Mitochondrial ROS-induced ROS release: an update and review.

Unstable mitochondrial membrane potential and redox transitions can occur following insults including ischemia/reperfusion injury and toxin exposure, with negative consequences for mitochondrial integrity and cellular survival. These transitions can involve mechanisms such as the recently described process, "Reactive Oxygen Species (ROS)-induced ROS-release" (RIRR), and be generated by circuits where the mitochondrial permeability transition (MPT) pore and the inner membrane anion channel (IMAC) are involved. The exposure to excessive oxidative stress results in an increase in ROS reaching a threshold level that triggers the opening of one of the requisite mitochondrial channels. In turn, this leads to the simultaneous collapse of the mitochondrial membrane potential and a transient increased ROS generation by the electron transfer chain. Generated ROS can be released into cytosol and trigger RIRR in neighboring mitochondria. This mitochondrion-to-mitochondrion ROS-signaling constitutes a positive feedback mechanism for enhanced ROS production leading to potentially significant mitochondrial and cellular injury. This review and update considers a variety of RIRR mechanisms (involving MPT, IMAC and episodes of mitochondrial transient hyperpolarization). RIRR could be a general cell biology phenomenon relevant to the processes of programmed mitochondrial destruction and cell death, and may contribute to other mechanisms of post-ischemic pathologies, including arrhythmias.