Migration Of Microvascular Endothelial Cells Research Articles

Non-peptide NK 1 receptor ligands based on the 4-phenylpyridine moiety

The quinoline nucleus of the previously described 4-phenylquinoline-3-carboxamides NK 1 receptor ligands 7 has been transformed into either substituted or azole—(i.e., triazole or tetrazole) fused pyridine moieties of compounds 9 and 10, respectively, in order to obtain NK 1 receptor ligands showing lower molecular weight or higher hydrophilicity. The program of molecular manipulations produced NK 1 receptor ligands showing affinity in the nanomolar range. In particular, 4-methyl-1-piperazinyl derivative 9j showed an IC 50 value of 4.8 nM and was proved to behave as a NK 1 antagonist blocking Sar 9-SP-sulfone induced proliferation and migration of microvascular endothelial cells. Therefore, compound 9j has been labeled with [ 11C]CH 3I ( t 1/2 = 20.4 min, β + = 99.8%) starting from the corresponding des-methyl precursor 9i using with a radiochemical yield of about 10% (not decay corrected) and a specific radioactivity >1 Ci/μmol in order to be used as a radiotracer in next PET studies.

PLD1-dependent PKCγ activation downstream to Src is essential for the development of pathologic retinal neovascularization

AbstractVascular endothelial growth factor (VEGF) appears to be an important mediator of pathologic retinal angiogenesis. In understanding the mechanisms of pathologic retinal neovascularization, we found that VEGF activates PLD1 in human retinal microvascular endothelial cells, and this event is dependent on Src. In addition, VEGF activates protein kinase C-γ (PKCγ) via Src-dependent PLD1 stimulation. Inhibition of Src, PLD1, or PKCγ via pharmacologic, dominant negative mutant, or siRNA approaches significantly attenuated VEGF-induced human retinal microvascular endothelial cell migration, proliferation, and tube formation. Hypoxia also induced Src-PLD1-PKCγ signaling in retina, leading to retinal neovascularization. Furthermore, siRNA-mediated down-regulation of VEGF inhibited hypoxia-induced Src-PLD1-PKCγ activation and neovascularization. Blockade of Src-PLD1-PKCγ signaling via the siRNA approach also suppressed hypoxia-induced retinal neovascularization. Thus, these observations demonstrate, for the first time, that Src-dependent PLD1-PKCγ activation plays an important role in pathologic retinal angiogenesis.

MVL-PLA2, a Snake Venom Phospholipase A2, Inhibits Angiogenesis through an Increase in Microtubule Dynamics and Disorganization of Focal Adhesions

Integrins are essential protagonists of the complex multi-step process of angiogenesis that has now become a major target for the development of anticancer therapies. We recently reported and characterized that MVL-PLA2, a novel phospholipase A2 from Macrovipera lebetina venom, exhibited anti-integrin activity. In this study, we show that MVL-PLA2 also displays potent anti-angiogenic properties. This phospholipase A2 inhibited adhesion and migration of human microvascular-endothelial cells (HMEC-1) in a dose-dependent manner without being cytotoxic. Using Matrigel™ and chick chorioallantoic membrane assays, we demonstrated that MVL-PLA2, as well as its catalytically inactivated form, significantly inhibited angiogenesis both in vitro and in vivo. We have also found that the actin cytoskeleton and the distribution of αvβ3 integrin, a critical regulator of angiogenesis and a major component of focal adhesions, were disturbed after MVL-PLA2 treatment. In order to further investigate the mechanism of action of this protein on endothelial cells, we analyzed the dynamic instability behavior of microtubules in living endothelial cells. Interestingly, we showed that MVL-PLA2 significantly increased microtubule dynamicity in HMEC-1 cells by 40%. We propose that the enhancement of microtubule dynamics may explain the alterations in the formation of focal adhesions, leading to inhibition of cell adhesion and migration.

CC-PLA2-1 and CC-PLA2-2, two Cerastes cerastes venom-derived phospholipases A2, inhibit angiogenesis both in vitro and in vivo

Integrins are essential in the complex multistep process of angiogenesis and are thus attractive targets for the development of antiangiogenic therapies. Integrins are antagonized by disintegrins and C-type lectin-like proteins, two protein families from snake venom. Here, we report that CC-PLA2-1 and CC-PLA2-2, two novel secreted phospholipases A2 (PLA2) isolated from Cerastes cerastes venom, also showed anti-integrin activity. Indeed, both PLA2s efficiently inhibited human brain microvascular endothelial cell adhesion and migration to fibrinogen and fibronectin in a dose-dependent manner. Interestingly, we show that this anti-adhesive effect was mediated by α5β1 and αv-containing integrins. CC-PLA2s also impaired in vitro human brain microvascular endothelial cell tubulogenesis on Matrigel and showed antiangiogenic activity in vivo in chicken chorioallantoic membrane assay. The complete PLA2 cDNAs were cloned from a venom gland cDNA library. Mature CC-PLA2-1 and CC-PLA2-2 contain 121 and 120 amino acids, respectively, including 14 cysteines each and showed 83% identity. Tertiary model structures of CC-PLA2-1 and CC-PLA2-2 were generated by homology modeling. This is thus the first study describing an antiangiogenic effect for snake venom PLA2s and reporting first clues to their mechanism of action on endothelial cells.

IL-17 Contributes to Angiogenesis in Rheumatoid Arthritis

Angiogenesis is an early and a critical event in the pathogenesis of rheumatoid arthritis (RA). Neovascularization is dependent on endothelial cell activation, migration and proliferation, and inhibition of angiogenesis may provide a novel therapeutic approach in RA. In this study, we document a novel role of IL-17 in mediating angiogenesis. Local expression of IL-17 in mouse ankles increases vascularity. We further demonstrate that IL-17 is angiogenic by showing its ability to promote blood vessel growth in Matrigel plugs in vivo. Additionally, IL-17, in concentrations present in the RA joint, induces human lung microvascular endothelial cell (HMVEC) migration mediated through the PI3K/AKT1 pathway. Furthermore, suppression of the PI3K pathway markedly reduces IL-17-induced tube formation. We also show that both IL-17-induced HMVEC chemotaxis and tube formation are mediated primarily through IL-17 receptor C. Neutralization of either IL-17 in RA synovial fluids or IL-17 receptor C on HMVECs significantly reduces the induction of HMVEC migration by RA synovial fluid. Finally, RA synovial fluid immunoneutralized with anti-IL-17 and antivascular endothelial growth factor does not reduce HMVEC migration beyond the effect detected by immunodepleting each factor alone. These observations identify a novel function for IL-17 as an angiogenic mediator in RA, supporting IL-17 as a therapeutic target in RA.

Chorioamnionitis stimulates angiogenesis in saccular stage fetal lungs via CC chemokines

The fetal lung vasculature forms in tandem with developing airways. Whereas saccular airway morphogenesis is arrested in bronchopulmonary dysplasia (BPD), the potential vascular phenotype in BPD at this stage of development is less well-understood. As inflammation increases the risk of BPD and induces arrest of saccular airway morphogenesis, we tested the effects of Escherichia coli LPS on fetal mouse lung vascular development. Injecting LPS into the amniotic fluid of Tie2-lacZ endothelial reporter mice at embryonic day 15 stimulated angiogenesis in the saccular stage fetal lung mesenchyme. LPS also increased the number of endothelial cells in saccular stage fetal mouse lung explants. Inflammation appeared to directly promote vascular development, as LPS stimulated pulmonary microvascular endothelial cell angiogenesis, cell migration, and proliferation in vitro. Whereas LPS did not increase expression of VEGF, angiopoietin-1 (Ang-1), Tie2, fetal liver kinase-1 (Flk-1), fms-like tyrosine kinase-1 (Flt-1), PDGFA, PDGFB, heparin-binding EGF-like growth factor (HB-EGF), or connective tissue growth factor (CTGF), LPS did stimulate the production of the angiogenic CC chemokines macrophage inflammatory protein-1α (MIP-1α) and monocyte chemoattractant protein-1 (MCP-1). Both MIP-1α and MCP-1 increased angiogenesis in fetal mouse lung explants. In addition, inhibitory antibodies against MIP-1α and MCP-1 blocked the effects of LPS on fetal lung vascular development, suggesting these chemokines are downstream mediators of LPS-induced angiogenesis. We speculate that an inflammation-mediated surge in angiogenesis could lead to formation of aberrant alveolar capillaries in the lungs of patients developing BPD.

Methylnaltrexone Potentiates the Anti-Angiogenic Effects of mTOR Inhibitors

BackgroundRecent cancer therapies include drugs that target both tumor growth and angiogenesis including mammalian target of rapamycin (mTOR) inhibitors. Since mTOR inhibitor therapy is associated with significant side effects, we examined potential agents that can reduce the therapeutic dose.MethodsMethylnaltrexone (MNTX), a peripheral mu opioid receptor (MOR) antagonist, in combination with the mTOR inhibitors temsirolimus and/or rapamycin, was evaluated for inhibition of VEGF-induced human pulmonary microvascular endothelial cell (EC) proliferation and migration as well as in vivo angiogenesis (mouse Matrigel plug assay).ResultsMNTX inhibited VEGF-induced EC proliferation and migration with an IC50 of ~100 nM. Adding 10 nM MNTX to EC shifted the IC50 of temsirolimus inhibition of VEGF-induced proliferation and migration from ~10 nM to ~1 nM and from ~50 to ~10 nM respectively. We observed similar effects with rapamycin. On a mechanistic level, we observed that MNTX increased EC plasma membrane-associated tyrosine phosphate activity. Inhibition of tyrosine phosphatase activity (3,4-dephostatin) blocked the synergy between MNTX and temsirolimus and increased VEGF-induced tyrosine phosphorylation of Src with enhanced PI3 kinase and mTOR Complex 2-dependent phosphorylation of Akt and subsequent activation of mTOR Complex 1 (rapamycin and temsirolimus target), while silencing Src, Akt or mTOR complex 2 components blocked VEGF-induced angiogenic events.ConclusionsOur data indicate that MNTX exerts a synergistic effect with rapamycin and temsirolimus on inhibition of VEGF-induced human EC proliferation and migration and in vivo angiogenesis. Therefore, addition of MNTX could potentially lower the dose of mTOR inhibitors which could improve therapeutic index.

Lysophosphatidic Acid Up-Regulates Expression of Growth-Regulated Oncogene-α, Interleukin-8, and Monocyte Chemoattractant Protein-1 in Human First-Trimester Trophoblasts: Possible Roles in Angiogenesis and Immune Regulation

The serum lysophospholipase D activity and production of lysophosphatidic acid (LPA) increase in women with pregnancy. The effects of LPA on human placenta tissue remained unclear. We investigate the expression of LPA receptors and function of LPA in human first-trimester trophoblasts. Normal villous trophoblasts were obtained from termination of first-trimester gestation. We examined the expression of LPA receptors in primary culture of trophoblasts and the tissue. The effects of LPA on the expressions of chemokines of trophoblasts were examined using RT-PCR and enzyme immunoassay. We delineate signal pathways of LPA-inducing relevant chemokines in trophoblasts. The secretory chemokines were tested for angiogenic function using human endometrial microvascular endothelial cells and for immunological chemotaxis using decidual natural killer cells and THP-1 monocytes. The results revealed the expression of LPA1 receptors in trophoblast cells. LPA enhanced growth-regulated oncogene (GRO)-alpha, IL-8 and monocyte chemoattractant protein (MCP)-1 expressions in a time- and dose-dependent manner. Mechanistic dissection disclosed that LPA functioned mainly via the LPA1 receptor, Gi protein, various signal mediators of ERK, protein kinase C, p38, Akt, and c-Jun N-terminal kinase, and nuclear factor-kappaB pathways to secrete these chemokines. LPA-induced IL-8 protein secretion of trophoblasts enhanced permeability, migration, proliferation, and capillary tube formation of human endometrial microvascular endothelial cells. LPA-induced GRO-alpha and MCP-1 incited chemotaxis of natural killer cells and monocytes. We demonstrate that LPA mediates trophoblast cells to produce GRO-alpha, IL-8, and MCP-1 via LPA1 receptors and nuclear factor-kappaB-dependent signal pathways. Through LPA-induced chemokine production, human first-trimester trophoblast cells may regulate angiogenesis and innate immune system in early pregnancy.

Blockade of Wnt Signaling Inhibits Angiogenesis and Tumor Growth in Hepatocellular Carcinoma

Aberrant activation of Wnt signaling plays an important role in hepatocarcinogenesis. In addition to direct effects on tumor cells, Wnt signaling might be involved in the organization of tumor microenvironment. In this study, we have explored whether Wnt signaling blockade by exogenous expression of Wnt antagonists could inhibit tumor angiogenesis and control tumor growth. Human Wnt inhibitory factor 1 (WIF1) and secreted frizzled-related protein 1 (sFRP1) were each fused with Fc fragment of human IgG1 to construct fusion proteins WIF1-Fc and sFRP1-Fc. The recombinant adenoviral vectors carrying WIF1-Fc and sFRP1-Fc driven by cytomegalovirus promoter were constructed. Ad-WIF1-Fc or Ad-sFRP1-Fc induced the expression and correct conformation of WIF1-Fc and sFRP1-Fc fusion proteins. These molecules caused down-regulation of E2F1, cyclin D1, and c-myc and promoted cell apoptosis in hepatocellular carcinoma cells. Treatment of established hepatocellular carcinoma tumors with Ad-WIF1-Fc and/or Ad-sFRP1-Fc resulted in significant inhibition of tumor growth and prolonged animal survival. The antineoplastic effect was associated with increased apoptosis of tumor cells, reduced microvessel density, and decreased expression of vascular endothelial growth factor and stromal cell-derived factor-1. Tube formation and migration of human microvascular endothelial cells and mouse endothelial progenitor cells (EPC) were significantly inhibited by both WIF1-Fc and sFRP1-Fc. In addition, these molecules blocked EPC differentiation and caused EPC apoptosis. Our data indicate that Wnt antagonists WIF1-Fc and sFRP1-Fc inhibit Wnt signaling and exert potent antitumor activity by increasing the apoptosis rate in tumor cells and by impairing tumor vascularization.

Thrombin induces fibronectin-specific migration of pulmonary microvascular endothelial cells: requirement of calcium/calmodulin-dependent protein kinase II

Pulmonary arterial hypertension (PAH) is a progressive disease of excess vasoconstriction and vascular cell proliferation that results in increased pulmonary vascular resistance and right heart failure. We have previously shown (66) that tissue factor expression is increased in the abnormal vessels of patients and rats with PAH. We hypothesized that tissue factor and its downstream mediator, thrombin, would promote migration of endothelial cells (EC) and the vascular pathology of PAH. Immunostaining revealed EC and a fibronectin-enriched matrix within the "plexiform-like" lesions in a rat model of severe PAH. In a modified Boyden assay, protease-activated receptor 1 (PAR1; thrombin receptor) stimulation by agonist peptide or thrombin induced pulmonary microvascular EC (PMVEC) migration when the cells were interacting with fibronectin, but not with other extracellular matrix proteins. Thrombin/fibronectin-induced migration was confirmed in wound healing and angiogenesis assays and was abrogated by the PAR1 antagonist SCH79797 and soluble RGD peptide. This fibronectin dependence was unique to PAR1 activation; other EC agonists evaluated did not induce migration on any matrix, and 10% FBS stimulated similar levels of migration on all matrix proteins tested. Thrombin/fibronectin stimulated autophosphorylation of calcium/calmodulin dependent protein kinase II (CaMKII) in PMVEC, and inhibitors of CaMKII blocked thrombin-induced migration on fibronectin, but had no effect on migration induced by 10% FBS. In contrast, EC isolated from the proximal pulmonary artery migrated in response to most agonists independent of the matrix substrate. Our findings illustrate EC heterogeneity in a single tissue and indicate a novel role for CaMKII in mediating EC migration. Because PMVEC have been shown to have impressive proliferative potential, thrombin/fibronectin-stimulated migration of these cells to a site of injured endothelium is a potential mechanism by which thrombin contributes to the development of vascular lesions in PAH.

Haptotactic Gradients for Directed Cell Migration: Stimulation and Inhibition Using Soluble Factors

A recently developed technique for the measurement of cell migration on surface bound gradients was used to assay the behavior of microvascular endothelial cells on a range of fibronectin gradient slopes in the presence of soluble promoters and inhibitors of chemotaxis. Directional microvascular endothelial cell migration was shown to increase with increasing gradient slope with no significant change in cellular persistence time or random cell speed. Uniformly distributed soluble chemotactic factor in the hMEC growth media enhanced directional migration. The addition of migration-inhibiting LY294002 eliminated the directional component of cell migration at a 5 microM dosing. These experiments broaden the understanding of the directional nature of cell motion and present a reliable system for the quantitative study of cell migration in complex conditions in vitro.

A novel role for activating transcription factor-2 in 15(S)-hydroxyeicosatetraenoic acid-induced angiogenesis

To investigate the mechanisms underlying 15(S)-HETE-induced angiogenesis, we have studied the role of the small GTPase, Rac1. We find that 15(S)-HETE activated Rac1 in human retinal microvascular endothelial cells (HRMVEC) in a time-dependent manner. Blockade of Rac1 by adenovirus-mediated expression of its dominant negative mutant suppressed HRMVEC migration as well as tube formation and Matrigel plug angiogenesis. 15(S)-HETE stimulated Src in HRMVEC in a time-dependent manner and blockade of its activation inhibited 15(S)-HETE-induced Rac1 stimulation in HRMVEC and the migration and tube formation of these cells as well as Matrigel plug angiogenesis. 15(S)-HETE stimulated JNK1 in Src-Rac1-dependent manner in HRMVEC and adenovirus-mediated expression of its dominant negative mutant suppressed the migration and tube formation of these cells and Matrigel plug angiogenesis. 15(S)-HETE activated ATF-2 in HRMVEC in Src-Rac1-JNK1-dependent manner and interference with its activation via adenovirus-mediated expression of its dominant negative mutant abrogated migration and tube formation of HRMVEC and Matrigel plug angiogenesis. In addition, 15(S)-HETE-induced MEK1 stimulation was found to be dependent on Src-Rac1 activation. Blockade of MEK1 activation inhibited 15(S)-HETE-induced JNK1 activity and ATF-2 phosphorylation. Together, these findings show that 15(S)-HETE activates ATF-2 via the Src-Rac1-MEK1-JNK1 signaling axis in HRMVEC leading to their angiogenic differentiation.

Focal adhesion kinase signaling pathway participates in the formation of choroidal neovascularization and regulates the proliferation and migration of choroidal microvascular endothelial cells by acting through HIF-1 and VEGF expression in RPE cells

Choroidal neovascularization (CNV) is one of the most frequent causes of severe and progressive vision loss, while its pathogenesis is still poorly understood. Focal adhesion kinase (FAK), a non-receptor tyrosine kinase, plays a crucial role in linking signals initiated by both the extracellular matrix (ECM) and soluble signaling factors and controls essential cellular processes. Extensive evidence has shown that FAK is activated in angiogenic response. This study aims to investigate the effect of FAK on CNV formation. The Brown-Norway (BN) rats underwent laser rupture of Bruch's membrane to induce CNV and were then killed at 1, 3, 7, and 14 days following laser injury. Immunofluorescence and Western blot were processed to detect FAK protein. Retinal pigment epithelial (RPE) cells were cultured under hypoxia and RNA interference (RNAi) technique was used to knock down the FAK gene in RPE cells. Expression of hypoxia inducible factor-1 (HIF-1alpha) and vascular endothelial growth factor (VEGF) in RPE cells were investigated by RT-PCR and Western blot. Two kinds of coculture models were used to observe the effects of specific blockade of FAK in RPE cells on the proliferation and migration of choroidal microvascular endothelial cells (CECs), respectively. FAK was highly expressed in the rat RPE-choroid tissue after photocoagulation. In vitro experiment showed that FAK was involved in hypoxia signaling in cultured RPE cells. The absence of FAK effectively reduced the expression of hypoxia-induced HIF-1alpha and VEGF in RPE cells, resulting in the inhibition of proliferation and migration of CECs. Our results suggest that FAK pathway activation plays a role in the development of CNV, and regulates the proliferation and migration of CECs by acting through HIF-1 and then up-regulating the expression of the angiogenic factor VEGF in RPE cells. It is reasonable to propose that FAK siRNA will potentially provides a means to attenuate the strong stimuli for neovascularization in CNV-dependent disorders, which could present a therapeutically relevant strategy for the inhibition of CNV.

Cell and molecular mechanisms of insulin‐induced angiogenesis

Angiogenesis, the development of new blood vessel from pre-existing vessels, is a key process in the formation of the granulation tissue during wound healing. The appropriate development of new blood vessels, along with their subsequent maturation and differentiation, establishes the foundation for functional wound neovasculature. We performed studies in vivo and used a variety of cellular and molecular approaches in vitro to show that insulin stimulates angiogenesis and to elucidate the signalling mechanisms by which this protein stimulates microvessel development. Mice skin injected with insulin shows longer vessels with more branches, along with increased numbers of associated α-smooth muscle actin-expressing cells, suggesting the appropriate differentiation and maturation of the new vessels. We also found that insulin stimulates human microvascular endothelial cell migration and tube formation, and that these effects occur independently of VEGF/VEGFR signalling, but are dependent upon the insulin receptor itself. Downstream signalling pathways involve PI3K, Akt, sterol regulatory element-binding protein 1 (SREBP-1) and Rac1; inhibition of these pathways results in elimination of endothelial cell migration and tube formation and significantly decreases the development of microvessels. Our findings strongly suggest that insulin is a good candidate for the treatment of ischaemic wounds and other conditions in which blood vessel development is impaired.

Green tea catechins inhibit angiogenesis through suppression of STAT3 activation

Previous studies indicate that green tea extract may inhibit breast cancer progression by blocking angiogenesis, although the molecular mechanisms are not well defined. We demonstrate that administration of Polyphenon E (Poly E), a standardized green tea extract, inhibited MDA-MB231 breast cancer and human dermal microvascular endothelial (HMVEC) cell migration and the expression of vascular endothelial growth factor (VEGF) and matrix metalloproteinase 9 (MMP9). In addition, Poly E inhibited VEGF-induced neovascularization in vivo. We also demonstrate that Poly E blocked signal transducers and activators of transcription (STAT) signaling by suppressing interferon-gamma (IFN-gamma)-induced gene transcription via IFN-gamma-activating sequence (GAS) elements and downstream STAT3 activation by inhibiting STAT1 and STAT3 dimerization in MDA-MB231 cells. Transient expression of constitutively active STAT3 significantly reduced the inhibitory effect of Poly E on cell migration and VEGF and MMP9 expression. Taken together, these observations indicate that green tea extract inhibits angiogenesis partly through the disruption of STAT3-mediated transcription of genes, including VEGF.

An RGD-Modified Endostatin-Derived Synthetic Peptide Shows Antitumor Activity in Vivo

It has been reported that an endostatin-derived synthetic peptide, named ES-2, that contains the amino acids 60-70 of endostatin from its N terminus, efficiently inhibits basic fibroblast growth factor-induced directional migration and tubular morphogenesis of microvascular endothelial cells. We found that the peptide had no effects on tumor growth in vivo. However, when the peptide Arg-Gly-Asp (RGD) was introduced into ES-2, the modified ES-2 showed significant antitumor results in animal models. Histochemical and immunohistochemical analysis showed that RGD-modified ES-2 induced large areas of continuous necrosis within tumors and significantly reduced the vessel density compared to control. Furthermore, only the peptides with RGD were able to bind tumor cells in vitro, suggesting that additional RGD domains may help in improving the receptor-binding ability and pharmacokinetic properties of ES-2 and preventing organic clearance, as well as enzymatic degradation of the peptide, thus enabling a greater fraction of the administered dose to be biologically available.

P.1.c.035 The role of nitric oxide in PC12 cells death. Protective effect of 12-lipoxygenase and cyclooxygenases inhibitors

Inhibitors of PARP-1(Poly(ADP-ribose) polymerase-1) act by competing with NAD+, the enzyme physiological substrate, which play a protective role in many pathological conditions characterized by PARP-1 overactivation. It has been shown that PARP-1 also promotes tumor growth and progression through its DNA repair activity. Since angiogenesis is an essential requirement for these activities, we sought to determine whether PARP inhibition might affect rat brain microvascular endothelial cells (GP8.3) migration, stimulated by C6-glioma conditioned medium (CM). Through wound-healing experiments and MTT analysis, we demonstrated that PARP-1 inhibitor PJ-34 [N-(6-Oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide] abolishes the migratory response of GP8.3 cells and reduces their viability. PARP-1 also acts in a DNA independent way within the Extracellular-Regulated-Kinase (ERK) signaling cascade, which regulates cell proliferation and differentiation. By western analysis and confocal laser scanning microscopy (LSM), we analyzed the effects of PJ-34 on PARP-1 expression, phospho-ERK and phospho-Elk-1 activation. The effect of MEK (mitogen-activated-protein-kinase-kinase) inhibitor PD98059 (2-(2-Amino-3-methoxyphenyl)-4 H-1-benzopyran-4-one) on PARP-1 expression in unstimulated and in CM-stimulated GP8.3 cells was analyzed by RT-PCR. PARP-1 expression and phospho-ERK activation were significantly reduced by treatment of GP8.3 cells with PJ-34 or PD98059. By LSM, we further demonstrated that PARP-1 and phospho-ERK are coexpressed and share the same subcellular localization in GP8.3 cells, in the cytoplasm as well as in nucleoplasm. Based on these data, we propose that PARP-1 and phospho-ERK interact in the cytosol and then translocate to the nucleus, where they trigger a proliferative response. We also propose that PARP-1 inhibition blocks CM-induced endothelial migration by interfering with ERK signal-transduction pathway.

Substance P-Mediated Expression of the Pro-Angiogenic Factor CCN1 Modulates the Course of Colitis

Substance P (SP) regulates important intestinal functions, such as mucosal permeability, motility, chloride secretion, and inflammation via the neurokinin-1 receptor (NK-1R). Previous reports showed that vascularization and expression of angiogenic factors are evident in the colonic mucosa of rats with colitis and patients with inflammatory bowel disease. Here we determined whether SP is associated with angiogenesis. Human NCM460 colonocytes stably transfected with the human NK-1R (NCM460-NK-1R cells) and mice with dextran sodium sulfate-induced colitis were used. We found that expression of the angiogenic factor CCN1 was increased in the colons of patients with Crohn's disease and ulcerative colitis. Mucosal extracts from inflammatory bowel disease patients induced human intestinal microvascular endothelial cell migration that was inhibited by blockade of CCN1 and its receptor integrin alphavbeta3. Both the degree of angiogenesis and CCN1 expression were elevated in the colons of mice with dextran sodium sulfate-induced colitis, which was reduced by treatment with the NK-1R antagonist CJ-12255. SP also increased CCN1 expression in NCM460-NK-1R colonocytes. SP exposure to human intestinal microvascular endothelial cells co-cultured with NCM460-NK-1R cells induced angiogenic activity that was inhibited by CCN1 silencing. In addition, intracolonic overexpression of CCN1 induced angiogenesis in mouse colon. Thus, SP mediates angiogenesis via CCN1 during colitis.

Role of αv integrin in osteoprotegerin-induced endothelial cell migration and proliferation

Osteoprotegerin (OPG) is a decoy receptor for the receptor activator of nuclear factor κB ligand (RANKL). However, the role of OPG in the endothelium remains unknown. In this study, we demonstrate that OPG stimulates the proliferation and migration of human microvascular endothelial cells (HMVECs). In addition, we show that treatment with integrin αvβ3 or integrin αvβ5 blocking antibody inhibits endothelial cell migration. In contrast, treatment with anti-αvβ3 antibody or anti-αvβ5 antibody alone did not inhibit OPG-induced proliferation. However, OPG-induced proliferation was inhibited when these antibodies were applied simultaneously. Furthermore, OPG evoked activation of extracellular signal-regulated kinase (ERK) 1/2, which has been linked to integrin αv activity. Taken together, these results suggest that integrins αvβ3 and/or αvβ5 contribute to endothelial cell proliferation and migration induced by OPG.

In-vitro-Untersuchungen zum Wirkungsmechanismus von VEGF und seinen Inhibitoren

VEGF expression and signalling are deregulated in diabetic retinopathy. Cellular processes like migration and proliferation as well as control of the permeability of the endothelium by VEGF are regulated as a consequence of its binding to the VEGF receptor 2. Proteins forming tight junctions between microvascular endothelial cells of the retina are delocated to the cytoplasm after treatment with VEGF(165), likely leading to the breakdown of the blood-retina barrier. VEGF-inhibitors such as a VEGF-aptamer (modified RNA-oligonucleotide; pegaptanib) or specific antibodies/antibody fragments (bevacizumab, ranibzumab) which directly interfere with the interaction of VEGF with its receptors are considered to be promising novel therapeutics to treat diabetic retinopathy and age-related macular degeneration. In vitro studies using microvascular endothelial cells will help to clarify the mechanisms of action of VEGF and its inhibitors. In particular, the influence of VEGF isoforms and the inhibitor ranibizumab on the proliferation and migration of bovine retinal microvascular endothelial cells was studied, as well as the rearrangement of tight-junction proteins after treatment of the cells with VEGF(165) and specific inhibitors. In addition to a review of recent publications in the field, primary data from our own studies are presented in this article.