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W.–K. Ju, Y. Kushnareva, B. Bossy, R. Schwarzenbacher, R. Liddington, A. White, M. Ellisman, G. Perkins, S. Lipton, E. Bossy–Wetzel; Opa1 Loss and Retinal Ganglion Cell Death . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5188.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Dominant optic atrophy (DOA) is the most common form of hereditary optic neuropathy, leading to vision loss in young children. To date, DOA is an incurable neurodegenerative disorder characterized by loss of retinal ganglion cells. The gene defective in DOA is Optic Atrophy Type–1 (OPA1). Interestingly, OPA1 encodes a large dynamin–related GTPase localized to the mitochondrial inner membrane and implicated in mitochondrial fusion. A balance between mitochondrial fission (division) and fusion is critical for normal neuronal function. OPA1 mutation causes DOA characterized by retinal ganglion cell degeneration. However, mechanisms of retinal ganglion cell death are unknown. Methods: By using siRNA mediated gene silencing, the effects of OPA1 loss were analyzed with 3D time–lapse deconvolution microscopy and electron microscope tomography. For structural analyses of OPA1, we synthesized recombinant OPA protein and GTPase activity was measured at physiological salt concentration. For bioenergetic analyses, mitochondrial respiration and ATP level were measured. Results: Most missense mutations in OPA1 cluster in the conserved GTPase domain. Intriguingly, several missense mutations map directly to the active site for GTP binding and therefore are likely to either alter enzymatic activity or result in its loss. We show that recombinant OPA1 protein reveals GTPase activity, similar to Dynamin. Importantly, OPA1 knockdown by siRNA results in dramatic mitochondrial fission characterized by a conversion of tubular, fused mitochondria into isolated small organelles. Mitochondrial fission after OPA1 loss is accompanied by a decrease of ATP, respiratory inhibition, and ultrastructural abnormalities of mitochondria. Dominant–negative Drp–1 overexpression prevents mitochondrial fission following OPA1 loss. Conclusions: OPA1 loss of function may impair normal mitochondrial and neuronal function and lead to neurodegeneration.
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