Department of Neurosurgery, University of California in San Diego, La Jolla, CA, USA.
Department of Developmental Biology, Washington University School of Medicine, St Louis, MO, USA.
BMC Biol. 2022 May 30;20(1):124. doi: 10.1186/s12915-022-01324-0.
Neurodevelopmental disorders increase brain tumor risk, suggesting that normal brain development may have protective properties. Mutations in epigenetic regulators are common in pediatric brain tumors, highlighting a potentially central role for disrupted epigenetic regulation of normal brain development in tumorigenesis. For example, lysine 27 to methionine mutation (H3K27M) in the H3F3A gene occurs frequently in Diffuse Intrinsic Pontine Gliomas (DIPGs), the most aggressive pediatric glioma. As H3K27M mutation is necessary but insufficient to cause DIPGs, it is accompanied by additional mutations in tumors. However, how H3K27M alone increases vulnerability to DIPG tumorigenesis remains unclear.
Here, we used human embryonic stem cell models with this mutation, in the absence of other DIPG contributory mutations, to investigate how H3K27M alters cellular proliferation and differentiation. We found that H3K27M increased stem cell proliferation and stem cell properties. It interfered with differentiation, promoting anomalous mesodermal and ectodermal gene expression during both multi-lineage and germ layer-specific cell specification, and blocking normal differentiation into neuroectoderm. H3K27M mutant clones exhibited transcriptomic diversity relative to the more homogeneous wildtype population, suggesting reduced fidelity of gene regulation, with aberrant expression of genes involved in stem cell regulation, differentiation, and tumorigenesis. These phenomena were associated with global loss of H3K27me3 and concordant loss of DNA methylation at specific genes in H3K27M-expressing cells.
Together, these data suggest that H3K27M mutation disrupts normal differentiation, maintaining a partially differentiated state with elevated clonogenicity during early development. This disrupted response to early developmental cues could promote tissue properties that enable acquisition of additional mutations that cooperate with H3K27M mutation in genesis of DMG/DIPG. Therefore, this work demonstrates for the first time that H3K27M mutation confers vulnerability to gliomagenesis through persistent clonogenicity and aberrant differentiation and defines associated alterations of histone and DNA methylation.
神经发育障碍会增加脑瘤风险，这表明正常的大脑发育可能具有保护作用。表观遗传调控因子的突变在小儿脑瘤中很常见，这突显了正常大脑发育的表观遗传调控失调在肿瘤发生中的潜在核心作用。例如，H3F3A 基因中的赖氨酸 27 到蛋氨酸突变（H3K27M）在弥漫性内在脑桥胶质瘤（DIPG）中频繁发生，这是最具侵袭性的小儿神经胶质瘤。由于 H3K27M 突变是导致 DIPG 所必需的，但并不足以导致 DIPG，因此它伴随着肿瘤中的其他突变。然而，单独的 H3K27M 如何增加易患 DIPG 肿瘤发生的风险仍不清楚。
在这里，我们使用在没有其他 DIPG 促成突变的情况下具有这种突变的人类胚胎干细胞模型，研究了 H3K27M 如何改变细胞增殖和分化。我们发现，H3K27M 增加了干细胞的增殖和干细胞特性。它干扰了分化，在多谱系和胚层特异性细胞特化过程中促进异常中胚层和外胚层基因表达，并阻止正常向神经外胚层分化。与更同质的野生型群体相比，H3K27M 突变克隆表现出转录组多样性，这表明基因调控的保真度降低，与干细胞调控、分化和肿瘤发生相关的基因表达异常。这些现象与 H3K27M 表达细胞中特定基因的 H3K27me3 整体丢失和 DNA 甲基化的一致性丢失有关。
总之，这些数据表明，H3K27M 突变破坏了正常分化，在早期发育过程中维持具有高克隆形成能力的部分分化状态。这种对早期发育信号的破坏反应可能会促进组织特性的获得，从而获得与 H3K27M 突变协同作用的其他突变，从而促进 DMG/DIPG 的发生。因此，这项工作首次表明，H3K27M 突变通过持续的克隆形成能力和异常分化赋予致胶质瘤易感性，并定义了组蛋白和 DNA 甲基化的相关改变。
