title: Oxidative stress is not a major contributor to somatic mitochondrial DNA mutations.
abstract: The accumulation of somatic mitochondrial DNA (mtDNA) mutations is implicated in aging and common diseases of the elderly, including cancer and neurodegenerative disease. However, the mechanisms that influence the frequency of somatic mtDNA mutations are poorly understood. To develop a simple invertebrate model system to address this matter, we used the Random Mutation Capture (RMC) assay to characterize the age-dependent frequency and distribution of mtDNA mutations in the fruit fly Drosophila melanogaster. Because oxidative stress is a major suspect in the age-dependent accumulation of somatic mtDNA mutations, we also used the RMC assay to explore the influence of oxidative stress on the somatic mtDNA mutation frequency. We found that many of the features associated with mtDNA mutations in vertebrates are conserved in Drosophila, including a comparable somatic mtDNA mutation frequency (∼10(-5)), an increased frequency of mtDNA mutations with age, and a prevalence of transition mutations. Only a small fraction of the mtDNA mutations detected in young or old animals were G∶C to T∶A transversions, a signature of oxidative damage, and loss-of-function mutations in the mitochondrial superoxide dismutase, Sod2, had no detectable influence on the somatic mtDNA mutation frequency. Moreover, a loss-of-function mutation in Ogg1, which encodes a DNA repair enzyme that removes oxidatively damaged deoxyguanosine residues (8-hydroxy-2'-deoxyguanosine), did not significantly influence the somatic mtDNA mutation frequency of Sod2 mutants. Together, these findings indicate that oxidative stress is not a major cause of somatic mtDNA mutations. Our data instead suggests that somatic mtDNA mutations arise primarily from errors that occur during mtDNA replication. Further studies using Drosophila should aid in the identification of factors that influence the frequency of somatic mtDNA mutations.
authors: Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America ; Molecular and Cellular Biology Program, University of Washington, Seattle, Washington, United States of America.
authors: Leslie S
authors: LS
authors: Itsara
authors: Department of Pathology, University of Washington, Seattle, Washington, United States of America.
authors: Scott R
authors: SR
authors: Kennedy
authors: Department of Pathology, University of Washington, Seattle, Washington, United States of America.
authors: Edward J
authors: EJ
authors: Fox
authors: Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America.
authors: Selina
authors: S
authors: Yu
authors: Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America ; Postbaccalaureate Research Education Program, University of Washington, Seattle, Washington, United States of America.
authors: Joshua J
authors: JJ
authors: Hewitt
authors: Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America.
authors: Monica
authors: M
authors: Sanchez-Contreras
authors: Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana, United States of America.
authors: Fernando
authors: F
authors: Cardozo-Pelaez
authors: Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America.
authors: Leo J
authors: LJ
authors: Pallanck
mesh_terms: D000375:Aging / Q000235:genetics* / Q000473:pathology; D000818:Animals; D045647:DNA Glycosylases / Q000235:genetics; D004260:DNA Repair / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics; D004331:Drosophila melanogaster; D006801:Humans; D008928:Mitochondria / Q000235:genetics / Q000473:pathology; D023421:Models, Animal; D009154:Mutation / Q000235:genetics*; D059645:Mutation Rate; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics; D000099156:Superoxide Dismutase 2
chemical_list: D045647:DNA Glycosylases; D004272:DNA, Mitochondrial; D029721:Drosophila Proteins; D017382:Reactive Oxygen Species; D013482:Superoxide Dismutase; D000099156:Superoxide Dismutase 2; C516999:Ogg1 protein, Drosophila