O Affects Mitochondrial Functionality Ex Vivo

Mitochondria have originated in eukaryotic cells by endosymbiosis of a specialized prokaryote approximately 2 billion years ago. They are essential for normal cell function by providing energy through their role in oxidizing carbon substrates. Glutathione (GSH) is a major thiol-disulfide redox buffer of the cell including the mitochondrial matrix and intermembrane space. We have generated cardiomyocyte-specific Grx1-roGFP2 GSH redox potential (E) biosensor mice in the past, in which the sensor is targeted to the mitochondrial matrix. Using this mouse model a distinct E of the mitochondrial matrix (-278.9 ± 0.4 mV) in isolated cardiomyocytes is observed. When analyzing the E in isolated mitochondria from the transgenic hearts, however, the E in the mitochondrial matrix is significantly oxidized (-247.7 ± 8.7 mV). This is prevented by adding N-Ethylmaleimide during the mitochondria isolation procedure, which precludes disulfide bond formation. A similar reducing effect is observed by isolating mitochondria in hypoxic (0.1-3% O) conditions that mimics mitochondrial pO levels in cellulo. The reduced E is accompanied by lower ROS production, reduced complex III activity but increased ATP levels produced at baseline and after stimulation with succinate/ADP. Altogether, we demonstrate that oxygenation is an essential factor that needs to be considered when analyzing mitochondrial function ex vivo.