Isolation, characterization, and biologic features of bone marrow endothelial cells

Consequences of HIV infection in the bone marrow niche

Dysregulation of the bone marrow niche resulting from the direct and indirect effects of HIV infection contributes to haematological abnormalities observed in HIV patients. The bone marrow niche is a complex, multicellular environment which functions primarily in the maintenance of haematopoietic stem/progenitor cells (HSPCs). These adult stem cells are responsible for replacing blood and immune cells over the course of a lifetime. Cells of the bone marrow niche support HSPCs and help to orchestrate the quiescence, self-renewal and differentiation of HSPCs through chemical and molecular signals and cell-cell interactions. This narrative review discusses the HIV-associated dysregulation of the bone marrow niche, as well as the susceptibility of HSPCs to infection by HIV.

Endothelial-to-osteoblast transition in normal mouse bone development

Metastatic prostate cancer (PCa) in bone induces bone-forming lesions. We have previously shown that PCa-induced bone originates from endothelial cells (ECs) that have undergone EC-to-osteoblast (OSB) transition. Here, we investigated whether EC-to-OSB transition also occurs during normal bone formation. We developed an EC and OSB dual-color reporter mouse (DRM) model that marks EC-OSB hybrid cells with red and green fluorescent proteins. We observed EC-to-OSB transition (RFP and GFP co-expression) in both endochondral and intramembranous bone formation during embryonic development and in adults. Co-expression was confirmed in cells isolated from DRM. Bone marrow- and lung-derived ECs underwent transition to OSBs and mineralization in osteogenic medium. RNA-sequencing revealed GATA family transcription factors were upregulated in EC-OSB hybrid cells and knockdown of GATA3 inhibited BMP4-induced mineralization. Our findings support that EC-to-OSB transition occurs during normal bone development and suggest a new paradigm regarding the endothelial origin of OSBs.

A potential area of use for immune checkpoint inhibitors: Targeting bone marrow microenvironment in acute myeloid leukemia

Acute myeloid leukemia (AML) arises from the cells of myeloid lineage and is the most frequent leukemia type in adulthood accounting for about 80% of all cases. The most common treatment strategy for the treatment of AML includes chemotherapy, in rare cases radiotherapy and stem cell and bone marrow transplantation are considered. Immune checkpoint proteins involve in the negative regulation of immune cells, leading to an escape from immune surveillance, in turn, causing failure of tumor cell elimination. Immune checkpoint inhibitors (ICIs) target the negative regulation of the immune cells and support the immune system in terms of anti-tumor immunity. Bone marrow microenvironment (BMM) bears various blood cell lineages and the interactions between these lineages and the noncellular components of BMM are considered important for AML development and progression. Administration of ICIs for the AML treatment may be a promising option by regulating BMM. In this review, we summarize the current treatment options in AML treatment and discuss the possible application of ICIs in AML treatment from the perspective of the regulation of BMM.

Integration of single-cell transcriptomes and biological function reveals distinct behavioral patterns in bone marrow endothelium

Heterogeneity of endothelial cell (EC) populations reflects their diverse functions in maintaining tissue's homeostasis. However, their phenotypic, molecular, and functional properties are not entirely mapped. We use the Tie2-CreERT2;Rosa26-tdTomato reporter mouse to trace, profile, and cultivate primary ECs from different organs. As paradigm platform, we use this strategy to study bone marrow endothelial cells (BMECs). Single-cell mRNA sequencing of primary BMECs reveals that their diversity and native molecular signatures is transitorily preserved in an ex vivo culture that conserves key cell-to-cell microenvironment interactions. Macrophages sustain BMEC cellular diversity and expansion and preserve sinusoidal-like BMECs ex vivo. Endomucin expression discriminates BMECs in populations exhibiting mutually exclusive properties and distinct sinusoidal/arterial and tip/stalk signatures. In contrast to arterial-like, sinusoidal-like BMECs are short-lived, form 2D-networks, contribute to in vivo angiogenesis, and support hematopoietic stem/progenitor cells in vitro. This platform can be extended to other organs' ECs to decode mechanistic information and explore therapeutics.

Bone Marrow Endothelial Cells Increase Prostate Cancer Cell Apoptosis in 3D Triculture Model of Reactive Stroma

Simple Summary

Prostate cancer (PCa) metastasizes preferentially to the bone marrow where it becomes difficult to treat. PCa cells in the bone marrow may survive, dormant and undetected for many years before patients eventually relapse with metastatic disease. Bone marrow is a complex tissue that initially is hostile to the PCa cells, Understanding how cancer cells survive in the bone marrow and what changes to the bone microenvironment permit them to switch to an actively growing state could offer new therapeutic strategies to combat metastatic PCa. In this study, we describe a method to culture PCa cells with two other cell types from the bone marrow, stromal cells and endothelial cells, as a way to study the interactions among these cell types. We found that factors produced by bone marrow endothelial cells, but not endothelial cells from other tissues, trigger PCa cells to either die or enter a dormant state, similar to what has been observed in patients when PCa cells initially colonize the bone marrow. Further analysis of the cell interactions within the culture model described in this study will offer increased understanding of PCa interaction with the bone marrow environment.

Abstract

The bone marrow tumor microenvironment (BMTE) is a complex network of cells, extracellular matrix, and sequestered signaling factors that initially act as a hostile environment for disseminating tumor cells (DTCs) from the cancerous prostate. Three-dimensional (3D) culture systems offer an opportunity to better model these complex interactions in reactive stroma, providing contextual behaviors for cancer cells, stromal cells, and endothelial cells. Using a new system designed for the triculture of osteoblastic prostate cancer (PCa) cells, stromal cells, and microvascular endothelial cells, we uncovered a context-specific pro-apoptotic effect of endothelial cells of the bone marrow different from those derived from the lung or dermis. The paracrine nature of this effect was demonstrated by observations that conditioned medium from bone marrow endothelial cells, but not from dermal or lung endothelial cells, led to PCa cell death in microtumors grown in 3D BMTE-simulating hydrogels. Analysis of the phosphoproteome by reverse phase protein analysis (RPPA) of PCa cells treated with conditioned media from different endothelial cells identified the differential regulation of pathways involved in proliferation, cell cycle regulation, and apoptosis. The findings from the RPPA were validated by western blotting for representative signaling factors identified, including forkhead box M1 (FOXM1; proliferation factor), pRb (cell cycle regulator), and Smac/DIABLO (pro-apoptosis) among treatment conditions. The 3D model presented here thus presents an accurate model to study the influence of the reactive BMTE, including stromal and endothelial cells, on the adaptive behaviors of cancer cells modeling DTCs at sites of bone metastasis. These findings in 3D culture systems can lead to a better understanding of the real-time interactions among cells present in reactive stroma than is possible using animal models.

Non-canonical EphA2 activation underpins PTEN-mediated metastatic migration and poor clinical outcome in prostate cancer

Background

The key process of mesenchymal to amoeboid transition (MAT), which enables prostate cancer (PCa) transendothelial migration and subsequent development of metastases in red bone marrow stroma, is driven by phosphorylation of EphA2^S897 by pAkt, which is induced by the omega-6 polyunsaturated fatty acid arachidonic acid. Here we investigate the influence of EphA2 signalling in PCa progression and long-term survival.

Methods

The mechanisms underpinning metastatic biopotential of altered EphA2 signalling in relation to PTEN status were assessed in vitro using canonical (EphA2^D739N) and non-canonical (EphA2^S897G) PC3-M mutants, interrogation of publicly available PTEN-stratified databases and clinical validation using a PCa TMA (n = 177) with long-term follow-up data. Spatial heterogeneity of EphA2 was assessed using a radical prostatectomy cohort (n = 67).

Results

Non-canonical EphA2 signalling via pEphA2^S897 is required for PCa transendothelial invasion of bone marrow endothelium. High expression of EphA2 or pEphA2^S897 in a PTEN^low background is associated with poor overall survival. Expression of EphA2, pEphA2^S897 and the associated MAT marker pMLC2 are spatially regulated with the highest levels found within lesion areas within 500 µm of the prostate margin.

Conclusion

EphA2 MAT-related signalling confers transendothelial invasion. This is associated with a substantially worse prognosis in PTEN-deficient PCa.

Bone Marrow Endothelial Cells Influence Function and Phenotype of Hematopoietic Stem and Progenitor Cells after Mixed Neutron/Gamma Radiation

The bone marrow (BM) microenvironment plays a crucial role in the maintenance and regeneration of hematopoietic stem (HSC) and progenitor cells (HSPC). In particular, the vascular niche is responsible for regulating HSC maintenance, differentiation, and migration of cells in and out of the BM. Damage to this niche upon exposure to ionizing radiation, whether accidental or as a result of therapy, can contribute to delays in HSC recovery and/or function. The ability of BM derived-endothelial cells (BMEC) to alter and/or protect HSPC after exposure to ionizing radiation was investigated. Our data show that exposure of BMEC to ionizing radiation resulted in alterations in Akt signaling, increased expression of PARP-1, IL6, and MCP-1, and decreased expression of MMP1 and MMP9. In addition, global analysis of gene expression of HSC and BMEC in response to mixed neutron/gamma field (MF) radiation identified 60 genes whose expression was altered after radiation in both cell types, suggesting that a subset of genes is commonly affected by this type of radiation. Focused gene analysis by RT-PCR revealed two categories of BMEC alterations: (a) a subset of genes whose expression was altered in response to radiation, with no additional effect observed during coculture with HSPC, and (b) a subset of genes upregulated in response to radiation, and altered when cocultured with HSPC. Coculture of BMEC with CD34+ HSPC induced HSPC proliferation, and improved BM function after MF radiation. Nonirradiated HSPC exhibited reduced CD34 expression over time, but when irradiated, they maintained higher CD34 expression. Nonirradiated HSPC cocultured with nonirradiated BMEC expressed lower levels of CD34 expression compared to nonirradiated alone. These data characterize the role of each cell type in response to MF radiation and demonstrate the interdependence of each cell’s response to ionizing radiation. The identified genes modulated by radiation and coculture provide guidance for future experiments to test hypotheses concerning specific factors mediating the beneficial effects of BMEC on HSPC. This information will prove useful in the search for medical countermeasures to radiation-induced hematopoietic injury.

Cell-based assays using calcein acetoxymethyl ester show variation in fluorescence with treatment conditions

The use of fluorogenic compounds in cell and molecular biology has increased in both frequency and range of applications. However, such compounds may introduce artifacts in intracellular fluorescence and cell number estimations as a consequence of interaction with exogenous stimulants, necessitating the use of adequate controls for accurate measurements and valid conclusions. Using calcein acetoxymethyl ester (AM) in combination with various exogenous cellular treatments, we report that the standard practice of direct normalization of experimental values to controls is insufficient for fluorogenic measurements. Treatments applied to cells may influence intracellular conversion of the fluorogenic compound, thereby enhancing or decreasing fluorescence relative to controls. We hereby encourage caution and recommend normalization of cellular fluorescence within each treatment group before comparison to controls.

Jeor S, Almeida-Porada G. Perivascular stromal cells as a potential reservoir of human cytomegalovirus

Human cytomegalovirus (HCMV) infection is an important cause of morbidity and mortality among both solid organ and hematopoietic stem cell transplant recipients. Identification of cells throughout the body that can potentially serve as a viral reservoir is essential to dissect mechanisms of cell tropism and latency and to develop novel therapies. Here, we tested and compared the permissivity of liver-, brain-, lung (LNG)- and bone marrow (BM)-derived perivascular mesenchymal stromal cells (MSC) to HCMV infection and their ability to propagate and produce infectious virus. Perivascular MSC isolated from the different organs have in common the expression of CD146 and Stro-1. While all these cells were permissive to HCMV infection, the highest rate of HCMV infection was seen with LNG-MSC, as determined by viral copy number and production of viral particles by these cells. In addition, we showed that, although the supernatants from each of the HCMV-infected cultures contained infectious virus, the viral copy number and the quantity and timing of virus production varied among the various organ-specific MSC. Furthermore, using quantitative polymerase chain reaction, we were able to detect HCMV DNA in BM-MSC isolated from 7 out of 19 healthy, HCMV-seropositive adults, suggesting that BM-derived perivascular stromal cells may constitute an unrecognized natural HCMV reservoir.

Panax ginseng modulates cytokines in bone marrow toxicity and myelopoiesis: ginsenoside Rg1 partially supports myelopoiesis

In this study, we have demonstrated that Korean Panax ginseng (KG) significantly enhances myelopoiesis in vitro and reconstitutes bone marrow after 5-flurouracil-induced (5FU) myelosuppression in mice. KG promoted total white blood cell, lymphocyte, neutrophil and platelet counts and improved body weight, spleen weight, and thymus weight. The number of CFU-GM in bone marrow cells of mice and serum levels of IL-3 and GM-CSF were significantly improved after KG treatment. KG induced significant c-Kit, SCF and IL-1 mRNA expression in spleen. Moreover, treatment with KG led to marked improvements in 5FU-induced histopathological changes in bone marrow and spleen, and partial suppression of thymus damage. The levels of IL-3 and GM-CSF in cultured bone marrow cells after 24 h stimulation with KG were considerably increased. The mechanism underlying promotion of myelopoiesis by KG was assessed by monitoring gene expression at two time-points of 4 and 8 h. Treatment with Rg1 (0.5, 1 and 1.5 µmol) specifically enhanced c-Kit, IL-6 and TNF-α mRNA expression in cultured bone marrow cells. Our results collectively suggest that the anti-myelotoxicity activity and promotion of myelopoiesis by KG are mediated through cytokines. Moreover, the ginsenoside, Rg1, supports the role of KG in myelopoiesis to some extent.

Soluble perlecan domain I enhances vascular endothelial growth factor-165 activity and receptor phosphorylation in human bone marrow endothelial cells

Background

Immobilized recombinant perlecan domain I (PlnDI) binds and modulates the activity of heparin-binding growth factors, in vitro. However, activities for PlnDI, in solution, have not been reported. In this study, we assessed the ability of soluble forms to modulate vascular endothelial growth factor-165 (VEGF₁₆₅) enhanced capillary tube-like formation, and VEGF receptor-2 phosphorylation of human bone marrow endothelial cells, in vitro.

Results

In solution, PlnDI binds VEGF₁₆₅ in a heparan sulfate and pH dependent manner. Capillary tube-like formation is enhanced by exogenous PlnDI; however, PlnDI/VEGF₁₆₅ mixtures combine to enhance formation beyond that stimulated by either PlnDI or VEGF₁₆₅ alone. PlnDI also stimulates VEGF receptor-2 phosphorylation, and mixtures of PlnDI/VEGF₁₆₅ reduce the time required for peak VEGF receptor-2 phosphorylation (Tyr-951), and increase Akt phosphorylation. PlnDI binds both immobilized neuropilin-1 and VEGF receptor-2, but has a greater affinity for neuropilin-1. PlnDI binding to neuropilin-1, but not to VEGF receptor-2 is dependent upon the heparan sulfate chains adorning PlnDI. Interestingly, the presence of VEGF₁₆₅ but not VEGF₁₂₁ significantly enhances PlnDI binding to Neuropilin-1 and VEGF receptor-2.

Conclusions

Our observations suggest soluble forms of PlnDI are biologically active. Moreover, PlnDI heparan sulfate chains alone or together with VEGF₁₆₅ can enhance VEGFR-2 signaling and angiogenic events, in vitro. We propose PlnDI liberated during basement membrane or extracellular matrix turnover may have similar activities, in vivo.

Novel surface expression of reticulocalbin 1 on bone endothelial cells and human prostate cancer cells is regulated by TNF-alpha

An unbiased cDNA expression phage library derived from bone-marrow endothelial cells was used to identify novel surface adhesion molecules that might participate in metastasis. Herein we report that reticulocalbin 1 (RCN1) is a cell surface-associated protein on both endothelial (EC) and prostate cancer (PCa) cell lines. RCN1 is an H/KDEL protein with six EF-hand, calcium-binding motifs, found in the endoplasmic reticulum. Our data indicate that RCN1 also is expressed on the cell surface of several endothelial cell lines, including human dermal microvascular endothelial cells (HDMVECs), bone marrow endothelial cells (BMEC), and transformed human bone marrow endothelial cells (TrHBMEC). While RCN1 protein levels were highest in lysates from HDMVEC, this difference was not statistically significant compared BMEC and TrHBMEC. Given preferential adhesion of PCa to bone-marrow EC, these data suggest that RCN1 is unlikely to account for the preferential metastasis of PCa to bone. In addition, there was not a statistically significant difference in total RCN1 protein expression among the PCa cell lines. RCN1 also was expressed on the surface of several PCa cell lines, including those of the LNCaP human PCa progression model and the highly metastatic PC-3 cell line. Interestingly, RCN1 expression on the cell surface was upregulated by tumor necrosis factor alpha treatment of bone-marrow endothelial cells. Taken together, we show cell surface localization of RCN1 that has not been described previously for either PCa or BMEC and that the surface expression on BMEC is regulated by pro-inflammatory TNF-alpha.

Tumor necrosis factor-alpha and endothelial cells modulate Notch signaling in the bone marrow microenvironment during inflammation

OBJECTIVE

Homeostasis of the hematopoietic compartment is challenged and maintained during conditions of stress by mechanisms that are poorly defined. To understand how the bone marrow (BM) microenvironment influences hematopoiesis, we explored the role of Notch signaling and BM endothelial cells in providing microenvironmental cues to hematopoietic cells in the presence of inflammatory stimuli.

MATERIALS AND METHODS

The human BM endothelial cell line (BMEC) and primary human BM endothelial cells were analyzed for expression of Notch ligands and the ability to expand hematopoietic progenitors in an in vitro coculture system. In vivo experiments were carried out to identify modulation of Notch signaling in BM endothelial and hematopoietic cells in mice challenged with tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS), or in Tie2-tmTNF-alpha transgenic mice characterized by constitutive TNF-alpha activation.

RESULTS

BM endothelial cells were found to express Jagged ligands and to greatly support progenitor's colony-forming ability. This effect was markedly decreased by Notch antagonists and augmented by increasing levels of Jagged2. Physiologic upregulation of Jagged2 expression on BMEC was observed upon TNF-alpha activation. Injection of TNF-alpha or LPS upregulated three- to fourfold Jagged2 expression on murine BM endothelial cells in vivo and resulted in increased Notch activation on murine hematopoietic stem/progenitor cells. Similarly, constitutive activation of endothelial cells in Tie2-tmTNF-alpha mice was characterized by increased expression of Jagged2 and by augmented Notch activation on hematopoietic stem/progenitor cells.

CONCLUSIONS

Our results provide the first evidence that BM endothelial cells promote expansion of hematopoietic progenitor cells by a Notch-dependent mechanism and that TNF-alpha and LPS can modulate the levels of Notch ligand expression and Notch activation in the BM microenvironment in vivo.

Nonlinear model-based estimates of IC(50) for studies involving continuous therapeutic dose-response data

We present statistical details for estimating an in vitro 50% inhibitory concentration (IC(50)), based on several models for continuous response data fit to bone-marrow endothelial cell lines replicated in vehicle and at several dose increments. Nonlinear models are fit via maximum likelihood assuming normal errors, and primary attention is given to exponential, Gompertz, and scaled logistic dose-response curves that admit increasing or decreasing monotonic and sigmoidal patterns. Careful consideration is given to dose axis scaling, comparative model fit via mean squared error and graphical assessment, analogues to weighted least squares analysis to address heterogeneity of variance across doses, and potential hormetic effects. Standard error estimation is discussed in detail, highlighting the advantage of reparameterizing dose-response models directly in terms of IC(50). Specific results for two cell lines are provided, along with a sample commercial software-based program for implementing a selection of the methods discussed.

Leukemia-stimulated bone marrow endothelium promotes leukemia cell survival

Extensive endothelial cell proliferation and marked neovascularization are the most pronounced microenvironmental changes consistently observed in the bone marrow (BM) of patients with acute lymphoblastic leukemia (ALL). It is not known whether ALL cells induce this phenotype and whether they receive critical signals from the tumor-associated BM endothelium. Here, we show that leukemia cells actively stimulate BM endothelium, promote de novo angiogenesis, and induce neovascularization in the leukemic BM. Soluble factors, present in the leukemic BM microenvironment, promote the proliferation, migration, and morphogenesis of BM endothelial cells, which are critical processes in tumor angiogenesis. We also show in vitro that leukemia cells display directional motion towards assembled BM endothelium and following adherence exhibit cell polarization, pseudopodia, and ultrastructural features that suggest the existence of leukemia-endothelium cross-talk. Finally, we show that BM endothelium promotes leukemia cell survival through a mechanism mediated through the anti-apoptotic molecule bcl-2. These studies indicate that ALL cells actively recruit BM endothelium and mediate the leukemia-associated neovascularization observed in ALL. Therefore, disruption of interactions between leukemia cells and BM endothelium may constitute a valid therapeutic strategy.

The bone marrow vascular niche: home of HSC differentiation and mobilization

The bone marrow vascular niche consists of a network of thin-walled and fenestrated sinusoidal vessels whose integrity is maintained and supported by surrounding hematopoietic cells. However, this dependence is highly reciprocal in that the bone marrow vasculature provides not only a conduit for mature hematopoietic cells to the peripheral circulation but also a site where hematopoietic progenitors, especially megakaryocytes, differentiate and set the stage for full reconstitution of hematopoiesis.

Invasive characteristics of human prostatic epithelial cells: understanding the metastatic process

Prostate cancer has a predilection to metastasise to the bone marrow stroma (BMS) by an as yet uncharacterised mechanism. We have defined a series of coculture models of invasion, which simulate the blood/BMS boundary and allow the elucidation of the signalling and mechanics of trans-endothelial migration within the complex bone marrow environment. Confocal microscopy shows that prostate epithelial cells bind specifically to bone marrow endothelial-to-endothelial cell junctions and initiate endothelial cell retraction. Trans-endothelial migration proceeds via an epithelial cell pseudopodial process, with complete epithelial migration occurring after 232±43 min. Stromal-derived factor-1 (SDF-1)/CXCR4 signalling induced PC-3 to invade across a basement membrane although the level of invasion was 3.5-fold less than invasion towards BMS (P=0.0007) or bone marrow endothelial cells (P=0.004). Maximal SDF-1 signalling of invasion was completely inhibited by 10 μM of the SDF-1 inhibitor T140. However, 10 μM T140 only reduced invasion towards BMS and bone marrow endothelial cells by 59% (P=0.001) and 29% (P=0.011), respectively. This study highlights the need to examine the potential roles of signalling molecules and/or inhibitors, not just in single-cell models but in coculture models that mimic the complex environment of the bone marrow.

Differential inhibition of invasion and proliferation by bisphosphonates: anti-metastatic potential of Zoledronic acid in prostate cancer

OBJECTIVES

To determine the mode of action of Zoledronic acid in the inhibition of metastasis in prostate cancer and the reduction of prostate cancer bone metastases.

METHODS

Benign and malignant primary prostatic epithelial cells (PEC) and the PC-3 prostate cancer cell line were studied in co-culture using human bone marrow stroma in the presence of escalating doses of EDTA, Clodronate, Pamidronate and Zoledronic acid. PEC binding and colony growth in bone marrow stroma was measured using standardised quantitative techniques. PEC cellular invasion through Matrigel and an endothelial monolayer was measured either in invasion chambers or by the measurement of endothelial monolayer permeability to fluorescent dextran. Co-culture supernatants were assayed for specific cytokine levels. Bone marrow cellular toxicity was assessed using a standard Mix assay.

RESULTS

Treatment of PEC with up to 100 microM bisphosphonate did not affect their ability to bind to bone marrow endothelium or stroma. Bone marrow endothelial permeability was reduced by 100 microM Zoledronic acid by 3.8% (p = 0.03856). Both Pamidronate (40% at 100 microM, p < or = 0.05) and Zoledronic acid inhibited PEC invasion, with Zoledronic acid being the most potent (40% at 10 microM, p < or = 0.05 rising to 91% at 100 microM, p < or = 0.001). Zoledronic acid inhibits malignant PEC proliferation in bone marrow stroma co-culture (26.5% at 10 microM rising to 66.5% at 40 microM). This was accompanied by changes within the cytokine milieu with a >800% rise in TIMP-2.

CONCLUSION

Zoledronic acid is a potent inhibitor of PEC invasion across bone marrow endothelium and colony formation with the bone marrow stroma, affecting the MMP: TIMP-2 balance to favour MMP inhibition.

Prostate Cancer Cell Adhesion to Bone Marrow Endothelium

Bone metastasis is the most frequent complication of prostate cancer (PC). Elucidation of the biological basis of this specificity is required for the development of approaches for metastatic inhibition. We investigated the possibility that the preferential attachment of PC cells to bone marrow endothelium (as opposed to endothelium from other organs) affects this specificity. We selected, from peptide phage-displayed libraries, peptide ligands to surfaces of PC cells (C4-2B) attenuated (30-40%) binding of C4-2B cells to bone marrow endothelial cells (BMECs). We then determined the molecules on the surface of C4-2B cells interacted with the selected peptides using column affinity chromatography and a cDNA expression phage-displayed library generated from C4-2B cells in T7 phage. We identified a phage from the cDNA library that specifically bound to one of the selected peptides-L11. This phage displayed the amino acid sequence homologous for the COOH-terminal portion of prostate-specific antigen (PSA). To examine the possible direct involvement of PSA in the interactions between PC and BMECs, we performed a cell-cell adhesion assay. Antibodies to PSA attenuated PC cells adhesion to BMECs. In addition, exogenous proteolytically active PSA modulated this adhesion. Finally, inactivation of mRNA coding PSA by a small interfering RNA (siRNA) diminished C4-2B cell adhesion to BMECs. These results indicate that PSA expressed as secreted and surface-associated molecules in C4-2B cells is involved in cell-cell interactions and/or digests components of bone marrow endothelium for preferential adhesion and penetration of PC cells. The suggested experimental approach is a promising strategy for identification of cell surface molecules involved in intercellular interactions.

Chemokine-mediated interaction of hematopoietic progenitors with the bone marrow vascular niche is required for thrombopoiesis

The molecular pathways involved in the differentiation of hematopoietic progenitors are unknown. Here we report that chemokine-mediated interactions of megakaryocyte progenitors with sinusoidal bone marrow endothelial cells (BMECs) promote thrombopoietin (TPO)-independent platelet production. Megakaryocyte-active cytokines, including interleukin-6 (IL-6) and IL-11, did not induce platelet production in thrombocytopenic, TPO-deficient (Thpo(-/-)) or TPO receptor-deficient (Mpl(-/-)) mice. In contrast, megakaryocyte-active chemokines, including stromal-derived factor-1 (SDF-1) and fibroblast growth factor-4 (FGF-4), restored thrombopoiesis in Thpo(-/-) and Mpl(-/-) mice. FGF-4 and SDF-1 enhanced vascular cell adhesion molecule-1 (VCAM-1)- and very late antigen-4 (VLA-4)-mediated localization of CXCR4(+) megakaryocyte progenitors to the vascular niche, promoting survival, maturation and platelet release. Disruption of the vascular niche or interference with megakaryocyte motility inhibited thrombopoiesis under physiological conditions and after myelosuppression. SDF-1 and FGF-4 diminished thrombocytopenia after myelosuppression. These data suggest that TPO supports progenitor cell expansion, whereas chemokine-mediated interaction of progenitors with the bone marrow vascular niche allows the progenitors to relocate to a microenvironment that is permissive and instructive for megakaryocyte maturation and thrombopoiesis. Progenitor-active chemokines offer a new strategy to restore hematopoiesis in a clinical setting.

Heterologous cells cooperate to augment stem cell migration, homing, and engraftment

T-lymphocyte depletion of bone marrow grafts compromises engraftment, suggesting a facilitating mechanism provided by the T cells that has been shown to associate with CD8(+) but not CD4(+) T cells. Explanations for this phenomenon have focused on immune targeting of residual host cells or cytokine production. We provide evidence for an alternative mechanism based on cooperative effects on cell motility. We observed that engraftment of CD34(+) cells in a beta(2)-microglobulin-deficient nonobese diabetic/severe combined immunodeficiency (beta(2)m(-/-) NOD/SCID) mouse model paralleled clinical observations in humans, with an enhancing effect noted from the addition of CD8(+) cells but not CD4(+) cells. This correlated with CD8(+) augmentation of CD34(+) cell homing to the bone marrow in vivo and CD8(+) cell-associated increases of CD34(+) cell transmigration through a bone marrow endothelial cell line in vitro. The cooperative interaction was not sensitive to brefeldin A inhibition of protein secretion. However, cytochalasin D-induced inhibition of CD8(+) cytoskeletal rearrangements abrogated CD34(+) transendothelial migration and impaired CD34(+) cell homing in vivo. CD8(+) cells did not migrate in tandem with CD34(+) cells or alter endothelial barrier integrity; rather, they affected phosphotyrosine-mediated signaling in CD34(+) cells in response to the chemokine stromal derived factor-1alpha (SDF-1alpha). These data demonstrate cell-cell cooperativity between different cell types in mediating chemotactic events and provide one potential explanation for the clinically observed effect of CD8(+) cells on bone marrow transplantation. This modification of cell migration by neighboring cells provides broad possibilities for combinatorial effects between cells of different types to influence cell localization.

Vascular endothelial growth factor (VEGF)-C signaling through FLT-4 (VEGFR-3) mediates leukemic cell proliferation, survival, and resistance to chemotherapy

Similar to solid tumors, growth of leukemias may also be angiogenesis dependent. Furthermore, tyrosine kinase receptors specific to endothelial cells are expressed on certain subsets of leukemias. We have previously demonstrated the existence of a VEGF/VEGFR-2 autocrine loop on leukemic cells that supports their growth and migration. Here, we demonstrate that in response to leukemia-derived proangiogenic and proinflammatory cytokines such as basic fibroblast growth factor and IL-1, endothelial cells release increasing amounts of another vascular endothelial growth factor (VEGF) family member, VEGF-C. In turn, interaction of VEGF-C with its receptor VEGFR-3 (FLT-4) promotes leukemia survival and proliferation. We demonstrate in 2 cell lines and 5 FLT-4(+) leukemias that VEGF-C and a mutant form of the molecule that lacks the KDR-binding motif induce receptor phosphorylation, leukemia proliferation, and increased survival, as determined by increased Bcl-2/Bax ratios. Moreover, VEGF-C protected leukemic cells from the apoptotic effects of 3 chemotherapeutic agents. Because most leukemic cells release proangiogenic as well as proinflammatory cytokines, our data suggest that the generation of a novel paracrine angiogenic loop involving VEGF-C and FLT-4 may promote the survival of a subset of leukemias and protect them from chemotherapy-induced apoptosis. These results identify the VEGF-C/FLT-4 pathway as a novel therapeutic target for the treatment of subsets of acute leukemia.

Primary culture of microvascular endothelial cells from human benign prostatic hyperplasia

BACKGROUND

Prostate growth seems to be influenced by paracrine factors like IL-6 originating from the microvascular endothelium. Therefore, our efforts were focused on the primary culture and behavior of microvascular endothelial cells (HPEC) derived from tissue of human benign prostatic hyperplasia (BPH). Until now, the isolation and culture of HPEC from BPH have not been reported.

METHODS

BPH tissue was cut into small cubes and gently squeezed after incubation with dispase. HPEC were cultured from the resulting cell suspension after a stepwise selection by use of superparamagnetic beads coated with antibodies against endothelial specific antigens. HPEC were characterized by flow cytometry and immunohistochemistry. gamma-Glutamyl transpeptidase activity (specific for microvascular endothelium) was measured after dissolution of the HPEC with Triton X-100. After the incubation of HPEC either with ATP, VEGF, or TNF-alpha, the release of IL-6 was measured by enzyme linked immunosorbent assay (ELISA).

RESULTS

HPEC showed a typical endothelial morphology. They were positive for von Willebrand factor, CD31, CD62E (after stimulation with TNF-alpha), alpha-actin and were negative for fibroblastic antigens and PSA. Proliferation was stimulated by vascular endothelial growth factor (VEGF). gamma-Glutamyl transpeptidase activity in HPEC was 6.3 microIU/microg protein, whereas in human umbilical vein endothelial cells (HUVEC) no gamma-glutamyl transpeptidase activity was detectable. The IL-6 secretion of HPEC was stimulated by VEGF and TNF-alpha, but not by ATP and bradykinin.

CONCLUSIONS

For the first time, the primary culture of microvascular endothelial cells from BPH tissue was successfully performed. Our results suggest that HPEC may be actively involved in prostate growth, due to the secretion of regulatory factors such as IL-6.

Positive and negative hematopoietic cytokines produced by bone marrow endothelial cells

Recently, cytokines and interleukins such as SCF, GM-CSF, G-CSF, TGF-beta, IL-6, IL-7, IL-8, IL-11 have been reported to be elaborated by endothelial cells. For further study, serum free bone marrow endothelial cell conditioned medium (BMEC-CM) was collected and ultrafiltrated by using a centriprep 10. The concentrated retentate (R-BMEC-CM) contained some substances whose molecular weight was more than 10 000 daltons. The filtrate (F-BMEC-CM) contained some substances whose molecular weight was less than 10 000 daltons. The effects of R-BMEC-CM and F-BMEC-CM on the growth of haematopoietic progenitors and the expression of cytokine and interleukin mRNAs of BMEC were investigated. The results showed that R-BMEC-CM stimulated the growth of CFU-GM, HPP-CFC, BFU-E, CFU-E, and CFU-Meg; while F-BMEC-CM inhibited the growth of these progenitors. Using the method of hybridizing to the Atlas cDNA Array, we were able to detect the presence of mRNAs of cytokines and interleukins in bone marrow endothelial cells. Our finding of the existence of mRNAs of SCF, GM-CSF, IL-6, TGF-beta, IL-1, and IL-11 in these cells was in agreement with the data reported previously. Furthermore, we detected mRNAs of MIP-2, Thymosion-beta4, PDGF, MSP-1, IFN-gamma, IL-13 and inhibin, which are related to haematopoiesis. Among these cytokines and interleukins, SCF, GM-CSF, IL-6, IL-1, and IL-11 are haematopoietic stimulators which may be responsible for the stimulative effects on the growth of haematopoietic progenitors. One of our new findings, the thymosin-beta4, is a small molecular haematopoietic inhibitor. It may be responsible for the inhibitory effect of F-BMEC-CM on haematopoietic progenitors. The presence of mRNAs of BMP, MSP-1, MIP-2, PDGF and IL-13 suggests that bone marrow endothelial cells might elaborate these substances. Their influence on haematopoietic progenitors needs further study.

Adoptive T-Cell Therapy for B-Cell Acute Lymphoblastic Leukemia: Preclinical Studies

We have previously shown that leukemia-specific cytotoxic T cells (CTL) can be generated from the bone marrow of most patients with B-cell precursor acute leukemias. If these antileukemia CTL are to be used for adoptive immunotherapy, they must have the capability to circulate, migrate through endothelium, home to the bone marrow, and, most importantly, lyse the leukemic cells in a leukemia-permissive bone marrow microenvironment. We demonstrate here that such antileukemia T-cell lines are overwhelmingly CD8+ and exhibit an activated phenotype. Using a transendothelial chemotaxis assay with human endothelial cells, we observed that these T cells can be recruited and transmigrate through vascular and bone marrow endothelium and that these transmigrated cells preserve their capacity to lyse leukemic cells. Additionally, these antileukemia T-cell lines are capable of adhering to autologous stromal cell layers. Finally, autologous antileukemia CTL specifically lyse leukemic cells even in the presence of autologous marrow stroma. Importantly, these antileukemia T-cell lines do not lyse autologous stromal cells. Thus, the capacity to generate anti–leukemia-specific T-cell lines coupled with the present findings that such cells can migrate, adhere, and function in the presence of the marrow microenvironment enable the development of clinical studies of adoptive transfer of antileukemia CTL for the treatment of ALL.

Preferential adhesion of prostate cancer cells to a human bone marrow endothelial cell line

BACKGROUND

In virtually all patients with advanced prostate cancer, the disease metastasizes to bone and causes osteoblastic growth. However, the mechanisms that contribute to bone metastasis are poorly understood. It has been hypothesized that the bone provides a favorable growth environment for prostate cancer cells, which nonselectively seed the bone marrow from the bloodstream. Alternatively, prostate cancer cells may preferentially bind to bone marrow endothelial cells. We developed an in vitro model of bone endothelium and tested the hypothesis that prostate cancer cells adhere preferentially to bone marrow endothelial cells.

METHODS

We isolated and characterized a human bone marrow endothelial (HBME-1) cell line. Cells were transfected with the simian virus 40 large T antigen for immortalization. Cell surface receptors were characterized by immunohistochemistry and flow cytometry. The adhesion of cancer cells to HBME-1 and to endothelial cell lines from other organs was tested in an in vitro binding assay as were inhibitors of adhesion.

RESULTS

The immortalized HBME-1 cell line demonstrated many properties characteristic of endothelial cells, including positive staining for von Willibrand factor and rapid formation of tubule structures when exposed to extracellular matrices. In an in vitro assay, prostate cancer cells adhered preferentially to human bone marrow endothelium when compared with endothelium derived from other sources. Preferential adhesion was blocked, in part, by antibodies to galectin-3 and LFA-1.

IMPLICATIONS

These data suggest that the propensity of prostate cancer cells to establish themselves in bone is due, at least in part, to their preferential adhesion to human bone marrow endothelial cells.