The malate-aspartate shuttle is a major electron shuttle that transfers reducing equivalents from the cytosol to the mitochondria, where they can be safely deposited onto the electron transport chain. Nevertheless, many proliferating cells discard reducing equivalents in the form of lactate, raising the question of what factors limit electron shuttle use. Here, we show that aspartate availability determines engagement of the malate-aspartate shuttle. In proliferating cells, increasing aspartate availability enhances use of the malate-aspartate shuttle and increases metabolism of glucose-derived pyruvate in mitochondria, a process that requires regeneration of oxidized electron carriers in the cytosol. During differentiation, elevated flux through the malate-aspartate shuttle cells enables cells to fuel mitochondrial networks from glucose-derived carbon. Engineering aspartate demand reverses this metabolic signature of differentiated cells. Together, these results demonstrate that cell-state-specific demand for aspartate is sufficient to determine use of the malate-aspartate shuttle and drives changing mitochondrial substrate preferences during differentiation. • Aspartate availability limits flux through the malate-aspartate shuttle • Malate-aspartate shuttle engagement increases during differentiation • The malate-aspartate shuttle supports glucose oxidation during differentiation • Increasing aspartate demands reverts metabolic signatures of differentiation Brunner et al. report that malate-aspartate shuttle engagement is cell-state dependent and can be modulated by the availability of the amino acid aspartate. In differentiated cells, malate-aspartate shuttle usage increases, enabling increased glucose oxidation in the TCA cycle, a known metabolic signature of differentiated cells.
Brunner et al. (Sun,) studied this question.