title: Dysregulated mitophagy and mitochondrial organization in optic atrophy due to OPA1 mutations.
abstract: OBJECTIVE
  To investigate mitophagy in 5 patients with severe dominantly inherited optic atrophy (DOA), caused by depletion of OPA1 (a protein that is essential for mitochondrial fusion), compared with healthy controls.
  
  
  METHODS
  Patients with severe DOA (DOA plus) had peripheral neuropathy, cognitive regression, and epilepsy in addition to loss of vision. We quantified mitophagy in dermal fibroblasts, using 2 high throughput imaging systems, by visualizing colocalization of mitochondrial fragments with engulfing autophagosomes.
  
  
  RESULTS
  Fibroblasts from 3 biallelic OPA1(-/-) patients with severe DOA had increased mitochondrial fragmentation and mitochondrial DNA (mtDNA)-depleted cells due to decreased levels of OPA1 protein. Similarly, in siRNA-treated control fibroblasts, profound OPA1 knockdown caused mitochondrial fragmentation, loss of mtDNA, impaired mitochondrial function, and mitochondrial mislocalization. Compared to controls, basal mitophagy (abundance of autophagosomes colocalizing with mitochondria) was increased in (1) biallelic patients, (2) monoallelic patients with DOA plus, and (3) OPA1 siRNA-treated control cultures. Mitophagic flux was also increased. Genetic knockdown of the mitophagy protein ATG7 confirmed this by eliminating differences between patient and control fibroblasts.
  
  
  CONCLUSIONS
  We demonstrated increased mitophagy and excessive mitochondrial fragmentation in primary human cultures associated with DOA plus due to biallelic OPA1 mutations. We previously found that increased mitophagy (mitochondrial recycling) was associated with visual loss in another mitochondrial optic neuropathy, Leber hereditary optic neuropathy (LHON). Combined with our LHON findings, this implicates excessive mitochondrial fragmentation, dysregulated mitophagy, and impaired response to energetic stress in the pathogenesis of mitochondrial optic neuropathies, potentially linked with mitochondrial mislocalization and mtDNA depletion.
authors.affiliation: Author affiliations are provided at the end of the article.
authors.forename: Chunyan
authors.initials: C
authors.lastname: Liao
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authors.forename: Neil
authors.initials: N
authors.lastname: Ashley
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authors.forename: Alan
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authors.lastname: Diot
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authors.forename: Karl
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authors.lastname: Morten
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authors.forename: Kanchan
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authors.lastname: Phadwal
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authors.forename: Andrew
authors.initials: A
authors.lastname: Williams
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authors.forename: Ian
authors.initials: I
authors.lastname: Fearnley
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authors.forename: Lyndon
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authors.lastname: Rosser
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authors.forename: Jo
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authors.lastname: Lowndes
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authors.forename: Carl
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authors.lastname: Fratter
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authors.forename: David J P
authors.initials: DJ
authors.lastname: Ferguson
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authors.forename: Laura
authors.initials: L
authors.lastname: Vay
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authors.forename: Gerardine
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authors.lastname: Quaghebeur
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authors.forename: Isabella
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authors.lastname: Moroni
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authors.forename: Stefania
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authors.lastname: Bianchi
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authors.forename: Costanza
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authors.lastname: Lamperti
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authors.forename: Susan M
authors.initials: SM
authors.lastname: Downes
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authors.forename: Kamil S
authors.initials: KS
authors.lastname: Sitarz
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authors.forename: Padraig J
authors.initials: PJ
authors.lastname: Flannery
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authors.forename: Janet
authors.initials: J
authors.lastname: Carver
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authors.forename: Eszter
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authors.lastname: Dombi
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authors.forename: Daniel
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authors.lastname: East
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authors.forename: Matilde
authors.initials: M
authors.lastname: Laura
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authors.forename: Mary M
authors.initials: MM
authors.lastname: Reilly
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authors.forename: Heather
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authors.lastname: Mortiboys
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authors.forename: Remko
authors.initials: R
authors.lastname: Prevo
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authors.forename: Michelangelo
authors.initials: M
authors.lastname: Campanella
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authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Daniels
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authors.forename: Massimo
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authors.lastname: Zeviani
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authors.forename: Patrick
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authors.lastname: Yu-Wai-Man
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authors.forename: Anna Katharina
authors.initials: AK
authors.lastname: Simon
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authors.forename: Marcela
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authors.lastname: Votruba
authors.affiliation: Author affiliations are provided at the end of the article. Joanna.Poulton@obs-gyn.ox.ac.uk.
authors.forename: Joanna
authors.initials: J
authors.lastname: Poulton
mesh_terms: D000975:Antioxidants / Q000494:pharmacology; D002478:Cells, Cultured; D003072:Cognition Disorders / Q000209:etiology; D004252:DNA Mutational Analysis; D004272:DNA, Mitochondrial / Q000235:genetics; D005192:Family Health; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure; D020558:GTP Phosphohydrolases / Q000235:genetics*; D006801:Humans; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000235:genetics; D024101:Mitochondrial Proteins / Q000235:genetics; D063306:Mitophagy / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D009896:Optic Atrophy / Q000150:complications / Q000235:genetics* / Q000473:pathology; D010375:Pedigree; D011494:Protein Kinases / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases / Q000235:genetics; D000099202:PTEN-Induced Putative Kinase
chemical_list: D000975:Antioxidants; D004272:DNA, Mitochondrial; D020558:GTP Phosphohydrolases; D024101:Mitochondrial Proteins; D011494:Protein Kinases; D034741:RNA, Small Interfering; D014451:Ubiquinone; D044767:Ubiquitin-Protein Ligases; D000099202:PTEN-Induced Putative Kinase; C111567:parkin protein; C470018:MFN2 protein, human; C415198:OPA1 protein, human; C036619:idebenone