Abstract 311: Signal Transducer and Activator of Transcription 3 Inhibits the Opening of Mitochondrial Calcium Uniporter Against Cardiac Ischemia/reperfusion in Hydrogen Peroxide Postconditioning

Reactive oxygen species (ROS) generated during early reperfusion activated signal transducer and activator of transcription 3 (STAT3) contribute to intermittent hypobaric hypoxia (IHH)-afforded cardioprotection against ischemia/reperfusion (I/R)-induced mitochondrial calcium overload, but its mechanisms are not fully understood. This study investigated whether ROS signaling activated STAT3 is involved in moderate hydrogen peroxide postconditioning (H 2 O 2 PoC) mimicked IHH against cardiac I/R injury and the possible downstream target of STAT3 in mitochondria that mediates H 2 O 2 PoC-afforded cardioprotection. Moderate H 2 O 2 PoC not only improved the post-ischemic recovery of myocardial contractile performance and reduce the infarct size in isolated rat I/R hearts, but also alleviated cytosolic Ca 2+ and mitochondrial Ca 2+ overload and improved Ca 2+ transients and cell contraction in rat I/R cardiomyocytes. However, the cardioprotective effects of moderate H 2 O 2 PoC was abrogated by janus kinase 2 (JAK2)/STAT3 inhibitor AG490 in rat hearts as well as adenovirus-delivered shRNAs specific for STAT3 and the opener of mitochondrial calcium uniporter (MCU) spermine, respectively, in rat adult cardiomyoctes with simulated I/R. Besides, the moderate H 2 O 2 PoC-afforded cardioprotection abrogated by spermine could be rescued by STAT3 overexpression in rat cardiomyoctes with simulated I/R. Moreover, H 2 O 2 PoC enhanced the expression of serine 727 phosphorylation of STAT3 and STAT3 in mitochondria of rat cardiomyoctes with simulated I/R. Furthermore, immunofluorescence and co-immunoprecipitation assay revealed a co-localization/interaction of STAT3 and MCU in rat cardiomyoctes with moderate H 2 O 2 PoC at reperfusion 5 min and reperfusion 30 min but not in I/R cells. Co-immunoprecipitation further confirmed that STAT3 interacted with the N-terminal domain (NTD) of MCU in rat cardiomyoctes with moderate H 2 O 2 PoC. These findings indicate that STAT3 mediates the cardioprotection of moderate H 2 O 2 PoC against I/R injury by alleviating mitochondrial calcium overload through inhibiting MCU opening via the interaction with the NTD of MCU. Our finds provide new insight into the mechanisms of STAT3 in the cardioprotection.