The Arthur and Sonia Labatt Brain Tumor Research Centre, Hospital for Sick Children Research Institute, University of Toronto, Toronto, 11-401E, 101 College Street, East Tower, Ontario, Canada, M5G 1L7.
Neurobiol Dis. 2011 Oct;44(1):84-91. doi: 10.1016/j.nbd.2011.06.007. Epub 2011 Jun 25.
Highly proliferating cells, normal or transformed, undergo aerobic glycolysis whereby glucose is metabolized to lactate rather than by oxidative metabolism, even in the presence of oxygen. This metabolic adaptation provides a survival advantage and facilitates synthesis of biosynthetic precursors required for continued cellular proliferation. An important mediator of aerobic glycolysis is our demonstration that in malignant gliomas there is over-expression of the glycolytic enzyme hexokinase 2 (HK2), phosphorylating glucose as the first step of the glycolytic pathway. In contrast, normal brain preferentially expresses HK1 and undergoes oxidative glucose metabolism. In this study, we examine whether this switch in HK isoform also occurs in the developing embryo and central nervous system (CNS). Bioinformatic analysis of available microarray data, including that of The Cancer Genome Atlas, demonstrated a ~17% overlap in metabolic-related genes in blastocyst stage embryo and human GBM tissue, including upregulation of HK2 and downregulation of HK1. Quantitative RT-PCR on mouse brains isolated at different embryonic and postnatal development time-points demonstrated HK2 expression was highest in the early embryo, while HK1 expression increased with CNS maturation. The downstream glycolytic enzymes PKM2 and LDHA had similar temporal profiles as HK2. Expression of the HK2 isoform was due in part to epigenetic regulation of HK2. In support, adult normal human brain and the few human GBM cell lines with low HK2 expression had methylation of CpG islands within intron 1 of HK2. In contrast, developing human fetal brain and GBM tissue expressing HK2 demonstrated significantly lower percent methylation. Furthermore, treatment of GBM cells lacking HK2 with 5-aza-2-deoxycytidine restored HK2 transcript expression. Overall, our results demonstrate that proliferative states including the developing embryo and malignant gliomas, which rely on aerobic glycolysis, preferentially express the HK2 isoform, found to be regulated in part epigenetically.
高度增殖的细胞，无论是正常的还是转化的，都会经历有氧糖酵解，即葡萄糖代谢为乳酸，而不是通过氧化代谢，即使在氧气存在的情况下也是如此。这种代谢适应为细胞增殖提供了生存优势，并促进了合成生物合成前体的合成，这些前体是持续细胞增殖所必需的。有氧糖酵解的一个重要介质是我们的证明，即在恶性神经胶质瘤中，糖酵解酶己糖激酶 2 (HK2) 的表达过度，将葡萄糖磷酸化为糖酵解途径的第一步。相比之下，正常大脑优先表达 HK1 并进行氧化葡萄糖代谢。在这项研究中，我们检查这种 HK 同工型的转换是否也发生在发育中的胚胎和中枢神经系统 (CNS) 中。对现有微阵列数据的生物信息学分析，包括癌症基因组图谱的数据，显示囊胚期胚胎和人类 GBM 组织中代谢相关基因的重叠约为 17%，包括 HK2 的上调和 HK1 的下调。对不同胚胎和产后发育时间点分离的小鼠大脑进行定量 RT-PCR 显示，HK2 表达在早期胚胎中最高，而随着中枢神经系统成熟，HK1 表达增加。下游糖酵解酶 PKM2 和 LDHA 的表达模式与 HK2 相似。HK2 同工型的表达部分归因于 HK2 的表观遗传调控。支持这一观点的是，成人正常人类大脑和少数 HK2 表达低的人类 GBM 细胞系中，HK2 内含子 1 内的 CpG 岛发生甲基化。相比之下，表达 HK2 的发育中的人类胎儿大脑和 GBM 组织表现出明显较低的甲基化百分比。此外，用 5-氮杂-2'-脱氧胞苷处理缺乏 HK2 的 GBM 细胞可恢复 HK2 转录本的表达。总的来说，我们的结果表明，包括胚胎发育和恶性神经胶质瘤在内的增殖状态，依赖于有氧糖酵解，优先表达 HK2 同工型，部分受表观遗传调控。
