Absence of the G Protein‐Coupled Receptor, G2A, Promotes Monocyte:Endothelial Interactions In Vivo

Abstract

Background: The G protein-coupled receptor G2A is highly expressed on macrophages and lymphocytes with lower expression on endothelium. G2A has been localized to atherosclerotic plaques. We examined the role of G2A in modulating monocyte:endothelial interactions in the vessel wall. Methods and Results: We examined adhesion of WEHI 78/24 monocytes to aorta of C57BL/6 (B6) and G2A-deficient (G2A−/−) mice using an ex vivo adhesion assay. G2A−/− mice had 10-fold elevations in adhesion of monocytes to aorta. Injection of GFP-expressing wild-type macrophages into B6 and G2A−/− mice in vivo showed increased macrophage accumulation in the aortic wall of G2A−/− mice. We isolated aortic endothelial cells (EC) from B6 and G2A−/− mice, and found a 2-fold increase in ICAM-1 and E-selectin surface expression on G2A−/− EC using flow cytometry. Using ELISA, we found a 3-fold increase in IL-6 and MCP-1 production by G2A−/− EC compared to B6 EC. We found a dramatic increase in nuclear localization of the p65 subunit of NFκB demonstrating increased NFκB activation in G2A−/− EC. Transfection of G2A into G2A−/− EC to restore normal expression levels reduced p65 nuclear localization to 35%. Restoration of G2A expression in G2A−/− EC significantly reduced ICAM-1 and E-selectin surface expression and reduced MCP-1 and IL-6 production. Restoring G2A to G2A−/− EC reduced monocyte adhesion by 80% compared to G2A−/− EC in a flow chamber assay. Conclusions: Absence of G2A in endothelium results in pro-inflammatory signaling and increased monocyte:endothelial interactions in the aortic wall. Thus, endothelial G2A expression may aid in prevention of vascular inflammation and atherosclerosis.