衰老细胞中关键代谢激酶PDK4的上调机制、病理意义及微环境中衰老细胞的靶向清除研究

Cellular senescence represents a passive status characterized by structural damages and functional deficiency caused by interior and/or exterior stimulating insults. Although cellular senescence is frequently correlated with tissue dysfunction and organ degeneration, the detailed mechanisms remain unclear. Our preliminary data indicated that anticancer agents used in clinics not only induce substantial apoptosis of malignant cells in the tumor foci, but also cause significant structual changes including DNA damage to stromal cells in the tumor microenvironment, thus triggering typical cellular senescence in vivo. Accompanying the development of a senescence-associated secretory phenotype (SASP), expression of the pyruvate dehydrogenase kinase 4 (PDK4) is markedly upregulated. PDK4 prevents pyruvate, the early product of glucose catabolism, from being metabolized in the mitochondria via oxidative phosphorylation (the Krebs cycle or TCA cycle), while allowing pyruvate to be converted to lactate in the cytoplasm by lactate dehydrogenase A (LDHA). Long term accumulation of lactate in the tissue may generate an acidic microenvironment, which holds the potential to enhance tissue dysfunction and drive organ degeneration. Meanwhile, senescent cells overexpress prostaglandin G/H synthase 2 (PTGS2), a bifunctional enzyme that can suppress cell apoptosis and promote cell survival. In this project, we propose to focus on the expression mechanism of key molecules associated with the regulation of metabolic pathways of senescent cells, and to address the biological implications of cellular senescence in the microenvironment. We also want to explore the technical strategy and realistic feasibility of selectively targeting senescent cells to postpone tissue dysfunction and organ degeneration. This project will provide an important baseline for elucidation of critical topics in current biomedicine including metabolic reprogramming of senescent cells and its pathophysiological impact on tissue homeostasis. Our study will also present critical clues for the establishment of novel therapeutic strategies that aim to effectively prevent and cure aging-associated disorders in future clinical practice.

细胞衰老是细胞在内外刺激作用下发生结构损伤和功能紊乱而进入的一种被动状态，同组织失调及器官退行密切关联，但具体机制并不清晰。我们前期发现临床抗癌药物不仅引起患者体内癌细胞大量凋亡，更造成微环境中基质细胞DNA损伤等深刻改变并导致细胞胁迫性衰老。伴随衰老相关分泌表型(SASP)出现的，是丙酮酸脱氢酶激酶4（PDK4）等蛋白的高度上调。PDK4阻抑丙酮酸在线粒体中经TCA循环的氧化磷酸化，促使丙酮酸在胞质中生成乳酸并形成酸性微环境，后者具有促进组织功能紊乱和器官退行的潜力。此外，衰老细胞上调表达前列腺素合成酶2（PTGS2），后者具有抑制细胞凋亡的活性。我们聚焦衰老细胞代谢通路相关分子的表达机制并阐明其生物学效应，探索通过特异性靶向衰老细胞从而延缓组织失调和器官退行的可行性。本项目将解析细胞衰老过程中关键代谢通路重编程等核心生物医学问题，为将来建立衰老相关疾病的临床防治策略提供重要依据。

细胞衰老是细胞周期阻滞的一种永久状态，发生在各种胁迫下的增殖细胞中。虽然衰老细胞仍然具有代谢活性，但我们对其代谢景观和体内病理生理学意义知之甚少。我们发现，丙酮酸脱氢酶（PDH）抑制剂，丙酮酸脱氢酶激酶4（PDK4）在人类衰老的基质细胞中表达显著上调。PDK4倾向于在基因毒诱导性衰老细胞中表达，与癌症患者治疗后生存呈负相关。在细胞衰老时，PDK4将葡萄糖代谢通量从氧化磷酸化（OXPHOS）转变为有氧糖酵解，导致乳酸产量增加，形成酸性微环境。然而，与以癌细胞为特征的“华堡效应”不同的是，衰老细胞通过三羧酸循环（TCA）维持了对丙酮酸的密集使用，显示出呼吸和氧化还原活性的增加，这表明了一种特殊形式的代谢重编程。来自PDK4基质细胞条件培养基在体外改变了整体表达，促进了受体癌细胞的恶性程度，并在体内加速了肿瘤进展。然而，在细胞检测中，特异性靶向PDK4减少了衰老细胞的不良影响，同时在临床前试验中促进肿瘤消退和延长治疗后生存期。值得注意的是，化疗后循环血液中乳酸水平上升预示着癌症患者较差生存率。因此，PDK4的上调和随后的乳酸产生是衰老的关键特征之一，而这项研究为未来的临床肿瘤学提供了一个新的治疗靶点。总之，我们的研究证实了衰老细胞的高分解代谢能力，并揭示了与衰老相关的酸性微环境和与年龄相关的病理之间的代谢联系，包括但不限于各种癌症。