A Novel Ubiquitin-Dependent Pathogenic Pathway in Spongiform Neurodegeneration

描述（由申请人提供）：海绵状神经变性是一种独特的神经变性形式，其特征是神经元空泡化、神经元细胞死亡和星形细胞增多。海绵状神经变性是众所周知的朊病毒疾病的标志，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（艾滋病）患者的大脑中。最常见的人类朊病毒疾病是克雅氏病（CJD），它以散发性、传染性和遗传性形式发生。散发的CJD形式占85%的病例，是一种病因不明的晚发性（平均发病年龄= 60岁）神经退行性疾病。尽管朊病毒蛋白已被广泛研究，但海绵状神经变性的致病机制仍不明确。有趣的是，最近的一项遗传研究表明，编码一种名为Mahogunin （Mgrn1）的新蛋白的基因的零突变导致小鼠年龄依赖性进行性海淀状神经变性，包括许多朊病毒疾病的特征，但没有蛋白酶抗性朊病毒蛋白的积累。目前，对Mgrn1的生物学功能以及Mgrn1功能丧失如何导致海绵状神经退行性变的了解甚少。Mgrn1含有一个环指，一个被认为是E3泛素蛋白连接酶活性的关键决定因素的基序。据推测，Mgrn1功能的丧失可能通过损害Mgrn1的泛素化和随后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在蛋白酶体独立的泛素信号通路中起作用，并提出了一种新的机制，通过这种机制，泛素化缺陷可能导致海森堡样神经变性。在这个项目中，申请人的小组将继续这些令人兴奋的结果，并使用生物化学，细胞生物学和分子遗传学方法的组合来研究Mgrn1 E3连接酶的细胞作用，确定其底物，并阐明Mgrn1功能丧失导致年龄依赖性海基状神经变性的分子机制。该项目的完成将促进我们对海绵状神经退行性疾病致病机制的理解，并促进治疗与年龄相关的神经退行性疾病的新治疗策略的发展。公共卫生相关性：海绵状神经变性最常与朊病毒疾病相关，但也发生在患有与年龄相关的神经退行性疾病（如阿尔茨海默病和弥漫性路易体病）的患者中。提出的研究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。拟议研究的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.