title: TRPV-5 mediates a receptor activator of NF-kappaB (RANK) ligand-induced increase in cytosolic Ca2+ in human osteoclasts and down-regulates bone resorption.
abstract: Most of the signaling effectors located downstream of receptor activator of NF-kappaB (RANK) activation are calcium-sensitive. However, the early signaling events that lead to the mobilization of intracellular calcium in human osteoclasts are still poorly understood. The Ca(2+)-sensitive fluorescent probe Fura2 was used to detect changes in the intracellular concentration of Ca(2+) ([Ca(2+)](i)) in a model of human osteoclasts. Stimulating these cells with receptor activator of NF-kappaB ligand (RANKL) induced a rapid and significant increase in [Ca(2+)](i). Adding extracellular Ca(2+) chelators, depleting intracellular stores, and the use of a phospholipase C inhibitor all indicated that the Ca(2+) was of extracellular origin, suggesting the involvement of a Ca(2+) channel. We showed that none of the classical Ca(2+) channels (L-, T-, or R-type) were involved in the RANKL-induced Ca(2+) spike. However, the effect of high doses of Gd(3+) did suggest that TRP family channels were present in human osteoclasts. The TRPV-5 channel was expressed in osteoclasts and was mainly located in the cellular area in contact with the bone surface. Furthermore, the RNA inactivation of TRPV-5 channel completely inhibited the RANKL-induced increase in [Ca(2+)](i), which was accompanied in the long term by marked activation of bone resorption. Overall, our results show that RANKL induced a significant increase in [Ca(2+)](i) of extracellular origin, probably as a result of the opening of TRPV-5 calcium channels on the surface of human osteoclasts. Our findings suggest that TRPV-5 contributes to maintaining the homeostasis of the human skeleton via a negative feedback loop in RANKL-induced bone resorption.
authors.affiliation: Division of Rheumatology, Faculty of Medicine, University of Sherbrooke,Sherbrooke, Quebec, Canada.
authors.forename: Estelle
authors.initials: E
authors.lastname: Chamoux
authors.forename: Martine
authors.initials: M
authors.lastname: Bisson
authors.forename: Marcel Daniel
authors.initials: MD
authors.lastname: Payet
authors.forename: Sophie
authors.initials: S
authors.lastname: Roux
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001862:Bone Resorption / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D018613:Microscopy, Confocal; D010010:Osteoclasts / Q000187:drug effects* / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D053245:RANK Ligand / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: D053245:RANK Ligand; D050916:TRPV Cation Channels; C492239:TRPV5 protein, human; D002118:Calcium