Dissecting the role of DNA Ligase 1 in Huntington's disease

亨廷顿病(HD)是一种毁灭性和致命性的神经退行性疾病，由 HTT基因CAG重复序列的多态。尽管潜在的基因突变是在25岁以上被发现的 几年前，尽管进行了广泛的努力，但仍然没有治愈或有效的治疗方法。CAG重复突变 经历依赖时间和CAG长度的体细胞扩张和最近的全基因组关联研究 (Gwas)支持体细胞CAG扩增作为致病过程的第一步，需要诱导细胞 毒性，最终导致临床疾病。Gwas发现了几个参与DNA修复的基因作为 发病年龄，其中LIG1，编码DNA连接酶1。DNA连接酶1的生物学功能 然而，该基因也可能改变影响细胞毒性的过程。 总体而言，疾病改良的机制基础仍然模糊不清。独立LIG1修改器 在人类遗传数据中可以区分出染色体：其中一个由预测的有害SNP标记 编码一个K854N替换是起始延迟，而另一个编码与LIG1表达增加有关 而且正在加速发病。在这项研究中，我们将进行实验，以检验植根于人类基因的假说 数据以了解这些LIG1修饰符效果的功能后果。在目标1中，我们将使用敲击 为检测K&gt；N替代突变引入小鼠Lig1基因对HD小鼠模型的影响， 并测试Lig1上调对体细胞CAG扩增和表型表达的影响。在AIM 2 我们将使用HD患者来源的和同基因的神经祖细胞和含有LIG1修饰物的神经元 等位基因，以确定它们的细胞和分子后果，并测试它们对由 HTT突变。在目标3中，我们将对LIG1 K845N进行生化、结构和功能分析 变种。综上所述，这些实验将提供新的洞察机制，通过这些机制遗传变异 LIG1修饰患者的疾病，最终揭示了可以用于疾病的治疗途径- 修改治疗方法。

Huntington’s disease (HD) is a devastating and fatal neurodegenerative disorder caused by the expansion of a polymorphic CAG repeat in the HTT gene. Although the underlying genetic mutation was discovered over 25 years ago, there is still no cure or effective treatment despite extensive efforts. The CAG repeat mutation undergoes time- and CAG length-dependent somatic expansion and recent genome-wide association studies (GWAS) support somatic CAG expansion as the first step of the pathogenic process, required to elicit cellular toxicity and ultimately clinical disease. GWAS identified several genes involved in DNA repair as modifiers of age of onset, among which is LIG1, encoding DNA ligase 1. The biological function of DNA ligase 1 implicates it in somatic CAG expansion, however this gene may also alter processes that impact on cellular toxicity. Overall, the mechanistic underpinnings of disease modification remain obscure. Independent LIG1 modifier chromosomes can be distinguished in the human genetic data: one, tagged by a predicted deleterious SNP encoding a K854N substitution, is onset-delaying, while another is associated with increased LIG1 expression and is onset-hastening. In this study, we will perform experiments to test hypotheses rooted in human genetic data to understand the functional consequences of these LIG1 modifier effects. In Aim 1 we will use a knock-in mouse model of HD to test the impact of the K>N substitution mutation introduced into the mouse Lig1 gene, and to test the impact of Lig1 upregulation, on somatic CAG expansion and phenotypic expression. In Aim 2 we will use HD patient-derived and isogenic neuronal progenitor cells and neurons harboring LIG1 modifier alleles to identify their cellular and molecular consequences and to test their impacts on phenotypes elicited by the HTT mutation. In Aim 3 we will perform biochemical, structural and functional analyses of the LIG1 K845N variant. Together, these experiments will provide novel insight into mechanisms by which genetic variation in LIG1 modifies disease in patients, ultimately revealing therapeutic avenues that can be pursued for disease- modifying treatments.