Mechanisms of motor neuron toxicity in Kennedy disease

摘要 脊髓延髓肌萎缩症（SBMA）是一种下运动神经元和骨骼肌的退行性疾病， 由雄激素受体（AR）基因中CAG/谷氨酰胺束扩张引起的肌肉。多聚谷氨酰胺 AR（polyQ AR）经历了依赖于细胞核转位和解折叠的过程，这些步骤对于 毒性和男性进行性肌无力的发展。虽然疾病导致 突变是在25年前发现的，目前只有支持性治疗可用于 SBMA患者。已用于研究疾病发病机理的模型系统显示激素和 谷氨酰胺在一系列下游途径中的长度依赖性变化，支持了不同的谷氨酰胺的作用。 毒性机制。这些观察结果促使我们转而关注于理解近端 调节突变雄激素受体蛋白降解的机制，希望利用这些机制， 发现有效的治疗方法。然而，这些清除途径尚未完全确定， 这种知识的缺乏阻碍了疾病改善疗法的发展。的目的 应用是定义热休克蛋白70在蛋白质质量控制决策中的作用， 全长polyQ AR.这种应用的科学前提是，通过免疫球蛋白Hsp 70， 基于Hsp 90/Hsp 70的机器和Hsp 70/Hsp 110解聚酶机器在 通过蛋白酶体控制polyQ AR降解。这一前提为我们的中央 假设Hsp 70靶向策略将促进突变蛋白的泛素化和清除。这 我们的初步数据显示与Hsp 90的结合稳定了polyQAR， 而突变蛋白的解折叠导致通过Hsp 70依赖性E3连接酶的泛素化。而且还要 基于我们已发表的研究，证明热休克蛋白70的变构调节增加与 错误折叠的蛋白质增强了细胞中polyQAR的清除，并在果蝇模型中降低了毒性。 拟议工作的基本原理是建立调节polyQ AR降解的机制 将确定可用于开发新疗法的靶点。结构、生化、遗传 和药理学方法将用于表征Hsp 70-CHIP与polyQ AR的复合物， 调节蛋白分类（目的1），建立遗传和小分子变构调节剂的作用， SBMA模型中的Hsp 70（目的2），并确定polyQ AR表达对泛素-蛋白酶体的影响 途径功能（目标3）。这些研究有望表征细胞的结构和功能， 调节polyQ AR降解的机制，并提供支持治疗的概念验证数据 方法以Hsp 70为靶点。由于该监护人还负责管理质量控制决策， 导致神经变性的其他突变蛋白质的周转，我们希望定义的方法 这里将告知适用于其他年龄依赖性神经系统疾病的治疗策略。

ABSTRACT Spinal and bulbar muscular atrophy (SBMA) is a degenerative disorder of lower motor neurons and skeletal muscle caused by a CAG/glutamine tract expansion in the androgen receptor (AR) gene. The polyglutamine AR (polyQ AR) undergoes hormone-dependent nuclear translocation and unfolding, steps that are essential to toxicity and to the development of progressive muscle weakness in men. Although the disease causing mutation was identified over two and a half decades ago, only supportive therapies are currently available to SBMA patients. Model systems that have been used to study disease pathogenesis show hormone and glutamine length-dependent changes in an array of downstream pathways, supporting a role for divergent mechanisms in toxicity. These observations prompted us to focus instead on understanding the proximal mechanisms that regulate degradation of the mutant androgen receptor protein in hopes of harnessing these for the discovery of effective treatments. However, these clearance pathways are incompletely defined, and this lack of knowledge hinders the development of disease-modifying therapies. The objective of this application is to define the role of Hsp70 in the protein quality control decisions that govern degradation of the full-length polyQ AR. The scientific premise of this application is that the Hsp70, acting through the Hsp90/Hsp70-based machinery and the Hsp70/Hsp110 disaggregase machinery, plays a critical role in controlling polyQ AR degradation through the proteasome. This premise provides the foundation for our central hypothesis that Hsp70 targeted strategies will promote ubiquitination and clearance of the mutant protein. This hypothesis springs from our preliminary data showing that association with Hsp90 stabilizes the polyQ AR, while unfolding of the mutant protein leads to ubiquitination by Hsp70-dependent E3 ligases. Moreover, we will build upon our published studies demonstrating that allosteric regulation of Hsp70 to increase binding to misfolded proteins enhances clearance of the polyQ AR in cells and alleviates toxicity in a Drosophila model. The rationale of the proposed work is that establishing the mechanisms that regulate polyQ AR degradation will identify targets that can be exploited for the development of new therapies. Structural, biochemical, genetic and pharmacological approaches will be used to characterize the Hsp70-CHIP complex with the polyQ AR that regulates protein triage (Aim 1), establish the effects of genetic and small molecule allosteric regulators of Hsp70 in SBMA models (Aim 2), and determine effects of polyQ AR expression on ubiquitin-proteasome pathway function (Aim 3). These studies are expected to characterize the structure and function of the cellular machinery that regulates polyQ AR degradation and provide proof-of-concept data supporting a therapeutic approach centered on targeting Hsp70. As this chaperone also regulates quality control decisions governing the turnover of other mutant proteins that cause neurodegeneration, we expect that the approaches defined here will inform therapeutic strategies that will be applicable to other age-dependent neurological diseases.