Overexpression of human mitochondrial valyl tRNA synthetase can partially restore levels of cognate mt-tRNAVal carrying the pathogenic C25U mutation.

Joanna Rorbach, Abdul Aziz Yusoff, Helen Tuppen, Dyg P Abg-Kamaludin, Zofia M A Chrzanowska-Lightowlers, Robert W Taylor, Douglass M Turnbull, Robert McFarland, Robert N Lightowlers

Nucleic acids research 2008 May

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Phenotypic diversity associated with pathogenic mutations of the human mitochondrial genome (mtDNA) has often been explained by unequal segregation of the mutated and wild-type genomes (heteroplasmy). However, this simple hypothesis cannot explain the tissue specificity of disorders caused by homoplasmic mtDNA mutations. We have previously associated a homoplasmic point mutation (1624C>T) in MTTV with a profound metabolic disorder that resulted in the neonatal deaths of numerous siblings. Affected tissues harboured a marked biochemical defect in components of the mitochondrial respiratory chain, presumably due to the extremely low (<1%) steady-state levels of mt-tRNA(Val). In primary myoblasts and transmitochondrial cybrids established from the proband (index case) and offspring, the marked respiratory deficiency was lost and steady-state levels of the mutated mt-tRNA(Val) were greater than in the biopsy material, but were still an order of magnitude lower than in control myoblasts. We present evidence that the generalized decrease in steady-state mt-tRNA(Val) observed in the homoplasmic 1624C>T-cell lines is caused by a rapid degradation of the deacylated form of the abnormal mt-tRNA(Val). By both establishing the identity of the human mitochondrial valyl-tRNA synthetase then inducing its overexpression in transmitochondrial cell lines, we have been able to partially restore steady-state levels of the mutated mt-tRNA(Val), consistent with an increased stability of the charged mt-tRNA. These data indicate that variations in the levels of VARS2L between tissue types and patients could underlie the difference in clinical presentation between individuals homoplasmic for the 1624C>T mutation.

Citation

Joanna Rorbach, Abdul Aziz Yusoff, Helen Tuppen, Dyg P Abg-Kamaludin, Zofia M A Chrzanowska-Lightowlers, Robert W Taylor, Douglass M Turnbull, Robert McFarland, Robert N Lightowlers. Overexpression of human mitochondrial valyl tRNA synthetase can partially restore levels of cognate mt-tRNAVal carrying the pathogenic C25U mutation. Nucleic acids research. 2008 May;36(9):3065-74