Investigating the role of dysfunctional histone H3.3 in driving early neuronal development and pediatric high-grade gliomas

摘要说明/摘要 儿童脑瘤是儿童最常见的实体肿瘤，约有5000例新病例 在美国每年确诊一次。在0-14岁的儿童中，大约17%的脑瘤是高级别的 胶质瘤(HGG)，目前是无法治愈的。缺乏有效的治疗方法突显出迫切需要 确定基于机制的治疗方法。大量的实验证据最近揭示了 携带H3.3-G34R的儿科HGGs(PHGGs)具有高基因组不稳定性和高水平表达 神经标志物的表达，表明这些肿瘤与其他肿瘤相比，代表了PHGG的一个不同的亚型 类型，包括H3.3-K27M突变的一例。超过90%的H3.3-G34R胶质瘤还存在ATRX 功能丧失突变。使用一种新建立的基因工程小鼠模型(GEMM)，我们 发现H3.3-G34R突变和ATRX缺失在癌前神经干细胞(PM-NSCs) TrP53-/-背景可强烈促进胶质瘤的形成。这些肿瘤表现出典型的人类特征。 H3.3-G34R-含有PHGGs，为我们研究分子提供了一个可靠的工具 H3.3-G34R突变和ATRX缺失协同作用的机制及鉴定 新的治疗靶点。我们发现H3.3-G34R突变改变了组蛋白的局部修饰 并导致早期神经元必需的转录因子FoxD1和HoxA1的高表达 发展。鉴于FoxD1和HoxA1的丰富与脑胶质瘤的预后不良相关 患者，他们为PHGGs提供了两个新的治疗靶点。此外，我们还发现ATRX缺失会导致ALT 激活，使肿瘤细胞对其线粒体功能的扰动敏感。在此基础上 观察到，我们假设由H3.3-G34R突变和ATRX丢失引起的独特的表观遗传学特征 导致胶质瘤形成，并导致涉及端粒功能障碍和受损的靶向易损性 线粒体活性。为了验证这一假设，我们计划1)确定FoxD1和HoxA1在H3.3中的作用- G34R驱动的胶质瘤发生，2)定义PHGGs中ATRX缺乏引起的治疗脆弱性，以及 3)阐明H3.3-G34R突变和ATRX缺失对小鼠表观遗传重编程的协同作用 神经胶质瘤。拟议研究的完成不仅将填补我们对H3.3-G34R如何 而ATRX的缺失改变了表观基因组，导致正常的神经元发育和胶质瘤形成，但也- 更重要的是-有助于开发针对PHGGs的治疗策略并提供 对表观遗传调控在脑发育和胶质瘤形成中的作用的洞察。

Summary Statement/Abstract Pediatric brain tumors are the most common solid tumors in children, with approximately 5000 new cases diagnosed per year in the United States. Around 17% of brain tumors in children age 0–14 years are high-grade gliomas (HGGs), which are currently incurable. The lack of effective treatments highlights the urgent need to identify mechanism-based therapeutic approaches. Substantial experimental evidence has recently revealed that H3.3-G34R–harboring pediatric HGGs (pHGGs) exhibit high genomic instability and high-level expression of neuronal markers, indicating that these tumors represent a distinct subtype of pHGG compared with other types, including the one with an H3.3-K27M mutation. More than 90% of H3.3-G34R gliomas also harbor ATRX loss-of-function mutations. Using a newly established genetically engineered murine model (GEMM), we demonstrated that H3.3-G34R mutation and ATRX deletion in premalignant neural stem cells (PM-NSCs) with the Trp53-/- background could strongly promote gliomagenesis. These tumors exhibit typical features of human H3.3-G34R–harboring pHGGs, so this GEMM provides us with a faithful tool for studying the molecular mechanisms underlying the synergistic effects of H3.3-G34R mutation and ATRX deletion and for identifying novel therapeutic targets. We have found that H3.3-G34R mutation changes histone modifications both locally and globally and leads to high expression of FoxD1 and HoxA1, transcription factors essential for early neuronal development. Given that enrichments of FoxD1 and HoxA1 are associated with worse prognosis in glioma patients, they provide 2 novel therapeutic targets for pHGGs. In addition, we found that ATRX loss leads to ALT activation, which makes tumor cells sensitive to perturbation of their mitochondrial function. On the basis of these observations, we hypothesize that distinctive epigenetic profiles induced by H3.3-G34R mutation and ATRX loss drive gliomagenesis and lead to targetable vulnerabilities involving dysfunctional telomeres and impaired mitochondrial activity. To test this hypothesis, we plan to 1) determine the roles of FoxD1 and HoxA1 in H3.3- G34R–driven gliomagenesis, 2) define the therapeutic vulnerability induced by ATRX deficiency in pHGGs, and 3) elucidate the synergistic effect of H3.3-G34R mutation and ATRX loss on epigenetic reprogramming in gliomas. The completion of the proposed studies will not only fill the gaps in our knowledge of how H3.3-G34R and ATRX loss change the epigenome to lead to normal neuronal development and gliomagenesis, but also— and more importantly—contribute to the development of therapeutic strategies that target pHGGs and provide insights into the role of epigenetic regulation in brain development and gliomagenesis.