title: Loss of the antioxidant enzyme CuZnSOD (Sod1) mimics an age-related increase in absolute mitochondrial DNA copy number in the skeletal muscle.
abstract: Mitochondria contain multiple copies of the circular mitochondrial genome (mtDNA) that encodes ribosomal RNAs and proteins locally translated for oxidative phosphorylation. Loss of mtDNA integrity, both altered copy number and increased mutations, is implicated in cellular dysfunction with aging. Published data on mtDNA copy number and aging is discordant which may be due to methodological limitations for quantifying mtDNA copy number. Existing quantitative PCR (qPCR) mtDNA copy number quantification methods provide only relative abundances and are problematic to normalize to different template input amounts and across tissues/sample types. As well, existing methods cannot quantify mtDNA copy number in subcellular isolates, such as isolated mitochondria and neuronal synaptic terminals, which lack nuclear genomic DNA for normalization. We have developed and validated a novel absolute mtDNA copy number quantitation method that uses chip-based digital polymerase chain reaction (dPCR) to count the number of copies of mtDNA and used this novel method to assess the literature discrepancy in which there is no clear consensus whether mtDNA numbers change with aging in skeletal muscle. Skeletal muscle in old mice was found to have increased absolute mtDNA numbers compared to young controls. Furthermore, young Sod1-/-mice were assessed and show an age-mimicking increase in skeletal muscle mtDNA. These findings reproduce a number of previous studies that demonstrate age-related increases in mtDNA. This simple and cost effective dPCR approach should enable precise and accurate mtDNA copy number quantitation in mitochondrial studies, eliminating contradictory studies of mitochondrial DNA content with aging.
authors.affiliation: Department of Physiology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.|Department of Geriatric Medicine, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.|Harold Hamm Diabetes Center, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.|Oklahoma Nathan Shock Center on Aging, Oklahoma City, OK, 73104, USA.
authors.forename: Dustin R
authors.initials: DR
authors.lastname: Masser
authors.affiliation: Department of Physiology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.
authors.forename: Nicholas W
authors.initials: NW
authors.lastname: Clark
authors.affiliation: Oklahoma Nathan Shock Center on Aging, Oklahoma City, OK, 73104, USA.|Oklahoma Medical Research Foundation, Oklahoma City, OK, 73102, USA.
authors.forename: Holly
authors.initials: H
authors.lastname: Van Remmen
authors.affiliation: Department of Physiology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA. wfreeman@ouhsc.edu.|Department of Geriatric Medicine, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA. wfreeman@ouhsc.edu.|Harold Hamm Diabetes Center, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA. wfreeman@ouhsc.edu.|Oklahoma Nathan Shock Center on Aging, Oklahoma City, OK, 73104, USA. wfreeman@ouhsc.edu.
authors.forename: Willard M
authors.initials: WM
authors.lastname: Freeman
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001921:Brain / Q000166:cytology / Q000502:physiology; D056915:DNA Copy Number Variations; D004272:DNA, Mitochondrial / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D000072105:Superoxide Dismutase-1 / Q000235:genetics*; D013574:Synaptosomes / Q000648:ultrastructure
chemical_list: D004272:DNA, Mitochondrial; C000606291:Sod1 protein, mouse; D000072105:Superoxide Dismutase-1
keywords: Aging; Digital PCR; Mitochondria; Sod1; Synaptosomes; mtDNA; mtDNA copy number