Voltage-gated sodium channel β1 subunit processing: downstream roles in regulating cardiac excitability

电压门控钠通道×1亚基处理：调节心脏兴奋性的下游作用

• 批准号: 9770543
• 负责人: Alexandra Ann Bouza
• 金额: $ 2.82万
• 依托单位: UNIVERSITY OF MICHIGAN AT ANN ARBOR
• 依托单位国家: 美国
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2020-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9770543
• 关键词: Acute; Amyloid beta-Protein Precursor; Arrhythmia; Ataxia; Behavioral; Binding Sites; Biochemical; Biological Markers; Brain; Brugada syndrome; Calcium; Cardiac; Cell Adhesion Molecules; Cell Fractionation; Cell Nucleus; Cells; ChIP-seq; Childhood; Cleaved cell; Comorbidity; Confocal Microscopy; DNA Binding; Data; Development; Developmental Delay Disorders; Electrocardiogram; Enzymes; Fractionation; Future; Genes; Genetic Transcription; Heart; Incidence; Intellectual functioning disability; Intercalated disc; Ion Channel; Kinetics; Knockout Mice; Lead; Life; Link; Mediating; Membrane Proteins; Methods; Mus; Muscle Cells; Mutation; Neurons; Nuclear; Patients; Phosphorylation; Physiological; Play; Positioning Attribute; Potassium; Resistance; Risk; Role; Seizures; Signal Transduction; Site; Sodium; Sodium Channel; Testing; Tetrodotoxin; Transcriptional Regulation; Ventricular; Ventricular Function; Western Blotting; Work; beta-site APP cleaving enzyme 1; biomarker identification; chromatin immunoprecipitation; dravet syndrome; epileptic encephalopathies; gamma secretase; high risk; immunocytochemistry; indium arsenide; insight; loss of function mutation; mouse model; mutant; new therapeutic target; novel therapeutics; prevent; sudden cardiac death; sudden unexpected death in epilepsy; voltage

Dravet syndrome (DS) is a severe, pediatric epileptic encephalopathy (EE) that typically presents in the first year of life. In addition to seizures, patients suffer from behavioral and developmental delay, ataxia, intellectual disability, and an increased risk (~18%) of Sudden Unexpected Death in EPilepsy (SUDEP). The mechanism of SUDEP is not clear and there are no biomarkers currently known to identify at risk patients. We study DS because of its high incidence of SUDEP to better understand SUDEP mechanisms. In most cases (>80%) DS is linked to mutations in genes which encode voltage-gated sodium channel (VGSC) subunits, SCN1A and SCN1B, which encode the Nav1.1 α subunit and the VGSC β1 subunit, respectively. SCN1A and SCN1B are expressed in both brain and heart. β1 regulates gating and kinetics of the ion channel pore, functions as a cell adhesion molecule (CAM), and initiates cell signaling. In ventricular myocytes, phosphorylated β1 localizes to intercalated disks and associates with the tetrodotoxin (TTX)- insensitive VGSC α subunit Nav1.5, while non-phosphorylated β1 localizes to t-tubules where it associates with the TTX-sensitive VGSC α subunits, Nav1.1, Nav1.3 and Nav1.6. We propose the high incidence of SUDEP in DS patients results from neuronal hyperexcitability and cardiac arrhythmia due to expression of mutant VGSC subunits in brain and heart. Scn1b null mice model DS. Scn1b null mice display prolonged QT intervals by electrocardiogram, abnormal calcium handling that is sensitive to TTX, and increased transient and persistent sodium currents in acutely isolated ventricular myocytes. Scn1b null mice show increased expression of Scn3a and Scn5a, encoding Nav1.3 and Nav1.5, respectively. β subunits are substrates for sequential cleavage by β-site APP cleaving enzyme 1 (BACE1) and γ-secretase. Sequential cleavage generates a soluble intracellular domain (ICD). We hypothesize that β1 cleavage in heart, followed by β1-ICD translocation to the nucleus, is critical for the transcriptional regulation of VGSC α subunits and potentially other genes important in regulating cardiac excitability. When β1 is not functional, as in DS, β1-mediated transcriptional regulation and β1-mediated current modulation are disrupted, resulting in changes in excitability and arrhythmias. Understanding the mechanism of β1-mediated signal transduction in heart may lead to new methods for the identification and treatment of patients at risk of SUDEP.

Dravet综合征（DS）是一种严重的儿童癫痫性脑病（EE）， 在生命的第一年。除了癫痫发作，患者还患有行为和发育障碍， 延迟、共济失调、智力残疾和意外猝死风险增加（约18%） 癫痫（Suepilepsy）SUDEP的发病机制尚不清楚，也没有生物标志物 目前已知用于识别高危患者。我们研究DS是因为它的SUDEP发生率很高 以更好地了解SUDEP机制。在大多数情况下（>80%），DS与以下突变有关： 编码电压门控钠通道（VGSC）亚单位SCN 1A和SCN 1B的基因， 分别编码Nav1.1 α亚基和VGSC β1亚基。SCN 1A和SCN 1B 在大脑和心脏中表达。β1调节离子通道孔的门控和动力学， 作为细胞粘附分子（CAM）起作用，并启动细胞信号传导。在心室肌细胞中， 磷酸化的β1定位于嵌入盘并与河豚毒素（TTX）缔合。 不敏感的VGSC α亚基Nav1.5，而非磷酸化的β1定位于t-小管， 与TTX敏感的VGSC α亚基Nav1.1、Nav1.3和Nav1.6相关。我们提出 DS患者中SUDEP的高发生率是由于神经元过度兴奋和心脏 VGSC亚基突变体在脑和心脏中的表达导致心律失常。Scn 1b基因敲除小鼠模型 DS. Scn 1b基因敲除小鼠心电图显示QT间期延长，钙异常 对TTX敏感的处理，以及增加的瞬时和持续钠电流， 急性分离的心室肌细胞。Scn 1b基因敲除小鼠显示Scn 3a表达增加， Scn 5a，分别编码Nav1.3和Nav1.5。β亚基是连续的 通过β-位点APP裂解酶1（BACE 1）和γ-分泌酶裂解。顺序裂解 产生可溶性胞内结构域（ICD）。我们假设心脏中的β1裂解， 随后β1-ICD易位到细胞核，对转录调控至关重要。 VGSC α亚基和其他可能在调节心脏兴奋性中重要的基因。当 β1无功能，如在DS、β1介导的转录调节和β1介导的电流中 调制被破坏，导致兴奋性和心律失常的变化。了解 β1介导的心脏信号转导机制可能为研究β1介导的心脏信号转导机制提供新的方法。 识别和治疗有SUDEP风险的患者。