Leber's hereditary optic neuropathy caused by a mutation in mitochondrial tRNAThr in eight Chinese pedigrees

Purpose: The purpose of this study was to investigate the pathophysiology underlying Leber's hereditary optic neuropathy (LHON)-associated mitochondrial tRNA mutation. Methods: Severn hundred ninety-seven Han Chinese subjects underwent clinical and genetic evaluation and analysis of mitochondrial DNA (mtDNA). The cybrid cell lines were constructed by transferring mitochondria from lymphoblastoid cell lines derived from a Chinese family into mtDNA-less (rho degrees) cells. These cell lines were assayed by tRNA Northern blot and Western blot analyses, respiratory enzymatic activities, the rate of ATP production and the generation of reactive oxygen species. Results: The tRNA(Thr) 15927G > A mutation was identified in eight probands with suggestively maternal inheritance among 352 Han Chinese probands lacking these known LHON-associated mtDNA mutations. The m.15927G > A mutation affected a highly conserved guanine at position 42 at the anticodon-stem of tRNA(Thr), destabilizing the conservative base pairing (28C-42G). We therefore hypothesized that the m.15927G > A mutation, and altered the structure and function of tRNA(Thr). Northern blot analysis revealed 60% decrease in the steady-state level of tRNA(Thr) in the mutant cell lines. Western blot analysis showed the variable reductions of 4 mtDNA encoding proteins, especially for marked decrease of ND1 and CYTB observed in mutant cell lines. Furthermore, we demonstrated that the m.15927G > A mutation decreased the activities of mitochondrial complexes I and III, markedly diminished mitochondria] ATP levels, and increased the production of reactive oxygen species in the mutant cells. Conclusions: Our data demonstrated the first mitochondrial tRNA mutation leading to LHON. Our findings may provide new insights into the understanding of pathophysiology of LHON.