A Deafness- and Diabetes-associated tRNA Mutation Causes Deficient Pseudouridinylation at Position 55 in tRNAGlu and Mitochondrial Dysfunction

Several mitochondrial tRNA mutations have been associated with maternally inherited diabetes and deafness. However, the pathophysiology of these tRNA mutations remains poorly understood. In this report, we identified the novel homoplasmic 14692A -> G mutation in the mitochondrial tRNA(Glu) gene among three Han Chinese families with maternally inherited diabetes and deafness. The m.14692A -> G mutation affected a highly conserved uridine at position 55 of the T Psi C loop of tRNA(Glu). The uridine is modified to pseudouridine (Psi 55), which plays an important role in the structure and function of this tRNA. Using lymphoblastoid cell lines derived from a Chinese family, we demonstrated that the m.14692A -> G mutation caused loss of Psi 55 modification and increased angiogenin-mediated endonucleolytic cleavage in mutant tRNA(Glu). The destabilization of base-pairing (18A-Psi 55) caused by the m.14692A -> G mutation perturbed the conformation and stability of tRNA(Glu). An approximately 65% decrease in the steady-state level of tRNA(Glu) was observed in mutant cells compared with control cells. A failure in tRNA(Glu) metabolism impaired mitochondrial translation, especially for polypeptides with a high proportion of glutamic acid codons such as ND1, ND6, and CO2 in mutant cells. An impairment of mitochondrial translation caused defective respiratory capacity, especially reducing the activities of complexes I and IV. Furthermore, marked decreases in the levels of mitochondrial ATP and membrane potential were observed in mutant cells. These mitochondrial dysfunctions caused an increasing production of reactive oxygen species in the mutant cells. Our findings may provide new insights into the pathophysiology of maternally inherited diabetes and deafness, which is primarily manifested by the deficient nucleotide modification of mitochondrial tRNA(Glu).