Abstract
The mechanisms involved in the cytotoxic action of oxysterols in the pathogenesis of atherosclerosis still remain poorly understood. Among the major oxysterols present in oxidized low-density lipoprotein, we show here that 7-ketocholesterol (7-Kchol) induces oxidative stress and/or apoptotic events in human aortic smooth muscle cells (SMCs). This specific effect of 7-Kchol is mediated by a robust upregulation (threefold from the basal level) of Nox-4, a reactive oxygen species (ROS)-generating NAD(P)H oxidase homologue. This effect was highlighted by silencing Nox-4 expression with a specific small interfering RNA, which significantly reduced the 7-Kchol-induced production of ROS and abolished apoptotic events. Furthermore, the 7-Kchol activating pathway included an early triggering of endoplasmic reticulum stress, as assessed by transient intracellular Ca(2+) oscillations, and the induction of the expression of the cell death effector CHOP and of GRP78/Bip chaperone via the activation of IRE-1, all hallmarks of the unfolded protein response (UPR). We also showed that 7-Kchol activated the IRE-1/Jun-NH(2)-terminal kinase (JNK)/AP-1 signaling pathway to promote Nox-4 expression. Silencing of IRE-1 and JNK inhibition downregulated Nox-4 expression and subsequently prevented the UPR-dependent cell death induced by 7-Kchol. These findings demonstrate that Nox-4 plays a key role in 7-Kchol-induced SMC death, which is consistent with the hypothesis that Nox-4/oxysterols are involved in the pathogenesis of atherosclerosis.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Aorta / cytology
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Apoptosis / drug effects*
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CCAAT-Enhancer-Binding Proteins / metabolism
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Calcium / analysis
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Calcium / metabolism
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Cells, Cultured
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Endoplasmic Reticulum / physiology*
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Endoplasmic Reticulum Chaperone BiP
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Endothelium, Vascular / cytology
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Fluorescent Antibody Technique, Indirect
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Gene Expression Regulation, Enzymologic*
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Genes, Reporter
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Heat-Shock Proteins / metabolism
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Humans
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Iron Regulatory Protein 1 / metabolism
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JNK Mitogen-Activated Protein Kinases / metabolism
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Ketocholesterols / metabolism
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Ketocholesterols / pharmacology*
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Kinetics
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Luciferases / metabolism
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Microscopy, Fluorescence
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Molecular Chaperones / metabolism
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Molecular Sequence Data
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Muscle, Smooth / drug effects*
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NADPH Oxidase 4
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NADPH Oxidases / metabolism*
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Oxidative Stress
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Protein Denaturation
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RNA, Messenger / metabolism
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RNA, Small Interfering / metabolism
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Reactive Oxygen Species / analysis
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Reactive Oxygen Species / metabolism
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Signal Transduction
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Transcription Factor CHOP
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Transcription Factors / metabolism
Substances
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CCAAT-Enhancer-Binding Proteins
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DDIT3 protein, human
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Endoplasmic Reticulum Chaperone BiP
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HSPA5 protein, human
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Heat-Shock Proteins
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Ketocholesterols
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Molecular Chaperones
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RNA, Messenger
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RNA, Small Interfering
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Reactive Oxygen Species
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Transcription Factors
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Transcription Factor CHOP
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Luciferases
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NADPH Oxidase 4
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NADPH Oxidases
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NOX4 protein, human
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JNK Mitogen-Activated Protein Kinases
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Iron Regulatory Protein 1
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Calcium
Associated data
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GENBANK/AF254621
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GENBANK/AF317889
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GENBANK/AJ438989