A Hypertension-Associated tRNA^Ala Mutation Alters tRNA Metabolism and Mitochondrial Function

In this report, we investigated the pathophysiology of a novel hypertension-associated mitochondrial tRNA(Ala) 5655A → G (m.5655A → G) mutation. The destabilization of a highly conserved base pairing (A1-U72) at the aminoacyl acceptor stem by an m.5655A → G mutation altered the tRNA(Ala) function. An in vitro processing analysis showed that the m.5655A → G mutation reduced the efficiency of tRNA(Ala) precursor 5' end cleavage catalyzed by RNase P. By using cybrids constructed by transferring mitochondria from lymphoblastoid cell lines derived from a Chinese family into mitochondrial DNA (mtDNA)-less (ρ(o)) cells, we showed a 41% reduction in the steady-state level of tRNA(Ala) in mutant cybrids. The mutation caused an improperly aminoacylated tRNA(Ala), as suggested by aberrantly aminoacylated tRNA(Ala) and slower electrophoretic mobility of mutated tRNA. A failure in tRNA(Ala) metabolism contributed to variable reductions in six mtDNA-encoded polypeptides in mutant cells, ranging from 21% to 37.5%, with an average of a 29.1% reduction, compared to levels of the controls. The impaired translation caused reduced activities of mitochondrial respiration chains. Furthermore, marked decreases in the levels of mitochondrial ATP and membrane potential were observed in mutant cells. These caused increases in the production of reactive oxygen species in the mutant cybrids. The data provide evidence for the association of the tRNA(Ala) 5655A → G mutation with hypertension.