title: MELAS mitochondrial DNA mutation A3243G reduces glutamate transport in cybrids cell lines.
abstract: MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) is commonly associated with the A3243G mitochondrial DNA (mtDNA) mutation encoding the transfer RNA of leucine (UUR) (tRNA (Leu(UUR))). The pathogenetic mechanisms of this mutation are not completely understood. Neuronal functions are particularly vulnerable to alterations in oxidative phosphorylation, which may affect the function of the neurotransmitter glutamate, leading to excitotoxicity. In order to investigate the possible effects of A3243G upon glutamate homeostasis, we assessed glutamate uptake in osteosarcoma-derived cytoplasmic hybrids (cybrids) expressing high levels of this mutation. High-affinity Na(+)-dependent glutamate uptake was assessed as radioactive [(3)H]-glutamate influx mediated by specific excitatory amino acid transporters (EAATs). The maximal rate (V(max)) of Na(+)-dependent glutamate uptake was significantly reduced in all the mutant clones. Although the defect did not relate to either the mutant load or magnitude of oxidative phosphorylation defect, we found an inverse relationship between A3243G mutation load and mitochondrial ATP synthesis, without any evidence of increased cellular or mitochondrial free radical production in these A3243G clones. These data suggest that a defect of glutamate transport in MELAS neurons may be due to decreased energy production and might be involved in mediating the pathogenic effects of the A3243G mtDNA mutation.
authors.affiliation: Department of Neuroscience and Biomedical Technologies, University of Milano-Bicocca, Monza, Italy. jacopo.difrancesco@unimib.it
authors.forename: Jacopo C
authors.initials: JC
authors.lastname: DiFrancesco
authors.forename: J Mark
authors.initials: JM
authors.lastname: Cooper
authors.forename: Amanda
authors.initials: A
authors.lastname: Lam
authors.forename: Paul E
authors.initials: PE
authors.lastname: Hart
authors.forename: Lucio
authors.initials: L
authors.lastname: Tremolizzo
authors.forename: Carlo
authors.initials: C
authors.lastname: Ferrarese
authors.forename: Antony H
authors.initials: AH
authors.lastname: Schapira
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D001692:Biological Transport / Q000235:genetics; D045744:Cell Line, Tumor; D004272:DNA, Mitochondrial / Q000235:genetics*; D015536:Down-Regulation / Q000235:genetics; D004734:Energy Metabolism / Q000235:genetics*; D050491:Glutamate Plasma Membrane Transport Proteins / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D006825:Hybridomas; D017241:MELAS Syndrome / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D011869:Radioligand Assay; D014316:Tritium
chemical_list: D004272:DNA, Mitochondrial; D050491:Glutamate Plasma Membrane Transport Proteins; D014316:Tritium; D018698:Glutamic Acid; D000255:Adenosine Triphosphate