title: The lipid moiety 7-ketocholesteryl-9-carboxynonanoate mediates binding interaction of oxLDL to LOX-1 and upregulates ABCA1 expression through PPARγ.
abstract: OBJECTIVE
  Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), a specific membrane receptor for oxidized low-density lipoprotein (oxLDL), plays a crucial role in atherosclerosis progression. The aim of this study was to elucidate the role of 7-ketocholesteryl-9-carboxynonanoate (oxLig-1), a lipid component of oxLDL, in the binding of oxLDL to LOX-1 and to determine whether oxLig-1 binding to LOX-1 is involved in the upregulation of ABCA1 expression.
  
  
  METHODS
  OxLig-1 binding to LOX-1 was analysed by AutoDock 4.2.6 and confirmed by fluorescence immunocytochemistry and enzyme-linked immunosorbent assays (ELISAs). LOX-1, LXRα and ABCA1 protein expression induced by oxLig-1 or methylated oxLig-1 was measured by western blotting. In addition, PPARγ activation was investigated using a dual-luciferase reporter system. Furthermore, the signalling cascade involved in oxLig-1-induced ABCA1 expression was assessed using inhibitors for PPARγ and LXRα and specific siRNAs against LOX-1, PPARγ and LXRα.
  
  
  RESULTS
  Docking, fluorescence immunocytochemistry and ELISA analyses showed that oxLig-1 bound LOX-1 and that the ω-carboxyl group was critical for this binding. Moreover, oxLig-1, but not methylated oxLig-1, increased LOX-1, LXRα, and ABCA1 expression. Luciferase reporter assays indicated that oxLig-1 activated PPARγ in the presence of LOX-1. Additionally, the inhibitor and siRNA experiments showed that oxLig-1 triggered the PPARγ-LXRα signalling pathway, leading to upregulation of ABCA1, and that this process required the participation of LOX-1.
  
  
  CONCLUSIONS
  Our observations indicate that oxLig-1 is a critical epitope of oxLDL that mediates the binding of oxLDL to LOX-1 and initiates PPARγ signal transduction to upregulate the expression of ABCA1.
authors.affiliation: School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116024, Liaoning, China.
authors.forename: Jingda
authors.initials: J
authors.lastname: Li
authors.affiliation: School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116024, Liaoning, China.
authors.forename: Zhilong
authors.initials: Z
authors.lastname: Xiu
authors.affiliation: Key Laboratory of Carbohydrate and Lipid Metabolism Research, College of Life Science and Technology, Dalian University, 10-Xuefu Avenue, Dalian Economical and Technological Development Zone, Liaoning 116622, China.
authors.forename: Renjun
authors.initials: R
authors.lastname: Wang
authors.affiliation: Key Laboratory of Carbohydrate and Lipid Metabolism Research, College of Life Science and Technology, Dalian University, 10-Xuefu Avenue, Dalian Economical and Technological Development Zone, Liaoning 116622, China.
authors.forename: Chengjie
authors.initials: C
authors.lastname: Yu
authors.affiliation: Key Laboratory of Carbohydrate and Lipid Metabolism Research, College of Life Science and Technology, Dalian University, 10-Xuefu Avenue, Dalian Economical and Technological Development Zone, Liaoning 116622, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Chi
authors.affiliation: Key Laboratory of Carbohydrate and Lipid Metabolism Research, College of Life Science and Technology, Dalian University, 10-Xuefu Avenue, Dalian Economical and Technological Development Zone, Liaoning 116622, China.
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Qin
authors.affiliation: Key Laboratory of Carbohydrate and Lipid Metabolism Research, College of Life Science and Technology, Dalian University, 10-Xuefu Avenue, Dalian Economical and Technological Development Zone, Liaoning 116622, China.
authors.forename: Changzhen
authors.initials: C
authors.lastname: Fu
authors.affiliation: Collaborative Research Centre, Department of Cell Chemistry, Okayama University, Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Okayama 700-8558, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Matsuura
authors.affiliation: Key Laboratory of Carbohydrate and Lipid Metabolism Research, College of Life Science and Technology, Dalian University, 10-Xuefu Avenue, Dalian Economical and Technological Development Zone, Liaoning 116622, China. Electronic address: qingpingliu40@126.com.
authors.forename: Qingping
authors.initials: Q
authors.lastname: Liu
mesh_terms: D064286:ATP Binding Cassette Transporter 1 / Q000235:genetics*; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002788:Cholesterol Esters / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism*; D051379:Mice; D062105:Molecular Docking Simulation; D047495:PPAR gamma / Q000378:metabolism*; D051127:Scavenger Receptors, Class E / Q000378:metabolism*; D015398:Signal Transduction; D015854:Up-Regulation
chemical_list: C510905:7-ketocholesteryl-9-carboxynonanoate; D064286:ATP Binding Cassette Transporter 1; D002788:Cholesterol Esters; D000939:Epitopes; D008077:Lipoproteins, LDL; C495137:OLR1 protein, human; D047495:PPAR gamma; D051127:Scavenger Receptors, Class E; C099252:oxidized low density lipoprotein
keywords: 7-Ketocholesteryl-9-carboxynonanoate; ABCA1; LOX-1; Oxidized low-density lipoprotein; PPARγ