Pathophysiology of Conduction Block in HNPP

描述(申请人提供)：人类PMP22基因突变导致最常见形式的遗传性周围神经疾病，包括遗传性神经病，易患 PMP22杂合缺失的压力性瘫痪(HNPP)。HNPP患者表现为局灶性感觉丧失和肌肉无力，这与传导阻滞有关。我们发现，在没有节段性脱髓鞘的情况下，PMP22缺乏会损害动作电位的传播。这种传导缺陷可能是由于髓鞘连接中断导致髓鞘通透性异常增加所致。在本研究中，我们将研究在PMP22缺乏的神经中，连接复合体是如何通过其异常维持而被破坏的。目的1：验证PMP22缺乏增加髓鞘连接肌动蛋白聚合，导致髓鞘连接蛋白复合体被移除的假说。我们的初步研究表明，F-肌动蛋白与显示连接蛋白复合体破坏的区域重叠显着增加。我们将利用基因标记的F-肌动蛋白小鼠模型来追踪F-肌动蛋白的形成动力学。我们将进一步测试PMP22缺乏如何激活肌动蛋白聚合。目的2：去除p21激活的激酶(PAK1)可逆转PMP22缺陷神经中F-肌动蛋白的增加，从而防止髓鞘连接复合体的破坏。我们的初步结果显示，PMP22/-神经中PAK1活性异常增加。去除PMP22/-小鼠中的Ak1可逆转异常的髓鞘通透性。我们将使用双基因敲除小鼠(PMP22/-/pak1-/-)来确定去除PAK1是否抑制HNPP小鼠模型中F-肌动蛋白的形成和连接复合体的错位。此外，利用我们新生产的表达PAK抑制肽的转基因小鼠，在可诱导的雪旺细胞特异性cre的控制下，我们将确定通过抑制PAK来挽救连接异常的时间需求。目的：全身应用PAK1抑制剂逆转HNPP小鼠模型的表型。在PMP22/-小鼠中，通过缺失pak1成功地逆转了异常的髓鞘渗透性，这有力地证明了在PMP22/-小鼠中使用PAK1抑制剂进行治疗试验的合理性。综上所述，这三个目标将进一步证实髓鞘连接中断和异常肌动蛋白聚合在HNPP中的致病作用。我们乐观地认为，通过这项研究可能会开发出一种治疗方法。因为髓鞘连接是封闭髓鞘的重要复合体，这项研究的结果可能在其他髓鞘疾病中有广泛的应用。

DESCRIPTION (provided by applicant): Mutations in human PMP22 cause the most common forms of inherited peripheral nerve diseases, which include hereditary neuropathy with liability to pressure palsies (HNPP) with heterozygous deletion of PMP22. Patients with HNPP presents with focal sensory loss and muscle weakness that are related to the conduction block. We have discovered that PMP22 deficiency impairs action potential propagation in the absence of segmental demyelination. This conduction defect is likely resulted from abnormally increased permeability of myelin through disruption of myelin junctions. In the present study, we will investigate how junction complexes are disrupted through their abnormal maintenance in PMP22 deficient nerves. Aim 1: Test the hypothesis that PMP22 deficiency increases actin polymerization at myelin junctions, leading to removal of myelin junction protein complexes. Our preliminary study has demonstrated a remarkable increase of F-actin overlaps with the areas that show disruption of junction protein complexes. We will utilize genetically labeled F-actin mouse model to track dynamics of F-actin formation. We will further test how PMP22 deficiency activates the actin polymerization. Aim 2: Removal of p21-activated kinase (PAK1) reverses the increase of F-actin in PMP22 deficient nerves, and thereby prevents myelin junction complexes from being disrupted. Our preliminary results show an abnormal increase of PAK1 activity in Pmp22+/- nerves. Ablation of Pak1 in Pmp22+/- mice reverses abnormal myelin permeability. We will use the double knockout mice (Pmp22+/- /Pak1-/-) to determine whether removal of PAK1 suppresses the formation of F-actin, and dislocation of junction complexes in HNPP mouse model. Moreover, utilizing our newly produced transgenic mouse expressing PAK-inhibiting peptides under the control of inducible Schwann cell-specific cre, we will determine the temporal requirement in rescuing junction abnormalities via PAK inhibition. Aim 3: Systemic administration of PAK1 inhibitor reverses the phenotype in the HNPP mouse model. A successful reversal of abnormal myelin permeability by deletion of Pak1 in Pmp22+/- mice strongly justifies a therapeutic trial in Pmp22+/- mice using PAK1 inhibitors. Taken together, these three aims will further substantiate the pathogenic roles of myelin junction disruption and abnormal actin polymerization in HNPP. We are optimistic that a therapy will likely be developed through this study. Because myelin junctions are essential complexes that seal myelin, results derived from this study may have broad applications in other myelin diseases.