Myeloma bone disease

Bone destruction is a hallmark of multiple myeloma, and recent studies demonstrated a strong interdependence between tumor progression and bone resorption. Increased bone resorption as a major characteristic of multiple myeloma is caused by osteoclast activation and osteoblast inhibition (uncoupling). Myeloma cells alter the local regulation of bone metabolism by increasing the receptor activator of NF-kappaB ligand (RANKL) and decreasing osteoprotegerin (OPG) expression within the bone marrow microenvironment, thereby stimulating the central pathway for osteoclast formation and activation. In addition, they produce the chemokines MIP-1alpha, MIP-1beta and SDF-1alpha, which also increase osteoclast activity. Furthermore, myeloma cells suppress osteoblast function by the secretion of osteoblast inhibiting factors, e.g. Dickkopf (DKK)-1. The resulting bone destruction releases several cytokines, which in turn promote myeloma cell growth. Therefore, the inhibition of bone resorption could stop this vicious circle and not only decrease myeloma bone disease, but also the tumor progression. Preclinical studies provided strong evidence that the suppression of the osteoclast activity using bisphosphonates, RANKL blockade or inhibition of MIP-1alpha or MIP-1beta is effective both in reducing myeloma bone disease and tumor growth and therefore may offer an important treatment strategy in multiple myeloma.     

IL-3 is a potential inhibitor of osteoblast differentiation in multiple myeloma

Bone destruction in multiple myeloma is characterized both by markedly increased osteoclastic bone destruction and severely impaired osteoblast activity. We reported that interleukin-3 (IL-3) levels are increased in bone marrow plasma of myeloma patients compared with healthy controls and that IL-3 stimulates osteoclast formation. However, the effects of IL-3 on osteoblasts are unknown. Therefore, to determine if IL-3 inhibits osteoblast growth and differentiation, we treated primary mouse and human marrow stromal cells with IL-3 and assessed osteoblast differentiation. IL-3 inhibited basal and bone morphogenic protein-2 (BMP-2)-stimulated osteoblast formation in a dose-dependent manner without affecting cell growth. Importantly, marrow plasma from patients with high IL-3 levels inhibited osteoblast differentiation, which could be blocked by anti-IL-3. However, IL-3 did not inhibit osteoblast differentiation of osteoblastlike cell lines. In contrast, IL-3 increased the number of CD45+ hematopoietic cells in stromal-cell cultures. Depletion of the CD45+ cells abolished the inhibitory effects of IL-3 on osteoblasts, and reconstitution of the cultures with CD45+ cells restored the capacity of IL-3 to inhibit osteoblast differentiation. These data suggest that IL-3 plays a dual role in the bone destructive process in myeloma by both stimulating osteoclasts and indirectly inhibiting osteoblast formation.     

Myeloma bone disease and proteasome inhibition therapies

Bone disease is one of the most debilitating manifestations of multiple myeloma. A complex interdependence exists between myeloma bone disease and tumor growth, creating a vicious circle of extensive bone destruction and myeloma progression. Proteasome inhibitors have recently been shown to promote bone formation in vitro and in vivo. Preclinical studies have demonstrated that proteasome inhibitors, including bortezomib, which is the first-in-class such agent, stimulate osteoblast differentiation while inhibiting osteoclast formation and bone resorption. Clinical studies are confirming these observations. Bortezomib counteracts the abnormal balance of osteoclast regulators (receptor activator of nuclear factor-kappaB ligand and osteoprotegerin), leading to osteoclast inhibition and decreased bone destruction, as measured by a reduction in markers of bone resorption. In addition, bortezomib stimulates osteoblast function, possibly through the reduction of dickkopf-1, leading to increased bone formation, as indicated by the elevation in bone-specific alkaline phosphatase and osteocalcin. The effect of bortezomib on bone disease is thought to be direct and not only a consequence of the agent's antimyeloma properties, making it an attractive agent for further investigation, as it may combine potent antimyeloma activity with beneficial effects on bone. However, the clinical implication of these effects requires prospective studies with specific clinical end points.     

Pathogenesis of myeloma bone disease

Myeloma bone disease is characterized by osteolytic bone destruction that is not followed by reactive new bone formation. This results in a purely lytic process, which differs from other cancers that metastasize to bone where bone destruction is followed by new bone formation. The bone destructive process in myeloma is mediated by the osteoclast (OCL), the normal bone resorbing cell. Factors that increase OCL formation and activity are produced by both myeloma cells themselves, as well as by marrow stromal cells when myeloma cells bind to marrow stromal cells. The bone destructive process releases factors that further increase the growth and survival of myeloma cells. Thus, there is a symbiotic relationship between the bone destructive process and increased growth of myeloma cells. Several studies have shown that blocking bone destruction can result in decreased tumor burden in animal models of myeloma. This overview will focus on the factors recently identified that appear to play an important role in the bone destructive process in myeloma.     

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.     

Mechanisms of bone loss in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease in which destruction of bone in the joints causes major morbidity. Recent research has shed light on the cell and molecular mechanisms that lead to this osteolysis, all due directly or indirectly to the chronic inflammation. The aspects of this research covered in this review include the alteration of cell proliferation and survival that results in growth of the RA synovium. This process depends upon an increase in angiogenesis and local blood flow, which is also a feature of increased bone turnover. In addition, the inflammatory environment increases expression of chemokines, which are involved in the recruitment of monocytic osteoclast precursors. Chronic inflammation also promotes an overall catabolic state, with increased osteoclast differentiation and resorptive activity, driven by disregulation of receptor activator of NF-κB ligand (RANKL) and the synergistic activity of inflammatory cytokines such as tumor necrosis factor-α and interleukin-1. Osteoclast survival is increased in this environment, but osteoblast differentiation and survival are decreased, with a consequent reduction in bone formation and a net loss of bone. Recognition of these processes and the factors involved will enable more effective and targeted treatments for RA.     

RANK ligand and osteoprotegerin in myeloma bone disease

Myeloma bone disease is due to interactions of myeloma cells with the bone marrow microenvironment, and is associated with pathologic fractures, neurologic symptoms and hypercalcemia. Adjacent to myeloma cells, the formation and activation of osteoclasts is increased, which results in enhanced bone resorption. The recent characterization of the essential cytokine of osteoclast cell biology, receptor activator of NF-kappa B ligand (RANKL) and its antagonist osteoprotegerin (OPG), have led to a detailed molecular and cellular understanding of myeloma bone disease. Myeloma cells induce RANKL expression in bone marrow stromal cells, and direct RANKL expression by myeloma cells may contribute to enhanced osteoclastogenesis in the bone microenvironment in myeloma bone disease. Furthermore, myeloma cells inhibit production and induce degradation of OPG. These effects result in an increased RANKL-to-OPG ratio that favors the formation and activation of osteoclasts. Patients with myeloma bone disease have inappropriately low serum and bone marrow levels of OPG. Specific blockade of RANKL prevented the skeletal complications in various animal models of myeloma, and suppressed bone resorption in a preliminary study of patients with myeloma bone disease.     

Proteasome inhibitors and bone disease

Bone disease in patients with multiple myeloma (MM) is characterized by increase in the numbers and activity of bone-resorpting osteoclasts and decrease in the number and function of bone-formation osteoblasts. MM-triggered inhibition of bone formation may stem from suppression of Wnt/β-catenin signaling, a pivotal pathway in the differentiation of mesenchymal stem cells (MSC) into osteoblasts, and regulating production of receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) axis by osteoblasts. Proteasome inhibitors (PIs), such as bortezomib (Bz), induce activation of Wnt/β-catenin pathway and MSC differentiation toward osteoblasts. PIs also suppress osteoclastogenesis, possibly through regulating multiple pathways including NF-κB, Bim, and the ratio of RANKL/OPG. The critical role of PI in increasing osteoblast function and suppression of osteoclast activity is highlighted by clinical evidence of increases in bone formation and decreases in bone resorption makers. This review will discuss the function of PIs in stimulating bone formation and suppression of bone resorption, and the mechanism underlying this process that leads to inhibition bone disease in MM patients.     

Immunomodulation of Multiple Myeloma Bone Disease

Multiple myeloma (MM) is a clonal malignancy of terminally differentiated plasma cells. Myeloma patients often have extensive skeletal complications, including bone pain, osteolytic lesions and pathological fractures, which represent the major cause of morbidity and possible mortality. Osteolysis is due to the uncoupling of bone cell activity, caused by osteoclast activation and osteoblast inhibition. Osteoclast biology is dominantly regulated by the RANK/RANKL/OPG axis. A disruption of RANKL/OPG ratio, due to the prevalence of RANKL and/or inactivation of OPG, has been reported in MM bone disease by different mechanisms involving either malignant plasma cells and/or other cells of immune system. Despite the major involvement of RANKL in MM is well documented, a dysregulated production of other cytokines either with pro- or anti-osteoclastogenic activity can also contribute to the development of osteolytic lesions by acting directly on bone cells or altering RANKL/OPG axis. This review focuses on molecules produced by cells of immune system able to induce bone destruction in MM bone disease.     

破骨细胞的研究进展

健康成人的骨骼在不断地重建，旧骨吸收和新骨形成处于动态平衡状态，破骨细胞在骨骼的形成和骨量的调节方面起着关键作用。近年来，破骨细胞的研究取得了相当大的进展。在破骨细胞增殖和分化过程中RANKL和M—CSF起到了重要的作用。骨吸收过程中破骨细胞与骨基质接触，在它自身与骨表面之间形成一个独立的微环境。破骨细胞对于骨的识别受到整合素的调控。PU．1基因、转录因子c-Fos、Fra-1、c-Jun可以通过调节破骨细胞前体的分化和成熟发挥吸收骨的作用。通过来源于脾干细胞的破骨细胞样细胞的诱导生成及其培养，可以获得大量的破骨细胞，从而用于实验室内分子生物学研究。     

Osteoprotegerin inhibits the development of osteolytic bone disease in multiple myeloma.

Multiple myeloma is a B-cell malignancy characterized by the accumulation of plasma cells in the bone marrow and the development of osteolytic bone disease. The present study demonstrates that myeloma cells express the critical osteoclastogenic factor RANKL (the ligand for receptor activator of NF-kappa B). Injection of 5T2MM myeloma cells into C57BL/KaLwRij mice resulted in the development of bone disease characterized by a significant decrease in cancellous bone volume in the tibial and femoral metaphyses, an increase in osteoclast formation, and radiologic evidence of osteolytic bone lesions. Dual-energy x-ray absorptiometry demonstrated a decrease in bone mineral density (BMD) at each of these sites. Treatment of mice with established myeloma with recombinant osteoprotegerin (OPG) protein, the soluble decoy receptor for RANKL, prevented the development of lytic bone lesions. OPG treatment was associated with preservation of cancellous bone volume and inhibition of osteoclast formation. OPG also promoted an increase in femoral, tibial, and vertebral BMD. These data suggest that the RANKL/RANK/OPG system may play a critical role in the development of osteolytic bone disease in multiple myeloma and that targeting this system may have therapeutic potential.     

Mechanisms of bone loss in rheumatoid arthritis

Abstract

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease in which destruction of bone in the joints causes major morbidity. Recent research has shed light on the cell and molecular mechanisms that lead to this osteolysis, all due directly or indirectly to the chronic inflammation. The aspects of this research covered in this review include the alteration of cell proliferation and survival that results in growth of the RA synovium. This process depends upon an increase in angiogenesis and local blood flow, which is also a feature of increased bone turnover. In addition, the inflammatory environment increases expression of chemokines, which are involved in the recruitment of monocytic osteoclast precursors. Chronic inflammation also promotes an overall catabolic state, with increased osteoclast differentiation and resorptive activity, driven by disregulation of receptor activator of NF-κB ligand (RANKL) and the synergistic activity of inflammatory cytokines such as tumor necrosis factor-α and interleukin-1. Osteoclast survival is increased in this environment, but osteoblast differentiation and survival are decreased, with a consequent reduction in bone formation and a net loss of bone. Recognition of these processes and the factors involved will enable more effective and targeted treatments for RA.     

RANKL: A therapeutic target for bone destruction in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder characterized by progressive joint destruction. Recent studies have indicated the critical involvement of osteoclasts in bone destruction in RA. The osteoclast differentiation factor receptor activator of NF-κB ligand (RANKL), which belongs to the tumor necrosis factor superfamily, plays a critical role in osteoclast differentiation and bone destruction in RA. Denosumab, an antibody against human RANKL, efficiently suppressed the progression of bone erosion in RA patients in randomized controlled studies, and is considered as a putative therapeutic option for preventing bone destruction in RA.     

Osteoblasts and bone formation

Bone is constantly being remodelled in a dynamic process where osteoblasts are responsible for bone formation and osteoclasts for its resorption. Osteoblasts are specialized mesenchymal cells that undergo a process of maturation where genes like core-binding factor alpha1 (Cbfa1) and osterix (Osx) play a very important role. Moreover, it was found recently that Wnt/ beta-catenin pathway plays a part on osteoblast differentiation and proliferation. In fact, mutations on some of the proteins involved in this pathway, like the low-density lipoprotein receptor related protein 5/6 (LRP5/6) lead to bone diseases. Osteoblast have also a role in regulation of bone resorption through receptor activator of nuclear factor-kappaB (RANK) ligand (RANKL), that links to its receptor, RANK, on the surface of pre-osteoblast cells, inducing their differentiation and fusion. On the other hand, osteoblasts secrete a soluble decoy receptor (osteoprotegerin, OPG) that blocks RANK/RANKL interaction by binding to RANKL and, thus, prevents osteoclast differentiation and activation. Therefore, the balance between RANKL and OPG determines the formation and activity of osteoclasts. Another factor that influences bone mass is leptin, a hormone produced by adipocytes that have a dual effect. It can act through the central nervous system and diminish osteoblasts activity, or can have an osteogenic effect by binding directly to its receptors on the surface of osteoblast cells.     

Rank/Rankl/opg: literature review

The discovery of the receptor activator of nuclear factor-kB (RANK)/RANK Ligand (RANKL)/osteoprotegerin (OPG) pathway contributed to the understanding of how bone formation and resorption were processed and regulated. RANKL and OPG are members of the tumor necrosis factor (TNF) and TNF receptor (TNFr) superfamilies, respectively, and binding to receptor activator of NF-kB (RANK) not only regulate osteoclast formation, activation and survival in normal bone modeling and remode-ling, but also in several other pathologic conditions characterized by increased bone turnover. There is accumulating evidence of the potential role of OPG and RANKL in other tissues. Looking beyond the RANK/RANKL/OPG axis, Wingless (Wnt) pathway emerged as the osteoblast differentiation way, and also as a bone mass regulator. Researchers have been discovering new molecules and cytokines interactions. Altogether, data suggest that RANK/RANKL/OPG system could be targeted as a new treatment strategy in bone conditions. FREEDOM is the more recently published clinical trial about a RANKL-specific recombinant fully human monoclonal antibody (denosumab). OPG is also a potential innovative therapeutic option to be investigated.     

Modulation of osteoclast differentiation and function by the new members of the tumor necrosis factor receptor and ligand families.

Osteoblasts/stromal cells are essentially involved in osteoclast differentiation and function through cell-to-cell contact (Fig. 8). Although many attempts have been made to elucidate the mechanism of the so-called "microenvironment provided by osteoblasts/stromal cells," (5-8) it has remained an open question until OPG and its binding molecule were cloned. The serial discovery of the new members of the TNF receptor-ligand family members has confirmed the idea that osteoclast differentiation and function are regulated by osteoblasts/stromal cells. RANKL, which has also been called ODF, TRANCE, or OPGL, is a member of the TNF ligand family. Expression of RANKL mRNA in osteoblasts/stromal cells is up-regulated by osteotropic factors such as 1 alpha, 25(OH)2D3, PTH, and IL-11. Osteoclast precursors express RANK, a TNF receptor family member, recognize RANKL through cell-to-cell interaction with osteoblasts/stromal cells, and differentiate into pOCs in the presence of M-CSF. RANKL is also involved in the survival and fusion of pOCs and activation of mature osteoclasts. OPG, which has also been called OCIF or TR1, is a soluble receptor for RANKL and acts as a decoy receptor in the RANK-RANKL signaling system (Fig. 8). In conclusion, osteoblasts/stromal cells are involved in all of the processes of osteoclast development, such as differentiation, survival, fusion, and activation of osteoclasts (Fig. 8). Osteoblasts/stromal cells can now be replaced with RANKL and M-CSF in dealing with the whole life of osteoclasts. RANKL, RANK, and OPG are three key molecules that regulate osteoclast recruitment and function. Further studies on these key molecules will elucidate the molecular mechanism of the regulation of osteoclastic bone resorption. This line of studies will establish new ways to treat several metabolic bone diseases caused by abnormal osteoclast recruitment and functions such as osteopetrosis, osteoporosis, metastatic bone disease, Paget's disease, rheumatoid arthritis, and periodontal bone disease.     

The antirheumatic drug leflunomide inhibits osteoclastogenesis by interfering with receptor activator of NF-kappa B ligand-stimulated induction of nuclear factor of activated T cells c1

OBJECTIVE: Suppression of bone destruction is required as part of an effective therapeutic strategy for autoimmune arthritis. Although numerous antirheumatic drugs are in clinical use, little is known about whether they inhibit bone destruction by acting on activated T cells or other cell types, such as bone-resorbing osteoclasts. This study was undertaken to determine whether leflunomide has a direct action on the osteoclast lineage and to gain insights into the molecular basis for the bone-protective effect of leflunomide. METHODS: The direct effect of leflunomide on osteoclast differentiation was investigated using an in vitro culture system of bone marrow monocyte/macrophages stimulated with receptor activator of NF-kappa B ligand (RANKL) and macrophage colony-stimulating factor. The molecular mechanism of the inhibition was analyzed by genome-wide screening. The T cell-independent effect of leflunomide was examined in rag-2(-/-) mice. RESULTS: Leflunomide blocked de novo pyrimidine synthesis and RANKL-induced calcium signaling in osteoclast precursor cells in vitro; hence, the induction of nuclear factor of activated T cells c1 (NF-ATc1) was strongly inhibited. The inhibition of this pathway is central to the action of leflunomide, since the inhibition was overcome by ectopic expression of NF-ATc1 in the precursor cells. Leflunomide suppressed endotoxin-induced inflammatory bone destruction even in rag-2(-/-) mice. CONCLUSION: Leflunomide has a direct inhibitory effect on RANKL-mediated osteoclast differentiation by inhibiting the induction of NF-ATc1, the master switch regulator for osteoclast differentiation. Our study suggests that the direct inhibitory action of leflunomide on osteoclast differentiation constitutes an important aspect in the amelioration of bone destruction, and that the RANKL-dependent NF-ATc1 induction pathway is a promising target for pharmacologic intervention in arthritic bone destruction.