Complement C3 interacts with cytochrome c to influence myocardial apoptosis during heart ischemia/reperfusion

Myocardial ischemia/reperfusion (I/R) elicits an acute inflammatory response involving complement factors. Previous animal studies showed that circulation complement C3 was deposited in the ischemic myocardium flooded with oxygenated blood upon reperfusion. Recently, we reported that myocardial necrosis was decreased in C3−/− mice after heart I/R. The current study used in the same heart model to test the effect of C3 on myocardial apoptosis. Our results showed that myocardial apoptosis was increased in C3−/− mice after heart I/R. Further, comparative proteomics analyses found that cytochrome c was present in the myocardial C3-complex following I/R. These results indicate that C3 can interact with cytochrome c in the cytosol of cardiomyocytes during myocardial I/R, which may sequester cytochrome c and thus reduce the number of cells undergoing apoptosis. In summary, our findings raise the possibility of a new mechanism affecting cell death relevant to pathologic conditions such as ischemia: a circulating innate immune factor, i.e. complement, can interact with intracellular factor(s), and influence the types of cell death that occur. ### Competing Interest Statement The authors have declared no competing interest.