Pathophysiology of Conduction Block in HNPP.

HNPP 传导阻滞的病理生理学。

基本信息

批准号：
8608012
负责人：
JUN LI
金额：
$ 34.09万
依托单位：
VANDERBILT UNIVERSITY
依托单位国家：
美国
项目类别：
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/8608012
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 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

项目摘要

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.

描述（由申请人提供）：传导阻滞（CB），即动作电位沿神经传播的失败，导致中枢和周围神经系统的许多脱髓鞘疾病的神经功能障碍，包括格林-巴利综合征、慢性炎症性脱髓鞘性多发性神经病和多发性硬化症。然而，CB 的分子基础尚不清楚。有趣的是，患有压力性麻痹的遗传性神经病 (HNPP) 的患者对外周神经的机械力异常敏感，并出现可逆性局灶性无力，HNPP 是一种遗传性疾病，含有 PMP22 基因的 17p11.2 染色体的一个拷贝被缺失。和感觉丧失，这可能是由于 CB 造成的。在过去的 4 年里，通过 NIH K08 拨款的支持，PI 的实验室使用 HNPP 的真实动物模型，即 pmp22 杂合基因敲除小鼠 (pmp22) 研究了 CB。我们发现 pmp22 小鼠中的 CB 机械诱导速度比野生型小鼠更快。我们发现了频繁出现的局灶性轴突收缩，其被结节旁黄斑（髓磷脂过度折叠）包裹，这是 HNPP 的病理标志。我们假设黄斑/轴突收缩使 PMP22 缺陷神经易于发生机械诱导的 CB。此外，我们还发现，在 PMP22 缺陷小鼠中去除 p21 激活激酶 1 型 (pak1) 基因可以消除毛斑/轴突收缩，这是一种新的信号传导机制。在本提案中，我们将进一步研究 CB 发育和恢复的细胞和分子基础、tomacula/轴突收缩的形成以及 PAK 抑制剂的治疗潜力。为此，我们提出以下具体目标：目标 1：检验以下假设：在 PMP22 缺陷中，斑膜/轴突收缩使神经易于机械诱导 CB。我们的初步结果表明，pmp22 小鼠的 tomacula 中机械诱导的 CB 和轴突收缩加速。为此，我们将首先使用具有斑斑/轴突收缩的附加动物模型和没有这些病理的动物模型来确定 CB 的易感性和斑斑/轴突收缩之间的关系。接下来我们将研究这种倾向的潜在机制；这些包括（1）由黄斑轴突畸形引起的电生理效应，以及（2）黄斑髓磷脂可能存在电流泄漏，分流去极化电流以降低动作电位传播的安全系数。这些机制将使用共焦显微镜和三维电镜进行研究，以描绘黄斑轴突畸形的详细几何特征。这些斑斑/轴突畸形的生理后果将通过阈值跟踪技术进行评估。这些结果将深入了解 PMP22 缺乏症中机械诱导 CB 倾向的潜在机制。目标 2：检验 PAK1 是形成小斑/轴突收缩所必需的假设。 PAK1 作为丝氨酸-苏氨酸激酶和 PAK 家族（从 PAK1 到 6）的成员，与小 GTP 酶（例如 cdc42 和 rac）相互作用以实现其激活。 pak1-/- 小鼠中 PAK1 缺陷不会导致任何表型。然而，在 pak1-/- 与 pmp22 小鼠杂交后，这两个基因的双敲除消除了 pmp22 小鼠中的 tomacula/axonal 收缩。为此，我们将测试去除毛斑是否会逆转 PMP22 缺陷小鼠对机械诱导的 CB 的易感性，并进一步探索这一新的信号通路。我们将尝试通过测试新合成的 PAK 抑制剂是否可以逆转 PMP22 缺陷中的黄斑/轴突收缩，将这一令人兴奋的发现转化为治疗。目标 3：确定 pmp22 单倍体不足延迟 CB 恢复的机制。我们的实验结果表明，pmp22 小鼠中机械诱导的 CB 恢复延迟。为此，我们将在 pmp22 小鼠中研究 CB 延迟恢复的细胞和分子机制。总而言之，这三个目标将定义使 pmp22 神经易受机械诱导的 CB 影响的细胞和分子因素，并建立 PMP22 缺陷中形成小斑/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，这可能有助于深入了解许多脱髓鞘疾病的发病机制。