Abstracts

Rationale: Patients with Tuberous Sclerosis Complex (TSC) often have severe, intractable epilepsy. Mutation of the TSC1 or TSC2 genes in TSC has recently been shown to cause hyperactivation of the mammalian target of rapamycin (mTOR) pathway, leading to a number of downstream cellular and molecular events related to glioneuronal growth and proliferation. mTOR inhibitors, such as rapamycin, have been proposed as novel therapeutic agents to prevent tumor growth in TSC, but the efficacy of such drugs in treating epilepsy has not been tested. In this study, we have evaluated the effect of rapamycin on seizures and other brain abnormalities in a mouse model of TSC with conditional inactivation of the Tsc1 gene primarily in glia (Tsc1^GFAPCKO mice).Methods: Tsc1^GFAPCKO mice and littermate controls were treated with rapamycin (3 mg/kg/d, i.p., 5 days/week) or vehicle starting at P14. Mice were monitored for seizures by video-EEG and survival from 4 weeks of age until 11 weeks or death. In other mice, brains were examined by immunohistochemical staining with GFAP-specific antibody and Nissl staining for glia and neuronal density in hippocampus and cortex. Phospho-S6 expression was also assayed by Western blotting to determine inhibition of the mTOR pathway by rapamycin.Results: Seizures developed in vehicle-treated Tsc1^GFAPCKO mice between 4-6 weeks of age and became progressively more frequent through 10 weeks of age, with most mice dying by 10 weeks. In contrast, rapamycin-treated mice exhibited no seizures during this time period. Furthermore, rapamycin caused a dramatic increase in survival, with only 1 of 10 mice dying prior to 5 months of age. Correspondingly, rapamycin prevented abnormal hyperactivation of phospho-S6, glial proliferation, neuronal disorganization, and increased brain size in Tsc1^GFAPCKO mice. Conclusions: Rapamycin has strong efficacy for preventing seizures and prolonging survival in Tsc1^GFAPCKO mice.