A Function-Centric Framework for Mitochondrial Quality Control.

Mitochondrial quality control (QC) comprises interconnected pathways that preserve organelle function by detecting damage and mediating repair, remodelling, or elimination of defective components. Although many sub-organellar QC mechanisms are well characterised, stress is often sensed first at the level of mitochondrial function rather than at individual molecular targets. Functional domains such as oxidative folding, bioenergetics, redox balance, pH, and thermogenesis act as sensory portals that detect perturbations and trigger adaptive reprogramming of mitochondrial activity. In this perspective, we provide a conceptual perspective for mitochondrial QC as a mechanistically integrated network, emphasising how changes in these functional states couple diverse QC modules-including proteases, antioxidant systems, mitochondrial dynamics, mitophagy, and mitochondrial-derived vesicles-into a unified surveillance system. We propose that primary stressors, such as redox imbalance, are progressively converted into secondary stress signals, including reactive oxygen species accumulation, membrane depolarisation, metabolite redistribution, and altered lipid or nucleic-acid structure. These secondary signals propagate across mitochondrial and cytosolic compartments, amplifying QC by coordinating the engagement of repair, remodelling, and organelle-elimination pathways. This cascading transformation of stress signals not only limits the impact of the initial insult but also enhances adaptive capacity by driving synergistic deployment of QC processes across multiple mechanistic layers.