Salubrinal-activated integrated stress response protects against doxorubicin-induced cardiotoxicity via activating transcription factor 4-mediated antioxidant defense and glutathione homeostasis

Doxorubicin is an effective chemotherapeutic agent; however, its use is limited by cardiotoxicity. Mitochondrial dysfunction is a central driver of doxorubicin-mediated cardiotoxicity. The role of the integrated stress response (ISR), a mitochondria-to-nucleus signaling pathway and crucial cellular defense mechanism in doxorubicin-induced cardiotoxicity, remains unclear. We investigated the pharmacological ISR activator salubrinal, a selective inhibitor of eukaryotic initiation factor 2α dephosphorylation with potential cardioprotective properties, to elucidate the molecular mechanisms underlying ISR-mediated cardioprotection in H9c2 cardiomyocytes, C57BL/6 mice, and HL-1 cell models. Doxorubicin disrupts ISR signaling, whereas salubrinal alleviates cardiotoxicity by activating transcription factor 4 (ATF4, a central ISR hub)-dependent pathways that suppress doxorubicin-induced apoptosis and preserve mitochondrial metabolism. The cystine/glutamate antiporter xCT, essential for glutathione (GSH) homeostasis, and growth differentiation factor 15 (GDF15), a mitochondrial stress-induced mitokine and potential biomarker of doxorubicin cardiotoxicity, are both regulated by ATF4. Mechanistically, we found that salubrinal contributes to cardioprotection against doxorubicin by enhancing the GSH-based antioxidant capacity via the ATF4-dependent GDF15–xCT axis. Further analysis of ATF4-associated GSH regulatory pathways revealed that enzymes involved in serine metabolism and glutathione peroxidase 4, a critical enzyme in GSH utilization that is upregulated by ATF4-mediated heat shock 70 kDa protein 5 and cystathionine gamma-lyase, contribute to the cardioprotective effects of salubrinal against doxorubicin-induced oxidative stress. Our findings highlight the ISR as a vital survival mechanism in cardiomyocytes exposed to doxorubicin. Regulating antioxidant defenses through enhanced GSH homeostasis and ISR activation, particularly via pharmacological agents such as salubrinal, may offer a promising therapeutic strategy for mitigating doxorubicin-induced cardiotoxicity.