V ascular calcification is highly correlated with cardiovascular mortality and associated with hypertension.1 Intima arterial calcification occurs in conjunction with atherosclerosis, and media calcification is usually present with systemic mineral imbalance caused by chronic renal disease. Although both types are pathologically distinct, there is an association between the molecular mechanism regulating vascular calcification in intima and media. We and others have described the involvement of receptor activator of nuclear factor κB ligand (RANKL) system with bone morphogenetic protein (BMP)-2 and BMP-4 axis in the development of intima and media calcification, respectively.
2,3RANKL system consists of a triad of proteins: the membrane-bound RANK, its ligand RANKL, and the decoy receptor osteoprotegerin (OPG). This system occurs in immune system, 4,5 mammary glands development, 6 and has been studied extensively in bone metabolism, where osteoblasts express RANKL and OPG, which regulate osteoclast differentiation via RANK activation. 7,8 The first insight about the importance of this system in vasculature came from studies in OPG −/− mice that show early onset of osteoporosis and severe media calcification. 9 The unopposed RANKL signaling present in OPG −/− mice was then related to the development of vascular calcification. Recently, we have described that RANKL plays an important role in aortic calcification under estrogen deficiency by acting on 2 important molecules of the calcification process: the inducer of calcification, BMP-2, and the inhibitor, matrix Gla protein. Objective-Vascular calcification is accelerated by hypertension and also contributes to hypertension; however, it is an enigma why hypertension and vascular calcification are a vicious spiral. The present study elucidates the cross-talk between renin-angiotensin II system and receptor activator of nuclear factor-κB ligand (RANKL) system in vascular calcification. Approach and Results-Angiotensin (Ang) II (10 −7 mol/L) significantly increased calcium deposition as assessed by Alizarin Red staining, associated with a significant increase in the expression of RANKL, RANK, and bone-related genes, such as cbfa1 and msx2, in human aortic vascular smooth muscle cells. Infusion of Ang II (100 ng/kg per minute) in ovariectomized ApoE −/− mice under high-fat diet significantly increased the expression of RANKL system and calcification in vivo, whereas administration of Ang II receptor blocker (olmesartan, 3 mg/kg per day) decreased the calcification and bone markers' expression. In addition, male OPG −/− mice showed a significant increase in vascular calcification followed by Ang II infusion as compared with wild type. Conversely, RANKL significantly increased Ang II type 1 receptor and angiotensin II-converting enzyme expression in vascular smooth muscle cells via extracellular signal-regulated protein kinase phosphorylation.Conclusions-The present study demonstrated that Ang II significantly induced vascular calcification in vitro and in vivo through...