Lee Eunhye, Kim Wonju, Beier David H, Lee Yejin, Kovalenko Marina, Saif Faaiza, Oliver Esaria, Murtha Ryan, Andrew Marissa A, Gillis Tammy, Demelo Brigitte, Srinageshwar Bhairavi, Ruliera Jayla, Lucente Diane, Kwak Seung, Lee Ramee, Pinto Ricardo Mouro, MacDonald Marcy E, Gusella James F, O'Brien Patrick J, Wheeler Vanessa C, Seong Ihn Sik
Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA.
Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
bioRxiv. 2025 Jul 18:2025.07.15.664798. doi: 10.1101/2025.07.15.664798.
Huntington's disease (HD) is a fatal neurodegenerative disorder caused by inheriting an expanded CAG repeat tract in the huntingtin gene () that further expands in somatic cells over an individual's lifetime. Genome-wide association studies have provided critical insight into factors that modify the course of disease. These include DNA repair genes that alter the rate of somatic expansion and other genes that do not appear to directly influence this process. One modifier gene is DNA ligase 1 (), in which a variant specifying a lysine to asparagine substitution (K845N) is associated with a profound (7-8 year) delay in the onset of motor signs. Here, we have taken a multifaceted approach to gain insight into the protective nature of this variant in HD. We demonstrate using ligase assays and enzyme kinetics that K845N enhances discrimination towards mismatched substrates and increases repair fidelity. Consistent with increased ligation fidelity, K845N confers protection against oxidative stress in cell-based assays. Finally, we demonstrate that the mouse LIG1 K843N orthologue suppresses somatic CAG expansion in HD knock-in mice. Overall, our data provide evidence that altered LIG1 function due to the K845N substitution may contribute to HD clinical delay by slowing somatic expansion in the brain and protecting the genome globally against damage. Significantly, our results provide a mechanistic foundation for considering DNA ligase fidelity as a therapeutic target in HD and potentially in other trinucleotide repeat disorders.
亨廷顿舞蹈症(HD)是一种致命的神经退行性疾病,由亨廷顿基因()中继承的一段CAG重复序列扩增引起,该序列在个体一生中会在体细胞中进一步扩增。全基因组关联研究为了解影响疾病进程的因素提供了关键见解。这些因素包括改变体细胞扩增速率的DNA修复基因以及其他似乎不直接影响这一过程的基因。其中一个修饰基因是DNA连接酶1(),其一个指定赖氨酸突变为天冬酰胺的变体(K845N)与运动症状发作的显著延迟(7 - 8年)相关。在此,我们采用了多方面的方法来深入了解该变体在HD中的保护性质。我们通过连接酶测定和酶动力学证明,K845N增强了对错配底物的识别能力并提高了修复保真度。与连接保真度的提高一致,在基于细胞的测定中,K845N赋予了对氧化应激的保护作用。最后,我们证明小鼠LIG1 K843N同源物可抑制HD基因敲入小鼠中的体细胞CAG扩增。总体而言,我们的数据表明,由于K845N替代导致的LIG1功能改变可能通过减缓大脑中的体细胞扩增并在整体上保护基因组免受损伤,从而导致HD临床症状延迟。重要的是,我们的结果为将DNA连接酶保真度作为HD以及潜在的其他三核苷酸重复疾病的治疗靶点提供了机制基础。