• Molecules and Cells
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• v.45 no.10
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• pp.749-760
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• 2022

Osteoclast generation from monocyte/macrophage lineage precursor cells needs to be tightly regulated to maintain bone homeostasis and is frequently over-activated in inflammatory conditions. PARK2, a protein associated with Parkinson's disease, plays an important role in mitophagy via its ubiquitin ligase function. In this study, we investigated whether PARK2 is involved in osteoclastogenesis. PARK2 expression was found to be increased during the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation. PARK2 gene silencing with siRNA significantly reduced osteoclastogenesis induced by RANKL, LPS (lipopolysaccharide), TNFα (tumor necrosis factor α), and IL-1β (interleukin-1β). On the other hand, overexpression of PARK2 promoted osteoclastogenesis. This regulation of osteoclastogenesis by PARK2 was mediated by IKK (inhibitory κB kinase) and NF-κB activation while MAPK (mitogen-activated protein kinases) activation was not involved. Additionally, administration of PARK2 siRNA significantly reduced osteoclastogenesis and bone loss in an in vivo model of inflammatory bone erosion. Taken together, this study establishes a novel role for PARK2 as a positive regulator in osteoclast differentiation and inflammatory bone destruction.

• Journal of Periodontal and Implant Science
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• v.32 no.4
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• pp.733-744
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• 2002

The fibroblasts are the principal cells in the periodontal ligament of peridontium. As the periodontal ligament fibroblasts (PDLF) show similar phenotype with osteoblasts, the PDLF are thought to play an important role in alveolar bone remodeling. Cell-to-cell contacted signaling is crucial for osteoclast formation. Recently it has been reported that PDLJ enhance the bone resorbing activity of osteoclasts differentiated from hematopoietic preosteoclasts. The aims of this study were to $clarify\;^{1)}$ the mechanism of PDLF-induced osteoclastogenesis $and\;^{2)}$ whether we can use preosteoclast cell line instead of primary hematopoietic preosteoclast cells for studying the mechanism of PDLF-induced osteoclastogenesis. Osteoclastic differentiation of mouse macrophage cell line RAW264.7 was compared with that of mouse bone marrow-derived M-CSF dependent cell (MDBM), a well-known hematopoietic preosteoclast model, by examining, 1) osteoclast-specific gene expression such as calcitonin receptor, M-CSF receptor (c-fms), cathepsin K, receptoractivator nuclear factor kappa B (RANK) ,2) generation of TRAP(+) multinucleated cells (MNCs), and 3) generation of resorption pit on the $OAAS^{TM}$ plate. RAW264.7 cultured in the medium containing of soluble osteoclast differentiation Factor (sODF) showed similar phenotype with MDBM-derived osteoclasts, those are mRNA expression pattern of osteoclast-specific genes, TRAP(+) MNCs generation, and bone resorbing abivity. Formation of resorption pits by osteoclastic MNCs differentiated from sODF-treated RAW264.7, was completely blocked by the addition of osteoprotegerin (OPG), a soluble decoy receptor for ODF, to the sODF-containing culture me야um. The effects of PDLF on differentiation of RAW264.7 into　the TRAP(+) multinucleated osteoclast-like cells were examined using coculture system. PDLF were fxed with paraformaldehyde, followed by coculture with RAW264.7, which induced formation of TRAP(+) MNCs in the absence of additional treatment of sODF. When compared with untreated and fixed PDLF (fPDLF), IL-1 ${\beta}$-treated, or lipopolysaccha-ride-treated and then fixed PDLF showed two-folld increase in the supporting activity of osteoclastogenesis from RAW264.7 coculture system. There were no TRAP(+) MNCs formation in coculture system of RAW264.7 with PDLF of no fixation. These findigs suggested that we can replace the primary hematopoietic preosteoclasts for RAW264. 7 cell line for studying the mechanism of PDLF-induced osteoclastogenesis, and we hypothesize that PDLF control osteoclastogenesis through ODF expression which might be enhanced by inflammatory signals.

• International Journal of Oral Biology
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• v.32 no.1
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• pp.1-5
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• 2007

Receptor activator of nuclear factor ${\kappa}B$ ligand (RANKL) induces osteoclast formation from hematopoietic cells via up-regulation of positive regulators, including $NF-{\kappa}B$, c-Fos, microphthalmia transcription factor (Mitf), PU.1, and nuclear factor of activated T cells (NFAT) c1. In addition to the positive regulation by these transcription factors, RANKL appears to regulate negative regulators such as MafB and inhibitors of differentiation (Ids). Ids and MafB are abundantly expressed in osteoclast precursors, bone marrowderived monocyte/macrophage lineage cells (BMMs). Expression levels of these genes are significantly reduced by RANKL during osteoclastogenesis. Overexpression of these genes in BMMs inhibits the formation of tartarate-resistant acid phosphatase (TRAP)-positive multinuclear osteoclasts by down-regulation of NFATc1 and osteoclast-associated receptor (OSCAR), which are important for osteoclast differentiation. Furthermore, reduced expression of these genes enhances osteoclastogenesis and increases expression of NFATc1 and OSCAR. Taken together, RANKL induces osteoclastogenesis via up-regulation of positive regulators as well as down-regulation of negative regulators.

• Food Science and Biotechnology
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• v.14 no.1
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• pp.94-98
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• 2005

Bone resorption surrounding tooth root causes tooth loss in periodontitis patients. Osteoclast has bone resorption activity. Effects of Artemisia asiatica on bone resorption induced by periodontopathogens, Porphyromonas gingivalis and Treponema denticola, were examined using co-culture systems of mouse osteoblasts and bone marrow cells. Addition of A. asiatica ethanol extract to bacterial sonicate abolished bacteria-induced osteoclastogenesis. To determine inhibitory mechanism of A. asiatica against osteoclastogenesis, effects of A. asiatica on expressions of osteoclastogenesis-inducing factors such as receptor activator of NF-${\kappa}B$ ligand (RANKL), prostaglandin $E_2\;(PGE_2)$, interleukin (IL)-1, and tumor necrosis factor (TNF)-${\alpha}$, in osteoblasts were examined. A. asiatica suppressed expressions of RANKL, $PGE_2$, IL-$1{\beta}$, and TNF-${\alpha}$ increased by each bacterial sonicate. These results suggest inhibitory action of A. asiatica against osteoclastogenesis is associated with down-regulations of RANKL, $PGE_2$ IL-$1{\beta}$, and TNF-${\alpha}$ expressions.

• International Journal of Oral Biology
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• v.44 no.3
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• pp.89-95
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• 2019

Piperlongumine (PL) is a natural product found in long pepper (Piper longum). The pharmacological effects of PL are well known, and it has been used for pain, hepatoprotection, and asthma in Oriental medicine. No studies have examined the effects of PL on bone tissue or bone-related diseases, including osteoporosis. The current study investigated for the first time the inhibitory effects of PL on osteoclast differentiation, bone resorption, and osteoclastogenesis-related factors in RAW264.7 macrophages stimulated by the receptor activator for nuclear factor-${\kappa}B$ ligand (RANKL). Cytotoxicity was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and osteoclast differentiation and bone resorption were confirmed by tartrate-resistant acid phosphatase (TRAP) staining and pit formation analysis. Osteoclast differentiation factors were confirmed by western blotting. PL exhibited toxicity in RAW264.7 macrophages, inhibiting osteoclast formation and bone resorption, in addition to inhibiting the expression of osteoclastogenesis-related factors, such as tumor necrosis factor receptor-associated factor 6 (TRAF6), c-Fos, and NFATc1, in RANKL-stimulated RAW264.7 macrophages. These findings suggest that PL is suitable for the treatment of osteoporosis, and it serves as a potential therapeutic agent for various bone diseases.

• Journal of Periodontal and Implant Science
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• v.37 no.3
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• pp.553-562
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• 2007

Osteoblasts regulate osteoclastogenesis by production of various cytokines. Aggregatibacter(A) ac-tinomycetemcomitans is one of periodontopathogens which invades gingival tissue. Therefore, clarifying the effect of alive A. actinomycetemcomitans on osteoblasts is important to understand the mechanism of alveolar bone resorption in periodontitis. We investigated induction of osteoclastogenesis-inducing cytokines, adherence, and invasion by A. actinomycetemcomitans in osteoblasts. Osteoblasts were isolated from mouse calvaria and expression of cytokines was determined by RT-PCR. When the ratio of the number of A. actinomycetemcomtians to the number of osteoblasts was 10:1, 50:1 and 100:1, RANKL mRNA expression was increased. A. actinomycetemcomitans also increased expression of macrophage inflammatory protein (MIP) -1${\alpha}$, interleukin (IL)-1${\beta}$, and tumor necrosis factor (TNF)-${\alpha}$. A. actinomycetemcomitans attached to and invaded osteoblasts at ratio of 1000:1. These results suggest that A. actinomycetemcomitans increases osteoclastogenesis-inducing ability of osteoblasts by stimulating the expression of RANKL, MIP-1${\alpha}$,IL-1${\beta}$, and TNF-${\alpha}$ and that invasion of A. actinomycetemcomitans provides a means by which the bacteria escape from immune system and antibiotic therapy.

• The Korean Journal of Physiology and Pharmacology
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• v.17 no.5
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• pp.427-433
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• 2013

Receptor activator of NF-${\kappa}B$ ligand (RANKL)-induced osteoclastogenesis is accompanied by intracellular $Ca^{2+}$ mobilization in a form of oscillations, which plays essential roles by activating sequentially $Ca^{2+}$/calmodulin-dependent protein kinase, calcineurin and NFATc1, necessary in the osteoclast differentiation. However, it is not known whether $Ca^{2+}$ mobilization which is evoked in RANKL-independent way induces to differentiate into osteoclasts. In present study, we investigated $Ca^{2+}$ mobilization induced by aluminum fluoride ($AlF_4^-$), a G-protein activator, with or without RANKL and the effects of $AlF_4^-$ on the osteoclastogenesis in primary cultured mouse bone marrow-derived macrophages (BMMs). We show here that $AlF_4^-$ induces intracellular $Ca^{2+}$ concentration ($[Ca^{2+}]_i$) oscillations, which is dependent on extracellular $Ca^{2+}$ influx. Notably, co-stimulation of $AlF_4^-$ with RANKL resulted in enhanced NFATc1 expression and formation of tartrate-resistant acid phosphatase (TRAP) positive multinucleated cells. Additionally, we confirmed that mitogen-activated protein kinase (MAPK) is also activated by $AlF_4^-$. Taken together, these results demonstrate that G-protein would be a novel modulator responsible for $[Ca^{2+}]_i$ oscillations and MAPK activation which lead to enhancement of RANKL-mediated osteoclastogenesis.

• International Journal of Oral Biology
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• v.40 no.1
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• pp.19-25
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• 2015

Osteocytes may function as mechanotransducers by regulating local osteoclastogenesis. Reduced availability of oxygen, i.e. hypoxia, could occur during disuse, bone development, and fracture. Receptor activator of nuclear factor-${\kappa}B$ ligand (RANKL) is an osteoblast/stromal cell derived essential factor for osteoclastogenesis. The hypoxia induced osteoclastogenesis via increased RANKL expression in osteoblasts was demonstrated. Hypoxic regulation of gene expression generally involves activation of the hypoxia-inducible factor (HIF) transcription pathway. In the present study, we investigated whether hypoxia regulates RANKL expression in murine osteocytes and HIF-$1{\alpha}$ mediates hypoxia-induced RANKL expression by transactivating RANKL promoter, to elucidate the role of osteocyte in osteoclastogenesis in the context of hypoxic condition. The expression levels of RANKL mRNA and protein, as well as hypoxia inducible factor-$1{\alpha}$ (HIF-$1{\alpha}$) protein, were significantly increased in hypoxic condition in MLO-Y4s. Constitutively active HIF-$1{\alpha}$ alone significantly increased the levels of RANKL expression in MLO-Y4s under normoxic conditions, whereas dominant negative HIF-$1{\alpha}$ blocked hypoxia-induced RANKL expression. To further explore to find if HIF-$1{\alpha}$ directly regulates RANKL transcription, a luciferase reporter assay was conducted. Hypoxia significantly increased RANKL promoter activity, whereas mutations of putative HIF-$1{\alpha}$ binding elements in RANKL promoter prevented this hypoxia-induced RANKL promoter activity in MLO-Y4s. These results suggest that HIF-$1{\alpha}$ mediates hypoxia-induced up-regulation of RANKL expression, and that in osteocytes of mechanically unloaded bone, hypoxia enhances osteoclastogenesis, at least in part, via an increased RANKL expression in osteocytes.

• Biomolecules & Therapeutics
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• v.19 no.2
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• pp.141-148
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• 2011

Osteoclasts are bone-resorbing cells of monocyte/macrophage origin and are culprits of bone destruction associated with osteoporosis, rheumatoid arthritis, and cancer bone metastasis. Recent advances in osteoclast biology revealed central roles of various cytokines in regulating osteoclastogenesis both in vitro and in vivo. However, exact underlying mechanisms including signaling pathways downstream of receptor ligation are still under pursuit. In the present review, the role of Jak/STAT proteins and their regulators will be discussed in connection with osteoclastogenesis, since growing evidence indicates that a number of cytokines and growth factors utilizing Jak/STAT signaling pathways affect osteoclastogenesis. A better understanding on the role of Jak/STAT pathways in osteoclast differentiation will not only strengthen our knowledge on osteoclast biology but also provide invaluable insights into the development of anti-resorptive strategies for treating bone-lytic diseases.

• Journal of Microbiology
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• v.45 no.6
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• pp.566-571
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• 2007

Bacterial lipopolysaccharide (LPS) is a potent stimulator of bone resorption in periodontitis. Co-culture systems of mouse calvaria-derived osteoblasts and bone marrow-derived preosteoclasts were used as an in vitro osteoclast differentiation. This study revealed that co-cultures using ddY or ICR mouse strain responded differently to LPS while responded equally to $1{\alpha},25(OH)_2D_3$. Thus, the different response to LPS indicates dissimilarity of two mouse stains in their capacity for generating osteoclasts while the two mouse strains share the similarity in response to $1{\alpha},25(OH)_2D_3$. To identify which cells between osteoblasts and preosteoclasts in the co-culture are responsible for the dissimilarity, the reciprocal co-cultures were performed between ddY and ICR mouse strains. The treatment of $1,25(OH)_2D_3$ to ddY/ICR (osteoblasts from ddY/preosteoclasts from ICR) and ICR/ddY reciprocal co-cultures also showed the similarity. In case of LPS treatment, the results of ddY/ICR were similar to ddY/ddY and the results of the other reciprocal co-culture, ICR/ddY combination, were consistent with those of ICR/ICR. It suggests that the dissimilarity between the two mouse strains may resident in osteoblasts but not in preosteoclasts. Therefore, the osteoblast is responsible for mouse strain-dependent osteoclastogenesis in response to LPS. Although mouse models will continue to provide insights into molecular mechanisms of osteoclastogenesis, caution should be exercised when using different mouse strains, especially ddY and ICR strains as models for osteoclast differentiation.