Receptor activator of NF-κB ligand induces the expression of carbonic anhydrase II, cathepsin K, and matrix metalloproteinase-9 in osteoclast precursor RAW264.7 cells

Osteoclast Generation and Cytokine Profile at Prosthetic Interfaces: A Study on Tissue of Patients with Aseptic Loosening or Implant-Associated Infections

Aseptic loosening of implants or loosening due to persistent bacterial infection remains a severe complication in orthopaedic surgery. To investigate underlying cellular and molecular mechanisms, particularly with regard to bone loss, tissue samples of patients requiring surgery were examined. By histological methods and by quantitative RT-PCR, respectively, infiltration of leukocytes, expression of osteoclast-typical genes and of proinflammatory cytokines was determined. Samples were taken directly from osteolytic sites and for comparison from adjacent sites, distant sites and from muscle. At osteolytic sites, cathepsin K and the metalloproteinases MMP1 and MMP9 were found, as was expression of inflammation-related cytokines, particularly of interleukin (IL)-1β, CXCL8, S100A9 and a very moderate expression of receptor activator of NfκB ligand (RANKL) and tumour necrosis factor (TNF) a. Of note, expression of these parameters gradually decreased from sites of osteolysis to adjacent tissue, to distant tissue to muscle. In patients with infection and osteolysis, expression of cytokines, notably of CXCL8, was markedly enhanced, especially in adjacent and distant tissues, where expression was 10- to 20-fold higher compared to tissue of aseptic patients. A possible source of CXCL8 could be infiltrated cells, particularly neutrophils, because they were found in infected tissue only. Histological examination of the biopsies revealed an additional CXCL8 source, namely endothelial cells of small blood vessels. In conclusion, aseptic loosening and implant-associated infection are associated with osteoclast generation and a local inflammatory response. The proinflammatory environment could promote the differentiation of precursor cells to osteoclasts, thereby linking inflammation to bone resorption. The higher expression of cytokines, particularly of CXCL8 in tissue of patients with bacterial infection, could explain the accelerated time course of bone resorption as it occurs in infection compared to aseptic loosening.

Regulation of matrix metalloproteinase-9 protein expression by 1α, 25-(OH)₂D₃ during osteoclast differentiation

To investigate 1α,25-(OH)₂D₃ regulation of matrix metalloproteinase-9 (MMP-9) protein expression during osteoclast formation and differentiation, receptor activator of nuclear factor kB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) were administered to induce the differentiation of RAW264.7 cells into osteoclasts. The cells were incubated with different concentrations of 1α,25-(OH)₂D₃ during culturing, and cell proliferation was measured using the methylthiazol tetrazolium method. Osteoclast formation was confirmed using tartrate-resistant acid phosphatase (TRAP) staining and assessing bone lacunar resorption. MMP-9 protein expression levels were measured with Western blotting. We showed that 1α,25-(OH)₂D₃ inhibited RAW264.7 cell proliferation induced by RANKL and M-CSF, increased the numbers of TRAP-positive osteoclasts and their nuclei, enhanced osteoclast bone resorption, and promoted MMP-9 protein expression in a concentration-dependent manner. These findings indicate that 1α,25-(OH)₂D₃ administered at a physiological relevant concentration promoted osteoclast formation and could regulate osteoclast bone metabolism by increasing MMP-9 protein expression during osteoclast differentiation.

The effect of alendronate on the expression of important cell factors in osteoclasts

This study investigated the effects of alendronate (ALN) on critical cell factors in osteoclasts. RAW 264.7 cells were induced by sRANKL to change to mature osteoclasts. On the sixth day of incubation, the osteoclasts were treated with ALN at various concentrations and for different incubation times. The concentration groups included 10-5 M, 10-6 M and 10-7 M ALN, respectively. The cells were incubated for 0 (control group), 2, 4, 6 and 8 h for each dose group. The mRNA and protein expression of tartrate‑resistant acid phosphatase, carbonic anhydrase II, osteoclast‑associated receptor and FAS/FASL genes in osteoclasts was analyzed. A concentration- and time‑dependent decrease in the mRNA and protein expression levels of the five genes was observed, and no significant difference between the two control groups was observed (P>0.05). Notably, significant differences between any two experimental groups were observed (P<0.05). Thus, ALN significantly decreased the expression of critical factors involved in osteoclast function.

Protease expression in giant cell tumour of bone: a comparative study on feline and human samples

Human giant cell tumour of bone (GCTB) is a rare low grade of malignancy tumour with tendency to recur. During tumourigenesis the bone remodeling balance is subverted by the tumour cellular components that interacting with bone matrix induce release of growth factors and cytokines, promoting cell proliferation and bone resorption. The master regulators of this positive feed-back are acid and neutral proteases that destroying extracellular matrix increase osteolysis. In contrast, in cats, very few data are reported on GCTB biological activity. In this study, histological features and metalloproteinase (MMPs) and urokinase plasminogen activator system (uPA) expression were compared in human and feline GCTB and differences in distribution and intensity related to histological pattern and clinical behaviour were determined. In both species, the overexpression of these molecules suggested a strong and complex cross-talk between tumour and microenvironment.

Vaspin attenuates RANKL-induced osteoclast formation in RAW264.7 cells

Visceral adipose tissue-derived serine protease inhibitor (vaspin), an adipokine that was recently identified in a rat model of type 2 diabetes, has been suggested to have an insulin-sensitizing effect. In this study, we investigated whether vaspin inhibits receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis using two types of osteoclast precursors: RAW264.7 cells and bone marrow cells (BMCs). Vaspin inhibited RANKL-induced osteoclastogenesis in RAW264.7 cells and BMCs. Interestingly, vaspin also inhibited the RANKL-induced expression of nuclear factor of activated T cells c1 (NFATc1) in RAW264.7 cells and BMCs. Furthermore, it inhibited the RANKL-induced upregulation of matrix metalloproteinase-9 and cathepsin K in RAW264.7 cells. Thus, we suggest that vaspin downregulates osteoclastogenesis in part by inhibiting expression of the transcription factor NFATc1.

Nicotine affects bone resorption and suppresses the expression of cathepsin K, MMP-9 and vacuolar-type H(+)-ATPase d2 and actin organization in osteoclasts

Tobacco smoking is an important risk factor for the development of several cancers, osteoporosis, and inflammatory diseases such as periodontitis. Nicotine is one of the major components of tobacco. In previous study, we showed that nicotine inhibits mineralized nodule formation by osteoblasts, and the culture medium from osteoblasts containing nicotine and lipopolysaccharide increases osteoclast differentiation. However, the direct effect of nicotine on the differentiation and function of osteoclasts is poorly understood. Thus, we examined the direct effects of nicotine on the expression of nicotine receptors and bone resorption-related enzymes, mineral resorption, actin organization, and bone resorption using RAW264.7 cells and bone marrow cells as osteoclast precursors. Cells were cultured with 10(-5), 10(-4), or 10(-3) M nicotine and/or 50 µM α-bungarotoxin (btx), an 7 nicotine receptor antagonist, in differentiation medium containing the soluble RANKL for up 7 days. 1-5, 7, 9, and 10 nicotine receptors were expressed on RAW264.7 cells. The expression of 7 nicotine receptor was increased by the addition of nicotine. Nicotine suppressed the number of tartrate-resistant acid phosphatase positive multinuclear osteoclasts with large nuclei(≥10 nuclei), and decreased the planar area of each cell. Nicotine decreased expression of cathepsin K, MMP-9, and V-ATPase d2. Btx inhibited nicotine effects. Nicotine increased CA II expression although decreased the expression of V-ATPase d2 and the distribution of F-actin. Nicotine suppressed the planar area of resorption pit by osteoclasts, but did not affect mineral resorption. These results suggest that nicotine increased the number of osteoclasts with small nuclei, but suppressed the number of osteoclasts with large nuclei. Moreover, nicotine reduced the planar area of resorption pit by suppressing the number of osteoclasts with large nuclei, V-ATPase d2, cathepsin K and MMP-9 expression and actin organization.

Angiotensin II induces the production of MMP-3 and MMP-13 through the MAPK signaling pathways via the AT(1) receptor in osteoblasts

Angiotensin II (Ang II) plays an important role in the maintenance of bone mass and integrity by activation of the mitogen-activated protein kinases (MAPKs) and by modulation of balance between resorption by osteoclasts and formation by osteoblasts. However, the role of Ang II in the turnover of extracellular matrix (ECM) in osteoid by osteoblasts remains unclear. Therefore, we examined the effect of Ang II on the expression of matrix metalloproteinases (MMPs), plasminogen activators (PAs), and their inhibitors [i.e., tissue inhibitors of metalloproteinases (TIMPs) and PA inhibitor-1 (PAI-1)] using osteoblastic ROS17/2.8 cells. Treatment with Ang II strikingly increased the expressions of MMP-3 and -13 and promoted cell proliferation associated with reduced alkaline phosphatase activity as well as enhanced phosphorylated expression of extracellular signal-regulated kinase (ERK)1/2, p38 MAPK, and stress-activated protein kinases/c-jun N-terminal kinases (SAPK/JNK) in ROS17/2.8 cells. However, Ang II had no effect on the expression of MMP-2, -9, -14, urokinase-type PA, tissue-type PA, TIMP-1, -2, -3, and PAI-1 in cells. Losartan (AT1 receptor blocker) blocked Ang II-induced expression of MMP-3 and -13, whereas PD123319 (AT2 receptor blocker) did not completely block these responses. Losartan also blocked the Ang II-induced phosphorylation of ERK1/2, p38 MAPK, and SAPK/JNK. MAPK kinase 1/2 inhibitor PD98059 and JNK inhibitor SP600125 suppressed Ang II-induced expression of MMP-3 and -13. These results suggested that Ang II stimulated the degradation process that occurs during ECM turnover in osteoid by increasing the production of MMP-3 and -13 through MAPK signaling pathways via the AT1 receptor in osteoblasts. Furthermore, our findings suggest that Ang II does not influence the plasminogen/plasmin pathway in osteoblasts.

Elevated circulating osteoprotegerin and reduced matrix-metalloprotease-9 in post-menopausal women with chronic Hepatitis C virus infection

The failure of the immune response to clear the Hepatitis C virus (HCV) results in chronic inflammation that leads to liver cirrhosis. In general, women have a better prognosis than men and this may be associated with increased levels of anti-inflammatory mediators that are positively regulated by female sex hormones. Our aim was to determine if a cohort of Irish women who acquired infection through administration of HCV genotype 1b-contaminated anti-D immunoglobulin from a single source, had altered levels of circulating cytokine levels compared to women who spontaneously resolved infection, men with HCV infection or age-matched healthy controls. Twenty post-menopausal women and 20 men with chronic HCV infection (genotype 1), 20 post-menopausal women who resolved infection and age and sex-matched controls were recruited for the study. Levels of circulating cytokines were assessed by ELISA. Circulating IL-6, Oncostatin-M, TNF-α, CXCL10, CCL18, VEGF and GM-CSF did not differ between groups. Both men and women with HCV had significantly elevated levels of circulating Osteoprotegerin (OPG). However, male but not female HCV patients had elevated levels of circulating Matrix Metalloprotease-9 (MMP-9). An increased OPG: MMP-9 ratio in the circulation of females compared to males with chronic HCV may help protect against HCV-associated liver disease and explain the slow progress of liver disease in this cohort.

Potential role of odanacatib in the treatment of osteoporosis

Cathepsin K is a key enzyme involved in the degradation of organic bone matrix by osteoclasts. Inhibition of bone resorption observed in human and animal models deficient for cathepsin K has identified this enzyme as a suitable target for intervention by small molecules with the potential to be used as therapeutic agents in the treatment of osteoporosis. Odanacatib (ODN) is a nonbasic selective cathepsin K inhibitor with good pharmacokinetic parameters such as minimal in vitro metabolism, long half-life, and oral bioavailability. In preclinical studies, ovariectomized monkeys and rabbits treated with ODN showed substantial inhibition of bone resorption markers along with increases in bone mineral density (BMD). Significant differences were observed in the effects of ODN treatment compared with those of other antiresorptive agents such as bisphosphonates and denosumab. ODN displayed compartment-specific effects on trabecular versus cortical bone formation, with treatment resulting in marked increases in periosteal bone formation and cortical thickness in ovariectomized monkeys whereas trabecular bone formation was reduced. Furthermore, osteoclasts remained viable. Phase I and II studies conducted in postmenopausal women showed ODN to be safe and well tolerated. After 5 years, women who received ODN 50 mg weekly continuously from year 1 (n = 13), showed BMD increases from baseline of 11.9% at the lumbar spine, 9.8% at the femoral neck, 10.9% at the hip trochanter, and 8.5% at the total hip. Additionally, these subjects maintained a low level of the urine bone resorption marker N-terminal telopeptide/creatinine (−67.4% from baseline) through 5 years of treatment, while levels of serum bone-specific alkaline phosphatase remained only slightly reduced relative to baseline (−15.3%). In women who were switched from ODN to placebo after 2 years, bone turnover markers were transiently increased and BMD gains reversed after 12 months off medication. Adverse experiences in the ODN-treated group were not significantly different from the placebo group. In conclusion, available data suggests that cathepsin K inhibition could be a promising intervention with which to treat osteoporosis. Ongoing studies are expected to provide information on the long-term efficacy in fracture reduction and safety of prolonged treatment with ODN.

OPG inhibits gene expression of RANK and CAII in mouse osteoclast-like cell

This study was designed to determine the effects of the osteoprotegerin (OPG) on the mRNA expression of carbonic anhydrase II (CAII) and the receptor activator of NF-κB (RANK) in mouse osteoclast-like cells. Marrow cells were harvested from femora and tibiae of mouse and cultured in 6-well chamber slides. After 1 day of incubation, the marrow cells were exposed to M-CSF (25 ng/ml), RANKL (50 ng/ml), and different concentrations of OPG (50, 75, and 100 ng/ml, respectively) for 3 days. Osteoclast-like cells were confirmed by both tartrate-resistant acid phosphatase (TRAP) stain and bone resorption assay. The expression of RANK and CAIImRNA was determined with real-time fluorescent quantitative polymerase chain reaction. The numbers of multinucleated, TRAP-positive osteoclast-like cells, and resorption pits formed were observed. Compared with the M-CSF + RANKL group, RANKmRNA expression was statistically decreased in the M-CSF and M-CSF + RANKL + OPG (100 ng/ml) groups (P = 0.004, P = 0.024, respectively); Compared with the M-CSF, M-CSF + RANKL, and M-CSF + RANKL + OPG (100 ng/ml) group, CAIImRNA expression in the M-CSF + RANKL + OPG (75 ng/ml) groups was statistically decreased (P = 0.001, P = 0.008, and P = 0.036, respectively). These data suggest that OPG could regulate the expression of RANK and CA II mRNA in the marrow culture system.

Interleukin-6 and soluble interleukin-6 receptor suppress osteoclastic differentiation by inducing PGE(2) production in chondrocytes

This study examined how interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6r) influence osteoclastic differentiation through the function of chondrocytes. Chondrocytes were cultured with or without IL-6 and/or sIL-6r in the presence or absence of NS398, a specific inhibitor of cyclooxygenase (COX)-2, for up to 28 days. Chondrocytes were also cultured with or without IL-6 and sIL-6r for 28 days, and the conditioned medium from cells cultured without IL-6 and sIL-6r was used to induce differentiation of RAW264.7 cells into osteoclast precursors. Osteoclastic differentiation was assessed by tartrate-resistant acid phosphatase (TRAP) staining. Expression of osteoprotegerin (OPG), receptor activator of NF-κB ligand (RANKL), COX-2, and prostaglandin E(2) (PGE(2)) increased in cells exposed to IL-6 and sIL-6r, whereas expression of macrophage colony-stimulating factor (M-CSF) and bone resorption-related enzymes decreased. NS398 blocked the stimulatory/suppressive effects of IL-6 and sIL-6r on the expression of OPG, RANKL, and M-CSF. Fewer TRAP-positive multinucleated cells were detected after treatment with conditioned medium from IL-6- and sIL-6r-treated chondrocytes than after treatment with conditioned medium from untreated chondrocytes. These results suggest that IL-6 and sIL-6r interfere with osteoclast function through the involvement of chondrocytes. Specifically, they appear to suppress the differentiation of osteoclast precursors into osteoclasts by inducing chondrocytic PGE(2) production, which, in turn, increases OPG secretion and decreases M-CSF secretion by chondrocytes.

Effects of pulsed electromagnetic fields on the mRNA expression of CAII and RANK in ovariectomized rats

The present study was designed to determine the effects of pulsed electromagnetic fields (PEMFs) on the mRNA expression of the carbonic anhydrase II (CAII) and receptor activator of NF-κB (RANK) in ovariectomized rats. A total of 48 SD rats were randomly divided into four groups [Sham, OVX, PEMFs, and E(2) (premarin)], 12 rats in each group. Rats in the Sham group received sham ovariectomy, while rats in OVX, PEMFs, and E(2) groups received ovariectomy. Twelve weeks following the surgery, rats (whole body) in the PEMFs group were exposed to PEMFs for 30 days with 3.8 mT, 8 Hz, and 40 min per day; rats in the E(2) group were administered premarin (0.0625 mg/kg/d; intragastric administration 1-2 ml/100 g). Rats in the Sham and OVX groups housed in the same conditions. At the end of intervention, the level of serum estradiol of rats was measured. The gene expression of CAII and RANK in the left ilium of rats was determined with real-time fluorescent-nested quantitative polymerase chain reaction. Compared with the Sham group, the level of serum estradiol in the ovariectomized group was significantly decreased (P < 0.05); compared with the OVX group, CAIImRNA expression was significantly decreased in the PEMFs group and E group (P < 0.05, 0.01, respectively). Compared with the E group, RANKmRNA expression was significantly higher in the PEMFs group (P < 0.05); although RANKmRNA expression decreased in PEMFs group, no statistically significant difference was found between PEMF group and OVX group (P = 0.82). These data suggest that PEMFs could regulate the expression of CAIImRNA in ovariectomized rats.

Study of the mechanisms by which Sambucus williamsii HANCE extract exert protective effects against ovariectomy-induced osteoporosis in vivo

The purpose of this study is to investigate the dose-dependent effects of SWH on bone properties and the mechanism involved in mediating the osteoprotective actions of SWH. The results indicated that SWH could improve bone properties by inhibiting the process of bone resorption and stimulating the process of bone formation.

INTRODUCTION

Our previous study showed that Sambucus williamsii HANCE (SWH) improved trabecular bone mass and cortical bone strength in ovariectomized (OVX) rats. The purpose of this study is to investigate the dose-dependent effects of SWH on bone properties and the mechanism involved in mediating the osteoprotective actions of SWH.

METHODS

Three-month-old C57BL/6J mice were fed a phytoestrogen-free diet and subjected to either ovariectomy or sham operation. OVX mice were treated with genistein (50 mg/kg), or a low (200 mg/kg), medium (500 mg/kg), or high (1,000 mg/kg) dose of SWH extract.

RESULTS

SWH could dose-dependently decrease urinary Ca excretion and increase serum Ca level in OVX mice. It could increase tibial bone mineral density and exert beneficial effects on the microarchitecture of trabecular bone in the OVX mice. SWH suppressed the ovariectomy-induced expression of Cbfa1 mRNA and cathepsin K mRNA and enhanced the ratio of OPG/RANKL mRNA expression in the tibia. In vitro study showed that SWH dramatically reduced the number of TRAP-positive cells in RANKL-induced RAW 264.7 cells.

CONCLUSIONS

The present study indicated that SWH could improve bone properties by inhibiting the process of bone resorption and stimulating the process of bone formation.

Identification of potential biomarkers for giant cell tumor of bone using comparative proteomics analysis

Giant cell tumor of bone can be locally aggressive and occasionally can metastasize in the lungs. To identify new markers predictive of aggressive behavior, we analyzed five patients who developed lung metastasis and five who remained disease free for a minimum of 5 years. Using two-dimensional electrophoresis, we detected 28 differentially expressed spots. Fourteen spots were identified using mass spectrometry, including seven up-regulated and seven down-regulated in metastatic samples and classified according to functional categories. We then selected five proteins involved in cell cycle or apoptosis. Thioredoxin peroxidase, allograft inflammatory factor 1, and ubiquitin E2N had more than threefold up-regulation; glutathione peroxidase 1 had 1.9-fold up-regulation; and heat shock protein 27 showed down-regulation in metastatic samples with a very low P value. After validation and analysis of protein levels, evaluation of clinical impact was assessed in a much wider cohort of primary archival specimens. Immunodetection showed a higher frequency of thioredoxin peroxidase, allograft inflammatory factor 1, ubiquitin E2N, and glutathione peroxidase 1 overexpression in primary tumors that developed into lung metastases or that locally relapsed than in the disease-free group, with variable stain intensity and distribution. Kaplan-Meier analysis showed that high expression of glutathione peroxidase 1 was strongly related to local recurrence and metastasis, suggesting that its up-regulation may identify a subset of high-risk patients with giant cell tumor prone to receive diverse clinical management.

Compressive force stimulates the gene expression of IL-17s and their receptors in MC3T3-E1 cells

During orthodontic tooth movement, cytokines released from periodontal ligament fibroblasts and alveolar bone osteoblasts can alter the process of bone remodeling. Recently, interleukin-17 (IL-17) was found to stimulate osteoclastic resorption through osteoblasts by inducing receptor activator of nuclear factor κB ligand (RANKL) expression. However, the relationship between mechanical stress and IL-17 production by osteoblasts is not clear. Therefore, we examined the effect of compressive force on the expressions of IL-17A, IL-17B, IL-17C, IL-17D, IL-17E, IL-17F, and their receptors (IL-17RA, IL-17RB, IL-17RC, IL-17RD, and IL-17RE) using MC3T3-E1 cells as osteoblast-like cells. We also examined the effect of IL-17A on the expression of IL-17Rs, RANKL, macrophage colony-stimulating factor (M-CSF), and osteoprotegerin (OPG). The cells were cultured with or without continuous compressive force (1.0 and 2.0 g/cm(2)) for up to 24 hr. The cells were also cultured with or without IL-17A (0.1, 1.0, or 10 ng/ml) for up to 72 hr. The mRNA expressions of IL-17s and their receptors were estimated by real-time polymerase chain reaction. The expression levels of IL-17s and their receptors increased depending on the compressive force. The addition of IL-17A increased the expression of IL-17RA, IL-17RB, IL-17RC, IL-17RE, RANKL, and M-CSF, whereas it decreased OPG expression. These results indicate that compressive force induces the expression of IL-17s and their receptors in osteoblast-like cells and that IL-17s and their receptors produced in response to compressive force may affect osteoclastogenesis through the expression of RANKL, M-CSF, and OPG.

Compressive force induces osteoclast differentiation via prostaglandin E(2) production in MC3T3-E1 cells

In orthodontic tooth movement, prostaglandin E(2) (PGE(2)) released from osteoblasts can alter the normal process of bone remodeling. We previously showed that compressive force (CF) controls bone formation by stimulating the production of PGE(2) and Ep2 and/or Ep4 receptors in osteoblasts. The present study was undertaken to examine the effect of CF on the production of PGE(2), cyclooxygenase-2 (COX-2), macrophage colony-stimulating factor (M-CSF), receptor activator of NF-kappaB ligand (RANKL), and osteoprotegerin (OPG) using osteoblastic MC3T3-E1 cells and to examine the indirect effect of CF on osteoclast differentiation using RAW264.7 cells as osteoclast precursors. MC3T3-E1 cells were cultured with or without continuous CF (1.0 or 3.0 g/cm(2)) for 24 hr, and PGE(2) production was determined using ELISA. The expression of COX-2, M-CSF, RANKL, and OPG genes and proteins was determined using real-time PCR and ELISA, respectively. Osteoclast differentiation was estimated using tartrate-resistant acid phosphatase (TRAP) staining of RAW 264.7 cells cultured for 10 days with conditioned medium from CF-treated MC3T3-E1 cells and soluble RANKL. As CF increased, PGE(2) production and the expression of COX-2, M-CSF, and RANKL increased, whereas OPG expression decreased. The number of TRAP-positive cells increased as CF increased. Celecoxib, a specific inhibitor of COX-2, blocked the stimulatory effect of CF on TRAP staining and the production of PGE(2), M-CSF, RANKL, and OPG. These results suggest that CF induces osteoclast differentiation by increasing M-CSF production and decreasing OPG production via PGE(2) in osteoblasts.

IL-1beta suppresses the formation of osteoclasts by increasing OPG production via an autocrine mechanism involving celecoxib-related prostaglandins in chondrocytes

Elevated interleukin (IL)-1 concentrations in synovial fluid have been implicated in joint bone and cartilage destruction. Previously, we showed that IL-1beta stimulated the expression of prostaglandin (PG) receptor EP4 via increased PGE(2) production. However, the effect of IL-1beta on osteoclast formation via chondrocytes is unclear. Therefore, we examined the effect of IL-1beta and/or celecoxib on the expression of macrophage colony-stimulating factor (M-CSF), receptor activator of NF-kappaB ligand (RANKL), and osteoprotegerin (OPG) in human chondrocytes, and the indirect effect of IL-1beta on osteoclast-like cell formation using RAW264.7 cells. OPG and RANKL expression increased with IL-1beta; whereas M-CSF expression decreased. Celecoxib blocked the stimulatory effect of IL-1beta. Conditioned medium from IL-1beta-treated chondrocytes decreased TRAP staining in RAW264.7 cells. These results suggest that IL-1beta suppresses the formation of osteoclast-like cells via increased OPG production and decreased M-CSF production in chondrocytes, and OPG production may increase through an autocrine mechanism involving celecoxib-related PGs.

Effects of pulsed electromagnetic fields on the mRNA expression of RANK and CAII in ovariectomized rat osteoclast-like cell

This study was designed to determine the effects of pulsed electromagnetic fields (PEMF) on the mRNA expression of the receptor activator of NF-kappa-B (RANK) and carbonic anhydrase II (CA II) in ovariectomized rat osteoclast-like cells. Marrow cells were harvested from femora and tibiae of rats, from which the ovaries had been totally excised, and cultured in 6-well chamber slides. After 1 day of incubation, the marrow cells were exposed to PEMF for 3 days with 3.8 mT, 8 Hz, and 40 min per day. Osteoclast-like cells were confirmed by both tartrate resistant acid phosphatase (TRAP) stain and bone resorption assay. The expression of RANK and CA II mRNA was determined with real-time fluorescent-nested quantitative polymerase chain reaction. Compared with the sham group, the level of serum estradiol in the ovariectomized group was significantly decreased ( p < 0.05). The numbers of multinucleated, TRAP-positive osteoclast-like cells and resorption pits formed were observed. In invitro study, the expression of RANK and CA II were measured in sham, ovariectomized without PEMF, and ovariectomized with PEMF treatment. Compared with the ovariectomized (PEMF) experimental group and sham group, CA II mRNA expression was significantly increased in the ovariectomized control group ( p < 0.05, 0.01, respectively). Compared with the sham group, RANK mRNA expression was significantly increased in the ovariectomized control group ( p < 0.05). These data suggest that PEMF could regulate the expression of RANK and CA II mRNA in the marrow culture system.

Genistein and a soy extract differentially affect three-dimensional bone parameters and bone-specific gene expression in ovariectomized mice

Soy isoflavone preparations, such as purified genistein and a soy extract (Novasoy), were reported previously to exert beneficial effects on bones. Our purpose in this study was to compare the effects of genistein and Novasoy on 3-dimensional trabecular bone parameters and the expression of bone-specific genes in ovariectomized (OVX) mice. The sham-operated mice were fed the control diet and OVX mice were fed diets containing genistein or Novasoy or the control diet, with or without 17beta-estradiol treatment, for 5 wk. Trabecular bone parameters of tibias were measured by microcomputed tomography and gene expression was assayed by real-time PCR. Consumption of diets containing genistein or Novasoy partially prevented the ovariectomy-induced increase in body weight but did not alter the uterus weight of the OVX mice. Novasoy, but not purified genistein, significantly preserved trabecular bone mass, bone volume, and trabecular bone separation in the proximal tibial metaphysis. Purified genistein decreased mRNA expression of receptor activator of nuclear factor-kappaB ligand (RANKL), carbonic anhydrase II, and cathepsin K and enhanced the ratio of osteoprotegrin:RANKL mRNA expression in the tibial head of the OVX mice. In contrast, the diet containing Novasoy suppressed the OVX-induced increase in serum alkaline phosphatase but did not alter bone-specific gene expression of tibia. Our study demonstrated that a soy extract containing a similar level of genistein in the form of Novasoy is more effective than purified genistein in improving tibial trabecular bone quality in OVX mice, but the mechanism of action might be distinct from that of genistein.

Cathepsin G-mediated activation of pro-matrix metalloproteinase 9 at the tumor-bone interface promotes transforming growth factor-beta signaling and bone destruction

Increased transforming growth factor-beta (TGF-beta) signaling has been observed at the tumor-bone interface of mammary tumor-induced osteolytic lesions despite no observed transcriptional up-regulation of TGF-beta. To this point, the mechanism for enhanced TGF-beta signaling remains unclear. The bulk of TGF-beta that is released at the tumor-bone interface is in an inactive form secondary to association with beta-latency-associated protein and latency TGF-beta binding protein. We hypothesized that the observed increase in TGF-beta signaling is due to increased cathepsin G-dependent, matrix metalloproteinase 9 (MMP9)-mediated activation of latent TGF-beta. MMP9 is capable of activating latent TGF-beta, and we observed that decreased production of MMP9 was associated with reduced TGF-beta signaling. Similar to TGF-beta, MMP9 is released in an inactive form and requires proteolytic activation. We showed that cathepsin G, which we have previously shown to be up-regulated at the tumor-bone interface, is capable of activating pro-MMP9. Inhibition of cathepsin G in vivo significantly reduced MMP9 activity, increased the ratio of latent TGF-beta to active TGF-beta, and reduced the level of TGF-beta signaling. Our proposed model based on these results is that cathepsin G is up-regulated through tumor-stromal interactions and activates pro-MMP9, active MMP9 cleaves and releases active TGF-beta, and active TGF-beta can then promote tumor growth and enhance osteoclast activation and subsequent bone resorption. Thus, for the first time, we have identified cathepsin G and MMP9 as proteases involved in enhanced TGF-beta signaling at the tumor-bone interface of mammary tumor-induced osteolytic lesions and have identified these proteases as potential therapeutic targets.

Cathepsin K inhibitors for osteoporosis and potential off-target effects

Cathepsin K is a highly potent collagenase and the predominant papain-like cysteine protease expressed in osteoclasts. Cathepsin K deficiencies in humans and mice have underlined the central role of this protease in bone resorption and, thus, have rendered the enzyme as an attractive target for anti-resorptive osteoporosis therapy. In the past decade, a lot of efforts have been made in developing highly potent, selective and orally applicable cathepsin K inhibitors. Some of these inhibitors have passed preclinical studies and are presently in clinical trials at different stages of advancement. The development of the inhibitors and preliminary results of the clinical trials revealed problems and lessons concerning the in situ specificity of the compounds and their tissue targeting. In this review, we briefly summarize the history of cathepsin K research and discuss the current development of cathepsin K inhibitors as novel anti-resorptives for the treatment of osteoporosis. We also discuss potential off-target effects of cathepsin K inhibition and alternative applications of cathepsin K inhibitors in arthritis, atherosclerosis, blood pressure regulation, obesity and cancer.

Differential mRNA expression profiles in proximal tibia of aged rats in response to ovariectomy and low-Ca diet

Both ovariectomized animals and animals fed with Ca-depleted diets are commonly used in vivo models for the investigation of osteoporosis-related bone loss. The present study aimed to study the genomic responses of bone in aged female rats to ovariectomy and dietary Ca deficiency in these models. Aged (11 months old) Sprague-Dawley rats were subjected to bilateral ovariectomy or sham-operation and fed with diets containing different dietary Ca content (LCD, 0.1% Ca or HCD, 1.2% Ca) for 12 weeks. Serum and urine were collected for biochemical marker measurement, and tibias were collected for bone mineral density (BMD) analysis by pQCT as well as for gene expression analysis by real-time PCR. Ovariectomy increased serum N-telopeptides of bone type I collagen (NTx) levels in aged rats fed with HCD (P<0.05). In addition, ovariectomy reduced BMD and predicted bone strength of tibial proximal metaphysis in aged rats fed with either LCD or HCD. Dietary Ca deficiency did not alter serum bone-specific alkaline phosphatase (BAP) or NTx levels, but induced a loss of BMD at tibia proximal metaphysis in aged rats. Ovariectomy promoted the mRNA expression of alpha-1 type I collagen (COL), osteoprotegerin (OPG) and receptor activator of nuclear factor-kappa B ligand (RANKL); and inhibited the mRNA expression of cathepsin K and matrix metalloproteinase-9 (MMP-9) in the proximal tibia of aged rats. Low-Ca diet significantly up-regulated the mRNA expression of COL, core binding factor I (Cbfa1), OPG and carbonic anhydrase II (CAII) in proximal tibia of aged rats. Our study revealed that the genomic responses of bone in proximal tibia to ovariectomy and dietary Ca deficiency were different. The bone loss induced by ovariectomy appears to be mediated primarily by an increase in RANKL mRNA expression; whereas the induction by dietary Ca restriction might be mediated by the induction of carbonic anhydrase II expression.

Proteases and bone remodelling

Bone remodelling is regulated by osteogenic cells which act individually through cellular and molecular interaction. These interactions can be established either through a cell-cell contact, involving molecules of the integrin family, or by the release of many polypeptidic factors and/or their soluble receptor chains. Proteolytic shedding of membrane-associated proteins regulates the physiological activity of numerous proteins. Proteases located on the plasma membrane, either as transmembrane proteins or anchored to cell-surface molecules, serve as activators or inhibitors of different cellular and physiological processes. This review will focus on the role of the proteases implicated in bone remodelling either through the proteolytic degradation of the extracellular matrix or through their relations with osteogenic factors. Their implication in bone tumor progression will be also considered.

Estrogen and testosterone attenuate extracellular matrix loss in collagen-induced arthritis in rats

Rheumatoid arthritis (RA) is a sexually dimorphic, autoimmune inflammatory disorder affecting the joints. Joint disability in RA results primarily from loss of matrix components (collagen and glycosoaminoglycan) in the cartilage and synovium. This study was carried out to understand the effect of physiological levels of testosterone, estrogen, and progesterone on oxidative stress-induced changes in matrix composition in rat synovium in arthritis. Arthritis induction in castrated and ovariectomized rats resulted in enhanced oxidative stress and this was assessed by lipid peroxidation levels and depletion of antioxidants. This, in turn, led to significantly (p < 0.01) increased levels of TNF-alpha and matrix metalloproteinase-2 (MMP-2), subsequently resulting in loss of collagen, elastin, and glycosoaminoglycan (GAG) and disorganization of reticulin as evidenced by biochemical quantitation and also by staining for collagen, reticulin, and elastin. Treatment with physiological doses of dihydrotestosterone (25 mg topically) and estrogen (5 microg/0.1 ml subcutaneously) restored the antioxidant levels significantly (p < 0.05) and reduced the levels of TNF-alpha and MMP-2, with estrogen exhibiting a higher potency. This, in turn, attenuated the damage to reticulin organization as well as the loss of collagen and GAG in the articular tissues. However, elastin loss could not be attenuated by either treatment. Progesterone (2 mg/0.1 ml subcutaneously) was not shown to have any significance in disease modification, and on the contrary, it inhibited the protective effects of estrogen. However, progesterone contributed to increased collagen levels in the tissues.

Cathepsin G enhances mammary tumor-induced osteolysis by generating soluble receptor activator of nuclear factor-kappaB ligand

Breast cancer commonly causes osteolytic metastases in bone, a process that is dependent on tumor-stromal interaction. Proteases play an important role in modulating tumor-stromal interactions in a manner that favors tumor establishment and progression. Whereas several studies have examined the role of proteases in modulating the bone microenvironment, little is currently known about their role in tumor-bone interaction during osteolytic metastasis. In cancer-induced osteolytic lesions, cleavage of receptor activator of nuclear factor-kappaB ligand (RANKL) to a soluble version (sRANKL) is critical for widespread osteoclast activation. Using a mouse model that mimics osteolytic changes associated with breast cancer-induced bone metastases, we identified cathepsin G, cathepsin K, matrix metalloproteinase (MMP)-9, and MMP13 to be proteases that are up-regulated at the tumor-bone interface using comparative cDNA microarray analysis and quantitative reverse transcription-PCR. Moreover, we showed that cathepsin G is capable of shedding the extracellular domain of RANKL, generating active sRANKL that is capable of inducing differentiation and activation of osteoclast precursors. The major source of cathepsin G at the tumor-bone interface seems to be osteoclasts that up-regulate production of cathepsin G via interaction with tumor cells. Furthermore, we showed that in vitro osteoclastogenesis is reduced by inhibition of cathepsin G in a coculture model and that in vivo inhibition of cathepsin G reduces mammary tumor-induced osteolysis. Together, our data indicate that cathepsin G activity at the tumor-bone interface plays an important role in mammary tumor-induced osteolysis and suggest that cathepsin G is a potentially novel therapeutic target in the treatment of breast cancer bone metastasis.

Sodium butyrate stimulates mineralized nodule formation and osteoprotegerin expression by human osteoblasts

OBJECTIVE

Butyric acid (sodium butyrate; BA) is a major metabolic by-product of main periodontopathic bacteria present in subgingival plaque. In the present study, we examined the effects of BA on cell proliferation, alkaline phosphatase (ALPase) activity, mineralized nodule formation, extracellular matrix protein expression, macrophage colony-stimulating factor (M-CSF), and osteoprotegerin (OPG) in normal human osteoblasts.

METHODS

The cells were cultured with 0, 10(-8), 10(-6) or 10(-4)M BA for up to 12 days. Mineralized nodule formation was detected by alizarin red staining, and the calcium content in mineralized nodules was determined using a calcium assay kit. The gene and protein expression levels for type I collagen, bone sialoprotein (BSP), osteopontin (OPN), M-CSF, and OPG were examined using real-time PCR and ELISA, respectively.

RESULTS

Mineralized nodule formation and the calcium content of mineralized nodules were increased by BA in a dose-dependent manner. Cell proliferation and ALPase activity were not affected by the addition of BA. Following the addition of 10(-4)M BA, the expression levels of BSP, OPN, and OPG increased, whereas the expression levels of type I collagen and M-CSF were not markedly affected.

CONCLUSION

These results suggest that BA stimulates bone formation by increasing the production of BSP and OPN, whereas it suppresses osteoclast differentiation by increasing the production of OPG by human osteoblasts.

The antibody MAB8051 directed against osteoprotegerin detects carbonic anhydrase II: implications for association studies with human cancers

A commonly used monoclonal antibody targeting osteoprotegerin (OPG), MAB8051, detects a truncated protein species in breast and prostate cancer cell lysates. OPG expression has been reported to contribute to cell survival of both of these cancers. We hypothesised that the truncated protein represented a unique tumour-associated OPG isoform. However, here we show that the truncated protein identified by MAB8051 in cancer cell lines is carbonic anhydrase II (CA II), also implicated in tumour biology. We clearly demonstrate cross-reactivity of this OPG antibody in western blots. OPG and CA II RNA-interference studies confirmed the identity of the bands. We show almost identical staining patterns between MAB8051 and CA II immunohistochemistry of different human tissue types and human tumour types using serial sections. We conclude that care should be exercised using this antibody for immunohistochemistry studies, without additional in situ hybridisation, or parallel use of other OPG-specific antibodies.

Biochemical properties and regulation of cathepsin K activity

Cysteine cathepsins (11 in humans) are mostly located in the acidic compartments of cells. They have been known for decades to be involved in intracellular protein degradation as housekeeping proteases. However, the discovery of new cathepsins, including cathepsins K, V and F, has provided strong evidence that they also participate in specific biological events. This review focuses on the current knowledge of cathepsin K, the major bone cysteine protease, which is a drug target of clinical interest. Nevertheless, we will not discuss recent developments in cathepsin K inhibitor design since they have been extensively detailed elsewhere. We will cover features of cathepsin K structure, cellular and tissue distribution, substrate specificity, and regulation (pH, propeptide, glycosaminoglycans, oxidants), and its putative roles in physiological or pathophysiological processes. Finally, we will review the kinetic data of its inhibition by natural endogenous inhibitors (stefin B, cystatin C, H- and L-kininogens).

Oligopotent Mesenchymal Stem Cell-Like Clone Becomes Multinucleated Following Phorbol Ester, TPA Stimulation

We established a mesenchymal stem cell clone, 5F9A, from rat bone marrow substrate adherent cells by repeated limiting dilutions. The cells have a fibroblastic shape and form intimate contacts with adjacent cells with interdigitations and junctions similar to adherence and tight junctions in a semi-confluent culture. Analysis of the phenotypes of these cells by RT-PCR and FACS demonstrated that they resembled mesenchymal stem cells, and the cells could differentiate into adiopocytes and osteoblasts under appropriate conditions in vitro showing their oligopotency. Furthermore, the cells were induced to become multinuclear cells by TPA (12-o-tetradecanoylphorbol 13-acetate) stimulation.