application): Mitochondrial DNA (mtDNA) mutations have been linked to a variety of clinical manifestations including neurodegenerative disease, but the pathophysiological mechanisms involved remain unclear. Particularly striking is the acute onset optic atrophy of Leber's Hereditary Optic Atrophy (LHON) and the basal ganglia degeneration of dystonia and Leigh's syndrome, both of which can result from missense mutations in subunits of respiratory Complex I. The investigators hypothesize that two factors influence clinical presentation: (1) the severity of the mtDNA mutation on mitochondrial energy generation and oxygen radical production, and (2) the sensitivity imparted by the mitochondrial defect to neuronal excitotoxic stimulation of NMDA receptors. LHON mutations are hypothesized to minimally affect energy output, but chronically increase oxygen radical production. The increased oxygen radicals might inactivate the vasodilator NO retinal vessel construction, resulting in ischemia, and optic nerve death. The dystonia and Leigh's syndrome mutations significantly reduce mitochondrial energy production and increase oxygen radical production, and rendering basal ganglia neurons sensitive to excitotoxicity. To test this hypothesis, the investigators propose four groups of experiments. First, they will identify additional mtDNA missense mutations associated with optic atrophy and basal ganglia degeneration, and compare them for genotype/ phenotype associations, defects in mitochondrial energy production, and increased oxygen radical production. Second, they will prepare lymphoblast and neuroblastoma cell lines harboring various mtDNA mutations and expressing NMDA receptors. These cells will then be assessed for their differential sensitivity to excitotoxic stimulation. Third, they will attempt to introduce various mtDNA mutations into the mouse germline via cybrid transfer to female ES cells and preparation of transgenic mice. Mice manifesting optic atrophy or basal ganglia disease will be analyzed for their bioenergetic defect, oxygen radical generation, and sensitivity to excitotoxic stimulation. Finally, mice prone to optic atrophy and basal ganglia degeneration will be treated with vasodilators and antioxidants plus NMDA receptor and antagonists, to determine if these therapies can prevent symptoms.
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