A general strategy for isolation of endothelial cells from murine tissues. Characterization of two endothelial cell lines from the murine lung and subcutaneous sponge implants

JunB is required for endothelial cell morphogenesis by regulating core-binding factor beta

The molecular mechanism triggering the organization of endothelial cells (ECs) in multicellular tubules is mechanistically still poorly understood. We demonstrate that cell-autonomous endothelial functions of the AP-1 subunit JunB are required for proper endothelial morphogenesis both in vivo in mouse embryos with endothelial-specific ablation of JunB and in in vitro angiogenesis models. By cDNA microarray analysis, we identified core-binding factor beta (CBFbeta), which together with the Runx proteins forms the heterodimeric core-binding transcription complex CBF, as a novel JunB target gene. In line with our findings, expression of the CBF target MMP-13 was impaired in JunB-deficient ECs. Reintroduction of CBFbeta into JunB-deficient ECs rescued the tube formation defect and MMP-13 expression, indicating an important role for CBFbeta in EC morphogenesis.

Tumour-mediated upregulation of chemoattractants and recruitment of myeloid cells predetermines lung metastasis

Primary tumours influence the environment in the lungs before metastasis. However, the mechanism of metastasis is not well understood. Here, we show that the inflammatory chemoattractants S100A8 and S100A9, whose expression is induced by distant primary tumours, attract Mac 1 (macrophage antigen 1)(+)-myeloid cells in the premetastatic lung. In addition, tumour cells use this mechanism, through activation of the mitogen-activated protein kinase (MAPK) p38, to acquire migration activity with pseudopodia for invasion (invadopodia). The expression of S100A8 and S100A9 was eliminated in lung Mac 1(+)-myeloid cells and endothelial cells deprived of soluble factors, such as vascular endothelial growth factor A (VEGF-A), tumour necrosis factor alpha (TNFalpha) and transforming growth factor beta (TGFbeta) both in vitro and in vivo. Neutralizing anti-S100A8 and anti-S100A9 antibodies blocked the morphological changes and migration of tumour cells and Mac 1(+)-myeloid cells. Thus, the S100A8 and S100A9 pathway may be common to both myeloid cell recruitment and tumour-cell invasion.

Endorepellin In Vivo: Targeting the Tumor Vasculature and Retarding Cancer Growth and Metabolism

BACKGROUND

The antiangiogenic approach to controlling cancer requires a better understanding of angiogenesis and the discovery of new compounds that modulate this key biological process. Here we investigated the role of endorepellin, an angiostatic protein fragment that is derived from the C-terminus of perlecan, a heparan sulfate proteoglycan, in controlling tumor angiogenesis in vivo.

METHODS

We administered human recombinant endorepellin systemically to mice bearing orthotopic squamous carcinoma xenografts or syngeneic Lewis lung carcinoma tumors. We monitored tumor growth, angiogenesis, metabolism, hypoxia, and mitotic index by using quantitative immunohistochemistry and positron emission tomography scan imaging. In addition, we determined the localization of injected endorepellin using near-infrared labeling and immunohistochemistry of frozen tumor sections. Finally, we isolated tumor-derived endothelial cells and tested whether endorepellin could interact with these cells and disrupt in vitro capillary morphogenesis. All statistical tests were two-sided.

RESULTS

Endorepellin specifically targeted the tumor vasculature as determined by immunohistochemical analysis and accumulated in the tumor perivascular zones where it persisted for several days as discrete deposits. This led to inhibition of tumor angiogenesis (as measured by decreased CD31-positive cells, mean control = 1902 CD31-positive pixels, mean endorepellin treated = 343.9, difference between means = 1558, 95% confidence interval [CI] = 1296 to 1820, P<.001), enhanced tumor hypoxia, and a statistically significant decrease in tumor metabolism and mitotic index (as measured by decreased Ki67-positive cells, mean control Ki67 pixels = 5970, mean endorepellin-treated Ki67 pixels = 3644, difference between means = 2326, 95% CI = 1904 to 2749, P<.001) compared to untreated controls. Endorepellin was actively internalized by tumor-derived endothelial cells causing a redistribution of alpha2beta1 integrin such that both proteins colocalized to punctate deposits in the perivascular region. Endorepellin treatment inhibited in vitro capillary morphogenesis of both normal and tumor-derived endothelia.

CONCLUSIONS

Our results provide support for the hypothesis that endorepellin is an effective antitumor vasculature agent that could be used as a therapeutic modality to combat cancer.

Bone morphogenic protein antagonist Drm/gremlin is a novel proangiogenic factor

Angiogenesis plays a key role in various physiologic and pathologic conditions, including tumor growth. Drm/gremlin, a member the Dan family of bone morphogenic protein (BMP) antagonists, is commonly thought to affect different processes during growth, differentiation, and development by heterodimerizing various BMPs. Here, we identify Drm/gremlin as a novel proangiogenic factor expressed by endothelium. Indeed, Drm/gremlin was purified to homogeneity from the conditioned medium of transformed endothelial cells using an endothelial-cell sprouting assay to follow protein isolation. Accordingly, recombinant Drm/gremlin stimulates endothelial-cell migration and invasion in fibrin and collagen gels, binds with high affinity to various endothelial cell types, and triggers tyrosine phosphorylation of intracellular signaling proteins. Also, Drm/gremlin induces neovascularization in the chick embryo chorioallantoic membrane. BMP4 does not affect Drm/gremlin interaction with endothelium, and both molecules exert a proangiogenic activity in vitro and in vivo when administered alone or in combination. Finally, Drm/gremlin is produced by the stroma of human tumor xenografts in nude mice, and it is highly expressed in endothelial cells of human lung tumor vasculature when compared with non-neoplastic lung. Our observations point to a novel, previously unrecognized capacity of Drm/gremlin to interact directly with target endothelial cells and to modulate angiogenesis.

Triggering CD40 on endothelial cells contributes to tumor growth

Inflammatory cells can either promote or inhibit tumor growth. Here we studied whether CD40, a key molecule for adaptive immune response, has any role in mammary carcinogenesis of BALB/NeuT transgenic tumor-prone mice. We transferred the HER2/neu oncogene into CD40-null background to obtain the CD40-KO/NeuT strain. CD40-KO/NeuT mice showed delayed tumor onset and reduced tumor multiplicity. BM (BM) transplantation experiments excluded a role of BM-derived cells in the reduced tumorigenicity associated with CD40 deficiency. Rather, CD40 expressed by endothelial cells (ECs) takes part to the angiogenic process. Accordingly, large vessels, well organized around the tumor lobular structures, characterize BALB/NeuT tumors, whereas tiny numerous vessels with scarce extracellular matrix are dispersed in the parenchyma of poorly organized CD40-KO/NeuT tumors.

Activated platelets, which may interact with and activate ECs, are a possible source of CD40L. Their localization within tumor vessels prompted the idea of treating BALB/NeuT and CD40-KO/NeuT mice chronically with the anti-platelet drug clopidogrel, known to inhibit platelet CD40L expression. Treatment of BALB/NeuT mice reduced tumor growth to a level similar to CD40-deficient mice, whereas CD40-KO/NeuT mice treated or not showed the same attenuated tumor outgrowth, indicating that activated platelets are the likely source of CD40L in this model. Collectively, these data point to a participation of CD40/CD40L in the angiogenic processes associated with mammary carcinogenesis of BALB/NeuT mice.

Redundant roles of Sox17 and Sox18 in postnatal angiogenesis in mice

Sox7, Sox17 and Sox18 constitute group F of the Sox family of HMG box transcription factor genes. Dominant-negative mutations in Sox18 underlie the cardiovascular defects observed in ragged mutant mice. By contrast, Sox18(-/-) mice are viable and fertile, and display no appreciable anomaly in their vasculature, suggesting functional compensation by the two other SoxF genes. Here, we provide direct evidence for redundant function of Sox17 and Sox18 in postnatal neovascularization by generating Sox17(+/-) -Sox18(-/-) double mutant mice. Whereas Sox18(-/-) and Sox17(+/-) -Sox18(+/-) mice showed no vascular defects, approximately half of the Sox17(+/-) -Sox18(-/-) pups died before postnatal day 21 (P21). They showed reduced neovascularization in the liver sinusoids and kidney outer medulla vasa recta at P7, which most likely caused the ischemic necrosis observed by P14 in hepatocytes and renal tubular epithelia. Those that survived to adulthood showed similar, but milder, vascular anomalies in both liver and kidney, and females were infertile with varying degrees of vascular abnormalities in the reproductive organs. These anomalies corresponded with sites of expression of Sox7 and Sox17 in the developing postnatal vasculature. In vitro angiogenesis assays, using primary endothelial cells isolated from the P7 livers, showed that the Sox17(+/-) -Sox18(-/-) endothelial cells were defective in endothelial sprouting and remodeling of the vasculature in a phenotype-dependent manner. Therefore, our findings indicate that Sox17 and Sox18, and possibly all three SoxF genes, are cooperatively involved in mammalian vascular development.

Generation and characterization of a mouse lymphatic endothelial cell line

Lymphatic vessels, by channeling fluid and leukocytes from the periphery into lymph nodes, play a central role in the development of the immune response. Despite their importance in homeostasis and disease, the difficulties in enriching and culturing lymphatic endothelial cells limit studies of their biology. Here, we report the isolation, stabilization, and characterization of a mouse lymphatic endothelial cell line (MELC) and the generated clones thereof. Cells were isolated from benign lymphangiomas induced by intraperitoneal injections of incomplete Freund's adjuvant. The MELC line expressed molecules typical of lymphatic endothelium, including VEGFR3/Flt-4, podoplanin, Prox-1, and D6, but not LYVE-1. It also expressed CD34, ICAM-1, VCAM, and JAM-A, but not CD31, VE-cadherin, E-selectin, or CX3CL1/fractalkine (both TNFalpha-induced), at variance with vascular endothelial cells tested in parallel. The inflammatory cytokines TNFalpha and IL-4 regulated production of selected adhesion molecules (VCAM), cytokines (IL-6), and chemokines (CCL2/JE). Whole genome transcriptional profiling identified a set of 150 known genes differentially expressed in MELC versus vascular endothelial cells. Thus, the MELC line may represent an invaluable source of lymphatic endothelium.

Vascular-specific quantification in an in vivo Matrigel chamber angiogenesis assay

The study of angiogenesis as a therapeutic target requires reliable in vivo assays that can provide physiologically relevant data. A murine in vivo Matrigel-based angiogenesis assay is presented here which includes the quantitative assessment of vascular-specific indicators of neovascularization. Matrigel containing 175 ng/ml bFGF is encapsulated in synthetic chambers which are implanted subcutaneously in C57/B16J mice. Ex vivo implants can be imaged to qualitatively view perfused vasculature within the chambers, or histologically processed to confirm the presence of vascular-specific tissue within the Matrigel. Viable cells are recovered from the excised chambers and quantified cytometrically using endothelial cell-specific markers CD34 and CD144, and for a marker of nucleated cells, Hoechst 33342. Thalidomide, 200 mg/kg/day, was tested using the assay and was found to inhibit angiogenesis by 46%. Angiogenesis inhibitors secreted by LL/M27 tumors were also characterized, where tumor-bearing mice showed a 73% inhibition of angiogenesis compared to tumor-free controls. Analysis of the number of nucleated cells in these samples failed to show a strong correlation with the number of endothelial cells, indicating that quantification of nonvascular-specific tissue in in vivo angiogenesis assays may not be sufficient. This new assay provides an objective, comprehensive determination of the vasculature-specific response of both endogenous and exogenous angiogenesis inhibitors in vivo, and also creates new opportunities for obtaining primary murine endothelial cells.

Overexpression of platelet-derived growth factor receptor alpha in endothelial cells of hepatocellular carcinoma associated with high metastatic potential

PURPOSE

Little information is available on the heterogeneity of the vascular endothelium in hepatocellular carcinoma. The aim of this study was to identify the differentially expressed genes in tumor endothelial cells from highly metastatic hepatocellular carcinoma.

EXPERIMENTAL DESIGN

Magnetic beads conjugated with anti-CD31 antibody were used to isolate vascular endothelial cells from hepatocellular carcinoma xenografts with different metastatic potentials in nude mice. Gene expression profiles for different endothelial cells were compared by use of cDNA microarray. The up-regulated gene was confirmed by reverse transcription-PCR, real-time PCR, and immunohistochemistry.

RESULTS

cDNA microarray analysis revealed differential expression patterns in seven genes consistently presented in endothelial cells isolated from hepatocellular carcinoma with different metastatic potentials. Overexpression of platelet-derived growth factor receptor alpha was found only in the endothelium of highly metastatic hepatocellular carcinoma, which was confirmed by reverse transcription-PCR, real-time PCR, and immunohistochemistry. Oral administration of STI571 (imatinib mesylate or Glivec), a protein tyrosine kinase inhibitor of platelet-derived growth factor receptor, combined with s.c. injection of IFN-alpha not only effectively reduced tumor weight (by 81.8%) and microvessel density (by 70.2%) but also inhibited lung metastasis (by 100%). Furthermore, immunohistochemical analysis of platelet-derived growth factor receptor alpha in human hepatocellular carcinoma tissues revealed its correlation with postoperative recurrence, especially in patients without microvessel invasion.

CONCLUSIONS

The gene expression of hepatocellular carcinoma vascular endothelium is different between tumors with different metastatic potential. Platelet-derived growth factor receptor alpha, which is overexpressed in endothelium of highly metastatic hepatocellular carcinoma, may serve as a biomarker for predicting metastasis and a therapeutic target for highly metastatic hepatocellular carcinoma.

Activation of endothelial NADPH oxidase during normoxic lung ischemia is KATP channel dependent

Previous studies have shown endothelial cell membrane depolarization and generation of reactive oxygen species (ROS) in endothelial cells with abrupt reduction in shear stress (ischemia). This study evaluated the role of ATP-sensitive potassium (K(ATP)) channels and NADPH oxidase in the ischemic response by using Kir6.2-/- and gp91(phox)-/- mice. To evaluate ROS generation, we subjected isolated perfused mouse lungs labeled with 2',7'-dichlorodihydrofluorescein (DCF), hydroethidine (HE), or diphenyl-1-pyrenylphosphine (DPPP) to control perfusion followed by global ischemia. In wild-type C57BL/6J mice, imaging of subpleural endothelial cells showed a time-dependent increase in intensity for all three fluorescence probes with ischemia, which was blocked by preperfusion with cromakalim (a K(ATP) channel agonist) or diphenyleneiodonium (DPI, a flavoprotein inhibitor). Endothelial cell fluorescence with bis-oxonol, a membrane potential probe, increased during lung ischemia indicating cell membrane depolarization. The change in membrane potential with ischemia in lungs of gp91(phox)-/- mice was similar to wild type, but ROS generation did not occur. Lungs from Kir6.2-/- showed marked attenuation of the change in both membrane potential and ROS production. Thus membrane depolarization during lung ischemia requires the presence of a K(ATP) channel and is required for activation of NADPH oxidase and endothelial ROS generation.

Cutting Edge: Extracellular High Mobility Group Box-1 Protein Is a Proangiogenic Cytokine

The chromosomal high mobility group box-1 (HMGB1) protein acts as a proinflammatory cytokine when released in the extracellular environment by necrotic and inflammatory cells. In the present study, we show that HMGB1 exerts proangiogenic effects by inducing MAPK ERK1/2 activation, cell proliferation, and chemotaxis in endothelial cells of different origin. Accordingly, HMGB1 stimulates membrane ruffling and repair of a mechanically wounded endothelial cell monolayer and causes endothelial cell sprouting in a three-dimensional fibrin gel. In keeping with its in vitro properties, HMGB1 stimulates neovascularization when applied in vivo on the top of the chicken embryo chorioallantoic membrane whose blood vessels express the HMGB1 receptor for advanced glycation end products (RAGE). Accordingly, RAGE blockade by neutralizing Abs inhibits HMGB1-induced neovascularization in vivo and endothelial cell proliferation and membrane ruffling in vitro. Taken together, the data identify HMGB1/RAGE interaction as a potent proangiogenic stimulus.

Primary and immortalised human pancreatic islet endothelial cells: phenotypic and immunological characterisation

AIMS/HYPOTHESIS

Studies on the biology of the microvascular endothelial cells (MECs) that surround and penetrate the pancreatic islets are hampered by difficulties in isolating and culturing large numbers of pure cells. We aimed to morphologically and functionally characterise primary MECs purified and cultured from human islets, and to establish a simian virus 40 (SV40)-immortalised cell line from these primary cultures.

MATERIALS AND METHODS

Human islet MECs were extracted and purified using anti-CD105 coated immunomagnetic beads, and endothelial markers and surface molecules analysed by flow cytometric analysis. An immortalised cell line was then established by using a chimeric adeno5/SV40 virus.

RESULTS

Islet MECs expressed classic and specific endothelial markers, a high basal level of intercellular adhesion molecule-1, and low levels of E-selectin and TNF (previously known as TNF-alpha) inducible vascular cell adhesion molecule-1. IFNG (previously known as IFN-gamma) induced expression of HLA class II molecules. The immortalised islet MECs expanded rapidly, exhibited increased DNA synthesis, and were passaged approximately 30 times, without signs of senescence. They retained the endothelial characteristics of the parental cells, and behaved as the primary cells in terms of TNF stimulation of expression of adhesion molecules and support of leucocyte adhesion and transmigration.

CONCLUSIONS/INTERPRETATION

The immortalised islet MECs that we have established could effectively represent a substitute for primary counterparts for in vitro studies on the role of the microvasculature in pathophysiological processes involved in type 1 and type 2 diabetes.

Isolation and characterization of coronary endothelial and smooth muscle cells from A1 adenosine receptor-knockout mice

Mice have been used widely in in vivo and in vitro cardiovascular research. The availability of knockout mice provides further clues to the physiological significance of specific receptor subtypes. Adenosine A(1) receptor (A(1)AR)-knockout (A(1)KO) mice and their wild-type (A(1)WT) controls were employed in this investigation. The heart and aortic arch were carefully removed and retroinfused with enzyme solution (1 mg/ml collagenase type I, 0.5 mg/ml soybean trypsin inhibitor, 3% BSA, and 2% antibiotics) through the aortic arch. The efflux was collected at 30-, 60-, and 90-min intervals. The cells were centrifuged, and the pellets were mixed with medium [medium 199-F-12 medium with 10% FBS and 2% antibiotics (for endothelial cells) and advanced DMEM with 10% FBS, 10% mouse serum, 2% GlutaMax, and 2% antibiotics (for smooth muscle cells)] and plated. Endothelial cells were characterized by a cobblestone appearance and positive staining with acetylated LDL labeled with 1,1'-dioctadecyl-3,3,3',3-tetramethylindocarbocyanine perchlorate. Smooth muscle cells were characterized by positive staining of smooth muscle alpha-actin and smooth muscle myosin heavy chain. Homogeneity of the smooth muscle cells was approximately 91%. Western blot analysis showed expression of smoothelin in the cells from passages 3, 7, and 11 in A(1)WT and A(1)KO mice. Furthermore, the A(1)AR was characterized by Western blot analysis using an A(1)AR-specific antibody. To our knowledge, this is the first isolation and successful characterization of smooth muscle cells from the mouse coronary system.

Impact of modeled microgravity on microvascular endothelial cells

Microvascular endothelial cells are protagonists in inflammation and angiogenesis. They contribute to the integrity of microvasculature by synthesizing a large array of cytokines, growth factors and mediators active on the endothelium itself, on smooth muscle cells and circulating leukocytes. Because space flight (i) associates with vascular impairment and (ii) modulates the cytokine network, we evaluated the effect of modeled microgravity on microvascular 1G11 cells. We found that modeled microgravity reversibly inhibits endothelial growth and this correlates with an upregulation of p21, a cyclin-dependent kinases inhibitor. By protein array, we found that microgravity inhibits the synthesis of interleukin 6, an event that may contribute to growth retardation. We also detected increased amounts of nitric oxide, a mediator of inflammatory responses, a potent vasodilator and a player in angiogenesis. The increased synthesis of nitric oxide is due, at least in part, to an upregulation of endothelial nitric oxide synthase. Because low levels of IL-6 might contribute to endothelial growth retardation as well as to the enhancement of nitric oxide synthesis, we hypothesize a central role of IL-6 in modulating microvascular endothelial cell behaviour in modeled microgravity.

Akt1 regulates pathological angiogenesis, vascular maturation and permeability in vivo

Akt kinases control essential cellular functions, including proliferation, apoptosis, metabolism and transcription, and have been proposed as promising targets for treatment of angiogenesis-dependent pathologies, such as cancer and ischemic injury. But their precise roles in neovascularization remain elusive. Here we show that Akt1 is the predominant isoform in vascular cells and describe the unexpected consequences of Akt1 knockout on vascular integrity and pathological angiogenesis. Angiogenic responses in three distinct in vivo models were enhanced in Akt1(-/-) mice; these enhanced responses were associated with impairment of blood vessel maturation and increased vascular permeability. Although impaired vascular maturation in Akt1(-/-) mice may be attributed to reduced activation of endothelial nitric oxide synthase (eNOS), the major phenotypic changes in vascular permeability and angiogenesis were linked to reduced expression of two endogenous vascular regulators, thrombospondins 1 (TSP-1) and 2 (TSP-2). Re-expression of TSP-1 and TSP-2 in mice transplanted with wild-type bone marrow corrected the angiogenic abnormalities in Akt1(-/-) mice. These findings establish a crucial role of an Akt-thrombospondin axis in angiogenesis.

Differential expression of EDF-1 and endothelial nitric oxide synthase by proliferating, quiescent and senescent microvascular endothelial cells

Endothelial Differentiation-related Factor (EDF)-1 is a low molecular weight polypeptide downregulated in endothelial cells exposed to HIV-1-Tat or the phorbol ester TPA. EDF-1 acts in the cytosol as a calmodulin binding protein, and in the nucleus as a transcriptional coactivator. Here, we show that EDF-1 is downregulated in non-proliferating microvascular endothelial cells. Indeed, both quiescence and senescence reduce the levels of EDF-1 and this is due to protein degradation through the proteasome. We also describe a different subcellular localization of EDF-1 which is mainly nuclear in senescent 1G11 cells. Since (i) endothelial nitric oxide (NO) seems to play a role in endothelial proliferation and (ii) NO is an important mediator involved in the control of vascular tone, inflammatory responses and angiogenesis, it is noteworthy that senescence downregulates the expression and the activity of endothelial nitric oxide synthase (eNOS) in microvascular endothelial cells. On the contrary, quiescence does not affect NOS expression and activity. The modulation of EDF-1 in microvascular endothelial cells might offer new insights into the molecular events involved in angiogenesis and in microvascular dysfunctions in the elderly.

A method of isolation and culture of microvascular endothelial cells from mouse skin

OBJECTIVES

The study of isolated microvascular endothelial cells from mice has long been impeded due to the many difficulties encountered in isolating and culturing these cells. We focused on developing a method to isolate microvascular endothelial cells from the skin fragments of newborn mice. We also aimed at establishing optimal culture conditions to sustain the growth of these cells.

METHODS AND RESULTS

Isolation of murine dermal microvascular endothelial cells (mDMEC) from P3 newborn mice was based first on enzymatic separation of the skin epidermal layer from the dermis using dispase and then on disaggregating dermal cellular elements using collagenase. The cells obtained from the dermis were subjected to a continuous density gradient centrifugation. Cells situated between densities 1.033 and 1.047 were then cultured on collagen IV-coated culture flasks using optimized growth culture conditions. Cells were characterized by endothelial appearance and by the presence and genetic expression of endothelial markers like CD31, NOS3, VEGFR-2 and Tie-2. Uptake of acetylated low-density lipoprotein (Ac-LDL) was used as a functional assay.

CONCLUSIONS

The methodology described herein for isolation and culture of murine microvascular endothelium offers a distinctive advantage for those using mouse models to study endothelial cell biology.

Lung endothelial cell proliferation with decreased shear stress is mediated by reactive oxygen species

Acute cessation of flow (ischemia) leads to depolarization of the endothelial cell (EC) membrane mediated by K(ATP) channels and followed by production of reactive oxygen species (ROS) from NADPH oxidase. We postulated that ROS are a signal for initiating EC proliferation associated with the loss of shear stress. Flow cytometry was used to identify proliferating CD31-positive pulmonary microvascular endothelial cells (mPMVECs) from wild-type, Kir6.2-/-, and gp91phox-/- mice. mPMVECs were labeled with PKH26 and cultured in artificial capillaries for 72 h at 5 dyn/cm2 (flow adaptation), followed by 24 h of stop flow or continued flow. ROS production during the first hour of ischemia was markedly diminished compared with wild-type mice in both types of gene-targeted mPMVECs. Cell proliferation was defined as the proliferation index (PI). After 72 h of flow, >98% of PKH26-labeled wild-type mPMVECs were at a single peak (PI 1.0) and the proportion of cells in the S+G2/M phases were at 5.8% on the basis of cell cycle analysis. With ischemia (24 h), PI increased to 2.5 and the ratio of cells in S+G2/M phases were at 35%. Catalase, diphenyleneiodonium, and cromakalim markedly inhibited ROS production and cell proliferation in flow-adapted wild-type mPMVECs. Significant effects of ischemia were not observed in Kir6.2-/- and gp91phox-/- cells. ANG II activation of NADPH oxidase was unaffected by KATP gene deletion. Thus loss of shear stress in flow-adapted mPMVECs results in cell division associated with ROS generated by NADPH oxidase. This effect requires a functioning cell membrane KATP channel.

Histone deacetylase activity is essential for the expression of HoxA9 and for endothelial commitment of progenitor cells

The regulation of acetylation is central for the epigenetic control of lineage-specific gene expression and determines cell fate decisions. We provide evidence that the inhibition of histone deacetylases (HDACs) blocks the endothelial differentiation of adult progenitor cells. To define the mechanisms by which HDAC inhibition prevents endothelial differentiation, we determined the expression of homeobox transcription factors and demonstrated that HoxA9 expression is down-regulated by HDAC inhibitors. The causal involvement of HoxA9 in the endothelial differentiation of adult progenitor cells is supported by the finding that HoxA9 overexpression partially rescued the endothelial differentiation blockade induced by HDAC inhibitors. Knockdown and overexpression studies revealed that HoxA9 acts as a master switch to regulate the expression of prototypical endothelial-committed genes such as endothelial nitric oxide synthase, VEGF-R₂, and VE-cadherin, and mediates the shear stress–induced maturation of endothelial cells. Consistently, HoxA9-deficient mice exhibited lower numbers of endothelial progenitor cells and showed an impaired postnatal neovascularization capacity after the induction of ischemia. Thus, HoxA9 is regulated by HDACs and is critical for postnatal neovascularization.

p130Rb2 and p27kip1 cooperate to control mobilization of angiogenic progenitors from the bone marrow

Neoangiogenesis involves both bone marrow-derived myelomonocytic and endothelial progenitor cells as well as endothelial cells coopted from surrounding vessels. Cytokines induce these cells to proliferate, migrate, and exit the cell cycle to establish the vasculature; however, which cell cycle regulators play a role in these processes is largely unknown. Here, we report that mice lacking the cell cycle inhibitors p130 and p27 show defects in tumor neoangiogenesis, both in xenografts and spontaneously arising tumors. This defect is associated with impaired mobilization of endothelial and myelomonocytic angiogenic progenitors from the bone marrow. This article documents the role of these molecules in angiogenesis and further suggests that cell expansion and mobilization from the bone marrow of angiogenic precursors are separable events.

Anti-oxidative vitamins prevent lipid-peroxidation and apoptosis in corneal endothelial cells

To determine the effects of vitamin supplementation on the lipid-peroxidation-mediated toxicity of iron-ions on corneal endothelial cells (CECs) leading to apoptosis, murine CECs were maintained in tissue culture medium supplemented with increasing concentrations of free iron-ions, a treatment known to lead to increased lipid-peroxidation. The concentration of anti-oxidative vitamins (ascorbic acid, tocopherol and retinoic acid) in the cell supernatant and in the cells was determined by high-pressure liquid chromatography. Apoptosis was assessed by quantification of caspase-3-like activity and by using annexin-V/propidium iodide stains for flow cytometry. Lipid-peroxidation was measured by the malondialdehyde method. Supplementation with anti-oxidative vitamins was tested for the ability to counteract the induction of apoptosis. The production of nitric oxide was assessed spectrophotometrically and the expression levels of inducible and endothelial nitric oxide synthase were determined by Western blot. Increasing levels of free iron led to a rapid loss of anti-oxidative vitamins in the supernatant and in the CECs. This was correlated with rising levels of malondialdehyde and increased apoptosis. Supplementation with ascorbic acid or alpha-tocopherol alone did not prevent lipid-peroxidation in the cells. A combination of vitamins C and E (ascorbic acid, tocopherol) or solitary supplementation with vitamin A (retinoic acid) prevented lipid-peroxidation. We thus present a novel in vitro model for testing the direct influence of pro-oxidative species on CECs. We also show that supplementation with anti-oxidative vitamins to CECs significantly prevents the generation of free-radical-induced oxidative injury and apoptosis. These findings may have important implications for the storage of human corneae prior to transplantation and for the prolongation of corneal graft survival.

Lack of oestrogen protection in amyloid-mediated endothelial damage due to protein nitrotyrosination

Amyloid beta-peptide (Abeta) cytotoxicity, the hallmark of Alzheimer's disease, implicates oxidative stress in both neurons and vascular cells, particularly endothelial cells. Consequently, antioxidants have shown neuroprotective activities against Abeta-induced cytotoxicity. Among the different antioxidants used in both in vitro and in vivo studies, 17beta-oestradiol (E2) has garnered the most attention. Oestrogen attenuated Abeta(E22Q)-induced toxicity in neurons but failed to protect endothelial cells. Here we show that E2-mediated activation of endothelial nitric oxide synthase (eNOS) increases the production of nitric oxide (NO), which, under Abeta(E22Q)-induced oxidative damage, results in the formation of peroxynitrite and increased nitration of tyrosine residues. Inhibition of eNOS prevents nitrotyrosination and permits E2-mediated protection against Abeta(E22Q) on endothelial cells. The main nitrotyrosinated proteins in the presence of E2 and Abeta(E22Q) were identified by MALDI-TOF mass spectrometry. These proteins are key players in the regulation of energy production, cytoskeletal integrity, protein metabolism and protection against oxidative stress. Our data highlight the potential damaging consequences of E2 in vascular disorders dealing with oxidative stress conditions, such as cerebral amyloid angiopathy, stroke and ischaemia-reperfusion conditions.

Loss of HIF-1alpha in endothelial cells disrupts a hypoxia-driven VEGF autocrine loop necessary for tumorigenesis

We deleted the hypoxia-responsive transcription factor HIF-1alpha in endothelial cells (EC) to determine its role during neovascularization. We found that loss of HIF-1alpha inhibits a number of important parameters of EC behavior during angiogenesis: these include proliferation, chemotaxis, extracellular matrix penetration, and wound healing. Most strikingly, loss of HIF-1alpha in EC results in a profound inhibition of blood vessel growth in solid tumors. These phenomena are all linked to a decreased level of VEGF expression and loss of autocrine response of VEGFR-2 in HIF-1alpha null EC. We thus show that a HIF-1alpha-driven, VEGF-mediated autocrine loop in EC is an essential component of solid tumor angiogenesis.

Monocyte chemoattractant protein-1 alters expression of tight junction-associated proteins in brain microvascular endothelial cells

The chemokine monocyte chemoattractant protein (MCP-1) is recognized to mediate extravasation of mononuclear leukocytes into the brain during a variety of neuroinflammatory conditions. In large part produced by parenchymal neural cells during these disease states, it is unclear how this chemokine can stimulate the migration of circulating leukocytes that lie behind the highly impermeant blood-brain barrier (BBB). Based on the premise that disruption of tight junctions (TJs) could foster leukocyte extravasation, experiments were conducted to test the hypothesis that MCP-1 alters the expression and/or distribution of the TJ-associated proteins zonulae occludens-1 (ZO-1) and occludin in brain microvascular endothelial cells (BMEC) comprising the BBB. Exposure to MCP-1 caused a loss in immunostaining of ZO-1 at inter-endothelial junctional regions in both cultured BMEC and isolated brain microvessels, as well as a similar effect on occludin in cultured BMEC, but did not alter occludin staining in microvessels. In cellular fractionation experiments, ZO-1 associated predominantly with the detergent-resistant cytoskeletal framework (CSK) in both cultured BMEC and brain microvessels, while a slimmer majority of occludin partitioned with the CSK. Following MCP-1 exposure, ZO-1 was reduced in the CSK fraction of cultured BMEC and microvessels, with a shift of ZO-1 to the detergent-soluble fraction in both cases. Occludin exhibited a similar pattern of MCP-1-induced loss and shift from the CSK in cultured BMEC, but remained nearly constant in microvessels. Lastly, expression of caveolin-1, a major structural component of membrane microdomains thought to be functionally complexed with TJs, was additionally altered by MCP-1 treatment of both cultured BMEC and microvessels. These results indicate that, in addition to its chemotactic activity, MCP-1 might alter BBB integrity during CNS inflammation.

cAMP inhibits TGFbeta1-induced in vitro angiogenesis

Transforming growth factor-beta (TGFbeta1) is a proangiogenic factor both, in vitro and in vivo, that is mainly involved in the later phases of angiogenesis. In an attempt to identify genes that participate in this effect, we found that TGFbeta1 down-regulates expression of adenylate cyclase VI. In addition, cAMP analogs (8-Bromo-cAMP) and forskolin (an adenylate cyclase activator) also reduced TGFbeta1-induced in vitro angiogenesis in mouse endothelial cell lines and in primary cultures of human umbilical vein endothelial cells on collagen gels. Induction of Ets-1 and plasminogen activator inhibitor-1 (PAI-1) by TGFbeta1 was blocked by these cAMP agonists and activators, in the absence of effects on endothelial cell viability. Moreover, the signal transduction pathways stimulated by TGFbeta1 were unaffected. Thus, Smad2 was normally phosphorylated and translocated to the nucleus in the presence of forskolin. In contrast, transfection studies using the PAI-1-promoter indicated that these cAMP analogues inhibit transcriptional stimulation by TGFbeta1. Electrophoretic mobility shift assay showed that Smad2/3 were bound normally to a TGFbeta1-response region in the presence of the cAMP analogs. In all, these data suggest that the cAMP pathway inhibits the transcriptional activity of Smads, that could be responsible for the block of the TGFbeta1-induced in vitro angiogenesis caused by this second messenger.

Culture of murine brain microvascular endothelial cells that maintain expression and cytoskeletal association of tight junction-associated proteins

A readily obtainable in vitro paradigm of the blood-brain barrier (BBB) would offer considerable benefits. Toward this end, in this study, we describe a novel method for purifying murine brain microvascular endothelial cells (BMEC) for culture. The method uses limited collagenase-dispase digestion of enriched brain microvessels, followed by immunoisolation of digested, microvascular fragments by magnetic beads coated with antibody to platelet-endothelial cell adhesion molecule-1. When plated onto collagen IV-coated surfaces, these fragments elaborated confluent monolayers of BMEC that expressed, as judged by immunocytochemistry, the adherens junction-associated proteins, VE-cadherin and beta-catenin, as well as the tight junction (TJ)-associated proteins, claudin-5, occludin, and zonula occludin-1 (ZO-1), in concentrated fashion along intercellular borders. In contrast, cultures of an immortalized and transformed line of murine brain capillary-derived endothelial cells, bEND.3, displayed diffuse cytoplasmic localization of occludin and ZO-1. This difference in occludin and ZO-1 staining between the two endothelial cell types was also reflected in the extent of association of these proteins with the detergent-resistant cytoskeletal framework (CSK). Although both occludin and ZO-1 largely partitioned with the CSK fraction in BMEC, they were found predominantly in the soluble fraction of bEND.3 cells, and claudin-5 was found associated equally with both fractions in BMEC and bEND.3 cells. Moreover, detergent-extracted cultures of the BMEC retained pronounced immunostaining of occludin and ZO-1, but not claudin-5, along intercellular borders. Because both occludin and ZO-1 are thought to be functionally coupled to the detergent-resistant CSK and high expression of TJs is considered a seminal characteristic of the BBB, these results impart that this method of purifying murine BMEC provides a suitable platform to investigate BBB properties in vitro.

“Lumen digestion” technique for isolation of aortic endothelial cells from heme oxygenase-1 knockout mice

Endothelial cell dysfunction plays a critical role in the pathogenesis of cardiovascular diseases. Gene targeted mutant, knockout, or transgenic mice are widely used in the laboratory investigation of these disorders. We describe a simple and reproducible “lumen digestion” technique to isolate aortic endothelial cells from mice that would be useful for researchers in endothelial cell biology. We used wild-type, homozygote, or heterozygote heme oxygenase-1 null mice from which the aorta is isolated and removed under anesthesia. After cauterizing all the branches, both ends of the aorta are cannulated using an Intramedic® PE-20 tube. After flushing the aorta with phosphate-buffered saline (PBS), the lumen is repeatedly instilled (five times) with 50 µL 0.25% trypsin in PBS, incubated for 2 min, and flushed with PBS. The outflow is collected in endothelial cell media with 20% fetal bovine serum. After centrifugation, the endothelial cells in the pellet are resuspended in media and plated in a 24-well tissue culture dish. Following culture for 2 to 3 weeks, the cells demonstrate typical cobblestone appearance, stain positive for the endothelial marker CD31, and are capable of low-density lipoprotein uptake. Following challenge with oxidized lipids, heme oxygenase-1 deficient endothelial cells demonstrate increased susceptibility to cell injury.

Isolation and transplantation of allogeneic pulmonary endothelium derived from GFP transgenic mice

The isolation of primary endothelial cells from murine tissues has long been a challenge and remains a difficult task. Using GFP transgenic C57/BL6 mice as donors, we describe a reliable method to isolate pulmonary endothelial cells by flow cytometry after staining with DiI-Ac-low density lipoprotein (LDL). After mechanical dissociation of murine lung tissue and enzymatic digestion, adherent cells can be quickly stained and sorted by flow cytometry. The isolated cells express endothelial cell markers such as CD31, MECA32 and CD106 and stained positive for Isolectin B4. After 50-fold expansion using standard endothelial growth media, cells could be transplanted into lethally irradiated allogeneic hosts and were detectable using fluorescence microscopy up to 24-h post-transplantation in pulmonary tissue.

ISOLATION AND MOLECULAR CHARACTERIZATION OF A MOUSE RENAL MICROVASCULAR ENDOTHELIAL CELL LINE

Murine endothelial cells (ECs) have proven difficult to obtain and maintain in culture. Long-term maintenance of normal ECs remains a difficult task. In this article we report the establishment of the first cellular line of renal microvascular endothelium obtained from normal tissue. Cells were isolated, cloned, and maintained by serial passages for longer than 24 mo, using endothelial cell growth supplement (ECGS) and gelatin-coated plates. Their morphology and ultrastructure, expression of von Willebrand factor, presence of smooth muscle alpha-actin, vimentin, cytokeratin filaments, capillary structures formed on Matrigel, and some typical ECs surface molecules were the criteria used to characterize cultured ECs. When examined for responsiveness to Shiga toxin-1, 13-20% of cytotoxicity was observed when coincubated with lipopolysaccharides. This cytotoxicity was not observed for normal lung ECs (1G11). Consequently, REC-A4 line retains characteristics of resting microvascular ECs and represents a useful in vitro model to study biological and physiopathological properties of renal endothelium.

Skeletal myogenic progenitors in the endothelium of lung and yolk sac

We previously showed that clonable skeletal myogenic cells can be derived from the embryonic aorta but become very rare in the more mature and structured fetal aorta. The aim of this study was to investigate whether, during fetal and postnatal development, these myogenic progenitors progressively disappear or may rather associate with the microvascular district, being thus distributed to virtually all tissues. To test this hypothesis, we used F1 embryos (or mice) from a transgenic line expressing a striated muscle-specific reporter gene (LacZ) crossed with a transgenic line expressing a different endothelial-specific reporter genes (GFP). Endothelial cells were isolated from yolk sac (at E11) and lung (at E11, E17, P1, P10, and P60), two organs embryologically unrelated to paraxial mesoderm, rich in vessels, and devoid of skeletal muscle. Endothelial cells, purified by magnetic bead selection (CD31/PECAM-1(+)) or cell sorting (Tie2-GFP(+)) were then challenged for their skeletal myogenic potential in vitro and in vivo. The results demonstrated that both yolk sac and lung contain progenitor cells, which express endothelial markers and are endowed with a skeletal myogenic potential that they reveal when in the presence of differentiating myoblasts, in vitro, and regenerating muscle, in vivo. The number (or potency to generate skeletal muscle) of these vessels associated cells decreases rapidly with age and is very low in mature animals, possibly correlating with reduced regenerative capacity of adult mammalian tissues.

Protease-activated receptors 1 and 4 mediate thrombin signaling in endothelial cells

Defining the relative importance of protease-activated receptors (PARs) for thrombin signaling in mouse endothelial cells is critical for a basic understanding of thrombin signaling in these cells and for the rational use of knockout mice to probe the roles of thrombin's actions on endothelial cells in vivo. We examined thrombin- and PAR agonist-induced increases in cytoplasmic calcium, phosphoinositide hydrolysis, extracellular signal-regulated kinase (ERK) phosphorylation, and gene expression in endothelial cells from wild-type and PAR-deficient mice. PAR1 and PAR4 agonists triggered responses in wild-type but not in Par1-/- and Par4-/- endothelial cells, respectively. Calcium imaging confirmed that a substantial fraction of individual endothelial cells responded to both agonists. Compared with wild-type cells, Par1-/- endothelial cells showed markedly decreased responses to low concentrations of thrombin, and cells that lacked both PAR1 and PAR4 showed no responses to even high concentrations of thrombin. Similar results were obtained when endothelial-dependent vasorelaxation of freshly isolated mouse aorta was used as an index of signaling in native endothelial cells. Thus PAR1 is the major thrombin receptor in mouse endothelial cells, but PAR4 also contributes. These receptors serve at least partially redundant roles in endothelial cells in vitro and in vivo and together are necessary for the thrombin responses measured.

Expression of genes involved in vascular development and angiogenesis in endothelial cells of adult lung

Profiling gene expression in endothelial cells advances the understanding of normal vascular physiology and disease processes involving angiogenesis. However, endothelial cell purification has been challenging because of the difficulty of isolating cells and their low abundance. Here we examine gene expression in endothelial cells freshly isolated from lung capillaries after in vivo labeling with fluorescent cationic liposomes and purification by fluorescence-activated cell sorting (FACS). Of the 39,000 genes and expressed sequence tags evaluated on custom oligonucleotide arrays, 555 were enriched in endothelial cell fraction. These included familiar endothelial cell-associated genes such as VEGF, VEGF receptor (VEGFR)-1, VEGFR-2, angiopoietin-2, Tie1, Tie2, Edg1 receptor, VE-cadherin, claudin 5, connexin37, CD31, and CD34. Also enriched were genes in semaphorin/neuropilin (Sema3c and Nrp1), ephrin/Eph (ephrin A1, B1, B2, and EphB4), delta/notch (Hey1, Jagged 2, Notch 1, Notch 4, Numb, and Siah1b), and Wingless (Frizzled-4 and Tle1) signaling pathways involved in vascular development and angiogenesis. Expression of representative genes in alveolar capillary endothelial cells was verified by immunohistochemistry. Such expression reflects features that endothelial cells of normal lung capillaries have in common with embryonic and growing blood vessels. About half of the enriched genes, including exostosin 2, lipocalin 7, phospholipid scramblase 2, pleckstrin 2, protocadherin 1, Ryk, scube 1, serpinh1, SNF-related kinase, and several tetraspanins, had little or no previous association with endothelial cells. This approach can readily be used to profile genes expressed in blood vessels in tumors, chronic inflammation, and other sites in which endothelial cells avidly take up cationic liposomes.

Age-associated impairment in TNF-alpha cardioprotection from myocardial infarction

Age-associated dysfunction in cardiac microvascular endothelial cells with impaired induction of cardioprotective platelet-derived growth factor (PDGF)-dependent pathways suggests that alterations in critical vascular receptor(s) may contribute to the increased severity of cardiovascular pathology in older persons. In vivo murine phage-display peptide library biopanning revealed a senescent decrease in cardiac microvascular binding of phage epitopes homologous to tumor necrosis factor-alpha (TNF-alpha), suggesting that its receptor(s) may be downregulated in older cardiac endothelial cells. Immunostaining demonstrated that TNF-receptor 1 (TNF-R1) density was significantly lower in the subendocardial endothelium of the aging murine heart. Functional studies confirmed the senescent dysregulation of TNF-alpha receptor pathways, demonstrating that TNF-alpha induced PDGF-B expression in cardiac microvascular endothelial cells of 4-mo-old, but not 24-mo-old, rats. Moreover, TNF-alpha mediated cardioprotective pathways were impaired in the aging heart. In young rat hearts, injection of TNF-alpha significantly reduced the extent of myocardial injury after coronary ligation: TNF-alpha, 7.9 +/- 1.9% left ventricular injury (n = 4) versus PBS, 16.2 +/- 7.9% (n = 10; P < 0.05). The addition of PDGF-AB did not augment the cardioprotective action of TNF-alpha. In myocardial infarctions of older hearts, however, TNF-alpha induced significant postcoronary occlusion mortality (TNF-alpha 80% vs. PBS 0%; n = 10 each, P < 0.05) that was reversed by the coadministration of PDGF-AB. Overall, these studies demonstrate that aging-associated alterations in TNF-alpha receptor cardiac microvascular pathways may contribute to the increased cardiovasular pathology of the aging heart. Strategies targeted at restoring TNF-alpha receptor-mediated expression of PDGF-B may improve cardiac microvascular function and provide novel approaches for treatment and possible prevention of cardiovascular disease in older individuals.

The role of endothelial insulin signaling in the regulation of vascular tone and insulin resistance

Insulin receptors (IRs) on vascular endothelial cells have been suggested to participate in insulin-regulated glucose homeostasis. To directly address the role of insulin action in endothelial function, we have generated a vascular endothelial cell IR knockout (VENIRKO) mouse using the Cre-loxP system. Cultured endothelium of VENIRKO mice exhibited complete rearrangement of the IR gene and a more than 95% decrease in IR mRNA. VENIRKO mice were born at the expected Mendelian ratio, grew normally, were fertile, and exhibited normal patterns of vasculature in the retina and other tissues. Glucose homeostasis under basal condition was comparable in VENIRKO mice. Both eNOS and endothelin-1 mRNA levels, however, were reduced by approximately 30-60% in endothelial cells, aorta, and heart, while vascular EGF expression was maintained at normal levels. Arterial pressure tended to be lower in VENIRKO mice on both low- and high-salt diets, and on a low-salt diet VENIRKO mice showed insulin resistance. Thus, inactivation of the IR on endothelial cell has no major consequences on vascular development or glucose homeostasis under basal conditions, but alters expression of vasoactive mediators and may play a role in maintaining vascular tone and regulation of insulin sensitivity to dietary salt intake.

Heterogeneity of endothelial cells from different organ sites in T-cell subset recruitment

Chemokines and adhesion molecules play a critical role in the recruitment of leukocytes into specific organ sites. Little is known, however, regarding the repertoire of chemokines and adhesion molecules expressed within different vascular beds. In this study, we compare adhesion molecule expression, chemokine induction, and T-cell subset-endothelial interactions under defined flow conditions on resting and tumor necrosis factor (TNF)-alpha-activated murine lung endothelial cells (MLECs) and heart endothelial cells (MHECs). Our study revealed that only MHECs exhibited high constitutive VCAM-1 expression. Exposure to TNF-alpha up-regulated adhesion molecule expression and chemokine production in both MLECs and MHECs. However, high levels of Regulated on Activation Normal T cell Expressed And Secreted (RANTES) expression were detected only in TNF-alpha-activated MHECs. TNF-alpha-stimulated MLECs and MHECs both supported T-helper cell interactions under defined flow conditions. Most T cells instantaneously arrested on MHECs but exhibited a rolling phenotype on MLECs. Blocking studies revealed that T-cell arrest on MHECs was mediated by constitutive VCAM-1 and TNF-alpha-induced RANTES. These findings are consistent with the hypothesis that functional heterogeneity of endothelial cells from different sites exists and some of it is retained in vitro. Furthermore, these results provide an insight into the molecular mechanisms that may mediate T-helper cell recruitment to these organs.

Isolation of murine aortic endothelial cells in culture and the effects of sex steroids on their growth

The lack of commercially available primary murine endothelial cells prompted us to isolate and cultivate this cell type. We report here the effect of sex steroids on the in vitro growth of murine aortic endothelial cells. Murine aortic endothelial cells were isolated by a combination of explant outgrowth from aortic rings and enzymatic digestion. The endothelial nature of the cells was verified by uptake of acylated low-density lipoprotein and positive staining for CD-31. Murine aortic endothelial cell growth is stimulated by physiological concentrations of estrogen. Progesterone, when given simultaneously with estrogen, inhibited the stimulatory growth effect of estrogen. Murine aortic endothelial cells grown in vitro continue to express messenger ribonucleic acid for proteins related to endothelial growth. These include vascular endothelial growth factor, its receptors Flt-1 and Flk-1, and the angiogenesis-associated transcription factor, Ets-1.

Insulin-like growth factor binding protein-3 is overexpressed in endothelial cells of mouse breast tumor vessels

Angiogenesis is a key process in a variety of human diseases, including cancer. The ability to target selectively the tumor vasculature is potentially useful for the diagnosis and treatment of cancer. Still, little information is available regarding markers that are restricted to the ECs of tumor vessels. cDNA array technology allows simultaneous analysis of relative expression levels of a broad spectrum of genes in 2 related cell populations. We used this technology with the aim of identifying markers specific for TECs. TECs were isolated by CD31-mediated immunomagnetic separation from tumors induced by s.c. injection of NF9006 breast carcinoma cells into syngeneic mice. NECs were isolated from lactating mammary glands. The endothelial nature of isolated cells was confirmed by RT-PCR using CD31-specific primers and by uptake of DiI-Ac-LDL. Macrophage contamination in the EC isolations could be reasonably ruled out by assessing the expression of the macrophage marker c-fms. (32)P-labeled cDNA probes generated by reverse transcription from total RNA were hybridized to mouse-specific gene arrays. Several genes consistently showed differential expression between TECs and NECs. However, expression of only 1 of these genes, IGFBP-3, was restricted exclusively to ECs. Semiquantitative RT-PCR revealed 22- to 33-fold differential expression of IGFBP-3 in the TEC fraction. IGFBP-3 was overexpressed by a factor of 5 in an additional mouse model of breast carcinoma induced by 4T1.2 tumor cells. These results indicate that IGFBP-3 is a potential novel marker of angiogenesis. Elucidation of its role in tumor neovascularization may open the possibility of IGFBP-3 as a therapeutic target for antiangiogenesis.

Papillary carcinoma of the thyroid: evidence for a role for hepatocyte growth factor (HGF) in promoting tumour angiogenesis

The pattern of vascularization of papillary carcinoma was investigated in tumour sections from 31 cases and in primary cultures from 12 cases. Tumour sections were immunostained for von Willebrand Factor (vWF) to visualize blood vessels; for endothelial-specific nitric-oxide-synthase (EC-NOS), as a marker of endothelial cell activation; and for Ki-67 to evaluate endothelial cell proliferation. It was found that endothelial cells lining venous vessels located in peritumoural fibrous tissue were intensely EC-NOS-positive and occasionally Ki-67-positive. Capillary vessels of tumour papillae were not stained for Ki-67 and were weakly EC-NOS-positive. Primary cultures of papillary carcinoma cells were used as a potential source of factors active on endothelial cells. It was found that thyroid tumour cells contain RNAs for angiopoietin, vascular endothelial growth factor (VEGF), and VEGF-C; moreover, they release large amounts of VEGF into culture supernatants and exert chemotactic activity in vitro for the endothelial cell line SIEC. The ability of papillary carcinoma cells to release angiogenic factors could be stimulated in vitro. Hepatocyte growth factor (HGF; 25 ng/ml) induced a 1.2- to 5-fold increase in the amount of VEGF released by tumour cells and a 1.2- to 4.2-fold increase in the amount of chemotactic activity present in culture supernatants. Met protein, the high affinity HGF-receptor, is overexpressed in a large proportion of cases of papillary carcinoma. These findings are consistent with the possibility that HGF-Met protein interaction is one of the molecular mechanisms promoting the vascularization of papillary carcinoma of the thyroid.

Prolonged gene expression in mouse lung endothelial cells following transfection with Epstein-Barr virus-based episomal plasmid

The development of a strategy to deliver a gene to pulmonary endothelium will be useful for gene function study and for pulmonary gene therapy. Cationic lipidic vectors are efficient in gene transfer to pulmonary endothelium via the vascular route; however, gene expression is transient and lasts for only a few days. In this study, we show that pulmonary gene transfer via cationic lipidic vectors can be significantly improved using an Epstein-Barr virus (EBV)-based expression plasmid. Systemic administration of cationic liposomes followed by the EBV-based plasmid led to gene expression in the lung that lasted for more than 3 weeks. Prolonged and high levels of gene expression can also be obtained in primary mouse lung endothelial cells (MLEC) following lipofection with an EBV-based plasmid. These results suggest the utility of this gene transfer protocol in studying the expression of cloned genes in lung endothelial cells and in pulmonary gene therapy.

A fluorescent Tie1 reporter allows monitoring of vascular development and endothelial cell isolation from transgenic mouse embryos

Tie1 is an endothelial receptor tyrosine kinase essential for development and maintenance of the vascular system. Here we report generation of transgenic mice expressing enhanced green fluorescent protein (EGFP) or a chimeric protein consisting of a Zeosin resistance marker and EGFP under the control of mouse Tie1 promoter. Intravital monitoring of fluorescence showed that the EGFP reporter recapitulates the Tie1 expression pattern in the developing vasculature, and flow cytometry using EGFP allowed the isolation of essentially pure Tie1-expressing endothelial cells from transgenic mouse embryos. However, EGFP and LacZ transgenic markers were strongly down-regulated in the adult vasculature; unlike the Tie1-LacZ knock-in locus, the promoter was not reactivated during tumor neovascularization, indicating the presence of additional regulatory elements in the Tie1 locus. Starting at midgestation, Tie1 promoter activity became stronger in the arterial than in the venous endothelium; in adult mice, promoter activity was observed in arterioles, capillaries, and lymphatic vessels, indicating a significant degree of specificity in different types of endothelial cells. Our results establish Tie1-Z/EGFP transgenic mice as a useful model to study embryonic vascular development and a convenient source for the isolation of primary endothelial cells.

Novel branching membrane translocational peptide as gene delivery vector

A fragment of HIV-tat protein, RKKRRQRRR, has been shown to have membrane penetration and nuclear localization properties, which are critical attributes of gene therapy agents. In this study, we designed a series of arborizing tat peptides, containing 1-8 tat moieties, and evaluated them as transfection enhancers in a variety of cell lines. We found that all compounds complexed with plasmid DNA, but only the molecule containing 8 tat-peptide chains shows significant transfection capabilities. Using rhodamine labeled plasmid and eight tat-peptide complex, we were also able to demonstrate intracellular delivery of the complex by fluorescence microscopy.

Vascular endothelial growth factor is expressed in endothelial cells isolated from skeletal muscles of nitric oxide synthase knockout mice during prazosin-induced angiogenesis

In skeletal muscles, angiogenesis can be induced by increases in wall shear stress. To identify molecules involved in the angiogenic process, a method based on the use of BS-1 lectin-coated magnetic beads was developed to isolate a cellular fraction enriched in microvascular endothelial cells which are directly exposed to wall shear stress. Using such cellular fractions from skeletal muscles of C57 mice in which angiogenesis was induced by administration with the alpha(1)-adrenergic antagonist prazosin, we found the concentration of vascular endothelial growth factor (VEGF) increased in correlation to the duration of the prazosin stimulus. In contrast, the angiopoietin-2/tie-2 system was not changed even after 4days of prazosin treatment. In neuronal nitric oxide synthase (nNOS) knockout mice, the VEGF concentration was also elevated after prazosin treatment but remained almost unchanged in endothelial nitric oxide synthase (eNOS) knockout mice. However, eNOS (and not nNOS) knockout mice expressed higher levels of VEGF under non-stimulated conditions as compared to C57 mice. These results suggest that VEGF produced in endothelial cells is involved in angiogenesis in skeletal muscles of mice responding to the administration of systemic vasodilators. NO derived from eNOS and nNOS may be an important regulator of the angiogenic response in skeletal muscles in vivo.

MMP9 induction by vascular endothelial growth factor receptor-1 is involved in lung-specific metastasis

The molecular mechanism of tissue-specific metastasis in tumors endogenously expressing members of the vascular endothelial growth factor (VEGF) family is not yet clear. Here we demonstrate that MMP9 is specifically induced in premetastatic lung endothelial cells and macrophages by distant primary tumors via VEGFR-1/Flt-1 tyrosine kinase (TK) and that it significantly promotes lung metastasis. In a genetic approach using mice, suppression of MMP9 induction by deletion of either VEGFR-1TK or MMP9 markedly reduced lung metastasis. Furthermore, the MMP9 levels in endothelial cells of normal lung lobes from patients carrying distant tumors were significantly elevated as compared with those from patients without tumors. Thus, a block of MMP9 induction via VEGFR-1 inhibition could be useful for the prevention of tumor metastasis in lung.

Isolation and characterization of large numbers of endothelial cells for studies of cell signaling

Studies of endothelial cell signaling involving cholesterol-rich domains require large numbers of cells of bona fide origin. The growth of any cell in culture, particularly for extended periods, results in an altered phenotype that could include changes in the properties of caveolae and lipid raft structures. While continuously propagated cells are used to study specific questions because their origin is known and because proteins of interest are still expressed, such reasoning is an oversimplification and can lead to findings that are descriptive of the cell's adaptation to culture rather than its original phenotype. We are particularly cognizant of this concern as we examine caveolar signaling domains in endothelial cells. Here we present a reproducible method for the isolation and characterization of large numbers of bona fide endothelial cells suitable for studies of the regulation of receptor signal transduction. Digestion of guinea pig hearts with collagenase results in the liberation of cells that adhere to collagen-coated plastic and express platelet-endothelial cell adhesion molecule 1 (PECAM-1) and binding sites for Ulex europaeus agglutinin 1 (UEA-1) that permit segregation of cells using fluorescence-activated cell sorting. Growth of cells over 7 doublings results in enrichment in the expression of both PECAM-1 and UEA-1 and retention of functional low-density lipoprotein receptor. The ability of cells to differentiate into endothelial tubes at any stage during their characterization up to 20 doublings in culture suggests that this method can be employed to generate endothelial cells that are minimally altered from their site of origin.

Histological markers for endothelial cells in endogenous and transplanted rodent pancreatic islets

BACKGROUND/AIMS

To obtain a selective marker to identify endothelial cells is difficult, due to the heterogeneity of these cells. Most described markers perform well in some applications, but fail in others. The aim of this study was to identify a selective and specific marker for rodent microvascular endothelial cells, especially for use in studies on the vascular system of pancreatic islets.

METHODS

A biotin-labelled form of the lectin Bandeiraea or Griffonia simplicifolia in combination with a streptAB-Complex with alkaline phosphatase was used to stain endothelium in paraffin-embedded tissue sections from C57BL/6 mice, Sprague-Dawley or Wistar-Furth rats.

RESULTS

We were consistently able to selectively stain microvascular endothelial cells in lungs, small intestines, white and brown adipose tissue, pancreas and islets of Langerhans with the lectin Bandeiraea simplicifolia. Furthermore, we were able to visualise the vasculature in syngenically transplanted islets of Langerhans in Wistar-Furth rats and C57BL/6 mice. Attempts to stain rodent endothelial cells with antibodies against CD34, CD31, CD200, Ox43, von Willebrand factor and the lectin Ulex europaeus were not uniformly successful.

CONCLUSION

The lectin Bandeiraea simplicifolia is a versatile marker for rodent endothelial cells, and may be used to study revascularisation after transplantation of pancreatic islet in rodents.

A monoclonal antibody to vascular endothelial-cadherin inhibits tumor angiogenesis without side effects on endothelial permeability

Vascular endothelial cadherin (VE-cadherin) is an endothelial-specific, trans-membrane protein that promotes homophilic cell adhesion. Inhibition of VE-cadherin by the blocking monoclonal antibody (mAb) BV13 inhibited angiogenesis and tumor growth in vivo. However, this effect was accompanied by a marked increase in lung and heart permeability. In the present paper, we characterize a different VE-cadherin mAb (BV14) that is able to inhibit angiogenesis without affecting vascular permeability. In vitro studies show that BV14, in contrast to BV13, did not increase paracellular permeability of endothelial monolayers and did not disrupt VE-cadherin clusters at junctions. However, both antibodies could inhibit formation of vascularlike structures in collagen gels and increase migration of endothelial cells into wounded areas. In vivo, BV14 and BV13 were equally active in inhibiting angiogenesis in the mouse cornea and in reducing the growth of hemangioma and C6 glioma. In contrast to BV13, BV14 did not change vascular permeability in all the organs tested and at any dose used. BV14 and BV13 bind to VE-cadherin extracellular repeats EC4 and EC1, respectively. We propose that, in resting vessels, where junctions are stable and well-structured, antibody binding to EC1 but not EC4 disrupts their organization and increases permeability. In contrast, in growing vessels, where endothelial cells are migrating and junctions are weaker, antibody binding to EC4 may be sufficient to disrupt cell-to-cell adhesion and inhibit assembly of new vascular structures.

Microarray technology and gene expression analysis for the study of angiogenesis

Angiogenesis plays a major role in multiple disease processes including cancer, and new agents that modulate angiogenesis are rapidly entering clinical trials. The understanding of the biological mechanisms and downstream effects for many of these agents is poorly understood. It is therefore important that methods evolve to understand how an agent regulates angiogenesis, in order to promote a higher percentage of successful drug candidates. With the emergence of microarray technology for the evaluation of gene expression, researchers have a powerful tool for dissecting the biological mechanisms of angiogenesis. However, huge data sets and complex statistics pose a hurdle for the investigator to obtain useful and meaningful data. To eliminate problems in data analysis, proper design and planning prior to performing a microarray experiment is crucial to making valid conclusions. This review will discuss the critical factors in designing, performing and analysing microarray experiments, and the utility of various models of angiogenesis for microarray analysis.