Distribution of platelet-derived growth factor (PDGF) A chain mRNA, protein, and PDGF-alpha receptor in rapidly forming human bone

Spatial Organization of Osteoclastic Coupling Factors and Their Receptors at Human Bone Remodeling Sites

The strictly regulated bone remodeling process ensures that osteoblastic bone formation is coupled to osteoclastic bone resorption. This coupling is regulated by a panel of coupling factors, including clastokines promoting the recruitment, expansion, and differentiation of osteoprogenitor cells within the eroded cavity. The osteoprogenitor cells on eroded surfaces are called reversal cells. They are intermixed with osteoclasts and become bone-forming osteoblast when reaching a critical density and maturity. Several coupling factors have been proposed in the literature, but their effects and expression pattern vary between studies depending on species and experimental setup. In this study, we investigated the mRNA levels of proposed secreted and membrane-bound coupling factors and their receptors in cortical bone remodeling events within the femur of healthy adolescent human controls using high-sensitivity RNA in situ hybridization. Of the proposed coupling factors, human osteoclasts showed mRNA-presence of LIF, PDGFB, SEMA4D, but no presence of EFNB2, and OSM. On the other hand, the osteoblastic reversal cells proximate to osteoclasts presented with LIFR, PDGFRA and PLXNB1, but not PDGFRB, which are all known receptors of the proposed coupling factors. Although EFNB2 was not present in mature osteoclasts, the mRNA of the ligand-receptor pair EFNB2:EPHB4 were abundant near the central blood vessels within intracortical pores with active remodeling. EPHB4 and SEMA4D were also abundant in mature bone-forming osteoblasts. This study highlights that especially LIF:LIFR, PDGFB:PDGFRA, SEMA4D:PLXNB1 may play a critical role in the osteoclast-osteoblast coupling in human remodeling events, as they are expressed within the critical cells.

Altered bone development with impaired cartilage formation precedes neuromuscular symptoms in spinal muscular atrophy

Spinal muscular atrophy (SMA) is a fatal neurodegenerative disease of newborns and children caused by mutations or deletions of the survival of motoneuron gene 1 resulting in low levels of the SMN protein. While neuromuscular degeneration is the cardinal symptom of the disease, the reduction of the ubiquitously expressed SMN additionally elicits non-motoneuron symptoms. Impaired bone development is a key feature of SMA, but it is yet unknown whether this is an indirect functional consequence of muscle weakness or caused by bone-intrinsic mechanisms. Therefore, we radiologically examined SMA patients in a prospective, non-randomized cohort study characterizing bone size and bone mineral density (BMD) and performed equivalent measurements in pre-symptomatic SMA mice. BMD as well as lumbar vertebral body size were significantly reduced in SMA patients. This growth defect but not BMD reduction was confirmed in SMA mice by μCT before the onset of neuromuscular symptoms indicating that it is at least partially independent of neuromuscular degeneration. Interestingly, the number of chondroblasts in the hypertrophic zone of the growth plate was significantly reduced. This was underlined by RNAseq and expression data from developing SMA mice vertebral bodies, which revealed molecular changes related to cell division and cartilage remodeling. Together, these findings suggest a bone intrinsic defect in SMA. This phenotype may not be rescued by novel drugs that enhance SMN levels in the central nervous system only.

Prognostic effects of cytokine levels on patients treated with taxane and zoledronic acid for metastatic breast cancer in bone (BEAT-ZO) (KCSG BR 10-13)

Advanced breast cancer frequently metastasizes to the skeleton causing major mobility issues and hazards to quality of life. To manage osteolytic bone metastasis, bone-modifying agents and chemotherapy are recommended as the standard of care. Here, we investigated serologic biomarkers that might be associated with prognosis in breast cancer patients treated with zoledronic acid (ZA) and taxane-based chemotherapy. We collected serum samples from breast cancer patients with bone metastasis who received taxane plus ZA as palliative treatment. Fourteen biomarkers of angiogenesis, immunogenicity, and apoptosis were assessed, and the correlation between serum cytokine levels and patient's prognosis was statistically analyzed. Sixty-six patients were enrolled, and samples from 40 patients were analyzed after laboratory quality control. Patients with low baseline PDGF-AA, high IFN-γ, low MCP-2, low TGF-β1, and low TNF-α were significantly associated with longer progression-free survival (PFS). Decreasing VEGF and TNF-α and increasing FGF-2 and PDGF-AA in the early treatment phase indicated longer PFS. In univariate and multivariate analyses, low TGF-β1 and TNF-α and high IFN-γ at baseline were associated with a significantly low hazard ratio for disease progression. Further, we designed a risk score with TGF-β1, TNF-α, and IFN-γ levels, which could prognosticate patients for PFS. In conclusion, serum cytokine level, such as TGF-β1, TNF-α, and IFN-γ, could be a potential prognostic biomarker for breast cancer patients with bone metastasis treated with ZA and taxane-based chemotherapy.

Postnatal expression of chondrogenic and osteogenic regulatory factor mRNA in the rat condylar cartilage

OBJECTIVES

The condylar cartilage is a key site of growth and development of the mandible. The aim of this research was to determine the mRNA expression levels of a number of chondrogenic and osteogenic regulatory factors in the condylar cartilage of the postnatal rat.

MATERIALS AND METHODS

Condyles were extracted from 40 rats aged 4, 10, 21 or 90 days with 10 rats assigned to each age group. The condyles from one rat from each age group was fixed and decalcified in 10% EDTA for histology. Using cryogenic grinding combined with QIAzol reagent total RNA was purified from pooled samples collected for each age group. Each pool contained six condyles (N = 3). mRNA expression levels for 28 genes were determined using qPCR.

RESULTS

Histological analysis revealed distinct morphological differences in the condyle tissue of the 4, 10, 21 and 90 day old postnatal rats. Expression of all examined genes was detected. High levels of mRNA for Alpl, Bglap, Col1a1, Col2a1, Runx2, Sox9 and Sp7 but not Msx1 were detected. Fgf1 and Fgf2 were expressed at a similar level. No significant difference (defined as ± fold-regulation > 2 and P < 0.05) in the gene mRNA expression levels was found when days 10, 21 or 90 were compared to day 4.

CONCLUSIONS

Apparent morphological changes of the rat condylar cartilage are not reflected in a change in the expression levels of the chondrogenic and osteogenic regulatory factor mRNA investigated in this study.

Low plasma PDGF-BB levels are associated with estradiol in postmenopausal osteoporosis: PDGF-BB mediated by estradiol in women

Objective This study aimed to investigate the association between low plasma Platelet-derived growth factor-BB (PDGF-BB) levels and oestradiol in Postmenopausal osteoporosis (PMOP). Methods This prospective study measured plasma PDGF-BB and oestradiol levels in outpatients who were admitted to our hospital. Participants were screened and then allocated to three groups: normal young women, postmenopausal control, and PMOP. Additionally, Sprague-Dawley rats underwent either sham surgery or bilateral ovariectomy (OVX), and were divided into the following groups: sham, OVX, OVX + oestradiol, and OVX + PDGF-BB. Plasma oestradiol and PDGF-BB levels were measured using commercially available ELISA kits. Results A total of 121 participants, including 69 normal young women, 28 patients with primary PMOP, and 24 age-matched postmenopausal women were enrolled. Plasma oestradiol and PDGF-BB levels were lower in postmenopausal women, especially in PMOP ( P < 0.01). Pearson correlations analysis showed that PDGF-BB levels were positively correlated with oestradiol levels and inversely correlated with age ( P < 0.01). The OVX rat model showed that oestradiol replacement increased plasma PDGF-BB levels, while PDGF-BB systematic treatment had no effect on plasma oestradiol levels. Conclusions Plasma PDGF-BB levels are maintained by oestrogen in normal young women and play a major role in PMOP.

Regulation of osteoblast development by Bcl-2-associated athanogene-1 (BAG-1)

BCL-2-associated athanogene-1 (BAG-1) is expressed by osteoblast-lineage cells; early embryonic lethality in Bag-1 null mice, however, has limited the investigation of BAG-1 function in osteoblast development. In the present study, bone morphogenetic protein-2/BMP-2-directed osteogenic differentiation of bone marrow stromal cells (BMSCs) of Bag-1^+/− (heterozygous) female mice was decreased significantly. Genes crucial for osteogenic differentiation, bone matrix formation and mineralisation were expressed at significantly lower levels in cultures of Bag-1^+/− BMSCs supplemented with BMP-2, while genes with roles in inhibition of BMP-2-directed osteoblastogenesis were significantly upregulated. 17-β-estradiol (E2) enhanced responsiveness of BMSCs of wild-type and Bag-1^+/− mice to BMP-2, and promoted robust BMP-2-stimulated osteogenic differentiation of BMSCs. BAG-1 can modulate cellular responses to E2 by regulating the establishment of functional estrogen receptors (ERs), crucially, via its interaction with heat shock proteins (HSC70/HSP70). Inhibition of BAG-1 binding to HSC70 by the small-molecule chemical inhibitor, Thioflavin-S, and a short peptide derived from the C-terminal BAG domain, which mediates binding with the ATPase domain of HSC70, resulted in significant downregulation of E2/ER-facilitated BMP-2-directed osteogenic differentiation of BMSCs. These studies demonstrate for the first time the significance of BAG-1-mediated protein-protein interactions, specifically, BAG-1-regulated activation of ER by HSC70, in modulation of E2-facilitated BMP-2-directed osteoblast development.

Autologous Osteophyte Grafting for Open-Wedge High Tibial Osteotomy

Osteophytes are physiological bony outgrowths that develop at the margins of the articular surfaces during the progression of osteoarthritis; they are associated with active endochondral bone formation processes and expressions of various growth factors. We believe they could be a source of bone grafts as a result of a potentially strong osteoinductive effect. Moreover, osteophytes can be easily harvested by arthroscopy in patients undergoing open-wedge high tibial osteotomy (OW-HTO) for medial unicompartmental knee osteoarthritis. Therefore, we have been using osteophyte autografts for osteotomy gaps in OW-HTO with positive preliminary results indicating rapid bone healing of osteotomy sites. In this technical note, we introduce a technique for harvesting autologous osteophytes by arthroscopy and implanting them into the gap formed after OW-HTO. We expect that autologous osteophyte grafting can be a useful method for accelerating bone union and therefore enabling weight bearing from an early stage after surgery, which will lead to an early return to social activities.

Osteoblast-derived paracrine factors regulate angiogenesis in response to mechanical stimulation

Angiogenesis is a process by which new blood vessels emerge from existing vessels through endothelial cell sprouting, migration, proliferation, and tubule formation. Angiogenesis during skeletal growth, homeostasis and repair is a complex and incompletely understood process. As the skeleton adapts to mechanical loading, we hypothesized that mechanical stimulation regulates "osteo-angio" crosstalk in the context of angiogenesis. We showed that conditioned media (CM) from osteoblasts exposed to fluid shear stress enhanced endothelial cell proliferation and migration, but not tubule formation, relative to CM from static cultures. Endothelial cell sprouting was studied using a dual-channel collagen gel-based microfluidic device that mimics vessel geometry. Static CM enhanced endothelial cell sprouting frequency, whereas loaded CM significantly enhanced both frequency and length. Both sprouting frequency and length were significantly enhanced in response to factors released from osteoblasts exposed to fluid shear stress in an adjacent channel. Osteoblasts released angiogenic factors, of which osteopontin, PDGF-AA, IGBP-2, MCP-1, and Pentraxin-3 were upregulated in response to mechanical loading. These data suggest that in vivo mechanical forces regulate angiogenesis in bone by modulating "osteo-angio" crosstalk through release of paracrine factors, which we term "osteokines".

Platelet‑derived growth factor promotes osteoblast proliferation by activating G‑protein‑coupled receptor kinase interactor‑1

Platelet‑derived growth factor (PDGF) has been reported to stimulate bone fracture‑healing. Multiple studies have demonstrated that PDGF has a critical role in osteoblast or osteoprogenitor cell activation, although the underlying mechanism remains unclear. Studies have found that G‑protein‑coupled receptor kinase interactor‑1 (GIT1) is activated by PDGF and described as an important factor in bone metabolism. In the present study, the effects of PDGF and GIT1 on the proliferation and apoptosis of osteoblasts were investigated in cultured osteoblasts isolated from rat calvaria with PDGF stimulation and GIT1 small interfering RNA transfection. The results demonstrated that PDGF rapidly stimulated GTI1 expression in osteoblasts, increased osteoblast proliferation and inhibited cell apoptosis. Furthermore, cyclin D1 expression was significantly upregulated, the number of cells in the G0/G1 phase was decreased, while the number in the S phase was increased. In cells with knockdown of GIT1, the change stimulated by PDGF was not evident. The results indicate that, PDGF stimulated GIT1 activation of cyclin D1 expression, thereby promoting osteoblasts to enter the S phase from the stationary G0/G1 phase, leading to the proliferation of osteoblasts.

[Effect of intramedullary reaming and nailing on the production of growth factors in the femur fracture callus in rats]

INTRODUCTION

Many studies have been conducted to determine the different effects that reaming or intramedullary nailing have on fracture healing, but there is no evidence in the literature of the effect of intramedullary reaming on osteogenesis. We performed a prospective study to analyse the effect of intramedullary reaming and nailing on the production of growth factors during the process of fracture healing in the femur of rats.

MATERIAL AND METHODS

A transverse mid-shaft non-comminuted femur fracture was produced in 64 rats; 34 rats did not receive any treatment, and a standardized surgical procedure was performed on 30 rats, by exposing the left knee, reaming the medullary canal from distal to proximal, and then fixing the fracture with a steel pin. The rats were sacrificed at the 24th hour, 4th, 7th and 15th days after the fracture. The amount of growth factors that appeared in the callus fracture was measured using histopathology studies. The primary categorical variables analysed were PDGFA, TGF2 and TGFβ-R2. These variables were analysed in each group at the different sacrifice times.

RESULTS

The results of the primary variables of the study, stratified by the time until sacrifice, showed no statistically significant differences.

DISCUSSION

Even if the presence of an intramedullary wire facilitates the fracture repair and the stabilising the bridge of bone between both edges of the fracture site, no evidence was found that reaming changes the expression of the growth factors studied (PDGFA, TGFβ-R2 and TGFβ2) during the callus formation in rats.

Gene expression profiling of articular cartilage reveals functional pathways and networks of candidate genes for osteochondrosis in pigs

Osteochondrosis (OC) is a joint disorder that frequently causes leg weakness in growing pigs, resulting in welfare problems and economic losses. We aimed to detect molecular pathways relevant to the emergence of the disease and to identify candidate genes for the liability to the disorder. Therefore, we compared microarray-based expression patterns of articular cartilage with (n=11) and without (n=11) histologically diagnosed OC lesions obtained from discordant sib-pairs. A total of 1,564 genes were found with different transcript abundance [differentially expressed (DE) genes] at q≤0.05. To further identify candidate genes, we integrated data from quantitative trait loci (QTL) and genome-wide association (GWA) studies with the expression analysis. We detected 317 DE genes within the QTL confidence intervals, of which 26 DE genes also overlapped GWA regions. Ingenuity Pathway Analysis suggests a pathogenic role of immune response, angiogenesis, and synthesis of extracellular matrix pathways for OC. These processes could facilitate the emergence of defects. But they may also promote the degradation of articular cartilage and the worsening of the disease. A functional network was derived that comprised genes with functional and positional clues of their role in bone and cartilage metabolisms and development, including extracellular matrix genes (e.g., LOX, OGN, and ASPN), angiogenesis genes (e.g., ANGPTL4 and PDGFA), and immune response genes (e.g., ICAM1, AZGP1, C1QB, C1QC, PDE4B, and CDA). The study identified molecular processes linked to OC and several genes with positional, genetic-statistical, and functional evidence for their role in the emergence of articular cartilage lesions and the liability to OC.

Controlled release strategies for bone, cartilage, and osteochondral engineering--Part I: recapitulation of native tissue healing and variables for the design of delivery systems

The potential of growth factors to stimulate tissue healing through the enhancement of cell proliferation, migration, and differentiation is undeniable. However, critical parameters on the design of adequate carriers, such as uncontrolled spatiotemporal presence of bioactive factors, inadequate release profiles, and supraphysiological dosages of growth factors, have impaired the translation of these systems onto clinical practice. This review describes the healing cascades for bone, cartilage, and osteochondral interface, highlighting the role of specific growth factors for triggering the reactions leading to tissue regeneration. Critical criteria on the design of carriers for controlled release of bioactive factors are also reported, focusing on the need to provide a spatiotemporal control over the delivery and presentation of these molecules.

The mesenchymal stem cell marker CD248 (endosialin) is a negative regulator of bone formation in mice

OBJECTIVE

CD248 (tumor endothelial marker 1/endosialin) is found on stromal cells and is highly expressed during malignancy and inflammation. Studies have shown a reduction in inflammatory arthritis in CD248-knockout (CD248(-/-) ) mice. The aim of the present study was to investigate the functional effect of genetic deletion of CD248 on bone mass.

METHODS

Western blotting, polymerase chain reaction, and immunofluorescence were used to investigate the expression of CD248 in humans and mice. Micro-computed tomography and the 3-point bending test were used to measure bone parameters and mechanical properties of the tibiae of 10-week-old wild-type (WT) or CD248(-/-) mice. Human and mouse primary osteoblasts were cultured in medium containing 10 mM β-glycerophosphate and 50 μg/ml ascorbic acid to induce mineralization, and then treated with platelet-derived growth factor BB (PDGF-BB). The mineral apposition rate in vivo was calculated by identifying newly formed bone via calcein labeling.

RESULTS

Expression of CD248 was seen in human and mouse osteoblasts, but not osteoclasts. CD248(-/-) mouse tibiae had higher bone mass and superior mechanical properties (increased load required to cause fracture) compared to WT mice. Primary osteoblasts from CD248(-/-) mice induced increased mineralization in vitro and produced increased bone over 7 days in vivo. There was no decrease in bone mineralization and no increase in proliferation of osteoblasts in response to stimulation with PDGF-BB, which could be attributed to a defect in PDGF signal transduction in the CD248(-/-) mice.

CONCLUSION

There is an unmet clinical need to address rheumatoid arthritis-associated bone loss. Genetic deletion of CD248 in mice results in high bone mass due to increased osteoblast-mediated bone formation, suggesting that targeting CD248 in rheumatoid arthritis may have the effect of increasing bone mass in addition to the previously reported effect of reducing inflammation.

PDGFs and PDGFRs in canine osteosarcoma: new targets for innovative therapeutic strategies in comparative oncology

Platelet derived growth factor receptor (PDGFR)α and PDGFRβ are tyrosine kinase receptors that are overexpressed in 70-80% of human osteosarcomas (OSAs) and may be suitable therapeutic targets for specific kinase inhibitors (TKIs). Canine OSA shows histopathological and clinical features similar to human OSA, and is considered an excellent model in comparative oncology. This study investigated PDGF-A, PDGF-B, PDGFRα and PDGFRβ expression in 33 canine OSA samples by immunohistochemistry and in seven primary canine OSA cell lines by Western blot and quantitative PCR analysis. Immunohistochemical data showed that PDGF-A and PDGF-B are expressed in 42% and 60% of the OSAs analysed, respectively, while PDGFRα and PDGFRβ were expressed in 78% and 81% of cases, respectively. Quantitative PCR data showed that all canine OSA cell lines overexpressed PDGFRα, while 6/7 overexpressed PDGFRβ and PDGF-A relative to a normal osteoblastic cell line. Moreover, in vitro treatment with a specific PDGFR inhibitor, AG1296, caused a dose- and time-dependent decrease in AKT phosphorylation. Collectively, these data show that PDGFRs/PDGFs are co-expressed in canine osteosarcomas, which suggests that an autocrine and/or paracrine loop is involved and that they play an important role in the aetiology of OSA. PDGFRs may be suitable targets for the treatment of canine OSA with a specific TKI.

Receptor tyrosine kinase inhibition causes simultaneous bone loss and excess bone formation within growing bone in rats

During postnatal skeletal growth, adaptation to mechanical loading leads to cellular activities at the growth plate. It has recently become evident that bone forming and bone resorbing cells are affected by the receptor tyrosine kinase (RTK) inhibitor imatinib mesylate (STI571, Gleevec®). Imatinib targets PDGF, ABL-related gene, c-Abl, c-Kit and c-Fms receptors, many of which have multiple functions in the bone microenvironment. We therefore studied the effects of imatinib in growing bone. Young rats were exposed to imatinib (150mg/kg on postnatal days 5-7, or 100mg/kg on postnatal days 5-13), and the effects of RTK inhibition on bone physiology were studied after 8 and 70days (3-day treatment), or after 14days (9-day treatment). X-ray imaging, computer tomography, histomorphometry, RNA analysis and immunohistochemistry were used to evaluate bone modeling and remodeling in vivo. Imatinib treatment eliminated osteoclasts from the metaphyseal osteochondral junction at 8 and 14days. This led to a resorption arrest at the growth plate, but also increased bone apposition by osteoblasts, thus resulting in local osteopetrosis at the osteochondral junction. The impaired bone remodelation observed on day 8 remained significant until adulthood. Within the same bone, increased osteoclast activity, leading to bone loss, was observed at distal bone trabeculae on days 8 and 14. Peripheral quantitative computer tomography (pQCT) and micro-CT analysis confirmed that, at the osteochondral junction, imatinib shifted the balance from bone resorption towards bone formation, thereby altering bone modeling. At distal trabecular bone, in turn, the balance was turned towards bone resorption, leading to bone loss.

The systemic angiogenic response during bone healing

INTRODUCTION

Angiogenesis is known to be a critical and closely regulated step during bone formation and fracture healing driven by a complex interaction of various cytokines. Delays in bone healing or even nonunion might therefore be associated with altered concentrations of specific angiogenic factors. These alterations might in turn be reflected by changes in serum concentrations.

METHOD

To determine physiological time courses of angiogenic cytokines during fracture healing as well as possible changes associated with failed consolidation, we prospectively collected serum samples from patients who had sustained surgical treatment for a long bone fracture. Fifteen patients without fracture healing 4 months after surgery (nonunion group) were matched to a collective of 15 patients with successful healing (union group). Serum concentrations of angiogenin (ANG), angiopoietin 2 (Ang-2), basic fibroblast growth factor (bFGF), platelet derived growth factor AB (PDGF-AB), pleiotrophin (PTN) and vascular endothelial growth factor (VEGF) were measured using enzyme linked immunosorbent assays over a period of 24 weeks.

RESULTS

Compared to reference values of healthy uninjured controls serum concentrations of VEGF, bFGF and PDGF were increased in both groups. Peak concentrations of these cytokines were reached during early fracture healing. Serum concentrations of bFGF and PDGF-AB were significantly higher in the union group at 2 and 4 weeks after the injury when compared to the nonunion group. Serum concentrations of ANG and Ang-2 declined steadily from the first measurement in normal healing fractures, while no significant changes over time could be detected for serum concentrations of these factures in nonunion patients. PTN serum levels increased asymptotically over the entire investigation in timely fracture healing while no such increase could be detected during delayed healing.

CONCLUSION

We conclude that fracture healing in human subjects is accompanied by distinct changes in systemic levels of specific angiogenic factors. Significant alterations of these physiologic changes in patients developing a fracture nonunion over time could be detected as early as 2 (bFGF) and 4 weeks (PDGF-AB) after initial trauma surgery.

Sustained platelet-derived growth factor receptor alpha signaling in osteoblasts results in craniosynostosis by overactivating the phospholipase C-gamma pathway

The development and growth of the skull is controlled by cranial sutures, which serve as growth centers for osteogenesis by providing a pool of osteoprogenitors. These osteoprogenitors undergo intramembranous ossification by direct differentiation into osteoblasts, which synthesize the components of the extracellular bone matrix. A dysregulation of osteoblast differentiation can lead to premature fusion of sutures, resulting in an abnormal skull shape, a disease called craniosynostosis. Although several genes could be linked to craniosynostosis, the mechanisms regulating cranial suture development remain largely elusive. We have established transgenic mice conditionally expressing an autoactivated platelet-derived growth factor receptor alpha (PDGFRalpha) in neural crest cells (NCCs) and their derivatives. In these mice, premature fusion of NCC-derived sutures occurred at early postnatal stages. In vivo and in vitro experiments demonstrated enhanced proliferation of osteoprogenitors and accelerated ossification of osteoblasts. Furthermore, in osteoblasts expressing the autoactivated receptor, we detected an upregulation of the phospholipase C-gamma (PLC-gamma) pathway. Treatment of differentiating osteoblasts with a PLC-gamma-specific inhibitor prevented the mineralization of synthesized bone matrix. Thus, we show for the first time that PDGFRalpha signaling stimulates osteogenesis of NCC-derived osteoblasts by activating the PLC-gamma pathway, suggesting an involvement of this pathway in the etiology of human craniosynostosis.

Regulation of immature cartilage growth by IGF-I, TGF-beta1, BMP-7, and PDGF-AB: role of metabolic balance between fixed charge and collagen network

Cartilage growth may involve alterations in the balance between the swelling tendency of proteoglycans and the restraining function of the collagen network. Growth factors, including IGF-I, TGF-beta1, BMP-7, and PDGF-AB, regulate chondrocyte metabolism and, consequently, may regulate cartilage growth. Immature bovine articular cartilage explants from the superficial and middle zones were incubated for 13 days in basal medium or medium supplemented with serum, IGF-I, TGF-beta1, BMP-7, or PDGF-AB. Variations in tissue size, accumulation of proteoglycan and collagen, and tensile properties were assessed. The inclusion of serum, IGF-I, or BMP-7 resulted in expansive tissue growth, stimulation of proteoglycan deposition but not of collagen, and a diminution of tensile integrity. The regulation of cartilage metabolism by TGF-beta1 resulted in tissue homeostasis, with maintenance of size, composition, and function. Incubation in basal medium or with PDGF-AB resulted in small volumetric and compositional changes, but a marked decrease in tensile integrity. These results demonstrate that the phenotype of cartilage growth, and the associated balance between proteoglycan content and integrity of the collagen network, is regulated differentially by certain growth factors.

Lipopolysaccharide stimulation of human aortic valve interstitial cells activates inflammation and osteogenesis

BACKGROUND

Calcific aortic stenosis may be an inflammatory disease with active bone formation in the valve leaflets rather than a disease of passive calcium deposition. Epidemiologic data demonstrating correlation of poor dental hygiene to atherosclerotic pathologies suggests that circulating bacterial products could be involved in the pathogenesis of aortic valve stenosis. We hypothesized that lipopolysaccharide (LPS) stimulation of human aortic valve interstitial cells (HAVICs) would induce inflammatory and osteogenic gene expression.

METHODS

The HAVICs were isolated from normal aortic valves obtained from explanted hearts during transplantation (n = 5) and grown in culture. Cells underwent 4 and 24 hours of LPS stimulation (LPS, 200 ng/mL) or beta-glycerol phosphate treatment (BGP) (osteogenic media as positive control). Media was removed for interleukin (IL)-6 and IL-8 immunoassay. Ribonucleic acid was extracted for microarray analysis. Statistics were by analysis of variance with post-hoc analysis (p < 0.05).

RESULTS

The LPS stimulation induced the gene expression of proinflammatory cytokines, chemokines, and adhesion molecules. Protein level confirmation by immunoassay demonstrated 3.4-fold (+/- 0.35, p < 0.01) and 9.5-fold (+/- 1.5 p < 0.01) increase over control of IL-6 and IL-8, respectively. The LPS and BGP both induced critical mediators of osteogenesis including bone morphogenetic protein 2 and platelet-derived growth factor alpha.

CONCLUSIONS

The LPS stimulation of HAVICs not only induces inflammatory mediators but also induces gene expression of osteogenic factors, similar to that induced by osteogenic media. Bacterial products stimulation, likely by toll-like receptor 4 and the innate immune system, may contribute to the pathogenesis of aortic valve stenosis.

Mechanical signals modulated vascular endothelial growth factor-A (VEGF-A) alternative splicing in osteoblastic cells through actin polymerisation

Since VEGF-A is involved in mechanically induced bone gain and because vegf exists under 6 isoforms exerting various biological effects, we studied vegf isoform expression and VEGF protein production in osteoblastic cells (rat Ros17/2.8 and human osteoblasts) submitted to 4 mechanical regimens. Mechanical regimens (1% stretch deformation) were designed with a fixed number of cycles (450) delivered at various frequencies (0.05 to 5 Hz). We found a negative correlation (R(2)=0.76, p<0.0001) between production of soluble VEGF and mechanical stretch frequency and a positive correlation (R(2)=0.99, p<0.0001) between production of matrix-bound VEGF and mechanical stretch frequency. mRNA expressions of soluble VEGF isoforms (121, 165) were specifically expressed under low frequency while matrix-bound VEGF isoforms (206, 189, 165, 145) were specifically expressed under high frequency in human osteoblasts. As f-actin stress fiber formation was significantly increased selectively in high frequency conditions, we disrupted actin fibers in Ros17/2.8 and found that immobilisation of VEGF was abolished. Conversely, Jasplakinolide treatment which increases stress fiber formation was able to mimic high frequency stretch-induced immobilisation of VEGF. Thus, we speculate that the stretch-induced increase in cell tension is responsible for matrix-bound vegf isoform production. Mechanically induced selection of soluble or matrix-bound VEGF production may modify osteoblast and endothelial cell crosstalk crucial during osteogenesis and fracture healing.

Upregulation of VEGF in subchondral bone of necrotic femoral heads in rabbits with use of extracorporeal shock waves

Extracorporeal shock wave treatment appears to be effective in patients with avascular necrosis of the femoral head. However, the pathway of biological events whereby this is accomplished has not been fully elucidated. The purpose of this study was to investigate the effect of extracorporeal shock waves on vascular endothelial growth factor (VEGF) expression in necrotic femoral heads of rabbits. VEGF expression was assessed by immunohistochemistry, quantitative real-time PCR, and Western blot analysis. The degree of angiogenesis was also assessed, as determined by the microvessel density (MVD), the assessment of which was based on CD31-expressing vessels. Bilateral avascular necrosis of femoral heads was induced with methylprednisolone and lipopolysaccharide in 30 New Zealand rabbits. The left limb (the study side) received shock wave therapy to the femoral head. The right limb (the control side) received no shock wave therapy. Biopsies of the femoral heads were performed at 1, 2, 4, 8, and 12 weeks. Western blot analysis and real-time PCR showed that shock wave therapy significantly increased VEGF protein and mRNA expression, respectively, in the subchondral bone of the treated necrotic femoral heads. Compared with the contralateral control without shock wave treatment, the VEGF mRNA expression levels increased to a peak at 2 weeks after the shock wave treatment and remained high for 8 weeks, then declined at 12 weeks, whereas the VEGF protein expression levels increased to a peak at 4 weeks after the shock wave treatment and remained high for 12 weeks. The immunostaining of VEGF was weak in the control group, and the immunoreactivity level in the shock-wave-treated group increased at 4 weeks and persisted for 12 weeks. The most intensive VEGF immunoreactivity was observed in the proliferative zone above the necrotic zone. At 4, 8, and 12 weeks after the shock wave treatment, MVD in subchondral bone from treated femoral heads was significantly higher than that in subchondral bone from untreated femoral heads. These data clearly show that extracorporeal shock waves can significantly upregulate the expression of VEGF. The upregulation of VEGF may play a role in inducing the ingrowth of neovascularization and in improving the blood supply to the femoral head.

Up-regulation of bone morphogenetic protein receptor IB by growth factors enhances BMP-2-induced human bone cell functions

Bone morphogenetic proteins (BMP) stimulate osteoblast differentiation by signal transduction via three BMP receptors (BMPR-IA, -IB, and -II). Several growth factors, including transforming growth factor-beta1 (TGF-beta1), fibroblast growth factor-2 (FGF-2) and platelet-derived growth factor-AB (PDGF-AB), have also been shown to play an important part in osteogenesis. The mechanism underlying these activities is unclear, but these growth factors could modulate the BMP/BMPR pathway by up-regulating BMPR expression, thereby enhancing the osteogenic responses of bone cells to the BMP. In this study we have therefore examined the effects of TGF-beta1, FGF-2, and PDGF-AB on BMPR expression and BMP-2-mediated osteoblast functions in primary human bone cells. The results showed that although the ligand BMP-2 and growth factors had little effect on BMPR-IA and -II transcript expression, they significantly up-regulated BMPR-IB mRNA specifically. However, only the growth factors, but not the ligand BMP-2, increased the surface expression of the BMPR-IB antigen, which was found to be due to a differential effect of BMP-2 and the growth factors on the Smurf1/Smad6-induced breakdown process. Pre-incubation of the cells with the growth factors significantly augmented BMP-2-induced Smad1/5/8 phosphorylation, and Dlx5 expression ALP activity, compared with that of cells treated with BMP-2 alone. When cells were transfected with siRNA targeting BMPR-IB, the growth factors neither up-regulated BMPR-IB transcript expression nor enhanced BMP-2-induced Smad1/5/8 phosphorylation, Dlx5 expression and ALP activity. The results indicate that increased BMPR-IB by TGF-beta1, FGF-2, and PDGF-AB significantly enhances BMP-2-induced osteogenic functions in vitro, suggesting that they might positively modulate bone formation by up-regulating BMPR-IB in vivo.

Chemotactic Migration of Human Mesenchymal Stem Cells and MC3T3-E1 Osteoblast-Like Cells Induced by COS-7 Cell Line Expressing rhBMP-7

During bone development, remodeling, and repair, bone morphogenetic proteins (BMPs) induce the differentiation of mesenchymal progenitor cells (MPCs) that enter into the osteoblastic lineage, and enhance the recruitment of MPCs and osteogenic cells. The process of migration is believed to be regulated, in part, by growth factors stored within the bone matrix, which are released by bone resorption. In this study, primary human mesenchymal stem cells (hMSCs) and MC3T3-E1 osteoblasts were examined for chemotaxis in response to recombinant human BMP-7 (rhBMP-7) produced in COS-7 cells (co-culture system). In order to produce BMP-7 transfected cells (BTCs), which serve as suppliers of rhBMP-7 under in vitro culture conditions, the encoding DNA was transferred into the pTARGET expression vector and introduced into COS-7 cells by conventional genetic engineering techniques. In cell culture studies, the rhBMP-7 produced in BTCs stimulated the specific activity of ALP, the production of cAMP in response to PTH, and the synthesis of osteocalcin. Migration assays were conducted with a computer-aided time-lapse video-microscopy system, to allow the rapid and precise analysis of cell migration and for the dynamic measurement of cell position and morphology. The migration distance and speed of the MC3T3-E1 cells, or hMSCs, co-cultured with BTCs, using a band-type seeding method, were significantly increased (p < 0.001), compared to those of the MC3T3-E1 cells (or hMSCs) only. In conclusion, these studies revealed that rhBMP-7 plays a role in the migration of bone-forming cells, and that the co-culture model (co-culture of bone-forming cells with BMP-7-producing cells) using a computer-aided, time-lapse video-microscopy system, is useful for the chemotactic migration assay of other chemotactic growth factors.

Microvascular adaptation to growth in rat humeral head

The aim of this work is to investigate the growth of the vasculature in the rat humeral head cartilage after the initial development of the secondary ossification centre until the adult organization. Rats aging from 5 weeks to 12 months were used. Histological observations on humeral heads were implemented with morphometrical analysis. Subsequently, vascular corrosion cast, that permits a three-dimensional observation of the vasculature, were prepared and observed by scanning electron microscopy. In young animals the epiphysis contains thin bone trabeculae and most of the epiphysis is occupied by bone marrow spaces. With age, the bone trabeculae progressively enlarge up to double their thickness. The percentage of bone tissue increases from 33.6 to 58.6% of the entire epiphysis, while the bone marrow spaces tend to increase very little in their mean dimension. Vascular corrosion casts show that the epiphyseal microcirculation is well distinguished from that of the diaphysis, and arises from the vessels present in the capsule and the periosteal networks. In young animals the only capillaries are bone marrow sinusoids and few subchondral capillaries. In adult animals small vessels run between the clusters of sinusoids forming the trabecular circulation. Capillary sprouts from sinusoids are always observed both in the young and adult animals. Thus, in adult rats different proper microcirculatory districts can be distinguished in the epiphysis: (a) the sinusoidal network, that supplies the hematopoiesis of the bone marrow and the adjacent osteogenic tissue; (b) the bone tissue microcirculation, limited to small vessels that supply the metabolism and the remodelling of the bone tissue. The reported microvascular organization and its adaptation to the epiphyseal growth represent the morphological basis for understanding the reciprocal interaction among the different tissues in developing and adult rat epiphysis.

Cyclooxygenase-2 inhibition selectively attenuates bone morphogenetic protein-6 synthesis and bone formation during guided tissue regeneration in a rat model

OBJECTIVES

Bone formation during guided tissue regeneration is a tightly regulated process involving cells, extracellular matrix and growth factors. The aims of this study were (i) to examine the expression of cyclooxygenase-2 (COX-2) during bone regeneration and (ii) the effects of selective COX-2 inhibition on osseous regeneration and growth factor expression in the rodent femur model.

MATERIAL AND METHODS

A standardized transcortical defect of 5 x 1.5 mm was prepared in the femur of 12 male rats and a closed half-cylindrical titanium chamber was placed over the defect. The expression of COX-2 and of platelet-derived growth factor-B (PDGF-B), bone morphogenetic protein-6 (BMP-6) and insulin-like growth factor-I/II (IGF-I/II) was analyzed at Days 3, 7, 21 and 28 semiquantitatively by reverse transcriptase-polymerase chain reaction and immunohistochemistry. The effects of COX-2 inhibition by intraperitoneal injection of NS-398 (3 mg/kg/day) were analyzed in five additional animals sacrificed at Day 14.

RESULTS

Histomorphometry revealed that new bone formation occurred in the cortical defect area as well as in the supracortical region, i.e. region within the chamber by Day 7 and increased through Day 28. Immunohistochemical evidence of COX-2 and PDGF-B levels were observed early (i.e. Day 3) and decreased rapidly by Day 7. BMP-6 expression was maximal at Day 3 and slowly declined by Day 28. In contrast, IGF-I/II expression gradually increased during the 28-day period. Systemic administration NS-398 caused a statistically significant reduction (P<0.05) in new bone formation (25-30%) and was associated with a statistically significant reduction in BMP-6 protein and mRNA expression (50% and 65% at P<0.05 and P<0.01, respectively). PDGF-B mRNA or protein expression was not affected by NS-398 treatment.

CONCLUSION

COX-2 inhibition resulted in reduced BMP-6 expression and impaired osseous regeneration suggesting an important role for COX-2-induced signaling in BMP synthesis and new bone formation.

To go or not to go: Migration of human mesenchymal progenitor cells stimulated by isoforms of PDGF

The recruitment of mesenchymal progenitor cells (MPCs) and their subsequent differentiation to osteoblasts is mandatory for bone development, remodeling, and repair. To study the possible involvement of platelet-derived growth factor (PDGF) isoforms, primary human MPCs and osteogenic differentiated progenitor cells (dOB) were examined for chemotaxic response to homodimeric human platelet-derived growth factor AA, -BB, and heterodimeric PDGF-AB. The role of PDGF receptors was addressed by preincubation with PDGF receptor alpha and beta chain specific antibodies. Migration of MPCs, dOB, and primary osteoblasts (OB) was stimulated by the addition of rhPDGF-AA, rhPDGF-BB, and rhPDGF-AB. The effect was highest in MPCs and for rhPDGF-BB, and declining with osteogenic differentiation. Preincubation with the receptor alpha specific antibody decreased the CI to borderline values while pretreatment with the receptor beta specific antibody led to a complete loss of chemotactic response to PDGF isoforms. In control experiments, basal migration values and rhBMP-2 as well as rxBMP-4 induced chemotaxis of MPC were not influenced by the addition of receptor alpha or beta antibodies. Interestingly, without preincubation the parallel exposure of MPC to rhTGF-beta1 instantaneously leads to a selective loss of migratory stimulation by rhPDGF-AA. The chemotactic effect of PDGF isoforms for primary human MPCs and the influence of osteogenic differentiation suggest a functional role for recruitment of MPCs during bone development and remodeling. Moreover, these observations may be useful for novel approaches towards guided tissue regeneration or tissue engineering of bone.

Combined low-dose imatinib mesylate and paclitaxel lack synergy in an experimental model of extra-osseous hormone-refractory prostate cancer

OBJECTIVE

To determine the efficacy of low-dose imatinib mesylate (STI571) alone or combined with a taxane (paclitaxel) in inhibiting the growth of experimental extra-osseous hormone-refractory prostate cancer.

MATERIALS AND METHODS

Orthotopic PC3 prostate tumours were established in male severe combined-immunodeficient mice; on day 3 the mice were randomly assigned to one of four groups: paclitaxel 10 mg/kg intraperitoneally once a week; STI571 50 mg/kg once a day for 6/7 weekdays; combined paclitaxel and STI571; and vehicle-treated controls. On day 40, the primary prostate tumour and metastatic lymphadenopathy were removed and measured. Effects were correlated with tumour cell proliferation and microvessel density.

RESULTS

Paclitaxel reduced the mean tumour weight and volume by 21.3% (not significant) and 73.7% (P < 0.05), respectively, compared to controls, and reduced the number of lymph node metastases by 49.1% (P < 0.05) and mean lymph node size by 13.5% (not significant). Adding low-dose STI571 had a small additive effect on tumour weight and the incidence of lymph node metastases, but this was not significant compared to paclitaxel alone. STI571 alone did not inhibit tumour progression. Antitumour effects were associated with parallel changes in tumour cell proliferation with no significant changes in neo-angiogenesis.

CONCLUSION

Combined low-dose STI571 and paclitaxel had little synergy in this experimental model. Low-dose STI571 monotherapy was not effective in extra-osseous disease, apparently due to a site-specific failure to up-regulate beta-platelet-derived growth factor receptor expression in prostate cancer cells and associated tumour stroma.

Inhibition of Platelet-Derived Growth Factor Receptor Signaling Restricts the Growth of Human Breast Cancer in the Bone of Nude Mice

Purpose: Bone is a common site for breast cancer metastasis. Platelet-derived growth factor (PDGF) and PDGF receptors (PDGFR) are involved in the regulation of bone resorption. This study examined the effects of STI571 (imatinib mesylate), which inhibits PDGFR tyrosine kinase signaling, on the growth of human breast cancer cells in the bone of nude mice with consequent osteolysis.

Experimental Design: Human breast cancer MDA-MB-435 cells were injected into the tibia of female nude mice. Two weeks later the mice were treated with p.o. and injected water (control), daily p.o. STI571, weekly injection of paclitaxel, or daily STI571, plus weekly paclitaxel, for up to 8 weeks. Growth of tumors in bones and osteolysis were monitored by digital radiography and tumors were collected for histochemical analysis.

Results: Mice treated with STI571 or STI571 plus paclitaxel had smaller bone tumors with less lytic bone destruction than did mice treated with water or paclitaxel alone. The results of treatment with paclitaxel plus STI571 did not differ from those with STI571 alone. Immunohistochemistry showed that PDGF-A, PDGF-B, PDGFRα, and PDGFRβ were expressed in the bone tumors. STI571 treatment inhibited PDGFR phosphorylation in tumor cells and tumor-associated endothelial cells, coincident with increased apoptosis, reduced proliferation, and lower microvessel density in the tumors.

Conclusions: Activated PDGFRs are expressed by endothelial and tumor cells in breast cancer tumors growing in the bone of nude mice. Interfering with PDGFR signaling may be an approach to control the progressive growth of breast cancer cells and thus reduce bone lysis.

Development of the microcirculation of the secondary ossification center in rat humeral head

This work investigated the origin and development of microcirculation in the rat humeral head and the expression of vascular endothelial growth factor (VEGF) as a factor supporting the vascular growth and the development of the secondary ossification centers. Sixty rats aging 1, 3-4, 6-8, 11, and 21 days, 5 weeks, and 4 and 8 months were used. Samples of humeral head were collected for histology and immunohistochemistry for VEGF. Some animals were perfused with Mercox resin in order to obtain vascular corrosion casts (vcc) observed by scanning electron microscopy (SEM). No cartilage canals were present at birth. At 6 days postnatal, blood vessels coming from the perichondrium and the region near the capsule attachment invaded the cartilage; at 11 days postnatal, signs of calcification were present and within the third week some bone trabeculae were formed. Just before the vascular invasion of the epiphysis, a positive reaction for VEGF was localized in chondrocytes of the epiphyseal cartilage close to the capsule insertion. During the development and expansion of the secondary ossification center, VEGF expression was higher in chondrocytes but decreased when epiphysis was diffusely ossified. VEGF was expressed also by mesenchymal cells present in and around the fibrous tissue where the secondary ossification center will develop. SEM vcc confirmed that vessels penetrating into the epiphysis arose merely from the periosteal and the capsular networks, and vascular connections with the diaphyseal circulation were not evident. These observations demonstrated that VEGF production by chondrocytes begun some days after birth, supported the rapid vascular growth from the surrounding soft tissues, and was chronologically related to the development of the secondary ossification center in rat proximal humerus. Finally, the possible role of VEGF as mediator of angiogenesis and, at least indirectly, as a trigger factor also in the ossification and the bone remodeling of the secondary ossification centers has been discussed.

Increase of both angiogenesis and bone mass in response to exercise depends on VEGF

Physiological angiogenesis during bone remodeling is undefined. Treadmill-running rats displayed bone marrow angiogenesis concomitant with bone formation increase and resorption decrease and upregulation of VEGF and its R1 receptor mRNA in proximal tibia. VEGF blockade over 5 weeks of training fully prevented the exercise-induced bone mass gain.

INTRODUCTION

We investigated the role of vascular endothelial growth factor (VEGF) and angiogenesis in the osteogenic response to exercise.

MATERIALS AND METHODS

Nine-week-old male Wistar rats were treadmill-trained at 60% Vo(2max) for various periods. Bone and vascular histomorphometry was performed after 2- and 5-week experiments. On-line RT PCR for VEGF and its receptors R1 and R2 was done after a 10-day experiment. In the 5-week experiment, running rats received either a VEGF inhibitory antibody or a placebo.

RESULTS

After 2 weeks, tibial BMD did not change; however, vessel number in the proximal metaphysis increased by 20% in running versus sedentary rats. In running rats, vessel number correlated positively (r = 0.88) with bone formation rate and negatively (r = -0.85) with active resorption surfaces. After 10 days of training, upregulation of VEGF and VEGF receptor R1 mRNA was detected in periosteum and metaphyseal bone. VEGF blockade in 5-week trained rats fully prevented the exercise-induced increase in metaphyseal BMD (9%) and cancellous bone volume (BV/TV; 25%), as well as the increased vessel number (25%). In 5-week placebo-treated running rats, bone formation rate returned to initial values, whereas osteoclastic surfaces continued to decline compared with both sedentary and anti-VEGF-treated running rats.

CONCLUSION

VEGF signaling-mediated bone angiogenesis is tightly related to exercise-induced bone cellular uncoupling and is indispensable for bone gain induced by exercise.

BMP-2, BMP-4, and PDGF-bb stimulate chemotactic migration of primary human mesenchymal progenitor cells

For bone development, remodeling, and repair; the recruitment of mesenchymal progenitor cells (MPC) and their differentiation to osteoblasts is mandatory. The process of migration is believed to be regulated in part by growth factors stored within the bone matrix and released by bone resorption. In this study, primary human MPCs and to osteoblasts differentiated progenitor cells were examined for chemotaxis in response to human basic fibroblast growth factor (rhbFGF), human transforming growth factor beta 1 (rhTGF-beta1), human platelet derived growth factor bb (rhPDGF-bb), human bone morphogenetic protein-2 (rhBMP-2), and recombinant bone morphogenetic protein-4 of Xenopus laevis (rxBMP-4) from 0.001 to 1.0 ng/ml each. The results of migration were expressed as a chemotactic index (CI). Migration of primary human progenitor cells was stimulated by rhBMP-2, rxBMP-4, and rhPDGF-bb in a dose-dependent manner. The increase of CI was up to 3.5-fold for rhBMP-2, 3.6-fold for rxBMP-4, and up to 22-fold for rhPDGF-bb, whereas rhTGF-beta1 and rhbFGF did not stimulate cell migration in the concentration range tested. In contrast differentiated progenitor cells behave similar to primary human osteoblasts. RhBMP-2, rhPDGF-bb, and rhTGF-beta1 stimulated the migration from 2.2 to 2.4-fold each, while rxBMP-4 and rhbFGF reached only a CI of 1.7-1.6. The effect of rhBMP-2, rxBMP-4, and rhPDGF-bb as chemoattractive proteins for primary human MPC, including the change in response to growth factors after differentiation suggests a functional role for recruitment of MPCs during bone development and remodeling, as well as fracture healing.

Expression of bone morphogenetic proteins and cartilage-derived morphogenetic proteins during osteophyte formation in humans

Bone- and cartilage-derived morphogenetic proteins (BMPs and CDMPs), which are TGFbeta superfamily members, are growth and differentiation factors that have been recently isolated, cloned and biologically characterized. They are important regulators of key events in the processes of bone formation during embryogenesis, postnatal growth, remodelling and regeneration of the skeleton. In the present study, we used immunohistochemical methods to investigate the distribution of BMP-2, -3, -5, -6, -7 and CDMP-1, -2, -3 in human osteophytes (abnormal bony outgrowths) isolated from osteoarthritic hip and knee joints from patients undergoing total joint replacement surgery. All osteophytes consisted of three different areas of active bone formation: (1) endochondral bone formation within cartilage residues; (2) intramembranous bone formation within the fibrous tissue cover and (3) bone formation within bone marrow spaces. The immunohistochemistry of certain BMPs and CDMPs in each of these three different bone formation sites was determined. The results indicate that each BMP has a distinct pattern of distribution. Immunoreactivity for BMP-2 was observed in fibrous tissue matrix as well as in osteoblasts; BMP-3 was mainly present in osteoblasts; BMP-6 was restricted to young osteocytes and bone matrix; BMP-7 was observed in hypertrophic chondrocytes, osteoblasts and young osteocytes of both endochondral and intramembranous bone formation sites. CDMP-1, -2 and -3 were strongly expressed in all cartilage cells. Surprisingly, BMP-3 and -6 were found in osteoclasts at the sites of bone resorption. Since a similar distribution pattern of bone morphogenetic proteins was observed during embryonal bone development, it is suggested that osteophyte formation is regulated by the same molecular mechanism as normal bone during embryogenesis.

Expression of platelet-derived growth factor-AA is associated with tumor progression in osteosarcoma

Platelet-derived growth factors are secreted by mesenchymal cells. The homodimer platelet-derived growth factor-AA especially stimulates bone cells through interaction with the platelet-derived growth factor-alpha receptor homodimer. In this study we wanted to determine the expression of the receptor and its ligand in human osteosarcomas and to correlate the expression of platelet-derived growth factor-AA and -alpha receptor with clinicopathological parameters. Fifty-seven osteosarcomas were immunohistochemically analyzed for expression of platelet-derived growth factor-AA and platelet-derived growth factor-alpha receptor. Spearman's correlation coefficient revealed a strong correlation between the expression of platelet-derived growth factor-AA and platelet-derived growth factor-alpha receptor (r = 0.867). No differences were observed relative to gender, age, tumor stage, tumor location, and response to neoadjuvant chemotherapy between high or low platelet-derived growth factor-AA and platelet-derived growth factor-alpha receptor expression. High platelet-derived growth factor-AA expression correlated with tumor progression in univariate analysis (P = .0415; log-rank test), whereas platelet-derived growth factor-alpha receptor expression showed a trend toward a shorter disease-free survival, which failed to reach significance (P = .0627, log-rank test). In multivariate analysis, platelet-derived growth factor-AA expression remained a significant independent predictor of tumor progression (P = .021, Cox regression). Immunohistochemical analysis of platelet-derived growth factor-AA expression in osteosarcoma may be a useful marker of prognosis and may be considered as a possible target for novel therapeutic strategies.

Distribution of genes for parathyroid hormone (PTH)-related peptide, Indian hedgehog, PTH receptor and patched in the process of experimental spondylosis in mice

OBJECT

Little is known about the molecular mechanisms underlying the process of spondylosis. The authors determined the extent of genetic localization of major regulators of chondrogenesis such as Indian hedgehog (Ihh) and parathyroid hormone (PTH)-related peptide (PTHrP) and their receptors during the development of spondylosis in their previously established experimental mouse model.

METHODS

Experimental spondylosis was induced in 5-week-old ICR mice. The cervical spines were chronologically harvested, and histological sections were prepared. Messenger (m) RNA for PTHrP, Ihh, PTH receptor (PTHR; a receptor for PTHrP), patched (Ptc; a receptor for Ihh), bone morphogenetic protein (BMP)-6, and collagen type X (COL10; a marker for mature chondrocyte) was localized in the tissue sections by performing in situ hybridization. In the early stage, mRNA for COL10, Ihh, and BMP-6 was absent; however, mRNA for PTHrP, PTHR, and Ptc was detected in the anterior margin of the cervical discs. In the late stage, evidence of COL10 mRNA began to be detected, and transcripts for Ihh, PTHrP, and BMP-6 were localized in hypertrophic chondrocytes adjacent to the bone-forming area in osteophyte. Messenger RNA for Ptc and PTHR continued to localize at this stage. In control mice, expression of these genes was absent.

CONCLUSIONS

The localization of PTHrP, Ihh, BMP-6, and the receptors PTHR and Ptc demonstrated in the present experimental model indicates the possible involvement of molecular signaling by PTHrP (through the PTHR), Ihh (through the Ptc), and BMP-6 in the regulation of chondrocyte maturation leading to endochondral ossification in spondylosis.

Platelet-derived growth factor-alpha receptor expression supports the growth of conventional chondrosarcoma and is associated with adverse outcome

Bone cells are important targets of platelet-derived growth factors (PDGFs) because they stimulate proliferation of osteoblasts and chondrocytes. In this study we wanted to determine the expression of PDGF-AA and PDGF-alpha receptor in conventional chondrosarcomas and to compare the results with those obtained from benign enchondromas and non-neoplastic cartilage tissue. Sixty-seven chondrosarcomas, 20 enchondromas, and 5 specimens of healthy cartilage as well as 7 specimens of hypertrophic callus cartilage were immunohistochemically analyzed for the expression of PDGF-AA and PDGF-alpha receptor, respectively. Additionally, the proliferation activity was examined with the MIB-1 antibody. Clinical follow-up data were available from 53 patients. A significant overexpression of receptor and factor was found in chondrosarcomas as compared with enchondromas (PDGF-AA p = 0.013, PDGF-alpha receptor p <0.001). MIB-1 values were significantly higher in chondrosarcomas (p <0.001). In healthy joint cartilage no staining was detectable, whereas reactive cartilage of callus formation showed high expression levels. PDGF-alpha receptor expression was significantly higher in grade 3 chondrosarcomas compared with grade 2 (p = 0.022) and grade 1 tumors (p = 0.002). Survival analysis documented a significantly shorter overall survival for patients with high PDGF-alpha receptor expression (p = 0.0172, log-rank test). Because PDGF-alpha receptor expression positively correlates with the aggressiveness of chondrosarcoma, it may be considered as a possible target for novel therapeutic strategies.

Mechanisms by which high-dose estrogen therapy produces anabolic skeletal effects in postmenopausal women: role of locally produced growth factors

Conventional hormone replacement therapy acts primarily by preserving bone, but cannot restore lost bone in women with established osteoporosis. Studies in rodents have shown that high doses of estrogens have anabolic skeletal effects, and recent observations in a group of women treated long term with high doses of estrogen indicated that similar effects occur in humans. This study examines the hypothesis that locally produced growth factors, including transforming growth factor-beta (TGF-beta) and platelet-derived growth factors (PDGFs), are involved in mediating the anabolic effects of high-dose estrogen. Transiliac-crest bone biopsies were taken from ten women, aged 52-67 years (mean 58 years), who had been treated with high-dose estrogen for 15 years. Control samples were obtained from four age-matched postmenopausal women not receiving estrogen therapy. TGF-betas and PDGFs were analyzed for mRNA and protein expression by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. Results showed both TGF-beta1 and -beta2 mRNA, expressed as a ratio to GAPDH, were increased in the estrogen-treated group with an eightfold increase for TGF-beta1 (0.258 +/- 0.246 [mean +/- SD] vs. 0.032 +/- 0.053 in the control group, p = 0.02) and a twofold increase for TGF-beta2 (p = n.s.). TGF-beta3 analysis showed only negligible amounts in both groups. Protein expression levels for TGF-beta1, -beta2, -betaRI and -RII were higher in the estrogen-treated group than in controls, the most marked effects being seen for TGF-beta1. PDGF-A protein expression was also significantly higher in osteoblasts and osteocytes in women treated with estrogen, whereas PDGF-B showed only modest differences. The percentage of bone surface occupied by osteoclasts, as determined by tartrate-resistant acid phosphatase (TRAP) staining, was significantly reduced in the estrogen-treated group (p = 0.001). These results demonstrate that high-dose estrogen therapy is associated with increased TGF-beta, TGF-betaR, and PDGF synthesis and decreased osteoclast activity, consistent with the hypothesis that these growth factors may mediate the actions of estrogen in bone.

Gene and protein expression of brain-derived neurotrophic factor and TrkB in bone and cartilage

Gene and protein expressions of brain-derived neurotrophic factor (BDNF) and TrkB, the high-affinity receptor of BDNF, were investigated in the femur and mandibular condyle of rats by in situ hybridization and immunohistochemistry. BDNF and TrkB mRNA showed overlapped expression in chondrocytes in proliferating and mature zones of the epiphyseal growth plate cartilage and mandibular condylar cartilage, and in cuboidal-shaped active osteoblasts at the site of endochondral and intramembranous ossification and in trabecular bone. Expression of BDNF protein also showed a similar localization. The present study suggests that BDNF may participate in regulating the development and remodeling of bony tissue in the developing rat.

Distribution of genes for bone morphogenetic protein-4, -6, growth differentiation factor-5, and bone morphogenetic protein receptors in the process of experimental spondylosis in mice

OBJECT

Because little is known about the molecular mechanisms underlying the process of spondylosis, the authors examined the extent of genetic localization of several members of bone morphogenetic protein (BMP) and BMP receptors in chondrogenesis during the process of inducing spondylosis in their previously established experimental mice model.

METHODS

Experimental spondylosis was induced in 5-week-old ICR mice. The cervical spine was harvested chronologically, and histological sections were prepared. Messenger RNA for BMP-4, growth and differentiation (GDF)-5, BMP-6, and BMP receptors (ALK-3, -6, and BMP-RII) was localized in the tissue sections by in situ hybridization. In the early stage, BMP-4-derived mRNA was localized mainly in cells in the anterior margin of the cervical discs, together with ALK-6 and BMP-RII mRNA. No GDF-5 and BMP-6 mRNA was detected at this stage. In the late stage, cells positive for BMP-4 decreased, whereas GDF-5 and BMP-6 mRNA were localized in cells undergoing chondrogenesis. The ALK-3 mRNA began to appear in this stage, as did ALK-6 and BMP-RII.

CONCLUSIONS

The localization of transcripts for BMP-4, -6, and GDF-5 as well as BMP receptors shown during the present experimental model indicate the possible involvement of molecular signaling by these BMPs in the chondrogenic progress in spondylosis.

Platelet-derived growth factor (PDGF)-AA: a self-imposed cytokine in the proliferation of human fetal osteoblasts

PDGF, a multiple mitogen, stimulates osteoblast replication and bone collagen degradation, and it has been described as a key factor in bone metabolism. Recently, PDGF was disclosed to be the autocrine cytokine of human osteoblasts. PDGF's effect on human bone development needs elucidation, and the mechanism of PDGF-AA autocrining remains unclear. In this work, osteoblasts were isolated from human fetal calvaria which resemble the cells in developing bone tissue. Using an in vitro model, the effect of PDGF-AA on the cells was investigated with the results showing that (i) after PDGF-AA was added into the medium for 24 h, PCI of the cells increased by 48.2% (P<0.05), and PCI decreased after the removal of PDGF-AA. (ii) 24 h after treatment with PDGF-AA, the percentage of osteoblasts in G(0)/G(1)phase decreased and that in S phase increased. (iii) The expression of PDGF-A mRNA was upregulated by PDGF-AA, PDGF-BB, TGFbeta,and bFGF respectively. These results proved that: (i) PDGF-AA enhances cell replication by accelerating cell recycle and inducing the quiescent cells into the proliferation portion of cell cycle. (ii) PDGF-AA is a self-imposed cytokine in human fetal osteoblast replication.

Platelet-derived growth factor-AA and -alpha receptor expression suggests an autocrine and/or paracrine loop in osteosarcoma

Platelet-derived growth factor (PDGF) is a major mitogen and chemotactic factor for mesenchymal cells such as fibroblasts, smooth muscle cells, and osteoblasts. PDGF exists as disulfide-linked homo- or heterodimers composed of two polypeptide chains encoded by distinct genes, designated PDGF-A and PDGF-B. Upon binding to its tyrosine kinase receptor PDGF-alpha, especially PDGF-AA stimulates the proliferation of osteoblastic cells and may exert autocrine and paracrine effects in regulating bone-forming processes. The purpose of this immunohistochemical study was to determine the expression of PDGF-AA and PDGF-alpha receptor in benign and malignant neoplastic bone lesions. Polyclonal antibodies to PDGF-AA and PDGF-alpha receptor were used on paraffin sections of 23 osteosarcomas and 17 osteoblastomas. Immunostaining was assessed quantitatively by evaluating the percentage of reactive tumor cells. In osteosarcomas, the mean expression of PDGF-AA and PDGF-alpha receptor was 33.97% (range, 2 to 80%; SD, 24.26%) and 27.13% (range, 3.2 to 72%; SD, 18.38%), respectively. Osteoblastomas showed significantly lower expression of PDGF-AA than osteosarcomas (mean, 15.71%; range, 5 to 34%; SD, 9.43%; P = .019). Although the mean expression of PDGF-alpha receptor in osteoblastomas was much lower than in osteosarcomas (mean, 17.55%; range, 3.6 to 26.8%; SD, 6.47%), the difference was not significant (P = .122). For osteosarcomas, Spearman correlation coefficient (two-tailed) revealed a significant correlation between the expression of PDGF-AA and PDGF-alpha receptor (r = .688), which was not the case for osteoblastomas (r = .267). These data suggest that in contrast to osteoblastoma, the growth of osteosarcoma may be supported by the coordinate expression of the potent mitogenic growth factor and its receptor that exert their functions by autocrine and paracrine mechanisms.

Quantification of growth factor levels using a simplified method of platelet-rich plasma gel preparation

PURPOSE

This study compared two methods of preparing platelet-rich plasma (PRP) gel and the levels of PDGF and TGFbeta in each preparation.

MATERIALS AND METHODS

Platelet-rich plasma gel was prepared by centrifugation and clotted using the ITA gelling agent (Natrex Technologies Inc, Greenville, NC) or by the addition of thrombin and calcium chloride. The levels of platelet-derived growth factor (PDGF) and transforming growth factor beta (TGFbeta) generated by clot formation were assayed by enzyme-linked immunoassay (ELISA).

RESULTS

Both methods of preparation yielded PRP gel in less than 30 minutes. However, the ITA preparation did not require thrombin to achieve adequate gel formation. The levels of PDGF and TGFbeta were similar regardless of which method was used for initiation of clot formation.

CONCLUSION

Use of ITA for gel preparation is equivalent to using calcium chloride and thrombin, without the need for special equipment and the risk of coagulopathy.

Effects of ultrasound and 1,25-dihydroxyvitamin D3 on growth factor secretion in co-cultures of osteoblasts and endothelial cells

It has been shown that low-intensity pulsed ultrasound (US) accelerates fracture healing in animal models and in clinical studies. However, the mechanism by which US accelerates fracture healing remains unclear. Systemic factors and several growth factors, such as platelet-derived growth factor (PDGF), are thought to be involved in the process of fracture healing. In the present study, we examined the effects of US and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on growth factor secretion in a co-culture system of human osteoblastic cells (SaOS-2) and endothelial cells (HUVEC). US was applied to cultured cells for 20 min daily for four consecutive days. US treatment increased the PDGF-AB level in the conditioned media. 1,25-(OH)2D3 (1 x 10(-8) M) also enhanced PDGF-AB secretion. The secretion of PDGF-AB was synergistically increased by the combination of US and 1,25-(OH)2D3. These results suggest that the stimulation of growth factor secretion from cells by US and 1,25-(OH)2D3 treatment may be involved in the acceleration of fracture healing.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Immunolocalisation of vascular endothelial growth factor (VEGF) in human neonatal growth plate cartilage

Angiogenesis is essential for the replacement of cartilage by bone during growth and repair. In order to obtain a better understanding of the mechanisms regulating vascular invasion at sites of endochondral ossification we have investigated the expression of the endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF), by chondrocytes in human neonatal growth plates. VEGF was absent from chondrocytes in the resting zone and only weakly expressed by occasional chondrocytes in the proliferating region. In the hypertrophic zone the number of chondrocytes stained and the intensity of staining for VEGF increased with chondrocyte hypertrophy, maximum expression of VEGF being observed in chondrocytes in the lower hypertrophic and mineralised regions of the cartilage. These observations provide the first demonstration of the presence of VEGF in situ in developing human bone and are consistent with in vitro observations demonstrating the upregulation of proangiogenic growth factor production with increasing chondrocyte hypertrophy. The presence of numerous small blood vessels and vascular structures in the subchondral region where VEGF expression was maximal indicates that VEGF produced by hypertrophic chondrocytes may play a key role in the regulation of vascular invasion of the growth plate.