Hippocampal Circuit Dysfunction in SCN8A Gain-of-Function Encephalopathy

项目总结/摘要 发育性癫痫性脑病（DEE）是一种以难治性癫痫发作为特征的复杂疾病， 发育迟缓、认知障碍、运动障碍和意外猝死风险增加 （SUDEP）（1 - 4）。钠通道基因SCN8A的新生错义突变已在更多的人中被发现。 300多例DEE患者，导致疾病早期婴儿癫痫性脑病13例（EIEE13; OMIM #614558）或SCN 8A脑病（3）。我们已经报道了最常见的致病性 SCN8A脑病的机制是钠通道Nav1.6的功能获得性（GOF）改变。我们 开发了一种表达患者突变p.Arg1872Trp（R1872W）的小鼠模型， Cre诱导的复合（5）。该模型允许在成人中以受控方式诱导癫痫发作。 动物，绕过组成型表达突变的早期致死性。通过交叉条件R1872W 我们用表达他莫昔芬诱导型Cre转基因的CAG-Cre-ER小鼠， 在成年小鼠中重现患者表型的癫痫发作。这些同类的相同遗传背景 小鼠有助于实验的可重复性。 海马波纹是在非快速眼动（NREM）睡眠和安静清醒时看到的快速振荡。行为 活动模式，如海马位置细胞在导航过程中的顺序放电，在一个 在涟漪期间压缩神经序列，帮助巩固相关记忆。波纹受损， 许多癫痫，可能导致患者的记忆和认知缺陷。虽然健康， 病理性波动动力学在颞叶癫痫中得到了很好的研究，最近在全球SCN 1A中也得到了很好的研究。 单倍不足模型，关于SCN8A对涟漪的影响的知识存在空白 脑病因此，重要的是研究SCN8A脑病对波纹的影响， 其他海马电路输出。我们的中心假设是，波纹（Aim 1）和海马位置细胞 在SCN8A脑病的发展过程中，放电（Aim 2）逐渐受损。的理由 这一假设来自我们发表的观察结果，即患者突变导致Nav1.6活性升高。 通道由于过早激活或失活受损，导致培养的海马神经元过度活跃， 锥体细胞这些目标的完成将导致大量数据集的收集，这些数据集将被共享 与癫痫社区，允许社区范围内的癫痫发作和发作间期动力学，癫痫发作- 发作和SUDEP预测算法，以及睡眠-觉醒节律随时间的变化。观察到的 海马回路动力学的变化将产生进一步的假设，这些假设可以用细胞类型来分析， 和区域特异性CRE转基因的后续R01应用。

PROJECT SUMMARY / ABSTRACT Developmental epileptic encephalopathy (DEE) is a complex disorder characterized by refractory seizures, developmental delay, cognitive disabilities, movement disorders and elevated risk of sudden unexpected death (SUDEP) (1-4). De novo missense mutations in the sodium channel gene SCN8A have been identified in more than 300 patients with DEE, resulting in the disorder early infantile epileptic encephalopathy 13 (EIEE13; OMIM #614558) or SCN8A encephalopathy (3). We have reported that the most common pathogenic mechanism of SCN8A encephalopathy is gain-of-function (GOF) changes in sodium channel Nav1.6. We developed a mouse model with expression of the patient mutation p.Arg1872Trp (R1872W) that is dependent on Cre-induced recombination (5). This model allows seizures to be induced in a controlled fashion in the adult animal, bypassing the early lethality of constitutively expressed mutations. By crossing conditional R1872W mice with CAG-Cre-ER mice expressing a tamoxifen-inducible Cre transgene, we can induce spontaneous seizures in adult mice that recapitulate patient phenotypes. The identical genetic background of these congenic mice contributes to experimental reproducibility. Hippocampal ripples are fast oscillations seen during non-REM (NREM) sleep and quiet wakefulness. Behavioral activity patterns, such as the sequential firing of hippocampal place cells during navigation, are replayed in a compressed neural sequence during ripples, helping to consolidate related memories. Ripples are impaired in a multitude of epilepsies, likely contributing to memory and cognitive deficits in patients. While healthy and pathological ripple dynamics are well studied in temporal lobe epilepsy and more recently in a global SCN1A haploinsufficiency model, there is a gap in knowledge regarding the impact on ripples of SCN8A encephalopathies. It is therefore important to investigate the effects of SCN8A encephalopathy on ripples and other hippocampal circuit output. Our central hypothesis is that both ripples (Aim 1) and hippocampal place cell firing (Aim 2) are progressively impaired during the development of SCN8A encephalopathy. The rationale for this hypothesis comes from our published observations that patient mutations cause elevated activity of Nav1.6 channels due to premature activation or impaired inactivation, resulting in hyperactivity of cultured hippocampal pyramidal cells. The completion of these Aims will result in the collection of massive datasets that will be shared with the epilepsy community, allowing for community-wide dissection of seizure and interictal dynamics, seizure- onset and SUDEP prediction algorithms, as well as changes in sleep-wake rhythms over time. The observed changes in hippocampal circuit dynamics will generate further hypotheses that can be dissected using cell type- and region-specific CRE transgenes in a follow-up R01 application.