Hyperbaric oxygen increases mitochondrial biogenesis and function with oxidative stress in HL-1 cardiomyocytes

Hyperbaric oxygen (HBO₂) therapy has been used to treat various pathological conditions, including carbon monoxide poisoning and ischemia-reperfusion injury. However, the molecular mechanisms underlying these therapeutic effects remain unclear. We investigated HBO₂-induced changes in mitochondrial function and biogenesis in a clonal cardiomyocyte cell line, HL-1. Cells were exposed to HBO₂ (3 atmospheres, 2,218 mmHg O₂, 39 mmHg CO₂) in a cell incubation chamber under controlled temperature and humidity conditions. Levels of reactive oxygen species (ROS), gene transcription and translation, mitochondrial membrane potential (ΔΨm), mitochondrial respiration, cellular ATP content, and spontaneous beating foci of HL-1 cells were measured. Exposure (2 or 6 h) to HBO₂ increased the cytosolic and mitochondrial ROS production, followed by upregulation of stress responses, including growth differentiation factor 15 and fibroblast growth factor 21. HBO₂ augmented antioxidant defense signaling through nuclear factor erythroid-2-related factor 2 and mitochondrial biogenesis through peroxisome proliferator-activated receptor-gamma coactivator-1α. HBO₂ exposure also elevated mitochondrial oxygen consumption, ΔΨm, and ATP production. To assess cardiomyocyte function, live cell imaging was performed, and the findings demonstrated an increase in the number of beating clusters in HL-1 cells following exposure to HBO₂. Notably, in HL-1 cells pre-treated with sublethal doses of mitochondrial electron transport chain inhibitors, further depolarization of ΔΨm was observed after HBO₂ exposure, implying exacerbation of mitochondrial dysfunction. Collectively, HBO₂-induced oxidative stress enhances mitochondrial biogenesis and function, possibly through a stress-mediated response. However, in the presence of defective mitochondrial function, cells may not be able to overcome the stress caused by HBO₂.NEW & NOTEWORTHY The molecular mechanisms underlying the beneficial effects of hyperbaric oxygen remain elusive. Here, we provide experimental evidence that hyperbaric oxygen induces oxidative stress in cardiac myocytes, triggering protective stress responses, enhancing antioxidant defense, and promoting mitochondrial biogenesis and function. However, hyperbaric oxygen can worsen mitochondrial function in cells with preexisting defects, suggesting an ambivalent consequence of hyperbaric oxygen on mitochondria that warrants consideration in therapeutic applications.