title: Bradykinin potentiates cytokine-induced prostaglandin biosynthesis in osteoblasts by enhanced expression of cyclooxygenase 2, resulting in increased RANKL expression.
abstract: OBJECTIVE
  Bradykinin (BK) stimulates bone resorption in vitro and synergistically potentiates interleukin-1 (IL-1)-induced bone resorption and prostaglandin (PG) formation, suggesting that kinins are important in inflammation-induced bone loss. The present study was undertaken to study 1) the role of the kinin B1 and B2 receptors in the synergistic interaction with IL-1 and tumor necrosis factor alpha (TNFalpha), 2) the molecular mechanisms involved in synergistic enhancement of PG formation, and 3) the effects of kinins on cytokine-induced expression of RANKL, RANK, and osteoprotegerin (OPG) (the latter being crucial molecules in osteoclast differentiation).
  
  
  METHODS
  Formation of PGs, expression of enzymes involved in arachidonic acid metabolism, and expression of RANKL, RANK, and OPG were assessed in the human osteoblastic cell line MG-63 and in mouse calvarial bones. The role of NF-kappaB and MAP kinases was studied using pharmacologic inhibitors.
  
  
  RESULTS
  PGE(2) formation and cyclooxygenase 2 (COX-2) protein expression were induced by IL-1beta and potentiated by kinins with affinity for the B1 or B2 receptors, resulting in PGE(2)-dependent enhancement of RANKL. The enhancements of PGE(2) formation and COX-2 were markedly decreased by inhibition of p38 and JNK MAP kinases, whereas inhibition of NF-kappaB resulted in abolishment of the PGE(2) response with only slight inhibition of COX-2.
  
  
  CONCLUSIONS
  Kinin B1 and B2 receptors synergistically potentiate IL-1- and TNFalpha-induced PG biosynthesis in osteoblasts by a mechanism involving increased levels of COX-2, resulting in increased RANKL. The synergistic stimulation is dependent on NF-kappaB and MAP kinases. These mechanisms might help to explain the enhanced bone resorption associated with inflammatory disorders, including that in rheumatoid arthritis.
authors.affiliation: Umeå University, Umeå, Sweden.
authors.forename: Anna Bernhold
authors.initials: AB
authors.lastname: Brechter
authors.forename: Ulf H
authors.initials: UH
authors.lastname: Lerner
mesh_terms: D000818:Animals; D001920:Bradykinin / Q000502:physiology*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism*; D016207:Cytokines / Q000502:physiology; D015232:Dinoprostone / Q000096:biosynthesis*; D006801:Humans; D053583:Interleukin-1beta / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D020929:Mitogen-Activated Protein Kinase Kinases / Q000502:physiology; D016328:NF-kappa B / Q000502:physiology; D010006:Osteoblasts / Q000378:metabolism*; D053244:Osteoprotegerin / Q000235:genetics / Q000378:metabolism; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D053246:Receptor Activator of Nuclear Factor-kappa B / Q000235:genetics / Q000378:metabolism; D043783:Receptor, Bradykinin B1 / Q000502:physiology*; D043782:Receptor, Bradykinin B2 / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology
chemical_list: D016207:Cytokines; D053583:Interleukin-1beta; D016328:NF-kappa B; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D043783:Receptor, Bradykinin B1; D043782:Receptor, Bradykinin B2; D014409:Tumor Necrosis Factor-alpha; D051546:Cyclooxygenase 2; D020929:Mitogen-Activated Protein Kinase Kinases; D015232:Dinoprostone; D001920:Bradykinin