Ischaemia-reperfusion (IR) injury, which occurs when blood supply to an organ is disrupted and then restored, underlies many disorders, notably heart attack and stroke. Thus while reperfusion of ischaemic tissue is essential for survival, it also initiates oxidative damage, cell death, and aberrant immune responses, driven in large part by generation of mitochondrial reactive oxygen species (ROS). Although mitochondrial ROS production in IR is established, it has generally been considered a non-specific response to reperfusion, consistent with the many apparently unconnected interventions that decrease IR damage. In contrast to this view, we have identified a critical post-translational modification on mitochondrial complex I that is sufficient to abolish mitochondrial ROS during IR. Using MitoSNO - a novel selective inhibitor of complex I - we establish that S-nitrosation of a single cysteine residue on the ND3 subunit sufficient to impair oxidoreductase activity on in the target protein.This inhibitory modification in turn diminished both ROS and tissue necrosis at reperfusion.
These findings led us to pursue the intriguing hypothesis that mitochondrial ROS production during IR could be controlled by a distinct metabolic process that interacts with mitochondrial complex I. We developed a comparative in vivo metabolomic analysis and unexpectedly identified conserved metabolic pathways responsible for controlling mitochondrial ROS production during IR. In doing so, we establish a universal metabolic signature of ischaemic injury in a range of tissues that are predictive for mitochondrial ROS production through mitochondrial complex I during reperfusion of ischaemic tissue. Pharmacological inhibition of these pathways is sufficient to ameliorate in vivo IR injury in murine models of heart attack, stroke and kidney damage. Thus our work identifies a general metabolic response of tissues to ischaemia and reperfusion that provides a unifying explanation for many hitherto unconnected aspects of IR injury.