Modifiers of Huntingtin and Alpha-synuclein Toxicity

描述（由申请人提供）：亨廷顿氏病（HD）是一种常染色体显性遗传疾病，其特征为不自主运动、人格改变和痴呆，由IT-15基因中CAG/多聚谷氨酰胺重复序列扩增引起。HD的一个主要神经病理学标志是出现含有亨廷顿蛋白（由IT-15编码的蛋白质）的核内和细胞质包涵体。胞质包涵体（Lewy小体）也是帕金森病（PD）的突出性质，帕金森病是一种以肌肉僵硬、运动迟缓、静止性震颤和姿势不稳定为特征的神经退行性疾病。路易体主要由蛋白质α-突触核蛋白组成，α-突触核蛋白基因中的两个点突变导致早发性遗传形式的帕金森病。α-突触核蛋白和亨廷顿蛋白聚集成有序的纤维状结构，具有淀粉样蛋白的特性。最初开发的“淀粉样蛋白假说”是为了描述β-淀粉样蛋白在阿尔茨海默病（AD）中的作用，该假说表明蛋白质聚集成有序的纤维状结构与异常蛋白质相互作用有因果关系，异常蛋白质相互作用最终导致神经元功能障碍和细胞死亡（哈代和Selkoe，2002）。蛋白质聚集、淀粉样蛋白形成和包涵体在神经变性中的确切作用仍有争议，目前尚不清楚HD和帕金森病的共同分子机制。 我们已经使用酵母作为真核生物的模型来测试以下假设：亨廷顿蛋白和α-突触核蛋白介导毒性的下游靶点和分子机制是独特的。在酵母中使用全基因组筛选方法，我们分离出52个修饰亨廷顿蛋白毒性的基因和86个修饰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%富集在蛋白质折叠和细胞应激的功能相关类别中，而修饰α-突触核蛋白毒性的基因中有29%涉及囊泡转运和脂质代谢。我们的初步结果令人惊讶地表明，基因和细胞途径，调节亨廷顿蛋白和α-突触核蛋白的毒性在酵母是完全不同的。我们分离的基因中有近一半被注释为具有一个或多个人类直系同源物，这表明我们可能在酵母中发现了与HD和帕金森病相关的亨廷顿蛋白和α-突触核蛋白的保守细胞生物学反应途径。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物化学技术来验证（或无效）我们已经确定的遗传修饰剂，来促进我们对HD和PD中发生的神经变性的理解。我们的长期目标是利用我们在这些研究中获得的信息来测试HD和帕金森病动物模型中的假设。

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.