RANKL, OPG, and RUNX2 expression and epigenetic modifications in giant cell tumour of bone in 32 patients

Aims

The present study investigated receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin (OPG), and Runt-related transcription factor 2 (RUNX2) gene expressions in giant cell tumour of bone (GCTB) patients in relationship with tumour recurrence. We also aimed to investigate the influence of CpG methylation on the transcriptional levels of RANKL and OPG.

Methods

A total of 32 GCTB tissue samples were analyzed, and the expression of RANKL, OPG, and RUNX2 was evaluated by quantitative polymerase chain reaction (qPCR). The methylation status of RANKL and OPG was also evaluated by quantitative methylation-specific polymerase chain reaction (qMSP).

Results

We found that RANKL and RUNX2 gene expression was upregulated more in recurrent than in non-recurrent GCTB tissues, while OPG gene expression was downregulated more in recurrent than in non-recurrent GCTB tissues. Additionally, we proved that changes in DNA methylation contribute to upregulating the expression of RANKL and downregulating the expression of OPG, which are critical for bone homeostasis and GCTB development.

Conclusion

Our results suggest that the overexpression of RANKL/RUNX2 and the lower expression of OPG are associated with recurrence in GCTB patients.

Effect of Periodontal Ligament Stem Cells-Derived Conditioned Medium on Gene Expression and Differentiation of Tumor Necrosis Factor-α-Challenged Osteoblasts

OBJECTIVES

 Tumor necrosis factor-α (TNF-α) causes bone resorption in periodontitis. It induces the production of receptor activator of NF-κB ligand (RANKL) from osteoblasts, leading to the disturbance of bone homeostasis through RANKL, RANK, and osteoprotegerin (OPG) axis. This study aimed to explore the effect of periodontal ligament stem cells-derived conditioned medium (PDLSCs-CM) on gene expression related to bone homeostasis and the differentiation of TNF-α-challenged osteoblasts.

MATERIALS AND METHODS

 Human osteoblasts were cultured with 50 ng/mL of TNF-α and 0, 1, 10, and 100 µg/ mL of PDLSCs-CM. Osteoblasts cultured without TNF-α and PDLSCs-CM were served as control. Gene expression of RANKL, OPG, and interleukin-1β (IL-1β) was evaluated by reverse transcription quantitative polymerase chain reaction at 48 hours. The early-stage and late-stage differentiation of TNF-α-challenged osteoblasts without or with PDLSCs-CM was explored by alkaline phosphatase (ALP) activity and alizarin red staining, respectively, at day 1, 3, 6, 9, and 12.

STATISTICAL ANALYSIS

 Mann-Whitney U test was used to analyze the differences in gene expression of TNF-α-challenged osteoblasts at 24 and 48 hours, and Kruskal-Wallis test was used to analyze the effect of PDLSCs-CM on gene expression and ALP activity among all experimental groups using SPSS software version 21.0. Statistical significance was considered with p-value less than 0.05.

RESULTS

 Expression of RANKL, OPG and IL-1β was significantly upregulated in TNF-α-challenged osteoblasts compared to the untreated control. The PDLSCs-CM at 1 and 10 μg/mL downregulated gene expression of TNF-α-challenged osteoblasts compared to the group without PDLSCs-CM, but the difference did not reach statistical significance. The ALP activity was decreased in TNF-α-challenged osteoblasts. The addition of PDLSCs-CM did not alter ALP activity of TNF-α-challenged osteoblasts. Alizarin red staining was comparable in the TNF-α-challenged osteoblasts cultured without or with PDLSCs-CM.

CONCLUSIONS

 The PDLSCs-CM did not alter gene expression involved in bone homeostasis and differentiation of TNF-α-challenged osteoblasts.

Boeravinone B, a natural rotenoid, inhibits osteoclast differentiation through modulating NF-κB, MAPK and PI3K/Akt signaling pathways

Osteoporosis is a major public health concern, which requires novel therapeutic strategies to prevent or mitigate bone loss. Natural compounds have attracted attention as potential therapeutic agents due to their safety and efficacy. In this study, we investigated the regulatory activities of boeravinone B (BOB), a natural rotenoid isolated from the medicinal plant Boerhavia diffusa, on the differentiation of osteoclasts and mesenchymal stem cells (MSCs), the two main cell components responsible for bone remodeling. We found that BOB inhibited osteoclast differentiation and function, as determined by TRAP staining and pit formation assay, with no significant cytotoxicity. Furthermore, our results showing that BOB ameliorates ovariectomyinduced bone loss demonstrated that BOB is also effective in vivo. BOB exerted its inhibitory effects on osteoclastogenesis by downregulating the RANKL/RANK signaling pathways, including NF-κB, MAPK, and PI3K/Akt, resulting in the suppression of osteoclast-specific gene expression. Further experiments revealed that, at least phenomenologically, BOB promotes osteoblast differentiation of bone marrow-derived MSCs but inhibits their differentiation into adipocytes. In conclusion, our study demonstrates that BOB inhibits osteoclastogenesis and promotes osteoblastogenesis in vitro by regulating various signaling pathways. These findings suggest that BOB has potential value as a novel therapeutic agent for the prevention and treatment of osteoporosis. [BMB Reports 2023; 56(10): 545-550].

Expression of osteogenic factors in FasL-deficient calvarial cells

During bone development, FasL acts not only through the traditional apoptotic mechanism regulating the amount of bone-resorbing osteoclasts, but there is also growing evidence about its effect on cell differentiation. Expression of osteoblastic factors was followed in non differentiated and differentiating primary calvarial cells obtained from FasL-deficient (gld) mice. The gld cells showed decreased expression of the key osteoblastic molecules osteocalcin (Ocn), osteopontin (Opn), and alkaline phosphatase (Alpl) in both groups. Notably, receptor activator of nuclear factor kappa-B ligand (Rankl) was unchanged in non-differentiated gld vs. wild type (wt) cells but decreased in differentiating gld cells. Osteoprotegerin (Opg) in the gld samples was increased in both groups. Opg vs. Rankl expression levels favored Opg in the case of non-differentiated cells but Rankl in differentiating ones. These results expand information on the involvement of FasL in non-apoptotic cell pathways related to osteoblastogenesis and consequently also osteoclastogenesis and pathologies such as osteoporosis.

Successful limb salvage in progressive proximal tibia osteosarcoma following denosumab chemotherapy: A case report

RATIONALE

Osteosarcoma (OS) is a primary malignant bone tumor that originates in the mesenchymal tissue. It is the most common type of pleomorphic tumor occurring in children and adolescents. Currently, there is no established systematic treatment for OS that progresses during standard preoperative chemotherapy.

PATIENT CONCERNS AND DIAGNOSES

We describe a 14-year-old male patient with a 4-month history of pain in the upper right leg. Based on the results of percutaneous biopsy, a diagnosis of OS was made. After admission, the patient was treated with first-line chemotherapy agents. After a single course of treatment, the tumor progressed locally and no limb salvage was feasible.

INTERVENTIONS AND OUTCOMES

Intervention with denosumab combined with chemotherapy led to a significant reduction in tumor volume and ossification of soft tissue, which successfully resulted in limb salvage rather than amputation. The patient showed no evidence of recurrent or distant metastasis at 6-month follow-up.

LESSONS

Treatment with receptor activator of nuclear factor-ĸB ligand inhibitor denosumab combined with standard chemotherapy is effective for advanced OS progressing after chemotherapy. We recommend denosumab therapy for successful limb salvage in patients with high-grade OS associated with osteolytic bone destruction and refractory to preoperative neoadjuvant chemotherapy.

Role of Hydroxyapatite and Ellagic Acid in the Osteogenesis

OBJECTIVE

 Ellagic acid (EA), a phenolic antioxidant, has benefits in bone health and wound healing. The combination of EA and hydroxyapatite (HA) (EA-HA) is expected to increase osteogenesis. The aim of this study was to analyze osteogenesis after application of EA-HA according to the number of osteoblasts and osteoclasts in the bone and the expression of the receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG), and osteocalcin (OCN) protein.

MATERIALS AND METHODS

 Thirty Wistar rats were assessed with bone defects created in the left femur. The defects were filled with EA-HA and then sutured. Control groups were filled with polyethylene glycol (PEG) or HA. Each group was sacrificed either 7 or 14 days after treatment.

RESULTS

 The defects filled with EA-HA exhibited the highest number of osteoblasts and the greatest expression of OPG and OCN at both day 7 and day 14 (p = 0.000). Conversely, treatment with EA-HA resulted in lower numbers of osteoclasts and reduced RANKL staining at both time points (p = 0.000).

CONCLUSIONS

 EA-HA can increase osteogenesis in bone defects by increasing the number of osteoblasts and the expression of OPG and OCN.

Guaiacol suppresses osteoclastogenesis by blocking interactions of RANK with TRAF6 and C-Src and inhibiting NF-κB, MAPK and AKT pathways

Angelica sinensis (AS; Dang Gui), a traditional Chinese herb, has for centuries been used for the treatment of bone diseases, including osteoporosis and osteonecrosis. However, the effective ingredient and underlying mechanisms remain elusive. Here, we identified guaiacol as the active component of AS by two‐dimensional cell membrane chromatography/C18 column/time‐of‐flight mass spectrometry (2D CMC/C18 column/TOFMS). Guaiacol suppressed osteoclastogenesis and osteoclast function in bone marrow monocytes (BMMCs) and RAW264.7 cells in vitro in a dose‐dependent manner. Co‐immunoprecipitation indicated that guaiacol blocked RANK‐TRAF6 association and RANK‐C‐Src association. Moreover, guaiacol prevented phosphorylation of p65, p50, IκB (NF‐κB pathway), ERK, JNK, c‐fos, p38 (MAPK pathway) and Akt (AKT pathway), and reduced the expression levels of Cathepsin K, CTR, MMP‐9 and TRAP. Guaiacol also suppressed the expression of nuclear factor of activated T‐cells cytoplasmic 1(NFATc1) and the RANKL‐induced Ca²⁺ oscillation. In vivo, it ameliorated ovariectomy‐induced bone loss by suppressing excessive osteoclastogenesis. Taken together, our findings suggest that guaiacol inhibits RANKL‐induced osteoclastogenesis by blocking the interactions of RANK with TRAF6 and C‐Src, and by suppressing the NF‐κB, MAPK and AKT signalling pathways. Therefore, this compound shows therapeutic potential for osteoclastogenesis‐related bone diseases, including postmenopausal osteoporosis.

Pulling RANK on Cancer: Blocking Aire-Mediated Central Tolerance to Enhance Immunotherapy

A major breakthrough in cancer treatment occurred with the development of strategies that overcome T-cell tolerance toward tumor cells. These approaches enhance antitumor immunity by overcoming mechanisms that are normally in place to prevent autoimmunity but simultaneously prevent rejection of tumor cells. Although tolerance mechanisms that restrict antitumor immunity take place both in the thymus and periphery, only immunotherapies that target peripheral tolerance mechanisms occurring outside of the thymus are currently available. We review here recent gains in our understanding of how thymic tolerance mediated by the autoimmune regulator (Aire) impedes antitumor immunity. It is now clear that transient depletion of Aire-expressing cells in the thymus can be achieved with RANKL blockade. Finally, we discuss key findings that support the repurposing of anti-RANKL as a cancer immunotherapy with a unique mechanism of action.

Evaluation of Bone Metabolism Biomarkers in Paget's Disease of Bone

Objective: To evaluate serum levels of bone metabolism biomarkers in patients with Paget's disease of bone (PDB).

Methods: Serum levels of osteopontin, sclerostin, receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin, Dickkopf-related protein 1 (DKK-1), and soluble frizzled-related protein 1 (sFRP-1) were measured in 57 patients with Paget’s disease of bone and 24 controls with primary osteoarthritis. Subgroup analysis was employed to identify any differences in bone metabolism biomarker levels according to disease activity or current treatment.

Results: Patients with PDB presented higher levels of osteopontin and RANKL. When compared with patients with inactive disease, patients with active disease presented higher levels of bone-specific alkaline phosphatase (BAP) and osteopontin. There was a significant correlation between serum levels of BAP and osteopontin. There was no significant correlation between levels of BAP and other bone metabolism biomarkers. Current disease extension on bone scintigraphy had a significant correlation with serum levels of osteopontin and BAP. There was no significant correlation between current disease extension and other bone metabolism biomarkers. Serum levels of osteopontin and RANKL were correlated to serum levels of BAP and disease extension.

Conclusion: Patients with PDB presented higher levels of osteopontin and RANKL. Osteopontin could be a useful biomarker for activity and extension of PDB.

Effects of Cinnamoyloxy-mammeisin from Geopropolis on Osteoclast Differentiation and Porphyromonas gingivalis-Induced Periodontitis

Bone-loss-related diseases such as rheumatoid arthritis, osteomyelitis, osteoporosis, and periodontitis are associated with high rates of morbidity worldwide. These disorders are characterized by an imbalance between the formation and activity of osteoblasts and osteoclasts, leading to bone loss. In this context, we evaluated the effect of cinnamoyloxy-mammeisin (CNM), an anti-inflammatory coumarin found in Melipona scutellaris geopropolis, on key targets related to bone remodeling. In the present study we investigated the in vitro effects of CNM on osteoclast differentiation and M-CSF+RANKL-induced osteoclastogenic marker expression. Additionally, the interference of CNM treatment on osteoclast activity was evaluated by zymography and resorption area. Finally, we assessed the capacity of the compound to mitigate alveolar bone loss in vivo in experimental murine periodontitis induced by Porphyromonas gingivalis. We observed that treatment with CNM impaired osteoclast differentiation, as evidenced by a reduced number of tartrate-resistant acid-phosphatase-positive multinucleated cells (TRAP+) as well as the expression of osteoclastogenic markers upon M-CSF+RANKL-induced stimulation. Similarly, we observed reduced gelatinolytic and resorption capacity in M-CSF+RANKL-induced cells in vitro. Lastly, CNM attenuated alveolar bone loss in an experimental murine periodontitis model. These findings indicate that CNM may be considered a promising treatment for bone loss diseases.

Molecular Mechanisms of Vascular Calcification in Chronic Kidney Disease: The Link between Bone and the Vasculature

Vascular calcification is highly prevalent in patients with chronic kidney disease (CKD) and increases mortality in those patients. Impaired calcium and phosphate homeostasis, increased oxidative stress, and loss of calcification inhibitors have been linked to vascular calcification in CKD. Additionally, impaired bone may perturb serum calcium/phosphate and their key regulator, parathyroid hormone, thus contributing to increased vascular calcification in CKD. Therapeutic approaches for CKD, such as phosphate binders and bisphosphonates, have been shown to ameliorate bone loss as well as vascular calcification. The precise mechanisms responsible for vascular calcification in CKD and the contribution of bone metabolism to vascular calcification have not been elucidated. This review discusses the role of systemic uremic factors and impaired bone metabolism in the pathogenesis of vascular calcification in CKD. The regulation of the key osteogenic transcription factor Runt-related transcription factor 2 (Runx2) and the emerging role of Runx2-dependent receptor activator of nuclear factor kappa-B ligand (RANKL) in vascular calcification of CKD are emphasized.

'Salvage Treatment' of Aggressive Giant Cell Tumor of Bones with Denosumab

Giant cell tumor of the bone (GCTB) presents as a lytic lesion of epiphyseometaphyseal regions of the long bones usually during the second to the fourth decade with female predilection. Histologically, they are formed of neoplastic mononuclear cells with a higher receptor activator of nuclear factor kappa-B ligand (RANKL) expression responsible for the aggressive osteolytic nature of the tumour. RANKL helps in the formation and functioning of osteoclasts. A newer molecule, Denosumab, is a monoclonal antibody directed against RANKL and thus prevents the formation and function of osteoclasts. Management of refractory, multicentric, recurrent, or metastatic GCTB remains challenging as achieving a tumor-free margin surgically is not always possible. Denosumab may play a crucial role, especially in the management of such difficult lesions. We present three cases of locally aggressive GCTB (involving proximal humerus, sacrum, and proximal femur) that were treated and responded very well to Denosumab therapy.

The Proteasome Inhibitor Carfilzomib Suppresses Parathyroid Hormone-induced Osteoclastogenesis through a RANKL-mediated Signaling Pathway

Parathyroid hormone (PTH) induces osteoclast formation and activity by increasing the ratio of RANKL/OPG in osteoblasts. The proteasome inhibitor carfilzomib (CFZ) has been used as an effective therapy for multiple myeloma via the inhibition of pathologic bone destruction. However, the effect of combination of PTH and CFZ on osteoclastogenesis is unknown. We now report that CFZ inhibits PTH-induced RANKL expression and secretion without affecting PTH inhibition of OPG expression, and it does so by blocking HDAC4 proteasomal degradation in osteoblasts. Furthermore, we used different types of culture systems, including co-culture, indirect co-culture, and transactivation, to assess the effect of CFZ on PTH action to induce osteoclastogenesis. Our results demonstrated that CFZ blocks PTH-induced osteoclast formation and bone resorption by its additional effect to inhibit RANKL-mediated IκB degradation and NF-κB activation in osteoclasts. This study showed for the first time that CFZ targets both osteoblasts and osteoclasts to suppress PTH-induced osteoclast differentiation and bone resorption. These findings warrant further investigation of this novel combination in animal models of osteoporosis and in patients.

Ubiquitin E3 Ligase LNX2 is Critical for Osteoclastogenesis In Vitro by Regulating M-CSF/RANKL Signaling and Notch2

The Notch signaling pathway plays a crucial role in skeletal development and homeostasis by regulating the proliferation and differentiation of osteoblasts and osteoclasts. However, the molecular mechanisms modulating the level and activity of Notch receptors in bone cells remain unknown. In this study, we uncovered that LNX2, an E3 ubiquitin ligase and Notch inhibitor Numb binding protein, was up-regulated during osteoclast differentiation. Knocking-down LNX2 expression in bone marrow macrophages by lentivirus-mediated short hairpin RNAs markedly inhibited osteoclast formation. Decreased LNX2 expression attenuated macrophage colony-stimulating factor (M-CSF)-induced ERK and AKT activation and RANKL-stimulated activation of NF-κB and JNK pathways; therefore, accelerated osteoclast apoptosis. Additionally, loss of LNX2 led to an increased accumulation of Numb, which promoted the degradation of Notch and caused a reduction of the expression of the Notch downstream target gene, Hes1. We conclude that LNX2 regulates M-CSF/RANKL and the Notch signaling pathways during osteoclastogenesis.

RANK/RANKL/OPG signaling pathways in necrotic jaw bone from bisphosphonate-treated subjects

Osteonecrosis of the jaw (ONJ) is a chronic complication affecting long-term bisphosphonate-treated subjects, recognized by non-healing exposed bone in the maxillofacial region. The pathophysiological mechanism underlying ONJ has not been fully elucidated. The aim of the present study was to investigate the role of RANK/RANKL/OPG signaling pathway and, in parallel, to evaluate angiogenic and matrix mineralization processes in jaw bone necrotic samples obtained from bisphosphonate-treated subjects with established ONJ. Necrotic bone samples and native bone samples were processed for Light and Field Emission in Lens Scanning Electron Microscope (FEISEM) analyses, for Real-Time RT-PCR to evaluate the gene expression of TNFRSF11A (RANK), TNFSF11 (RANKL), and TNFSF11B (OPG) and for immunohistochemical analyses of VEGF and BSP expression. Morphological analyses performed by Light microscope and FEISEM show empty osteocytic lacunae and alteration of lamellar organization with degradation of the mineralized bone matrix in necrotic bone samples. A significant increase in TNFRSF11A, TNFSF11, TRAF6 and NFAT2 gene expression, and a reduction of TNFSF11B gene transcription level compared is also showed in necrotic bone compared to control samples. No significant difference of VEGF expression is evidenced, while lower BSP expression in necrotic bone compared to healthy samples is found. Even if the pathogenesis of bisphosphonate-associated ONJ remains unknown, a link between oral pathogens and its development seems to exist. We suppose lipopolysaccharide produced by bacteria colonizing and infecting necrotic bone and the surrounding viable area could trigger RANK/RANKL/OPG signaling pathway and, in this context, osteoclasts activation could be considered as a protective strategy carried out by the host bone tissue to delimitate the necrotic area and to counteract infection.

Interactomics profiling of the negative regulatory function of carbon monoxide on RANKL-treated RAW 264.7 cells during osteoclastogenesis

BACKGROUND

During osteoclastogenesis, the maturation of osteoclast (OC) progenitors is stimulated by the receptor activator of nuclear factor-κB ligand (RANKL). Excess OC production plays a critical role in the pathogenesis of inflammatory bone disorders. Conversely, the inhibition of abnormal OC proliferation reduces inflammation-induced bone loss. Low concentrations of carbon monoxide (CO) are known to decrease inflammation and OC-mediated bone erosion but the molecular mechanism is unknown.

RESULTS

To obtain insight into the biological function of CO, cultured RANKL-treated RAW 264.7 cells were used in an in vitro experimental model of osteoclastogenesis. The results showed that CO inhibited: 1) tartrate-resistant acid phosphatase (TRAP)-positive cell formation; 2) F-actin ring production; 3) c-fos pathway activation; 4) the expression of cathepsin K, TRAP, calcitonin receptor, and matrix metalloproteinase-9 mRNAs; 5) the expression of nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent 1 in translation. Protein-protein interaction analysis predicted mitogen-activated protein kinase kinase kinase 4 as the controlling hub.

CONCLUSIONS

Low-concentrations of CO (250 ppm) may inhibit osteoclastogenesis. Data from STRING- and IPA-based interactome analyses suggested that the expression of proteins with the functions of signal transduction, enzymes, and epigenetic regulation are significantly altered by CO during RANKL-induced osteoclastogenesis. Our study provides the first interactome analysis of osteoclastogenesis, the results of which supported the negative regulation of OC differentiation by CO.

Osteocyte-driven bone remodeling

Osteocytes, the most abundant cells in bone, have been long postulated to detect and respond to mechanical and hormonal stimuli and to coordinate the function of osteoblasts and osteoclasts. The discovery that the inhibitor of bone formation sclerostin is primarily expressed in osteocytes in bone and downregulated by anabolic stimuli provided a mechanism by which osteocytes influence the activity of osteoblasts. Advances of the last few years provided experimental evidence demonstrating that osteocytes also participate in the recruitment of osteoclasts and the initiation of bone remodeling. Apoptotic osteocytes trigger yet-to-be-identified signals that attract osteoclast precursors to specific areas of bone, which in turn differentiate to mature, bone-resorbing osteoclasts. Osteocytes are also the source of molecules that regulate the generation and activity of osteoclasts, such as OPG and RANKL; and genetic manipulations of the mouse genome leading to loss or gain of function or to altered expression of either molecule in osteocytes markedly affect bone resorption. This review highlights these investigations and discusses how the novel concept of osteocyte-driven bone resorption and formation impacts our understanding of the mechanisms by which current therapies control bone remodeling.

Denosumab and giant cell tumour of bone-a review and future management considerations

Giant cell tumour of bone (gctb) is one type of giant-cell-rich bone lesion characterized by the presence of numerous multinucleated osteoclast-type giant cells. Giant cells are known to express rankl (receptor activator of nuclear factor κB ligand) and are responsible for the aggressive osteolytic nature of the tumour. No available treatment option is definitively effective in curing this disease, especially in surgically unsalvageable cases. In recent years, several studies of denosumab in patients with advanced or unresectable gctb have shown objective changes in tumour composition, reduced bony destruction, and clinical benefit. Denosumab is a fully human monoclonal antibody that targets and binds with high affinity and specificity to rankl. Several large phase iii studies have shown that denosumab is more effective than bisphosphonates in reducing skeletal morbidity arising from a wide range of tumours and that it can delay bone metastasis. The relevant articles are reviewed here. The controversies related to the future use of denosumab in the treatment of gctb are discussed.

Labisia pumila regulates bone-related genes expressions in postmenopausal osteoporosis model

BACKGROUND

Labisia Pumila var. alata (LPva) has shown potential as an alternative to estrogen replacement therapy (ERT) in prevention of estrogen-deficient osteoporosis. In earlier studies using postmenopausal model, LPva was able to reverse the ovariectomy-induced changes in biochemical markers, bone calcium, bone histomorphometric parameters and biomechanical strength. The mechanism behind these protective effects is unclear but LPva may have regulated factors that regulate bone remodeling. The aim of this study is to determine the bone-protective mechanism of LPva by measuring the expressions of several factors involved in bone formative and resorptive activities namely Osteoprotegerin (OPG), Receptor Activator of Nuclear Factor kappa-B Ligand (RANKL), Macrophage-Colony Stimulating Factor (MCSF) and Bone Morphogenetic Protein-2 (BMP-2).

METHODS

Thirty-two female Wistar rats were randomly divided into four groups: Sham-operated (Sham), ovariectomized control (OVXC), ovariectomized with Labisia pumila var. alata (LPva) and ovariectomized with ERT (Premarin) (ERT). The LPva and ERT were administered via daily oral gavages at doses of 17.5 mg/kg and 64.5 μg/kg, respectively. Following two months of treatment, the rats were euthanized and the gene expressions of BMP-2, OPG, RANKL and MCSF in the femoral bones were measured using a branch - DNA technique.

RESULTS

The RANKL gene expression was increased while the OPG and BMP-2 gene expressions were reduced in the OVXC group compared to the SHAM group. There were no significant changes in the MCSF gene expressions among the groups. Treatment with either LPva or ERT was able to prevent these ovariectomy-induced changes in the gene expressions in ovariectomized rats with similar efficacy.

CONCLUSION

LPva may protect bone against estrogen deficiency-induced changes by regulating the RANKL, OPG and BMP-2 gene expressions.

SLAT negatively regulates RANKL-induced osteoclast differentiation

RANKL induces the formation of osteoclasts, which are responsible for bone resorption. Herein, we investigated the role of SWAP-70-like adapter of T cells (SLAT) in RANKL-induced osteoclastogenesis. Expression levels of SLAT were reduced during RANKL-induced osteoclastogenesis. Overexpression of SLAT in BMMs inhibited TRAP-positive multinuclear osteoclast formation and attenuated the expression of NFATc1, which is an important modulator in osteoclastogenesis. Furthermore, silencing of SLAT by RNA interference enhanced osteoclast formation as well as NFATc1 expression. In addition, SLAT was involved in RANKL-induced JNK activation in osteoclasts. Taken together, our data suggest that SLAT acts as a negative modulator of RANKL-induced osteoclastogenesis.

Selective induction of P2Y14 receptor by RANKL promotes osteoclast formation

The purinergic receptor P2Y, G protein coupled, 14 (P2Y14) receptor for UDP-glucose and other UDP-sugars has been implicated in the regulation of the stem cell compartment as well as neuroimmune function. However, the role of P2Y14 in osteoclast formation is completely unknown. We found that RANKL selectively induced P2Y14 among seven mammalian P2Y receptors when analysed at both the mRNA and protein level, but inhibitors of the mitogenactivated protein (MAP) kinase pathway suppressed induction of P2Y14 proteins. Extracellular addition of UDP-sugars such as UDP-glucose, UDP-galactose, UDP-glucuronic acid, and UDP-N-acetyl glucosamine promoted RANKL-induced osteoclastogenesis, while P2Y14 downregulation by RNA interference inhibited osteoclast formation. Taken together, these results suggest that P2Y14 may act as the receptor for UDP-sugars in osteoclast precusors and may regulate RANKL-induced osteoclastogenesis.

Osteocyte apoptosis

Apoptotic death of osteocytes was recognized over 15 years ago, but its significance for bone homeostasis has remained elusive. A new paradigm has emerged that invokes osteocyte apoptosis as a critical event in the recruitment of osteoclasts to a specific site in response to skeletal unloading, fatigue damage, estrogen deficiency and perhaps in other states where bone must be removed. This is accomplished by yet to be defined signals emanating from dying osteocytes, which stimulate neighboring viable osteocytes to produce osteoclastogenic cytokines. The osteocyte apoptosis caused by chronic glucocorticoid administration does not increase osteoclasts; however, it does negatively impact maintenance of bone hydration, vascularity, and strength.

Osteocyte control of osteoclastogenesis

Multiple lines of evidence support the idea that osteocytes act as mechanosensors in bone and that they control bone formation, in part, by expressing the Wnt antagonist sclerostin. However, the role of osteocytes in the control of bone resorption has been less clear. Recent studies have demonstrated that osteocytes are the major source of the cytokine RANKL involved in osteoclast formation in cancellous bone. The goal of this review is to discuss these and other studies that reveal mechanisms whereby osteocytes control osteoclast formation and thus bone resorption.

Advances in osteoclast biology reveal potential new drug targets and new roles for osteoclasts

Osteoclasts are multinucleated myeloid lineage cells formed in response to macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) by fusion of bone marrow-derived precursors that circulate in the blood and are attracted to sites of bone resorption in response to factors, such as sphingosine-1 phosphate signaling. Major advances in understanding of the molecular mechanisms regulating osteoclast functions have been made in the past 20 years, mainly from mouse and human genetic studies. These have revealed that osteoclasts express and respond to proinflammatory and anti-inflammatory cytokines. Some of these cytokines activate NF-κB and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) signaling to induce osteoclast formation and activity and also regulate communication with neighboring cells through signaling proteins, including ephrins and semaphorins. Osteoclasts also positively and negatively regulate immune responses and osteoblastic bone formation. These advances have led to development of new inhibitors of bone resorption that are in clinical use or in clinical trials; and more should follow, based on these advances. This article reviews current understanding of how bone resorption is regulated both positively and negatively in normal and pathologic states.

The deep-sea natural products, biogenic polyphosphate (Bio-PolyP) and biogenic silica (Bio-Silica), as biomimetic scaffolds for bone tissue engineering: fabrication of a morphogenetically-active polymer

Bone defects in human, caused by fractures/nonunions or trauma, gain increasing impact and have become a medical challenge in the present-day aging population. Frequently, those fractures require surgical intervention which ideally relies on autografts or suboptimally on allografts. Therefore, it is pressing and likewise challenging to develop bone substitution materials to heal bone defects. During the differentiation of osteoblasts from their mesenchymal progenitor/stem cells and of osteoclasts from their hemopoietic precursor cells, a lineage-specific release of growth factors and a trans-lineage homeostatic cross-talk via signaling molecules take place. Hence, the major hurdle is to fabricate a template that is functioning in a way mimicking the morphogenetic, inductive role(s) of the native extracellular matrix. In the last few years, two naturally occurring polymers that are produced by deep-sea sponges, the biogenic polyphosphate (bio-polyP) and biogenic silica (bio-silica) have also been identified as promoting morphogenetic on both osteoblasts and osteoclasts. These polymers elicit cytokines that affect bone mineralization (hydroxyapatite formation). In this manner, bio-silica and bio-polyP cause an increased release of BMP-2, the key mediator activating the anabolic arm of the hydroxyapatite forming cells, and of RANKL. In addition, bio-polyP inhibits the progression of the pre-osteoclasts to functionally active osteoclasts. Based on these findings, new bioinspired strategies for the fabrication of bone biomimetic templates have been developed applying 3D-printing techniques. Finally, a strategy is outlined by which these two morphogenetically active polymers might be used to develop a novel functionally active polymer.

Targeting bone physiology for the treatment of metastatic prostate cancer

Metastatic prostate cancer has a unique predilection for bone that can lead to significant clinical sequelae, such as fracture and cord compression. This tropism for bone yields not only clinical challenges, but also opportunities to understand the tumor biology in bone and to develop relevant therapeutic strategies. The process by which tumor cells migrate to bone, remain dormant, and then colonize and expand is based on complex interactions between prostate cancer tumor cells and the host microenvironment. This review will provide an overview of these interactions as well as therapies targeting osseous metastases in castration-resistant prostate cancer.

Human apolipoprotein E isoforms differentially affect bone mass and turnover in vivo

The primary role of apolipoprotein E (apoE) is to mediate the cellular uptake of lipoproteins. However, a new role for apoE as a regulator of bone metabolism in mice has recently been established. In contrast to mice, the human APOE gene is characterized by three common isoforms APOE ε2, ε3, and ε4 that result in different metabolic properties of the apoE isoforms, but it remains controversial whether the APOE polymorphism influences bone traits in humans. To clarify this, we investigated bone phenotypes of apoE knock-in (k.i.) mice, which express one human isoform each (apoE2 k.i., apoE3 k.i., apoE4 k.i.) in place of the mouse apoE. Analysis of 12-week-old female k.i. mice revealed increased levels of biochemical bone formation and resorption markers in apoE2 k.i. animals as compared to apoE3 k.i. and apoE4 k.i., with a reduced osteoprotegerin (OPG)/receptor activator of NF-κB ligand (RANKL) ratio in apoE2 k.i., indicating increased turnover with prevailing resorption in apoE2 k.i. Accordingly, histomorphometric and micro-computed tomography (µCT) analyses demonstrated significantly lower trabecular bone mass in apoE2 than in apoE3 and apoE4 k.i. animals, which was reflected by a significant reduction of lumbar vertebrae maximum force resistance. Unlike trabecular bone, femoral cortical thickness, and stability was not differentially affected by the apoE isoforms. To extend these observations to the human situation, plasma from middle-aged healthy men homozygous for ε2/ε2, ε3/ε3, and ε4/ε4 (n = 21, n = 80, n = 55, respectively) was analyzed with regard to bone turnover markers. In analogy to apoE2 k.i. mice, a lower OPG/RANKL ratio was observed in the serum of ε2/ε2 carriers as compared to ε3/ε3 and ε4/ε4 individuals (p = 0.02 for ε2/ε2 versus ε4/ε4). In conclusion, the current data strongly underline the general importance of apoE as a regulator of bone metabolism and identifies the APOE ε2 allele as a potential genetic risk factor for low trabecular bone mass and vertebral fractures in humans.

Enhanced mineralization potential of vascular cells from SM22α-Rankl (tg) mice

Vascular calcification, prevalent in diabetes and chronic kidney disease, contributes to morbidity and mortality. To investigate the effect of receptor activator of NF-kB ligand (RANKL) on vascular calcification in vivo, transgenic mice, where RANKL expression was targeted to vascular smooth muscle cells using the SM22α promoter (SM22α-Rankl ( tg )), were created. Sixteen-month-old male SM22α-Rankl ( tg ) mice had higher body weight and higher serum calcium levels but lower lumbar bone mineral density (BMD) compared with age- and gender-matched wild-type (WT) littermates. BMD of long bones, body fat (percent of weight) of the leg, and serum levels of phosphate and RANKL were not significantly different. No significant differences in these parameters were observed in female mice. Histological analysis did not reveal calcium deposits in the aortic roots of SM22α-Rankl ( tg ) mice. To analyze the osteoblastic differentiation and mineralization potentials of vascular cells, aortic smooth muscle cells (SMCs) were isolated and cultured. Results showed that SM22α-Rankl ( tg ) SMCs had higher baseline alkaline phosphatase (ALP) activity but not baseline matrix calcification. When induced by the PKA agonist forskolin, ALP activity was greater in SM22α-Rankl ( tg ) than in WT SMCs. Real-time RT-qPCR revealed higher baseline expression of ALP and ankylosis genes but lower osteoprotegerin gene in SM22α-Rankl ( tg ) SMCs. Matrix mineralization induced by inorganic phosphate or forskolin was greater in SM22α-Rankl ( tg ) than in WT SMCs. Treatment of these cells with the ALP inhibitor levamisole abolished forskolin-induced matrix mineralization but not inorganic phosphate-induced matrix mineralization. These findings suggest that RANKL overexpression in the vasculature may promote mineralization potential.

Integrin αvβ3 and CD44 pathways in metastatic prostate cancer cells support osteoclastogenesis via a Runx2/Smad 5/receptor activator of NF-κB ligand signaling axis

BACKGROUND

Bone loss and pathological fractures are common skeletal complications associated with androgen deprivation therapy and bone metastases in prostate cancer patients. We have previously demonstrated that prostate cancer cells secrete receptor activator of NF-kB ligand (RANKL), a protein essential for osteoclast differentiation and activation. However, the mechanism(s) by which RANKL is produced remains to be determined. The objective of this study is to gain insight into the molecular mechanisms controlling RANKL expression in metastatic prostate cancer cells.

RESULTS

We show here that phosphorylation of Smad 5 by integrin αvβ3 and RUNX2 by CD44 signaling, respectively, regulates RANKL expression in human-derived PC3 prostate cancer cells isolated from bone metastasis. We found that RUNX2 intranuclear targeting is mediated by phosphorylation of Smad 5. Indeed, Smad5 knock-down via RNA interference and inhibition of Smad 5 phosphorylation by an αv inhibitor reduced RUNX2 nuclear localization and RANKL expression. Similarly, knockdown of CD44 or RUNX2 attenuated the expression of RANKL. As a result, conditioned media from these cells failed to support osteoclast differentiation in vitro. Immunohistochemistry analysis of tissue microarray sections containing primary prostatic tumor (grade2-4) detected predominant localization of RUNX2 and phosphorylated Smad 5 in the nuclei. Immunoblotting analyses of nuclear lysates from prostate tumor tissue corroborate these observations.

CONCLUSIONS

Collectively, we show that CD44 signaling regulates phosphorylation of RUNX2. Localization of RUNX2 in the nucleus requires phosphorylation of Smad-5 by integrin αvβ3 signaling. Our results suggest possible integration of two different pathways in the expression of RANKL. These observations imply a novel mechanistic insight into the role of these proteins in bone loss associated with bone metastases in patients with prostate cancer.

The biology of progesterone receptor in the normal mammary gland and in breast cancer

This paper reviews work on progesterone and the progesterone receptor (PR) in the mouse mammary gland that has been used extensively as an experimental model. Studies have led to the concept that progesterone controls proliferation and morphogenesis of the luminal epithelium in a tightly orchestrated manner at distinct stages of development by paracrine signaling pathways, including receptor activator of nuclear factor κB ligand (RANKL) as a major paracrine factor. Progesterone also drives expansion of stem cells by paracrine signals to generate progenitors required for alveologenesis. During mid-to-late pregnancy, progesterone has another role to suppress secretory activation until parturition mediated in part by crosstalk between PR and prolactin/Stat5 signaling to inhibit induction of milk protein gene expression, and by inhibiting tight junction closure. In models of hormone-dependent mouse mammary tumors, the progesterone/PR signaling axis enhances pre-neoplastic progression by a switch from a paracrine to an autocrine mode of proliferation and dysregulation of the RANKL signaling pathway. Limited experiments with normal human breast show that progesterone/PR signaling also stimulates epithelial cell proliferation by a paracrine mechanism; however, the signaling pathways and whether RANKL is a major mediator remains unknown. Work with human breast cancer cell lines, patient tumor samples and clinical studies indicates that progesterone is a risk factor for breast cancer and that alteration in progesterone/PR signaling pathways contributes to early stage human breast cancer progression. However, loss of PR expression in primary tumors is associated with a less differentiated more invasive phenotype and worse prognosis, suggesting that PR may limit later stages of tumor progression.

Activation of resorption in fatigue-loaded bone involves both apoptosis and active pro-osteoclastogenic signaling by distinct osteocyte populations

Osteocyte apoptosis is required to initiate osteoclastic bone resorption following fatigue-induced microdamage in vivo; however, it is unclear whether apoptotic osteocytes also produce the signals that induce osteoclast differentiation. We determined the spatial and temporal patterns of osteocyte apoptosis and expression of pro-osteoclastogenic signaling molecules in vivo. Ulnae from female Sprague-Dawley rats (16-18weeks old) were cyclically loaded to a single fatigue level, and tissues were analyzed 3 and 7days later (prior to the first appearance of osteoclasts). Expression of genes associated with osteoclastogenesis (RANKL, OPG, VEGF) and apoptosis (caspase-3) were assessed by qPCR using RNA isolated from 6mm segments of ulnar mid-diaphysis, with confirmation and spatial localization of gene expression performed by immunohistochemistry. A novel double staining immunohistochemistry method permitted simultaneous localization of apoptotic osteocytes and osteocytes expressing pro-osteoclastogenic signals relative to microdamage sites. Osteocyte staining for caspase-3 and osteoclast regulatory signals exhibited different spatial distributions, with apoptotic (caspase 3-positive) cells highest in the damage region and declining to control levels within several hundred microns of the microdamage focus. Cells expressing RANKL or VEGF peaked between 100 and 300μm from the damage site, then returned to control levels beyond this distance. Conversely, osteocytes in non-fatigued control bones expressed OPG. However, OPG staining was reduced markedly in osteocytes immediately surrounding microdamage. These results demonstrate that while osteocyte apoptosis triggers the bone remodeling response to microdamage, the neighboring non-apoptotic osteocytes are the major source of pro-osteoclastogenic signals. Moreover, both the apoptotic and osteoclast-signaling osteocyte populations are localized in a spatially and temporally restricted pattern consistent with the targeted nature of this remodeling response.

The transmembrane adaptor protein, linker for activation of T cells (LAT), regulates RANKL-induced osteoclast differentiation

RANKL induces the formation of osteoclasts, which are responsible for bone resorption. Herein we investigate the role of the transmembrane adaptor proteins in RANKL-induced osteoclastogenesis. LAT positively regulates osteoclast differentiation and is up-regulated by RANKL via c-Fos and NFATc1, whereas LAB and LIME act as negative modulators of osteoclastogenesis. In addition, silencing of LAT by RNA interference or overexpression of a LAT dominant negative in bone marrow-derived macrophage cells attenuates RANKL-induced osteoclast formation. Furthermore, LAT is involved in RANKL-induced PLC(γ) activation and NFATc1 induction. Thus, our data suggest that LAT acts as a positive regulator of RANKL-induced osteoclastogenesis.

Infections in postmenopausal women with osteoporosis treated with denosumab or placebo: coincidence or causal association?

Serious adverse events of infections that occurred in subjects receiving denosumab or placebo in the Fracture Reduction Evaluation of Denosumab in Osteoporosis every 6 Months (FREEDOM) study were examined in detail. Serious adverse events of infections in denosumab subjects had heterogeneous etiology, with no clear clinical pattern to suggest a relationship to time or duration of exposure to denosumab.

INTRODUCTION

Denosumab reduces the risk for new vertebral, hip, and nonvertebral fractures compared with placebo. In the pivotal phase 3 fracture trial (FREEDOM), the overall safety profile and incidence of adverse events including adverse events of infections were similar between groups. Serious adverse events of erysipelas and cellulitis were more frequent in denosumab-treated subjects. In this report, we further evaluate the details of infectious events in FREEDOM to better understand if RANKL inhibition with denosumab influences infection risk.

METHODS

FREEDOM was an international multicenter, randomized, double-blind, placebo-controlled study in postmenopausal women with osteoporosis randomly assigned to receive placebo (n = 3,906) or denosumab 60 mg every 6 months (n = 3,902). The incidence of adverse events and serious adverse events categorized within the Medical Dictionary for Regulatory Activities system organ class, "Infections and Infestations," was compared between the placebo and denosumab groups by body systems and preferred terms. The temporal relationship between occurrence of serious adverse events of infections of interest and administration of denosumab was explored.

RESULTS

Serious adverse events of infections involving the gastrointestinal system, renal and urinary system, ear, and endocarditis were numerically higher in the denosumab group compared with placebo, but the number of events was small. No relationship was observed between serious adverse events of infections and timing of administration or duration of exposure to denosumab.

CONCLUSIONS

Serious adverse events of infections that occurred with denosumab treatment had heterogeneous etiology, with no clear clinical pattern to suggest a relationship to time or duration of exposure to denosumab.

WITHDRAWN: Cardamonin Inhibits Osteoclastogenesis Induced by Tumor Cells Through Interruption of the Signaling Pathway Activated by Receptor Activator of NF-κB Ligand

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Decreased SH3BP2 inhibits osteoclast differentiation and function

Germline mutations in SH3BP2 gene have been identified in patients with cherubism, a skeletal disorder characterized by excessive osteoclastic bone resorption that is limited to the mandible and maxilla. We previously demonstrated that SH3BP2 overexpression in Raw264.7 cells increased RANKL-induced osteoclastogenesis. Here, we examine the effect of decreased SH3BP2 on osteoclastogenesis. shRNA knockdown of SH3BP2 decreased PLCγ2 phosphorylation and NFATc1 expression, and reduced the expression of osteoclast-specific genes. In BMMs knockdown of SH3BP2 led to reductions in both the number and the surface area of TRAP positive and multinucleated osteoclasts. Bone resorptive activity was also dramatically blocked by shRNA knockdown of SH3BP2. Similarly Sh3bp2(-/-) deficient mice BMMs formed smaller osteoclasts that stained less with TRAP than wild-type mice. Taken together, this study demonstrates that SH3BP2 knockdown significantly decreases osteoclast differentiation and function. These results suggest that SH3BP2 plays a critical role in osteoclastogenesis and is a potential target for suppression of pathologic bone resorption.

A new regulator of osteoclastogenesis: estrogen response element-binding protein in bone

The heterogeneous nuclear ribonucleoprotein (hnRNP)-like estrogen response element-binding protein (ERE-BP) competes with estrogen receptor α (ERα) for occupancy of estrogen response elements (EREs). Here we report that ERE-BP potently stimulates osteoclastogenesis. ERE-BP mRNA and protein were found to be expressed ubiquitously in bone. Overexpression of ERE-BP in cultured osteoblasts stimulated expression of the receptor activator of NF-κB ligand (RANKL) and decreased osteoprotegerin (OPG). The effect of ERE-BP on RANKL was shown to be transcriptional in transient transfection assay and competed with via the ER. Constitutive expression of ERE-BP increased the sensitivity of cells toward 1,25-dihydroxyvitamin D(3) stimulation of RANKL expression. In contrast, knockdown of ERE-BP in stromal ST-2 cells decreased basal RANKL promoter activity. Cocultures of ERE-BP lentivirus-transduced ST-2 cells with spleen monocytes induced formation of multinucleated osteoclasts (OCs) characterized by tartrate-resistant acid phosphatase, calcitonin receptors, and functional calcium resorption from bone slices. Although ERα competed with ERE-BP for an ERE in a dose-dependent manner, ERE-BP was an independent and potent regulator of RANKL and osteoclastogenesis. In preosteoclastic RAW cells, overexpression of ERE-BP increased RANK, upregulated NF-κB signaling, and enhanced differentiation toward a mature OC phenotype independent of RANKL. These results identify ERE-BP as a potent modulator of osteoclastogenesis. We hypothesize that ERE-BP may play a critical role in the regulation of bone homeostasis as a modulator of estrogen sensitivity as well as by direct action on the transcription of critical osteoclastogenic genes.

Central giant cell lesion

A classic case of central giant cell lesion (CGCL) is presented with emphasis on clinical, radiologic, and histologic features. The differential is discussed including peripheral giant cell granuloma, brown tumor of hyperparathyroidism, and giant cell tumor of bone. The molecular pathway of osteoclastogenesis is selectively reviewed and applied to suggest possible etiologies of the giant cell lesions. CGCL syndromes and treatment are also discussed.

The role of RANK/RANKL/OPG signalling pathways in osteoclastogenesis in odontogenic keratocysts, radicular cysts, and ameloblastomas

The aim of this study was to evaluate the immunohistochemical expression of molecules involved in osteoclastogenesis, including the receptor activator of nuclear factor kappa B (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) in odontogenic keratocysts (OKCs), which has been named as a keratocystic odontogenic tumour by the WHO, and compare their expression with radicular cysts and ameloblastomas. RANK is a member of tumour necrosis factor receptor family and it is activated by RANK ligand. OPG binds to RANKL and inactivates it. The imbalance of these factors could cause the differential bone resorption activity in some diseases and tumours. The expression of these molecules was evaluated in ameloblastomas (n = 20), OKCs (n = 20), and radicular cysts (n = 20) by immunohistochemistry. Immunohistochemical reactivity for RANK, RANKL, and OPG was detected in neoplastic and nonneoplastic epithelium and connective tissue cells. RANK showed the greatest expression in OKCs followed by ameloblastomas, with the lowest expression seen in radicular cysts. Expression of RANKL was detected in all lesions and no significant differences were observed between groups. OPG was expressed very low in all groups. In the stroma, the number of RANK positive cells was higher in OKCs when compared with ameloblastomas and radicular cysts but radicular cyst had higher numbers of RANKL positive cells in the stroma than ameloblastomas. The molecular system of RANK/RANKL/OPG is variably expressed in OKCs, radicular cysts, and ameloblastomas and this system may be involved in the osteoclastogenic mechanisms in OKCs and ameloblastomas. Advanced studies could further clarify the role of RANK, RANKL, and OPG in mediating tumour associated bone osteolysis.

Reduced osteoclastogenesis and RANKL expression in marrow from women taking alendronate

Alendronate (AL) is commonly used for the prevention and treatment of osteoporotic fractures. Little is known about the effects of AL administration on osteoclast differentiation from human marrow progenitor cells. We used marrow discarded during orthopedic surgery to test the hypothesis that cultures of bone marrow-derived stem cells (BMCs) from subjects receiving AL (+AL) may differ from control subjects with respect to in vitro osteoclast differentiation and regulatory factors. The number of osteoclasts generated in BMC cultures from control subjects was 4.7-fold greater than that from +AL subjects (P = 0.015). RANKL expression in +AL BMCs was 57% of that in controls (P = 0.001), and OPG expression in +AL BMCs was greater than in controls (153%, P = 0.01). The mean RANKL/OPG ratio in BMCs was 0.65 ± 0.35 for +AL specimens and 1.28 ± 0.53 for controls (P = 0.031). In addition, we assessed the direct effect of AL on expression of RANKL and OPG in marrow stromal cells isolated from nine control women. Treatment with AL downregulated RANKL expression and upregulated OPG expression, with an average 50% decrease in RANKL/OPG ratio at 10(-7) M (P = 0.004). These results show that osteoclast differentiation is dysregulated in marrow isolated from +AL subjects. Furthermore, AL may inhibit human osteoclastogenesis by affecting the key regulatory genes in marrow cells.

Treatment and prevention of bone complications from prostate cancer

Bone metastases and skeletal complications are major causes of morbidity in prostate cancer patients. Despite the osteoblastic appearance of bone metastases on imaging studies, patients have elevated serum and urinary markers of bone resorption, indicative of high osteoclast activity. Increased osteoclast activity is independently associated with higher risk of subsequent skeletal complications, disease progression, and death. Osteoclast-targeted therapies are therefore a rational approach to reduction of risk for disease-related skeletal complications, bone metastases, and treatment-related fractures. This review focuses on recent advances in osteoclast-targeted therapy in prostate cancer. Bisphosphonates have been extensively studied in men with prostate cancer. Zoledronic acid significantly decreased the risk of skeletal complications in men with castration-resistant prostate cancer and bone metastases, and it is FDA-approved for this indication. Denosumab is a human monoclonal antibody that binds and inactivates RANKL, a critical mediator of osteoclast differentiation, activation, and survival. Recent global phase 3 clinic trials demonstrated an emerging role for denosumab in the treatment of prostate cancer bone metastases and prevention of fractures associated with androgen deprivation therapy.

HIV-1 infection and antiretroviral therapies: risk factors for osteoporosis and bone fracture

PURPOSE OF REVIEW

Patients with HIV-1 infection/AIDS are living longer due to the success of highly active antiretroviral therapy (HAART). However, serious metabolic complications including bone loss and fractures are becoming common. Understanding the root causes of bone loss and its potential implications for aging AIDS patients will be critical to the design of effective interventions to stem a tidal wave of fractures in a population chronically exposed to HAART.

RECENT FINDINGS

Paradoxically, bone loss may occur not only due to HIV/AIDS but also as a consequence of HAART. The cause and mechanisms driving these distinct forms of bone loss, however, are complex and controversial. This review examines our current understanding of the underlying causes of HIV-1 and HAART-associated bone loss, and recent findings pertaining to the relevance of the immuno-skeletal interface in this process.

SUMMARY

It is projected that by 2015 more than half of the HIV/AIDS population in the USA will be over the age of 50 and the synergy between HIV and/or HAART-related bone loss with age-associated bone loss could lead to a significant health threat. Aggressive antiresorptive therapy may be warranted in high-risk patients.

Osteopontin is required for unloading-induced osteoclast recruitment and modulation of RANKL expression during tooth drift-associated bone remodeling, but not for super-eruption

Unloading of teeth results in extensive alveolar bone remodeling, causing teeth to move in both vertical ("super-eruption") and horizontal direction ("drift"). In order to decipher the molecular mechanisms of unloading-induced bone remodeling during tooth movement, we focused on the role of osteopontin (OPN) in the un-opposed molar model, comparing wild-type (WT) and OPN-null mice. Our data indicated that OPN was not required for the continuous eruption of un-opposed teeth while OPN was necessary for the drift of teeth. OPN expression and osteoclast counts were greatly increased on alveolar bone surfaces facing the direction of the drift in WT mice, while osteoclast counts were diminished in OPN-/- mice. RANKL expression in the distal periodontal ligament of WT molars increased significantly by day 6 following unloading, while overall levels of RANKL expression were decreased in both WT and OPN-null mice. In vitro treatment of MC3T3 cells, WT BMCs and OPN-/- BMCs with recombinant OPN resulted in significantly increased RANKL expression in all three cell types. The PI3K and MEK/ERK pathway inhibitors Ly294002 and U0126 reduced RANKL expression levels in vitro. Treatment of BMCs and MC3T3 with OPN also resulted in increased ERK phosphorylation and reduced OPG levels. Together, our studies suggest that increased OPN expression during unloading-induced drifting of teeth enhances localized RANKL expression and osteoclast activity on drift-direction alveolar bone surfaces via extracellular matrix signaling pathways.

Dysosteosclerosis presents as an "osteoclast-poor" form of osteopetrosis: comprehensive investigation of a 3-year-old girl and literature review

Dysosteosclerosis (DSS), an extremely rare dense bone disease, features short stature and fractures and sometimes optic atrophy, cranial nerve palsy, developmental delay, and failure of tooth eruption in infancy or early childhood consistent with osteopetrosis (OPT). Bone histology during childhood shows unresorbed primary spongiosa from deficient osteoclast action. Additionally, there is remarkable progressive flattening of all vertebrae and, by adolescence, paradoxical metaphyseal osteopenia with thin cortical bone. Reports of consanguinity indicate autosomal recessive inheritance, yet more affected males than females suggest X-linked recessive inheritance. We investigated a nonconsanguineous girl with DSS. Osteosclerosis was discovered at age 7 months. Our studies, spanning ages 11 to 44 months, showed weight at approximately 50th percentile, and length diminishing from approximately 30th percentile to -2.3 SD. Head circumference was +4 SD. The patient had frontal bossing, blue sclera, normal teeth, genu valgum, and unremarkable joints. Radiographs showed orbital and facial sclerosis, basilar thickening, bone-in-bone appearance of the pelvis, sclerotic long bone ends, and fractures of ribs and extremities. Progressive metaphyseal widening occurred as vertebrae changed from ovoid to flattened and became beaked anteriorly. A hemogram was normal. Consistent with OPT, serum parathyroid hormone (PTH) concentrations reflected dietary calcium levels. Serum bone alkaline phosphatase, osteocalcin, and TRACP-5b were subnormal. The iliac crest contained excessive primary spongiosa and no osteoclasts. No mutations were identified in the splice sites or exons for the genes encoding chloride channel 7, T-cell immune regulator 1, OPT-associated transmembrane protein 1, and monocyte colony-stimulating factor (M-CSF) and its receptor C-FMS, ANKH, OPG, RANK, and RANKL. Genomic copy-number microarray was unrevealing. Hence, DSS is a distinctive OPT of unknown etiology featuring osteoclast deficiency during early childhood. How osteopenia follows is an enigma of human skeletal pathobiology.

Inhibition of osteoclastogenesis by mechanically loaded osteocytes: involvement of MEPE

In regions of high bone loading, the mechanoresponsive osteocytes inhibit osteoclastic bone resorption by producing signaling molecules. One possible candidate is matrix extracellular phosphoglycoprotein (MEPE) because acidic serine- and aspartate-rich MEPE-associated motif peptides upregulate osteoprotegerin (OPG) gene expression, a negative regulator of osteoclastogenesis. These peptides are cleaved from MEPE when relatively more MEPE than PHEX (phosphate-regulating gene with homology to endopeptidases on the X chromosome) is present. We investigated whether mechanical loading of osteocytes affects osteocyte-stimulated osteoclastogenesis by involvement of MEPE. MLO-Y4 osteocytes were mechanically loaded by 1-h pulsating fluid flow (PFF; 0.7 ± 0.3 Pa, 5 Hz) or kept under static control conditions. Recombinant MEPE (0.05, 0.5, or 5 μg/ml) was added to some static cultures. Mouse bone marrow cells were seeded on top of the osteocytes to determine osteoclastogenesis. Gene expression of MEPE, PHEX, receptor activator of nuclear factor kappa-B ligand (RANKL), and OPG by osteocytes was determined after PFF. Osteocytes supported osteoclast formation under static control conditions. Both PFF and recombinant MEPE inhibited osteocyte-stimulated osteoclastogenesis. PFF upregulated MEPE gene expression by 2.5-fold, but not PHEX expression. PFF decreased the RANKL/OPG ratio at 1-h PFF treatment. Our data suggest that mechanical loading induces changes in gene expression by osteocytes, which likely contributes to the inhibition of osteoclastogenesis after mechanical loading of bone. Because mechanical loading upregulated gene expression of MEPE but not PHEX, possibly resulting in the upregulation of OPG gene expression, we speculate that MEPE is a soluble factor involved in the inhibition of osteoclastogenesis by osteocytes.

Extracellular microfibrils control osteoblast-supported osteoclastogenesis by restricting TGF{beta} stimulation of RANKL production

Mutations in fibrillin-1 or fibrillin-2, the major structural components of extracellular microfibrils, cause pleiotropic manifestations in Marfan syndrome and congenital contractural arachnodactyly, respectively. We recently found that fibrillin-1 and fibrillin-2 control bone formation by regulating osteoblast differentiation through the differential modulation of endogenous TGFβ and bone morphogenetic protein signals. Here, we describe in vivo and ex vivo experiments that implicate the fibrillins as negative regulators of bone resorption. Adult Fbn2(-/-) mice display a greater than normal osteolytic response to locally implanted lipopolysaccharide-coated titanium particles. Although isolated cultures of Fbn2(-/-) preosteoclasts exhibited normal differentiation and activity, these features were substantially augmented when mutant or wild-type preosteoclasts were co-cultured with Fbn2(-/-) but not wild-type osteoblasts. Greater osteoclastogenic potential of Fbn2(-/-) osteoblasts was largely accounted for by up-regulation of the Rankl gene secondary to heightened TGFβ activity. This conclusion was based on the findings that blockade of TGFβ signaling blunts Rankl up-regulation in Fbn2(-/-) osteoblasts and bones and that systemic TGFβ antagonism improves locally induced osteolysis in Fbn2(-/-) mice. Abnormally high Rankl expression secondary to elevated TGFβ activity was also noted in cultured osteoblasts from Fbn1(-/-) mice. Collectively our data demonstrated that extracellular microfibrils balance local catabolic and anabolic signals during bone remodeling in addition to implying distinct mechanisms of bone loss in Marfan syndrome and congenital contractural arachnodactyly.

Are osteoclasts needed for the bone anabolic response to parathyroid hormone? A study of intermittent parathyroid hormone with denosumab or alendronate in knock-in mice expressing humanized RANKL

PTH stimulates osteoblastic cells to form new bone and to produce osteoblast-osteoclast coupling factors such as RANKL. Whether osteoclasts or their activity are needed for PTH anabolism remains uncertain. We treated ovariectomized huRANKL knock-in mice with a human RANKL inhibitor denosumab (DMAb), alendronate (Aln), or vehicle for 4 weeks, followed by co-treatment with intermittent PTH for 4 weeks. Loss of bone mass and microarchitecture was prevented by Aln and further significantly improved by DMAb. PTH improved bone mass, microstructure, and strength, and was additive to Aln but not to DMAb. Aln inhibited biochemical and histomorphometrical indices of bone turnover,--i.e. osteocalcin and bone formation rate (BFR) on cancellous bone surfaces-, and Dmab inhibited them further. However Aln increased whereas Dmab suppressed osteoclast number and surfaces. PTH significantly increased osteocalcin and bone formation indices, in the absence or presence of either antiresorptive, although BFR remained lower in presence of Dmab. To further evaluate PTH effects in the complete absence of osteoclasts, high dose PTH was administered to RANK(-/-) mice. PTH increased osteocalcin similarly in RANK(-/-) and WT mice. It also increased BMD in RANK(-/-) mice, although less than in WT. These results further indicate that osteoclasts are not strictly required for PTH anabolism, which presumably still occurs via stimulation of modeling-based bone formation. However the magnitude of PTH anabolic effects on the skeleton, in particular its additive effects with antiresorptives, depends on the extent of the remodeling space, as determined by the number and activity of osteoclasts on bone surfaces.

Selective targeting of RANK signaling pathways as new therapeutic strategies for osteoporosis

IMPORTANCE OF THE FIELD

Osteoporosis has become a worldwide health and social issue due to an aging population. Four major antiresorptive drugs (agents capable of inhibiting osteoclast formation and/or function) are currently available on the market: estrogen, selective estrogen receptor modulators (SERMs), bisphosphonates and calcitonin. These drugs either lack satisfactory efficacy or have potential to cause serious side effects. Thus, development of more efficacious and safer drugs is warranted.

AREAS COVERED IN THIS REVIEW

The discovery of the receptor activator of NF-kappaB ligand (RANKL) and its two receptors, RANK and osteoprotegerin (OPG), has not only established a crucial role for the RANKL/RANK/OPG axis in osteoclast biology but also created a great opportunity to develop new drugs targeting this system for osteoporosis therapy. This review focuses on discussion of therapeutic targeting of RANK signaling.

WHAT THE READER WILL GAIN

An update on the functions of RANKL and an overview of the known RANK signaling pathways in osteoclasts. A discussion of rationales for exploring RANK signaling pathways as potent and specific therapeutic targets to promote future development of better drugs for osteoporosis.

TAKE HOME MESSAGE

Several RANK signaling components have the potential to serve as potent and specific therapeutic targets for osteoporosis.

Systemic effects of ulna loading in male rats during functional adaptation

Functional skeletal adaptation is thought to be a local phenomenon controlled by osteoctyes. However, the nervous system also may have regulatory effects on adaptation. The aim of this study was to determine the effects of loading of a single bone on adaptation of other appendicular long bones and whether these responses were neuronally regulated. Young male Sprague-Dawley rats were used. The right ulna was loaded to induce a modeling response. In other rats, a second regimen was used to induce bone fatigue with a mixed modeling/remodeling response; a proportion of rats from each group received brachial plexus anesthesia to induce temporary neuronal blocking during bone loading. Sham groups were included. Left and right long bones (ulna, humerus, tibia, and femur) from each rat were examined histologically 10 days after loading. In fatigue- and sham-loaded animals, blood plasma concentrations of TNF-α, RANKL, OPG, and TRAP5b were determined. We found that loading the right ulna induced an increase in bone formation in distant long bones that were not loaded and that this effect was neuronally regulated. Distant effects were most evident in the rats that received loading without bone fatigue. In the fatigue-loaded animals, neuronal blocking induced a significant decrease in plasma TRAP5b at 10 days. Histologically, bone resorption was increased in both loaded and contralateral ulnas in fatigue-loaded rats and was not significantly blocked by brachial plexus anesthesia. In young, growing male rats we conclude that ulna loading induced increased bone formation in multiple bones. Systemic adaptation effects were, at least in part, neuronally regulated.

Comparison of low-intensity pulsed ultrasound and pulsed electromagnetic field treatments on OPG and RANKL expression in human osteoblast-like cells

OBJECTIVE

To compare two clinically applied treatments to stimulate bone healing-low-intensity pulsed ultrasound (LIPUS) and pulsed electromagnetic field (PEMF)-for their effects on RANKL and OPG expression in osteoblast-like cells in vitro.

MATERIALS AND METHODS

LIPUS or PEMF was applied to Saos-2 cells for 10 minutes or 3 hours. RANKL and OPG expressions were analyzed at 0, 4, 8, or 12 hours after treatment with real-time PCR. Secreted protein levels in culture supernatant were analyzed at the same posttreatment time points using specific ELISA assays.

RESULTS

Neither LIPUS nor PEMF had an effect on RANKL protein expression. OPG protein was significantly increased by LIPUS after 0 and 4 hours (brief short-term effect) and was increased almost 2.5-fold by PEMF after 8 hours. The mRNA levels of OPG and RANKL were hardly affected by LIPUS treatment at any time point. PEMF induced a fivefold increase in RANKL mRNA expression at t = 0. A brief PEMF treatment of 10 minutes resulted in downregulation of RANKL expression after 0 and 4 hours and upregulation at 12 hours. OPG mRNA was downregulated after 8 hours.

CONCLUSION

The effects of LIPUS or PEMF expression on OPG and RANKL are limited. From our experiments, it seems that LIPUS treatment resulted in a quick protein response, while the response of cells to PEMF (3 hours) was delayed. The increase in OPG protein at 8 hours post PEMF treatment is indicative of reduction of osteolysis.

Effects and mechanism of aromatic aminoketone SY0916 on osteoclastic bone destruction

AIM

To study the effects and mechanism of aromatic aminoketone (SY0916) on bone destruction in vitro.

METHODS

MC3T3-E1 cells and bone marrow cells were co-cultured to obtain purified osteoclasts. The proliferation of osteoclast-like cells (OCLs) was determined by MTT assay. The number of osteoclasts was measured by tartrate-resistant acid phosphatase (TRAP) staining. The functioning of osteoclasts was determined by measuring the area of bone resorption pits on bone slices. MMP-9 secretion by osteoclasts was measured by an ELISA kit. Osteoclast apoptosis was detected by flow cytometry using an AnnexinV-FITC kit. Gene expression of RANK and MMP-9 in osteoclasts as well as RANKL and OPG in MC3T3-E1 cells was determined by real-time PCR.

RESULTS

SY0916 significantly inhibited the proliferation of OCLs, decreased both the total and average area of bone resorption pits, and dramatically inhibited the number of osteoclasts between concentrations of 0.01 and 10 micromol/L. Furthermore, SY0916 reversed IL-1 beta-mediated inhibition of osteoclast apoptosis and shortened osteoclast lifespan. In addition, SY0916 significantly inhibited the mRNA expression of RANK, RANKL, OPG, and MMP-9. However, the inhibition of OPG was weaker than that of RANKL. Accordingly, the ratio of RANKL to OPG mRNA expression in MC3T3-E1 cells was significantly decreased by SY0916. Meanwhile, the expression of MMP-9 protein in osteoclasts was inhibited by SY0916 between 0.01 and 10 micromol/L.

CONCLUSION

SY0916 prevents osteoclastic bone destruction by inhibiting the proliferation and function of osteoclasts. The underlying mechanism for this effect involves the regulation of the RANKL-OPG-RANK axis, which determines the direction of bone metabolism.