-
[show abstract]
[hide abstract]
ABSTRACT: Mitochondrial cytopathies are associated with increased free radical generation and paracrystalline inclusions. Paracrystalline inclusions were serendipitously found in a young male athlete with a very high respiratory exchange ratio during steady-state exercise; he also had an unusually low aerobic capacity. Direct sequencing of the mitochondrial DNA (mtDNA) coding regions revealed a novel missense mutation (G15497A) resulting in a glycine-->serine conversion at a highly conserved site in the cytochrome b gene in the subject, his mother, and sister. Cybrids, prepared by fusion of the subject's platelets with either U87MG rho degrees or SH-SY5Y rho degrees cells, generated higher basal levels of reactive oxygen species (ROS), had a lower adenosine triphosphate (ATP) content, and were more sensitive to oxygen and glucose deprivation and peroxynitrite generation compared to control cybrids with wild-type mtDNA. Cell survival was significantly enhanced with 50 mmol/L creatine monohydrate (CM) administration. The subject was also treated with CM (10 g/d) for a period of 5 weeks and a repeat muscle biopsy showed no paracrystalline inclusions. The results suggest that the development of exercise-induced paracrystalline inclusions may be influenced by the G15497A mtDNA mutation, and that CM mitigates against the pathological consequences of this mutation.
Muscle & Nerve 04/2004; 29(4):537-47. · 2.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Oxidative damage to mitochondrial DNA (mtDNA) increases with age in the brain and can induce G:C to T:A and T:A to G:C point mutations. Though rare at any particular site, multiple somatic mtDNA mutations induced by oxidative damage or by other mechanisms may accumulate with age in the brain and thus could play a role in aging and neurodegenerative diseases. However, no prior study has quantified the total burden of mtDNA point mutation subtypes in the brain. Using a highly sensitive cloning and sequencing strategy, we find that the aggregate levels of G:C to T:A and T:A to G:C transversions and of all point mutations increase with age in the frontal cortex (FCtx). In the substantia nigra (SN), the aggregate levels of point mutations in young controls are similar to the levels in the SN or FCtx of elderly subjects. Extrapolation from our data suggests an average of 2.7 (FCtx) to 3.2 (SN) somatic point mutations per mitochondrial genome in elderly subjects. There were no significant differences between Parkinson's disease (PD) patients and age-matched controls in somatic mutation levels. These results indicate that individually rare mtDNA point mutations reach a high aggregate burden in FCtx and SN of elderly subjects.
Neurobiology of Aging 02/2004; 25(1):71-81. · 6.19 Impact Factor
-
David K Simon,
Jennifer Friedman,
Xandra O Breakefield,
Joseph Jankovic,
Mitchell F Brin,
John Provias,
Susan B Bressman,
Michael E Charness,
Daniel Tarsy, Donald R Johns,
Mark A Tarnopolsky
[show abstract]
[hide abstract]
ABSTRACT: Mitochondrial DNA (mtDNA) mutations can cause rare forms of dystonia, but the role of mtDNA mutations in other types of dystonia is not well understood. We now report identification by sequencing, restriction endonuclease analyses, and clonal analyses of a heteroplasmic missense A to G base pair substitution at nucleotide position 3796 (A3796G) in the gene encoding the ND1 subunit of mitochondrial complex I in a patient with adult-onset dystonia, spasticity, and core-type myopathy. The mutation converts a highly conserved threonine to an alanine. The same mutation subsequently was identified in 2 of 74 additional unrelated adult-onset dystonia patients. A muscle biopsy was obtained from 1 of these 2 subjects and this revealed abnormalities of electron transport chain (ETC) activities. The mutation was absent in 64 subjects with early onset dystonia, 82 normal controls, and 65 subjects with Parkinson's disease or multiple system atrophy. The A3796G mutation previously has been reported in 3 of 226 subjects from mitochondrial haplogroup H. Each of the 3 subjects in our study harboring the A3796G mutation was also from haplogroup H. However, a subgroup analysis of haplogroup H subjects from our study indicates that the A3796G mutation is significantly overrepresented among haplogroup H adult-onset dystonia subjects compared with haplogroup H controls (P<0.01). This difference remains significant even after excluding the index patient (P=0.04). These data suggest that, among haplogroup H subjects, the presence of the A3796G mutation increases the risk of developing adult-onset dystonia.
Neurogenetics 09/2003; 4(4):199-205. · 3.35 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Dramatic advances in our understanding of the molecular genetic basis of Leber's hereditary optic neuropathy (LHON) have revolutionized our ability to diagnose and prognosticate this disease. Unfortunately no corresponding advances in the treatment of LHON have emerged. Glaucoma is a prevalent form of optic neuropathy that has been studied extensively. Lessons learned from treatment of LHON and glaucoma may have important implications for both diseases. LHON presents formidable challenges to the design and conduct of clinical trials. The acutely symptomatic LHON patient with monocular vision loss provides a unique clinical situation in which to test an agent during a critical therapeutic window. Advances in neuroprotection, apoptosis, and neurodegenerative diseases may provide important clues for potential therapeutic agents for LHON. Antioxidants and agents that interfere with the critical steps of mitochondrial-dependent, oxidative stress-induced apoptosis are candidates for future LHON therapy. A variety of neuroprotective agents, under active investigation in other diseases, may be useful in LHON therapy. Effective pharmacotherapy will complement the current management approach that has changed little in the 130 years since LHON was originally described.
Seminars in Ophthalmology 03/2002; 17(1):33-8. · 0.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Somatic mitochondrial DNA (mtDNA) point mutations reach high levels in the brain. However, the cell types that accumulate mutations and the patterns of mutations within individual cells are not known. We have quantified somatic mtDNA mutations in 28 single neurons and in 18 single glia from post-mortem human substantia nigra of six control subjects. Both neurons and glia contain mtDNA with somatic mutations. Single neurons harbor a geometric mean (95% CI) of 200.3 (152.9-262.4) somatic mtDNA point mutations per million base pairs, compared to 133.8 (97.5-184.9) for single glia (p=0.0251). If mutations detected multiple times in the same cell are counted only once, the mean mutation level per million base pairs remains elevated in single neurons (146.9; 124.0-174.2) compared to single glia (100.5; 81.5-126.5; p=0.009). Multiple distinct somatic point mutations are present in different cells from the same subject. Most of these mutations are individually present at low levels (less than 10-20% of mtDNA molecules), but with high aggregate mutation levels, particularly in neurons. These mutations may contribute to changes in brain function during normal aging and neurodegenerative disorders.
Neurobiology of Aging 26(10):1343-55. · 6.19 Impact Factor
