mTORC1-dependent translational control in developmental epilepsy

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PROJECT SUMMARY Malformation of cortical development (MCD) is the leading cause of intractable epilepsy in children. Seizures due to MCD are severe and frequently resistant to antiepileptic drugs, and the only definitive treatment option is often surgery to remove the abnormal brain regions responsible for seizure generation. These therapeutic limitations highlight the need for novel approaches to treat MCD-related epilepsy. Recent studies in humans and animal models have identified pathogenic mutations leading to aberrant hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway in several MCD subtypes that are highly linked to epilepsy, including tuberous sclerosis complex, focal cortical dysplasia, and hemimegalencephaly, demonstrating an important role for mTORC1 dysregulation in the pathogenesis of epilepsy. However, the mechanisms by which mTORC1 dysregulation contributes to epilepsy are not well understood. Since current mTORC1 inhibitors such as rapamycin and its analogs can have serious side effects, do not fully block all of mTORC1’s functions, and have limited efficacy, a more specific understanding of the downstream molecular players responsible for epilepsy development is crucial in order to develop more effective therapies. mTORC1 regulates many cellular processes, with the best studied function being mRNA cap-dependent translational control. Activation of mTORC1 promotes mRNA translation via inactivation of the translational suppressor 4EBP. Thus, one working hypothesis is that upregulated mTORC1-dependent translation leads to exaggerated protein synthesis that contributes to the neuronal defects underlying epilepsy. Interestingly, normalizing translation via 4EBP overexpression during cortical development prevented mTORC1-induced cytoarchitectural abnormalities associated with MCD. However, the effects on neuronal excitability and seizures have not been investigated. The overall goal of this research is to delineate the contribution of increased mTORC1-dependent translation to hyperexcitability and seizures (Aim 1) and to identify the specific molecules that are abnormally expressed as a result of this aberrant increase in translation (Aim 2). A canonical activator of mTORC1, Rheb, will be constitutively expressed in neurons to mimic the persistent activation of mTORC1 in disease states in mouse models. Complementing genetic and pharmacological approaches will then be used to target mTORC1-induced translation and the resulting effects on neuronal excitability and seizures will be assessed. In parallel, mRNAs that are actively translated in neurons under different conditions of mTORC1 activity will be isolated and identified by microarray analysis and biochemical validation. The proposed research will advance our understanding of how altered intracellular signaling pathways and translational control mechanisms modulate neuronal excitability and seizures and provide mechanistic insights into the pathogenesis of epilepsy associated with MCD. Knowledge gained from this study will help uncover novel targets for the treatment of intractable epilepsy and potentially other neurodevelopmental disorders caused by mTORC1 dysregulation.