title: 7-Ketocholesterol induces autophagy in vascular smooth muscle cells through Nox4 and Atg4B.
abstract: Oxidized lipoproteins stimulate autophagy in advanced atherosclerotic plaques. However, the mechanisms underlying autophagy induction and the role of autophagy in atherogenesis remain to be determined. This study was designed to investigate the mechanisms by which 7-ketocholesterol (7-KC), a major component of oxidized lipoproteins, induces autophagy. This study was also designed to determine the effect of autophagy induction on apoptosis, a central event in the development of atherosclerosis. Exposure of human aortic smooth muscle cells to 7-KC increased autophagic flux. Autophagy induction was suppressed by treating the cells with either a reactive oxygen species scavenger or an antioxidant. Administration of 7-KC concomitantly up-regulated Nox4 expression, increased intracellular hydrogen peroxide levels, and inhibited autophagy-related gene 4B activity. Catalase overexpression to remove hydrogen peroxide or Nox4 knockdown with siRNA reduced intracellular hydrogen peroxide levels, restored autophagy-related gene 4B activity, and consequently attenuated 7-KC-induced autophagy. Moreover, inhibition of autophagy aggravated both endoplasmic reticulum (ER) stress and cell death in response to 7-KC. In contrast, up-regulation of autophagic activity by rapamycin had opposite effects. Finally, activation of autophagy by chronic rapamycin treatment attenuated ER stress, apoptosis, and atherosclerosis in apolipoprotein E knockout (ApoE(-/-)) mouse aortas. In conclusion, we demonstrate that up-regulation of autophagy is a cellular protective response that attenuates 7-KC-induced cell death in human aortic smooth muscle cells.
authors.affiliation: Section of Molecular Medicine, Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
authors.forename: Chaoyong
authors.initials: C
authors.lastname: He
authors.forename: Huaiping
authors.initials: H
authors.lastname: Zhu
authors.forename: Wencheng
authors.initials: W
authors.lastname: Zhang
authors.forename: Imoh
authors.initials: I
authors.lastname: Okon
authors.forename: Qilong
authors.initials: Q
authors.lastname: Wang
authors.forename: Hongliang
authors.initials: H
authors.lastname: Li
authors.forename: Yun-Zheng
authors.initials: YZ
authors.lastname: Le
authors.forename: Zhonglin
authors.initials: Z
authors.lastname: Xie
mesh_terms: D000818:Animals; D001011:Aorta; D017209:Apoptosis; D050197:Atherosclerosis / Q000517:prevention & control; D001343:Autophagy / Q000187:drug effects*; D000071183:Autophagy-Related Proteins; D002317:Cardiovascular Agents / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D007653:Ketocholesterols / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D000071183:Autophagy-Related Proteins; D002317:Cardiovascular Agents; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D007653:Ketocholesterols; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C498910:NOX4 protein, human; C422943:Nox4 protein, mouse; C507524:ATG4B protein, human; C582881:Atg4b protein, mouse; D003546:Cysteine Endopeptidases; C003001:7-ketocholesterol; D020123:Sirolimus