Interaction of Fas ligand and Fas expressed on osteoclast precursors increases osteoclastogenesis.
We incidentally found that osteoclast precursors and mature osteoclasts express Fas ligand (FasL) as well as Fas, which was confirmed by flow cytometry, immunofluorescent staining, and RT-PCR. The aim of this study was to determine the role of FasL in differentiation and cell death of osteoclasts. To study the role of FasL in osteoclastogenesis, neutralizing anti-FasL mAb or rFasL was added during receptor activator of NF-kappaB ligand (RANKL)-induced osteoclastogenesis using bone marrow-derived macrophages. Neutralization of endogenous FasL by anti-FasL mAb decreased osteoclastogenesis, whereas rFasL enhanced osteoclast differentiation in a dose-dependent manner. In addition, rFasL up-regulated the secretion of osteoclastogenic cytokines, such as IL-1beta and TNF-alpha, and the activation of NF-kappaB. Functional blocking of IL-1beta and TNF-alpha using IL-1 receptor antagonist and soluble TNFR confirmed that those cytokines mediated the effect of FasL on osteoclastogenesis. The osteoclast precursors were relatively resistant to rFasL-induced apoptosis especially before RANKL treatment, resulting in minimal cell loss by rFasL treatment during osteoclastogenesis. Although rFasL increased the cell death of mature osteoclasts, growth factor withdrawal induced much more cell death. However, anti-FasL mAb did not affect the survival of mature osteoclasts, suggesting that the endogenous FasL does not have a role in the apoptosis of osteoclasts. Finally, in contrast to the effect on apoptosis, rFasL-assisted osteoclastogenesis was not mediated by caspases. In conclusion, FasL has a novel function in bone homeostasis by enhancing the differentiation of osteoclasts, which was not considered previously.
Park
Hyewon
H
Department of Oromaxillofacial Infection & Immunity and Dental Research Institute, School of Dentistry, Seoul National University, Jongro-gu, Seoul, Republic of Korea.
Jung
Youn-Kwan
YK
Park
Ok-Jin
OJ
Lee
Yeon Ju
YJ
Choi
Je-Yong
JY
Choi
Youngnim
Y
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology*; D016207:Cytokines / Q000096:biosynthesis; D024202:Electrophoretic Mobility Shift Assay; D004797:Enzyme-Linked Immunosorbent Assay; D053222:Fas Ligand Protein; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000378:metabolism; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism; D048069:Tumor Necrosis Factors / Q000378:metabolism*; D019014:fas Receptor
D002352:Carrier Proteins; D016207:Cytokines; D053222:Fas Ligand Protein; C491899:Fas protein, mouse; C505658:Fasl protein, mouse; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018124:Receptors, Tumor Necrosis Factor; C505687:Tnfrsf11a protein, mouse; C505689:Tnfsf11 protein, mouse; D048069:Tumor Necrosis Factors; D019014:fas Receptor