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Borreguero CF, Wueest S, Hantel C, Schneider H, Konrad D, Beuschlein F, Spyroglou A. Deoxyguanosine kinase mutation F180S is associated with a lean phenotype in mice. Int J Obes (Lond) 2023; 47:215-223. [PMID: 36709400 PMCID: PMC10023562 DOI: 10.1038/s41366-023-01262-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2022] [Revised: 01/14/2023] [Accepted: 01/17/2023] [Indexed: 01/29/2023]
Abstract
BACKGROUND Deoxyguanosine kinase (DGUOK) deficiency is one of the genetic causes of mitochondrial DNA depletion syndrome (MDDS) in humans, leading to the hepatocerebral or the isolated hepatic form of MDDS. Mouse models are helpful tools for the improvement of understanding of the pathophysiology of diseases and offer the opportunity to examine new therapeutic options. METHODS Herein, we describe the generation and metabolic characterization of a mouse line carrying a homozygous DguokF180S/F180S mutation derived from an N-ethyl-N-nitrosourea-mutagenesis screen. Energy expenditure (EE), oxygen consumption (VO2) and carbon dioxide production (VCO2) were assessed in metabolic cages. LC-MS/MS was used to quantify plasma adrenal steroids. Plasma insulin and leptin levels were quantified with commercially available assay kits. RESULTS Mutant animals displayed significantly lower body weights and reduced inguinal fat pad mass, in comparison to unaffected littermates. Biochemically, they were characterized by significantly lower blood glucose levels, accompanied by significantly lower insulin, total cholesterol, high density lipoprotein and triglyceride levels. They also displayed an almost 2-fold increase in transaminases. Moreover, absolute EE was comparable in mutant and control mice, but EE in mutants was uncoupled from their body weights. Histological examination of inguinal white adipose tissue (WAT) revealed adipocytes with multilocular fat droplets reminiscent of WAT browning. In addition, mRNA and protein expression of Ucp1 was increased. Mutant mice also presented differing mitochondrial DNA content in various tissues and altered metabolic activity in mitochondria, but no further phenotypical or behavioral abnormalities. Preliminary data imply normal survival of DguokF180S/F180S mutant animals. CONCLUSION Taken together, DGUOK mutation F180S leads to a lean phenotype, with lower glucose, insulin, and lipid levels rendering this mouse model not only useful for the study of MDDS forms but also for deciphering mechanisms resulting in a lean phenotype.
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Affiliation(s)
- Cédric Francis Borreguero
- Klinik für Endokrinologie, Diabetologie und Klinische Ernährung, University Hospital Zurich (USZ), University of Zurich (UZH), Zurich, Switzerland
| | - Stephan Wueest
- Division of Pediatric Endocrinology and Diabetology, University Children's Hospital, University of Zurich, Zurich, Switzerland
- Children's Research Center, University Children's Hospital, University of Zurich, Zurich, Switzerland
| | - Constanze Hantel
- Klinik für Endokrinologie, Diabetologie und Klinische Ernährung, University Hospital Zurich (USZ), University of Zurich (UZH), Zurich, Switzerland
- Medizinische Klinik und Poliklinik III, University Hospital Carl Gustav Carus Dresden, Dresden, Germany
| | - Holger Schneider
- Medizinische Klinik und Poliklinik IV, Ludwig-Maximilians-University (LMU), Munich, Germany
| | - Daniel Konrad
- Division of Pediatric Endocrinology and Diabetology, University Children's Hospital, University of Zurich, Zurich, Switzerland
- Children's Research Center, University Children's Hospital, University of Zurich, Zurich, Switzerland
| | - Felix Beuschlein
- Klinik für Endokrinologie, Diabetologie und Klinische Ernährung, University Hospital Zurich (USZ), University of Zurich (UZH), Zurich, Switzerland.
| | - Ariadni Spyroglou
- Klinik für Endokrinologie, Diabetologie und Klinische Ernährung, University Hospital Zurich (USZ), University of Zurich (UZH), Zurich, Switzerland
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Molina-Granada D, González-Vioque E, Dibley MG, Cabrera-Pérez R, Vallbona-Garcia A, Torres-Torronteras J, Sazanov LA, Ryan MT, Cámara Y, Martí R. Most mitochondrial dGTP is tightly bound to respiratory complex I through the NDUFA10 subunit. Commun Biol 2022; 5:620. [PMID: 35739187 PMCID: PMC9226000 DOI: 10.1038/s42003-022-03568-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Accepted: 06/08/2022] [Indexed: 12/30/2022] Open
Abstract
Imbalanced mitochondrial dNTP pools are known players in the pathogenesis of multiple human diseases. Here we show that, even under physiological conditions, dGTP is largely overrepresented among other dNTPs in mitochondria of mouse tissues and human cultured cells. In addition, a vast majority of mitochondrial dGTP is tightly bound to NDUFA10, an accessory subunit of complex I of the mitochondrial respiratory chain. NDUFA10 shares a deoxyribonucleoside kinase (dNK) domain with deoxyribonucleoside kinases in the nucleotide salvage pathway, though no specific function beyond stabilizing the complex I holoenzyme has been described for this subunit. We mutated the dNK domain of NDUFA10 in human HEK-293T cells while preserving complex I assembly and activity. The NDUFA10E160A/R161A shows reduced dGTP binding capacity in vitro and leads to a 50% reduction in mitochondrial dGTP content, proving that most dGTP is directly bound to the dNK domain of NDUFA10. This interaction may represent a hitherto unknown mechanism regulating mitochondrial dNTP availability and linking oxidative metabolism to DNA maintenance.
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Affiliation(s)
- David Molina-Granada
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Emiliano González-Vioque
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
- Department of Clinical Biochemistry, Hospital Universitario Puerta del Hierro-Majadahonda, Madrid, Spain
| | - Marris G Dibley
- Department of Biochemistry and Molecular Biology, Monash Biomedicine Discovery Institute, Monash University, Melbourne, Australia
| | - Raquel Cabrera-Pérez
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Antoni Vallbona-Garcia
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain
| | - Javier Torres-Torronteras
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Leonid A Sazanov
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Michael T Ryan
- Department of Biochemistry and Molecular Biology, Monash Biomedicine Discovery Institute, Monash University, Melbourne, Australia
| | - Yolanda Cámara
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain.
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.
| | - Ramon Martí
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain.
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.
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3
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Lin S, Huang C, Sun J, Bollt O, Wang X, Martine E, Kang J, Taylor MD, Fang B, Singh PK, Koomen J, Hao J, Yang S. The mitochondrial deoxyguanosine kinase is required for cancer cell stemness in lung adenocarcinoma. EMBO Mol Med 2019; 11:e10849. [PMID: 31633874 PMCID: PMC6895611 DOI: 10.15252/emmm.201910849] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Revised: 09/17/2019] [Accepted: 09/20/2019] [Indexed: 12/14/2022] Open
Abstract
The mitochondrial deoxynucleotide triphosphate (dNTP) is maintained by the mitochondrial deoxynucleoside salvage pathway and dedicated for the mtDNA homeostasis, and the mitochondrial deoxyguanosine kinase (DGUOK) is a rate-limiting enzyme in this pathway. Here, we investigated the role of the DGUOK in the self-renewal of lung cancer stem-like cells (CSC). Our data support that DGUOK overexpression strongly correlates with cancer progression and patient survival. The depletion of DGUOK robustly inhibited lung adenocarcinoma tumor growth, metastasis, and CSC self-renewal. Mechanistically, DGUOK is required for the biogenesis of respiratory complex I and mitochondrial OXPHOS, which in turn regulates CSC self-renewal through AMPK-YAP1 signaling. The restoration of mitochondrial OXPHOS in DGUOK KO lung cancer cells using NDI1 was able to prevent AMPK-mediated phosphorylation of YAP and to rescue CSC stemness. Genetic targeting of DGUOK using doxycycline-inducible CRISPR/Cas9 was able to markedly induce tumor regression. Our findings reveal a novel role for mitochondrial dNTP metabolism in lung cancer tumor growth and progression, and implicate that the mitochondrial deoxynucleotide salvage pathway could be potentially targeted to prevent CSC-mediated therapy resistance and metastatic recurrence.
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Affiliation(s)
- Shengchen Lin
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
| | - Chongbiao Huang
- Key Laboratory of Cancer Prevention and Therapy, Department of Pancreatic Cancer, Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, Tianjin, China
| | - Jianwei Sun
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
- State Key Laboratory of Natural Resource Conservation and Utilization in Yunnan and Center for Life Science, School of Life Sciences, Yunnan University, Kunming, China
- South China Agricultural University, Guangzhou, China
| | - Oana Bollt
- Department of Surgery, The Pennsylvania State University College of Medicine, Hershey, PA, USA
| | - Xiuchao Wang
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
- Key Laboratory of Cancer Prevention and Therapy, Department of Pancreatic Cancer, Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, Tianjin, China
| | - Eric Martine
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
| | - Jiaxin Kang
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
- South China Agricultural University, Guangzhou, China
| | - Matthew D Taylor
- Department of Surgery, The Pennsylvania State University College of Medicine, Hershey, PA, USA
| | - Bin Fang
- Department of Molecular Oncology, Proteomics & Metabolomics Core, H. Lee Moffitt Cancer Center, Tampa, FL, USA
| | - Pankaj K Singh
- Department of Pathology and Microbiology, Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, USA
| | - John Koomen
- Department of Molecular Oncology, Proteomics & Metabolomics Core, H. Lee Moffitt Cancer Center, Tampa, FL, USA
| | - Jihui Hao
- Key Laboratory of Cancer Prevention and Therapy, Department of Pancreatic Cancer, Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, Tianjin, China
| | - Shengyu Yang
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
- Department of Tumor Biology, H. Lee Moffitt Cancer Center, Tampa, FL, USA
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4
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Mahjoub G, Habibzadeh P, Dastsooz H, Mirzaei M, Kavosi A, Jamali L, Javanmardi H, Katibeh P, Faghihi MA, Dastgheib SA. Clinical and molecular characterization of three patients with Hepatocerebral form of mitochondrial DNA depletion syndrome: a case series. BMC MEDICAL GENETICS 2019; 20:167. [PMID: 31664948 PMCID: PMC6819644 DOI: 10.1186/s12881-019-0893-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Accepted: 09/10/2019] [Indexed: 12/31/2022]
Abstract
Background Mitochondrial DNA depletion syndromes (MDS) are clinically and phenotypically heterogeneous disorders resulting from nuclear gene mutations. The affected individuals represent a notable reduction in mitochondrial DNA (mtDNA) content, which leads to malfunction of the components of the respiratory chain. MDS is classified according to the type of affected tissue; the most common type is hepatocerebral form, which is attributed to mutations in nuclear genes such as DGUOK and MPV17. These two genes encode mitochondrial proteins and play major roles in mtDNA synthesis. Case presentation In this investigation patients in three families affected by hepatocerebral form of MDS who were initially diagnosed with tyrosinemia underwent full clinical evaluation. Furthermore, the causative mutations were identified using next generation sequencing and were subsequently validated using sanger sequencing. The effect of the mutations on the gene expression was also studied using real-time PCR. A pathogenic heterozygous frameshift deletion mutation in DGUOK gene was identified in parents of two affected patients (c.706–707 + 2 del: p.k236 fs) presenting with jaundice, impaired fetal growth, low-birth weight, and failure to thrive who died at the age of 3 and 6 months in family I. Moreover, a novel splice site mutation in MPV17 gene (c.461 + 1G > C) was identified in a patient with jaundice, muscle weakness, and failure to thrive who died due to hepatic failure at the age of 4 months. A 5-month-old infant presenting with jaundice, dark urine, poor sucking, and feeding problems was also identified to have another novel mutation in MPV17 gene leading to stop gain mutation (c.277C > T: p.(Gln93*)). Conclusions These patients had overlapping clinical features with tyrosinemia. MDS should be considered a differential diagnosis in patients presenting with signs and symptoms of tyrosinemia.
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Affiliation(s)
- Ghazale Mahjoub
- Persian BayanGene Research and Training Center, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Parham Habibzadeh
- Persian BayanGene Research and Training Center, Shiraz University of Medical Sciences, Shiraz, Iran.,Student Research Committee, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Hassan Dastsooz
- Persian BayanGene Research and Training Center, Shiraz University of Medical Sciences, Shiraz, Iran.,Italian Institute for Genomic Medicine (IIGM), University of Turin, Turin, Italy
| | - Malihe Mirzaei
- Persian BayanGene Research and Training Center, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Arghavan Kavosi
- Persian BayanGene Research and Training Center, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Laila Jamali
- Persian BayanGene Research and Training Center, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Haniyeh Javanmardi
- Student Research Committee, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Pegah Katibeh
- Department of Pediatrics, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Mohammad Ali Faghihi
- Persian BayanGene Research and Training Center, Shiraz University of Medical Sciences, Shiraz, Iran.,Center for Therapeutic Innovation, Department of Psychiatry and Behavioral Sciences, University of Miami Miller School of Medicine, Miami, USA
| | - Seyed Alireza Dastgheib
- Department of Medical Genetics, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.
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5
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Al-Hussaini A, Faqeih E, El-Hattab AW, Alfadhel M, Asery A, Alsaleem B, Bakhsh E, Ali A, Alasmari A, Lone K, Nahari A, Eyaid W, Al Balwi M, Craig K, Butterworth A, He L, Taylor RW. Clinical and molecular characteristics of mitochondrial DNA depletion syndrome associated with neonatal cholestasis and liver failure. J Pediatr 2014; 164:553-9.e1-2. [PMID: 24321534 DOI: 10.1016/j.jpeds.2013.10.082] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Revised: 09/23/2013] [Accepted: 10/29/2013] [Indexed: 11/17/2022]
Abstract
OBJECTIVE To determine the frequency of mitochondrial DNA depletion syndrome (MDS) in infants with cholestasis and liver failure and to further clarify the clinical, biochemical, radiologic, histopathologic, and molecular features associated with MDS due to deoxyguanosine kinase (DGUOK) and MPV17 gene mutations. STUDY DESIGN We studied 20 infants with suspected hepatocerebral MDS referred to our tertiary care center between 2007 and 2013. Genomic DNA was isolated from blood leukocytes, liver, and/or skeletal muscle samples by standard methods. Mitochondrial DNA copy number relative to nuclear DNA levels was determined in muscle and/or liver DNA using real-time quantitative polymerase chain reaction and compared with age-matched controls. Nuclear candidate genes, including polymerase γ, MPV17, and DGUOK were sequenced using standard analyses. RESULTS We identified pathogenic MPV17 and DGUOK mutations in 11 infants (6 females) representing 2.5% of the 450 cases of infantile cholestasis and 22% of the 50 cases of infantile liver failure referred to our center during the study period. All of the 11 patients manifested cholestasis that was followed by a rapidly progressive liver failure and death before 2 years of life. Mitochondrial DNA depletion was demonstrated in liver or muscle for 8 out of the 11 cases where tissue was available. Seven patients had mutations in the MPV17 gene (3 novel mutations), 4 patients had DGUOK mutations (of which 2 were novel mutations). CONCLUSION Mutations in the MPV17 and DGUOK genes are present in a significant percentage of infants with liver failure and are associated with poor prognosis.
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Affiliation(s)
- Abdulrahman Al-Hussaini
- Division of Pediatric Gastroenterology, The Children's Hospital, King Fahad Medical City, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia.
| | - Eissa Faqeih
- Division of Medical Genetics, The Children's Hospital, King Fahad Medical City, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia
| | - Ayman W El-Hattab
- Division of Medical Genetics, The Children's Hospital, King Fahad Medical City, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia
| | - Majid Alfadhel
- Division of Genetics, Department of Pediatrics, King Saud bin Abdulaziz University for Health Sciences, King Abdulaziz Medical City, Riyadh, Saudi Arabia
| | - Ali Asery
- Division of Pediatric Gastroenterology, The Children's Hospital, King Fahad Medical City, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia
| | - Badr Alsaleem
- Division of Pediatric Gastroenterology, The Children's Hospital, King Fahad Medical City, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia
| | - Eman Bakhsh
- Department of Radiology, King Saud bin Abdulaziz University for Health Sciences, King Fahad Medical City, Riyadh, Saudi Arabia
| | - Ashraf Ali
- Department of Pathology, King Saud bin Abdulaziz University for Health Sciences, King Abdulaziz Medical City, Riyadh, Saudi Arabia
| | - Ali Alasmari
- Division of Medical Genetics, The Children's Hospital, King Fahad Medical City, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia
| | - Khurram Lone
- Division of Pediatric Gastroenterology, The Children's Hospital, King Fahad Medical City, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia
| | - Ahmed Nahari
- Division of Pediatric Gastroenterology, The Children's Hospital, King Fahad Medical City, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia
| | - Wafaa Eyaid
- Division of Genetics, Department of Pediatrics, King Saud bin Abdulaziz University for Health Sciences, King Abdulaziz Medical City, Riyadh, Saudi Arabia
| | - Mohammed Al Balwi
- Department of Pathology, King Saud bin Abdulaziz University for Health Sciences, King Abdulaziz Medical City, Riyadh, Saudi Arabia; King Abdullah International Medical Research Center, King Saud bin Abdulaziz University for Health Sciences, King Abdulaziz Medical City, Riyadh, Saudi Arabia
| | - Kate Craig
- Newcastle Mitochondrial Highly Specialized Services Diagnostic Laboratory, Wellcome Trust Centre for Mitochondrial Research, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Anna Butterworth
- Newcastle Mitochondrial Highly Specialized Services Diagnostic Laboratory, Wellcome Trust Centre for Mitochondrial Research, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Langping He
- Newcastle Mitochondrial Highly Specialized Services Diagnostic Laboratory, Wellcome Trust Centre for Mitochondrial Research, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Robert W Taylor
- Newcastle Mitochondrial Highly Specialized Services Diagnostic Laboratory, Wellcome Trust Centre for Mitochondrial Research, Newcastle University, Newcastle upon Tyne, United Kingdom
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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.
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Affiliation(s)
- William C Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Durham, North Carolina 27709, USA.
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7
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Leung GPH. Iatrogenic mitochondriopathies: a recent lesson from nucleoside/nucleotide reverse transcriptase inhibitors. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 942:347-69. [PMID: 22399431 DOI: 10.1007/978-94-007-2869-1_16] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The use of nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) has revolutionized the treatment of infection by human immunodeficiency virus (HIV) and hepatitis-B virus. NRTIs can suppress viral replication in the long-term, but possess significant toxicity that can seriously compromise treatment effectiveness. The major toxicity of NRTIs is mitochondrial toxicity. This manifests as serious side effects such as myopathy, peripheral neuropathy and lactic acidosis. In general, it is believed that the mitochondrial pathogenesis is closely related to the effect of NRTIs on mitochondrial DNA polymerase-γ. Depletion and mutation of mitochondrial DNA during chronic NRTI therapy may lead to cellular respiratory dysfunction and release of reactive oxidative species, resulting in cellular damage. It is now apparent that the etiology is far more complex than originally thought. It appears to involve multiple mechanisms as well as host factors such as HIV per se, inborn mitochondrial mutation, and sex. Management of mitochondrial toxicity during NRTI therapy remains a challenge. Interruption of NRTI therapy and substitution of the causative agents with alternative better-tolerated NRTIs represents the mainstay of management for mitochondrial toxicity and its clinical manifestations. A range of pharmacological approaches has been proposed as treatments and prophylaxes.
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Affiliation(s)
- George P H Leung
- Department of Pharmacology and Pharmacy, The University of Hong Kong, Hong Kong, China.
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8
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Antes A, Tappin I, Chung S, Lim R, Lu B, Parrott AM, Hill HZ, Suzuki CK, Lee CG. Differential regulation of full-length genome and a single-stranded 7S DNA along the cell cycle in human mitochondria. Nucleic Acids Res 2010; 38:6466-76. [PMID: 20530535 PMCID: PMC2965228 DOI: 10.1093/nar/gkq493] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Mammalian mitochondria contain full-length genome and a single-stranded 7S DNA. Although the copy number of mitochondrial DNA (mtDNA) varies depending on the cell type and also in response to diverse environmental stresses, our understanding of how mtDNA and 7S DNA are maintained and regulated is limited, partly due to lack of reliable in vitro assay systems that reflect the in vivo functionality of mitochondria. Here we report an in vitro assay system to measure synthesis of both mtDNA and 7S DNA under a controllable in vitro condition. With this assay system, we demonstrate that the replication capacity of mitochondria correlates with endogenous copy numbers of mtDNA and 7S DNA. Our study also shows that higher nucleotide concentrations increasingly promote 7S DNA synthesis but not mtDNA synthesis. Consistently, the mitochondrial capacity to synthesize 7S DNA but not mtDNA noticeably varied along the cell cycle, reaching its highest level in S phase. These findings suggest that syntheses of mtDNA and 7S DNA proceed independently and that the mitochondrial capacity to synthesize 7S DNA dynamically changes not only with cell-cycle progression but also in response to varying nucleotide concentrations.
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Affiliation(s)
- Anita Antes
- Department of Biochemistry and Molecular Biology, UMDNJ-New Jersey Medical School, Newark, NJ 07103, USA
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9
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Camici M, Micheli V, Ipata PL, Tozzi MG. Pediatric neurological syndromes and inborn errors of purine metabolism. Neurochem Int 2009; 56:367-78. [PMID: 20005278 DOI: 10.1016/j.neuint.2009.12.003] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2009] [Revised: 11/25/2009] [Accepted: 12/03/2009] [Indexed: 11/17/2022]
Abstract
This review is devised to gather the presently known inborn errors of purine metabolism that manifest neurological pediatric syndromes. The aim is to draw a comprehensive picture of these rare diseases, characterized by unexpected and often devastating neurological symptoms. Although investigated for many years, most purine metabolism disorders associated to psychomotor dysfunctions still hide the molecular link between the metabolic derangement and the neurological manifestations. This basically indicates that many of the actual functions of nucleosides and nucleotides in the development and function of several organs, in particular central nervous system, are still unknown. Both superactivity and deficiency of phosphoribosylpyrophosphate synthetase cause hereditary disorders characterized, in most cases, by neurological impairments. The deficiency of adenylosuccinate lyase and 5-amino-4-imidazolecarboxamide ribotide transformylase/IMP cyclohydrolase, both belonging to the de novo purine synthesis pathway, is also associated to severe neurological manifestations. Among catabolic enzymes, hyperactivity of ectosolic 5'-nucleotidase, as well as deficiency of purine nucleoside phosphorylase and adenosine deaminase also lead to syndromes affecting the central nervous system. The most severe pathologies are associated to the deficiency of the salvage pathway enzymes hypoxanthine-guanine phosphoribosyltransferase and deoxyguanosine kinase: the former due to an unexplained adverse effect exerted on the development and/or differentiation of dopaminergic neurons, the latter due to a clear impairment of mitochondrial functions. The assessment of hypo- or hyperuricemic conditions is suggestive of purine enzyme dysfunctions, but most disorders of purine metabolism may escape the clinical investigation because they are not associated to these metabolic derangements. This review may represent a starting point stimulating both scientists and physicians involved in the study of neurological dysfunctions caused by inborn errors of purine metabolism with the aim to find novel therapeutical approaches.
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Affiliation(s)
- Marcella Camici
- Dipartimento di Biologia, Unità di Biochimica, Via S Zeno 51, 56127 Pisa, Italy.
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10
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Liu HL, Xu JJ, Dai XM, Shi JB, Xu S, Gao J, Yao QZ, Liu F. Both DNA damage and mitochondrial dysfunction are involved in novel oxadiazolo[3,4-d]pyrimidine nucleoside derivatives-induced cancer cell death. J Appl Toxicol 2009; 29:489-95. [DOI: 10.1002/jat.1433] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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11
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Eriksson S, Wang L. Molecular mechanisms of mitochondrial DNA depletion diseases caused by deficiencies in enzymes in purine and pyrimidine metabolism. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2008; 27:800-8. [PMID: 18600543 DOI: 10.1080/15257770802146197] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Mitochondrial DNA depletion syndrome (MDS), a reduction of mitochondrial DNA copy number, often affects muscle or liver. Mutations in enzymes of deoxyribonucleotide metabolism give MDS, for example, the mitochondrial thymidine kinase 2 (TK2) and deoxyguanosine kinase (dGK) genes. Sixteen TK2 and 22 dGK alterations are known. Their characteristics and symptoms are described. Levels of five key deoxynucleotide metabolizing enzymes in mouse tissues were measured. TK2 and dGK levels in muscles were 5- to 10-fold lower than other nonproliferating tissues and 100-fold lower compared to spleen. Each type of tissue apparently relies on de novo and salvage synthesis of DNA precursors to varying degrees.
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Affiliation(s)
- Staffan Eriksson
- Department of Anatomy, Physiology & Biochemistry, Swedish University of Agricultural Sciences, Uppsala, Sweden.
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Abstract
Mitochondrial genetic diseases can result from defects in mitochondrial DNA (mtDNA) in the form of deletions, point mutations, or depletion, which ultimately cause loss of oxidative phosphorylation. These mutations may be spontaneous, maternally inherited, or a result of inherited nuclear defects in genes that maintain mtDNA. This review focuses on our current understanding of nuclear gene mutations that produce mtDNA alterations and cause mitochondrial depletion syndrome (MDS), progressive external ophthalmoplegia (PEO), ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). To date, all of these etiologic nuclear genes fall into one of two categories: genes whose products function directly at the mtDNA replication fork, such as POLG, POLG2, and TWINKLE, or genes whose products supply the mitochondria with deoxynucleotide triphosphate pools needed for DNA replication, such as TK2, DGUOK, TP, SUCLA2, ANT1, and possibly the newly identified MPV17.
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Affiliation(s)
- William C Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
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13
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Leung GPH, Tse CM. The role of mitochondrial and plasma membrane nucleoside transporters in drug toxicity. Expert Opin Drug Metab Toxicol 2008; 3:705-18. [PMID: 17916056 DOI: 10.1517/17425255.3.5.705] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Many anticancer and antiviral drugs are nucleoside analogues, which interfere with nucleotide metabolism and DNA replication to produce pharmacological effects. Clinical efficacy and toxicity of nucleoside drugs are closely associated with nucleoside transporters because they mediate the transport of nucleoside drugs across biological membranes. Two families of human nucleoside transporters (equilibrative nucleoside transporters and concentrative nucleoside transporters) have been extensively studied for several decades. They are widely distributed, from the plasma membrane to membranes of organelles such as mitochondria, and the distribution differs in different tissues. In addition, they have different specificities to nucleoside drugs. The characteristics of equilibrative and concentrative nucleoside transporters affect the therapeutic outcomes achieved with anticancer and antiviral nucleoside drugs. In this review, an overview of the role of mitochondrial and plasma membrane nucleoside transporters in nucleoside drug toxicity is provided. Rational design and therapeutic application of nucleoside analogues are also discussed.
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Affiliation(s)
- George P H Leung
- The University of Hong Kong, Department of Pharmacology, Hong Kong.
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14
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Abstract
Among the human diseases that result from abnormalities in mitochondrial genome stability or maintenance are several that result from mutations affecting enzymes of deoxyribonucleoside triphosphate (dNTP) metabolism. In addition, it is evident that the toxicity of antiviral nucleoside analogs is determined in part by the extent to which their intracellular conversion to dNTP analogs occurs within the mitochondrion. Finally, recent work from this laboratory has shown considerable variation among different mammalian tissues with respect to mitochondrial dNTP pool sizes and has suggested that natural asymmetries in mitochondrial dNTP concentrations may contribute to the high rates at which the mitochondrial genome undergoes mutation. These factors suggest that much more information is needed about maintenance and regulation of dNTP pools within mammalian mitochondria. This review summarizes our current understanding and suggests directions for future research.
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Affiliation(s)
- Christopher K Mathews
- Department of Biochemistry and Biophysics, Oregon State University, 2011 Agricultural and Life Sciences Bldg., Corvallis, OR 97331-7305, USA.
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15
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Mousson de Camaret B, Taanman JW, Padet S, Chassagne M, Mayençon M, Clerc-Renaud P, Mandon G, Zabot MT, Lachaux A, Bozon D. Kinetic properties of mutant deoxyguanosine kinase in a case of reversible hepatic mtDNA depletion. Biochem J 2007; 402:377-85. [PMID: 17073823 PMCID: PMC1798436 DOI: 10.1042/bj20060705] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
DGUOK [dG (deoxyguanosine) kinase] is one of the two mitochondrial deoxynucleoside salvage pathway enzymes involved in precursor synthesis for mtDNA (mitochondrial DNA) replication. DGUOK is responsible for the initial rate-limiting phosphorylation of the purine deoxynucleosides, using a nucleoside triphosphate as phosphate donor. Mutations in the DGUOK gene are associated with the hepato-specific and hepatocerebral forms of MDS (mtDNA depletion syndrome). We identified two missense mutations (N46S and L266R) in the DGUOK gene of a previously reported child, now 10 years old, who presented with an unusual revertant phenotype of liver MDS. The kinetic properties of normal and mutant DGUOK were studied in mitochondrial preparations from cultured skin fibroblasts, using an optimized methodology. The N46S/L266R DGUOK showed 14 and 10% residual activity as compared with controls with dG and deoxyadenosine as phosphate acceptors respectively. Similar apparent negative co-operativity in the binding of the phosphate acceptors to the wild-type enzyme was found for the mutant. In contrast, abnormal bimodal kinetics were shown with ATP as the phosphate donor, suggesting an impairment of the ATP binding mode at the phosphate donor site. No kinetic behaviours were found for two other patients with splicing defects or premature stop codon. The present study represents the first characterization of the enzymatic kinetic properties of normal and mutant DGUOK in organello and our optimized protocol allowed us to demonstrate a residual activity in skin fibroblast mitochondria from a patient with a revertant phenotype of MDS. The residual DGUOK activity may play a crucial role in the phenotype reversal.
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16
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Abstract
Intracellular concentrations of the four deoxyribonucleoside triphosphates (dNTPs) are closely regulated, and imbalances in the four dNTP pools have genotoxic consequences. Replication errors leading to mutations can occur, for example, if one dNTP in excess drives formation of a non-Watson-Crick base pair or if it forces replicative DNA chain elongation past a mismatch before DNA polymerase can correct the error by 3' exonuclease proofreading. This review focuses on developments since 1994, when the field was last reviewed comprehensively. Emphasis is placed on the following topics: 1) novel aspects of dNTP pool regulation, 2) dNTP pool asymmetries as mutagenic determinants, 3) dNTP metabolism and hypermutagenesis of retroviral genomes, 4) dNTP metabolism and mutagenesis in the mitochondrial genome, 5) chemical modification of nucleotides as a premutagenic event, 6) relationships between dNTP metabolism, genome stability, aging, and cancer.
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Affiliation(s)
- Christopher K Mathews
- Department of Biochemistry and Biophysics, Oregon State University, 2011 Agricultural & Life Sciences Bldg., Corvallis, Oregon 97331-7305, USA.
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Galbiati S, Bordoni A, Papadimitriou D, Toscano A, Rodolico C, Katsarou E, Sciacco M, Garufi A, Prelle A, Aguennouz M', Bonsignore M, Crimi M, Martinuzzi A, Bresolin N, Papadimitriou A, Comi GP. New mutations in TK2 gene associated with mitochondrial DNA depletion. Pediatr Neurol 2006; 34:177-85. [PMID: 16504786 DOI: 10.1016/j.pediatrneurol.2005.07.013] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 06/14/2005] [Accepted: 07/11/2005] [Indexed: 11/17/2022]
Abstract
Mitochondrial deoxyribonucleic acid depletion syndromes are autosomal recessive disorders characterized by a reduction of the amount of mitochondrial deoxyribonucleic acid, which impairs the synthesis of respiratory chain complexes. Mutations in the deoxyguanosine kinase and polymerase gamma genes have been identified in hepatocerebral forms, whereas thymidine kinase 2 gene mutations have been found in patients with isolated myopathy, encephalomyopathy, or spinal muscular atrophy. Mutations in the gene encoding the beta subunit of the adenosine diphosphate-forming succinyl-coenzyme A synthetase have also been reported in a family. In this report, the clinical, molecular, morphologic, and biochemical features of five children from two independent families with an infantile encephalomyopathy are characterized. The affected children manifested muscle mitochondrial deoxyribonucleic acid depletion and three novel thymidine kinase 2 gene mutations. They consist of a homozygous substitution resulting in Ala to Val change at the highly conserved position 181 of thymidine kinase in the first family, and two heterozygous substitutions in the second family: a Cys to Trp change at residue 108 and a Leu to Pro change at residue 257 of the enzyme. Common clinical features associated with these TK2 mutations are a normal early developmental phase followed by psychomotor regression, encephalopathy often with epileptic seizures, and myopathy with features of a progressive dystrophic process.
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Affiliation(s)
- Sara Galbiati
- Centro Dino Ferrari, Department of Neurological Sciences, University of Milan, I.R.C.C.S. Ospedale Maggiore Policlinico, Milano, Italy.
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Labarthe F, Dobbelaere D, Devisme L, De Muret A, Jardel C, Taanman JW, Gottrand F, Lombès A. Clinical, biochemical and morphological features of hepatocerebral syndrome with mitochondrial DNA depletion due to deoxyguanosine kinase deficiency. J Hepatol 2005; 43:333-41. [PMID: 15964659 DOI: 10.1016/j.jhep.2005.03.023] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 03/10/2005] [Accepted: 03/14/2005] [Indexed: 12/04/2022]
Abstract
BACKGROUND/AIMS The aim of this study was to delineate the specific clinical, biological and liver morphological alterations of the hepatocerebral syndrome due to alterations in the deoxyguanosine kinase gene, a rare and severe form of mitochondrial DNA depletion syndrome. METHODS We report seven cases from three unrelated families with the same mutation in the deoxyguanosine kinase gene. RESULTS All the patients presented in the first weeks of life with hepatomegaly and progressive liver failure that led to death few months later. Major psychomotor delay and multidirectional nystagmus were reported shortly after onset of the disease. Severe hyperlactacidaemia was constant. Histological examination of the liver disclosed a multifocal injury of hepatocytes with irregular foamy steatosis, cholestasis, and fibrosis, associated with different degrees of hepatosiderosis and glycogen depletion. Liver respiratory chain activities were abnormal in all analysed patients and the amount of liver mitochondrial DNA was severely decreased. An identical homozygous 4bp GATT duplication was identified in the deoxyguanosine kinase gene of all the cases. CONCLUSIONS These patients, together with patients reported in the literature, permit to delineate the specific features of the hepatocerebral form of mitochondrial DNA depletion syndrome and to differentiate them from other causes of neonatal liver failure.
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Affiliation(s)
- François Labarthe
- Groupement de Médecine Pédiatrique, Hôpital Clocheville, CHU Tours, France
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Activity profiles of deoxynucleoside kinases and 5'-nucleotidases in cultured adipocytes and myoblastic cells: insights into mitochondrial toxicity of nucleoside analogs. Biochem Pharmacol 2005; 69:951-60. [PMID: 15748706 DOI: 10.1016/j.bcp.2004.12.010] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2004] [Accepted: 12/28/2004] [Indexed: 10/25/2022]
Abstract
Nucleoside reverse transcriptase inhibitor (NRTI) treatment of HIV is associated with complications, including lipodystrophy (LD) and myopathy. Inhibition of mitochondrial DNA polymerase and depletion of mtDNA by NRTI triphosphates are believed to be key mechanisms in NRTI toxicity. Here, we determined the activities and mRNA levels of deoxynucleoside kinases (dNK) and 5'-nucleotidases (5'-NT) controlling the rate-limiting step in intracellular phosphorylation of NRTIs in cell models representing adipose, muscle tissue and peripheral blood cells using specific assays and Taqman RT-PCR. In vitro phosphorylation of 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-didehydro-2',3'-dideoxythymidine (d4T) in extracts was also determined. 3T3-L1 adipocytes showed similar activity of mitochondrial thymidine kinase-2 (TK2) and deoxyguanosine kinase (dGK) but 3- to 36-fold lower levels of cytosolic deoxycytidine kinase (dCK), thymidine kinase-1 (TK1) and thymidine monophosphate kinase (TMPK) and higher levels of deoxyribonucleotidase activity compared to proliferating 3T3-L1. dCK, dGK and TK2 activities correlated with their mRNA levels in proliferating, resting and differentiating 3T3-L1. Differentiated L6 myoblasts had lower activities of cytosolic dNK's and TMPK, higher dGK and similar TK2 and deoxyribonucleotidases (dNT) activities compared to proliferating myoblasts. TK2 was the limiting dNK activity while dGK was predominant in adipocytes and myocytes. Activity profiles revealed limited capacity to phosphorylate dThd and dCyd in adipocytes and myocytes compared to proliferating cells and CEM lymphocytes. Phosphorylation of AZT and d4T was low in adipocytes and myocytes, and the presence of these analogs inhibited the phosphorylation of dThd by TK2 suggesting that mitochondrial toxicity of some NRTIs in adipocytes and myocytes is due to the depletion of normal mitochondrial dNTP pools.
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Abstract
Mitochondrial DNA (mtDNA) depends on numerous nuclear encoded factors and a constant supply of deoxyribonucleoside triphosphates (dNTP), for its maintenance and replication. The function of proteins involved in nucleotide metabolism is perturbed in a heterogeneous group of disorders associated with depletion, multiple deletions, and mutations of the mitochondrial genome. Disturbed homeostasis of the mitochondrial dNTP pools are likely the underlying cause. Understanding of the biochemical and molecular basis of these disorders will promote the development of new therapeutic approaches. This article reviews the current knowledge of deoxyribonucleotide metabolism in relation to disorders affecting mtDNA integrity.
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Affiliation(s)
- Ann Saada
- Metabolic Disease Unit, Shaare Zedek Medical Center, Jerusalem, Israel.
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Bradshaw PC, Samuels DC. A computational model of mitochondrial deoxynucleotide metabolism and DNA replication. Am J Physiol Cell Physiol 2005; 288:C989-1002. [PMID: 15634740 DOI: 10.1152/ajpcell.00530.2004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We present a computational model of mitochondrial deoxynucleotide metabolism and mitochondrial DNA (mtDNA) synthesis. The model includes the transport of deoxynucleosides and deoxynucleotides into the mitochondrial matrix space, as well as their phosphorylation and polymerization into mtDNA. Different simulated cell types (cancer, rapidly dividing, slowly dividing, and postmitotic cells) are represented in this model by different cytoplasmic deoxynucleotide concentrations. We calculated the changes in deoxynucleotide concentrations within the mitochondrion during the course of a mtDNA replication event and the time required for mtDNA replication in the different cell types. On the basis of the model, we define three steady states of mitochondrial deoxynucleotide metabolism: the phosphorylating state (the net import of deoxynucleosides and export of phosphorylated deoxynucleotides), the desphosphorylating state (the reverse of the phosphorylating state), and the efficient state (the net import of both deoxynucleosides and deoxynucleotides). We present five testable hypotheses based on this simulation. First, the deoxynucleotide pools within a mitochondrion are sufficient to support only a small fraction of even a single mtDNA replication event. Second, the mtDNA replication time in postmitotic cells is much longer than that in rapidly dividing cells. Third, mitochondria in dividing cells are net sinks of cytoplasmic deoxynucleotides, while mitochondria in postmitotic cells are net sources. Fourth, the deoxynucleotide carrier exerts the most control over the mtDNA replication rate in rapidly dividing cells, but in postmitotic cells, the NDPK and TK2 enzymes have the most control. Fifth, following from the previous hypothesis, rapidly dividing cells derive almost all of their mtDNA precursors from the cytoplasmic deoxynucleotides, not from phosphorylation within the mitochondrion.
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Affiliation(s)
- Patrick C Bradshaw
- Virginia Bioinformatics Institute, Virginia Polytechnic and State Univ., Bioinformatics Facility I (0477 Blacksburg, VA 24061, USA
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