Cellular events in heritable peripheral neuropathies

摘要 遗传性脱髓鞘神经病，包括Charcot-Marie-Tooth病1A型(CMT1A)， 在导致肌肉萎缩和功能性功能障碍的周围神经疾病中占很大比例 减损。外周髓鞘蛋白22(PMP22)是雪旺氏细胞内的一种疏水性完整膜蛋白 细胞，其异常表达与大多数CMT1A病例有关。在大多数患者中， 在脱髓鞘神经病中，PMP22基因是复制的，而在CMT1A和 DeJerine-Sottas综合征，PMP22中存在单一氨基酸替换。神经活检的研究 从神经病患者身上发现PMP22在雪旺细胞胞浆中异常滞留，而缺乏 正确的髓鞘蛋白表达。为了了解PMP22的亚细胞发病机制- 相关的神经病变，我们已经表征了PMP22的翻译后处理，并发现 神经病雪旺细胞内蛋白质的降解和异常积聚 小鼠，包括点突变震颤器J和PMP22过表达模型。由于胞浆PMP22是 仅在神经病小鼠的神经组织中检测到，而不是在正常小鼠的神经组织中检测到，异常的细胞内聚集 PMP22可能参与了该病的发病机制。事实上，在压倒泛素蛋白酶体的基础上 途径，PMP22的胞浆聚集体形成和招募基本的雪旺细胞分子，包括 伴侣蛋白和髓鞘蛋白，它们改变细胞的蛋白质平衡。在允许的条件下， 从新生神经分离的雪旺细胞具有清除这些异常胞浆蛋白的能力。 通过一种由伴侣和自噬辅助的机制聚集。在当前的这个周期中 项目中，我们在颤抖者J和PMP22的样本中刺激了伴侣和自噬反应 过度表达的小鼠，并发现PMP22的异常胞浆聚集可以被抑制和 髓磷脂的产生有所改善。此外，我们已经表明，对这些途径的饮食刺激具有 证明对这些神经病小鼠是有益的。这些原则证明实验的成功设置了 在神经病小鼠中推进特定药物治疗范例的阶段，并进行评估 对神经肌肉功能、神经形态及相关亚细胞机制的治疗结果。 这个项目的总体目标是确定伴侣和自噬的药理增强 蛋白质降解可以减缓或阻止幼鼠神经病变的进展，并研究 来自疾病晚期的样本对这种方法的反应。我们将在药理上使用 特征性的已知小分子刺激幼虫的伴侣和自噬途径 神经病变小鼠和晚期疾病状态小鼠的体外样本。这些研究将确定是否 通过刺激PMP22内的蛋白质平衡机制改善PMP22的亚细胞加工 雪旺细胞可为CMT1a及相关神经疾病的治疗提供一种可行的方法。

Abstract Heritable demyelinating neuropathies, including Charcot-Marie-Tooth disease type 1A (CMT1A), account for a significant portion of peripheral nerve disorders leading to muscle atrophy and functional impairment. Peripheral myelin protein 22 (PMP22) is a hydrophobic integral membrane protein within Schwann cells, whose abnormal expression is associated with the majority of CMT1A cases. In most patients with demyelinating neuropathy, the PMP22 gene is duplicated, while in a smaller fraction of CMT1A and in Dejerine-Sottas Syndrome, single amino acid substitutions in PMP22 are present. Studies of nerve biopsies from neuropathic patients revealed abnormal retention of PMP22 within the Schwann cell cytosol, and the lack of correct myelin protein expression. To gain understanding into the subcellular pathogenesis of PMP22- associated neuropathies, we have characterized the posttranslational processing of PMP22 and found slowed degradation and abnormal intracellular accumulation of the protein within Schwann cells from neuropathic mice, including the point mutant Trembler J and the PMP22 overexpressor models. Since cytosolic PMP22 is only detected in nerve tissue from neuropathic and not normal mice, the abnormal intracellular accumulation of PMP22 likely contributes to the disease pathogenesis. Indeed, upon overwhelming the ubiquitin-proteasome pathway, cytosolic aggregates of PMP22 form and recruit essential Schwann cell molecules, including chaperones and myelin proteins, which alter the protein balance of the cell. Under permissive conditions, Schwann cells isolated from neonatal nerves have the ability to clear these abnormal cytosolic protein aggregates by a mechanism that is assisted by chaperones and autophagy. During the current cycle of this project, we stimulated the chaperone and autophagic responses within samples from Trembler J and PMP22 overexpressor mice, and found that the abnormal cytosolic aggregation of PMP22 can be suppressed and myelin production improved. Furthermore, we have shown that dietary stimulation of these pathways has proven beneficial to these neuropathic mice. The success of these proof-of-principle experiments sets the stage to move forward with specific pharmacologic treatment paradigms in neuropathic mice, and evaluate treatment outcome on neuromuscular function, nerve morphology and associated subcellular mechanisms. The overall aim of this project is to determine if pharmacologic enhancement of chaperones and autophagic protein degradation can slow or halt the progression of the neuropathy in young mice, and to investigate the response of samples from advanced disease stages to this approach. We will use pharmacologically characterized, known small molecules to stimulate the chaperone and autophagy pathways in young neuropathic mice and in ex vivo samples from advanced disease state mice. These studies will determine if improving the subcellular processing of PMP22 by stimulation of protein homeostatic mechanisms within Schwann cells could provide a viable approach for therapy in CMT1A and related neuropathies.