Expression of osteocalcin and its transcriptional regulators core-binding factor alpha 1 and MSX2 in osteoid-forming tumours

The influence on surface characteristic and biocompatibility of nano-SnO2-modified titanium implant material using atomic layer deposition technique

BACKGROUND/PURPOSE

To investigate the surface characteristics of titanium (Ti) implant materials, which were coated with different thicknesses of nanoscale tin oxide (SnO₂) using the atomic layer deposition technique, and evaluated its biological performance on human embryonic palatal mesenchyme (HEPM) cells.

METHODS

The thickness of the coating layer on Ti was 0 (Ti0), 20 nm (Ti20), 50 nm (Ti50), and 100 nm (Ti100), respectively. The surface morphology was observed with an SEM and AFM. The root mean square roughness of micron-scale (mRq) and nanoroughness (nRq) of Ti discs' surface were measured. The Alamar blue (AB) assay and F-actin fluorescence staining were used to evaluate the biocompatibility, and the osteocalcin (OCN) was measured to clarify the differentiation of HEPM cells on materials.

RESULTS

In the coating groups, the mRq was decreased, but the nRq was increased. The spreading and polygonal morphology of HEPMs was apparent in coating groups. On Day 4, the survival rate of HEPM cells on Ti0 was higher than on Ti20 and Ti50. There was no significant difference on Day 7, Day 10, and Day 14. The OCN was significantly higher on Day 14 in all the coating groups than Ti0.

CONCLUSION

The results showed that the cell growth was intensified with rough surfaces. However, the OCN and morphology change was prominent when the nanoroughness was increased, which meant the increased nanoroughness might enhance OCN production and improve the tendency of osseointegration. The nanoscale SnO₂ coating could increase the ability of bone formation but not cell growth.

Risk factors for fracture in patients with fibrous dysplasia of the proximal femur

OBJECTIVE

The primary aim of this retrospective observational clinical study was to explore the risk factors for fracture in patients with fibrous dysplasia (FD) of the proximal femur.

METHODS

We investigated body mass index, bilateral radiographs on both sides, femoral neck shaft angle measurements, and markers of bone metabolism in patients with FD of the proximal femur according to whether or not they had sustained a hip fracture. Nine clinical parameters (age, sex, clinical classification, anatomic classification, femoral neck shaft angle, and procollagen type 1 N-terminal propeptide, C-terminal telopeptide of type I collagen, and osteocalcin levels) were selected for univariate analysis. Factors that were significant in univariate analysis were then subjected to multivariate logistic analysis.

RESULTS

Clinical classification, anatomic classification, femoral neck shaft angle, and the osteocalcin level were identified to be statistically significant risk factors for fracture in univariate analysis. Anatomic classification, femoral neck shaft angle, and the osteocalcin level remained significant risk factors in multivariate analysis.

CONCLUSIONS

Anatomic classification, femoral neck shaft angle, and the osteocalcin level are important risk factors for fracture in patients with FD of the proximal femur and could be used to guide implementation of a fracture prevention strategy in these patients.

Osteosarcoma: prognosis plateau warrants retinoblastoma pathway targeted therapy

Osteosarcoma (OS) is the most common primary bone cancer in children and adolescents, affecting ~560 young patients in the United States annually. The term OS describes a diverse array of subtypes with varying prognoses, but the majority of tumors are high grade and aggressive. Perhaps because the true etiology of these aggressive tumors remains unknown, advances in OS treatment have reached a discouraging plateau, with only incremental improvements over the past 40 years. Thus, research surrounding the pathogenesis of OS is essential, as it promises to unveil novel therapeutic targets that can attack tumor cells with greater specificity and lower toxicity. Among the candidate molecular targets in OS, the retinoblastoma (RB) pathway demonstrates the highest frequency of inactivation and thus represents a particularly promising avenue for molecular targeted therapy. This review examines the present thinking and practices in OS treatment and specifically highlights the relevance of the RB pathway in osteosarcomagenesis. Through further investigation into RB pathway-related novel therapeutic targets, we believe that a near-term breakthrough in improved OS prognosis is possible.

The impact of osteoblastic differentiation on osteosarcomagenesis in the mouse

Osteosarcomas remain an enigmatic group of malignancies that share in common the presence of transformed cells producing osteoid matrix, even if these cells comprise a minority of the tumor volume. The differentiation state of osteosarcomas has therefore become a topic of interest and challenge to those who study this disease. In order to test how the cell of origin contributes to the final state of differentiation in the transformed cells, we compared the relative tumorigenicity of Cre-LoxP conditional disruption of the cell cycle checkpoint tumor-suppressor genes Trp53 and Rb1 using Prx1-Cre, Collagen-1α1-Cre and Osteocalcin-Cre to transform undifferentiated mesenchyme, preosteoblasts and mature osteoblasts, respectively. The Prx1 and Col1α1 lineages developed tumors with nearly complete penetrance, as anticipated. Osteosarcomas also developed in 44% of Oc-Cre;Rb1(fl/fl);Trp53(fl/fl) mice. We confirmed using 5-ethynyl-2'-deoxyuridine click chemistry that the Oc-Cre lineage includes very few actively cycling cells. By assessing radiographic mineralization and histological osteoid production, the differentiation state of tumors did not correlate with the differentiation state of the lineage of origin. Some of the osteocalcin-lineage-derived osteosarcomas were among the least osteoblastic. Osteocalcin immunohistochemistry in tumors correlated well with the expression of DNA methyl transferases, suggesting that silencing of these epigenetic regulators may influence the final differentiation state of an osteosarcoma. Transformation of differentiated, minimally proliferative osteoblasts is possible but may require such an epigenetic reprogramming that the tumors no longer resemble their differentiated origins.

Coleusin factor, a novel anticancer diterpenoid, inhibits osteosarcoma growth by inducing bone morphogenetic protein-2-dependent differentiation

Coleusin factor is a diterpenoid compound isolated from the root of a tropical plant, Coleus forskohlii. Although Coleusin factor has been reported to suppress proliferation of and induce apoptosis in several types of cancer cells, the effects of Coleusin factor on osteosarcoma and the underlying mechanism are still not fully understood. In this study, we show that Coleusin factor treatment potently inhibits the growth of osteosarcoma cells associated with G(1) cell-cycle arrest. Interestingly, apoptosis and cell death are not induced. Instead, Coleusin factor causes osteosarcoma cells to exhibit typical properties of differentiated osteoblasts, including a morphologic alteration resembling osteoblasts, the expression of osteoblast differentiation markers, elevated alkaline phosphatase activity, and increased cellular mineralization. Coleusin factor treatment significantly increases the expression of bone morphogenetic protein-2 (BMP-2), a crucial osteogenic regulator, and runt-related transcription factor 2 (RUNX2), one of the key transcription factors of the BMP pathway. When BMP-2 signaling is blocked, Coleusin factor fails to inhibit cell proliferation and to induce osteoblast differentiation. Thus, upregulation of BMP-2 autocrine is critical for Coleusin factor to induce osteoblast differentiation and exert its anticancer effects on osteosarcoma. Importantly, administration of Coleusin factor inhibits the growth of osteosarcoma xenografted in nude mice without systemic or immunologic toxicity. Osteosarcoma is a highly aggressive cancer marked by the loss of normal differentiation. Coleusin factor represents a new type of BMP-2 inducer that restores differentiation in osteosarcoma cells. It may provide a promising therapeutic strategy against osteosarcoma with minimal side effects.

In vascular smooth muscle cells paricalcitol prevents phosphate-induced Wnt/β-catenin activation

The present study investigates the differential effect of two vitamin D receptor agonists, calcitriol and paricalcitol, on human aortic smooth muscle cells calcification in vitro. Human vascular smooth muscle cells were incubated in a high phosphate (HP) medium alone or supplemented with either calcitriol 10(-8)M (HP + CTR) or paricalcitol 3·10(-8) M (HP + PC). HP medium induced calcification, which was associated with the upregulation of mRNA expression of osteogenic factors such as bone morphogenetic protein 2 (BMP2), Runx2/Cbfa1, Msx2, and osteocalcin. In these cells, activation of Wnt/β-catenin signaling was evidenced by the translocation of β-catenin into the nucleus and the increase in the expression of direct target genes as cyclin D1, axin 2, and VCAN/versican. Addition of calcitriol to HP medium (HP + CTR) further increased calcification and also enhanced the expression of osteogenic factors together with a significant elevation of nuclear β-catenin levels and the expression of cyclin D1, axin 2, and VCAN. By contrast, the addition of paricalcitol (HP + PC) not only reduced calcification but also downregulated the expression of BMP2 and other osteoblastic phenotype markers as well as the levels of nuclear β-catenin and the expression of its target genes. The role of Wnt/β-catenin on phosphate- and calcitriol-induced calcification was further demonstrated by the inhibition of calcification after addition of Dickkopf-related protein 1 (DKK-1), a specific natural antagonist of the Wnt/β-catenin signaling pathway. In conclusion, the differential effect of calcitriol and paricalcitol on vascular calcification appears to be mediated by a distinct regulation of the BMP and Wnt/β-catenin signaling pathways.

The MET oncogene transforms human primary bone-derived cells into osteosarcomas by targeting committed osteo-progenitors

The MET oncogene is aberrantly overexpressed in human osteosarcomas. We have previously converted primary cultures of human bone-derived cells into osteosarcoma cells by overexpressing MET. To determine whether MET transforms mesenchymal stem cells or committed progenitor cells, here we characterize distinct MET overexpressing osteosarcoma (MET-OS) clones using genome-wide expression profiling, cytometric analysis, and functional assays. All the MET-OS clones consistently display mesenchymal and stemness markers, but not most of the mesenchymal–stem cell-specific markers. Conversely, the MET-OS clones express genes characteristic of early osteoblastic differentiation phases, but not those of late phases. Profiling of mesenchymal stem cells induced to differentiate along osteoblast, adipocyte, and chondrocyte lineages confirms that MET-OS cells are similar to cells at an initial phase of osteoblastic differentiation. Accordingly, MET-OS cells cannot differentiate into adipocytes or chondrocytes, but can partially differentiate into osteogenic-matrix-producing cells. Moreover, in vitro MET-OS cells form self-renewing spheres enriched in cells that can initiate tumors in vivo. MET kinase inhibition abrogates the self-renewal capacity of MET-OS cells and allows them to progress toward osteoblastic differentiation. These data show that MET initiates the transformation of a cell population that has features of osteo-progenitors and suggest that MET regulates self-renewal and lineage differentiation of osteosarcoma cells.

p53 and MDM2 are involved in the regulation of osteocalcin gene expression

Osteocalcin (OC) is a major noncollagenous bone matrix protein and an osteoblast marker whose expression is limited to mature osteoblasts during the late differentiation stage. In previous studies we have shown osteosarcomas to lose p53 function with a corresponding loss of osteocalcin gene expression. Introduction of wild type p53 resulted in re expression of the osteocalcin gene. Using gel shift and chromatin immunoprecipitation assays, we have identified a putative p53 binding site within the rat OC promoter region and observed an increase in OC promoter activity when p53 accumulates using a CAT assay. The p53 inducible gene Mdm2 is a well-known downstream regulator of p53 levels. Our results showed a synergistic increase in the OC promoter activity when both p53 and MDM2 were transiently overexpressed. We further demonstrate that p53 is not degraded during overexpression of MDM2 protein. Increased OC expression was observed with concomitantly increased p53, VDR, and MDM2 levels in ROS17/2.8 cells during treatment with differentiation promoting (DP) media, but was significantly decreased when co-treated with DP media and the small molecule inhibitor of MDM2-p53 interaction, Nutlin-3. We have also observed a dramatic increase of the OC promoter activity in the presence of p53 and Mdm2 with inclusion of Cbfa-1 and p300 factors. Our results suggest that under some physiological conditions the oncoprotein MDM2 may cooperate with p53 to regulate the osteocalcin gene during osteoblastic differentiation.

Analysis of stromal cells in osteofibrous dysplasia and adamantinoma of long bones

Adamantinoma of long bones and osteofibrous dysplasia are rare, osteolytic primary bone tumours of uncertain origin containing areas of fibrous and fibro-osseous proliferation. We investigated the nature of the stromal cells in adamantinoma of long bones and osteofibrous dysplasia, and determined cellular and molecular mechanisms of osteolysis in these tumours. Cell culture, molecular (RT-PCR, western blot) and immunohistochemical studies on cases of adamantinoma of long bones and of osteofibrous dysplasia were undertaken to determine the expression of epithelial, osteoblast and osteoclast markers. Ultrastructural and immunophenotypic studies on cultured adamantinoma and osteofibrous dysplasia stromal cells showed that these cells were mainly fibroblast-like with few cells expressing epithelial markers. Osteofibrous dysplasia but not adamantinoma cells expressed alkaline phosphatase. Both osteofibrous dysplasia and adamantinoma cells expressed the ostoclastogenic factors M-CSF and RANKL. Adamantinoma and osteofibrous dysplasia cells also expressed messenger RNA for osteocalcin, osteonectin, osteopontin, osterix and collagen type 1. Adamantinoma and osteofibrous dysplasia cells cultured alone on dentine slices were not capable of lacunar resorption, but in co-cultures with monocytes induced formation of osteoclast-like cells was observered. Cultured osteofibrous dysplasia and adamantinoma stromal cells show similar ultrastructural and immunophenotypic characteristics, and differentially express osteoblast markers. Promotion of osteoclastogenesis by stromal cells may contribute to osteolysis in adamantinoma of long bones and osteofibrous dysplasia.

Osteocalcin gene expression is regulated by wild-type p53

The tumor-suppressor p53 is a transcription factor that regulates a number of genes in the process of cell-cycle inhibition, apoptosis, and DNA damage. Recent studies have revealed a crucial role for p53 in bone remodeling. In our previous studies we have shown that p53 is an important regulator of osteoblast differentiation. In this study we investigated the role of p53 in the regulation of human osteocalcin gene expression. We observed that osteocalcin promoter activity could be upregulated by both exogenous and endogenous p53 and downregulated by p53-specific small interfering RNA. DNA affinity immunoblotting assay showed that p53 can bind to the human osteocalcin promoter in vitro. We further identified a p53 response element within the osteocalcin promoter region using a chromatin immunoprecipitation assay. Furthermore, we observed an additive effect of p53 and VDR on the regulation of osteocalcin promoter activity. Our findings suggest that p53 may directly target the human osteocalcin gene and positively affect osteocalcin gene expression.

Proteasome inhibition with bortezomib suppresses growth and induces apoptosis in osteosarcoma

Osteosarcomas are primary bone tumors of osteoblastic origin that mostly affect adolescent patients. These tumors are highly aggressive and metastatic. Previous reports indicate that gain of function of a key osteoblastic differentiation factor, Runx2, leads to growth inhibition in osteosarcoma. We have previously established that Runx2 transcriptionally regulates expression of a major proapoptotic factor, Bax. Runx2 is regulated via proteasomal degradation, and proteasome inhibition has a stimulatory effect on Runx2. In this study, we hypothesized that proteasome inhibition will induce Runx2 and Runx2-dependent Bax expression sensitizing osteosarcoma cells to apoptosis. Our data showed that a proteasome inhibitor, bortezomib, increased Runx2 and Bax in osteosarcoma cells. In vitro, bortezomib suppressed growth and induced apoptosis in osteosarcoma cells but not in nonmalignant osteoblasts. Experiments involving intratibial tumor xenografts in nude mice demonstrated significant tumor regression in bortezomib-treated animals. Immunohistochemical studies revealed that bortezomib inhibited cell proliferation and induced apoptosis in osteosarcoma xenografts. These effects correlated with increased immunoreactivity for Runx2 and Bax. In summary, our results indicate that bortezomib suppresses growth and induces apoptosis in osteosarcoma in vitro and in vivo suggesting that proteasome inhibition may be effective as an adjuvant to current treatment regimens for these tumors. Published 2009 UICC. This article is a US Government work and, as such, is in the public domain in the United States of America.

Potential of chemically modified hydrophilic surface characteristics to support tissue integration of titanium dental implants

In the past, several modifications of specific surface properties such as topography, structure, chemistry, surface charge, and wettability have been investigated to predictably improve the osseointegration of titanium implants. The aim of the present review was to evaluate, based on the currently available evidence, the impact of hydrophilic surface modifications of titanium for dental implants. A surface treatment was performed to produce hydroxylated/hydrated titanium surfaces with identical microstructure to either acid-etched, or sand-blasted, large grit and acid-etched substrates, but with hydrophilic character. Preliminary in vitro studies have indicated that the specific properties noted for hydrophilic titanium surfaces have a significant influence on cell differentiation and growth factor production. Animal experiments have pointed out that hydrophilic surfaces improve early stages of soft tissue and hard tissue integration of either nonsubmerged or submerged titanium implants. This data was also corroborated by the results from preliminary clinical studies. In conclusion, the present review has pointed to a potential of hydrophilic surface modifications to support tissue integration of titanium dental implants.

Bone regeneration in dehiscence-type defects at non-submerged and submerged chemically modified (SLActive) and conventional SLA titanium implants: an immunohistochemical study in dogs

OBJECTIVES

The aim of the present study was to evaluate bone regeneration in dehiscence-type defects at non-submerged and submerged titanium implants with chemically modified (mod) and conventional sandblasted/acid-etched (SLA) surfaces.

MATERIAL AND METHODS

Standardized buccal dehiscence defects were surgically created following implant site preparation in both the upper and lower jaws of 12 beagle dogs. Both types of implants were randomly assigned to either a non-submerged or a submerged healing procedure. After 1, 2, 4, and 8 weeks, dissected blocks were processed for histomorphometrical [e.g. new bone height (NBH), per cent linear fill (PLF), percentage of bone to implant contact (BIC-D), area of new bone fill (BF)] and immunohistochemical analysis.

RESULTS

At 8 weeks, non-submerged and submerged SLA implants revealed significantly lower mean NBH (1.1+/-0.8-1.9+/-1.2 mm), PLF (27.7+/-20.3-46.0+/-28.5%), BIC-D (26.8+/-10.4-46.2+/-16.2%), and BF (1.3+/-0.9-3.4+/-2.8 mm(2)) values than respective modSLA implants [NBH (2.6+/-0.8-4.3+/-0.1 mm), PLF (64.2+/-19.4-107.2+/-4.7%), BIC-D (67.5+/-18.8-82.1+/-14.8%), BF (2.9+/-1.0-6.7+/-1.1 mm(2))]. Within modSLA groups, significantly highest BF values were observed at submerged implants.

CONCLUSION

It was concluded that (i) modSLA titanium surfaces promoted bone regeneration in acute-type buccal dehiscence defects and (ii) a submerged healing procedure improved the outcome of healing additionally.

Histological and immunohistochemical analysis of initial and early osseous integration at chemically modified and conventional SLA titanium implants: preliminary results of a pilot study in dogs

OBJECTIVES

The aim of the present pilot study was to investigate initial and early tissue reactions to modified (mod) and conventional sand-blasted, large grit and acid-etched (SLA) titanium implants.

MATERIAL AND METHODS

Implantation of modSLA and SLA implants was performed bilaterally in both the mandible and maxilla of dogs. The animals were sacrificed after a healing period of 1, 4, 7 and 14 days, respectively. Peri-implant tissue reactions were assessed in non-decalcified tissue sections using conventional histology (Toluidine blue-TB and Masson Goldner Trichrome stain-MG) and immunohistochemistry using monoclonal antibodies to transglutaminase II (TG) (angiogenesis) and osteocalcin (OC). Bone density (BD) and bone to implant contact (BIC) were assessed histomorphometrically.

RESULTS

Day 1 revealed an early TG antigen reactivity in the provisional fibrin matrix adjacent to both implant surfaces. Day 4 was characterized by the formation of a collagen-rich connective tissue (MG), which revealed the first signs of OC synthesis adjacent to modSLA surfaces. Immunohistochemical staining for TG revealed a direct correlation between angiogenesis and new bone formation, which was clearly identifiable after 7 days by means of increasing BD, BIC and OC values. After 14 days, modSLA surfaces seemed to be surrounded by a firmly attached mature, parallel-fibered woven bone.

CONCLUSIONS

Within the limits of the present study, it might be concluded that the combination of immunohistochemical and conventional histological stainings in non-decalcified tissue sections is a valuable technique to evaluate the initial and early stages of wound healing around endosseous titanium implants.

Epigenetic modifications in osteogenic differentiation and transformation

Almost all tumors are characterized by both architectural and cellular abnormalities in differentiation. Osteoblast development is relatively well understood, making osteosarcoma a good model for understanding how tumorigenesis perturbs normal differentiation. We argue that there are two key transition points in normal cellular differentiation that are the focus of oncogenic events, in both of which epigenetic processes are critical. The first is the transition from an uncommitted pluripotent precursor (mesenchymal stem cell) to the 'transit-amplifying compartment' of the osteoblast lineage. This transition, normally exquisitely regulated in space and time, is abnormal in cancer. The second involves termination of lineage expansion, equally tightly regulated under normal circumstances. In cancer, the mechanisms that mandate eventual cessation of cell division are almost universally disrupted. This model predicts that key differentiation genes in bone, such as RUNX2, act in an oncogenic fashion to initiate entry into a proliferative phase of cell differentiation, and anti-oncogenically into the post-mitotic state, resulting in ambivalent roles in tumorigenesis. Polycomb genes exemplify epigenetic processes in the stem cell compartment and tumorigenesis, and are implicated in skeletal development in vivo. The epigenetic functions of the retinoblastoma protein, which plays a key role in tumorigenesis in bone, is discussed in the context of terminal cell cycle exit.

Osteoblast differentiation and skeletal development are regulated by Mdm2-p53 signaling

Mdm2 is required to negatively regulate p53 activity at the peri-implantation stage of early mouse development. However, the absolute requirement for Mdm2 throughout embryogenesis and in organogenesis is unknown. To explore Mdm2–p53 signaling in osteogenesis, Mdm2-conditional mice were bred with Col3.6-Cre–transgenic mice that express Cre recombinase in osteoblast lineage cells. Mdm2-conditional Col3.6-Cre mice die at birth and display multiple skeletal defects. Osteoblast progenitor cells deleted for Mdm2 have elevated p53 activity, reduced proliferation, reduced levels of the master osteoblast transcriptional regulator Runx2, and reduced differentiation. In contrast, p53-null osteoprogenitor cells have increased proliferation, increased expression of Runx2, increased osteoblast maturation, and increased tumorigenic potential, as mice specifically deleted for p53 in osteoblasts develop osteosarcomas. These results demonstrate that p53 plays a critical role in bone organogenesis and homeostasis by negatively regulating bone development and growth and by suppressing bone neoplasia and that Mdm2-mediated inhibition of p53 function is a prerequisite for Runx2 activation, osteoblast differentiation, and proper skeletal formation.

RhoA GTPase inactivation by statins induces osteosarcoma cell apoptosis by inhibiting p42/p44-MAPKs-Bcl-2 signaling independently of BMP-2 and cell differentiation

Osteosarcoma is the most common primary bone tumour in young adults. Despite improved prognosis, resistance to chemotherapy remains responsible for failure of osteosarcoma treatment. The identification of signals that promote apoptosis may provide clues to develop new therapeutic strategies for chemoresistant osteosarcoma. Here, we show that lipophilic statins (atorvastatin, simvastatin, cerivastatin) markedly induce caspases-dependent apoptosis in various human osteosarcoma cells, independently of bone morphogenetic protein (BMP)-2 signaling and cell differentiation. Although statins increased BMP-2 expression, the proapoptotic effect of statins was not prevented by the BMP antagonist noggin, and was abolished by mevalonate and geranylgeranylpyrophosphate, suggesting the involvement of defective protein geranylgeranylation. Consistently, lipophilic statins induced membrane RhoA relocalization to the cytosol and inhibited RhoA activity, which resulted in decreased phospho-p42/p44- mitogen-activated protein kinases (MAPKs) and Bcl-2 levels. Constitutively active RhoA rescued phospho-p42/p44-MAPKs and Bcl-2 and abolished statin-induced apoptosis. Thus, lipophilic statins induce caspase-dependent osteosarcoma cell apoptosis by a RhoA-p42/p44 MAPKs-Bcl-2-mediated mechanism, independently of BMP-2 signaling and cell differentiation.

Constitutive hedgehog signaling in chondrosarcoma up-regulates tumor cell proliferation

Chondrosarcoma is a malignant cartilage tumor that may arise from benign precursor lesions, such as enchondromas. Some cases of multiple enchondromas are caused by a mutation that results in constitutive activation of Hedgehog-mediated signaling. We found that chondrosarcomas expressed high levels of the Hedgehog target genes PTCH1 and GLI1. Treatment with parathyroid hormone-related protein down-regulated Indian Hedgehog (IHH) expression in normal growth plates but not in chondrosarcoma or enchondroma organ cultures. Treatment of the chondrosarcoma organ cultures with Hedgehog protein increased cell proliferation rate, whereas addition of chemical inhibitors of Hedgehog signaling decreased the proliferation rate. Chondrosarcoma xenografts from 12 different human tumors were established in NOD-SCID mice. Treatment with triparanol, an inhibitor of Hedgehog signaling, resulted in a 60% decrease in tumor volume, a 30% decrease in cellularity, and a 20% reduction in proliferation rate. These results show that Hedgehog signaling is active in chondrosarcoma and benign cartilage tumors and regulates tumor cell proliferation. Our data raise the intriguing possibility that Hedgehog blockade could serve as an effective treatment for chondrosarcoma, a tumor for which there are currently no universally effective nonsurgical management options.

Autogenous bone chips: influence of a new piezoelectric device (PiezosurgeryR) on chip morphology, cell viability and differentiation

AIM

The aim of the present study was to investigate the influence of a new piezoelectric device, designed for harvesting autogenous bone chips from intra-oral sites, on chip morphology, cell viability and differentiation.

METHODS

A total of 69 samples of cortical bone chips were randomly gained by either (1) a piezoelectric device (PS), or (2) conventional rotating drills (RD). Shape and size of the bone chips were compared by means of morphometrical analysis. Outgrowing osteoblasts were identified by means of alkaline phosphatase activity (AP), immunhistochemical staining for osteocalcin (OC) synthesis and reverse transcriptase-polymerase chain reaction phenotyping.

RESULTS

In 88.9% of the RD and 87.9% of the PS specimens, an outgrowth of adherent cells nearby the bone chips was observed after 6-19 days. Confluence of cells was reached after 4 weeks. Positive staining for AP and OC identified the cells as osteoblasts. The morphometrical analysis revealed a statistically significant more voluminous size of the particles collected with PS than RD.

CONCLUSION

Within the limits of the present study, it may be concluded that both the harvesting methods are not different from each other concerning their detrimental effect on viability and differentiation of cells growing out of autogenous bone chips derived from intra-oral cortical sites.

von Willebrand factor expression in osteosarcoma metastasis

A number of genes are implicated in the initiation and progression of osteosarcoma; however, cytogenetic and comparative genomic hybridization studies indicate the involvement of additional unidentified genes. An examination of gene expression profiles in 22 high-grade osteosarcoma tumor specimens from 15 patients (including paired primary and metastatic samples from five patients) indicated that von Willebrand factor (vWF) mRNA expression may increase during tumor progression. vWF, a large glycoprotein previously considered to be expressed exclusively by endothelial cells and megakaryocytes, is involved in platelet aggregation and adhesion to the subendothelial matrix, processes critical to hematogenous tumor cell metastasis to the lung. Analysis of paired primary and metastatic osteosarcoma tumor samples from 10 patients revealed an increase in vWF gene expression in metastases (P=0.005). Immunohistochemistry showed that, in addition to the endothelial cells, vWF protein was also detected in osteosarcoma cells in vivo in 13 of 29 tumor specimens as well as in SAOS2, an osteosarcoma cell line. The tumor cell staining correlated positively with high vWF expression in the sample (P=0.006). Although vascular endothelial cells contribute to the vWF mRNA detected in the tumor samples, there was neither any correlation between vascular density (VD) and vWF mRNA expression nor between VD and clinical outcome. These findings suggest that vWF expression is deregulated in osteosarcoma tumors, potentially contributing to metastasis.

Prolonged beta-catenin stabilization and tcf-dependent transcriptional activation in hyperplastic cutaneous wounds

Mesenchymal cells that accumulate during the proliferative phase of wound healing and that are present in hyperplastic wounds share cytologic similarities with the cells from fibroproliferative lesions in which there is activation of beta-catenin-mediated transcription. Re-excision wounds from a previous biopsy and samples from hyperplastic cutaneous wounds were studied along with normal tissues. During normal wound healing, there was an increase in beta-catenin protein level, peaking 4 weeks following the insult and returning towards baseline level by 12 weeks. Hyperplastic wounds exhibited a prolonged duration of elevated beta-catenin, lasting more than 2 years following the initial injury. The level of expression of genes known to be upregulated in the proliferative phase of wound healing (alpha-smooth muscle actin and type three collagen), correlated with beta-catenin protein level. The phosphorylation level of glycogen synthase kinase-3-beta, a kinase important for beta-catenin protein destabilization, correlated with beta-catenin protein level. Beta-catenin was transcriptionally active in these wounds as demonstrated by the expression of the beta-catenin target genes (MMP-7 and FN) and by activation of a tcf-reporter in primary cell cultures. Beta-catenin stabilization increases cell proliferation and motility in fibroblasts in vitro, and likely has a similar function during its transient elevation in the proliferative phase of normal wound healing. In hyperplastic wounds, there is dysregulation of beta-catenin, maintaining the mesenchymal cells in a prolonged proliferative state. As such, beta-catenin likely plays a central role in mesenchymal cells during the healing process, and is an appealing therapeutic target for disorders of wound healing.

Terminal osteoblast differentiation, mediated by runx2 and p27KIP1, is disrupted in osteosarcoma

The molecular basis for the inverse relationship between differentiation and tumorigenesis is unknown. The function of runx2, a master regulator of osteoblast differentiation belonging to the runt family of tumor suppressor genes, is consistently disrupted in osteosarcoma cell lines. Ectopic expression of runx2 induces p27^KIP1, thereby inhibiting the activity of S-phase cyclin complexes and leading to the dephosphorylation of the retinoblastoma tumor suppressor protein (pRb) and a G1 cell cycle arrest. Runx2 physically interacts with the hypophosphorylated form of pRb, a known coactivator of runx2, thereby completing a feed-forward loop in which progressive cell cycle exit promotes increased expression of the osteoblast phenotype. Loss of p27^KIP1 perturbs transient and terminal cell cycle exit in osteoblasts. Consistent with the incompatibility of malignant transformation and permanent cell cycle exit, loss of p27^KIP1 expression correlates with dedifferentiation in high-grade human osteosarcomas. Physiologic coupling of osteoblast differentiation to cell cycle withdrawal is mediated through runx2 and p27^KIP1, and these processes are disrupted in osteosarcoma.

Altered expression and deletion of RMO1 in osteosarcoma

In order to increase our understanding of the molecular events underlying osteosarcoma progression, the expression of approximately 950 genes was examined in 24 primary and metastatic osteosarcoma tumor specimens. A gene, RMO1, was isolated with decreased expression in metastatic samples. Real-Time PCR corroborated this pattern, revealing lower expression in the primary sample in 6 of 7 cases for which both primary and metastatic osteosarcoma samples were available from the same patient (p = 0.034). RMO1 is located at 2q33, a region of frequent loss of heterozygosity in cancer, and exhibited loss of heterozygosity in 6 out of 9 primary osteosarcoma tumor samples (67%). Loss of heterozygosity is evident in primary tumors while the decrease in gene expression is seen in the metastatic samples, indicating that these 2 events are separately implicated in cancer progression. Cloning of RMO1 revealed an open reading frame with multiple splice forms with significant homology to GRB7, 10 and 14 and MIG10 in the region containing a Pleckstrin homology domain and a Ras association domain, suggestive of a role in cell signaling and migration. Northern blot analysis indicated that RMO1 mRNA is ubiquitously expressed in tissues except for peripheral blood leukocytes. These data suggest that RMO1 may be a candidate for a protein involved in inhibiting tumor progression.

Growth factors regulate beta-catenin-mediated TCF-dependent transcriptional activation in fibroblasts during the proliferative phase of wound healing

Beta-catenin is a critical regulator of cell behavior during embryogenesis and neoplastic processes. It also plays a crucial role in repair by modulating dermal fibroblast activity during the proliferative phase of cutaneous wound healing. We hypothesize that growth factors liberated during the initial phase of wound healing convey signals to induce activation of beta-catenin-mediated TCF-dependent signaling during the proliferative phase. Dermal fibroblasts were isolated and cultured from mice containing a beta-galactosidase reporter responsive to beta-catenin-TCF transactivation (TCF-beta-gal). Cells were stimulated with growth factors present at the initial phase of wound healing. EGF and TGF-beta1 significantly increased beta-catenin protein levels and transcriptional activity, whereas beta-catenin mRNA expression was unaffected. This increase was attributed to inactivation of GSK-3beta, a kinase important for beta-catenin destabilization. Subcutaneous injection of EGF or TGF-beta1 before wounding of TCF-beta-gal mice resulted in larger scars and fibroblasts within these wounds that strongly stained for beta-galactosidase, indicating significant beta-catenin transcriptional activity in vivo. Thus, beta-catenin-mediated signaling is activated downstream of growth factors released during the initial phase of wound repair, and may act during the proliferative phase of wound healing to integrate signals from initial phase factors into the expression of genes important during the later, remodeling phase.

Intraclonal plasticity for bone, smooth muscle, and adipocyte lineages in bone marrow stroma fibroblastoid cells

Bone marrow stroma fibroblastoid cells (BMSFC) develop from a single clone of cells within each of the in vitro fibroblastoid colonies (CFU-F) derived from either murine or human bone marrow. All of the clones represented by these colonies displayed antigenic and product markers for osteoblast, smooth muscle, and adipocyte lineages when tested separately for each marker. Separate sets of fibroblastoid colonies derived from the same individual donor's culture tested positive with antibodies specific for smooth muscle-specific heavy chain myosin (SMMHC), smooth muscle alpha actin-1, bone sialoprotein, osteocalcin, or alkaline phosphatase, and developed von Kossa-positive deposits shown by X-ray microanalysis and electron diffraction to be hydroxyapatite. Individual cells were positive for both SMMHC and osteocalcin. All cells in the multiple clones tested were capable of metabolizing a fatty acid to form intracellular lipid droplets. PCR transcripts obtained from the human cell cultures that provided these BMSFC clones were consistent with the immunocytochemical findings. Transcripts for PPAR (gamma)-2 and Cbfa-1 were dependent upon the culture medium content, suggesting an osteoblast/adipocyte differentiation switch point. Cell lineage specificity for markers and RNA transcripts was determined by comparison to skin fibroblast controls. These findings demonstrate a high degree of interlineage plasticity in vitro for BMSFC.

Genetic deletion of receptor for hyaluronan-mediated motility (Rhamm) attenuates the formation of aggressive fibromatosis (desmoid tumor)

Aggressive fibromatosis (desmoid tumor) is a locally invasive soft tissue neoplasm associated with mutations resulting in beta-catenin-mediated transcriptional activation. This tumor is composed of cells with histological and molecular characteristics common to proliferating mesenchymal cells of dermal wounds. Using immunohistochemistry and RT-PCR, we show that Rhamm, a protein with an important role in wound healing and neoplastic progression, is also expressed at high levels in aggressive fibromatosis. A mouse harboring a targeted deletion in Rhamm was generated, resulting in viable Rhamm-/- animals. Rhamm-/- mice were crossed with Apc/Apc1638N mice, which harbor a targeted mutation in the Apc gene predisposing animals to gastrointestinal and aggressive fibromatosis tumors. Rhamm deficiency significantly decreased the number of aggressive fibromatosis tumors formed, but did not alter the number of gastrointestinal polyps. Cell culture studies show that Rhamm regulates cell proliferation in both fibroblasts and fibromatosis cells under conditions of low density, but not high density. These results suggest that Rhamm regulates proliferation of cells with sparse cell-cell contacts, such as occurs in aggressive fibromatosis; provides the first genetic evidence implicating Rhamm in tumor pathology; and suggest Rhamm blockade as a potential therapeutic target for this otherwise difficult-to-treat neoplasm.

Osteo/chondrocytic transcription factors and their target genes exhibit distinct patterns of expression in human arterial calcification

OBJECTIVE

Mineralization-regulating proteins are found deposited at sites of vascular calcification. However, the relationship between the onset of calcification in vivo and the expression of genes encoding mineralization-regulating proteins is unknown. This study aimed to determine the temporal and spatial pattern of expression of key bone and cartilage proteins as atherosclerotic calcification progresses.

METHODS AND RESULTS

Using reverse transcription-polymerase chain reaction on a panel of noncalcified and calcified human arterial samples, two classes of proteins could be identified: (1) Matrix Gla protein, osteonectin, osteoprotegerin, and aggrecan were constitutively expressed by vascular smooth muscle cells (VSMCs) in the normal vessel media but downregulated in calcified arteries whereas (2) alkaline phosphatase, bone sialoprotein, osteocalcin, and collagen II were expressed predominantly in the calcified vessel together with Cbfa1, Msx2, and Sox9, transcription factors that regulate expression of these genes. In the calcified plaque in situ hybridization identified subsets of VSMCs expressing osteoblast and chondrocyte-like gene expression profiles whereas osteoclast-like macrophages were present around sites of calcification.

CONCLUSIONS

These observations suggest a sequence of molecular events in vascular calcification beginning with the loss of expression by VSMCs, of constitutive inhibitory proteins, and ending with expression by VSMCs and macrophages of chondrocytic, osteoblastic, and osteoclastic-associated proteins that orchestrate the calcification process.

Regulation of osteocalcin gene expression by a novel Ku antigen transcription factor complex

We previously described an osteocalcin (OC) fibroblast growth factor (FGF) response element (FRE) DNA binding activity as a target of Msx2 transcriptional regulation. We now identify Ku70, Ku80, and Tbdn100, a variant of Tubedown-1, as constituents of the purified OCFRE-binding complex. Northern and Western blot analyses demonstrate expression of Ku and Tbdn100 in MC3T3E1 osteoblasts. FGF2 treatment regulates Ku, but not Tbdn100, protein accumulation. Gel supershift studies confirm sequence-specific DNA binding of Ku in the OCFRE complex; chromatin immunoprecipitation assays confirm association of Ku and Tbdn100 with the endogenous OC promoter. In the promoter region -154 to -113, the OCFRE is juxtaposed to OSE2, an osteoblast-specific element that binds Runx2 (Osf2, Cbfa1). Expression of the Ku.Tbdn100 complex up-regulates both the basal and Runx2-dependent transcription driven by this 42-bp OC promoter element, reconstituted in CV-1 cells. Synergistic transactivation occurs in the presence of activated FGF receptor 2 signaling. Msx2 suppresses Ku- and Runx2-dependent transcription; suppression is dependent upon the Msx2 homeodomain NH(2)-terminal arm and extension. Pull-down assays confirm physical interactions between Ku and these co-regulatory transcription factors, consistent with the functional interactions identified. Finally, cultured Ku70 -/- calvarial cells exhibit a profound, selective deficiency in OC expression as compared with wild-type calvarial cells, confirming the biochemical data showing a role for Ku in OC transcription. In toto, these data indicate that a novel Ku antigen complex assembles on the OC promoter, functioning in concert with Msx2 and Runx2 to regulate OC gene expression.

Morphological and biological heterogeneity of three tumorigenic cell lines derived from a single p53-/- osteoblast-like cell line, MMC2

Osteosarcoma is a malignant tumor with heterogeneous features both in histological and biological aspects. We have established three tumorigenic cell lines, MMOS1, MMOS2, and MMOS3, from three independent tumors that developed in nude mice after the inoculation of MMC2, an osteoblast-like cell line derived from p53-/- mice. Expression patterns of the osteoblast-related genes showed a marked difference between MMOS2 and the other two cell lines, and were correlated well with the features of the original tumors, ranging from an osteoblastic osteosarcoma (MMOS2) to tumors with scarce or no osteoid formation (MMOS1 and MMOS3). The properties of malignant cells also varied in the three cell lines. MMOS1, which was the most serum-dependent in vitro, developed markedly larger tumors in vivo than the other two cell lines. MMOS3 showed the fastest growth in low-serum conditions and produced the largest number of colonies in soft agar, but did not develop lung metastases, whereas MMOS1 and MMOS2 developed lung metastases with a frequency of 30 and 50%. These data suggest that the biological activities in vivo do not necessarily reflect those in vitro. Because the three tumorigenic cell lines share MMC2 as a common precursor, our data showed an example that the heterogeneity of osteosarcoma was created by genetic alterations that took place during the transformation process of each tumor.

A mutant PTH/PTHrP type I receptor in enchondromatosis

Enchondromas are common benign cartilage tumors of bone. They can occur as solitary lesions or as multiple lesions in enchondromatosis (Ollier and Maffucci diseases). Clinical problems caused by enchondromas include skeletal deformity and the potential for malignant change to chondrosarcoma. The extent of skeletal involvement is variable in enchondromatosis and may include dysplasia that is not directly attributable to enchondromas. Enchondromatosis is rare, obvious inheritance of the condition is unusual and no candidate loci have been identified. Enchondromas are usually in close proximity to, or in continuity with, growth-plate cartilage. Consequently, they may result from abnormal regulation of proliferation and terminal differentiation of chondrocytes in the adjoining growth plate. In normal growth plates, differentiation of proliferative chondrocytes to post-mitotic hypertrophic chondrocytes is regulated in part by a tightly coupled signaling relay involving parathyroid hormone related protein (PTHrP) and Indian hedgehog (IHH). PTHrP delays the hypertrophic differentiation of proliferating chondrocytes, whereas IHH promotes chondrocyte proliferation. We identified a mutant PTH/PTHrP type I receptor (PTHR1) in human enchondromatosis that signals abnormally in vitro and causes enchondroma-like lesions in transgenic mice. The mutant receptor constitutively activates Hedgehog signaling, and excessive Hedgehog signaling is sufficient to cause formation of enchondroma-like lesions.

The retinoblastoma protein acts as a transcriptional coactivator required for osteogenic differentiation

The incidence of osteosarcoma is increased 500-fold in patients who inherit mutations in the RB gene. To understand why the retinoblastoma protein (pRb) is specifically targeted in osteosarcoma, we studied its function in osteogenesis. Loss of pRb but not p107 or p130 blocks late osteoblast differentiation. pRb physically interacts with the osteoblast transcription factor, CBFA1, and associates with osteoblast-specific promoters in vivo in a CBFA1-dependent fashion. Association of pRb with CBFA1 and promoter sequences results in synergistic transactivation of an osteoblast-specific reporter. This transactivation function is lost in tumor-derived pRb mutants, underscoring a potential role in tumor suppression. Thus, pRb functions as a direct transcriptional coactivator promoting osteoblast differentiation, which may contribute to the targeting of pRb in osteosarcoma.