1
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Dubie JJ, Katju V, Bergthorsson U. Dissecting the sequential evolution of a selfish mitochondrial genome in Caenorhabditis elegans. Heredity (Edinb) 2024; 133:186-197. [PMID: 38969772 PMCID: PMC11349875 DOI: 10.1038/s41437-024-00704-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2024] [Revised: 06/24/2024] [Accepted: 06/25/2024] [Indexed: 07/07/2024] Open
Abstract
Mitochondrial genomes exist in a nested hierarchy of populations where mitochondrial variants are subject to genetic drift and selection at each level of organization, sometimes engendering conflict between different levels of selection, and between the nuclear and mitochondrial genomes. Deletion mutants in the Caenorhabditis elegans mitochondrial genome can reach high intracellular frequencies despite strongly detrimental effects on fitness. During a mutation accumulation (MA) experiment in C. elegans, a 499 bp deletion in ctb-1 rose to 90% frequency within cells while significantly reducing fitness. During the experiment, the deletion-bearing mtDNA acquired three additional mutations in nd5, namely two single insertion frameshift mutations in a homopolymeric run, and a base substitution. Despite an additional fitness cost of these secondary mutations, all deletion-bearing molecules contained the nd5 mutations at the termination of the MA experiment. The presence of mutant mtDNA was associated with increased mtDNA copy-number. Variation in mtDNA copy-number was greater in the MA lines than in a wildtype nuclear background, including a severe reduction in copy-number at one generational timepoint. Evolutionary replay experiments using different generations of the MA experiment as starting points suggests that two of the secondary mutations contribute to the proliferation of the original ctb-1 deletion by unknown mechanisms.
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Affiliation(s)
- Joseph J Dubie
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX, USA
- Department of Integrative Biology, University of Texas, Austin, TX, USA
| | - Vaishali Katju
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX, USA.
- Evolutionary Biology, Department of Ecology and Genetics, Uppsala University, Norbyvägen 18D, 752 36, Uppsala, Sweden.
| | - Ulfar Bergthorsson
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX, USA.
- Evolutionary Biology, Department of Ecology and Genetics, Uppsala University, Norbyvägen 18D, 752 36, Uppsala, Sweden.
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2
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Bury A, Pyle A, Vincent AE, Actis P, Hudson G. Nanobiopsy investigation of the subcellular mtDNA heteroplasmy in human tissues. Sci Rep 2024; 14:13789. [PMID: 38877095 PMCID: PMC11178779 DOI: 10.1038/s41598-024-64455-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 06/10/2024] [Indexed: 06/16/2024] Open
Abstract
Mitochondrial function is critical to continued cellular vitality and is an important contributor to a growing number of human diseases. Mitochondrial dysfunction is typically heterogeneous, mediated through the clonal expansion of mitochondrial DNA (mtDNA) variants in a subset of cells in a given tissue. To date, our understanding of the dynamics of clonal expansion of mtDNA variants has been technically limited to the single cell-level. Here, we report the use of nanobiopsy for subcellular sampling from human tissues, combined with next-generation sequencing to assess subcellular mtDNA mutation load in human tissue from mitochondrial disease patients. The ability to map mitochondrial mutation loads within individual cells of diseased tissue samples will further our understanding of mitochondrial genetic diseases.
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Affiliation(s)
- Alexander Bury
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle, UK
- NIHR Biomedical Research Centre, Faculty of Medical Science, Newcastle University, Newcastle, UK
- School of Electronic and Electrical Engineering and Pollard Institute, University of Leeds, Leeds, UK
- Bragg Centre for Materials Research, Leeds, UK
| | - Angela Pyle
- Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle, UK
| | - Amy E Vincent
- Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle, UK.
- NIHR Biomedical Research Centre, Faculty of Medical Science, Newcastle University, Newcastle, UK.
| | - Paolo Actis
- School of Electronic and Electrical Engineering and Pollard Institute, University of Leeds, Leeds, UK.
- Bragg Centre for Materials Research, Leeds, UK.
| | - Gavin Hudson
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle, UK.
- NIHR Biomedical Research Centre, Faculty of Medical Science, Newcastle University, Newcastle, UK.
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3
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Bernardino Gomes TM, Vincent AE, Menger KE, Stewart JB, Nicholls TJ. Mechanisms and pathologies of human mitochondrial DNA replication and deletion formation. Biochem J 2024; 481:683-715. [PMID: 38804971 PMCID: PMC11346376 DOI: 10.1042/bcj20230262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2024] [Revised: 05/13/2024] [Accepted: 05/14/2024] [Indexed: 05/29/2024]
Abstract
Human mitochondria possess a multi-copy circular genome, mitochondrial DNA (mtDNA), that is essential for cellular energy metabolism. The number of copies of mtDNA per cell, and their integrity, are maintained by nuclear-encoded mtDNA replication and repair machineries. Aberrant mtDNA replication and mtDNA breakage are believed to cause deletions within mtDNA. The genomic location and breakpoint sequences of these deletions show similar patterns across various inherited and acquired diseases, and are also observed during normal ageing, suggesting a common mechanism of deletion formation. However, an ongoing debate over the mechanism by which mtDNA replicates has made it difficult to develop clear and testable models for how mtDNA rearrangements arise and propagate at a molecular and cellular level. These deletions may impair energy metabolism if present in a high proportion of the mtDNA copies within the cell, and can be seen in primary mitochondrial diseases, either in sporadic cases or caused by autosomal variants in nuclear-encoded mtDNA maintenance genes. These mitochondrial diseases have diverse genetic causes and multiple modes of inheritance, and show notoriously broad clinical heterogeneity with complex tissue specificities, which further makes establishing genotype-phenotype relationships challenging. In this review, we aim to cover our current understanding of how the human mitochondrial genome is replicated, the mechanisms by which mtDNA replication and repair can lead to mtDNA instability in the form of large-scale rearrangements, how rearranged mtDNAs subsequently accumulate within cells, and the pathological consequences when this occurs.
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Affiliation(s)
- Tiago M. Bernardino Gomes
- Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
- Wellcome Centre for Mitochondrial Research, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
- NHS England Highly Specialised Service for Rare Mitochondrial Disorders, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne NE2 4HH, U.K
| | - Amy E. Vincent
- Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
- Wellcome Centre for Mitochondrial Research, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
| | - Katja E. Menger
- Wellcome Centre for Mitochondrial Research, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
- Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
| | - James B. Stewart
- Wellcome Centre for Mitochondrial Research, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
- Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
| | - Thomas J. Nicholls
- Wellcome Centre for Mitochondrial Research, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
- Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
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4
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Carey AR, Miller NR, Cui H, Allis K, Balog A, Bai R, Vernon HJ. Myopathy and Ophthalmologic Abnormalities in Association With Multiple Skeletal Muscle Mitochondrial DNA Deletions. J Neuroophthalmol 2024; 44:247-252. [PMID: 37665646 DOI: 10.1097/wno.0000000000001984] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/06/2023]
Abstract
BACKGROUND Establishing a molecular diagnosis of mitochondrial diseases due to pathogenic mitochondrial DNA (mtDNA) variants can be difficult because of varying levels of tissue heteroplasmy, and identifying these variants is important for clinical management. Here, we present clinical and molecular findings in 8 adult patients with classical features of mitochondrial ophthalmologic and/or muscle disease and multiple mtDNA deletions isolated to muscle. METHODS The patients were identified via a retrospective review of patients seen in both a tertiary ophthalmology center and a genetics clinic with a clinical diagnosis of chronic progressive external ophthalmoplegia, optic nerve abnormalities, and/or mitochondrial myopathy. Age at onset of symptoms ranged from 18 to 61 years. Ocular manifestations included bilateral optic neuropathy in one patient, bilateral optic disc cupping without optic neuropathy in 2 patients, ptosis in 4 patients, and ocular motility deficits in 2 patients. Five patients had generalized weakness. RESULTS Pathogenic variants in mtDNA were not found in the blood or buccal sample from any patient, but 7 of 8 patients had multiple mtDNA deletions identified in muscle tissue. One patient had a single mtDNA deletion identified in the muscle. Heteroplasmy was less than 15% for all of the identified deletions, with the exception of one deletion that had a heteroplasmy of 50%-60%. None of the patients were found to have a nuclear gene variant known to be associated with mitochondrial DNA maintenance. CONCLUSIONS mtDNA deletions were identified in adult patients with ophthalmologic and/or musle abnormalities and may underlie their clinical presentations.
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Affiliation(s)
- Andrew R Carey
- Neuro-Ophthalmology Division (ARC, NRM), Department of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland; GeneDx (HC, KA, AB, RB), Gaithersburg, Maryland; and Department of Genetic Medicine (HJV), Johns Hopkins University School of Medicine, Baltimore, Maryland
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5
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Whitehall JC, Smith ALM, Greaves LC. Mitochondrial DNA Mutations and Ageing. Subcell Biochem 2023; 102:77-98. [PMID: 36600130 DOI: 10.1007/978-3-031-21410-3_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Mitochondria are subcellular organelles present in most eukaryotic cells which play a significant role in numerous aspects of cell biology. These include carbohydrate and fatty acid metabolism to generate cellular energy through oxidative phosphorylation, apoptosis, cell signalling, haem biosynthesis and reactive oxygen species production. Mitochondrial dysfunction is a feature of many human ageing tissues, and since the discovery that mitochondrial DNA mutations were a major underlying cause of changes in oxidative phosphorylation capacity, it has been proposed that they have a role in human ageing. However, there is still much debate on whether mitochondrial DNA mutations play a causal role in ageing or are simply a consequence of the ageing process. This chapter describes the structure of mammalian mitochondria, and the unique features of mitochondrial genetics, and reviews the current evidence surrounding the role of mitochondrial DNA mutations in the ageing process. It then focusses on more recent discoveries regarding the role of mitochondrial dysfunction in stem cell ageing and age-related inflammation.
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Affiliation(s)
- Julia C Whitehall
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Newcastle University, Newcastle Upon Tyne, UK
| | - Anna L M Smith
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Newcastle University, Newcastle Upon Tyne, UK
| | - Laura C Greaves
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Newcastle University, Newcastle Upon Tyne, UK.
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6
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Stochastic survival of the densest and mitochondrial DNA clonal expansion in aging. Proc Natl Acad Sci U S A 2022; 119:e2122073119. [PMID: 36442091 PMCID: PMC9894218 DOI: 10.1073/pnas.2122073119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The expansion of mitochondrial DNA molecules with deletions has been associated with aging, particularly in skeletal muscle fibers; its mechanism has remained unclear for three decades. Previous accounts have assigned a replicative advantage (RA) to mitochondrial DNA containing deletion mutations, but there is also evidence that cells can selectively remove defective mitochondrial DNA. Here we present a spatial model that, without an RA, but instead through a combination of enhanced density for mutants and noise, produces a wave of expanding mutations with speeds consistent with experimental data. A standard model based on RA yields waves that are too fast. We provide a formula that predicts that wave speed drops with copy number, consonant with experimental data. Crucially, our model yields traveling waves of mutants even if mutants are preferentially eliminated. Additionally, we predict that mutant loads observed in single-cell experiments can be produced by de novo mutation rates that are drastically lower than previously thought for neutral models. Given this exemplar of how spatial structure (multiple linked mtDNA populations), noise, and density affect muscle cell aging, we introduce the mechanism of stochastic survival of the densest (SSD), an alternative to RA, that may underpin other evolutionary phenomena.
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7
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Chiaratti MR, Chinnery PF. Modulating mitochondrial DNA mutations: factors shaping heteroplasmy in the germ line and somatic cells. Pharmacol Res 2022; 185:106466. [PMID: 36174964 DOI: 10.1016/j.phrs.2022.106466] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 09/21/2022] [Accepted: 09/23/2022] [Indexed: 11/30/2022]
Abstract
Until recently it was thought that most humans only harbor one type of mitochondrial DNA (mtDNA), however, deep sequencing and single-cell analysis has shown the converse - that mixed populations of mtDNA (heteroplasmy) are the norm. This is important because heteroplasmy levels can change dramatically during transmission in the female germ line, leading to high levels causing severe mitochondrial diseases. There is also emerging evidence that low level mtDNA mutations contribute to common late onset diseases such as neurodegenerative disorders and cardiometabolic diseases because the inherited mutation levels can change within developing organs and non-dividing cells over time. Initial predictions suggested that the segregation of mtDNA heteroplasmy was largely stochastic, with an equal tendency for levels to increase or decrease. However, transgenic animal work and single-cell analysis have shown this not to be the case during germ-line transmission and in somatic tissues during life. Mutation levels in specific mtDNA regions can increase or decrease in different contexts and the underlying molecular mechanisms are starting to be unraveled. In this review we provide a synthesis of recent literature on the mechanisms of selection for and against mtDNA variants. We identify the most pertinent gaps in our understanding and suggest ways these could be addressed using state of the art techniques.
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Affiliation(s)
- Marcos R Chiaratti
- Departamento de Genética e Evolução, Centro de Ciências Biológicas e da Saúde, Universidade Federal de São Carlos, São Carlos, Brazil.
| | - Patrick F Chinnery
- Department of Clinical Neurosciences, School of Clinical Medicine, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK; Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK.
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8
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Chen TH, Koh KY, Lin KMC, Chou CK. Mitochondrial Dysfunction as an Underlying Cause of Skeletal Muscle Disorders. Int J Mol Sci 2022; 23:12926. [PMID: 36361713 PMCID: PMC9653750 DOI: 10.3390/ijms232112926] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 10/21/2022] [Accepted: 10/21/2022] [Indexed: 09/19/2023] Open
Abstract
Mitochondria are an important energy source in skeletal muscle. A main function of mitochondria is the generation of ATP for energy through oxidative phosphorylation (OXPHOS). Mitochondrial defects or abnormalities can lead to muscle disease or multisystem disease. Mitochondrial dysfunction can be caused by defective mitochondrial OXPHOS, mtDNA mutations, Ca2+ imbalances, mitochondrial-related proteins, mitochondrial chaperone proteins, and ultrastructural defects. In addition, an imbalance between mitochondrial fusion and fission, lysosomal dysfunction due to insufficient biosynthesis, and/or defects in mitophagy can result in mitochondrial damage. In this review, we explore the association between impaired mitochondrial function and skeletal muscle disorders. Furthermore, we emphasize the need for more research to determine the specific clinical benefits of mitochondrial therapy in the treatment of skeletal muscle disorders.
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Affiliation(s)
- Tsung-Hsien Chen
- Department of Internal Medicine, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi 60002, Taiwan
| | - Kok-Yean Koh
- Division of Gastroenterology and Hepatology, Department of Internal Medicine, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi 60002, Taiwan
| | - Kurt Ming-Chao Lin
- Institute of Biomedical Engineering and Nanomedicine, National Health Research Institutes, Zhunan 35053, Taiwan
| | - Chu-Kuang Chou
- Division of Gastroenterology and Hepatology, Department of Internal Medicine, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi 60002, Taiwan
- Obesity Center, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi 60002, Taiwan
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9
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Biallelic Variants in ENDOG Associated with Mitochondrial Myopathy and Multiple mtDNA Deletions. Cells 2022; 11:cells11060974. [PMID: 35326425 PMCID: PMC8946636 DOI: 10.3390/cells11060974] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2022] [Revised: 03/07/2022] [Accepted: 03/09/2022] [Indexed: 12/02/2022] Open
Abstract
Endonuclease G (ENDOG) is a nuclear-encoded mitochondrial-localized nuclease. Although its precise biological function remains unclear, its proximity to mitochondrial DNA (mtDNA) makes it an excellent candidate to participate in mtDNA replication, metabolism and maintenance. Indeed, several roles for ENDOG have been hypothesized, including maturation of RNA primers during mtDNA replication, splicing of polycistronic transcripts and mtDNA repair. To date, ENDOG has been deemed as a determinant of cardiac hypertrophy, but no pathogenic variants or genetically defined patients linked to this gene have been described. Here, we report biallelic ENDOG variants identified by NGS in a patient with progressive external ophthalmoplegia, mitochondrial myopathy and multiple mtDNA deletions in muscle. The absence of the ENDOG protein in the patient’s muscle and fibroblasts indicates that the identified variants are pathogenic. The presence of multiple mtDNA deletions supports the role of ENDOG in mtDNA maintenance; moreover, the patient’s clinical presentation is very similar to mitochondrial diseases caused by mutations in other genes involved in mtDNA homeostasis. Although the patient’s fibroblasts did not present multiple mtDNA deletions or delay in the replication process, interestingly, we detected an accumulation of low-level heteroplasmy mtDNA point mutations compared with age-matched controls. This may indicate a possible role of ENDOG in mtDNA replication or repair. Our report provides evidence of the association of ENDOG variants with mitochondrial myopathy.
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10
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Pereira CV, Gitschlag BL, Patel MR. Cellular mechanisms of mtDNA heteroplasmy dynamics. Crit Rev Biochem Mol Biol 2021; 56:510-525. [PMID: 34120542 DOI: 10.1080/10409238.2021.1934812] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Heteroplasmy refers to the coexistence of more than one variant of the mitochondrial genome (mtDNA). Mutated or partially deleted mtDNAs can induce chronic metabolic impairment and cause mitochondrial diseases when their heteroplasmy levels exceed a critical threshold. These mutant mtDNAs can be maternally inherited or can arise de novo. Compelling evidence has emerged showing that mutant mtDNA levels can vary and change in a nonrandom fashion across generations and amongst tissues of an individual. However, our lack of understanding of the basic cellular and molecular mechanisms of mtDNA heteroplasmy dynamics has made it difficult to predict who will inherit or develop mtDNA-associated diseases. More recently, with the advances in technology and the establishment of tractable model systems, insights into the mechanisms underlying the selection forces that modulate heteroplasmy dynamics are beginning to emerge. In this review, we summarize evidence from different organisms, showing that mutant mtDNA can experience both positive and negative selection. We also review the recently identified mechanisms that modulate heteroplasmy dynamics. Taken together, this is an opportune time to survey the literature and to identify key cellular pathways that can be targeted to develop therapies for diseases caused by heteroplasmic mtDNA mutations.
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Affiliation(s)
- Claudia V Pereira
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA
| | - Bryan L Gitschlag
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA
| | - Maulik R Patel
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA.,Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, USA.,Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, TN, USA
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11
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Bagge EK, Fujimori-Tonou N, Kubota-Sakashita M, Kasahara T, Kato T. Unbiased PCR-free spatio-temporal mapping of the mtDNA mutation spectrum reveals brain region-specific responses to replication instability. BMC Biol 2020; 18:150. [PMID: 33097039 PMCID: PMC7585204 DOI: 10.1186/s12915-020-00890-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Accepted: 10/06/2020] [Indexed: 12/24/2022] Open
Abstract
Background The accumulation of mtDNA mutations in different tissues from various mouse models has been widely studied especially in the context of mtDNA mutation-driven ageing but has been confounded by the inherent limitations of the most widely used approaches. By implementing a method to sequence mtDNA without PCR amplification prior to library preparation, we map the full unbiased mtDNA mutation spectrum across six distinct brain regions from mice. Results We demonstrate that ageing-induced levels of mtDNA mutations (single nucleotide variants and deletions) reach stable levels at 50 weeks of age but can be further elevated specifically in the cortex, nucleus accumbens (NAc), and paraventricular thalamic nucleus (PVT) by expression of a proof-reading-deficient mitochondrial DNA polymerase, PolgD181A. The increase in single nucleotide variants increases the fraction of shared SNVs as well as their frequency, while characteristics of deletions remain largely unaffected. In addition, PolgD181A also induces an ageing-dependent accumulation of non-coding control-region multimers in NAc and PVT, a feature that appears almost non-existent in wild-type mice. Conclusions Our data provide a novel view of the spatio-temporal accumulation of mtDNA mutations using very limited tissue input. The differential response of brain regions to a state of replication instability provides insight into a possible heterogenic mitochondrial landscape across the brain that may be involved in the ageing phenotype and mitochondria-associated disorders.
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Affiliation(s)
- Emilie Kristine Bagge
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Center for Brain Science, Wako, Saitama, Japan
| | - Noriko Fujimori-Tonou
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Center for Brain Science, Wako, Saitama, Japan.,Current address: Support Unit for Bio-Material Analysis, Research Resources Division, RIKEN Center for Brain Science, Wako, Saitama, Japan
| | - Mie Kubota-Sakashita
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Center for Brain Science, Wako, Saitama, Japan
| | - Takaoki Kasahara
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Center for Brain Science, Wako, Saitama, Japan.,Current address: Career Development Program, RIKEN Center for Brain Science, Wako, Saitama, Japan
| | - Tadafumi Kato
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Center for Brain Science, Wako, Saitama, Japan. .,Department of Psychiatry and Behavioral Science, Juntendo University, Graduate School of Medicine, Hongo 2-1-1, Bunkyo, Tokyo 113-8421, Japan.
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12
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Lawless C, Greaves L, Reeve AK, Turnbull DM, Vincent AE. The rise and rise of mitochondrial DNA mutations. Open Biol 2020; 10:200061. [PMID: 32428418 PMCID: PMC7276526 DOI: 10.1098/rsob.200061] [Citation(s) in RCA: 75] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Accepted: 04/23/2020] [Indexed: 12/24/2022] Open
Abstract
How mitochondrial DNA mutations clonally expand in an individual cell is a question that has perplexed mitochondrial biologists for decades. A growing body of literature indicates that mitochondrial DNA mutations play a major role in ageing, metabolic diseases, neurodegenerative diseases, neuromuscular disorders and cancers. Importantly, this process of clonal expansion occurs for both inherited and somatic mitochondrial DNA mutations. To complicate matters further there are fundamental differences between mitochondrial DNA point mutations and deletions, and between mitotic and post-mitotic cells, that impact this pathogenic process. These differences, along with the challenges of investigating a longitudinal process occurring over decades in humans, have so far hindered progress towards understanding clonal expansion. Here we summarize our current understanding of the clonal expansion of mitochondrial DNA mutations in different tissues and highlight key unanswered questions. We then discuss the various existing biological models, along with their advantages and disadvantages. Finally, we explore what has been achieved with mathematical modelling so far and suggest future work to advance this important area of research.
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Affiliation(s)
| | | | | | - Doug M. Turnbull
- Wellcome Centre for Mitochondrial Research, Clinical and Translational Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle NE2 4HH, UK
| | - Amy E. Vincent
- Wellcome Centre for Mitochondrial Research, Clinical and Translational Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle NE2 4HH, UK
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13
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van den Ameele J, Li AY, Ma H, Chinnery PF. Mitochondrial heteroplasmy beyond the oocyte bottleneck. Semin Cell Dev Biol 2020; 97:156-166. [DOI: 10.1016/j.semcdb.2019.10.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 09/17/2019] [Accepted: 10/01/2019] [Indexed: 12/31/2022]
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14
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Lehmann D, Tuppen HAL, Campbell GE, Alston CL, Lawless C, Rosa HS, Rocha MC, Reeve AK, Nicholls TJ, Deschauer M, Zierz S, Taylor RW, Turnbull DM, Vincent AE. Understanding mitochondrial DNA maintenance disorders at the single muscle fibre level. Nucleic Acids Res 2019; 47:7430-7443. [PMID: 31147703 PMCID: PMC6698645 DOI: 10.1093/nar/gkz472] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Revised: 05/12/2019] [Accepted: 05/16/2019] [Indexed: 01/07/2023] Open
Abstract
Clonal expansion of mitochondrial DNA (mtDNA) deletions is an important pathological mechanism in adults with mtDNA maintenance disorders, leading to a mosaic mitochondrial respiratory chain deficiency in skeletal muscle. This study had two aims: (i) to determine if different Mendelian mtDNA maintenance disorders showed similar pattern of mtDNA deletions and respiratory chain deficiency and (ii) to investigate the correlation between the mitochondrial genetic defect and corresponding respiratory chain deficiency. We performed a quantitative analysis of respiratory chain deficiency, at a single cell level, in a cohort of patients with mutations in mtDNA maintenance genes. Using the same tissue section, we performed laser microdissection and single cell genetic analysis to investigate the relationship between mtDNA deletion characteristics and the respiratory chain deficiency. The pattern of respiratory chain deficiency is similar with different genetic defects. We demonstrate a clear correlation between the level of mtDNA deletion and extent of respiratory chain deficiency within a single cell. Long-range and single molecule PCR shows the presence of multiple mtDNA deletions in approximately one-third of all muscle fibres. We did not detect evidence of a replicative advantage for smaller mtDNA molecules in the majority of fibres, but further analysis is needed to provide conclusive evidence.
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Affiliation(s)
- Diana Lehmann
- Department of Neurology, University of Ulm, 89075, Ulm, Germany.,Department of Neurology, University of Halle-Wittenberg, 06120, Halle/Saale, Germany
| | - Helen A L Tuppen
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Georgia E Campbell
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Charlotte L Alston
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.,NHS Highly Specialised Mitochondrial Diagnostic Laboratory, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, NE2 4HH, UK
| | - Conor Lawless
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Hannah S Rosa
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Mariana C Rocha
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Amy K Reeve
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.,Centre for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Thomas J Nicholls
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Marcus Deschauer
- Department of Neurology, Technical University Munich, 81675, Munich, Germany
| | - Stephan Zierz
- Department of Neurology, University of Halle-Wittenberg, 06120, Halle/Saale, Germany
| | - Robert W Taylor
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.,NHS Highly Specialised Mitochondrial Diagnostic Laboratory, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, NE2 4HH, UK
| | - Doug M Turnbull
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.,Centre for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Amy E Vincent
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.,Centre for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
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15
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Dubie JJ, Caraway AR, Stout MM, Katju V, Bergthorsson U. The conflict within: origin, proliferation and persistence of a spontaneously arising selfish mitochondrial genome. Philos Trans R Soc Lond B Biol Sci 2019; 375:20190174. [PMID: 31787044 DOI: 10.1098/rstb.2019.0174] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Mitochondrial genomes can sustain mutations that are simultaneously detrimental to individual fitness and yet, can proliferate within individuals owing to a replicative advantage. We analysed the fitness effects and population dynamics of a mitochondrial genome containing a novel 499 bp deletion in the cytochrome b(1) (ctb-1) gene (Δctb-1) encoding the cytochrome b of complex III in Caenorhabditis elegans. Δctb-1 reached a high heteroplasmic frequency of 96% in one experimental line during a mutation accumulation experiment and was linked to additional spontaneous mutations in nd5 and tRNA-Asn. The Δctb-1 mutant mitotype imposed a significant fitness cost including a 65% and 52% reduction in productivity and competitive fitness, respectively, relative to individuals bearing wild-type (WT) mitochondria. Deletion-bearing worms were rapidly purged within a few generations when competed against WT mitochondrial DNA (mtDNA) bearing worms in experimental populations. By contrast, the Δctb-1 mitotype was able to persist in large populations comprising heteroplasmic individuals only, although the average intracellular frequency of Δctb-1 exhibited a slow decline owing to competition among individuals bearing different frequencies of the heteroplasmy. Within experimental lines subjected to severe population bottlenecks (n = 1), the relative intracellular frequency of Δctb-1 increased, which is a hallmark of selfish drive. A positive correlation between Δctb-1 and WT mtDNA copy-number suggests a mechanism that increases total mtDNA per se, and does not discern the Δctb-1 mitotype from the WT mtDNA. This study demonstrates the selfish nature of the Δctb-1 mitotype, given its transmission advantage and substantial fitness load for the host, and highlights the importance of population size for the population dynamics of selfish mtDNA. This article is part of the theme issue 'Linking the mitochondrial genotype to phenotype: a complex endeavour'.
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Affiliation(s)
- Joseph James Dubie
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
| | - Avery Robert Caraway
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
| | - McKenna Margaret Stout
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
| | - Vaishali Katju
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
| | - Ulfar Bergthorsson
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
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16
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Vincent AE, White K, Davey T, Philips J, Ogden RT, Lawless C, Warren C, Hall MG, Ng YS, Falkous G, Holden T, Deehan D, Taylor RW, Turnbull DM, Picard M. Quantitative 3D Mapping of the Human Skeletal Muscle Mitochondrial Network. Cell Rep 2019; 26:996-1009.e4. [PMID: 30655224 PMCID: PMC6513570 DOI: 10.1016/j.celrep.2019.01.010] [Citation(s) in RCA: 100] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Revised: 10/11/2018] [Accepted: 01/02/2019] [Indexed: 01/07/2023] Open
Abstract
Genetic and biochemical defects of mitochondrial function are a major
cause of human disease, but their link to mitochondrial morphology in
situ has not been defined. Here, we develop a quantitative
three-dimensional approach to map mitochondrial network organization in human
muscle at electron microscopy resolution. We establish morphological differences
between human and mouse and among patients with mitochondrial DNA (mtDNA)
diseases compared to healthy controls. We also define the ultrastructure and
prevalence of mitochondrial nanotunnels, which exist as either free-ended or
connecting membrane protrusions across non-adjacent mitochondria. A multivariate
model integrating mitochondrial volume, morphological complexity, and branching
anisotropy computed across individual mitochondria and mitochondrial populations
identifies increased proportion of simple mitochondria and nanotunnels as a
discriminant signature of mitochondrial stress. Overall, these data define the
nature of the mitochondrial network in human muscle, quantify human-mouse
differences, and suggest potential morphological markers of mitochondrial
dysfunction in human tissues. Vincent et al. use 3D electron microscopy to provide a quantitative
morphometric assessment of human skeletal muscle mitochondria. They find that
healthy human muscle mitochondria differ from mouse mitochondria and show that
primary mtDNA defects are associated with a distinct morphological signature
including increased abundance of mitochondrial nanotunnels.
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Affiliation(s)
- Amy E Vincent
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK; MRC Centre for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, UK
| | - Kathryn White
- EM Research Services, Newcastle University, Newcastle upon Tyne, UK
| | - Tracey Davey
- EM Research Services, Newcastle University, Newcastle upon Tyne, UK
| | - Jonathan Philips
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - R Todd Ogden
- Institute of Child Health, University College London, London, UK
| | - Conor Lawless
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Charlotte Warren
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK; MRC Centre for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, UK
| | - Matt G Hall
- National Physical Laboratory, Teddington, UK; Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Yi Shiau Ng
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Gavin Falkous
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Thomas Holden
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - David Deehan
- Department of Biostatistics, Columbia University Mailman School of Public Health, New York, NY, USA
| | - Robert W Taylor
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Doug M Turnbull
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK; MRC Centre for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, UK.
| | - Martin Picard
- Department of Psychiatry, Division of Behavioral Medicine, Columbia University Irving Medical Center, New York, NY, USA; Department of Neurology and Columbia Translational Neuroscience Initiative, H. Houston Merritt Center, Columbia University Irving Medical Center, New York, NY, USA; Columbia University Aging Center, Columbia University, New York, NY, USA.
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17
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Abstract
Mitochondrial myopathies are progressive muscle conditions caused primarily by the impairment of oxidative phosphorylation (OXPHOS) in the mitochondria. This causes a deficit in energy production in the form of adenosine triphosphate (ATP), particularly in skeletal muscle. The diagnosis of mitochondrial myopathy is reliant on the combination of numerous techniques including traditional histochemical, immunohistochemical, and biochemical testing combined with the fast-emerging molecular genetic techniques, namely next-generation sequencing (NGS). This has allowed for the diagnosis to become more effective in terms of determining causative or novel genes. However, there are currently no effective or disease-modifying treatments available for the vast majority of patients with mitochondrial myopathies. Existing therapeutic options focus on the symptomatic management of disease manifestations. An increasing number of clinical trials have investigated the therapeutic effects of various vitamins, cofactors, and small molecules, though these trials have failed to show definitive outcome measures for clinical practice thus far. In addition, new molecular strategies, specifically mtZFNs and mtTALENs, that cause beneficial heteroplasmic shifts in cell lines harboring varying pathogenic mtDNA mutations offer hope for the future. Moreover, recent developments in the reproductive options for patients with mitochondrial myopathies mean that for some families, the possibility of preventing transmission of the mutation to the next generation is now possible.
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Affiliation(s)
- Syeda T Ahmed
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Lyndsey Craven
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Oliver M Russell
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Doug M Turnbull
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
- MRC Centre for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, UK
| | - Amy E Vincent
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK.
- MRC Centre for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, UK.
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18
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Vincent AE, Rosa HS, Pabis K, Lawless C, Chen C, Grünewald A, Rygiel KA, Rocha MC, Reeve AK, Falkous G, Perissi V, White K, Davey T, Petrof BJ, Sayer AA, Cooper C, Deehan D, Taylor RW, Turnbull DM, Picard M. Subcellular origin of mitochondrial DNA deletions in human skeletal muscle. Ann Neurol 2018; 84:289-301. [PMID: 30014514 PMCID: PMC6141001 DOI: 10.1002/ana.25288] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 07/02/2018] [Accepted: 07/02/2018] [Indexed: 01/07/2023]
Abstract
OBJECTIVE In patients with mitochondrial DNA (mtDNA) maintenance disorders and with aging, mtDNA deletions sporadically form and clonally expand within individual muscle fibers, causing respiratory chain deficiency. This study aimed to identify the sub-cellular origin and potential mechanisms underlying this process. METHODS Serial skeletal muscle cryosections from patients with multiple mtDNA deletions were subjected to subcellular immunofluorescent, histochemical, and genetic analysis. RESULTS We report respiratory chain-deficient perinuclear foci containing mtDNA deletions, which show local elevations of both mitochondrial mass and mtDNA copy number. These subcellular foci of respiratory chain deficiency are associated with a local increase in mitochondrial biogenesis and unfolded protein response signaling pathways. We also find that the commonly reported segmental pattern of mitochondrial deficiency is consistent with the three-dimensional organization of the human skeletal muscle mitochondrial network. INTERPRETATION We propose that mtDNA deletions first exceed the biochemical threshold causing biochemical deficiency in focal regions adjacent to the myonuclei, and induce mitochondrial biogenesis before spreading across the muscle fiber. These subcellular resolution data provide new insights into the possible origin of mitochondrial respiratory chain deficiency in mitochondrial myopathy. Ann Neurol 2018;84:289-301.
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Affiliation(s)
- Amy E Vincent
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Hannah S Rosa
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Kamil Pabis
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Conor Lawless
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Chun Chen
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Anne Grünewald
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom.,Institute of Neurogenetics, University of Lübeck, Lübeck, Germany.,Molecular and Functional Neurobiology Group, Luxembourg Center for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Karolina A Rygiel
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Mariana C Rocha
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Amy K Reeve
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Gavin Falkous
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Valentina Perissi
- Department of Biochemistry, Boston University School of Medicine, Boston, MA
| | - Kathryn White
- Electron Microscopy Research Services, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Tracey Davey
- Electron Microscopy Research Services, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Basil J Petrof
- Meakins-Christie Laboratories, Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada
| | - Avan A Sayer
- National Institute for Health Research Newcastle Biomedical Research Centre, Newcastle upon Tyne Hospitals National Health Service Foundation Trust and Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Cyrus Cooper
- Medical Research Council Lifecourse Epidemiology Unit, University of Southampton, Southampton, United Kingdom
| | - David Deehan
- Institute of Cellular Medicine, Newcastle University, Newcastle Upon Tyne, United Kingdom
| | - Robert W Taylor
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Doug M Turnbull
- Wellcome Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Martin Picard
- Department of Psychiatry, Division of Behavioral Medicine, Columbia University Medical Center, New York, NY.,Department of Neurology and Columbia Translational Neuroscience Initiative, H. Houston Merritt Center, Columbia University Medical Center, New York, NY.,Columbia University Aging Center, Columbia University, New York, NY
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19
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Clonal expansion of mtDNA deletions: different disease models assessed by digital droplet PCR in single muscle cells. Sci Rep 2018; 8:11682. [PMID: 30076399 PMCID: PMC6076247 DOI: 10.1038/s41598-018-30143-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 07/18/2018] [Indexed: 01/07/2023] Open
Abstract
Deletions in mitochondrial DNA (mtDNA) are an important cause of human disease and their accumulation has been implicated in the ageing process. As mtDNA is a high copy number genome, the coexistence of deleted and wild-type mtDNA molecules within a single cell defines heteroplasmy. When deleted mtDNA molecules, driven by intracellular clonal expansion, reach a sufficiently high level, a biochemical defect emerges, contributing to the appearance and progression of clinical pathology. Consequently, it is relevant to determine the heteroplasmy levels within individual cells to understand the mechanism of clonal expansion. Heteroplasmy is reflected in a mosaic distribution of cytochrome c oxidase (COX)-deficient muscle fibers. We applied droplet digital PCR (ddPCR) to single muscle fibers collected by laser-capture microdissection (LCM) from muscle biopsies of patients with different paradigms of mitochondrial disease, characterized by the accumulation of single or multiple mtDNA deletions. By combining these two sensitive approaches, ddPCR and LCM, we document different models of clonal expansion in patients with single and multiple mtDNA deletions, implicating different mechanisms and time points for the development of COX deficiency in these molecularly distinct mitochondrial cytopathies.
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20
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Clinical syndromes associated with mtDNA mutations: where we stand after 30 years. Essays Biochem 2018; 62:235-254. [DOI: 10.1042/ebc20170097] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Revised: 05/29/2018] [Accepted: 05/30/2018] [Indexed: 01/16/2023]
Abstract
The landmark year 1988 can be considered as the birthdate of mitochondrial medicine, when the first pathogenic mutations affecting mtDNA were associated with human diseases. Three decades later, the field still expands and we are not ‘scraping the bottom of the barrel’ yet. Despite the tremendous progress in terms of molecular characterization and genotype/phenotype correlations, for the vast majority of cases we still lack a deep understanding of the pathogenesis, good models to study, and effective therapeutic options. However, recent technological advances including somatic cell reprogramming to induced pluripotent stem cells (iPSCs), organoid technology, and tailored endonucleases provide unprecedented opportunities to fill these gaps, casting hope to soon cure the major primary mitochondrial phenotypes reviewed here. This group of rare diseases represents a key model for tackling the pathogenic mechanisms involving mitochondrial biology relevant to much more common disorders that affect our currently ageing population, such as diabetes and metabolic syndrome, neurodegenerative and inflammatory disorders, and cancer.
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21
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Resolving the Enigma of the Clonal Expansion of mtDNA Deletions. Genes (Basel) 2018; 9:genes9030126. [PMID: 29495484 PMCID: PMC5867847 DOI: 10.3390/genes9030126] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Revised: 02/14/2018] [Accepted: 02/16/2018] [Indexed: 12/31/2022] Open
Abstract
Mitochondria are cell organelles that are special since they contain their own genetic material in the form of mitochondrial DNA (mtDNA). Damage and mutations of mtDNA are not only involved in several inherited human diseases but are also widely thought to play an important role during aging. In both cases, point mutations or large deletions accumulate inside cells, leading to functional impairment once a certain threshold has been surpassed. In most cases, it is a single type of mutant that clonally expands and out-competes the wild type mtDNA, with different mutant molecules being amplified in different cells. The challenge is to explain where the selection advantage for the accumulation comes from, why such a large range of different deletions seem to possess this advantage, and how this process can scale to species with different lifespans such as those of rats and man. From this perspective, we provide an overview of current ideas, present an update of our own proposal, and discuss the wider relevance of the phenomenon for aging.
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22
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Preferential amplification of a human mitochondrial DNA deletion in vitro and in vivo. Sci Rep 2018; 8:1799. [PMID: 29379065 PMCID: PMC5789095 DOI: 10.1038/s41598-018-20064-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Accepted: 12/27/2017] [Indexed: 01/19/2023] Open
Abstract
We generated induced pluripotent stem cells (iPSCs) from patient fibroblasts to yield cell lines containing varying degrees of heteroplasmy for a m.13514 A > G mtDNA point mutation (2 lines) and for a ~6 kb single, large scale mtDNA deletion (3 lines). Long term culture of the iPSCs containing a single, large-scale mtDNA deletion showed consistent increase in mtDNA deletion levels with time. Higher levels of mtDNA heteroplasmy correlated with increased respiratory deficiency. To determine what changes occurred in deletion level during differentiation, teratomas comprising all three embryonic germ layers were generated from low (20%) and intermediate heteroplasmy (55%) mtDNA deletion clones. Regardless of whether iPSCs harbouring low or intermediate mtDNA heteroplasmy were used, the final levels of heteroplasmy in all teratoma germ layers increased to a similar high level (>60%). Thus, during human stem cell division, cells not only tolerate high mtDNA deletion loads but seem to preferentially replicate deleted mtDNA genomes. This has implications for the involvement of mtDNA deletions in both disease and ageing.
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23
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Origins of mtDNA mutations in ageing. Essays Biochem 2017; 61:325-337. [PMID: 28698307 DOI: 10.1042/ebc20160090] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 05/24/2017] [Accepted: 05/26/2017] [Indexed: 12/21/2022]
Abstract
MtDNA mutations are one of the hallmarks of ageing and age-related diseases. It is well established that somatic point mutations accumulate in mtDNA of multiple organs and tissues with increasing age and heteroplasmy is universal in mammals. However, the origin of these mutations remains controversial. The long-lasting hypothesis stating that mtDNA mutations emanate from oxidative damage via a self-perpetuating mechanism has been extensively challenged in recent years. Contrary to this initial ascertainment, mtDNA appears to be well protected from action of reactive oxygen species (ROS) through robust protein coating and endomitochondrial microcompartmentalization. Extensive development of scrupulous high-throughput DNA sequencing methods suggests that an imperfect replication process, rather than oxidative lesions are the main sources of mtDNA point mutations, indicating that mtDNA polymerase γ (POLG) might be responsible for the majority of mtDNA mutagenic events. Here, we summarize the recent knowledge in prevention and defence of mtDNA oxidative lesions and discuss the plausible mechanisms of mtDNA point mutation generation and fixation.
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24
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Abstract
Mitochondria were first postulated to contribute to aging more than 40 years ago. During the following decades, multiple lines of evidence in model organisms and humans showed that impaired mitochondrial function can contribute to age-associated disease phenotypes and aging. However, in contrast to the original theory favoring oxidative damage as a cause for mtDNA mutations, there are now strong data arguing that most mammalian mtDNA mutations originate as replication errors made by the mtDNA polymerase. Currently, a substantial amount of mitochondrial research is focused on finding ways to either remove or counteract the effects of mtDNA mutations with the hope of extending the human health- and lifespan. This review summarizes the current knowledge regarding the formation of mtDNA mutations and their impact on mitochondrial function. We also critically discuss proposed pathways interlinked with mammalian mtDNA mutations and suggest future research strategies to elucidate the role of mtDNA mutations in aging.
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Affiliation(s)
- Timo E S Kauppila
- Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, D-50931 Cologne, Germany
| | - Johanna H K Kauppila
- Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, D-50931 Cologne, Germany
| | - Nils-Göran Larsson
- Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, D-50931 Cologne, Germany; Department of Medical Biochemistry and Biophysics, Karolinska Institutet, 171 77 Stockholm, Sweden.
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25
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Abstract
Clonal expansion of mtDNA deletions compromises mitochondrial function in human disease and aging, but how deleterious mtDNA genomes propagate has remained unclear. In this issue (Gitschlag et al., 2016) and in a recent Nature publication, C. elegans studies implicate the mitochondrial unfolded protein response (UPR(mt)) and offer mechanistic insights into this process.
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Affiliation(s)
- Martin Picard
- Department of Psychiatry, Division of Behavioral Medicine, Columbia University Medical Center, New York, NY 10032, USA; Department of Neurology and Columbia Translational Neuroscience Initiative, H. Houston Merritt Center, Columbia University Medical Center, New York, NY 10032, USA; Wellcome Trust Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neurosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - Amy E Vincent
- Wellcome Trust Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neurosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - Doug M Turnbull
- Wellcome Trust Centre for Mitochondrial Research and Newcastle Centre for Ageing and Vitality, Institute of Neurosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
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26
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Digital PCR methods improve detection sensitivity and measurement precision of low abundance mtDNA deletions. Sci Rep 2016; 6:25186. [PMID: 27122135 PMCID: PMC4848546 DOI: 10.1038/srep25186] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2015] [Accepted: 04/12/2016] [Indexed: 02/05/2023] Open
Abstract
Mitochondrial DNA (mtDNA) mutations are a common cause of primary mitochondrial disorders, and have also been implicated in a broad collection of conditions, including aging, neurodegeneration, and cancer. Prevalent among these pathogenic variants are mtDNA deletions, which show a strong bias for the loss of sequence in the major arc between, but not including, the heavy and light strand origins of replication. Because individual mtDNA deletions can accumulate focally, occur with multiple mixed breakpoints, and in the presence of normal mtDNA sequences, methods that detect broad-spectrum mutations with enhanced sensitivity and limited costs have both research and clinical applications. In this study, we evaluated semi-quantitative and digital PCR-based methods of mtDNA deletion detection using double-stranded reference templates or biological samples. Our aim was to describe key experimental assay parameters that will enable the analysis of low levels or small differences in mtDNA deletion load during disease progression, with limited false-positive detection. We determined that the digital PCR method significantly improved mtDNA deletion detection sensitivity through absolute quantitation, improved precision and reduced assay standard error.
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27
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Rocha MC, Grady JP, Grünewald A, Vincent A, Dobson PF, Taylor RW, Turnbull DM, Rygiel KA. A novel immunofluorescent assay to investigate oxidative phosphorylation deficiency in mitochondrial myopathy: understanding mechanisms and improving diagnosis. Sci Rep 2015; 5:15037. [PMID: 26469001 PMCID: PMC4606788 DOI: 10.1038/srep15037] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 09/04/2015] [Indexed: 02/07/2023] Open
Abstract
Oxidative phosphorylation defects in human tissues are often challenging to quantify due to a mosaic pattern of deficiency. Biochemical assays are difficult to interpret due to the varying enzyme deficiency levels found in individual cells. Histochemical analysis allows semi-quantitative assessment of complex II and complex IV activities, but there is no validated histochemical assay to assess complex I activity which is frequently affected in mitochondrial pathology. To help improve the diagnosis of mitochondrial disease and to study the mechanisms underlying mitochondrial abnormalities in disease, we have developed a quadruple immunofluorescent technique enabling the quantification of key respiratory chain subunits of complexes I and IV, together with an indicator of mitochondrial mass and a cell membrane marker. This assay gives precise and objective quantification of protein abundance in large numbers of individual muscle fibres. By assessing muscle biopsies from subjects with a range of different mitochondrial genetic defects we have demonstrated that specific genotypes exhibit distinct biochemical signatures in muscle, providing evidence for the diagnostic use of the technique, as well as insight into the underlying molecular pathology. Stringent testing for reproducibility and sensitivity confirms the potential value of the technique for mechanistic studies of disease and in the evaluation of therapeutic approaches.
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Affiliation(s)
- Mariana C Rocha
- Newcastle University Centre for Ageing and Vitality, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.,Wellcome Trust Centre for Mitochondrial Research, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - John P Grady
- Wellcome Trust Centre for Mitochondrial Research, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Anne Grünewald
- Wellcome Trust Centre for Mitochondrial Research, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Amy Vincent
- Wellcome Trust Centre for Mitochondrial Research, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Philip F Dobson
- Newcastle University Centre for Ageing and Vitality, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Robert W Taylor
- Wellcome Trust Centre for Mitochondrial Research, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Doug M Turnbull
- Newcastle University Centre for Ageing and Vitality, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.,Wellcome Trust Centre for Mitochondrial Research, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Karolina A Rygiel
- Newcastle University Centre for Ageing and Vitality, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.,Wellcome Trust Centre for Mitochondrial Research, Institute for Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
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28
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Abstract
Because of their high-energy metabolism, neurons are strictly dependent on mitochondria, which generate cellular ATP through oxidative phosphorylation. The mitochondrial genome encodes for critical components of the oxidative phosphorylation pathway machinery, and therefore, mutations in mitochondrial DNA (mtDNA) cause energy production defects that frequently have severe neurological manifestations. Here, we review the principles of mitochondrial genetics and focus on prototypical mitochondrial diseases to illustrate how primary defects in mtDNA or secondary defects in mtDNA due to nuclear genome mutations can cause prominent neurological and multisystem features. In addition, we discuss the pathophysiological mechanisms underlying mitochondrial diseases, the cellular mechanisms that protect mitochondrial integrity, and the prospects for therapy.
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Affiliation(s)
- Valerio Carelli
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy; Neurology Unit, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - David C Chan
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
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Carelli V, Maresca A, Caporali L, Trifunov S, Zanna C, Rugolo M. Mitochondria: Biogenesis and mitophagy balance in segregation and clonal expansion of mitochondrial DNA mutations. Int J Biochem Cell Biol 2015; 63:21-4. [PMID: 25666555 DOI: 10.1016/j.biocel.2015.01.023] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Revised: 01/20/2015] [Accepted: 01/29/2015] [Indexed: 12/31/2022]
Abstract
Mitochondria are cytoplasmic organelles containing their own multi-copy genome. They are organized in a highly dynamic network, resulting from balance between fission and fusion, which maintains homeostasis of mitochondrial mass through mitochondrial biogenesis and mitophagy. Mitochondrial DNA (mtDNA) mutates much faster than nuclear DNA. In particular, mtDNA point mutations and deletions may occur somatically and accumulate with aging, coexisting with the wild type, a condition known as heteroplasmy. Under specific circumstances, clonal expansion of mutant mtDNA may occur within single cells, causing a wide range of severe human diseases when mutant overcomes wild type. Furthermore, mtDNA deletions accumulate and clonally expand as a consequence of deleterious mutations in nuclear genes involved in mtDNA replication and maintenance, as well as in mitochondrial fusion genes (mitofusin-2 and OPA1), possibly implicating mtDNA nucleoids segregation. We here discuss how the intricacies of mitochondrial homeostasis impinge on the intracellular propagation of mutant mtDNA. This article is part of a Directed Issue entitled: Energy Metabolism Disorders and Therapies.
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Affiliation(s)
- Valerio Carelli
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy; Unit of Neurology, Department of Biomedical and NeuroMotor Sciences (DIBINEM), University of Bologna, Bologna, Italy.
| | - Alessandra Maresca
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy; Unit of Neurology, Department of Biomedical and NeuroMotor Sciences (DIBINEM), University of Bologna, Bologna, Italy
| | - Leonardo Caporali
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy; Unit of Neurology, Department of Biomedical and NeuroMotor Sciences (DIBINEM), University of Bologna, Bologna, Italy
| | - Selena Trifunov
- Unit of Neurology, Department of Biomedical and NeuroMotor Sciences (DIBINEM), University of Bologna, Bologna, Italy; Unit of Cellular Biochemistry, Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Claudia Zanna
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy; Unit of Cellular Biochemistry, Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Michela Rugolo
- Unit of Cellular Biochemistry, Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
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Khrapko K, Turnbull D. Mitochondrial DNA mutations in aging. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 127:29-62. [PMID: 25149213 DOI: 10.1016/b978-0-12-394625-6.00002-7] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The relationship of mitochondrial DNA mutations to aging is still debated. Most mtDNA mutations are recessive: there are multiple copies per cell and mutation needs to clonally expand to cause respiratory deficiency. Overall mtDNA mutant loads are low, so effects of mutations are limited to critical areas where mutations locally reach high fractions. This includes respiratory chain deficient zones in muscle fibers, respiratory-deficient crypts in colon, and massive expansions of deleted mtDNA in substantia nigra neurons. mtDNA "mutator" mouse with increased rate of mtDNA mutations is a useful model, although rates and distribution of mutations may significantly deviate from what is observed in human aging. Comparison of species with different longevity reveals intriguing longevity-related traits in mtDNA sequence, although their significance is yet to be evaluated. The impact of somatic mtDNA mutations rapidly increases with age, so their importance is expected to grow as human life expectancy increases.
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Affiliation(s)
- Konstantin Khrapko
- Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
| | - Doug Turnbull
- LLHW Centre for Ageing and Vitality, Newcastle University, Newcastle, United Kingdom
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