Basic fibroblast growth factor induces osteoclast formation in murine bone marrow cultures

Extremely low-frequency electromagnetic fields facilitate both osteoblast and osteoclast activity through Wnt/β-catenin signaling in the zebrafish scale

Electromagnetic fields (EMFs) have received widespread attention as effective, noninvasive, and safe therapies across a range of clinical applications for bone disorders. However, due to the various frequencies of devices, their effects on tissues/cells are vary, which has been a bottleneck in understanding the effects of EMFs on bone tissue. Here, we developed an in vivo model system using zebrafish scales to investigate the effects of extremely low-frequency EMFs (ELF-EMFs) on fracture healing. Exposure to 10 millitesla (mT) of ELF-EMFs at 60 Hz increased the number of both osteoblasts and osteoclasts in the fractured scale, whereas 3 or 30 mT did not. Gene expression analysis revealed that exposure to 10 mT ELF-EMFs upregulated wnt10b and Wnt target genes in the fractured scale. Moreover, β-catenin expression was enhanced by ELF-EMFs predominantly at the fracture site of the zebrafish scale. Inhibition of Wnt/β-catenin signaling by IWR-1-endo treatment reduced both osteoblasts and osteoclasts in the fractured scale exposed to ELF-EMFs. These results suggest that ELF-EMFs promote both osteoblast and osteoclast activity through activation of Wnt/β-catenin signaling in fracture healing. Our data provide in vivo evidence that ELF-EMFs generated with a widely used commercial AC power supply have a facilitative effect on fracture healing.

Functional Heterogeneity Within Osteoclast Populations-a Critical Review of Four Key Publications that May Change the Paradigm of Osteoclasts

PURPOSE OF REVIEW

In this review, we critically evaluate the literature for osteoclast heterogeneity, including heterogeneity in osteoclast behavior, which has hitherto been unstudied and has only recently come to attention. We give a critical review centered on four recent high-impact papers on this topic and aim to shed light on the elusive biology of osteoclasts and focus on the variant features of osteoclasts that diverge from the classical viewpoint.

RECENT FINDINGS

Osteoclasts originate from the myeloid lineage and are best known for their unique ability to resorb bone. For decades, osteoclasts have been defined simply as multinucleated cells positive for tartrate-resistant acid phosphatase activity and quantified relative to the bone perimeter or surface in histomorphometric analyses. However, several recent, high-profile studies have demonstrated the existence of heterogeneous osteoclast populations, with variable origins and functions depending on the microenvironment. This includes long-term persisting osteoclasts, inflammatory osteoclasts, recycling osteoclasts (osteomorphs), and bone resorption modes. Most of these findings have been revealed through murine studies and have helped identify new targets for human studies. These studies have also uncovered distinct sets of behavioral patterns in heterogeneous osteoclast cultures. The underlying osteoclast heterogeneity likely drives differences in bone remodeling, altering patient risk for osteoporosis and fracture. Thus, identifying the underlying key features of osteoclast heterogeneity may help in better targeting bone diseases.

Endogenous FGF-2 levels impact FGF-2/BMP-2 growth factor delivery dosing in aged murine calvarial bone defects

Bone repair in elderly mice has been shown to be improved or negatively impacted by supplementing the highly osteogenic bone morphogenetic protein-2 (BMP-2) with fibroblast growth factor-2 (FGF-2). To better predict the outcome of FGF-2 supplementation, we investigated whether endogenous levels of FGF-2 play a role in optimal dosing of FGF-2 for augmenting BMP-2 activity in elderly mice. In vivo calvarial bone defect studies in Fgf2 knockout mice with wildtype controls were conducted with the growth factors delivered in a highly localized manner from a biomimetic calcium phosphate/polyelectrolyte multilayer coating applied to a bone graft substitute. Endogenous FGF-2 levels were measured in old mice versus young and found to decrease with age. Optimal dosing for improving bone defect repair correlated with levels of endogenous FGF-2, with a larger dose of FGF-2 required to have a positive effect on bone healing in the Fgf2 knockout mice. The same dose in wildtype old mice, with higher levels of FGF-2, promoted chondrogenesis and increased osteoclast activity. The results suggest a personalized medicine approach, based on a knowledge of endogenous levels of FGF-2, should guide FGF-2 supplementation in order to avoid provoking excessive bone resorption and cartilage formation, both of which inhibited calvarial bone repair.

FGF2 disruption enhances thermogenesis in brown and beige fat to protect against adiposity and hepatic steatosis

Objective

Fibroblast growth factor 2 (FGF2) has been reported to play divergent roles in white adipogenic differentiation, however, whether it regulates thermogenesis of fat tissues remains largely unknown. We therefore aimed to investigate the effect of FGF2 on fat thermogenesis and elucidate the underlying mechanisms.

Methods

FGF2-KO and wild-type (WT) mice were fed with chow diet and high-fat diet (HFD) for 14 weeks. The brown and white fat mass, thermogenic capability, respiratory exchange ratio, and hepatic fat deposition were determined. In vitro experiments were conducted to compare the thermogenic ability of FGF2-KO- with WT-derived brown and white adipocytes. Exogenous FGF2 was supplemented to in vitro-cultured WT brown and ISO-induced beige adipocytes. The FGFR inhibitor, PPARγ agonist, and PGC-1α expression lentivirus were used with the aid of technologies including Co-IP, ChIP, and luciferase reporter assay to elucidate the mechanisms underlying the FGF2 regulation of thermogenesis.

Results

FGF2 gene disruption results in increased thermogenic capability in both brown and beige fat, supporting by increased UCP1 expression, enhanced respiratory exchange ratio, and elevated thermogenic potential in response to cold exposure. Thus, the deletion of FGF2 protects mice from high fat-induced adiposity and hepatic steatosis. Mechanistically, in vitro investigations indicated FGF2 acts in autocrine/paracrine fashions. Exogenous FGF2 supplementation inhibits both PGC-1α and PPARγ expression, leading to suppression of UCP1 expression in brown and beige adipocytes.

Conclusions

These findings demonstrate that FGF2 is a novel thermogenic regulator, suggesting a viable potential strategy for using FGF2-selective inhibitors in combat adiposity and associated hepatic steatosis.

•

FGF2-KO mice show potentiated stimulation on thermogenic capability under both basal and cold challenge stimulation.

•

FGF2 disruption protected mice against HFD-induced adiposity and hepatic steatosis.

•

FGF2 acts in autocrine/paracrine fashions in vitro.

•

Both PPARγ and PGC-1α play roles in FGF2 suppression of thermogenesis.

Bone Disruption and Environmental Pollutants

BACKGROUND

Endocrine Disrupting Chemicals (EDCs) are ubiquitous and may significantly contribute in environmental pollution, thus contaminating humans and wildlife. Environmental pollutants could interfere with bone homeostasis by means of different mechanisms, which include hormonal imbalance, direct osteoblasts toxicity and enanchment of osteoclasts activity, thus leading to osteopenia or osteoporosis. Among these, bisphenols, dioxins, polycyclic aromatic hydrocarbons, polychlorobiphenyls, poly- and perfluoroalkyls, phthalates, parabens, organotins and cadmium may play a role in bone distuption.

METHODS

PubMed/MEDLINE, ISI-web of knowledge and Google scholar databases were searched for medical subject headings terms and free-text word related to the aforementioned classes of chemicals and bone metabolism and remodelling for better clarifying and understanding the main mechanisms of bone disruption.

RESULTS

Several of EDCs act as xenoestrogens. Considering that estrogens play a significant role in regulating bone remodeling, most of these chemicals generate hormonal imbalance with possible detrimental consequences on bone tissue structure and its mechanical and non-mechanical properties.

DISCUSSION

A lot of evidences about bone distruptors came from in vitro studies or animal models, and conduct to equivocal results. In addition, a few data derived form humans and most of these data focused on the impact of EDCs on bone mineral density without considering their influence on long-term fracture risk. Moreover, it should be taken into account that humans are exposed to a mixture of EDCs and the final effect on bone metabolism might be the result of either a synergism or antagonist effects among them. Age of first exposure, cumulative dose exposure over time, and the usually observed non-monotonic dose-response curve for EDCs should be considered as other important variable influencing the final effect on bone metabolism.

CONCLUSION

Taking into account these variables, observational studies are needed to better analyze this issue both for echological purpose and to preserve bone health.

Pentraxin 3 inhibits fibroblast growth factor 2 induced osteoclastogenesis in rheumatoid arthritis

BACKGROUND

Synovial fibroblasts (SFs) act as key effector cells mediating synovial inflammation and joint destruction in rheumatoid arthritis (RA). Fibroblast growth factor 2 (FGF2) and its receptors (FGFRs) play important roles in RASF-mediated osteoclastogenesis. Pentraxin 3 (PTX3) is a soluble pattern recognition receptor with nonredundant roles in inflammation and innate immunity. PTX3 is produced by various cell types, including SFs and is highly expressed in RA. However, the role of PTX3 in FGF2-induced osteoclastogenesis in RA and the underlying mechanism have been poorly elucidated.

METHODS

We first determined the expression of FGF2 and RANKL in synovial tissue and synovial fluid of RA patients. We then examined the effect of PTX3 on RASF osteoclastogenesis induced by endogenous and exogenous FGF2 in isolated RASF cells treated with FGF2 and/or recombinant PTX3 (rPTX3). Thirdly, we analyzed the effect of PTX3 on FGF2 binding to FGFR-1 and HSPG receptors on RASFs. Lastly, we evaluated joint morphology after injection of rPTX3 into collagen-induced arthritis (CIA) mice.

RESULTS

FGF2 was confirmed to be highly expressed in both synovial tissue and synovial fluid of RA patients. FGF2 promoted cell proliferation and increased the expressions of RANKL and ICAM-1 and RANKL/OPG to induce osteoclastogenesis in RASF, while anti-FGF2 neutralized this effect. PTX3 significantly inhibited FGF2-induced RASF cell growth and osteoclastogenesis by preventing the interaction of ¹²⁵I-FGF2 and FGFRs on the same cells. In addition, administration of rPTX3 significantly ameliorated cartilage and bone destruction in mice with CIA.

CONCLUSIONS

PTX3 exhibited an inhibitory effect on the autocrine and paracrine stimulation of FGF2 on SFs, and ameliorated bone destruction in CIA mice. PTX3 may be implicated in bone destruction in RA, which may provide theoretical evidence and potential therapeutic targets for RA treatment.

Switching Homes: How Cancer Moves to Bone

Bone metastases (BM) are a very common complication of the most prevalent human cancers. BM are extremely painful and may be life-threatening when associated with hypercalcaemia. BM can lead to kidney failure and cardiac arrhythmias and arrest, but why and how do cancer cells decide to "switch homes" and move to bone? In this review, we will present what answers science has provided so far, with focus on the molecular mechanisms and cellular aspects of well-established findings, such as the concept of "vicious cycle" and "osteolytic" vs. "osteosclerotic" bone metastases; as well as on novel concepts, such as cellular dormancy and extracellular vesicles. At the molecular level, we will focus on hypoxia-associated factors and angiogenesis, the Wnt pathway, parathyroid hormone-related peptide (PTHrP) and chemokines. At the supramolecular/cellular level, we will discuss tumour dormancy, id est the mechanisms through which a small contingent of tumour cells coming from the primary site may be kept dormant in the endosteal niche for many years. Finally, we will present a potential role for the multimolecular mediators known as extracellular vesicles in determining bone-tropism and establishing a premetastatic niche by influencing the bone microenvironment.

Comparison of the Effects of Two Different Analgesics on Bone Regeneration During Mandibular Distraction Osteogenesis

INTRODUCTION

Mandibular distraction osteogenesis (DO) is frequently used in the management of bone defects and craniofacial deformities, with analgesics commonly administered to relieve acute postoperative pain. This experimental animal study investigated the effects of 2 analgesics, acetaminophen and acemetacin, on bone regeneration after DO.

MATERIALS AND METHODS

This study was conducted with 14 mature male New Zealand rabbits (2.8-3.2 kg) randomized into 2 groups of 7. Mandibular osteotomies were performed under optimal operating conditions, and a custom-made distractor was applied to the mandible of each subject, with distraction initiated after a 5-day latency period at a rate of 1.0 mm/d (2 × 0.5 mm/d) for 10 days. Analgesics were administered via oral gavage during the latency period and for the first 5 days of the distraction period for 10 days in total, with group I receiving acetaminophen (200 mg/kg/d) and group II receiving acemetacin (5 mg/kg/d). Subjects were sacrificed and their mandibles dissected at the end of 4 weeks postoperatively. Bone mineral density (BMD) and bone mineral content (BMC) were measured using dual-energy X-ray absorptiometry (DEXA), and histomorphometric analysis was performed to evaluate the quality of newly formed bone. Paired group comparisons of non-normally distributed numerical variables were made using the Mann-Whitney U test, with a P value of <0.05 considered statistically significant.

RESULTS

No significant differences in BMC and BMD values of intact bone, newly formed bone, or bone around the pin site were observed between the 2 groups. Histometric analysis also indicated acetaminophen and acemetacin to have similar effects on bone regeneration during distraction.

CONCLUSION

Acemetacin may be an alternative to acetaminophen for treating pain associated with DO, given the similarities in the effects of the 2 analgesics on bone regeneration. However, this finding should be supported by further experimental and human studies.

Opposing effects of Sca-1(+) cell-based systemic FGF2 gene transfer strategy on lumbar versus caudal vertebrae in the mouse

Our previous work showed that a Sca-1⁺ cell-based FGF2 therapy was capable of promoting robust increases in trabecular bone formation and connectivity on the endosteum of long bones. Past work reported that administration of FGF2 protein promoted bone formation in red marrow but not in yellow marrow. The issue as to whether the Sca-1⁺ cell-based FGF2 therapy is effective in yellow marrow is highly relevant to its clinical potential for osteoporosis, as most red marrows in a person of an advanced age, are converted to yellow marrows. Accordingly, this study sought to compare the osteogenic effects of this stem cell-based FGF2 therapy on red marrow-filled lumbar vertebrae with those on yellow marrow-filled caudal vertebrae of young adult W⁴¹/W⁴¹ mice. The Sca-1⁺ cell-based FGF2 therapy drastically increased trabecular bone formation in lumbar vertebrae, but the therapy not only did not promote bone formation but instead caused substantial loss of trabecular bone in caudal vertebrae. The lack of an osteogenic response was not due to insufficient engraftment of FGF2-expressing Sca-1⁺ cells or inadequate FGF2 expression in caudal vertebrae. Previous studies have demonstrated that recipient mice of this stem cell-based FGF2 therapy developed secondary hyperparathyroidism and increased bone resorption. Thus, the loss of bone mass in caudal vertebrae might in part be due to an increase in resorption without a corresponding increase in bone formation. In conclusion, the Sca-1⁺ cell-based FGF2 therapy is osteogenic in red marrow but not in yellow marrow.

Oxysterols and EBI2 promote osteoclast precursor migration to bone surfaces and regulate bone mass homeostasis

The mechanisms guiding cells toward bone surfaces are generally unknown. Here, Nevius et al. show that the Gαi protein–coupled receptor EBI2 is expressed in mouse osteoclast precursors to guide these cells toward bone surfaces. Defective EBI2 signaling increased bone mass in male mice and protected female mice from age- and estrogen deficiency–induced osteoporosis.

Bone surfaces attract hematopoietic and nonhematopoietic cells, such as osteoclasts (OCs) and osteoblasts (OBs), and are targeted by bone metastatic cancers. However, the mechanisms guiding cells toward bone surfaces are essentially unknown. Here, we show that the Gαi protein–coupled receptor (GPCR) EBI2 is expressed in mouse monocyte/OC precursors (OCPs) and its oxysterol ligand 7α,25-dihydroxycholesterol (7α,25-OHC) is secreted abundantly by OBs. Using in vitro time-lapse microscopy and intravital two-photon microscopy, we show that EBI2 enhances the development of large OCs by promoting OCP motility, thus facilitating cell–cell interactions and fusion in vitro and in vivo. EBI2 is also necessary and sufficient for guiding OCPs toward bone surfaces. Interestingly, OCPs also secrete 7α,25-OHC, which promotes autocrine EBI2 signaling and reduces OCP migration toward bone surfaces in vivo. Defective EBI2 signaling led to increased bone mass in male mice and protected female mice from age- and estrogen deficiency–induced osteoporosis. This study identifies a novel pathway involved in OCP homing to the bone surface that may have significant therapeutic potential.

Core–shell microspheres delivering FGF-2 and BMP-2 in different release patterns for bone regeneration

Sequential delivery of FGF-2 and BMP-2 efficiently bridged the bone defects and remodeled the bone graft.

Role of angiogenesis in bone repair. Arch Biochem Biophys. 2014;561:109-117. [PMID: 25034215 DOI: 10.1016/j.abb.2014.07.006]

Bone vasculature plays a vital role in bone development, remodeling and homeostasis. New blood vessel formation is crucial during both primary bone development as well as fracture repair in adults. Both bone repair and bone remodeling involve the activation and complex interaction between angiogenic and osteogenic pathways. Interestingly studies have demonstrated that angiogenesis precedes the onset of osteogenesis. Indeed reduced or inadequate blood flow has been linked to impaired fracture healing and old age related low bone mass disorders such as osteoporosis. Similarly the slow penetration of host blood vessels in large engineered bone tissue grafts has been cited as one of the major hurdle still impeding current bone construction engineering strategies. This article reviews the current knowledge elaborating the importance of vascularization during bone healing and remodeling, and the current therapeutic strategies being adapted to promote and improve angiogenesis.

SOCS-1/3 participation in FGF-2 signaling to modulate RANK ligand expression in paget's disease of bone

Paget's disease of bone (PDB) is a chronic focal skeletal disorder characterized by excessive bone resorption followed by disorganized new bone formation. Measles virus nucleocapsid (MVNP) is implicated in pathogenesis of PDB. RANK ligand (RANKL), a critical osteoclastogenic factor expressed on bone marrow stromal/preosteoblast cells is upregulated in PDB. We recently demonstrated that fibroblast growth factor-2 (FGF-2) which induces RANKL expression is elevated in PDB. In this study, we hypothesized that FGF-2 modulates suppressors of cytokine signaling (SOCS) to induce RANKL expression in PDB. We identified increased levels of SOCS-1/3 mRNA expression in bone marrow mononuclear cells derived from patients with PDB compared to normal subjects. Interestingly, conditioned media obtained from MVNP transduced osteoclast progenitor cells significantly increased SOCS-1/3 mRNA expression in stromal/preosteoblast cells. We next examined if SOCS participates in FGF-2 signaling to modulate RANKL gene expression. We showed that FGF-2 stimulation significantly increased SOCS-1/3 expression in human bone marrow stromal/preosteoblast cells. In addition, co-expression of SOCS-1/3 with hRANKL gene promoter-luciferase reporter plasmid in marrow stromal cells demonstrated a significant increase in promoter activity without FGF-2 stimulation. Furthermore, siRNA inhibition of STAT-1 suppresses FGF-2 increased SOCS-1/3 expression in these cells. Thus, our results suggest that SOCS participates in FGF-2 modulation of RANKL expression in PDB.

Deletion of CD74, a putative MIF receptor, in mice enhances osteoclastogenesis and decreases bone mass

CD74 is a type II transmembrane protein that can act as a receptor for macrophage migration inhibitory factor (MIF) and plays a role in MIF-regulated responses. We reported that MIF inhibited osteoclast formation and MIF knockout (KO) mice had decreased bone mass. We therefore examined if CD74 was involved in the ability of MIF to alter osteoclastogenesis in cultured bone marrow (BM) from wild-type (WT) and CD74-deficient (KO) male mice. We also measured the bone phenotype of CD74 KO male mice. Bone mass in the femur of 8-week-old mice was measured by micro-computed tomography and histomorphometry. Bone marrow cells from CD74 KO mice formed 15% more osteoclast-like cells (OCLs) with macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) (both at 30 ng/mL) compared to WT. Addition of MIF to WT cultures inhibited OCL formation by 16% but had no effect on CD74KO cultures. The number of colony forming unit granulocyte-macrophage (CFU-GM) in the bone marrow of CD74 KO mice was 26% greater than in WT controls. Trabecular bone volume (TBV) in the femurs of CD74 KO male mice was decreased by 26% compared to WT. In addition, cortical area and thickness were decreased by 14% and 11%, respectively. Histomorphometric analysis demonstrated that tartrate-resistant acid phosphatase (TRAP)(+) osteoclast number and area were significantly increased in CD74 KO by 35% and 43%, respectively compared to WT. Finally, we examined the effect of MIF on RANKL-induced-signaling pathways in bone marrow macrophage (BMM) cultures. MIF treatment decreased RANKL-induced nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) and c-Fos protein in BMM cultures by 70% and 41%, respectively. Our data demonstrate that CD74 is required for MIF to affect in vitro osteoclastogenesis. Further, the bone phenotype of CD74 KO mice is similar to that of MIF KO mice. MIF treatment of WT cultures suppressed RANKL-induced activator protein 1 (AP-1) expression, which resulted in decreased osteoclast differentiation in vitro. We propose that CD74 plays a critical role in the MIF inhibition of osteoclastogenesis.

Endocrine disruptors and bone metabolism

Bone microenvironment is a complex dynamic equilibrium between osteoclasts and osteoblasts and is modulated by a wide variety of hormones and osteocyte mediators secreted in response to physiological and pathological conditions. The rate of remodeling involves tight coupling and regulation of both cells population and is regulated by a wide variety of hormones and mediators such as parathyroid hormone, prostaglandins, thyroid hormone, sex steroids, etc. It is also well documented that bone formation is easily influenced by the exposure of osteoblasts and osteoclasts to chemical compounds. Currently, humans and wildlife animals are exposed to various environmental xenoestrogens typically at low doses. These compounds, known as endocrine disruptor chemicals (EDCs), can alter the systemic hormonal regulation of the bone remodeling process and the skeletal formation. This review highlights the effects of the EDCs on mammalian bone turnover and development providing a macro and molecular view of their action.

Biological apatite (BAp) crystallographic orientation and texture as a new index for assessing the microstructure and function of bone regenerated by tissue engineering

Recently, there have been remarkable advances in medical techniques for regenerating bone defects. To determine the degree of bone regeneration, it is essential to develop a new method that can analyze microstructure and related mechanical function. Here, quantitative analysis of the orientation distribution of biological apatite (BAp) crystallites by a microbeam X-ray diffractometer system is proposed as a new index of bone quality for the evaluation of regenerated bone microstructure. Preferential alignment of the BAp c-axis in the rabbit ulna and skull bone, regenerated by controlled release of basic fibroblast growth factor (bFGF) was investigated. The BAp c-axis orientation was evaluated by the relative intensity between the (002) and (310) diffraction peaks, or the three-dimensional texture for the (002) peak. It was found that new bone in the defects was initially produced without preferential alignment of the BAp c-axis, and subsequently reproduced to recover towards the original alignment. In other words, the BAp density recovered prior to the BAp orientation. Perfect recovery of BAp alignment was not achieved in the ulna and skull defects after 4 weeks and 12 weeks, respectively. Apparent recovery of the macroscopic shape and bio-mineralization of BAp was almost complete in the ulna defect after 4 weeks. However, an additional 2 weeks was required for complete repair of BAp orientation. It is finally concluded that orientation distribution of BAp crystallites offers an effective means of evaluating the degree of microstructural regeneration, and also the related mechanical function, in regenerated hard tissues.

The calcium-sensing receptor complements parathyroid hormone-induced bone turnover in discrete skeletal compartments in mice

Although the calcium-sensing receptor (CaSR) and parathyroid hormone (PTH) may each exert skeletal effects, it is uncertain how CaSR and PTH interact at the level of bone in primary hyperparathyroidism (PHPT). Therefore, we simulated PHPT with 2 wk of continuous PTH infusion in adult mice with deletion of the PTH gene (Pth(-/-) mice) and with deletion of both PTH and CaSR genes (Pth(-/-)-Casr (-/-) mice) and compared skeletal phenotypes. PTH infusion in Pth(-/-) mice increased cortical bone turnover, augmented cortical porosity, and reduced cortical bone volume, femoral bone mineral density (BMD), and bone mineral content (BMC); these effects were markedly attenuated in PTH-infused Pth(-/-)-Casr(-/-) mice. In the absence of CaSR, the PTH-stimulated expression of receptor activator of nuclear factor-κB ligand and tartrate-resistant acid phosphatase and PTH-stimulated osteoclastogenesis was also reduced. In trabecular bone, PTH-induced increases in bone turnover, trabecular bone volume, and trabecular number were lower in Pth(-/-)-Casr(-/-) mice than in Pth(-/-) mice. PTH-stimulated genetic markers of osteoblast activity were also lower. These results are consistent with a role for CaSR in modulating both PTH-induced bone resorption and PTH-induced bone formation in discrete skeletal compartments.

A bone-seeking clone exhibits different biological properties from the ACHN parental human renal cell carcinoma in vivo and in vitro

Metastatic bone disease caused by renal cell carcinoma (RCC) occurs frequently. Very little is currently known about the mechanism of preferential metastasis of RCC to bone. We hypothesize that RCCs that develop bone metastases have the capacity to facilitate their colonization in bone. To examine this hypothesis, we established bone-seeking (ACHN-BO) clones of the human RCC cell line ACHN by repeated four passages in nude mice and in vitro of metastatic cells obtained from bone. These clones were examined for distinguishing biological characteristics and compared with the ACHN parental cells (ACHN-P) in vivo and in vitro. Our results showed that the ACHN-BO cell line could be successfully obtained by in vivo selection through the lateral tail vein. This approach results in the development of multiple osteolytic lesions in the distal femora and proximal tibiae within four weeks after inoculation, with a success rate of 85-100% and no additional comorbidity. ACHN-P cells developed metastases in lung, bone, brain, ovary and adrenal glands. Conversely, ACHN-BO cells exclusively metastasized to bones with larger osteolytic lesions. Compared with the ACHN-P cell line, the proliferation ability in ACHN-BO6 was increased by 9.68 and 6.42%, respectively (P<0.05), while the apoptotic ratio decreased significantly (P<0.05) and cells were blocked in the S phase with suppressed migration and invasion capacities. The ACHN-BO₆ cell line produced greater amounts of the pro-angiogenic factors VEGF and TGF-β than ACHN-P. Our data suggest that these phenotypic changes allow RCC cells to promote osteoclastic bone resorption, survive and proliferate in bone, which consequently leads to the establishment of bone metastases. This model provides a reliable reproduction of the clinical situation and, therefore, is suitable for designing and evaluating more effective treatments for RCC bone metastasis.

Regulation of osteoblast and osteoclast functions by FGF-6

Fibroblast growth factor-6 (FGF-6) is known to be the key ligand for fibroblast growth factor receptor 4 (FGFR4) during muscle regeneration but its role in bone has yet to be verified. FGFR signaling is known to be important in the initiation and regulation of osteogenesis, so in this study the actions of FGF-6 on human osteoblasts and osteoclasts were investigated. Human primary osteoblasts (hOB) were used to study the effect of FGF-6 on proliferation (by ATP quantification), signal transduction (by ERK and AKT phosphorylation), differentiation (by alkaline phosphatase activity, APA), and mineralization (by calcein staining). To study FGF-6 activity on osteoclast differentiation, human bone marrow cells were used and tartrate-resistant acid phosphatase (TRAP) multinucleated cells together with actin filaments arrangements were quantified. Human primary mature osteoclasts were used to evaluate the effect of FGF-6 on osteoclast reabsorbing activity by reabsorbed pit measurements. FGF-6 >10(-9) M as FGF-2 10(-7) M induced hOB proliferation mediated by pERK together with a reduction in APA and reduced mineralization of the treated cells. Moreover FGF-6 increased the formation of TRAP-positive multinucleated cells in a dose-dependent manner (maximal effect at 10(-8) M). FGF-6-treated cells showed also a greater percentage of cells that formed typical osteoclast sealing zones. Mature osteoclasts cultured on dentine slice increased the area of reabsorption with a maximal effect of FGF-6 at 10(-12) M. FGF-6 may be considered a regulator of bone metabolism as shown by its activity on both osteoblasts and osteoclasts.

Disruption of the Fgf2 gene activates the adipogenic and suppresses the osteogenic program in mesenchymal marrow stromal stem cells

Here we determine the Fibroblast Growth Factor-2 (FGF2) dependency of the time course of changes in bone mass in female mice. This study extends our earlier reports that knockout of the FGF2 gene (Fgf2) caused low turnover bone loss in Fgf2(-/-) male mice by examining bone loss with age in Fgf2(-/-) female mice, and by assessing whether reduced bone formation is associated with differentiation of bone marrow stromal cells (BMSCs) towards the adipocyte lineage. Bone mineral density (BMD) was similar in 3-month-old female Fgf2(+/+) and Fgf2(-/-) mice but was significantly reduced as early as 5 months of age in Fgf2(-/-) mice. In vivo studies showed that there was a greater accumulation of marrow fat in long bones of 14 and 20 month old Fgf2(-/-) mice compared with Fgf2(+/+) littermates. To study the effect of disruption of FGF2 on osteoblastogenesis and adipogenesis, BMSCs from both genotypes were cultured in osteogenic or adipogenic media. Reduced alkaline phosphatase positive (ALP), mineralized colonies and a marked increase in adipocytes were observed in Fgf2(-/-) BMSC cultures. These cultures also showed an increase in the mRNA of the adipogenic transcription factor PPARgamma2 as well as the downstream target genes aP2 and adiponectin. Treatment with exogenous FGF2 blocked adipocyte formation and increased ALP colony formation and ALP activity in BMSC cultures of both genotypes. These results support an important role for endogenous FGF2 in osteoblast (OB) lineage determination. Alteration in FGF2 signaling may contribute to impaired OB bone formation capacity and to increased bone marrow fat accumulation both of which are characteristics of aged bone.

Effect of recombinant human fibroblast growth factor-2 on bone formation in rabbit mandibular distraction models using beta-tricalcium phosphate

This study was designed to evaluate the effect of recombinant human fibroblast growth factor-2 (rhFGF-2) on the amount and period of new bone formation in rabbit mandibular distraction models using beta-tricalcium phosphate (beta-TCP) as a bone graft substitute. Sixteen male Japanese White rabbits were divided into the following four experimental groups: 1, distraction alone; 2, distraction with beta-TCP granules; 3, distraction with rhFGF-2 (25 microg/50 microL) injected into beta-TCP granules; and 4, distraction with rhFGF-2 (100 microg/50 microL) injected into beta-TCP granules. The bones were harvested at 4 weeks after the operation and examined using soft radiography, micro-computed tomography (micro-CT), and peripheral quantitative computed tomography (pQCT). The dissected mandibles were stained using the Villanueva bone staining method, and the amount of new bone formed, bioresorption of beta-TCP, and new blood vessel formation were morphometrically calculated using bone histomorphometry. Radiopaque areas were observed more frequently in the distracted area of groups 3 and 4. Micro-CT analysis revealed partial new bone formation in the central region of the distracted area in groups 3 and 4. pQCT analysis revealed increased bone mineral density in groups 3 and 4. Histomorphometric analysis revealed increased newly formed bone and blood vessel areas in groups 3 and 4. In group 4, the number of osteoclasts around the beta-TCP granules had significantly increased. The present findings suggested that the combined use of rhFGF-2 and beta-TCP reduced the treatment period for distraction osteogenesis and accelerated the formation of a new high-quality bone.

Characterization of a new renal cell carcinoma bone metastasis mouse model

Metastatic bone disease caused by renal cell carcinoma (RCC) occurs frequently and becomes more and more prevalent presumably because survival times among patients with disseminated cancers are increasing. Patients with bone metastases from renal cell carcinoma suffer from severe pain, nerve compression syndromes and pathologic fractures. Very little is known about the mechanisms of skeletal metastases of RCC. Thus, to better understand the molecular mechanism of renal cell cancer (RCC) bone metastasis, it is crucial to develop new animal models. We have established a new animal model of RCC metastasis to bone by inoculation of human 786-O/luciferase cells into the left cardiac ventricle of athymic nude mice. The animals developed aggressive osteolytic bone destruction as monitored by radiography and micro-CT-scans with the mean endpoint at 62 +/- 8 days. The extensive bone destruction observed was comparable to the clinical setting and mainly occurred in hind limbs, forelimbs and the spine. The tumors were primarily located within the bone and resulted in destruction of cortical bone. No soft tissue metastases were detected by BLI or histomorphometry. To increase the bone-metastatic potential of the 786-O cell line, an in vivo selection was done yielding a subpopulation causing osteolytic lesions with the mean endpoint of 47 +/- 3 days. The selected subline secreted more proangiogenic factors VEGF and bFGF in vitro compared to the parental cell line suggesting that these tumors are highly vascular. This model provides a reliable reproduction of the clinical situation and therefore, is suitable for designing and evaluating more effective treatments for RCC bone metastasis.

Phosphatidylserine-containing liposomes inhibit the differentiation of osteoclasts and trabecular bone loss

Liposomes containing phosphatidylserine (PS) are engulfed by phagocytes including macrophages, microglia, and dendritic cells. PS liposomes (PSLs) mimic the effects of apoptotic cells on these phagocytes to induce the secretion of anti-inflammatory molecules and to inhibit the maturation of dendritic cells. However, the effects of PSLs on osteoclasts, which are also differentiated from the common myeloid precursors, remain to be determined. This study investigated the effects of PSLs on the osteoclastogenesis. In the rat bone marrow culture system, osteoclast precursors phagocytosed PSLs to secrete TGF-beta1 and PGE(2), which in turn inhibited osteoclastogenesis through the downregulation of receptor activator for NF-kappaB ligand, receptor activator of NF-kappaB, ICAM-1, and CD44. Consistent with these in vitro observations, i.m. injection of PSLs significantly increased the plasma level of TGF-beta1 and PGE(2) and decreased the expression of receptor activator for NF-kappaB ligand, receptor activator of NF-kappaB, and ICAM-1 in the skeletal tissues of ankle joints of rats with adjuvant arthritis (AA). A quantitative analysis using microcomputed tomography revealed that PSLs as well as TGF-beta1 together with PGE(2) significantly inhibited AA-induced trabecular bone loss. These observations strongly suggest that PSLs generate TGF-beta1 and PGE(2) release, leading to inhibit osteoclastogenesis and AA-induced trabecular bone loss. Because PS is a component of the cell membrane, PSLs therefore can be a potentially effective pharmacological intervention against abnormal bone loss, such as osteoporosis without deleterious side effects.

Anti-arthritic effect of scopoletin, a coumarin compound occurring in Erycibe obtusifolia Benth stems, is associated with decreased angiogenesis in synovium

Scopoletin is the main constituent of coumarin found in the stems of Erycibe obtusifolia Benth, a traditional Chinese medicine used in the treatment of rheumatoid arthritis. We have previously demonstrated that scopoletin is able to decrease the serum level of uric acid in hyperuricemic mice induced by potassium oxonate, and attenuate croton oil-induced inflammation. In the present study, we evaluated the anti-arthritic effects of scopoletin in rat adjuvant-induced arthritis by assessing paw swelling, pathology, and synovial angiogenesis. It was found that scopoletin, injected intraperitoneally at doses of 50, 100 mg/kg, reduced both inoculated and non-inoculated paw swelling as well as articular index scores, and elevated the mean body weight of adjuvant-induced arthritic rats. Rats treated with higher dose of scopoletin showed a near-normal histological architecture of the joints and a reduced new blood vessel formation in the synovial tissues. Furthermore, scopoletin downregulated the overexpression of vascular endothelial growth factor, basic fibroblast growth factor and interleukin 6 in the synovial tissues of adjuvant-induced arthritic rats. In conclusion, scopoletin is capable of ameliorating clinical symptoms of rat adjuvant-induced arthritis, by reducing numbers of new blood vessels in the synovium and the production of important endogenous angiogenic inducers. Therefore, this compound may be a potential agent for angiogenesis-related diseases and could serve as a structural base for screening more potent synthetic analogs.

Establishment of an animal model of a pasteurized bone graft, with a preliminary analysis of muscle coverage or FGF-2 administration to the graft

Background

Pasteurized bone grafting is used following the excision of a bone tumor for the purpose of eliminating neoplastic cells while preserving bone-inducing ability. In the hopes of guaranteeing the most favourable results, the establishment of an animal model has been urgently awaited. In the course of establishing such a model, we made a preliminary examination of the effect of muscle coverage or fibroblast growth factor 2 (FGF-2) administration radiographically.

Methods

Forty pasteurized intercalary bone grafts of the Wistar rat femur treated at 60°C for 30 min were reimplanted and stabilized with an intramedullary nail (1.1 mm in diameter). Some grafts were not covered by muscle after the implantation, so that they could act as a clinical model for wide resection, and/or these were soaked with FGF-2 solution prior to implantation. The grafts were then divided into 3 groups, comprising 12 grafts with muscle-covering but without FGF-2 (MC+; FGF2-), 12 grafts without muscle-covering and without FGF-2 (MC-; FGF2-) and 16 grafts without muscle covering but with FGF-2 (MC-; FGF2+).

Results

At 2 weeks after grafting, the pasteurized bone model seemed to be successful in terms of eliminating living cells, including osteocytes. At 4 weeks after grafting, partial bone incorporation was observed in half the (MC+; FGF2-) cases and in half the (MC-; FGF2+) cases, but not in any of the (MC-; FGF2-) cases. At 12 weeks after grafting, bone incorporation was seen in 3 out of 4 in the (MC+; FGF2-) group (3/4: 75%) and in 3 out of 8 in the (MC-; FGF2+) group (3/8: 38%). However, most of the grafted bones without FGF-2 were absorbed in all the cases, massively, regardless of whether there had been muscle-covering (MC+; FGF2-; 4/4: 100%) or no muscle-covering (MC-; FGF2-; 4/4: 100%), while bone absorption was noted at a lower frequency (2/8: 25%) and to a lower degree in the (MC-; FGF2+) group.

Conclusion

In conclusion, we have established an animal pasteurized bone graft model in rats. Pasteurized bone was able to maintain bone induction ability. Despite the low number of cases in each group, the results of each group suggest that muscle-covering has an effect on bone incorporation, but that it is not able to prevent bone absorption to the pasteurized bone. However, an application of FGF-2 may have a positive effect on bone incorporation and may be able to prevent bone absorption of the graft in cases of pasteurized bone graft.

Actions of fibroblast growth factor-8 in bone cells in vitro

The fibroblast growth factors (FGFs) are a group of at least 25 structurally related peptides that are involved in many biological processes. Some FGFs are active in bone, including FGF-1, FGF-2, and FGF-18, and recent evidence indicates that FGF-8 is osteogenic, particularly in mesenchymal stem cells. In the current study, we found that FGF-8 was expressed in rat primary osteoblasts and in osteoblastic UMR-106 and MC3T3-E1 cells. Both FGF-8a and FGF-8b potently stimulated the proliferation of osteoblastic cells, whereas they inhibited the formation of mineralized bone nodules in long-term cultures of osteoblasts and reduced the levels of osteoblast differentiation markers, osteocalcin, and bone sialoprotein. FGF-8a induced the phosphorylation of p42/p44 mitogen-activated protein kinase (MAPK) in osteoblastic cells; however, its mitogenic actions were not blocked by either the MAPK kinase (MEK) inhibitor U-0126 or the PI 3-kinase (PI3K) inhibitor LY-294002. Interestingly, FGF-8a, unlike FGF-8b and other members of the family, inhibited osteoclastogenesis in mouse bone marrow cultures, and this was via a receptor activator of NF-kappaB ligand (RANKL)/osteoprotegerin (OPG)-independent manner. However, FGF-8a did not affect osteoclastogenesis in RAW 264.7 cells (a macrophage cell line devoid of stromal cells) exogenously stimulated by RANKL, nor did it affect mature osteoclast function as assessed in rat calvarial organ cultures and isolated mature osteoclasts. In summary, we have demonstrated that FGF-8 is active in bone cells, stimulating osteoblast proliferation in a MAPK-independent pathway and inhibiting osteoclastogenesis via a RANKL/OPG-independent mechanism. These data suggest that FGF-8 may have a physiological role in bone acting in an autocrine/paracrine manner.

FGF-2 stimulation of RANK ligand expression in Paget's disease of bone

Receptor activator for nuclear factor-kappaB ligand (RANKL), a critical osteoclastogenic factor expressed in marrow stromal/preosteoblast cells is up-regulated in Paget's disease of bone (PDB). We previously demonstrated that heat-shock factor-2 (HSF-2) is a downstream target of fibroblast growth factor-2 (FGF-2) signaling to induce RANKL expression in bone marrow stromal/preosteoblast cells. In this study, we identified a 2.5-fold increase in serum FGF-2 levels in patients (n = 8) with PDB compared with normal subjects (n = 10). We showed that HSF-2 co-immunoprecipitates with heat-shock protein-27 (HSP-27) and that FGF-2 stimulation significantly increased phospho-HSP-27 levels in marrow stromal cells. Confocal microscopy revealed HSF-2 colocalization with HSP-27 in unstimulated cells and HSF-2 nuclear translocation upon FGF-2 stimulation. We further show that FGF-2 stimulation significantly increased the levels of phosphorylated signal transducers and activators of the transcription (p-STAT-1) in these cells. Western blot analysis confirmed that small interfering RNA suppression of STAT-1 significantly decreased (3.2-fold) RANKL expression and promoter activity in FGF-2-stimulated cells. Chromatin immunoprecipitation assay revealed STAT-1 binding to a putative motif located far upstream (-8 kb) in the hRANKL gene promoter region. These results suggest STAT-1 is a downstream effector of FGF-2 signaling and that elevated levels of FGF-2 stimulates RANKL expression in PDB.

The investigation of synovial genomic targets of bucillamine with microarray technique

OBJECTIVE

To identify the molecular mechanisms of bucillamine activity, global gene expression analysis and pathway analysis were conducted using IL-1 beta-stimulated human fibroblast-like synovial cells (FLS).

METHODS

Normal human FLS were treated with IL-1 beta in the presence or absence of 10 and 100 microM bucillamine for 6 h. Total RNA was extracted and global gene expression levels were detected using a 44 k human whole genome array. Data were analyzed using Ingenuity pathway analysis.

RESULTS

Numerous pathways were activated by IL-1 beta stimulation. At both concentrations, bucillamine suppressed nine signal pathways stimulated by IL-1 beta.

CONCLUSIONS

Bucillamine effectively inhibited fibroblast growth factor (FGF) signaling and tight junction signaling activated by IL-1 beta in FLS. Suppression of these signal pathways may correlate with the pharmacologic mechanisms of bucillamine. In particular, the suppression of FGF signaling by bucillamine is remarkable because the activation of FGF signaling may be involved in rheumatoid arthritis pathology.

DACH1 negatively regulates the human RANK ligand gene expression in stromal/preosteoblast cells

Receptor activator of NF-kappaB ligand (RANKL) is a critical osteoclastogenic factor that is expressed on bone marrow stromal/preosteoblast cells. Most bone resorption stimuli induce osteoclast formation by modulating RANKL expression in these cells. However, little is known about the mechanisms regulating RANKL gene expression. We recently reported that heat shock factor-2 (HSF-2) is a downstream target for FGF-2 signaling to enhance RANKL gene transcription in marrow stromal/preosteoblast cells. In this study, we show that DACH1 (human homologue of Drosophila dachshund gene) negatively regulates RANKL gene expression and suppresses FGF-2-enhanced RANKL gene expression in these cells. DACH1 contains a conserved dachshund domain (DS) in the N-terminal region, which interacts with the nuclear co-repressor (NCoR) to repress gene expression. Co-expression of DACH1 with hRANKL promoter-luciferase reporter plasmid in normal human bone marrow-derived stromal cells significantly decreased (3.3-fold) FGF-2-stimulated hRANKL gene promoter activity. Deletion of DS domain abolished DACH1 inhibition of FGF-2-enhanced RANKL gene promoter activity. Western blot analysis confirmed that DACH1 suppressed FGF-2-stimulated RANKL expression in marrow stromal/preosteoblast cells. We show HSF-2 co-immune precipitated with DACH1 and that FGF-2 stimulation significantly increased (2.7-fold) HSF-2 binding to DACH1. Confocal microscopy analysis further demonstrated that FGF-2 promotes HSF-2 nuclear transport and co-localization with DACH1 in marrow stromal cells. Co-expression of NCoR with DACH1 significantly decreased (5.3-fold) and siRNA suppression of NCoR in DACH1 co-transfected cells increased (3.6-fold) RANKL promoter activity. Furthermore, DACH1 co-expression with NCoR significantly decreased (7.5-fold) RANKL mRNA expression in marrow stromal cells. Collectively, these studies indicate that NCoR participates in DACH1 repression of RANKL gene expression in marrow stromal/preosteoblast cells. Thus, DACH1 plays an important role in negative regulation of RANKL gene expression in marrow stromal/preosteoblast cells in the bone microenvironment.

Reduced expression and function of bone morphogenetic protein-2 in bones of Fgf2 null mice

Disruption of the fibroblast growth factor 2 (FGF-2) gene results in reduced bone mass in mice and impairs expression of bone morphogenic protein-2 (BMP-2) an important mediator of osteoblast and osteoclast differentiation. Since the relationship between FGF-2 and BMP-2 in bone remodeling has not been fully determined, in this study we examined whether endogenous FGF-2 was necessary for maximal effect of BMP-2 on periosteal bone formation in vivo and bone nodule formation and osteoclast formation in vitro in Fgf2-/- mice. We showed that BMP-2 significantly increased periosteal bone formation by 57% in Fgf2+/+ mice but the changes were not significant in Fgf2-/- littermates. In line with these results we found no significant increase in alkaline phosphatase positive (ALP) activity in calvarial osteoblasts or ALP mineralized colonies in stromal cultures from Fgf2-/- mice after BMP-2 treatment. Moreover, BMP-2 induced osteoclast formation was also impaired in marrow stromal cultures from Fgf2-/- mice. Interestingly, BMP-2 induced nuclear accumulation of the runt related transcription factor (Runx2) was markedly impaired in osteoblasts from Fgf2-/- mice. Examination of the effect of loss of FGF-2 on BMP-2 signaling pathway showed that BMP-2 caused a similar induction of phospho-Smad1/5/8 within 30 min in calvarial osteoblasts from both genotypes. In contrast BMP-2-induced p42/44 MAPK was reduced in Fgf2-/- mice. These findings strongly demonstrated that endogenous FGF-2 is important in the maximal responses of BMP-2 in bone and that this may be dependent on the p42/44 MAPK signaling pathway and downstream modulation of Runx2.

Distribution of inositol 1,4,5-trisphosphate receptors in rat osteoclasts

Inositol 1,4,5-trisphosphate (IP₃) receptors (IP₃Rs) are Ca²⁺ channels that localize to intracellular Ca²⁺ stores such as the endoplasmic reticulum (ER). Recently, IP₃Rs were found to participate in the formation of the cytoskeleton and cellular adhesions. In this study, we examined the cellular localization of type I, II, and III IP₃Rs to assess their role in cellular adhesion in rat osteoclasts. Rat bone marrow cells were cultured in α-MEM with 10% fetal bovine serum, M-CSF, RANKL, and 1,25(OH)₂D₃ for 1 week to promote osteoclast formation. Type I, II, and III IP₃R expression in the osteoclasts was then examined by RT-PCR. Double-staining was performed using antibodies against type I, II, and III IP₃Rs and DiOC₆, an ER marker, or TRITC-phalloidin, an actin filament marker. Expression of all three IP₃Rs was detected in the newly formed osteoclasts; however, the localization of the type I and II IP₃Rs was predominantly close to nuclear, and possibly colocalized with the ER, while the type III IP₃Rs were localized to the ER and podosomes, actin-rich adhesion structures in osteoclasts. These findings suggest that type III IP₃Rs are associated with osteoclast adhesion.

Role of Sandhika: A Polyherbal Formulation on MC3T3-E1 Osteoblast-like Cells

Sandhika is a polyherbal formulation, (water soluble fraction of Commiphora mukul, Boswellia serrata, Semecarpus anacardium and Strychnos nux vomica), which has been in clinical use in India for last 20 years. Its modified formulation BHUx has shown specific inhibition of cyclooxygenase (COX)-2 and lipoxygenase (LOX)-15 and has prevented diet-induced atherosclerosis in rabbits. In order to explore the possibility of the use of Sandhika for the management of osteoporosis, we have examined its influence on MC3T3-E1 osteoblast-like cells in presence of lipopolysaccharide (1 microg/ml) in terms of calcium nodule formation and alkaline phosphatase activity. MC3T3-E1 osteoblast-like cells (80% confluence in 6-well plates) were treated with water extract of Sandhika, for 10 days, in the concentration range of 0.5 to 16 mg/ml final concentration, in presence of LPS. Media was changed on every third day and culture supernatant was collected after every change to assess the alkaline phosphatase activity and on the tenth day, cells were washed and stained with "Alizarin S" for visualization of calcium nodules by using Meta Morph software (Universal Imaging, Downingtown, PA). The results showed significant enhancement in calcium nodule formation in the dose dependent manner up to 2 mg/ml, followed by gradual decrease at higher concentrations. This change was accompanied with the increase in the alkaline phosphatase activity in these plates, indicating a potential anabolic effect of this polyherbal formulation on osteoblast-like cells under inflammatory conditions induced by LPS.

Effect of conjugated linoleic acid on bone formation and rheumatoid arthritis

Conjugated linoleic acid (CLA) has shown a variety of biologically beneficial effects. Dietary CLA inhibits eddosteal bone resorption, increases endocortical bone formation, and modulates the action and expression of cyclooxygenase (COX) enzyme, thereby decreasing prostaglandin-dependent bone resorption. CLA also enhances calcium absorption and may improve bone formation in animals, although results are not consistent. Since CLA can also affect inflammatory cytokines, it is hypothesized that CLA may be a good tool for prevention or reduction of rheumatoid arthritis symptoms. The possible mechanisms by which CLA prevents rheumatoid arthritis as well as other inflammatory diseases is discussed.

Effects of basic fibroblast growth factor and a prostaglandin E2 receptor subtype 4 agonist on osteoblastogenesis and adipogenesis in aged ovariectomized rats

bFGF stimulates osteo- and adipogenesis concurrently at skeletal sites with red but not with fatty marrow, whereas a PGE2 receptor subtype 4 agonist has bone anabolic effects at both skeletal sites and decreases adipose tissue within red and fatty marrow.

INTRODUCTION

Basic fibroblast growth factor (bFGF) stimulates osteogenesis at skeletal sites with hematopoietic but not with fatty marrow. The prostaglandin E2 (PGE2) receptor subtype 4 agonist (EP4A) stimulates osteogenesis at the former skeletal sites, but its effects at fatty marrow sites are unknown. In addition, both bFGF and PGE2 through the EP4 receptor have also been implicated in adipogenesis. However, their specific effects on bone marrow adipogenesis and the inter-relationship with osteogenesis have never been studied in vivo.

MATERIALS AND METHODS

Female Sprague-Dawley rats were ovariectomized (OVX) or sham-operated and maintained for 1 yr after surgery. OVX rats were then injected daily with bFGF or with EP4A SC for 3 wk. The osteo- and adipogenic effects of these agents were assessed by histomorphometry and by determining changes in expression of genes associated with these events by real-time PCR in the lumbar and caudal vertebrae, bones with a predominance of hematopoietic and fatty marrow, respectively. Expression of FGFR1-4 and the EP4 receptor were also evaluated by real-time PCR and immunocytochemistry.

RESULTS

bFGF and EP4A stimulated bone formation at skeletal sites with hematopoietic marrow, but only the later anabolic agent is also effective at fatty marrow sites. The diminished bone anabolic effect of bFGF at the fatty marrow site was not caused by a lack of cell surface receptors for the growth factor at this site. Interestingly, whereas EP4A decreased fatty marrow area and the number of adipocytes, bFGF increased osteogenesis and adipogenesis within the bone marrow.

CONCLUSIONS

bFGF can stimulate osteogenesis and bone marrow adipogenesis concurrently at red marrow sites, but not at fatty marrow sites. In contrast, EP4A stimulates bone formation at skeletal sites with hematopoietic and fatty marrow and simultaneously decreased fatty marrow area and the number of adipocytes in the bone marrow, suggesting that osteogenesis occurs at the expense of adipogenesis.

Fidgetin-like 1 gene inhibited by basic fibroblast growth factor regulates the proliferation and differentiation of osteoblasts

The FIGNL1 gene was proven to be a new subfamily member of ATPases associated with diverse cellular activities (AAA proteins). In this in vitro study, the AAA proteins inhibited osteoblast proliferation and stimulated osteoblast differentiation. We showed that FIGNL1 may play some regulatory role in osteoblastogenesis.

INTRODUCTION

The fidgetin-like 1 (FIGNL1) gene encodes a new subfamily member of ATPases associated with diverse cellular activities (AAA proteins). Although the FIGNL1 protein localizes to both the nucleus and cytoplasm, the function of FIGNL1 remains unknown. In a previous study, we identified several genes that mediate the anabolic effects of basic fibroblast growth factor (bFGF) on bone by using microarray data. FIGNL1 was one of the genes that downregulated >2-fold in MC3T3-E1 cells after treatment with bFGF. Therefore, this study was aimed to identify and confirm the function of FIGNL1 on osteoblastogenesis.

MATERIALS AND METHODS

We examined the effect of the FIGNL1 gene on proliferation, differentiation, and apoptosis in mouse osteoblast cells (MC3T3-E1 and mouse primary calvarial cells) using flow cytometry, RT-PCR, cell proliferation assay, and cell death assay. MC3T3-E1 cells and mouse calvarial cells were transfected with small interfering RNA (siRNA) directed against the FIGNL1 or nontargeting control siRNA and examined by cell proliferation and cell death assays. Also, FIGNL1 was fused to enhance green fluorescent protein (EGFP), and the EGFP-fused protein was transiently expressed in MC3T3-E1 cells.

RESULTS

Reduced expression of FIGNL1 by bFGF and TGF-beta1 treatment was verified by RT-PCR analysis. Overexpression of FIGNL1 reduced the proliferation of MC3T3-E1 and calvarial cells, more than the mock transfected control cells did. In contrast, siFIGNL1 transfection significantly increased the proliferation of osteoblasts, whereas overexpression of FIGNL1 did not seem to alter apoptosis in osteoblasts. Meanwhile, overexpression of FIGNL1 enhanced the mRNA expression of alkaline phosphatase (ALP) and osteocalcin (OCN) in osteoblasts. In contrast, siFIGNL1 decreased the expression of ALP and OCN. A pEGFP-FIGNL1 transfected into MCT3-E1 cells had an initially ubiquitous distribution and rapidly translocated to the nucleus 1 h after bFGF treatment.

CONCLUSIONS

From these results, we proposed that FIGNL1, a subfamily member of the AAA family of proteins, might play some regulatory role in osteoblast proliferation and differentiation. Further analyses of FIGNL1 will be needed to better delineate the mechanisms contributing to the inhibition of proliferation and stimulation of osteoblast differentiation.

Repair of segmental bone defects in rabbit tibiae using a complex of beta-tricalcium phosphate, type I collagen, and fibroblast growth factor-2

The objective of this study was to evaluate the effects of a complex of beta-tricalcium phosphate (beta-TCP) granules, collagen, and fibroblast growth factor-2 (FGF-2) on cortical bone repair in rabbits. Segmental bone defects of 5 mm in length were created in the middle of the tibial shaft. The defect was stabilized with a plate and screws, and was filled with 0.3 ml of a complex of beta-TCP granules and 5% collagen, with or without 200 microg of recombinant human fibroblast growth factor-2 (rhFGF-2). Bone regeneration and beta-TCP resorption were assessed by X-ray and micro-CT scanner. A three-point bending test was also performed. The results showed that the segmental bone defect was not only radiologically, but also mechanically healed with cortical bone 12 weeks after implantation of the complex with rhFGF-2. In contrast, after implantation of the complex without rhFGF-2, most of the defect was filled with beta-TCP and only a small amount of bone formation was found. These results suggest that resorption of beta-TCP is important for bone formation and may be promoted by FGF-2 in the beta-TCP implantation site. In addition, the complex of beta-TCP granules and collagen combined with rhFGF-2 provides a paste-like material that is easy to handle. This material may be of considerable use in the treatment of cortical bone defects.

RANK ligand expression in heat shock factor-2 deficient mouse bone marrow stromal/preosteoblast cells

Heat Shock Proteins (HSP) are molecular chaperones activated upon cellular stress/stimuli. HSP gene expression is regulated by Heat Shock Factors (HSF). We have recently demonstrated a functional role for heat shock factor-2 (HSF-2) in fibroblast growth factor-2 (FGF-2)-induced RANK ligand (RANKL), a critical osteoclastogenic factor expression on stromal/preosteoblast cells. In the present study, we show that FGF-2 treatment did not induce RANKL expression in HSF-2-/-stromal/preosteoblast cells. Interestingly, HSF-2 deficiency resulted in rapid induction of alkaline phosphatase (ALP) activity and osteocalcin mRNA expression in these cells. Furthermore, FGF-2 did not induce osteoclast formation in co-culture of normal mouse spleen cells and HSF-2-/-stromal/preosteoblast cells. Electron microscopy analysis demonstrated that osteoclasts from HSF-2-/-mice have poorly developed ruffled borders. These data further confirm that HSF-2 plays an important role in FGF-2-induced RANKL expression in stromal/preosteoblast cells. HSF-2 deficiency has pleotropic effects on gene expression during osteoblast differentiation and osteoclastogenesis in the bone microenvironment. Novel therapeutic agents that modulate HSF-2 activation may have therapeutic utility against increased levels of FGF-2 and bone destruction associated with pathologic conditions.

RANKL-stimulated osteoclast-like cell formation in vitro is partially dependent on endogenous interleukin-1 production

Receptor activator of NF-kappaB ligand (RANKL) and interleukin-1 (IL-1) individually plays a critical role in the differentiation and activation of osteoclasts in bone. In addition, both RANKL and IL-1 activate similar signal transduction pathways including p38 MAP kinase and c-Jun NH(2) terminal kinase (JNK). We examined if endogenously produced IL-1 influenced osteoclast-like cell (OCL) formation in murine bone marrow and bone marrow monocyte (BMM) cultures that were stimulated with M-CSF and RANKL. RANKL stimulated OCL formation in a dose-dependent manner in bone marrow cultures, and this response was significantly inhibited by IL-1 RA (100 ng/ml), a specific IL-1 antagonist. Interleukin-1 further increased OCL formation in BMM cultures that were treated with M-CSF (30 ng/ml) and RANKL (1, 3, 10 and 30 ng/ml). In addition, BMM cultures from IL-1 type I receptor-deficient mice, which do not respond to IL-1, demonstrated significantly less OCL formation compared to wild-type BMM cultures. We examined the time course and dose response of IL-1alpha protein expression by ELISA in BMM cultures that were treated with or without M-CSF and RANKL. RANKL dose dependently stimulated IL-1alpha protein significantly (up to 46%) in 6-day cultures. The interaction of RANKL and IL-1 on osteoclastogenesis did not appear significantly dependent on prostaglandin synthesis since PGE(2) expression in the conditioned medium of BMM cultures was nearly undetectable and the PGHS-2 specific inhibitor, NS-398, was without effect. We also investigated the effect of IL-1 on p38 MAP kinase and JNK in BMM cultures. The combination of RANKL and IL-1 had additive effects on JNK but not p38 MAP kinase compared to results in cultures treated with RANKL or IL-1 alone. In addition, SP600125, a specific JNK inhibitor, markedly reduced OCL formation in BMM cultures that were treated with RANKL or the combination of RANKL and IL-1. These findings demonstrate that endogenously produced IL-1 augments the response of bone marrow cells to RANKL, and this effect appears mediated by mechanisms that are associated with enhancement of JNK activity.

Transforming growth factor-beta1 to the bone

TGF-beta1 is a ubiquitous growth factor that is implicated in the control of proliferation, migration, differentiation, and survival of many different cell types. It influences such diverse processes as embryogenesis, angiogenesis, inflammation, and wound healing. In skeletal tissue, TGF-beta1 plays a major role in development and maintenance, affecting both cartilage and bone metabolism, the latter being the subject of this review. Because it affects both cells of the osteoblast and osteoclast lineage, TGF-beta1 is one of the most important factors in the bone environment, helping to retain the balance between the dynamic processes of bone resorption and bone formation. Many seemingly contradictory reports have been published on the exact functioning of TGF-beta1 in the bone milieu. This review provides an overall picture of the bone-specific actions of TGF-beta1 and reconciles experimental discrepancies that have been reported for this multifunctional cytokine.

Over-expression of fibroblast growth factor-2 causes defective bone mineralization and osteopenia in transgenic mice

Over-expression of human FGF-2 cDNA linked to the phosphoglycerate kinase promoter in transgenic (TgFGF2) mice resulted in a dwarf mouse with premature closure of the growth plate and shortening of bone length. This study was designed to further characterize bone structure and remodeling in these mice. Bones of 1-6 month-old wild (NTg) and TgFGF2 mice were studied. FGF-2 protein levels were higher in bones of TgFGF2 mice. Bone mineral density was significantly decreased as early as 1 month in femurs from TgFGF2 mice compared with NTg mice. Micro-CT of trabecular bone of the distal femurs from 6-month-old TgFGF2 mice revealed significant reduction in trabecular bone volume, trabecular number (Tb.N), and increased trabecular separation (Tb.Sp). Osteoblast surface/bone surface, double-labeled surface, mineral apposition rate, and bone formation rates were all significantly reduced in TgFGF2 mice. There were fewer TRAP positive osteoclasts in calvaria from TgFGF2 mice. Quantitative histomorphometry showed that total bone area was similar in both genotypes, however percent osteoclast surface, and osteoclast number/bone surface were significantly reduced in TgFGF2 mice. Increased replication of TgFGF2 calvarial osteoblasts was observed and primary cultures of bone marrow stromal cells from TgFGF2 expressed markers of mature osteoblasts but formed fewer mineralized nodules. The data presented indicate that non-targeted over-expression of FGF-2 protein resulted in decreased endochondral and intramembranous bone formation. These results are consistent with FGF-2 functioning as a negative regulator of postnatal bone growth and remodeling in this animal model.

Polyunsaturated fatty acids: biochemical, nutritional and epigenetic properties

Dietary polyunsaturated fatty acids (PUFA) have effects on diverse physiological processes impacting normal health and chronic diseases, such as the regulation of plasma lipid levels, cardiovascular and immune function, insulin action and neuronal development and visual function. Ingestion of PUFA will lead to their distribution to virtually every cell in the body with effects on membrane composition and function, eicosanoid synthesis, cellular signaling and regulation of gene expression. Cell specific lipid metabolism, as well as the expression of fatty acid-regulated transcription factors, likely play an important role in determining how cells respond to changes in PUFA composition. This review will focus on recent advances on the essentiality of these molecules and on their interplay in cell physiology, leading to new perspective in different therapeutic fields.

Pax5-deficient mice exhibit early onset osteopenia with increased osteoclast progenitors

Pax5 encodes BSAP, a member of the paired box domain transcription factors, whose expression is restricted to B lymphocyte lineage cells. Pax5(-/-) mice have a developmental arrest of the B cell lineage at the pro-B cell stage. We show here that Pax5(-/-) mice are severely osteopenic, missing 60% of their bone mass. The osteopenia can be accounted for by a >100% increase in the number of osteoclasts in bone measured histomorphometrically. This is not due to a lack of B cells, because other strains of B cell-deficient mice do not exhibit this phenotype. There was no difference in the number of osteoclasts produced in vitro by wild-type and Pax5(-/-) bone marrow cells. In contrast, spleen cells from Pax5(-/-) mice produce as much as five times the number of osteoclasts as control spleen cells. Culture of Pax5(-/-) spleen cells yields a population of adherent cells that grow spontaneously in culture without added growth factors for >4 wk. These cells have a monocyte phenotype, produce large numbers of osteoclasts when induced in vitro, and therefore are highly enriched in osteoclast precursors. These data demonstrate a previously unsuspected connection between B cell and osteoclast development and a key role for Pax5 in the control of osteoclast development.

Induction of RANKL expression and osteoclast maturation by the binding of fibroblast growth factor 2 to heparan sulfate proteoglycan on rheumatoid synovial fibroblasts

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by progressive joint destruction. The aim of this study was to clarify the relevance of RA synovial fibroblasts (RASFs) and fibroblast growth factor 2 (FGF-2), which is produced abundantly by RASFs, to the osteoclastogenesis and bone resorption in RA.

METHODS

Synovial fibroblasts were prepared from the synovial tissues of 10 patients with active RA and 7 patients with osteoarthritis (OA). The expression of RANKL, intercellular adhesion molecule 1 (ICAM-1), FGF receptor 1 (FGFR-1), and heparan sulfate proteoglycan (HSPG) on synovial fibroblasts was measured by FACScan. Osteoclast formation in cocultures of RASFs and peripheral blood mononuclear cells (PBMCs) was evaluated by tartrate-resistant acid phosphatase staining and a pit-formation assay using dentin slices.

RESULTS

FGF-2 induced the expression of both RANKL and ICAM-1 on RASFs more so than on OA synovial fibroblasts (OASFs). FGF-2-induced up-regulation of RANKL and ICAM-1 was inhibited by anti-FGF-2 antibody. Although FGFR-1 was equally expressed on RASFs and OASFs, HSPG was highly expressed on RASFs. Up-regulation of RANKL by FGF-2 on RASFs was diminished by the removal of heparan sulfate with heparitinase. Osteoclast formation from PBMCs induced by RASFs was inhibited by the addition of either heparitinase, anti-ICAM-1 antibody, anti-FGF-2 antibody, or osteoprotegerin. FGF-2-induced RANKL on RASFs and osteoclast formation were suppressed by an inhibitor of ERK.

CONCLUSION

FGF-2 was transferred to FGFR-1 through binding to HSPG, which is characteristically expressed on RASFs, resulting in RANKL- and ICAM-1-mediated maturation of osteoclasts via ERK activation. Thus, we propose that FGF-2 not only augments the proliferation of RASFs, but also is involved in osteoclast maturation, which leads to bone destruction in RA.