Scn8a and Seizure Resistance

描述（由申请人提供）：几种癫痫综合征，包括婴儿严重肌阵挛性癫痫（SMEI）和全身性癫痫伴发热性癫痫发作（GEFS+），是由电压门控钠通道突变引起的。钠通道SCN1A的突变是GEFS+和SMEI的主要原因，尽管其他三种钠通道（SCN2A、SCN3A和SCN8A）在中枢神经系统（CNS）中表达。携带Scn1a和Scn2a基因突变的小鼠表现出较低的癫痫发作阈值和自发性癫痫发作。与之形成鲜明对比的是，我们发现小鼠Scn8a基因突变导致癫痫发作阈值升高。此外，改变Scn8a活性可以恢复Scn1a突变小鼠的正常癫痫阈值和寿命，作为GEFS+和SMEI的模型。这项应用的目的是测试Scn8a突变可以预防癫痫发作的假设，并研究这种保护的机制。这可以通过两个具体目标来实现。在第一个目标中，我们将确定Scn8a表达减少导致更高癫痫阈值和防止癫痫诱导的机制。第一个目标将确定癫痫发作阈值的增加是由于Scn8a表达减少对神经元兴奋性的直接影响，还是其他三个CNS钠通道表达代偿性增加的间接影响，或者可能两者兼而有之。然后，我们将利用电生理记录确定Scn8a表达的减少是否会导致海马和皮质脑切片中网络兴奋性的改变。第二个目的是确定导致Scn8a突变小鼠癫痫发作阈值升高的神经元细胞类型。这将通过选择性地从锥体细胞或皮层和海马体的中间神经元中删除Scn8a来实现，然后评估小鼠癫痫发作阈值升高和网络兴奋性改变。最后，我们将使用分子遗传学和电生理学方法来研究Scn8a活性改变导致SMEI小鼠癫痫发作表型显著改善的机制。这些研究将为改变Scn8a功能导致癫痫发作阈值升高的机制提供重要的和临床相关的见解，使人们能够追求急需的转化研究，以开发新的癫痫治疗方法。公共卫生相关性：我们观察到，钠通道基因Scn8a活性降低的小鼠更耐癫痫发作。我们将研究这一观察结果背后的机制。本研究将提供Scn8a对癫痫抵抗的重要临床相关信息，并为进一步研究降低人类Scn8a基因活性治疗人类癫痫的可行性奠定基础。

DESCRIPTION (provided by applicant): Several epilepsy syndromes, including severe myoclonic epilepsy in infancy (SMEI) and generalized epilepsy with febrile seizures plus (GEFS+), are caused by mutations in the voltage-gated sodium channels. Mutations in the sodium channel SCN1A are a major cause of GEFS+ and SMEI, even though three other sodium channels (SCN2A, SCN3A, and SCN8A) are expressed in the central nervous system (CNS). Mice with mutations in Scn1a and Scn2a exhibit lower seizure thresholds and spontaneous seizures. In marked contrast, we have shown that mutations in the mouse Scn8a gene lead to elevated seizure thresholds. Furthermore, altering Scn8a activity can restore normal seizure thresholds and life spans in mice with Scn1a mutations that serve as models of GEFS+ and SMEI. The goal of this application is to test the hypothesis that mutations in Scn8a can protect against seizures and to investigate the mechanism underlying such protection. This can be achieved in two specific aims. In the first aim we will determine the mechanism by which decreased Scn8a expression leads to higher seizure thresholds and protection against seizure induction. The first objective will establish whether the increase in seizure thresholds is due either to a direct effect of decreased Scn8a expression on neuronal excitability or an indirect effect of a compensatory increase in the expression of any of the other three CNS sodium channels, or possibly both. We will then determine whether reduced Scn8a expression leads to altered network excitability in hippocampal and cortical brain slices using electrophysiological recordings. The purpose of the second aim is to identify the neuronal cell types responsible for the elevation in seizure thresholds of Scn8a mutant mice. This will be accomplished by selectively deleting Scn8a from either pyramidal cells or interneurons in the cortex and hippocampus, and then evaluating the mice for elevated seizure thresholds and altered network excitability. Finally, we will use molecular genetic and electrophysiological approaches to investigate the mechanism by which altered Scn8a activity leads to the dramatic improvements seen in the seizure phenotype of an SMEI mouse model. These studies will provide important and clinically relevant insight into the mechanism by which altered Scn8a function leads to elevated seizure thresholds, enabling the pursuit of much-needed translational studies into the development of novel treatments for epilepsy. PUBLIC HEALTH RELEVANCE: We have observed that mice with reduced activity of the sodium channel gene Scn8a are more seizure resistant. We will investigate the mechanism that underlies this observation. This study will provide important, clinically relevant information on the contribution of Scn8a to seizure resistance and will lay the foundation for further research on the feasibility of reducing the activity of the human SCN8A gene as a treatment for human epilepsy.