Secreted frizzled-related protein-1 inhibits RANKL-dependent osteoclast formation

Karl D Häusler, Nicole J Horwood, Yoshiro Chuman, Jane L Fisher, Jennifer Ellis, T John Martin, Jeffrey S Rubin, Matthew T Gillespie

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112 Citations (Scopus)

Abstract

UNLABELLED: We determined that sFRP-1 mRNA was differentially expressed by osteoblast/stromal cell lines and that sFRP-1 neutralizing antibodies and siRNA complementary to sFRP-1 coding sequence enhanced, while recombinant sFRP-1 inhibited, osteoclast formation. In studying the mechanism of action for sFRP-1, we found that sFRP-1 could bind recombinant RANKL. These results suggest potential cross-talk between Wnt and RANKL pathways.

INTRODUCTION: Osteoclast formation in normal bone remodeling requires the presence of osteoblast lineage cells that express RANKL and macrophage-colony-stimulating factor (M-CSF), which interact with their cognate receptors on the osteoclast precursor. We identified secreted Frizzled-related protein-1 (sFRP-1), which is known to bind to Wnt and inhibit the Wnt signaling pathway, as an osteoblast-derived factor that impinges on osteoclast formation and activity.

MATERIALS AND METHODS: Differential display of mRNA from osteoblast lineage cell lines established sFRP-1 to be highly expressed in an osteoclast supporting cell line. sFRP-1 expression in bone was determined by in situ hybridization, and the effects of sFRP-1 on osteoclast formation were determined using a neutralizing antibody, siRNA, for sFRP-1 and recombinant protein.

RESULTS: In situ hybridization revealed sFRP-1 mRNA expression in osteoblasts and chondrocytes in murine bone. sFRP-1 mRNA expression could be elevated in calvarial primary osteoblasts in response to prostaglandin E2 (PGE2) or interleukin (IL)-11, whereas many other osteotropic agents (e.g., IL-1, IL-6, calcitrol, parathyroid hormone) were without any effect. In vitro assays of osteoclast formation established sFRP-1 to be an inhibitor of osteoclast formation. Neutralizing antibodies against sFRP-1 enhanced TRACP+ mononuclear and multinuclear osteoclast formation (3- and 2-fold, respectively) in co-cultures of murine osteoblasts with spleen cells, whereas siRNA complementary to sFRP-1 coding sequence significantly enhanced osteoclast formation in co-cultures of KUSA O (osteoblast/stromal cell line) and bone marrow cells, cultured in the presence of PGE2 and 1,25(OH)2 vitamin D3. Recombinant sFRP-1 dose-dependently inhibited osteoclast formation in osteoblast/spleen co-cultures, RANKL + M-CSF-treated splenic cultures, and RANKL-treated RAW264.7 cell cultures, indicating a direct action of sFRP-1 on hematopoietic cells. Consistent with this, sFRP-1 was found to bind to RANKL in ELISAs.

CONCLUSION: sFRP-1 is expressed by osteoblasts and inhibits osteoclast formation. While sFRP-1 activity might involve the blocking of endogenous Wnt signaling, our results suggest that, alternatively, it could be because of direct binding to RANKL. This study describes a new mechanism whereby osteoblasts regulate osteoclastogenesis through the expression and release of sFRP-1.

Original languageEnglish
Pages (from-to)1873-1881
Number of pages9
JournalJournal of Bone and Mineral Research
Volume19
Issue number11
Early online date16 Aug 2004
DOIs
Publication statusPublished - Nov 2004

Keywords

  • Animals
  • Bone Marrow Cells/metabolism
  • Bone and Bones/metabolism
  • Calcitriol/metabolism
  • Carrier Proteins/antagonists & inhibitors
  • Cell Line
  • Chondrocytes/metabolism
  • Dose-Response Relationship, Drug
  • Enzyme-Linked Immunosorbent Assay
  • Escherichia coli/metabolism
  • Gene Expression Profiling
  • Gene Expression Regulation
  • Glutathione Transferase/metabolism
  • In Situ Hybridization
  • Intercellular Signaling Peptides and Proteins/metabolism
  • Interleukin-11/metabolism
  • Interleukin-6/metabolism
  • Macrophage Colony-Stimulating Factor/metabolism
  • Male
  • Membrane Glycoproteins/antagonists & inhibitors
  • Membrane Proteins/metabolism
  • Mice
  • Mice, Inbred C57BL
  • Osteoblasts/metabolism
  • Osteoclasts/metabolism
  • Parathyroid Hormone/metabolism
  • Polymerase Chain Reaction
  • RANK Ligand
  • RNA, Messenger/metabolism
  • RNA, Small Interfering/metabolism
  • Receptor Activator of Nuclear Factor-kappa B
  • Recombinant Fusion Proteins/metabolism
  • Recombinant Proteins/chemistry
  • Signal Transduction
  • Wnt Proteins

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