title: Release of OPA1 during apoptosis participates in the rapid and complete release of cytochrome c and subsequent mitochondrial fragmentation.
abstract: Mitochondria are important participants in apoptosis, releasing cytochrome c into the cytoplasm and undergoing extensive fragmentation. However, mechanisms underlying these processes remain unclear. Here, we demonstrate that cytochrome c release during apoptosis precedes mitochondrial fragmentation. Unexpectedly, OPA1, a dynamin-like GTPase of the mitochondrial intermembrane space important for maintaining cristae structure, is co-released with cytochrome c. To mimic the loss of OPA1 occurring after its release, we knocked down OPA1 expression using RNA interference. This triggered structural changes in the mitochondrial cristae and caused increased fragmentation by blocking mitochondrial fusion. Because cytochrome c is mostly sequestered within cristae folds but released rapidly and completely during apoptosis, we examined the effect of OPA1 loss on cytochrome c release, demonstrating that it is accelerated. Thus, our results suggest that an initial mitochondrial leak of OPA1 leads to cristae structural alterations and exposure of previously sequestered protein pools, permitting continued release in a feed-forward manner to completion. Moreover, our findings indicate that the resulting OPA1 depletion causes a block in mitochondrial fusion, providing a compelling mechanism for the prominent increase in mitochondrial fragmentation seen during apoptosis.
authors.affiliation: Cellular Neurology Unit, Surgical Neurology Branch, NINDS, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Damien
authors.initials: D
authors.lastname: Arnoult
authors.forename: Alain
authors.initials: A
authors.lastname: Grodet
authors.forename: Yang-Ja
authors.initials: YJ
authors.lastname: Lee
authors.forename: Jérôme
authors.initials: J
authors.lastname: Estaquier
authors.forename: Craig
authors.initials: C
authors.lastname: Blackstone
mesh_terms: D017209:Apoptosis; D002244:Carbon / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019286:Endopeptidase K / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D013997:Time Factors; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D051028:bcl-2-Associated X Protein; D049452:Green Fluorescent Proteins; D011189:Potassium Chloride; D002244:Carbon; D045304:Cytochromes c; D019286:Endopeptidase K; D020558:GTP Phosphohydrolases; C415198:OPA1 protein, human