Huntington's Disease Repeat Instability and Pathogenesis

描述（由申请人提供）：亨廷顿氏病（HD）是一种毁灭性的致命神经退行性疾病，由HD基因中多态CAG重复扩增引起，该重复扩增对纹状体和皮层中的神经元具有特异性，可触发细胞死亡。尽管这种潜在的基因突变在15年前就被发现了，但尽管人们努力了解导致神经变性的分子途径，但仍然没有治愈或有效的治疗方法。近年来，HD CAG重复突变经历了显著的组织特异性体细胞扩增，特别是在受该疾病影响的大脑区域。这提出了靶组织中体细胞HD CAG长度增加有助于HD发病的假设。在过去的资助周期中，我们在HD的精确遗传Hdh CAG敲入小鼠模型和HD个体的死后大脑中获得的数据都有力地支持了这一假设，这意味着改变体细胞不稳定性的因素也可能是疾病的修饰因素。在此，我们提出了进一步阐明a)体细胞不稳定性和HD发病机制的因素，以及b)体细胞不稳定性与疾病表型的关系的实验。在Aim 1中，我们将识别和表征两种近交遗传背景下的先天性Hdh CAG敲入小鼠品系之间的体细胞不稳定性差异和早期表型差异的遗传变异。在目标2中，我们将把Hdh CAG敲入小鼠与小鼠背景（Msh3-/-）杂交，该背景没有表现出体细胞不稳定性，并确定对行为表型和晚期病理的影响。在Aim 3中，我们将量化大量HD死后大脑的体细胞不稳定性，并对HD患者体细胞不稳定性的修饰因子进行全基因组关联研究。我们还将研究来自HD患者的诱导多能干细胞（iPS）衍生的神经元的不稳定性，目的是建立不稳定性的细胞培养模型，作为筛选人类不稳定性修饰因子的替代方法。总之，这些研究将有助于深入了解促成体细胞不稳定和HD致病过程的因素。这将基于攻击DNA突变本身的策略，为HD和其他三核苷酸重复疾病带来新的治疗靶点。

DESCRIPTION (provided by applicant): Huntington's disease (HD) is a devastating fatal neurodegenerative disorder caused by the expansion of a polymorphic CAG repeat in the HD gene that triggers cell death with a specificity towards neurons in the striatum and cortex. Although the underlying genetic mutation was discovered over 15 years ago, there is still no cure or effective treatment despite extensive efforts to understand the molecular pathways that lead to neurodegeneration. In recent years it has become apparent that the HD CAG repeat mutation undergoes dramatic tissue-specific somatic expansion, particularly in the brain regions affected in the disorder. This raises the hypothesis that somatic HD CAG length increases in target tissues contribute to HD pathogenesis. Data that we have generated during the past funding cycle both in accurate genetic Hdh CAG knock-in mouse models of HD and in postmortem brain from HD individuals strongly support this hypothesis, implying that factors that modify somatic instability may also be modifiers of disease. Here we propose experiments to elucidate further a) the factors that contribute to somatic instability and HD pathogenesis, and b) the relationship of somatic instability to disease phenotypes. In Aim 1 we will identify and characterize the genetic variants that underlie the difference in somatic instability and the difference in an early phenotype between congenic Hdh CAG knock-in mouse strains on two inbred genetic backgrounds. In Aim 2 we will cross Hdh CAG knock-in mice onto a mouse background (Msh3-/-) that displays no somatic instability and determine the effect on behavioral phenotypes and late-stage pathology. In Aim 3 we will quantify somatic instability in a large collection of HD postmortem brains and perform a genome-wide association study for modifiers of somatic instability in HD patients. We will also investigate instability in neurons derived from induced pluripotent stem (iPS) cells from HD patients with the aim of generating a cell culture model of instability as an alternative to screen for modifiers of instability in humans. Together, these studies will provide insight into the factors that contribute to somatic instability and the HD pathogenic process. This will lead to novel therapeutic targets both for HD and other trinucleotide repeat diseases based upon a strategy of attacking the DNA mutation itself. PUBLIC HEALTH RELEVANCE: Huntington's disease is a devastating, fatal neurodegenerative disorder for which there is no cure or effective treatment. The combination of emotional, cognitive and motor symptoms, leading to long-term care needs results in an extremely high healthcare cost, estimated at 25 billion dollars a year. This study is aimed at identifying early modifiers of disease with the potential of discovering novel targets for early therapeutic intervention.