Mitochondrial competence determines responses to metabolic interventions during aging

Cellular responses to metabolic interventions vary across physiological contexts, but the basis for this variability remains unclear. Here, we show that mitochondrial competence determines whether cells can engage adaptive metabolic states that support survival during aging. Using 4-methylbenzoic acid (4-MBA), identified as a lifespan-extending compound, as a perturbation probe, we find that modulation of Target of Rapamycin Complex 1 (TORC1) signaling induces a shift from anabolic growth to maintenance-associated metabolism; however, signaling output alone does not predict outcomes. Instead, survival closely correlates with mitochondrial function, with its disruption abolishing adaptive responses. Genetic and biochemical analyses define a mitochondrial regulatory circuit that constrains signaling dynamics and governs state transitions. This regulatory logic is conserved across mammalian systems and operates under oxidative stress, replicative aging, and Hutchinson-Gilford progeria syndrome (HGPS), extending to proliferative cancer cells. These findings establish mitochondrial competence as a key determinant of cellular responsiveness and provide a framework for understanding context-dependent effects of metabolic interventions during aging.