Origins of DNA damage driving pathology in human neurodegeneration

编码共济失调-毛细血管扩张突变(ATM)基因的两个等位基因丢失或突变 在人类中，激酶会导致早发性小脑性共济失调和进行性神经变性。 这种表型的机制解释，以及相关的A-T样障碍(ATLD) 由Mre11基因罕见突变引起的，尽管多年来一直在研究，但一直难以捉摸 酵素。ATM是DNA损伤反应的主要调节器，控制着检查点 DNA损伤在所有细胞类型中的反应和存活率。我们之前已经将 ATM蛋白激酶在体外，使用纯化的蛋白来确定ATM在 DNA双链断裂，也可以独立于氧化断裂而被激活 压力。在最近的工作中，我们发现ATM激酶活性的丧失会导致 蛋白质聚集体.富含多肽的不溶于洗涤剂的蛋白质 具有本质上无序的结构域。这些聚集体是对超激活的反应形成的 多聚-ADP-核糖聚合酶(PARP)，在转录应激位点被激活。 对21例患者小脑组织样本的分析也显示出大量的聚集体 与对照组相比，也出现了过度PAR化，这与这些观察结果一致。基座 根据这一证据，我们认为蛋白质聚集可能在 与其他形式的小脑性共济失调类似，出现在这种疾病中的神经退行性变 更常见的迟发性神经变性在人类人群中。在此，我们建议 描述在缺乏ATM功能的情况下发生的单链DNA断裂的来源 检验氧化应激和转录依赖的联合作用的假设 损伤是造成链断裂和所观察到的蛋白质聚集体的原因。 伴随着人类神经元ATM的丢失。我们还将确定位置和要求 在表达Mre11的ATLD等位基因的神经元中发现链断裂，并检验这一假设 Mre11-Rad50-Nbs1(MRN)复合体促进单链断裂修复的体外研究 纯化蛋白质的生物化学。这些实验将检验关于 ATM和MRN在神经元中的作用及小脑DNA损伤的起源 神经退行性变。

Loss or mutations in both alleles of the gene encoding ataxia-telangiectasia mutated (ATM) kinase results in early-onset cerebellar ataxia and progressive neurodegeneration in humans. Mechanistic explanations for this phenotype, as well as for the related A-T like Disorder (ATLD) caused by rare mutations in the MRE11 gene, have been elusive despite years of work on these enzymes. ATM is a master regulator of the DNA damage response, controlling checkpoint responses and survival of DNA damage in all cell types. We have previously characterized the ATM protein kinase in vitro, using purified proteins to determine that ATM is activated at sites of DNA double-strand breaks and can also be activated independently of breaks by oxidative stress. In recent work we found that loss of ATM kinase activity results in the formation of protein aggregates—detergent-resistant insoluble forms of proteins—enriched for polypeptides with intrinsically disordered domains. These aggregates form in response to hyperactivation of poly-ADP-ribose polymerases (PARPs) that are activated at sites of transcriptional stress. Analysis of 21 patient cerebellum tissue samples also showed massive levels of aggregates as well as hyperPARylation in comparison to controls, consistent with these observations. Based on this evidence we propose that protein aggregation may play a causal role in the neurodegeneration that occurs in this disorder, similar to other forms of cerebellar ataxia and to more common late-onset neurodegeneration in the human population. Here we propose to characterize the origin of single-strand DNA breaks that occur in the absence of ATM function to test the hypothesis that the combined effects of oxidative stress and transcription-dependent damage is responsible for the strand breaks and resulting protein aggregates that are observed with loss of ATM in human neurons. We will also characterize the locations and requirements for strand breaks seen in neurons expressing ATLD alleles of MRE11 and test the hypothesis that the Mre11-Rad50-Nbs1 (MRN) complex promotes single-strand break repair using in vitro biochemistry with purified proteins. These experiments will test novel hypotheses about the functions of ATM and MRN in neurons and the origins of DNA damage during cerebellar neurodegeneration.