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Finsterer J. Double Trouble from
POLG1
and
CLCN1
Variants with Intrafamilial Phenotypic Heterogeneity. Mov Disord Clin Pract 2020; 7:575-576. [DOI: 10.1002/mdc3.12962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 02/19/2020] [Indexed: 11/09/2022] Open
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Toompuu M, Tuomela T, Laine P, Paulin L, Dufour E, Jacobs HT. Polyadenylation and degradation of structurally abnormal mitochondrial tRNAs in human cells. Nucleic Acids Res 2019. [PMID: 29518244 PMCID: PMC6007314 DOI: 10.1093/nar/gky159] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
RNA 3' polyadenylation is known to serve diverse purposes in biology, in particular, regulating mRNA stability and translation. Here we determined that, upon exposure to high levels of the intercalating agent ethidium bromide (EtBr), greater than those required to suppress mitochondrial transcription, mitochondrial tRNAs in human cells became polyadenylated. Relaxation of the inducing stress led to rapid turnover of the polyadenylated tRNAs. The extent, kinetics and duration of tRNA polyadenylation were EtBr dose-dependent, with mitochondrial tRNAs differentially sensitive to the stress. RNA interference and inhibitor studies indicated that ongoing mitochondrial ATP synthesis, plus the mitochondrial poly(A) polymerase and SUV3 helicase were required for tRNA polyadenylation, while polynucleotide phosphorylase counteracted the process and was needed, along with SUV3, for degradation of the polyadenylated tRNAs. Doxycycline treatment inhibited both tRNA polyadenylation and turnover, suggesting a possible involvement of the mitoribosome, although other translational inhibitors had only minor effects. The dysfunctional tRNALeu(UUR) bearing the pathological A3243G mutation was constitutively polyadenylated at a low level, but this was markedly enhanced after doxycycline treatment. We propose that polyadenylation of structurally and functionally abnormal mitochondrial tRNAs entrains their PNPase/SUV3-mediated destruction, and that this pathway could play an important role in mitochondrial diseases associated with tRNA mutations.
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Affiliation(s)
- Marina Toompuu
- Faculty of Medicine and Life Sciences, BioMediTech Institute and Tampere University Hospital, FI-33014 University of Tampere, Finland
| | - Tea Tuomela
- Faculty of Medicine and Life Sciences, BioMediTech Institute and Tampere University Hospital, FI-33014 University of Tampere, Finland
| | - Pia Laine
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Lars Paulin
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Eric Dufour
- Faculty of Medicine and Life Sciences, BioMediTech Institute and Tampere University Hospital, FI-33014 University of Tampere, Finland
| | - Howard T Jacobs
- Faculty of Medicine and Life Sciences, BioMediTech Institute and Tampere University Hospital, FI-33014 University of Tampere, Finland.,Institute of Biotechnology, FI-00014 University of Helsinki, Finland
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Phillips J, Courel S, Rebelo AP, Bis-Brewer DM, Bardakjian T, Dankwa L, Hamedani AG, Züchner S, Scherer SS. POLG mutations presenting as Charcot-Marie-Tooth disease. J Peripher Nerv Syst 2019; 24:213-218. [PMID: 30843307 DOI: 10.1111/jns.12313] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 02/27/2019] [Accepted: 03/02/2019] [Indexed: 12/15/2022]
Abstract
We report on two patients, with different POLG mutations, in whom axonal neuropathy dominated the clinical picture. One patient presented with late onset sensory axonal neuropathy caused by a homozygous c.2243G>C (p.Trp748Ser) mutation that resulted from uniparental disomy of the long arm of chromosome 15. The other patient had a complex phenotype that included early onset axonal Charcot-Marie-Tooth disease (CMT) caused by compound heterozygous c.926G>A (p.Arg309His) and c.2209G>C (p.Gly737Arg) mutations.
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Affiliation(s)
- Jade Phillips
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Steve Courel
- Department of Human Genetics and Hussman Institute for Human Genomics, University of Miami, Miami, Florida
| | - Adriana P Rebelo
- Department of Human Genetics and Hussman Institute for Human Genomics, University of Miami, Miami, Florida
| | - Dana M Bis-Brewer
- Department of Human Genetics and Hussman Institute for Human Genomics, University of Miami, Miami, Florida
| | - Tanya Bardakjian
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Lois Dankwa
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Ali G Hamedani
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Stephan Züchner
- Department of Human Genetics and Hussman Institute for Human Genomics, University of Miami, Miami, Florida
| | - Steven S Scherer
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
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DeBalsi KL, Longley MJ, Hoff KE, Copeland WC. Synergistic Effects of the in cis T251I and P587L Mitochondrial DNA Polymerase γ Disease Mutations. J Biol Chem 2017; 292:4198-4209. [PMID: 28154168 DOI: 10.1074/jbc.m116.773341] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 01/26/2017] [Indexed: 01/28/2023] Open
Abstract
Human mitochondrial DNA (mtDNA) polymerase γ (Pol γ) is the only polymerase known to replicate the mitochondrial genome. The Pol γ holoenzyme consists of the p140 catalytic subunit (POLG) and the p55 homodimeric accessory subunit (POLG2), which enhances binding of Pol γ to DNA and promotes processivity of the holoenzyme. Mutations within POLG impede maintenance of mtDNA and cause mitochondrial diseases. Two common POLG mutations usually found in cis in patients primarily with progressive external ophthalmoplegia generate T251I and P587L amino acid substitutions. To determine whether T251I or P587L is the primary pathogenic allele or whether both substitutions are required to cause disease, we overproduced and purified WT, T251I, P587L, and T251I + P587L double variant forms of recombinant Pol γ. Biochemical characterization of these variants revealed impaired DNA binding affinity, reduced thermostability, diminished exonuclease activity, defective catalytic activity, and compromised DNA processivity, even in the presence of the p55 accessory subunit. However, physical association with p55 was unperturbed, suggesting intersubunit affinities similar to WT. Notably, although the single mutants were similarly impaired, a dramatic synergistic effect was found for the double mutant across all parameters. In conclusion, our analyses suggest that individually both T251I and P587L substitutions functionally impair Pol γ, with greater pathogenicity predicted for the single P587L variant. Combining T251I and P587L induces extreme thermal lability and leads to synergistic nucleotide and DNA binding defects, which severely impair catalytic activity and correlate with presentation of disease in patients.
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Affiliation(s)
- Karen L DeBalsi
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - Matthew J Longley
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - Kirsten E Hoff
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - William C Copeland
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
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The in cis T251I and P587L POLG1 base changes: Description of a new family and literature review. Neuromuscul Disord 2015; 25:333-9. [DOI: 10.1016/j.nmd.2015.01.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Revised: 01/07/2015] [Accepted: 01/14/2015] [Indexed: 11/19/2022]
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Abstract
To highlight differences between early-onset and adult mitochondrial depletion syndromes (MDS) concerning etiology and genetic background, pathogenesis, phenotype, clinical presentation and their outcome. MDSs most frequently occur in neonates, infants, or juveniles and more rarely in adolescents or adults. Mutated genes phenotypically presenting with adult-onset MDS include POLG1, TK2, TyMP, RRM2B, or PEO1/twinkle. Adult MDS manifest similarly to early-onset MDS, as myopathy, encephalo-myopathy, hepato-cerebral syndrome, or with chronic progressive external ophthalmoplegia (CPEO), fatigue, or only minimal muscular manifestations. Diagnostic work-up or treatment is not at variance from early-onset cases. Histological examination of muscle may be normal but biochemical investigations may reveal multiple respiratory chain defects. The outcome appears to be more favorable in adult than in early-onset forms. Mitochondrial depletion syndromes is not only a condition of neonates, infants, or juveniles but rarely also occurs in adults, presenting with minimal manifestations or manifestations like in the early-onset forms. Outcome of adult-onset MDS appears more favorable than early-onset MDS.
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Nanau RM, Neuman MG. Adverse drug reactions induced by valproic acid. Clin Biochem 2013; 46:1323-38. [PMID: 23792104 DOI: 10.1016/j.clinbiochem.2013.06.012] [Citation(s) in RCA: 188] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 06/11/2013] [Accepted: 06/12/2013] [Indexed: 12/11/2022]
Abstract
Valproic acid is a widely-used first-generation antiepileptic drug, prescribed predominantly in epilepsy and psychiatric disorders. VPA has good efficacy and pharmacoeconomic profiles, as well as a relatively favorable safety profile. However, adverse drug reactions have been reported in relation with valproic acid use, either as monotherapy or polytherapy with other antiepileptic drugs or antipsychotic drugs. This systematic review discusses valproic acid adverse drug reactions, in terms of hepatotoxicity, mitochondrial toxicity, hyperammonemic encephalopathy, hypersensitivity syndrome reactions, neurological toxicity, metabolic and endocrine adverse events, and teratogenicity.
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Affiliation(s)
- Radu M Nanau
- Department of Pharmacology and Toxicology, Faculty of Medicine, University of Toronto, In Vitro Drug Safety and Biotechnology, Toronto, Ontario, Canada
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Roos S, Macao B, Fusté JM, Lindberg C, Jemt E, Holme E, Moslemi AR, Oldfors A, Falkenberg M. Subnormal levels of POLγA cause inefficient initiation of light-strand DNA synthesis and lead to mitochondrial DNA deletions and progressive external ophthalmoplegia [corrected]. Hum Mol Genet 2013; 22:2411-22. [PMID: 23446635 DOI: 10.1093/hmg/ddt094] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The POLG1 gene encodes the catalytic subunit of mitochondrial DNA (mtDNA) polymerase γ (POLγ). We here describe a sibling pair with adult-onset progressive external ophthalmoplegia, cognitive impairment and mitochondrial myopathy characterized by DNA depletion and multiple mtDNA deletions. The phenotype is due to compound heterozygous POLG1 mutations, T914P and the intron mutation c.3104 + 3A > T. The mutant genes produce POLγ isoforms with heterozygous phenotypes that fail to synthesize longer DNA products in vitro. However, exon skipping in the c.3104 + 3A > T mutant is not complete, and the presence of low levels of wild-type POLγ explains patient survival. To better understand the underlying pathogenic mechanisms, we characterized the effects of POLγ depletion in vitro and found that leading-strand DNA synthesis is relatively undisturbed. In contrast, initiation of lagging-strand DNA synthesis is ineffective at lower POLγ concentrations that uncouples leading strand from lagging-strand DNA synthesis. In vivo, this effect leads to prolonged exposure of the heavy strand in its single-stranded conformation that in turn can cause the mtDNA deletions observed in our patients. Our findings, thus, suggest a molecular mechanism explaining how POLγ mutations can cause mtDNA deletions in vivo.
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Affiliation(s)
- Sara Roos
- Department of Pathology, Institute of Biomedicine, The Sahlgrenska Academy at the University of Gothenburg, Gula Stråket 8, Gothenburg SE-413 45, Sweden.
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Fuke S, Kubota-Sakashita M, Kasahara T, Shigeyoshi Y, Kato T. Regional variation in mitochondrial DNA copy number in mouse brain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1807:270-4. [PMID: 21145305 DOI: 10.1016/j.bbabio.2010.11.016] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 11/10/2010] [Accepted: 11/30/2010] [Indexed: 11/17/2022]
Abstract
Mitochondria have their own DNA (mitochondrial DNA [mtDNA]). Although mtDNA copy number is dependent on tissues and its decrease is associated with various neuromuscular diseases, detailed distribution of mtDNA copies in the brain remains uncertain. Using real-time quantitative PCR assay, we examined regional variation in mtDNA copy number in 39 brain regions of male mice. A significant regional difference in mtDNA copy number was observed (P<4.8×10(-35)). High levels of mtDNA copies were found in the ventral tegmental area and substantia nigra, two major nuclei containing dopaminergic neurons. In contrast, cerebellar vermis and lobes had significantly lower copy numbers than other regions. Hippocampal dentate gyrus also had a relatively low mtDNA copy number. This study is the first quantitative analysis of regional variation in mtDNA copy number in mouse brain. Our findings are important for the physiological and pathophysiological studies of mtDNA in the brain.
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Affiliation(s)
- Satoshi Fuke
- Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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Sanaker PS, Toompuu M, Hogan VE, He L, Tzoulis C, Chrzanowska-Lightowlers ZMA, Taylor RW, Bindoff LA. Differences in RNA processing underlie the tissue specific phenotype of ISCU myopathy. Biochim Biophys Acta Mol Basis Dis 2010; 1802:539-44. [PMID: 20206689 DOI: 10.1016/j.bbadis.2010.02.010] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2009] [Revised: 02/26/2010] [Accepted: 02/26/2010] [Indexed: 10/19/2022]
Abstract
Hereditary myopathy with lactic acidosis, or myopathy with exercise intolerance, Swedish type (OMIM #255125) is caused by mutations in the iron-sulfur cluster scaffold (ISCU) gene. The g.7044G>C ISCU mutation induces a splicing error in the pre-mRNA that strengthens a weak intronic splice site leading to inclusion of a new exon and subsequent loss of mRNA and protein. While ISCU is widely expressed, homozygosity for this particular intronic mutation gives rise to a pure myopathy. In order to investigate tissue specificity and disease mechanism, we studied muscle, myoblasts, fibroblasts and blood cells from the first non-Swedish case of this disease. Consistent with the recognised role of ISCU, we found abnormal activities of respiratory chain complexes containing iron-sulfur clusters in patient muscle. We confirmed that, in the presence of the g.7044G>C mutation, splicing produces both abnormally and normally spliced mRNA in all tissues. The ratio of these products varies dramatically between tissues, being most abnormal in mature skeletal muscle that also has the lowest relative starting levels of ISCU mRNA compared with other tissues. Myoblasts and fibroblasts have more of the normally spliced variant as well as higher starting levels of ISCU mRNA. Up-regulation of mtDNA copy number was found in skeletal muscle and myoblasts, but not fibroblasts, and is thought to represent a compensatory response. Tissue specificity in this disorder appears therefore to be dependent on the mRNA starting level, the amount of remaining normally spliced RNA, and the degree to which compensatory mechanisms can respond.
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