Moderate Hydrogen Peroxide Postconditioning Ameliorates Ischemia/Reperfusion Injury in Cardiomyocytes via STAT3-Induced Calcium, ROS, and ATP Homeostasis

Introduction: Moderate hydrogen peroxide postconditioning (H₂O₂PoC) activates signal transducer and activator of transcription 3 (STAT3) to alleviate mitochondrial calcium overload during cardiac ischemia/reperfusion (I/R). However, the initial time window of STAT3-induced calcium hemostasis, the production of reactive oxygen species (ROS) and adenosine triphosphate (ATP) in H₂O₂PoC, and its regulated mechanism remain unknown. This study aimed to investigate H₂O₂PoC-induced homeostasis of calcium, ROS and ATP, and the role of STAT3 in the regulation. Methods: Isolated rat cardiomyocytes were exposed to H₂O₂PoC and Janus kinase 2 (JAK2)/STAT3 inhibitor AG490 during I/R. Ca²⁺ transients, cell contraction, intracellular calcium concentration, ROS production, ATP contents, phosphorylation of STAT3, gene and protein expression of manganese superoxide dismutase (MnSOD), metallothionein 1 (MT1) and metallothionein 2 (MT2), as well as activities of mitochondrial complex I and complex II were detected. Results: Moderate H₂O₂PoC improved post-ischemic Ca²⁺ transients and cell contraction recovery as well as alleviated cytosolic and mitochondrial calcium overload, which were abrogated by AG490 in rat cardiomyocytes. Moderate H₂O₂PoC increased ROS production and rate of ROS production at early reperfusion in rat I/R cardiomyocytes, and this phenomenon was also abrogated by AG490. Notably, the expression of phosphorylated nuclear STAT3; gene and protein expression of MnSOD, MT1, and MT2; and activities of mitochondrial complex I and complex II were upregulated by moderate H₂O₂PoC but downregulated by AG490. Conclusion: These findings indicated that the cardioprotection of moderate H₂O₂PoC against cardiac I/R could be associated with activated STAT3 at early reperfusion to maintain calcium, ROS, and ATP homeostasis in rat cardiomyocytes.