Lectin-like Oxidized LDL Receptor 1 Is Involved in CRP-Mediated Complement Activation

BACKGROUND: C-reactive protein (CRP) is purported to be a risk factor that acts independently of LDL cholesterol in predicting all-cause mortality in patients with ischemic heart disease. Lectin-like oxidized LDL receptor 1 (LOX-1) impairs endothelial function and exacerbates myocardial injury. We recently demonstrated that CRP increased vascular permeability through direct binding to LOX-1. Here we examined, using a hypertensive rat model, whether LOX-1 is involved in CRP-induced complement activation. METHODS AND RESULTS: In the cultured LOX-1-expressing cell line hLOX-1-CHO, CRP increased complement activation, but did not do so in native CHO cells. Depleting C1q from serum abolished CRP-induced complement activation. Incubation of CRP with serum on immobilized recombinant LOX-1 similarly showed that CRP activated C1q-requiring classical complement pathway in a LOX-1-dependent manner. Interestingly, the interaction between CRP and LOX-1 was dependent on Ca(2+) ion and competed with phosphocholine, suggesting that LOX-1 bound to the B-face of CRP with a phosphocholine-binding domain. This was in contrast to Fc gamma receptors, to which CRP bound in A-face with complement-binding domain. In vivo, intradermal injection of CRP to hypertensive SHRSP rats induced complement activation detected by C3d deposition and leukocyte infiltration around the injected area. Anti-LOX-1 antibody reduced the extent of complement activation and leukocyte infiltration. CONCLUSIONS: LOX-1 appears to be involved in CRP-induced complement activation, and thus may serve to locate the site of CRP-induced complement activation and inflammation. (C) 2011 American Association for Clinical Chemistry