CAL72: a human osteosarcoma cell line with unique effects on hematopoietic cells

Alginate-Chitosan Microencapsulated Cells for Improving CD34+ Progenitor Maintenance and Expansion

Protocols for isolation, characterization, and transplantation of hematopoietic stem cells (HSCs) have been well established. However, difficulty in finding human leucocyte antigens (HLA)-matched donors and scarcity of HSCs are still the major obstacles of allogeneic transplantation. In this study, we developed a double-layered microcapsule to deliver paracrine factors from non-matched or low-matched HSCs to other cells. The umbilical cord blood-derived hematopoietic progenitor cells, identified as CD34+ cells, were entrapped in alginate polymer and further protected by chitosan coating. The microcapsules showed no toxicity for surrounding CD34+ cells. When CD34+ cells-loaded microcapsules were co-cultured with bare CD34+ cells that have been collected from unrelated donors, the microcapsules affected surrounding cells and increased the percentage of CD34+ cell population. This study is the first to report the potency of alginate-chitosan microcapsules containing non-HLA-matched cells for improving proliferation and progenitor maintenance of CD34+ cells.

Using a combination of gangliosides and cell surface vimentin as surface biomarkers for isolating osteosarcoma cells in microfluidic devices

Background

Osteosarcoma (OS) is the most common primary bone tumor and the third leading cause of pediatric cancer deaths. Liquid biopsies are an alternative to current diagnostic imaging modalities that can be used to monitor treatment efficacy and the development of metastases. This study addresses the use of novel biomarkers to detect circulating osteosarcoma cells.

Procedures

Flow cytometry was used to evaluate the relative expression of epithelial cell adhesion molecule (EpCAM), ganglioside 2 and 3 (GD2/3), and cell surface vimentin (CSV) on a panel of OS cell lines. A microfluidic device was used to affirm the efficacy of GD2/3 and CSV to capture CTCs. Once captured, CTCs on the device are enumerated and the capture efficiency for each marker is measured. Patient samples were captured using the LFAM chip.

Results

We report the evaluation of GD2, GD3, and CSV as markers for OS cell capture in cell lines and in patient samples. The results of our capture studies correlate with our flow cytometry data and have shown a low capture efficiency of OS cells using EpCAM antibodies, while showing a moderate capture efficiency of OS cells using the GD2, GD3, and CSV antibodies independently. The combination of biomarkers demonstrate a high capture efficiency of approximately 80%. This is further supported by the detection of 1-1.5 CTCs per mL of blood using GD2 + CSV in OS patient samples.

Conclusions

The combination of GD2 + CSV significantly increased the capture efficacy of OS cells. The detection of CTCs through routine blood sampling may be used clinically for earlier detection of metastases and monitoring the therapeutic effect of treatments in metastatic osteosarcomas.

Use of in vitro bone models to screen for altered bone metabolism, osteopathies, and fracture healing: challenges of complex models

Approx. every third hospitalized patient in Europe suffers from musculoskeletal injuries or diseases. Up to 20% of these patients need costly surgical revisions after delayed or impaired fracture healing. Reasons for this are the severity of the trauma, individual factors, e.g, the patients’ age, individual lifestyle, chronic diseases, medication, and, over 70 diseases that negatively affect the bone quality. To investigate the various disease constellations and/or develop new treatment strategies, many in vivo, ex vivo, and in vitro models can be applied. Analyzing these various models more closely, it is obvious that many of them have limits and/or restrictions. Undoubtedly, in vivo models most completely represent the biological situation. Besides possible species-specific differences, ethical concerns may question the use of in vivo models especially for large screening approaches. Challenging whether ex vivo or in vitro bone models can be used as an adequate replacement for such screenings, we here summarize the advantages and challenges of frequently used ex vivo and in vitro bone models to study disturbed bone metabolism and fracture healing. Using own examples, we discuss the common challenge of cell-specific normalization of data obtained from more complex in vitro models as one example of the analytical limits which lower the full potential of these complex model systems.

Material-Dependent Formation and Degradation of Bone Matrix-Comparison of Two Cryogels

Cryogels represent ideal carriers for bone tissue engineering. We recently described the osteogenic potential of cryogels with different protein additives, e.g., platelet-rich plasma (PRP). However, these scaffolds raised concerns as different toxic substances are required for their preparation. Therefore, we developed another gelatin (GEL)-based cryogel. This study aimed to compare the two scaffolds regarding their physical characteristics and their influence on osteogenic and osteoclastic cells. Compared to the PRP scaffolds, GEL scaffolds had both larger pores and thicker walls, resulting in a lower connective density. PRP scaffolds, with crystalized calcium phosphates on the surface, were significantly stiffer but less mineralized than GEL scaffolds with hydroxyapatite incorporated within the matrix. The GEL scaffolds favored adherence and proliferation of the osteogenic SCP-1 and SaOS-2 cells. Macrophage colony-stimulating factor (M-CSF) and osteoprotegerin (OPG) levels seemed to be induced by GEL scaffolds. Levels of other osteoblast and osteoclast markers were comparable between the two scaffolds. After 14 days, mineral content and stiffness of the cryogels were increased by SCP-1 and SaOS-2 cells, especially of PRP scaffolds. THP-1 cell-derived osteoclastic cells only reduced mineral content and stiffness of PRP cryogels. In summary, both scaffolds present powerful advantages; however, the possibility to altered mineral content and stiffness may be decisive when it comes to using PRP or GEL scaffolds for bone tissue engineering.

Biomimetic Macroporous PCL Scaffolds for Ex Vivo Expansion of Cord Blood-Derived CD34+ Cells with Feeder Cells Support

Ex vivo expansion of hematopoietic stem cells (HSCs) with most current methods can hardly satisfy clinical application requirement. While in vivo, HSCs efficiently self-renew in niche where they interact with 3D extracellular matrix and stromal cells. Therefore, co-cultures of CD34⁺ cells and mesenchyme stem cells derived from human amniotic membrane (hAMSCs) on the basis of biomimetic macroporous three-dimensional (3D) poly(ε-caprolactone) (PCL) scaffolds are developed, where scaffolds and hAMSCs are applied to mimic structural and cellular microenvironment of HSCs. The influence of scaffolds, feeder cells, and contact manners on expansion and stemness maintenance of CD34⁺ cells is investigated in this protocol. Biomimetic scaffolds-dependent co-cultures of CD34⁺ cells and hAMSCs can effectively promote the expansion of CD34⁺ cells; meanwhile, indirect contact is superior to direct contact. The combination of biomimetic scaffolds and hAMSCs represents a new strategy for achieving clinical-scale ex vivo expansion of CD34⁺ cells.

Biocompatible hollow-strut, silica enriched zirconia foams

BACKGROUND

Porous ceramic biomaterials structures are accepted components in applied research in the field of tissue engineering due to their mechanical properties being closer to structural tissue like bone or other properties related to improved biocompatibility.

OBJECTIVE

Hollow-strut, silica enriched zirconia foams were made by replication of polyurethane via impregnation with a suspension of zirconia-particles in polysiloxane.

METHODS

Two-step heat treatment allowed conversion of the precursor structures into hollow-strut ceramic foams which were tested for their biocompatibility using an osteoblast cell line. Further, the material was characterized via different spectroscopic (Raman-spectroscopy, EDX) and imaging (SEM, μCT) methods.

RESULTS

The material shows open cell porosity with hollow struts and sufficient structural integrity for handling and an expected chemistry as investigated by Raman and EDX spectroscopy. The material further supported cell growth and overall good biocompatibility.

CONCLUSIONS

The investigated composite foam shows promising properties and is potentially interesting as candidate material for future bone tissue engineering applications.

Strontium doped poly-ε-caprolactone composite scaffolds made by reactive foaming

In the reconstruction and regeneration of bone tissue, a primary goal is to initiate bone growth and to stabilize the surrounding bone. In this regard, a potentially useful component in biomaterials for bone tissue engineering is strontium, which acts as cationic active agent, triggering certain intracellular pathways and acting as so called dual action bone agent which inhibits bone resorption while stimulating bone regeneration. In this study we established a novel processing for the foaming of a polymer (poly-ε-caprolactone) and simultaneous chemical reaction of a mixture of calcium and strontium hydroxides to the respective carbonates using supercritical carbon dioxide. The resultant porous composite scaffold was optimized in composition and strontium content and was characterized via different spectroscopic (infrared and Raman spectroscopy, energy dispersive X-ray spectroscopy), imaging (SEM, μCT), mechanical testing and in vitro methods (fluorescence vital staining, MTT-assay). As a result, the composite scaffold showed good in vitro biocompatibility with partly open pore structure and the expected chemistry. First mechanical testing results indicate sufficient mechanical stability to support future in vivo applications.

Pharmacological targeting of the PI3K/mTOR pathway alters the release of angioregulatory mediators both from primary human acute myeloid leukemia cells and their neighboring stromal cells

Acute myeloid leukemia (AML) is a heterogeneous and aggressive malignancy with poor overall survival. Constitutive as well as cytokine-initiated activation of PI3K/Akt/mTOR signaling is a common feature of AML patients, and inhibition of this pathway is considered as a possible therapeutic strategy in AML. Human AML cells and different stromal cell populations were cultured under highly standardized in vitro conditions. We investigated the effects of mTOR inhibitors (rapamycin and temsirolimus) and PI3K inhibitors (GDC-0941 and 3-methyladenin (3-MA)) on cell proliferation and the constitutive release of angioregulatory mediators by AML and stromal cells.

Primary human AML cells were heterogeneous, though most patients showed high CXCL8 levels and detectable release of CXCL10, Ang-1, HGF and MMP-9. Hierarchical clustering analysis showed that disruption of PI3K/Akt/mTOR pathways decreased AML cell release of CXCL8-11 for a large subset of patients, whereas the effects on other mediators were divergent. Various stromal cells (endothelial cells, fibroblasts, cells with osteoblastic phenotype) also showed constitutive release of angioregulatory mediators, and inhibitors of both the PI3K and mTOR pathway had anti-proliferative effects on stromal cells and resulted in decreased release of these angioregulatory mediators. PI3K and mTOR inhibitors can decrease constitutive cytokine release both by AML and stromal cells, suggesting potential direct and indirect antileukemic effects.

In Vitro Characterization of Valproic Acid, ATRA, and Cytarabine Used for Disease-Stabilization in Human Acute Myeloid Leukemia: Antiproliferative Effects of Drugs on Endothelial and Osteoblastic Cells and Altered Release of Angioregulatory Mediators by Endothelial Cells

The combined use of the histone deacetylase inhibitor valproic acid (VPA), the retinoic acid receptor- α agonist all-trans retinoic acid (ATRA), and the deoxyribonucleic acid polymerase- α inhibitor cytarabine (Ara-C) is now considered for disease-stabilizing treatment of acute myeloid leukemia (AML). Leukemogenesis and leukemia cell chemoresistance seem to be supported by neighbouring stromal cells in the bone marrow, and we have therefore investigated the effects of these drugs on primary human endothelial cells and the osteoblastic Cal72 cell line. The results show that VPA and Ara-C have antiproliferative effects, and the antiproliferative/cytotoxic effect of Ara-C was seen at low concentrations corresponding to serum levels found during low-dose in vivo treatment. Furthermore, in functional assays of endothelial migration and tube formation VPA elicited an antiangiogenic effect, whereas ATRA elicited a proangiogenic effect. Finally, VPA and ATRA altered the endothelial cell release of angiogenic mediators; ATRA increased levels of CXCL8, PDGF-AA, and VEGF-D, while VPA decreased VEGF-D and PDGF-AA/BB levels and both drugs reduced MMP-2 levels. Several of these mediators can enhance AML cell proliferation and/or are involved in AML-induced bone marrow angiogenesis, and direct pharmacological effects on stromal cells may thus indirectly contribute to the overall antileukemic activity of this triple drug combination.

Identification of an aptamer binding to human osteogenic-induced progenitor cells

The aim of this study was to generate a specific aptamer against human jaw periosteal cells (JPCs) for tissue engineering applications in oral and maxillofacial surgery. This aptamer should serve as a capture molecule to enrich or even purify osteogenic progenitor cells from JPCs or from adult stem cells of other sources. Using systematic evolution of ligands by exponential enrichment (SELEX), we generated the first aptamer to specifically bind to human osteogenically induced JPCs. We did not detect any binding of the aptamer to undifferentiated JPCs, adipogenically and chondrogenically induced JPCs, or to any other cell line tested. However, similar binding patterns of the identified aptamer 74 were detected with mesenchymal stromal cells (MSCs) derived from placental tissue and bone marrow. After cell sorting, we analyzed the expression of osteogenic marker genes in the aptamer 74-positive and aptamer 74-negative fractions and detected no significant differences. Additionally, the analysis of the mineralization capacity revealed a slight tendency for the aptamer positive fraction to have a higher osteogenic potential. In terms of proliferation, JPCs growing in aptamer-coated wells showed increased proliferation rates compared with the controls. Herein, we report the development of an innovative approach for tissue engineering applications. Further studies should be conducted to modify and improve the specificity of the generated aptamer.

Fra-2/AP-1 controls bone formation by regulating osteoblast differentiation and collagen production

The activator protein-1 (AP-1) transcription factor complex, in particular the Fos proteins, is an important regulator of bone homeostasis. Fra-2 (Fosl2), a Fos-related protein of the AP-1 family, is expressed in bone cells, and newborn mice lacking Fra-2 exhibit defects in chondrocytes and osteoclasts. Here we show that Fra-2-deficient osteoblasts display a differentiation defect both in vivo and in vitro. Moreover, Fra-2-overexpressing mice are osteosclerotic because of increased differentiation of osteoblasts, which appears to be cell autonomous. Importantly, the osteoblast-specific osteocalcin (Oc) gene and collagen1α2 (col1α2) are transcriptional targets of Fra-2 in both murine and human bone cells. In addition, Fra-2, Oc, and col1 are expressed in stromal cells of human chondroblastic and osteoblastic osteosarcomas (Os's) as well as during osteoblast differentiation of human Os cell lines. These findings reveal a novel function of Fra-2/AP-1 as a positive regulator of bone and matrix formation in mice and humans.

Maintenance and expansion of hematopoietic stem/progenitor cells in biomimetic osteoblast niche

In this study, we employed bio-derived bone scaffold and composited with the marrow mesenchymal stem cell induced into osteoblast to replicate a "biomimetic niche." The CD34(+) cells or mononuclear cells (MNC) from umbilical cord blood were cultured for 2-5 weeks in the biomimetic niche (3D system) was compared with conventional two dimensional cultures (2D system) without adding cytokine supplement. After 2 weeks in culture, the CD34(+) cells from umbilical cord blood in the 3D system increased 3.3-4.8 folds when compared with the initial CD34(+) cells. CD34(+)/CD38(-) cells accounted for 82-90% of CD34(+) cells. After 5 weeks, CD34(+)/CD38(-) cells in the 3D system increased when compared with initial (1.3 ± 0.3 × 10(3) vs. 1.0 ± 0.5 × 10(4), p < 0.05), but were decreased in the 2D system (1.3 ± 0.3 × 10(3) vs. 2.5 ± 0.7 × 10(2), p < 0.05). The CFU progenitors were produced more in the 3D system than in the 2D system (4.6-9.3 folds vs. 1.0-1.5 folds) after 2 weeks in culture, and the colony distribution in the 3D system manifested higher percentage of BFU-E and CFU-GEMM, but in the 2D system was mainly CFU-GM. The LTC-ICs in the 3D system showed 5.2-7.2 folds increase over input at 2 weeks in culture, and maintain the immaturation of hematopoietic progenitor cells (HPCs) over 5 weeks. In conclusion, this new 3D hematopoietic progenitor cell culture system is the first to utilize natural cancellous bone as scaffold with osteoblasts as supporting cells; it is mimicry of natural bone marrow HSC niche. Our primary work has demonstrated it could maintain and expand HSC/HPC in vitro.

Behavior of CAL72 osteoblast-like cells cultured on zirconia ceramics with different surface topographies

OBJECTIVES

Because of its inherent strength, biocompatibility, and tooth-like color, zirconia ceramics have the potential to become an alternative to titanium as dental implant material. This study aimed at investigating the osteoblastic response to yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) with different surface topographies.

METHODS

CAL72 osteoblast-like cells were cultured on machined (TZP-m), airborne particle abraded (TZP-s), and airborne particle abraded and acid-etched Y-TZP (TZP-sa) surfaces. Polystyrene and airborne particle abraded with large grit and acid-etched (SLA) titanium served as a reference control. The surface topography was examined by scanning electron microscopy (SEM) and profilometry. At culture days 3, 6, and 12, cell proliferation, at day 12 cell morphology, and cell-covered surface area were determined.

RESULTS

The surface roughness of Y-TZP was increased by airborne particle abrasion and additionally by acid etching. No statistically significant differences were found between average roughness (R(a)) and maximum peak-to-valley height (R(p-v)) values of airborne particle abraded and acid-etched Y-TZP and SLA titanium. Whereas the cell proliferation assay revealed statistically significant greater values at day 3 for surface-treated Y-TZP and polystyrene cultures as compared with machined Y-TZP, no differences between the Y-TZP groups, SLA titanium, and polystyrene were observed at culture days 6 and 12.

CONCLUSIONS

Cell morphology and cell-covered surface area were not affected by the type of substrate. The results suggest that roughened Y-TZP is an appropriate substrate for the proliferation and spreading of osteoblastic cells.

Effects of interferon gamma on native human acute myelogenous leukaemia cells

T cell targeting immunotherapy is now considered a possible strategy in acute myelogenous leukaemia (AML), and IFNgamma release may then contribute to the antileukaemic effects. We investigated the effects of IFNgamma on native human AML cells. Normal T cells could be activated to release IFNgamma in the presence of AML cells. Furthermore, high levels of CD119 (IFNgamma receptor alpha chain) expression were observed for all 39 patients examined. Receptor expression was decreased after exposure to exogenous IFNgamma, and receptor ligation caused Stat1 phosphorylation but no phosphorylation of the alternative messengers Erk1/2. The effect of exogenous IFNgamma on AML blast proliferation was dependent on the local cytokine network and IFNgamma (1) inhibited proliferation in the presence of exogenous IL1beta, GM-CSF, G-CSF and SCF; (2) had divergent effects in the presence of IL3 and Flt3 (65 patients examined); (3) inhibited proliferation in the presence of endothelial cells but had divergent effects in the presence of fibroblasts, osteoblasts and normal stromal cells (65 patients examined). IFNgamma increased stress-induced (spontaneous) in vitro apoptosis as well as cytarabine-induced apoptosis only for a subset of patients. Furthermore, IFNgamma decreased the release of proangiogenic CXCL8 and increased the release of antiangiogenic CXCL9-11. We conclude that IFNgamma can be released in the presence of native human AML cells and affect AML cell proliferation, regulation of apoptosis and the balance between pro- and antiangiogenic chemokine release.

T lymphocyte chemotactic chemokines in acute myelogenous leukemia (AML): local release by native human AML blasts and systemic levels of CXCL10 (IP-10), CCL5 (RANTES) and CCL17 (TARC)

T cell targeting immunotherapy is now considered in acute myelogenous leukemia (AML), and local recruitment of antileukemic T cells to the AML microcompartment will then be essential. This process is probably influenced by both intravascular as well as extravascular levels of T cell chemotactic chemokines. We observed that native human AML cells usually showed constitutive secretion of the chemotactic chemokines CXCL10 and CCL5, whereas CCL17 was only released for a subset of patients and at relatively low levels. Coculture of AML cells with nonleukemic stromal cells (i.e., fibroblasts, osteoblasts) increased CXCL10 and CCL17 levels whereas CCL5 levels were not altered. However, a wide variation between patients in both CXCL10 and CCL5 levels persisted even in the presence of the stromal cells. Neutralization of CXCL10 and CCL5 inhibited T cell migration in the presence of native human AML cells. Furthermore, serum CCL17 and CXCL10 levels varied between AML patients and were determined by disease status (both chemokines) as well as patient age, chemotherapy and complicating infections (only CCL17). Thus, extravascular as well as intravascular levels of T cell chemotactic chemokines show a considerable variation between patients that may be important for T cell recruitment and the effects of antileukemic T cell reactivity in local AML compartments.

In vitro culture of human osteosarcoma cell lines: a comparison of functional characteristics for cell lines cultured in medium without and with fetal calf serum

PURPOSE

Experimental in vitro models including well-characterised cell lines can be used to identify possible new therapeutic targets for the treatment of osteosarcoma. Culture media including inactivated serum is often recommended for in vitro culture of osteosarcoma cells, but the serum component then represents a nonstandardised parameter including a wide range of unidentified mediators. To improve the standardisation we have investigated whether serum-free culture media can be used in experimental in vitro studies of osteosarcoma cell lines.

METHODS

The seven osteosarcoma cell lines Cal72, SJSA-1, Saos-2, SK-ES-1, U2OS, 143.98.2, and KHOS-32IH were cultured in vitro in various serum-free media and media supplemented with 10% heat-inactivated fetal calf serum (FCS).

RESULTS

Although proliferation often was relatively low in serum-free media (X-vivo 10, X-vivo 15, X-vivo 20, Stem Span SFEM), some cell lines (Cal72, KHOS-32IH, Saos-2) showed proliferation comparable with the recommended FCS-containing media even when using serum-free conditions. The optimal serum-free medium then varied between cell lines. We also compared 6 different FCS-containing media (including Stem Span with 10% FCS) and the optimal FCS-containing medium varied between cell lines. However, all cell lines proliferated well in Stem Span with FCS, and this medium was regarded as optimal for four of the lines. FCS could not be replaced by fatty acids or low density lipoprotein when testing the Stem Span medium. The release of a wide range of soluble mediators showed only minor differences when using serum-free and FCS-containing media (including Stem Span with and without FCS), and serum-free Stem Span could also be used for in vitro studies of mitogen-stimulated T cell activation in the presence of accessory osteosarcoma cells. The use of Stem Span with 10% FCS allowed the release of a wide range of chemokines by osteosarcoma cell lines (Cal72, SJSA-1), and the chemokine release profile was very similar to the fibroblast lines Hs27 and HFL1.

CONCLUSIONS

Serum-free culture media can be used for in vitro studies of several osteosarcoma cell lines, but the optimal medium varies between cell lines and thus depends on: (i) the cell lines to be investigated/compared; (ii) the functional characteristic that is evaluated (proliferation, cytokine release); and (iii) whether coculture experiments are included.

Coculture of native human acute myelogenous leukemia blasts with fibroblasts and osteoblasts results in an increase of vascular endothelial growth factor levels

OBJECTIVES

Angiogenesis seems important in the development of acute myelogenous leukemia (AML). Proangiogenic vascular endothelial growth factor (VEGF) is constitutively secreted by the AML blasts for a subset of patients, but it can also be released by non-leukemic bone marrow cells.

METHODS

VEGF levels were determined after coculture of native human AML blasts with fibroblast lines, osteoblastic sarcoma cell lines, normal bone marrow stromal cells and normal osteoblasts. Cultures were prepared with leukemic and non-leukemic cells separated by a semipermeable membrane or in direct contact.

RESULTS

The non-leukemic cells usually showed higher spontaneous VEGF release than AML cell populations. Coculture of AML blasts with HFL1 fibroblasts caused a supra-additive increase of VEGF levels when the cell populations were cultured separately, and the increase was also observed when cells were cultured in direct contact. An increase was also observed when AML blasts were cultured with osteoblastic sarcoma cells, normal bone marrow stromal cells and normal osteoblasts. Coculture had divergent effects on VEGF mRNA levels both for leukemic and non-leukemic cells, but increased mRNA levels were commonly observed especially for the non-leukemic cells. Cytokine inhibition experiments suggest that IL1 is important for the VEGF-increasing crosstalk, whereas the mechanisms are probably heterogeneous for coculture with osteoblasts.

CONCLUSION

The bi-directional crosstalk via local cytokine networks between AML blasts and non-leukemic cells results in increased local VEGF levels, an observation suggesting that VEGF-targeting antiangiogenic therapy should be considered as a general therapeutic strategy in AML.

Cell lines and primary cell cultures in the study of bone cell biology

Bone is a metabolically active and highly organized tissue consisting of a mineral phase of hydroxyapatite and amorphous calcium phosphate crystals deposited in an organic matrix. Bone has two main functions. It forms a rigid skeleton and has a central role in calcium and phosphate homeostasis. The major cell types of bone are osteoblasts, osteoclasts and chondrocytes. In the laboratory, primary cultures or cell lines established from each of these different cell types provide valuable information about the processes of skeletal development, bone formation and bone resorption, leading ultimately, to the formulation of new forms of treatment for common bone diseases such as osteoporosis.

Blood and bone: two tissues whose fates are intertwined to create the hematopoietic stem-cell niche

The mechanisms of bone and blood formation have traditionally been viewed as distinct, unrelated processes, but compelling evidence suggests that they are intertwined. Based on observations that hematopoietic precursors reside close to endosteal surfaces, it was hypothesized that osteoblasts play a central role in hematopoiesis, and it has been shown that osteoblasts produce many factors essential for the survival, renewal, and maturation of hematopoietic stem cells (HSCs). Preceding these observations are studies demonstrating that the disruption or perturbation of normal osteoblastic function has a profound and central role in defining the operational structure of the HSC niche. These observations provide a glimpse of the dimensions and ramifications of HSC-osteoblast interactions. Although more research is required to secure a broader grasp of the molecular mechanisms that govern blood and bone biology, the central role for osteoblasts in hematopoietic stem cell regulation is reviewed herein from the perspectives of (1) historical context; (2) the role of the osteoblast in supporting stem cell survival, proliferation, and maintenance; (3) the participation, if any, of osteoblasts in the creation of a stem cell niche; (4) the molecules that mediate HSC-osteoblast interactions; (5) the role of osteoblasts in stem cell transplantation; and (6) possible future directions for investigation.

In vitro effects of native human acute myelogenous leukemia blasts on fibroblasts and osteoblasts

Bone marrow stromal cells constitute a heterogeneous population, and in the present study we investigated intercellular crosstalk via release of soluble mediators between native human AML blasts and fibroblasts/osteoblasts. Coculture of nonleukemic stromal cells and AML blasts separated by a semipermeable membrane decreased proliferation of the fibroblast line HFL1, and the inhibition was maintained when HFL1 and AML cells were cultured in direct contact. A similar inhibitory effect was observed for osteoblastic sarcoma cell lines (Cal72, SJSA-1) and normal osteoblasts. GM-CSF was released by both nonleukemic cells and a subset of AML blast populations, and increased levels of GM-CSF were detected in AML cocultures with fibroblasts and osteoblastic sarcoma cells when testing AML cell populations with constitutive GM-CSF release. Furthermore, constitutive IL-1beta secretion by AML blasts was detected only for a subset of patients, whereas relatively high levels of IL-1RA were observed for all patients; coculture of AML blasts with HFL1 fibroblasts and osteoblastic sarcoma cells increased IL-1beta levels for patients with constitutive IL-1beta secretion, whereas IL-1RA levels were slightly decreased but still generally higher than IL-1beta levels (tested only for HFL1 fibroblasts). The bidirectional crosstalk between AML blasts and stromal cells with increased release of AML growth factors may be important in leukemogenesis, whereas the decreased stromal cell proliferation combined with the persistent release of IL-1RA may in addition inhibit remaining normal hematopoiesis and thereby contribute to bone marrow failure in AML.

Down-regulation of Hox A7 is required for cell adhesion and migration on fibronectin during early HL-60 monocytic differentiation

Hox genes, which are key regulators of cell fate and pattern formation during embryogenesis, are also important regulators of hematopoiesis, and different combinations of Hox gene products are involved in lineage commitment or maturation. However, their molecular and cellular modes of action are not yet completely understood. Recent studies have indicated that Hox genes are involved in the regulation of cell-extracellular matrix (ECM) interactions and cell migration. Here, we report that Hox A7, a gene frequently overexpressed in acute myeloid leukemia, is down-regulated during HL-60 monocytic differentiation. Using a model in which HL-60 cells are induced to differentiate toward the monocytic lineage with bone marrow stromal-like cells, we demonstrate that Hox A7-sustained expression disturbs the regulation of cell adhesive and migratory capacities on fibronectin during early differentiation. We show that this is accompanied by a partial blockage of the transcriptional induction of proline-rich tyrosine kinase 2, a gene coding for a focal adhesion kinase active in monocytes, and of tissue transglutaminase, a gene coding for a fibronectin coreceptor in monocytes. This is the first report that demonstrates the involvement of a Hox gene in the regulation of adhesion and migration of hematopoietic cells and that links it to the deregulation of genes involved in cell-ECM interactions and downstream signaling pathways.

Modification of gene expression induced in human osteogenic and osteosarcoma cells by culture on a biphasic calcium phosphate bone substitute

Bone hybrids made of bioceramics seeded with mesenchymal or osteoblastic cells are very promising alternatives to autologous bone graft. Along this line, the development of in vitro models, dedicated to analyze the influence of these biomaterials on osteogenic cells, will help to improve the performance of these bone substitutes. In the present work we analyzed the effects of a macroporous biphasic calcium phosphate ceramic (BCP, Triosite) on three different human osteosarcoma cell lines and on human primary osteogenic cells and compared this culture substratum to traditional culture on plastic. We showed that all these osteoblastic cells adhere and proliferate on the trabecular BCP blocks, with a different spatial organization for osteosarcoma cells compared to normal osteogenic cells. We also demonstrated that osteoblastic marker genes such as Cbfa1, type I collagen, osteonectin, osteopontin, and osteocalcin were expressed at similar levels by these cells cultured on either substratum, suggesting that adhesion to BCP does maintain the osteoblastic phenotype of these cells. Next, we provided the first evidence of differences of cytokine expression profiles revealed on this Ca-P ceramic as compared to expression in classical culture. These modifications affected the expression of cytokines such as TGF-beta1, G-CSF, and IL-3 and were quantitatively different between osteosarcoma cells and normal osteogenic cells. Given the role of these cytokines in bone biology and in hematopoiesis, these results obtained in vitro suggest that the BCP ceramic studied here could stimulate osteogenesis in vivo by activating cellular processes during bone formation and healing. This study highlights the notion that the nature of the culture substratum must be taken into account when studying bone cell biology in vitro. Owing to the nature and spatial organization of the BCP, our hypothesis is that culture on BCP is closer to the physiological situation than culture on plastic.