涉及烟酰胺腺嘌呤二核苷酸 (NAD) 的酶活性的复杂编排对于维持代谢稳态和保持基因组完整性至关重要。作为一种辅酶，NAD 在调节代谢途径（如糖酵解和克雷布循环）中发挥着关键作用。 ADP-核糖基转移酶 (PARP) 和 Sirtuins 依赖 NAD 介导靶蛋白的翻译后修饰。 DNA 断裂后 PARP1 的激活会导致细胞 NAD 快速耗尽，从而损害细胞活力。因此，必须严格控制NAD的水平。在这里，我们证明外源性 NAD（而不是其前体）对线粒体活性有直接影响。与 NAD 短期孵育可促进克雷布循环和电子传递链，并增强嘧啶生物合成。延长与 NAD 的孵育会导致嘧啶耗尽、嘌呤积累、复制应激反应激活和细胞周期停滞。此外，NAD 和 5-氟尿苷的组合可以选择性地杀死依赖从头合成嘧啶的癌细胞。我们提出了一个 NAD 如何调节核苷酸代谢的综合模型，该模型与健康寿命、衰老和癌症治疗相关。© 2023。作者。

The intricate orchestration of enzymatic activities involving nicotinamide adenine dinucleotide (NAD+) is essential for maintaining metabolic homeostasis and preserving genomic integrity. As a co-enzyme, NAD+ plays a key role in regulating metabolic pathways, such as glycolysis and Kreb's cycle. ADP-ribosyltransferases (PARPs) and sirtuins rely on NAD+ to mediate post-translational modifications of target proteins. The activation of PARP1 in response to DNA breaks leads to rapid depletion of cellular NAD+ compromising cell viability. Therefore, the levels of NAD+ must be tightly regulated. Here we show that exogenous NAD+, but not its precursors, has a direct effect on mitochondrial activity. Short-term incubation with NAD+ boosts Kreb's cycle and the electron transport chain and enhances pyrimidine biosynthesis. Extended incubation with NAD+ results in depletion of pyrimidines, accumulation of purines, activation of the replication stress response and cell cycle arrest. Moreover, a combination of NAD+ and 5-fluorouridine selectively kills cancer cells that rely on de novo pyrimidine synthesis. We propose an integrated model of how NAD+ regulates nucleotide metabolism, with relevance to healthspan, ageing and cancer therapy.© 2023. The Author(s).