Huntington's Disease Repeat Instability and Pathogenesis

描述（由申请人提供）：亨廷顿病（HD）是一种致命的神经退行性疾病，由多态性CAG重复序列扩增超过约36个单位的阈值引起。扩增的CAG重复序列被翻译成亨廷顿蛋白氨基末端的多聚谷氨酰胺片段，引发纹状体和皮质中神经元亚群的细胞死亡。扩增的CAG重复序列在生殖系和体细胞组织中也表现出显著的不稳定性。这项研究的长期目标是阐明HD CAG重复序列不稳定性和突变亨廷顿蛋白引发的特异性神经变性的分子途径。在HD基因敲入小鼠中，其准确地再现了人类HD突变，Msh 2基因是重复不稳定性和早期纹状体表型的修饰物。在这项研究中，我们将测试的假设，Msh 2的行为在错配修复途径，以修改CAG重复不稳定性和早期表型在HD敲入小鼠。我们将用缺乏特定错配修复基因的小鼠和携带Msh 2 ATP酶结构域突变的小鼠系进行遗传杂交。这些实验将提供Msh 2在CAG重复不稳定性和突变型HD等位基因表型表达中的作用的机制性见解。为了确定候选DNA修复基因是否是人类HD发病年龄的修饰因子，将使用发病年龄偏离CAG重复序列预测值的“极端”个体进行遗传关联研究。为了进一步了解Msh 2修饰小鼠重复不稳定性和早期纹状体疾病的机制，我们将使用Cre-loxP系统产生Msh 2基因的条件性敲除。我们将使用Camklla驱动的Cre转基因在前脑神经元中特异性地抑制Msh 2，以测试Msh 2在纹状体神经元中起作用以改变不稳定性和早期表型的假设。总之，这些研究将深入了解重复不稳定性和发病机制，从而制定合理的治疗策略，旨在减缓或阻止这种毁灭性疾病。

DESCRIPTION (provided by applicant): Huntington's disease (HD) is a fatal neurodegenerative disorder caused by the expansion of a polymorphic CAG repeat tract beyond a threshold of ~ 36 units. The expanded CAG repeat is translated into a polyglutamine stretch at the amino-terminus of the huntingtin protein, triggering cell death in a subset of neurons in the striatum and cortex. The expanded CAG repeat also exhibits dramatic instability in the germline and in somatic tissues. The long-term goals of this research are to elucidate the molecular pathways that underlie the instability of the HD CAG repeat and the specific neurodegeneration triggered by mutant huntingtin. In HD knock-in mice, which accurately recapitulate the human HD mutation, the Msh2 gene is a modifier of repeat instability and an early striatal phenotype. In this study, we will test the hypothesis that Msh2 acts in the mismatch repair pathway to modify CAG repeat instability and early phenotypes in HD knock-in mice. We will perform genetic crosses with mice deficient in specific mismatch repair genes and mouse line carrying a mutation in Msh2's ATPase domain. These experiments will provide mechanistic insight into Msh2's role in CAG repeat instability and phenotypic expression of the mutant HD allele. To determine whether candidate DNA repair genes are modifiers of the age of onset of HD in humans genetic association studies will be performed using 'extreme' individuals with onset ages deviating from values predicted by CAG repeat size. To gain further insight into the mechanism by which Msh2 modifies repeat instability and early striatal disease in the mouse we will generate a conditional knockout of the Msh2 gene using the Cre-loxP system. We will specifically inactivate Msh2 in forebrain neurons using a Camklla-driven Cre transgene to test the hypothesis that Msh2 acts in striatal neurons to modify instability and early phenotypes. Together, these studies will provide insight into mechanisms of repeat instability and pathogenesis, leading to rational therapeutic strategies aimed at slowing or halting this devastating disease.