Investigating SCN8A developmental and epileptic encephalopathy mechanisms and treatments in a human cellular model of the thalamocortical circuit

Columbia University Health Sciences, New York NY

Investigators

Abstract

PROJECT SUMMARY/ABSTRACT Mutations in the voltage-gated sodium channel (VGSC) gene, SCN8A, are associated with developmental and epileptic encephalopathy (DEE). DEE is a severe condition, characterized by neurodevelopmental delay, behavioral and intellectual impairment, and seizures. Despite the availability of several VGSC-targeting pharmacological agents, no effective treatment exists for patients with SCN8A-DEE. Additionally, seizure-altering medication rarely ameliorates DEE-associated cognitive and behavioral comorbidities. To better understand the etiology of SCN8A-DEE and to test novel gene therapy approaches as alternatives to pharmacological interventions, I have generated a novel human induced pluripotent stem cell (hiPSC)-derived organoid model of the thalamocortical circuit (hTCO). This human cellular thalamocortical system produces rhythmic oscillations that resemble those that are affected in animal models of Scn8a- associated epilepsy. Here, I will interrogate the underlying physiology of altered thalamocortical cellular and network activity using whole-cell patch-clamp and two-photon calcium imaging techniques, as well as immunohistochemical and transcriptomic analysis of control and SCN8A-DEE mutant hTCOs. My preliminary work has already established that cells required for thalamocortical rhythm generation are present in hTCOs and that hTCOs exhibit mature thalamocortical-like network activity. Using this model, I will test the hypothesis that SCN8A-DEE hTCOs demonstrate hypersynchronous oscillatory activity and delayed neural maturation in comparison to control hTCOs. In addition to assessing circuit physiology, I will also examine the effects of two SCN8A-targeted gene therapies on neuronal and network physiology in SCN8A-DEE and control hTCOs. The first approach uses short hairpin RNAs (shRNAs) to knockdown SCN8A gene expression in order to reduce the amount of hyperactive mutant SCN8A within neurons. The second approach involves the use of a novel peptide that interacts with the intracellular inactivation gate to reduce SCN8A-DEE-associated increased persistent sodium current. This study will provide valuable training opportunities for me to learn cutting-edge approaches while I interrogate the mechanisms that lead to SCN8A-DEE. Exploration of SCN8A-DEE pathogenesis and examinations of genetic therapeutic efficacy to treat SCN8A-DEE pathologies in a construct-valid, human cellular model system have strong potential to yield insights into SCN8A-DEE and improve the quality of life for patients living with genetic epilepsies.