Received on October 27, 2008
Accepted on November 18, 2008

Lipids, Lipoproteins, and Cardiovascular Risk Factors

Oxidized LDL Receptor LOX-1 Binds to C-reactive Protein and Mediates its Vascular Effects

¹ Department of Vascular Physiology, National Cardiovascular Center Research Institute, Suita, Osaka, Japan
² Laboratory of Immunobiology, Department of Molecular and Applied Biosciences, Graduate School of Biosphere Science, Hiroshima University, Hiroshima, Japan
³ National Food Research Institute, Tsukuba, Japan
⁴ Department of Biomedical and Surgical Sciences, University of Verona, Verona, Italy
⁵ INSERM, U564, University of Angers, Angers, France, and Immunology and Allergology Laboratory, University Hospital of Angers, Angers, France

^* To whom correspondence should be addressed. E-mail: t-sawamura{at}umin.ac.jp.

BACKGROUND: C-reactive protein (CRP) exerts biological activity on vascular endothelial cells. This activity may promote atherothrombosis, but the effects of this activity are still controversial. Lectin-like oxidized LDL receptor-1 (LOX-1), the oxidized LDL receptor on endothelial cells, is involved in endothelial dysfunction induced by oxidized LDL.

METHODS: We used laser confocal microscopy to examine and fluorescence cell image analysis to quantify the binding of fluorescently labeled CRP to cells expressing LOX-1. We then examined the binding of unlabeled CRP to recombinant human LOX-1 in a cell-free system. Small interfering RNAs (siRNAs) against LOX-1 were applied to cultured bovine endothelial cells to analyze the role of LOX-1 in native cells. To observe its in vivo effects, we injected CRP intradermally in stroke-prone spontaneously hypertensive (SHR-SP) rats and analyzed vascular permeability.

RESULTS: CRP bound to LOX-1–expressing cells in parallel with the induction of LOX-1 expression. CRP dose-dependently bound to the cell line and recombinant LOX-1, with significant binding detected at 0.3 mg/L CRP concentration. The K_d value of the binding was calculated to be 1.6 x 10^–7 mol/L. siRNA against LOX-1 significantly inhibited the binding of fluorescently labeled CRP to the endothelial cells, whereas control RNA did not. In vivo, intradermal injection of CRP-induced vascular exudation of Evans blue dye in SHR-SP rats, in which expression of LOX-1 is greatly enhanced. Anti–LOX-1 antibody significantly suppressed vascular permeability.

CONCLUSIONS: CRP and oxidized LDL-receptor LOX-1 directly interact with each other. Two risk factors for ischemic heart diseases, CRP and oxidized LDL, share a common molecule, LOX-1, as their receptor.