Lack of receptor activator of nuclear factor-kB ligand (RANKL) expression and functional production by human multiple myeloma cells

The direct expression and production of the critical osteoclastogenic factor, the receptor activator of NF-kB ligand (RANKL), is a matter of controversy. In this study we definitively demonstrate by both qualitative and quantitative polymerase chain reaction analysis that human myeloma cells do not express significant levels of RANKL mRNA or produce RANKL able to stimulate osteoclast formation.     

RANK (receptor activator of nuclear factor-kappaB) and RANKL expression in multiple myeloma

The new members of the tumour necrosis factor (TNF) receptor-ligand family, receptor activator of nuclear factor-kappaB ligand (RANKL) and its receptor RANK, play a crucial role in osteoclast differentiation and activation. An increased expression of RANKL and/or RANK may be involved in the excessive bone resorption observed in multiple myeloma (MM). We used immunohistochemistry to study RANK and RANKL expression in bone marrow (BM) biopsies obtained at diagnosis in 15 MM patients, six patients with monoclonal gammopathy of undetermined significance (MGUS) and 10 normal BM biopsies. Plasma cells were not labelled with anti-RANKL or anti-RANK antibodies. In all biopsies, RANKL was expressed in endosteal bone surface, around vessels and in cells characterized by cytoplasmic expansions. These last cells did not express CD45 and were vimentin positive, corresponding to bone marrow stromal cells. Numerous stromal cells expressed RANKL in MM and MGUS specimens, with a greater expression in MM than in MGUS. Very few cells were stained with anti-RANKL in normal BM specimens. With the anti-RANK antibody, small mononuclear cells in the bone microenvironment were positive and were identified as erythroblast cells. In conclusion, we showed that RANKL was expressed in reticular stromal cells, with a greater intensity in myeloma specimens. These results suggest that RANKL overexpressed by bone marrow stromal cells may contribute to the high rate of bone resorption observed in MM.     

Receptor activator of nuclear factor kappa B ligand (RANKL): another link between breast and bone.

Mice rendered null for the genes encoding receptor activator of nuclear factor kappa B ligand (RANKL) or its receptor, RANK, are osteopetrotic because of failure of osteoclast development. The failure of lactation owing to the lack of development of lobulo-alveolar structures during pregnancy, despite earlier stages of mammary gland development being normal, is now added to each of these phenotypes. The breast phenotype in RANKL-/- (but not in RANK-/-) mice is rescued by treatment of pregnant mice with RANKL, indicating a key role for these tumour necrosis factor (TNF) ligand and receptor family members in a crucial terminal step in breast development and lactation. Both RANKL and RANK are synthesized by mammary epithelial cells, with both prolactin and parathyroid hormone-related protein (PTHrP) able to enhance production of mRNA for RANKL. These findings reveal a paracrine-autocrine system in lactation control, with novel signalling pathways that reflect intercellular communication processes in bone.     

Role of receptor activator of nuclear factor-kappa B ligand (RANKL), osteoprotegerin and macrophage protein 1-alpha (MIP-1a) in monoclonal gammopathy of undetermined significance (MGUS)

The aim of this study was to evaluate the role of markers of bone remodelling, and osteoclast activation/function in patients with monoclonal gammopathy of undetermined significance (MGUS). We have measured serum levels of soluble RANKL (sRANKL), osteoprotegerin (OPG), macrophage inflammatory protein-1alpha (MIP-1alpha), markers of bone resorption [N-telopeptide of collagen type-I (NTX), and tartrate-resistant acid phosphatase isoform-5b (TRACP-5b)] and bone formation [bone-alkaline phosphatase (bALP)] in 40 MGUS patients. These parameters were compared with those of 42 newly diagnosed myeloma patients, and 45 healthy, gender- and age-matched controls. MGUS patients had elevated levels of NTX, sRANKL, and sRANKL/OPG ratio compared with controls (P < 0.0001). Furthermore, TRACP-5b, MIP-1alpha and NTX were decreased in patients with MGUS compared with myeloma patients (P < 0.001), while OPG and bALP were increased (P < 0.001). Serum levels of MIP-1alpha, as well as TRACP-5b, and sRANKL/OPG ratio were reduced, while bALP was increased in MGUS patients, even when compared with myeloma patients who had stage I/II disease. These results demonstrate that increased osteoclastogenesis leading to increased bone resorption is present in MGUS but seems to be compensated for by normal bone formation, which is absent in MM. Furthermore MIP-1alpha, bALP, and sRANKL/OPG may be useful tools for distinguishing between cases of MGUS and early myeloma.     

破骨细胞分化因子和护骨素 mRNA在OVX小鼠骨组织的相对表达

目的　研究破骨细胞分化因子 (ODF)和护骨素 (OPG)mRNA在OVX小鼠骨组织中的相对表达水平 ,探讨ODF和OPG在绝经后骨质疏松 (PMO)发病中的意义。　方法　将 4 0只小鼠随机分为 5组 ,第Ⅰ、Ⅴ组行假手术 ,两组小鼠分别在术后 1周和 5周处死 ;第Ⅱ、Ⅲ组行卵巢切除手术 ,分别在术后 1周和 5周处死 ;Ⅳ组行卵巢切除手术 ,术后第 2天给苯甲酸雌二醇治疗 ,5周后处死。小鼠处死后 ,提取其骨组织总RNA ,RT PCR检测ODF和OPGmRNA表达水平。　结果　去卵巢后Ⅱ、Ⅲ、Ⅳ组ODF与OPGmRNA比值 (分别为 1 16 78± 0 2 873、0 80 93± 0 14 14、0 6 6 4 0± 0 0 935 )显著增高 ,采用雌激素防治可使其一定程度上恢复。　结论　PMO发病中雌激素减退所导致的骨丢失与骨组织ODF和OPG的mRNA相对表达水平紊乱有关     

New insight in the mechanism of osteoclast activation and formation in multiple myeloma: focus on the receptor activator of NF-kappaB ligand (RANKL)

The increase of osteoclast activation and formation is mainly involved in the development of the osteolytic bone lesions that characterize multiple myeloma (MM) patients. The mechanisms by which myeloma cells induce bone resorption have not been clear for many years. Recently, new evidence has elucidated which factors are critically involved in the activation of osteoclastic cells in MM. The potential role of the critical osteoclastogenic factor, the receptor activator of NF-kappaB ligand (RANKL), and its soluble antagonist osteoprotegerin (OPG) in the activation of bone resorption in MM is summarized in this review. It has been demonstrated that human MM cells induce an imbalance in the bone marrow environment of the RANKL/OPG ratio in favor of RANKL that triggers the osteoclast formation and activation leading to bone destruction. The direct production of the chemokine macrophage inflammatory protein-1 alpha (MIP-1alpha) by myeloma cells, in combination with the RANKL induction in BM stromal cells in response to myeloma cells, are critical in osteoclast activation and osteoclastogenesis.     

Methylation of receptor activator of nuclear factor kappa ligand (RANKL) gene in rheumatoid arthritis patients

BackgroundRheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by synovitis, cartilage damage and bone resorption. Methylation of deoxyribonucleic acid plays a crucial role in repressing gene expression. Receptor activator of nuclear factor-kappa ligand (RANKL) controls bone homeostasis.Aim of the workTo assess the serum level of RANKL and its gene promoter methylation in RA patients and to determine its association with clinical characteristics and disease activity.Patients and methodsThe study included 40 RA patients and 40 control. The disease activity score (DAS28) was assessed. Frequency of RANKL gene promoter methylation was determined by quantitative methylation specific PCR (QMSP) and serum RANKL level by enzyme linked immunosorbant assay (ELISA).ResultsPatients mean age was 46.8 ± 10.6 years, 36 females and 4 males (F:M 9:1) with median disease duration 4.5 years. Positive rheumatoid factor, anti-cyclic citrullinated peptide and C-reactive protein were present in 65 %, 75 % and 55 % of cases. Methylation percentage of RANKL gene promoter was significantly lower in patients (3.4 %) than in controls (3.7 %)(p = 0.035) while serum level was significantly increased in patients (9.1 ng/ml,5.3–11.8 ng/ml) than in controls (5.7 ng/ml, 4.5–8 ng/ml)(p = 0.003). RANKL methylation frequency was inversely associated with serum level (rs = -0.21,p = 0.06). There was no significant correlation of RANKL serum level and methylation with DAS28 (r = 0.03,p = 0.87 and r = 0.06,p = 0.73 respectively). RANKL serum level (>9.5 ng/ml) and methylation percentage (≤9%) significantly discriminate RA cases from control (sensitivity 47.5 %, specificity 91.9 %; p = 0.001 and sensitivity 100 %, specificity 40 %; p = 0.03 respectively).ConclusionRA patients expressed elevated serum RANKL with low methylation.     

破骨细胞和骨保护素/细胞核因子-κB受体活化因子配体系统在银屑病关节炎骨质破坏中的作用

目的 探讨银屑病关节炎( PsA)患者体内破骨细胞和骨保护素/细胞核因子-κB受体活化因子配体(OPG/RANKL)系统的水平与骨质破坏的关系.方法 分离41例PsA患者、20例骨关节炎患者及24名健康对照者的外周血单个核细胞诱导生成破骨细胞,采用耐酒石酸酸性磷酸酶染色法进行鉴定.运用酶联免疫吸附试验( ELISA)法测定3组患者血清中的骨保护素和RANKL的水平,同时收集PsA患者的临床实验室资料.采用单因素方差分析和直线回归分析进行统计学处理.结果 PsA组的破骨细胞数目[(17.7±4.8)个,视野]明显多于骨关节炎组[(6.5±1.6)个,视野]和健康对照组[(6.4±1.6)个,视野],差异有统计学意义(P＜0.05).PsA组的RANKL水平[(178±38) pg/ml]明显高于骨关节炎组[( 32±4) pg/ml]和健康对照组[(67±17) pg/ml],差异有统计学意义(P＜0.05).与无骨质破坏的PsA组相比较,破骨细胞和RANKL的水平在有骨质破坏的PsA组中明显增高[(17.6±0.9)个／视野与(7.9±1.3)个／视野和(199±72) pg/ml与(128±44) pg/ml],差异有统计学意义(P＜0.01).PsA患者的影像学评分和破骨细胞、RANKL的水平呈正相关(r=0.83,0.76;P＜0.05).结论 PsA患者外周血中的破骨细胞数目和RANKL水平显著升高,PsA患者体内的破骨细胞和RANKL水平升高与骨质破坏相关密切,提示破骨细胞及RANKL水平的变化可以反映骨质破坏的严重程度.     

前列腺素E2调节大鼠成骨细胞RANKL/OPG mRNA表达的信号通路研究

目的 探讨前列腺素E2(PGE2)对大鼠成骨细胞RANKL和OPG mRNA表达的调节及其信号转导机制.方法 培养大鼠UMR106成骨细胞,采用不同浓度的PGE2、不同信号通路的激动剂和阻断剂干预细胞不同时间后收集细胞提取总RNA,实时荧光定量PCR检测RANKL和OPG mRNA的表达水平.结果PGE2、Forskolin和db-cAMP均可促进RANKL mRNA表达,抑制OPG mRNA的表达.PMA促进RANKL和OPG mRNA表达而A23187则下调RANKL和OPG表达.KT-5720下调PGE2诱导的RANKL mRNA表达约53%(P<0.001),而chelerythrine、维拉帕米、W7、KN-62和PD98059则对PGE2>诱导的RANKL mRNA表达无明显影响(P>0.05).KT-5720(P=0.01)、维拉帕米(P=0.029)和W7(P<0.001)均能部分阻断PGE2对OPG mRNA表达的下调作用,KN-62、PD98059和chelerythrine则不影响PGE2对OPG表达的调节(P>0.05).结论 PGE2诱导的RANKL表达是由PKA信号通路介导的,而PKA和钙/钙调蛋白信号通路则介导了PGE2对OPG表达的抑制作用.     

Structure-based development of a receptor activator of nuclear factor-kappaB ligand (RANKL) inhibitor peptide and molecular basis for osteopetrosis

The receptor activator of nuclear factor-κB (RANK) and its ligand RANKL, which belong to the tumor necrosis factor (TNF) receptor-ligand family, mediate osteoclastogenesis. The crystal structure of the RANKL ectodomain (eRANKL) in complex with the RANK ectodomain (eRANK) combined with biochemical assays of RANK mutants indicated that three RANK loops (Loop1, Loop2, and Loop3) bind to the interface of a trimeric eRANKL. Loop3 is particularly notable in that it is structurally distinctive from other TNF-family receptors and forms extensive contacts with RANKL. The disulfide bond (C125-C127) at the tip of Loop3 is important for determining the unique topology of Loop3, and docking E126 close to RANKL, which was supported by the inability of C127A or E126A mutants of RANK to bind to RANKL. Inhibitory activity of RANK mutants, which contain loops of osteoprotegerin (OPG), a soluble decoy receptor to RANKL, confirmed that OPG shares the similar binding mode with RANK and OPG. Loop3 plays a key role in RANKL binding. Peptide inhibitors designed to mimic Loop3 blocked the RANKL-induced differentiation of osteoclast precursors, suggesting that they could be developed as therapeutic agents for the treatment of osteoporosis and bone-related diseases. Furthermore, some of the RANK mutations associated with autosomal recessive osteopetrosis (ARO) resulted in reduced RANKL-binding activity and failure to induce osteoclastogenesis. These results, together with structural interpretation of eRANK-eRANKL interaction, provided molecular understanding for pathogenesis of ARO.     

The differential expression of osteoprotegerin (OPG) and receptor activator of nuclear factor kappaB ligand (RANKL) in human osteoarthritic subchondral bone osteoblasts is an indicator of the metabolic state of these disease cells

OBJECTIVE: We previously reported that human OA subchondral bone osteoblasts could be discriminated into two subpopulations identified by their levels of endogenous production (low [L] or high [H]) of PGE(2). Here, we investigated the OPG and RANKL expression levels, the histologic analysis of the subchondral bone as well as the osteoclast differentiation effect of osteoblasts on normal and both OA subpopulations (L and H), and further examined on the L OA osteoblasts the modulation of bone remodelling factors on the OPG and RANKL levels, as well as on the resorption activity. METHODS: Gene expression was determined using real-time PCR, PGE2 and OPG levels by specific ELISA, and membranous RANKL by flow cytometry. Histological observation of the subchondral bone was performed on human knee specimens. Osteoclast differentiation and formation was assayed by using the pre-osteoclastic cell line RAW 264.7. OPG and RANKL modulation on L OA osteoblasts was monitored following treatment with osteotropic factors, and the resorption activity was studied by the co-culture of differentiated PBMC/osteoblasts. RESULTS: Human OA subchondral bone osteoblasts expressed less OPG than normal. Compared to normal, RANKL gene expression levels were increased in L OA and decreased in H OA cells. The OPG/RANKL mRNA ratio was significantly diminished in L OA compared to normal or H OA (p<0.02, p<0.03), and markedly increased in H OA compared to normal. Inhibition of endogenous PGE(2) levels by indomethacin markedly decreased the ratio of OPG/RANKL on the H OA. In contrast to H OA osteoblasts, L OA cells induced a significantly higher level of osteoclast differentiation and formation (p<0.05).Histological analysis showed a reduced subchondral bone on the L OA and an increased bone mass on the H OA compared to normal. Treatment of L OA osteoblasts with osteotropic factors revealed that the OPG/RANKL mRNA expression ratio was significantly reduced by vitamin D(3) and significantly increased by TNF-alpha, PTH and PGE(2), while IL-1Beta demonstrated no effect. OPG protein levels showed similar profiles. No true effect was noted on membranous RANKL upon treatment with IL-1Beta, PGE(2) and PTH, but a significant increase was observed with vitamin D3 and TNF-alpha. The resorption activity of the L OA cells was significantly inhibited by all treatments except IL-1Beta, with maximum effect observed with vitamin D(3) and PGE(2). CONCLUSION: OPG and RANKL levels, and consequently the OPG/RANKL ratio, differed according to human OA subchondral bone osteoblast classification; it is decreased in L and increased in H OA. These findings, in addition to those showing that L OA osteoblasts have a reduced subchondral bone mass and induce a higher level of osteoclast differentiation, strongly suggest that the metabolic state of the L OA osteoblasts favours bone resorption.     

Role of osteoprotegerin/receptor activator of nuclear factor kappa B/receptor activator of nuclear factor kappa B ligand axis in nonalcoholic fatty liver disease

Concomitantly with the increase in the prevalences of overweight/obesity, nonalcoholic fatty liver disease(NAFLD) has worldwide become the main cause of chronic liver disease in both adults and children. Patients with fatty liver display features of metabolic syndrome(Met S), like insulin resistance(IR), glucose intolerance, hypertension and dyslipidemia. Recently, epidemiological studies have linked obesity, Met S, and NAFLD to decreased bone mineral density and osteoporosis, highlighting an intricate interplay among bone, adipose tissue, and liver. Osteoprotegerin(OPG), an important symbol of the receptor activator of nuclear factor-B ligand/receptor activator of nuclear factor kappa B/OPG system activation, typically considered for its role in bone metabolism, may also play critical roles in the initiation and perpetuation of obesityrelated comorbidities. Clinical data have indicated that OPG concentrations are associated with hypertension, left ventricular hypertrophy, vascular calcification, endothelial dysfunction, and severity of liver damage in chronic hepatitis C. Nonetheless, the relationship between circulating OPG and IR as a key feature of Met S as well as between OPG and NAFLD remains uncertain. Thus, the aims of the present review are to provide the existent knowledge on these associations and to discuss briefly the underlying mechanisms linking OPG and NAFLD.     

Bortezomib reduces serum dickkopf-1 and receptor activator of nuclear factor-kappaB ligand concentrations and normalises indices of bone remodelling in patients with relapsed multiple myeloma

The effect of bortezomib on bone remodelling was evaluated in 34 relapsed myeloma patients. At baseline, patients had increased serum concentrations of dickkopf-1 (DKK-1), soluble receptor activator of nuclear factor-kappaB ligand (sRANKL), sRANKL/osteoprotegerin ratio, C-telopeptide of type-I collagen (CTX) and tartrate-resistant acid phosphatase isoform-5b (TRACP-5b); bone-alkaline phosphatase and osteocalcin were reduced. Serum DKK-1 correlated with CTX and severe bone disease. Bortezomib administration significantly reduced serum DKK-1, sRANKL, CTX, and TRACP-5b after four cycles, and dramatically increased bone-alkaline phosphatase and osteocalcin, irrespective of treatment response. This is the first study showing that bortezomib reduces DKK-1 and RANKL serum levels, leading to the normalisation of bone remodelling in relapsed myeloma.     

Circulating osteoprotegerin and receptor activator for nuclear factor kappaB ligand: clinical utility in metabolic bone disease assessment

CONTEXT: The discovery of the receptor activator for nuclear factor kappaB (RANK) ligand (RANKL)/RANK signaling pathway has marked a major advance in our understanding of the mechanisms controlling osteoclastogenesis. RANKL, expressed by preosteoblasts and stromal cells, binds to RANK, expressed by cells of the osteoclast lineage, inducing a signaling cascade leading to the differentiation and fusion of osteoclast precursor cells and stimulating the activity of the mature osteoclast. The effects of RANKL are counteracted by osteoprotegerin (OPG), a soluble neutralizing decoy receptor. EVIDENCE: This paper reviews the literature surrounding the use of circulating OPG and soluble RANKL (sRANKL) measurements and assesses their potential as markers of bone disease. Original clinical and basic research articles and reviews were identified using a Pubmed search strategy (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi) and cover the time period up until January 2005. Search terms osteoprotegerin, OPG, RANK, RANKL, and RANK ligand were used alone and in combination with bone, osteoporosis, and disease. EVIDENCE SYNTHESIS: Assays for detecting OPG and sRANKL in the circulation in humans have been developed, and differences in the circulating concentrations of OPG and sRANKL have been observed in different disease states. There are, however, some inconsistencies in study outcome. These may relate to differences in study design, methodology, and other unknown factors influencing the variability of these measurements. CONCLUSIONS: The clinical utility of serum OPG and sRANKL measurements as markers of disease activity requires additional investigation. In particular, rigorous testing of assays and identification of the sources of measurement variability are required.