Molecular mechanisms of neuronal hyperactivity in Tuberous Sclerosis Complex

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Epilepsy and Autism spectrum disorder are among the most common neurological disorders that affect children, and there is increasing evidence that dysregulation of the mechanistic target of rapamycin (mTOR) is involved in the development of both disorders. Tuberous Sclerosis Complex (TSC) is an ideal model in which to study the effects of abnormal mTOR signaling in the brain because dysregulation of this pathway has been implicated in the neurological symptoms of both animal models and patients. Although the TSC-mTOR signaling pathway has been well studied, the downstream effect of dysregulation of this pathway on neurons is not completely understood. We have found that loss of Tsc2 in an animal model of TSC leads to down- regulation of the critical transcription factor, Egr1, in certain sub-types of pyramidal neurons. In addition, we have observed down-regulation of EGR1 in cortical neurons differentiated from induced pluripotent stem cells (iPSCs) from patients with TSC, coincident with increased activity in these neurons. We hypothesize that down-regulation of EGR1 occurs due to dysregulation of mTOR in two separate signaling complexes and contributes to neuronal abnormalities observed in TSC, such excitatory-inhibitory imbalance. To demonstrate the clinical relevance of this finding, we propose to confirm our observation in iPSC-derived neurons from patients with TSC and cortical tubers from individuals with TSC. We will then examine the mechanism by which loss of TSC2 alters EGR1 expression in iPSC-derived neurons. Finally, we will examine excitability in iPSC- derived neurons and determine the effect of rescuing EGR1 expression on this phenotype using extracellular recordings. The candidate is currently a Neurogenetics fellow at Boston Children's Hospital, and this proposal builds upon his skills in bioinformatics and extends his skillset to the use of iPSC-derived neurons to model genetic disease, molecular and cellular techniques to study dysregulated signaling pathways, single cell sequencing, and basic electrophysiological concepts and techniques. His proposal includes a comprehensive mentoring and didactic plan that will allow him to successfully learn new skills and gain expertise in each of these important areas. His primary mentor, Dr. Mustafa Sahin, is a translational neuroscientist and expert in both the clinical research and molecular biology of TSC. In addition, the candidate has assembled a K08 advisory committee consisting of Dr. Lee Rubin, Dr. Elizabeth Engle, and Dr. Alexander Rotenberg, who each have specific expertise in various aspects of this proposal, such as differentiation and study of iPSC-derived neurons, single cell sequencing, and electrophysiology. The candidate is committed to a career in translation research focusing on neurogenetic disorders in children, and the proposed research and career development plans will enable him to successfully transition to become an independent investigator in this field.