Breathing disorders in a mouse model of Rett syndrome

描述（由申请人提供）：Rett综合征（RS）是一种由编码甲基-CpG结合蛋白2（MeCP 2）的X连锁基因破坏引起的神经发育疾病。RS患者除了自闭症症状外，还表现出呼吸不稳定，如呼吸过度、呼吸暂停、呼吸暂停、Valsalva呼吸、屏气、空气吞咽等，在Mecp 2-/Y小鼠中重现。呼吸紊乱是导致不明原因猝死和脑发育异常的重要原因之一。脑源性神经营养因子（BDNF）、神经递质系统、神经元活动异常和呼吸神经元网络重塑均参与呼吸系统疾病的发生。我们最近发现的呼吸障碍的另一个潜在的重要机制是中枢CO2化学敏感性（CCS）的缺陷。我们的初步研究表明，Mecp 2-/Y小鼠失去了对中度高碳酸血症的敏感性，而它们对重度高碳酸血症的敏感性似乎正常，这似乎至少部分是由于pH敏感性离子通道的表达缺陷。结果，只有当高碳酸血症变得严重时，才在小鼠中检测到CO2，并且累积的CO2导致过度通气。在从体内排出过量的CO2后，恢复了换气不足。因此，对中度PCO 2的不良反应可导致周期性换气过度和换气不足。然而，异常CO2敏感性的细胞和分子机制仍不清楚。最近的研究表明，生理和病理生理PCO 2光谱检测不同的pH敏感的离子通道在野生型（WT）哺乳动物。CCS可以被破坏时，传感分子之一，通常覆盖PCO 2光谱的一部分，是有缺陷的，没有足够的补偿，由其他传感分子，导致零星的CO2化学感受和不稳定的呼吸活动，我们认为发生在RS。因此，我们设计了实验来测试这一假设，这是创新的呼吸障碍的RS的理解，并没有被测试过。研究的中心主题是MeCP 2缺乏导致脑干中pH敏感性离子通道的异常表达，导致脑干神经元的CO2化学敏感性缺陷和呼吸不稳定。我们的具体目标是解决以下问题：1）Mecp 2基因敲除如何影响全身CO2敏感性和呼吸节律？2)Mecp 2-/Y小鼠CO2敏感性受损是由于中枢CO2化学感受、外周CO2化学感受还是两者共同作用？3)Mecp 2-/Y小鼠蓝斑（LC）神经元CCS缺陷的离子基础是什么？涉及哪些离子通道？4)Mecp 2-/Y小鼠pH敏感性离子通道缺陷的机制是什么？所产生的信息应对RS呼吸障碍的病因学、呼吸障碍治疗干预的分子靶点识别以及pH敏感离子通道介导的CCS的脑干机制产生影响。

DESCRIPTION (provided by applicant): Rett Syndrome (RS) is a neurodevelopmental disease caused by the disruption of the X- linked gene encoding methyl-CpG-binding protein 2 (MeCP2). People with RS show breathing instability in addition to autistic symptoms, such as hyperpnea, apnea, apneusis, Valsalva breathing, breath-holding, air swallowing, etc., which are recapitulated in the Mecp2-/Y mice. The breathing disturbances play a role in the high incidence rate of sudden unexplained death and the abnormal brain development. The involvement of brain-derived neurotrophic factor (BDNF), neurotransmitter systems, abnormal neuronal activity and remodeling of respiratory neuronal networks have been suggested. Another potentially important mechanism for the breathing disorders that we have recently found is the defect in central CO2 chemosensitivity (CCS). Our preliminary studies indicated that the Mecp2-/Y mice lost their sensitivity to moderate hypercapnia, while their sensitivity to severe hypercapnia appeared normal, which seems to be due, at least in part, to the defective expression of pH-sensitive ion channels. As a result, CO2 was detected in the mice only when hypercapnia became severe, and the accumulated CO2 caused hyperventilation. After the excessive CO2 was removed from the body, hypoventilation was resumed. The defective response to moderate PCO2 thus can lead to periodical hyper- and hypoventilation. However, the cellular and molecular mechanisms underlying the abnormal CO2 sensitivity are still unclear. Recent studies suggest that the physiologic and pathophysiologic PCO2 spectrum is detected by different pH-sensitive ion channels in wild-type (WT) mammals. The CCS can be disrupted when one of the sensing molecules, that normally covers a part of the PCO2 spectrum, is defective without adequate compensation by other sensing molecules, resulting in sporadic CO2 chemoreception and instable breathing activity, which we believe occurs in RS. We have therefore designed experiments to test this hypothesis that is innovative in the understanding of the breathing disorders in RS and has not been tested before. The central theme of the studies is that the MeCP2 deficiency causes abnormal expression of the pH-sensitive ion channels in the brainstem, leading to defective CO2 chemosensitivity of brainstem neurons and breathing instability. Our specific aims are to address the following questions: 1) How does the Mecp2 knockout affect systemic CO2 sensitivity and breathing rhythmicity? 2) Does the impaired CO2 sensitivity of Mecp2-/Y mice attribute to the central CO2 chemoreception, the peripheral CO2 chemoreception or both? 3) What ionic basis is responsible for the CCS defects in locus coeruleus (LC) neurons of Mecp2-/Y mice, and what ion channels are involved? 4) What mechanisms underlie the defects of the pH-sensitive ion channels in Mecp2-/Y mice? The information to be generated should have impacts on the etiology of the breathing disturbances in RS, the identification of molecular target(s) for therapeutic intervention to the breathing disturbances and the brainstem mechanisms for the CCS mediated by the pH-sensitive ion channels.