BMEC-1: a human bone marrow microvascular endothelial cell line with primary cell characteristics

Toxicological evaluation of therapeutically active zinc oxide nanoflowers in pre-clinical mouse model

Our earlier reports established that zinc oxide nanoflowers (ZONF) show significant pro-angiogenic properties, where reactive oxygen species, nitric oxide and MAPK-AKT-eNOS cell signaling axis play an essential task. Considering the significance of angiogenesis in healthcare, our research group has recently demonstrated the in vivo therapeutic application of ZONF (10 mg/kg b.w.) for treating peripheral artery disease. Moreover, based on the angio-neural crosstalk between vascular and neuronal systems, we have further demonstrated the neuritogenic and neuroprotective characteristics of pro-angiogenic nanoflowers (10 mg/kg b.w.) for the treatment of cerebral ischemia. However, it is crucial for a therapeutic material to be non-toxic for its practical clinical applications and therefore assessment of its in vivo toxicity and adverse effect is highly important. Herein, for the first time, we investigate a detailed nanotoxicology of therapeutically active ZONF in Swiss albino mice to evaluate their safety profile and comprehend their aspects for future clinical applications. The maximum tolerated dose (MTD) of ZONF was found to be 512.5 mg/kg b.w. which was employed for acute exposure (2 weeks), showing slight toxicity. However, sub-chronic (4 weeks) and long term chronic (8-12 weeks) studies of nanoflowers exhibited their non-toxic nature particularly at lower therapeutic doses (1-10 mg/kg b.w.). Additionally, in depth genotoxicity study revealed that lower therapeutic dose of ZONF (10 mg/kg b.w.) did not exhibit significant toxicity even in genetic level. Overall, the present nanotoxicology of ZONF suggests their high biocompatible nature at therapeutic dose, offering the basis of their future clinical applications in ischemic and other vascular diseases.

Studying the potential of upregulated PTGS2 and VEGF-C besides hyper-methylation of PTGS2 promoter as biomarkers of Acute myeloid leukemia

Hereby, we aimed to investigate the expression of prostaglandin-endoperoxide synthase 2 (PTGS2) and Vascular Endothelial Factor-C (VEGF-C) besides the methylation of PTGS2 in AML patients. VEGF-C and PTGS2 expression analysis were evaluated in newly diagnosed AML patients and healthy controls by quantitative Reverse Transcriptase PCR method. Also, PTGS2 methylation status was evaluated by Methylation-Sensitive High-Resolution Melting Curve Analysis (MS-HRM). While 34% of patients were female, the mean age of the patients was 43.41 ± 17.60 years suffering mostly from M4 (48.21%) type of AML. Although methylation level between patients and controls was not significantly different, none of the normal controls showed methylation in the PTGS2 promoter. PTGS2 and VEGF-C levels were elevated in AML cases and correlated with WBC, Platelet, and Hemoglobin levels. The survival of patients with overexpressed VEGF-C and PTGS2 was poorer than others. It can be concluded that PTGS2 and especially VEGF-C expression but not PTGS2 methylation can be considered as diagnostic biomarkers for AML.

Long-Lived Human Lymphatic Endothelial Cells to Study Lymphatic Biology and Lymphatic Vessel/Tumor Coculture in a 3D Microfluidic Model

The lymphatic system is essential in maintaining tissue fluid homeostasis as well as antigen and immune cell transport to lymph nodes. Moreover, lymphatic vasculature plays an important role in various pathological processes, such as cancer. Fundamental to this research field are representative in vitro models. Here we present a microfluidic lymphatic vessel model to study lymphangiogenesis and its interaction with colon cancer organoids using a newly developed lymphatic endothelial cell (LEC) line. We generated immortalized human LECs by lentiviral transduction of human telomerase (hTERT) and BMI-1 expression cassettes into primary LECs. Immortalized LECs showed an increased growth potential, reduced senescence, and elongated lifespan with maintenance of typical LEC morphology and marker expression for over 12 months while remaining nontransformed. Immortalized LECs were introduced in a microfluidic chip, comprising a free-standing extracellular matrix, where they formed a perfusable vessel-like structure against the extracellular matrix. A gradient of lymphangiogenic factors over the extracellular matrix gel induced the formation of luminated sprouts. Adding mouse colon cancer organoids adjacent to the lymphatic vessel resulted in a stable long-lived coculture model in which cancer cell-induced lymphangiogenesis and cancer cell motility can be investigated. Thus, the development of a stable immortalized lymphatic endothelial cell line in a membrane-free, perfused microfluidic chip yields a highly standardized lymphangiogenesis and lymphatic vessel-tumor cell coculture assay.

Plasmodium vivax Gametocytes Adherence to Bone Marrow Endothelial Cells

In a Plasmodium vivax infection, it was shown a proportionally increased on gametocyte distribution within the bone marrow aspirant, suggesting a role of this organ as a reservoir for this parasite stage. Here, we evaluated the ex vivo cytoadhesive capacity of P. vivax gametocytes to bone marrow endothelial cells (HBMEC) and investigated the involvement of some receptors in the cytoadhesion process by using transfected CHO cells (CHO-ICAM1, CHO-CD36 and CHO-VCAM), wild type (CHO-K1) or deficient in heparan and chondroitin sulfate (CHO-745). Ex-vivo cytoadhesion assays were performed using a total of 44 P. vivax isolates enriched in gametocyte stages by Percoll gradient in the different cell lines. The majority of isolates (88.9%) were able to adhere to HBMEC monolayer. ICAM1 seemed to be the sole receptor significantly involved. CD-36 was the receptor with higher adhesion rate, despite no significance was noticed when compared to CHO-745. We demonstrated that gametocyte P. vivax adheres ex vivo to bone marrow endothelial cells. Moreover, P. vivax gametocytes display the ability to adhere to all CHO cells investigated, especially to CHO-ICAM1. These findings bring insights to the comprehension of the role of the bone marrow as a P. vivax reservoir and the potential impact on parasite transmission to the vector.

Extrusion-based printing of sacrificial Carbopol ink for fabrication of microfluidic devices

Current technologies for manufacturing of microfluidic devices include soft-lithography, wet and dry etching, thermoforming, micro-machining and three-dimensional (3D) printing. Among them, soft-lithography has been the mostly preferred one in medical and pharmaceutical fields due to its ability to generate polydimethylsiloxane (PDMS) devices with resin biocompatibility, throughput and transparency for imaging. It is a multi-step process requiring the preparation of a silicon wafer pattern, which is fabricated using photolithography according to a defined mask. Photolithography is a costly, complicated and time-consuming process requiring a clean-room environment, and the technology is not readily accessible in most of the developing countries. In addition, generated patterns on photolithography-made silicon wafers do not allow building 3D intricate shapes and silicon direct bonding is thus utilized for closed fluid channels and complex 3D structures. 3D Printing of PDMS has recently gained significant interest due to its ability to define complex 3D shapes directly from user-defined designs. In this work, we investigated Carbopol as a sacrificial gel in order to create microfluidic channels in PDMS devices. Our study demonstrated that Carbopol ink possessed a shear-thinning behavior and enabled the extrusion-based printing of channel templates, which were overlaid with PDMS to create microfluidic devices upon curing of PDMS and removal of the sacrificial Carbopol ink. To demonstrate the effectiveness of the fabricated devices, channels were lined up with human umbilical vein endothelial cells (HUVECs) and human bone marrow endothelial cells (BMECs) in separate devices, where both HUVECs and BMECs demonstrated the formation of endothelium with highly aligned cells in the direction of fluid flow. Overall, we here present a highly affordable and practical approach in fabrication of PDMS devices with closed fluid channels, which have great potential in a myriad of applications from cancer treatments to infectious disease diagnostics to artificial organs.

VEGF/PKD-1 signaling mediates arteriogenic gene expression and angiogenic responses in reversible human microvascular endothelial cells with extended lifespan

Microvascular ECs (MVECs) are an ideal model in angiogenesis research. The aim of this study was to determine vascular endothelial growth factor (VEGF)/protein kinase D1 (PKD-1) signaling in expression of arteriogenic genes in human MVECs. To achieve this aim, we transduced specific SV40 large T antigen and telomerase into primary human dermal MVECs (HMVEC-D) to establish reversible HMVECs with extended lifespan (HMVECi-D). HMVECi-D was then exposed to VEGF/VEGF-inducer GS4012 or transduced with constitutively active protein kinase PKD-1 (PKD-CA). Quantitative RT-PCR was performed to detect arteriogenic gene expression. Furthermore, the angiogenic capacity in response to VEGF pathway was evaluated by Matrigel tube-formation and proliferation assays. We observed that VEGF/PKD-1 signaling axis significantly stimulated the expression of arteriogenic genes and promoted EC proliferation, along with downregulation of CD36 expression. Intriguingly, overexpression of PKD-CA also resulted in formation of tip cell morphology, accompanied by increased mRNA of delta-like ligand 4 (DLL4). In conclusion, we have successfully established and characterized HMVECi-D, and showed that VEGF/PKD-1 signaling axis increases angiogenic and arteriogenic gene expression. These studies suggest that the axis may regulate arteriolar differentiation through changing MVEC gene expression.

Activated ovarian endothelial cells promote early follicular development and survival

Background

New data suggests that endothelial cells (ECs) elaborate essential “angiocrine factors”. The aim of this study is to investigate the role of activated ovarian endothelial cells in early in-vitro follicular development.

Methods

Mouse ovarian ECs were isolated using magnetic cell sorting or by FACS and cultured in serum free media. After a constitutive activation of the Akt pathway was initiated, early follicles (50–150 um) were mechanically isolated from 8-day-old mice and co-cultured with these activated ovarian endothelial cells (AOEC) (n = 32), gel (n = 24) or within matrigel (n = 27) in serum free media for 14 days. Follicular growth, survival and function were assessed.

Results

After 6 passages, flow cytometry showed 93% of cells grown in serum-free culture were VE-cadherin positive, CD-31 positive and CD 45 negative, matching the known EC profile. Beginning on day 4 of culture, we observed significantly higher follicular and oocyte growth rates in follicles co-cultured with AOECs compared with follicles on gel or matrigel. After 14 days of culture, 73% of primary follicles and 83% of secondary follicles co-cultured with AOEC survived, whereas the majority of follicles cultured on gel or matrigel underwent atresia.

Conclusions

This is the first report of successful isolation and culture of ovarian ECs. We suggest that co-culture with activated ovarian ECs promotes early follicular development and survival. This model is a novel platform for the in vitro maturation of early follicles and for the future exploration of endothelial-follicular communication.

Capsule

In vitro development of early follicles necessitates a complex interplay of growth factors and signals required for development. Endothelial cells (ECs) may elaborate essential “angiocrine factors” involved in organ regeneration. We demonstrate that co-culture with ovarian ECs enables culture of primary and early secondary mouse ovarian follicles.

Modeling human endothelial cell transformation in vascular neoplasias

Endothelial cell (EC)-derived neoplasias range from benign hemangioma to aggressive metastatic angiosarcoma, which responds poorly to current treatments and has a very high mortality rate. The development of treatments that are more effective for these disorders will be expedited by insight into the processes that promote abnormal proliferation and malignant transformation of human ECs. The study of primary endothelial malignancy has been limited by the rarity of the disease; however, there is potential for carefully characterized EC lines and animal models to play a central role in the discovery, development and testing of molecular targeted therapies for vascular neoplasias. This review describes molecular alterations that have been identified in EC-derived neoplasias, as well as the processes that underpin the immortalization and tumorigenic conversion of ECs. Human EC lines, established through the introduction of defined genetic elements or by culture of primary tumor tissue, are catalogued and discussed in relation to their relevance as models of vascular neoplasia.

DC8 and DC13 var genes associated with severe malaria bind avidly to diverse endothelial cells

During blood stage infection, Plasmodium falciparum infected erythrocytes (IE) bind to host blood vessels. This virulence determinant enables parasites to evade spleen-dependent killing mechanisms, but paradoxically in some cases may reduce parasite fitness by killing the host. Adhesion of infected erythrocytes is mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1), a family of polymorphic adhesion proteins encoded by var genes. Whereas cerebral binding and severe malaria are associated with parasites expressing DC8 and DC13 var genes, relatively little is known about the non-brain endothelial selection on severe malaria adhesive types. In this study, we selected P. falciparum-IEs on diverse endothelial cell types and demonstrate that DC8 and DC13 var genes were consistently among the major var transcripts selected on non-brain endothelial cells (lung, heart, bone marrow). To investigate the molecular basis for this avid endothelial binding activity, recombinant proteins were expressed from the predominant upregulated DC8 transcript, IT4var19. In-depth binding comparisons revealed that multiple extracellular domains from this protein bound brain and non-brain endothelial cells, and individual domains largely did not discriminate between different endothelial cell types. Additionally, we found that recombinant DC8 and DC13 CIDR1 domains exhibited a widespread endothelial binding activity and could compete for DC8-IE binding to brain endothelial cells, suggesting they may bind the same host receptor. Our findings provide new insights into the interaction of severe malaria adhesive types and host blood vessels and support the hypothesis that parasites causing severe malaria express PfEMP1 variants with a superior ability to adhere to diverse endothelial cell types, and may therefore endow these parasites with a growth and transmission advantage.

Alteration in endoglin-related angiogenesis in refractory cytopenia with multilineage dysplasia

The functional mechanisms involved in angiogenesis and the potential role of endoglin (ENG), recently described as a new marker for this process, have not been explored in Myelodysplastic Syndromes (MDS). In order to gain insight in MDS angiogenesis a combined analysis in bone marrow (BM) of gene expression levels, angiogenesis-related soluble factors and functional angiogenesis-related studies was carried out. Ninety-seven MDS patients and forty-two normal BM samples were studied. The morphology of the capillary-like structures originated by two endothelial cells lines in the BM environment of patients with refractory cytopenia with multilineage dysplasia (RCMD) was different from those of the remaining MDS. In addition, the BM mononuclear cells from RCMD patients displayed over-expression of VEGF, HIF and FN1 while they showed reduced expression of ENG in contrast to the normal ENG expression of the remaining low-risk MDS and the high expression of ENG in high-risk MDS subtype. Moreover, higher soluble ENG and soluble FLT-1 levels in BM microenvironment were observed in RCMD cases, which distinguished them from other individuals. Therefore, the present study suggests that the patterns of angiogenesis are different between the MDS subtypes. The differences in angiogenesis observed in RCMD patients could be related to ENG abnormalities.

Context- and cell-dependent effects of Delta-like 4 targeting in the bone marrow microenvironment

Delta-like 4 (Dll4) is a ligand of the Notch pathway family which has been widely studied in the context of tumor angiogenesis, its blockade shown to result in non-productive angiogenesis and halted tumor growth. As Dll4 inhibitors enter the clinic, there is an emerging need to understand their side effects, namely the systemic consequences of Dll4:Notch blockade in tissues other than tumors. The present study focused on the effects of systemic anti-Dll4 targeting in the bone marrow (BM) microenvironment. Here we show that Dll4 blockade with monoclonal antibodies perturbs the BM vascular niche of sub-lethally irradiated mice, resulting in increased CD31⁺, VE-Cadherin⁺ and c-kit⁺ vessel density, and also increased megakaryocytes, whereas CD105⁺, VEGFR3⁺, SMA⁺ and lectin⁺ vessel density remained unaltered. We investigated also the expression of angiocrine genes upon Dll4 treatment in vivo, and demonstrate that IGFbp2, IGFbp3, Angpt2, Dll4, DHH and VEGF-A are upregulated, while FGF1 and CSF2 are reduced. In vitro treatment of endothelial cells with anti-Dll4 reduced Akt phosphorylation while maintaining similar levels of Erk 1/2 phosphorylation. Besides its effects in the BM vascular niche, anti-Dll4 treatment perturbed hematopoiesis, as evidenced by increased myeloid (CD11b⁺), decreased B (B220⁺) and T (CD3⁺) lymphoid BM content of treated mice, with a corresponding increase in myeloid circulating cells. Moreover, anti-Dll4 treatment also increased the number of CFU-M and -G colonies in methylcellulose assays, independently of Notch1. Finally, anti-Dll4 treatment of donor BM improved the hematopoietic recovery of lethally irradiated recipients in a transplant setting. Together, our data reveals the hematopoietic (BM) effects of systemic anti-Dll4 treatment result from qualitative vascular changes and also direct hematopoietic cell modulation, which may be favorable in a transplant setting.

Effect of palmitic acid and linoleic acid on expression of ICAM-1 and VCAM-1 in human bone marrow endothelial cells (HBMECs)

INTRODUCTION

The amount and type of fatty acids (FAs) in the diet influence the risk of atherosclerosis. Palmitic acid and linoleic acid exist at high levels in Iranian edible oils. In this study, we investigated the effect of palmitic acid and linoleic acid on expression of soluble and cell-associated forms of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in human bone marrow endothelial cells (HBMECs).

MATERIAL AND METHODS

The endothelial cells were induced with bacterial lipopolysaccharide (LPS) or tumor necrosis factor α (TNF-α), and thereafter incubated with palmitic or linoleic acid. The level of soluble and cell-associated VCAM-1 and ICAM-1 were analyzed using ELISA and western blot.

RESULTS

Our findings indicated that palmitic acid up-regulates the expression of ICAM-1 and VCAM-1 in HBMECs when these cells are induced with TNF-α or LPS. In addition, the results suggest that linoleic acid could sustain up-regulated ICAM-1 and VCAM-1 in activated endothelial cells.

CONCLUSIONS

Chronic activation of endothelial cells in the presence of palmitic and linoleic may account for pathogenesis of cardiovascular events. These findings provide further support for the detrimental effects of these fatty acids, especially palmitic acid, in promotion and induction of cardiovascular diseases which are prevalent in the Iranian population.

CD45 regulates homing and engraftment of immature normal and leukemic human cells in transplanted immunodeficient mice

Bone marrow homing and engraftment by clinically transplanted hematopoietic stem and progenitor cells is a complex process that is not fully understood. We report that the pan-leukocyte CD45 phosphatase plays an essential role in trafficking and repopulation of the bone marrow by immature human CD34(+) cells and leukemic cells in transplanted nonobese diabetic severe combined immunodeficient mice. Inhibiting CD45 function by blocking antibodies or a CD45 inhibitor impaired the motility of both normal and leukemic human cells. Blocking CD45 inhibited homing and repopulation by immature human CD34(+) cells as well as homing of primary patient leukemic cells. In addition, CD45 inhibition negatively affected development of hematopoietic progenitors in vitro and their recovery in transplanted recipients in vivo, revealing the central role of CD45 in the regulation of hematopoiesis. Moreover, CD45 blockage induced a hyperadhesive phenotype in immature human progenitor cells as well as in murine leukocytes, leading to their defective adhesion interactions with endothelial cells. This phenotype was further manifested by the ability of CD45 blockage to prevent breakdown of adhesion interactions in the BM, which inhibited murine progenitor mobilization. The substantial effects of a direct CD45 inhibition point at its essential roles in cell trafficking, including murine progenitor cell mobilization and both normal immature and leukemic human hematopoietic cells as well as regulation of hematopoiesis and engraftment potential.

Endothelial cells regulate cardiomyocyte development from embryonic stem cells

The molecules and environment that direct pluripotent stem cell differentiation into cardiomyocytes are largely unknown. Here, we determined a critical role of receptor tyrosine kinase, EphB4, in regulating cardiomyocyte generation from embryonic stem (ES) cells through endothelial cells. The number of spontaneous contracting cardiomyocytes, and the expression of cardiac-specific genes, including alpha-MHC and MLC-2V, was significantly decreased in EphB4-null ES cells. EphB4 was expressed in endothelial cells underneath contracting cardiomyocytes, but not in cardiomyocytes. Angiogenic inhibitors, including endostatin and angiostatin, inhibited endothelial cell differentiation and diminished cardiomyogenesis in ES cells. Generation of functional cardiomyocytes and the expression of cardiac-specific genes were significantly enhanced by co-culture of ES cells with human endothelial cells. Furthermore, the defects of cardiomyocyte differentiation in EphB4-deficient ES cells were rescued by human endothelial cells. For the first time, our study demonstrated that endothelial cells play an essential role in facilitating cardiomyocyte differentiation from pluripotent stem cells. EphB4 signaling is a critical component of the endothelial niche to regulate regeneration of cardiomyocytes.

Instructive role of the vascular niche in promoting tumour growth and tissue repair by angiocrine factors

The precise mechanisms whereby anti-angiogenesis therapy blocks tumour growth or causes vascular toxicity are unknown. We propose that endothelial cells establish a vascular niche that promotes tumour growth and tissue repair not only by delivering nutrients and O2 but also through an 'angiocrine' mechanism by producing stem and progenitor cell-active trophogens. Identification of endothelial-derived instructive angiocrine factors will allow direct tumour targeting, while diminishing the unwanted side effects associated with the use of anti-angiogenic agents.

The CysLT1 ligand leukotriene D4 supports alpha4beta1- and alpha5beta1-mediated adhesion and proliferation of CD34+ hematopoietic progenitor cells

Cytokines and chemokines control hematopoietic stem and progenitor cell (HPC) proliferation and trafficking. However, the role of nonpeptide mediators in the bone marrow microenvironment has remained elusive. Particularly CysLT(1), a G protein-coupled receptor recognizing inflammatory mediators of the cysteinyl leukotriene family, is highly expressed in HPCs. We therefore analyzed the effects of its ligands on human CD34(+) HPCs. The most potent CysLT(1) ligand, LTD(4), rapidly and significantly up-regulated alpha(4)beta(1) and alpha(5)beta(1) integrin-dependent adhesion of both primitive and committed HPC. LTD(4)-triggered adhesion was inhibited by specific CysLT(1) antagonists. The effects of other CysLT(1) ligands were weak (LTC(4)) or absent (LTE(4)). In serum-free liquid cultures supplemented with various hematopoietic cytokines including IL-3, only LTD(4) significantly augmented the expansion of HPCs in a dose-dependent manner comparable to that of peptide growth factors. LTC(4) and LTE(4) were less effective. In CD34(+) cell lines and primary HPCs, LTD(4) induced phosphorylation of p44/42 ERK/MAPK and focal adhesion kinase-related tyrosine kinase Pyk2, which is linked to integrin activation. Bone marrow stromal cells produced biologically significant amounts of cysteinyl leukotrienes only when hematopoietic cells were absent, suggesting a regulatory feedback mechanism in the hematopoietic microenvironment. In contrast to antagonists of the homing-related G protein-coupled receptor CXCR4, administration of a CysLT(1) antagonist failed to induce human CD34(+) HPC mobilization in vivo. Our results suggest that cysteinyl leukotriene may contribute to HPC retention and proliferation only when cysteinyl leukotriene levels are increased either systemically during inflammation or locally during marrow aplasia.

Bovine microvascular endothelial cells immortalized with human telomerase

Primary cultures of bovine microvascular endothelial cells (BME) isolated from the adrenal cortex, are commonly used to study vascular endothelium, but have a limited life span. To circumvent these limitations, we have immortalized BME cells with either simian virus 40 (SV40) or with a retrovirus containing the coding region of human telomerase reverse transcriptase (hTERT), and have investigated whether the clonal populations obtained, maintain differentiated properties characteristic of microvascular endothelium. Immortalized cells were characterized for maintenance of typical endothelial morphology, marker expression, and functional characteristics including uptake of Acetylated low-density lipoprotein (Ac-LDL), capillary-like tube formation in three-dimensional collagen gels, as well as metalloproteinase (MMP) and plasminogen activator (PA)-mediated extracellular proteolysis. Whilst immortalization of BME cells with SV40 was associated with loss of endothelial-specific properties, hTERT-BME exhibited an endothelial phenotype similar to that of wild-type endothelial cells. Specifically, they showed a typical cobblestone morphology, were contact-inhibited, expressed endothelial cell-specific markers (e.g., CD31, vWF) and both fibroblast growth factor receptor 1 (FGFR-1) and vascular endothelial growth factor receptor-2 (VEGFR-2). In addition, they expressed receptors for LDL. Importantly, when grown on collagen gels, hTERT-BME cells underwent MMP-dependent tube-like structure formation in response to VEGFR-2 activation. In a collagen gel sandwich assay, hTERT-BME formed tubular structures in the absence of exogenously added angiogenic cytokines. Sustained tube formation was induced by VEGF-A alone or in combination with FGF-2. From 17 sub-clones that displayed a non-transformed phenotype, a high proliferative capacity and tubulogenic properties in three-dimensional collagen gels, we isolated two distinct subpopulations that display a highly specific response to VEGF-A or to FGF-2. We have generated hTERT-BME cells that maintain endothelial-specific properties and function and have isolated clones that respond differentially to VEGF-A or FGF-2. These immortalized cell lines will facilitate the study of endothelial cell biology.

Inhibition of human prostate cancer growth, osteolysis and angiogenesis in a bone metastasis model by a novel mechanism-based selective gelatinase inhibitor

Metastasis to the bone is a major clinical complication in patients with prostate cancer (PC). However, therapeutic options for treatment of PC bone metastasis are limited. Gelatinases are members of the matrix metalloproteinase (MMP) family and have been shown to play a key role in PC metastasis. Herein, we investigated the effect of SB-3CT, a covalent mechanism-based MMP inhibitor with high selectivity for gelatinases, in an experimental model of PC bone metastases. Intraperitoneal (i.p.) treatment with SB-3CT (50 mg/kg) inhibited intraosseous growth of human PC3 cells within the marrow of human fetal femur fragments previously implanted in SCID mice, as demonstrated by histomorphometry and Ki-67 immunohistochemistry. The anti-osteolytic effect of SB-3CT was confirmed by radiographic images. Treatment with SB-3CT also reduced intratumoral vascular density and bone degradation in the PC3 bone tumors. A direct inhibition of bone marrow endothelial cell invasion and tubule formation in Matrigel by SB-3CT in vitro was also demonstrated. The use of the highly selective gelatinase inhibitors holds the promise of effective intervention of metastases of PC to the bone.

Etoposide differentially affects bone marrow and dermal derived endothelial cells

Chemotherapy alteration of the bone marrow microenvironment has the potential to influence hematopoietic recovery following transplantation. To discern the effect of specific drugs on components of the complex marrow microenvironment, in vitro models have significant utility. In the current study we sought to determine whether dermal (HMEC-1) and marrow derived endothelial cells (BMEC-1) respond differently to identical chemotherapy exposure. BMEC-1 cells were consistently more sensitive to etoposide exposure than HMEC-1 cells, measured as reduced viability. BMEC-1 also had reduced focal adhesion kinase (FAK) and VCAM-1 protein expression following chemotherapy, in contrast to dermal derived endothelial cells in which neither protein was influenced dramatically by etoposide. The two endothelial cell lines had markedly different levels of baseline VE-Cadherin protein, which was modestly altered by treatment. These data indicate that marrow derived endothelial cells have disruption of specific proteins following chemotherapy that may influence their ability to facilitate hematopoietic cell entry or egress from the marrow. In addition, these observations suggest that while BMEC-1 and HMEC-1 share a variety of characteristics, they differ significantly in their response to stress and should be incorporated into specific models with this consideration.

Expansion of cord blood CD34+ hematopoietic progenitor cells in coculture with autologous umbilical vein endothelial cells (HUVEC) is superior to cytokine-supplemented liquid culture

Expansion of hematopoietic progenitor cells (HPC) in the presence of endothelium has been shown to result in grafts capable of restoring hematopoiesis in a myeloablated host. However, the use of xenogeneic endothelium or cell lines may carry risks in a clinical transplantation setting. We explored the feasibility of cord blood progenitor cell expansion in vitro in an autologous coculture system using umbilical vein endothelial cells (HUVEC). CD34+ HPC and HUVEC were isolated from the same umbilical cord. For 3 days, HPC were maintained in serum-free medium supplemented with a single cytokine (SCF) or a cytokine combination (SCF, Flt3-ligand, IL-6). Meanwhile, adherent HUVEC cultures were established. After addition of VEGF and IL-1 at day 3, the cells were either added to HUVEC cultures or grown without endothelial cells for further 7 days. Total cells, CD34+ and clonogenic progenitors were significantly increased when coculture was compared to liquid culture. Long-term culture-initiating cells (LTC-IC) and cobble stone area-forming cells (CAFC, limiting dilution analysis) were detected more frequently after coculture with endothelial cells. Also precursors and mature myeloid cells were observed after expansion. We conclude that coculture with autologous HUVEC represents a feasable approach for ex vivo expansion of cord blood HPC.

Thrombospondin 1, produced by endothelial cells under the action of erythropoietin, stimulates thymidine incorporation into erythroid cells and counteracts the inhibitory action of insulin-like growth factor binding protein 3

The nature of erythropoietin (EPO)-dependent, erythroid cell regulatory factors secreted by endothelial cells is largely unknown. The production of thrombospondin 1 (TSP-1) and insulin-like growth factor binding protein 3 (IGFBP-3) is increased in cultures of human umbilical vein endothelial cells (HUVEC) incubated with erythropoietin (EPO). Simultaneous incubation of HUVEC with EPO and interleukin 3 (IL-3) resulted in a decreased production, suggesting that both TSP-1 and IGFBP-3 belong to the EPO- and IL-3-dependent erythroid regulatory factors previously described in cultures of bone marrow endothelial cells. TSP-1 and TSP-1 derived synthetic peptides based on the CD36 and CD47 binding sites of TSPs increased thymidine incorporation into bovine erythroid cells of fetal liver. IGBBP-3 inhibited thymidine incorporation in the same cells. Preincubation of erythroid cells with TSP-1 eliminated the inhibitory activity of IGFBP-3. We suggest that EPO-dependent, endothelial-derived TSP-1 may play a positive role in red cell production by acting directly on erythroid cells, stimulating DNA synthesis and preventing the inhibitory action of IGFBP-3.

Role of ChemR23 in directing the migration of myeloid and plasmacytoid dendritic cells to lymphoid organs and inflamed skin

Chemerin is a chemotactic agent that was recently identified as the ligand of ChemR23, a serpentine receptor expressed by activated macrophages and monocyte-derived dendritic cells (DCs). This paper shows that blood plasmacytoid and myeloid DCs express functional ChemR23. Recombinant chemerin induced the transmigration of plasmacytoid and myeloid DCs across an endothelial cell monolayer. In secondary lymphoid organs (lymph nodes and tonsils), ChemR23 is expressed by CD123⁺ plasmacytoid DCs and by CD1a⁺ DC-SIGN⁺ DCs in the interfollicular T cell area. ChemR23⁺ DCs were also observed in dermis from normal skin, whereas Langerhans cells were negative. Chemerin expression was selectively detected on the luminal side of high endothelial venules in secondary lymphoid organs and in dermal endothelial vessels of lupus erythematosus skin lesions. Chemerin⁺ endothelial cells were surrounded by ChemR23⁺ plasmacytoid DCs. Thus, ChemR23 is expressed and functional in plasmacytoid DCs, a property shared only by CXCR4 among chemotactic receptors. This finding, together with the selective expression of the cognate ligand on the luminal side of high endothelial venules and inflamed endothelium, suggests a key role of the ChemR23/chemerin axis in directing plasmacytoid DC trafficking.

Production of hemo- and immunoregulatory cytokines by erythroblast antigen+ and glycophorin A+ cells from human bone marrow

BACKGROUND

Erythroid nuclear cells (ENC) of the bone marrow (BM) have not previously been considered as important producers of wide spectrum of haemo- and immunoregulatory cytokines. The aim of the current work was to confirm the production of the main hemo- and immunoregulatory cytokines in human ENC from BM.

RESULTS

We used native human BM ENC in our experiments. We for the first time have shown, that the unstimulated erythroblasts (Gl A+ or AG-EB+) produced a wide spectrum of immunoregulatory cytokines. Human BM ENC produce cytokines such as interleukin (IL)-1beta, IL-2, IL-4, IL-6, interferon (IFN)-gamma, transforming growth factor (TGF)-beta1, tumor necrosis factor (TNF)-alpha and IL-10. They can be sub-divided into glycophorin A positive (Gl A+) and erythroblast antigen positive (AG-EB+) cells. To study potential differences in cytokine expression between these subsets, ENC were isolated and purified using specific antibodies to Gl A and AG-EB and the separated cells were cultivated for 24 hours. The cytokine contents of the supernatant were measured by electrochemiluminescence immunoassay. Quantitative differences in TGF-beta1 and TNF-alpha production were found between Gl A+ and AG-EB+ BM ENC. Furthermore, in vitro addition of erythropoietin (EPO) reduced IFN-gamma and IL-2 production specifically by the AG-EB+ ENC. Thus, Gl A+ and AG-EB+ ENC produce IL-1beta, IL-2, IL-4, IL-6, IFN-gamma, TGF-beta1 and TNF-alpha. Gl A+ ENC also produce IL-10.

CONCLUSION

Cytokine production by erythroid nuclear cells suggests that these cells might be involved in regulating the proliferation and differentiation of hematopoietic and immunocompetent cells in human BM.

Generation and characterization of telomerase-transfected human lymphatic endothelial cells with an extended life span

The study of lymphatic endothelial cells and lymphangiogenesis has, in the past, been hampered by the lack of lymphatic endothelial-specific markers. The recent discovery of several such markers has permitted the isolation of lymphatic endothelial cells (LECs) from human skin. However, cell numbers are limited and purity is variable with the different isolation procedures. To overcome these problems, we have transfected human dermal microvascular endothelial cells (HDMVECs) with a retrovirus containing the coding region of human telomerase reverse transcriptase (hTERT), and have produced a cell line, hTERT-HDLEC, with an extended lifespan. hTERT-HDLEC exhibit a typical cobblestone morphology when grown in culture, are contact-inhibited, and express endothelial cell-specific markers. hTERT-HDLEC also express the recognized lymphatic markers, Prox-1, LYVE-1 and podoplanin, as well as integrin alpha9, but do not express CD34. They also form tube-like structures in three-dimensional collagen gels when stimulated with vascular endothelial growth factors -A and -C. Based on these currently recognized criteria, these cells are LEC. Surprisingly, we also found that the widely studied HMEC-1 cell line expresses recognized lymphatic markers; however, these cells are also CD34-positive. In summary, the ectopic expression of hTERT increases the life span of LECs and does not affect their capacity to form tube-like structures in a collagen matrix. The production and characterization of hTERT-HDLEC will facilitate the study of the properties of lymphatic endothelium in vitro.

Suspended cells from trabecular bone by collagenase digestion become virtually identical to mesenchymal stem cells obtained from marrow aspirates

Several reports describe that the explant culture of the trabecular bone after collagenase treatment produces mesenchymal stem cells (MSCs). However, the suspended cells had not been intensively examined concerning MSCs. We hypothesized that the cells would acquire the properties of MSCs during their expansion and therefore compared them with marrow aspirate-derived MSCs. Human trabecular bones were washed, digested, filtered, and expanded clonally for 14 days. Their proliferation ability (n = 9) and differentiation potentials for chondrocyte, adipocyte, and osteoblast (n = 6) were similar with those of marrow aspirate-derived MSCs. Epitope and mRNA analysis revealed some differences in both types of cells, which disappeared with expansion and subcultivation. A mixed population of collagenase-released (CR) cells had similar differentiation potentials with CR clone, CD31(+) fraction, and osteoblastic cells. For quantitative study, trabecular bone and bone marrow were harvested by single aspiration using a biopsy needle (n = 16). Although the total nucleated cell number harvested was similar, the colony-forming efficiency of CR cells was approximately 100-fold higher than that of BM cells and more than 1 million CR cells could be obtained in 14 days from all donors. Enzymatically released cells from trabecular bone became virtually identical to marrow aspirate-derived MSCs, demonstrating that a trabecular bone fragment can be an alternative source of MSCs.

The bHLH TAL-1/SCL regulates endothelial cell migration and morphogenesis

The basic helix-loop-helix tal-1 gene (or scl), known for its fundamental role in embryonic and adult hematopoiesis in vertebrates, is also required for embryonic vascular remodeling. In adults, TAL-1 protein is undetectable in quiescent endothelium but it is present in newly formed vessels including tumoral vasculature, indicating its involvement in angiogenesis. Here, we demonstrate that TAL-1 expression is tightly regulated during in vitro angiogenesis: it is low during the initial step of migration and is upregulated during formation of capillary-like structures. We investigated whether ectopic expression of either wild-type TAL-1 or a dominant-negative mutant lacking the DNA-binding domain (Delta-bas) modulates the activity of human primary endothelial cells in the angiogenic processes of migration, proliferation and cell morphogenesis. Overexpression of either wild-type or Delta-bas TAL-1 affected chemotactic migration of primary endothelial cells without modifying their proliferative properties. Ectopic expression of wild-type TAL-1 accelerated the formation of capillary-like structures in vitro and, in vivo, enhanced vascularisation in mice (Matrigel implants) associated with a general enlargement of capillary lumens. Importantly, transduction of the mutant Delta-bas completely impaired in vitro angiogenesis and strongly inhibited vascularisation in mice. Taken together, our data show that TAL-1 modulates the angiogenic response of endothelial cells by stimulating cell morphogenesis and by influencing their behavior in migration. This study highlights the importance of TAL-1 regulation in postnatal vascular remodeling and provides the first physiological evidence that links TAL-1 activity to endothelial cell morphogenic processes.

Human bone marrow endothelial cells elaborate non-stromal-cell-derived factor-1 (SDF-1)-dependent chemoattraction and SDF-1-dependent transmigration of haematopoietic progenitors

This study investigated human bone marrow endothelial cells (BMEC) chemoattractive activity in relation to haematopoietic cell trafficking. BMEC-conditioned medium induced chemoattraction of haematopoietic progenitor cells. Migration was not inhibited by pretreating the cells with pertussis toxin (PTX) or 12G5, indicating that the chemoattractive activity was not dependent on stromal-cell-derived factor-1 (SDF-1). Spontaneous migration, but not SDF-1-mediated chemotaxis of haematopoietic progenitors, was better supported by BMEC as compared with umbilical vein endothelial cells. The superior migration was abolished by pretreating the cells with PTX, indicating that BMEC-derived SDF-1 favours bone marrow endothelium, with better transmigration of haematopoietic progenitors.

Immortalization of bovine capillary endothelial cells by hTERT alone involves inactivation of endogenous p16INK4A/pRb

Recent studies show that stable expression of the human telomerase catalytic subunit, hTERT, alone can lead several types of normal human somatic cells to bypass replicative senescence and become immortal. The molecular mechanisms by which telomerase immortalizes cells are not fully understood, although a key function of telomerase is to maintain a critical length of telomeres in order to preserve the stability and integrity of the genome. Here we report that stable transfection of hTERT alone was sufficient to allow bovine capillary endothelial (BCE) cells to bypass senescence and acquire immortality. Surprisingly, telomere lengths in these stable transfectants were progressively shortened during an increasing number of population doublings (PDLs), despite high telomerase activity. The expression of the cyclin-dependent kinase inhibitors (CDKIs) p16INK4A and p21CIP1/WAF1 was concomitantly repressed, and the retinoblastoma protein (pRb) was maintained in a hyperphosphorylated state in the telomerase-expressing cells. Re-expression of p16INK4A in these cells by either treatment with a demethylating agent or by adenovirus-mediated expression reinduced a senescence-like phenotype, suggesting that the inactivation of p16INK4A was due to DNA methylation and was crucial for the immortalization process. In agreement with this finding, the expression levels of the prototypic DNA methyltransferase DNMT1 were elevated in the hTERT-positive cells.

Multiple stages of malignant transformation of human endothelial cells modelled by co-expression of telomerase reverse transcriptase, SV40 T antigen and oncogenic N-ras

We have modelled multiple stages of malignant transformation of human endothelial cells (ECs) by overexpressing the catalytic subunit of human telomerase (hTERT), together with SV40 T antigen (SV40T) and oncogenic N-ras. Transfection with hTERT alone, led to the immortalization of two out of three cultures of bone marrow-derived ECs (BMECs). One hTERT transduced BMEC culture underwent a long proliferative lag before resuming proliferation. BMECs transfected with hTERT alone were functionally and phenotypically normal. BMECs transfected with SV40T (BMSVTs) had an extended lifespan, but eventually succumbed to crisis. BMSVTs exhibited a partially transformed phenotype, demonstrating growth factor independence, altered antigen expression and forming tiny, infrequent colonies in vitro. Transduction of BMSVTs with hTERT resulted in immortalization of 4 out of 4 cultures. BMSVTs immortalized with hTERT formed large colonies in vitro and small transient tumours in vivo. BMECs co-expressing SV40T, hTERT and N-ras exhibited an overtly transformed phenotype; forming very large colonies with an altered morphology and generating rapidly growing tumours in vivo. These investigations demonstrate transformation of human ECs to an overtly malignant phenotype. This model will be useful for understanding mechanisms underlying vascular and angiogenic neoplasias, as well as for testing drugs designed to curtail aberrant EC growth.

Phosphorylation by mitogen-activated protein kinase mediates the hypoxia-induced turnover of the TAL1/SCL transcription factor in endothelial cells

The basic helix-loop-helix transcription factor TAL1 (or SCL), originally identified from its involvement by a chromosomal rearrangement in T-cell acute lymphoblastic leukemia, is required for hematopoietic development. TAL1 also has a critical role in embryonic vascular remodeling and is expressed in endothelial cells postnatally, although little is known about its function or regulation in this cell type. We report here that the important proangiogenic stimulus hypoxia stimulates phosphorylation, ubiquitination, and proteasomal breakdown of TAL1 in endothelial cells. Tryptic phosphopeptide mapping and chemical inhibitor studies showed that hypoxia induced the mitogen-activated protein kinase-mediated phosphorylation of a single serine residue, Ser(122), in the protein, and site-directed mutagenesis demonstrated that Ser(122) phosphorylation was necessary for hypoxic acceleration of TAL1 turnover in an immortalized murine endothelial cell line. Finally, whereas TAL1 expression was detected in endothelial cells from both large and small vessels, hypoxia-induced TAL1 turnover was observed only in microvascular endothelial cells. Besides their implications for TAL1 function in angiogenic processes, these results demonstrate that a protein kinase(s) important for mitogenic signaling is also utilized in hypoxic endothelial cells to target a transcription factor for destruction.

Efficient mobilization and recruitment of marrow-derived endothelial and hematopoietic stem cells by adenoviral vectors expressing angiogenic factors

Adult bone marrow (BM) is a rich reservoir for endothelial and hematopoietic stem and progenitor cells that contribute to revascularization of injured and tumor tissue. Physiological stress results in the release of specific chemo-cytokines that promote mobilization of stem cells to the circulation and direct their incorporation into the target tissues. In order to dissect the mechanism and identify the cellular mediators that regulate stem cell recruitment, we have developed an in vivo murine model, in which the plasma levels of chemokines are elevated by introducing adenoviral vectors (Advectors) expressing such chemokines. Among the known stem cell-active chemokines, the angiogenic factor VEGF through interaction with its receptors, VEGFR2 and VEGFR1 expressed on endothelial and hematopoietic stem cells, promotes mobilization and recruitment of these cells into the neo-angiogenic sites, thereby accelerating the revascularization process. Based on these studies, it has become apparent that mobilization of stem cells is a dynamic process and requires sequential release of chemocytokines, expression of adhesion molecules and activation of proteases that facilitate egress of cells from the BM to the circulation. Chemokine-activation of metalloproteinases is essential for the release of bio-active cytokines, thereby enhancing stem cell mobilization potential. Advectors are ideal for delivery of chemocytokines since they allow for long-term robust expression facilitating in vivo proliferation and mobilization of large numbers of an otherwise rare population of stem cells. VEGF-mobilized endothelial and hematopoietic stem cells provide for an enriched source of adult pluripotent cells that can be used for revascularization, tissue regeneration or gene therapy.

The regulation of prostate cancer cell adhesion to human bone marrow endothelial cell monolayers by androgen dihydrotestosterone and cytokines

A previous study from our laboratory suggested that prostate cancer metastasis to bone may be mediated, in part, by preferential adhesion to human bone marrow endothelial (HBME) cells. Tumor cell adhesion to endothelial cells may be modulated by the effect of cytokines on cell adhesion molecules (CAMs). Tumor necrosis factor-alpha (TNF-alpha) regulates VCAM expression on the endothelium and this effect is enhanced by dihydrotestosterone (DHT). Transforming growth factor-beta (TGF-beta) stimulates the expression of alpha2beta1 integrin on PC-3 cells. The current study investigated the effects of the above cytokines and DHT (singularly and in various combinations) upon HBME and prostate cancer cell expression of VCAM, alpha2 integrin subunit, and beta1 integrin subunit by flow cytometry. We also monitored the effects of the above treatments on PC-3 cell adhesion to HBME monolayers. The data demonstrate that none of the treatments significantly altered the expression of selected CAMs on HBME cell and neoplastic prostate cell lines. The treatment of HBME monolayers with various combinations of cytokines and DHT prior to performing adhesion assays with PC-3 demonstrates that treatments containing TGF-beta reduced PC-3 cell adhesion to HBME monolayers by 32% or greater (P < 0.05). The reduction in PC-3 cell adhesion to TGF-beta-treated HBME monolayers was dose dependent. Interestingly, LNCaP cells but not PC-3 cells treated with TGF-beta had a reduced ability to adhere to untreated HBME monolayers. These results suggest that TGF-beta may reduce tumor cell adhesion to bone marrow microvascular endothelium, in vivo. The biological significance of this observation is discussed.

Antagonism between interleukin 3 and erythropoietin in mice with azidothymidine-induced anemia and in bone marrow endothelial cells

Azidothymidine (AZT)-induced anemia in mice can be reversed by the administration of IGF-IL-3 (fusion protein of insulin-like growth factor II (IGF II) and interleukin 3). Although interleukin 3 (IL-3) and erythropoietin (EPO) are known to act synergistically on hematopoietic cell proliferation in vitro, injection of IGF-IL-3 and EPO in AZT-treated mice resulted in a reduction of red cells and an increase of plasma EPO levels as compared to animals treated with IGF-IL-3 or EPO alone. We tested the hypothesis that the antagonistic effect of IL-3 and EPO on erythroid cells may be mediated by endothelial cells. Bovine liver erythroid cells were cultured on monolayers of human bone marrow endothelial cells previously treated with EPO and IGF-IL-3. There was a significant reduction of thymidine incorporation into both erythroid and endothelial cells in cultures pre-treated with IGF-IL-3 and EPO. Endothelial cell culture supernatants separated by ultrafiltration and ultracentrifugation from cells treated with EPO and IL-3 significantly reduced thymidine incorporation into erythroid cells as compared to identical fractions obtained from the media of cells cultured with EPO alone. These results suggest that endothelial cells treated simultaneously with EPO and IL-3 have a negative effect on erythroid cell production.

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.

Functional murine leukemia virus vectors pseudotyped with the visna virus envelope show expanded visna virus cell tropism

Pseudotype virus vectors serve as a powerful tool for the study of virus receptor usage and entry. We describe the development of murine leukemia virus (MuLV) particles pseudotyped with the visna virus envelope glycoprotein and encoding a green fluorescent protein reporter as a tool to study the expression of the visna virus receptor. Functional MuLV/visna virus pseudotypes were obtained when the cytoplasmic tail of the visna virus envelope TM protein was truncated to 3, 7, or 11 amino acids in length. MuLV/visna virus particles were used to transduce a panel of cell types from various organisms, including sheep, goat, human, hamster, mouse, monkey, and quail. The majority of the cells examined were susceptible to MuLV/visna pseudotype viruses, supporting the notion that the visna virus cellular receptor is a widely expressed protein found in many species. Of 16 different cell types tested, only mouse embryo fibroblast NIH 3T3 cells, hamster ovary CHO cells, and the human promonocyte cell line U937 cells were not susceptible to transduction by the pseudotyped virus. The production of functional MuLV/visna virus pseudotypes has provided a sensitive, biologically relevant system to study visna virus cell entry and envelope-receptor interactions.

CD44 is a major E-selectin ligand on human hematopoietic progenitor cells

E-selectin plays a critical role in mediating tissue-specific homing of T cells into skin, and of primitive hematopoietic progenitor cells (HPCs) into bone marrow (BM). Though it is known that a glycoform of PSGL-1 (CLA) functions as the principal E-selectin ligand on human T lymphocytes, the E-selectin ligand(s) of human HPCs has not been identified. We used a shear-based adherence assay to analyze and define the E-selectin ligand activity of membrane proteins from human HPCs. Our data show that PSGL-1 expressed on human HPCs is an E-selectin ligand, and that HPCs also express a previously unrecognized E-selectin ligand, CD44. The E-selectin ligand activity of CD44 is conferred by the elaboration of sialylated, fucosylated binding determinants on N-glycans. This glycoform of CD44 is expressed on primitive CD34+ human HPCs, but not on more mature hematopoietic cells. Under physiologic flow conditions, this molecule mediates E-selectin-dependent rolling interactions over a wider shear range than that of PSGL-1, and promotes human HPC rolling interactions on E-selectin expressed on human BM endothelial cells. These findings offer new insights into the structural biology and physiology of CD44, and into the molecular basis of E-selectin-dependent adhesive interactions that direct homing of human HPC to BM.

Shear forces promote lymphocyte migration across vascular endothelium bearing apical chemokines

Leukocyte transendothelial migration (TEM) is thought to be a chemotactic process controlled by chemokine gradients across the endothelium. Using cytokine-activated human umbilical vascular endothelial cells (HUVECs) as a model of inflamed endothelium, we have shown that apical endothelial chemokines can trigger robust peripheral blood lymphocyte (PBL) migration across endothelial cells. Lymphocyte TEM was promoted by physiological shear stress applied continuously to migrating lymphocytes. Lymphocyte integrins, intact actin cytoskeleton and G(i) protein-mediated chemokine signaling, but not a chemotactic gradient, were mandatory for TEM. PBL TEM did not require intracellular free calcium or intact phosphatidyl inositol kinase activity in migrating lymphocytes. Thus, lymphocyte TEM is promoted by fluid shear-induced mechanical signals coupled to G(i) protein signals at apical endothelial zones.

Hyaluronan synthase elevation in metastatic prostate carcinoma cells correlates with hyaluronan surface retention, a prerequisite for rapid adhesion to bone marrow endothelial cells

Bone marrow is the primary site of metastasis in patients with advanced stage prostate cancer. Prostate carcinoma cells metastasizing to bone must initially adhere to endothelial cells in the bone marrow sinusoids. In this report, we have modeled that interaction in vitro using two bone marrow endothelial cell (BMEC) lines and four prostate adenocarcinoma cell lines to investigate the adhesion mechanism. Highly metastatic PC3 and PC3M-LN4 cells were found to adhere rapidly and specifically (70-90%) to BMEC-1 and trHBMEC bone marrow endothelial cells, but not to human umbilical vein endothelial cells (15-25%). Specific adhesion to BMEC-1 and trHBMEC was dependent upon the presence of a hyaluronan (HA) pericellular matrix assembled on the prostate carcinoma cells. DU145 and LNCaP cells were only weakly adherent and retained no cell surface HA. Maximal BMEC adhesion and HA encapsulation were associated with high levels of HA synthesis by the prostate carcinoma cells. Up-regulation of HA synthase isoforms Has2 and Has3 relative to levels expressed by normal prostate corresponded to elevated HA synthesis and avid BMEC adhesion. These results support a model in which tumor cells with up-regulated HA synthase expression assemble a cell surface hyaluronan matrix that promotes adhesion to bone marrow endothelial cells. This interaction could contribute to preferential bone metastasis by prostate carcinoma cells.

Telomerized human microvasculature is functional in vivo

Previously we showed the superior in vitro survival of human telomerase reverse transcriptase (hTERT)-transduced human endothelial cells (EC). Here we show that retroviral-mediated transduction of hTERT in human dermal microvascular EC (HDMEC) results in cell lines that form microvascular structures when subcutaneously implanted in severe combined immunodeficiency (SCID) mice. Anti-human type IV collagen basement membrane immunoreactivity and visualization of enhanced green fluorescent protein (eGFP)-labeled microvessels confirmed the human origin of these capillaries. No human vasculature was observed after implantation of HT1080 fibrosarcoma cells, 293 human embryonic kidney cells, or human skin fibroblasts. Intravascular red fluorescent microspheres injected into host circulation were found within green "telomerized" microvessels, indicating functional murine-human vessel anastamoses. Whereas primary HDMEC-derived vessel density decreased with time, telomerized HDMEC maintained durable vessels six weeks after xenografting. Modulation of implant vessel density by exposure to different angiogenic and angiostatic factors demonstrated the utility of this system for the study of human microvascular remodeling in vivo.

The role of endothelium in the regulation of hematopoietic stem cell migration

Mobilization of hematopoietic progenitor cells appears to be a multifactorial process which is at least partially regulated at the level of bone marrow microvascular endothelium (BMEC). In order to study the regulation of progenitor cell migration by endothelium in vitro, methods have been developed to isolate BMEC from bone marrow aspirates. In addition, immortalized BMEC cell lines have been generated. Using an in vitro model of migration across bone marrow endothelium, we demonstrate that only a small number of more mature, committed progenitors migrate spontaneously. In this model, adhesion molecules of the beta2-integrin family and the corresponding endothelial ligands are involved. The low spontaneous migratory capacity suggests that, in addition to adhesion molecules which mediate direct cellular contacts, paracrine cytokines and chemokines may play a role in progenitor migration across endothelium. Growth-factor-stimulated hematopoietic cells can produce cytokines which act on endothelial cells (e.g., vascular endothelial growth factor, VEGF), modifying their motility, growth, permeability, and fenestration. Therefore, VEGF might be involved in the mobilization and homing of hematopoietic progenitor cells. Furthermore, transendothelial migration of progenitors in vitro is substantially enhanced by the chemokine stromal-cell-derived factor-1 (SDF-1), which is produced by bone marrow stromal cells. More primitive progenitors, which do not migrate spontaneously, also respond to this chemokine. We conclude that transendothelial progenitor cell migration is regulated by adhesion molecules, paracrine cytokines, and chemokines. Mobilizing hematopoietic growth factors stimulate proliferation of hematopoietic cells, which may indirectly result in changes of the local cytokine and chemokine milieu, adhesion molecule expression, and eventually the mobilization of hematopoietic progenitor cells.

Mass cultured human fibroblasts overexpressing hTERT encounter a growth crisis following an extended period of proliferation

During the process of immortalization, at least two mortality checkpoints, M1 and M2, must be bypassed. Cells that have bypassed M1 (senescence) have an extended life span, but are not necessarily immortal. Recent studies have shown that ectopic expression of the catalytic subunit of telomerase (hTERT) enables normal human cells to bypass senescence (M1) and oncogene transformed cells to avert crisis (M2) and become immortal. However, it is unclear whether hTERT expression is sufficient for normal human fibroblasts to overcome both M1 and M2 and become immortal. We have investigated the role of telomerase in immortalization by maintaining mass cultures of hTERT-transduced primary human fetal lung fibroblasts (MRC-5 cells) for very long periods of time (more than 2 years). In the present studies, up to 70% of MRC-5 cells were transduced with retroviral vectors that express hTERT. hTERT-transduced cells exhibited high levels of telomerase activity, elongation of telomeres, and proliferation beyond senescence. However, after proliferating for more than 36 population doublings (PDLs) beyond senescence, the overall growth rate of hTERT-expressing cells declined. During theses periods of reduced growth, hTERT-transduced MRC-5 cells exhibited features typical of cells in crisis, including an increased rate of cell death and polyploidy. In some instances, very late passage cells acquired a senescence-like phenotype characterized by arrest in the G1 phase of the cell cycle and greatly reduced DNA synthesis. At the onset of crisis, hTERT-transduced cells expressed high levels of telomerase and had very long telomeres, ranging up to 30 kb. Not all cells succumbed to crisis and, consequently, some cultures have proliferated beyond 240 PDLs, while another culture appears to be permanently arrested at 160 PDLs. Late passage MRC-5 cells, including postcrisis cells, displayed no signs of malignant transformation. Our results are consistent with the model in which telomerase and telomere elongation greatly extends cellular life span without inducing malignant changes. However, these investigations also indicate that hTERT-expressing cells may undergo crisis following an extended life span and that immortality is not the universal outcome of hTERT expression in normal diploid fibroblasts.

Immortalisation of human bone marrow endothelial cells: characterisation of new cell lines

BACKGROUND

Adhesion of haematopoietic progenitor cells (HPC) to human bone marrow endothelial cells (HBMEC) plays a key role in homing of HPC to bone marrow. Here we describe four new HBMEC cell lines that can be used to study the (specific) adhesion of HPC to HBMEC.

DESIGN

HBMEC were immortalised with a retroviral construct containing the human papilloma virus 16 E6/E7 genes. Four cell lines were characterised.

RESULTS

The cell lines showed their endothelial nature by the expression of von Willebrand Factor and VE-cadherin (CD144). Electron microscopic analysis revealed normal endothelial-cell characteristics, including the presence of Weibel-Palade bodies and intercellular junction structures. An extensive phenotypic analysis of the cell-lines was performed, they were found to resemble primary HBMEC. The only difference found was the absence of expression of E-selectin (CD62e) and VCAM-1 (CD106) on resting HBMEC cell lines. Upon stimulation with IL-1beta the expression of E-selectin, VCAM-1 and ICAM-1 (CD54) was upregulated. All resting cell lines bound CD34+ HPC. Adhesion was increased by addition of the phorbol ester PMA. Two cell lines showed increased binding upon IL-1beta prestimulation. Highest adhesion was observed after the combination of IL-1beta prestimulation of the endothelial cells and addition of PMA. Binding of CD34+ HPC to HBMEC was compared with the binding to human umbilical vein endothelial cell lines and to a human dermal microvascular endothelial cell line (HMEC-1). So far, we have only found relatively less binding of HPC to IL-1beta prestimulated HMEC-1 cells, which could be explained by a reduced induction of E-selectin and VCAM-1 upon IL-1beta stimulation of these cells.

CONCLUSION

The immortalised HBMEC cell lines have maintained their normal phenotype for the majority of characteristics examined. The expression of E-selectin and VCAM-1, which are not constitutively expressed on the cell lines, can be induced by stimulation of the endothelial cells with IL-1beta. The cell lines have furthermore maintained their capability to bind HPC. They will therefore be useful to investigate the interactions between HPC and HBMEC involved in homing of HPC.

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.

Characterization of novel clonal murine endothelial cell lines with an extended life span

A murine endothelial cell line was recently established from microvessels that had invaded a subcutaneous sponge implant (Dong, Q. G.; Bernasconi, S.; Lostaglio, S., et al. Arterioscl. Thromb. Vasc. Biol. 17:1599-1604; 1997). From these sponge-induced endothelial (SIE) cells, we have isolated two subpopulations endowed with different phenotypic properties. Clone SIE-F consists of large, highly spread cells that have a relatively slow growth rate, form contact-inhibited monolayers, do not grow under anchorage-independent conditions, express elevated levels of thrombospondin-1 (TSP-1) and are not tumorigenic in vivo. In contrast, clone SIE-S2 consists of small, spindle-shaped cells that have a high proliferation rate, do not show contact-inhibition, grow under anchorage-independent conditions, express very low levels of TSP-1 and are tumorigenic in vivo. Both clones express the endothelial markers vascular endothelial-cadherin and vascular intercellular adhesion molecule-1, but do not express CD31 and E-selectin. In addition, SIE-S2 cells, but not SIE-F cells, express the alpha-smooth muscle actin isoform. SIE-S2 cells, but not SIE-F cells, are able to form branching tubes in fibrin gels. The SIE-F and SIE-S2 clones, which have properties of nontransformed and transformed cells, respectively, should provide useful tools to investigate physiological and pathological processes involving vascular endothelium.

Stromal Derived Factor-1–Induced Chemokinesis of Cord Blood CD34+ Cells (Long-Term Culture-Initiating Cells) Through Endothelial Cells Is Mediated by E-Selectin

Homing of hematopoietic stem cells to the bone marrow (BM) involves sequential interaction with adhesion molecules expressed on BM endothelium (BMEC) and chemokine stromal derived factor-1 (SDF-1). However, the mechanism whereby adhesion molecules regulate the SDF-1–induced transendothelial migration process is not known. E-selectin is an endothelial-specific selectin that is constitutively expressed by the BMEC in vivo. Hence, we hypothesized that E-selectin may mediate SDF-1–induced transendothelial migration of CD34+ cells. We show that CD34+ cells express both E-selectin ligand and fucosyltransferase-VII (FucT-VII). Soluble E-selectin–IgG chimera binds avidly to 75% ± 10% of CD34+ cells composed mostly of progenitors and cells with long-term culture-initiating cell (LTC-IC) potential. To assess the functional capacity of E-selectin to mediate CD34+ cell migration in a transendothelial migration system, CD34+ cells were placed on transwell plates coated with interleukin-1β–activated BMEC. In the absence of SDF-1, there was spontaneous migration of 7.0% ± 1.4% of CD34+ cells and 14.1% ± 2.2% of LTC-IC. SDF-1 induced migration of an additional 23.0% ± 4.4% of CD34+cells and 17.6% ± 3.6% of LTC-IC. Blocking MoAb to E-selectin inhibited SDF-1–induced migration of CD34+ cells by 42.0% ± 2.5% and LTC-IC by 90.9% ± 16.6%. To define the mechanism of constitutive expression of E-selectin by the BMEC in vivo, we have found that vascular endothelial growth factor (VEGF165) induces E-selectin expression by cultured endothelial cells. VEGF-stimulated endothelial cells support transendothelial migration of CD34+ cells that could be blocked by MoAb to E-selectin. These results suggest that trafficking of subsets of CD34+ cells with LTC-IC potential is determined in part by sequential interactions with E-selectin and SDF-1.

Stromal Derived Factor-1–Induced Chemokinesis of Cord Blood CD34+ Cells (Long-Term Culture-Initiating Cells) Through Endothelial Cells Is Mediated by E-Selectin

Homing of hematopoietic stem cells to the bone marrow (BM) involves sequential interaction with adhesion molecules expressed on BM endothelium (BMEC) and chemokine stromal derived factor-1 (SDF-1). However, the mechanism whereby adhesion molecules regulate the SDF-1–induced transendothelial migration process is not known. E-selectin is an endothelial-specific selectin that is constitutively expressed by the BMEC in vivo. Hence, we hypothesized that E-selectin may mediate SDF-1–induced transendothelial migration of CD34+ cells. We show that CD34+ cells express both E-selectin ligand and fucosyltransferase-VII (FucT-VII). Soluble E-selectin–IgG chimera binds avidly to 75% ± 10% of CD34+ cells composed mostly of progenitors and cells with long-term culture-initiating cell (LTC-IC) potential. To assess the functional capacity of E-selectin to mediate CD34+ cell migration in a transendothelial migration system, CD34+ cells were placed on transwell plates coated with interleukin-1β–activated BMEC. In the absence of SDF-1, there was spontaneous migration of 7.0% ± 1.4% of CD34+ cells and 14.1% ± 2.2% of LTC-IC. SDF-1 induced migration of an additional 23.0% ± 4.4% of CD34+cells and 17.6% ± 3.6% of LTC-IC. Blocking MoAb to E-selectin inhibited SDF-1–induced migration of CD34+ cells by 42.0% ± 2.5% and LTC-IC by 90.9% ± 16.6%. To define the mechanism of constitutive expression of E-selectin by the BMEC in vivo, we have found that vascular endothelial growth factor (VEGF165) induces E-selectin expression by cultured endothelial cells. VEGF-stimulated endothelial cells support transendothelial migration of CD34+ cells that could be blocked by MoAb to E-selectin. These results suggest that trafficking of subsets of CD34+ cells with LTC-IC potential is determined in part by sequential interactions with E-selectin and SDF-1.

Human endothelial cell life extension by telomerase expression

Normal human endothelial cells, like other somatic cells in culture, divide a limited number of times before entering a nondividing state called replicative senescence. Expression of the catalytic component of human telomerase, human telomerase reverse transcriptase (hTERT), extends the life span of human fibroblasts and retinal pigment epithelial cells beyond senescence without causing neoplastic transformation (Bodnar, A. G., Ouellette, M., Frolkis, M., Holt, S. E., Chiu, C. P., Morin, G. B., Harley, C. B., Shay, J. W., Lichtsteiner, S., and Wright, W. E. (1998) Science 279, 349-352; Jiang, X., Jimenez, G., Chang, E., Frolkis, M., Kusler, B., Sage, M., Beeche, M., Bodnar, A., Wahl, G., Tlsty, T., and Chiu, C.-P. (1999) Nat. Genet. 21, 111-114). Here, we show that both human large vessel and microvascular endothelial cells also bypass replicative senescence after introduction of hTERT. For the first time, we report that hTERT expression in these life-extended vascular cells does not affect their differentiated and functional phenotype and that these cells maintain their angiogenic potential in vitro. Furthermore, hTERT(+) microvascular endothelial cells have normal karyotype, and hTERT(+) endothelial cell strains do not exhibit a transformed phenotype. Relative to parental cells at senescence, hTERT-expressing endothelial cells exhibit resistance to induction of apoptosis by a variety of different conditions. Such characteristics are highly desirable for designing vascular transplantation and gene therapy delivery systems in vivo.

Regulation of transendothelial migration of hematopoietic progenitor cells

Transendothelial migration of hematopoietic progenitor cells occurs in the bone marrow during mobilization and homing, and may therefore play a key role in the trafficking of hematopoietic stem cells. We hypothesize that adhesion molecules, chemokines, and paracrine cytokines are involved in this multifactorial process. As suggested in several studies, downregulation of adhesion molecules (e.g., integrins) may contribute to mobilization of progenitors due to a decreased avidity to bone marrow stromal and endothelial cells, which express the corresponding ligands. Using an in vitro model of transendothelial migration, we have shown that only a small number of more mature, committed progenitors migrates spontaneously under the control of adhesion molecules of the beta-2-integrin family and their corresponding endothelial/stromal ligands. However, transendothelial migration of progenitors in vitro is substantially enhanced by the chemokine stromal cell-derived factor-1 (SDF-1), which is constitutively produced by bone marrow stromal cells. More primitive progenitors also respond to this chemokine. In addition, the ligand for SDF-1, the chemokine receptor CXCR-4, is expressed in greater levels on bone marrow CD34+ cells as compared to mobilized progenitors, suggesting that downregulation of chemokine receptors occurs during progenitor mobilization. Indeed, bone marrow CD34+ cells migrate more avidly in response to SDF-1 than mobilized progenitors. Paracrine cytokines may also play a role in hematopoietic stem cell trafficking, since growth factor-stimulated hematopoietic cells produce cytokines that act on endothelial cells (e.g., vascular endothelial growth factor, VEGF), modifying their proliferation, motility, permeability, and fenestration. We conclude that transendothelial migration of hematopoietic progenitor cells is regulated by adhesion molecules, paracrine cytokines, and chemokines. Cytotoxic therapy as well as exogenously administered hematopoietic growth factors may affect adhesion molecule expression, the local cytokine and chemokine milieu, and chemokine receptor expression, which indirectly results in mobilization of hematopoietic stem cells.