Pathophysiology of Conduction Block in HNPP

描述（由申请人提供）：人PMP 22突变引起最常见形式的遗传性周围神经疾病，包括易患 具有PMP 22杂合缺失的压力性麻痹（HNPP）。HNPP患者表现为与传导阻滞相关的局灶性感觉丧失和肌无力。我们已经发现，在没有节段性脱髓鞘的情况下，PMP 22缺陷损害动作电位传播。这种传导缺陷可能是由于髓鞘连接破坏导致髓鞘渗透性异常增加所致。在本研究中，我们将研究如何通过其异常维护在PMP 22缺陷的神经连接复合物被破坏。目标1：检验以下假设：PMP 22缺乏会增加髓鞘连接处的肌动蛋白聚合，导致髓鞘连接蛋白复合物的去除。 我们的初步研究已经证明了一个显着增加的F-肌动蛋白重叠的地区，显示中断的连接蛋白复合物。我们将利用基因标记的F-actin小鼠模型来跟踪F-actin形成的动力学。我们将进一步测试PMP 22缺陷如何激活肌动蛋白聚合。目标二：去除p21激活激酶（PAK 1）逆转了PMP 22缺陷神经中F-肌动蛋白的增加，从而防止髓鞘连接复合物被破坏。 我们的初步结果表明，PAK 1活性异常增加Pmp 22 +/-神经。Pmp 22 +/-小鼠中Pak 1的消融逆转了异常的髓鞘渗透性。我们将使用双基因敲除小鼠（Pmp 22 +/- /Pak 1-/-）来确定PAK 1的去除是否抑制HNPP小鼠模型中F-肌动蛋白的形成和连接复合物的脱位。此外，利用我们新生产的转基因小鼠表达PAK抑制肽的控制下，诱导的雪旺细胞特异性cre，我们将确定时间的要求，通过PAK抑制拯救连接异常。目的3：PAK 1抑制剂的全身给药逆转HNPP小鼠模型中的表型。 通过缺失Pak 1在Pmp 22 +/-小鼠中成功逆转异常髓鞘渗透性，有力地证明了使用PAK 1抑制剂在Pmp 22 +/-小鼠中进行治疗试验的合理性。 这三个目标将进一步证实髓鞘连接破坏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。由于髓鞘连接是密封髓鞘的基本复合物，因此这项研究的结果可能在其他髓鞘疾病中具有广泛的应用。

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.