Activation of protease-activated receptor-2 leads to inhibition of osteoclast differentiation

J Bone Miner Res. 2004 Mar;19(3):507-16. doi: 10.1359/JBMR.0301248. Epub 2003 Dec 22.

Abstract

PAR-2 is expressed by osteoblasts and activated by proteases present during inflammation. PAR-2 activation inhibited osteoclast differentiation induced by hormones and cytokines in mouse bone marrow cultures and may protect bone from uncontrolled resorption.

Introduction: Protease-activated receptor-2 (PAR-2), which is expressed by osteoblasts, is activated specifically by a small number of proteases, including mast cell tryptase and factor Xa. PAR-2 is also activated by a peptide (RAP) that corresponds to the "tethered ligand" created by cleavage of the receptor's extracellular domain. The effect of activating PAR-2 on osteoclast differentiation was investigated.

Materials and methods: Mouse bone marrow cultures have been used to investigate the effect of PAR-2 activation on osteoclast differentiation induced by parathyroid hormone (PTH), 1,25 dihydroxyvitamin D3 [1,25(OH)2D3], and interleukin-11 (IL-11). Expression of PAR-2 by mouse bone marrow, mouse bone marrow stromal cell-enriched cultures, and the RAW264.7 osteoclastogenic cell line was demonstrated by RT-PCR.

Results: RAP was shown to inhibit osteoclast differentiation induced by PTH, 1,25(OH)2D3, or IL-11. Semiquantitative RT-PCR was used to investigate expression of mediators of osteoclast differentiation induced by PTH, 1,25(OH)2D3, or IL-11 in mouse bone marrow cultures and primary calvarial osteoblast cultures treated simultaneously with RAP. In bone marrow and osteoblast cultures treated with PTH, 1,25(OH)2D3, or IL-11, RAP inhibited expression of RANKL and significantly suppressed the ratio of RANKL:osteoprotegerin expression. Activation of PAR-2 led to reduced expression of prostaglandin G/H synthase-2 in bone marrow cultures treated with PTH, 1,25(OH)2D3, or IL-11. RAP inhibited PTH- or 1,25(OH)2D3-induced expression of IL-6 in bone marrow cultures. RAP had no effect on osteoclast differentiation in RANKL-treated RAW264.7 cells.

Conclusion: These observations indicate that PAR-2 activation inhibits osteoclast differentiation by acting on cells of the osteoblast lineage to modulate multiple mediators of the effects of PTH, 1,25(OH)2D3, and IL-11. Therefore, the role of PAR-2 in bone may be to protect it from uncontrolled resorption by limiting levels of osteoclast differentiation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bone Marrow Cells / cytology
  • Carrier Proteins / metabolism
  • Cell Differentiation / drug effects
  • Cell Line
  • Cells, Cultured
  • Cyclooxygenase 1
  • Cyclooxygenase 2
  • Interleukin-6 / metabolism
  • Isoenzymes / metabolism
  • Macrophages / cytology
  • Macrophages / metabolism
  • Membrane Glycoproteins / metabolism
  • Membrane Proteins
  • Mice
  • Osteoblasts / cytology
  • Osteoclasts / cytology
  • Osteoclasts / metabolism*
  • Prostaglandin-Endoperoxide Synthases / metabolism
  • RANK Ligand
  • Receptor Activator of Nuclear Factor-kappa B
  • Receptor, PAR-2 / metabolism*

Substances

  • Carrier Proteins
  • Interleukin-6
  • Isoenzymes
  • Membrane Glycoproteins
  • Membrane Proteins
  • RANK Ligand
  • Receptor Activator of Nuclear Factor-kappa B
  • Receptor, PAR-2
  • Tnfrsf11a protein, mouse
  • Tnfsf11 protein, mouse
  • Cyclooxygenase 1
  • Cyclooxygenase 2
  • Prostaglandin-Endoperoxide Synthases
  • Ptgs1 protein, mouse