Role of KCNQ2 Channels in Control of Breathing

总结 与KCNQ 2通道相关的发育性和癫痫性脑病主要与以下因素有关： KCNQ 2基因突变。然而，越来越多的复发性KCNQ 2功能获得性 变体（即，R201 C）的特性。KCNQ 2 R201 C突变患者表现出严重的肌阵挛 以及由于化学反射减少而导致的早期严重换气不足。目前，KCNQ 2 控制呼吸动力的通道尚不清楚。斜方后核（RTN）是重要的呼吸核， 该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CO2的变化。化学敏感的RTN神经元被CO2/H+的增加激活，而CO2/H+的增加激活RTN神经元。 功能缺失型Kcnq 2突变可能使RTN神经元过度增殖，使其对CO2/H+的反应更加困难。 事实上，来自父母资助的工作表明，RTN中复发性Kcnq 2突变Kcnq 2 R201 C的表达 神经元对CO2的反应减弱。令人兴奋的是，我们还发现RTN中的Kcnq 2通道活性 神经元由H+-肌醇协同转运蛋白（HMIT）调节，HMIT输入肌醇以支持 产生磷脂酰肌醇4，5-二磷酸（PIP 2），一种Kcnq 2通道的变构激活剂。HMIT RTN区域的表达仅限于化学敏感的神经元。因此，我们假设， HMIT是RTN神经元中Kcnq 2通道活动所需的。特别是，我们提出H+依赖的肌细胞， 通过HMIT将肌醇转运到RTN神经元中将增加PIP 2水平并激活Kcnq 2通道以限制 CO2/H+刺激的活动，以及通过神经递质维持神经调制， Gq偶联受体和PIP 2水解。因此，本申请的目的是确定 在正常条件下，哪些Kcnq 2通道和HMIT相互作用以控制RTN化学感受，以及是否 HMIT可以靶向改善表达Kcnq 2 R201 C的小鼠的呼吸。这三个具体目标 项目是：1）确定HMIT影响Kcnq 2通道调节化学敏感性的程度， RTN神经元; 2）确定Kcnq 2通道和HMIT相互作用对RTN化学受体的贡献 网络兴奋性; 3）在RTN神经元中建立HMIT作为Kcnq 2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Kcnq 2， RTN神经元中的通道活动，我们可以为开发呼吸问题的治疗方法奠定基础 与Kcnq 2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.