Three prevalent mitochondrial DNA pathogenic mutations at positions 11778, 3460, and 14484, which affect different subunits of Complex I, cause retinal ganglion cell death and optic nerve atrophy in Leber's hereditary optic neuropathy (LHON). The cell death is painless and without inflammation, consistent with an apoptotic mechanism. We have investigated the possibility that the LHON mutation confers a pro-apoptotic stimulus and have tested the sensitivity of osteosarcoma-derived cybrid cells carrying the most common and severe mutations (11778 and 3460) to cell death induced by Fas. We observed that LHON cybrids were sensitized to Fas-dependent death. Control cells that bear the same mitochondrial genetic background (the J haplogroup) without the pathogenic 11778 mutation are no more sensitive than other controls, indicating that increased Fas-dependent death in LHON cybrids was induced by the LHON pathogenic mutations. The type of death was apoptotic by several criteria, including induction by Fas, inhibition by the caspase inhibitor zVAD-fmk (zVal-Ala-Asp-fluoro-methyl ketone), activation of DEVDase activity (Asp-Glu-Val-Asp protease), specific cleavage of caspase-3, DNA fragmentation, and increased Annexin-V labeling. These data indicate that the most common and severe LHON pathogenic mutations 11778 and 3460 predispose cells to apoptosis, which may be relevant for the pathophysiology of cell death in LHON, and potential therapy.
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