title: Deoxynucleoside stress exacerbates the phenotype of a mouse model of mitochondrial neurogastrointestinal encephalopathy.
abstract: Balanced pools of deoxyribonucleoside triphosphate precursors are required for DNA replication, and alterations of this balance are relevant to human mitochondrial diseases including mitochondrial neurogastrointestinal encephalopathy. In this disease, autosomal recessive TYMP mutations cause severe reductions of thymidine phosphorylase activity; marked elevations of the pyrimidine nucleosides thymidine and deoxyuridine in plasma and tissues, and somatic multiple deletions, depletion and site-specific point mutations of mitochondrial DNA. Thymidine phosphorylase and uridine phosphorylase double knockout mice recapitulated several features of these patients including thymidine phosphorylase activity deficiency, elevated thymidine and deoxyuridine in tissues, mitochondrial DNA depletion, respiratory chain defects and white matter changes. However, in contrast to patients with this disease, mutant mice showed mitochondrial alterations only in the brain. To test the hypothesis that elevated levels of nucleotides cause unbalanced deoxyribonucleoside triphosphate pools and, in turn, pathogenic mitochondrial DNA instability, we have stressed double knockout mice with exogenous thymidine and deoxyuridine, and assessed clinical, neuroradiological, histological, molecular, and biochemical consequences. Mutant mice treated with exogenous thymidine and deoxyuridine showed reduced survival, body weight, and muscle strength, relative to untreated animals. Moreover, in treated mutants, leukoencephalopathy, a hallmark of the disease, was enhanced and the small intestine showed a reduction of smooth muscle cells and increased fibrosis. Levels of mitochondrial DNA were depleted not only in the brain but also in the small intestine, and deoxyribonucleoside triphosphate imbalance was observed in the brain. The relative proportion, rather than the absolute amount of deoxyribonucleoside triphosphate, was critical for mitochondrial DNA maintenance. Thus, our results demonstrate that stress of exogenous pyrimidine nucleosides enhances the mitochondrial phenotype of our knockout mice. Our mouse studies provide insights into the pathogenic role of thymidine and deoxyuridine imbalance in mitochondrial neurogastrointestinal encephalopathy and an excellent model to study new therapeutic approaches.
authors.affiliation: 1 Department of Neurology, Columbia University Medical Centre, New York, NY, 10032, USA.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Garcia-Diaz
authors.forename: Caterina
authors.initials: C
authors.lastname: Garone
authors.forename: Emanuele
authors.initials: E
authors.lastname: Barca
authors.forename: Hamed
authors.initials: H
authors.lastname: Mojahed
authors.forename: Purification
authors.initials: P
authors.lastname: Gutierrez
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pizzorno
authors.forename: Kurenai
authors.initials: K
authors.lastname: Tanji
authors.forename: Fernando
authors.initials: F
authors.lastname: Arias-Mendoza
authors.forename: Caterina M
authors.initials: CM
authors.lastname: Quinzii
authors.forename: Michio
authors.initials: M
authors.lastname: Hirano
mesh_terms: D000367:Age Factors; D000818:Animals; D001835:Body Weight / Q000187:drug effects / Q000235:genetics; D001921:Brain / Q000473:pathology; D003853:Deoxyribonucleosides / Q000009:adverse effects* / Q000378:metabolism; D004195:Disease Models, Animal; D007418:Intestinal Pseudo-Obstruction / Q000139:chemically induced* / Q000235:genetics* / Q000401:mortality / Q000503:physiopathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D028361:Mitochondrial Diseases / Q000209:etiology / Q000235:genetics; D017237:Mitochondrial Encephalomyopathies / Q000139:chemically induced* / Q000235:genetics* / Q000401:mortality / Q000503:physiopathology; D009043:Motor Activity / Q000187:drug effects; D053580:Muscle Strength / Q000187:drug effects / Q000235:genetics; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology; D039141:Muscular Dystrophy, Oculopharyngeal; D009886:Ophthalmoplegia / Q000151:congenital; D011596:Psychomotor Disorders / Q000209:etiology / Q000235:genetics; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013936:Thymidine / Q000009:adverse effects / Q000378:metabolism; D013939:Thymidine Phosphorylase / Q000172:deficiency; D014543:Uridine Phosphorylase / Q000172:deficiency
chemical_list: D003853:Deoxyribonucleosides; D013385:Succinate Dehydrogenase; D014543:Uridine Phosphorylase; D013939:Thymidine Phosphorylase; D013936:Thymidine
keywords: MNGIE; animal model; deoxynucleotide; deoxyuridine; mitochondrial DNA; thymidine
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