SCN8A encephalopathy: disease mechanisms and treatment

项目总结 哺乳动物基因组包含四个电压门控钠通道，它们在细胞内高水平表达 中枢神经系统：SCN1A、SCN2A、SCN3A、SCN8A。这个基因家族在人类进化过程中起着重要作用。 人类癫痫的病因和每个基因的突变与不同类型的癫痫有关。然而， SCN8A功能改变与癫痫之间的关系似乎更为复杂。虽然我们已经展示了 具有功能丧失的Scn8a突变的小鼠对诱导癫痫发作更具抵抗力，许多从头开始获得的 已经在具有一系列临床特征的患者中发现了功能性SCN8A突变，包括灾难性的 儿童癫痫、自闭症、智力残疾和发育迟缓。携带SCN8A突变的个体 还面临癫痫突发意外死亡(SUDEP)的风险增加。它们的作用机制 SCN8A突变导致观察到的一系列具有临床挑战性的特征仍然知之甚少，并且 目前的治疗方法往往严重不足。我们的中心假设是，大多数 SCN8A疾病的有效治疗需要对精确的细胞类型有机械上的了解 以及作为SCN8A病理基础的大脑区域。我们的建议建立在我们最近的研究之上，在这些研究中，我们 分离了细胞类型、回路和潜在的癫痫产生与癫痫抵抗的关系，这是由于 Scn8a单倍体不全。我们将通过研究三种不同的SCN8A变体来扩展这些发现：R850Q -最严重和最反复发生的SCN8A突变之一，R1620L-一种与相对轻微的 癫痫，但智力残疾和社会功能障碍，以及与癫痫相关的N1768D突变 脑病。我们将通过使用条件性敲入(CKI)小鼠品系来研究AIM 1中的R850Q突变 启用该变体的细胞和区域选择性表达，直到现在还不可能研究，因为 当在小鼠中全局表达时，严重的表型和过早的死亡。长江基建R850Q系列将用于 确定不同细胞类型对癫痫发作、行为和生物物理表型的影响 伴有SCN8A功能障碍。在目标2中，我们将实施两种并行方法来指导识别更多 在R1620L和R1620L中使用药理学和细胞特异性操作的有效SCN8A治疗 N1768D品系，从而跨越了SCN8A临床表现的范围。鉴于缺乏优化的治疗方法 策略针对SCN8A突变患者，我们将首先进行系统比对 抗癫痫药物和候选药物降低自发性癫痫发作和SUDEP风险的能力，以及 使行为正常化。我们还将使用化学遗传学方法进一步询问特定类型的细胞 对疾病机制的贡献，并建立有选择性地调节 兴奋性神经元的兴奋性，以及小白蛋白、生长抑素和血管活性肠肽 表达中间神经元。提出的实验为SCN8A的个性化用药提供了一条途径 患者和其他神经疾病的治疗发展蓝图。

PROJECT SUMMARY The mammalian genome contains four voltage-gated sodium channels that are expressed at high levels in the central nervous system: SCN1A, SCN2A, SCN3A and SCN8A. This gene family plays an important role in the etiology of human epilepsy and mutations in each gene are associated with different types of epilepsy. However, the relationship between altered SCN8A function and epilepsy appears more complex. While we have shown that mice with loss-of-function Scn8a mutations are more resistant to induced seizures, many de novo gain-of- function SCN8A mutations have been identified in patients with a range of clinical features including catastrophic childhood epilepsy, autism, intellectual disability and developmental delay. Individuals with SCN8A mutations also face an increased risk for sudden unexpected death in epilepsy (SUDEP). The mechanisms by which SCN8A mutations lead to the observed range of clinically challenging features remain poorly understood, and current therapies are often woefully inadequate. Our central hypothesis is that the development of the most effective therapy for SCN8A disorders requires a mechanistic understanding of the precise cell types and brain regions underlying SCN8A pathologies. Our proposal builds on our recent studies in which we decoupled the cell types, circuits, and regions underlying seizure generation versus seizure resistance due to Scn8a haploinsufficiency. We will expand on these findings by studying three different SCN8A variants: R850Q – one of the most severe and recurrent SCN8A mutations, R1620L – a mutation associated with relatively mild epilepsy, yet intellectual disability and social dysfunction, and N1768D – a mutation associated with epileptic encephalopathy. We will study the R850Q mutation in Aim 1 by using a conditional knock-in (CKI) mouse line to enable cell- and region-selective expression of this variant, which until now was not possible to study due to the severe phenotype and premature lethality when globally expressed in mice. The CKI R850Q line will be used to establish the contribution of different cell types to the seizure, behavioral, and biophysical phenotypes associated with SCN8A dysfunction. In Aim 2, we will implement two parallel approaches to guide the identification of more efficacious SCN8A therapies using pharmacological and cell-specific manipulations in both the R1620L and N1768D lines, thereby spanning the range of SCN8A clinical presentations. Given the lack of optimized treatment strategies for patients with SCN8A mutations, we will conduct the first systematic comparison of selected antiepileptic and candidate drugs for their ability to decrease spontaneous seizures and SUDEP risk, and normalize behavior. We will also use a chemogenetic approach to further interrogate cell type-specific contributions to disease mechanisms and establish the therapeutic potential of selectively modulating the excitability of excitatory neurons, as well as parvalbumin, somatostatin, and vasoactive intestinal peptide- expressing interneurons. The proposed experiments provide a path towards personalized medicine for SCN8A patients and a blueprint for treatment development in other neurological disorders.