title: The mitochondrial disease associated protein Ndufaf2 is dispensable for Complex-1 assembly but critical for the regulation of oxidative stress.
abstract: Deficiency in human mitochondrial Complex-1 has been linked to a wide variety of neurological disorders. Homozygous deletion of the Complex-1 associated protein, Ndufaf2, leads to a severe juvenile onset encephalopathy involving degeneration of the substantia nigra and other sub-cortical regions resulting in adolescent lethality. To understand the precise role of Ndufaf2 in Complex-1 function and its links to neurologic disease, we studied the effects on Complex-1 assembly and function, as well as pathological consequences at the cellular level, in multiple in vitro models of Ndufaf2 deficiency. Using both Ndufaf2-deficient human neuroblastoma cells and primary fibroblasts cultured from Ndufaf2 knock-out mice we found that Ndufaf2-deficiency selectively reduces Complex-1 activity. While Ndufaf2 is traditionally referred to as an assembly factor of Complex-1, surprisingly, however, Ndufaf2-deficient cells were able to assemble a fully mature Complex-1 enzyme, albeit with reduced kinetics. Importantly, no evidence of intermediate or incomplete assembly was observed. Ndufaf2 deficiency resulted in significant increases in oxidative stress and mitochondrial DNA deletion, consistent with contemporary hypotheses regarding the pathophysiology of inherited mutations in Complex-1 disorders. These data suggest that Ndufaf2, unlike other Complex-1 assembly factors, may be more accurately described as a chaperone involved in proper folding during Complex-1 assembly, since it is dispensable for Complex-1 maturation but not its proper function.
authors.affiliation: Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Julia S
authors.initials: JS
authors.lastname: Schlehe
authors.forename: Marion S M
authors.initials: MS
authors.lastname: Journel
authors.forename: Kelsey P
authors.initials: KP
authors.lastname: Taylor
authors.forename: Katherine D
authors.initials: KD
authors.lastname: Amodeo
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: LaVoie
mesh_terms: D000818:Animals; D053148:Caspase 3 / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology; D016923:Cell Death; D045744:Cell Line, Tumor; D002950:Citrate (si)-Synthase / Q000378:metabolism; D042967:Electron Transport Complex I / Q000235:genetics / Q000378:metabolism*; D042963:Electron Transport Complex II / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D024101:Mitochondrial Proteins / Q000172:deficiency / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000378:metabolism; D009447:Neuroblastoma / Q000473:pathology; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D010101:Oxygen Consumption; D013997:Time Factors
chemical_list: D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; C098483:NADH dehydrogenase subunit 4; C501824:NDUFAF2 protein, human; D042963:Electron Transport Complex II; D009245:NADH Dehydrogenase; C515075:NADH dehydrogenase subunit 1, human; D002950:Citrate (si)-Synthase; D053148:Caspase 3; D042967:Electron Transport Complex I
keywords: Complex-1 assembly; Complex-1 disease; KO; Mitochondria; Mitochondrial DNA mutations; OCR; Oxidative stress; PBS; PVDF; ROS; WT; knockout; mitochondrial DNA; mtDNA; not significant; ns; oxygen consumption rate; phosphate buffered saline; polyvinylidene fluoride; reactive oxygen species; wildtype