title: Somatic mitochondrial DNA deletions accumulate to high levels in aging human extraocular muscles.
abstract: PURPOSE. Mitochondrial function and the presence of somatic mitochondrial DNA (mtDNA) defects were investigated in extraocular muscles (EOMs) collected from individuals covering a wide age range, to document the changes seen with normal aging. METHODS. Cytochrome c oxidase (COX) and succinate dehydrogenase (SDH) histochemistry was performed on 46 EOM samples to determine the level of COX deficiency in serial cryostat muscle sections (mean age, 42.6 years; range, 3.0-96.0 years). Competitive three-primer and real-time PCR were performed on single-fiber lysates to detect and quantify mtDNA deletions. Whole-genome mitochondrial sequencing was also performed to evaluate the contribution of mtDNA point mutations to the overall mutational load. RESULTS. COX-negative fibers were seen in EOMs beginning in the third decade of life, and there was a significant age-related increase: <30 years, 0.05% (n = 17); 30 to 60 years, 1.94% (n = 13); and >60 years, 3.34% (n = 16, P = 0.0001). Higher levels of COX deficiency were also present in EOM than in skeletal muscle in all three age groups (P < 0.0001). Most of the COX-negative fibers harbored high levels (>70%) of mtDNA deletions (206/284, 72.54%) and the mean deletion level was 66.64% (SD 36.45%). The mutational yield from whole mitochondrial genome sequencing was relatively low (1/19, 5.3%), with only a single mtDNA point mutation identified among COX-negative fibers with low deletion levels < or =70%. CONCLUSIONS. The results show an exponential increase in COX deficiency in EOMs beginning in early adulthood, which suggests an accelerated aging process compared with other postmitotic tissues.
authors.affiliation: Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle-upon-Tyne, United Kingdom. patrick.yu-wai-man@ncl.ac.uk
authors.forename: Patrick
authors.initials: P
authors.lastname: Yu-Wai-Man
authors.forename: Joey
authors.initials: J
authors.lastname: Lai-Cheong
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Borthwick
authors.forename: Langping
authors.initials: L
authors.lastname: He
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Taylor
authors.forename: Laura C
authors.initials: LC
authors.lastname: Greaves
authors.forename: Robert W
authors.initials: RW
authors.lastname: Taylor
authors.forename: Philip G
authors.initials: PG
authors.lastname: Griffiths
authors.forename: Douglass M
authors.initials: DM
authors.lastname: Turnbull
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D002872:Chromosome Deletion; D030401:Cytochrome-c Oxidase Deficiency / Q000378:metabolism; D004272:DNA, Mitochondrial / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008931:Mitochondria, Muscle / Q000201:enzymology / Q000235:genetics*; D009801:Oculomotor Muscles / Q000201:enzymology / Q000502:physiology*; D017354:Point Mutation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013385:Succinate Dehydrogenase / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D013385:Succinate Dehydrogenase; D003576:Electron Transport Complex IV