Effects on mitochondrial transcription of manipulating mTERF protein levels in cultured human HEK293 cells

Peer reviewe

Acquisition of the wobble . . .

The A3243G mutation in the mitochondrial gene for human mitochondrial (mt) tRNA Leu(UUR) , responsible for decoding of UUR codons, is associated with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). We previously demonstrated that this mutation causes defects in 5-taurinomethyluridine (τm 5 U) modification at the anticodon first (wobble) position of the mutant mt tRNA Leu(UUR) , leading to a UUG decoding deficiency and entraining severe respiratory defects. In addition, we previously identified a heteroplasmic mutation, G12300A, in the other mt leucine tRNA gene, mt tRNA Leu(CUN) , which functions as a suppressor of the A3243G respiratory defect in cybrid cells containing A3243G mutant mtDNA. Although the G12300A mutation converts the anticodon sequence of mt tRNA Leu(CUN) from UAG to UAA, this tRNA carrying an unmodified wobble uridine still cannot decode the UUG codon. Mass spectrometric analysis of the suppressor mt tRNA Leu(CUN) carrying the G12300A mutation from the phenotypically revertant cells revealed that the wobble uridine aquires de novo τm 5 U modification. I

A mouse model of mitochondrial complex III dysfunction induced by myxothiazol.

Myxothiazol is a respiratory chain complex III (CIII) inhibitor that binds to the ubiquinol oxidation site Qo of CIII. It blocks electron transfer from ubiquinol to cytochrome b and thus inhibits CIII activity. It has been utilized as a tool in studies of respiratory chain function in in vitro and cell culture models. We developed a mouse model of biochemically induced and reversible CIII inhibition using myxothiazol. We administered myxothiazol intraperitoneally at a dose of 0.56mg/kg to C57Bl/J6 mice every 24h and assessed CIII activity, histology, lipid content, supercomplex formation, and gene expression in the livers of the mice. A reversible CIII activity decrease to 50% of control value occurred at 2h post-injection. At 74h only minor histological changes in the liver were found, supercomplex formation was preserved and no significant changes in the expression of genes indicating hepatotoxicity or inflammation were found. Thus, myxothiazol-induced CIII inhibition can be induced in mice for four days in a row without overt hepatotoxicity or lethality. This model could be utilized in further studies of respiratory chain function and pharmacological approaches to mitochondrial hepatopathies

Characterization of complex III deficiency and liver dysfunction in GRACILE syndrome caused by a BCS1L mutation

A homozygous mutation in the complex III chaperone BCS1L causes GRACILE syndrome (intrauterine growth restriction, aminoaciduria, cholestasis, hepatic iron overload, lactacidosis). In control and patient fibroblasts we localized BCS1L in inner mitochondrial membranes. In patient liver, kidney, and heart BCS1L and Rieske protein levels, as well as the amount and activity of complex III, were decreased. Major histopathology was found in kidney and liver with cirrhosis and iron deposition, but of iron-related proteins only ferritin levels were high. In placenta from a GRACILE fetus, the ferrooxidases ceruloplasmin and hephaestin were upregulated suggesting association between iron overload and placental dysfunction