The effect of triptolide （TP） on the expression of receptor activator of nuclear factor-κB ligand （RANKL） and osteoprotegerin （OPG） was explored in rat adjuvant induced arthritis （AA）. AA was induced in Wista...The effect of triptolide （TP） on the expression of receptor activator of nuclear factor-κB ligand （RANKL） and osteoprotegerin （OPG） was explored in rat adjuvant induced arthritis （AA）. AA was induced in Wistar rats. Arthritis rats were treated with TP and methotrexate （MTX） at the onset （day 9） of arthritis. On the peak of arthritis （day 24）, the expression of RANKL and OPG protein in the joints and RANKL mRNA in peripheral blood mononuclear cells （PBMC） was detected. TNF-α and IL-1β levels in peripheral blood were determined. Bone erosion scores were also evaluated. The results showed that bone erosion scores in TP and MTX groups were lower than in AA group （.P〈0.01） ; The expression levels of RANKL in the synovium （P〈0.01） and bone （P〈0.05）, and OPG level in synovium （P〈0.05） were lower in TP group than in AA group （P〈0.05）. In TP group, the expression levels of RANKL mRNA and TNF-α, IL-1β in PBMC were lower than in AA group （all P〈0.01）. It was concluded that TP could inhibit rat adjuvant arthritis bone erosion by suppressing the expression of RANKL.展开更多
Objective To study the effect of baicalin on the expression of receptor activator of nuclear factor-κB ligand(RANKL)and osteoprotegerin(OPG)in cultured human periodontal ligament(HPDL)cells.Methods Small interfering ...Objective To study the effect of baicalin on the expression of receptor activator of nuclear factor-κB ligand(RANKL)and osteoprotegerin(OPG)in cultured human periodontal ligament(HPDL)cells.Methods Small interfering RNA(siRNA)eukaryotic expression vector targeted transforming growth factor βⅡ receptor(TGF-β RⅡ)was constructed and transfected into T cells.HPDL cells with T cells transfected with siRNA or not were placed in the culture medium that had been added with lipopolysaccharide(LPS)and baicalin.The obtained solution was divided into six groups according to the components(group Ⅰ:HPDL cells+LPS+T cells transfected with siRNA1+baicalin;group Ⅱ:HPDL cells+LPS+T cells transfected with siRNA1;group Ⅲ:HPDL cells+LPS+T cells+baicalin;group Ⅳ:HPDL cells+LPS+T cells;group Ⅴ:HPDL cells+baicalin;group Ⅵ:HPDL cells)and was cultured for 48 hours.RT-PCR was used to observe the effect of baicalin on the expression of OPG-RANKL in HPDL cells.Results The ratio of RANKL/OPG in group Ⅰ was lower than that in group Ⅱ(P<0.01)and higher than that in group Ⅲ(P<0.01);The ratio of RANKL/OPG in group Ⅲ was lower than that in group Ⅳ(P<0.01);the ratio of RANKL/OPG in group Ⅳ was higher than that in group Ⅵ(P<0.01);the ratio of RANKL/OPG in group Ⅴ was lower than that in group Ⅵ(P<0.05).Conclusion ① Baicalin could decrease the ratio of RANKL/OPG in HPDL cells.② The TGF-β signaling transduction plays an important role in the effect of baicalin on the RANKL/OPG ratio in HPDL cells.③ Baicalin acts not only through TGF-β to regulate RANKL/OPG in HPDL cells,but also through other pathways.展开更多
Background:Obstructive sleep apnea-hypopnea syndrome (OSAHS) is associated with a higher prevalence of osteoporosis.However,the underlying mechanisms linking OSAHS with bone loss are still unclear.The aim of this stud...Background:Obstructive sleep apnea-hypopnea syndrome (OSAHS) is associated with a higher prevalence of osteoporosis.However,the underlying mechanisms linking OSAHS with bone loss are still unclear.The aim of this study was to investigate the changes of receptor activator of nuclear factor-κB ligand (RANKL,an osteoclastogenesis-promoting factor) and osteoprotegerin (OPG,the decoy receptor for RANKL),oxidative stress and bone metabolism markers in OSAHS,in order to understand the potential mechanisms underlying bone loss in OSAHS patients.Methods:Forty-eight male patients with OSAHS,confirmed by polysomnography (PSG) study,were enrolled.Twenty male subjects who were confirmed as not having OSAHS served as the controls.The subjects’bone mineral density (BMD) was assessed in lumbar spine and femoral neck using dual-energy X-ray absorptiometry (DXA).Blood samples were collected from all subjects for measurement of RANKL,OPG,the bone formation marker bone-specific alkaline phosphatase (BAP),the bone resorption marker tartrate-resistant acid phosphatase 5b (TRAP-5b),and total antioxidant capacity (TAOC).Results:The BMD and the T-score of the femoral neck and the lumbar spine were significantly lower in OSAHS patients as compared to the control group (P< 0.05).The serum level of BAP was significantly decreased in the OSAHS group (15.62 ± 5.20 μg/L) as compared to the control group (18.83 ± 5.50 μg/L,t= -2.235,P< 0.05),while the levels of TRAP-5b did not differ between the two groups (t= -1.447,P> 0.05).The serum level of OPG and the OPG/RANKL ratio were lower in the OSAHS group compared to the control group (bothP< 0.05).TAOC level was also decreased significantly in the OSAHS group (P< 0.05).Correlation analysis showed that the TAOC level was positively correlated with BAP in the OSAHS group (r= 0.248,P= 0.04),but there were no correlations between TAOC and the BMD or the T-scores.The correlations between the level of OPG (or the OPG/RANKL ratio) and BMD or TAOC did not reach significance.Conclusion:In OSAHS patients,lower levels of TAOC were associated with decreased bone formation,suggesting a role of oxidative stress in bone loss,while the role of OPG/RANKL imbalance in bone metabolism in OSAHS needs further evaluation .展开更多
Osteoporosis is a common bone disease characterized by reduced bone and increased risk of fracture. In postmenopausal women, osteoporosis results from bone loss attributable to estrogen deficiency. Osteoclast differen...Osteoporosis is a common bone disease characterized by reduced bone and increased risk of fracture. In postmenopausal women, osteoporosis results from bone loss attributable to estrogen deficiency. Osteoclast differentiation and activation is mediated by receptor activator of nuclear factor-κB ligand(RANKL), its receptor receptor activator of nuclear factor-κB(RANK), and a decoy receptor for RANKL, osteoprotegerin(OPG). The OPG/RANKL/RANK system plays a pivotal role in osteoclast biology. Currently, a fully human antiRANKL monoclonal antibody named denosumab is being clinically used for the treatment of osteoporosis and cancer-related bone disorders. This review describes recent advances in RANKL-related research, a story from bench to bedside. First, the discovery of the key factors, OPG/RANKL/RANK, revealed the molecular mechanism of osteoclastogenesis. Second, we established three animal models:(1) a novel and rapid bone loss model by administration of glutathione-S transferase-RANKL fusion protein to mice;(2) a novel mouse model of hypercalcemia with anorexia by overexpression of soluble RANKL using an adenovirus vector; and(3) a novel mouse model of osteopetrosis by administration of a denosumab-like anti-mouse RANKL neutralizing monoclonal antibody. Lastly, anti-human RANKL monoclonal antibody has been successfully applied to the treatment of osteoporosis and cancer-related bone disorders in many countries. This is a real example of applying basic science to clinical practice.展开更多
Objective: To investigate the effect of recombinant human osteoprotegerin combined with tinidazole on mice with periodontitis and the effect on serum RANKL and MCP-1 levels. Methods: 80 SPF-cleaned mice were randomly ...Objective: To investigate the effect of recombinant human osteoprotegerin combined with tinidazole on mice with periodontitis and the effect on serum RANKL and MCP-1 levels. Methods: 80 SPF-cleaned mice were randomly divided into 4 groups, 20 each, model group, tinidazole group and recombinant human osteoprotegerin group were modeled by Kimura et al., and tinidazole group received tinidazole. After intragastric administration, the recombinant human osteoprotegerin group was injected with recombinant human osteoprotegerin in the periodontal pocket according to the tinidazole group. The periodontal changes of the four groups of mice were observed and recorded, and the gingival rating was performed. Epithelial tissue morphology was observed by hematoxylin-eosin (HE) staining. Serum levels of IL-4, IL-6, RANKL and MCP-1 were measured by enzyme-linked immunosorbent assay. Results:After the intervention, the model group developed severe inflammatory reactions, including redness, hemorrhage, and deep periodontal pockets. The teeth were significantly loosened. The mice in the tinidazole group and the recombinant human osteoprotegerin group recovered substantially, and the gingival rating of the recombinant human osteoprotegerin group was better than that. The tinidazole group and the model group (P<0.05). The results of HE staining showed that the model group had edema, vasodilation and a large amount of inflammatory infiltration. The epithelial structure of the mice in the tinidazole group and the recombinant human osteoprotegerin group was intact and arranged closely and orderly. After intervention, the IL-4 in the tinidazole group and the recombinant human osteoprotegerin group was significantly higher than the model group and IL-6 was significantly lower than the model group (P<0.05), and the recombinant human osteoprotegerin group IL-4 was significantly higher after the intervention. IL-6 was significantly lower in the tinidazole group than in the tinidazole group (P<0.05). After the intervention, the tinidazole group and the recombinant human osteoprotegerin group were significantly reduced, and the recombinant human osteoprotegerin group RAKNL and MCP-1 were significantly lower than the model group (P>0.05). Conclusion: Recombinant human osteoprotegerin combined with tinidazole has a better therapeutic effect on gums and teeth in mice with periodontitis, and can lower the levels of RAKNL and MCP-1 in serum, inhibit bone resorption and protect teeth.展开更多
目的研究初发系统性红斑狼疮（systemic lupus erythematosus，SLE）患者外周血淋巴细胞中细胞核因子-κB受体激活剂配体（receptor activator of nuclear factor kappa B ligand，RANKL）、护骨素（osteoprotegerin，OPG）基因mRNA的...目的研究初发系统性红斑狼疮（systemic lupus erythematosus，SLE）患者外周血淋巴细胞中细胞核因子-κB受体激活剂配体（receptor activator of nuclear factor kappa B ligand，RANKL）、护骨素（osteoprotegerin，OPG）基因mRNA的表达情况，探讨其表达水平与初发SLE患者骨质疏松的关系。方法选择初发SLE患者45例及正常对照42例，运用实时定量PCR方法检测患者外周血淋巴细胞RANKL、OPG的mRNA表达水平。采用双能X线骨密度仪分别检测患者腰椎（L1-4）和股骨近端2个部位的骨密度，单因素分析RANKL、OPG基因mRNA表达水平与SLE患者骨密度的关系。结果SLE患者RANKL、OPG基因mRNA表达水平较正常对照组明显减低（P〈0．01）；SLE患者2个部位的骨密度均低于正常对照组（P〈0．05），骨量异常发生率为28-89％，骨量异常降低的SLE患者OPG基因mRNA的表达水平比骨量正常的患者显著降低，两者间的差异有统计学意义（P〈0．01）；而RANKL基因mRNA表达水平的差异无统计学意义（P〉0．05）；OPG基因mRNA表达水平与初发SLE患者骨密度间存在正相关（r=0．461；P=0．001），即OPG表达水平越低，骨量减少越明显；而RANKL基因mRNA表达降低与初发SLE患者骨密度无明显相关性（r=-0．189，P=0．214）；初发SLE患者疾病活动度与骨量减少、RANKL及OPG基因表达水平间不存在相关性（r=0．293，P=0．138；r=-0．099，P=0．493；，=0．138，P=0．493）。结论初发SLE患者骨量减少的发病率较正常人群增高，并且初发SLE患者体内RANKL和OPG基因表达存在异常；其中OPG表达水平的降低可能与初发SLE患者的骨量减少有密切关系。展开更多
目的:研究人牙囊细胞白细胞介素-10(interleukin-10,IL-10)蛋白的表达及其对破骨细胞分化因子(receptor activator of nuclear factor kappa B ligand,RANKL)表达的影响。方法:采用组织块加胶原酶消化法培养人牙囊细胞,进行IL-10免疫组...目的:研究人牙囊细胞白细胞介素-10(interleukin-10,IL-10)蛋白的表达及其对破骨细胞分化因子(receptor activator of nuclear factor kappa B ligand,RANKL)表达的影响。方法:采用组织块加胶原酶消化法培养人牙囊细胞,进行IL-10免疫组化染色。25ng/mlIL-10作用于牙囊细胞0、1、3、6 h,用RT-PCR检测RANKL mRNA表达的变化。结果:人牙囊细胞IL-10表达阳性。25ng/ml IL-10降低人牙囊细胞RANKL的表达,且具有时间依赖性。结论:人牙囊细胞表达IL-10,IL-10通过降低人牙囊细胞RANKL的表达,在牙齿萌出过程中起重要的调控作用。展开更多
Bone-resorbing osteoclasts are formed from a monocyte/macrophage lineage under the strict control o bone-forming osteoblasts. So far,macrophage colonystimulating factor(M-CSF),receptor activator o nuclear factor-κB l...Bone-resorbing osteoclasts are formed from a monocyte/macrophage lineage under the strict control o bone-forming osteoblasts. So far,macrophage colonystimulating factor(M-CSF),receptor activator o nuclear factor-κB ligand(RANKL),and osteoprotegerin(OPG) produced by osteoblasts play major roles in the regulation of osteoclast differentiation. Recent studies have shown that osteoblasts regulate osteoclastogenesis through several mechanisms independent o M-CSF,RANKL,and OPG production. Identification o osteoclast-committed precursors in vivo demonstrated that osteoblasts are involved in the distribution o osteoclast precursors in bone. Interleukin 34(IL-34)a novel ligand for c-Fms,plays a pivotal role in maintaining the splenic reservoir of osteoclast-committed precursors in M-CSF deficient mice. IL-34 is also able to act as a substitute for osteoblast-producing M-CSF in osteoclastogenesis. Wnt5 a,produced by osteoblasts,enhances osteoclast differentiation by upregulating RANK expression through activation of the noncanonical Wnt pathway. Semaphorin 3A produced by osteoblasts inhibits RANKL-induced osteoclast differentiation through the suppression of immunoreceptortyrosine-based activation motif signals. Thus,recent findings show that osteoclast differentiation is tightly regulated by osteoblasts through several different mechanisms. These newly identified molecules are expected to be promising targets of therapeutic agents in bone-related diseases.展开更多
文摘The effect of triptolide （TP） on the expression of receptor activator of nuclear factor-κB ligand （RANKL） and osteoprotegerin （OPG） was explored in rat adjuvant induced arthritis （AA）. AA was induced in Wistar rats. Arthritis rats were treated with TP and methotrexate （MTX） at the onset （day 9） of arthritis. On the peak of arthritis （day 24）, the expression of RANKL and OPG protein in the joints and RANKL mRNA in peripheral blood mononuclear cells （PBMC） was detected. TNF-α and IL-1β levels in peripheral blood were determined. Bone erosion scores were also evaluated. The results showed that bone erosion scores in TP and MTX groups were lower than in AA group （.P〈0.01） ; The expression levels of RANKL in the synovium （P〈0.01） and bone （P〈0.05）, and OPG level in synovium （P〈0.05） were lower in TP group than in AA group （P〈0.05）. In TP group, the expression levels of RANKL mRNA and TNF-α, IL-1β in PBMC were lower than in AA group （all P〈0.01）. It was concluded that TP could inhibit rat adjuvant arthritis bone erosion by suppressing the expression of RANKL.
基金supported by the Foundation of Stomatology Hospital,Xi'an Jiaotong University
文摘Objective To study the effect of baicalin on the expression of receptor activator of nuclear factor-κB ligand(RANKL)and osteoprotegerin(OPG)in cultured human periodontal ligament(HPDL)cells.Methods Small interfering RNA(siRNA)eukaryotic expression vector targeted transforming growth factor βⅡ receptor(TGF-β RⅡ)was constructed and transfected into T cells.HPDL cells with T cells transfected with siRNA or not were placed in the culture medium that had been added with lipopolysaccharide(LPS)and baicalin.The obtained solution was divided into six groups according to the components(group Ⅰ:HPDL cells+LPS+T cells transfected with siRNA1+baicalin;group Ⅱ:HPDL cells+LPS+T cells transfected with siRNA1;group Ⅲ:HPDL cells+LPS+T cells+baicalin;group Ⅳ:HPDL cells+LPS+T cells;group Ⅴ:HPDL cells+baicalin;group Ⅵ:HPDL cells)and was cultured for 48 hours.RT-PCR was used to observe the effect of baicalin on the expression of OPG-RANKL in HPDL cells.Results The ratio of RANKL/OPG in group Ⅰ was lower than that in group Ⅱ(P<0.01)and higher than that in group Ⅲ(P<0.01);The ratio of RANKL/OPG in group Ⅲ was lower than that in group Ⅳ(P<0.01);the ratio of RANKL/OPG in group Ⅳ was higher than that in group Ⅵ(P<0.01);the ratio of RANKL/OPG in group Ⅴ was lower than that in group Ⅵ(P<0.05).Conclusion ① Baicalin could decrease the ratio of RANKL/OPG in HPDL cells.② The TGF-β signaling transduction plays an important role in the effect of baicalin on the RANKL/OPG ratio in HPDL cells.③ Baicalin acts not only through TGF-β to regulate RANKL/OPG in HPDL cells,but also through other pathways.
文摘Background:Obstructive sleep apnea-hypopnea syndrome (OSAHS) is associated with a higher prevalence of osteoporosis.However,the underlying mechanisms linking OSAHS with bone loss are still unclear.The aim of this study was to investigate the changes of receptor activator of nuclear factor-κB ligand (RANKL,an osteoclastogenesis-promoting factor) and osteoprotegerin (OPG,the decoy receptor for RANKL),oxidative stress and bone metabolism markers in OSAHS,in order to understand the potential mechanisms underlying bone loss in OSAHS patients.Methods:Forty-eight male patients with OSAHS,confirmed by polysomnography (PSG) study,were enrolled.Twenty male subjects who were confirmed as not having OSAHS served as the controls.The subjects’bone mineral density (BMD) was assessed in lumbar spine and femoral neck using dual-energy X-ray absorptiometry (DXA).Blood samples were collected from all subjects for measurement of RANKL,OPG,the bone formation marker bone-specific alkaline phosphatase (BAP),the bone resorption marker tartrate-resistant acid phosphatase 5b (TRAP-5b),and total antioxidant capacity (TAOC).Results:The BMD and the T-score of the femoral neck and the lumbar spine were significantly lower in OSAHS patients as compared to the control group (P< 0.05).The serum level of BAP was significantly decreased in the OSAHS group (15.62 ± 5.20 μg/L) as compared to the control group (18.83 ± 5.50 μg/L,t= -2.235,P< 0.05),while the levels of TRAP-5b did not differ between the two groups (t= -1.447,P> 0.05).The serum level of OPG and the OPG/RANKL ratio were lower in the OSAHS group compared to the control group (bothP< 0.05).TAOC level was also decreased significantly in the OSAHS group (P< 0.05).Correlation analysis showed that the TAOC level was positively correlated with BAP in the OSAHS group (r= 0.248,P= 0.04),but there were no correlations between TAOC and the BMD or the T-scores.The correlations between the level of OPG (or the OPG/RANKL ratio) and BMD or TAOC did not reach significance.Conclusion:In OSAHS patients,lower levels of TAOC were associated with decreased bone formation,suggesting a role of oxidative stress in bone loss,while the role of OPG/RANKL imbalance in bone metabolism in OSAHS needs further evaluation .
文摘Osteoporosis is a common bone disease characterized by reduced bone and increased risk of fracture. In postmenopausal women, osteoporosis results from bone loss attributable to estrogen deficiency. Osteoclast differentiation and activation is mediated by receptor activator of nuclear factor-κB ligand(RANKL), its receptor receptor activator of nuclear factor-κB(RANK), and a decoy receptor for RANKL, osteoprotegerin(OPG). The OPG/RANKL/RANK system plays a pivotal role in osteoclast biology. Currently, a fully human antiRANKL monoclonal antibody named denosumab is being clinically used for the treatment of osteoporosis and cancer-related bone disorders. This review describes recent advances in RANKL-related research, a story from bench to bedside. First, the discovery of the key factors, OPG/RANKL/RANK, revealed the molecular mechanism of osteoclastogenesis. Second, we established three animal models:(1) a novel and rapid bone loss model by administration of glutathione-S transferase-RANKL fusion protein to mice;(2) a novel mouse model of hypercalcemia with anorexia by overexpression of soluble RANKL using an adenovirus vector; and(3) a novel mouse model of osteopetrosis by administration of a denosumab-like anti-mouse RANKL neutralizing monoclonal antibody. Lastly, anti-human RANKL monoclonal antibody has been successfully applied to the treatment of osteoporosis and cancer-related bone disorders in many countries. This is a real example of applying basic science to clinical practice.
文摘Objective: To investigate the effect of recombinant human osteoprotegerin combined with tinidazole on mice with periodontitis and the effect on serum RANKL and MCP-1 levels. Methods: 80 SPF-cleaned mice were randomly divided into 4 groups, 20 each, model group, tinidazole group and recombinant human osteoprotegerin group were modeled by Kimura et al., and tinidazole group received tinidazole. After intragastric administration, the recombinant human osteoprotegerin group was injected with recombinant human osteoprotegerin in the periodontal pocket according to the tinidazole group. The periodontal changes of the four groups of mice were observed and recorded, and the gingival rating was performed. Epithelial tissue morphology was observed by hematoxylin-eosin (HE) staining. Serum levels of IL-4, IL-6, RANKL and MCP-1 were measured by enzyme-linked immunosorbent assay. Results:After the intervention, the model group developed severe inflammatory reactions, including redness, hemorrhage, and deep periodontal pockets. The teeth were significantly loosened. The mice in the tinidazole group and the recombinant human osteoprotegerin group recovered substantially, and the gingival rating of the recombinant human osteoprotegerin group was better than that. The tinidazole group and the model group (P<0.05). The results of HE staining showed that the model group had edema, vasodilation and a large amount of inflammatory infiltration. The epithelial structure of the mice in the tinidazole group and the recombinant human osteoprotegerin group was intact and arranged closely and orderly. After intervention, the IL-4 in the tinidazole group and the recombinant human osteoprotegerin group was significantly higher than the model group and IL-6 was significantly lower than the model group (P<0.05), and the recombinant human osteoprotegerin group IL-4 was significantly higher after the intervention. IL-6 was significantly lower in the tinidazole group than in the tinidazole group (P<0.05). After the intervention, the tinidazole group and the recombinant human osteoprotegerin group were significantly reduced, and the recombinant human osteoprotegerin group RAKNL and MCP-1 were significantly lower than the model group (P>0.05). Conclusion: Recombinant human osteoprotegerin combined with tinidazole has a better therapeutic effect on gums and teeth in mice with periodontitis, and can lower the levels of RAKNL and MCP-1 in serum, inhibit bone resorption and protect teeth.
文摘目的研究初发系统性红斑狼疮（systemic lupus erythematosus，SLE）患者外周血淋巴细胞中细胞核因子-κB受体激活剂配体（receptor activator of nuclear factor kappa B ligand，RANKL）、护骨素（osteoprotegerin，OPG）基因mRNA的表达情况，探讨其表达水平与初发SLE患者骨质疏松的关系。方法选择初发SLE患者45例及正常对照42例，运用实时定量PCR方法检测患者外周血淋巴细胞RANKL、OPG的mRNA表达水平。采用双能X线骨密度仪分别检测患者腰椎（L1-4）和股骨近端2个部位的骨密度，单因素分析RANKL、OPG基因mRNA表达水平与SLE患者骨密度的关系。结果SLE患者RANKL、OPG基因mRNA表达水平较正常对照组明显减低（P〈0．01）；SLE患者2个部位的骨密度均低于正常对照组（P〈0．05），骨量异常发生率为28-89％，骨量异常降低的SLE患者OPG基因mRNA的表达水平比骨量正常的患者显著降低，两者间的差异有统计学意义（P〈0．01）；而RANKL基因mRNA表达水平的差异无统计学意义（P〉0．05）；OPG基因mRNA表达水平与初发SLE患者骨密度间存在正相关（r=0．461；P=0．001），即OPG表达水平越低，骨量减少越明显；而RANKL基因mRNA表达降低与初发SLE患者骨密度无明显相关性（r=-0．189，P=0．214）；初发SLE患者疾病活动度与骨量减少、RANKL及OPG基因表达水平间不存在相关性（r=0．293，P=0．138；r=-0．099，P=0．493；，=0．138，P=0．493）。结论初发SLE患者骨量减少的发病率较正常人群增高，并且初发SLE患者体内RANKL和OPG基因表达存在异常；其中OPG表达水平的降低可能与初发SLE患者的骨量减少有密切关系。
文摘Bone-resorbing osteoclasts are formed from a monocyte/macrophage lineage under the strict control o bone-forming osteoblasts. So far,macrophage colonystimulating factor(M-CSF),receptor activator o nuclear factor-κB ligand(RANKL),and osteoprotegerin(OPG) produced by osteoblasts play major roles in the regulation of osteoclast differentiation. Recent studies have shown that osteoblasts regulate osteoclastogenesis through several mechanisms independent o M-CSF,RANKL,and OPG production. Identification o osteoclast-committed precursors in vivo demonstrated that osteoblasts are involved in the distribution o osteoclast precursors in bone. Interleukin 34(IL-34)a novel ligand for c-Fms,plays a pivotal role in maintaining the splenic reservoir of osteoclast-committed precursors in M-CSF deficient mice. IL-34 is also able to act as a substitute for osteoblast-producing M-CSF in osteoclastogenesis. Wnt5 a,produced by osteoblasts,enhances osteoclast differentiation by upregulating RANK expression through activation of the noncanonical Wnt pathway. Semaphorin 3A produced by osteoblasts inhibits RANKL-induced osteoclast differentiation through the suppression of immunoreceptortyrosine-based activation motif signals. Thus,recent findings show that osteoclast differentiation is tightly regulated by osteoblasts through several different mechanisms. These newly identified molecules are expected to be promising targets of therapeutic agents in bone-related diseases.
