The Dectin 1 Agonist Curdlan Regulates Osteoclastogenesis by Inhibiting Nuclear Factor of Activated T cells Cytoplasmic 1 (NFATc1) through Syk Kinase

Toru Yamasaki,Wataru Ariyoshi,Toshinori Okinaga,Yoshiyuki Adachi,Ryuji Hosokawa,Shinichi Mochizuki,Kazuo Sakurai,Tatsuji Nishihara

doi:10.1074/jbc.m114.551416

Abstract

Several immune system cell surface receptors are reported to be associated with osteoclastogenesis. Dectin 1, a lectin receptor for β-glucan, is found predominantly on cells of the myeloid lineage. In this study, we examined the effect of the dectin 1 agonist curdlan on osteoclastogenesis. In mouse bone marrow cells and dectin 1-overexpressing RAW 264.7 cells (d-RAWs), curdlan suppressed receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation, bone resorption, and actin ring formation in a dose-dependent manner. This was achieved within non-growth inhibitory concentrations at the early stage. Conversely, curdlan had no effect on macrophage colony-stimulating factor-induced differentiation. Furthermore, curdlan inhibited RANKL-induced nuclear factor of activated T cell cytoplasmic 1 (NFATc1) expression, thereby decreasing osteoclastogenesis-related marker gene expression, including tartrate-resistant acid phosphatase, osteoclast stimulatory transmembrane protein, cathepsin K, and matrix metallopeptidase 9. Curdlan inhibited RANKL-induced c-fos expression, followed by suppression of NFATc1 autoamplification, without significantly affecting the NF-κB signaling pathway. We also observed that curdlan treatment decreased Syk protein in d-RAWs. Inhibition of the dectin 1-Syk kinase pathway by Syk-specific siRNA or chemical inhibitors suppressed osteoclast formation and NFATc1 expression stimulated by RANKL. In conclusion, our results demonstrate that curdlan potentially inhibits osteoclast differentiation, especially NFATc1 expression, and that Syk kinase plays a crucial role in the transcriptional pathways. This suggests that the activation of dectin 1-Syk kinase interaction critically regulates the genes required for osteoclastogenesis.

Highlights

Dectin 1 is found on myeloid lineage cells and contains an immunoreceptor tyrosine-based activation motif from which signals are associated with bone homeostasis
Curdlan Inhibits the RANKL-mediated activator protein 1 (AP-1) Signaling Pathway via Dectin-1—To investigate the molecular mechanism by which curdlan inhibits osteoclastogenesis, we evaluated the effect of curdlan on the activation of NF-␬B and AP-1, which is required for induction of NFATc1, by Western blotting
Curdlan Inhibits Osteoclastogenesis via Degradation of Syk Protein—To clarify the role of Syk on osteoclastogenesis, we examined Syk expression in dectin 1-overexpressing RAW 264.7 cells (d-RAWs) incubated with curdlan by immunoblot analysis

Summary

Background

Dectin 1 is found on myeloid lineage cells and contains an immunoreceptor tyrosine-based activation motif from which signals are associated with bone homeostasis. In mouse bone marrow cells and dectin 1-overexpressing RAW 264.7 cells (d-RAWs), curdlan suppressed receptor activator of NF-␬B ligand (RA NKL)-induced osteoclast differentiation, bone resorption, and actin ring formation in a dose-dependent manner. Our results demonstrate that curdlan potentially inhibits osteoclast differentiation, especially NFATc1 expression, and that Syk kinase plays a crucial role in the transcriptional pathways. This suggests that the activation of dectin 1-Syk kinase interaction critically regulates the genes required for osteoclastogenesis. RANKL interacts with the osteoclast cell surface receptor RANK, which, in turn, recruits cytosolic TNF receptor-associated factors [3], prior to activation of downstream signaling pathways. Dectin 1 is known to mediate its own signaling through its cytoplasmic tail [10], and tyrosine residues within its receptor

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EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION