低氧适应的分子机制初探
文献类型：学位论文
| 作者 | 李越 |
| 学位类别 | 硕士 |
| 答辩日期 | 2014 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 孔庆鹏 |
| 关键词 | 缺氧 适应 藏族 高原 肿瘤细胞 糖酵解 |
| 中文摘要 | 光合作用的演化以及地球上大气中氧化反应的发生大概是生命史上最为重要的转折。氧气参与着呼吸功能，使呼吸产能更加高效。然而人类却无时无刻不在面对着各种程度的低氧挑战，如世居高原的藏族和安第斯人以及普遍有糖酵解上调现象的肿瘤微环境。他们的相似之处在于都受到自然选择的驱动力，展现出了对环境/微环境的适应性表型，这也使他们成为了研究低氧适应机制的良好模型。本文主要就藏族和乳腺癌细胞对低氧适应（尤其是能量代谢适应）的分子机制进行了探讨。当低海拔人群到达高海拔，其线粒体含量降低。然而，世居高海拔人群的线粒体DNA含量是否也有着类似的特征还不得而知。同时线粒体DNA含量的变化伴随着血液中的哪些物质变化也值得探究。因此我们选取了241例高海拔世居藏族人群以及220例低海拔陕西汉族群体以检测其线粒体DNA含量以及相应的相关血液指标。结果显示藏族的相对线粒体DNA拷贝数显著低于低海拔陕西汉族，同时年龄、性别、血糖、甘油三酯以及总胆固醇都与线粒体DNA含量无关，但二氧化碳结合力显示出与线粒体DNA拷贝数显著的负相关。这些结果提示二氧化碳结合力增加与低线粒体DNA拷贝数可能为高原人群适应机制提供了潜力。此外，高原藏族呼吸的氧含量较低，动脉血含量较少，但其能量代谢阈值并为显著降低，这暗示藏族对于高海拔的适应可能伴随着能量代谢途径的特殊适应机制。在藏族人群低氧的生理环境下可能作为能量生产补充途径的糖酵解成为我们的关注点。我们对丙酮酸和乳酸间相互转换的关键酶——乳酸脱氢酶LDH的两个亚基的编码基因启动子区域进行了检测，结果发现LDHA启动子区并未显示出强烈的受选择趋势，而LDHB启动子区有两个多态性位点在藏族群体中显示出了较高的频率，其中LDHB-3041G>R突变被证明可以增强启动子效率。我们推测这种现象可能导致体内乳酸积累减少，从而降低糖酵解的负效应，体现了藏族人群对低氧环境的适应能力。最后我们还检测了LDHB-3041G>R突变在三阴乳腺癌中的频率，发现在三阴乳腺癌中此突变频率显著高于健康汉族、食管癌患者、良性乳腺肿瘤患者以及非三阴乳腺癌患者，暗示LDHB在三阴乳腺癌中表达增加，与前期研究结果相一致，并且含有LDHB-3041G>R突变的患者总体治疗效果较差。由于LDHB-3041G>R附近可能为c-Myc的调控区域，因此LDHB在三阴乳腺癌中的过表达可能受到c-Myc的直接调控。另外我们的结果可能为反向Warburg效应提供了证据，三阴乳腺癌癌细胞可能将周围基质糖酵解产生的乳酸转化为丙酮酸并将此作为能量原料。本研究揭示了三阴乳腺癌独特的能量适应机制，并为未来三阴乳腺癌的诊断和治疗提供了新的靶标。总的来说，我们发现无论是藏族群体还是癌症细胞，其对于低氧的适应机制比想象中更为复杂，其在面对低氧环境时并非单纯利用糖酵解补充产能，而是伴随着其他适应机制以抵抗糖酵解的负效应。 |
| 英文摘要 | The evolution of oxygenic photosynthesis and ensuing oxygenation of Earth’s atmosphere is probably the most important transition in the history of life. Oxygen participates in the respiratory function, making it more highly exergonic. However, human beings are facing different levels of hypoxic challenges constantly, like Tibetans and Andeans who have inhabited in high altitude long time ago and cancer cells growing in a microenvironment where glycolysis is universally upregulated. They are analogous to each other since they have both developed adaptive phenotypes to hypoxic environment/microenvironment resulted from the selective force, which makes them perfect models to study the mechanisms for adapting to hypoxia. In this paper, we mainly focus on the molecular mechanisms of hypoxia adaptation, especially metabolism adaptation. When lowlanders arrive at high altitude, the mitochondrial content tends to decrease. However, whether the mtDNA content of native highlanders share the same feature as lowlanders remains unknown. It is also interesting to dissect what other changes in blood plasma might accompany the change of mtDNA content. To address these issues, we recruited 241 Tibetan subjects in Tibet and 220 Han subjects in Shaanxi province. Relative mtDNA copy number and blood biochemical indexes were measured. Results show that relative mtDNA copy number in Tibetans is significantly lower as compared to Han subjects; sex, age, blood glucose, triglyceride and total cholesterol show no influence on mtDNA content, but carbon dioxide combining power is negatively correlated with mtDNA content. These results indicate that an increase in CO2 combining power along with lower mtDNA content may provide adaptive potential. Besides, Tibetans’ inspired air contains less oxygen, resulting in less oxygen in arterial blood. However, their basal metabolic rate does not lowered significantly, suggesting their unique adaptation mechanism to hypoxic metabolism. Glycolysis, a potential pathway that could compensate for energy production, got our attention. We examined the promoters of two genes encoding the subunits of LDH, a key enzyme who can reversibly convert pyruvate to lactate. We did not find a selective trend in LDHA promoter, but we did find two SNPs in LDHB promoter showing significantly high frequency in Tibetans, among which, LDHB-3041G>R was proved to enhance the promoter’s activity. This finding may reveal a mechanism to reduce the lactate accumulation and counteract the negative effect of glycolysis, which could be an adaptive potential for Tibetans. Finally we determined the frequency of this mutation in triple-negative breast cancer (TNBC). The results suggested that the frequency of LDHB-3041G>R in TNBC was significantly higher than healthy controls, esophagus cancer, benign breast tumor and non-TNBC breast cancer patients. Our result is in accordance with previous studies, which shows LDHB was specifically overexpressed in TNBC. Furthermore, patients with this mutation often show poor prognosis. The region around LDHB-3041G>R was suggested to be directly regulated by c-Myc, so LDHB overexpression in TNBC could be directly regulated by the c-Myc pathway. Our results could offer new evidence to support the “reverse Warburg effect”, which suggest that tumor cells that are hypoxic and glucose-deprived can use lactate that was derived from aerobic glycolysis from surrounding stromal or tumor cells. Our study revealed a unique metabolic adaptation mechanism and a new target for diagnosis and treatment of triple-negative breast cancer. Over all, we find that both Tibetans and cancer cells have more complicated adaptive mechanism than expected. They can not only use glycolysis as a compensatory pathway to produce energy, but also other adaptive pathways to counteract the side effect of glycolysis. |
| 语种 | 中文 |
| 源URL | [http://159.226.149.26:8080/handle/152453/10085]  |
| 专题 | 昆明动物研究所_分子人类学 |
| 作者单位 | 中国科学院昆明动物研究所 |
| 推荐引用方式 GB/T 7714 | 李越. 低氧适应的分子机制初探[D]. 北京. 中国科学院研究生院. 2014. |
入库方式： OAI收割
来源：昆明动物研究所
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