FHF2A and FHF2B in sensory neurons: potential regulators of resurgent currents

 描述(由申请者提供)：疼痛是美国人寻求医疗服务的最普遍原因之一。虽然众所周知，背根神经节(DRG)感觉神经元的超兴奋性可导致神经病理性和炎症性疼痛，但这种超兴奋性背后的细胞和分子变化尚不完全清楚。这种知识的缺乏阻碍了更好的疗法的发展。一个明显导致疼痛的机制是含有外周感觉神经元的背根节中电活动的增加。电压门控钠通道(VGSC)有助于感觉神经元的兴奋性，因为它们是动作电位上冲所必需的。一种独特的VGSC电流类型，即复活电流，通过另一种称为开放通道阻挡的失活机制，在再极化电压下产生内向电流。复苏性电流被认为与DRG感觉神经元的自发放电、超兴奋性和痛觉的启动有关。感觉神经元复苏电流的增加与阵发性极端疼痛障碍(PEPD)、海葵毒素ATX-II诱导的疼痛以及奥沙利铂急性降温加重痛性神经病变有关。不幸的是，我们对复活电流背后的分子机制的了解很差，特别是在DRG神经元中。我们认为，结合VGSC C末端的成纤维细胞生长因子同源因子(FHF)2可以实质上调节感觉神经元的复苏性电流。具体地说，我们假设FHF2A通过介导长期失活来限制感觉神经元的复活电流产生，而FHF2B通过调节失活的电压依赖性来增强复活电流的产生。因此，在这项NRSA奖学金中，申请者将：1)下调FHF2A蛋白的表达，并使用针对FHF2A N端的抗体来确定对复苏电流产生的功能影响；2)过度表达FHF2A以确定增加FHF2A活性是否会减少复苏电流；以及3)下调FHF2B蛋白表达并过度表达FHF2B以确定调制这种变体是否会增强复苏电流。我们还将测量测试复苏电流的DRG神经元中FHF2A和FHF2B的内源性水平，以评估表达谱和复苏电流特性之间的相关性。这项提议的结果应该有助于我们找到新的方法来研究与复苏电流增加相关的超兴奋性，并有助于开发治疗疼痛疾病的方法，如PEPD、急性奥沙利铂诱导的痛性神经病以及可能的炎症性疼痛。

 DESCRIPTION (provided by applicant): Pain is one of the most prevalent reasons people in the US seek medical care. Although it is well known that hyperexcitability of dorsal root ganglion (DRG) sensory neurons can contribute to neuropathic and inflammatory pain, the cellular and molecular changes that underlie this hyperexcitability are not fully understood. This lack of knowledge has hindered the development of better therapeutics. One mechanism that clearly contributes to pain is increased electrical activity in DRG containing peripheral sensory neurons. Voltage gated sodium channels (VGSC) contribute to the excitability of sensory neurons, as they are essential for the upstroke of the action potential. A unique type of VGSC current, resurgent current, generates an inward current at repolarizing voltages through an alternate mechanism of inactivation termed open channel block. Resurgent currents are thought to contribute to spontaneous firing, hyperexcitability and the initiation of pain sensations in DRG sensory neurons. Increased resurgent currents in sensory neurons have been implicated in Paroxysmal Extreme Pain Disorder (PEPD), sea-anemone toxin ATX-II induced pain, and oxaliplatin acute- cooling aggravated painful neuropathy. Unfortunately, our understanding of the molecular mechanisms that underlie resurgent currents, especially in DRG neurons, is poor. We propose that Fibroblast Growth Factor Homologous Factors (FHF) 2 that bind the C-terminus of VGSC can substantially modulate resurgent currents in sensory neurons. Specifically, we hypothesize that FHF2A limits resurgent current generation in sensory neurons by mediating long-term inactivation and that FHF2B enhances resurgent currents generation by modulating the voltage dependence of inactivation. Therefore in this NRSA fellowship the applicant will: 1) knockdown FHF2A protein expression and use an antibody targeted to the N-terminus of FHF2A to determine the functional effect on resurgent current generation, 2) overexpress FHF2A to determine if increasing FHF2A activity reduces resurgent currents and 3) knockdown FHF2B protein expression and overexpress FHF2B to determine if modulation this variant enhances resurgent currents. We will also measure endogenous levels of FHF2A and FHF2B in DRG neurons tested for resurgent current to assess correlations between expression profiles and resurgent current properties. The results of this proposal should help us identify novel approaches for the study of hyperexcitability associated with increased resurgent currents, and aid the development of treatments for painful conditions such as PEPD, acute oxaliplatin-induced painful neuropathy and possibly inflammatory pain.