Proliferating cells exhibit a metabolic phenotype known as “aerobic glycolysis,” which is characterized by an elevated rate of glucose fermentation to lactate irrespective of oxygen availability. Although several theories have been proposed, a rationalization for why proliferating cells seemingly waste glucose carbon by excreting it as lactate remains elusive. Using the NCI-60 cell lines, we determined that lactate excretion is strongly correlated with the activity of mitochondrial NADH shuttles, but not proliferation. Quantifying the fluxes of the malate-aspartate shuttle (MAS), the glycerol 3-phosphate shuttle (G3PS), and lactate dehydrogenase under various conditions demonstrated that proliferating cells primarily transform glucose to lactate when glycolysis outpaces the mitochondrial NADH shuttles. Increasing mitochondrial NADH shuttle fluxes decreased glucose fermentation but did not reduce the proliferation rate. Our results reveal that glucose fermentation, a hallmark of cancer, is a secondary consequence of MAS and G3PS saturation rather than a unique metabolic driver of cellular proliferation.

增殖细胞表现出一种称为“有氧糖酵解”的代谢表型，其特征是无论氧气供应情况如何，葡萄糖发酵成乳酸的速率都会升高。尽管已经提出了几种理论，但对于为什么增殖细胞似乎通过将葡萄糖碳以乳酸形式排出来浪费葡萄糖碳的合理化仍然难以捉摸。使用 NCI-60 细胞系，我们确定乳酸排泄与线粒体 NADH 穿梭的活性密切相关，但与增殖无关。对各种条件下苹果酸-天冬氨酸穿梭机 (MAS)、甘油 3-磷酸穿梭机 (G3PS) 和乳酸脱氢酶的通量进行定量表明，当糖酵解速度超过线粒体 NADH 穿梭机时，增殖细胞主要将葡萄糖转化为乳酸。增加线粒体 NADH 穿梭通量会减少葡萄糖发酵，但不会降低增殖率。我们的结果表明，作为癌症标志的葡萄糖发酵是 MAS 和 G3PS 饱和的次要结果，而不是细胞增殖的独特代谢驱动因素。