VGSC Modulation by FHFs: Neural Functions and Mechanisms

描述（由申请人提供）：电压门控钠通道（VGSCs）在可兴奋细胞中产生和传播电活动。VGSC在闭合、打开和失活状态之间转换的精确动力学对脑、神经、心脏和肌肉功能至关重要，这已被广泛的临床钠通道病变所证实。虽然分离的VGSC α亚基包括通道孔、电压传感器和失活机制，但与成纤维细胞生长因子同源因子（FHFs）的相互作用对VGSC失活的动力学具有巨大而复杂的影响。事实上，FHF突变是人类脊髓小脑性共济失调的一个原因，并导致神经元内在兴奋性缺陷。虽然所有FHF亚型都与VGSC结合，但它们调节VGSC快速失活和诱导新特征的长期失活通道状态的能力不同。本应用程序提出了实验来扩展对FHF神经元功能和FHF诱导VGSC调制的物理机制的分析。AIM 1：我们的总体生物学假设是，FHF亚型在不同神经元及其亚细胞区室中的差异表达决定了细胞的兴奋和传导特性。我们将测试：（I-A）轴突初始段不同长型FHFs （a型FHFs， FHF4B）的相对丰度是否指定神经元的兴奋特性？（I-B） a型FHFs的体树突膜定位是否限制了神经元重复放电时钠动作电位的反向传播？（I-C）动作电位轴突传导不需要长形式FHFs，并且对其可能有害吗？目的II：更清楚地了解fhf调节VGSC的物理机制将进一步深入了解VGSC构象动力学，并为设计治疗高兴奋性疾病（如癫痫和心律失常）的合理方法提供建议。我们将测试：（II-A） a型FHFs远端n端的长期失活颗粒是否停靠在VGSC的细胞质腔内？（II-B）对接的a型FHF失活颗粒中的阳离子残基是否对钠离子传导起到屏蔽作用？（II-C）阳离子区如何靠近？FHFs -三叶核心调节VGSC快速失活？

DESCRIPTION (provided by applicant): Voltage-gated sodium channels (VGSCs) generate and propagate electrical activity in excitable cells. The precise dynamics of VGSC transitions among closed, open, and inactivated states are essential for brain, nerve, heart, and muscle function, as documented by a wide range of clinical sodium channelopathy disorders. While the VGSC alpha subunit in isolation comprises the channel's pore, its voltage sensors, and its inactivation machinery, interaction with fibroblast growth factor homologous factors (FHFs) has large and complex effects on the dynamics of VGSC inactivation. Indeed, FHF mutations are a cause of human spinocerebellar ataxia and cause defects in neuronal intrinsic excitability. While all FHF isoforms bind VGSCs, they differ in their abilities to modulate VGSC fast inactivation and to induce a newly characterized long-term inactivated channel state. This application proposes experiments to expand analysis of FHF neuronal functions and physical mechanisms of FHF- induced VGSC modulation. AIM I: Our overall biological hypothesis is that differential expression of FHF isoforms in different neurons and their subcellular compartments acts to determine excitation and conduction properties of cells. We will test: (I-A) Does the relative abundance of different long-form FHFs (A-type FHFs, FHF4B) at the axon initial segment specify the excitation properties of a neuron? (I-B) Does somatodendritic membrane localization of A-type FHFs act to limit sodium action potential backpropagation during repetitive firing of neurons? (I-C) Are long-form FHFs not required for, and potentially deleterious to, action potential axonal conduction? AIM II: A clearer understanding of physical mechanisms for VGSC modulation by FHFs will provide further insight into VGSC conformation dynamics and suggest rational approaches for designing therapeutics for managing disorders of hyperexcitability, such as epilepsies and arrhythmias. We will test: (II-A) Does the long- term inactivation particle at the distal N-terminus of A-type FHFs dock within the cytoplasmic cavern of a VGSC? (II-B) Do the cationic residues in the docked A-type FHF inactivation particle act as a shield against sodium ion conduction? (II-C) How does a cationic region near the ?-trefoil core of FHFs modulate VGSC fast inactivation?