title: Defects in mitochondrial DNA replication and oxidative damage in muscle of mtDNA mutator mice.
abstract: A causal role for mitochondrial dysfunction in mammalian aging is supported by recent studies of the mtDNA mutator mouse ("PolG" mouse), which harbors a defect in the proofreading-exonuclease activity of mitochondrial DNA polymerase gamma. These mice exhibit accelerated aging phenotypes characteristic of human aging, including systemic mitochondrial dysfunction, exercise intolerance, alopecia and graying of hair, curvature of the spine, and premature mortality. While mitochondrial dysfunction has been shown to cause increased oxidative stress in many systems, several groups have suggested that PolG mutator mice show no markers of oxidative damage. These mice have been presented as proof that mitochondrial dysfunction is sufficient to accelerate aging without oxidative stress. In this study, by normalizing to mitochondrial content in enriched fractions we detected increased oxidative modification of protein and DNA in PolG skeletal muscle mitochondria. We separately developed novel methods that allow simultaneous direct measurement of mtDNA replication defects and oxidative damage. Using this approach, we find evidence that suggests PolG muscle mtDNA is indeed oxidatively damaged. We also observed a significant decrease in antioxidants and expression of mitochondrial biogenesis pathway components and DNA repair enzymes in these mice, indicating an association of maladaptive gene expression with the phenotypes observed in PolG mice. Together, these findings demonstrate the presence of oxidative damage associated with the premature aging-like phenotypes induced by mitochondrial dysfunction.
authors.affiliation: Department of Animal Biology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104, USA.
authors.forename: Jill E
authors.initials: JE
authors.lastname: Kolesar
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, ON L8N 3Z5, Canada; Department of Pediatrics, McMaster University, Hamilton, ON L8N 3Z5, Canada; Department of Medicine, McMaster University, Hamilton, ON L8N 3Z5, Canada.
authors.forename: Adeel
authors.initials: A
authors.lastname: Safdar
authors.affiliation: Department of Pediatrics, McMaster University, Hamilton, ON L8N 3Z5, Canada.
authors.forename: Arkan
authors.initials: A
authors.lastname: Abadi
authors.affiliation: Department of Pediatrics, McMaster University, Hamilton, ON L8N 3Z5, Canada.
authors.forename: Lauren G
authors.initials: LG
authors.lastname: MacNeil
authors.affiliation: Department of Pediatrics, McMaster University, Hamilton, ON L8N 3Z5, Canada; Department of Medicine, McMaster University, Hamilton, ON L8N 3Z5, Canada.
authors.forename: Justin D
authors.initials: JD
authors.lastname: Crane
authors.affiliation: Department of Pediatrics, McMaster University, Hamilton, ON L8N 3Z5, Canada; Department of Medicine, McMaster University, Hamilton, ON L8N 3Z5, Canada. Electronic address: tarnopol@mcmaster.ca.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Tarnopolsky
authors.affiliation: Department of Animal Biology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104, USA. Electronic address: bkauf@vet.upenn.edu.
authors.forename: Brett A
authors.initials: BA
authors.lastname: Kaufman
mesh_terms: D000375:Aging / Q000235:genetics; D019588:Aging, Premature / Q000235:genetics; D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D002460:Cell Line; D053960:DNA Breaks; D000074002:DNA Polymerase gamma; D004261:DNA Replication / Q000235:genetics; D004272:DNA, Mitochondrial / Q000096:biosynthesis / Q000235:genetics*; D004259:DNA-Directed DNA Polymerase / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008931:Mitochondria, Muscle / Q000235:genetics / Q000473:pathology*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology*; D009154:Mutation; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000235:genetics*
chemical_list: D000975:Antioxidants; D004272:DNA, Mitochondrial; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase; C498803:Polg protein, mouse