that could be used for seizure analysis in the P35-54 age range. Mice were administered AAV1-Cre at postnatal day one and underwent implantation of EEG headset at postnatal day 21 for seizure assessment. Treatment groups received mTOR inhibitor everolimus (0.3 or 0.03 mg/kg, IP 3x per week) beginning at postnatal day 28 through day 54. EEG recordings occurred continuously from day 35-55.
Results:
There were no seizures detected in the cohort of animals that did not receive AAV1-Cre. Seizures were detected in 12/16 animals receiving AAV1-Cre only, in 5/8 animals receiving AAV1-Cre + 0.03 mg/kg everolimus and in 4/8 animals receiving AAV1-Cre + 0.3 mg/kg everolimus. The average number of seizures in 48 hours in the untreated animals was 1.35 and an observed dose response effect of everolimus (0.03 and 0.3 mg/kgk) with 0.50, and 0.24 seizures/48 hours. However, there was no significant effect on seizure duration.
Conclusions:
This data is consistent with other TSC epilepsy models, supporting the utility of the TSC1 stochastic mouse model for assessment of seizures.
Funding: N/A