Mapping Leak Electron Pathways from Mitochondria to the Outer Cell Membrane in Human Embryonic Lung Fibroblasts.

Background: It is widely accepted that the inevitable leakage of electrons from mitochondria during respiratory metabolism is managed intracellularly through a complex cascade involving the conversion and transport of reactive oxygen species (ROS) and antioxidant mechanisms. However, considering that electrons can travel through various media, including biomacromolecules, do leaked electrons from the electron transport chain necessarily undergo complicated intracellular disposal processes? Here, we demonstrate that leaked electrons may actually be transported out of the cell. Methods: By expressing circularly permuted yellow fluorescent protein (cpYFP), a superoxide indicator, at the microtubules, actin, and integrin of human embryonic lung fibroblasts. Results: All three corresponding transgenic strains emitted fluorescent light, illuminating an ROS pathway from mitochondria to the outer cell membrane. The fluorescent intensity was positively correlated with mitochondrial superoxide content and aerobic respiratory intensity but was independent of cytosolic ROS levels. Conclusion: These results suggest that leaked electrons are transported out of the cell in their electron form. We anticipate that our findings will serve as a starting point for revising the understanding of ROS generation and homeostasis, implicating various physiological and pathological processes.