Abstracts

Rationale: Several growth disorders and cancers have been linked to aberrant regulation of the PI3K-mTOR signaling pathway. More recently, a number of diseases associated with epilepsy have also been linked to this pathway, including Tuberous Sclerosis Complex (TSC) and cortical dysplasia (CD). Many characteristics of CD, including large cytomegalic (CM) neurons with upregulated mTOR pathway activation and epilepsy, are recapitulated in mice by a neuronal subset-specific conditional knockout of the negative PI3K-mTOR regulator, PTEN (NS-PTEN knockout mice). In the studies presented here, we evaluated the epilepsy phenotype and candidate mechanisms of hyperexcitability, and then examined the effects of transient mTOR pathway inhibition using the mTOR-specific inhibitor, rapamycin. Methods: Video-EEG recordings, biochemical assays, and Timm staining were employed to examine the short and long-term effects of treatment with rapamycin. Study groups consisted of naïve, vehicle-, and rapamycin-treated wild type (WT) and knockout (KO) mice. Treatment consisted of 10mg/kg daily I.P. injections of rapamycin or vehicle for 5 days per week during postnatal weeks 4-5. Results: Video-EEG analysis confirmed that KO mice have epilepsy, as they all exhibited interictal spikes, repetitive spikes, and spike and wave discharges. These indicators of epilepsy were fully penetrant by 6 weeks, and grew more prevalent with age. We also found mossy fiber sprouting by 6 weeks, which has been linked to recurrent excitation in temporal lobe epilepsy patients and other animal models. Treatment with rapamycin decreased cortical pS6 levels, a downstream effector of mTORC1, indicating a successful inhibition of the PI3K-mTORC1 pathway. Epileptiform activity was also significantly reduced both immediately following treatment and 3 weeks after treatment termination, such that there was no significant difference between the pre-treatment and post-treatment epileptiform activity in the rapamycin-treated group. Rapamycin treatment also significantly reduced the mossy fiber sprouting. Conclusions: Our findings demonstrate that NS/PTEN KO mice have epilepsy, and inhibition of the mTOR pathway not only attenuates epileptiform activity in this model, but also reduces aberrant mossy fiber sprouting. These results suggest that rapamycin may function as a novel treatment for some forms of epilepsy. Studies are currently underway to assess when rapamycin treatment alters mossy fiber sprouting in this model. Changes in potential molecular mTOR substrates of excitability are also being evaluated.