Dose-dependent mitochondrial H₂O₂ signaling drives toxicity or stress adaptation and longevity in fission yeast

The spatiotemporal dynamics of hydrogen peroxide (H₂O₂) signaling and its effects on gene expression and cell fitness remain unclear. Using fission yeast, we applied genetic tools to control and monitor intracellular H₂O₂ levels. We expressed the H₂O₂ biosensor HyPer7 in four subcellular compartments, overexpressed D-amino acid oxidase (Dao1) in specific locations to induce localized H₂O₂ production, and modulated H₂O₂ detoxification or sensing. H₂O₂ concentrations showed 2- to 5-fold reductions across membranes, and D-amino acid treatments generated nanomolar H₂O₂ levels in Dao1-expressing cells. Mitochondrial-targeted Dao1 produced H₂O₂ fluxes capable of reaching the nucleus. While high mitochondrial H₂O₂ disrupted mitochondrial morphology and respiration, lower levels triggered antioxidant defenses, enhancing stress resistance and longevity. These findings establish a quantitative framework for mitochondrial H₂O₂ signaling and demonstrate that localized redox signals from mitochondria can either promote or impair cellular fitness depending on their intensity.