Modifiers of Huntingtin and Alpha-synuclein Toxicity

描述(申请人提供)：亨廷顿病(HD)是一种常染色体显性遗传性疾病，特征是不自主运动、个性变化和痴呆症，由IT-15基因中CAG/聚谷氨酰胺重复序列的扩大引起。HD的一个主要神经病理特征是核内和胞浆内含有亨廷顿蛋白(由IT-15编码的蛋白质)的包涵体。胞浆包涵体也是帕金森病(PD)的显著特征，帕金森病是一种神经退行性疾病，以肌肉僵硬、运动迟缓、静止性震颤和姿势不稳定为特征。路易小体主要由α-突触核蛋白蛋白组成，α-突触核蛋白基因的两个点突变会导致早发性、遗传性帕金森氏病。α-突触核蛋白和亨廷顿蛋白聚集成有序的纤维结构，具有淀粉样蛋白的特性。“淀粉样假说”最初是为了描述β-淀粉样蛋白在阿尔茨海默病(AD)中的作用，它认为蛋白质聚集成有序的纤维结构与异常的蛋白质相互作用有因果关系，最终导致神经元功能障碍和细胞死亡(Hardy和Selkoe，2002)。蛋白质聚集、淀粉样蛋白形成和包涵体在神经退行性变中的确切作用仍存在争议，目前尚不清楚HD和帕金森病是否存在共同的分子机制。 我们使用酵母作为真核生物的模型来检验这一假设，即亨廷顿蛋白和共核蛋白介导毒性的下游靶点和分子机制是独特的。使用酵母全基因组筛选方法，我们分离了52个改变亨廷顿蛋白毒性的基因，以及86个改变α-突触核蛋白毒性的基因。影响亨廷顿蛋白毒性的基因中有30%集中在蛋白质折叠和细胞应激等功能相关的类别中，而改变α-突触核蛋白毒性的基因中有29%涉及囊泡运输和脂质代谢。我们的初步结果令人惊讶地表明，调节酵母中亨廷顿蛋白和α-突触核蛋白毒性的基因和细胞途径完全不同。我们分离的近一半基因被注释为具有一个或多个人类同源基因，这表明我们可能在酵母中发现了与HD和帕金森病相关的保守的细胞生物反应途径，即亨廷顿蛋白和α-突触核蛋白。利用我们已经产生的资源和信息，我们现在希望通过应用分子遗传学和生化技术来验证(或无效)我们已经确定的遗传修饰物，来促进我们对HD和PD中发生的神经退行性变的理解。我们的长期目标是利用我们在这些研究中获得的信息，在HD和帕金森病的动物模型中测试假说。

DESCRIPTION (provided by applicant): Huntington's disease (HD) is an autosomal dominant inherited disorder characterized by involuntary movements, personality changes and dementia, and is caused by an expansion of a CAG/polyglutamine repeat in the IT-15 gene. A major neuropathological hallmark in HD is the occurrence of intranuclear and cytoplasmic inclusion bodies that contain huntingtin (the protein encoded by IT-15). Cytoplasmic inclusion bodies (Lewy bodies) are also a prominent nature of Parkinson's disease (PD), a neurodegenerative disorder characterized by muscle rigidity, bradykinesia, resting tremor and postural instability. Lewy bodies are composed primarily of the protein alpha-synuclein, and two point mutations in the alpha-synuclein gene cause early-onset, inherited forms of Parkinson's disease. Alpha-synuclein and huntingtin aggregate into ordered fibrillar structures with properties characteristic of amyloid. The 'amyloid hypothesis', developed originally to describe the role of beta-amyloid in Alzheimer's Disease (AD), suggests that the aggregation of proteins into an ordered fibrillar structure is causally related to aberrant protein interactions that culminate in neuronal dysfunction and cell death (Hardy and Selkoe, 2002). The precise roles of protein aggregation, amyloid formation and inclusion bodies in neurodegeneration remain controversial, and it is not yet clear if common molecular mechanisms underlie HD and Parkinson's disease. We have used yeast as a model eukaryotic organism to test the hypothesis that the downstream targets and molecular mechanisms by which huntingtin and ot-synuclein mediate toxicity are unique. Using a genome-wide screening approach in yeast we isolated 52 genes that modify huntingtin toxicity, and 86 genes that modify alpha-synuclein toxicity. 30% of genes that affect huntingtin toxicity are enriched in the functionally related categories of protein folding and cell stress, while 29% of genes that modify alpha-synuclein toxicity are involved in vesicular transport and lipid metabolism. Our preliminary results indicate surprisingly that the genes and cellular pathways that modulate huntingtin and alpha-synuclein toxicity in yeast are completely divergent. Nearly half of the genes we isolated are annotated as having one or more human ortholog, suggesting we may have discovered in yeast conserved cell-biological response pathways to huntingtin and alpha-synuclein that are relevant to HD and Parkinson's disease. Using the resources and information that we have generated, we now wish to advance our understanding of the neurodegeneration that occurs in HD and PD by applying molecular genetic and biochemical techniques to validate (or invalidate) the genetic modifiers we have identified. Our long-term goal is to use the information we gain in these studies to test hypotheses in animal models of HD and Parkinson's disease.