FIG. 2.

Pathways activated in response to different degree of oxidative stress. When low oxidative stress is just enough to lead to the mitochondrial permeability transition (MPT), and autophagy and mitophagy are likely induced (261). As the oxidative damage increases, molecules such as cytochrome c may be released from mitochondria activating the caspase cascade and triggering apoptosis. At the extreme, oxidative stress causes severe MPT or even the rupture of the mitochondrial membrane, and neither autophagy nor apoptosis can provide an adequate response. The Bcl-2 proteins are a family of proteins involved in the response to autophagy and apoptosis, and play important roles in regulating MPT. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article at www.liebertonline.com/ars).