Neuronal channelopathies cause various brain disorders including epilepsy, migraine and ataxia. Despite the development of mouse models, pathophysiological mechanisms for these disorders are poorly understood. One particularly devastating channelopathy is Dravet Syndrome (DS), a severe childhood epileptic encephalopathy typically caused by de novo dominant mutations in SCN1A, encoding the voltage-gated Na+ channel (VGSC) Nav1.1. Heterologous expression of mutant channels suggests haploinsufficiency, raising the question of how loss of VGSCs underlying action potentials (APs) produces hyperexcitability. Data from DS mouse models indicate both decreased Na+ current in interneurons, implicating disinhibition, and increased Na+ current in pyramidal cells, implicating hyperexcitability, depending on genetic background, brain area, and animal age. To understand the effects of SCN1A DS mutations in human neurons we derived forebrain-like neurons from two DS subjects by induced pluripotent stem cell (iPSC) reprogramming of patient fibroblasts and compared them with iPSC-derived neurons from human controls. We found that DS patient-derived neurons have increased Na+ current density in both bipolar- and pyramidal-shaped neurons. Consistent with increased Na+ current, both putative excitatory and inhibitory patient-derived neurons showed spontaneous bursting and other evidence of hyperexcitability. Our data provided some of the first evidence that epilepsy patient-specific neurons obtained via the iPSC method are useful for modeling epileptic-like hyperactivity. Moreover, our findings revealed a previously unrecognized potential epilepsy mechanism underlying DS and offered a platform for future screening of novel anti-epileptic therapies using patient-derived neurons. The long-term goal of this research is to understand the molecular basis of genetic epilepsies. Our objective is to determine epilepsy mechanisms of SCN1A-linked DS in humans. We will test the central hypothesis that SCN1A haploinsufficiency leads to paradoxically increased Na+ current in excitatory and inhibitory neurons, as well as alterations in other ionic currents that underlie neuronal hyperexcitability in DS. The rationale fr this work is that identifying the role of SCN1A haploinsufficiency in the development of hyperexcitability may lead to novel treatments for DS as well as related pediatric epilepsies. We will test our hypothesis by pursuing three specific aims: 1: To determine whether SCN1A haploinsufficiency causes alterations in the expression of other VGSC ?-subunits that lead to increased Na+ current in DS patient-specific iPSC neurons. 2: To investigate changes in synaptic function in DS patient-specific iPSC neurons. 3: To determine the electrophysiological characteristics of DS patient-specific and control iPSC neurons differentiated in the rodent brain. This work is expected to reveal how SCN1A haploinsufficiency contributes to epilepsy in humans. Our results will have positive impact because this work will lead to a greater understanding of the mechanisms of DS and related diseases and may lead to novel therapeutic agents for epilepsy.
Dravet Syndrome is a severe childhood epileptic encephalopathy typically caused by de novo dominant mutations in SCN1A, the gene encoding the voltage-gated Na+ channel Nav1.1. The objective of this research is to determine epilepsy mechanisms of Dravet Syndrome in humans. We will test the central hypothesis that increased Na+ current expression in both excitatory and inhibitory neurons underlies neuronal hyperexcitability in Dravet Syndrome. Identifying the mechanism of hyperexcitability may lead to novel treatments for Dravet Syndrome as well as related pediatric epilepsies.
|Lopez-Santiago, Luis F; Yuan, Yukun; Wagnon, Jacy L et al. (2017) Neuronal hyperexcitability in a mouse model of SCN8A epileptic encephalopathy. Proc Natl Acad Sci U S A 114:2383-2388|