Complex genetic interactions in mouse model of sudden death in epilepsy (SUDEP)

描述(由申请人提供)：这项工作的总体目标是在癫痫猝死(SUDEP)的背景下检查KcNA1和SCN2A离子通道基因突变之间的双基因相互作用。癫痫患者因不明原因突然死亡的可能性是普通人群的24倍；这些死亡被归类为SUDEP，是癫痫相关死亡的主要原因。据传闻，有几个基因与SUDEP有关，但其遗传病因在很大程度上尚不清楚，可能涉及多个易感基因变异的共同遗传。这项建议调查了亚临床SCN2A零杂合子在SUDEP KcNA1基因敲除小鼠模型中作为癫痫和过早死亡的保护性遗传修饰物的能力。SCN2A是一种人类癫痫基因，编码Nav1.2电压门控钠通道Alpha亚基，但这里使用的敲除突变尚未发现会导致癫痫。Kcna1也是人类癫痫基因，编码Kv1.1电压门控钾通道Alpha-亚基，通常作用于抑制神经元的兴奋性。KcNA1基因敲除小鼠通过表现出严重的癫痫、脑驱动的心功能障碍和过早死亡来准确地模拟人类SUDEP。鉴于这两个基因的表达重叠和相互对立的兴奋性效应，拟议的研究测试了以下假设：亚临床SCN2A零杂合性通过抑制与Kv1.1通道缺失相关的神经心脏功能障碍和神经元过度兴奋来降低KcNA1基因缺失小鼠的SUDEP发生率。初步数据显示，SCN2A零杂合性阻止了KcNA1基因敲除中的SUDEP，使他们的存活率提高了三倍。在目标1中，使用视频脑电-心电图仪(EEG-ECG)来确定SCN2A缺失杂合子是否减少KcNA1缺失小鼠的癫痫样放电和/或心脏异常。目的2通过分析c-Fos等与神经元异常激活相关的分子生物标志物的表达变化，寻找SCN2A和KcNA1之间功能相互作用的神经元网络。这项研究利用一种新的双基因小鼠模型作为了解SUDEP背后复杂的遗传相互作用的重要第一步，最终目标是改进基于基因的癫痫风险预测、预防和治疗。SCN2A零杂合子抑制Kcna1 SUDEP表型的能力将证明一项原则证明，即使是没有明显表型的亚临床基因变异也必须在评估癫痫患者的遗传风险谱时考虑，因为这些等位基因也可以是疾病易感性的关键修饰因素。此外，在这个双基因模型中对分子生物标记物内表型的检查有可能识别以前未被识别的脑网络，这些网络对于SUDEP病理生理学和未来研究的候选治疗靶点是重要的。

DESCRIPTION (provided by applicant): The overall goal of this work is to examine digenic interactions between mutations in the Kcna1 and Scn2a ion channel genes in the context of sudden unexpected death in epilepsy (SUDEP). People with epilepsy are 24 times more likely than the general population to die suddenly for unknown pathological reasons; these deaths are classified as SUDEP and represent the leading cause of epilepsy-related mortality. Several genes have been linked anecdotally to SUDEP, but its genetic etiology is largely unknown and likely complex involving the co-inheritance of multiple susceptibility gene variants. This proposal investigates the ability of subclinical Scn2a-null heterozygosity to act as a protective genetic modifier of epilepsy and premature death in the Kcna1 knockout mouse model of SUDEP. Scn2a, a human epilepsy gene, encodes Nav1.2 voltage-gated sodium channel Alpha-subunits but the knockout mutation utilized here has not been found to cause epilepsy. Kcna1, also a human epilepsy gene, encodes Kv1.1 voltage-gated potassium channel Alpha-subunits that normally act to dampen neuronal excitability. Kcna1 knockout mice accurately model human SUDEP by exhibiting severe epilepsy, brain-driven cardiac dysfunction, and premature death. Given the expression overlap and mutually opposing excitability effects of the two genes, the proposed research tests the hypothesis that subclinical Scn2a-null heterozygosity reduces SUDEP incidence in Kcna1-null mice by suppressing neurocardiac dysfunction and neuronal hyperexcitability associated with the absence of Kv1.1 channels. Preliminary data shows that Scn2a-null heterozygosity prevents SUDEP in Kcna1 knockouts increasing their survival threefold. In Aim 1, video electroencephalography-electrocardiography (EEG-ECG) is used to determine whether Scn2a-null heterozygosity reduces epileptiform discharges and/or cardiac abnormalities in Kcna1-null mice. Aim 2 seeks to identify neuronal networks exhibiting functional interaction between Scn2a and Kcna1 by analyzing changes in expression of molecular biomarkers associated with abnormal neuronal activation, such as c-Fos. This research utilizes a novel digenic mouse model as an important first step towards understanding the complex genetic interactions underlying SUDEP with the ultimate goal of improving genotype-based risk prediction, prevention, and therapy in epilepsy. The ability of Scn2a-null heterozygosity to suppress the Kcna1 SUDEP phenotype would demonstrate a proof-of-principle that even subclinical gene variants without obvious phenotypes must be considered when evaluating the genetic risk profiles of epilepsy patients since those alleles can also be critical modifiers of disease susceptibility. Furthermore, the examination of molecular biomarker endophenotypes in this digenic model has the potential to identify previously unrecognized brain networks that are important for SUDEP pathophysiology and candidate therapeutic targets for future studies.