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

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Abstract

Aim:

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.

Main 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.

Key findings:

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.

Significance:

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.

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