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van Karnebeek CDM, Ramos RJ, Wen XY, Tarailo-Graovac M, Gleeson JG, Skrypnyk C, Brand-Arzamendi K, Karbassi F, Issa MY, van der Lee R, Drögemöller BI, Koster J, Rousseau J, Campeau PM, Wang Y, Cao F, Li M, Ruiter J, Ciapaite J, Kluijtmans LAJ, Willemsen MAAP, Jans JJ, Ross CJ, Wintjes LT, Rodenburg RJ, Huigen MCDG, Jia Z, Waterham HR, Wasserman WW, Wanders RJA, Verhoeven-Duif NM, Zaki MS, Wevers RA. Bi-allelic GOT2 Mutations Cause a Treatable Malate-Aspartate Shuttle-Related Encephalopathy. Am J Hum Genet 2019; 105:534-548. [PMID: 31422819 DOI: 10.1016/j.ajhg.2019.07.015] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Accepted: 07/22/2019] [Indexed: 11/30/2022] Open
Abstract
Early-infantile encephalopathies with epilepsy are devastating conditions mandating an accurate diagnosis to guide proper management. Whole-exome sequencing was used to investigate the disease etiology in four children from independent families with intellectual disability and epilepsy, revealing bi-allelic GOT2 mutations. In-depth metabolic studies in individual 1 showed low plasma serine, hypercitrullinemia, hyperlactatemia, and hyperammonemia. The epilepsy was serine and pyridoxine responsive. Functional consequences of observed mutations were tested by measuring enzyme activity and by cell and animal models. Zebrafish and mouse models were used to validate brain developmental and functional defects and to test therapeutic strategies. GOT2 encodes the mitochondrial glutamate oxaloacetate transaminase. GOT2 enzyme activity was deficient in fibroblasts with bi-allelic mutations. GOT2, a member of the malate-aspartate shuttle, plays an essential role in the intracellular NAD(H) redox balance. De novo serine biosynthesis was impaired in fibroblasts with GOT2 mutations and GOT2-knockout HEK293 cells. Correcting the highly oxidized cytosolic NAD-redox state by pyruvate supplementation restored serine biosynthesis in GOT2-deficient cells. Knockdown of got2a in zebrafish resulted in a brain developmental defect associated with seizure-like electroencephalography spikes, which could be rescued by supplying pyridoxine in embryo water. Both pyridoxine and serine synergistically rescued embryonic developmental defects in zebrafish got2a morphants. The two treated individuals reacted favorably to their treatment. Our data provide a mechanistic basis for the biochemical abnormalities in GOT2 deficiency that may also hold for other MAS defects.
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Affiliation(s)
- Clara D M van Karnebeek
- Departments of Pediatrics & Clinical Genetics, Emma Children's Hospital, Amsterdam University Medical Centres, Amsterdam Gastro-enterology and Metabolism, University of Amsterdam, 1105 AZ Amsterdam, the Netherlands; Department of Pediatrics / Medical Genetics, BC Children's Hospital Research Institute, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, BC V5Z 4H4, Canada; On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Amalia Children's Hospital, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands.
| | - Rúben J Ramos
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Genetics, University Medical Center Utrecht, 3584 EA Utrecht, the Netherlands
| | - Xiao-Yan Wen
- Zebrafish Centre for Advanced Drug Discovery, Keenan Research Centre for Biomedical Science, Li Ka Sheng Knowledge Institute, St. Michael's Hospital, Toronto, ON M5B 1T8, Canada; Department of Medicine, Physiology and LMP & Institute of Medical Science, University of Toronto, Toronto, ON M5G 2C4, Canada
| | - Maja Tarailo-Graovac
- Departments of Biochemistry, Molecular Biology and Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada; Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB T2N 4N1, Canada
| | - Joseph G Gleeson
- Department Neurosciences and Pediatric, Howard Hughes Medical Institute, University of California; Rady Children's Institute for Genomic Medicine, San Diego, CA 92093, USA
| | - Cristina Skrypnyk
- Department of Molecular Medicine and Al Jawhara Center for Molecular Medicine, Genetics and Inherited Diseases, College of Medicine and Medical Sciences, Arabian Gulf University, Postal Code 328, Bahrain
| | - Koroboshka Brand-Arzamendi
- Zebrafish Centre for Advanced Drug Discovery, Keenan Research Centre for Biomedical Science, Li Ka Sheng Knowledge Institute, St. Michael's Hospital, Toronto, ON M5B 1T8, Canada
| | - Farhad Karbassi
- Zebrafish Centre for Advanced Drug Discovery, Keenan Research Centre for Biomedical Science, Li Ka Sheng Knowledge Institute, St. Michael's Hospital, Toronto, ON M5B 1T8, Canada
| | - Mahmoud Y Issa
- Clinical Genetics Department, Human Genetics and Genome Research Division, National Research Centre, Cairo 12311, Egypt
| | - Robin van der Lee
- Centre for Molecular Medicine and Therapeutics, Department of Medical Genetics, BC Children's Hospital Research Institute, University of British Columbia, Vancouver, BC V5Z 4H4, Canada
| | - Britt I Drögemöller
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; BC Children's Hospital Research Institute, Vancouver, BC V5Z 4H4, Canada
| | - Janet Koster
- Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam University Medical Centres, University of Amsterdam, Amsterdam Gastro-enterology and Metabolism, 1105 AZ Amsterdam, the Netherlands
| | - Justine Rousseau
- CHU Sainte-Justine Research Center, Montreal, QC H3T 1C5, Canada
| | | | - Youdong Wang
- Zebrafish Centre for Advanced Drug Discovery, Keenan Research Centre for Biomedical Science, Li Ka Sheng Knowledge Institute, St. Michael's Hospital, Toronto, ON M5B 1T8, Canada
| | - Feng Cao
- Department of Neuroscience & Mental Health, The Hospital for Sick Children & Department of Physiology, University of Toronto, Toronto, ON M5G 1X8, Canada
| | - Meng Li
- Zebrafish Centre for Advanced Drug Discovery, Keenan Research Centre for Biomedical Science, Li Ka Sheng Knowledge Institute, St. Michael's Hospital, Toronto, ON M5B 1T8, Canada
| | - Jos Ruiter
- Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam University Medical Centres, University of Amsterdam, Amsterdam Gastro-enterology and Metabolism, 1105 AZ Amsterdam, the Netherlands
| | - Jolita Ciapaite
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Genetics, University Medical Center Utrecht, 3584 EA Utrecht, the Netherlands
| | - Leo A J Kluijtmans
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands
| | - Michel A A P Willemsen
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Amalia Children's Hospital, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands
| | - Judith J Jans
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Genetics, University Medical Center Utrecht, 3584 EA Utrecht, the Netherlands
| | - Colin J Ross
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Liesbeth T Wintjes
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands; Radboud Center for Mitochondrial Medicine, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands
| | - Richard J Rodenburg
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands; Amalia Children's Hospital, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands; Radboud Center for Mitochondrial Medicine, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands
| | - Marleen C D G Huigen
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands
| | - Zhengping Jia
- Department of Neuroscience & Mental Health, The Hospital for Sick Children & Department of Physiology, University of Toronto, Toronto, ON M5G 1X8, Canada
| | - Hans R Waterham
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam University Medical Centres, University of Amsterdam, Amsterdam Gastro-enterology and Metabolism, 1105 AZ Amsterdam, the Netherlands
| | - Wyeth W Wasserman
- Centre for Molecular Medicine and Therapeutics, Department of Medical Genetics, BC Children's Hospital Research Institute, University of British Columbia, Vancouver, BC V5Z 4H4, Canada
| | - Ronald J A Wanders
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam University Medical Centres, University of Amsterdam, Amsterdam Gastro-enterology and Metabolism, 1105 AZ Amsterdam, the Netherlands
| | - Nanda M Verhoeven-Duif
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Genetics, University Medical Center Utrecht, 3584 EA Utrecht, the Netherlands
| | - Maha S Zaki
- Clinical Genetics Department, Human Genetics and Genome Research Division, National Research Centre, Cairo 12311, Egypt
| | - Ron A Wevers
- On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands.
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Ramos RJ, Albersen M, Vringer E, Bosma M, Zwakenberg S, Zwartkruis F, Jans JJM, Verhoeven-Duif NM. Discovery of pyridoxal reductase activity as part of human vitamin B6 metabolism. Biochim Biophys Acta Gen Subj 2019; 1863:1088-1097. [PMID: 30928491 DOI: 10.1016/j.bbagen.2019.03.019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 03/15/2019] [Accepted: 03/26/2019] [Indexed: 10/27/2022]
Abstract
BACKGROUND Pyridoxal 5'-phosphate (PLP) is the active form of vitamin B6. Mammals cannot synthesize vitamin B6, so they rely on dietary uptake of the different B6 forms, and via the B6 salvage pathway they interconvert them into PLP. Humans possess three enzymes in this pathway: pyridoxal kinase, pyridox(am)ine phosphate oxidase and pyridoxal phosphatase. Besides these, a fourth enzyme has been described in plants and yeast but not in humans: pyridoxal reductase. METHODS We analysed B6 vitamers in remnant CSF samples of PLP-treated patients and four mammalian cell lines (HepG2, Caco2, HEK293 and Neuro-2a) supplemented with PL as the sole source of vitamin B6. RESULTS Strong accumulation of pyridoxine (PN) in CSF of PLP-treated patients was observed, suggesting the existence of a PN-forming enzyme. Our in vitro studies show that all cell lines reduce PL to PN in a time- and dose-dependent manner. We compared the amino acid sequences of known PL reductases to human sequences and found high homology for members of the voltage-gated potassium channel beta subunits and the human aldose reductases. Pharmacological inhibition and knockout of these proteins show that none of the candidates is solely responsible for PL reduction to PN. CONCLUSIONS We show evidence for the presence of PL reductase activity in humans. Further studies are needed to identify the responsible protein. GENERAL SIGNIFICANCE This study expands the number of enzymes with a role in B6 salvage pathway. We hypothesize a protective role of PL reductase(s) by limiting the intracellular amount of free PL and PLP.
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Affiliation(s)
- Rúben J Ramos
- Department of Genetics, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Monique Albersen
- Department of Genetics, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Esmee Vringer
- Department of Genetics, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Marjolein Bosma
- Department of Genetics, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Susan Zwakenberg
- Department of Molecular Cancer Research and Center for Molecular Medicine, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Fried Zwartkruis
- Department of Molecular Cancer Research and Center for Molecular Medicine, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Judith J M Jans
- Department of Genetics, University Medical Center Utrecht, Utrecht, the Netherlands
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Ramos RJ, Pras-Raves ML, Gerrits J, van der Ham M, Willemsen M, Prinsen H, Burgering B, Jans JJ, Verhoeven-Duif NM. Vitamin B6 is essential for serine de novo biosynthesis. J Inherit Metab Dis 2017; 40:883-891. [PMID: 28801717 DOI: 10.1007/s10545-017-0061-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 05/29/2017] [Accepted: 05/31/2017] [Indexed: 11/30/2022]
Abstract
Pyridoxal 5'-phosphate (PLP), the metabolically active form of vitamin B6, plays an essential role in brain metabolism as a cofactor in numerous enzyme reactions. PLP deficiency in brain, either genetic or acquired, results in severe drug-resistant seizures that respond to vitamin B6 supplementation. The pathogenesis of vitamin B6 deficiency is largely unknown. To shed more light on the metabolic consequences of vitamin B6 deficiency in brain, we performed untargeted metabolomics in vitamin B6-deprived Neuro-2a cells. Significant alterations were observed in a range of metabolites. The most surprising observation was a decrease of serine and glycine, two amino acids that are known to be elevated in the plasma of vitamin B6 deficient patients. To investigate the cause of the low concentrations of serine and glycine, a metabolic flux analysis on serine biosynthesis was performed. The metabolic flux results showed that the de novo synthesis of serine was significantly reduced in vitamin B6-deprived cells. In addition, formation of glycine and 5-methyltetrahydrofolate was decreased. Thus, vitamin B6 is essential for serine de novo biosynthesis in neuronal cells, and serine de novo synthesis is critical to maintain intracellular serine and glycine. These findings suggest that serine and glycine concentrations in brain may be deficient in patients with vitamin B6 responsive epilepsy. The low intracellular 5-mTHF concentrations observed in vitro may explain the favourable but so far unexplained response of some patients with pyridoxine-dependent epilepsy to folinic acid supplementation.
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Affiliation(s)
- Rúben J Ramos
- Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands
| | - Mia L Pras-Raves
- Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands
| | - Johan Gerrits
- Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands
| | - Maria van der Ham
- Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands
| | - Marcel Willemsen
- Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands
| | - Hubertus Prinsen
- Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands
| | - Boudewijn Burgering
- Department of Molecular Cancer Research and Center for Molecular Medicine, University Medical Center Utrecht, Utrecht, 3584 EA, The Netherlands
| | - Judith J Jans
- Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands.
| | - Nanda M Verhoeven-Duif
- Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands
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