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Secondary mtDNA defects do not cause optic nerve dysfunction in a mouse model of dominant optic atrophy.

ABSTRACT: PURPOSE:The majority of patients with autosomal dominant optic atrophy (DOA) harbor pathogenic OPA1 mutations and certain missense mutations, mostly within the GTPase domain, have recently been shown to cause multiple mitochondrial DNA (mtDNA) deletions in skeletal muscle. This raises the possibility that the optic neuropathy could be the result of secondary mtDNA defects accumulating within retinal ganglion cells (RGCs). To explore this hypothesis, the authors looked for evidence of mitochondrial dysfunction in a mouse model of DOA and documented the visual and neurologic progression in aging mutant mice. METHODS:Visual function was assessed with a rotating optokinetic (OKN) drum at ages 13 and 18 months and neurologic phenotyping was performed using the primary SHIRPA screen at age 13 months, comparing mutant Opa1(+/)(-) mice with wild-type C57Bl/6 mice. The presence of cytochrome c oxidase (COX) deficiency and multiple mtDNA deletions was investigated in gastrocnemius muscle and eye specimens harvested from 2- and 11-month-old Opa1(+/+) and Opa1(+/)(-) mice. RESULTS:At age 13 months, Opa1(+/)(-) mice had a statistically significant reduction in OKN responses compared to C57Bl/6 controls with both 2 degrees and 8 degrees gratings (P < 0.001). At age 18 months, the difference between the two groups was significant for the 8 degrees grating (P = 0.003) but not for the 2 degrees grating (P = 0.082). Opa1(+/)(-) mice did not exhibit any significant neuromuscular deficits and no COX deficient areas or secondary mtDNA deletions were identified in skeletal muscle or the RGC layer. There was also no evidence of significant mtDNA depletion or proliferation in skeletal muscle from Opa1(+/)(-) mice. CONCLUSIONS:COX deficiency and mtDNA abnormalities do not contribute to optic nerve dysfunction in pure DOA.

SUBMITTER: Yu-Wai-Man P

PROVIDER: S-EPMC4034167 | biostudies-literature | 2009 Oct

REPOSITORIES: biostudies-literature

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Secondary mtDNA defects do not cause optic nerve dysfunction in a mouse model of dominant optic atrophy.

Yu-Wai-Man Patrick P Davies Vanessa J VJ Piechota Malgorzata J MJ Cree Lynsey M LM Votruba Marcela M Chinnery Patrick F PF

Investigative ophthalmology & visual science 20090514 10

<h4>Purpose</h4>The majority of patients with autosomal dominant optic atrophy (DOA) harbor pathogenic OPA1 mutations and certain missense mutations, mostly within the GTPase domain, have recently been shown to cause multiple mitochondrial DNA (mtDNA) deletions in skeletal muscle. This raises the possibility that the optic neuropathy could be the result of secondary mtDNA defects accumulating within retinal ganglion cells (RGCs). To explore this hypothesis, the authors looked for evidence of mit ...[more]

PMID: 19443720

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Project description:DEFINITION OF THE DISEASE: Dominant Optic Atrophy (DOA) is a neuro-ophthalmic condition characterized by a bilateral degeneration of the optic nerves, causing insidious visual loss, typically starting during the first decade of life. The disease affects primary the retinal ganglion cells (RGC) and their axons forming the optic nerve, which transfer the visual information from the photoreceptors to the lateral geniculus in the brain.The prevalence of the disease varies from 1/10000 in Denmark due to a founder effect, to 1/30000 in the rest of the world.DOA patients usually suffer of moderate visual loss, associated with central or paracentral visual field deficits and color vision defects. The severity of the disease is highly variable, the visual acuity ranging from normal to legal blindness. The ophthalmic examination discloses on fundoscopy isolated optic disc pallor or atrophy, related to the RGC death. About 20% of DOA patients harbour extraocular multi-systemic features, including neurosensory hearing loss, or less commonly chronic progressive external ophthalmoplegia, myopathy, peripheral neuropathy, multiple sclerosis-like illness, spastic paraplegia or cataracts.Two genes (OPA1, OPA3) encoding inner mitochondrial membrane proteins and three loci (OPA4, OPA5, OPA8) are currently known for DOA. Additional loci and genes (OPA2, OPA6 and OPA7) are responsible for X-linked or recessive optic atrophy. All OPA genes yet identified encode mitochondrial proteins embedded in the inner membrane and ubiquitously expressed, as are the proteins mutated in the Leber Hereditary Optic Neuropathy. OPA1 mutations affect mitochondrial fusion, energy metabolism, control of apoptosis, calcium clearance and maintenance of mitochondrial genome integrity. OPA3 mutations only affect the energy metabolism and the control of apoptosis.Patients are usually diagnosed during their early childhood, because of bilateral, mild, otherwise unexplained visual loss related to optic discs pallor or atrophy, and typically occurring in the context of a family history of DOA. Optical Coherence Tomography further discloses non-specific thinning of retinal nerve fiber layer, but a normal morphology of the photoreceptors layers. Abnormal visual evoked potentials and pattern ERG may also reflect the dysfunction of the RGCs and their axons. Molecular diagnosis is provided by the identification of a mutation in the OPA1 gene (75% of DOA patients) or in the OPA3 gene (1% of patients).Visual loss in DOA may progress during puberty until adulthood, with very slow subsequent chronic progression in most of the cases. On the opposite, in DOA patients with associated extra-ocular features, the visual loss may be more severe over time.To date, there is no preventative or curative treatment in DOA; severely visually impaired patients may benefit from low vision aids. Genetic counseling is commonly offered and patients are advised to avoid alcohol and tobacco consumption, as well as the use of medications that may interfere with mitochondrial metabolism. Gene and pharmacological therapies for DOA are currently under investigation.

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Secondary mtDNA defects do not cause optic nerve dysfunction in a mouse model of dominant optic atrophy.

Publications

Secondary mtDNA defects do not cause optic nerve dysfunction in a mouse model of dominant optic atrophy.

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