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Eur J Immunol. 2008 Jun;38(6):1598-609. doi: 10.1002/eji.200737650.

The 4-1BB ligand and 4-1BB expressed on osteoclast precursors enhance RANKL-induced osteoclastogenesis via bi-directional signaling.

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1
Department of Oromaxillofacial Infection and Immunity, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Korea.

Abstract

The 4-1BB is a costimulatory molecule similar to the receptor activator of NF-kappaB ligand (RANKL), both of which are key factors for the differentiation of osteoclasts and are expressed mainly by activated T cells. The 4-1BB shares common signaling pathways with RANK, suggesting a potential role in osteoclastogenesis. In this study, the role of 4-1BB and 4-1BB ligand (4-1BBL) in osteoclastogenesis was investigated using 4-1BB(-/-) and 4-1BB(+/+) mice. Osteoclast precursors normally express 4-1BB and 4-1BBL after exposure to RANKL, which was confirmed by semi-quantitative RT-PCR and flow cytometry. The 4-1BB(-/- )mice had a slightly increased bone mass accompanied by a reduced osteoclastogenic ability of 4-1BB(-/-) bone marrow-derived macrophages (BMM) ex vivo. In addition, 4-1BB(-/-) BMM demonstrated hypophosphorylation of JNK and p38 and decreased induction of c-Fos in response to RANKL stimulation. Retroviral transduction of wild-type as well as partial-length 4-1BB, which lacks TNF receptor-associated factor 2-binding sites for signaling, restored the osteoclastogenic ability of 4-1BB(-/-) BMM. Furthermore, both recombinant 4-1BB and 4-1BBL enhanced RANKL-induced osteoclastogenesis by 4-1BB(+/+) BMM and the induction of c-Fos and NFATc1.Together, these results indicate that 4-1BBL and 4-1BB expressed on osteoclast precursors enhance RANKL-induced osteoclastogenesis via bi-directional signaling, findings that may delineate the complex nature of the 4-1BBL and 4-1BB interaction.

PMID:
18421790
DOI:
10.1002/eji.200737650
[Indexed for MEDLINE]
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