Electron leak from NDUFA13 within mitochondrial complex I attenuates ischemia-reperfusion injury via dimerized STAT3

The causative relationship between specific mitochondrial molecular structure and reactive oxygen species (ROS) generation has attracted much attention. NDUFA13 is a newly identified accessory subunit of mitochondria complex I with a unique molecular structure and a location that is very close to the subunits of complex I of low electrochemical potentials. It has been reported that down-regulated NDUFA13 rendered tumor cells more resistant to apoptosis. Thus, this molecule might provide an ideal opportunity for us to investigate the profile of ROS generation and its role in cell protection against apoptosis. In the present study, we generated cardiac-specific tamoxifen-inducible NDUFA13 knockout mice and demonstrated that cardiac-specific heterozygous knockout (cHet) mice exhibited normal cardiac morphology and function in the basal state but were more resistant to apoptosis when exposed to ischemia-reperfusion (I/R) injury. cHet mice showed a preserved capacity of oxygen consumption rate by complex I and II, which can match the oxygen consumption driven by electron donors of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD)+ascorbate. Interestingly, at basal state, cHet mice exhibited a higher H₂O₂ level in the cytosol, but not in the mitochondria. Importantly, increased H₂O₂ served as a second messenger and led to the STAT3 dimerization and, hence, activation of antiapoptotic signaling, which eventually significantly suppressed the superoxide burst and decreased the infarct size during the I/R process in cHet mice.