title: Osteoprotegerin (OPG) is localized to the Weibel-Palade bodies of human vascular endothelial cells and is physically associated with von Willebrand factor.
abstract: Recent studies demonstrate roles for osteoprotegerin (OPG) in both skeletal and extra-skeletal tissues. Although its role in preventing osteoclast (OC) formation and activity is well documented, emerging evidence suggests a role of OPG in endothelial cell survival and the prevention of arterial calcification. In this communication, we show that vascular endothelial cells in situ, and human umbilical vein endothelial cells (HUVEC) in vitro, express abundant OPG. In HUVEC, OPG co-localizes with P-selectin and von Willebrand factor (vWF), within the Weibel-Palade bodies (WPB). Treatment of HUVEC with the pro-inflammatory cytokines, tumor necrosis factor (TNF)-alpha and IL-1beta, resulted in mobilization from the WPBs and subsequent secretion of OPG protein into the culture supernatant. Furthermore, TNF-alpha treatment of HUVEC resulted in a sustained increase in OPG mRNA levels and protein secretion over the 24-h treatment period. Reciprocal immunoprecipitation experiments revealed that while not associated with P-Selectin, OPG is physically complexed with vWF both within the WPB and following secretion from endothelial cells. Interestingly, this association was also identified in human peripheral blood plasma. In addition to its interaction with vWF, we show that OPG also binds with high avidity to the vWF reductase, thrombospondin (TSP-1), raising the intriguing possibility that OPG may provide a link between TSP-1 and vWF. In summary, the intracellular localization of OPG in HUVEC, in association with vWF, together with its rapid and sustained secretory response to inflammatory stimuli, strongly support a modulatory role in vascular injury, inflammation and hemostasis.
authors.affiliation: Myeloma and Mesenchymal Research Laboratory, Division of Haematology, Institute of Medical and Veterinary Science, and Hanson Institute, Adelaide, South Australia, Australia. andrew.zannettino@imvs.sa.gov.au
authors.forename: A C W
authors.initials: AC
authors.lastname: Zannettino
authors.forename: C A
authors.initials: CA
authors.lastname: Holding
authors.forename: P
authors.initials: P
authors.lastname: Diamond
authors.forename: G J
authors.initials: GJ
authors.lastname: Atkins
authors.forename: P
authors.initials: P
authors.lastname: Kostakis
authors.forename: A
authors.initials: A
authors.lastname: Farrugia
authors.forename: J
authors.initials: J
authors.lastname: Gamble
authors.forename: L B
authors.initials: LB
authors.lastname: To
authors.forename: D M
authors.initials: DM
authors.lastname: Findlay
authors.forename: D R
authors.initials: DR
authors.lastname: Haynes
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D006023:Glycoproteins / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger / Q000378:metabolism; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D019700:Thrombospondin 1 / Q000378:metabolism; D013997:Time Factors; D014018:Tissue Distribution; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D020302:Weibel-Palade Bodies / Q000378:metabolism*; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; C505686:TNFRSF11A protein, human; C506030:TNFRSF11B protein, human; C505688:TNFSF11 protein, human; D019700:Thrombospondin 1; D014409:Tumor Necrosis Factor-alpha; D014841:von Willebrand Factor