bims-cytox1 2017-07-30 papers

Issue of 2017‒07‒30
three papers selected by
Gavin McStay
New York Institute of Technology

PLoS Genet. 2017 Jul 21. 13(7): e1006921

Mutations in the Caenorhabditis elegans orthologs of human genes required for mitochondrial tRNA modification cause similar electron transport chain defects but different nuclear responses.

Carmen Navarro-González, Ismaïl Moukadiri, Magda Villarroya, Ernesto López-Pascual, Simon Tuck, M-Eugenia Armengod.

Several oxidative phosphorylation (OXPHOS) diseases are caused by defects in the post-transcriptional modification of mitochondrial tRNAs (mt-tRNAs). Mutations in MTO1 or GTPBP3 impair the modification of the wobble uridine at position 5 of the pyrimidine ring and cause heart failure. Mutations in TRMU affect modification at position 2 and cause liver disease. Presently, the molecular basis of the diseases and why mutations in the different genes lead to such different clinical symptoms is poorly understood. Here we use Caenorhabditis elegans as a model organism to investigate how defects in the TRMU, GTPBP3 and MTO1 orthologues (designated as mttu-1, mtcu-1, and mtcu-2, respectively) exert their effects. We found that whereas the inactivation of each C. elegans gene is associated with a mild OXPHOS dysfunction, mutations in mtcu-1 or mtcu-2 cause changes in the expression of metabolic and mitochondrial stress response genes that are quite different from those caused by mttu-1 mutations. Our data suggest that retrograde signaling promotes defect-specific metabolic reprogramming, which is able to rescue the OXPHOS dysfunction in the single mutants by stimulating the oxidative tricarboxylic acid cycle flux through complex II. This adaptive response, however, appears to be associated with a biological cost since the single mutant worms exhibit thermosensitivity and decreased fertility and, in the case of mttu-1, longer reproductive cycle. Notably, mttu-1 worms also exhibit increased lifespan. We further show that mtcu-1; mttu-1 and mtcu-2; mttu-1 double mutants display severe growth defects and sterility. The animal models presented here support the idea that the pathological states in humans may initially develop not as a direct consequence of a bioenergetic defect, but from the cell's maladaptive response to the hypomodification status of mt-tRNAs. Our work highlights the important association of the defect-specific metabolic rewiring with the pathological phenotype, which must be taken into consideration in exploring specific therapeutic interventions.

DOI: https://doi.org/10.1371/journal.pgen.1006921

J Mol Diagn. 2017 Jul 18. pii: S1525-1578(17)30217-9. [Epub ahead of print]

A Method for Next-Generation Sequencing of Paired Diagnostic and Remission Samples to Detect Mitochondrial DNA Mutations Associated with Leukemia.

Ilaria S Pagani, Chung H Kok, Verity A Saunders, Mark B Van der Hoek, Susan L Heatley, Anthony P Schwarer, Christopher N Hahn, Timothy P Hughes, Deborah L White, David M Ross.

Somatic mitochondrial DNA (mtDNA) mutations have been identified in many human cancers, including leukemia. To identify somatic mutations, it is necessary to have a control tissue from the same individual for comparison. When patients with leukemia achieve remission, the remission peripheral blood may be a suitable and easily accessible control tissue, but this approach has not previously been applied to the study of mtDNA mutations. We have developed and validated a next-generation sequencing approach for the identification of leukemia-associated mtDNA mutations in 26 chronic myeloid leukemia patients at diagnosis using either nonhematopoietic or remission blood samples as the control. The entire mt genome was amplified by long-range PCR and sequenced using Illumina technology. Variant caller software was used to detect mtDNA somatic mutations, and an empirically determined threshold of 2% was applied to minimize false-positive results because of sequencing errors. Mutations were called against both nonhematopoietic and remission controls: the overall concordance between the two approaches was 81% (73/90 mutations). Some discordant results were because of the presence of somatic mutations in remission samples, because of either minimal residual disease or nonleukemic hematopoietic clones. This method could be applied to study somatic mtDNA mutations in leukemia patients who achieve minimal residual disease, and in patients with nonhematopoietic cancers who have a matched uninvolved tissue available.

DOI: https://doi.org/10.1016/j.jmoldx.2017.05.009

Neurochem Int. 2017 Jul 18. pii: S0197-0186(17)30062-1. [Epub ahead of print]

Pharmacologic modeling of primary mitochondrial respiratory chain dysfunction in zebrafish.

James Byrnes, Rebecca Ganetzky, Richard Lightfoot, Michael Tzeng, Eiko Nakamaru-Ogiso, Christoph Seiler, Marni J Falk.

Mitochondrial respiratory chain (RC) disease is a heterogeneous and highly morbid group of energy deficiency disorders for which no proven effective therapies exist. Robust vertebrate animal models of primary RC dysfunction are needed to explore the effects of variation in RC disease subtypes, tissue-specific manifestations, and major pathogenic factors contributing to each disorder, as well as their pre-clinical response to therapeutic candidates. We have developed a series of zebrafish (Danio rerio) models that inhibit, to variable degrees, distinct aspects of RC function, and enable quantification of animal development, survival, behaviors, and organ-level treatment effects on function as well as mitochondrial biochemistry and physiology. Here, we characterize four pharmacologic inhibitor models of mitochondrial RC dysfunction in early larval zebrafish, including rotenone (complex I inhibitor), azide (complex IV inhibitor), oligomycin (complex V inhibitor), and chloramphenicol (mitochondrial translation inhibitor that leads to multiple RC dysfunction). A range of concentrations and exposure times of each RC inhibitor were systematically evaluated on early larval development, animal survival, integrated behaviors (touch and startle responses), organ physiology (brain death, neurologic tone, heart rate), and fluorescence-based mitochondrial physiology in zebrafish skeletal muscle. Pharmacologic RC inhibitor effects were validated by spectrophotometric analysis of Complex I, II and IV activities, or relative quantitation of ATP levels in larvae. Outcomes were prioritized that utilize in vivo animal imaging and quantitative behavioral assessments, as may optimally inform the translational potential of pre-clinical drug screens for future clinical study in human mitochondrial disease subjects. The RC complex inhibitors each delayed early embryo development, with short-term exposures of these three agents or chloramphenicol from 5 to 7 days post fertilization also causing reduced larval survival and organ-specific defects ranging from brain death, behavioral and neurologic alterations, reduced mitochondrial membrane potential in skeletal muscle (rotenone), and/or cardiac edema with visible blood pooling (oligomycin). Remarkably, we demonstrate that treating animals with probucol, a nutrient-sensing signaling network modulating drug that has been shown to yield therapeutic effects in a range of other RC disease cellular and animal models, both prevented acute rotenone-induced brain death in zebrafish larvae, and significantly rescued early embryo developmental delay from either rotenone or oligomycin exposure. Overall, these zebrafish pharmacologic RC function inhibition models offer a unique opportunity to gain novel insights into diverse developmental, survival, organ-level, and behavioral defects of varying severity, as well as their individual response to candidate therapies, in a highly tractable and cost-effective vertebrate animal model system.

Keywords: Chloramphenicol (PubChem CID: 5959); Complex I; Complex IV; Complex V; D. rerio; Mitochondrial translation; Mitotracker green FM (PubChem CID: 59705974); Oligomycin (PubChem CID: 16760598); Probucol (PubChem CID: 4912); Rotenone (PubChem CID: 6758); Sodium azide (PubChem CID: 33557); TMRE (PubChem CID: 2762682)

DOI: https://doi.org/10.1016/j.neuint.2017.07.008