Human Mitochondrial Leucyl-tRNA Synthetase Corrects Mitochondrial Dysfunctions Due to the tRNA^Leu(UUR) A3243G Mutation, Associated with Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Symptoms and Diabetes

Abstract

Mutations in mitochondrial tRNA genes are associated with a wide spectrum of human diseases. In particular, the tRNA Leu(UUR) A3243G mutation causes mitochondrial encephalomyopathy, lactic acidosis, and stroke-like symptoms (MELAS) and 2% of cases of type 2 diabetes. The primary defect in this mutation was an inefficient aminoacylation of the tRNA Leu(UUR) . In the present study, we have investigated the molecular mechanism of the A3243G mutation and whether the overexpression of human mitochondrial leucyl-tRNA synthetase (LARS2) in the cytoplasmic hybrid (cybrid) cells carrying the A3243G mutation corrects the mitochondrial dysfunctions. Human LARS2 localizes exclusively to mitochondria, and LARS2 is expressed ubiquitously but most abundantly in tissues with high metabolic rates. We showed that the alteration of aminoacylation tRNA Leu(UUR) caused by the A3243G mutation led to mitochondrial translational defects and thereby reduced the aminoacylated efficiencies of tRNA Leu(UUR) as well as tRNA Ala and tRNA Met . We demonstrated that the transfer of human mitochondrial leucyl-tRNA synthetase into the cybrid cells carrying the A3243G mutation improved the efficiency of aminoacylation and stability of mitochondrial tRNAs and then increased the rates of mitochondrial translation and respiration, consequently correcting the mitochondrial dysfunction. These findings provide new insights into the molecular mechanism of maternally inherited diseases and a step toward therapeutic interventions for these disorders.

Mutations of human NARS2, encoding the mitochondrial asparaginyl-tRNA synthetase, cause nonsyndromic deafness and Leigh syndrome

“…Decreased mt-tRNAs levels secondary to defects in a mt-tRNA's cognate ARS2, have been observed in several other ARS2-related diseases [13,46]. Intriguingly, recent studies have shown that overexpression of cognate and non-cognate ARS2 can rescue mitochondrial dysfunction secondary to mt-tRNA mutations [47,48], further reinforcing the importance of the interaction between ARS2 and their cognate mt-tRNAs. The absence of hearing deficit in the family studied by Vanlander and co-authors, while the two families described in our study exhibit hearing loss, is an additional example of the pleiotropism of ARS2 associated disease.…”

Emerging therapeutic approaches to mitochondrial diseases

“…Interestingly, the rates of oxygen consumption in suppressed cells were directly proportional to the levels of leucyl-tRNA synthetase in A3243G mutant cells and could even reach wild-type respiratory function. The suppressed cells had increased steady-state levels of tRNA (Leu(UUR)) and up to threefold higher steady-state levels of mitochondrial translation products, but rates of protein synthesis did not differed from those in parental mutant cells [Li and Guan, 2010;Park et al, 2008].…”

Trends in Mitochondrial Therapeutics for Neurological Disease

“…Overexpression of human mitochondrial valyl-or leucyl-tRNA synthetases increased, respectively, the steady-state levels of mutant mt-tRNA Val [71] or mt-tRNA Leu(UUR) [72], consistent with increased stability of the charged mt-tRNA. Also, overexpression of mitochondrial leucyl-tRNA synthetase rescued mitochondrial translation and respiration in cells carrying the A3243G MELAS mutation in mt-tRNA Leu(UUR) [73]. A related strategy consists in the allotopic expression of recombinant and importable tRNAs with altered aminoacylation identity.…”