The lipid moiety 7-ketocholesteryl-9-carboxynonanoate mediates binding interaction of oxLDL to LOX-1 and upregulates ABCA1 expression through PPARγ

• Published in: Life sciences (1973) Vol. 177; pp. 27 - 40
• Main Authors: Li, Jingda, Xiu, Zhilong, Wang, Renjun, Yu, Chengjie, Chi, Yan, Qin, Jianzhong, Fu, Changzhen, Matsuura, Eiji, Liu, Qingping
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 15.05.2017
• Subjects: 7-Ketocholesteryl-9-carboxynonanoate; ABCA1; Animals; ATP Binding Cassette Transporter 1 - genetics; Blotting, Western; Cell Line; Cholesterol Esters - metabolism; Enzyme-Linked Immunosorbent Assay; Epitopes; Humans; Lipoproteins, LDL - metabolism; LOX-1; Mice; Molecular Docking Simulation; Oxidized low-density lipoprotein; PPAR gamma - metabolism; PPARγ; Scavenger Receptors, Class E - metabolism; Signal Transduction; Up-Regulation; ABCA1; 7-Ketocholesteryl-9-carboxynonanoate; Oxidized low-density lipoprotein; LOX-1; PPARγ
• ISSN: 0024-3205; 1879-0631
• DOI: 10.1016/j.lfs.2017.03.024

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. 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. 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. 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.