Disease Mechanisms in Human Ubiquilinopathy

描述（由申请人提供）：肌萎缩性侧索硬化症（ALS）的特征是大脑和脊髓中的大运动神经元变性，导致进行性萎缩和随意肌麻痹，呼吸衰竭，最终死亡。家族性ALS （FALS）约占所有ALS病例的10%，其中大多数（90%）的疾病表现为散发性ALS （SALS）。肌萎缩性侧索硬化症遗传病因的发现是近20年来肌萎缩性侧索硬化症研究的主要推动力。这些发现为研究发病机制和动物模型提供了新的思路。然而，尽管有这样的努力，ALS的全球治疗还不可能，因为从不同的病因下游的共同分子机制还没有变得明显。很明显，发现其他病因和常见的下游机制将极大地促进对ALS的分子理解和寻找适当治疗的目标。在这个应用程序中，我们提出了朝着这些目标前进的方向。我们已经发现UBQLN2突变是x连锁显性ALS和FTD型ALS/痴呆的原因。ALS患者的脊髓和皮层中有泛素2阳性包裹体，ALS/FTD患者的海马中有额外的包裹体，这种病理是新颖、独特和独特的。令我们惊讶的是，到目前为止，我们在所有的SALS、ALS/FTD和FALS病例中发现了相似的泛素2阳性包裹体。这些病例中没有UBQLN2突变，这表明泛素2在整个ALS中具有翻译后作用。我们最初的体外和体内数据表明，在突变的泛素2存在下，泛素蛋白酶体综合征（UPS）和自噬功能障碍。此外，表达致病UBQLN2突变（P497H）的转基因小鼠在远场记录中观察到认知和行为缺陷以及长时程增强减弱。在本项目中，我们提出了四个具体目标来了解突变体泛素2的致病机制。我们将建立病理，认知和其他行为表型及其电生理相关性在我们目前和有待开发的突变型小鼠模型中。我们还将使用我们已经建立的ubqln2敲除小鼠模型，并开发ubqln1敲除和ubqln1/ubqln2的双敲除，以测试突变型ubiquilin2缺陷是否是与UPS和自噬系统相关的ubiquilin2功能丧失的表现，或者突变型ubiquilin2是否表现出新的毒性。该项目的成功完成不仅将有助于深入了解x连锁ALS的致病机制，而且还将迅速为更广泛的研究界提供有用的试剂，用于未来的研究以及筛选和测试潜在的治疗方法。该项目的结果也将对理解其他神经退行性疾病的发病机制和治疗具有重要意义。

DESCRIPTION (provided by applicant): Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of large motor neurons in the brain and spinal cord, resulting in progressive wasting and paralysis of voluntary muscles, respiratory failure and ultimately death. Familial ALS (FALS) accounts for around 10% of all ALS cases, with the majority (90%) of the disease presenting as sporadic ALS (SALS). Discovery of genetic etiologies of ALS has been the driving force in ALS research for the last 20 years. These discoveries have provided fresh insight into pathogenesis and animal models. However, in spite of this effort, global treatments have not been possible for ALS because a common molecular mechanism downstream from the distinct etiologies has not become apparent. It is clear that discovery of additional etiologies and common downstream mechanisms will greatly advance the goals for a molecular understanding of ALS and in finding appropriate treatments. In this application we propose an advance in direction of those goals. We have discovered mutations in UBQLN2 as cause of X-linked dominant ALS and ALS/dementia of the FTD type. The pathology is novel, distinct and unique with ubiquilin2 positive inclusions in the spinal cord and cortex in ALS patients and additional inclusions in the hippocampus of patients with ALS/FTD. To our surprise we found similar ubiquilin2 positive inclusions in all cases of SALS and ALS/FTD and FALS cases studied thus far. None of those cases had mutations in UBQLN2, arguing for a posttranslational role for ubiquilin2 in ALS as a whole. Our initial in vitro and in vivo data suggest a dysfunction of the ubiquilin proteasome syndrome (UPS) and autophagy in the presence of mutant ubiquilin2. In addition, cognitive and behavioral deficits and decreased long term potentiation in far field recordings were observed in transgenic mice expressing a pathogenic UBQLN2 mutation (P497H). In this project, we propose four specific aims to understand the disease causing mechanism(s) of mutant ubiquilin2. We will establish pathological, cognitive and other behavioral phenotypes and their electrophysiological correlates in our current and to be developed mouse models of mutant ubiquiln2. We will also use our already established ubqln2 knockout mouse model and develop ubqln1 knockout and double knockouts of ubqln1/ubqln2 to test if mutant ubiquilin2 defects are manifestation of a loss of function of ubiquilin2 in relationto the UPS and autophagy systems or whether mutant ubiquilin2 exhibits a novel toxic property. Successful completion of this project will not only provide insight into understanding the pathogenic mechanism of X-linked ALS, but also rapidly provide the wider research community with useful reagents for future studies and for screening and testing potential therapies. The outcome of this project will also have important implications in the understanding of the pathogenesis and treatment of other neurodegenerative diseases. PUBLIC HEALTH RELEVANCE: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder affecting an estimated 350,000 individuals worldwide, with 50% dying within 3 years of onset. The cost to the family approaches $200,000 per year in the final years of illness and the disease defies all treatment. Discovery of diverse genetic causes of ALS has been the driving force in ALS research for the last 20 years by providing fresh insight into mechanisms of disease. It is clear that discovery of additional causes of ALS and unifying mechanisms of disease will greatly advance the goals for a molecular understanding of ALS and in finding appropriate treatments. We have discovered mutations in a gene called UBQLN2 as a cause of a form of inherited ALS and ALS/dementia and an exciting and unique pathology in sporadic and familial ALS as well as ALS/dementia. Functional studies have revealed an impairment of protein degradation pathways in the presence of mutant form of ubiquilin2. Though impaired protein degradation is thought to be associated with the formation of detrimental protein inclusions in the development of many neurodegenerative disorders, direct evidence of mutations in this pathway is limited. Hence, ubiquilin2, by virtue of a common pathology across ALS and ALS/dementia presents a unique opportunity to study the effect of its mutations on cellular protein quality control with a view to understand the pathogenic mechanism by which the UBQLN2 mutations cause neurodegeneration. We will develop and analyze appropriate animal models in this study to identify molecular mechanisms by which mutant ubiquilin2 causes imbalance in the protein economy of neurons which result in impaired synapse formation and leads to clinical syndromes of ALS and dementia.