Pathophysiology of Conduction Block in HNPP.

HNPP 传导阻滞的病理生理学。

• 批准号: 8043536
• 负责人: JUN LI
• 金额: $ 34.3万
• 依托单位: VANDERBILT UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-03-15 至 2015-02-28
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8043536
• 关键词: 17p11.2; Action Potentials; Animal Model; Axon; Chromosome Deletion; Chromosomes; Chronic Inflammatory Demyelinating Polyneuropathy; Confocal Microscopy; Crossbreeding; Deformity; Demyelinating Diseases; Development; Excision; Extravasation; Failure; Family; Functional disorder; Genes; Grant; Guillain-Barré Syndrome; Inherited; Knock-out; Knockout Mice; Laboratories; Mechanics; Molecular; Monomeric GTP-Binding Proteins; Multiple Sclerosis; Mus; Myelin; Myelin Associated Glycoprotein; Myelin P0 Protein; Myelin Proteins; Nerve; Nerve Fibers; Nerve compression syndrome; Neurologic; Paralysed; Pathogenesis; Pathology; Patients; Peripheral Nerves; Peripheral Nervous System; Phenotype; Physiological; Predisposing Factor; Predisposition; Principal Investigator; Protein-Serine-Threonine Kinases; Recovery; Safety; Sensory; Shunt Device; Signal Pathway; Signal Transduction; Techniques; Testing; Therapeutic; Translating; United States National Institutes of Health; Wild Type Mouse; axonal degeneration; base; constriction; disability; hereditary neuropathy; inhibitor/antagonist; insight; member; nervous system disorder; novel; p21 activated kinase; pressure; public health relevance

DESCRIPTION (provided by applicant): Conduction block (CB), a failure of action potential propagation along the nerve, causes neurological disabilities in a number of demyelinating diseases of the central and peripheral nervous systems, including Guillain-Barre syndrome, chronic inflammatory demyelinating polyneuropathy, and multiple sclerosis. The molecular basis for CB, however, is not well understood. Interestingly, patients with hereditary neuropathy with liability to pressure palsies (HNPP), an inherited condition with a deletion of one copy of chromosome 17p11.2 containing the PMP22 gene, are abnormally sensitive to mechanical force on the peripheral nerve, and develop reversible focal weakness and sensory loss which are probably due to CB. In the past 4 years, through the support of an NIH K08 grant, the PI's laboratory has studied CB using an authentic animal model of HNPP, the pmp22 heterozygous knockout mouse (pmp22). We found that CB can be mechanically induced more rapidly in the pmp22 mice than that in wild-type mice. We have identified frequent focal axonal constrictions encased by paranodal tomacula (excessive myelin folding), a pathological hallmark of HNPP. We hypothesize that the tomacula/axonal constrictions predispose the PMP22 deficient nerves to develop mechanically induced CB. Moreover, we have shown that removal of the p21-activated kinase type-1 (pak1) gene in PMP22 deficient mice eliminates tomacula/axonal constrictions, a novel signaling mechanism. In this proposal we will further investigate the cellular and molecular basis for the development and recovery of CB, the formation of tomacula/axonal constrictions, and the therapeutic potential of PAK inhibitors. Toward these ends, we propose the following specific aims: Aim 1: Test the hypothesis that tomacula/axonal constrictions predispose nerves to mechanically induced CB in PMP22 deficiency. Our preliminary results have shown a hastened mechanically-induced CB and axonal constrictions in tomacula in pmp22 mice. In this aim, we will first determine the relationship between the predisposition of CB and tomacula/axonal constrictions using an additional animal model with tomacula/axonal constrictions and an animal model without these pathologies. We will next investigate potential mechanisms for this predisposition; these include (1) electrophysiological effects caused by axonal deformities in tomacula and (2) possible current leakage out of tomaculous myelin that shunts the depolarizing current to reduce the safety factor for action potential propagation. These mechanisms will be investigated using confocal microscopy and 3-dimentional EM to delineate detail geometric features of axonal deformities in tomacula. Physiological consequences of these tomacula/axon deformities will be evaluated by threshold tracking technique. These results will provide insights into the mechanisms underlying the propensity to mechanically-induce CB in PMP22 deficiency. Aim 2: Test the hypothesis that PAK1 is required for the formation of tomaculum/axonal constriction. PAK1, as a serine-threonine kinase and a member of the PAK family (from PAK1 to 6), interacts with small GTPases for its activation, such as cdc42 and rac. Deficiency of PAK1 in the pak1-/- mice causes no phenotype. After crossbreeding pak1-/- with pmp22 mice, however, double-knockout of both genes eliminates tomacula/axonal constrictions in pmp22 mice. In this aim, we will test whether removal of tomacula will reverse the susceptibility to mechanically-induced CB in PMP22 deficient mice, and further explore this novel signaling pathway. We will attempt to translate this exciting finding to therapy by testing whether newly synthesized PAK inhibitor can reverse tomacula/axonal constrictions in PMP22 deficiency. Aim 3: Identify the mechanisms by which haploinsufficiency of pmp22 delays the recovery of CB. Our experimental results have shown a delayed recovery of mechanically-induced CB in the pmp22 mice. In this aim, cellular and molecular mechanisms that underlie the delayed recovery of CB will be investigated in pmp22 mice. Taken together, these three aims will define cellular and molecular factors that predispose pmp22 nerves to mechanically induced CB, and establish molecular signaling pathway for the formation of tomaculum/axonal constriction in the PMP22 deficiency. Results are expected to deepen our understanding on the molecular basis of CB, which may render insights into the pathogenesis for many demyelinating diseases. PUBLIC HEALTH RELEVANCE: Conduction block (CB), a failure of propagation of electrical signal along nerve fibers, causes disabilities in a variety of neurological disorders. Patients with hereditary neuropathy with liability to pressure palsies present with frequent focal weakness and sensory loss, which are likely caused by CB. Our study investigates molecular mechanisms responsible for the CB using HNPP and its animal model.

描述（由申请人提供）：传导阻滞（CB），沿神经沿神经的动作电位传播失败，导致中枢和周围神经系统的多种脱髓鞘疾病中的神经障碍，包括吉列兰 - 巴雷综合征，慢性炎性炎性炎症性脱氧化的多余的神经疗法以及多发性硬化。然而，CB的分子基础尚不清楚。有趣的是，遗传性神经病患者对压力麻痹的责任（HNPP）是一种遗传状况，该疾病的遗传疾病删除了一份含有PMP22基因的染色体17p11.2副本，对外周神经对机械力异常敏感，并且可能会导致可反抗的局灶性弱点和感官损失和感官损失。在过去的四年中，通过NIH K08赠款的支持，PI的实验室使用了HNPP的真实动物模型，PMP22杂合敲除小鼠（PMP22）研究了CB。我们发现，与野生型小鼠相比，PMP22小鼠的CB可以机械诱导的速度更快。我们已经确定了由旁丙诺拉曲霉（HNPP）的病理标志（过度髓磷脂折叠）所包围的频繁焦距轴突收缩。我们假设曲曲霉/轴突收缩易感PMP22缺乏神经，以发展机械诱导的Cb。此外，我们已经表明，在PMP22缺乏小鼠中，去除P21激活的激酶类型1（PAK1）基因可消除一种新型的信号传导机制，消除了Tomacula/axonal限制。在此提案中，我们将进一步研究CB发育和恢复，曲折/轴突收缩的形成和恢复的细胞和分子基础以及PAK抑制剂的治疗潜力。在这些目的方面，我们提出了以下特定目的：目标1：测试假设的假设，即tomacula/轴突收缩易感神经对PMP22缺乏症的机械诱导的CB。我们的初步结果表明，在PMP22小鼠中，在Tomacula中迅速诱发了机械诱导的CB和轴突收缩。在此目标中，我们将首先确定使用带有Tomacula/轴突限制的其他动物模型，而没有这些病理的动物模型，CB和Tomacula/Axonal限制的易感性之间的关系。我们接下来将研究这种易感性的潜在机制。其中包括（1）由tomacula中的轴突畸形引起的电生理效应，以及（2）可能会泄漏出干性髓磷脂的电流泄漏，从而使去极化电流分流，从而降低了动作电位传播的安全系数。这些机制将使用共聚焦显微镜和三维EM进行研究，以描绘tomacula轴突畸形的细节几何特征。这些tomacula/轴突畸形的生理后果将通过阈值跟踪技术评估。这些结果将提供有关在PMP22缺乏症中机械诱导CB倾向的基础机制的见解。 AIM 2：检验假设，即形成tomaculum/轴突收缩需要PAK1。 Pak1作为丝氨酸 - 硫代激酶和PAK家族的成员（从PAK1到6），与小的GTPases相互作用以激活其激活，例如CDC42和RAC。 PAK1中PAK1的缺乏不会引起表型。然而，在与PMP22小鼠杂交PAK1 - / - 之后，这两个基因的双重敲除消除了PMP22小鼠中的tomacula/轴突收缩。在此目标中，我们将测试tomacula的去除是否会扭转对PMP22缺乏小鼠机械诱导的CB的敏感性，并进一步探索这种新型的信号传导途径。我们将尝试通过测试新合成的PAK抑制剂是否可以逆转PMP22缺乏症中的Tomacula/轴突收缩来将这一令人兴奋的发现转化为治疗。 AIM 3：确定PMP22单倍不足的机制延迟了CB的恢复。我们的实验结果表明，在PMP22小鼠中机械诱导的CB恢复延迟。在此目标中，将在PMP22小鼠中研究CB延迟恢复的基础的细胞和分子机制。 综上所述，这三个目标将定义细胞和分子因子，使PMP22神经易于机械诱导CB，并为在PMP22缺乏症中形成tomaculum/轴突收缩的分子信号传导途径。预计结果将加深我们对CB分子基础的理解，这可能会使许多脱髓鞘疾病对发病机理有所了解。 公共卫生相关性： 传导阻滞（CB）是沿神经纤维传播的传播失败，导致多种神经系统疾病的残疾。遗传性神经病患者对存在频繁的局灶性无力和感觉丧失的压力麻痹责任，这可能是由CB引起的。我们的研究研究了使用HNPP及其动物模型来调查负责CB的分子机制。