Mitochondrial morphological dynamics in apoptosis

Mitochondrial damage, characterized by outer membrane permeabilization, is a key to apoptosis. Recently, it has been recognized that changes of mitochondrial morphological dynamics play an important role in the regulation of mitochondrial membrane integrity. In normal healthy cells, mitochondria form long tubular structures that are usually interconnected into a dynamic network. This tubular morphology is controlled by constant fission and fusion of the mitochondria. Fission involves the cleavage of mitochondria into smaller fragments and fusion involves the connection and lengthening of adjacent mitochondria. A finely-tuned balance between mitochondrial fission and fusion is important to the maintenance of mitochondrial motility, homeostasis, health and integrity. During the early stages of apoptosis, tubular mitochondria break down into punctate organellar fragments. The fragmentation may involve the activation of mitochondrial fission and suppression of fusion. Importantly, mitochondrial fragmentation has been shown to facilitate mitochondrial membrane permeabilization, the release of cytochrome c, and apoptosis induction.