Anti-epileptogenic role of mTOR activation among hippocampal interneurons

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PROJECT SUMMARY Epilepsy can be a debilitating and sometimes fatal disease for which there are no preventatives, no cure, and for which existing medications fail in one third of patients. Development of preventative treatments for epilepsy is a key NINDS goal (Benchmark II. Prevent epilepsy and its progression; Galanopoulou et al., 2016; Binder et al., 2020). The mechanistic target of rapamycin (mTOR) pathway has emerged as a promising target for epilepsy prevention. mTOR acts as a relatively ubiquitous promotor of cell growth; enhancing neuronal connectivity, excitability and metabolism. Activation of the mTOR pathway occurs during epileptogenesis and appears to regulate pro-excitatory changes implicated in the process. Moreover, blocking mTOR signaling with the antagonist rapamycin mitigates epilepsy development in many epilepsy models. Blocking mTOR signaling, however, does not work in all models, and there is evidence that this pathway may also act to reduce brain excitability. To explain these conflicting effects, we hypothesize that increased mTOR activation among excitatory neurons is pro-epileptogenic, while activation among GABAergic interneurons is anti-epileptogenic. Systemic mTOR antagonists, therefore, block epileptogenic changes among excitatory cells, but also block compensatory protective changes among interneurons. To test this hypothesis, we will use intersectional genetic approaches to selectively delete the obligate mTOR regulatory proteins Raptor or Rictor from vesicular GABA transporter-, parvalbumin-, and somatostatin-expressing interneurons in mice. We will also examine the impact of enhancing mTOR signaling in interneurons by deleting the mTOR negative regulator Tsc2. Studies will be conducted using both acquired and genetic models of epilepsy. We predict that blocking mTOR signaling in interneurons will make epilepsy worse, while enhancing signaling will improve outcomes. Studies will advance understanding of the role of mTOR in epileptogenesis and will have direct implications for ongoing clinical use of mTOR antagonists.