Nrf2 participates in the protective effect of exogenous mitochondria against mitochondrial dysfunction in myocardial ischaemic and hypoxic injury

Coronary artery disease is one of the leading causes of death worldwide. Treatments including coronary artery intervention can cause complications, such as myocardial ischaemia-reperfusion injury (MIRI). Mitochondrial injury or dysfunction is a key pathology of MIRI. Mitochondrial transplantation is considered a promising therapeutic strategy for cardiac-related diseases, but its mechanism is still unclear. Nrf2 is a prominent player in supporting the structural and functional integrity of mitochondria. In our research, we focused on the effect of Nrf2 in the treatment of MIRI by mitochondrial transplantation. H9C2 cells were subjected to hypoxia/reoxygenation (H/R) and MIRI was induced in wild-type and Nrf2-/- mice by surgical ligation of the left coronary artery to elucidate the mechanism in vitro and in vivo, respectively. Exogenous mitochondria were extracted from healthy H9C2 cells and the pectoralis major and administered to H9C2 cells and mice with MIRI, respectively. Mitochondrial internalization, H9C2 cell injury or apoptosis, cardiac injury/function, mitochondrial function, morphology, mitochondrial dynamics, and the expression of components of the Nrf2 pathway were assessed. We found that exogenous mitochondria were internalized into H9C2 cardiomyocytes. Exogenous mitochondrial transplantation attenuated cardiomyocyte injury, cardiomyocyte apoptosis, and mitochondrial dysfunction. Exogenous mitochondrial transplantation increased the expression of Nrf2 and its downstream targets, attenuated cardiomyocyte injury, cardiac dysfunction, apoptosis, mitochondrial dysfunction, and mitochondrial fusion and fission imbalance, and improved mitophagy after MIRI in wild-type mice but not in Nrf2-/- mice. These results suggested that exogenous mitochondria can be internalized into cardiomyocytes and activate the Nrf2 pathway and that exogenous mitochondria improve cardiac function and ameliorate mitochondrial dysfunction via the Nrf2 pathway.