title: Role of oxidative stress in intermittent hypoxia-induced immediate early gene activation in rat PC12 cells.
abstract: Intermittent hypoxia (IH) occurs in many pathophysiological conditions. The molecular mechanisms associated with IH, however, have received little attention. Previous studies have reported that the c-fos gene via formation of activator protein-1 (AP-1) transcription factor contributes to adaptive responses to continuous hypoxia. In the present study, using a cell culture model we examined whether IH activates c-fos and AP-1 and if so, by what mechanisms. Experiments were performed on rat phaeochromocytoma cells exposed to 21% O(2) (normoxia) or 60 and 120 cycles of IH, each cycle consisting 15 s of hypoxia followed by 4 min of normoxia. IH resulted in a significant elevation of c-fos mRNA as well as transcriptional activation. IH was more potent and induced a longer lasting activation of c-fos than comparable cumulative duration of continuous hypoxia. IH increased AP-1 activity and tyrosine hydroxylase (TH) mRNA, an AP-1-regulated downstream gene, and these effects were prevented by antisense c-fos. Superoxide dismutase mimetic, a potent scavenger of superoxide anions, prevented IH-induced c-fos, AP-1 and TH activations. IH increased superoxide anion levels in mitochondria as evidenced by decreased aconitase enzyme activity and increased levels of hydrogen peroxide, a stable dismutated product of superoxide anions. Complex I of the mitochondrial electron transport chain was markedly inhibited in IH exposed cells. Pharmacological inhibitors of complex I mimicked the effects of IH during normoxia and occluded the effects of IH on c-fos activation, suggesting the involvement of the mitochondrial electron transport chain in the generation of superoxide anions during IH. These results suggest IH-induced c-fos-mediated transcriptional activation involves oxidative stress.
authors.affiliation: Department of Physiology, Case Western Reserve, University, Cleveland, OH 44106, USA.
authors.forename: Guoxiang
authors.initials: G
authors.lastname: Yuan
authors.forename: Gautam
authors.initials: G
authors.lastname: Adhikary
authors.forename: Andrew A
authors.initials: AA
authors.lastname: McCormick
authors.forename: John J
authors.initials: JJ
authors.lastname: Holcroft
authors.forename: Ganesh K
authors.initials: GK
authors.lastname: Kumar
authors.forename: Nanduri R
authors.initials: NR
authors.lastname: Prabhakar
mesh_terms: D000154:Aconitate Hydratase / Q000378:metabolism; D000818:Animals; D002470:Cell Survival / Q000502:physiology; D042967:Electron Transport Complex I / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D017781:Genes, Immediate-Early / Q000502:physiology*; D016762:Genes, fos / Q000235:genetics; D006861:Hydrogen Peroxide / Q000378:metabolism; D000860:Hypoxia / Q000503:physiopathology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D018384:Oxidative Stress / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D016716:PC12 Cells; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000235:genetics; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D018808:Transcription Factor AP-1; D013481:Superoxides; D006861:Hydrogen Peroxide; D007770:L-Lactate Dehydrogenase; D014446:Tyrosine 3-Monooxygenase; D000154:Aconitate Hydratase; D042967:Electron Transport Complex I