51
|
Varma H, Faust PL, Iglesias AD, Lagana SM, Wou K, Hirano M, DiMauro S, Mansukani MM, Hoff KE, Nagy PL, Copeland WC, Naini AB. Whole exome sequencing identifies a homozygous POLG2 missense variant in an infant with fulminant hepatic failure and mitochondrial DNA depletion. Eur J Med Genet 2016; 59:540-5. [PMID: 27592148 DOI: 10.1016/j.ejmg.2016.08.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Revised: 08/04/2016] [Accepted: 08/31/2016] [Indexed: 11/26/2022]
Abstract
Mitochondrial DNA (mtDNA) depletion syndrome manifests as diverse early-onset diseases that affect skeletal muscle, brain and liver function. Mutations in several nuclear DNA-encoded genes cause mtDNA depletion. We report on a patient, a 3-month-old boy who presented with hepatic failure, and was found to have severe mtDNA depletion in liver and muscle. Whole-exome sequencing identified a homozygous missense variant (c.544C > T, p.R182W) in the accessory subunit of mitochondrial DNA polymerase gamma (POLG2), which is required for mitochondrial DNA replication. This variant is predicted to disrupt a critical region needed for homodimerization of the POLG2 protein and cause loss of processive DNA synthesis. Both parents were phenotypically normal and heterozygous for this variant. Heterozygous mutations in POLG2 were previously associated with progressive external ophthalmoplegia and mtDNA deletions. This is the first report of a patient with a homozygous mutation in POLG2 and with a clinical presentation of severe hepatic failure and mitochondrial depletion.
Collapse
Affiliation(s)
- Hemant Varma
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA; Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, USA
| | - Phyllis L Faust
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA
| | - Alejandro D Iglesias
- Division of Medical Genetics, Columbia University, New York Presbyterian Hospital, USA
| | - Stephen M Lagana
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA
| | - Karen Wou
- Division of Genetics, New York Presbyterian Hospital, USA
| | - Michio Hirano
- Department of Neurology, Columbia University Medical Center, USA
| | | | - Mahesh M Mansukani
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA; Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, USA
| | - Kirsten E Hoff
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
| | - Peter L Nagy
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA; Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, USA
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA.
| | - Ali B Naini
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA; Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, USA.
| |
Collapse
|
52
|
Abstract
Recent advances in the field of mitochondrial DNA (mtDNA) replication highlight the diversity of both the mechanisms utilized and the structural and functional organization of the proteins at mtDNA replication fork, despite the relative simplicity of the animal mtDNA genome. DNA polymerase γ, mtDNA helicase and mitochondrial single-stranded DNA-binding protein-the key replisome proteins, have evolved distinct structural features and biochemical properties. These appear to be correlated with mtDNA genomic features in different metazoan taxa and with their modes of DNA replication, although substantial integrative research is warranted to establish firmly these links. To date, several modes of mtDNA replication have been described for animals: rolling circle, theta, strand-displacement, and RITOLS/bootlace. Resolution of a continuing controversy relevant to mtDNA replication in mammals/vertebrates will have a direct impact on the mechanistic interpretation of mtDNA-related human diseases. Here we review these subjects, integrating earlier and recent data to provide a perspective on the major challenges for future research.
Collapse
Affiliation(s)
- G L Ciesielski
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland; Michigan State University, East Lansing, MI, United States
| | - M T Oliveira
- Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista "Júlio de Mesquita Filho", Jaboticabal, SP, Brazil
| | - L S Kaguni
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland; Michigan State University, East Lansing, MI, United States.
| |
Collapse
|
53
|
Young MJ, Copeland WC. Human mitochondrial DNA replication machinery and disease. Curr Opin Genet Dev 2016; 38:52-62. [PMID: 27065468 DOI: 10.1016/j.gde.2016.03.005] [Citation(s) in RCA: 129] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 03/03/2016] [Accepted: 03/08/2016] [Indexed: 12/21/2022]
Abstract
The human mitochondrial genome is replicated by DNA polymerase γ in concert with key components of the mitochondrial DNA (mtDNA) replication machinery. Defects in mtDNA replication or nucleotide metabolism cause deletions, point mutations, or depletion of mtDNA. The resulting loss of cellular respiration ultimately induces mitochondrial genetic diseases, including mtDNA depletion syndromes (MDS) such as Alpers or early infantile hepatocerebral syndromes, and mtDNA deletion disorders such as progressive external ophthalmoplegia, ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy. Here we review the current literature regarding human mtDNA replication and heritable disorders caused by genetic changes of the POLG, POLG2, Twinkle, RNASEH1, DNA2, and MGME1 genes.
Collapse
Affiliation(s)
- Matthew J Young
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709, United States
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709, United States.
| |
Collapse
|
54
|
Paramasivam A, Meena AK, Pedaparthi L, Jyothi V, Uppin MS, Jabeen SA, Sundaram C, Thangaraj K. Novel mutation in C10orf2 associated with multiple mtDNA deletions, chronic progressive external ophthalmoplegia and premature aging. Mitochondrion 2015; 26:81-5. [PMID: 26689116 DOI: 10.1016/j.mito.2015.12.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 12/11/2015] [Accepted: 12/11/2015] [Indexed: 11/15/2022]
Abstract
Chronic progressive external ophthalmoplegia (CPEO) is caused by defects in both mitochondrial and nuclear genes, however, the causal genetic factors in large number of patients remains undetermined. Therefore, our aim was to screen 12 unrelated patients with CPEO for mutation/multiple deletions in mtDNA and mutations in the coding regions of C10orf2, which is essential for mtDNA replication. Histopathological study of muscle biopsy revealed cytochrome c oxidase-deficient fibers and ragged blue fibers in all the patients. Long-range PCR of DNA from skeletal muscle revealed multiple mtDNA deletions in all the 12 patients. Further, sequencing coding regions of C10orf2 revealed three variants in three different patients, of which two were novel (c.1964G>A/p.G655D; c.204G>A/p.G68G) variants and one was reported (c.1052A>G/p. N351S). Sequencing of other nuclear genes that are associated with CPEO and multiple mtDNA deletions, such as; POLG1, POLG2, TK2, ANT1, DGUOK, MPV17 and RRM2B did not reveal any pathogenic mutation in patients with C10orf2 mutation. Since in silico analyses revealed p.G655D could be a potentially pathogenic and it was absent in 200 healthy controls, p.G655D could be the causative factor for CPEO. Therefore, we suggest that C10orf2 gene should be screened in CPEO individuals with multiple mtDNA deletions, which might help in prognosis of this disease and appropriate genetic counseling.
Collapse
Affiliation(s)
| | | | - Lalitha Pedaparthi
- Department of Neurology, Nizam's Institute of Medical Sciences, Hyderabad, India
| | | | - Megha S Uppin
- Department of Pathology, Nizam's Institute of Medical Sciences, Hyderabad, India
| | - Shaikh Afshan Jabeen
- Department of Neurology, Nizam's Institute of Medical Sciences, Hyderabad, India
| | - Challa Sundaram
- Department of Pathology, Nizam's Institute of Medical Sciences, Hyderabad, India
| | | |
Collapse
|
55
|
Cabrera-Pérez R, Torres-Torronteras J, Vila-Julià F, Ortega FJ, Cámara Y, Barquinero J, Martí R. Prospective therapeutic approaches in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). Expert Opin Orphan Drugs 2015. [DOI: 10.1517/21678707.2015.1090307] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
|
56
|
Young MJ, Humble MM, DeBalsi KL, Sun KY, Copeland WC. POLG2 disease variants: analyses reveal a dominant negative heterodimer, altered mitochondrial localization and impaired respiratory capacity. Hum Mol Genet 2015; 24:5184-97. [PMID: 26123486 PMCID: PMC4550827 DOI: 10.1093/hmg/ddv240] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Revised: 06/02/2015] [Accepted: 06/22/2015] [Indexed: 01/14/2023] Open
Abstract
Human mitochondrial DNA (mtDNA) is replicated and repaired by the mtDNA polymerase gamma, polγ. Polγ is composed of three subunits encoded by two nuclear genes: (1) POLG codes for the 140-kilodalton (kDa) catalytic subunit, p140 and (2) POLG2 encodes the ∼110-kDa homodimeric accessory subunit, p55. Specific mutations are associated with POLG- or POLG2-related disorders. During DNA replication the p55 accessory subunit binds to p140 and increases processivity by preventing polγ's dissociation from the template. To date, studies have demonstrated that homodimeric p55 disease variants are deficient in the ability to stimulate p140; however, all patients currently identified with POLG2-related disorders are heterozygotes. In these patients, we expect p55 to occur as 25% wild-type (WT) homodimers, 25% variant homodimers and 50% heterodimers. We report the development of a tandem affinity strategy to isolate p55 heterodimers. The WT/G451E p55 heterodimer impairs polγ function in vitro, demonstrating that the POLG2 c.1352G>A/p.G451E mutation encodes a dominant negative protein. To analyze the subcellular consequence of disease mutations in HEK293 cells, we designed plasmids encoding p55 disease variants tagged with green fluorescent protein (GFP). P205R and L475DfsX2 p55 variants exhibit irregular diffuse mitochondrial fluorescence and unlike WT p55, they fail to form distinct puncta associated with mtDNA nucleoids. Furthermore, homogenous preparations of P205R and L475DfsX2 p55 form aberrant reducible multimers. We predict that abnormal protein folding or aggregation or both contribute to the pathophysiology of these disorders. Examination of mitochondrial bioenergetics in stable cell lines overexpressing GFP-tagged p55 variants revealed impaired mitochondrial reserve capacity.
Collapse
Affiliation(s)
- Matthew J Young
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| | - Margaret M Humble
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| | - Karen L DeBalsi
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| | - Kathie Y Sun
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| |
Collapse
|
57
|
Nagappa M, Bindu PS, Taly AB, Sonam K, Shwetha C, Kumar R, Gayathri N, Srinivas‐Bharath M, Arvinda HR, Sinha S, Paramasivam A, Thangaraj K. Palatal Tremor in POLG-Associated Ataxia. Mov Disord Clin Pract 2015; 2:318-320. [PMID: 30363534 PMCID: PMC6178733 DOI: 10.1002/mdc3.12195] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2015] [Revised: 03/22/2015] [Accepted: 03/25/2015] [Indexed: 11/08/2022] Open
Affiliation(s)
- Madhu Nagappa
- Department of NeurologyNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Parayil Sankaran Bindu
- Department of NeurologyNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Arun B. Taly
- Department of NeurologyNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Kothari Sonam
- Department of Clinical NeurosciencesNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Chiplunkar Shwetha
- Department of Clinical NeurosciencesNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Rakesh Kumar
- Department of NeurologyNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Narayanappa Gayathri
- Department of NeuropathologyNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - M.M. Srinivas‐Bharath
- Department of NeurochemistryNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Hanumanthapura R. Arvinda
- Department of Neuroimaging and Interventional RadiologyNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Sanjib Sinha
- Department of NeurologyNational Institute of Mental Health and NeurosciencesBangaloreIndia
| | - Arumugam Paramasivam
- Center for Scientific and Industrial Research–Center for Cellular and Molecular Biology (CSIR‐CCMB)HyderabadIndia
| | - Kumarasamy Thangaraj
- Center for Scientific and Industrial Research–Center for Cellular and Molecular Biology (CSIR‐CCMB)HyderabadIndia
| |
Collapse
|
58
|
Ahmed N, Ronchi D, Comi GP. Genes and Pathways Involved in Adult Onset Disorders Featuring Muscle Mitochondrial DNA Instability. Int J Mol Sci 2015; 16:18054-76. [PMID: 26251896 PMCID: PMC4581235 DOI: 10.3390/ijms160818054] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Revised: 07/27/2015] [Accepted: 07/28/2015] [Indexed: 12/31/2022] Open
Abstract
Replication and maintenance of mtDNA entirely relies on a set of proteins encoded by the nuclear genome, which include members of the core replicative machinery, proteins involved in the homeostasis of mitochondrial dNTPs pools or deputed to the control of mitochondrial dynamics and morphology. Mutations in their coding genes have been observed in familial and sporadic forms of pediatric and adult-onset clinical phenotypes featuring mtDNA instability. The list of defects involved in these disorders has recently expanded, including mutations in the exo-/endo-nuclease flap-processing proteins MGME1 and DNA2, supporting the notion that an enzymatic DNA repair system actively takes place in mitochondria. The results obtained in the last few years acknowledge the contribution of next-generation sequencing methods in the identification of new disease loci in small groups of patients and even single probands. Although heterogeneous, these genes can be conveniently classified according to the pathway to which they belong. The definition of the molecular and biochemical features of these pathways might be helpful for fundamental knowledge of these disorders, to accelerate genetic diagnosis of patients and the development of rational therapies. In this review, we discuss the molecular findings disclosed in adult patients with muscle pathology hallmarked by mtDNA instability.
Collapse
Affiliation(s)
- Naghia Ahmed
- Neurology Unit, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, Dino Ferrari Centre, Department of Pathophysiology and Transplantation, Università degli Studi di Milano, via Francesco Sforza 35, Milan 20122, Italy.
| | - Dario Ronchi
- Neurology Unit, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, Dino Ferrari Centre, Department of Pathophysiology and Transplantation, Università degli Studi di Milano, via Francesco Sforza 35, Milan 20122, Italy.
| | - Giacomo Pietro Comi
- Neurology Unit, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, Dino Ferrari Centre, Department of Pathophysiology and Transplantation, Università degli Studi di Milano, via Francesco Sforza 35, Milan 20122, Italy.
| |
Collapse
|
59
|
Carelli V, Musumeci O, Caporali L, Zanna C, La Morgia C, Del Dotto V, Porcelli AM, Rugolo M, Valentino ML, Iommarini L, Maresca A, Barboni P, Carbonelli M, Trombetta C, Valente EM, Patergnani S, Giorgi C, Pinton P, Rizzo G, Tonon C, Lodi R, Avoni P, Liguori R, Baruzzi A, Toscano A, Zeviani M. Syndromic parkinsonism and dementia associated with OPA1 missense mutations. Ann Neurol 2015; 78:21-38. [PMID: 25820230 PMCID: PMC5008165 DOI: 10.1002/ana.24410] [Citation(s) in RCA: 137] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Revised: 03/23/2015] [Accepted: 03/24/2015] [Indexed: 01/07/2023]
Abstract
Objective Mounting evidence links neurodegenerative disorders such as Parkinson disease and Alzheimer disease with mitochondrial dysfunction, and recent emphasis has focused on mitochondrial dynamics and quality control. Mitochondrial dynamics and mtDNA maintenance is another link recently emerged, implicating mutations in the mitochondrial fusion genes OPA1 and MFN2 in the pathogenesis of multisystem syndromes characterized by neurodegeneration and accumulation of mtDNA multiple deletions in postmitotic tissues. Here, we report 2 Italian families affected by dominant chronic progressive external ophthalmoplegia (CPEO) complicated by parkinsonism and dementia. Methods Patients were extensively studied by optical coherence tomography (OCT) to assess retinal nerve fibers, and underwent muscle and brain magnetic resonance spectroscopy (MRS), and muscle biopsy and fibroblasts were analyzed. Candidate genes were sequenced, and mtDNA was analyzed for rearrangements. Results Affected individuals displayed a slowly progressive syndrome characterized by CPEO, mitochondrial myopathy, sensorineural deafness, peripheral neuropathy, parkinsonism, and/or cognitive impairment, in most cases without visual complains, but with subclinical loss of retinal nerve fibers at OCT. Muscle biopsies showed cytochrome c oxidase‐negative fibers and mtDNA multiple deletions, and MRS displayed defective oxidative metabolism in muscle and brain. We found 2 heterozygous OPA1 missense mutations affecting highly conserved amino acid positions (p.G488R, p.A495V) in the guanosine triphosphatase domain, each segregating with affected individuals. Fibroblast studies showed a reduced amount of OPA1 protein with normal mRNA expression, fragmented mitochondria, impaired bioenergetics, increased autophagy and mitophagy. Interpretation The association of CPEO and parkinsonism/dementia with subclinical optic neuropathy widens the phenotypic spectrum of OPA1 mutations, highlighting the association of defective mitochondrial dynamics, mtDNA multiple deletions, and altered mitophagy with parkinsonism. Ann Neurol 2015;78:21–38
Collapse
Affiliation(s)
- Valerio Carelli
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy.,Unit of Neurology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Olimpia Musumeci
- Department of Neuroscience, University of Messina, Messina, Italy
| | - Leonardo Caporali
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy
| | - Claudia Zanna
- Unit of Neurology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Chiara La Morgia
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy.,Unit of Neurology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Valentina Del Dotto
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Anna Maria Porcelli
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Michela Rugolo
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Maria Lucia Valentino
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy.,Unit of Neurology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Luisa Iommarini
- Department of Pharmacy and Biotechnology, 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, University of Bologna, Bologna, Italy
| | | | | | | | - Enza Maria Valente
- Mendel Laboratory, IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Foggia, Italy
| | - Simone Patergnani
- Department of Morphology, Surgery, and Experimental Medicine, University of Ferrara, Ferrara, Italy
| | - Carlotta Giorgi
- Department of Morphology, Surgery, and Experimental Medicine, University of Ferrara, Ferrara, Italy
| | - Paolo Pinton
- Department of Morphology, Surgery, and Experimental Medicine, University of Ferrara, Ferrara, Italy
| | - Giovanni Rizzo
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy.,Unit of Neurology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Caterina Tonon
- Functional Magnetic Resonance Unit, St Orsola-Malpighi Polyclinic, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Raffaele Lodi
- Functional Magnetic Resonance Unit, St Orsola-Malpighi Polyclinic, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Patrizia Avoni
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy.,Unit of Neurology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Rocco Liguori
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy.,Unit of Neurology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Agostino Baruzzi
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy.,Unit of Neurology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy
| | - Antonio Toscano
- Department of Neuroscience, University of Messina, Messina, Italy
| | - Massimo Zeviani
- Mitochondrial Biology Unit, Medical Research Council, Cambridge, United Kingdom
| |
Collapse
|
60
|
Szymanski MR, Kuznetsov VB, Shumate C, Meng Q, Lee YS, Patel G, Patel S, Yin YW. Structural basis for processivity and antiviral drug toxicity in human mitochondrial DNA replicase. EMBO J 2015; 34:1959-70. [PMID: 26056153 DOI: 10.15252/embj.201591520] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Accepted: 05/18/2015] [Indexed: 11/09/2022] Open
Abstract
The human DNA polymerase gamma (Pol γ) is responsible for DNA replication in mitochondria. Pol γ is particularly susceptible to inhibition by dideoxynucleoside-based inhibitors designed to fight viral infection. Here, we report crystal structures of the replicating Pol γ-DNA complex bound to either substrate or zalcitabine, an inhibitor used for HIV reverse transcriptase. The structures reveal that zalcitabine binds to the Pol γ active site almost identically to the substrate dCTP, providing a structural basis for Pol γ-mediated drug toxicity. When compared to the apo form, Pol γ undergoes intra- and inter-subunit conformational changes upon formation of the ternary complex with primer/template DNA and substrate. We also find that the accessory subunit Pol γB, which lacks intrinsic enzymatic activity and does not contact the primer/template DNA directly, serves as an allosteric regulator of holoenzyme activities. The structures presented here suggest a mechanism for processivity of the holoenzyme and provide a model for understanding the deleterious effects of Pol γ mutations in human disease. Crystal structures of the mitochondrial DNA polymerase, Pol γ, in complex with substrate or antiviral inhibitor zalcitabine provide a basis for understanding Pol γ-mediated drug toxicity.
Collapse
Affiliation(s)
- Michal R Szymanski
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA
| | - Vladmir B Kuznetsov
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA
| | - Christie Shumate
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA
| | - Qingchao Meng
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA
| | - Young-Sam Lee
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA
| | - Gayatri Patel
- Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ, USA
| | - Smita Patel
- Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ, USA
| | - Y Whitney Yin
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA
| |
Collapse
|
61
|
Iommarini L, Peralta S, Torraco A, Diaz F. Mitochondrial Diseases Part II: Mouse models of OXPHOS deficiencies caused by defects in regulatory factors and other components required for mitochondrial function. Mitochondrion 2015; 22:96-118. [PMID: 25640959 DOI: 10.1016/j.mito.2015.01.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Accepted: 01/22/2015] [Indexed: 01/21/2023]
Abstract
Mitochondrial disorders are defined as defects that affect the oxidative phosphorylation system (OXPHOS). They are characterized by a heterogeneous array of clinical presentations due in part to a wide variety of factors required for proper function of the components of the OXPHOS system. There is no cure for these disorders owing to our poor knowledge of the pathogenic mechanisms of disease. To understand the mechanisms of human disease numerous mouse models have been developed in recent years. Here we summarize the features of several mouse models of mitochondrial diseases directly related to those factors affecting mtDNA maintenance, replication, transcription, translation as well as other proteins that are involved in mitochondrial dynamics and quality control which affect mitochondrial OXPHOS function without being intrinsic components of the system. We discuss how these models have contributed to our understanding of mitochondrial diseases and their pathogenic mechanisms.
Collapse
Affiliation(s)
- Luisa Iommarini
- Department of Pharmacy and Biotechnology (FABIT), University of Bologna, Via Irnerio 42, 40128 Bologna, Italy.
| | - Susana Peralta
- Department of Neurology, University of Miami, Miller School of Medicine, Miami, FL 33136, USA.
| | - Alessandra Torraco
- Unit for Neuromuscular and Neurodegenerative Disorders, Laboratory of Molecular Medicine, Bambino Gesù Children's Hospital, IRCCS, Viale di San Paolo, 15 - 00146, Rome, Italy.
| | - Francisca Diaz
- Department of Neurology, University of Miami, Miller School of Medicine, Miami, FL 33136, USA.
| |
Collapse
|
62
|
Stumpf JD, Copeland WC. MMS exposure promotes increased MtDNA mutagenesis in the presence of replication-defective disease-associated DNA polymerase γ variants. PLoS Genet 2014; 10:e1004748. [PMID: 25340760 PMCID: PMC4207668 DOI: 10.1371/journal.pgen.1004748] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 09/11/2014] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial DNA (mtDNA) encodes proteins essential for ATP production. Mutant variants of the mtDNA polymerase cause mutagenesis that contributes to aging, genetic diseases, and sensitivity to environmental agents. We interrogated mtDNA replication in Saccharomyces cerevisiae strains with disease-associated mutations affecting conserved regions of the mtDNA polymerase, Mip1, in the presence of the wild type Mip1. Mutant frequency arising from mtDNA base substitutions that confer erythromycin resistance and deletions between 21-nucleotide direct repeats was determined. Previously, increased mutagenesis was observed in strains encoding mutant variants that were insufficient to maintain mtDNA and that were not expected to reduce polymerase fidelity or exonuclease proofreading. Increased mutagenesis could be explained by mutant variants stalling the replication fork, thereby predisposing the template DNA to irreparable damage that is bypassed with poor fidelity. This hypothesis suggests that the exogenous base-alkylating agent, methyl methanesulfonate (MMS), would further increase mtDNA mutagenesis. Mitochondrial mutagenesis associated with MMS exposure was increased up to 30-fold in mip1 mutants containing disease-associated alterations that affect polymerase activity. Disrupting exonuclease activity of mutant variants was not associated with increased spontaneous mutagenesis compared with exonuclease-proficient alleles, suggesting that most or all of the mtDNA was replicated by wild type Mip1. A novel subset of C to G transversions was responsible for about half of the mutants arising after MMS exposure implicating error-prone bypass of methylated cytosines as the predominant mutational mechanism. Exposure to MMS does not disrupt exonuclease activity that suppresses deletions between 21-nucleotide direct repeats, suggesting the MMS-induce mutagenesis is not explained by inactivated exonuclease activity. Further, trace amounts of CdCl2 inhibit mtDNA replication but suppresses MMS-induced mutagenesis. These results suggest a novel mechanism wherein mutations that lead to hypermutation by DNA base-damaging agents and associate with mitochondrial disease may contribute to previously unexplained phenomena, such as the wide variation of age of disease onset and acquired mitochondrial toxicities. Thousands of mitochondrial DNA (mtDNA) per cell are necessary to maintain energy required for cellular survival in humans. Interfering with the mtDNA polymerase can result in mitochondrial diseases and mitochondrial toxicity. Therefore, it is important to explore new genetic and environmental mechanisms that alter the effectiveness and accuracy of mtDNA replication. This genetic study uses the budding yeast to demonstrate that heterozygous strains harboring disease-associated mutations in the mtDNA polymerase gene in the presence of a wild type copy of the mtDNA polymerase are associated with increased mtDNA point mutagenesis in the presence of methane methylsulfonate, a known base damaging agent. Further observations suggest that the inability of disease-associated variants to replicate mtDNA resulted in increased vulnerability to irreparable base damage that was likely to result in mutations when replicated. Also, this study showed that trace amounts of the environmental contaminant cadmium chloride impairs mtDNA replication but eliminates damage-induced mutagenesis in the remaining functional mitochondria. This interplay between disease-associated variant and wild type polymerase offers new insights on possible disease variation and implicates novel environmental consequences for compound heterozygous patients.
Collapse
Affiliation(s)
- Jeffrey D. Stumpf
- Mitochondrial DNA Replication Group, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, NIH, DHHS, Research Triangle Park, North Carolina, United States of America
| | - William C. Copeland
- Mitochondrial DNA Replication Group, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, NIH, DHHS, Research Triangle Park, North Carolina, United States of America
- * E-mail:
| |
Collapse
|
63
|
Fuke S, Kametani M, Yamada K, Kasahara T, Kubota-Sakashita M, Kujoth GC, Prolla TA, Hitoshi S, Kato T. Heterozygous Polg mutation causes motor dysfunction due to mtDNA deletions. Ann Clin Transl Neurol 2014; 1:909-20. [PMID: 25540805 PMCID: PMC4265062 DOI: 10.1002/acn3.133] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Revised: 09/25/2014] [Accepted: 09/25/2014] [Indexed: 12/27/2022] Open
Abstract
Objective Mutations in nuclear-encoded mitochondrial DNA (mtDNA) polymerase (POLG) are known to cause autosomal dominant chronic progressive external ophthalmoplegia (adCPEO) with accumulation of multiple mtDNA deletions in muscles. However, no animal model with a heterozygous Polg mutation representing mtDNA impairment and symptoms of CPEO has been established. To understand the pathogenic mechanism of CPEO, it is important to determine the age dependency and tissue specificity of mtDNA impairment resulting from a heterozygous mutation in the Polg gene in an animal model. Methods We assessed behavioral phenotypes, tissue-specific accumulation of mtDNA deletions, and its age dependency in heterozygous PolgD257A knock-in mice carrying a proofreading-deficient mutation in the Polg. Results Heterozygous PolgD257A knock-in mice exhibited motor dysfunction in a rotarod test. Polg+/D257A mice had significant accumulation of multiple mtDNA deletions, but did not show significant accumulation of point mutations or mtDNA depletion in the brain. While mtDNA deletions increased in an age-dependent manner regardless of the tissue even in Polg+/+ mice, the age-dependent accumulation of mtDNA deletions was enhanced in muscles and in the brain of Polg+/D257A mice. Interpretation Heterozygous PolgD257A knock-in mice showed tissue-specific, age-dependent accumulation of multiple mtDNA deletions in muscles and the brain which was likely to result in neuromuscular symptoms. Polg+/D257A mice may be used as an animal model of adCPEO associated with impaired mtDNA maintenance.
Collapse
Affiliation(s)
- Satoshi Fuke
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Brain Science Institute Wako, Saitama, Japan, 351-0198 ; Department of Integrative Physiology, Shiga University of Medical Science Otsu, Shiga, Japan, 520-2192
| | - Mizue Kametani
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Brain Science Institute Wako, Saitama, Japan, 351-0198
| | - Kazuyuki Yamada
- Research Resources Center, RIKEN Brain Science Institute Wako, Saitama, Japan, 351-0198
| | - Takaoki Kasahara
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Brain Science Institute Wako, Saitama, Japan, 351-0198
| | - Mie Kubota-Sakashita
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Brain Science Institute Wako, Saitama, Japan, 351-0198
| | - Gregory C Kujoth
- Department of Neurological Surgery, University of Wisconsin Madison, Wisconsin, 53792
| | - Tomas A Prolla
- Departments of Genetics and Medical Genetics, University of Wisconsin Madison, Wisconsin, 53706
| | - Seiji Hitoshi
- Department of Integrative Physiology, Shiga University of Medical Science Otsu, Shiga, Japan, 520-2192
| | - Tadafumi Kato
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Brain Science Institute Wako, Saitama, Japan, 351-0198
| |
Collapse
|
64
|
Lee SK, Zhao MH, Zheng Z, Kwon JW, Liang S, Kim SH, Kim NH, Cui XS. Polymerase subunit gamma 2 affects porcine oocyte maturation and subsequent embryonic development. Theriogenology 2014; 83:121-30. [PMID: 25308052 DOI: 10.1016/j.theriogenology.2014.08.019] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Revised: 07/16/2014] [Accepted: 08/31/2014] [Indexed: 01/30/2023]
Abstract
Deoxyribonucleic acid polymerase subunit gamma (POLG) is an enzyme encoded by the mitochondrial Polg gene. Polymerase (DNA directed), gamma 2, accessory subunit, also known as POLG2, is involved in mitochondrial replication. In the present study, we examined the role of Polg2 in the maturation of porcine oocytes. After Polg2 knockdown, the mitochondrial DNA copy number was significantly (P < 0.05) lower than that in the control group. However, there was no decrease in mitochondrial membrane potential. The decrease in mitochondrial DNA copy number led to reductions in adenosine-5'-triphosphate content (P < 0.05) and the maturation rate (P < 0.05) of oocytes. Furthermore, in the Polg2-knockdown group, maturation-promoting factor activity was decreased (P < 0.05) and the percentage of oocytes displaying abnormal actin filaments and microtubules was significantly increased (P < 0.05). This likely led to the reduced development rate and number of cells per blastocyst in this group (P < 0.05). In conclusion, Polg2 seems to be critical for mitochondrial replication and regulation of adenosine-5'-triphosphate content and affects porcine oocyte maturation and subsequent embryonic development.
Collapse
Affiliation(s)
- Seul-Ki Lee
- Department of Animal Sciences, Chungbuk National University, Cheongju, South Korea; Brain Korea 21 Center for Bio-Resource Development, Cheongju, South Korea
| | - Ming-Hui Zhao
- Department of Animal Sciences, Chungbuk National University, Cheongju, South Korea; Brain Korea 21 Center for Bio-Resource Development, Cheongju, South Korea
| | - Zhong Zheng
- Department of Animal Sciences, Chungbuk National University, Cheongju, South Korea; Brain Korea 21 Center for Bio-Resource Development, Cheongju, South Korea
| | - Jung-Woo Kwon
- Department of Animal Sciences, Chungbuk National University, Cheongju, South Korea; Brain Korea 21 Center for Bio-Resource Development, Cheongju, South Korea
| | - Shuang Liang
- Department of Animal Sciences, Chungbuk National University, Cheongju, South Korea; Brain Korea 21 Center for Bio-Resource Development, Cheongju, South Korea
| | - Seon-Hyang Kim
- Department of Animal Sciences, Chungbuk National University, Cheongju, South Korea; Brain Korea 21 Center for Bio-Resource Development, Cheongju, South Korea
| | - Nam-Hyung Kim
- Department of Animal Sciences, Chungbuk National University, Cheongju, South Korea; Brain Korea 21 Center for Bio-Resource Development, Cheongju, South Korea
| | - Xiang-Shun Cui
- Department of Animal Sciences, Chungbuk National University, Cheongju, South Korea; Brain Korea 21 Center for Bio-Resource Development, Cheongju, South Korea.
| |
Collapse
|
65
|
Abstract
Mitochondrial DNA is replicated by DNA polymerase γ in concert with accessory proteins such as the mitochondrial DNA helicase, single-stranded DNA binding protein, topoisomerase, and initiating factors. Defects in mitochondrial DNA replication or nucleotide metabolism can cause mitochondrial genetic diseases due to mitochondrial DNA deletions, point mutations, or depletion, which ultimately cause loss of oxidative phosphorylation. These genetic diseases include mitochondrial DNA depletion syndromes such as Alpers or early infantile hepatocerebral syndromes, and mitochondrial DNA deletion disorders, such as progressive external ophthalmoplegia, ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy. This review focuses on our current knowledge of genetic defects of mitochondrial DNA replication (POLG, POLG2, C10orf2, and MGME1) that cause instability of mitochondrial DNA and mitochondrial disease.
Collapse
Affiliation(s)
- William C. Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
| |
Collapse
|
66
|
Nicholls TJ, Zsurka G, Peeva V, Schöler S, Szczesny RJ, Cysewski D, Reyes A, Kornblum C, Sciacco M, Moggio M, Dziembowski A, Kunz WS, Minczuk M. Linear mtDNA fragments and unusual mtDNA rearrangements associated with pathological deficiency of MGME1 exonuclease. Hum Mol Genet 2014; 23:6147-62. [PMID: 24986917 PMCID: PMC4222359 DOI: 10.1093/hmg/ddu336] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
MGME1, also known as Ddk1 or C20orf72, is a mitochondrial exonuclease found to be involved in the processing of mitochondrial DNA (mtDNA) during replication. Here, we present detailed insights on the role of MGME1 in mtDNA maintenance. Upon loss of MGME1, elongated 7S DNA species accumulate owing to incomplete processing of 5′ ends. Moreover, an 11-kb linear mtDNA fragment spanning the entire major arc of the mitochondrial genome is generated. In contrast to control cells, where linear mtDNA molecules are detectable only after nuclease S1 treatment, the 11-kb fragment persists in MGME1-deficient cells. In parallel, we observed characteristic mtDNA duplications in the absence of MGME1. The fact that the breakpoints of these mtDNA rearrangements do not correspond to either classical deletions or the ends of the linear 11-kb fragment points to a role of MGME1 in processing mtDNA ends, possibly enabling their repair by homologous recombination. In agreement with its functional involvement in mtDNA maintenance, we show that MGME1 interacts with the mitochondrial replicase PolgA, suggesting that it is a constituent of the mitochondrial replisome, to which it provides an additional exonuclease activity. Thus, our results support the viewpoint that MGME1-mediated mtDNA processing is essential for faithful mitochondrial genome replication and might be required for intramolecular recombination of mtDNA.
Collapse
Affiliation(s)
| | - Gábor Zsurka
- Department of Epileptology, Life and Brain Center and
| | | | | | - Roman J Szczesny
- Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Warsaw, Poland, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland and
| | - Dominik Cysewski
- Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Warsaw, Poland, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland and
| | - Aurelio Reyes
- Mitochondrial Biology Unit, Medical Research Council, Cambridge, UK
| | - Cornelia Kornblum
- Department of Neurology, University of Bonn Medical Center, Bonn, Germany
| | - Monica Sciacco
- Neuromuscular Unit, Fondazione IRCCS Ca' Granda, Ospedale Maggiore Policlinico, Centro Dino Ferrari, University of Milan, Milan, Italy
| | - Maurizio Moggio
- Neuromuscular Unit, Fondazione IRCCS Ca' Granda, Ospedale Maggiore Policlinico, Centro Dino Ferrari, University of Milan, Milan, Italy
| | - Andrzej Dziembowski
- Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Warsaw, Poland, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland and
| | | | - Michal Minczuk
- Mitochondrial Biology Unit, Medical Research Council, Cambridge, UK,
| |
Collapse
|
67
|
Vartiainen S, Chen S, George J, Tuomela T, Luoto KR, O'Dell KMC, Jacobs HT. Phenotypic rescue of a Drosophila model of mitochondrial ANT1 disease. Dis Model Mech 2014; 7:635-48. [PMID: 24812436 PMCID: PMC4036471 DOI: 10.1242/dmm.016527] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
A point mutation in the Drosophila gene that codes for the major adult isoform of adenine nuclear translocase (ANT) represents a model for human diseases that are associated with ANT insufficiency [stress-sensitive B1 (sesB1)]. We characterized the organismal, bioenergetic and molecular phenotype of sesB1 flies then tested strategies to compensate the mutant phenotype. In addition to developmental delay and mechanical-stress-induced seizures, sesB1 flies have an impaired response to sound, defective male courtship, female sterility and curtailed lifespan. These phenotypes, excluding the latter two, are shared with the mitoribosomal protein S12 mutant, tko25t. Mitochondria from sesB1 adults showed a decreased respiratory control ratio and downregulation of cytochrome oxidase. sesB1 adults exhibited ATP depletion, lactate accumulation and changes in gene expression that were consistent with a metabolic shift towards glycolysis, characterized by activation of lactate dehydrogenase and anaplerotic pathways. Females also showed downregulation of many genes that are required for oogenesis, and their eggs, although fertilized, failed to develop to the larval stages. The sesB1 phenotypes of developmental delay and mechanical-stress-induced seizures were alleviated by an altered mitochondrial DNA background. Female sterility was substantially rescued by somatic expression of alternative oxidase (AOX) from the sea squirt Ciona intestinalis, whereas AOX did not alleviate developmental delay. Our findings illustrate the potential of different therapeutic strategies for ANT-linked diseases, based on alleviating metabolic stress.
Collapse
Affiliation(s)
- Suvi Vartiainen
- BioMediTech and Tampere University Hospital, FI-33014 University of Tampere, Finland
| | - Shanjun Chen
- BioMediTech and Tampere University Hospital, FI-33014 University of Tampere, Finland
| | - Jack George
- BioMediTech and Tampere University Hospital, FI-33014 University of Tampere, Finland
| | - Tea Tuomela
- BioMediTech and Tampere University Hospital, FI-33014 University of Tampere, Finland
| | - Kaisa R Luoto
- BioMediTech and Tampere University Hospital, FI-33014 University of Tampere, Finland
| | - Kevin M C O'Dell
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow G12 8QQ, Scotland, UK
| | - Howard T Jacobs
- BioMediTech and Tampere University Hospital, FI-33014 University of Tampere, Finland. Research Program of Molecular Neurology, FI-00014 University of Helsinki, Finland.
| |
Collapse
|
68
|
Chaussenot A, Paquis-Flucklinger V. An overview of neurological and neuromuscular signs in mitochondrial diseases. Rev Neurol (Paris) 2014; 170:323-38. [DOI: 10.1016/j.neurol.2014.03.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Accepted: 03/24/2014] [Indexed: 01/10/2023]
|
69
|
Pfeffer G, Gorman GS, Griffin H, Kurzawa-Akanbi M, Blakely EL, Wilson I, Sitarz K, Moore D, Murphy JL, Alston CL, Pyle A, Coxhead J, Payne B, Gorrie GH, Longman C, Hadjivassiliou M, McConville J, Dick D, Imam I, Hilton D, Norwood F, Baker MR, Jaiser SR, Yu-Wai-Man P, Farrell M, McCarthy A, Lynch T, McFarland R, Schaefer AM, Turnbull DM, Horvath R, Taylor RW, Chinnery PF. Mutations in the SPG7 gene cause chronic progressive external ophthalmoplegia through disordered mitochondrial DNA maintenance. Brain 2014; 137:1323-36. [PMID: 24727571 PMCID: PMC3999722 DOI: 10.1093/brain/awu060] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 01/12/2014] [Accepted: 01/30/2014] [Indexed: 12/12/2022] Open
Abstract
Despite being a canonical presenting feature of mitochondrial disease, the genetic basis of progressive external ophthalmoplegia remains unknown in a large proportion of patients. Here we show that mutations in SPG7 are a novel cause of progressive external ophthalmoplegia associated with multiple mitochondrial DNA deletions. After excluding known causes, whole exome sequencing, targeted Sanger sequencing and multiplex ligation-dependent probe amplification analysis were used to study 68 adult patients with progressive external ophthalmoplegia either with or without multiple mitochondrial DNA deletions in skeletal muscle. Nine patients (eight probands) were found to carry compound heterozygous SPG7 mutations, including three novel mutations: two missense mutations c.2221G>A; p.(Glu741Lys), c.2224G>A; p.(Asp742Asn), a truncating mutation c.861dupT; p.Asn288*, and seven previously reported mutations. We identified a further six patients with single heterozygous mutations in SPG7, including two further novel mutations: c.184-3C>T (predicted to remove a splice site before exon 2) and c.1067C>T; p.(Thr356Met). The clinical phenotype typically developed in mid-adult life with either progressive external ophthalmoplegia/ptosis and spastic ataxia, or a progressive ataxic disorder. Dysphagia and proximal myopathy were common, but urinary symptoms were rare, despite the spasticity. Functional studies included transcript analysis, proteomics, mitochondrial network analysis, single fibre mitochondrial DNA analysis and deep re-sequencing of mitochondrial DNA. SPG7 mutations caused increased mitochondrial biogenesis in patient muscle, and mitochondrial fusion in patient fibroblasts associated with the clonal expansion of mitochondrial DNA mutations. In conclusion, the SPG7 gene should be screened in patients in whom a disorder of mitochondrial DNA maintenance is suspected when spastic ataxia is prominent. The complex neurological phenotype is likely a result of the clonal expansion of secondary mitochondrial DNA mutations modulating the phenotype, driven by compensatory mitochondrial biogenesis.
Collapse
Affiliation(s)
- Gerald Pfeffer
- 1 Wellcome Centre for Mitochondrial Research, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
70
|
Genetics of mitochondrial respiratory chain deficiencies. Rev Neurol (Paris) 2014; 170:309-22. [DOI: 10.1016/j.neurol.2013.11.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Accepted: 11/27/2013] [Indexed: 01/21/2023]
|
71
|
Tanaka K, Tateishi T, Kawamura N, Ohyagi Y, Urata M, Kira JI. [A case of sensory ataxic neuropathy, dysarthria, and ophthalmoparesis with multiple mitochondrial DNA deletions]. Rinsho Shinkeigaku 2014; 53:205-11. [PMID: 23524600 DOI: 10.5692/clinicalneurol.53.205] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
We report the case of a 62-year-old man with sensory ataxic neuropathy, dysarthria, and ophthalmoparesis (SANDO). He developed gait disturbance at 54 years of age, muscle weakness at 56 years, and difficulty hearing at 58 years. His brother had muscle weakness in both legs from age 20 years, and was diagnosed with Charcot-Marie-Tooth disease because he had muscle weakness of the four extremities, decreased CMAP and SNAP amplitudes on peripheral nerve conduction tests, and loss of large myelinated fibers and onion-bulb formations on sural nerve biopsy. His brother died aged 46 years, but no accurate cause of death was identified. Neurological examination of the present patient revealed bilateral ptosis, external ophthalmoparesis, dysarthria, dysphagia, sensorineural hearing loss, mild weakness and atrophy of proximal muscles in all four limbs, severe sensory ataxia, and disturbance of deep sensation in his legs. He showed elevation of lactate and pyruvate levels in cerebrospinal fluid and serum. An aerobic exercise test disclosed a marked increase in lactate and pyruvate levels in serum. On nerve conduction study, amplitudes of CMAP and SNAP, and F wave-evoked frequency were decreased. Needle electromyography showed chronic neurogenic patterns with fibrillation potentials in the extremity muscles. Head MRI demonstrated T2 prolonged lesions in the bilateral basal ganglia, while brain MRS revealed a small lactate peak. Biopsy of his left lateral vastus muscle showed ragged-red fibers and group atrophy, and some muscle fibers had decreased cytochrome c activity. Left sural nerve biopsy revealed a marked loss of large myelinated fibers, and some onion-bulb formations. Genetic testing disclosed a large mtDNA deletion in the biopsied muscle. Among nuclear genes, we found point mutations in ANT-1 (exon 1 c.105G>A, 5' untranslated region) and POLG-1 (exon 4, c.1218G>A, p. and exon 23 c.3920C>T, p.A1217V). We diagnosed SANDO. This is the first case of SANDO with large mitochondrial DNA deletions in Japanese.
Collapse
Affiliation(s)
- Koji Tanaka
- Department of Neurology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University
| | | | | | | | | | | |
Collapse
|
72
|
Siciliano G, Pasquali L, Mancuso M, Murri L. Molecular diagnostics and mitochondrial dysfunction: a future perspective. Expert Rev Mol Diagn 2014; 8:531-49. [DOI: 10.1586/14737159.8.4.531] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
73
|
Ohnuki Y, Takahashi K, Iijima E, Takahashi W, Suzuki S, Ozaki Y, Kitao R, Mihara M, Ishihara T, Nakamura M, Sawano Y, Goto YI, Izumi S, Kulski JK, Shiina T, Takizawa S. Multiple deletions in mitochondrial DNA in a patient with progressive external ophthalmoplegia, leukoencephalopathy and hypogonadism. Intern Med 2014; 53:1365-9. [PMID: 24930659 DOI: 10.2169/internalmedicine.53.1320] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Progressive external ophthalmoplegia (PEO) is one of a number of major types of mitochondrial disorders. Most sporadic PEO patients have a heteroplasmic large deletion of mitochondrial DNA (mtDNA) in the mitochondria in skeletal muscles. We herein analyzed mtDNA deletions using sub-cloning and Sanger sequencing of PCR products in a 31-year-old Japanese man with multiple symptoms, including PEO, muscle weakness, hearing loss, leukoencephalopathy and hypogonadism. A large number of multiple deletions was detected, as well as four kinds of deletion breakpoints identified in different locations, including m.3347_12322, m.5818_13964, m.5829_13964 and m.5837_13503.
Collapse
Affiliation(s)
- Yuko Ohnuki
- Department of Molecular Life Science, Basic Medical Science and Molecular Medicine, Tokai University School of Medicine, Japan
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
74
|
Jackson AP, Laskey RA, Coleman N. Replication proteins and human disease. Cold Spring Harb Perspect Biol 2014; 6:cshperspect.a013060. [PMID: 23881941 DOI: 10.1101/cshperspect.a013060] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
In this article, we discuss the significance of DNA replication proteins in human disease. There is a broad range of mutations in genes encoding replication proteins, which result in several distinct clinical disorders that share common themes. One group of replication proteins, the MCMs, has emerged as effective biomarkers for early detection of a range of common cancers. They offer practical and theoretical advantages over other replication proteins and have been developed for widespread clinical use.
Collapse
Affiliation(s)
- Andrew P Jackson
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | | | | |
Collapse
|
75
|
Bouchard C, Rankinen T, Timmons JA. Genomics and genetics in the biology of adaptation to exercise. Compr Physiol 2013; 1:1603-48. [PMID: 23733655 DOI: 10.1002/cphy.c100059] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
This article is devoted to the role of genetic variation and gene-exercise interactions in the biology of adaptation to exercise. There is evidence from genetic epidemiology research that DNA sequence differences contribute to human variation in physical activity level, cardiorespiratory fitness in the untrained state, cardiovascular and metabolic response to acute exercise, and responsiveness to regular exercise. Methodological and technological advances have made it possible to undertake the molecular dissection of the genetic component of complex, multifactorial traits, such as those of interest to exercise biology, in terms of tissue expression profile, genes, and allelic variants. The evidence from animal models and human studies is considered. Data on candidate genes, genome-wide linkage results, genome-wide association findings, expression arrays, and combinations of these approaches are reviewed. Combining transcriptomic and genomic technologies has been shown to be more powerful as evidenced by the development of a recent molecular predictor of the ability to increase VO2max with exercise training. For exercise as a behavior and physiological fitness as a state to be major players in public health policies will require that the role of human individuality and the influence of DNA sequence differences be understood. Likewise, progress in the use of exercise in therapeutic medicine will depend to a large extent on our ability to identify the favorable responders for given physiological properties to a given exercise regimen.
Collapse
Affiliation(s)
- Claude Bouchard
- Human Genomics Laboratory, Pennington Biomedical Research Center, Baton Rouge, Louisiana, USA.
| | | | | |
Collapse
|
76
|
Cámara Y, González-Vioque E, Scarpelli M, Torres-Torronteras J, Martí R. Feeding the deoxyribonucleoside salvage pathway to rescue mitochondrial DNA. Drug Discov Today 2013; 18:950-7. [DOI: 10.1016/j.drudis.2013.06.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Revised: 05/27/2013] [Accepted: 06/19/2013] [Indexed: 12/16/2022]
|
77
|
Milone M, Wong LJ. Diagnosis of mitochondrial myopathies. Mol Genet Metab 2013; 110:35-41. [PMID: 23911206 DOI: 10.1016/j.ymgme.2013.07.007] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2013] [Revised: 07/10/2013] [Accepted: 07/10/2013] [Indexed: 01/01/2023]
Abstract
Mitochondria are ubiquitous organelles and play crucial roles in vital functions, most importantly, the oxidative phosphorylation and energy metabolism. Therefore, mitochondrial dysfunction can affect multiple tissues, with muscle and nerve preferentially affected. Mitochondrial myopathy is a common clinical phenotype, which is characterized by early fatigue and/or fixed muscle weakness; rhabdomyolysis can seldom occur. Muscle biopsy often identifies signs of diseased mitochondria by morphological studies, while biochemical analysis may identify respiratory chain deficiencies. The clinical, morphological and biochemical data guide molecular analysis. Being the mitochondrial function under the control of both mitochondrial DNA and nuclear DNA, the search for mitochondrial DNA mutations and mitochondrial DNA quantitation, may not be sufficient for the molecular diagnosis of mitochondrial myopathies. Approximately 1500 nuclear genes can affect mitochondrial structure and function and the targeting of such genes may be necessary to reach the diagnosis. The identification of causative molecular defects in nuclear or mitochondrial genome leads to the definite diagnosis of mitochondrial myopathy.
Collapse
Affiliation(s)
- Margherita Milone
- Department of Neurology, Neuromuscular Division, Mayo Clinic, Rochester, MN, USA
| | | |
Collapse
|
78
|
Swett RJ, Elias A, Miller JA, Dyson GE, Andrés Cisneros G. Hypothesis driven single nucleotide polymorphism search (HyDn-SNP-S). DNA Repair (Amst) 2013; 12:733-40. [PMID: 23830898 DOI: 10.1016/j.dnarep.2013.06.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 05/27/2013] [Accepted: 06/11/2013] [Indexed: 12/28/2022]
Abstract
The advent of complete-genome genotyping across phenotype cohorts has provided a rich source of information for bioinformaticians. However the search for SNPs from this data is generally performed on a study-by-study case without any specific hypothesis of the location for SNPs that are predictive for the phenotype. We have designed a method whereby very large SNP lists (several gigabytes in size), combining several genotyping studies at once, can be sorted and traced back to their ultimate consequence in protein structure. Given a working hypothesis, researchers are able to easily search whole genome genotyping data for SNPs that link genetic locations to phenotypes. This allows a targeted search for correlations between phenotypes and potentially relevant systems, rather than utilizing statistical methods only. HyDn-SNP-S returns results that are less data dense, allowing more thorough analysis, including haplotype analysis. We have applied our method to correlate DNA polymerases to cancer phenotypes using four of the available cancer databases in dbGaP. Logistic regression and derived haplotype analysis indicates that ~80SNPs, previously overlooked, are statistically significant. Derived haplotypes from this work link POLL to breast cancer and POLG to prostate cancer with an increase in incidence of 3.01- and 9.6-fold, respectively. Molecular dynamics simulations on wild-type and one of the SNP mutants from the haplotype of POLL provide insights at the atomic level on the functional impact of this cancer related SNP. Furthermore, HyDn-SNP-S has been designed to allow application to any system. The program is available upon request from the authors.
Collapse
Affiliation(s)
- Rebecca J Swett
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, MI 48202, USA
| | | | | | | | | |
Collapse
|
79
|
Affiliation(s)
- Jin-Hong Shin
- Department of Neurology, Pusan National University Yangsan Hospital, Yangsan, Korea
| | - Dae-Seong Kim
- Department of Neurology, Pusan National University Yangsan Hospital, Yangsan, Korea
| |
Collapse
|
80
|
Zsurka G, Kunz WS. Mitochondrial involvement in neurodegenerative diseases. IUBMB Life 2013; 65:263-72. [PMID: 23341346 DOI: 10.1002/iub.1126] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 12/06/2012] [Accepted: 12/06/2012] [Indexed: 01/12/2023]
Abstract
The classical bioenergetical view of the involvement of mitochondria in neurogeneration is based on the fact that mitochondria are the central players of ATP synthesis in neurons and their failure leads to neuronal dysfunction and eventually to cell death. Mutations in at least 39 genes in inherited neurodegenerative disorders seem to alter directly or indirectly mitochondrial function. Most of these mutations do not directly affect oxidative phosphorylation, but act through disturbed mitochondrial dynamics and quality control. This, however, does not invalidate the bioenergetic hypothesis. Neurodegeneration is not necessarily associated with a gross failure of ATP production, but might rather be a consequence of local insufficiencies of ATP supply in critical compartments of neurons, like the presynaptic terminal. We hypothesize that slow disease progression, at least in a subgroup of neurodegenerative diseases, can be explained by the parallel action of subcellular ATP insufficiency and clonal expansion of somatic mitochondrial DNA mutations, and particularly deletions.
Collapse
Affiliation(s)
- Gábor Zsurka
- Department of Epileptology and Life and Brain Center, University Bonn, Bonn, Germany
| | | |
Collapse
|
81
|
Loss-of-function mutations in MGME1 impair mtDNA replication and cause multisystemic mitochondrial disease. Nat Genet 2013; 45:214-9. [PMID: 23313956 DOI: 10.1038/ng.2501] [Citation(s) in RCA: 163] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Accepted: 11/28/2012] [Indexed: 12/17/2022]
Abstract
Known disease mechanisms in mitochondrial DNA (mtDNA) maintenance disorders alter either the mitochondrial replication machinery (POLG, POLG2 and C10orf2) or the biosynthesis pathways of deoxyribonucleoside 5'-triphosphates for mtDNA synthesis. However, in many of these disorders, the underlying genetic defect has yet to be discovered. Here, we identify homozygous nonsense and missense mutations in the orphan gene C20orf72 in three families with a mitochondrial syndrome characterized by external ophthalmoplegia, emaciation and respiratory failure. Muscle biopsies showed mtDNA depletion and multiple mtDNA deletions. C20orf72, hereafter MGME1 (mitochondrial genome maintenance exonuclease 1), encodes a mitochondrial RecB-type exonuclease belonging to the PD-(D/E)XK nuclease superfamily. We show that MGME1 cleaves single-stranded DNA and processes DNA flap substrates. Fibroblasts from affected individuals do not repopulate after chemically induced mtDNA depletion. They also accumulate intermediates of stalled replication and show increased levels of 7S DNA, as do MGME1-depleted cells. Thus, we show that MGME1-mediated mtDNA processing is essential for mitochondrial genome maintenance.
Collapse
|
82
|
Sohl CD, Kasiviswanathan R, Copeland WC, Anderson KS. Mutations in human DNA polymerase γ confer unique mechanisms of catalytic deficiency that mirror the disease severity in mitochondrial disorder patients. Hum Mol Genet 2012. [PMID: 23208208 DOI: 10.1093/hmg/dds509] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Human mitochondrial DNA polymerase γ (pol γ) is solely responsible for the replication and repair of the mitochondrial genome. Unsurprisingly, alterations in pol γ activity have been associated with mitochondrial diseases such as Alpers syndrome and progressive external ophthalmoplegia. Thus far, predicting the severity of mitochondrial disease based the magnitude of deficiency in pol γ activity has been difficult. In order to understand the relationship between disease severity in patients and enzymatic defects in vitro, we characterized the molecular mechanisms of four pol γ mutations, A957P, A957S, R1096C and R1096H, which have been found in patients suffering from aggressive Alpers syndrome to mild progressive external ophthalmoplegia. The A957P mutant showed the most striking deficiencies in the incorporation efficiency of a correct deoxyribonucleotide triphosphate (dNTP) relative to wild-type pol γ, with less, but still significant incorporation efficiency defects seen in R1096H and R1096C, and only a small decrease in incorporation efficiency observed for A957S. Importantly, this trend matches the disease severity observed in patients very well (approximated as A957P ≫ R1096C ≥ R1096H ≫ A957S, from most severe disease to least severe). Further, the A957P mutation conferred a two orders of magnitude loss of fidelity relative to wild-type pol γ, indicating that a buildup of mitochondrial genomic mutations may contribute to the death in infancy seen with these patients. We conclude that characterizing the unique molecular mechanisms of pol γ deficiency for physiologically important mutant enzymes is important for understanding mitochondrial disease and for predicting disease severity.
Collapse
Affiliation(s)
- Christal D Sohl
- Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520, USA
| | | | | | | |
Collapse
|
83
|
Menezes MR, Sweasy JB. Mouse models of DNA polymerases. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2012; 53:645-665. [PMID: 23001998 DOI: 10.1002/em.21731] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Revised: 08/01/2012] [Accepted: 08/07/2012] [Indexed: 06/01/2023]
Abstract
In 1956, Arthur Kornberg discovered the mechanism of the biological synthesis of DNA and was awarded the Nobel Prize in Physiology or Medicine in 1959 for this contribution, which included the isolation and characterization of Escherichia coli DNA polymerase I. Now there are 15 known DNA polymerases in mammalian cells that belong to four different families. These DNA polymerases function in many different cellular processes including DNA replication, DNA repair, and damage tolerance. Several biochemical and cell biological studies have provoked a further investigation of DNA polymerase function using mouse models in which polymerase genes have been altered using gene-targeting techniques. The phenotypes of mice harboring mutant alleles reveal the prominent role of DNA polymerases in embryogenesis, prevention of premature aging, and cancer suppression.
Collapse
Affiliation(s)
- Miriam R Menezes
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT, USA
| | | |
Collapse
|
84
|
Humble MM, Young MJ, Foley JF, Pandiri AR, Travlos GS, Copeland WC. Polg2 is essential for mammalian embryogenesis and is required for mtDNA maintenance. Hum Mol Genet 2012. [PMID: 23197651 DOI: 10.1093/hmg/dds506] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Mammalian mitochondrial DNA (mtDNA) is replicated by the heterotrimeric Pol γ comprised of a single catalytic subunit, encoded by Polg, and a homodimeric accessory subunit encoded by the Polg2 gene. While the catalytic subunit has been shown to be essential for embryo development, genetic data regarding the accessory subunit are lacking in mammalian systems. Here, we describe the generation of heterozygous (Polg2(+/-)) and homozygous (Polg2(-/-)) knockout (KO) mice. Polg2(+/-) mice are haplosufficient and develop normally with no discernable difference in mitochondrial function through 2 years of age. In contrast, the Polg2(-/-) is embryonic lethal at day 8.0-8.5 p.c. with concomitant loss of mtDNA and mtDNA gene products. Electron microscopy shows severe ultra-structural defects and loss of organized cristae in mitochondria of the Polg2(-/-) embryos as well as an increase in lipid accumulation compared with both wild-type (WT) and Polg2(+/-) embryos. Our data indicate that Polg2 function is critical to mammalian embryogenesis and mtDNA replication, and that a single copy of Polg2 is sufficient to sustain life.
Collapse
Affiliation(s)
- Margaret M Humble
- Mitochondrial DNA Replication Group, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, NIH, DHHS, Research Triangle Park, NC 27709, USA
| | | | | | | | | | | |
Collapse
|
85
|
Pitceathly RDS, Smith C, Fratter C, Alston CL, He L, Craig K, Blakely EL, Evans JC, Taylor J, Shabbir Z, Deschauer M, Pohl U, Roberts ME, Jackson MC, Halfpenny CA, Turnpenny PD, Lunt PW, Hanna MG, Schaefer AM, McFarland R, Horvath R, Chinnery PF, Turnbull DM, Poulton J, Taylor RW, Gorman GS. Adults with RRM2B-related mitochondrial disease have distinct clinical and molecular characteristics. ACTA ACUST UNITED AC 2012; 135:3392-403. [PMID: 23107649 PMCID: PMC3501970 DOI: 10.1093/brain/aws231] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Mutations in the nuclear-encoded mitochondrial maintenance gene RRM2B are an important cause of familial mitochondrial disease in both adults and children and represent the third most common cause of multiple mitochondrial DNA deletions in adults, following POLG [polymerase (DNA directed), gamma] and PEO1 (now called C10ORF2, encoding the Twinkle helicase) mutations. However, the clinico-pathological and molecular features of adults with RRM2B-related disease have not been clearly defined. In this multicentre study of 26 adult patients from 22 independent families, including five additional cases published in the literature, we show that extra-ocular neurological complications are common in adults with genetically confirmed RRM2B mutations. We also demonstrate a clear correlation between the clinical phenotype and the underlying genetic defect. Myopathy was a prominent manifestation, followed by bulbar dysfunction and fatigue. Sensorineural hearing loss and gastrointestinal disturbance were also important findings. Severe multisystem neurological disease was associated with recessively inherited compound heterozygous mutations with a mean age of disease onset at 7 years. Dominantly inherited heterozygous mutations were associated with a milder predominantly myopathic phenotype with a later mean age of disease onset at 46 years. Skeletal muscle biopsies revealed subsarcolemmal accumulation of mitochondria and/or cytochrome c oxidase-deficient fibres. Multiple mitochondrial DNA deletions were universally present in patients who underwent a muscle biopsy. We identified 18 different heterozygous RRM2B mutations within our cohort of patients, including five novel mutations that have not previously been reported. Despite marked clinical overlap between the mitochondrial maintenance genes, key clinical features such as bulbar dysfunction, hearing loss and gastrointestinal disturbance should help prioritize genetic testing towards RRM2B analysis, and sequencing of the gene may preclude performance of a muscle biopsy.
Collapse
Affiliation(s)
- Robert D S Pitceathly
- MRC Centre for Neuromuscular Diseases, UCL Institute of Neurology and National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
86
|
Ronchi D, Garone C, Bordoni A, Gutierrez Rios P, Calvo SE, Ripolone M, Ranieri M, Rizzuti M, Villa L, Magri F, Corti S, Bresolin N, Mootha VK, Moggio M, DiMauro S, Comi GP, Sciacco M. Next-generation sequencing reveals DGUOK mutations in adult patients with mitochondrial DNA multiple deletions. Brain 2012; 135:3404-15. [PMID: 23043144 DOI: 10.1093/brain/aws258] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The molecular diagnosis of mitochondrial disorders still remains elusive in a large proportion of patients, but advances in next generation sequencing are significantly improving our chances to detect mutations even in sporadic patients. Syndromes associated with mitochondrial DNA multiple deletions are caused by different molecular defects resulting in a wide spectrum of predominantly adult-onset clinical presentations, ranging from progressive external ophthalmoplegia to multi-systemic disorders of variable severity. The mutations underlying these conditions remain undisclosed in half of the affected subjects. We applied next-generation sequencing of known mitochondrial targets (MitoExome) to probands presenting with adult-onset mitochondrial myopathy and harbouring mitochondrial DNA multiple deletions in skeletal muscle. We identified autosomal recessive mutations in the DGUOK gene (encoding mitochondrial deoxyguanosine kinase), which has previously been associated with an infantile hepatocerebral form of mitochondrial DNA depletion. Mutations in DGUOK occurred in five independent subjects, representing 5.6% of our cohort of patients with mitochondrial DNA multiple deletions, and impaired both muscle DGUOK activity and protein stability. Clinical presentations were variable, including mitochondrial myopathy with or without progressive external ophthalmoplegia, recurrent rhabdomyolysis in a young female who had received a liver transplant at 9 months of age and adult-onset lower motor neuron syndrome with mild cognitive impairment. These findings reinforce the concept that mutations in genes involved in deoxyribonucleotide metabolism can cause diverse clinical phenotypes and suggest that DGUOK should be screened in patients harbouring mitochondrial DNA deletions in skeletal muscle.
Collapse
Affiliation(s)
- Dario Ronchi
- Dino Ferrari Centre, Neuroscience Section, Department of Pathophysiology and Transplantation, University of Milan, Neurology Unit, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, 20122 Milan, Italy.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
87
|
Ronchi D, Fassone E, Bordoni A, Sciacco M, Lucchini V, Di Fonzo A, Rizzuti M, Colombo I, Napoli L, Ciscato P, Moggio M, Cosi A, Collotta M, Corti S, Bresolin N, Comi GP. Two novel mutations in PEO1 (twinkle) gene associated with chronic external ophthalmoplegia. J Neurol Sci 2012; 308:173-6. [PMID: 21689831 PMCID: PMC3158327 DOI: 10.1016/j.jns.2011.05.042] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2010] [Revised: 05/25/2011] [Accepted: 05/26/2011] [Indexed: 12/02/2022]
Abstract
Maintenance and replication of mitochondrial DNA require the concerted action of several factors encoded by nuclear genome. The mitochondrial helicase Twinkle is a key player of replisome machinery. Heterozygous mutations in its coding gene, PEO1, are associated with progressive external ophthalmoplegia (PEO) characterised by ptosis and ophthalmoparesis, with cytochrome c oxidase (COX)-deficient fibres, ragged-red fibres (RRF) and multiple mtDNA deletions in muscle. Here we describe clinical, histological and molecular features of two patients presenting with mitochondrial myopathy associated with PEO. PEO1 sequencing disclosed two novel mutations in exons 1 and 4 of the gene, respectively. Although mutations in PEO1 exon 1 have already been described, this is the first report of mutation occurring in exon 4.
Collapse
Affiliation(s)
- Dario Ronchi
- Dino Ferrari Centre, Department of Neurological Sciences, University of Milan, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
88
|
Abstract
Mitochondrial DNA (mtDNA) is replicated by the DNA polymerase g in concert with accessory proteins such as the mtDNA helicase, single stranded DNA binding protein, topoisomerase, and initiating factors. Nucleotide precursors for mtDNA replication arise from the mitochondrial salvage pathway originating from transport of nucleosides, or alternatively from cytoplasmic reduction of ribonucleotides. Defects in mtDNA replication or nucleotide metabolism can cause mitochondrial genetic diseases due to mtDNA deletions, point mutations, or depletion which ultimately cause loss of oxidative phosphorylation. These genetic diseases include mtDNA depletion syndromes such as Alpers or early infantile hepatocerebral syndromes, and mtDNA deletion disorders, such as progressive external ophthalmoplegia (PEO), ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). This review focuses on our current knowledge of genetic defects of mtDNA replication (POLG, POLG2, C10orf2) and nucleotide metabolism (TYMP, TK2, DGOUK, and RRM2B) that cause instability of mtDNA and mitochondrial disease.
Collapse
Affiliation(s)
- William C Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Durham, North Carolina 27709, USA.
| |
Collapse
|
89
|
Craig K, Young MJ, Blakely EL, Longley MJ, Turnbull DM, Copeland WC, Taylor RW. A p.R369G POLG2 mutation associated with adPEO and multiple mtDNA deletions causes decreased affinity between polymerase γ subunits. Mitochondrion 2012; 12:313-9. [PMID: 22155748 PMCID: PMC3824628 DOI: 10.1016/j.mito.2011.11.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2011] [Revised: 11/18/2011] [Accepted: 11/28/2011] [Indexed: 11/16/2022]
Abstract
Human mitochondrial DNA (mtDNA) polymerase γ (pol γ) is the sole enzyme required to replicate and maintain the integrity of the mitochondrial genome. It comprises two subunits, a catalytic p140 subunit and a smaller p55 accessory subunit encoded by the POLG2 gene. We describe the molecular characterization of a potential dominant POLG2 mutation (p.R369G) in a patient with adPEO and multiple mtDNA deletions. Biochemical studies of the recombinant mutant p55 protein showed a reduced affinity to the pol γ p140 subunit, leading to impaired processivity of the holoenzyme complex but did not show sensitivity to N-ethylmalaimide (NEM) inhibition, inferring a novel disease mechanism.
Collapse
Affiliation(s)
- Kate Craig
- Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Framlington Place, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | | | | | | | | | | | | |
Collapse
|
90
|
Martikainen MH, Hinttala R, Röyttä M, Jääskeläinen S, Wendelin-Saarenhovi M, Parkkola R, Majamaa K. Progressive external ophthalmoplegia in southwestern Finland: a clinical and genetic study. Neuroepidemiology 2012; 38:114-9. [PMID: 22377773 DOI: 10.1159/000336112] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Accepted: 12/12/2011] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Progressive external ophthalmoplegia (PEO) is a common phenotype of mitochondrial disease. Molecular etiologies include sporadic, large-scale deletions in mitochondrial DNA (mtDNA), multiple mtDNA deletions secondary to autosomal dominant or recessive mutations and mtDNA point mutations. METHODS We studied the prevalence and clinical and genetic characteristics of PEO in a defined population in southwestern Finland. A total of 620 patients were first identified from the patient registry at the Turku University Hospital over an 18-year period. The medical records of these patients were scrutinized, and those with clinical features compatible with PEO were ascertained. RESULTS We identified 10 patients with possible PEO. The patients were examined clinically, and DNA was analyzed for mtDNA deletions and for the m.3243A>G and m.8344A>G mtDNA point mutations. The ANT1, PEO1, POLG1 and POLG2 genes were sequenced. We confirmed the clinical diagnosis of PEO in 6 patients. Large-scale mtDNA deletions were detected in 3 out of 6 PEO patients and mutations in the POLG1 gene in 1 out of 6. We did not find any mutations in the ANT1, PEO1 or POLG2 genes. CONCLUSIONS Our results suggest that molecular investigation of patients with PEO, either sporadic or familial, should start with an analysis for mtDNA deletions, followed by an analysis of the POLG1 gene.
Collapse
|
91
|
Abstract
Mitochondria are essential organelles with multiple functions, the most well known being the production of adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS). The mitochondrial diseases are defined by impairment of OXPHOS. They are a diverse group of diseases that can present in virtually any tissue in either adults or children. Here we review the main molecular mechanisms of mitochondrial diseases, as presently known. A number of disease-causing genetic defects, either in the nuclear genome or in the mitochondria's own genome, mitochondrial DNA (mtDNA), have been identified. The most classical genetic defect causing mitochondrial disease is a mutation in a gene encoding a structural OXPHOS subunit. However, mitochondrial diseases can also arise through impaired mtDNA maintenance, defects in mitochondrial translation factors, and various more indirect mechanisms. The putative consequences of mitochondrial dysfunction on a cellular level are discussed.
Collapse
Affiliation(s)
- Emil Ylikallio
- Research Programs Unit, Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, Finland.
| | | |
Collapse
|
92
|
Yu-Wai-Man P, Chinnery PF. Dysfunctional mitochondrial maintenance: what breaks the circle of life? Brain 2012; 135:9-11. [PMID: 22271662 DOI: 10.1093/brain/awr352] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
93
|
Limongelli G, Masarone D, D’Alessandro R, Elliott PM. Mitochondrial diseases and the heart: an overview of molecular basis, diagnosis, treatment and clinical course. Future Cardiol 2012; 8:71-88. [DOI: 10.2217/fca.11.79] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The mitochondrion is the main site of production of ATP that represents the source of energy for a large number of cellular processes. Mitochondrial diseases that result in a deficit in ATP production can affect almost every organ system with a large spectrum of clinical phenotypes. Cardiomyocytes are particularly vulnerable to limited ATP supply because of their large energy requirement. Abnormalities in the mitochondrial function are increasingly recognized in association with dilated and hypertrophic cardiomyopathy, cardiac conduction defects, endothelial dysfunction and coronary artery disease. Cardiologists should, therefore, be alerted to symptoms and signs suggestive of mitochondrial diseases and become familiar with the general issues related to multisystem disease management, genetic counseling and testing.
Collapse
Affiliation(s)
- Giuseppe Limongelli
- Monaldi Hospital Second University of Naples (SUN), Naples, Italy
- The Heart Hospital, University College of London (UCL), London, UK
| | - Daniele Masarone
- Monaldi Hospital Second University of Naples (SUN), Naples, Italy
| | | | - Perry M Elliott
- The Heart Hospital, University College of London (UCL), London, UK
| |
Collapse
|
94
|
Kasiviswanathan R, Gustafson MA, Copeland WC, Meyer JN. Human mitochondrial DNA polymerase γ exhibits potential for bypass and mutagenesis at UV-induced cyclobutane thymine dimers. J Biol Chem 2011; 287:9222-9. [PMID: 22194617 DOI: 10.1074/jbc.m111.306852] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Cyclobutane thymine dimers (T-T) comprise the majority of DNA damage caused by short wavelength ultraviolet radiation. These lesions generally block replicative DNA polymerases and are repaired by nucleotide excision repair or bypassed by translesion polymerases in the nucleus. Mitochondria lack nucleotide excision repair, and therefore, it is important to understand how the sole mitochondrial DNA polymerase, pol γ, interacts with irreparable lesions such as T-T. We performed in vitro DNA polymerization assays to measure the kinetics of incorporation opposite the lesion and bypass of the lesion by pol γ with a dimer-containing template. Exonuclease-deficient pol γ bypassed thymine dimers with low relative efficiency; bypass was attenuated but still detectable when using exonuclease-proficient pol γ. When bypass did occur, pol γ misincorporated a guanine residue opposite the 3'-thymine of the dimer only 4-fold less efficiently than it incorporated an adenine. Surprisingly, the pol γ exonuclease-proficient enzyme excised the incorrectly incorporated guanine at similar rates irrespective of the nature of the thymines in the template. In the presence of all four dNTPs, pol γ extended the primer after incorporation of two adenines opposite the lesion with relatively higher efficiency compared with extension past either an adenine or a guanine incorporated opposite the 3'-thymine of the T-T. Our results suggest that T-T usually stalls mitochondrial DNA replication but also suggest a mechanism for the introduction of point mutations and deletions in the mitochondrial genomes of chronically UV-exposed cells.
Collapse
Affiliation(s)
- Rajesh Kasiviswanathan
- Laboratory of Molecular Genetics, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
| | | | | | | |
Collapse
|
95
|
Kasiviswanathan R, Collins TRL, Copeland WC. The interface of transcription and DNA replication in the mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2011; 1819:970-8. [PMID: 22207204 DOI: 10.1016/j.bbagrm.2011.12.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2011] [Revised: 12/09/2011] [Accepted: 12/12/2011] [Indexed: 11/30/2022]
Abstract
DNA replication of the mitochondrial genome is unique in that replication is not primed by RNA derived from dedicated primases, but instead by extension of processed RNA transcripts laid down by the mitochondrial RNA polymerase. Thus, the RNA polymerase serves not only to generate the transcripts but also the primers needed for mitochondrial DNA replication. The interface between this transcription and DNA replication is not well understood but must be highly regulated and coordinated to carry out both mitochondrial DNA replication and transcription. This review focuses on the extension of RNA primers for DNA replication by the replication machinery and summarizes the current models of DNA replication in mitochondria as well as the proteins involved in mitochondrial DNA replication, namely, the DNA polymerase γ and its accessory subunit, the mitochondrial DNA helicase, the single-stranded DNA binding protein, topoisomerase I and IIIα and RNaseH1. This article is part of a Special Issue entitled: Mitochondrial Gene Expression.
Collapse
Affiliation(s)
- Rajesh Kasiviswanathan
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | | | | |
Collapse
|
96
|
Greaves LC, Reeve AK, Taylor RW, Turnbull DM. Mitochondrial DNA and disease. J Pathol 2011; 226:274-86. [PMID: 21989606 DOI: 10.1002/path.3028] [Citation(s) in RCA: 199] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Revised: 09/27/2011] [Accepted: 10/05/2011] [Indexed: 12/28/2022]
Abstract
Mitochondrial DNA (mtDNA) defects are a relatively common cause of inherited disease and have been implicated in both ageing and cancer. MtDNA encodes essential subunits of the mitochondrial respiratory chain and defects result in impaired oxidative phosphorylation (OXPHOS). Similar OXPHOS defects have been shown to be present in a number of neurodegenerative conditions, including Parkinson's disease, as well as in normal ageing human tissues. Additionally, a number of tumours have been shown to contain mtDNA mutations and an altered metabolic phenotype. In this review we outline the unique characteristics of mitochondrial genetics before detailing important pathological features of mtDNA diseases, focusing on adult neurological disease as well as the role of mtDNA mutations in neurodegenerative diseases, ageing and cancer.
Collapse
Affiliation(s)
- Laura C Greaves
- Mitochondrial Research Group, Institute for Ageing and Health, Newcastle University, UK.
| | | | | | | |
Collapse
|
97
|
Tyynismaa H, Sun R, Ahola-Erkkilä S, Almusa H, Pöyhönen R, Korpela M, Honkaniemi J, Isohanni P, Paetau A, Wang L, Suomalainen A. Thymidine kinase 2 mutations in autosomal recessive progressive external ophthalmoplegia with multiple mitochondrial DNA deletions. Hum Mol Genet 2011; 21:66-75. [PMID: 21937588 DOI: 10.1093/hmg/ddr438] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Autosomal-inherited progressive external ophthalmoplegia (PEO) is an adult-onset disease characterized by the accumulation of multiple mitochondrial DNA (mtDNA) deletions in post-mitotic tissues. Mutations in six different genes have been described to cause the autosomal dominant form of the disease, but only mutations in the DNA polymerase gamma gene are known to cause autosomal recessive PEO (arPEO), leaving the genetic background of arPEO mostly unknown. Here we used whole-exome sequencing and identified compound heterozygous mutations, leading to two amino acid alterations R225W and a novel T230A in thymidine kinase 2 (TK2) in arPEO patients. TK2 is an enzyme of the mitochondrial nucleotide salvage pathway and its loss-of-function mutations have previously been shown to underlie the early-infantile myopathic form of mtDNA depletion syndrome (MDS). Our TK2 activity measurements of patient fibroblasts and mutant recombinant proteins show that the combination of the identified arPEO variants, R225W and T230A, leads to a significant reduction in TK2 activity, consistent with the late-onset phenotype, whereas homozygosity for R225W, previously associated with MDS, leads to near-total loss of activity. Our finding identifies a new genetic cause of arPEO with multiple mtDNA deletions. Furthermore, MDS and multiple mtDNA deletion disorders are manifestations of the same pathogenic pathways affecting mtDNA replication and repair, indicating that MDS-associated genes should be studied when searching for genetic background of PEO disorders.
Collapse
Affiliation(s)
- Henna Tyynismaa
- Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, Haartmaninkatu 8, Helsinki 00290, Finland.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
98
|
Zhang L, Chan SSL, Wolff DJ. Mitochondrial disorders of DNA polymerase γ dysfunction: from anatomic to molecular pathology diagnosis. Arch Pathol Lab Med 2011. [PMID: 21732785 DOI: 10.1043/2010-0356-rar.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
CONTEXT Primary mitochondrial dysfunction is one of the most common causes of inherited disorders predominantly involving the neuromuscular system. Advances in the molecular study of mitochondrial DNA have changed our vision and our approach to primary mitochondrial disorders. Many of the mitochondrial disorders are caused by mutations in nuclear genes and are inherited in an autosomal recessive pattern. Among the autosomal inherited mitochondrial disorders, those related to DNA polymerase γ dysfunction are the most common and the best studied. Understanding the molecular mechanisms and being familiar with the recent advances in laboratory diagnosis of this group of mitochondrial disorders are essential for pathologists to interpret abnormal histopathology and laboratory results and to suggest further studies for a definitive diagnosis. OBJECTIVES To help pathologists better understand the common clinical syndromes originating from mutations in DNA polymerase γ and its associated proteins and use the stepwise approach of clinical, laboratory, and pathologic diagnosis of these syndromes. DATA SOURCES Review of pertinent published literature and relevant Internet databases. CONCLUSIONS Mitochondrial disorders are now better recognized with the development of molecular tests for clinical diagnosis. A cooperative effort among primary physicians, diagnostic pathologists, geneticists, and molecular biologists with expertise in mitochondrial disorders is required to reach a definitive diagnosis.
Collapse
Affiliation(s)
- Linsheng Zhang
- Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29425, USA.
| | | | | |
Collapse
|
99
|
Say RE, Whittaker RG, Turnbull HE, McFarland R, Taylor RW, Turnbull DM. Mitochondrial disease in pregnancy: a systematic review. Obstet Med 2011; 4:90-4. [PMID: 27579099 PMCID: PMC4989604 DOI: 10.1258/om.2011.110008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/22/2011] [Indexed: 01/08/2023] Open
Abstract
Mitochondrial diseases are heterogeneous in clinical presentation and genotype. The incidence of known pathogenic mitochondrial DNA mutations in the general population is 1 in 500. Little is known about the implications of pregnancy for women with mitochondrial disease. We undertook a systematic review of the literature on mitochondrial disease in pregnancy. Ten case reports were identified. The most common complications were threatened preterm labour (5 women) and preeclampsia (4 women). Two women experienced magnesium sulphate toxicity. Pregnancy had a varied effect on mitochondrial disease with some women being asymptomatic; others developing mild symptoms such as exercise intolerance or muscle weakness which resolved postnatally; and others developed more serious, persistent symptoms such as symptomatic Wolff-Parkinson-White syndrome, persistent paraesthesia and focal segmental glomerulosclerosis. Women with mitochondrial disease appear to be at increased risk of complications during pregnancy and labour but further prospective cohort studies are needed.
Collapse
Affiliation(s)
- R E Say
- Institute of Cellular Medicine
| | - R G Whittaker
- Mitochondrial Research Group, Newcastle University, Newcastle upon Tyne, UK
| | - H E Turnbull
- Mitochondrial Research Group, Newcastle University, Newcastle upon Tyne, UK
| | - R McFarland
- Mitochondrial Research Group, Newcastle University, Newcastle upon Tyne, UK
| | - R W Taylor
- Mitochondrial Research Group, Newcastle University, Newcastle upon Tyne, UK
| | - D M Turnbull
- Mitochondrial Research Group, Newcastle University, Newcastle upon Tyne, UK
| |
Collapse
|
100
|
Biochemical analysis of the G517V POLG variant reveals wild-type like activity. Mitochondrion 2011; 11:929-34. [PMID: 21856450 DOI: 10.1016/j.mito.2011.08.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Revised: 07/13/2011] [Accepted: 08/04/2011] [Indexed: 11/22/2022]
Abstract
The c.1550g→t mutation in the POLG gene causing the G517V substitution has been reported by many groups to be associated with a variety of mitochondrial diseases, including autosomal dominant and recessive forms of ataxia neuropathy, myopathy and microcephaly, progressive external ophthalmoplegia, diabetes, strokes, hypotonia, and epilepsy. However, the variable disease presentation and age of onset raises suspicion of its pathogenicity. Because of the varied reported associated symptoms and request from physicians to address the consequence of this mutation, we have carried out the biochemical analysis of the purified recombinant human DNA polymerase γ protein harboring the G517V substitution. These analyses revealed that the G517V mutant enzyme retained 80-90% of wild-type DNA polymerase activity, in addition to its functional interaction with the p55 accessory subunit. DNA binding by the mutant was also only slightly lower than the wild-type enzyme. Our data suggest that the G517V mutation by itself in pol γ most likely does not have a role in mitochondrial disorders.
Collapse
|