Preincubation Of Human Umbilical Vein Endothelial Cells Research Articles

Fibulin-5 Regulates Angiopoietin-1/Tie-2 Receptor Signaling in Endothelial Cells.

BackgroundFibulin-5 is an extracellular matrix glycoprotein that plays critical roles in vasculogenesis and embryonic development. Deletion of Fibulin-5 in mice results in enhanced skin vascularization and upregulation of the angiogenesis factor angiopoietin-1 (Ang-1), suggesting that Fibulin-5 functions as an angiogenesis inhibitor. In this study, we investigate the inhibitory effects of Fibulin-5 on Ang-1/TIE-2 receptor pathway signaling and cell survival in human endothelial cells.Methodology/Principal FindingsRecombinant wild-type and RGE-mutant Fibulin-5 proteins were generated through stable transfection of HEK293 and CHO cells, respectively. In vitro solid phase binding assays using pure proteins revealed that wild-type Fibulin-5 does not bind to Ang-1 or TIE-2 proteins but strongly binds to heparin. Binding assays using human umbilical vein endothelial cells (HUVECs) indicated that wild-type Fibulin-5 strongly binds to cells but RGE-mutant Fibulin-5, which is incapable of binding to integrins, does not. Pre-incubation of HUVECs for 1 hr with Fibulin-5 significantly increased caspase 3/7 activity, ERK1/2 phosphorylation, and expressions of the transcription factor early growth response 1 (EGR1) and the dual-specificity phosphatase 5 (DUSP5). Fibulin-5 also strongly attenuated Ang-1-induced TIE-2 and AKT phosphorylation, decreased Ang-1-induced expressions of the transcription factors Inhibitor of DNA Binding 1 (ID1) and Kruppel-like Factor 2 (KLF2), and reversed the inhibitory effect of Ang-1 on serum deprivation-induced cytotoxicity and caspase 3/7 activity.Conclusion/SignificanceWe conclude that Fibulin-5 strongly binds to the endothelial cell surface through heparin-sulfate proteoglycans and possibly integrins and that it exerts strong anti-angiogenic effects by reducing endothelial cell viability and interfering with the signaling pathways of the Ang-1/TIE-2 receptor axis.

ZEB1 Upregulates VEGF Expression and Stimulates Angiogenesis in Breast Cancer.

Although zinc finger E-box binding homeobox 1 (ZEB1) has been identified as a key factor in the regulation of breast cancer differentiation and metastasis, its potential role in modulating tumor angiogenesis has not been fully examined. Here, we present the novel finding that conditioned medium derived from ZEB1-expressing MDA-MB-231 cells significantly increased the capillary tube formation of human umbilical vein endothelial cells (HUVECs), whereas ZEB1 knockdown by RNA interference had the opposite effect. ZEB1 caused marked upregulation of the expression of vascular endothelial growth factor A (VEGFA) at both mRNA and protein levels. Pre-incubation of HUVECs with anti-VEGFA neutralized antibody attenuated ZEB1-mediated tube formation of HUVECs. In breast cancer tissues, expression of ZEB1 was positively correlated with those of VEGFA and CD31. At the molecular level, ZEB1 activated VEGFA transcription by increasing SP1 recruitment to its promoter, which was mediated via the activation of PI3K and p38 pathways. Using a nude mouse xenograft model, we demonstrated that elevated expression of ZEB1 promotes in vivo tumorigenesis and angiogenesis in breast cancer. Collectively, we found that ZEB1-expressing breast cancer cells increase VEGFA production and thus stimulate tumor growth and angiogenesis via a paracrine mechanism.

43 A novel role for small molecule glycomimetics in the protection against lipid-induced endothelial dysfunction

Glycomimetics are molecules that mimic the structure of carbohydrates involved in important biological processes. Small molecule glycomimetics are an untapped source of novel therapies for endothelial dysfunction, a hallmark of cardiovascular complications associated with diabetes. The current study aims to investigate the possible protective effects of newly synthesised small molecule glycomimetics against lipid-induced endothelial dysfunction, with an emphasis on nitric oxide (NO) and induced oxidative stress. Glycomimetics were synthesised by the stepwise transformation of 2,5-dihydroxybenzoic acid to a range of 2,5-substituted benzoic acid derivatives incorporating the key sulfate groups to mimic the interactions of heparan sulfate. Acetylcholine-induced endothelium-dependent relaxation in mouse thoracic aortic rings was measured using wire myography, and human umbilical vein endothelial cells (HUVECs) function was assessed in the presence or absence of palmitate, with or without the test glycomimetics. NO and reactive oxygen species (ROS) production was measured using DAF-2 and H2DCF-DA, respectively. Colorimetric assays were used to determine lipid peroxidation and activity of the antioxidant enzymes. Expression of Akt, eNOS, Nrf-2, NQO-1 and HO-1 were assessed using RT-PCR and western blotting. At 1 µM concentration, the synthesised glycomimetics significantly improved endothelium-dependent relaxation ex vivo and protected HUVECs against palmitate-induced oxidative stress and reduced NO production. Pre-incubation of HUVECs with all compounds upregulated Akt/eNOS signalling, activated Nrf2/ARE pathway, and suppressed ROS-induced lipid peroxidation. In conclusion, our newly synthesised small molecule glycomimetics protect against lipid-induced endothelial dysfunction. These novel cytoprotective effects open the door to a new class of therapeutic drugs to target endothelial dysfunction.

Astaxanthin decreases inflammatory biomarkers associated with cardiovascular disease in human umbilical vein endothelial cells

As a potent antioxidant, astaxanthin may downregulate inflammation‐associated factors involved in endothelial dysfunction and cardiovascular disease progression. We studied the possible protective effects of astaxanthin against endothelial dysfunction in human umbilical vein endothelial cells (HUVEC) induced with H2O2. Cells were pre‐incubated with 0, 0.01, 0.1, or 1.0 μmol/L astaxanthin for 48 h, then oxidative stress induced with 100 μmol/L H2O2 overnight. Uptake kinetics showed a time‐dependent accumulation of astaxanthin (1.0 μmol/L) by HUVEC over the 48 h period. Oxidative stress induction with H2O2 decreased intracellular antioxidant activity (SOD and GPx) and increased the production of reactive oxygen species (ROS), inflammatory cytokines and mediators. In contrast, pre‐incubation of HUVEC with astaxanthin prior to H2O2 stress increased (P < 0.05) SOD, but not GPx activity, and decreased the production of ROS, PGE2, LTB4, NO, IL‐8, and IFN‐γ. Pre‐treatment with astaxanthin also downregulated transcriptional activation of NF‐κB and activator protein‐1, thereby inhibiting downstream production of inflammatory cytokines and mediators. Therefore, astaxanthin inhibits inflammatory biomarkers upregulated by H2O2, likely by scavenging ROS required for transcriptional activation. Supported by the University of Washington and Washington State University.

Astaxanthin Decreases Inflammatory Biomarkers Associated with Cardiovascular Disease in Human Umbilical Vein Endothelial Cells

Oxidative stress and inflammation are strongly linked to the development of cardiovascular disease (CVD). As a potent antioxidant, astaxanthin may downregulate inflammation-associated factors involved in endothelial dysfunction and CVD progression. We studied the possible protective effects of astaxanthin against endothelial dysfunction in human umbilical vein endothelial cells (HUVEC) induced with hydrogen peroxide (H2O2). Cells were pre-incubated with 0, 0.01, 0.1, or 1.0 μmol/L astaxanthin for 48 h, then oxidative stress induced with 100 μmol/L H2O2 overnight. Uptake kinetics of astaxanthin showed a time-dependent uptake of astaxanthin (1.0 μmol/L) by HUVEC over the 48 h incubation period. Oxidative stress induction with H2O2 in HUVEC decreased intracellular antioxidant activity and increased the production of inflammatory biomarkers and reactive oxygen species (ROS). In contrast, pre-incubation of HUVEC with astaxanthin prior to H2O2 stress increased (P < 0.05) superoxide dismutase activity and decreased ROS, prostaglandin E2, leukotriene B4, NO, IL-8, and IFN- production. Pre-treatment with astaxanthin also downregulated the transcriptional activation of NF-κB and activator protein-1, thereby inhibiting downstream production of inflammatory mediators and cytokines. Therefore, astaxanthin protects against factors initiated by H2O2 addition, likely by scavenging ROS required for transcriptional activation and inhibiting the production of inflammatory biomarkers involved in endothelial dysfunction and CVD. Abbreviations: AP-1: activator protein-1; CVD: cardiovascular disease; CS: culture supernatant; EGM-2: endothelial growth medium-2; GPx: glutathione peroxidase; H2O2: hydrogen peroxide; HUVEC: human umbilical vein endothelial cell; LTB4: leukotriene B4; PGE2: prostaglandin E2; ROS: reactive oxygen species; SOD: superoxide dismutase; THF: tetrahydrofuran.

Temporally resolved cAMP monitoring in endothelial cells uncovers a thrombin‐induced [cAMP] elevation mediated via the Ca2+‐dependent production of prostacyclin

The barrier function of the endothelium is controlled by the second messengers Ca2+ and cAMP that differentially regulate the permeability of endothelial cells. The Ca2+-elevating agent thrombin has been demonstrated to increase endothelial permeability and to decrease cAMP levels as detected via enzyme immunoassays. To study the effects of thrombin on cAMP with high temporal resolution, we utilised the FRET-based cAMP sensor Epac1-camps in single intact human umbilical vein endothelial cells (HUVECs). In these cells, thrombin induced a delayed increase in [cAMP], initiating after about 40 s, with maximum cAMP levels after 130 s of thrombin application. This increase of cAMP levels was Ca2+-dependent, but did not require calmodulin (CaM). Pharmacological approaches revealed that phospholipase A2 (PLA2) activity and cyclooxygenase (COX)-mediated synthesis of prostaglandins was required for the thrombin-induced elevation of [cAMP]. Furthermore, preincubation of HUVECs with a prostacyclin-receptor antagonist significantly reduced the thrombin-induced increase in [cAMP]. We conclude that thrombin causes the synthesis of prostacyclin in endothelial cells and that the subsequent stimulation of Gs-coupled prostacyclin receptors then results in an increase in [cAMP].

Factor Xa Induces Tissue Factor Expression in Endothelial Cells by P44/42 MAPK and NF-κB-Dependent Pathways

Tissue factor (TF) is an initiator of coagulation. The serine protease factor Xa (FXa) is the convergence point of the extrinsic and intrinsic components of the coagulation cascade. In addition to its hemostatic function, FXa elicits inflammatory responses in endothelial cells that may be important in surgical procedures in which inflammation is triggered. This study tested the hypothesis that FXa can up-regulate TF on vascular endothelial cells by a mitogen-activated protein kinase (MAPK)- and NF-κB-dependent pathway. Incubation of cultured human umbilical vein endothelial cells (HUVECs) with FXa increased TF protein expression and activity in a dose-dependent manner. Pre-incubation of HUVECs with the serine protease inhibitor antithrombin, which targets not only thrombin but also FXa and FIXa, inhibited FXa-induced TF expression, but the selective thrombin inhibitor hirudin did not inhibit FXa-induced TF expression, ruling out a thrombin-mediated pathway. After 10 min incubation with HUVECs, FXa rapidly induced P44/42 MAPK activation (immunoblotting of phosphorylated P44/42 MAPK) with a peak at 30 min. The MEK 1/2 inhibitor PD98059 partially reduced FXa-induced TF expression and activity (3.82 ± 0.11 vs 6.54 ± 0.08 fmol/min/cm(2), P < 0.05). NF-κB was activated by FXa, confirmed by cytoplasmic IkBα degradation and increased NF-κB P65 nuclear translocation. Interruption of the NF-κB pathway by the IkBα phosphorylation inhibitor Bay 11-7802 abrogated FXa-induced TFprotein expression and activity (1.93 ± 0.02 versus 6.54 ± 0.08 fmol/min/cm(2), P < 0.05). However, inhibition of PI3 kinase by LY 294002 did not attenuate FXa-induced TF protein expression and activity. (1) FXa up-regulates TF protein expression and activity in HUVECs, (2) FXa-induced up-regulation of TF is independent of the thrombin-PAR1 pathway, and (3) the MAPK and NF-κB pathways, but not PI3 kinase pathway, are involved in FXa-induced TF expression on human umbilical endothelial cells. FXa may be a feed-forward alternative mechanism of activating TF expression and activity, thereby increasing a procoagulant state or inflammation. This mechanism may be important in the pro-inflammatory state initiated by cardiac surgical procedures.

Retinoic acid decreases endothelial permeability and fenestrae‐associated protein PV‐1 expression in human umbilical vein endothelial cells (HUVEC)

Vascular endothelial growth factor (VEGF), recognized as a growth factor secreted by tumor cells, increases PV‐1 expression and endothelial permeability. Retinoic acid (RA), a vitamin A derivative, regulates cell differentiation and is implicated in obesity, diabetes and cardiovascular disease. We postulated that RA may alter the effects of VEGF on HUVEC. To test this hypothesis we measured if administration of RA modulates PV‐1 expression and endothelial permeability in cell culture. HUVEC cultures were treated with 1 and 10 μM of RA. mRNA and protein levels of PV‐1 were detected with real‐time PCR and western blot, respectively. Permeability of endothelial monolayer was determined using 40 kDa FITC‐labeled dextran. 10 μM of RA significantly decreased the mRNA and protein level of PV‐1 and this effect was most pronounced after 48 hours. 10 μM of RA also decreased significantly the permeability of endothelial monolayer. Preincubation of HUVEC for 30 minutes with RA increased cell proliferation and blocked the endothelial permeability induced by 100 ng/ml VEGF. We demonstrated that RA decreased permeability and PV‐1 expression and blocked the effect of VEGF on endothelial permeability. Our results also suggest that RA may modulate the endothelial permeability effect of VEGF which at least partly induced by PV‐1 protein. Further studies needed to clarify the functional consequences of this striking phenomenon.

The bio-complex "reaction pattern in vertebrate cells" reduces cytokine-induced cellular adhesion molecule mRNA expression in human endothelial cells by attenuation of NF-kappaB translocation

The bio-complex "reaction pattern in vertebrate cells" (RiV) is mainly represented by characteristic exosome-like particles--probably as reaction products of cells to specific stress. The transcription factor NF-kappaB plays a central role in inflammation. We tested the hypothesis that RiV particle preparations (RiV-PP) reduce cellular adhesion molecule (CAM) expression (ICAM-1, VCAM-1, E-selectin) by the attenuation of NF-kappaB translocation in human umbilical vein endothelial cells (HUVEC). After 4 hours, pre-incubation of HUVEC with RiV-PP before stimulation with TNF-alpha significantly reduced ICAM-1 (65.5+/-10.3%) and VCAM-1 (71.1+/-12.3%) mRNA expression compared to TNF-alpha-treated cells (100%, n=7). ICAM-1 surface expression was significantly albeit marginally reduced in RiV/TNF-alpha- treated cells (92.0+/-5.6%, n=4). No significant effect was observed on VCAM-1 surface expression. In RiV/TNF-alpha-treated cells (n=4), NF-kappaB subunits p50 (85.7+/-4.1%) and p65 (85.0+/-1.8%) nuclear translocation was significantly reduced. RiV-PP may exert an anti-inflammatory effect in HUVEC by reducing CAM mRNA expression via attenuation of p50 and p65 translocation.

Lectin-like oxidized low density lipoprotein receptor-1 mediates effects of bezatibrate on the apoptosis of endothelial cells

Objective To observe the influence of bezafibrate on the apoptosis and expression of lectin-like oxidized low density lipoprotein receptor-1(LOX-1) mediated by oxidized low density lipoprotein(ox-LDL) in cultured human umbilical vein endothelial cells(HUVECs).Methodes The apoptosis of HUVECs mediated by ox-LDL were evaluated by flow cytometry and the expression of LOX-1 mRNA were detected by RT-PCR.Results Compared with the control group,ox-LDL could increase apoptosis and the expression of LOX-1(P<0.05),and Bezafibrate could decrease the apoptosis and the expression of LOX-1 in a concentration -dependent manner(P<0.05).Preincubation of HUVECs with polyinosinic acid for 2 hours,the apoptosis and the expression of LOX-1 decreased(P<0.05).Conclusions Bezafibrate inhibits the apoptosis of HUVECs mediated by ox-LDL by reducing the expression of LOX-1,which may be part of the reasons for bezafibrate to prevent and treat atherosclerosis. Key words: Bezafibrate/PD; Receptors,LDL; Apoptosis

Lysophosphatidylglycerol stimulates chemotactic migration and tube formation in human umbilical vein endothelial cells

In this study, we observed that lysophosphatidylglycerol (LPG) stimulates extracellular signal-regulated kinase (ERK) in human umbilical vein endothelial cells (HUVECs). LPG-stimulated ERK activity was not inhibited by pertussis toxin (PTX), indicating PTX-sensitive G-proteins-independent manner. In terms of functional aspect, LPG induced chemotactic migration of HUVECs in a PTX-insensitive manner. Preincubation of HUVECs with an ERK inhibitor (PD98059) completely inhibited LPG-induced chemotactic migration, suggesting the crucial role of ERK in the process. LPG-induced ERK activation and chemotactic migration in HUVECs were not affected by an lysophosphatidic acid receptor-selective antagonist (Ki16425), indicating lysophosphatidic acid receptors-independency. We also found that LPG stimulated tube formation in HUVECs. Taken together we suggest that LPG stimulates HUVECs and result in chemotactic migration and tube formation, suggesting a new aspect of LPG as a modulator of endothelial cell functioning.

Tumor necrosis factor‐alpha (TNF‐α)‐induced cell adhesion was inhibited by an aqueous extract of Buddleia officinalis in HUVECs

Cell adhesion is involved in the initiation and progression of cardiovascular disease including atherosclerosis. While conducting an in vitro screening of 600 medicinal plant extracts, an aqueous extract of Buddleia officinalis (ABO) was found to exhibit an anti-vascular inflammatory activity in human umbilical vein endothelial cells (HUVECs). In the present study, therefore, the anti-vascular inflammatory activity of ABO and possible mechanisms responsible for this effect were investigated in HUVECs. Preincubation of HUVECs with ABO (10 μg/ml) suppressed the protein and mRNA expression levels of adhesion molecules including intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) induced by tumor necrosis factor-alpha (TNF-α) in HUVECs. ABO also attenuated TNF-α-induced cell adhesion of monocytic U937 cells to HUVECs in a dose-dependent manner. In addition, ABO significantly inhibited TNF-α-induced translocation of Nuclear Factor-κB (NF-κB) p65 from cytoplasm to nuclei in HUVECs. Taken together, the present data suggest that ABO suppresses the vascular inflammatory process through the inhibition of NF-κB activation.

Mesenchymal stem cells display coordinated rolling and adhesion behavior on endothelial cells

AbstractTo explore the initial steps by which transplanted mesenchymal stem cells (MSCs) interact with the vessel wall in the course of extravasation, we studied binding of human MSCs to endothelial cells (ECs). In a parallel plate flow chamber, MSCs bound to human umbilical vein ECs (HUVECs) similar to peripheral-blood mononuclear cells (PBMCs) or CD34+ hematopoietic progenitors at shear stresses of up to 2 dynes/cm2. This involved rapid extension of podia, rolling, and subsequent firm adhesion that was increased when ECs were prestimulated with TNF-α. MSC binding was suppressed when ECs were pretreated with function-blocking anti–P-selectin antibody, and rolling of MSCs was induced on immobilized P-selectin, indicating that P-selectin was involved in this process. Preincubation of HUVECs with anti–VCAM-1 or of MSCs with anti–VLA-4 antibodies suppressed binding of MSCs to HUVECs but did not enhance inhibition by anti–P-selectin, indicating that both P-selectin and VCAM-1 are equally required for this process. Intravital microscopy demonstrated the capacity of MSCs to roll and adhere to postcapillary venules in vivo in a mouse model in a P-selectin–dependent manner. Thus, MSCs interact in a coordinated fashion with ECs under shear flow, engaging P-selectin and VCAM-1/VLA-4.

MBL and C1q compete for interaction with human endothelial cells

C1q, the recognition molecule of the classical pathway of complement, binds to endothelial cells, leading to cell activation. Mannose-binding lectin (MBL), a recognition molecule of the lectin pathway, is structurally and functionally related to C1q. Therefore, we investigated the interaction of MBL with human umbilical vein endothelial cells (HUVEC). C1q and MBL were purified from normal human plasma and binding to HUVEC was evaluated by flow cytometry. Cross-competition experiments were performed using MBL and C1q labeled with digoxygenin. MBL, similar to C1q, exhibited a dose-dependent binding to HUVEC under calcium-free conditions, suggesting involvement of its collagenous domains. Pre-incubation of HUVEC with MBL inhibited the binding of digoxygenin-labeled MBL at equimolar concentrations, confirming the specificity of the interaction. Pre-incubation of HUVEC with MBL inhibited the binding of C1q and vice versa. Activation of HUVEC with LPS resulted in increased C1q and MBL binding. Stimulation of HUVEC with MBL did not result in a detectable increase in cytokine production. Based on these results, we propose that MBL and C1q bind to a shared receptor on endothelial cells. Interaction of MBL and C1q with receptors on endothelial cells may be involved in inflammatory processes, and in clearance of pathogens and apoptotic cells.

The 4G/5G PAI-1 polymorphism influences the endothelial response to IL-1 and the modulatory effect of pravastatin.

Increased plasminogen activator inhibitor (PAI-1) levels lead to impaired fibrinolytic function associated with higher cardiovascular risk. PAI-1 expression may be regulated by different inflammatory cytokines such as interleukin-1alpha (IL-1). Several polymorphisms have been described in the PAI-1 gene. We examined the influence of the 4G/5G polymorphism in the promoter region on IL-1alpha-induced PAI-1 expression by human umbilical vein endothelial cells (HUVEC) in presence or absence of pravastatin. Genotyped HUVEC were incubated with IL-1alpha (500 U mL(-1)) in presence or absence of pravastatin (1-10 microm). PAI-1 expression was analyzed by real time polymerase chain reaction (PCR), and PAI-1 antigen measured in supernatants by ELISA. IL-1alpha increased PAI-1 secretion in a genotype-dependent manner, and higher values were observed for 4G/4G compared with both 4G/5G and 5G/5G cultures (P < 0.05). Preincubation of HUVEC with 10 microm pravastatin significantly reduced IL-1-induced PAI-1 expression in 4G/4G HUVEC compared with untreated cultures (177.5% +/- 24.5% vs. 257.9% +/- 39.0%, P < 0.05). Pravastatin also attenuated the amount of secreted PAI-1 by 4G/4G HUVEC after IL-1 stimulation (5020.6 +/- 165.7 ng mL(-1) vs. 4261.1 +/- 309.8 ng mL(-1), P < 0.05). This effect was prevented by coincubation with mevalonate, indicating a dependence on HMG-CoA reductase inhibition. The endothelial 4G/5G PAI-1 genotype influences the PAI-1 response to IL-1alpha and the modulatory effect of pravastatin. As increased PAI-1 levels have been linked to cardiovascular disease the observed endothelial modulation by pravastatin may have potential clinical implications.

CML-1 inhibits TNF-α-induced NF-κB activation and adhesion molecule expression in endothelial cells through inhibition of IkBα kinase

CML-1 is a purified extract from a mixture of 13 oriental herbs (Achyranthis Radix, Angelicae Gigantis Radix, Cinnamomi Cortex Spissus, Eucommiae Cortex, Glycyrrhizae Radix, Hoelen, Lycii Fructus, Paeoniae Radix, Rehmanniae Radix Preparata and Atractylodis Rhizoma, Zingiberis Rhizoma, Zizyphi Semen, Acori Graminei Rhizoma) that have been widely used for the treatment of inflammatory diseases in Asia. Since our previous study has been shown to have the anti-inflammatory activity of CML-1 in vivo and the upregulation of adhesion molecules in response to numerous inducing factors is associated with inflammation, this study examined the effect of CML-1 on the expression of adhesion molecules induced by TNF-α in cultured human umbilical vein endothelial cells (HUVECs). Preincubation of HUVECs for 20 h with CML-1 (1–100 μg/ml) dose-dependently inhibited TNF-α (10 ng/ml)-induced adhesion of THP-1 monocytic cells, as well as mRNA and protein expression of E-selectin, vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). CML-1 was also shown to inhibit NK-kB activation induced by TNF-α. Furthermore, CML-1 inhibited TNF-α-induced IkB kinase activation, subsequent degradation of IkBα, and nuclear translocation of NK-kB. Evidence presented in this report demonstrated that CML-1 inhibited the adhesive capacity of HUVEC and the TNF-α-mediated induction of E-selectin, ICAM-1 and VCAM-1 in HUVEC by inhibiting the IkB/NF-kB signaling pathway at the level of IkB kinase, which may explain the ability of CML-1 to suppress inflammation and modulate the immune response.

VEGF-E activates endothelial nitric oxide synthase to induce angiogenesis via cGMP and PKG-independent pathways

Vascular endothelial growth factor-A (VEGF), which binds to both VEGF receptor-1 (Flt1) and VEGFR-2 (KDR/Flk-1), requires nitric oxide (NO) to induce angiogenesis in a cGMP-dependent manner. Here we show that VEGF-E, a VEGFR-2-selective ligand stimulates NO release and tube formation in human umbilical vein endothelial cells (HUVEC). Inhibition of phospholipase Cγ (PLCγ) with U73122 abrogated VEGF-E induced endothelial cell migration, tube formation and NO release. Inhibition of endothelial nitric oxide synthase (eNOS) using l-NNA blocked VEGF-E-induced NO release and angiogenesis. Pre-incubation of HUVEC with the soluble guanylate cyclase inhibitor, ODQ, or the protein kinase G (PKG) inhibitor, KT-5823, had no effect on angiogenesis suggesting that the action of VEGF-E is cGMP-independent. Our data provide the first demonstration that VEGFR-2-mediated NO signaling and subsequent angiogenesis is through a mechanism that is dependent on PLCγ but independent of cGMP and PKG.

Nitric oxide donor-induced persistent inhibition of cell adhesion protein expression and NFκB activation in endothelial cells

Nitric oxide (NO), applied by inhalation or released from NO donors, has been used to reduce the expression of cell adhesion molecules (CAM) and ameliorate other consequences of ischemia/reperfusion (I/R) injury. In this study, we have assessed the time frames of pretreatment and of the duration of the preconditioned state using human umbilical vein endothelial cells (HUVECs) and the NO donor, SNAP, in combination with cysteine. The induction of vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM) and E-selectin by the cytokines TNFalpha and IL-1beta, and by bacterial lipopolysaccharide (LPS) was reduced by SNAP/Cys preincubation (30 min, 1mM) to less than 10% of controls. This refractory state in respect to cytokine-induced CAM expression persisted for 6h after washout of the NO donor in the combination TNFalpha/VCAM, and a partial block was still observed after 8h. The effect was not mediated by the cGMP pathway, as was demonstrated by using the inhibitor of guanylyl cyclase, ODQ, and the cGMP analogue, 8-Br-cGMP. The TNFalpha-induced expression of CAM was exclusively dependent on the transcription factor NFkappaB since the inhibitor of NFkappaB activation, BAY 11-7082, completely blocked the induction. The TNFalpha-induced phosphorylation and degradation of the inhibitor of kappaB (IkappaBalpha) was suppressed for up to 8h after SNAP/Cys pretreatment. The inhibitory S-nitrosation of IkappaB kinase (IKKbeta), as assessed by the biotin-switch-procedure and immunoprecipitation, was only detectable immediately after SNAP/Cys incubation but not at later time points. In summary, a short preincubation of HUVEC with SNAP/Cys results in a persistent suppression of NFkappaB-dependent expression of CAM. The stabilization of IkappaBalpha over the same time span may be causally related to this effect.

Lovastatin Reduces Nuclear Factor &amp;kappa;B Activation Induced by C-Reactive Protein in Human Vascular Endothelial Cells

The role of C-reactive protein (CRP) in atherogenesis has been supported by more recent data. Some studies have demonstrated marked up-regulation inflammatory responses in endothelial cells subjected to CRP. The nuclear factor-kappaB (NF-kappaB) signal transduction is known to play a key role in the expression of these proatherogenic entities. Statins have anti-inflammatory properties independent of their cholesterol-lowering effects. Therefore, we studied the effects of CRP and lovastatin on NF-kappaB activation in human umbilical vein endothelial cells (HUVECs). By using an electrophoretic mobility shift assays (EMSA), we found that CRP (50 microg/ml) increased activation of NF-kappaB and degradation of inhibitory kappa B (IkappaB) in HUVECs, reaching a maximal effect after the incubation with CRP for 1 h. Lovastatin (10(-5) mol/l) diminished NF-kappaB activation induced by CRP. Furthermore, lovastatin may block NF-kappaB activation by causing a stabilization of the IkappaB-alpha in cellular cytoplasm with western blotting analysis. Preincubation of HUVECs with pyrrolidinethiocarbamate (PDTC, NF-kappaB inhibitor) diminished CD40 expression induced by CRP with flow cytometry. Our results suggest that CRP increases activation of NF-kappaB and induces CD40 expression in HUVECs partly via activation of NF-kappaB. Lovastatin, through the inhibition of NF-kappaB activation, reduces the inflammation involved in the pathogenesis of atherosclerosis.

Synergy between anti‐endoglin (CD105) monoclonal antibodies and TGF‐β in suppression of growth of human endothelial cells

Endoglin (CD105) is a proliferation-associated cell membrane antigen of endothelial cells and strongly expressed in the angiogenic vasculature of solid tumors. Endoglin is essential for angiogenesis/vascular development and an ancillary transforming growth factor beta (TGF-beta) receptor. Certain anti-endoglin monoclonal antibodies (mAbs), termed SN6 series mAbs, inhibited angiogenesis, tumor growth and metastasis in mice. We investigated the mechanisms by which anti-endoglin mAbs suppress growth of proliferating endothelial cells. We found that 4 SN6 series mAbs suppressed growth of human umbilical vein endothelial cells (HUVECs) in a dose-dependent manner in the absence of any effector cells or complement. Significant differences in the growth suppression between the 4 anti-endoglin mAbs defining different epitopes were observed. These differences were not determined by antigen-binding avidities of the mAbs. Combination of TGF-beta1 and each of the 4 anti-endoglin mAbs exerted synergistic growth suppression of HUVECs. Binding of anti-endoglin mAbs to endoglin-expressing cells did not block the subsequent binding of TGF-beta1. Conversely, preincubation of HUVECs with TGF-beta1 did not change cell surface expression of endoglin. The present results suggest that direct suppression of the endothelial cell growth by SN6 series mAbs is one of the underlying mechanisms by which anti-endoglin mAbs exert antiangiogenic and tumor-suppressive activity in vivo. The results further suggest that TGF-beta1 plays an important role in the in vivo antiangiogenic efficacy of anti-endoglin mAbs by synergistically enhancing the activity of these mAbs. Further studies of the present novel findings may provide valuable information about the functional roles of endoglin and anti-endoglin mAbs in the TGF-beta-mediated cell regulation.