Functions of RANKL/RANK/OPG in bone modeling and remodeling

The discovery of the RANKL/RANK/OPG system in the mid 1990s for the regulation of bone resorption has led to major advances in our understanding of how bone modeling and remodeling are regulated. It had been known for many years before this discovery that osteoblastic stromal cells regulated osteoclast formation, but it had not been anticipated that they would do this through expression of members of the TNF superfamily: receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG), or that these cytokines and signaling through receptor activator of NF-κB (RANK) would have extensive functions beyond regulation of bone remodeling. RANKL/RANK signaling regulates osteoclast formation, activation and survival in normal bone modeling and remodeling and in a variety of pathologic conditions characterized by increased bone turnover. OPG protects bone from excessive resorption by binding to RANKL and preventing it from binding to RANK. Thus, the relative concentration of RANKL and OPG in bone is a major determinant of bone mass and strength. Here, we review our current understanding of the role of the RANKL/RANK/OPG system in bone modeling and remodeling.     

仙灵骨葆对骨质疏松大鼠OPG/RANK/RANKL 表达的影响

目的:观察仙灵骨葆治疗骨质疏松模型大鼠后,对大鼠体内OPG/RANKL/RANK表达的影响。方法:卵巢摘除法建立SD大鼠骨质疏松模型,设立假手术组、对照组(单纯去卵巢组)、雌激素组(给予17β-雌二醇)和治疗组(给予仙灵骨葆)。术后1周开始给药,给药12周后检测各组大鼠股骨骨密度,ELISA法检测血清中OPG/RANKL含量,RT-PCR检测骨组织中OPG/RANK/RAN-KL mRNA表达,免疫组化检测骨组织中RANK的表达。结果:对照组大鼠骨密度显著低于假手术组;治疗组和雌激素组大鼠O-PG表达显著高于对照组,RANK及RANKL的表达显著低于对照组。结论:采用卵巢摘除法成功建立大鼠骨质疏松模型;仙灵骨葆可促进骨质疏松大鼠OPG的表达,并抑制RANK及RANKL的表达,对骨质疏松模型大鼠有治疗作用。     

OPG、RANK、RANKL的结构、作用机制和在骨疾病中的作用

破骨细胞和成骨细胞分别介导骨的吸收过程和合成过程,而OPG、RANK、RANKL在调节二者的比例中发挥非常重要的作用.RANKL与RANK结合后可能通过三种途径:JNK途径、NF-κB途径和蛋白激酶B途径参与破骨细胞的分化,促进骨质的吸收;RANKL与OPG结合后能阻断RANKL与RANK的结合,由于缺乏RANKL-RANK产生的转录活化信号,破骨细胞分化成熟发生障碍,骨质的吸收受到抑制.OPG、RANK、RANKL同时也是免疫分子,在淋巴细胞、淋巴器官的分化、发育中起重要的作用,骨疾病与免疫系统之间存在着一定的关系.RANMKL/RANK与RANKI/OPG在生物体内保持着一定的比率,如果比率失衡,就会引起各种骨疾病.本篇综述总结了近年来OPG、RANK、RANKL结构、作用的新进展以及它们在骨疾病中的作用.     

Changes in RANKL/OPG/RANK gene expression in peripheral mononuclear cells following treatment with estrogen or raloxifene

The RANKL/OPG/RANK pathway is the key mediator of osteoclastogenesis. Mononuclear cells may be implicated in post-menopausal osteoporosis. The effect of estrogen or raloxifene on bone resorption and the expression of RANKL/OPG/RANK in peripheral blood mononuclear cells (PBMCs) was examined. Twenty-nine women with post-menopausal osteoporosis were treated with estrogen (HRT) or raloxifene for 12 months. Bone mineral density (BMD) was measured at baseline and at 12 months at the spine and hip. Serum C-terminal telopeptide (CTX) and OPG were measured at baseline and at 1, 3, 6 and 12 months. PBMCs were isolated from 17 women and changes in RANKL, OPG and RANK mRNA were determined. The effects of estrogen or raloxifene in PBMCs in vitro were also assessed. BMD increased following treatment (lumbar spine % change mean [S.E.M.]: 4.3% [0.9], p<0.001). Serum CTX decreased (6 months: -43.7% [6.0], p<0.0001). Serum OPG declined gradually (12 months: -26.4% [4.4], p<0.001). RANKL, OPG and RANK gene expression decreased (6 months: RANKL 50.0% [24.8] p<0.001, OPG: 21.7% [28] p<0.001, RANK: 76.6% [10.2] p=0.015). Changes in OPG mRNA correlated with changes in BMD (r=-0.53, p=0.027) and CTX (r=0.7, p=0.0044). Down-regulation in RANKL, OPG, RANK mRNA and reduction in bone resorption was also seen in vitro. These results suggest that the expression of RANKL/OPG/RANK in PBMCs are responsive to the slowing in bone turnover/remodeling associated with treatment with estrogen or raloxifene. Further confirmatory studies are needed.     

Imbalance of RANK,RANKL and OPG expression during tibial fracture repair in diabetic rats

To clarify the mechanisms of altered bone repair in the diabetic state, we investigated RANK, RANKL and OPG expression by immunohistochemistry and RT-PCR in the fracture sites of rats that were either healthy or made diabetic by alloxan. Histomorphometric analysis of the fracture site at 7 days after fracture revealed that diabetic rats (db) have significantly less hard tissue formation at the fracture site, compared to controls. The number of RANK, RANKL and OPG positive cells was decreased in the db group; however, the RANKL/OPG ratio was similar in controls and db at this time. At day 14, numbers of RANKL and OPG positive cells and the mRNA expression for these markers were higher in the control group than in db (P = 0.008). The RANKL/OPG ratio in the db group was greater than in controls. Our results demonstrate an imbalance of RANKL/OPG expression associated with diabetes that may contribute to the delay of fracture repair during the course of diabetes.     

OPG/RANK/RANKL系统与骨质疏松研究最新进展

骨质疏松是严重威胁中老年人健康的骨科常见病,OPG/RANK/RANKL是参与调节骨重建的最重要的分子系统之一,与骨疾病相关的骨质疏松有密切联系,并已成为药物设计的新靶点.因此,对该系统的深入研究将为骨生理、病理机制阐明及骨疾病防治带来积极影响.     

Assessment and clinical implications of RANK/RANKL/OPG pathway as markers of bone tumor progression in patients with NET harboring bone metastases

Abstract

Introduction: The impact on the survival of bone metastases (BM) in patients with neuroendocrine tumor (NET) is a matter of debate. BM have a key role in causing symptoms and in decreasing patients’ quality of life. Although the mechanisms of the development of BM are not completely clear, it is now well understood that the Receptor Activator of Nuclear factor Kappa-B-/Ligand (RANK/RANKL)/osteoprotegerin (OPG) pathway plays a relevant role.

Aim: To characterize the RANK/RANKL/OPG pathway in patients affected with NET.

Patients and methods: Two cohorts of 15 patients each were enrolled in the study; one cohort was affected with NET without BM and the second cohort was affected with NET with BM. The serum RANK/RANKL/OPG pathway was assessed in both the groups.

Results: Serum OPG levels and RANKL/OPG ratio were lower and higher, respectively, in NET patients harboring BM than in those without BM. During the ROC analysis, a cut-off value of 1071?pg/ml for OPG and 0.62 for RANKL/OPG ratio were able to significantly distinguish between the two groups.

Conclusions: This study indicates that RANK/RANKL/OPG pathway is imbalanced in patients with NET harboring BM. Specific alterations of this pathway could predict an early development of BM.     

Involvement of integrin up‐regulation in RANKL/RANK pathway of chondrosarcomas migration

Invasion of tumor cells is the primary cause of therapeutic failure in malignant chondrosarcomas treatment. Receptor activator of nuclear factor‐κB ligand (RANKL) and its receptor, RANK, play a key roles in osteoclastogenesis and tumor metastasis. We found that the RANKL and RANK expression in human chondrosarcoma tissues was higher than that in normal cartilage. We also found that RANKL directed the migration and increased cell surface expression of β1 integrin in human chondrosarcoma cells (JJ012 cells). Pretreatment of JJ012 cells with MAPK kinase (MEK) inhibitors, PD98059 or U0126, inhibited the RANKL‐induced migration and integrin expression. Stimulation of cells with RANKL increased the phosphorylation of MEK and extracellular signal‐regulating kinase (ERK). In addition, NF‐κB inhibitor (PDTC) or IκB protease inhibitor (TPCK) also inhibited RANKL‐induced cells migration and integrin up‐regulation. Taken together, these results suggest that the RANKL acts through MEK/ERK, which in turn activates IKKα/β and NF‐κB, resulting in the activation of β1 integrin and contributing to the migration of human chondrosarcoma cells. J. Cell. Biochem. 111: 138–147, 2010. © 2010 Wiley‐Liss, Inc.     

胰岛素对2型糖尿病骨质疏松大鼠血清与骨OPG、RANKL表达的影响

目的:探讨胰岛素对2型糖尿病骨质疏松大鼠血清及骨OPG(osteoprotegerin)、RANKL(OPG receptor activator nuclear factork B)表达水平的影响。方法:以高脂高糖饲料喂养4周同时饮用3%果糖水导致胰岛素抵抗小鼠,再以小剂量链脲佐菌素(30mg/kg)腹腔注射1次,2周后诱导建立2型糖尿病小鼠模型。对照组动物则给予正常饲料及饮用水进行喂养。模型建立成功后,对模型2组大鼠进行胰岛素治疗,分别采用OPG和RANKLelisa试剂盒对正常动物模型和糖尿病动物模型血清和骨组织中OPG,RANKL含量进行比较分析,采用血糖分析仪对不同组动物的血糖进行比较分析,采用骨密度分析仪对动物的骨密度进行分析,了解高血糖对于骨密度及血清,骨组织中OPG,RANKL含量的影响以及胰岛素对高血糖骨质疏松造成的结果的影响。结果:相较于正常组大鼠,模型组大鼠血清及髂骨中OPG、血糖、糖化血红蛋白、髂骨密度表达显著下调(P0.05),而RANKL表达显著上调(P0.05),胰岛素处理的模型大鼠血清及骨中OPG含量较模型组大鼠显著升高,血清及骨组织中RANKL表达显著下调(P0.05)。结论:胰岛素能够显著降低2型糖尿病骨质疏松大鼠血清及骨组织中RANKL的表达,显著上调OPG的表达。     

钛颗粒对小鼠颅骨OPG/RANKL mRNA及蛋白表达的影响

目的:观察钛颗粒对小鼠颅骨中OPG/RANKL mRNA及其蛋白表达的影响,探讨关节置换术后骨溶解的发生机制。方法:取成年BALB/C小鼠40只,随机分为假手术组、钛颗粒低剂量组、钛颗粒中剂量组及高剂量组,每组10只。除假手术组外,其余各组分别将钛颗粒15、30、60 mg涂抹于小鼠颅骨表面后缝合切口。8周后取颅骨组织及外周血,运用real-time PCR及ELISA技术测定OPG/RANKL基因及蛋白表达情况。结果:与假手术组相比,钛颗粒低剂量组外周血中OPG蛋白表达及颅骨组织中OPG mRNA的表达均显著上升(P0.01),外周血中RANKL蛋白表达降低,但无统计学差异,颅骨组织中RANKL mRNA表达无显著差异;中剂量组及高剂量组外周血中OPG蛋白表达显著降低(p0.01),RANKL蛋白表达显著升高(P0.01),OPG mRNA表达显著降低(P0.01),RANKL mRNA表达显著升高(P0.01)。低中高三种不同剂量钛颗粒组组间相比,外周血中OPG、RAKNL蛋白及颅骨组织中其mRNA表达均存在明显差异(P0.01),高剂量组对OPG、RANKL蛋白及mRNA表达的影响更显著。结论:钛颗粒可以改变OPG/RANKL的mRNA及蛋白表达量,这可能是其导致关节置换术后体骨溶解进而产生松动的原因之一。     

兔膝关节损伤后软骨细胞中OPG与RANKL表达

目的:随着中国经济的高速发展,人民生活水平日益增高。体育运动,高能量机动车造成的膝关节损伤数量不断增加,关节软骨的损伤恢复一直不是很理想。针对其后期的恢复研究做了许多相关的实验。本实验通过对兔膝关节软骨细胞损伤后软骨细胞中OPG(骨保护素)与RANKL(核激活因子受体配体)两种因子在损伤后与正常软骨细胞中的表达的比较,探讨损伤后软骨细胞中OPG和RANKL的表达。方法:25只大耳白兔随机分成5组,每组5只。前4组在10天完成20只兔左后腿膝关节软骨损伤动物模型,最后1组5只做手术对照组,术后处置相同。在术后1周,2周,4周,8周时取膝关节软骨损伤处关节软骨制成标本对照组取正常膝关节软骨制成标本。应用HE染色观察软骨细胞恢复情况及SP免疫组化法检测软骨细胞中OPG与RANKL的表达。在光镜下观察,通过医学图像分析软件(media cybernetics image-proplus6.0)图片分析,测定镜下相对灰度值并计算每个标本的平均灰度值,单因素方差分析法进行数据分析。结果:OPG在膝关节损伤后2-4周表达最高,4-8周有下降趋势。RANKL在膝关节软骨损伤后明显表达并逐步的呈升高趋势。实验组镜下观察表达较强烈,测定镜下平均灰度值与对照组有显著性差异(P0.05)。结论:1.OPG在膝关节软骨损伤后显著性表达。2-4周表达较高,4-8周趋于降低。2.RANKL在膝关节软骨损伤后显著表达,1-8周呈平稳上升趋势。     

黄芩苷对慢性萎缩性胃炎模型鼠OPG/RANKL轴的影响

摘要 目的：探讨黄芩苷对慢性萎缩性胃炎模型鼠OPG/RANKL轴的影响。方法：将建模成功的大鼠(n=42)平分为三组-模型组、雷尼替丁组与黄芩苷组,黄芩苷组灌胃6.3 g/kg体重的黄芩苷溶液(5 mg?kg^-1),雷尼替丁组灌胃6.3 g/kg体重的雷尼替丁生理盐水溶液(150 mg?kg^-1),模型组灌胃与同容积的生理盐水,记录不同时间点OPG/RANKL轴表达变化情况。结果：雷尼替丁组与黄芩苷组治疗后2 w与4 w的体重高于模型组(P<0.05),黄芩苷组高于雷尼替丁组(P<0.05)。雷尼替丁组与黄芩苷组治疗后2 w与4 w的胃黏膜组织评分低于模型组(P<0.05),黄芩苷组低于雷尼替丁组(P<0.05)。雷尼替丁组与黄芩苷组治疗后2 w与4 w的血清NO与SOD含量高于模型组(P<0.05),黄芩苷组高于雷尼替丁组(P<0.05)。雷尼替丁组与黄芩苷组治疗后2 w与4 w的胃窦组织OPG、RANKL蛋白相对表达水平高于对照组,黄芩苷组高于雷尼替丁组(P<0.05)。结论：黄芩苷治疗慢性萎缩性胃炎模型鼠能激活OPG/RANKL轴,提高血清NO与SOD含量,能减少胃黏膜组织损伤,提高大鼠体重。     

吸烟对种植体周围炎患者龈下菌群、龈沟液炎症因子和RANKL/OPG比值的影响

摘要 目的：探讨吸烟对种植体周围炎患者龈下菌群分布、龈沟液炎症因子白细胞介素-4（IL-4）、白细胞介素-5（IL-5）、白细胞介素-6（IL-6）、白细胞介素-8（IL-8）、白细胞介素-17（IL-17）和核因子-κB受体活化因子配体/骨保护素（RANKL/OPG）比值的影响。方法：选择2019年3月至2022年3月首都医科大学附属北京友谊医院口腔科收治的种植体周围炎患者99例（共151颗种植体）,根据是否吸烟分为吸烟组（45例,68颗种植体）和非吸烟组（54例,83颗种植体）,比较两组患者种植体牙周改良菌斑指数（mPLI）、牙龈出血指数（GBI）、种植体周围探诊深度（PPD）,采集两组龈下菌斑进行细胞培养并进行菌种鉴定,分析两组龈下菌群分布情况,比较两组龈沟液中IL-4、IL-5、IL-6、IL-8、IL-17、RANKL/OPG比值。结果：吸烟组mPLI、GBI、PPD高于不吸烟组（P＜0.05）。吸烟组厌氧菌检出率高于非吸烟组（P＜0.05）,有益菌检出率低于非吸烟组（P＜0.05）,两组需氧菌检出率比较差异无统计学意义（P＞0.05）。吸烟组龈沟液IL-4、IL-5、IL-6、IL-8、IL-17水平均高于非吸烟组（P＜0.05）。吸烟组龈沟液RANKL水平、RANKL/OPG比值高于非吸烟组（P＜0.05）,OPG水平低于非吸烟组（P＜0.05）。结论：吸烟可导致种植体周围炎患者龈下厌氧菌增加,加重炎症反应,增加牙槽骨吸收风险。     

Expression of RANKL/OPG during bone remodeling in vivo

The interaction between receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG) plays a dominant role in osteoclastogenesis. As both proteins are produced by osteoblast lineage cells, they are considered to represent a key link between bone formation and resorption. In this study, we investigated the expression of RANKL and OPG during bone remodeling in vivo to determine the relationship between osteoclastogenic stimulation and osteoblastic differentiation.Total RNA was prepared from rat femurs after marrow ablation on days 0, 3, 6, and 9. The temporal activation patterns of osteoblast-related genes (procollagen α1 (I), alkaline phosphatase, osteopontin, and osteocalcin) were examined by Northern blot analysis. An appreciable increase in the expression of these osteoblast markers was observed on day 3. The peak increase in gene expression was observed on day 6 followed by a slight reduction by day 9. Real-time PCR analysis showed that the OPG mRNA expression was markedly upregulated on day 6 and slightly decreased on day 9. In contrast, RANKL mRNA expression was increased by more than 20-fold on day 9. The RANKL/OPG ratio, an index of osteoclastogenic stimulation, peaked on day 9. Histological analysis showed that RANKL and OPG immunoreactivity were predominantly associated with bone marrow cells. The expression of bone formation markers was activated in the bone formation phase, followed by the stimulation of RANKL/OPG expression in the bone resorption phase, which confirmed that these molecules are key factors linking bone formation to resorption during bone remodeling.     

不同温度下成骨细胞增殖及其OPG/RANKL mRNA表达的影响

目的:探讨不同温度下对小鼠成骨细胞MC3T3-E1的增殖以及OPG/RANKL表达水平的影响。方法:1.以小鼠成骨细胞MC3T3-E1为体外实验模型,MTT法检检测细胞的增殖情况。2.RT-PCR方法检测MC3T3-E1OPG/RANKL mRNA的表达水平。结果:设定对照组为37℃,高于对照组(38℃-39℃-40℃-41℃-42℃)分别作用于MC3T3-E1细胞1小时/天,连续1周,可刺激细胞增殖,OD值显著增加(P<0.05)。同时可增加OPG mRNA表达,降低RANKL mRNA表达,呈温度梯度依赖性。结论:热刺激促进MC3T3-E1细胞增殖,同时通过调节OPG/RANKL mRNA的表达,直接促进骨形成,抑制骨吸收。     

Elastase induced lung epithelial cell apoptosis and emphysema through placenta growth factor

Chronic pulmonary obstructive disease (COPD) is the fourth leading cause of death worldwide, however, the pathogenic factors and mechanisms are not fully understood. Pulmonary emphysema is one of the major components of COPD and is thought to result from oxidative stress, chronic inflammation, protease–antiprotease imbalance and lung epithelial (LE) cell apoptosis. In our previous studies, COPD patients were noted to have higher levels of placenta growth factor (PlGF) in serum and bronchoalveolar lavage fluid than controls. In addition, transgenic mice overexpressing PlGF developed pulmonary emphysema and exposure to PlGF in LE cells induced apoptosis. Furthermore, intratracheal instillation of porcine pancreatic elastase (PPE) on to PlGF wild type mice induced emphysema, but not in PlGF knockout mice. Therefore, we hypothesized that PPE generates pulmonary emphysema through the upregulation of PlGF expression in LE cells. The elevation of PlGF then leads to LE cell apoptosis. In the present study, we investigated whether PPE induces PlGF expression, whether PlGF induces apoptosis and whether the downstream mechanisms of PlGF are related to LE cell apoptosis. We found that PPE increased PlGF secretion and expression both in vivo and in vitro. Moreover, PlGF-induced LE cell apoptosis and PPE-induced emphysema in the mice were mediated by c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) pathways. Given these findings, we suggest that the increase in PlGF and PlGF-induced JNK and p38 MAPK pathways contribute to PPE-induced LE cell apoptosis and emphysema. Regulatory control of PlGF and agents against its downstream signals may be potential therapeutic targets for COPD.     

Differential coexpression networks in bronchiolitis and emphysema phenotypes reveal heterogeneous mechanisms of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease with multiple molecular mechanisms. To investigate and contrast the molecular processes differing between bronchiolitis and emphysema phenotypes of COPD, we downloaded the GSE69818 microarray data set from the Gene Expression Omnibus (GEO), which based on lung tissues from 38 patients with emphysema and 32 patients with bronchiolitis. Then, weighted gene coexpression network analysis (WGCNA) and differential coexpression (DiffCoEx) analysis were performed, followed by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes enrichment analysis (KEGG) analysis. Modules and hub genes for bronchiolitis and emphysema were identified, and we found that genes in modules linked to neutrophil degranulation, Rho protein signal transduction and B cell receptor signalling were coexpressed in emphysema. DiffCoEx analysis showed that four hub genes (IFT88, CCDC103, MMP10 and Bik) were consistently expressed in emphysema patients; these hub genes were enriched, respectively, for functions of cilium assembly and movement, proteolysis and apoptotic mitochondrial changes. In our re‐analysis of GSE69818, gene expression networks in relation to emphysema deepen insights into the molecular mechanism of COPD and also identify some promising therapeutic targets.     

Pro-inflammatory phenotype of COPD fibroblasts not compatible with repair in COPD lung

Chronic obstructive pulmonary disease (COPD) is characterized by loss of elastic fibres from small airways and alveolar walls, with the decrease in elastin increasing with disease severity. It is unclear why there is a lack of repair of elastic fibres. We have examined fibroblasts cultured from lung tissue from subjects with or without COPD to determine if the secretory profile explains lack of tissue repair. In this study, fibroblasts were cultured from lung parenchyma of patients with mild COPD [Global initiative for chronic Obstructive Lung Disease (GOLD) 1, n= 5], moderate to severe COPD (GOLD 2-3, n= 12) and controls (non-COPD, n= 5). Measurements were made of proliferation, senescence-associated β-galactosidase-1, mRNA expression of IL-6, IL-8, MMP-1, tropoelastin and versican, and protein levels for IL-6, IL-8, PGE(2,) tropoelastin, insoluble elastin, and versican. GOLD 2-3 fibroblasts proliferated more slowly (P < 0.01), had higher levels of senescence-associated β-galactosidase-1 (P < 0.001) than controls and showed significant increases in mRNA and/or protein for IL-6 (P < 0.05), IL-8 (P < 0.01), MMP-1 (P < 0.05), PGE(2) (P < 0.05), versican (P < 0.05) and tropoelastin (P < 0.05). mRNA expression and/or protein levels of tropoelastin (P < 0.01), versican (P < 0.05), IL-6 (P < 0.05) and IL-8 (P < 0.05) were negatively correlated with FEV1% of predicted. Insoluble elastin was not increased. In summary, fibroblasts from moderate to severe COPD subjects display a secretory phenotype with up-regulation of inflammatory molecules including the matrix proteoglycan versican, and increased soluble, but not insoluble, elastin. Versican inhibits assembly of tropoelastin into insoluble elastin and we conclude that the pro-inflammatory phenotype of COPD fibroblasts is not compatible with repair of elastic fibres.