Regulation of osteoclast protease expression by RANKL

Computational exploration of Eucommia ulmoides flavonoids as potential RANKL inhibitors via molecular docking and dynamics simulations

Osteoporosis, characterized by excessive osteoclast activation, is mediated through the RANKL/RANK/OPG signaling axis. While flavonoids from Eucommia ulmoides (EU) have demonstrated anti-osteoclastogenic activity, their atomic-level mechanisms remain elusive. Here, we investigated six EU-derived flavonoids (cyrtominetin, quercetin, syringetin, genistein, ombuin, and kaempferol) targeting RANKL using integrated computational approaches. Molecular docking revealed strong binding affinities (Total_Score > 4.0) for all compounds, with cyrtominetin exhibiting the highest affinity (-50.205 kJ/mol via MM-PBSA), primarily through hydrogen bonds with Gly178, His180, Lys181, and Asn295. Moreover, most flavonoids interacted with RANKL by forming strong hydrogen bonds with Gly178 and Asn295, exhibiting higher binding affinity that was identified as essential for the activity. All-atom molecular dynamics simulations (100 ns) confirmed complex stability, demonstrating: low RMSD fluctuations (< 4.0 Å) and compact Rg values (16.0-17.0 Å). Notably, binding free energy decomposition identified both electrostatic and van der Waals contributions as critical for stabilization. These results identify cyrtominetin as a promising lead compound for RANKL inhibition, providing structural insights for designing flavonoid-based therapeutics against osteoporosis.

Water Extract of Mentha arvensis L. Attenuates Estrogen Deficiency-Induced Bone Loss by Inhibiting Osteoclast Differentiation

Mentha arvensis L., is an aromatic herb that belongs to the Lamiaceae family and is widely used in medicinal applications, essential oil applications, and food flavoring. The extract of M. arvensis has been reported to exert sedative-hypnotic, anti-inflammatory, anti-fungal, and anti-bacterial effects. However, its effects on bone metabolism have not yet been studied. Here, we investigated the effects of the water extract of M. arvensis (WEMA) on osteoclast formation in vitro and bone loss in an ovariectomized mouse model. We found that WEMA inhibited osteoclast differentiation by directly acting on osteoclast precursor cells. WEMA inhibited receptor activator of nuclear factor-κB ligand (RANKL)-induced the expression of cellular oncogene fos (c-Fos) and nuclear factor of activated T cells c1 (NFATc1), crucial transcription factors for osteoclast differentiation, by suppressing RANKL-induced activation of early signaling pathways such as those of mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB). In addition, oral administration of WEMA suppressed ovariectomy-induced trabecular bone loss in mice. We additionally identified phytochemicals in WEMA that are known to have anti-osteoclastogenic or anti-osteoporotic properties. Collectively, these results suggest that WEMA is a promising herbal candidate that can be used to prevent or treat postmenopausal osteoporosis.

Role of vasodilator-stimulated phosphoprotein in RANKL-differentiated murine macrophage RAW264.7 cells: Modulation of NF-κB, c-Fos and NFATc1 transcription factors

Vasodilator-stimulated phosphoprotein (VASP) is essential for osteoclast differentiation, and reduced VASP expression results in depressed osteoclast differentiation. Previously, we demonstrated the importance of VASP and Ras-related C3 botulinum toxin substrate 1 interactions in osteosarcoma cell migration and metastasis using Mg-63 and Saos2 cells. However, the molecular details of the functional role of VASP in cell motility and migration remain to be elucidated. The present study demonstrated that VASP affects the expression of αV-integrin, tartrate-resistant acid phosphatase (TRAP) and lamellipodia protrusion in RAW 264.7 murine macrophage cells. The RAW 264.7 mouse monocyte macrophage cell line was used as an osteoclast precursor. RAW 264.7 cells were treated with 50 ng/ml of receptor activator of nuclear factor κ-Β ligand (RANKL) in order to induce cell differentiation (osteoclastogenesis). Small interfering RNA (siRNA) was used to silence VASP, and RT-PCR and western blotting were used to determine the expression for genes and proteins, respectively. TRAP staining as a histochemical marker for osteoclast and fluorescent microscopy for lamellipodia protrusion was performed. RANKL treatment significantly increased the gene and protein expression of VASP, αV-integrin and TRAP in RAW 264.7 cells. Silencing of VASP significantly reduced the RANKL-induced expression of αV-integrin, TRAP and lamellipodia protrusion. In addition, knockdown of VASP attenuated RANKL-stimulated activation of NF-κB, c-Fos and nuclear factor of activated T cells cytoplasmic 1 transcription factors, and the phosphorylation of the p65 and IκBα. These results suggest the critical role of VASP in regulating osteoclast differentiation, which should be further explored in osteosarcoma research.

Dysregulated healing response participates in the pathophysiology of temporomandibular joint ankylosis

This study aimed to characterize samples from patients diagnosed with TMJ ankylosis, using both clinical and histological data. Both clinical and histological analyses of retrieved tissue samples from patients with primary TMJ ankyloses were performed retrospectively (1980-2012). All patients had been subjected to primary arthroplasty. Our study analyzed connective tissue differentiation, ossification patterns, and bone resorption, using histology and immunohistochemistry. Fifteen case records, with a sex ratio of 4:1 (men:woman) and a median age of 8 years, were collected. Six patient samples reported a previous inflammatory event. Histologically, 15 samples exhibited fibrous tissue. Among these, 13 displayed bone at different stages of maturity (fibrous/bony ankylosis). Eleven samples showed aberrant cartilage, characterized by hypertrophic chondrocyte-like cells at the bone/cartilage interface. Four samples revealed inflammatory infiltrate; in one case, this was organized as a lymphoid follicle. Eleven samples showed bone resorption by attached osteoclasts. Interestingly, non-attached osteoclasts were detected, suggesting locally impaired bone remodeling. An association between the presence of mature/lamellar bone and the presence of osteoclasts was observed (p = 0.03). No association was found between previous history of either trauma or infection and the histological type of ankylosis (p = 0.74). There was no association between the histological presence of inflammation or infection and the type of ankylosis (p = 0.63 and p = 0.87, respectively). Retrieved TMJ ankylosis tissues displayed both aberrant ossification and reduced focal bone resorption, suggesting a dysregulated healing response.

Effects of Probiotic Culture Supernatant on Cariogenic Biofilm Formation and RANKL-Induced Osteoclastogenesis in RAW 264.7 Macrophages

Postbiotics are a promising functional ingredient that can overcome the limitations of viability and storage stability that challenge the production of probiotics. To evaluate the effects of postbiotics on oral health, eight spent culture supernatants (SCSs) of probiotics were prepared, and the effects of SCSs on Streptococcus mutans-induced cariogenic biofilm formation and the receptor activator of the nuclear factor κB ligand (RANKL)-induced osteoclastogenesis were evaluated in RAW 264.7 macrophages. SCS of Lactobacillus salivarius MG4265 reduced S. mutans-induced biofilm formation by 73% and significantly inhibited tartrate-resistant acid phosphatase (TRAP) activity, which is a biomarker of mature osteoclasts in RAW 264.7 macrophages. The suppression of RANKL-induced activation of mitogen activated the protein kinases (c-Jun N-terminal kinase, extracellular signal-regulated kinase, and p38) and nuclear factor κB pathways, as well as the upregulation of heme oxygenase-1 expression. The suppression of RANK-L-induced activation of mitogen also inhibited the expression of transcriptional factors (c-fos and nuclear factor of activated T cells cytoplasmic 1) and, subsequently, osteoclastogenesis-related gene expression (tartrate-resistant acid phosphatase-positive (TRAP), cathepsin K, and matrix metalloproteinase-9).Therefore, SCS of L. salivarius MG4265 has great potential as a multifunctional oral health ingredient that inhibits biofilm formation and suppresses the alveolar bone loss that is associated with periodontitis.

Poncirin Inhibits Osteoclast Differentiation and Bone Loss through Down-Regulation of NFATc1 In Vitro and In Vivo

Activation of osteoclast and inactivation of osteoblast result in loss of bone mass with bone resorption, leading to the pathological progression of osteoporosis. The receptor activator of NF-κB ligand (RANKL) is a member of the TNF superfamily, and is a key mediator of osteoclast differentiation. A flavanone glycoside isolated from the fruit of Poncirus trifoliata, poncirin has anti-allergic, hypocholesterolemic, anti-inflammatory and anti-platelet activities. The present study investigates the effect of poncirin on osteoclast differentiation of RANKL-stimulated RAW264.7 cells. We observed reduced formation of RANKL-stimulated TRAP-positive multinucleated cells (a morphological feature of osteoclasts) after poncirin exposure. Real-time qPCR analysis showed suppression of the RANKL-mediated induction of key osteoclastogenic molecules such as NFATc1, TRAP, c-Fos, MMP9 and cathepsin K after poncirin treatment. Poncirin also inhibited the RANKL-mediated activation of NF-κB and, notably, JNK, without changes in ERK and p38 expression in RAW264.7 cells. Furthermore, we assessed the in vivo efficacy of poncirin in the lipopolysaccharide (LPS)-induced bone erosion model. Evaluating the micro-CT of femurs revealed that bone erosion in poncirin treated mice was markedly attenuated. Our results indicate that poncirin exerts anti-osteoclastic effects in vitro and in vivo by suppressing osteoclast differentiation. We believe that poncirin is a promising candidate for inflammatory bone loss therapeutics.

Absence of α-calcitonin gene-related peptide modulates bone remodeling properties of murine osteoblasts and osteoclasts in an age-dependent way

Mice with an overall deletion of the sensory neuropeptide α-calcitonin gene-related peptide (α-CGRP) develop an age-dependent osteopenic bone phenotype. Underlying molecular mechanisms of how αCGRP affects bone cell metabolism are not well understood. This study aims to characterize differences in metabolic parameters of osteoblast-like cells (OB) and differentiated bone marrow-derived macrophages (BMM)/osteoclast (OC) cultures isolated from 3 month (3 m) and 9 month old (9 m) α-CGRP-deficient mice (-/-) and age-matched WT controls. All WT bone cell cultures endogenously produced and secreted α-CGRP. We found higher BMM but reduced OB numbers and reduced OB vitality after isolation from 9 m compared to 3 m mice, independent of genotype. Absence of α-CGRP reduced cell spreading, increased apoptosis rate throughout osteogenic differentiation, and reduced ALP activity during late osteogenic differentiation in 9 m OB-/- cultures, whereas minor effects were found in 3 m OB-/- cultures. Cathepsin K activity was reduced in 3 m OC-/- cultures. On the contrary, 9 m OC-/- cells demonstrated increased proliferation and caspase3/7 activity. The absence of α-CGRP influenced bone formation and resorption rate differently in bone cells from 3 and 9 m old mice. In summary we suggest, that an increase of dysfunctional mature osteoblasts might occur during aging and contribute to the development of the osteopenic bone phenotype in mature adult (9 m) α-CGRP-deficient mice.

Substance P modulates bone remodeling properties of murine osteoblasts and osteoclasts

Clinical observations suggest neuronal control of bone remodeling. Sensory nerve fibers innervating bone, bone marrow and periosteum signal via neurotransmitters including substance P (SP). In previous studies we observed impaired biomechanical and structural bone parameters in tachykinin (Tac) 1-deficient mice lacking SP. Here, we aim to specify effects of SP on metabolic parameters of bone marrow macrophage (BMM)/osteoclast cultures and osteoblasts isolated from Tac1-deficient and wildtype (WT) mice. We demonstrated endogenous SP production and secretion in WT bone cells. Absence of SP reduced bone resorption rate, as we found reduced numbers of precursor cells (BMM) and multinucleated osteoclasts and measured reduced cathepsin K activity in Tac1-/- BMM/osteoclast cultures. However, this might partly be compensated by reduced apoptosis rate and increased fusion potential of Tac1-/- precursor cells to enlarged "super" osteoclasts. Contrarily, increased ALP enzyme activity and apoptosis rate during early osteoblast differentiation accelerated osteogenesis and cell death in the absence of SP together with reduced ALP activity of Tac1-/- osteoblasts during late osteogenic differentiation resulting in reduced bone formation at later stages. Therefore, we suggest that absence of SP presumably results in a slight reduction of bone resorption rate but concomitantly in a critical reduction of bone formation and mineralization rate.

A single-nucleotide polymorphism in MMP9 is associated with decreased risk of steroid-induced osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is a common hip joint disease, and steroid-induced ONFH accounts for a large number of cases. Here, we examined eight previously-identified single-nucleotide polymorphisms (SNPs) in the MPP2 and MPP9 genes of 285 steroid-induced ONFH patients and 507 healthy controls from northern China to determine whether these SNPs were associated with the risk of developing steroid-induced ONFH. Chi-squared tests and genetic model and haplotype analyses were used to evaluate associations. The rs2274755 SNP in MMP9 was associated with a decreased risk of steroid-induced ONFH in the allele, dominant, and additive models. Additionally, the “CGC” MMP9 haplotype was associated with a 0.69-fold decrease in the risk of steroid-induced ONFH. Although additional, larger population-based studies are needed to confirm these findings, our results reveal for the first time an association between a MMP9 SNP at the rs2274755 locus and a decreased risk of steroid-induced ONFH in a northern Chinese population.

MMP9 polymorphism is associated with susceptibility to non-traumatic osteonecrosis of femoral head in a Chinese Han population

Non-traumatic osteonecrosis of femoral head (ONFH) is an orthopedic refractory disease with escalating morbidity in Chinese Han population. In our case-control study, we examined eight previously identified MMP9 single-nucleotide polymorphisms (SNPs) in 585 non-traumatic ONFH patients and 507 healthy individuals from northern China to determine whether these SNPs associated with the risk of developing non-traumatic ONFH. Genetic model and haplotype analyses were used to evaluate the association between SNPs and non-traumatic ONFH. MMP9 rs2274755 (OR, 0.740; 95% CI, 0.578-0.949; p = 0.017) was associated with a reduced risk of non-traumatic ONFH. After adjusting for age and gender, the logistic regression results showed that rs2274755 associated with a lower risk of non-traumatic ONFH in the dominant (OR=0.71, 95% CI: 0.54-0.94, p=0.016), overdominant (OR=0.73, 95% CI: 0.55-0.96, p=0.026) and log-additive (OR=0.74740; 95% CI, 0.578-0.949; p=0.017) models. In addition, the “TGC” haplotype of rs2274755 was associated with a 0.79-fold decrease in risk while the “CTC” haplotype associated with a 0.65-fold decrease risk of the non-traumatic ONFH. These results provide evidence that the MMP9 SNP at the rs2274755 locus is associated with a decreased risk of non-traumatic ONFH in a Chinese Han population.

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.

The Elusive Antifibrotic Macrophage

Fibrotic diseases, especially of the liver, the cardiovascular system, the kidneys, and the lungs, account for approximately 45% of deaths in Western societies. Fibrosis is a serious complication associated with aging and/or chronic inflammation or injury and cannot be treated effectively yet. It is characterized by excessive deposition of extracellular matrix (ECM) proteins by myofibroblasts and impaired degradation by macrophages. This ultimately destroys the normal structure of an organ, which leads to loss of function. Most efforts to develop drugs have focused on inhibiting ECM production by myofibroblasts and have not yielded many effective drugs yet. Another option is to stimulate the cells that are responsible for degradation and uptake of excess ECM, i.e., antifibrotic macrophages. However, macrophages are plastic cells that have many faces in fibrosis, including profibrotic behavior-stimulating ECM production. This can be dependent on their origin, as the different organs have tissue-resident macrophages with different origins and a various influx of incoming monocytes in steady-state conditions and during fibrosis. To be able to pharmacologically stimulate the right kind of behavior in fibrosis, a thorough characterization of antifibrotic macrophages is necessary, as well as an understanding of the signals they need to degrade ECM. In this review, we will summarize the current state of the art regarding the antifibrotic macrophage phenotype and the signals that stimulate its behavior.

Sympathetic Neurotransmitters Modulate Osteoclastogenesis and Osteoclast Activity in the Context of Collagen-Induced Arthritis

Excessive synovial osteoclastogenesis is a hallmark of rheumatoid arthritis (RA). Concomitantly, local synovial changes comprise neuronal components of the peripheral sympathetic nervous system. Here, we wanted to analyze if collagen-induced arthritis (CIA) alters bone marrow-derived macrophage (BMM) osteoclastogenesis and osteoclast activity, and how sympathetic neurotransmitters participate in this process. Therefore, BMMs from Dark Agouti rats at different CIA stages were differentiated into osteoclasts in vitro and osteoclast number, cathepsin K activity, matrix resorption and apoptosis were analyzed in the presence of acetylcholine (ACh), noradrenaline (NA) vasoactive intestinal peptide (VIP) and assay-dependent, adenylyl cyclase activator NKH477. We observed modulation of neurotransmitter receptor mRNA expression in CIA osteoclasts without affecting protein level. CIA stage-dependently altered marker gene expression associated with osteoclast differentiation and activity without affecting osteoclast number or activity. Neurotransmitter stimulation modulated osteoclast differentiation, apoptosis and activity. VIP, NA and adenylyl cyclase activator NKH477 inhibited cathepsin K activity and osteoclastogenesis (NKH477, 10(-6) M NA) whereas ACh mostly acted pro-osteoclastogenic. We conclude that CIA alone does not affect metabolism of in vitro generated osteoclasts whereas stimulation with NA, VIP plus specific activation of adenylyl cyclase induced anti-resorptive effects probably mediated via cAMP signaling. Contrary, we suggest pro-osteoclastogenic and pro-resorptive properties of ACh mediated via muscarinic receptors.

Effects of 1α,25-(OH)2D3 on the formation and activity of osteoclasts in RAW264.7 cells

The hormonally active form of vitamin D3, 1α,25-(OH)2D3, has an important role in bone metabolism. This study examined the effects of 1α,25-(OH)2D3 on the ability of two cytokines, receptor activator of nuclear factor-κB ligand (RANKL) and macrophage-colony stimulating factor (M-CSF), to induce RAW 264.7 cells to form osteoclasts. A TRAP histochemical staining assay and bone resorption analysis were used to identify the rate of formation and activity of osteoclasts. The numbers of osteoclasts formed, and their bone resorption activity, was enhanced by the addition of 1α,25-(OH)2D3. The expression levels of osteoclast-specific proteins that are essential for bone resorption, integrin β3, V-ATPase, CAII, CTSK, TRAP and MMP-9, were detected by western blotting. During 48 h, the expression levels of all these proteins significantly increased. Quantitative real-time polymerase chain reaction was used to determine the expression levels of the transcription factors, c-Fos and NFATcl. The expression levels of c-Fos and NFATc1 also increased 24h after treatment with 1α,25-(OH)2D3. These results suggest that 1α,25-(OH)2D3 can regulate bone metabolism by directly enhancing the formation and maturation of osteoclasts.

Absence of substance P and the sympathetic nervous system impact on bone structure and chondrocyte differentiation in an adult model of endochondral ossification

OBJECTIVE

Sensory and sympathetic nerve fibers (SNF) innervate bone and epiphyseal growth plate. The role of neuronal signals for proper endochondral ossification during skeletal growth is mostly unknown. Here, we investigated the impact of the absence of sensory neurotransmitter substance P (SP) and the removal of SNF on callus differentiation, a model for endochondral ossification in adult animals, and on bone formation.

METHODS

In order to generate callus, tibia fractures were set in the left hind leg of wild type (WT), tachykinin 1-deficient (Tac1-/-) mice (no SP) and animals without SNF. Locomotion was tested in healthy animals and touch sensibility was determined early after fracture. Callus tissue was prepared for immunofluorescence staining for SP, neurokinin1-receptor (NK1R), tyrosine-hydroxylase (TH) and adrenergic receptors α1, α2 and β2. At the fracture site, osteoclasts were stained for TRAP, osteoblasts were stained for RUNX2, and histomorphometric analysis of callus tissue composition was performed. Primary murine bone marrow derived macrophages (BMM), osteoclasts, and osteoblasts were tested for differentiation, activity, proliferation and apoptosis in vitro. Femoral fractures were set in the left hind leg of all the three groups for mechanical testing and μCT-analysis.

RESULTS

Callus cells stained positive for SP, NK1R, α1d- and α2b adrenoceptors and remained β2-adrenoceptor and TH-negative. Absence of SP and SNF did not change the general locomotion but reduces touch sensitivity after fracture. In mice without SNF, we detected more mesenchymal callus tissue and less cartilaginous tissue 5 days after fracture. At day 13 past fracture, we observed a decrease of the area covered by hypertrophic chondrocytes in Tac1-/- mice and mice without SNF, a lower number of osteoblasts in Tac1-/- mice and an increase of osteoclasts in mineralized callus tissue in mice without SNF. Apoptosis rate and activity of osteoclasts and osteoblasts isolated from Tac1-/- and sympathectomized mice were partly altered in vitro. Mechanical testing of fractured- and contralateral legs 21 days after fracture, revealed an overall reduced mechanical bone quality in Tac1-/- mice and mice without SNF. μCT-analysis revealed clear structural alteration in contralateral and fractured legs proximal of the fracture site with respect to trabecular parameters, bone mass and connectivity density. Notably, structural parameters are altered in fractured legs when related to unfractured legs in WT but not in mice without SP and SNF.

CONCLUSION

The absence of SP and SNF reduces pain sensitivity and mechanical stability of the bone in general. The micro-architecture of the bone is profoundly impaired in the absence of intact SNF with a less drastic effect in SP-deficient mice. Both sympathetic and sensory neurotransmitters are indispensable for proper callus differentiation. Importantly, the absence of SP reduces bone formation rate whereas the absence of SNF induces bone resorption rate. Notably, fracture chondrocytes produce SP and its receptor NK1 and are positive for α-adrenoceptors indicating an endogenous callus signaling loop. We propose that sensory and sympathetic neurotransmitters have crucial trophic effects which are essential for proper bone formation in addition to their classical neurological actions.

Targeting bone remodeling by isoflavone and 3,3'-diindolylmethane in the context of prostate cancer bone metastasis

Prostate cancer (PCa) bone metastases have long been believed to be osteoblastic because of bone remodeling leading to the formation of new bone. However, recent studies have shown increased osteolytic activity in the beginning stages of PCa bone metastases, suggesting that targeting both osteolytic and osteoblastic mediators would likely inhibit bone remodeling and PCa bone metastasis. In this study, we found that PCa cells could stimulate differentiation of osteoclasts and osteoblasts through the up-regulation of RANKL, RUNX2 and osteopontin, promoting bone remodeling. Interestingly, we found that formulated isoflavone and 3,3′-diindolylmethane (BR-DIM) were able to inhibit the differentiation of osteoclasts and osteoblasts through the inhibition of cell signal transduction in RANKL, osteoblastic, and PCa cell signaling. Moreover, we found that isoflavone and BR-DIM down-regulated the expression of miR-92a, which is known to be associated with RANKL signaling, EMT and cancer progression. By pathway and network analysis, we also observed the regulatory effects of isoflavone and BR-DIM on multiple signaling pathways such as AR/PSA, NKX3-1/Akt/p27, MITF, etc. Therefore, isoflavone and BR-DIM with their multi-targeted effects could be useful for the prevention of PCa progression, especially by attenuating bone metastasis mechanisms.

Blood-derived human osteoclast resorption activity is impaired by Hyaluronan-CD44 engagement via a p38-dependent mechanism

The control of bone resorption is crucial in osteolytic diseases. Once attached to bone, osteoclasts (OCs) initiate the resorption process through the activation of a complex cascade of morphological and biochemical changes. Hyaluronan (HA), an extracellular glycosaminoglycan long non-branching polysaccharide, is expressed in bone matrices. Here we demonstrate that HA counter-balances the erosion activity of human mature OCs by significantly reducing their degradative potential. HA treatment of fully differentiated OCs derived from human peripheral blood monocytes inhibited migration on collagen as well as bone resorption. HA-mediated effects were primarily due to TRAcP, MMP-9, and cathepsin K down-regulation and to the increased levels of TIMP-1, a natural MMP-9 inhibitor. Binding of HA to mature OCs was entirely mediated by CD44: function-blocking anti-CD44 antibodies fully abrogated HA effects, and the engagement of HA receptor caused a rapid de-phosphorylation of Ser325 in the CD44 cytoplasmic tail. The inhibitory action by HA was associated with a transient up-phosphorylation of Pyk2, a novel persistent phosphorylation of p38 and the down-regulation of NFATc1 transcription factor. Our results provide a direct evidence for the involvement of CD44 in the HA-dependent regulation of OC activity and suggest a signaling pathway that could be unique in OC function inhibition.

Differential expression of tartrate-resistant acid phosphatase isoforms 5a and 5b by tumor and stromal cells in human metastatic bone disease

Tartrate-resistant acid phosphatase (TRAP) exists in human serum as two major isoforms, monomeric 5a and proteolytically processed enzymatically active 5b. The 5b isoform is secreted by osteoclasts and has recently been advocated as a serum marker for bone metastasis in breast cancer patients. The 5a isoform, on the other hand, is not bone-derived and has been proposed to be a marker of activated macrophages and chronic inflammation. In this study, expression of TRAP protein and enzymatic activity in bone metastases from different primary sites was examined. TRAP activity was high in bone metastases from prostate cancer, intermediate in breast cancer, and low in lung and kidney cancers. The partially purified TRAP from breast cancer bone metastasis samples exhibited the enzymatic characteristics of purple acid phosphatase. Both 5a and 5b isoforms were expressed in bone metastases of different histogenetic origins, i.e. prostate, breast, lung and kidney, and also a novel previously unreported 42 kDa variant of the TRAP 5a isoform was identified in bone metastases. This novel TRAP 5a isoform was absent in human bone, indicating that the 42 kDa variant is specific to metastatic cancer tissue. Immunohistochemistry revealed that metastatic cancer cells were the predominant source of TRAP 5a, whereas tumor-associated macrophages and occasionally multinucleated giant cells in the tumor stroma preferentially expressed the proteolytically processed TRAP 5b variant. Our results indicate the presence of a previously unstudied variant of monomeric TRAP 5a in cancer cells, which may have functional and diagnostic implications. Moreover, the presence of TRAP-positive macrophages in bone metastases could, together with cancer cells and osteoclasts, contribute to the elevated levels of serum TRAP activity observed in patients with bone metastases.

Cancer prevention with natural compounds

Botanical and nutritional compounds have been used for the treatment of cancer throughout history. These compounds also may be useful in the prevention of cancer. Population studies suggest that a reduced risk of cancer is associated with high consumption of vegetables and fruits. Thus, the cancer chemopreventive potential of naturally occurring phytochemicals is of great interest. There are numerous reports of cancer chemopreventive activity of dietary botanicals, including cruciferous vegetables such as cabbage and broccoli, Allium vegetables such as garlic and onion, green tea, Citrus fruits, soybeans, tomatoes, berries, and ginger, as well as medicinal plants. Several lead compounds, such as genistein (from soybeans), lycopene (from tomatoes), brassinin (from cruciferous vegetables), sulforaphane (from asparagus), indole-3-carbinol (from broccoli), and resveratrol (from grapes and peanuts) are in preclinical or clinical trials for cancer chemoprevention. Phytochemicals have great potential in cancer prevention because of their safety, low cost, and oral bioavailability. In this review, we discuss potential natural cancer preventive compounds and their mechanisms of action.

RANK-Fc inhibits malignancy via inhibiting ERK activation and evoking caspase-3-mediated anoikis in human osteosarcoma cells

Osteosarcoma (OS) is the most common primary malignant bone tumour, mainly afflicting the young. While there has been substantial improvement in treatment of OS with surgery and chemotherapy in the past two decades, this disease remains a significant health problem, warranting efforts to find better therapeutic options. In this study, we examined the RANK/RANKL axis in OS cells, using a RANK-Fc protein to perturb this coupling in an effort to reduce OS cell growth. RANK-Fc suppressed OS cell migration (P < 0.005), invasion ability (P < 0.05), and anchorage-independent ability in collagen-1 gel (P < 0.005) following induction of anoikis and activation of caspase-3. OS cell proliferation was not perturbed by RANK-Fc. The anti-invasion and anti-metastasis capability of RANK-Fc is attributed to reduced extracellular signal-regulated protein kinase (ERK) signaling via RANK-Fc, though activation of NFkappaB, and altered expression of Akt, p38, JNK, and matrix metalloproteinase (MMP)-2 and -9 were ruled out. In vivo, activity of the RANK-Fc against OS cell migration and invasion was confirmed in a model strictly monitoring metastasis. Thus, RANK-Fc, given its ability to directly reduce OS aggression, is a potential drug candidate.

Low-energy laser irradiation facilitates the velocity of tooth movement and the expressions of matrix metalloproteinase-9, cathepsin K, and alpha(v) beta(3) integrin in rats

It has previously been reported that low-energy laser irradiation stimulated the velocity of tooth movement via the receptor activator of nuclear factor kappa B (RANK)/RANK ligand and the macrophage colony-stimulating factor/its receptor (c-Fms) systems. Matrix metalloproteinase (MMP)-9, cathepsin K, and alpha(v) beta(3) [alpha(v)beta3] integrin are essential for osteoclastogenesis; therefore, the present study was designed to examine the effects of low-energy laser irradiation on the expression of MMP-9, cathepsin K, and alpha(v)beta3 integrin during experimental tooth movement. Fifty male, 6-week-old Wistar strain rats were used in the experiment. A total force of 10g was applied to the rat molars to induce tooth movement. A Ga-Al-As diode laser was used to irradiate the area around the moving tooth and, after 7 days, the amount of tooth movement was measured. To determine the amount of tooth movement, plaster models of the maxillae were made using a silicone impression material before (day 0) and after tooth movement (days 1, 2, 3, 4, and 7). The models were scanned using a contact-type three-dimensional (3-D) measurement apparatus. Immunohistochemical staining for MMP-9, cathepsin K, and integrin subunits of alpha(v)beta3 was performed. Intergroup comparisons of the average values were conducted with a Mann-Whitney U-test for tooth movement and the number of tartrate-resistant acid phosphatase (TRAP), MMP-9, cathepsin K, and integrin subunits of alpha(v)beta3-positive cells. In the laser-irradiated group, the amount of tooth movement was significantly greater than that in the non-irradiated group at the end of the experiment (P < 0.05). Cells positively stained with TRAP, MMP-9, cathepsin K, and integrin subunits of alpha(v)beta3 were found to be significantly increased in the irradiated group on days 2-7 compared with those in the non-irradiated group (P < 0.05). These findings suggest that low-energy laser irradiation facilitates the velocity of tooth movement and MMP-9, cathepsin K, and integrin subunits of alpha(v)beta3 expression in rats.

Modeled gravitational unloading triggers differentiation and apoptosis in preosteoclastic cells

Gravity acts permanently on organisms as either static or dynamic stimulation. Understanding the influence of gravitational and mechanical stimuli on biological systems is an intriguing scientific problem. More than two decades of life science studies in low g, either real or modeled by clinostats, as well as experimentation with devices simulating different types of controlled mechanical stimuli, have shown that important biological functions are altered at the single cell level. Here, we show that the human leukemic line FLG 29.1, characterized as an osteoclastic precursor model, is directly sensitive to gravitational unloading, modeled by a random positioning machine (RPM). The phenotypic expression of cytoskeletal proteins, osteoclastic markers, and factors regulating apoptosis was investigated using histochemical and immunohistochemical methods, while the expression of the corresponding genes was analyzed using RT-PCR. A quantitative bone resorption assay was performed. Autofluorescence spectroscopy and imaging were applied to gain information on cell metabolism. The results show that modeled hypogravity may trigger both differentiation and apoptosis in FLG 29.1 cells. Indeed, when comparing RPM versus 1 x g cultures, in the former we found cytoskeletal alterations and a marked increase in apoptosis, but the surviving cells showed an osteoclastic-like morphology, overexpression of osteoclastic markers and the ability to resorb bone. In particular, the overexpression of both RANK and its ligand RANKL, maintained even after return to 1 x g conditions, is consistent with the firing of a differentiation process via a paracrine/autocrine mechanism.

High d(+)glucose concentration inhibits RANKL-induced osteoclastogenesis

Diabetes is a chronic disease associated with hyperglycemia and altered bone metabolism that may lead to complications including osteopenia, increased risk of fracture and osteoporosis. Hyperglycemia has been implicated in the pathogenesis of diabetic bone disease; however, the biologic effect of glucose on osteoclastogenesis is unclear. In the present study, we examined the effect of high d(+)glucose (d-Glc) and l(-)glucose (l-Glc; osmotic control) on RANKL-induced osteoclastogenesis using RAW264.7 cells and Bone Marrow Macrophages (BMM) as models. Cells were exposed to sustained high glucose levels to mimic diabetic conditions. Osteoclast formation was analyzed using tartrate resistant acid phosphatase (TRACP) assay, expression of calcitonin receptor (CTR) and cathepsin K mRNAs, and cultures were examined for reactive oxygen species (ROS) using dichlorodihydrofluorescein diacetate (DCF-DA) fluorescence, caspase-3 and Nuclear Factor kappaB (NF-kappaB) activity. Cellular function was assessed using a migration assay. Results show, for the first time, that high d-Glc inhibits osteoclast formation, ROS production, caspase-3 activity and migration in response to RANKL through a metabolic pathway. Our findings also suggest that high d-Glc may alter RANKL-induced osteoclast formation by inhibiting redox-sensitive NF-kappaB activity through an anti-oxidative mechanism. This study increases our understanding of the role of glucose in diabetes-associated bone disease. Our data suggest that high glucose levels may alter bone turnover by decreasing osteoclast differentiation and function in diabetes and provide new insight into the biologic effects of glucose on osteoclastogenesis.

Tartrate-resistant acid phosphatase (TRAP) and the osteoclast/immune cell dichotomy

Tartrate-resistant acid phosphatase (TRAP), once considered to be just a histochemical marker of osteoclasts is now recognised to be a molecule of widespread occurrence with functions in both the skeleton and the immune system. TRAP is expressed by osteoclasts, macrophages, dendritic cells and a number of other cell types. It has a critical role in many biological processes including skeletal development, collagen synthesis and degradation, the mineralisation of bone, cytokine production by macrophages and dendritic cells, macrophage recruitment, dendritic cell maturation and a role in the development of Th1 responses. TRAP is able to degrade skeletal phosphoproteins including osteopontin (OPN), identical to the T-cell cytokine, Eta-1. In this review, we discuss the role of TRAP in bone and immune cells and suggest that TRAP may be implicated in autoimmune disorders regulated by Th1 inflammatory responses as well as certain cancers.

Cathepsin K predicts femoral neck bone mineral density change in nonosteoporotic peri- and early postmenopausal women

OBJECTIVE

Cathepsin K is a cysteine protease that plays an essential role in organic bone matrix degradation. The aim of our study was to seek correlation of serum cathepsin K levels and a change in bone mineral density (BMD) over a 3-year period in a population of healthy nonosteoporotic women. The secondary end points were the correlations of serum cathepsin K with cross-sectional BMD and with other serum bone turnover markers and age.

DESIGN

In 43 healthy women aged 42 to 57 years, blood samples for determination of cathepsin K, osteocalcin, bone alkaline phosphatase, C-terminal cross-linking telopeptide of type I collagen, osteoprotegerin, and nuclear factor kappaB ligand were collected at the time of the first BMD measurement. BMD measurements were repeated after 3 years.

RESULTS

We found a moderate negative correlation of serum cathepsin K levels with change in femoral neck BMD, but none with change in spinal BMD. There were no significant correlations between cross-sectional BMD of the spine or femoral neck and serum levels of cathepsin K. Serum levels of cathepsin K were not significantly correlated with any bone turnover markers studied or with age.

CONCLUSIONS

Serum cathepsin K does not seem to represent a surrogate for bone turnover markers used at present, but it might be useful as a predictor of cortical bone loss.

Expression of bone resorption genes in osteoarthritis and in osteoporosis

Cathepsin K and MMP-9 are considered to be the most abundant proteases in osteoclasts. TRAP is a marker for osteoclasts, and there is increasing evidence of its proteolytic role in bone resorption. RANKL is a recently discovered regulator of osteoclast maturation and activity and induces expression of many genes. This study compared cathepsin K, MMP-9, TRAP, RANKL, OPG, and osteocalcin gene expression in the proximal femur of patients with osteoarthritis with that of patients with femoral neck fracture. Fifty-six patients undergoing arthroplasty because of osteoarthritis or femoral neck fracture were included in the study. Total mRNA was extracted from the bone samples obtained from the intertrochanteric region of the proximal femur. Real-time RT-PCR was used to quantify CTSK (cathepsin K), MMP-9 (matrix metalloproteinase 9), ACP5 (TRAP), TNFSF11 (RANKL), TNFRSF11B (OPG), and BGLAP (osteocalcin) mRNAs. The levels of mRNAs coding for MMP-9 and osteocalcin indicated higher expression in the osteoarthritic group (P = 0.011, P = 0.001, respectively), whereas RANKL expression and the ratio RANKL/OPG were both significantly lower in the osteoarthritic group than in the fracture group. Expression of cathepsin K, MMP-9, and TRAP relative to RANKL was significantly higher in the osteoarthritic group. Ratios of all three proteolytic enzymes relative to formation marker osteocalcin were higher in the fracture group. Gene expression of cathepsin K, MMP-9, TRAP, RANKL, OPG, and osteocalcin and the association between their mRNA levels pointed to higher bone resorption and bone formation in osteoarthritis, differences in balance between them, and differences in regulation of bone resorption in osteoarthritic and osteoporotic bone.

Trigger osteoclast formation and activation: Molecular treatment strategy of delayed tooth eruption

Delayed tooth eruption (DTE) is the emergence of a tooth into the oral cavity at a time that delays significantly from norms. It causes a significant impact on a patient's oral health. Some methods have been suggested to rescue the delayed tooth eruption. However, no approach aims to accelerate the biological process of tooth eruption and rescue these eruption disorders. Recent researches have shown that tooth eruption depends on the presence of osteoclasts to create an eruption pathway through the alveolar bone. We postulate a new approach that targets osteoclast formation and activation to accelerate the eruption of the affected tooth. These strategies include stimulating osteoclastogenesis by applying the cytokines or small molecules, such as TNF-alpha, IL-1 alpha and MCP-1; triggering osteoclast differentiation by applying molecules associated RANKL signaling, such as RANKL-Fc and OPG antibody; enhancing the function of osteoclasts by applying proteinases, such as CTSK. For the clinical point of view, we can inject these molecules in the oral mucosa of the affected tooth to induce bone resorption, then to rebuild the pathway of tooth eruption.

Increased expression of activating factors in large osteoclasts could explain their excessive activity in osteolytic diseases

Large osteoclasts (>or=10 nuclei) predominate at sites of pathological bone resorption. We hypothesized this was related to increased resorptive activity of large osteoclasts and have demonstrated previously that larger osteoclasts are 8-fold more likely to be resorbing than small osteoclasts (2-5 nuclei). Here we ask whether these differences in resorptive activity can be explained by differences in expression of factors involved in osteoclast signaling, fusion, attachment, and matrix degradation. Authentic rabbit osteoclasts and osteoclasts derived from RAW264.7 cells showed similar increases in c-fms expression (1.7- to 1.8-fold) in large osteoclasts suggesting that RAW cells are a viable system for further analysis. We found 2- to 4.5-fold increases in the expression of the integrins alpha(v) and beta(3), the proteases proMMP9, matMMP9 and pro-cathepsinK, and in activating receptors RANK, IL-1R1, and TNFR1 in large osteoclasts. In contrast, small osteoclasts had higher expression of the fusion protein SIRPalpha1 and the decoy receptor IL-1R2. The higher expression of activation receptors and lower expression of IL-1R2 in large osteoclasts suggest they are hyperresponsive to extracellular factors. This is supported by the observation that the resorptive activity in large osteoclasts was more responsive to IL-1beta, and that this increased activity was inhibited by the IL-1 receptor antagonist, IL-1ra. This increased responsiveness of large osteoclasts to IL-1 may, in part, explain the pathological bone loss noted in inflammatory diseases. The heterogeneity in receptor expression and the differential response to cytokines and their antagonists could prove useful for selective inhibition of large osteoclasts actively engaged in pathological bone loss.

RANK ligand signaling modulates the matrix metalloproteinase-9 gene expression during osteoclast differentiation

Osteoclast differentiation is tightly regulated by receptor activator of NF-kappaB ligand (RANKL) signaling. Matrix metalloproteinase-9 (MMP-9), a type IV collagenase is highly expressed in osteoclast cells and plays an important role in degradation of extracellular matrix; however, the molecular mechanisms that regulate MMP-9 gene expression are unknown. In this study, we demonstrate that RANKL signaling induces MMP-9 gene expression in osteoclast precursor cells. We further show that RANKL regulates MMP-9 gene expression through TRAF6 but not TRAF2. Interestingly, blockade of p38 MAPK activity by pharmacological inhibitor, SB203580 increases MMP-9 activity whereas ERK1/2 inhibitor, PD98059 decreases RANKL induced MMP-9 activity in RAW264.7 cells. These data suggest that RANKL differentially regulates MMP-9 expression through p38 and ERK signaling pathways during osteoclast differentiation. Transient expression of MMP-9 gene (+1 to -1174 bp relative to ATG start codon) promoter-luciferase reporter plasmids in RAW264.7 cells and RANKL stimulation showed significant increase (20-fold) of MMP-9 gene promoter activity; however, there is no significant change with respect to +1 bp to -446 bp promoter region and empty vector transfected cells. These results indicated that MMP-9 promoter sequence from -446 bp to -1174 bp relative to start codon is responsive to RANKL stimulation. Sequence analysis of the mouse MMP-9 gene promoter region further identified the presence of binding motif (-1123 bp to -1153 bp) for the nuclear factor of activated T cells 1 (NFATc1) transcription factor. Inhibition of NFATc1 using siRNA and VIVIT peptide inhibitor significantly decreased RANKL stimulation of MMP-9 activity. We further confirm by oligonucleotide pull-down assay that RANKL stimuli enhanced NFATc1 binding to MMP-9 gene promoter element. In addition, over-expression of constitutively active NFAT in RAW264.7 cells markedly increased (5-fold) MMP-9 gene promoter activity in the absence of RANKL. Taken together, our results suggest that RANKL signals through TRAF6 and that NFATc1 is a downstream effector of RANKL signaling to modulate MMP-9 gene expression during osteoclast differentiation.

Calvarial osteoclasts express a higher level of tartrate-resistant acid phosphatase than long bone osteoclasts and activation does not depend on cathepsin K or L activity

Bone resorption by osteoclasts depends on the activity of various proteolytic enzymes, in particular those belonging to the group of cysteine proteinases. Next to these enzymes, tartrate-resistant acid phosphatase (TRAP) is considered to participate in this process. TRAP is synthesized as an inactive proenzyme, and in vitro studies have shown its activation by cysteine proteinases. In the present study, the possible involvement of the latter enzyme class in the in vivo modulation of TRAP was investigated using mice deficient for cathepsin K and/or L and in bones that express a high (long bone) or low (calvaria) level of cysteine proteinase activity. The results demonstrated, in mice lacking cathepsin K but not in those deficient for cathepsin L, significantly higher levels of TRAP activity in long bone. This higher activity was due to a higher number of osteoclasts. Next, we found considerable differences in TRAP activity between calvarial and long bones. Calvarial bones contained a 25-fold higher level of activity than long bones. This difference was seen in all mice, irrespective of genotype. Osteoclasts isolated from the two types of bone revealed that calvarial osteoclasts expressed higher enzyme activity as well as a higher level of mRNA for the enzyme. Analysis of TRAP-deficient mice revealed higher levels of nondigested bone matrix components in and around calvarial osteoclasts than in long bone osteoclasts. Finally, inhibition of cysteine proteinase activity by specific inhibitors resulted in increased TRAP activity. Our data suggest that neither cathepsin K nor L is essential in activating TRAP. The findings also point to functional differences between osteoclasts from different bone sites in terms of participation of TRAP in degradation of bone matrix. We propose that the higher level of TRAP activity in calvarial osteoclasts compared to that in long bone cells may partially compensate for the lower cysteine proteinase activity found in calvarial osteoclasts and TRAP may contribute to the degradation of noncollagenous proteins during the digestion of this type of bone.

[Effects of kangfengshi granules on expressions of osteoprotegerin, RANKL and M-CSF in bone tissues of rats with collagen-induced arthritis]

OBJECTIVE

To observe the effects of Kangfengshi Granules (KFSG) on expressions of the mRNAs of osteoprotegerin (OPG), receptor activator of nuclear factor-kappaB ligand (RANKL) and macrophage colony stimulating factor (M-CSF) in bone tissues of rats with collagen-induced arthritis.

METHODS

Forty SD rats were randomly divided into four groups: normal control group, untreated group, cyclosporine A (CsA)-treated group and KFSG-treated group. Except the rats in the normal control group, all the other rats received subcutaneous injection of collagen II to establish collagen-induced arthritis (CIA) models. Then the rats in each group were fed normal saline or corresponding drugs for four weeks. Total RNA was extracted from carpal and digital bones. The expressions of OPG, RANKL and M-CSF mRNAs were examined by real-time PCR.

RESULTS

The total incidence of arthritis induced by collagen II in the rats was approximately 90%. The expression levels of RANKL and M-CSF mRNAs and the RANKL mRNA/OPG mRNA ratio in the untreated group, KFSG-treated group and CsA-treated group were all significantly higher than those in the normal control group, while the expression levels of OPG mRNA in those three groups were significantly lower than that in the normal control group. The expression level of OPG mRNA in the KFSG-treated group was obviously higher while the expression level of M-CSF mRNA and the RANKL mRNA/OPG mRNA ratio in the same group were both lower as compared with those in the untreated group.

CONCLUSION

The molecular mechanism of effects of KFSG on bone erosion and destruction induced by rheumatoid arthritis is closely correlated with up-regulating the expression of OPG mRNA, down-regulating the expression of M-CSF mRNA and RANKL mRNA/OPG mRNA ratio.

Antitumor and antimetastatic activities of docetaxel are enhanced by genistein through regulation of osteoprotegerin/receptor activator of nuclear factor-kappaB (RANK)/RANK ligand/MMP-9 signaling in prostate cancer

Bone metastasis is very common in advanced prostate cancer. Docetaxel has been shown to improve survival in patients with metastatic prostate cancer. However, treatment with docetaxel is associated with a certain degree of toxicity. Genistein, derived from soybeans, has been found to inhibit cancer cell growth without toxicity. We have recently reported that genistein could potentiate the antitumor activity of chemotherapeutic agents both in vitro and in vivo. However, the molecular mechanism of this novel effect of genistein has not been fully elucidated. In this study, we found that genistein significantly potentiated the antitumor, anti-invasive, and antimetastatic activities of docetaxel both in culture and in severe combined immunodeficient (SCID)-human model of experimental prostate cancer bone metastasis. We further conducted microarray analysis, real-time reverse transcription-PCR, Western blot analysis, small interfering RNA and cDNA transfection, matrix metalloproteinase-9 (MMP-9) activity assay, and invasion assay. We found that the expression of osteoprotegerin (OPG) was induced by genistein and inhibited by docetaxel, whereas genistein significantly down-regulated the expression and secretion of receptor activator of nuclear factor-kappaB (RANK) ligand (RANKL) and inhibited osteoclast formation. Moreover, genistein down-regulated the expression and activity of MMP-9, which was induced by docetaxel treatment, and inhibited invasion of PC-3 cells. These results suggest that the observed potentiation of antitumor activity of docetaxel by genistein in the SCID-human model of experimental bone metastasis could be mediated by regulation of OPG/RANK/RANKL/MMP-9 signaling, resulting in the inhibition of osteoclastic bone resorption and prostate cancer bone metastasis. From these results, we conclude that genistein could be a promising nontoxic agent to improve the treatment outcome of metastatic prostate cancer with docetaxel.

Osteoclasts from patients with autosomal dominant osteopetrosis type I caused by a T253I mutation in low-density lipoprotein receptor-related protein 5 are normal in vitro, but have decreased resorption capacity in vivo

Autosomal dominant osteopetrosis type I (ADOI) is presumably caused by gain-of-function mutations in the LRP5 gene. Patients with a T253I mutation in LRP5 have a high bone mass phenotype, characterized by increased mineralizing surface index but abnormally low numbers of small osteoclasts. To investigate the effect of the T253I mutation in LRP5 on osteoclasts, we isolated CD14+ monocytes from ADOI patients and assessed their ability to generate osteoclasts when treated with RANKL and M-CSF compared to that of age- and sex-matched control osteoclasts. We found normal osteoclastogenesis, expression of osteoclast markers, morphology, and localization of proteins involved in bone resorption, such as ClC-7 and cathepsin K. The ability to resorb bone was also normal. In vivo, we compared the bone resorption and bone formation response to T3 in ADOI patients and age- and sex-matched controls. We found attenuated resorptive response to T3 stimulation, despite a normal bone formation response, in alignment with the reduced number of osteoclasts in vivo. These data demonstrate that ADOI osteoclasts are normal with respect to all aspects investigated in vitro. We speculate that the mutations causing ADOI alter the osteoblastic phenotype toward a smaller potential for supporting osteoclastogenesis.

Serum levels of osteoprotegerin and RANKL in patients with ST elevation acute myocardial infarction

OPG (osteoprotegerin) has been suggested to have an important role in atherogenesis and vascular calcification. In the present study, we have investigated serum OPG and RANKL (receptor activator of nuclear factor kappaB ligand) concentrations in patients with ST elevation AMI (acute myocardial infarction) and established CAD (coronary artery disease). OPG and RANKL were measured in 58 male patients hospitalized in the coronary care unit with ST elevation AMI, in 52 asymptomatic male patients with an established diagnosis of CAD and in 52 healthy male controls. These last two groups were matched with the AMI patients for age and body mass index. OPG was significantly (P<0.05) higher in patients with AMI at 1 h after AMI (8.04+/-4.86 pmol/l) than in both patients with established CAD (4.92+/-1.65 pmol/l) and healthy subjects (3.15+/-1.01 pmol/l). Subjects with established CAD had significantly (P<0.05) increased OPG levels compared with controls. RANKL levels in patients with established CAD (0.02+/-0.05 pmol/l) and with AMI (0.11+/-0.4 pmol/l) were significantly (P<0.05) lower compared with controls (0.32+/-0.35 pmol/l). In the AMI group, OPG decreased significantly (P<0.05) at 1 and 4 weeks after infarction (8.04+/-4.86 compared with 6.38+/-3.87 and 6.55+/-2.6 pmol/l respectively), but OPG levels, either at 1 h or 1-4 weeks after AMI, remained significantly (P<0.05) higher compared with established CAD (4.92+/-1.65 pmol/l) and controls (3.15+/-1.01 pmol/l). Our data show for the first time that OPG levels are increased in ST elevation AMI within 1 h of infarction. Whether the increase in OPG is a consequence or a causal factor of plaque destabilization deserves further investigation.

Prostate cancer mediates osteoclastogenesis through two different pathways

The present study was undertaken to test the effects of prostate cancer cell lines (LNCaP, DU145, PC3, and MDA PCa 2b) on osteoclastogenesis. Crude conditioned medium (CM) from all four prostate cancer cell lines enhanced expression of the mRNA for receptor activator of NF-kappaB ligand (RANKL) in a mouse osteoblast cell line, MC3T3-E1; however, CM had no effect on expression of osteoprotegerin (OPG) mRNA. Coculture of MC3T3-E1 with prostate cancer cells yielded similar results. The number of mature osteoclasts induced by soluble RANKL increased significantly when osteoclast precursor cells were cultured with CM from LNCaP and DU145 cells. CM from LNCaP and DU145 cells also induced maturation from precursor in the absence of soluble RANKL, and this effect was not blocked by OPG. Addition of CM from DU145 cells increased expression of MMP-9 mRNA by osteoclast precursors. Our findings indicate that prostate cancer mediates osteoclastogenesis through induction of RANKL expression by osteoblasts and through direct actions on osteoclast precursors mediated by some factors other than RANKL.

Dysregulated osteoprotegerin/RANK ligand/RANK axis in clinical and experimental heart failure

BACKGROUND

Persistent inflammation appears to play a role in the development of heart failure (HF). Osteoprotegerin (OPG), the receptor activator of nuclear factor-kappaB (RANK), and RANK ligand (RANKL) are newly discovered members of the tumor necrosis factor superfamily that are critical regulators in bone metabolism but appear also to be involved in immune responses. We hypothesized that the OPG/RANK/RANKL axis could be involved in the pathogenesis of heart failure (HF), and this hypothesis was investigated in both experimental and clinical studies.

METHODS AND RESULTS

Our main and novel findings were as follows: (1) In a rat model of postinfarction HF, we found persistently increased gene expression of OPG, RANK, and RANKL in the ischemic part of the left ventricle (LV) and, for OPG, in the nonischemic part that involved both noncardiomyocyte and in particular cardiomyocyte tissue. (2) Enhanced myocardial protein levels of OPG, RANK, and RANKL, in particular, were also seen in human HF, and using immunohistochemistry, we localized these mediators to cardiomyocytes within the LV in both experimental and clinical HF. (3) In human HF, we also found increased systemic expression of RANKL (T cells and serum) and OPG (serum), with increasing levels according to functional, hemodynamic, and neurohormonal disease severity. (4) RANKL increased total matrix metalloproteinase activity in human fibroblasts, which indicates a matrix-degrading net effect and suggests a potential mechanism by which enhanced RANKL expression in HF may contribute to LV dysfunction.

CONCLUSIONS

These findings suggest a potential role for known mediators of bone homeostasis in the pathogenesis of HF and possibly represents new targets for therapeutic intervention in this disorder.

Impaired bone resorption in cathepsin K-deficient mice is partially compensated for by enhanced osteoclastogenesis and increased expression of other proteases via an increased RANKL/OPG ratio

Previous reports indicate that mice deficient for cathepsin K (Ctsk), a key protease in osteoclastic bone resorption, develop osteopetrosis due to their inability to properly degrade organic bone matrix. Some features of the phenotype of Ctsk knockout mice, however, suggest the presence of mechanisms by which Ctsk-deficient mice compensate for the lack of cathepsin K. To study these mechanisms in detail, we generated Ctsk-deficient (Ctsk-/-) mice and analyzed them at the age of 2, 7, and 12 months using peripheral quantitative computed tomography, histomorphometry, resorption marker measurements, osteoclast and osteoblast differentiation cultures, and gene expression analyses. The present study verified the previously published osteopetrotic features of Ctsk-deficient mice. However, these changes did not exacerbate during aging indicating the absence of Ctsk to have its most severe effects during the rapid growth period. Resorption markers ICTP and CTX were decreased in the media of Ctsk-/- osteoclasts cultured on bone slices indicating impaired bone resorption. Ctsk-/- mice exhibited several mechanisms attempting to compensate for Ctsk deficiency. The number of osteoclasts in trabecular bone was significantly increased in Ctsk-/- mice compared to controls, as was the number of osteoclast precursors in bone marrow. The mRNA levels for receptor activator of nuclear factor (kappa)B ligand (RANKL) in Ctsk-/- bones were increased resulting in increased RANKL/OPG ratio favoring osteoclastogenesis. In addition, expression of mRNAs of osteoclastic enzymes (MMP-9, TRACP) and for osteoblastic proteases (MMP-13, MMP-14) were increased in Ctsk-/- mice compared to controls. Impaired osteoclastic bone resorption in Ctsk-/- mice results in activation of osteoblastic cells to produce increased amounts of other proteolytic enzymes and RANKL in vivo. We suggest that increased RANKL expression mediates enhanced osteoclastogenesis and increased protease expression by osteoclasts. These observations underline the important role of osteoblastic cells in regulation of osteoclast activity and bone turnover.

Optimised real-time quantitative PCR assays for RANKL regulated genes

Osteoclasts are multinucleated giant cells that differentiate from precursors of the monocyte-macrophage lineage. We used receptor activator of NF-kappa B ligand (RANKL) and macrophage colony stimulating factor (M-CSF) to differentiate authentic human osteoclasts from peripheral blood mononuclear cells (PBMCs). We previously described a series of genes that are strongly regulated by RANKL. Here, we provide a set of reliable quantitative real-time PCR based assays of RANKL regulated genes as reference genes that may prove useful in the study of human osteoclasts. The SYBR-green I assays are free of primer dimer and other artefacts, and are designed to amplify in parallel, thus permitting simultaneous analysis of 12 genes. Optimised primers for 18S rRNA provide a valid housekeeping reference gene. Standard curves have been constructed for all assays, thus allowing for absolute quantification of mRNA transcript copy number. As an example, the regulation of expression of the chemokine RANTES in osteoclasts is demonstrated. These gene assays have potential utility in a variety of cell types, tissues and organs, in addition to macrophages and osteoclasts.

The molecular triad OPG/RANK/RANKL: involvement in the orchestration of pathophysiological bone remodeling

The past decade has seen an explosion in the field of bone biology. The area of bone biology over this period of time has been marked by a number of key discoveries that have opened up entirely new areas for investigation. The recent identification of the receptor activator of nuclear factor kappaB ligand (RANKL), its cognate receptor RANK, and its decoy receptor osteoprotegerin (OPG) has led to a new molecular perspective on osteoclast biology and bone homeostasis. Specifically, the interaction between RANKL and RANK has been shown to be required for osteoclast differentiation. The third protagonist, OPG, acts as a soluble receptor antagonist for RANKL that prevents it from binding to and activating RANK. Any dysregulation of their respective expression leads to pathological conditions such as bone tumor-associated osteolysis, immune disease, or cardiovascular pathology. In this context, the OPG/RANK/RANKL triad opens novel therapeutic areas in diseases characterized by excessive bone resorption. The present article is an update and extension of an earlier review published by Kwan Tat et al. [Kwan Tat S, Padrines M, Theoleyre S, Heymann D, Fortun Y. IL-6, RANKL, TNF-alpha/IL-1: interrelations in bone resorption pathophysiology. Cytokine Growth Factor Rev 2004;15:49-60].

Relevance of an in vitro osteoclastogenesis system to study receptor activator of NF-kB ligand and osteoprotegerin biological activities

Receptor activator of NF-kB Ligand (RANKL) is an essential requirement for osteoclastogenesis and its activity is neutralized by binding to the soluble decoy receptor osteoprotegerin (OPG). The purpose of this work was to study the effects of RANKL and OPG during osteoclastogenesis using the murine monocytic cell line RAW 264.7 that can differentiate into osteoclasts in vitro. RAW 264.7 cells plated at 10(4) cells/cm(2) and cultured for 4 days in the presence of RANKL represent the optimal culture conditions for osteoclast differentiation, with an up-regulation of all parameters related to bone resorption: tartrate resistant acid phosphatase (TRAP), calcitonin receptor (CTR), RANK, cathepsin K, matrix metalloproteinase (MMP)-9 mRNA expressions. RANKL and OPG biological effects vary according to the differentiation state of the cells: in undifferentiated RAW 264.7 cells, TRAP expression was decreased by OPG and RANKL, RANK expression was inhibited by OPG, while MMP-9 and cathepsin K mRNA expressions were not modulated. In differentiated RAW 264.7 cells, RANKL and OPG both exert an overall inhibitory effect on the expression of all the parameters studied. In these experimental conditions, OPG-induced MMP-9 inhibition was abrogated in the presence of a blocking anti-RANKL antibody, suggesting that part of OPG effects are RANKL-dependent.