PCR phenotyping of cytokines, growth factors and their receptors and bone matrix proteins in human osteoblast-like cell lines

Layer-by-layer assembly of nanotheranostic particles for simultaneous delivery of docetaxel and doxorubicin to target osteosarcoma

Osteosarcoma (OS) is a rare form of primary bone cancer, impacting approximately 3.4 × 106 individuals worldwide each year, primarily afflicting children. Given the limitations of existing cancer therapies, the emergence of nanotheranostic platforms has generated considerable research interest in recent decades. These platforms seamlessly integrate therapeutic potential of drug compounds with the diagnostic capabilities of imaging probes within a single construct. This innovation has opened avenues for enhanced drug delivery to targeted sites while concurrently enabling real-time monitoring of the vehicle's trajectory. In this study, we developed a nanotheranostic system employing the layer-by-layer (LbL) technique on a core containing doxorubicin (DOXO) and in-house synthesized carbon quantum dots. By utilizing chitosan and chondroitin sulfate as polyelectrolytes, we constructed a multilayered coating to encapsulate DOXO and docetaxel, achieving a coordinated co-delivery of both drugs. The LbL-functionalized nanoparticles exhibited an approximate size of 150 nm, manifesting a predominantly uniform and spherical morphology, with an encapsulation efficiency of 48% for both drugs. The presence of seven layers in these systems facilitated controlled drug release over time, as evidenced by in vitro release tests. Finally, the impact of the LbL-functionalized nanoparticles was evaluated on U2OS and Saos-2 osteosarcoma cells. The synergistic effect of the two drugs was found to be crucial in inducing cell death, particularly in Saos-2 cells treated with nanoparticles at concentrations higher than 10 μg/ml. Transmission electron microscopy analysis confirmed the internalization of the nanoparticles into both cell types through endocytic mechanisms, revealing an underlying mechanism of necrosis-induced cell death.

Invasion and Secondary Site Colonization as a Function of In Vitro Primary Tumor Matrix Stiffness: Breast to Bone Metastasis

Increased breast tissue stiffness is correlated with breast cancer risk and invasive cancer progression. However, its role in promoting bone metastasis, a major cause of mortality, is not yet understood. It is previously identified that the composition and stiffness of alginate-based hydrogels mimicking normal (1-2 kPa) and cancerous (6-10 kPa) breast tissue govern phenotype of breast cancer cells (including MDA-MB-231) in vitro. Here, to understand the causal effect of primary tumor stiffness on metastatic potential, a new breast-to-bone in vitro model is described. Together with alginate-gelatin hydrogels to mimic breast tissue, 3D printed biohybrid poly-caprolactone (PCL)-composite scaffolds, decellularized following bone-ECM deposition through Saos-2 engraftment, are used to mimic the bone tissue. It is reported that higher hydrogel stiffness results in the increased migration and invasion capacity of MDA-MB 231 cells. Interestingly, increased expression of osteolytic factors PTHrP and IL-6 is observed when MDA-MB-231 cells pre-conditioned in stiffer hydrogels (10 kPa, 3% w/v gelatin) colonize the bone/PCL scaffolds. The new breast-to-bone in vitro models herein described are designed with relevant tissue microenvironmental factors and could emerge as future non-animal technological platforms for monitoring metastatic processes and therapeutic efficacy.

Biological Response to Bioinspired Microporous 3D-Printed Scaffolds for Bone Tissue Engineering

The scaffold is a key element in the field of tissue engineering, especially when large defects or substitutions of pathological tissues or organs need to be clinically addressed. The expected outcome is strongly dependent on the cell–scaffold interaction and the integration with the surrounding biological tissue. Indeed, mimicking the natural extracellular matrix (ECM) of the tissue to be healed represents a further optimization that can limit a possible morphological mismatch between the scaffold and the tissue itself. For this aim, and referring to bone tissue engineering, polylactic acid (PLA) scaffolds were 3D printed with a microstructure inspired by the trabecular architecture and biologically evaluated by means of human osteosarcoma SAOS-2 cells. The cells were seeded on two types of scaffolds differing for the designed pore size (i.e., 400 and 600 µm), showing the same growth exponential trend found in the control and no significant alterations in the actin distribution. The microporous structure of the two tested samples enhanced the protein adsorption capability and mRNA expression of markers related to protein synthesis, proliferation, and osteoblast differentiation. Our findings demonstrate that 3D-printed scaffolds support the adhesion, growth, and differentiation of osteoblast-like cells and the microporous architecture, mimicking the natural bone hierarchical structure, and favoring greater bioactivity. These bioinspired scaffolds represent an interesting new tool for bone tissue engineering and regenerative medicine applications.

β-catenin mediates fluoride-induced aberrant osteoblasts activity and osteogenesis

Excess fluoride in drinking water is an environmental issue of increasing worldwide concern, because of its adverse effect on human health. Skeletal fluorosis caused by chronic exposure to excessive fluoride is a metabolic bone disease characterized by accelerated bone turnover accompanied by aberrant activation of osteoblasts. It is not clear whether Wnt/β-catenin signaling, an important signaling pathway regulating the function of osteoblasts, mediates the pathogenesis of skeletal fluorosis. A cross-sectional case-control study was conducted in Tongyu County, Jilin Province, China showed that fluoride stimulated the levels of OCN and OPG, resulting in accelerated bone turnover in patients with skeletal fluorosis. To investigate the influence of fluoride on Wnt/β-catenin signaling pathway, 64 male BALB/c mice were allotted randomly to four groups and treated with deionized water containing 0, 55, 110 and 221 mg/L NaF for 3 months, respectively. The results demonstrated that fluoride significantly increased mouse cancellous bone formation and the protein expression of Wnt3a, phospho-GSK3β (ser 9) and Runx2. Moreover, partial correlation analysis indicated that there was no significant correlation between fluoride exposure and Runx2 protein levels, after adjusting for β-catenin, suggesting that β-catenin might play a crucial role in fluoride-induced aberrant osteogenesis. In vivo, viability of SaoS2 cells was significantly facilitated by 4 mg/L NaF, and fluoride could induce the abnormal activation of Wnt/β-catenin signaling, the expression of its target gene Runx2 and significantly increased Tcf/Lef reporter activity. Importantly, inhibition of β-catenin suppressed fluoride-induced Runx2 protein expression and the osteogenic phenotypes. Taken together, the present study provided in vivo and in vitro evidence reveals a potential mechanism for fluoride-induced aberrant osteoblast activation and indicates that β-catenin is the pivot molecule mediating viability and differentiation of osteoblasts and might be a therapeutic target for skeletal fluorosis.

Expression dynamics of integrin α2, α3, and αV upon osteogenic differentiation of human mesenchymal stem cells

Background

The differentiation of human mesenchymal stem cells (hMSCs) into osteoblasts (OBs) is a prerequisite for bone formation. However, little is known about the definitive surface markers for OBs during osteogenesis.

Methods

To study the surface markers on OBs, we generated and used monoclonal antibodies (MAbs) against surface molecules on transforming growth factor-β1 (TGF-β1)-treated cancer cells. The generated MAbs were further selected toward expression changes on hMSCs cultured with TGF-β1/bone morphogenetic protein-2 (BMP-2) or osteogenic differentiation medium (ODM) by flow cytometry. Immunoprecipitation and mass spectrometry were performed to identify target antigens of selected MAbs. Expression changes of the target antigens were evaluated in hMSCs, human periodontal ligament cells (hPDLCs), and human dental pulp cells (hDPCs) during osteogenic and adipogenic differentiation by quantitative polymerase chain reaction (qPCR) and flow cytometry. hMSCs were also sorted by the MAbs using magnetic-activated cell sorting system, and osteogenic potential of sorted cells was evaluated via Alizarin Red S (ARS) staining and qPCR.

Results

The binding reactivity of MR14-E5, one of the MAbs, was downregulated in hMSCs with ODM while the binding reactivity of ER7-A7, ER7-A8, and MR1-B1 MAbs was upregulated. Mass spectrometry and overexpression identified that MR14-E5, ER7-A7/ER7-A8, and MR1-B1 recognized integrin α2, α3, and αV, respectively. Upon osteogenic differentiation of hMSCs, the expression of integrin α2 was drastically downregulated, but the expression of integrin α3 and αV was upregulated in accordance with upregulation of osteogenic markers. Expression of integrin α3 and αV was also upregulated in hPDLCs and hDPCs during osteogenic differentiation. Cell sorting showed that integrin αV-high hMSCs have a greater osteogenic potential than integrin αV-low hMSCs upon the osteogenic differentiation of hMSCs. Cell sorting further revealed that the surface expression of integrin αV is more dramatically induced even in integrin αV-low hMSCs.

Conclusion

These findings suggest that integrin α3 and αV induction is a good indicator of OB differentiation. These findings also shed insight into the expression dynamics of integrins upon osteogenic differentiation of hMSCs and provide the reason why different integrin ligands are required for OB differentiation of hMSCs.

Lycopene and bone: an in vitro investigation and a pilot prospective clinical study

Background

There are several effective therapies for osteoporosis but these agents might cause serious adverse events. Lycopene intake could prevent bone loss, however studies on its effects on bone are scarce. Our aim was to investigate the effects of lycopene on osteoblast cells as well as bone mineral density and bone turnover markers in postmenopausal women.

Methods

We investigated the effect of lycopene on the Wnt/β-catenin and ERK 1/2 pathways, RUNX2, alkaline phosphatase, RANKL and COL1A of Saos-2. We also carried out a pilot controlled clinical study to verify the feasibility of an approach for bone loss prevention through the intake of a lycopene-rich tomato sauce in 39 postmenopausal women.

Results

Lycopene 10 µM resulted in higher β-catenin and phERK1/2 protein Vs the vehicle (p = 0.04 and p = 0.006). RUNX2 and COL1A mRNA was induced by both 5 and 10 µM doses (p = 0.03; p = 0.03 and p = 0.03; p = 0.05) while RANKL mRNA was reduced (p < 0.05). A significant bone density loss was not detected in women taking the tomato sauce while the control group had bone loss (p = 0.002). Tomato sauce intake resulted in a greater bone alkaline phosphatase reduction than the control (18% vs 8.5%, p = 0.03).

Conclusions

Lycopene activates the WNT/β-catenin and ERK1/2 pathways, upregulates RUNX2, alkaline phosphatase, COL1A and downregulates RANKL Saos-2. These processes contributed to prevent bone loss in postmenopausal women.

Bile acids and bilirubin effects on osteoblastic gene profile. Implications in the pathogenesis of osteoporosis in liver diseases

Osteoporosis in advanced cholestatic and end-stage liver disease is related to low bone formation. Previous studies have demonstrated the deleterious consequences of lithocholic acid (LCA) and bilirubin on osteoblastic cells. These effects are partially or completely neutralized by ursodeoxycholic acid (UDCA). We have assessed the differential gene expression of osteoblastic cells under different culture conditions. The experiments were performed in human osteosarcoma cells (Saos-2) cultured with LCA (10 μM), bilirubin (50 μM) or UDCA (10 and 100 μM) at 2 and 24 h. Expression of 87 genes related to bone metabolism and other signalling pathways were assessed by TaqMan micro fluidic cards. Several genes were up-regulated by LCA, most of them pro-apoptotic (BAX, BCL10, BCL2L13, BCL2L14), but also MGP (matrix Gla protein), BGLAP (osteocalcin), SPP1 (osteopontin) and CYP24A1, and down-regulated bone morphogenic protein genes (BMP3 and BMP4) and DKK1 (Dickkopf-related protein 1). Parallel effects were observed with bilirubin, which up-regulated apoptotic genes and CSF2 (colony-stimulating factor 2) and down-regulated antiapoptotic genes (BCL2 and BCL2L1), BMP3, BMP4 and RUNX2. UDCA 100 μM had specific consequences since differential expression was observed, up-regulating BMP2, BMP4, BMP7, CALCR (calcitonin receptor), SPOCK3 (osteonectin), BGLAP (osteocalcin) and SPP1 (osteopontin), and down-regulating pro-apoptotic genes. Furthermore, most of the differential expression changes induced by both LCA and bilirubin were partially or completely neutralized by UDCA. Conclusion: Our observations reveal novel target genes, whose regulation by retained substances of cholestasis may provide additional insights into the pathogenesis of osteoporosis in cholestatic and end-stage liver diseases.

Effects of glucocorticoids on vitamin D3-metabolizing 24-hydroxylase (CYP24A1) in Saos-2 cells and primary human osteoblasts

Vitamin D is essential for bone function and deficiency in active vitamin D hormone can lead to bone disorders. Long-term treatment with glucocorticoids results in osteoporosis and increased risk of fractures. Much remains unclear regarding the effects of these compounds in bone cells. In the current study, human osteosarcoma Saos-2 cells and primary human osteoblasts were found to express mRNA for the vitamin D receptor as well as activating and deactivating enzymes in vitamin D₃ metabolism. These bone cells exhibited CYP24A1-mediated 24-hydroxylation which is essential for deactivation of the active vitamin form. However, bioactivating vitamin D₃ hydroxylase activities could not be detected in either of these cells. Several glucocorticoids, including prednisolone, down regulated CYP24A1 mRNA and CYP24A1-mediated 24-hydroxylase activity in both Saos-2 and primary human osteoblasts. Also, prednisolone significantly suppressed a human CYP24A1 promoter-luciferase reporter gene in Saos-2 cells co-transfected with the glucocorticoid receptor. Thus, the results of the present study show suppression by glucocorticoids on CYP24A1 mRNA, CYP24A1-mediated metabolism and CYP24A1 promoter activity in human osteoblast-like cells. As part of this study we examined if glucocorticoids are formed locally in Saos-2 cells. The experiments indicate formation of 11-deoxycortisol, a steroid with glucocorticoid activity, which can bind the glucocorticoid receptor. Our data showing suppression by glucocorticoids on CYP24A1 expression in human osteoblasts suggest a previously unknown mechanism for effects of glucocorticoids in human bone, where these compounds may interfere with regulation of active vitamin D levels.

Focused Ultrasound Effects on Osteosarcoma Cell Lines

MRI guided Focused Ultrasound (MRgFUS) has shown to be effective therapeutic modality for non-invasive clinical interventions in ablating of uterine fibroids, in bone metastasis palliative treatments, and in breast, liver, and prostate cancer ablation. MRgFUS combines high intensity focused ultrasound (HIFU) with MRI images for treatment planning and real time thermometry monitoring, thus enabling non-invasive ablation of tumor tissue. Although in the literature there are several studies on the Ultrasound (US) effects on cell in culture, there is no systematic evidence of the biological effect of Magnetic Resonance guided Focused Ultrasound Surgery (MRgFUS) treatment on osteosarcoma cells, especially in lower dose regions, where tissues receive sub-lethal acoustic power. The effect of MRgFUS treatment at different levels of acoustic intensity (15.5-49 W/cm²) was investigated on Mg-63 and Saos-2 cell lines to evaluate the impact of the dissipation of acoustic energy delivered outside the focal area, in terms of cell viability and osteogenic differentiation at 24 h, 7 days, and 14 days after treatment. Results suggested that the attenuation of FUS acoustic intensities from the focal area (higher intensities) to the “far field” (lower intensities) zones might determine different osteosarcoma cell responses, which range from decrease of cell proliferation rates (from 49 W/cm² to 38.9 W/cm²) to the selection of a subpopulation of heterogeneous and immature living cells (from 31.1 W/cm² to 15.5 W/cm²), which can clearly preserve bone tumor cells.

KIT as a therapeutic target for non-oncological diseases

KIT is a receptor tyrosine kinase that after binding to its ligand stem cell factor activates signaling cascades linked to biological processes such as proliferation, differentiation, migration and cell survival. Based on studies performed on SCF and/or KIT mutant animals that presented anemia, sterility, and/or pigmentation disorders, KIT signaling was mainly considered to be involved in the regulation of hematopoiesis, gametogenesis, and melanogenesis. More recently, novel animal models and ameliorated cellular and molecular techniques have led to the discovery of a widen repertoire of tissue compartments and functions that are being modulated by KIT. This is the case for the lung, heart, nervous system, gastrointestinal tract, pancreas, kidney, liver, and bone. For this reason, the tyrosine kinase inhibitors that were originally developed for the treatment of hemato-oncological diseases are being currently investigated for the treatment of non-oncological disorders such as asthma, rheumatoid arthritis, and alzheimer's disease, among others. The beneficial effects of some of these tyrosine kinase inhibitors have been proven to depend on KIT inhibition. This review will focus on KIT expression and regulation in healthy and pathologic conditions other than cancer. Moreover, advances in the development of anti-KIT therapies, including tyrosine kinase inhibitors, and their application will be discussed.

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin increases the activation of aryl hydrocarbon receptor and is associated with the aggressiveness of osteosarcoma MG-63 osteoblast-like cells

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor whose activity is modulated by xenobiotics and physiological ligands. Activation of the AhR by environmental xenobiotics may induce a conformational change in AhR and has been implicated in a variety of cellular processes, including inflammation and tumorigenesis. It is unknown whether the activation of AhR serves a role in modulating the progression of osteosarcoma. The osteosarcoma cell line MG-63, was treated with AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD treatment degrades AhR expression through activation of the AhR signaling pathway, however there were no survival differences observed in MG-63 cells. There were concomitant elevations of cyclooxygenase-2 and receptor activator of nuclear factor-κB ligand secretion from MG-63 cells upon TCDD treatment on a protein and mRNA level at 24 and 72 h. In addition, TCDD treatment also increases the production of prostaglandin E2 on MG-63 cells, and induces the expression of chemokine receptor CXCR4. However, CXCL12 production was not altered in MG-63 cells when stimulated with TCDD. The AhR antagonist CH-223191, blocks the effects on TCDD-induced RANKL, COX-2, PGE2 and CXCR4 changes. In conclusion, these findings suggest that AhR signal therapy should be further explored as a therapeutic option for the treatment of osteosarcoma.

M2 polarization of macrophages by Oncostatin M in hypoxic tumor microenvironment is mediated by mTORC2 and promotes tumor growth and metastasis

Oncostatin M (OSM), an inflammatory cytokine belonging to the interleukin-6 (IL-6) superfamily, plays a vital role in multitude of physiological and pathological processes. Its role in breast tumor progression and metastasis to distant organs is well documented. Recent reports implicate OSM in macrophage M2 polarization, a key pro-tumoral phenomenon. M2 polarization of macrophages is believed to promote tumor progression by potentiating metastasis and angiogenesis. In the current study, we delineated the mechanism underlying OSM induced macrophage M2 polarization. The findings revealed that OSM skews macrophages towards an M2 polarized phenotype via mTOR signaling complex 2 (mTORC2). mTORC2 relays signals through two effector kinases i.e. PKC-α and Akt. Our results indicated that mTORC2 mediated M2 polarization of macrophages is not dependent on PKC-α and is primarily affected via Akt, particularly Akt1. In vivo studies conducted on 4T1/BALB/c mouse orthotropic model of breast cancer further corroborated these observations wherein i.v. reintroduction of mTORC2 abrogated monocytes into orthotropic mouse model resulted in diminished acquisition of M2 specific attributes by tumor associated macrophages. Metastasis to distant organs like lung, liver and bone was reduced as evident by decrease in formation of focal metastatic lesions in mTORC2 abrogated monocytes mice. Our study pinpoints key role of mTORC2-Akt1 axis in OSM induced macrophage polarization and suggests for possible usage of Oncostatin-M blockade and/or selective mTORC2 inhibition as a potential anti-cancer strategy particularly with reference to metastasis of breast cancer to distant organs such as lung, liver and bone.

Oncostatin M upregulates HIF-1α in breast tumor associated macrophages independent of intracellular oxygen concentration

AIMS

HIF is an important transcription-regulator for adaptation to cellular stress in cells of myeloid origin. Classically, expression and activity of HIF1-α is regulated by oxygen-concentration within cell. However, there exists an alternative regulatory mechanism affecting HIF1-α levels independent of oxygen concentration particularly in inflammatory cells like macrophages. Here we report the mechanism of HIF1-α upregulation in TAMs by Oncostatin-M (OSM) independent of cellular oxygen concentration.

MAIN METHODS

THP-1 derived macrophages were treated with OSM. HIF1-α levels and interaction with pVHL were evaluated via immunoblot-analysis and Co-immunoprecipitation. Translocation of HIF1-α to nucleus was visualized using confocal-microscopy. Fold change in mRNA levels of ARG-1 and COX-2 was analyzed using RT-PCR.

KEY FINDINGS

Current study demonstrates that OSM treatment to TAMs led to an increased expression of HIF1-α under normoxic conditions via activation of mTORC2. This HIF1-α upregulation was dependent on both de novo synthesis of HIF1-α and its enhanced stability due to disruption of its binding to pVHL. Furthermore, we evaluated that OSM not only enhances the expression of HIF1-α but also increases its localization to nucleus where it acts as a transcription factor regulating expression of genes like ARG-1 and COX-2.

SIGNIFICANCE

Inflammation is a critical hallmark of cancer as tumor microenvironment is largely infiltrated with macrophages. These tumor associated macrophages (TAMs) display a M2 skewed phenotype. Many target genes of TAMs are HIF1-α responsive. These TAMs are involved in tumor progression, metastasis and angiogenesis. Targeting of HIF1-α/OSM can lead to devising of better therapeutic strategy against cancer.

Different Modulatory Effects of IL-17, IL-22, and IL-23 on Osteoblast Differentiation

OBJECTIVES

To examine the expressions of IL-17, IL-22, and IL-23 receptors in four osteoblast models and the effects of IL-17, IL-22, and IL-23 on osteoblasts.

METHODS

Gene expression levels of receptors, alkaline phosphatase (ALP), osteocalcin (OCN), and Runt-related transcription factor 2 (Runx-2), were evaluated by RT-PCR and real-time RT-PCR. Proliferative responses and cell cycle analysis were detected by a CCK-8 assay and flow cytometry, respectively. ALP activity and ALP mass were detected by an ALP activity assay and ALP staining, respectively.

RESULTS

In primary osteoblasts, only the IL-17 receptor was expressed. In C2C12, MC3T3-E1, and Saos-2 cells, the genes of IL-17, IL-22, and IL-23 receptors were not detectable. None of IL-17, IL-22, and IL-23 had an obvious effect on the proliferation of primary osteoblasts, but IL-17 exhibited an inhibitory effect on the gene expression of ALP, OCN, and Runx-2. The ALP activity and ALP mass of primary osteoblasts were downregulated by IL-17 treatment in a dose-dependent manner, and IL-17 failed to inhibit BMP-2-induced phosphorylation of Smad.

CONCLUSION

Primary osteoblasts constitutively express IL-17 receptors, but none of C2C12 cells, MC3T3-E1 cells, and Saos-2 cells express any receptors for IL-17, IL-22, and IL-23. IL-17 inhibits BMP-2-induced osteoblast differentiation via the BMP/Smad-independent pathway.

Cytokine, Chemokine, and Growth Factor Profile Characterization of Undifferentiated and Osteoinduced Human Adipose-Derived Stem Cells

Bone is the second most manipulated tissue after blood. Adipose-derived stem cells (ASCs) may become a convenient source of MSC for bone regenerative protocols. Surprisingly, little is known about the most significant biomolecules these cells produce and release after being osteoinduced. Therefore, the present study aimed at dosing 13 candidates chosen among the most representative cytokines, chemokines, and growth factors within the conditioned media of osteodifferentiated and undifferentiated ASCs. Two acknowledged osteoblastic cell models, that is, MG-63 and SaOs-2 cells, were compared. Notably, IL-6, IL-8, MCP-1, and VEGF were highly produced and detectable in ASCs. In addition, while IL-6 and IL-8 seemed to be significantly induced by the osteogenic medium, no such effect was seen for MCP-1 and VEGF. Overall SaOS-2 had a poor expression profile, which may be consistent with the more differentiated phenotype of SaOs-2 compared to ASCs and MG-63. Instead, in maintaining medium, MG-63 displayed a very rich production of IL-12, MCP-1, IP-10, and VEGF, which were significantly reduced in osteogenic conditions, with the only exception of MCP-1. The high expression of MCP-1 and VEGF, even after the osteogenic commitment, may support the usage of ASCs in bone regenerative protocols by recruiting both osteoblasts and osteoclasts of the host.

Platelet-functionalized three-dimensional poly-ε-caprolactone fibrous scaffold prepared using centrifugal spinning for delivery of growth factors

Bone and cartilage are tissues of a three-dimensional (3D) nature. Therefore, scaffolds for their regeneration should support cell infiltration and growth in all 3 dimensions. To fulfill such a requirement, the materials should possess large, open pores. Centrifugal spinning is a simple method for producing 3D fibrous scaffolds with large and interconnected pores. However, the process of bone regeneration is rather complex and requires additional stimulation by active molecules. In the current study, we introduced a simple composite scaffold based on platelet adhesion to poly-ε-caprolactone 3D fibers. Platelets were used as a natural source of growth factors and cytokines active in the tissue repair process. By immobilization in the fibrous scaffolds, their bioavailability was prolonged. The biological evaluation of the proposed system in the MG-63 model showed improved metabolic activity, proliferation and alkaline phosphatase activity in comparison to nonfunctionalized fibrous scaffold. In addition, the response of cells was dose dependent with improved biocompatibility with increasing platelet concentration. The results demonstrated the suitability of the system for bone tissue.

Overcoming physical constraints in bone engineering: ‘the importance of being vascularized’

Bone plays several physiological functions and is the second most commonly transplanted tissue after blood. Since the treatment of large bone defects is still unsatisfactory, researchers have endeavoured to obtain scaffolds able to release growth and differentiation factors for mesenchymal stem cells, osteoblasts and endothelial cells in order to obtain faster mineralization and prompt a reliable vascularization. Nowadays, the application of osteoblastic cultures spans from cell physiology and pharmacology to cytocompatibility measurement and osteogenic potential evaluation of novel biomaterials. To overcome the simple traditional monocultures in vitro, co-cultures of osteogenic and vasculogenic precursors were introduced with very interesting results. Increasingly complex culture systems have been developed, where cells are seeded on proper scaffolds and stimulated so as to mimic the physiological conditions more accurately. These bioreactors aim at enabling bone regeneration by incorporating different cells types into bio-inspired materials within a surveilled habitat. This review is focused on the most recent developments in the organomimetic cultures of osteoblasts and vascular endothelial cells for bone tissue engineering.

Behavior of bone cells in contact with magnesium implant material

Magnesium-based implants exhibit several advantages, such as biodegradability and possible osteoinductive properties. Whether the degradation may induce cell type-specific changes in metabolism still remains unclear. To examine the osteoinductivity mechanisms, the reaction of bone-derived cells (MG63, U2OS, SaoS2, and primary human osteoblasts (OB)) to magnesium (Mg) was determined. Mg-based extracts were used to mimic more realistic Mg degradation conditions. Moreover, the influence of cells having direct contact with the degrading Mg metal was investigated. In exposure to extracts and in direct contact, the cells decreased pH and osmolality due to metabolic activity. Proliferating cells showed no significant reaction to extracts, whereas differentiating cells were negatively influenced. In contrast to extract exposure, where cell size increased, in direct contact to magnesium, cell size was stable or even decreased. The amount of focal adhesions decreased over time on all materials. Genes involved in bone formation were significantly upregulated, especially for primary human osteoblasts. Some osteoinductive indicators were observed for OB: (i) an increased cell count after extract addition indicated a higher proliferation potential; (ii) increased cell sizes after extract supplementation in combination with augmented adhesion behavior of these cells suggest an early switch to differentiation; and (iii) bone-inducing gene expression patterns were determined for all analyzed conditions. The results from the cell lines were inhomogeneous and showed no specific stimulus of Mg. The comparison of the different cell types showed that primary cells of the investigated tissue should be used as an in vitro model if Mg is analyzed. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 165-179, 2017.

Curcumin in Combination with Piperine Suppresses Osteoclastogenesis In Vitro

INTRODUCTION

The dietary pigment curcumin is a natural polyphenol extracted from the Curcuma longa rhizomes native to South Asia. The antioxidative, antimicrobial, and anti-inflammatory activities besides its unknown side effects suggest that curcumin could be a promising antiresorptive agent to prevent replacement resorption in replanted teeth after traumatic avulsion. Piperine, an alkaloid present in black pepper, seems to enhance the bioavailability and activity of curcumin. Therefore, this study evaluated the biocompatibility of curcumin and piperine in cultures of periodontal ligament cells as well as their effects in an in vitro osteoclastogenesis model of RAW 264.7 macrophages.

METHODS

The cytotoxicity in human periodontal ligament fibroblasts, human osteogenic sarcoma cells (SAOS-2), and murine osteoclastic precursors (RAW 264.7) was analyzed by using cell number determination and proliferation assays. The ability of curcumin and its conjugate to suppress the receptor activator of nuclear factor kappa B ligand-induced osteoclastogenesis was assessed by tartrate-resistant acid phosphatase (TRAP) staining and activity as well as real-time polymerase chain reaction.

RESULTS

Curcumin at concentrations ≥ 10 μmol/L was cytotoxic in all cell types tested, whereas piperine showed only slight cytotoxicity at 30 μmol/L in RAW and SAOS cultures. Although curcumin caused already significant effects, the combination with piperine completely suppressed the osteoclastogenesis by decreasing the TRAP activity and inhibiting the expression of the specific osteoclast markers TRAP, cathepsin K, and calcitonin receptor.

CONCLUSIONS

We demonstrated that curcumin combined with piperine suppressed the osteoclastogenesis in vitro without causing cytotoxic effects in periodontal ligament cells. These findings suggest its potential therapeutic application for the prevention and treatment of replacement resorption in replanted avulsed teeth.

Effect of Fluoride-Modified Titanium Surface on Early Adhesion of Irradiated Osteoblasts

Objective. The present study aimed to investigate the effect of fluoride-modified titanium surface on adhesion of irradiated osteoblasts. Materials and Methods. Fluoride-modified surface was obtained and the morphology, roughness, and chemical composition of the surface were evaluated by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy, respectively. The adhesion of irradiated osteoblast-like cells, in terms of number, area, and fluorescence intensity on the titanium surface, was evaluated using immunofluorescence staining. Results. Numerous nanosize pits were seen only in the F-TiO surface. The pits were more remarkable and uniform on F-TiO surface than on TiO surface; however, the amplitude of peaks and bottoms on F-TiO surface appeared to be smaller than on TiO surface. The Sa value and Sdr percentage of TiO surfaces were significantly higher than those of F-TiO surface. The concentrations of main elements such as titanium, oxygen, and carbon were similar on both surfaces. The number of irradiated osteoblasts adhered on the control surface was larger than on fluoride-modified surface. Meanwhile, the cells on the fluoride-modified surface formed more actin filaments. Conclusions. The fluoride-modified titanium surface alters the adhesion of irradiated osteoblasts. Further studies are needed to investigate the proliferation, differentiation, maturation, gene expression, and cytokine production of irradiated osteoblasts on fluoride-modified titanium surface.

Comparison of the reaction of bone-derived cells to enhanced MgCl2-salt concentrations

Magnesium-based implants exhibit various advantages such as biodegradability and potential for enhanced in vivo bone formation. However, the cellular mechanisms behind this possible osteoconductivity remain unclear. To determine whether high local magnesium concentrations can be osteoconductive and exclude other environmental factors that occur during the degradation of magnesium implants, magnesium salt (MgCl₂) was used as a model system. Because cell lines are preferred targets in studies of non-degradable implant materials, we performed a comparative study of 3 osteosarcoma-derived cell lines (MG63, SaoS2 and U2OS) with primary human osteoblasts. The correlation among cell count, viability, cell size and several MgCl₂ concentrations was used to examine the influence of magnesium on proliferation in vitro. Moreover, bone metabolism alterations during proliferation were investigated by analyzing the expression of genes involved in osteogenesis. It was observed that for all cell types, the cell count decreases at concentrations above 10 mM MgCl₂. However, detailed analysis showed that MgCl₂ has a relevant but very diverse influence on proliferation and bone metabolism, depending on the cell type. Only for primary cells was a clear stimulating effect observed. Therefore, reliable results demonstrating the osteoconductivity of magnesium implants can only be achieved with primary osteoblasts.

Influence of ARHGEF3 and RHOA knockdown on ACTA2 and other genes in osteoblasts and osteoclasts

Osteoporosis is a common bone disease that has a strong genetic component. Genome-wide linkage studies have identified the chromosomal region 3p14-p22 as a quantitative trait locus for bone mineral density (BMD). We have previously identified associations between variation in two related genes located in 3p14-p22, ARHGEF3 and RHOA, and BMD in women. In this study we performed knockdown of these genes using small interfering RNA (siRNA) in human osteoblast-like and osteoclast-like cells in culture, with subsequent microarray analysis to identify genes differentially regulated from a list of 264 candidate genes. Validation of selected findings was then carried out in additional human cell lines/cultures using quantitative real-time PCR (qRT-PCR). The qRT-PCR results showed significant down-regulation of the ACTA2 gene, encoding the cytoskeletal protein alpha 2 actin, in response to RHOA knockdown in both osteoblast-like (P<0.001) and osteoclast-like cells (P = 0.002). RHOA knockdown also caused up-regulation of the PTH1R gene, encoding the parathyroid hormone 1 receptor, in Saos-2 osteoblast-like cells (P<0.001). Other findings included down-regulation of the TNFRSF11B gene, encoding osteoprotegerin, in response to ARHGEF3 knockdown in the Saos-2 and hFOB 1.19 osteoblast-like cells (P = 0.003–0.02), and down-regulation of ARHGDIA, encoding the Rho GDP dissociation inhibitor alpha, in response to RHOA knockdown in osteoclast-like cells (P<0.001). These studies identify ARHGEF3 and RHOA as potential regulators of a number of genes in bone cells, including TNFRSF11B, ARHGDIA, PTH1R and ACTA2, with influences on the latter evident in both osteoblast-like and osteoclast-like cells. This adds further evidence to previous studies suggesting a role for the ARHGEF3 and RHOA genes in bone metabolism.

Human endogenous peptide p33 inhibits detrimental effects of LL-37 on osteoblast viability

BACKGROUND AND OBJECTIVE

High levels of the antimicrobial peptide, LL-37, are detected in gingival crevicular fluid from patients with chronic periodontitis. LL-37 not only shows antimicrobial activity but also affects host-cell viability. The objective of the present study was to identify endogenous mechanisms that antagonize the detrimental effects of LL-37 on osteoblast viability, focusing on the human peptide p33 expressed on the surface of various cell types.

MATERIAL AND METHODS

Human osteoblast-like MG63 cells and human hFOB1.19 osteoblasts were treated with or without LL-37 in the presence or absence of p33. Recombinant human p33 was expressed in an Escherichia coli expression system. Lactate dehydrogenase (LDH) was assessed using an enzymatic spectrophotometric assay. DNA synthesis was determined by measuring [(3) H]-thymidine incorporation. Cell number was assessed by counting cells in a Bürker chamber. Intracellular Ca(2+) was monitored by recording Fluo 4-AM fluorescence using a laser scanning confocal microscope. Cellular expression of p33 was determined by western blotting.

RESULTS

LL-37 caused a concentration-dependent release of LDH from human osteoblasts, showing a half-maximal response value (EC50 ) of 4 μm and a rapid and sustained rise in the intracellular Ca(2+) concentration of osteoblasts, suggesting that LL-37 forms pores in the cell membrane. p33 (10 μm) inhibited the LL-37-induced LDH release and LL-37-evoked rise in intracellular Ca(2+) concentration, suggesting that p33 prevents LL-37-induced permeabilization of the cell membrane. Moreover, p33 blocked LL-37-induced attenuation of osteoblast numbers. Also, mucin antagonized, at concentrations representative for nonstimulated whole saliva, LL-37-evoked LDH release, whilst cationic endogenous polyamines had no impact on LL-37-induced LDH release from osteoblasts.

CONCLUSIONS

The endogenous peptide p33 prevents LL-37-induced reduction of human osteoblast viability. Importantly, this mechanism may protect the osteoblasts from LL-37-induced cell damage in patients suffering from chronic periodontitis associated with high levels of LL-37 locally.

Maintenance of a bone collagen phenotype by osteoblast-like cells in 3D periodic porous titanium (Ti-6Al-4 V) structures fabricated by selective electron beam melting

Regular 3D periodic porous Ti-6Al-4 V structures were fabricated by the selective electron beam melting method (EBM) over a range of relative densities (0.17-0.40) and pore sizes (500-1500 µm). Structures were seeded with human osteoblast-like cells (SAOS-2) and cultured for four weeks. Cells multiplied within these structures and extracellular matrix collagen content increased. Type I and type V collagens typically synthesized by osteoblasts were deposited in the newly formed matrix with time in culture. High magnification scanning electron microscopy revealed cells attached to surfaces on the interior of the structures with an increasingly fibrous matrix. The in-vitro results demonstrate that the novel EBM-processed porous structures, designed to address the effect of stress-shielding, are conducive to osteoblast attachment, proliferation and deposition of a collagenous matrix characteristic of bone.

Differences in proliferation, differentiation, and cytokine production by bone cells seeded on titanium-nitride and cobalt-chromium-molybdenum surfaces

Titanium-nitride coating is used to improve cobalt-chromium-molybdenum implant survival in total knee arthroplasty, but its effect on osteoconduction is unknown. Chromium and cobalt ions negatively affect the growth and metabolism of cultured osteoblasts while enhancing osteoclastogenic cytokine production. Therefore, it was hypothesized that a titanium-nitride surface would enhance osteoblast proliferation and/or differentiation and reduce osteoclastogenic cytokine production compared with a cobalt-chromium-molybdenum surface. MC3T3-E1 osteoblasts showed increased proliferation and decreased differentiation on titanium-nitride, while cytokine interleukin-6 production was higher on porous cobalt-chromium-molybdenum (p < 0.05), though interleukin-1β was occasionally detected on both surfaces. These findings suggest improved osteoconduction on titanium-nitride compared with cobalt-chromium-molybdenum surface.

Primary human osteoblast cultures

Osteoblast cultures can be used to investigate the mechanisms of bone formation, to probe the cellular and molecular basis of bone disease, and to screen for potential therapeutic agents that affect bone formation. Here, we describe the methods for establishing and characterising primary human osteoblast cultures.

In search of representative models of human bone-forming cells for cytocompatibility studies

Osteosarcoma-derived cells have been routinely used for studying osteoblastic functions, but it remains unclear to what extent they mimic the behavior of primary osteoblasts in the study of cells and materials interactions. This study reports comparatively on the responses of three human osteosarcoma cell lines, MG-63, Saos-2 and U-2 OS, and human primary osteoblasts cultured on Ti6Al4V surfaces or exposed to Ti particles. Phenotypic characterization of the cell lines revealed that Saos-2 cells and primary osteoblasts displayed similar expression patterns of Cbfa1, SP7 and osteocalcin. Unlike primary cells, the cell lines expressed markers of undifferentiated cells, had high proliferative rates and poor fibronectin matrix assembly. None of the three cell lines faithfully reproduced the adhesive behavior of primary osteoblasts when cultured on Ti6Al4V surfaces or exposed to Ti particles. Differences in cell growth between the cell lines and primary osteoblasts cultured on Ti6Al4V surfaces were also observed. Ti particles inhibited the growth of Saos-2 cells and primary osteoblasts to a similar extent, while no such effect was observed in U-2 OS and MG-63 cells. Saos-2 cells reproduced the alkaline phosphatase (ALP) activity profile of primary osteoblasts cultured on metallic surfaces or exposed to particles. Altogether, these results show that none of the osteoblast-like cells studied perfectly mimic the behavior of human osteoblast cells (hOB) on Ti6Al4V surfaces or exposed to Ti particles. Saos-2 cells reproduce some of the hOB responses such as the profile of enzymatic ALP activity when cultured on the surfaces or treated with particles as well as cell growth inhibition when exposed to Ti particles. Although in vitro cytocompatibility studies involve the evaluation of multiple parameters, Saos-2 cells may be used as representative of human osteoblasts when these standard tests are evaluated.

Oncostatin M promotes STAT3 activation, VEGF production, and invasion in osteosarcoma cell lines

Background

We have previously demonstrated that both canine and human OSA cell lines, as well as 8 fresh canine OSA tumor samples, exhibit constitutive phosphorylation of STAT3, and that this correlates with enhanced expression of matrix metalloproteinase-2 (MMP2). While multiple signal transduction pathways can result in phosphorylation of STAT3, stimulation of the cytokine receptor gp130 through either IL-6 or Oncostatin M (OSM) is the most common mechanism through which STAT3 is activated. The purpose of this study was to evaluate the role of IL-6 and OSM stimulation on both canine and human OSA cell lines to begin to determine the role of these cytokines in the biology of OSA.

Methods

RT-PCR and Western blotting were used to interrogate the consequences of OSM and IL-6 stimulation of OSA cell lines. OSA cells were stimulated with OSM and/or hepatocyte growth factor (HGF) and the effects on MMP2 activity (gel zymography), proliferation (CyQUANT), invasion (Matrigel transwell assay), and VEGF production (Western blotting, ELISA) were assessed. The small molecule STAT3 inhibitor LLL3 was used to investigate the impact of STAT3 inhibition following OSM stimulation of OSA cells.

Results

Our data demonstrate that the OSM receptor (OSMR), but not IL-6 or its receptor, is expressed by all human and canine OSA cell lines and canine OSA tumor samples; additionally, OSM expression was noted in all tumor samples. Treatment of OSA cell lines with OSM induced phosphorylation of STAT3, Src, and JAK2. OSM stimulation also resulted in a dose dependent increase in MMP2 activity and VEGF expression that was markedly reduced following treatment with the small molecule STAT3 inhibitor LLL3. Lastly, OSM stimulation of OSA cell lines enhanced invasion through Matrigel, particularly in the presence of rhHGF. In contrast, both OSM and HGF stimulation of OSA cell lines did not alter their proliferative capacity.

Conclusions

These data indicate OSM stimulation of human and canine OSA cells induces STAT3 activation, thereby enhancing the expression/activation of MMP2 and VEGF, ultimately promoting invasive behavior and tumor angiogenesis. As such, OSM and its receptor may represent a novel target for therapeutic intervention in OSA.

Lnk-dependent axis of SCF-cKit signal for osteogenesis in bone fracture healing

The therapeutic potential of hematopoietic stem cells/endothelial progenitor cells (HSCs/EPCs) for fracture healing has been demonstrated with evidence for enhanced vasculogenesis/angiogenesis and osteogenesis at the site of fracture. The adaptor protein Lnk has recently been identified as an essential inhibitor of stem cell factor (SCF)–cKit signaling during stem cell self-renewal, and Lnk-deficient mice demonstrate enhanced hematopoietic reconstitution. In this study, we investigated whether the loss of Lnk signaling enhances the regenerative response during fracture healing. Radiological and histological examination showed accelerated fracture healing and remodeling in Lnk-deficient mice compared with wild-type mice. Molecular, physiological, and morphological approaches showed that vasculogenesis/angiogenesis and osteogenesis were promoted in Lnk-deficient mice by the mobilization and recruitment of HSCs/EPCs via activation of the SCF–cKit signaling pathway in the perifracture zone, which established a favorable environment for bone healing and remodeling. In addition, osteoblasts (OBs) from Lnk-deficient mice had a greater potential for terminal differentiation in response to SCF–cKit signaling in vitro. These findings suggest that inhibition of Lnk may have therapeutic potential by promoting an environment conducive to vasculogenesis/angiogenesis and osteogenesis and by facilitating OB terminal differentiation, leading to enhanced fracture healing.

Prostate cancer cells modulate osteoblast mineralisation and osteoclast differentiation through Id-1

Background:

Id-1 is overexpressed in and correlated with metastatic potential of prostate cancer. The role of Id-1 in this metastatic process was further analysed.

Methods:

Conditioned media from prostate cancer cells, expressing various levels of Id-1, were used to stimulate pre-osteoclast differentiation and osteoblast mineralisation. Downstream effectors of Id-1 were identified. Expressions of Id-1 and its downstream effectors in prostate cancers were studied using immunohistochemistry in a prostate cancer patient cohort (N=110).

Results:

We found that conditioned media from LNCaP prostate cancer cells overexpressing Id-1 had a higher ability to drive osteoclast differentiation and a lower ability to stimulate osteoblast mineralisation than control, whereas conditioned media from PC3 prostate cancer cells with Id-1 knockdown were less able to stimulate osteoclast differentiation. Id-1 was found to negatively regulate TNF-β and this correlation was confirmed in human prostate cancer specimens (P=0.03). Furthermore, addition of recombinant TNF-β to LNCaP Id-1 cell-derived media blocked the effect of Id-1 overexpression on osteoblast mineralisation.

Conclusion:

In prostate cancer cells, the ability of Id-1 to modulate bone cell differentiation favouring metastatic bone disease is partially mediated by TNF-β, and Id-1 could be a potential therapeutic target for prostate cancer to bone metastasis.

Immobilization of poly (ethylene imine) on poly (L-lactide) promotes MG63 cell proliferation and function

Poly (ethylene imine) (PEI) is a polycation widely used for DNA transfection to cells but also applied as primary polycation for layer-by-layer (LBL) assembly of polyelectrolytes. The aim of the present study was to investigate the effect of modification with PEI on the biocompatibility of poly (L-lactide) (PLLA) films. PEI with different molecular weight was immobilized on PLLA by either adsorption or covalent binding. Cell morphologies, immuno-fluorescence staining, cell proliferation by lactate dehydrogenase assay and cell differentiation by alkaline phosphatase assay were utilized to assess the biocompatibility of the modified PLLA using osteoblast cell line MG63. Results revealed that PEI modification remarkably improved cell adhesion, viability, proliferation and function compared with plain PLLA. Hence, PEI-modified PLLA is acceptable as transfection vehicle for engineering of bone and other tissues, or as primary layer to allow LBL assembly to generate biomimetic surface coatings.

The tumor necrosis factor-{alpha}-blocking agent infliximab inhibits interleukin 1beta (IL-1beta) and IL-6 gene expression in human osteoblastic cells

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine involved in the pathogenesis of several rheumatic diseases, including rheumatoid arthritis (RA), associated with systemic bone loss and subchondral bone erosions. TNF-alpha-blocking agents such as infliximab have been successful in treatment of disease-modifying antirheumatic drug-resistant rheumatic diseases. Infliximab therapy in RA also had beneficial effects on local bone destruction and bone mineral density. We assessed effects of infliximab treatment on the bone tissue compartment and cytokine profile expression in vitro.

METHODS

Osteoblast-like cells were exposed for 24 h to sera of RA patients collected at baseline and after 1 month (T1) and 3 years (T2) of infliximab treatment. Total RNA was extracted, and expression of interleukin 1beta (IL-1beta), IL-6, and osteoprotegerin (OPG) was measured by RT-PCR.

RESULTS

IL-1beta gene expression was significantly reduced by the T1 serum, and the same decrease was elicited by the T2 serum. IL-6 downregulation was evident with the T2 serum. OPG was unaffected.

CONCLUSION

The finding of downregulation of inflammatory cytokines was interesting, particularly IL-6, which plays a crucial role in arthritis-related bone loss due to its involvement in osteoclast recruitment and activation. These results may represent a biological explanation and a link for the clinical observation of the beneficial effects of anti-TNF-alpha agents on the progression of rheumatic diseases at the bone level.

Establishment of a new human osteosarcoma cell line, UTOS-1: cytogenetic characterization by array comparative genomic hybridization

The cytogenetic characteristics of osteosarcoma (OS) remain controversial. The establishment of a new human OS cell line may improve the characterization. We report the establishment of a new human osteosarcoma cell line, UTOS-1, from a typical osteoblastic OS of an 18-year-old man. Cultured UTOS-1 cells are spindle-shaped, and have been maintained in vitro for over 50 passages in more than 2 years. Xenografted UTOS-1 cells exhibit features typical of OS, such as production of osteoid or immature bone matrix, and proliferation potency in vivo. UTOS-1 also exhibit morphological and immunohistochemical characteristics typical of osteoblastic OS. Chromosomal analysis by G-band show 73~85 chromosomes with complicated translocations. Array CGH show frequent gains at locus DAB2 at chromosome 5q13, CCND2 at 12p13, MDM2 at 12q14.3-q15, FLI and TOP3A at 17p11.2-p12 and OCRL1 at Xq25, and show frequent losses at HTR1B at 6q13, D6S268 at 6q16.3-q21, SHGC17327 at 18ptel, and STK6 at 20q13.2-q13.3. The UTOS-1 cell line may prove useful for biologic and molecular pathogenetic investigations of human OS.

Glycosaminoglycan composition changes with MG-63 osteosarcoma osteogenesis in vitro and induces human mesenchymal stem cell aggregation

Osteogenic differentiation is coordinated by the exposure of cells to temporal changes in a combination of growth factors and elements within the extracellular matrix (ECM). Many of the key proteins that drive these changes share the property of being dependent on ECM glycosaminoglycans (GAGs) for their activity. Here, we examined whether GAGs isolated from proliferating, differentiating and mineralizing MG-63 osteosarcoma cells differed in their physical properties, and thus in their capacities to coordinate the osteogenic cascade both in human MG-63 osteosarcoma cells and primary human mesenchymal stem cells (hMSCs). Our results show that the size distribution of GAGs, the expression of GAG-carrying proteoglycan cores and the expression of enzymes involved in their modification systematically change as MG-63 cells mature in culture. When dosed back onto cells exogenously in soluble form, GAGs regulated MG-63 survival and growth in a dose-dependent manner, but not differentiation in either cell type. In contrast, hMSCs aggregated into distinct colonies when grown on GAG-coated substrates, while MG-63 cells did not. Heparin-coated substrates improved hMSC viability without inducing aggregation. These results suggest a complex role for GAGs in coordinating the emergence of the osteoblast phenotype, and provide further evidence for the use of heparans in bone tissue repair applications.

Osteoimmunology: interactions of the bone and immune system

Bone and the immune system are both complex tissues that respectively regulate the skeleton and the body's response to invading pathogens. It has now become clear that these organ systems often interact in their function. This is particularly true for the development of immune cells in the bone marrow and for the function of bone cells in health and disease. Because these two disciplines developed independently, investigators in each don't always fully appreciate the significance that the other system has on the function of the tissue they are studying. This review is meant to provide a broad overview of the many ways that bone and immune cells interact so that a better understanding of the role that each plays in the development and function of the other can develop. It is hoped that an appreciation of the interactions of these two organ systems will lead to better therapeutics for diseases that affect either or both.

Establishment and characterization of OS 99-1, a cell line derived from a highly aggressive primary human osteosarcoma

Osteosarcoma is the most common form of primary bone cancer. In this study, we established a human osteosarcoma cell line (OS 99-1) from a highly aggressive primary tumor. G-banding karyotype analysis demonstrated a large number of clonal abnormalities, as well as extensive intercellular heterogeneity. Through the use of immunologic, molecular, and biochemical analyses, we characterized protein and gene expression profiles confirming the osteogenic nature of the cells. Further evaluation indicated that OS 99-1 cells maintain the capacity to differentiate in an in vitro mineralization assay as well as form tumors in the in vivo chicken embryo model. This cell line provides a useful tool to investigate the molecular mechanisms contributing to osteosarcoma and may have the potential to serve as a culture system for studies involving bone physiology.

A low level of reactive oxygen species selects for primitive hematopoietic stem cells that may reside in the low-oxygenic niche

A low-oxygenic niche in bone marrow limits reactive oxygen species (ROS) production, thus providing long-term protection for hematopoietic stem cells (HSCs) from ROS stress. Although many approaches have been used to enrich HSCs, none has been designed to isolate primitive HSCs located within the low-oxygenic niche due to difficulties of direct physical access. Here we show that an early HSC population that might reside in the niche can be functionally isolated by taking advantage of the relative intracellular ROS activity. Many attributes of primitive HSCs in the low-oxygenic osteoblastic niche, such as quiescence, and calcium receptor, N-cadherin, Notch1, and p21 are higher in the ROS(low) population. Intriguingly, the ROS(low) population has a higher self-renewal potential. In contrast, significant HSC exhaustion in the ROS(high) population was observed following serial transplantation, and expression of activated p38 mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) was higher in this population. Importantly, treatment with an antioxidant, a p38 inhibitor, or rapamycin was able to restore HSC function in the ROS(high) population. Thus, more potent HSCs associated with the low-oxygenic niche can be isolated by selecting for the low level of ROS expression. The ROS-related signaling pathways together with specific characteristics of niche HSCs may serve as targets for beneficial therapies.

Biology of umbilical cord blood progenitors in bone marrow niches

Within the bone marrow (BM), hematopoietic progenitor cells (HPCs) are localized in poorly oxygenated niches where they interact with the surrounding osteoblasts (OBs) through VLA4/VCAM-1 engagement, and are exposed to interleukin-6 (IL-6), stem cell factor (SCF), and chemokines such as CXCL12 (OB factors). Umbilical cord (UC) is more highly oxygenated that the BM microenvironment. When UC-HPCs are exposed to the 2% to 3% O(2) concentration found in the bone endosteum, their survival is significantly decreased. However, engagement of VLA-4 integrins on UCB-derived CD34(+) cells reduced cell death in 2% to 3% O(2) conditions, which was associated with an increase in phospho-Ser473 AKT and an increase in phospho-Ser9 GSK3b. Consistent with the role of GSK3b in destabilizing beta-catenin, there was more cytoplasmic beta-catenin in UC-HPCs exposed to 2% to 3% O(2) on fibronectin, compared with suspension culture. UC-HPCs cultured at 2% to 3% O(2) with OB factors showed an increase in nuclear beta-catenin and persistence of a small pool of CD34(+)38(-) HPCs. CFU assays followed by surface phenotyping of the plated colonies showed improved maintenance of mixed lineage colonies with both erythroid and megakaryocytic precursors. These studies provide a biologic perspective for how UC-derived HPCs adapt to the bone endosteum, which is low in oxygen and densely populated by osteoblasts.