title: Osteoprotegerin expressed by osteoclasts: an autoregulator of osteoclastogenesis.
abstract: Osteoprotegerin (OPG) is secreted by stromal and osteoblastic lineage cells and inhibits osteoclastogenesis by preventing the interaction of receptor activator of nuclear factor-κB ligand (RANKL) with receptor activator of nuclear factor-κB (RANK). In this study, the expression of OPG in osteoclasts themselves and its biological functions during osteoclastogenesis were investigated for the first time. OPG expression in vivo in the developing rat maxilla was examined by immunofluorescence analysis. OPG expression in osteoclasts during in vitro osteoclastogenesis was determined by reverse-transcription polymerase chain-reaction (RT-PCR), Western blot, and immunofluorescence staining. We determined the function of OPG produced by osteoclasts during osteoclastogenesis by silencing the OPG gene. The effects of OPG on bone-resorbing activity and apoptosis of mature osteoclasts were examined by the assay of resorptive pit formation on calcium-phosphate-coated plate and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining, respectively. In the immunofluorescence findings, strong immunoreactivities were unexpectedly seen in multinucleated tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts around the growing and erupting tooth germs in the rat alveolar bone. In vitro, OPG expression was significantly increased during the differentiation of osteoclasts from mouse bone-marrow-derived cells treated with a combination of macrophage colony-stimulating factor (M-CSF) and RANKL. Interestingly, it was found that OPG small interfering (si)RNA treatment during osteoclastogenesis enhanced the sizes of osteoclasts, but attenuated their bone-resorbing activity. Also, the increased chromosomal DNA fragmentation and caspase-3 activity in the late phase of osteoclastogenesis were found to be decreased by treatment with OPG siRNA. Furthermore, effects of OPG siRNA treatment on osteoclastogenesis and bone-resorbing activity were recovered by the treatment of exogenous OPG. These results suggest that OPG, expressed by the osteoclasts themselves, may play an auto-regulatory role in the late phase of osteoclastogenesis through the induction of apoptosis.
authors.affiliation: Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: J H
authors.initials: JH
authors.lastname: Kang
authors.affiliation: Department of Microbiology, College of Medicine, Seonam University, Namwon, Korea;
authors.forename: H M
authors.initials: HM
authors.lastname: Ko
authors.affiliation: Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: J S
authors.initials: JS
authors.lastname: Moon
authors.affiliation: Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: H I
authors.initials: HI
authors.lastname: Yoo
authors.affiliation: Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: J Y
authors.initials: JY
authors.lastname: Jung
authors.affiliation: Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: M S
authors.initials: MS
authors.lastname: Kim
authors.affiliation: Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: J T
authors.initials: JT
authors.lastname: Koh
authors.affiliation: Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: W J
authors.initials: WJ
authors.lastname: Kim
authors.affiliation: Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea ksh@jnu.ac.kr.
authors.forename: S H
authors.initials: SH
authors.lastname: Kim
mesh_terms: D000135:Acid Phosphatase / Q000032:analysis; D000539:Alveolar Process / Q000166:cytology; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001854:Bone Marrow Cells / Q000187:drug effects; D001862:Bone Resorption / Q000378:metabolism; D002130:Calcium Phosphates / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D048429:Cell Size; D002478:Cells, Cultured; D020099:Coated Materials, Biocompatible / Q000378:metabolism; D020868:Gene Silencing; D006706:Homeostasis / Q000502:physiology; D007527:Isoenzymes / Q000032:analysis; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008297:Male; D008437:Maxilla / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D053244:Osteoprotegerin / Q000032:analysis* / Q000235:genetics; D053245:RANK Ligand / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D000071681:Tartrate-Resistant Acid Phosphatase; D014078:Tooth Eruption / Q000502:physiology; D014083:Tooth Germ / Q000166:cytology
chemical_list: D002130:Calcium Phosphates; D020099:Coated Materials, Biocompatible; D007527:Isoenzymes; D053244:Osteoprotegerin; D053245:RANK Ligand; C506031:Tnfrsf11b protein, mouse; C506032:Tnfrsf11b protein, rat; C505689:Tnfsf11 protein, mouse; D016173:Macrophage Colony-Stimulating Factor; C020243:calcium phosphate; D000135:Acid Phosphatase; C000605511:Acp5 protein, mouse; D000071681:Tartrate-Resistant Acid Phosphatase
keywords: M-CSF; OPG; RANKL; apoptosis; autoregulation; resorption