Expression of bone morphogenetic proteins by osteoinductive and non-osteoinductive human osteosarcoma cells

Influence of Chinese Herbal Formula on Bone Characteristics of Cobb Broiler Chickens

To evaluate the prevention and treatment effect of a Chinese herbal formula (CHF) on the bone disease of Cobb broiler chickens, compare its efficacy with Bisphosphonates (BPs), and provide a theoretical basis for studying the nutritional regulation technology of CHF to improve the bone characteristics of broiler chickens. In this study, 560 one-day-old Cobb broiler chickens were examined for the influence of Chinese herbal formula (CHF) and Bisphosphonates (BPs). Different doses of CHF and BPs were added to the diet, and the 30- and 60-day-old live weight, tibial bone strength, the microstructure of the distal femur cancellous bone, blood biochemical indexes related to bone metabolism, and genes related to bone metabolism were determined and analyzed. The results showed that the live weight of Cobb broilers fed with CHF and BPs in the diet was as follows: The live weight of the CHF group was higher than that of the normal control (NC) group, while the live weight of the BPs group was lower than that of the NC group; the CHF and BPs improved the bone strength of Cobb broilers and increased the elastic modulus, yield strength, and maximum stress of the tibia. CHF and BPs increased the cancellous bone mineral density (BMD), bone tissue ratio (BV/TV), bone surface area tissue volume ratio (BS/TV), bone trabecular thickness (Tb.Th), and bone trabecular number (Tb.N) in the distal femur, and decreased the bone surface area bone volume ratio (BS/BV) and bone trabecular separation (Tb.Sp). Thus, the microstructure of the bone tissue of the distal femur was improved to a certain extent. Both the CHF and the BPs also increased the serum levels of the vitamin D receptor (VDR), osteoprotegerin (OPG), and alkaline phosphatase (ALP), and decreased the content of osteocalcin (OT). Meanwhile, CHF and BPs upregulated the expression of osteogenic genes (BMP-2, OPG, Runx-2) to promote bone formation and downregulated the expression of osteoclastic genes (RANK, RANKL, TNF-α) to inhibit bone resorption, thus affecting bone metabolism. Conclusion: The CHF could improve the skeletal characteristics of Cobb broilers by upregulating the expression of bone-forming-related genes and downregulating the expression of bone-breaking-related genes, thus preventing and controlling skeletal diseases in Cobb broilers. Its effect was comparable to that of BPs. Meanwhile, the CHF-H group achieved the best results in promoting the growth and improvement of the skeletal characteristics of Cobb broilers based on the live weight and skeletal-characteristics-related indexes.

The Epstein-Barr Virus-Encoded EBNA1 Protein Activates the Bone Morphogenic Protein (BMP) Signalling Pathway to Promote Carcinoma Cell Migration

The Epstein-Barr virus (EBV)-encoded nuclear antigen 1 (EBNA1) protein is expressed in all virus-associated malignancies, where it performs an essential role in the maintenance, replication and transcription of the EBV genome. In recent years, it has become apparent that EBNA1 can also influence cellular gene transcription. Here, we demonstrate that EBNA1 is able to stimulate the expression of the Transforming growth factor-beta (TGFβ) superfamily member, bone morphogenic protein 2 (BMP2), with consequential activation of the BMP signalling pathway in carcinoma cell lines. We show that BMP pathway activation is associated with an increase in the migratory capacity of carcinoma cells, an effect that can be ablated by the BMP antagonist, Noggin. Gene expression profiling of authentic EBV-positive nasopharyngeal carcinoma (NPC) tumours revealed the consistent presence of BMP ligands, established BMP pathway effectors and putative target genes, constituting a prominent BMP “signature” in this virus-associated cancer. Our findings show that EBNA1 is the major viral-encoded protein responsible for activating the BMP signalling pathway in carcinoma cells and supports a role for this pathway in promoting cell migration and possibly, metastatic spread.

Bone morphogenetic proteins mediate crosstalk between cancer cells and the tumour microenvironment at primary tumours and metastases (Review)

Bone morphogenetic proteins (BMP) are pluripotent molecules, co‑ordinating cellular functions from early embryonic and postnatal development to tissue repair, regeneration and homeostasis. They are also involved in tumourigenesis, disease progression and the metastasis of various solid tumours. Emerging evidence has indicated that BMPs are able to promote disease progression and metastasis by orchestrating communication between cancer cells and the surrounding microenvironment. The interactions occur between BMPs and epidermal growth factor receptor, hepatocyte growth factor, fibroblast growth factor, vascular endothelial growth factor and extracellular matrix components. Overall, these interactions co‑ordinate the cellular functions of tumour cells and other types of cell in the tumour to promote the growth of the primary tumour, local invasion, angiogenesis and metastasis, and the establishment and survival of cancer cells in the metastatic niche. Therefore, the present study aimed to provide an informative summary of the involvement of BMPs in the tumour microenvironment.

Deregulated bone morphogenetic proteins and their receptors are associated with disease progression of gastric cancer

Bone morphogenetic proteins (BMP) are members of the transforming growth factor β superfamily (TGF-β). BMPs are involved in tumourigenesis and disease progression of certain malignancies. To date, the role played by BMPs in gastric cancer (GC) remains largely unknown. In the present study, we systematically analysed the expression and clinical significance of BMP and BMP receptors (BMPR) in TCGA gastric cancer database and GEO database and explored the possible mechanism of action. BMP5 is reduced in gastric cancer tissues, while ACVRL1, ACVR1, TGFBR1, and BMPR2 were significantly increased in the gastric tumours. BMP3, ACVR1, TGFBR1, BMPR1B (also known as ALK6), TGFBR2 and BMPR2 were significantly associated with poorer overall survival of GC patients. A negative correlation was seen between BMP/BMPR and proliferation markers which was supported by their correlation with the cell cycle promoters and inhibitors. More interestingly, further analyses showed that BMPs and their receptors are positively correlated with matrix metalloproteinases (MMPs), epithelial mesenchymal transition (EMT) markers and stemness in GC. Furthermore, positive correlations were also frequently seen between BMP receptors and markers/regulators of angiogenesis and lymphangiogenesis in the gastric tumours. Taken together, these findings suggest that BMPs play dual roles in GC. They may inhibit proliferation of GC cells. On the other hand, they can also promote disease progression through a promotion of invasion, EMT and stemness. The elevated expression of BMP receptors in GC were also highly associated with tumour associated angiogenesis and lymphangiogenesis which facilitate tumour growth, expansion and spread.

Immunohistochemical Validation of Spontaneously Arising Canine Osteosarcoma as a Model for Human Osteosarcoma

Osteosarcoma (OS) originates from bone-forming mesenchymal cells and represents one of the primary bone tumours. It is the most common primary bone tumour in dogs and man. The characterization of an appropriate natural disease animal model to study human OS is essential to elucidate the pathogenesis of the disease. This study aimed to validate canine OS as a model for the human disease by evaluating immunohistochemically the expression of markers known to be important in human OS. The immunohistochemical panel included vimentin, alkaline phosphatase (ALP), desmin, S100, neuron-specific enolase (NSE), runt-related transcription factor 2 (Runx2) and bone morphogenetic protein 4 (BMP4). Immunohistochemistry was conducted on formalin-fixed, paraffin wax-embedded tissue sections from 59 dogs with confirmed primary OS. Vimentin, ALP, Runx2 and BMP4 were highly expressed by all tumours, while desmin, S100 and NSE were expressed variably. The findings were similar to those described previously for human OS and suggest that canine OS may represent a useful model for the study of the human disease.

Recombinant human bone morphogenic protein-2 Induces the Differentiation and Mineralization of Osteoblastic Cells Under Hypoxic Conditions via Activation of Protein Kinase D and p38 Mitogen-Activated Protein Kinase Signaling Pathways

Hypoxia suppresses osteoblastic differentiation and the bone-forming capacity. As the leading osteoinductive growth factor used clinically in bone-related regenerative medicine, recombinant human bone morphogenic protein-2 (rhBMP-2) has yielded promising results in unfavorable hypoxic clinical situations. Although many studies have examined the effects of rhBMP-2 on osteoblastic differentiation, mineralization and the related signaling pathways, those of rhBMP-2 on osteoblastic cells remain unknown, particularly under hypoxic conditions. Therefore, this study was conducted under a 1% oxygen tension to examine the differentiating effects of rhBMP-2 on osteoblastic cells under hypoxia. rhBMP-2 could also induce the differentiation and mineralization of Osteoblastic (MC3T3-E1) cells under 1% hypoxic conditions. rhBMP-2 could also induce the differentiation and mineralization of MC3T3-E1 cells under 1% hypoxic conditions. rhBMP-2 increased the alkaline phosphatase {ALP} activity in a time dependent manner, and expression of ALP, collagen type-1 (Col-1) and osteocalcin (OC) mRNA were up-regulated significantly in a time- and concentration-dependent manner. In addition, the area of the mineralized nodules increased gradually in a concentration-dependent manner. Western blot analysis, which was performed to identify the signaling pathways underlying rhBMP-2-induced osteoblastic differentiation under hypoxic conditions, showed that rhBMP-2 significantly promoted the phosphorylation of the p38 mitogen-activated protein kinase (MAPK) in a time-dependent manner. A pretreatment with SB203580, a p38 MAPK inhibitor, inhibited the rhBMP-2-mediated differentiation and mineralization. Moreover, the phosphorylation of p38 induced by rhBMP-2 was inhibited in response to a pretreatment of the cells with Go6976, a protein kinase D {PKD) inhibitor. These findings suggest that rhBMP-2 induces the differentiation and mineralization of MC3T3-E1 cells under hypoxic conditions via activation of the PKD and p38 MAPK signaling pathways.

Bone morphogenetic protein signaling in musculoskeletal cancer

PURPOSE

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor-β (TGF-β) superfamily of proteins; they were initially named after their ability to induce ectopic bone formation. Published studies have proved BMPs' role in a variety of biological processes such as embryogenesis and patterning of body axes, and maintaining adult tissue homeostasis. Other studies have focused on BMPs properties, functions and possible involvement in skeletal diseases, including cancer.

METHODS

A literature search mainly paying attention to the role of BMPs in musculoskeletal tumors was performed in electronic databases.

RESULTS

This article discusses BMPs synthesis and signaling, and summarizes their prominent roles in the skeletal system for the differentiation of osteoblasts, osteocytes and chondrocytes.

CONCLUSIONS

The review emphasizes on the role of BMP signaling in the initiation and progression of musculoskeletal cancer.

Roles of bone morphogenetic protein signaling in osteosarcoma

PURPOSE

Since the original extraction of bone morphogenetic proteins (BMPs) from bovine bone, research interest and clinical use has increased exponentially. With this, a concomitant analysis of BMP expression in bone tumours has been performed. BMP ligands, receptors, and signaling activity have been observed in diverse benign and malignant bone tumours. However, the reported expression, function, and importance of BMPs in bone tumours, and specifically osteosarcomas, have been far from uniform. This review highlights recent advances in understanding the role of BMP signaling in osteosarcoma biology, focusing on the sometimes divergent findings by various researchers and the challenges inherent in the study of osteosarcoma.

METHODS

We performed a literature review of all studies examining BMP signaling in osteosarcoma.

RESULTS

Overall, multiple BMP ligands and receptors are expressed in most osteosarcoma cell lines and subtypes, although BMP signaling may be reduced in comparison with benign bone-forming tumours. Studies suggest that osteosarcomas with different lineages of differentiation may have differential expression of BMP ligands. Although significant disagreement in the literature exists, the presence of BMP signaling in osteosarcoma may impart a worse prognosis. On the cellular level, BMP signaling appears to mediate promigratory effects in osteosarcoma and chondrosarcoma cell types, possibly via interaction and activation of Integrin β1.

CONCLUSIONS

BMP signaling has clear biologic importance in osteosarcoma, although it is not yet fully understood. Future questions for study include assessing the utility of BMP signaling in prognostication of osteosarcoma and the potential modulation of BMP signaling for inhibition of osteosarcomagenesis, growth and invasion.

Can heparins stimulate bone cancer stem cells and interfere with tumorigenesis?

Heparin and heparan sulfate, a variety of negatively charged highly sulfated polysaccharides, can influence the biological functions of human bone morphogenetic proteins (BMPs). Notably, BMPs control numerous essential biological activities and processes, such as bone formation, bone turnover, brain development, tumor initiation, and progression. BMPs also enhance the repair of bone tissue injuries and are used in bone remodeling alongside implantable prosthetic devices. BMPs either potentiate or inhibit the growth of cancer stem cells (CSCs). This dual biological effect appears to depend upon the cell type, underlying cytogenetic and biochemical aberrations in various distinct malignancies. Similarly, heparins may modulate CSCs positively or negatively through BMPs. The primary aims of this review are to investigate whether heparin prophylaxis would likely stimulate the propagation of a chemotherapy-resistant subpopulation of CSCs and aggravate tumor response to treatment, and result in tumor expansion, tumor recurrence and metastasis. The secondary aim is to document whether such detrimental effects surpass their beneficial effects as anticoagulants in primary bone cancers such as osteosarcoma. The current state of scientific knowledge based on key published articles from the standpoint of rigidity of data and identification of data gaps is discussed.

Dose- and time-dependent effects of recombinant human bone morphogenetic protein-2 on the osteogenic and adipogenic potentials of alveolar bone-derived stromal cells

BACKGROUND AND OBJECTIVE

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a well-known growth factor that can induce robust bone formation, and recent studies have shown that rhBMP-2-induced osteogenesis is closely related to adipogenesis. The aim of the present study was to determine the dose- and time-dependent effects of rhBMP-2 on the osteogenic and adipogenic differentiation of human alveolar bone-derived stromal cells (hABCs) in vivo and in vitro.

MATERIAL AND METHODS

hABCs were isolated and cultured, and then transplanted using a carrier treated either with or without rhBMP-2 (100 μg/mL) into an ectopic subcutaneous mouse model. Comprehensive histologic and histometric analyses were performed after an 8-wk healing period. To further understand the dose-dependent (0, 10, 50, 200, 500 and 1000 ng/mL) and time-dependent (0, 3, 5, 7 and 14 d) effects of rhBMP-2 on osteogenic and adipogenic differentiation, in vitro osteogenic and adipogenic differentiation of hABCs were evaluated, and the expression of related mRNAs, including those for alkaline phosphatase, osteocalcin, bone sialoprotein, peroxisome-proliferator-activated receptor gamma-2 and lipoprotein lipase, were assessed using quantitative RT-PCR.

RESULTS

rhBMP-2 significantly promoted the osteogenic and adipogenic differentiation of hABCs in vivo, and gradually increased both the osteogenic and adipogenic potential in a dose- and time-dependent manner with minimal deviation in vitro. The expression of osteogenesis- and adipogenesis-associated mRNAs were concomitantly up-regulated by rhBMP-2.

CONCLUSION

The findings of the present study showed that rhBMP-2 significantly enhanced the adipogenic as well as the osteogenic potential of hABCs in dose- and time-dependent manner. The control of adipogenic differentiation of hABCs should be considered when regenerating the alveolar bone using rhBMP-2.

A clinically relevant model of osteoinduction: a process requiring calcium phosphate and BMP/Wnt signalling

In this study, we investigated a clinically relevant model of in vivo ectopic bone formation utilizing human periosteum derived cells (HPDCs) seeded in a Collagraft™ carrier and explored the mechanisms by which this process is driven. Bone formation occurred after eight weeks when a minimum of one million HPDCs was loaded on Collagraft™ carriers and implanted subcutaneously in NMRI nu/nu mice. De novo bone matrix, mainly secreted by the HPDCs, was found juxta-proximal of the calcium phosphate (CaP) granules suggesting that CaP may have triggered the ‘osteoinductive program’. Indeed, removal of the CaP granules by ethylenediaminetetraacetic acid decalcification prior to cell seeding and implantation resulted in loss of bone formation. In addition, inhibition of endogenous bone morphogenetic protein and Wnt signalling by overexpression of the secreted antagonists Noggin and Frzb, respectively, also abrogated osteoinduction. Proliferation of the engrafted HPDCs was strongly reduced in the decalcified scaffolds or when seeded with adenovirus-Noggin/Frzb transduced HPDCs indicating that cell division of the engrafted HPDCs is required for the direct bone formation cascade. These data suggest that this model of bone formation is similar to that observed during physiological intramembranous bone development and may be of importance when investigating tissue engineering strategies.

Immunohistochemical localization of bone morphogenetic proteins (BMPs) 2, 4, 6, and 7 during induced heterotopic bone formation

The distribution and staining intensity of bone morphogenetic proteins (BMPs) 2, 4, 6, and 7 were assessed by immunohistochemistry in ectopic bone induced in Nu/Nu mice by Saos-2 cell derived implants. Devitalized Saos-2 cells or their extracts can induce endochondral bone formation when implanted subcutaneously into Nu/Nu mice. BMP staining was mostly cytoplasmic. The most intense BMP staining was seen in hypertrophic and apoptotic chondrocytes, osteoprogenitor cells such as periosteal and perivascular cells, and osteoblasts. BMP staining in osteocytes and osteoclasts was variable, ranging from undetectable to intensely stained, and from minimal to moderately stained in megakaryocytes of the induced bone marrow. BMP-2, 4, 6, and 7 staining in Saos-2 implant-induced bone indicates the following: (1) Saos-2 cell products promote expression of BMPs by host osteoprogenitor cells, which in turn, leads to bone and marrow formation at ectopic sites; (2) strong BMP staining is seen in maturing chondrocytes, and thus may play a role in chondrocyte differentiation and/or apoptosis; (3) BMP expression in perivascular and periosteal cells indicates that osteoprogenitor cells also express BMP; (4) BMP release by osteoclasts may promote osteoblastic differentiation at sites of bone remodeling. These new data can be useful in understanding the role of BMPs in promoting clinical bone repair and in various pathologic conditions.

Antisense targeting of TGF-beta1 augments BMP-induced upregulation of osteopontin, type I collagen and Cbfa1 in human Saos-2 cells

Despite commonalities in signal transduction in osteoblasts from different species, the role of TGF-beta1 on bone formation remains elusive. In particular, the role of autocrine TGF-beta1 on human osteoblasts is largely unknown. Here we show the effect of TGF-beta1 knock-down on the proliferation and differentiation of osteoblasts induced by BMP2. Treatment with antisense TGF-beta1 moderately increased the rate of cell proliferation, which was completely reversed by the exogenous addition of TGF-beta1. Notably, TGF-beta1 blockade significantly enhanced BMP2-induced upregulation of mRNAs encoding osteopontin, type I collagen and Cbfa1, which was suppressed by exogenous TGF-beta1. Moreover, TGF-beta1 knock-down increased BMP2-induced phosphorylation of Smad1/5 as well as their nuclear import, which paralleled a reduction of inhibitory Smad6. These data suggest autocrine TGF-beta1 antagonizes BMP signaling through modulation of inducible Smad6 and the activity of BMP specific Smad1/5.

Establishment and Characterization of a Cell Line, MCO-Y4, Derived from Canine Mammary Gland Osteosarcoma

A cell line, MCO-Y4, was established from a mammary gland osteosarcoma of a 16-year-old female mongrel dog. Histopathologically the tumor was composed of osteoblastic cells with an osteoid meshwork and chondroid matrix. The mean doubling time of the cells at the 93rd passage was 32.39+/-4.66 hr. Immunohistochemically, the osteoblastic and chondroblastic cells were positive for bone morphogenetic protein (BMP)-2/4 and BMP receptor (BMPR) II. The cultured cells were spindle in shape during the growth and the confluent phases. No tumor matrix was detected in the culture dish by alcian blue staining or von-Kossa silver impregnation. MCO-Y4 cells on the chamber slides showed intense immunoreactivity for BMP-2/4 and BMPR II. Noggin, an antagonist for BMP-2/4, showed the growth inhibition on MCO-Y4 cells. In addition, fibronectin might be potential for stimulating growth of MCO-Y4 cells. When transplanted into severe combined immunodeficiency mice, the cells formed tumors consisting of solid proliferation of osteoblastic and fibroblastic cells with woven-bone trabeculae. These tumor cells were intensely positive for BMP-2/4 and BMPR II. Our results suggested that the cell line might be useful for studying the role of BMPs in canine osteosarcoma and the mechanism of ossification.

Evolving concepts in bone tissue engineering

The field of tissue engineering integrates the latest advances in molecular biology, biochemistry, engineering, material science, and medical transplantation. Researchers in the developing field of regenerative medicine have identified bone tissue engineering as an attractive translational target. Clinical problems requiring bone regeneration are diverse, and no single regeneration approach will likely resolve all defects. Recent advances in the field of tissue engineering have included the use of sophisticated biocompatible scaffolds, new postnatal multipotent cell populations, and the appropriate cellular stimulation. In particular, synthetic polymer scaffolds allow for fast and reproducible construction, while still retaining biocompatible characteristics. These criteria relate to the immediate goal of determining the ideal implant. The search is becoming a reality with widespread availability of biocompatible scaffolds; however, the desired parameters have not been clearly defined. Currently, most research focuses on the use of bone morphogenetic proteins (BMPs), specifically BMP-2 and BMP-7. These proteins induce osteogenic differentiation in vitro, as well as bone defect healing in vivo. Protein-scaffold interactions that enhance BMP binding are of the utmost importance, since prolonged BMP release creates the most osteogenic microenvironment. Transition into clinical studies has had only mild success and relies on large doses of BMPs for bone formation. Advances within the field of bone tissue engineering will likely overcome these challenges and lead to more clinically relevant therapies.

BMP4 inhibits proliferation and promotes myocyte differentiation of lung fibroblasts via Smad1 and JNK pathways

Fibroblast proliferation, differentiation, and migration contribute to the characteristic pulmonary vascular remodeling seen in primary pulmonary hypertension (PPH). The identification of mutations in the bone morphogenetic protein type II receptor (BMPRII) in PPH have led us to question what role BMPRII and its ligands play in pulmonary vascular remodeling. Thus, to further understand the functional significance of BMPRII in the pulmonary vasculature, we examined the expression of TGF-beta superfamily receptors in human fetal lung fibroblasts (HFL) and investigated the role of BMP4 on cell cycle regulation, fibroblast proliferation, and differentiation. Furthermore, signaling pathways involved in these processes were examined. HFL expressed BMPRI and BMPRII mRNA and demonstrated specific I(125)-BMP4 binding sites. BMP4 inhibited [(3)H]thymidine incorporation and proliferation of HFL; protein expression was increased for the cell cycle inhibitor p21 and reduced for the positive regulators cyclin D and cdk2 by BMP4. BMP4 induced differentiation of HFL into a smooth muscle cell phenotype since protein expression of alpha-smooth muscle actin and smooth muscle myosin was increased. Furthermore, p38(MAPK), ERK1/2, JNK, and Smad1 were phosphorylated by BMP4. Using specific MAPK inhibitors, a dominant negative Smad1 construct, and Smad1 siRNA, we found that the antiproliferative and prodifferentiation effects of BMP4 were Smad1 dependent with JNK also contributing to differentiation. Because failure of Smad phosphorylation is a major feature of BMPRII mutations, these results imply that BMPRII mutations may promote the expansion of fibroblasts resistant to the antiproliferative, prodifferentiation effects of BMPs and suggest a mechanism for the vascular obliteration seen in familial PPH.

Bone morphogenetic proteins in bone tumors

Bone morphogenetic proteins (BMPs), inducers of ectopic bone formation in vivo, are present in a number of osteosarcomas. BMPs are responsible for reactive bone formation, including periosteal reactions by normal osteoblasts, rather than production of tumorous osteoid by tumor cells. Osteosarcomas producing BMPs contain less-differentiated mesenchymal cells, resulting in a poorer prognosis for those patients. BMPs are also expressed in malignant fibrous histiocytomas (MFHs) of bone and dedifferentiated chondrosarcomas exhibiting undifferentiated features. However, BMPs in MFH do not show any osteoinductive activity in vivo, suggesting that those BMPs may be inactive forms and have additional functions unrelated to bone formation. Among benign bone tumors, BMPs are expressed in osteoid osteomas or osteoblastomas and effect reactive bone formation such as a surrounding sclerosis. BMPs and a BMP receptor (BMPRIB) are also detected in the cartilage cap in osteochondroma, suggesting that BMP signaling via BMPRIB might be involved in the pathogenesis of osteochondroma. Clinically, BMPs have utility as diagnostic and prognostic markers for characterizing the stage of differentiation of mesenchymal cells and mesenchymal tumors, and they may be of value in predicting the prognosis of sarcoma patients. This article reviews the accumulated information on BMPs in bone tumors, including the most recent findings, and discusses the biological and clinical significance of BMPs in bone tumors.

Prostate cancer bone metastases promote both osteolytic and osteoblastic activity

Advanced prostate cancer is frequently accompanied by the development of metastasis to bone. In the past, prostate cancer bone metastases were characterized as being osteoblastic (i.e., increasing bone density) based on radiographs. However, emerging evidence suggests that development of prostate cancer bone metastases requires osteoclastic activity in addition to osteoblastic activity. The complexities of how prostate tumor cells influence bone remodeling are just beginning to be elucidated. Prostate cancer cells produce a variety of pro-osteoblastic factors that promote bone mineralization. For example, both bone morphogenetic proteins and endothelin-1 have well recognized pro-osteoblastic activities and are produced by prostate cancer cells. In addition to factors that enhance bone mineralization prostate cancer cells produced factors that promote osteoclast activity. Perhaps the most critical pro-osteoclastogenic factor produced by prostate cancer cells is receptor activator of NFkappaB ligand (RANKL), which has been shown to be required for the development of osteoclasts. Blocking RANKL results in inhibiting prostate cancer-induced osteoclastogenesis and inhibits development and progression of prostate tumor growth in bone. These findings suggest that targeting osteoclast activity may be of therapeutic benefit. However, it remains to be defined how prostate cancer cells synchronize the combination of osteoclastic and osteoblastic activity. We propose that as the bone microenvironment is changed by the developing cancer, this in turn influences the prostate cancer cells' balance between pro-osteoclastic and pro-osteoblastic activity. Accordingly, the determination of how the prostate cancer cells and bone microenvironment crosstalk are important to elucidate how prostate cancer cells modulate bone remodeling.

Differential expression of osteogenic factors associated with osteoinductivity of human osteosarcoma cell lines

Differential expression of multiple osteogenic factors may be responsible for the different osteoinductivity of osteosarcoma cell lines. We compared in vivo osteoinductivity of human osteosarcoma cell lines (Saos-2 vs. U-2 OS) in nude mice, and their in vitro expression of various osteogenic factors of protein level by quantitative immunocytochemistry and mRNA level by RT-PCR and/or in situ hybridization. Saos-2 cells, but not U-2 OS, were osteoinductive in vivo. Significantly higher expression (independent t-test, all p < 0.005) of osteogenic factors were observed in Saos-2 cells compared with U-2 OS, which included bone morphogenetic proteins (particularly BMPs-2, 3, 4, and 7), transforming growth factor-beta (TGF-beta), BMP receptor (BMPR)-1A, receptor-regulated Smads (R-Smads), Smads 1, 2, and 5, and common-mediator Smad (Co-Smad), Smad 4. In contrast, U-2 OS cells expressed higher levels of inhibitory Smad 6 (I-Smad) protein than Saos-2 cells (p < 0.001). These results suggest that a combination of osteogenic factors (BMPs, TGF-beta, BMPRs, and R/Co-Smads) against I-Smad may play important roles in the Saos-2 cell osteoinductivity. This may have a clinical implication in selecting key osteogenic factors for combined therapy for bone defect diseases. The characterized cell lines can be used as positive and negative controls for the assessments of both in vitro and in vivo bone formation capabilities of designed tissues or biomaterials.

Bone morphogenetic protein 2 induces placental growth factor in mesenchymal stem cells

Bone-forming osteoblasts differentiate from pluripotent mesenchymal stem cells (MSCs) in a multistage process that can be modeled in vitro using MSCs isolated from adult human trabecular bone or bone marrow. To identify new genes involved in osteoblast differentiation, we have performed large-scale gene expression profiling using high-density cDNA microarrays in primary human MSCs treated with the known osteogenic agent bone morphogenetic protein 2 (BMP-2). The vascular endothelial growth factor (VEGF) family member placental growth factor (PlGF) was found as an early regulated gene whose induction was already detected after 2 h treatment with BMP-2. Tissue distribution analysis of PlGF mRNA expression using microarrays revealed a very restricted expression of PlGF only in BMP-2-treated MSCs and in placenta as expected. Ribonuclease protection assay (RPA) confirmed the induction of PlGF and showed preferential expression of the PlGF-1 isoform over PLGF-2 in MSCs and MG63 cells. BMP-2 stimulated PlGF expression in MG63 cells with an EC50 of about 50 ng/ml and mRNA levels peaked between 24 and 32 h after stimulation. Furthermore, induction of PlGF by BMP-2 appeared specific, as other osteogenic agents including vitamin D3, transforming growth factor beta, and basic fibroblast growth factor were inactive. BMP-2 stimulated PlGF secretion from MG63 and MSC cells, but PlGF had no effect on MSC proliferation and osteoblastic differentiation. Based on the known function of PlGF in the recruitment of endothelial and hematopoietic stem cells, these results suggest a paracrine role for MSC-derived PlGF in the angiogenesis and hematopoiesis that accompany BMP-2-induced bone formation.

Effects of transforming growth factor-beta 1 (TGF-beta1) on in vitro mineralization of human osteoblasts on implant materials

An in vitro cell-implant mineralization model system was used to study the effect of transforming growth factor-beta 1(TGF-beta1) on mineralization in human osteoblast cultures. SaOs-2 and primary human osteoblast (HOB) cells were cultured on Tivanium (Ti-6Al-4V) disks. Administration of different concentrations of TGF-beta1 (0.02, 0.01, 0.2, 1.0, 2.0ng/ml) to these cultures demonstrated a biphasic dose response with 0.2ng/ml TGF-beta1 maximally increasing the calcium content compared to control culture. Results with SaOs-2 and HOB cultures were similar. An optimal dose of TGF-beta1 (0.2ng/ml) was provided to the cultures either in one single dose or multiple doses. Continuous administration of 0.2ng/ml TGF-beta1 caused 77% (SaOs-2) and 60% (HOB) increases in calcification compared to the control and 0.2ng/ml single dose groups. Single administration of the accumulative dose at 1.6ng/ml had no significant effect on the calcium content in either cell culture compared to control. Two weeks continuous administration of 0.2ng/ml TGF-beta1 in both cell cultures resulted in significant increases in the expression of bone specific extracellular matrix proteins which included alkaline phosphatase, Type I collagen, and osteocalcin as measured by Northern blot analysis and RT-PCR. At 4 weeks, the mRNA level of Type I collagen was still significantly higher in the TGF-beta1 treatment group compared to control. In conclusion, TGF-beta1 enhances mineralization of HOB on implant materials.

Testing of skeletal implant surfaces with human fetal osteoblasts

The effect of standard orthopaedic implant materials on osteoblast proliferation and differentiation was investigated using a human osteoblast cell culture system. Human fetal osteoblasts 1.19 were cultured on stainless steel, cobalt-chrome-molybdenum, and commercially pure titanium for 12 days. Tissue culture polystyrene was used as a control. Cell proliferation was measured by electronic cell counting and by a colorimetric proliferation assay. To assess the degree of differentiation, levels of alkaline phosphatase activity, collagen Type I, and osteocalcin production were measured. Osteocalcin gene expression was measured by reverse transcriptase-polymerase chain reaction. Electronic cell counting and proliferation assays showed lower cell numbers and delayed proliferation on stainless steel and cobalt-chrome-molybdenum compared with titanium and polystyrene. Alkaline phosphatase and osteocalcin were measured higher on titanium than on stainless steel or cobalt-chrome-molybdenum. Differences in collagen Type I production were not found. Reverse transcriptase-polymerase chain reaction showed the highest osteocalcin gene expression on titanium. The human fetal osteoblast cell line 1.19 provides a rapidly proliferating and differentiating system for testing biomaterials in which differences in osteoblast proliferation and differentiation on orthopaedic implant materials could be revealed, suggesting that the chemistry of biomaterials has a dynamic effect on proliferation and differentiation of human osteoblasts.

BMP-4 and BMP-6 involvement in the osteogenic properties of the HeLa cell line

The heterotopically induced ossicles are used in our research on bone tissue. The ossicles are formed in the thigh muscle of BALB/c mice under the influence of injected suspension of 3 x 10(6) HeLa cells. We postulate that the mechanism of bone induction is based on the secretion of bone morphogenetic proteins BMP-4 and BMP-6 by the grafted HeLa cells. This was proved by the use of specific immunohistochemical reaction and Western blots of conditioned culture medium. It seems that HeLa cells secrete BMPs continuously into the culture medium, even without contact with the mice muscle tissue, were induction of bone tissue is observed.

A murine osteosarcoma cell line with a potential to develop ossification upon transplantation

An osteosarcoma cell line has been established from a soft tissue tumor that occurred spontaneously in a BALB / c mouse. This cell line showed ossification when transplanted into syngeneic mice. To examine the mechanism of bone formation, the expression of mRNAs for osteoblastic and chondroblastic markers and factors associated with ossification has been investigated. In culture, the cells exhibited a spindle shape in the growth phase, but had a polygonal shape in the stationary phase. Reverse transcription-polymerase chain reaction analysis showed that the cells expressed mRNAs for pro-alpha1(I) chain of type I collagen, alkaline phosphatase, osteopontin, osteocalcin, and core binding factor alpha1, suggesting differentiation into the stage of osteoblasts during the stationary phase. After transplantation, histological examination revealed small foci of pale blue material and basophilic networks that were scattered in the tumor tissues at one week. The former stained positive with alcian blue, suggesting a chondroid matrix. Pro-alpha1(II) chain of type II collagen mRNA was expressed at one week. A large part of tumors at two and three weeks consisted of basophilic networks, which stained positive via von Kossa's method, indicating a calcified woven bone. In situ hybridization analysis showed strong expression of osteopontin and osteocalcin mRNAs in tumor cells surrounding the bone matrix. Bone morphogenetic protein-6 and -7 mRNAs were detected in transplanted tumors, but not in cultured cells. These results suggest that the cell line has the properties of an osteoblastic lineage when cultured in vitro and has an ossifying ability through endochondral bone formation processes when transplanted in vivo.

Rapid quantitative bioassay of osteoinduction

We developed a reproducible, relatively rapid bioassay that quantitatively correlates with the osteoinductive capacity of demineralized bone matrix obtained from human long bones. We have found that Saos human osteosarcoma cells proliferate in response to incubation with demineralized bone matrix and that an index of this proliferative activity correlates with demineralized bone matrix-induced osteogenesis in vivo. The bioassay (Saos cell proliferation) had an interassay coefficient of variation of 23 +/- 2% and an intra-assay coefficient of 11 +/- 1%. Cell proliferation was normalized to a standard sample of demineralized bone matrix with a clinically high osteoinductive capacity, which was assigned a value of one. The Saos cell proliferation for each sample was related to the standard and assigned a value placing it into the low (0.00-0.39), intermediate (0.40-0.69), or high (0.70-1.49) osteoinductive index group. Osteoinduction of human demineralized bone matrix was quantitated by expressing new bone formation as a function of the total bone volume (new bone plus the demineralized bone powder). The demineralized bone matrix was placed in pouches formed in the rectus abdominis muscles of athymic rats, and endochondral bone formation was assessed at 35 days following implantation, when marrow spaces in the ossicles were formed by new bone bridging the spaces between demineralized bone matrix particles. The proliferative index correlated with the area of new bone formation in histological sections of the newly formed ossicles. When the proliferative index (the osteoinductive index) was divided into low, intermediate, and high groups, the correlation between it and new bone formation (osteoinduction) was 0.850 (p < 0.0005) in 25 samples of demineralized bone matrix. There was no overlap in the osteoinduction stimulated between the samples with low and high osteoinductive indices. We conclude that the proliferation assay is useful for the routine screening of bone allograft donors for osteoinductive potential. Furthermore, the two-dimensional area of new bone formation, as it relates to total new bone area, is a quantitative measure of osteoinduction.

The role of transforming growth factor-beta on retarded osteoblastic differentiation in vitro

Various matrix growth factors play important roles in the development and growth of cartilage and bone. Among them transforming growth factor-beta superfamily and especially bone morphogenetic proteins are known to be important factors, since they induce bone and cartilage formation in ectopic sites in vivo. We have previously shown that the human osteosarcoma cell line Saos-2 expresses molecules that in vivo induce new bone formation with asymmetric bone maturation. In this study we examined the role of Saos-2-conditioned medium in prolonged cultures of mesenchymal C3H/10T1/2 cells. The C3H/10T1/2 cells were cultured with Saos-2-conditioned medium for 28 days. We show that Saos-2-treated C3H/10T1/2 cells performed retarded osteoblastic differentiation when compared to recombinant BMP-2 and -4 induced differentiation. We further show that this retardation is due to excessive amounts of transforming growth factor-beta in Saos-2-conditioned medium. Our results also suggest that this model can well be used to study additional cofactors involved in retarded osteogenesis.

Immunohistochemical demonstration of bone morphogenetic protein in odontogenic tumors

The aim of the present study was to describe the expression and distribution of bone morphogenetic protein (BMP) in odontogenic tumors by immunohistochemistry using monoclonal antibody against bovine BMP (BMPMcAb). Eight types of odontogenic tumors (44 cases), including ameloblastoma (20 cases), cementifying fibroma (8 cases), benign cementoblastoma (5 cases), dentinoma (3 cases), compound odontoma (2 cases), adenomatoid odontogenic tumor (2 cases), calcifying epithelial odontogenic tumor (2 cases) and odontogenic fibroma (2 cases), were studied. The results showed that, according to the immunostaining pattern of BMPMcAb, tumors could be classified into two types: all cementifying fibromas, benign cementoblastomas, dentinomas, odontogenic fibromas, and compound odontomas demonstrated a positive reaction, whereas all ameloblastomas, adenomatoid odontogenic tumors, and calcifying epithelial odontogenic tumors were negative. BMPMcAb-positive odontogenic tumors were those tumors with formation of enamel, dentin, cementum or bone. Therefore, BMP might play an important role in the formation of calcified dental tissues and the development of odontogenic tumors contaning such tissues.