Role of the OPG/RANK/RANKL triad in calcifications of the atheromatous plaques: Comparison between carotid and femoral beds

Recent works demonstrated the difference of calcification genesis between carotid and femoral plaques, femoral plaques being more calcified. It has been clearly demonstrated that the molecular triad osteoprotegerin (OPG)/Receptor Activator of NFkB (RANK)/RANK Ligand (RANKL) exerts its activities in the osteoimmunology and vascular system. The aim of this study was to determine their expression and their potential role in calcifications of the atheromatous plaques located in two different peripheral arterial beds, carotid and femoral. The expression of OPG, RANK and RANKL was analyzed by immunochemistry in 40 carotid and femoral samples. Blood OPG and RANKL were quantified using specific ELISA assays. OPG staining was more frequently observed in carotid than in femoral plaques, especially in lipid core. Its expression correlated with macrophage infiltration more abundantly observed in carotid specimens. Surprisingly, serum OPG concentration was significantly lower in carotid population compared to femoral population while RANK and RANKL were equally expressed in both arterial beds. Carotid plaques that are less rich in calcium than femoral specimens, express more frequently OPG, this expression being correlated with the abundance of macrophages in the lesions. These data strengthen the key role played by OPG in the differential calcification in carotid and femoral plaques.