101
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Ugalde C, Morán M, Blázquez A, Arenas J, Martín MA. Mitochondrial Disorders Due to Nuclear OXPHOS Gene Defects. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2009; 652:85-116. [DOI: 10.1007/978-90-481-2813-6_7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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102
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Abstract
Mitochondria possess two elongation factor Gs: one with translocation activity (EF-G1(mt)) and the other with no confirmed activity (EF-G2(mt)). Tsuboi et al. (2009) now show that the function of EF-G2(mt) is not in elongation but, rather, in ribosome recycling.
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103
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Tsuboi M, Morita H, Nozaki Y, Akama K, Ueda T, Ito K, Nierhaus KH, Takeuchi N. EF-G2mt is an exclusive recycling factor in mammalian mitochondrial protein synthesis. Mol Cell 2009; 35:502-10. [PMID: 19716793 DOI: 10.1016/j.molcel.2009.06.028] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2009] [Revised: 05/04/2009] [Accepted: 06/18/2009] [Indexed: 11/30/2022]
Abstract
Bacterial translation elongation factor G (EF-G) catalyzes translocation during peptide elongation and mediates ribosomal disassembly during ribosome recycling in concert with the ribosomal recycling factor (RRF). Two homologs of EF-G have been identified in mitochondria from yeast to man, EF-G1mt and EF-G2mt. Here, we demonstrate that the dual function of bacterial EF-G is divided between EF-G1mt and EF-G2mt in human mitochondria (RRFmt). EF-G1mt specifically catalyzes translocation, whereas EF-G2mt mediates ribosome recycling with human mitochondrial RRF but lacks translocation activity. Domain swapping experiments suggest that the functional specificity for EF-G2mt resides in domains III and IV. Furthermore, GTP hydrolysis by EF-G2mt is not necessary for ribosomal splitting, in contrast to the bacterial-recycling mode. Because EF-G2mt represents a class of translational GTPase that is involved in ribosome recycling, we propose to rename this factor mitochondrial ribosome recycling factor 2 (RRF2mt).
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Affiliation(s)
- Masafumi Tsuboi
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa-shi, Chiba 277-8562, Japan
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104
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Bykhovskaya Y, Mengesha E, Fischel-Ghodsian N. Phenotypic expression of maternally inherited deafness is affected by RNA modification and cytoplasmic ribosomal proteins. Mol Genet Metab 2009; 97:297-304. [PMID: 19482502 PMCID: PMC2728627 DOI: 10.1016/j.ymgme.2009.05.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Revised: 04/30/2009] [Accepted: 05/02/2009] [Indexed: 01/06/2023]
Abstract
The homoplasmic mitochondrial A1555G mutation in the 12S rRNA gene leads to a mitochondrial translation disorder associated with deafness. The absence of disease in non-cochlear tissues in all patients, and in the cochlea in some patients, is not well understood. We used a system-based approach, including whole genome expression and biological function analysis, to elucidate the pathways underlying tissue specificity and clinical severity of this condition. Levels of over 48K RNA transcripts from EBV-transformed lymphoblasts of deaf and hearing individuals with the A1555G mutation and controls were obtained. Differentially expressed transcripts were functionally grouped using gene set enrichment analysis. Over 50 RNA binding proteins were differentially expressed between deaf and hearing individuals with the A1555G mutation (P-value of 2.56E-7), confirming previous genetic data implicating this pathway in the determination of the severity of hearing loss. Unexpectedly, the majority of cytoplasmic ribosomal genes were up-regulated in a coordinated fashion in individuals with the A1555G mutation versus controls (P-value of 3.91E-135). This finding was verified through real time RT-PCR, and through measuring of protein levels by flow cytometry. Analysis of expression levels of other differentially expressed genes suggests that this coordinated over-expression of cytoplasmic ribosomal proteins might occur through the Myc/Max pathway. We propose that expression levels of RNA binding proteins help determine the severity of the cochlear phenotype, and that coordinated up-regulation of the cytoplasmic translation apparatus operates as a compensation mechanism in unaffected tissues of patients with maternal deafness associated with the A1555G mutation.
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Affiliation(s)
- Yelena Bykhovskaya
- Medical Genetics Institute, Ahmanson Department of Pediatrics, Steven Spielberg Pediatric Research Center, Cedars-Sinai Medical Center and David Geffen School of Medicine at UCLA, 8700 Beverly Blvd, Los Angeles, California, 90048 USA
| | - Emebet Mengesha
- Medical Genetics Institute, Ahmanson Department of Pediatrics, Steven Spielberg Pediatric Research Center, Cedars-Sinai Medical Center and David Geffen School of Medicine at UCLA, 8700 Beverly Blvd, Los Angeles, California, 90048 USA
| | - Nathan Fischel-Ghodsian
- Medical Genetics Institute, Ahmanson Department of Pediatrics, Steven Spielberg Pediatric Research Center, Cedars-Sinai Medical Center and David Geffen School of Medicine at UCLA, 8700 Beverly Blvd, Los Angeles, California, 90048 USA
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105
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Valente L, Shigi N, Suzuki T, Zeviani M. The R336Q mutation in human mitochondrial EFTu prevents the formation of an active mt-EFTu.GTP.aa-tRNA ternary complex. Biochim Biophys Acta Mol Basis Dis 2009; 1792:791-5. [PMID: 19524667 DOI: 10.1016/j.bbadis.2009.06.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Revised: 05/06/2009] [Accepted: 06/08/2009] [Indexed: 11/18/2022]
Abstract
The mitochondrial translational machinery allows the genes encoded by mitochondrial DNA (mtDNA) to be translated in situ. Mitochondrial translation requires a number of nucleus-encoded protein factors, some of which have been found to carry mutations in patients affected by mitochondrial encephalomyopathies. We have previously described the first, and so far only, mutation in the mitochondrial elongation factor Tu, mt-EFTu, in a baby girl with polycystic encephalopathy, micropolygyria, and leukodystrophic changes. Despite that the mutant mt-EFTu was present in normal amount in the patient's tissues, mitochondrial translation was severely reduced, determining multiple defects in the amount and activity of mtDNA-dependent respiratory chain complexes. By an in-vitro reconstructed translational system, we here provide evidence that the mutant mt-EFTu variant fails to bind to aminoacylated mitochondrial tRNAs, thus explaining the observed impairment of mitochondrial translation. This is the first analysis on the molecular mechanism of a mtDNA translation defect due to a nuclear gene mutation.
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Affiliation(s)
- Lucia Valente
- Unit of Molecular Neurogenetics, IRCCS Foundation, Neurological Institute C. Besta, 20126 Milano, Italy
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106
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Zhu X, Peng X, Guan MX, Yan Q. Pathogenic mutations of nuclear genes associated with mitochondrial disorders. Acta Biochim Biophys Sin (Shanghai) 2009; 41:179-87. [PMID: 19280056 DOI: 10.1093/abbs/gmn021] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mitochondrial disorders are clinical phenotypes associated with mitochondrial dysfunction, which can be caused by mutations in mitochondrial DNA (mtDNA) or nuclear genes. In this review, we summarized the pathogenic mutations of nuclear genes associated with mitochondrial disorders. These nuclear genes encode, components of mitochondrial translational machinery and structural subunits and assembly factors of the oxidative phosphorylation, that complex. The molecular mechanisms, that nuclear modifier genes modulate the phenotypic expression of mtDNA mutations, are discussed in detail.
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Affiliation(s)
- Xiaoyu Zhu
- College of Life Science, Zhejiang University, Hangzhou 310058, Peopleos Republic of China
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107
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Abstract
In the course of evolution, mitochondria lost their independence, and mitochondrial DNA (mtDNA) became the 'slave' of nuclear DNA, depending on numerous nucleus-encoded factors for its integrity, replication and expression. Mutations in any of these factors may alter the cross-talk between the two genomes and cause Mendelian disorders characterized by qualitative (multiple deletions) or quantitative (depletion) alterations of mtDNA, or by defective translation of mtDNA-encoded respiratory chain components.
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Affiliation(s)
- A Spinazzola
- Unit of Molecular Neurogenetics, C. Besta Neurological Institute, Foundation IRCCS, Milano, Italy
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108
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Abstract
Research of patients with defects in cellular energy metabolism (mitochondrial disease) has led to a better understanding of mitochondrial biology in health and disease. The obtained knowledge is of increasing importance for physicians of all medical disciplines. It assists in enabling the development of rational treatment strategies for diseases or conditions caused by mitochondrial dysfunction. The still frequently used classical interventions with vitamins or co-factors are only beneficial in some rare mitochondrial disease conditions, like coenzyme Q biosynthesis defects. For that reason alternative strategies to correct disturbed energy metabolism have to be developed. New approaches in this direction include nutrition and exercise therapies, alternative gene expression, enzyme-replacement, scavenging of potentially toxic compounds and modulating cell signalling. The effect of some of these interventions has already been explored in humans whilst others are still at the level of single cell research. We review the state of the art of the development of mitochondrial treatment strategies and discuss what steps need to be taken to efficiently approach the huge burden of disease caused by dysfunctional mitochondria.
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Affiliation(s)
- S Koene
- Radboud University Nijmegen Medical Centre, Nijmegen Centre for Mitochondrial Disorders, Nijmegen, The Netherlands
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109
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Kirby DM, Thorburn DR. Approaches to finding the molecular basis of mitochondrial oxidative phosphorylation disorders. Twin Res Hum Genet 2009; 11:395-411. [PMID: 18637740 DOI: 10.1375/twin.11.4.395] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Inherited disorders of mitochondrial oxidative phosphorylation are the most common group of inborn errors of metabolism and cause a wide range of clinical presentations. Mitochondrial DNA encodes 13 protein subunits required for oxidative phosphorylation plus 22 transfer RNAs and two ribosomal RNAs, and mutations in most of these genes cause human disease. Nuclear genes encode most of the protein subunits and all other proteins required for mitochondrial biogenesis and mitochondrial DNA replication and expression. Mutations in 64 nuclear genes and 34 mitochondrial genes are now known to cause mitochondrial disease and many novel mitochondrial disease genes await discovery. The genetic complexity of oxidative phosphorylation means that maternal, autosomal recessive, autosomal dominant and X-linked modes of inheritance can occur, along with de novo mutations. This complexity presents a challenge in planning efficient molecular genetic diagnosis of patients with suspected mitochondrial disease. In some situations, clinical phenotype can be strongly predictive of the underlying genotype. However, more often this is not the case and it is usually helpful, particularly with pediatric patients, to determine whether the activity of one or more of the individual oxidative phosphorylation enzymes is deficient before proceeding with mutation analysis. In this review we will summarize the genetic bases of mitochondrial disease and discuss some approaches to integrate information from clinical presentation, laboratory findings, family history, and imaging to guide molecular investigation.
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Affiliation(s)
- Denise M Kirby
- 1 Murdoch Childrens Research Institute and Genetic Health Services Victoria, Royal Children's Hospital, Melbourne, Australia
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110
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Zecic A, Smet JE, Praeter CMD, Vanhaesebrouck P, Viscomi C, Broecke CVD, Paepe BD, Lohse P, Martin JJ, Jackson JG, Campbell CR, Meirleir LJD, Zeviani M, Seneca SH, Lissens W, Coster RNV. Lactic acidosis in a newborn with adrenal calcifications. Pediatr Res 2009; 66:317-22. [PMID: 19581830 PMCID: PMC7101825 DOI: 10.1203/pdr.0b013e3181b40a80] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
A patient is reported who presented in the newborn period with an unusual combination of congenital lactic acidosis and bilateral calcifications in the adrenal medulla, visible on standard abdominal x-ray and ultrasound examination. At birth, the proband was hypotonic and dystrophic. She developed respiratory insufficiency, cardiomegaly, and hepatomegaly and died at the age of 38 d. Examination of postmortem heart muscle revealed multiple areas of myocardial infarction with dystrophic calcifications. In the medulla of the adrenal glands, foci of necrosis and calcifications, and in the liver, multiple zones of necrosis and iron deposition were detected. Biochemical analysis in heart muscle revealed a decreased activity of complex IV of the oxidative phosphorylation (OXPHOS) and in liver a combined deficiency involving the complexes I, III, IV, and V. The findings were suggestive of a defect in biosynthesis of the mitochondrially encoded subunits of the OXPHOS complexes. Extensive analysis of the proband's mitochondrial DNA revealed neither pathogenic deletions and point mutations nor copy number alterations. Relative amounts of mitochondrial transcripts for the ribosomal mitochondrial 12S rRNA (12S) and mitochondrial 16S rRNA (16S) were significantly increased suggesting a compensatory mechanism involving the transcription machinery to low levels of translation. The underlying molecular defect has not been identified yet.
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Affiliation(s)
- Alexandra Zecic
- Departments of Neonatology, Ghent University Hospital, Ghent, 9000 Belgium
| | - Joél E Smet
- Pediatric Neurology and Metabolism, Ghent University Hospital, Ghent, 9000 Belgium
| | | | | | - Carlo Viscomi
- Department of Molecular Neurogenetics, Istituto Nazionale Neurologico “C. Besta,”, Milan, 20126 Italy
| | | | - Boel De Paepe
- Pediatric Neurology and Metabolism, Ghent University Hospital, Ghent, 9000 Belgium
| | - Peter Lohse
- Department of Clinical Chemistry, University of Munich, Munich, 81377 Germany
| | | | - Joshua G Jackson
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455
| | - Colin R Campbell
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455
| | - Linda J De Meirleir
- Department of Medical Genetics, University Hospital Brussels, Brussels, 1090 Belgium
| | - Massimo Zeviani
- Department of Molecular Neurogenetics, Istituto Nazionale Neurologico “C. Besta,”, Milan, 20126 Italy
| | - Sara H Seneca
- Department of Medical Genetics, University Hospital Brussels, Brussels, 1090 Belgium
| | - Willy Lissens
- Department of Medical Genetics, University Hospital Brussels, Brussels, 1090 Belgium
| | - Rudy N Van Coster
- Pediatric Neurology and Metabolism, Ghent University Hospital, Ghent, 9000 Belgium
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111
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GeneDistiller--distilling candidate genes from linkage intervals. PLoS One 2008; 3:e3874. [PMID: 19057649 PMCID: PMC2587712 DOI: 10.1371/journal.pone.0003874] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2008] [Accepted: 11/10/2008] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Linkage studies often yield intervals containing several hundred positional candidate genes. Different manual or automatic approaches exist for the determination of the gene most likely to cause the disease. While the manual search is very flexible and takes advantage of the researchers' background knowledge and intuition, it may be very cumbersome to collect and study the relevant data. Automatic solutions on the other hand usually focus on certain models, remain "black boxes" and do not offer the same degree of flexibility. METHODOLOGY We have developed a web-based application that combines the advantages of both approaches. Information from various data sources such as gene-phenotype associations, gene expression patterns and protein-protein interactions was integrated into a central database. Researchers can select which information for the genes within a candidate interval or for single genes shall be displayed. Genes can also interactively be filtered, sorted and prioritised according to criteria derived from the background knowledge and preconception of the disease under scrutiny. CONCLUSIONS GeneDistiller provides knowledge-driven, fully interactive and intuitive access to multiple data sources. It displays maximum relevant information, while saving the user from drowning in the flood of data. A typical query takes less than two seconds, thus allowing an interactive and explorative approach to the hunt for the candidate gene. ACCESS GeneDistiller can be freely accessed at http://www.genedistiller.org.
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112
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Ferreiro-Barros CC, Tengan CH, Barros MH, Palenzuela L, Kanki C, Quinzii C, Lou J, El Gharaby N, Shokr A, De Vivo DC, DiMauro S, Hirano M. Neonatal mitochondrial encephaloneuromyopathy due to a defect of mitochondrial protein synthesis. J Neurol Sci 2008; 275:128-32. [PMID: 18835491 DOI: 10.1016/j.jns.2008.08.028] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2007] [Revised: 07/26/2008] [Accepted: 08/08/2008] [Indexed: 11/17/2022]
Abstract
Mitochondrial diseases are clinically and genetically heterogeneous disorders due to primary mutations in mitochondrial DNA (mtDNA) or nuclear DNA (nDNA). We studied a male infant with severe congenital encephalopathy, peripheral neuropathy, and myopathy. The patient's lactic acidosis and biochemical defects of respiratory chain complexes I, III, and IV in muscle indicated that he had a mitochondrial disorder while parental consanguinity suggested autosomal recessive inheritance. Cultured fibroblasts from the patient showed a generalized defect of mitochondrial protein synthesis. Fusion of cells from the patient with 143B206 rho(0) cells devoid of mtDNA restored cytochrome c oxidase activity confirming the nDNA origin of the disease. Our studies indicate that the patient has a novel autosomal recessive defect of mitochondrial protein synthesis.
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113
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Abstract
Mitochondrial diseases (encephalomyopathies) have traditionally been ascribed to defects of the respiratory chain, which has helped researchers explain their genetic and clinical complexity. However, other mitochondrial functions are greatly important for the nervous system, including protein importation, organellar dynamics, and programmed cell death. Defects in genes controlling these functions are attracting increasing attention as causes not only of neurological (and psychiatric) diseases but also of age-related neurodegenerative disorders. After discussing some pathogenic conundrums regarding the neurological manifestations of the respiratory chain defects, we review altered mitochondrial dynamics in the etiology of specific neurological diseases and in the physiopathology of more common neurodegenerative disorders.
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Affiliation(s)
- Salvatore DiMauro
- Department of Neurology, Columbia University Medical Center, New York, NY 10032, USA.
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114
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Staley KJ, Sims KB, Grant PE, Hedley-Whyte ET. Case records of the Massachusetts General Hospital. Case 28-2008. An 8-day-old infant with congenital deafness, lethargy, and hypothermia. N Engl J Med 2008; 359:1156-67. [PMID: 18784106 DOI: 10.1056/nejmcpc0804642] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- Kevin J Staley
- Department of Pediatric Neurology, Massachusetts General Hospital, USA
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115
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Sasarman F, Antonicka H, Shoubridge EA. The A3243G tRNALeu(UUR) MELAS mutation causes amino acid misincorporation and a combined respiratory chain assembly defect partially suppressed by overexpression of EFTu and EFG2. Hum Mol Genet 2008; 17:3697-707. [DOI: 10.1093/hmg/ddn265] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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116
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Abstract
PURPOSE OF REVIEW Mitochondrial diseases are a major category of childhood illness that produce a wide variety of symptoms and multisystemic disorders. This review highlights recent clinically important developments in diagnostic evaluation and treatment of mitochondrial diseases. RECENT FINDINGS Major advances have been made in understanding the genetic bases of mitochondrial diseases. Molecular defects have recently been reported in mitochondrial DNA maintenance, RNA translation and protein import and in mitochondrial fusion and fission, opening new areas of cell disorder. Diagnostic testing is struggling to keep pace with these fundamental discoveries. The diagnostic approach to children suspected of mitochondrial disease is rapidly evolving but few patients have a molecular diagnosis. A better notion of the prognosis of affected children is emerging from studies of long-term outcome. Some therapeutic successes are reported, such as in coenzyme Q deficiency conditions. SUMMARY Mitochondrial diseases can present with signs in almost any organ. Well planned clinical evaluation is the key to successful diagnostic work-up of mitochondrial diseases. An approach is presented for further testing in specialized laboratories. Mitochondrial diseases can be caused by mutations in mitochondrial DNA or, more commonly in children, in nuclear genes. Mitochondrial DNA mutations pose special challenges for genetic counseling and prenatal diagnosis. Supportive treatment and avoidance of environmental stresses are important aspects of patient care. Specific treatment of mitochondrial diseases is in its infancy and is a major challenge for pediatric medicine.
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117
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Koopman WJH, Distelmaier F, Hink MA, Verkaart S, Wijers M, Fransen J, Smeitink JAM, Willems PHGM. Inherited complex I deficiency is associated with faster protein diffusion in the matrix of moving mitochondria. Am J Physiol Cell Physiol 2008; 294:C1124-32. [DOI: 10.1152/ajpcell.00079.2008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mitochondria continuously change shape, position, and matrix configuration for optimal metabolite exchange. It is well established that changes in mitochondrial metabolism influence mitochondrial shape and matrix configuration. We demonstrated previously that inhibition of mitochondrial complex I (CI or NADH:ubiquinone oxidoreductase) by rotenone accelerated matrix protein diffusion and decreased the fraction and velocity of moving mitochondria. In the present study, we investigated the relationship between inherited CI deficiency, mitochondrial shape, mobility, and matrix protein diffusion. To this end, we analyzed fibroblasts of two children that represented opposite extremes in a cohort of 16 patients, with respect to their residual CI activity and mitochondrial shape. Fluorescence correlation spectroscopy (FCS) revealed no relationship between residual CI activity, mitochondrial shape, the fraction of moving mitochondria, their velocity, and the rate of matrix-targeted enhanced yellow fluorescent protein (mitoEYFP) diffusion. However, mitochondrial velocity and matrix protein diffusion in moving mitochondria were two to three times higher in patient cells than in control cells. Nocodazole inhibited mitochondrial movement without altering matrix EYFP diffusion, suggesting that both activities are mutually independent. Unexpectedly, electron microscopy analysis revealed no differences in mitochondrial ultrastructure between control and patient cells. It is discussed that the matrix of a moving mitochondrion in the CI-deficient state becomes less dense, allowing faster metabolite diffusion, and that fibroblasts of CI-deficient patients become more glycolytic, allowing a higher mitochondrial velocity.
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118
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Abstract
PURPOSE OF REVIEW Mitochondrial disorders are increasingly acknowledged as a major category in clinical neurology. In this review we highlight the most recent advances in the field, including the characterization of new disease genes, new physiopathological insights, and the role of mitochondrial dysfunction in neurodegeneration. RECENT FINDINGS Substantial progress has been made on the genetic basis and pathogenic mechanisms in disorders associated with altered mitochondrial DNA stability and expression. These defects include a wide spectrum of neurological conditions caused by genetic abnormalities of the mitochondrial replication and translation machineries, and of the metabolic pathways controlling the nucleotide supply to organelles, cells and tissues. Another relevant contribution has been given to the molecular dissection of coenzyme Q deficiency, a clinically heterogeneous, potentially treatable condition, thanks to the biochemical and genetic characterization of the first defects in coenzyme Q biosynthesis. Finally, the genetic determinants controlling the penetrance of mitochondrial disorders, as well as the role of mitochondrial dysfunction in neurodegenerative conditions such as Parkinson's and Huntington's diseases, have been investigated in both patients and animal models. SUMMARY The dual genetic contribution controlling mitochondrial biogenesis, and the intricacy and universality of the metabolic pathways operating in the mitochondrion explain the complexity of what is now known as 'mitochondrial medicine'.
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Affiliation(s)
- Massimo Zeviani
- Unit of Molecular Neurogenetics, Institute of Neurology C. Besta, Foundation IRCCS, Milan, Italy.
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119
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Soleimanpour-Lichaei HR, Kühl I, Gaisne M, Passos JF, Wydro M, Rorbach J, Temperley R, Bonnefoy N, Tate W, Lightowlers R, Chrzanowska-Lightowlers Z. mtRF1a is a human mitochondrial translation release factor decoding the major termination codons UAA and UAG. Mol Cell 2007; 27:745-57. [PMID: 17803939 PMCID: PMC1976341 DOI: 10.1016/j.molcel.2007.06.031] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2007] [Revised: 05/30/2007] [Accepted: 06/21/2007] [Indexed: 11/28/2022]
Abstract
Human mitochondria contain their own genome, encoding 13 polypeptides that are synthesized within the organelle. The molecular processes that govern and facilitate this mitochondrial translation remain unclear. Many key factors have yet to be characterized—for example, those required for translation termination. All other systems have two classes of release factors that either promote codon-specific hydrolysis of peptidyl-tRNA (class I) or lack specificity but stimulate the dissociation of class I factors from the ribosome (class II). One human mitochondrial protein has been previously identified in silico as a putative member of the class I release factors. Although we could not confirm the function of this factor, we report the identification of a different mitochondrial protein, mtRF1a, that is capable in vitro and in vivo of terminating translation at UAA/UAG codons. Further, mtRF1a depletion in HeLa cells led to compromised growth in galactose and increased production of reactive oxygen species.
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Affiliation(s)
| | - Inge Kühl
- Centre de Génétique Moléculaire, CNRS Batiment 26, Avenue de la Terrasse, 91198 Gif sur Yvette Cedex, France
| | - Mauricette Gaisne
- Centre de Génétique Moléculaire, CNRS Batiment 26, Avenue de la Terrasse, 91198 Gif sur Yvette Cedex, France
| | - Joao F. Passos
- Centre for Integrated Systems Biology of Ageing and Nutrition, Newcastle University, Newcastle upon Tyne NE4 6BE, UK
| | - Mateusz Wydro
- Mitochondrial Research Group, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Joanna Rorbach
- Mitochondrial Research Group, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Richard Temperley
- Mitochondrial Research Group, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Nathalie Bonnefoy
- Centre de Génétique Moléculaire, CNRS Batiment 26, Avenue de la Terrasse, 91198 Gif sur Yvette Cedex, France
| | - Warren Tate
- Department of Biochemistry, University of Otago, P.O. Box 56, 710 Cumberland Street, Dunedin 9016, New Zealand
| | - Robert Lightowlers
- Mitochondrial Research Group, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Zofia Chrzanowska-Lightowlers
- Mitochondrial Research Group, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
- Corresponding author
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120
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Maassen JA, 't Hart LM, Ouwens DM. Lessons that can be learned from patients with diabetogenic mutations in mitochondrial DNA: implications for common type 2 diabetes. Curr Opin Clin Nutr Metab Care 2007; 10:693-7. [PMID: 18089949 DOI: 10.1097/mco.0b013e3282f0b774] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW To discuss the role of mitochondria in the development of type 2 diabetes. RECENT FINDINGS Some mutations in mitochondrial DNA are diabetogenic due to a gradual decline in insulin secretion by the pancreas. These mutations also result in abnormalities in lipid metabolism. A similar situation is seen in patients treated with nucleoside analogues as part of highly active antiretroviral therapy to suppress human immunodeficiency virus infection. These drugs induce a 30-50% reduction in mitochondrial DNA copy number in multiple tissues. Treated individuals develop a redistribution of body fat with concomitant development of markers of the metabolic syndrome and an elevated risk of developing type 2 diabetes. Studies have also shown the presence of reduced mitochondrial activity in muscle and adipose tissue in individuals with type 2 diabetes. SUMMARY These observations suggest a pathogenic model for obesity-associated type 2 diabetes, in which mitochondrial activity in peripheral adipocytes is essential to keep triacylglycerol stored within these cells. Mitochondria protect the organism against fatty acid-induced insulin resistance and lipotoxicity to the pancreas. In adipocytes, mitochondria may remove fatty acids through uncoupled beta oxidation, whereas in muscle fatty acids, removal is largely driven by adenosine diphosphate production through physical activity.
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Affiliation(s)
- Johannes A Maassen
- Department of Molecular Cell Biology, Leiden University Medical Centre, Albinusdreef 2, 2300RC Leiden, the Netherlands.
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121
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Edvardson S, Shaag A, Kolesnikova O, Gomori JM, Tarassov I, Einbinder T, Saada A, Elpeleg O. Deleterious mutation in the mitochondrial arginyl-transfer RNA synthetase gene is associated with pontocerebellar hypoplasia. Am J Hum Genet 2007; 81:857-62. [PMID: 17847012 PMCID: PMC2227936 DOI: 10.1086/521227] [Citation(s) in RCA: 264] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2007] [Accepted: 06/28/2007] [Indexed: 01/09/2023] Open
Abstract
Homozygosity mapping was performed in a consanguineous Sephardic Jewish family with three patients who presented with severe infantile encephalopathy associated with pontocerebellar hypoplasia and multiple mitochondrial respiratory-chain defects. This resulted in the identification of an intronic mutation in RARS2, the gene encoding mitochondrial arginine-transfer RNA (tRNA) synthetase. The mutation was associated with the production of an abnormally short RARS2 transcript and a marked reduction of the mitochondrial tRNA(Arg) transcript in the patients' fibroblasts. We speculate that missplicing mutations in mitochondrial aminoacyl-tRNA synthethase genes preferentially affect the brain because of a tissue-specific vulnerability of the splicing machinery.
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Affiliation(s)
- Simon Edvardson
- Pediatric Neurology Unit, Hadassah-Hebrew University Medical Center, Jerusalem, 91120, Israel
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122
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Saada A, Shaag A, Arnon S, Dolfin T, Miller C, Fuchs-Telem D, Lombes A, Elpeleg O. Antenatal mitochondrial disease caused by mitochondrial ribosomal protein (MRPS22) mutation. J Med Genet 2007; 44:784-6. [PMID: 17873122 PMCID: PMC2652816 DOI: 10.1136/jmg.2007.053116] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Three patients born to the same set of consanguineous parents presented with antenatal skin oedema, hypotonia, cardiomyopathy and tubulopathy. The enzymatic activities of multiple mitochondrial respiratory chain complexes were reduced in muscle. Marked reduction of 12s rRNA, the core of the mitochondrial small ribosomal subunit, was found in fibroblasts. Homozygosity mapping led to the identification of a mutation in the MRPS22 gene, which encodes a mitochondrial ribosomal protein. Transfection of the patient cells with wild-type MRPS22 cDNA increased the 12s rRNA content and normalised the enzymatic activities. Quantification of mitochondrial transcripts is advisable in patients with multiple defects of the mitochondrial respiratory chain.
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Affiliation(s)
- A Saada
- Metabolic Disease Unit, Hadassah - Hebrew University Medical Center, Jerusalem, 91120, Israel
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123
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Abstract
In this issue of Cell, Park et al. (2007) describe the nuclear encoded protein MTERF3 as a negative regulator of mitochondrial DNA transcription initiation. This study highlights a mechanism by which mitochondrial DNA transcription (and therefore oxidative phosphorylation) may be regulated in response to alterations in the cell's physiological and metabolic demands.
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Affiliation(s)
- Robert W Taylor
- Mitochondrial Research Group, School of Neurology, Neurobiology and Psychiatry, The Medical School, Newcastle University, Newcastle upon Tyne, UK
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124
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Scheper GC, van der Knaap MS, Proud CG. Translation matters: protein synthesis defects in inherited disease. Nat Rev Genet 2007; 8:711-23. [PMID: 17680008 DOI: 10.1038/nrg2142] [Citation(s) in RCA: 194] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The list of genetic diseases caused by mutations that affect mRNA translation is rapidly growing. Although protein synthesis is a fundamental process in all cells, the disease phenotypes show a surprising degree of heterogeneity. Studies of some of these diseases have provided intriguing new insights into the functions of proteins involved in the process of translation; for example, evidence suggests that several have other functions in addition to their roles in translation. Given the numerous proteins involved in mRNA translation, it is likely that further inherited diseases will turn out to be caused by mutations in genes that are involved in this complex process.
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Affiliation(s)
- Gert C Scheper
- Department of Child Neurology/Center for Neurogenomics and Cognitive Research, Vrije Universiteit Medical Center, De Boelelaan 1117, 1081HV Amsterdam, The Netherlands
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125
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Moslemi AR, Darin N. Molecular genetic and clinical aspects of mitochondrial disorders in childhood. Mitochondrion 2007; 7:241-52. [PMID: 17376748 DOI: 10.1016/j.mito.2007.02.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Revised: 01/17/2007] [Accepted: 02/02/2007] [Indexed: 12/21/2022]
Abstract
Mitochondrial OXPHOS disorders are caused by mutations in mitochondrial or nuclear genes, which directly or indirectly affect mitochondrial oxidative phosphorylation (OXPHOS). Primary mtDNA abnormalities in children are due to rearrangements (deletions or duplications) and point mutations or insertions. Mutations in the nuclear-encoded polypeptide subunits of OXPHOS result in complex I and II deficiency, whereas mutations in the nuclear proteins involved in the assembly of OXPHOS subunits cause defects in complexes I, III, IV, and V. Here, we review recent progress in the identification of mitochondrial and nuclear gene defects and the associated clinical manifestations of these disorders in childhood.
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Affiliation(s)
- Ali-Reza Moslemi
- Department of Pathology, Göteborg University, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden.
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126
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Smits P, Smeitink JAM, van den Heuvel LP, Huynen MA, Ettema TJG. Reconstructing the evolution of the mitochondrial ribosomal proteome. Nucleic Acids Res 2007; 35:4686-703. [PMID: 17604309 PMCID: PMC1950548 DOI: 10.1093/nar/gkm441] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
For production of proteins that are encoded by the mitochondrial genome, mitochondria rely on their own mitochondrial translation system, with the mitoribosome as its central component. Using extensive homology searches, we have reconstructed the evolutionary history of the mitoribosomal proteome that is encoded by a diverse subset of eukaryotic genomes, revealing an ancestral ribosome of alpha-proteobacterial descent that more than doubled its protein content in most eukaryotic lineages. We observe large variations in the protein content of mitoribosomes between different eukaryotes, with mammalian mitoribosomes sharing only 74 and 43% of its proteins with yeast and Leishmania mitoribosomes, respectively. We detected many previously unidentified mitochondrial ribosomal proteins (MRPs) and found that several have increased in size compared to their bacterial ancestral counterparts by addition of functional domains. Several new MRPs have originated via duplication of existing MRPs as well as by recruitment from outside of the mitoribosomal proteome. Using sensitive profile-profile homology searches, we found hitherto undetected homology between bacterial and eukaryotic ribosomal proteins, as well as between fungal and mammalian ribosomal proteins, detecting two novel human MRPs. These newly detected MRPs constitute, along with evolutionary conserved MRPs, excellent new screening targets for human patients with unresolved mitochondrial oxidative phosphorylation disorders.
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Affiliation(s)
- Paulien Smits
- Nijmegen Center for Mitochondrial Disorders, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert–Grooteplein-Zuid 10 and Center for Molecular and Biomolecular Informatics, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert-Grooteplein 28, 6525 GA Nijmegen, The Netherlands
| | - Jan A. M. Smeitink
- Nijmegen Center for Mitochondrial Disorders, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert–Grooteplein-Zuid 10 and Center for Molecular and Biomolecular Informatics, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert-Grooteplein 28, 6525 GA Nijmegen, The Netherlands
| | - Lambert P. van den Heuvel
- Nijmegen Center for Mitochondrial Disorders, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert–Grooteplein-Zuid 10 and Center for Molecular and Biomolecular Informatics, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert-Grooteplein 28, 6525 GA Nijmegen, The Netherlands
| | - Martijn A. Huynen
- Nijmegen Center for Mitochondrial Disorders, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert–Grooteplein-Zuid 10 and Center for Molecular and Biomolecular Informatics, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert-Grooteplein 28, 6525 GA Nijmegen, The Netherlands
| | - Thijs J. G. Ettema
- Nijmegen Center for Mitochondrial Disorders, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert–Grooteplein-Zuid 10 and Center for Molecular and Biomolecular Informatics, Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Geert-Grooteplein 28, 6525 GA Nijmegen, The Netherlands
- *To whom correspondence should be addressed.
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127
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Abstract
In the course of evolution, mitochondria lost their independence, and mtDNA became “slave” of nDNA, depending on numerous nucleus-encoded factors for its integrity, replication and expression. Mutations in any of these factors may alter the cross-talk between the two genomes and cause diseases that affect mtDNA integrity or expression, being inherited as mendelian traits.
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Affiliation(s)
- Antonella Spinazzola
- Unit of Molecular Neurogenetics, C. Besta Neurological Institute-Foundation IRCCS, via Libero Temolo 4, Milano, 20126, Italy
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128
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Vogel RO, van den Brand MAM, Rodenburg RJ, van den Heuvel LPWJ, Tsuneoka M, Smeitink JAM, Nijtmans LGJ. Investigation of the complex I assembly chaperones B17.2L and NDUFAF1 in a cohort of CI deficient patients. Mol Genet Metab 2007; 91:176-82. [PMID: 17383918 DOI: 10.1016/j.ymgme.2007.02.007] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2006] [Revised: 02/13/2007] [Accepted: 02/13/2007] [Indexed: 11/15/2022]
Abstract
Dysfunction of complex I (NADH:ubiquinone oxidoreductase; CI), the largest enzyme of the oxidative phosphorylation (OXPHOS) system, often results in severe neuromuscular disorders and early childhood death. Mutations in its seven mitochondrial and 38 nuclear DNA-encoded structural components can only partly explain these deficiencies. Recently, CI assembly chaperones NDUFAF1 and B17.2L were linked to CI deficiency, but it is still unclear by which mechanism. To better understand their requirement during assembly we have studied their presence in CI subcomplexes in a cohort of CI deficient patients using one- and two-dimensional blue-native PAGE. This analysis revealed distinct differences between their associations to subcomplexes in different patients. B17.2L occurred in a 830 kDa subcomplex specifically in patients with mutations in subunits NDUFV1 and NDUFS4. Contrasting with this seemingly specific requirement, the previously described NDUFAF1 association to 500-850 kDa intermediates did not appear to be related to the nature and severity of the CI assembly defect. Surprisingly, even in the absence of assembly intermediates in a patient harboring a mutation in translation elongation factor G1 (EFG1), NDUFAF1 remained associated to the 500-850 kDa subcomplexes. These findings illustrate the difference in mechanism between B17.2L and NDUFAF1 and suggest that the involvement of NDUFAF1 in the assembly process could be indirect rather than direct via the binding to assembly intermediates.
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Affiliation(s)
- Rutger O Vogel
- Nijmegen Centre for Mitochondrial Disorders, Department of Paediatrics, Radboud University Nijmegen Medical Centre, 6500 HB, Nijmegen, The Netherlands
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129
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Scheper GC, van der Klok T, van Andel RJ, van Berkel CGM, Sissler M, Smet J, Muravina TI, Serkov SV, Uziel G, Bugiani M, Schiffmann R, Krägeloh-Mann I, Smeitink JAM, Florentz C, Van Coster R, Pronk JC, van der Knaap MS. Mitochondrial aspartyl-tRNA synthetase deficiency causes leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation. Nat Genet 2007; 39:534-9. [PMID: 17384640 DOI: 10.1038/ng2013] [Citation(s) in RCA: 345] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Accepted: 02/23/2007] [Indexed: 11/08/2022]
Abstract
Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) has recently been defined based on a highly characteristic constellation of abnormalities observed by magnetic resonance imaging and spectroscopy. LBSL is an autosomal recessive disease, most often manifesting in early childhood. Affected individuals develop slowly progressive cerebellar ataxia, spasticity and dorsal column dysfunction, sometimes with a mild cognitive deficit or decline. We performed linkage mapping with microsatellite markers in LBSL families and found a candidate region on chromosome 1, which we narrowed by means of shared haplotypes. Sequencing of genes in this candidate region uncovered mutations in DARS2, which encodes mitochondrial aspartyl-tRNA synthetase, in affected individuals from all 30 families. Enzyme activities of mutant proteins were decreased. We were surprised to find that activities of mitochondrial complexes from fibroblasts and lymphoblasts derived from affected individuals were normal, as determined by different assays.
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Affiliation(s)
- Gert C Scheper
- Department of Pediatrics and Child Neurology, Vrije University Medical Center, 1081 HV Amsterdam, The Netherlands.
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130
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Auré K, Mamchaoui K, Frachon P, Butler-Browne GS, Lombès A, Mouly V. Impact on oxidative phosphorylation of immortalization with the telomerase gene. Neuromuscul Disord 2007; 17:368-75. [PMID: 17383182 DOI: 10.1016/j.nmd.2007.01.019] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2006] [Revised: 11/03/2006] [Accepted: 01/29/2007] [Indexed: 11/25/2022]
Abstract
Skin fibroblasts are essential tools for biochemical, genetic and physiopathological investigations of mitochondrial diseases. Their immortalization has been previously performed to overcome the limited number of divisions of these primary cells but it has never been systematically evaluated with respect to efficacy and impact on the oxidative phosphorylation (OXPHOS) characteristics of the cells. We successfully immortalized with the human telomerase gene 15 human fibroblasts populations, 4 derived from controls and 11 from patients with diverse respiratory chain defects. Immortalization induced significant but mild modification of the OXPHOS characteristics of the cells with lower rates of oxygen consumption and ATP synthesis associated with their loose coupling. However, it never significantly altered the type and severity of any genetic OXPHOS defect present prior to immortalization. Furthermore, it did not significantly modify the cells' dependence on glucose and sensitivity to galactose thus showing that immortalized cells could be screened by their nutritional requirement. Immortalized skin fibroblasts with significant OXPHOS defect provide reliable tools for the diagnosis and research of the genetic cause of mitochondrial defects. They also represent precious material to investigate the cellular responses to these defects, even though these should afterwards be verified in unmodified primary cells.
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Affiliation(s)
- K Auré
- Inserm, U582, Institut de Myologie, Paris F-75013, France
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131
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Morava E, Bongers EMHF, Kress W, Sie L, Rodenburg R, Heuvel LVD, Brunner HG. Encephalomyopathy and optic atrophy with tall stature and mitochondrial dysfunction: a new syndrome. Clin Dysmorphol 2007; 16:131-134. [PMID: 17351361 DOI: 10.1097/mcd.0b013e328014715e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Eva Morava
- Departments of Pediatrics Human Genetics Child Neurology, Nijmegen Centre for Mitochondrial Disorders, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands Department of Human Genetics, University Biocenter Am Hubland, Wurzburg, Germany
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132
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Affiliation(s)
- Patrick F Chinnery
- Mitochondrial Research Group and Institute of Human Genetics, Newcastle University, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
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133
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Valente L, Tiranti V, Marsano RM, Malfatti E, Fernandez-Vizarra E, Donnini C, Mereghetti P, De Gioia L, Burlina A, Castellan C, Comi GP, Savasta S, Ferrero I, Zeviani M. Infantile encephalopathy and defective mitochondrial DNA translation in patients with mutations of mitochondrial elongation factors EFG1 and EFTu. Am J Hum Genet 2007; 80:44-58. [PMID: 17160893 PMCID: PMC1785320 DOI: 10.1086/510559] [Citation(s) in RCA: 155] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Accepted: 10/25/2006] [Indexed: 11/03/2022] Open
Abstract
Mitochondrial protein translation is a complex process performed within mitochondria by an apparatus composed of mitochondrial DNA (mtDNA)-encoded RNAs and nuclear DNA-encoded proteins. Although the latter by far outnumber the former, the vast majority of mitochondrial translation defects in humans have been associated with mutations in RNA-encoding mtDNA genes, whereas mutations in protein-encoding nuclear genes have been identified in a handful of cases. Genetic investigation involving patients with defective mitochondrial translation led us to the discovery of novel mutations in the mitochondrial elongation factor G1 (EFG1) in one affected baby and, for the first time, in the mitochondrial elongation factor Tu (EFTu) in another one. Both patients were affected by severe lactic acidosis and rapidly progressive, fatal encephalopathy. The EFG1-mutant patient had early-onset Leigh syndrome, whereas the EFTu-mutant patient had severe infantile macrocystic leukodystrophy with micropolygyria. Structural modeling enabled us to make predictions about the effects of the mutations at the molecular level. Yeast and mammalian cell systems proved the pathogenic role of the mutant alleles by functional complementation in vivo. Nuclear-gene abnormalities causing mitochondrial translation defects represent a new, potentially broad field of mitochondrial medicine. Investigation of these defects is important to expand the molecular characterization of mitochondrial disorders and also may contribute to the elucidation of the complex control mechanisms, which regulate this fundamental pathway of mtDNA homeostasis.
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Affiliation(s)
- Lucia Valente
- Pierfranco and Luisa Mariani Center for Research on Children's Mitochondrial Disorders, Division of Molecular Neurogenetics, National Neurological Institute "Carlo Besta," Milano, Italy
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134
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Abstract
Mitochondria are ubiquitous organelles that are intimately involved in many cellular processes, but whose principal task is to provide the energy necessary for normal cell functioning and maintenance. Disruption of this energy supply can have devastating consequences for the cell, organ, and individual. Over the last two decades, mutations in both mitochondrial DNA (mtDNA) and nuclear DNA have been identified as causative in a number of well-characterized clinical syndromes, although for mtDNA mutations in particular, this relationship between genotype and phenotype is often not straightforward. Despite this, a number of epidemiological studies have been undertaken to assess the prevalence of mtDNA mutations and these have highlighted the impact that mtDNA disease has on both the community and individual families. Although there has been considerable improvement in the diagnosis of mitochondrial disorders, disappointingly this has not been matched by developments toward effective treatment. Nevertheless, our understanding of mitochondrial biology is gathering pace and progress in this area will be crucial to devising future treatment strategies. In addition to mitochondrial disease, evidence for a central role of mitochondria in other processes, such as aging and neurodegeneration, is slowly accumulating, although their role in cancer remains controversial. In this chapter, we discuss these issues and offer our own views based on our cumulative experience of investigating and managing these diseases over the last 20 years.
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Affiliation(s)
- R McFarland
- Mitochondrial Research Group, School of Neurology, Neurobiology, and Psychiatry, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom
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135
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Oldfors A, Tulinius M. Mitochondrial encephalomyopathies. HANDBOOK OF CLINICAL NEUROLOGY 2007; 86:125-165. [PMID: 18808998 DOI: 10.1016/s0072-9752(07)86006-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
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136
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Fernández-Silva P, Acín-Pérez R, Fernández-Vizarra E, Pérez-Martos A, Enriquez JA. In Vivo and In Organello Analyses of Mitochondrial Translation. Methods Cell Biol 2007; 80:571-88. [PMID: 17445714 DOI: 10.1016/s0091-679x(06)80028-2] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- P Fernández-Silva
- Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, Zaragoza 50013, Spain
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137
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Smeitink JAM, Elpeleg O, Antonicka H, Diepstra H, Saada A, Smits P, Sasarman F, Vriend G, Jacob-Hirsch J, Shaag A, Rechavi G, Welling B, Horst J, Rodenburg RJ, van den Heuvel B, Shoubridge EA. Distinct clinical phenotypes associated with a mutation in the mitochondrial translation elongation factor EFTs. Am J Hum Genet 2006; 79:869-77. [PMID: 17033963 PMCID: PMC1698578 DOI: 10.1086/508434] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2006] [Accepted: 08/14/2006] [Indexed: 01/06/2023] Open
Abstract
The 13 polypeptides encoded in mitochondrial DNA (mtDNA) are synthesized in the mitochondrial matrix on a dedicated protein-translation apparatus that resembles that found in prokaryotes. Here, we have investigated the genetic basis for a mitochondrial protein-synthesis defect associated with a combined oxidative phosphorylation enzyme deficiency in two patients, one of whom presented with encephalomyopathy and the other with hypertrophic cardiomyopathy. Sequencing of candidate genes revealed the same homozygous mutation (C997T) in both patients in TSFM, a gene coding for the mitochondrial translation elongation factor EFTs. EFTs functions as a guanine nucleotide exchange factor for EFTu, another translation elongation factor that brings aminoacylated transfer RNAs to the ribosomal A site as a ternary complex with guanosine triphosphate. The mutation predicts an Arg333Trp substitution at an evolutionarily conserved site in a subdomain of EFTs that interacts with EFTu. Molecular modeling showed that the substitution disrupts local subdomain structure and the dimerization interface. The steady-state levels of EFTs and EFTu in patient fibroblasts were reduced by 75% and 60%, respectively, and the amounts of assembled complexes I, IV, and V were reduced by 35%-91% compared with the amounts in controls. These phenotypes and the translation defect were rescued by retroviral expression of either EFTs or EFTu. These data clearly establish mutant EFTs as the cause of disease in these patients. The fact that the same mutation is associated with distinct clinical phenotypes suggests the presence of genetic modifiers of the mitochondrial translation apparatus.
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Affiliation(s)
- Jan A M Smeitink
- Nijmegen Centre for Mitochondrial Disorders, Department of Pediatrics, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
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138
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Wittig I, Carrozzo R, Santorelli FM, Schägger H. Supercomplexes and subcomplexes of mitochondrial oxidative phosphorylation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:1066-72. [PMID: 16782043 DOI: 10.1016/j.bbabio.2006.05.006] [Citation(s) in RCA: 171] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2006] [Revised: 04/07/2006] [Accepted: 05/03/2006] [Indexed: 10/24/2022]
Abstract
Dimerization or oligomerization of ATP synthase has been proposed to play an important role for mitochondrial cristae formation and to be involved in regulating ATP synthase activity. We found comparable oligomycin-sensitive ATPase activity for monomeric and oligomeric ATP synthase suggesting that oligomerization/monomerization dynamics are not directly involved in regulating ATP synthase activity. Binding of the natural IF1 inhibitor protein has been shown to induce dimerization of F1-subcomplexes. This suggested that binding of IF1 might also dimerize holo ATP synthase, and possibly link dimerization and inhibition. Analyzing mitochondria of human rho zero cells that contain mitochondria but lack mitochondrial DNA, we identified three subcomplexes of ATP synthase: (i) F1 catalytic domain, (ii) F1-domain with bound IF1, and (iii) F1-c subcomplex with bound IF1 and a ring of subunits c. Since both IF1 containing subcomplexes were present in monomeric state and exhibited considerably reduced ATPase activity as compared to the third subcomplex lacking IF1, we postulate that inhibition and induction of dimerization of F1-subcomplexes by IF1 are independent events. F1-subcomplexes were also found in mitochondria of patients with specific mitochondrial disorders, and turned out to be useful for the clinical differentiation between various types of mitochondrial biosynthesis disorders. Supramolecular associations of respiratory complexes, the "respirasomes", seem not to be the largest assemblies in the structural organization of the respiratory chain, as suggested by differential solubilization of mitochondria and electron microscopic analyses of whole mitochondria. We present a model for a higher supramolecular association of respirasomes into a "respiratory string".
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Affiliation(s)
- Ilka Wittig
- Molekulare Bioenergetik, Zentrum der Biologischen Chemie, Universitätsklinikum Frankfurt, Theodor-Stern-Kai 7, Haus 26, D-60590 Frankfurt, Germany.
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139
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Rugarli EI, Langer T. Translating m-AAA protease function in mitochondria to hereditary spastic paraplegia. Trends Mol Med 2006; 12:262-9. [PMID: 16647881 DOI: 10.1016/j.molmed.2006.04.002] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2006] [Revised: 03/16/2006] [Accepted: 04/13/2006] [Indexed: 12/26/2022]
Abstract
Hereditary spastic paraplegia (HSP) is a genetically heterogeneous neurodegenerative disorder that is characterized by progressive and cell-specific axonal degeneration. An autosomal recessive form of the disease is caused by mutations in paraplegin, which is a conserved subunit of the ubiquitous and ATP-dependent m-AAA protease in mitochondria. The m-AAA protease carries out protein quality control in the inner membrane of the mitochondria, suggesting a pathogenic role of misfolded proteins in HSP. A recent study demonstrates that the m-AAA protease regulates ribosome assembly and translation within mitochondria by controlling proteolytic maturation of a ribosomal subunit. Here, we will discuss implications of the dual role of the m-AAA protease in protein activation and degradation for mitochondrial dysfunction and axonal degeneration.
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Affiliation(s)
- Elena I Rugarli
- Istituto Nazionale Neurologico C. Besta, Division of Biochemistry and Genetics, 20126 Milan, Italy
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140
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Antonicka H, Sasarman F, Kennaway NG, Shoubridge EA. The molecular basis for tissue specificity of the oxidative phosphorylation deficiencies in patients with mutations in the mitochondrial translation factor EFG1. Hum Mol Genet 2006; 15:1835-46. [PMID: 16632485 DOI: 10.1093/hmg/ddl106] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Defects in mitochondrial translation are associated with a remarkable, but unexplained diversity of clinical phenotypes. Here we have investigated the molecular basis for tissue specificity in patients with a fatal hepatopathy due to mutations in the mitochondrial translation elongation factor EFG1. Blue-native gel electrophoresis revealed unique, tissue-specific patterns in the nature and severity of the defect. Liver was the most severely affected tissue, with less than 10% residual assembly of complexes I and IV, and a 50% decrease in complex V. Skeletal muscle showed a 50% reduction in complex I, and complexes IV and V were 20% of control. In fibroblasts, complexes I and IV were 20% of control, and there was a 40-60% reduction in complexes III and V. In contrast, except for a 50% decrease in complex IV, all complexes were near normal in heart. The severity of the defect paralleled the steady-state level of the mutant EFG1 protein, which varied from 60% of control in heart to undetectable in liver. The ratio of translation elongation factors EFTu:EFTs increased from 1:6 to 1:2 in patient heart, whereas in liver it decreased from 1:1 to 1:4. Over-expression of either EFTu or EFTs in control and patient fibroblasts produced dominant negative effects, indicating that the relative abundance of these factors is an important determinant of translation efficiency. Our results demonstrate marked differences among tissues in the organization of the mitochondrial translation system and its response to dysfunction, and explain the severe hepatopathy, but normal cardiac function in EFG1 patients.
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Affiliation(s)
- Hana Antonicka
- Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, Quebec, Canada
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141
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Carrozzo R, Wittig I, Santorelli FM, Bertini E, Hofmann S, Brandt U, Schägger H. Subcomplexes of human ATP synthase mark mitochondrial biosynthesis disorders. Ann Neurol 2005; 59:265-75. [PMID: 16365880 DOI: 10.1002/ana.20729] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE METHODS We describe biochemically and clinically relevant aspects of mitochondrial ATP synthase, the enzyme that supplies most ATP for the cells energy demand. RESULTS Analyzing human Rho zero cells we could identify three subcomplexes of ATP synthase: F1 catalytic domain, F1 domain with bound natural IF1 inhibitor protein, and F1-c subcomplex, an assembly of F1 domain and a ring of F(O)-subunits c. Large amounts of F1 subcomplexes accumulated also in mitochondria of patients with specific mitochondrial disorders. By quantifying the F1 subcomplexes and other oxidative phosphorylation complexes in parallel, we were able to discriminate three classes of defects in mitochondrial biosynthesis, namely, mitochondrial DNA depletion, mitochondrial transfer RNA (tRNA) mutations, and mutations in the mitochondrial ATP6 gene. INTERPRETATION The relatively simple electrophoretic assay used here is a straightforward approach to differentiate between various types of genetic alterations affecting the biosynthesis of oxidative phosphorylation complexes and will be useful to guide molecular genetic diagnostics in the field of mitochondrial neuromuscular disorders.
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Affiliation(s)
- Rosalba Carrozzo
- Unit of Molecular Medicine, Bambino Gesù Hospital and Research Institute, Rome, Italy
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142
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Abstract
The human mitochondrial genome is extremely small compared with the nuclear genome, and mitochondrial genetics presents unique clinical and experimental challenges. Despite the diminutive size of the mitochondrial genome, mitochondrial DNA (mtDNA) mutations are an important cause of inherited disease. Recent years have witnessed considerable progress in understanding basic mitochondrial genetics and the relationship between inherited mutations and disease phenotypes, and in identifying acquired mtDNA mutations in both ageing and cancer. However, many challenges remain, including the prevention and treatment of these diseases. This review explores the advances that have been made and the areas in which future progress is likely.
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143
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DiMauro S, Hirano M. Mitochondrial encephalomyopathies: an update. Neuromuscul Disord 2005; 15:276-86. [PMID: 15792866 DOI: 10.1016/j.nmd.2004.12.008] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2004] [Revised: 12/10/2004] [Accepted: 12/10/2004] [Indexed: 01/10/2023]
Abstract
A genetic classification of the mitochondrial encephalomyopathies includes disorders due to defects of mitochondrial DNA (mtDNA) and disorders due to defects of nuclear DNA (nDNA). Recent progress in mtDNA-related diseases includes: (i) new pathogenic mutations in protein-coding genes, especially those encoding subunits of complex I (ND genes); (ii) the pathogenic nature of homoplasmic mutations, whose expression is regulated by environmental and genetic factors; (iii) increasing interest in the functional and pathophysiological role of haplotypes. Advances in mendelian mitochondrial diseases include: (i) new mutations in genes for complex I subunits; (ii) identification of new mutant ancillary proteins associated with complex IV and complex V deficiencies; (iii) better molecular understanding of disorders due to faulty intergenomic communication, which are associated with multiple mtDNA deletions, mtDNA depletion, or defects of mtDNA translation; (iv) the pathogenic role of alterations of the inner mitochondrial membrane phospholipid components, especially cardiolipin; (v) the emerging importance of defects in mitochondrial motility, fission, or fusion.
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Affiliation(s)
- Salvatore DiMauro
- Department of Neurology, Columbia University Medical Center, College of Physicians and Surgeons, Room 4-420, 630 West 168th Street, New York, NY 10032, USA.
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144
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Coenen MJH, Smeitink JAM, Smeets R, Trijbels FJM, van den Heuvel LP. Mutation detection in four candidate genes (OXA1L, MRS2L, YME1L and MIPEP) for combined deficiencies in the oxidative phosphorylation system. J Inherit Metab Dis 2005; 28:1091-7. [PMID: 16435202 DOI: 10.1007/s10545-005-4483-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2005] [Accepted: 11/08/2005] [Indexed: 10/25/2022]
Abstract
Mitochondria are the main energy-producing organelles of the cell. Five complexes embedded in the mitochondrial inner membrane, together constituting the oxidative phosphorylation (OXPHOS) system, comprise the final steps in cellular energy production. Many patients with a mitochondrial defect suffer from a so-called combined deficiency, meaning that the enzymatic activities of two or more complexes of the OXPHOS system are decreased. Numerous mutations have been described in nuclear genes that are involved in the functioning of a single complex of the OXPHOS system. However, little attention has been paid to patients with a deficiency of more than one complex of this particular system. In this study we have investigated four nuclear genes (OXA1L, MRS2L, YME1L and MIPEP) that might be involved in the pathology of combined enzymatic deficiencies of the OXPHOS system. Based on the results of yeast knockouts of these four proteins, we have sequenced the open reading frame of OXA1L in eight patients with an enzymatic deficiency of complexes I and IV. MRS2L, YME1L and MIPEP have been sequenced in three patients with a combined defect of complexes III and IV. No mutations were detected in these patients, showing that at least in these patients the OXPHOS system deficiency cannot be explained by a mutation in these four genes.
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Affiliation(s)
- M J H Coenen
- Nijmegen Centre for Mitochondrial Disorders, Department of Paediatrics, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
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