The tricarboxylic acid (TCA) cycle converts the end products of glycolysis and fatty acid β-oxidation into the reducing equivalents NADH and FADH2 Although mitochondrial matrix uptake of Ca2+ enhances ATP production, it remains unclear whether deprivation of mitochondrial TCA substrates alters mitochondrial Ca2+ flux. We investigated the effect of TCA cycle substrates on MCU-mediated mitochondrial matrix uptake of Ca2+, mitochondrial bioenergetics, and autophagic flux. Inhibition of glycolysis, mitochondrial pyruvate transport, or mitochondrial fatty acid transport triggered expression of the MCU gatekeeper MICU1 but not the MCU core subunit. Knockdown of mitochondrial pyruvate carrier (MPC) isoforms or expression of the dominant negative mutant MPC1R97W resulted in increased MICU1 protein abundance and inhibition of MCU-mediated mitochondrial matrix uptake of Ca2+ We also found that genetic ablation of MPC1 in hepatocytes and mouse embryonic fibroblasts resulted in reduced resting matrix Ca2+, likely because of increased MICU1 expression, but resulted in changes in mitochondrial morphology. TCA cycle substrate-dependent MICU1 expression was mediated by the transcription factor early growth response 1 (EGR1). Blocking mitochondrial pyruvate or fatty acid flux was linked to increased autophagy marker abundance. These studies reveal a mechanism that controls the MCU-mediated Ca2+ flux machinery and that depends on TCA cycle substrate availability. This mechanism generates a metabolic homeostatic circuit that protects cells from bioenergetic crisis and mitochondrial Ca2+ overload during periods of nutrient stress.

中文翻译：

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线粒体丙酮酸和脂肪酸通量调节 MICU1 依赖性的 MCU 活性控制。

三羧酸 (TCA) 循环将糖酵解和脂肪酸 β-氧化的终产物转化为还原当量 NADH 和 FADH2。尽管线粒体基质对 Ca2+ 的摄取增强了 ATP 的产生，但线粒体 TCA 底物的剥夺是否会改变线粒体 Ca2+ 通量仍不清楚。我们研究了 TCA 循环底物对 MCU 介导的线粒体基质 Ca2+ 吸收、线粒体生物能和自噬通量的影响。糖酵解、线粒体丙酮酸转运或线粒体脂肪酸转运的抑制会触发 MCU 看门人 MICU1 的表达，但不会触发 MCU 核心亚基的表达。线粒体丙酮酸载体（MPC）亚型的敲除或显性失活突变体MPC1R97W的表达导致MICU1蛋白丰度增加，并抑制MCU介导的线粒体基质对Ca2+的吸收。我们还发现肝细胞和小鼠胚胎成纤维细胞中MPC1的基因消除导致静息基质 Ca2+ 减少，可能是因为 MICU1 表达增加，但导致线粒体形态发生变化。TCA 循环底物依赖性 MICU1 表达由转录因子早期生长反应 1 (EGR1) 介导。阻断线粒体丙酮酸或脂肪酸流动与自噬标记物丰度增加有关。这些研究揭示了一种控制 MCU 介导的 Ca2+ 通量机制的机制，该机制取决于 TCA 循环底物的可用性。这种机制产生代谢稳态回路，在营养应激期间保护细胞免受生物能量危机和线粒体 Ca2+ 过载的影响。