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.     

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.     

人骨保护素(OPG)重组腺病毒的制备及其生物活性研究

采用RT-PCR法得到人OPG的编码区cDNA,克隆至穿梭质粒pShuttle,构建重组有OPG编码区cDNA的腺病毒DNA,经Pac I 酶切线性化,在脂质体介导下转染HEK293细胞,制备重组腺病毒并测定病毒滴度约为5×10⁶～1.5×10⁷ pfu/mL。体外感染小鼠成肌细胞C2C12,Western blot及ELISA检测证实有OPG蛋白的表达,并可在细胞培养上清中持续表达6周。感染OPG重组腺病毒的C2C12细胞生长状态良好、细胞周期无明显变化。将重组腺病毒加入体外培养的小鼠骨髓细胞的培养基中,诱导形成的破骨细胞数量及在象牙片上形成的吸收陷窝的数量显著减少（P<0.01）。      

RANKL/RANK/OPG信号通路对骨代谢和血管钙化作用机制的研究现状

核因子-κB受体活化因子配体(receptor activator of nuclear factor-kappa B ligand,RANKL)/核因子-κB受体活化因子(receptor activator of nuclear factor kappa B,RANK)/骨保护素(osteoprotegerin,OPG)信号通路是调节骨代谢过程中破骨细胞功能的重要通路。OPG能够与RANKL结合并阻止其与RANK结合,抑制破骨细胞生成从而抑制骨吸收,增加骨密度,改善骨质疏松。其中,RANKL/OPG的比值是骨吸收和骨形成平衡的关键。目前血管钙化已不再被看作是单纯的钙磷的被动沉积,而是由血管平滑肌细胞和内皮细胞主动参与的一种与骨形成相似的病理生理过程。在这个过程中,RANKL/RANK/OPG信号通路也起到重要作用。本文就RANKL/RANK/OPG信号通路在骨代谢和血管钙化中的作用机制进行了综述。     

RANKL与骨重建

骨是一种动态更新的组织,它不断进行骨吸收（bone resorption）与骨形成（bone formation）的平衡,这个过程称之为骨重建（bone remodeling）．核因子κB受体活化因子配体（receptor activator of nuclear factor κB ligand,RANKL）是骨吸收和骨形成耦联的关键,具有诱导破骨细胞（osteoclast, OC）生成、活化,抑制破骨细胞凋亡的作用．RANKL最初发现于活化的T细胞,但骨重建过程中RANKL主要来源于骨细胞、成骨细胞和骨髓基质细胞．RANKL/核因子κB受体活化因子（receptor activator of nuclear factor κB,RANK）/骨保护素（osteoprotegerin, OPG）信号通路在成骨细胞调控破骨细胞生成的过程中起着重要的调节作用,是维持骨重建平衡的关键．本文就RANKL及其在骨中的分子作用机制作一综述.     

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。     

破骨细胞骨吸收功能的检测方法

破骨细胞是一种多核的,具有骨吸收功能的骨组织细胞,在骨吸收过程中起着至关重要的作用.破骨细胞骨吸收功能的异常会引发一系列的临床病症,如骨质疏松症、关节置换术后假体松动、骨硬化症和牙周病变等.破骨细胞骨吸收功能的进一步研究对于各类骨疾病的防治具有重要的意义.然而破骨细胞骨吸收功能的检测方法一直以来是制约破骨细胞研究的瓶颈之一.为此,围绕破骨细胞骨吸收功能的检测方法做一综述.     

丹参素抑制RANKL诱导的破骨细胞分化

目的：研究丹参素对RANKL诱导的破骨细胞分化的影响。方法：运用冲洗法从股骨、胫骨中获得小鼠骨髓源性单核巨噬细 胞用于体外RANKL 诱导的破骨细胞分化,同时,施加不同剂量的丹参素干预,经TRAP染色法在形态学上观察观,蛋白印迹法检 测蛋白水平的变化,实时定量PCR 检测mRNA 水平变化来研究丹参素对RANKL诱导的骨髓源单核巨噬细胞破骨分化的影响。 结果：①不同剂量丹参素干预组与对照组相比,TRAP 阳性破骨细胞数量得到了明显抑制（P<0.05）。②不同剂量丹参素干预组与 对照组相比,磷酸化Akt的上调量被明显的降低。磷酸化p38 MAPK,JNK和ERK 的变化则不明显。③不同剂量丹参素干预组与 对照组相比,c-fos,TRAP,CTSK 等参与破骨细胞分化的重要基因表达减少,NFATc1 变化不明显。结论：丹参素通过下调磷酸化 Akt水平的途径抑制了RANKL诱导的破骨细胞分化。     

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。     

巴戟天及其糖提取物对于体外培养成骨细胞OPG/RANKL基因系统表达的影响

目的:探讨巴戟天及多糖提取物对成骨细胞骨保护素(OPG)/核因子κB受体活化因子配体(RANKL)基因系统表达的影响。方法:取2~3天的SD大鼠5只分离原代成骨细胞,再取8周龄SD大鼠35只随机分为七组,对照组不进行处理,三组给予10 g/L、50 g/L、100 g/L巴戟天水灌胃,其余三组分别给予10 g/L、50 g/L、100 g/L巴戟天多糖灌胃,72 h后采用采用ELISA法测定培养液中OPG、RANKL及骨钙素的含量,采用MTT法检测不同浓度巴戟天水及多糖提取物对大鼠成骨细胞增殖的影响,采用荧光定量PCR检测OPG和RANKL mRNA表达情况;通过Westernblot检测OPG和RANKL蛋白表达水平。结果:巴戟天水及多糖提取物组A570nm、ALP活性、骨钙素含量、OPG/RANKL mRNA表达量、OPG和RANKL蛋白表达阳性密度均高于对照组(P0.05);A 570 nm、ALP活性、骨钙素含量、OPG/RANKL mRNA表达量、OPG和RANKL蛋白表达阳性密度均高于同等剂量的水提取物各组(P0.05);巴戟天多糖组中随着多糖剂量的升高A 570 nm、ALP活性、骨钙素含量、OPG/RANKL mRNA表达量、OPG和RANKL蛋白表达阳性密度,差异比较有统计学意义(P0.05)。结论:巴戟天水及多糖提取物均能促进体外培养成骨细胞的增殖,提高成骨细胞活性。     

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.     

Ligustilide suppresses RANKL-induced osteoclastogenesis and bone resorption via inhibition of RANK expression

Osteoclast (OC) is the only cell involved in bone resorption. Dysfunction of OCs leads to a variety of bone diseases. Ligustilide (LIG) is the main component of the volatile oil isolated and purified from Angelica sinensis. LIG exerts many pharmacological activities, but its effects on osteoclastogenesis and bone resorption are still unclear. Our study showed that LIG inhibited receptor activator of nuclear factor-κB (NF-κB) ligand-induced OC formation and activation in a dose-dependent manner. Additionally, LIG downregulated the messenger RNA (mRNA) expression of OC-specific genes, such as V-ATPase d2, tartrate-resistant acid phosphatase, a dendritic cell-specific transmembrane protein, cathepsin K, and nuclear factor of activated T cells cl. Furthermore, LIG blocked the activation of NF-κB/extracellular signal-regulated kinase/p38/immunoreceptor tyrosine-based activation motif signaling pathways. Crucially, the expression of tumor necrosis factor receptor-associated factor 6 proteins and the expression of receptor activator of NF-κB mRNA were inhibited by LIG. However, LIG did not affect the formation and mineralization of osteoblasts. Collectively, this observation suggests that LIG may serve as a promising agent for the prevention and treatment of diseases caused by abnormal bone resorption.     

The OPG/RANKL/RANK system in metabolic bone diseases

The OPG/RANKL/RANK cytokine system is essential for osteoclast biology. Various studies suggest that human metabolic bone diseases are related to alterations of this system. Here we summarize OPG/RANKL/RANK abnormalities in different forms of osteoporoses and hyperparathyroidism. Skeletal estrogen agonists (including 17beta-estradiol, raloxifene, and genistein) induce osteoblastic OPG production through estrogen receptor-alpha activation in vitro, while immune cells appear to over-express RANKL in estrogen deficiency in vivo. Of note, OPG administration can prevent bone loss associated with estrogen deficiency as observed in both animal models and a small clinical study. Glucocorticoids and immunosuppressants concurrently up-regulate RANKL and suppress OPG in osteoblastic cells in vitro, and glucocorticoids are among the most powerful drugs to suppress OPG serum levels in vivo. As for mechanisms of immobilization-induced bone loss, it appears that mechanical strain inhibits RANKL production through the ERK 1/2 MAP kinase pathway and up-regulates OPG production in vitro. Hence, lack of mechanical strainduring immobilization may favor an enhanced RANKL-to-OPG ratio leading to increased bone loss. As for hyperparathyroidism, chronic PTH exposure concurrently enhances RANKL production and suppresses OPG secretion through activation of osteoblastic protein kinase A in vitro which would favour increased osteoclastic activity. In sum, the capacity for OPG to antagonize the increases in bone loss seen in many rodent models of metabolic bone disease implicates RANKL/OPG imbalances as the likely etiology and supports the potential role for a RANKL antagonist as a therapeutic intervention in these settings.     

The effects of fatty acids consumption on OPG/RANKL/RANK system in cardiovascular diseases: Current status and future perspectives for the impact of diet-gene interaction

Cardiovascular disease (CVD) is an overall term that comprises a number of related pathologies, these include peripheral arterial disease, cerebrovascular disease, coronary heart disease (CHD), venous thromboembolism, and rheumatic and congenital heart diseases. Fatty acids in the diet have been reported to affect CVD. The OPG/RANKL/RANK system appears to have a role in CVD outcomes. However, there have been few studies on the impact of diet-gene interaction for effects of fatty acids consumption on the OPG/RANKL/RANK system in CVD. This review focuses on the effects of fatty acids on OPG/RANKL/RANK in CVD.     

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.     

Hyperbaric oxygen therapy modulates serum OPG/RANKL in femoral head necrosis patients

Hyperbaric oxygen therapy (HBOT) has beneficial effects on avascular necrosis of femoral head (ANFH), but its mechanism of action is still unclear. We investigated if HBOT upregulates serum osteoprotegerin (OPG) and/or inhibits osteoclast activation. 23 patients with unilateral ANFH at stage I, II and III consented to the study: the patients received standard HBOT. Serum OPG levels were obtained at the beginning of HBOT (T0), after 15 sessions (T1), 30 sessions (T2), after a 30-day break (T3), and after 60 sessions (T4). Magnetic resonance imaging (MRI) was obtained at T0 and about one year from the end of HBO treatments. Lesion size was compared between pre- and post-HBOT. 19 patients completed the study. HBOT reduced pain symptoms in all patients. HBOT significantly reduced lesion size in all stage I and II patients and in 2 of 11 stage III patients. HBOT increased serum OPG levels but receptor activator of nuclear factor kappa-B ligand (RANKL) levels did not change.