Functional consequences of HSPB1 mutations that result in motor neuron disease

描述（由申请人提供）：运动神经元疾病（MND）是一种神经退行性疾病，可导致肌肉无力，通常伴有呼吸衰竭和死亡。MND分子遗传学的快速进展揭示了至少22种不同的基因，它们在所有细胞中表达，但在突变时仅导致运动神经元（MN）丢失。小热休克蛋白B1（HSPB1，以前的HSP 27）在遗传性运动神经病（HMN）患者中发生突变。HSPB1在MND引起基因中是独特的，因为已知野生型HSPB1的过表达在MN中具有神经保护作用，而突变对MN是有毒的。该提案的主要目标是确定与运动神经元存活相关的HSPB1的分子功能。为了做到这一点，我们已经开发了一种运动神经病的小鼠模型，其在神经元中表达最常见的HSPB1突变（R136W）。我们发现，HSPB1突变小鼠表现出轻度虚弱的表型，模仿HMN。我们建议开发在所有细胞中表达突变HSPB1的第二系小鼠，以便我们可以区分MN和非MN对MN损伤的贡献。非神经元细胞在MND进展中的作用正在成为一个重要的概念，特别是小胶质细胞表达的基因可能是减少MND中MN丢失的重要靶点。我们假设在所有细胞中表达HSPB1（R136W）的动物将具有比仅在神经元中表达HSPB1（R136W）的动物更严重的表型。HSPB1是一种特异性的mRNA衰变途径，称为富含AU元件（ARE）依赖性mRNA衰变。富含AU的元件mRNA衰变是所有细胞中控制一组选定mRNA表达的关键机制。我们的初步数据表明，HSPB1（R136W）在这种RNA衰变途径中是有缺陷的，这提高了含ARE的mRNA（通常通过这种途径降解）可能在MN病理中发挥作用的可能性。这些基因中的许多编码蛋白质，如干扰素和炎性细胞因子，其在损伤和感染期间具有保护功能，但当上调时可能具有破坏性。我们假设，与野生型HSPB1相比，表达突变型HSPB1的MN和小胶质细胞中含有ARE的mRNA的mRNA水平将升高。为了测试这一点，我们将直接测量小鼠MN和小胶质细胞中含有ARE的mRNA。这些动物的发展和对HSPB1分子功能的鉴定对MN存活至关重要，这将为HMN患者带来新的治疗靶点和治疗方法，并有很大的潜力促进我们对所有MND的理解并提供新的治疗策略。 公共卫生相关性：HSPB1蛋白在重要的RNA衰变途径中起关键作用，并在运动神经元中具有神经保护作用。HSPB1功能的研究很可能为正常运动神经元功能和运动神经元疾病的发病机制提供新的见解。最终，该项目将导致确定治疗这种毁灭性神经系统疾病的新靶点。

DESCRIPTION (provided by applicant): Motor neuron diseases (MNDs) are neurodegenerative disorders that cause muscle weakness and often respiratory failure and death. Rapid progress in the molecular genetics of MNDs has revealed at least 22 distinct genes that are expressed in all cells and yet result exclusively in motor neuron (MN) loss when mutated. The small heat shock protein B1 (HSPB1, formerly HSP27) is mutated in patients with hereditary motor neuropathy (HMN). HSPB1 is unique among MND-causing genes in that overexpression of the wild type HSPB1 is known to be neuroprotective in MNs whereas mutations are toxic to MNs. The primary goal of this proposal is to determine the molecular function of HSPB1 that is relevant to motor neuron survival. To do this, we have developed a mouse model of motor neuropathy expresing the most common HSPB1 mutation (R136W) in neurons. We find that HSPB1 mutant mice display a phenotype of mild weakness that mimics HMN. We propose to develop a second line of mice expressing mutant HSPB1 in all cells so that we may distinguish between MN and non-MN contributions to MN injury. The role of non-neuronal cells in the progression of MND is emerging as an important concept and genes expressed by microglia in particular may be important targets in reducing MN loss in MNDs. We hypothesize that animals expressing HSPB1(R136W) in all cells will have a phenotype that is more severe than animals expressing HSPB1(R136W) exclusively in neurons. HSPB1 is required for a specific mRNA decay pathway caled AU-rich element (ARE)-dependent mRNA decay. AU-rich element mRNA decay is a critical mechanism in all cells to control the expression of a select group of mRNAs. Our preliminary data demonstrate that HSPB1(R136W) is defective in this RNA decay pathway, which raises the possibility that ARE-containing mRNAs (normally degraded via this pathway) may play a role in MN pathology. Many of these genes encode proteins such as interferons and inflammatory cytokines which have protective functions during injury and infections, but can be damaging when upregulated. We hypothesize that mRNA levels of ARE-containing mRNAs will be elevated in MNs and microglia expressing mutant HSPB1 compared to wild type HSPB1. To test this, we will directly measure ARE-containing mRNAs in MNs and microglia in mice. The development of these animals and the identification of the molecular function of HSPB1 that is important for MN survival will lead to new therapeutic targets and treatments for patients with HMN and has great potential to advance our understanding of and provide novel treatment strategies for all MNDs. PUBLIC HEALTH RELEVANCE: The HSPB1 protein plays a critical role in an important RNA decay pathway and is neuroprotective in motor neurons. The proposed studies of HSPB1 function are highly likely to provide novel insights into normal motor neuron function and to the pathogenesis of motor neuron diseases. Ultimately, this project will lead to the identification of novel targets for the treatment of this devastating class of nervous system disease.