title: Interleukin-6 inhibits receptor activator of nuclear factor kappaB ligand-induced osteoclastogenesis by diverting cells into the macrophage lineage: key role of Serine727 phosphorylation of signal transducer and activator of transcription 3.
abstract: Osteoclasts are bone-resorptive cells that differentiate from hematopoietic precursors upon receptor activator of nuclear factor kappaB ligand (RANKL) activation. Previous studies demonstrated that IL-6 indirectly stimulates osteoclastogenesis through the production of RANKL by osteoblasts. However, few data described the direct effect of IL-6 on osteoclasts. To investigate this effect, we used several models: murine RAW264.7 cells, mouse bone marrow, and human blood monocytes. In the three models used, the addition of IL-6 inhibited RANKL-induced osteoclastogenesis. Furthermore, IL-6 decreased the expression of osteoclast markers and up-modulated macrophage markers. To elucidate this inhibition, signal transducer and activator of transcription (STAT) 3, the main signaling molecule activated by IL-6, was analyzed. Addition of two STAT3 inhibitors completely abolished RANKL-induced osteoclastogenesis, revealing a key role of STAT3. We demonstrated that a basal level of phosphorylated-STAT3 on Serine(727) associated with an absence of phosphorylation on Tyrosine(705) is essential for osteoclastogenesis. Furthermore, a decrease of Serine(727) phosphorylation led to an inhibition of osteoclast differentiation, whereas an increase of Tyrosine(705) phosphorylation upon IL-6 stimulation led to the formation of macrophages instead of osteoclasts. In conclusion, we showed for the first time that IL-6 inhibits RANKL-induced osteoclastogenesis by diverting cells into the macrophage lineage, and demonstrated the functional role of activated-STAT3 and its form of phosphorylation in the control of osteoclastogenesis.
authors.affiliation: EA3822-INSERM 7, ERI 7, and Laboratoire de Physiopathologie de la Résorption Osseuse et Thérapie des Tumeurs Osseuses Primitives, Université de Nantes, 1 rue Gaston Veil, Nantes Cedex 1, France. laurence.duplomb@univ-nantes.fr
authors.forename: Laurence
authors.initials: L
authors.lastname: Duplomb
authors.forename: Marc
authors.initials: M
authors.lastname: Baud'huin
authors.forename: Céline
authors.initials: C
authors.lastname: Charrier
authors.forename: Martine
authors.initials: M
authors.lastname: Berreur
authors.forename: Valérie
authors.initials: V
authors.lastname: Trichet
authors.forename: Frédéric
authors.initials: F
authors.lastname: Blanchard
authors.forename: Dominique
authors.initials: D
authors.lastname: Heymann
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D039481:CD11b Antigen / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D005434:Flow Cytometry; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology*; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D009000:Monocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D053245:RANK Ligand / Q000494:pharmacology*; D053246:Receptor Activator of Nuclear Factor-kappa B / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor / Q000378:metabolism; D012694:Serine / Q000378:metabolism
chemical_list: D039481:CD11b Antigen; D015850:Interleukin-6; D018950:Lipopolysaccharide Receptors; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D050796:STAT3 Transcription Factor; C505687:Tnfrsf11a protein, mouse; D012694:Serine