Despite availability of anti-epileptic drugs, one-third of the 3.4 million US patients with epilepsy have medically intractable epilepsy and still experience seizures despite treatment. There are no effective treatments to prevent the development of this debilitating condition (antiepileptogenic) in at-risk patients. The mechanistic target of rapamycin (mTOR) pathway, which regulates neuronal plasticity and growth, has emerged as a promising candidate for the development of anti-epileptogenic therapies. Pharmacological antagonists of the mTOR pathway have shown efficacy at preventing seizure occurrence in animal models of epilepsy, however, the cellular targets and signaling complexes mediating these effects are unclear. Hippocampal dentate granule cells (DGCs) may be prime targets of mTOR mediated pathological changes seen in temporal lobe epilepsy (TLE). mTOR signaling is increased among DGCs during the development of TLE, and treatment with rapamycin can block the formation of atypical DGC morphology. Our lab has shown that deletion of mTOR inhibitor, phosphatase and tensin homolog (PTEN) from newborn hippocampal dentate granule cells (DGCs) resulted in the mossy fiber sprouting and soma hypertrophy associated with epilepsy. These abnormalities exhibited in DGCs are thought to be associated with breakdown of the dentate gyrus? ability to filter incoming information from the entorhinal cortex, creating hyper-excitable hippocampal circuits, resulting in spontaneous recurrent seizures. We hypothesize that rapamycin produces its diseasing modifying effects by blocking mTOR signaling in DGCs. To test this hypothesis, we will genetically delete the essential mTORC1 adaptor protein raptor from granule cells in a mouse TLE model and determine whether the treatment reduces seizure incidence and prevents dysmorphogenesis in DGCs (Aim 1). To assess the role of raptor in epileptogenesis, we have developed a viral strategy in which LoxP-flanked raptor can be deleted after pilocarpine-induced status epilepticus by injecting transgenic animals with AAV9.CamKII.HI.eGFP-Cre. Cre- mediated recombination in hippocampal neurons will lead to the deletion of raptor, preventing mTORC1 activity in these cells.
(Aim 2) We predict that blocking hippocampal DGCs plays a role in the pathogenesis of TLE. Our proposal leverages collaborative, conceptual, and methodological innovation to make meaningful progress towards delineating the roles of mTORC1 and mTORC2 in the pathogenesis of epilepsy. The results, together with mentored training, will provide a foundation for working toward new solutions for epilepsy and other neurological disorders.
This study will directly test the hypothesis that disease modifying effects from rapamycin treatment occur by blocking mTORC1 signaling in dentate granule cells. Using a novel viral strategy we will be able to determine the affect the mTORC1 adaptor protein, Raptor, will have upon measurable forms of epileptiform activity, seizure frequencies, and morphology. This approach allows a better understanding of the role of mTORC1 activity in epileptogenesis, which may potentially lead to the development of improved treatment options for individuals suffering from epilepsy
