A Novel Ubiquitin-Dependent Pathogenic Pathway in Spongiform Neurodegeneration

描述(申请人提供)：海绵状神经变性是一种独特的神经变性形式，其特征是神经元中的空泡化、神经元细胞死亡和星形胶质细胞增多。海绵状神经变性最为人所知的是Pron病的特征，这种病理也存在于阿尔茨海默病、弥漫性路易体病和获得性免疫缺陷综合征(AIDS)患者的大脑中。人类最常见的Pron病是克雅氏病(CJD)，它以散发性、传染性和遗传性的形式发生。散发性CJD占病例的85%，是一种起病晚(平均发病年龄=60岁)、原因不明的神经退行性疾病。尽管普恩蛋白已经得到了广泛的研究，但海绵状神经变性的致病机制仍不清楚。有趣的是，最近的一项遗传学研究显示，编码一种名为Mahogunin(Mgrn1)的新蛋白质的基因零突变会导致小鼠年龄相关的进行性海绵状神经退行性变，这种变性包括Pron病的许多特征，但没有积累抗蛋白酶的Prion蛋白。目前，对Mgrn1的生物学功能以及Mgrn1功能缺失如何导致海绵状神经变性的研究甚少。Mgrn1含有一个无名指，这个基序被认为是E3泛素蛋白连接酶活性的关键决定因素。已经推测，Mgrn1功能的丧失可能通过损害Mgrn1的泛素化和随后尚未确定的底物(S)的蛋白酶体降解而导致海绵状神经变性。相比之下，申请人的初步结果导致了一个有趣的假设，即Mgrn1在非蛋白酶体、泛素信号通路中发挥功能，并提出了一种新的机制，通过这种机制，有缺陷的泛素化可能会导致海绵状神经退化。在这个项目中，申请人的团队将在这些令人兴奋的结果的基础上，结合生化、细胞生物学和分子遗传学的方法来研究Mgrn1 E3连接酶的细胞作用，鉴定其底物，并阐明Mgrn1功能丧失导致年龄依赖性海绵状神经变性的分子机制。拟议项目的完成将促进我们对海绵状神经变性发病机制的了解，并有助于开发治疗与年龄相关的神经退行性疾病的新治疗策略。公共卫生相关性：海绵状神经退行性变最常与普恩病毒病有关，但也会发生在患有与年龄相关的神经退行性疾病的患者中，如阿尔茨海默病和弥漫性路易体病。这项拟议研究的目标是确定导致年龄依赖性海绵状神经变性的分子致病机制。拟议的研究结果将为开发有效的治疗方法以对抗与年龄相关的神经退行性疾病提供所需的基本信息。

DESCRIPTION (provided by applicant): Spongiform neurodegeneration is a unique form of neurodegeneration characterized by vacuolation in neurons, neuronal cell death, and astrocytosis. Spongiform neurodegeneration is best known as the hallmark of prion disease, and this pathology is also present in the brains of patients suffering from Alzheimer's disease, diffuse Lewy body disease, and acquired immune deficiency syndrome (AIDS). The most common human prion disease is Creutzfeldt-Jakob disease (CJD), which occurs in sporadic, infectious, and inherited forms. The sporadic CJD form accounts for 85% of cases and is a late-onset (average age of onset = 60 years) neurodegenerative disorder of unknown cause. Although the prion protein has been extensively studied, the pathogenic mechanism underlying spongiform neurodegeneration remains elusive. Interestingly, a recent genetic study reveals that a null mutation in the gene encoding a novel protein called Mahogunin (Mgrn1) causes age-dependent, progressive spongiform neurodegeneration in mice that includes many features of prion disease but without accumulation of protease-resistant prion protein. At present, very little is known about the biological function of Mgrn1 and how loss of Mgrn1 function causes spongiform neurodegeneration. Mgrn1 contains a RING finger, a motif thought to be the key determinant of E3 ubiquitin-protein ligase activity. It has been speculated that loss of Mgrn1 function may cause spongiform neurodegeneration by impairing the ubiquitination and subsequent proteasomal degradation of yet-to-be-identified substrate(s) of Mgrn1. In contrast, the applicant's preliminary results have led to an intriguing hypothesis that Mgrn1 functions in a proteasome-independent, ubiquitin signalling pathway and suggest a novel mechanism by which defective ubiquitination may cause spongiform neurodegeneration. In this project, the applicant's group will follow up on these exciting results and use a combination of biochemical, cell biological, and molecular genetic approaches to investigate the cellular role of Mgrn1 E3 ligase, identify its substrates, and elucidate the molecular mechanism by which loss of Mgrn1 function causes age-dependent spongiform neurodegeneration. Completion of the proposed project should advance our understanding of the pathogenic mechanism underlying spongiform neurodegeneration and facilitate the development of new therapeutic strategies for treating age-related neurodegenerative disorders. PUBLIC HEALTH RELEVANCE: Spongiform neurodegeneration is most commonly associated with prion disease, but also occurs in patients suffering from age-related neurodegenerative disorders, such as Alzheimer's disease and diffuse Lewy body disease. The goal of the proposed research is to define the molecular pathogenic mechanism that causes age-dependent spongiform neurodegeneration. The results of the proposed studies will provide fundamental information needed for the development of effective therapeutics to combat age-related neurodegenerative diseases.