Functional analysis of lymphoblast and cybrid mitochondria containing the 3460, 11778, or 14484 Leber's hereditary optic neuropathy mitochondrial DNAmutation

Leber's hereditary optic neuropathy (LHON) is a form of blindness caused by mitochondrial DNA (mtDNA) mutations in complex I genes. We report an exten sive biochemical analysis of the mitochondrial defects in lymphoblasts and transmitochondrial cybrids harboring the three most common LHON mutations: 3460A, 11778A, and 14484C. Respiration studies revealed that the 3460A muta tion reduced the maximal respiration rate 20-28%, the 11778A mutation 30-36 %, and the 14484C mutation 10-15%. The respiration defects of the 3460A and 11778A mutations transferred in cybrid experiments linking these defects t o the mtDNA. Complex I enzymatic assays revealed that the 3460A mutation re sulted in a 79% reduction in specific activity and the 11778A mutation resu lted in a 20% reduction, while the 14484C mutation did not affect the compl ex I activity. The enzyme defect of the 3460A mutation transferred with the mtDNA in cybrids. Overall, these data support the conclusion that the 3460 A and 11778A mutants result in complex I defects and that the 14484C mutati on causes a much milder biochemical defect. These studies represent the fir st direct comparison of oxidative phosphorylation defects among all of the primary LHON mtDNA mutations, thus permitting insight into the underlying p athophysiological mechanism of the disease.