Functional consequences of HSPB1 mutations that result in motor neuron disease

描述(申请人提供)：运动神经元病(MND)是一种神经退行性疾病，会导致肌肉无力，通常是呼吸衰竭和死亡。MND分子遗传学的快速发展揭示了至少22个不同的基因，这些基因在所有细胞中表达，但在突变时仅导致运动神经元(MN)丢失。小分子热休克蛋白B1(HSPB1，前身为HSP27)在遗传性运动神经病(HMN)患者中发生突变。在引起MND的基因中，HSPB1是独一无二的，因为已知野生型HSPB1的过度表达在MNS中具有神经保护作用，而突变对MNS是有毒的。这项建议的主要目标是确定HSPB1与运动神经元生存相关的分子功能。为此，我们开发了一种运动神经病的小鼠模型，该模型表达神经元中最常见的HSPB1突变(R136W)。我们发现，HSPB1突变小鼠表现出轻度虚弱的表型，类似于HMN。我们建议建立在所有细胞中表达突变HSPB1的第二系小鼠，以便我们能够区分MN和非MN在MN损伤中的作用。非神经细胞在MND进展中的作用正在成为一个重要的概念，尤其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是一种特定的被称为富含AU元素(ARE)的mRNA衰变途径所必需的。富含Au元素的mRNA衰变是所有细胞中控制一组特定mRNAs表达的关键机制。我们的初步数据表明，HSPB1(R136W)在这一RNA衰退途径中存在缺陷，这增加了含有ARE的mRNAs(通常通过这一途径降解)在MN病理中发挥作用的可能性。其中许多基因编码干扰素和炎症细胞因子等蛋白质，这些蛋白质在损伤和感染过程中具有保护功能，但当上调时可能具有破坏性。我们推测，与野生型HSPB1相比，表达突变型HSPB1的MNS和小胶质细胞中含有ARE的mRNAs的mRNA水平将会升高。为了验证这一点，我们将直接测量小鼠MNS和小胶质细胞中含有ARE的mRNAs。这些动物的发展和对MN生存至关重要的HSPB1分子功能的鉴定将为HMN患者带来新的治疗靶点和治疗方法，并具有促进我们对所有MND的理解和提供新的治疗策略的巨大潜力。 公共卫生相关性：HSPB1蛋白在重要的RNA衰变途径中发挥关键作用，并对运动神经元具有神经保护作用。HSPB1功能的研究很可能为了解运动神经元的正常功能和运动神经元疾病的发病机制提供新的见解。最终，该项目将为治疗这种毁灭性的神经系统疾病确定新的靶点。

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.