Role of KCNQ2 Channels in Control of Breathing

摘要 与KCNQ2通道相关的发育性和癫痫性脑病主要与 功能丧失的KCNQ2突变。然而，越来越多的复发KCNQ2功能增益 已经确定了变异体(即R201C)。KCNQ2R201C突变患者表现出严重的肌阵挛 以及早期由于化学反射减弱而导致的严重换气不足。目前，KCNQ2通过哪些机制 控制呼吸动力的通道尚不清楚。梯形后核(RTN)是一种重要的呼吸系统 中枢；这一区域的神经元作为呼吸化学感受器，通过调节呼吸来响应 组织中二氧化碳的变化。化学敏感的RTN神经元被CO2/H+的增加所激活，而增益- 功能缺失的KCNQ2突变可能使RTN神经元超极化，使其对CO2/H+的反应更加困难。 事实上，父母赠款的工作表明，KCNQ2反复突变Kcnq2R201C在RTN中的表达 神经元削弱了对二氧化碳的换气反应。令人兴奋的是，我们还发现在RTN中KCNQ2通道活动 神经元受H+-肌醇共转运体(HMIT)的调节，该转运体进口肌醇以支持 生产KCNQ2通道的变构激活剂磷脂酰肌醇4，5-二磷酸(PIP2)。HMIT 在RTN区域的表达仅限于对化疗敏感的神经元。因此，我们假设 HMIT是RTN神经元KCNQ2通道活动所必需的。特别地，我们提出了H+依赖的肌电活动。 HMIT将肌醇转运到RTN神经元将增加PIP2水平并激活KCNQ2通道以限制 CO2/H+刺激的活动，以及维持神经递质的神经调节信号通过 GQ偶联受体与PIP2的水解性。因此，本申请的目标是确定 在正常情况下，哪些KCNQ2通道和HMIT相互作用来控制RTN化学接收，以及 HMIT可以靶向改善表达Kcnq2R201C的小鼠的呼吸。这一行动的三个具体目标 项目有：1)确定HMIT对化疗药物KCNQ2通道调节的影响程度 2)测定KCNQ2通道和HMIT相互作用对RTN化学受体的作用 网络兴奋性；以及3)在RTN神经元中建立HMIT作为KCNQ2相关的治疗靶点 呼吸异常。这项研究的基本原理是，通过了解HMIT如何调节KCNQ2 RTN神经元的通道活动，我们可以为开发呼吸疾病的治疗方法奠定基础 与KCNQ2突变相关。

SUMMARY Developmental and epileptic encephalopathy associated with KCNQ2 channels has been primarily linked to loss-of-function KCNQ2 mutations. However, an increasing number of recurrent KCNQ2 gain-of-function variants (i.e., R201C) have been identified. Patients with the KCNQ2R201C mutation display severe myoclonus and early profound hypoventilation due to reduced chemoreflex. Currently, mechanisms by which KCNQ2 channels control the drive to breathe are unclear. The retrotrapezoid nucleus (RTN) is an important respiratory center; neurons in this region function as respiratory chemoreceptors by regulating breathing in response to changes in tissue CO2. Chemosensitive RTN neurons are activated by an increase in CO2/H+, whereas a gain- of-function Kcnq2 mutation might hyperpolarize RTN neurons and make it more difficult to respond to CO2/H+. Indeed, work from the parent grant showed that expression of the recurrent Kcnq2 mutation Kcnq2R201C in RTN neurons blunted the ventilatory response to CO2. Excitingly, we also found that Kcnq2 channel activity in RTN neurons is regulated by a H+-myo-inositol cotransporter (HMIT) which imports myo-inositol to support production of phosphatidylinositol 4,5-bisphosphate (PIP2), an allosteric activator of Kcnq2 channels. HMIT expression in the RTN region is restricted only to chemosensitive neurons. Therefore, we hypothesize that HMIT is required for Kcnq2 channel activity in RTN neurons. In particular, we propose that H+-dependent myo- inositol transport into RTN neurons by HMIT will increase PIP2 levels and activate Kcnq2 channels to limit CO2/H+-stimulated activity, as well as to maintain neural modulation by neurotransmitters that signal through Gq-coupled receptors and PIP2 hydrolysis. Thus, the objective of this application is to determine the extent to which Kcnq2 channels and HMIT interact to control RTN chemoreception under normal conditions and whether HMIT can be targeted to improve breathing in mice that express Kcnq2R201C. The three Specific Aims of this project are: 1) determine the extent to which HMIT influences Kcnq2 channel regulation of chemosensitive RTN neurons; 2) determine contributions of Kcnq2 channels and HMIT interactions to RTN chemoreceptor network excitability; and 3) to establish HMIT in RTN neurons as a therapeutic target for Kcnq2 associated breathing abnormalities. The rationale for this research is that by understanding how HMIT regulates Kcnq2 channel activity in RTN neurons, we can lay a foundation for developing treatments for respiratory problems associated with Kcnq2 mutations.