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(Circulation Research. 2009;104:1041.)
© 2009 American Heart Association, Inc.

Molecular Medicine

RANKL Increases Vascular Smooth Muscle Cell Calcification Through a RANK-BMP4–Dependent Pathway

Sara Panizo, Anna Cardus, Mario Encinas, Eva Parisi, Petya Valcheva, Susana López-Ongil, Blai Coll, Elvira Fernandez^*, Jose M. Valdivielso^*

From the Department of Medicine (S.P., A.C., E.P., P.V.), University of Lleida; Research Laboratory (S.P., A.C., M.E., E.P., P.V., J.M.V.), Hospital Universitari Arnau de Vilanova; Research Unit and Nephrology Section (S.L.-O.), Hospital Universitario Príncipe de Asturias, Alcala de Henares, Madrid; and Unitat de Diagnòstic i Tractament de Malaties Aterotrombòtiques (UDETMA) (B.C., E.F., J.M.V.), Nephrology Department, Hospital Universitari Arnau de Vilanova, Institut de Recerca Biomèdica de Lleida (IRBLLEIDA), Spain.

Correspondence to Dr Jose M. Valdivielso, Laboratorio de Investigación HUAV-UDL, Hospital Universitari Arnau de Vilanova, Rovira Roure 80, 25198 Lleida, Spain. E-mail Valdivielso{at}medicina.udl.es

Vascular calcification commonly associated with several pathologies and it has been suggested to be similar to bone mineralization. The axis RANKL-OPG (receptor activator of nuclear factor B ligand–osteoprotegerin) finely controls bone turnover. RANKL has been suggested to increase vascular calcification, but direct evidence is missing. Thus, in the present work, we assess the effect of RANKL in vascular smooth muscle cell (VSMC) calcification. VSMCs incubated with RANKL showed a dose-dependent increase in calcification, which was abolished by coincubation with OPG. To test whether the effect was mediated by signaling to its receptor, knockdown of RANK was accomplished by short hairpin (sh)RNA. Indeed, cells lacking RANK showed no increases in vascular calcification when incubated with RANKL. To further elucidate the mechanism by which RANK activation increases calcification, we blocked both nuclear factor (NF)-B activation pathways. Only IKK inactivation inhibited calcification, pointing to an involvement of the alternative NF-B activation pathway. Furthermore, RANKL addition increased bone morphogenetic protein (BMP)4 expression in VSMCs, and that increase disappeared in cells lacking RANK or IKK. The increase in calcification was also blunted by Noggin, pointing to a mediation of BMP4 in the calcification induced by RANKL. Furthermore, in an in vivo model, the increase in vascular calcium content was parallel to an increase in RANKL and BMP4 expression, which was localized in calcified areas. However, blood levels of the ratio RANKL/OPG did not change. We conclude that RANKL increases vascular smooth muscle cell calcification by binding to RANK and increasing BMP4 production through activation of the alternative NF-B pathway.

Key Words: vascular calcification • RANKL • BMP4 • NF-B

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