Mitochondrial DNA repair in aging and disease

Mitochondria are organelles which, according to the endosymbiosis theory, evolved from purpurbacteria approximately 1.5 billion years ago. One of the unique features of mitochondria is that they have their own genome. Mitochondria replicate and transcribe their DNA semiautonomously. Like nuclear DNA, mitochondrial DNA (mtDNA) is constantly exposed to DNA damaging agents. Regarding the repair of mtDNA, the prevailing concept for many years was that mtDNA molecules suffering an excess of damage would simply be degraded to be replaced by newly generated successors copied from undamaged genomes. However, evidence now clearly shows that mitochondria contain the machinery to repair the damage to their genomes caused by certain endogenous or exogenous damaging agents. The link between mtDNA damage and repair to aging, neurodegeneration, and carcinogenesis-associated processes is the subject of this review. (C) 2008 Elsevier Ireland Ltd. All rights reserved.