Figure 2. . A simplified fusion–fission cycle of mitochondria.
Mitochondria are dynamically regulated to maintain cellular homeostasis. Mitochondrial biogenesis increases mitochondrial numbers and replaces damaged mitochondria. MFN1 and MFN2 and OPA1-mediated fusion dilutes damage that accumulates in the mitochondria, including mitochondrial DNA mutations and reactive oxygen species. In contrast, the excessive mitochondrial damages can promote fission mediated through DRP1 and FIS1. Repaired polarized mitochondria re-enter the mitochondrial pool by fusion, and remaining depolarized mitochondria are transported to lysosomes for elimination by mitophagy (autophagy).