Ritterhoff Julia, McMillen Timothy, Foundas Hanna, Palkovacs Roland, Poschet Gernot, Caudal Arianne, Liu Yaxin, Most Patrick, Walker Matthew, Tian Rong
Department of Anesthesiology and Pain Medicine, Mitochondria and Metabolism Center, University of Washington, Seattle, Washington, United States.
Molecular and Translational Cardiology, Department of Internal Medicine III, University Hospital Heidelberg, Heidelberg, Germany.
Am J Physiol Cell Physiol. 2025 Jan 1;328(1):C168-C178. doi: 10.1152/ajpcell.00611.2023. Epub 2024 Nov 29.
The TCA cycle serves as a central hub to balance catabolic and anabolic needs of the cell, where carbon moieties can either contribute to oxidative metabolism or support biosynthetic reactions. This differential TCA cycle engagement for glucose-derived carbon has been extensively studied in cultured cells, but the fate of fatty acid (FA)-derived carbons is poorly understood. To fill the knowledge gap, we have developed a strategy to culture cells with long-chain FAs without altering cell viability. By tracing C-FA, we show that FA oxidation (FAO) is robust in both proliferating and oxidative cells while the metabolic pathway after citrate formation is distinct. In proliferating cells, a significant portion of carbon derived from FAO exits canonical TCA cycle as citrate and converts to unlabeled malate in cytosol. Increasing FA supply or β-oxidation does not change the partition of FA-derived carbon between cytosol and mitochondria. Oxidation of glucose competes with FA-derived carbon for the canonical TCA pathway thus promoting FA carbon flowing into the alternative TCA pathway. Moreover, the coupling between FAO and the canonical TCA pathway changes with the state of oxidative energy metabolism. By using C stable isotope-resolved metabolomics and FA-driven oxygen consumption rate analysis, our study provides novel insights into the fate of FA carbon through β-oxidation and downstream TCA cycle in proliferative and oxidative cells. Although both proliferative and oxidative cells demonstrate robust β-oxidation, they demonstrate distinct metabolic carbon fate downstream of citrate during TCA cycle oxidation. This differential TCA cycle engagement is likely to be important to balance catabolic and anabolic demands of the cell.
三羧酸循环作为一个核心枢纽，用于平衡细胞的分解代谢和合成代谢需求，其中碳部分既可以参与氧化代谢，也可以支持生物合成反应。在培养细胞中，已对源自葡萄糖的碳在三羧酸循环中的这种差异参与进行了广泛研究，但对源自脂肪酸（FA）的碳的去向却知之甚少。为了填补这一知识空白，我们开发了一种用长链脂肪酸培养细胞而不改变细胞活力的策略。通过追踪碳 - 脂肪酸，我们发现脂肪酸氧化（FAO）在增殖细胞和氧化细胞中都很活跃，而柠檬酸形成后的代谢途径却有所不同。在增殖细胞中，源自脂肪酸氧化的很大一部分碳以柠檬酸的形式离开经典三羧酸循环，并在细胞质中转化为未标记的苹果酸。增加脂肪酸供应或β - 氧化不会改变源自脂肪酸的碳在细胞质和线粒体之间的分配。葡萄糖氧化与源自脂肪酸的碳竞争经典三羧酸途径，从而促进脂肪酸碳流入替代三羧酸途径。此外，脂肪酸氧化与经典三羧酸途径之间的耦合随氧化能量代谢状态而变化。通过使用碳稳定同位素分辨代谢组学和脂肪酸驱动的氧消耗率分析，我们的研究为增殖细胞和氧化细胞中通过β - 氧化和下游三羧酸循环的脂肪酸碳去向提供了新的见解。尽管增殖细胞和氧化细胞都表现出强大的β - 氧化，但在三羧酸循环氧化过程中，它们在柠檬酸下游表现出不同的代谢碳去向。这种三羧酸循环的差异参与可能对平衡细胞的分解代谢和合成代谢需求很重要。
