In vitro endothelial wound repair. Interaction of cell migration and proliferation

Paclitaxel Enhances Thrombin-Induced Endothelial Tissue Factor Expression via c-Jun Terminal NH 2 Kinase Activation

Paclitaxel is used on drug-eluting stents because it inhibits proliferation of vascular cells. Stent thrombosis remains a concern with this compound, particularly with higher dosages. This study investigates the effect of paclitaxel on tissue factor (TF) expression in human endothelial cells. Paclitaxel enhanced thrombin-induced endothelial TF protein expression in a concentration- and time-dependent manner. A concentration of 10 −5 mol/L elicited a 2.1-fold increase in TF protein and a 1.6-fold increase in TF surface activity. The effect was similar after a 1 hour as compared with a 25-hour pretreatment period. Real-time polymerase chain reaction revealed that paclitaxel increased thrombin-induced TF mRNA expression. Paclitaxel potently activated c-Jun terminal NH 2 kinase (JNK) as compared with thrombin alone, whereas the thrombin-mediated phosphorylation of p38 and extracellular signal-regulated kinase remained unaffected. Similar to paclitaxel, docetaxel enhanced both TF expression and JNK activation as compared with thrombin alone. The JNK inhibitor SP600125 reduced thrombin-induced TF expression by 35%. Moreover, SP600125 blunted the effect of paclitaxel and docetaxel on thrombin-induced TF expression. Paclitaxel increases endothelial TF expression via its stabilizing effect on microtubules and selective activation of JNK. This observation provides novel insights into the pathogenesis of thrombus formation after paclitaxel-eluting stent deployment and may have an impact on drug-eluting stent design.

The role of laser fluence in cell viability, proliferation, and membrane integrity of wounded human skin fibroblasts following helium-neon laser irradiation

BACKGROUND

In medicine, lasers have been used predominantly for applications, which are broadly termed low level laser therapy (LLLT), phototherapy or photobiomodulation. This study aimed to establish cellular responses to Helium-Neon (632.8 nm) laser irradiation using different laser fluences (0.5, 2.5, 5, 10, and 16 J/cm(2)) with a single exposure on 2 consecutive days on normal and wounded human skin fibroblasts.

MATERIALS AND METHODS

Changes in normal and wounded fibroblast cell morphology were evaluated by light microscopy. Changes following laser irradiation were evaluated by assessing the mitochondrial activity using adenosine triphosphate (ATP) luminescence, cell proliferation using neutral red and an alkaline phosphatase (ALP) activity assay, membrane integrity using lactate dehydrogenase (LDH), and percentage cytotoxicity and DNA damage using the Comet assay.

RESULTS

Morphologically, wounded cells exposed to 5 J/cm(2) migrate rapidly across the wound margin indicating a stimulatory or positive influence of phototherapy. A dose of 5 J/cm(2) has a stimulatory influence on wounded fibroblasts with an increase in cell proliferation and cell viability without adversely increasing the amount of cellular and molecular damage. Higher doses (10 and 16 J/cm(2)) were characterized by a decrease in cell viability and cell proliferation with a significant amount of damage to the cell membrane and DNA.

CONCLUSIONS

Results show that 5 J/cm(2) stimulates mitochondrial activity, which leads to normalization of cell function and ultimately stimulates cell proliferation and migration of wounded fibroblasts to accelerate wound closure. Laser irradiation can modify cellular processes in a dose or fluence (J/cm(2)) dependent manner.

Characterization of the activities of actin-affecting drugs on tumor cell migration

Metastases kill 90% of cancer patients. It is thus a major challenge in cancer therapy to inhibit the spreading of tumor cells from primary tumor sites to those particular organs where metastases are likely to occur. Whereas the actin cytoskeleton is a key component involved in cell migration, agents targeting actin dynamics have been relatively poorly investigated. Consequently, valuable in vitro pharmacological tools are needed to selectively identify this type of agent. In response to the absence of any standardized process, the present work aims to develop a multi-assay strategy for screening actin-affecting drugs with anti-migratory potentials. To validate our approach, we used two cancer cell lines (MCF7 and A549) and three actin-affecting drugs (cytochalasin D, latrunculin A, and jasplakinolide). We quantified the effects of these drugs on the kinetics of actin polymerization in tubes (by means of spectrofluorimetry) and on the dynamics of actin cytoskeletons within whole cells (by means of fluorescence microscopy). Using quantitative videomicroscopy, we investigated the actual effects of the drugs on cell motility. Finally, the combined drug effects on cell motility and cell growth were evaluated by means of a scratch-wound assay. While our results showed concordant drug-induced effects on actin polymerization occurring in vitro in test tubes and within whole cells, the whole cell assay appeared more sensitive than the tube assay. The inhibition of actin polymerization induced by cytochalasin D was paralleled by a decrease in cell motility for both cell types. In the case of jasplakinolide, which induces actin polymerization, while it significantly enhanced the locomotion of the A549 cells, it significantly inhibited that of the MCF-7 ones. All these effects were confirmed by means of the scratch-wound assay except of the jasplakinolide-induced effects on MCF-7 cell motility. These later seemed compensated by an additional effect occurring during wound recolonization (possibly acting on the cell growth features). In conclusion, the use of multi-assays with different levels of sophistication and biological relevance is recommended in the screening of new actin-affecting drugs with potentially anti-migratory effects.

ADAM10 mediates E-cadherin shedding and regulates epithelial cell-cell adhesion, migration, and beta-catenin translocation

E-cadherin controls a wide array of cellular behaviors, including cell-cell adhesion, differentiation, and tissue development. We show here that E-cadherin is cleaved specifically by ADAM (a disintegrin and metalloprotease) 10 in its ectodomain. Analysis of ADAM10-deficient fibroblasts, inhibitor studies, and RNA interference-mediated down-regulation of ADAM10 demonstrated that ADAM10 is responsible not only for the constitutive shedding but also for the regulated shedding of this adhesion molecule in fibroblasts and keratinocytes. ADAM10-mediated E-cadherin shedding affects epithelial cell-cell adhesion as well as cell migration. Furthermore, the shedding of E-cadherin by ADAM10 modulates the beta-catenin subcellular localization and downstream signaling. ADAM10 overexpression in epithelial cells increased the expression of the beta-catenin downstream gene cyclin D1 dose-dependently and enhanced cell proliferation. In ADAM10-deficient mouse embryos, the C-terminal E-cadherin fragment is not generated, and the full-length protein accumulates, highlighting the in vivo relevance for ADAM10 in E-cadherin shedding. Our data strongly suggest that this protease constitutes a major regulatory element for the multiple functions of E-cadherin under physiological as well as pathological conditions.

Endothelial Cell Confluence Regulates Cyclooxygenase-2 and Prostaglandin E2 Production That Modulate Motility

Endothelial cells line the vasculature and, after mechanical denudation during invasive procedures or cellular loss from natural causes, migrate to reestablish a confluent monolayer. We find confluent monolayers of human umbilical vein endothelial cells were quiescent and expressed low levels of cyclooxygenase-2, but expressed cyclooxygenase-2 at levels comparable with cytokine-stimulated cells when present in a subconfluent culture. Mechanically wounding endothelial cell monolayers stimulated rapid cyclooxygenase-2 expression that increased with the level of wounding. Cyclooxygenase-2 re-expression occurred throughout the culture, suggesting signaling from cells proximal to the wound to distal cells. Media from wounded monolayers stimulated cyclooxygenase-2 expression in confluent monolayers, which correlated with the level of wounding of the donor monolayer. Wounded monolayers and cells in subconfluent cultures secreted enhanced levels of prostaglandin (PG) E(2) that depended on cyclooxygenase-2 activity, and PGE(2) stimulated cyclooxygenase-2 expression in confluent endothelial cell monolayers. Cells from subconfluent monolayers migrated through filters more readily than those from confluent monolayers, and the cyclooxygenase-2-selective inhibitor NS-398 suppressed migration. Adding PGE(2) to NS-398-treated cells augmented migration. Endothelial cells also migrated into mechanically denuded areas of confluent monolayers, and this too was suppressed by NS-398. We conclude that endothelial cells not in contact with neighboring cells express cyclooxygenase-2 that results in enhanced release of PGE(2), and that this autocrine and paracrine loop enhances endothelial cell migration to cover denuded areas of the endothelium.

A high-throughput cell migration assay using scratch wound healing, a comparison of image-based readout methods

BACKGROUND

Cell migration is a complex phenomenon that requires the coordination of numerous cellular processes. Investigation of cell migration and its underlying biology is of interest to basic scientists and those in search of therapeutics. Current migration assays for screening small molecules, siRNAs, or other perturbations are difficult to perform in parallel at the scale required to screen large libraries.

RESULTS

We have adapted the commonly used scratch wound healing assay of tissue-culture cell monolayers to a 384 well plate format. By mechanically scratching the cell substrate with a pin array, we are able to create characteristically sized wounds in all wells of a 384 well plate. Imaging of the healing wounds with an automated fluorescence microscope allows us to distinguish perturbations that affect cell migration, morphology, and division. Readout requires ~1 hr per plate but is high in information content i.e. high content. We compare readouts using different imaging technologies, automated microscopy, scanners and a fluorescence macroscope, and evaluate the trade-off between information content and data acquisition rate.

CONCLUSIONS

The adaptation of a wound healing assay to a 384 well format facilitates the study of aspects of cell migration, tissue reorganization, cell division, and other processes that underlie wound healing. This assay allows greater than 10,000 perturbations to be screened per day with a quantitative, high-content readout, and can also be used to characterize small numbers of perturbations in detail.

Irradiation of mechanically-injured human arterial endothelial cells leads to increased gene expression and secretion of inflammatory and growth promoting cytokines

Radiation therapy is applied to inhibit neointima formation after percutaneous transluminal coronary angioplasty (PTCA). In this study, we evaluated the effect of irradiation on re-endothelialisation of circular denuded tracks made in post-confluent cultures of arterial endothelial cells (ECs) and on cellular factors involved in this process. Image analysis and time-lapse microcinematography revealed cell migration into denuded areas starting 4h after injury. Fifty percent coverage was achieved at 14.8 +/- 2.0 h. Using competitive PCR and flow cytometry techniques, no significant changes in mRNA expression of interleukin-1beta (IL-1beta), interleukin-8 (IL-8), basic fibroblast growth factor (bFGF or FGF-2), transforming growth factor-beta1 (TGF-beta1), platelet-derived growth factor A (PDGF-A), platelet-derived growth factor B (PDGF-B) and tissue factor (TF), and surface molecule expression of anti-intercellular adhesion molecule-1 (ICAM-1), anti-vascular cell adhesion molecule-1 (VCAM-1), anti-platelet/endothelial cell adhesion molecule-1 (PECAM-1), MHC-1, TF and Fas were observed. However, injury did significantly (P < 0.05) elevate the release of IL-8 and FGF-2 protein in the cell culture supernatant, as assessed by ELISA. Radiation (15Gy) given immediately after injury did not affect the kinetics of re-endothelialisation up to 48 h, in spite of the fact that no cell divisions were observed. Thereafter cell density decreased and cultures deteriorated. Compared to cultures exposed to injury alone, radiation induced significant (P < 0.05) increases in mRNA levels of IL-8 (1.35 +/- 0.10-fold increase at 4h), FGF-2 (1.62 +/- 0.10-fold at 4h; 1.76 +/- 0.33-fold at 24h) and IL-1beta (2.76 +/- 0.40-fold at 24h), whereas mRNA levels of TGF-beta1, PDGF-A and PDGF-B increased about 1.2-fold. IL-8 and FGF-2 protein concentrations in the media were higher than those observed in non-irradiated injured cell cultures; however, this difference was not significant. Radiation induced a 2.3 +/- 0.3-fold increase (P < 0.05) in Fas surface expression only. In conclusion, irradiation of mechanically-injured human EC leads to increased gene expression and protein secretion of inflammatory and growth promoting cytokines.

Angiotensin II inhibits endothelial cell motility through an AT1-dependent oxidant-sensitive decrement of nitric oxide availability

OBJECTIVE

The migratory capability of vascular endothelial cells plays a pivotal role in the maintenance of vessel wall integrity and is stimulated by nitric oxide (NO). Angiotensin II increases NAD(P)H oxidase activity in endothelial cells, thereby promoting reactive oxygen species (ROS) generation. Because ROS can both reduce NO synthase activity and increase NO breakdown, thus impairing NO availability in endothelial cells, we evaluated the effect of angiotensin II on human vascular endothelial cell (HUVEC) motility.

METHODS AND RESULTS

Angiotensin II dose- and time-dependently reduced HUVEC migration. Besides inhibiting HUVEC motility, angiotensin II altered intracellular glutathione redox status. The generation of ROS by cultured HUVECs was significantly increased by angiotensin II. Furthermore, angiotensin II reduced NO metabolite concentrations in culture media. The angiotensin II type 1 receptor antagonist candesartan cilexetil attenuated the inhibitory action exerted by angiotensin II on HUVEC motility, reversed the angiotensin II-induced increase in intracellular oxidative stress, and restored NO availability. Similar effects were exerted by the flavonoid inhibitor diphenylene iodinium and the antioxidant agent N-acetyl-L-cysteine.

CONCLUSIONS

All together, our data demonstrate that angiotensin II inhibits HUVEC motility by reducing NO availability. Such reduction is due to an angiotensin II type 1 receptor-dependent increment in intracellular ROS generation.

An antibody to VEGF upregulates factor VIII via interleukin-1 in activated adrenal cortex-derived capillary endothelial cells

We have previously shown in an in vitro wounding system of cultured endothelial cells (EC) that vascular endothelial growth factor (VEGF(165)) treatment upregulated the level of factor VIII (FVIII) in the cells facing an experimental wound. The FVIII upregulation induced by VEGF(165) could be abolished by rhuMab VEGF, a humanized antibody that blocks VEGF functions and inhibits tumorigenesis. Because the thrombotic system is actively involved in angiogenesis, we further investigated the effects of rhuMab VEGF on the regulation of FVIII. Although non-disturbed cells distant from a wound were not affected by rhuMab VEGF treatment, FVIII was also significantly upregulated in the cells along the wound in cultures treated with the antibody alone. RhuMab VEGF stimulation of FVIII could be blocked by VEGF(165). When cells were treated with rhuMab VEGF and VEGF(165) combined together, the stimulation or inhibition of FVIII expression was dose-related and dependent on the amount of excess free rhuMab VEGF and rhuMab VEGF:VEGF(165) immune complexes. Thus, both VEGF(165) and rhuMab VEGF used as single reagents enhanced FVIII in activated endothelial cells, while the immune complexes suppressed the upregulation. Following rhuMab VEGF treatment, two distinct activated endothelial subpopulations that differ in their ability to internalize rhuMab VEGF and express interleukin-1 (IL-1) were identified. IL-1beta but not IL-1alpha appeared to be acting as a mediator between the two endothelial subpopulations as the FVIII upregulation induced by rhuMab VEGF could be totally abolished by treatment with type II soluble IL-1 receptor (sIL-1RII).

Focal adhesion kinase is a key mediator of human trophoblast development

Trophoblast differentiation during the first trimester of pregnancy involves cell proliferation and invasion and extracellular matrix (ECM) remodeling. Reports have indicated that, in a variety of cell types, processes such as proliferation, invasion, and ECM remodeling require the turnover of focal adhesions mediated by a cytoplasmic tyrosine kinase named focal adhesion kinase (FAK). Therefore, in the present study we examined the expression and spatial localization of FAK during early human placental development. Immunocytochemical and immunoblot analysis showed that FAK and a focal adhesion-associated protein named paxillin were highly expressed between the 5th and 8th weeks of gestation, specifically in villous cytotrophoblast and extravillous trophoblast (EVT) cells. Activated FAK, phosphorylated on Tyr-397, colocalized with alpha5 integrin and matrix metalloproteinase-2 (MMP2) expression in EVT cells within a previously characterized intermediate, invasive-restrained region. FAK and paxillin expression dramatically decreased after 10 to 12 weeks of gestation coincident with increasing pO(2) levels. Exposure of human villous explants of 5 to 8 weeks to a 3% O(2) environment resulted in increased trophoblast outgrowth, cell proliferation, and detection of alpha5 integrin and MMP2, as well as increased activation of FAK in EVT cells compared with explants grown in a 20% O(2) environment. To determine whether FAK was a key requisite for trophoblast differentiation, villous explants of 5 weeks gestation were grown in Matrigel in a 3% O(2) environment and incubated with 20-mer antisense FAK oligonucleotides. A dramatic reduction of trophoblast outgrowth was observed in antisense-treated explants compared with missense and control cultures, and, in addition, cell proliferation and MMP2 activity in antisense-treated explants were dramatically reduced. These data suggest that FAK is a key kinase involved in early trophoblast cell differentiation and plays a role in regulating cell proliferation and motility during early placental development.

Cell motility in a new single-cell wound model

Until now researchers have used a monolayer of cultured cells to investigate cell motility toward an injured cell. However, we suspect that, when using this method, adjacent cells move to the free space due to relief of contact inhibition. The current study was designed to investigate the cell motility nearby an injured cell in varying cell connectivity. A low-power laser beam was used to damage one cell selectively with the silver coating beads. After injury, we observed the cell motility in three different cell types: (1) those immediately adjacent to the injured cell, (2) those removed from the injured cell by interposition of another cell, and (3) those removed from the injured cell by free space. The cells that are in direct contact with the injured cell moved toward the injured cell within 1.5-3.0 h. Indirectly connected cells and cells with no contact, on the other hand, showed no significant movement toward the injured cell. This suggests that the cell motility toward the cell injury is not only due to relief of contact inhibition but might also be caused by cell-to-cell signaling via cell connection. The current method will provide a tool to create a cell injury without damaging adjacent cells.

Formation of stress fibres in human endothelial cells infected with Bartonella bacilliformis is associated with altered morphology, impaired migration and defects in cell morphogenesis

Bartonella bacilliformis, a Gram-negative, flagellated bacterium, infects human erythrocytes (haematic phase) and endothelial cells (tissue phase), resulting in a biphasic disease. In the tissue phase of disease (verruga peruana), infection leads to infection of endothelial cells and a pronounced proliferation of these cells, resulting in characteristic skin eruptions of papules and nodules. We have studied the properties of endothelial cells infected in vitro. Extensive cytoskeletal remodelling of endothelial cells occurred after infection in vitro with B. bacilliformis. The cells became spindle shaped and contained arrays of actin stress fibres orientated parallel to the long axis of the cell. Cell-cell contacts were disrupted, along with the distribution of the plasma membrane marker protein, PECAM-1, which participates in cell-cell junctions. The prominent stress fibres terminated in an increased number of focal contacts, which were studied using immunofluorescent staining for paxillin, a cytoplasmic protein that localizes in the focal adhesions. These morphological changes are consistent with activation of intracellular Rho by B. bacilliformis. Formation of stress fibres and the increased number of focal adhesions could be prevented by preincubation of the endothelial cells with C3 exoenzyme, which inactivates intracellular Rho by ADP ribosylation. Endothelial cell motility was greatly diminished in infected cells and the cells did not respond effectively to a stimulus that would evoke motility. In addition, infection of endothelial cells interfered with their ability to form networks of capillary tubes when suspended within three-dimensional collagen matrices. If the properties of infected endothelial cells in vivo are similar, the infected cells will probably not participate effectively in angiogenesis.

Spontaneous and flow-induced Ca2+ transients in retracted regions in endothelial cells

Changes in intracellular calcium concentration ([Ca2+]i) and focal adhesion sites of cultured bovine aortic endothelial cells (BAECs) were simultaneously visualized in real time. Local [Ca2+]i transients were observed at the rear edges of spontaneously migrating BAECs. Furthermore, the majority of starting regions of [Ca2+]i transients retracted continuously. Frequency of [Ca2+]i transients increased with the application of fluid flow. The majority of starting regions of flow-induced [Ca2+]i transients retracted following the occurrence of [Ca2+]i transients. In addition, retracted areas were distributed in the upstream regions of the cell. Application of GdCl3, a mechanosensitive cation channel blocker, resulted in a clear reduction of [Ca2+]i transients and rear retractions in cases of spontaneous and flow-induced BAEC migration. Flow-induced directional rear retractions were also inhibited. Consequently, we conclude that local [Ca2+]i transients play an important role in the migration of BAECs with respect to rear retraction. Furthermore, flow-induced [Ca2+]i transients regulate directional rear retraction under flow conditions.

Novel method for the quantitative assessment of cell migration: a study on the motility of rabbit anterior cruciate (ACL) and medial collateral ligament (MCL) cells

A novel method of quantitating cell migration has been proposed for the potential utilization of tissue engineered scaffolds. Applying Alt's conservation law to describe the motion of first passage ACL and MCL cells, we have developed a quantitative method to assess innate differences in the motility of cells from these two ligamentous tissues. In this study, first passage ACL and MCL cells were cultured from four mature New Zealand white rabbits. One side of the cell monolayer was scraped completely away to create a wound model. The cell moved into the cell-free area, and cell density profiles were analyzed at 6 h and 12 h. Values of the random motility coefficient (mu) were then estimated by curve fitting the 6 h and 12 h data to a mathematical model, derived from the conservation law of cell flux. During 6 h of incubation in medium supplemented with 1% FBS, MCL cells (mu(MCL) = 4.63 +/- 0.65 X 10(-6) mm(2)/sec) were significantly (p < 0.05) more mobile than ACL cells (mu(ACL) = 2.51 +/- 0.31 X 10(-6) mm(2)/sec). At 12 h, the MCL cells also appeared to move faster (mu(ACL) = 4.39 +/- 0.63 X 10(-6) mm(2)/sec, mu(MCL) = 6.59 +/- 1.47 X 10(-6) mm(2)/sec), but the difference was not statistically significant (p = 0.18). Exposure of the cells to growth factors PDGF-BB or bFGF for 6 h had no significant effect on the migration of the ACL and MCL cells. However, exposure of the ACL cells (p < 0.05) and the MCL cells (p = 0.19) to 1 ng/mL of PDGFBB for 12 h enhanced their migration. Incubation with a high concentration (100 ng/mL) of PDGF-BB or bFGF at concentrations tested (1 or 100 ng/mL) for 12 h, produced little or no migratory stimulation on these ligament cells. Our findings support the previous qualitative observations made by numerous investigators. The novel methodology developed in this study may provide a basis for tissue engineering, and the results may be applied to tissue reconstruction techniques of the knee ligaments.

Calcium influx triggers the sequential proteolysis of extracellular and cytoplasmic domains of E-cadherin, leading to loss of beta-catenin from cell-cell contacts

Cadherins are major cell-cell adhesion molecules in both tumor and normal tissues. Although serum levels of soluble E-cadherin have been shown to be higher in the cancer patients than in healthy volunteers, the detail mechanism regulating release of soluble E-cadherin remains to be elucidated. Here we show that the ectodomain of E-cadherin is proteolytically cleaved from some cancer cells by a membrane-bound metalloprotease to yield soluble form, and the residual membrane-tethered cleavage product is subsequently degraded by intracellular proteolytic pathway. Futhermore, we show that extracellular calcium influx, that is induced by mechanical scraping of cells or ionomycin treatment, enhances the metalloprotease-mediated E-cadherin cleavage and the subsequent degradation of the cytoplasmic domain. Immunocytochemical analysis demonstrates that the sequential proteolysis of E-cadherin triggered by the calcium influx results in translocation of beta-catenin from the cell-cell contacts to cytoplasm. Our data suggest that calcium influx-induced proteolysis of E-cadherin not only disrupts the cell-cell adhesion but also activates beta-catenin-mediated intracellular signaling pathway, potentially leading to alterations in motility and proliferation activity of cells.

Expression of CCR2 by endothelial cells : implications for MCP-1 mediated wound injury repair and In vivo inflammatory activation of endothelium

Endothelial cell proliferation and migration may play a central role in angiogenesis, wound healing, and atherosclerosis. Although CXC chemokines can act on endothelial cells by influencing proliferation, an involvement of CC chemokines and endothelial expression of chemokine receptors remains to be elucidated. Reverse transcription-polymerase chain reaction, RNase protection, Western blot, and flow cytometric analysis showed that human umbilical vein endothelial cells express mRNA and surface protein of the monocyte chemotactic protein-1 (MCP-1) receptor CCR2, which was upregulated by inflammatory cytokines. MCP-1 induced migration of endothelial cells in a transwell assay, which was inhibited by the 9-76 MCP-1 receptor antagonist. Increased secretion of MCP-1 or interleukin-8, but not RANTES, on endothelial injury suggested a functional role of CCR2 in wound repair as measured by ELISA. After mechanical injury to endothelial monolayers, which spontaneously closed within 24 hours, wound repair was delayed by the 9-76 antagonist and by a blocking monoclonal antibody to MCP-1, but not to interleukin-8, and was improved by exogenous MCP-1. This was confirmed by quantification of cell migration into the wound area, whereas proliferation and viability were unaltered by MCP-1 or its analogue. Notably, immunohistochemistry of inflamed tissue revealed CCR2 staining on arterial, venous, and venular endothelium affected by cellular infiltration. This is the first demonstration of endothelial CCR2 expression ex vivo, inferring its involvement in inflammatory conditions. Thus endothelial cells express functional CCR2 that may have important implications for endothelial wound repair and inflammatory reactions.

Fibroblast growth factor 2 enhances early stages of in vitro endothelial repair by microfilament bundle reorganization and cell elongation

As endothelial cells convert from quiescent to migrating cells over 8 h along a wound edge, actin microfilaments undergo well-defined sequential changes characterized by an initial random distribution followed by a parallel and then a perpendicular orientation of microfilaments with respect to the wound edge. The latter is associated with subsequent cell migration. We tested the hypothesis that fibroblast growth factor 2 (FGF-2) can enhance the very early stages of wound repair even prior to migration and that FGF-2 enhancement of wound repair is associated with changes in the endothelial actin cytoskeleton. Using an in vitro two-sided wound model, the addition of FGF-2 at the time of wounding enhanced the extent of wound closure over 8 h. Treatment with FGF-2 was associated with significantly longer cells along the wound edge at 4 and 8 h after wounding. When treated with increasing concentrations of neutralizing FGF-2 antibody, the extent of wound closure decreased over 8 h and was associated with a decrease in cell length along the wound edge. Actin microfilaments were localized using rhodamine phalloidin and viewed using laser confocal microscopy. At 4 h after wounding, FGF-2 treatment was associated with significantly more cells along the wound expressing perpendicular microfilaments compared to untreated cells, which suggested a more rapid transition of parallel to perpendicular microfilament distribution. Thus, FGF-2 affects the very early stages of wound repair prior to migration by enhancing wound closure due to the early appearance of perpendicular microfilaments and lengthening of cells along the wound edge.

Reduced in vitro repair in endothelial cells harvested from the intercostal ostia of porcine thoracic aorta

The ability of large-vessel endothelium to repair itself rapidly after injury is important in the maintenance of its barrier function and in limiting the development and progression of atherosclerosis. Because dysfunctional repair may be involved in the pathogenesis of some atherosclerotic plaques, including those at the ostia of aortic branches, linear mechanical denuding wounds were made in confluent monolayers of endothelial cells harvested by scraping from the flow divider, the upstream wall of the intercostal branch and unbranched regions in the thoracic aorta. The extent of wound closure was significantly lower in cells derived from either side of the intercostal branches, compared with cells from unbranched areas. The wound edge of cells harvested from the flow divider and its opposite wall closed by 22+/-0.084 microm and 22+/-1.3 microm, respectively, versus control, unbranched endothelial cells (30+/-2.2 microm) at 24 hours and by 48 hours, 48+/-3.4 microm and 47+/-3.6 microm compared with control (61+/-3.4 microm). Extent of wound closure in cells harvested by scraping from unbranched regions was comparable with collagenase-harvested endothelial cells at 24 and 48 hours. Distribution of F-actin microfilaments, tubulin and centrosomes have been shown to be disrupted at the wound edge in poorly migrating cells. In our study, however, no differences were observed in cytoskeletal distribution between cells from branched, unbranched and control areas. Thus, aortic endothelial cells from the intercostal branch region show a reduced ability to repair wounds compared with cells harvested from unbranched aorta. The mechanism for this difference is currently unknown.

A wound-induced [Ca2+]i increase and its transcriptional activation of immediate early genes is important in the regulation of motility

Upon mechanical wounding of a confluent quiescent monolayer, cells move into the denuded zone. However, it is not well known what signaling cascade connects release from contact inhibition to cell movement at the wound edge. Mechanical wounding induced an increase in the concentration of intracellular free Ca2+ ([Ca2+]i) in endothelial cells at the wound edge. The [Ca2+]i signal was required for the transcriptional activation of two immediate early genes (IEGs), c-fos and c-jun, since blocking Ca2+ influx with Gd3+ or EGTA reduced IEG transcription, while augmenting Ca2+ influx increased IEG transcription. The transcriptional activation of the IEGs depended on protein kinase C and calmodulin-dependent protein kinase since treatment with the inhibitors Calphostin C and KN-62 significantly reduced IEG expression. Briefly blocking Ca2+ influx also produced a long-term reduction of cell motility, while augmenting Ca2+ influx increased cell motility. To evaluate whether expression of IEGs might control cell movement, we microinjected sense or antisense cDNA to c-fos into cells after wounding. Antisense c-fos cDNA inhibited motility, while sense cDNA increased motility rates. These results suggested that the [Ca2+]i rise, induced by wounding, regulated the initiation of subsequent motility through the transcriptional activation of IEGs during wounding.

Stimulatory effects of lipoprotein(a) and low-density lipoprotein on human umbilical vein endothelial cell migration and proliferation are partially mediated by fibroblast growth factor-2

We previously reported a transient increase in plasma lipoprotein(a) (Lp(a)) concentrations following acute myocardial infarction and surgical operations, and demonstrated Lp(a) accumulation in healing tissues. In the present study, the stimulatory effect of Lp(a) on migration and proliferation of human umbilical vein endothelial cells (HUVEC) was assessed by quantitative assay methods and compared it with that of LDL. Lp(a) stimulated both migration and proliferation of HUVEC in a dose-dependent manner and the stimulatory activities for migration and proliferation were two times higher than those of LDL in terms of moles of apoB. In addition, this stimulatory activity of Lp(a) was not affected by the difference of Lp(a) phenotype. Although each neutralizing antibody to hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF) and interleukin-1beta (IL-1beta) had no further effect on migration and proliferation of HUVEC treated with Lp(a), only antibody to fibroblast growth factor-2 (FGF-2) partially suppressed them. Moreover, pertussis toxin, which inhibits FGF-2-stimulated endothelial cell movement, also partially suppressed Lp(a)-induced HUVEC migration. FGF-2 concentrations in the medium of HUVEC treated with Lp(a) were constant in spite of the increase in FGF-2 mRNA levels in HUVEC. Taken together, it is suggest that Lp(a) stimulates HUVEC migration and proliferation, which is mediated, at least in part, by FGF-2 and may promote the angiogenesis during wound healing.

Reactivity patterns of antiphospholipid antibodies and endothelial cells: effect of antiendothelial antibodies on cell migration

Antiphospholipid syndrome (APS) is characterized by the presence of a heterogeneous class of antibodies directed against phospholipids and associated with high occurrence of thrombotic complications. Antiendothelial cell antibodies (AECAs) have been identified in various autoimmune disorders including APS, but their reactivity patterns remain unclear. We used eluted endothelial membrane-bound antibodies (EC eluates) to investigate possible cross-reactivity of AECAs and their pathogenic effects on endothelial cell integrity. The heterogeneous and nonspecific nature of AECAs was confirmed by our finding that they cross-react with fibroblasts and platelets and bind to cardiolipin. In addition, platelet-bound antibodies from sera of patients with APS reacted with endothelial cells. A dose-dependent binding of human monoclonal anticardiolipin antibody was demonstrated, but this antibody did not compete with AECAs in EC eluates, indicating that only small portion of AECAs are directed against cardiolipin. Although sera from APS patients prolonged coagulation tests, EC eluates did not affect coagulation, suggesting that AECAs may belong to antiphospholipid antibodies subsets that does not interfere with coagulation. Vascular damage is a common feature of autoimmune disorders associated with AECAs. Possible effects of AECAs on vascular perturbance were investigated by cytotoxicity, attachment, and migration assays. Although AECAs were not shown to be cytotoxic or to affect cell attachment, sera from APS patients caused reduced cellular migration (by 30%), and EC eluates caused even more significant inhibition (by 50%). These findings suggest possible interference of AECAs in vascular repair mechanisms and provide an explanation for the thrombotic complications frequently seen in APS patients.

Arachidonic acid pretreatment enhances smooth muscle cell migration via increased Ca2+ influx

It is well known that vascular smooth muscle cell (SMC) migration is an initial step in atheromatous plaque formation. In the present study, we investigated the effects of arachidonic acid (AA, 20:4 n-6) on bovine carotid artery SMC migration using the modified Boyden chamber technique. SMCs pretreated with 2.5 microg/ml of AA for 2 days, showed an enhanced migration response to fetal bovine serum. AA pretreatment (0.5-5.0 microg/ml) increased fetal bovine serum-induced SMC migration dose-dependently, and maximum stimulation was observed at a concentration of 2.5 microg/ml. However, AA pretreatment did not enhance fetal bovine serum-induced endothelial cell migration. Using lipid analysis, we found that AA was substantially incorporated into cellular phospholipids. When SMC migration was induced by platelet derived growth factor (PDGF)-BB, instead of serum, the stimulative effect of AA pretreatment was retained. SMCs pretreated with AA showed greater mobilization of intracellular Ca2+ in response to PDGF-BB than SMCs without AA pretreatment (controls). Nifedipine, a Ca2+ channel blocker, and glycoletherdiamine-tetraacetic acid (EGTA) had no effect on PDGF-induced migration of controls but both drugs reduced the enhanced PDGE-induced migration of AA-pretreated SMCs to the control level. Baicalein, an inhibitor of 12-lipoxygenase, reduced PDGF-BB-induced migration of both control and AA pretreated SMCs, however the AA-pretreated cells still showed enhanced migration compared to control cells. These findings suggest that AA accelerates SMC migration in the thickening of the intima during atheroma formation, via stimulation of extracellular Ca2+ influx.

Requirement for protein kinase C theta for cell cycle progression and formation of actin stress fibers and filopodia in vascular endothelial cells

Activation of the protein kinase C (PKC) family with phorbol esters induces endothelial proliferation and angiogenesis, but which of the events that constitute angiogenesis are affected by individual members of the PKC family is unknown. In rat capillary endothelial (RCE) cells, serum stimulation increased expression of a single PKC isoenzyme, PKCtheta, and its translocation to the periphery. Conditional overexpression of a dominant-negative mutant of PKCtheta markedly inhibited RCE proliferation, as well as closure of a "wound" by RCE migration and formation of capillary rings and tubules in vitro. PKCtheta inhibition delayed the endothelial cell cycle at the G2/M phase and prevented formation of actin stress fibers and filopodia but not lamellipodia. The defect in cell morphology and wound closure in PKCtheta-kn cells was reversed by overexpressing kinase-active PKCtheta, indicating that these RCE functions depend upon PKCtheta substrates. Thus, PKCtheta is required for multiple processes essential for angiogenesis and wound repair, including endothelial mitosis, maintenance of a normal actin cytoskeleton, and formation of an enclosed tube.

Bacterial toxins block endothelial wound repair. Evidence that Rho GTPases control cytoskeletal rearrangements in migrating endothelial cells

We investigated the effect of bacterial toxins that modify and inactivate Rho GTP-binding proteins on the migratory response of endothelial cells to wounding. C3-transferase from Clostridium botulinum, EDIN from Staphylococcus aureus, and toxin A from Clostridium difficile blocked migration of human umbilical vein endothelial cells (HUVECs) in an in vitro wound repair assay. Migrating HUVECs expressed actin microspikes (maximum at 10 minutes after wounding), ruffles (maximum at 12 hours), and fibers (maximum at 24 hours), and within these actin structures, vinculin-containing focal complexes/adhesions were formed. C3-Transferase ADP ribosylated RhoA, RhoB, and RhoC in HUVECs and abolished the formation of actin stress fibers/focal adhesions but had no effect on expression of microspikes, ruffles, or the associated vinculin-containing focal complexes. Similar results were obtained with EDIN and toxin A. These results indicate that endothelial cells migrating into a wounded area express distinct combinations of actin/vinculin structures in a spatially and temporally coordinated manner. The GTPase Rho selectively controls the formation of actin fibers/focal adhesions that occurs 2 to 24 hours after wounding. A mechanism is proposed by which Rho-specific bacterial toxins could influence vascular repair, angiogenesis, or atherosclerosis.

Paclitaxel inhibits arterial smooth muscle cell proliferation and migration in vitro and in vivo using local drug delivery

BACKGROUND

The antineoplastic compound paclitaxel (Taxol) causes an increased assembly of extraordinarily stable microtubules. The present study was designed to characterize the effects of paclitaxel on proliferation and migration of human arterial smooth muscle cells (haSMCs) in vitro and on neointima formation in an in vivo experimental rabbit model.

METHODS AND RESULTS

Both monocultures of haSMCs and cocultures with human arterial endothelial cells (haECs) were used. Cell growth after 4, 8, and 14 days was determined in the absence or presence of platelet-derived growth factor-AB (PDGF-AB), basic fibroblast growth factor (bFGF), or thrombin. Nonstop paclitaxel exposure, as well as single-dose applications of paclitaxel for 24 hours or even 20 minutes (0.1 to 10.0 micromol/L), caused a complete and prolonged inhibition of haSMC growth up to day 14, with an IC50 of 2.0 nmol/L. Mitogens or cocultures with stimulating haECs did not significantly attenuate paclitaxel-induced effects. Immunohistochemistry showed characteristic cytoskeletal changes predominantly in the microtubule network. Additionally, in 20 male New Zealand White rabbits, intimal plaques were produced by electrical stimulation. In 10 animals, paclitaxel was locally applied by use of microporous balloons. Histologically, the intima wall area, wall thickness, and degree of stenosis were reduced significantly in paclitaxel-treated animals compared with controls.

CONCLUSIONS

Our data show that paclitaxel inhibits haSMC proliferation and migration in a dose-dependent manner in monocultures and cocultures even in the presence of mitogens. Furthermore, paclitaxel prevents neointima formation in rabbits after balloon angioplasty. The long-lasting effect after just several minutes' exposure time makes this lipophilic substance a promising candidate for local antiproliferative therapy of restenosis.

How do injured cells communicate with the surviving cell monolayer?

Mechanically scratching cell monolayers relieves contact inhibition and induces surviving cells near the wound edge to move and proliferate. The present work was designed to test whether surviving cells passively respond to newly available space, or whether cells are actively stimulated by signals from injured cells nearby. We monitored intracellular free Ca2+ ([Ca2+]i) while scratching confluent monolayers of bovine pulmonary endothelial cells and mouse mammary epithelial cells. Within seconds after wounding, a transient elevation of [Ca2+]i was observed in surviving cells. In endothelial cells, the [Ca2+]i elevation propagated into the monolayer for a distance of 10 to 12 cell rows at a speed of 20 to 28 microm/second. The amplitude of the wave of [Ca2+]i was reduced as it propagated into the monolayer, but the velocity of the wave was nearly constant. Cells that experienced the [Ca2+]i elevation had intact plasma membranes, and survived for over 24 hours post wounding. Removing extracellular Ca2+ decreased the amplitude by two-thirds and reduced the propagation rate by half, suggesting that Ca2+ influx contributed to the increased [Ca2+]i. To determine how [Ca2+]i waves were stimulated, we blocked extracellular communication by fluid perfusion or intercellular communication by breaks in the monolayer. In bovine pulmonary artery endothelial cultures, the [Ca2+]i wave passed over breaks in the monolayer, and was prevented from traveling upstream in a perfusion chamber. Conditioned media from injured cells also elevated [Ca2+]i in unwounded reporter cultures. In mouse mammary epithelial monolayers with established cell-cell contacts, the [Ca2+]i wave passed over breaks in the monolayer, but was only partially prevented from traveling upstream during perfusion. These experiments showed that mechanical wounds lead to long distance, [Ca2+]i-dependent communication between the injured cells and the surviving cell monolayer through at least two mechanisms: first, extracellular release of a chemical stimulus from wounded cells that diffused to neighboring cells (present in both monolayers); second, transmission of an intercellular signal through cell-cell junctions (present in the mammary epithelial monolayers). Thus, mechanical injury provided a direct, chemical stimulus to nearby cells which have not themselves been damaged.

Inhibition of focal adhesion kinase (FAK) signaling in focal adhesions decreases cell motility and proliferation

It has been proposed that the focal adhesion kinase (FAK) mediates focal adhesion formation through tyrosine phosphorylation during cell adhesion. We investigated the role of FAK in focal adhesion structure and function. Loading cells with a glutathione-S-transferase fusion protein (GST-Cterm) containing the FAK focal adhesion targeting sequence, but not the kinase domain, decreased the association of endogenous FAK with focal adhesions. This displacement of endogenous FAK in both BALB/c 3T3 cells and human umbilical vein endothelial cells loaded with GST-Cterm decreased focal adhesion phosphotyrosine content. Neither cell type, however, exhibited a reduction in focal adhesions after GST-Cterm loading. These results indicate that FAK mediates adhesion-associated tyrosine phosphorylation, but not the formation of focal adhesions. We then examined the effect of inhibiting FAK function on other adhesion-dependent cell behavior. Cells microinjected with GST-Cterm exhibited decreased migration. In addition, cells injected with GST-Cterm had decreased DNA synthesis compared with control-injected or noninjected cells. These findings suggest that FAK functions in the regulation of cell migration and cell proliferation.

Role of lysophosphatidylcholine in the inhibition of endothelial cell motility by oxidized low density lipoprotein

Endothelial cell (EC) movement is required for the development and repair of blood vessels. We have previously shown that LDL oxidized by transition metals almost completely suppressed the wound-healing migratory response of vascular EC in vitro. We now report that lysophosphatidylcholine (lysoPC), a lipid component of oxidized LDL, has an important role in the antimigratory activity of the lipoprotein. Purified 1-palmitoyl lysoPC inhibited movement with a half-maximal activity at 12-15 micrometers, and near complete inhibition at 20 micrometers; the inhibitory concentration of lysoPC was consistent with its abundance in oxidized LDL. The inhibition was not due to cytotoxicity since protein synthesis was unaffected and since EC movement was restored after removal of lysoPC. Lysophospholipid activity was dependent on lipid structure. LysoPC's containing 1-position C16 or C18 saturated fatty acids were antimigratory, but those containing C < or = 14 saturated fatty acids or polyunsaturated fatty acids were not. The activity of 1-palmitoyl lysolipids with various head groups was examined. Lysophosphatidylinositol was more antimigratory than lysophosphatidylglycerol and lysophosphatidylcholine, which were more potent than lysophosphatidylserine and lysophosphatidylethanolamine. Monoglyceride was inactive while lysophosphatidate had promigratory activity. These results are consistent with head group size rather than charge as a critical determinant of activity. To show that lysophospholipids within an intact lipoprotein were active, LDL was treated with bee venom phospholipase A2 (PLA2). The modified lipoprotein inhibited EC movement to the same extent as iron-oxidized LDL and antimigratory activity correlated with the amount of lysoPC formed. To determine antimigratory activity of lysoPC present in oxidized LDL, lipid extracts from oxidized LDL were fractionated by normal phase HPLC. The fraction comigrating with lysoPC had nearly the same activity as the total extract confirming that lysoPC (or a co-eluting lipid) was a major antimigratory molecule in oxidized LDL. These studies demonstrate that lysoPC in oxidized LDL limit EC wound healing responses in vitro, and suggest a possible role for lysolipids in limiting endothelial regeneration after a denuding injury in vivo.

Gelatinase B is involved in the in vitro wound repair of human respiratory epithelium

Following epithelial injury, extracellular matrix undergoes imposing remodelings. We examined the contribution of matrix metalloproteinases, gelatinases A and B, in an in vitro wound repair model of human respiratory epithelium. Confluent human surface respiratory epithelial (HSRE) cells cultured from dissociated surface cells of human nasal polyps were chemically injured. Over the next 3 to 5 days, cells migrated onto the injured area to repair the circular wound. Repair kinetics of these wounds was monitored until wound closure occurred. Gelatinolytic activities were analysed in culture supernates and in cell protein extracts derived from repairing migratory and non repairing stationary cells. Small amounts of gelatinase A were expressed by HSRE cells, and variations of this gelatinase remained very weak for the time of the wound repair. In contrast, gelatinase B was upregulated during the wound repair process, with a maximum peak observed at wound closure. A marked gelatinase B activation occurred only in cells involved in the repair process. Gelatinase B was localized in some migratory basal cells, recognized by an anti-cytokeratin 14 antibody and located around the wound. We could not detect any gelatinase A in repairing or in stationary HSRE cells. Addition of the 6-6B monoclonal antibody, known to inhibit gelatinase B activation, to the culture medium during the repair process resulted in a dose-dependent decrease of the wound repair speed. These results suggest that gelatinase B, produced by epithelial cells, actively contributes to the wound repair process of the respiratory epithelium.

Immunosuppressive agents and endothelial repair. Prednisolone delays migration and cytoskeletal rearrangement in wounded porcine aortic monolayers

Endothelial denudation at areas of predilection to atherosclerosis is balanced by an active repair process that may be inhibited under conditions of accelerated atherosclerosis. After cardiac transplantation, the accelerated atherosclerotic process that develops may be enhanced by immunosuppressive agents that have nonspecific effects on cell signaling, proliferation, and response to injury. To study subtle effects of cyclosporine A, azathioprine, and 6 alpha-methylprednisolone on normal endothelial repair processes, confluent porcine endothelial monolayers were denuded in the presence of clinically relevant concentrations of these agents. The rate of endothelial wound repair was compared and the effects on cell spreading, proliferation, and the cytoskeleton assessed. 6 alpha-Methylprednisolone at concentrations of 1.25 to 50 mumol/L was associated with a transient 30% to 60% inhibition of endothelial wound repair. This was associated with increased cell size at the wound edge and a delay in centrosomal reorientation toward the wound, without any effect on cell proliferation. Cyclosporine and azathioprine in clinically relevant concentrations did not affect endothelial repair. Thus, corticosteroids transiently inhibit endothelial cytoskeletal alterations that are important in endothelial repair after a denuding injury.

Suramin inhibits C6 glioma-induced angiogenesis in vitro

Aspects of tumor-induced angiogenesis in vitro were examined using an assay involving collagen gel invasion by a surface monolayer of bovine endothelial cells under the influence of serum free conditioned medium produced by C6 cells, an experimentally derived rat glial tumor cell line. The effects of the polyanionic compound suramin, known to interfere with growth factor/cell signaling on this process were evaluated. Collagen gel invasion was quantified by adding C6 conditioned medium with or without various doses of suramin to monolayers of bovine aortic endothelial cells grown on type I collagen gels in transwell inserts. Cultures were monitored with phase-contrast microscopy. After various periods of incubation collagen gels were fixed, embedded in epoxy resin, and 1-micron thick sections were stained with toluidine blue. Additional cultures were used to evaluate the effects of C6 conditioned medium and suramin on endothelial cell proliferation, and on chemotaxis through 8-microns pores. C6 glioma cell conditioned medium induced large vessel endothelial cells to sprout into the underlying collagen matrix and subsequently form networks of capillary like tubes. Conditioned medium was also chemotactic and mitogenic for these cells. The addition of suramin to C6 glioma conditioned medium prevents tube formation in collagen gels, and inhibits both endothelial cell proliferation and chemotaxis in a dose dependent manner. These results suggest that glial tumor cell conditioned medium induces angiogenesis in large vessel endothelial cells in vitro via mechanisms which are disrupted by suramin, most likely involving tumor-derived growth factor release and/or endothelium-mediated matrix proteolysis.

Establishment of an outgrowth culture system to study growth regulation of normal human epithelium

To study the growth regulation of epithelial cells as a sheet, I developed an outgrowth culture system for normal human ectocervical epithelial (NHCE) cells, whereby outgrowths from tissue explants increase their radius in a constant rate over time. Cinematographic observation revealed that throughout the outgrowths the cells coordinately migrate and proliferate. To date, all 59 specimens examined have shown similar growth characteristics, with explant size not causing any difference in the growth rate; 10(8) cells/specimen can easily be obtained in 3 wk. Cell densities of outgrowths also remain constant. Moreover, there is no fibroblast contamination, and removal of explants does not affect growth rate. Therefore, pure epithelial outgrowth in uniform growth condition can be prepared for further experiments. The results demonstrate that the outgrowth culture system is an attractive model for analysis of growth control mechanisms in normal human epithelium in vitro.

Migration of retinal pigment epithelium cells in vitro is regulated by protein kinase C

The migration of retinal pigment epithelial (RPE) cells is an important step in various pathologic conditions, including subretinal neovascularization (SRN) and proliferative vitreoretinopathy (PVR). Therefore, elucidation of the mechanism of RPE migration may be useful in devising effective treatment for these disorders. Since protein kinase C (PKC) has been shown to regulate the migration of other cell types, we studied the effects of PKC agonists and antagonists on RPE migration. We used an in vitro wound healing model in which a small area of a confluent monolayer of bovine RPE cells was denuded with a razor blade. The cultures were subsequently incubated with agents known to stimulate [phorbol 12-myristate 13-acetate (PMA)] or inhibit (calphostin C, staurosporine) PKC. After 20 hr, migration was measured as the number of cells that had entered the denuded area. We also measured the translocation of PKC from the cytosol to the membrane in order to determine the activation or inhibition of PKC by PMA and calphostin C in the cells. The phorbol ester PMA stimulated migration by 41%, and calphostin C and staurosporine inhibited migration by 38% and 31%, respectively, in a medium supplemented with 10% serum. To determine the requirement for serum in this modulation, we also measured the effects of PMA and calphostin C on RPE migration in serum-free medium. Under these conditions, basal migration was greatly decreased, but PMA stimulated migration by 177% and calphostin C inhibited migration by 93%. Since PKC modulation is known to induce the proliferation of cells, we also tested the effects of these agents on growth-inhibited migration by pretreating the cells with the antiproliferative drug mitomycin C. We found that modulation of PKC under these conditions equally affected growth-inhibited and growth-dependent migration. Therefore, based on the increase in RPE migration induced by a PKC agonist, and the decrease in migration caused by PKC antagonists, it is suggested that PKC-mediated signal transduction plays a crucial role in RPE cell migration. This knowledge may be useful in devising effective treatments for SRN and PVR.

Enhanced migratory activity of vascular smooth muscle cells with high expression of platelet-derived growth factor A and B

Proliferation and migration of vascular smooth muscle cells (SMCs) are major events in atherogenesis. It is known that platelet-derived growth factor (PDGF) stimulates both of these processes in a paracrine fashion, whereas autocrine stimulation has been shown only for proliferation. The aim of this study was to investigate the influence of PDGF expression in SMCs on migratory activity of these cells. SMCs were cultivated from the vascular tissue of 23 patients. Cellular motility was analyzed by a computer-assisted motion analysis system; 54 images per sample, obtained during an observation period of eighteen hours, were analyzed. PDGF-A and PDGF-B mRNA levels were determined by quantitative polymerase chain reaction (PCR) following reverse transcription. To quantitate mRNA content of SMCs, the authors coamplified cDNA copies of mRNA from cells and from a synthetic reference RNA in the same reaction vessel. Cells derived from atherosclerotic lesions produced a 1.6-fold increase of PDGF-A (P < 0.05) and a 5-fold increase of PDGF-B mRNA (P < 0.05) as compared with those from normal vessels. The migratory velocity (range 11.1-49.2 microns/hr) was independent of PDGF-A and PDGF-B mRNA expression. A significant correlation between levels of PDGF-A mRNA and PDGF-B mRNA and the degree of directional changes of SMCs on the covered track (klinokinesis) was found (P < 0.05).

CONCLUSION

PDGF-A and PDGF-B mRNA expression is significantly correlated with positive klinokinesis without affecting migratory velocity. This finding reflects enhanced migratory activity of SMCs. Besides its known mitogenic effects, the authors present evidence that PDGF may act as an autocrine motogen* in SMCs.

Role of thrombin in endothelial cell monolayer repair in vitro

PURPOSE

We examined the effect of thrombin on human iliac artery endothelial cell monolayer repair and proliferation after denuding vascular injury.

METHODS

Human iliac artery endothelial cell monolayer repair was determined by scrape wounding confluent monolayers and measuring the advancement of the cells into the wounded area for 3 days. Proliferation studies involved plating human iliac artery endothelial cells at one tenth confluence and counting the increase in cell number every 2 days for a 2-week period. Proliferation during monolayer repair was examined by determining bromodeoxyuridine uptake in cells located at the leading edge of a scrape-wounded monolayer.

RESULTS

Thrombin (1 to 8 U/ml) inhibited human iliac artery endothelial cell monolayer repair in a concentration-related, reversible manner. The effect was augmented by decreasing serum concentration and was independent of the presence of endothelial cell growth supplement. Inactivation of thrombin's proteolytic site with diisopropylfluorophosphate eliminated its effect on monolayer repair. Thrombin (0.5 to 8 U/ml) inhibited human iliac artery endothelial cell proliferation in a dose-related manner. This effect was augmented by decreasing serum concentration. Finally, thrombin (4 U/ml) inhibited the proliferative response of cells located at the leading edge of wounded monolayers compared with control groups.

CONCLUSION

Thrombin inhibits human arterial endothelial cell monolayer repair and proliferation after denuding vascular injury.

Angiogenesis inhibition: a review

In this review we discuss the concept of anti-angiogenesis, which is the inhibition of neovascularization. Anti-angiogenic agents are viewed from the standpoint of their effect on various elements of the angiogenic process, including induction of vascular discontinuity, endothelial cell movement, endothelial cell proliferation, and three-dimensional restructuring of patent vessels. An effort is made to place the many different approaches to anti-angiogenesis research into a comprehensible structure, in order to identify problems of evaluation and interpretation, thereby providing a clearer basis for determining promising and needed directions for further investigation.

High-density lipoprotein stimulates endothelial cell movement by a mechanism distinct from basic fibroblast growth factor

Endothelial cell (EC) migration is a regulatory event in the formation and repair of blood vessels. Although serum contains substantial promigratory activity, the responsible components and especially the role of lipoproteins have not been determined. We examined the effect of plasma high-density lipoprotein (HDL) on the movement of ECs in vitro. Confluent cultures of bovine aortic ECs in serum-free medium were "wounded," and migration was measured after 24 hours. HDL stimulated migration in a concentration-dependent manner with a half-maximal response at 25 to 40 micrograms cholesterol per milliliter and a maximal twofold stimulation at approximately 150 micrograms cholesterol per milliliter. HDL-stimulated migration was not due to cell proliferation, since migration was increased in the presence of hydroxyurea at a concentration that blocked proliferation. At optimal concentrations, HDL was at least as stimulatory as basic fibroblast growth factor (FGF). However, the activity of HDL was not due to contamination by basic FGF, since antibodies to basic FGF did not block HDL-stimulated movement and since the maximum promigratory activities of basic FGF and HDL were additive. These results indicate that HDL and basic FGF may use distinct signaling pathways to initiate EC movement. This possibility was confirmed by results showing that pertussis toxin suppressed basic FGF-stimulated but not HDL-stimulated EC motility and that inhibitors of phospholipase A2, aristolochic acid and ONO-RS-082, also blocked the promigratory activity of basic FGF but had no effect on the activity of HDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Tyrosine kinase activity, cytoskeletal organization, and motility in human vascular endothelial cells

Tyrosine phosphorylation of cytoskeletal proteins occurs during integrin-mediated cell adhesion to extracellular matrix proteins. We have investigated the role of tyrosine phosphorylation in the migration and initial spreading of human umbilical vein endothelial cells (HUVEC). Elevated phosphotyrosine concentrations were noted in the focal adhesions of HUVEC migrating into wounds. Anti-phosphotyrosine Western blots of extracts of wounded HUVEC monolayers demonstrated increased phosphorylation at 120-130 kDa when compared with extracts of intact monolayers. The pp125FAK immunoprecipitated from wounded monolayers exhibited increased kinase activity as compared to pp125FAK from intact monolayers. The time to wound closure in HUVEC monolayers was doubled by tyrphostin AG 213 treatment. The same concentration of AG 213 interfered with HUVEC focal adhesion and stress fiber formation. AG 213 inhibited adhesion-associated tyrosine phosphorylation of pp125FAK in HUVEC. Tyrphostins AG 213 and AG 808 inhibited pp125FAK activity in in vitro kinase assays. pp125FAK immunoprecipitates from HUVEC treated with both of these inhibitors also had kinase activity in vitro that was below levels seen in untreated HUVEC. These findings suggest that tyrosine phosphorylation of cytoskeletal proteins may be important in HUVEC spreading and migration and that pp125FAK may mediate phosphotyrosine formation during these processes.

Taxol and embryonic development in the chick

Taxol, an inhibitor of microtubule disassembly, is currently under investigation in the therapy of several human cancers. The current investigation was undertaken to characterize potential taxol developmental toxicity in chicks. On one of days 1-4 of incubation, taxol was administered in dimethylsulfoxide (DMSO) or olive oil in a range of doses, the highest of which produced a high incidence of early embryo death. Production of gross structural malformations was sporadic and occurred in vehicle-treated as well as taxol-treated embryos. A more common manifestation of taxol toxicity was a syndrome of visceral abnormalities, including regression of the vitelline circulation, dilatation of the atria, and hemorrhage in the left side of the head and thorax, often with decreased eye pigmentation. Regardless of the day of treatment, this syndrome occurred at 4.5-5 days. To investigate the possibility that taxol induced its effect through disruption of angiogenesis in the vitelline circulation, filters soaked in taxol were applied to the margin of the germ disc. No inhibition of vessel development was demonstrated. We conclude that taxol decreases the viability of embryos and that this impairment of survival precludes the development of birth defects. Solvent toxicity is an important confounder in the investigation of taxol embryotoxicity.

Molecular and cellular concepts in atherosclerosis

Atherosclerosis is a complex disease of uncertain cause. Its pathobiology is believed to represent an abnormal expression of the processes of vascular healing. Etiologic models derive from a 'response to injury' paradigm and can be divided into three separate disease stages: endothelial dysfunction, smooth muscle proliferation and architectural disruption. The initiating event of endothelial dysfunction is unknown, but is believed to be related to low-density lipoproteins and/or their oxidized derivatives. Endothelial injury is signalled to the smooth muscle cells of the media by three routes: direct cell-cell interaction, secretion of soluble growth factors and monocyte-derived cytokines. Monocytes are recruited by the endothelium and invade the subintimal space by a complex interaction of a variety of adhesion proteins and receptors on both cell types. Smooth muscle cell proliferation is initiated by a change in phenotype expression from 'contractile' to 'synthetic' resulting from the binding of fibronectin to specific integrin receptors. Three functionally distinct activities may represent separate subtypes of the 'synthetic phenotype': migration from the media to the intima, increased proliferation and inappropriate extracellular matrix synthesis. The loss of normal regulatory control and anchorage independence of proliferation suggest a relationship to oncogenic transformation. Both migration and proliferation result from the binding of platelet-derived growth factor-like factors to smooth muscle cell receptors, which initiates a cascade of intracellular molecular events leading either to cytoskeletal locomotory restructuring or cell cycle activation. Both pathways also appear to be coregulated by integrin receptors and both depend upon phosphorylation of cell membrane, cytosolic and nuclear regulatory proteins. Clinical expression of atherosclerosis may follow sudden loss of architectural integrity of the intimal plaque by three different mechanisms: plaque fissuring, intraluminal plaque rupture or intramural hemorrhage related to abnormal vessel wall stress and/or biochemistry.

Fibroblast migration and proliferation during in vitro wound healing. A quantitative comparison between various growth factors and a low molecular weight blood dialysate used in the clinic to normalize impaired wound healing

During the formation of granulation tissue in a dermal wound, platelets, monocytes and other cellular blood constituents release various peptide growth factors to stimulate fibroblasts to migrate into the wound site and proliferate, in order to reconstitute the various connective tissue components. The effect on fibroblast migration and proliferation of these growth factors, and of Solcoseryl (HD), a deproteinized fraction of calf blood used to normalize wound granulation and scar tissue formation, was quantified in vitro. The presence of basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta) and hemodialysate (HD) increased the number of cells in the denuded area, i.e., in the "wound space" of an artificially ruptured monolayer of LM-fibroblasts (mouse lung fibroblasts). When cell proliferation was blocked with Mitomycin C, in the first 24 h all factors, i.e., bFGF, PDGF, TGF-beta and HD, promoted cell migration, whereas after 48 h it became obvious that each factor stimulated both migration and proliferation, each in a characteristic way. The effects were significant and more distinct after 48 h, following the order: PDGF (46%) approximately bFGF (87%) > HD (45%) approximately TGF-beta (40%) > control (62%). The relative contributions of migration after inhibiting proliferation are given in brackets. The modulatory activity of HD was localized in its hydrophilic fraction. It was destroyed by acid hydrolysis. Furthermore, this activity could be blocked by protamine sulfate, an inhibitor blocking peptide growth factor receptor binding.

Transient effect of epidermal growth factor on the motility of an immortalized mammary epithelial cell line

The effects of growth factors on epithelial cell motility and dispersion have been examined on an immortalized human mammary epithelial cell line, the 184A1 nontumorigenic cell line. Among all the molecules tested, epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) were demonstrated to stimulate an increase in mammary epithelial cell motility and wound closure that was associated with a morphological transformation of the cells and was accompanied by modifications in cell-cell and cell-substrate adhesion systems. The EGF-induced increase in cell motility and monolayer wound closure occurred over a 24 hour period and was not dependent on an increase in cell number. The effect of EGF was abolished by inhibiting alpha 2 integrins with specific antibodies, indicating that part of the mechanism for the increase in cell motility and accelerated wound closure depends on alpha 2 integrin functional expression. After 72 hours of exposure to EGF, the EGF-induced alterations in cell morphology, motility and cell adhesion systems underwent a spontaneous reversion that was correlated with a 10-fold reduction in the number of EGF receptors. The ability to regulate the scattering response induced by growth factors might be an important feature distinguishing normal epithelial cells from their tumoral counterparts.

In vitro large-wound re-endothelialization. Inhibition of centrosome redistribution by transient inhibition of transcription after wounding prevents rapid repair

Rapid, efficient re-endothelialization of large wounds is characterized by a specific sequence of cytoskeletal events that occur after wounding. Wounds 1.5 mm wide were created down the middle of confluent porcine aortic endothelial monolayers to study regulation of repair. The wounded cultures were incubated for short periods with cycloheximide or actinomycin D to test the hypothesis that transient inhibition of translation and transcription at the time of wounding disrupts rapid repair by interfering with centrosome redistribution to the front of the cell, an early event associated with cell migration. Although centrosome reorientation did not occur when protein synthesis was inhibited with 20 micrograms/mL cycloheximide for 1 hour before and for up to 4 hours after wounding, reorientation did occur by 2 hours after cycloheximide was washed out. The times taken for the wound to close for cycloheximide-treated and control cells did not differ (60 +/- 1.1 vs 60 +/- 0.8 hours). When transcription was inhibited with 0.25 micrograms/mL actinomycin D for 1 hour before and for 1 hour after wounding, re-endothelialization was dramatically reduced. The time taken for the wound to close was almost five times longer (288 +/- 5.3 hours) than for control cells. The cells moved very slowly, maintaining a flattened, spread-out shape, as opposed to being elongated. The centrosomes did not reorient to the front of the cell throughout the entire period. However, addition of actinomycin D for 2 hours when centrosomes had already moved to the front of the cells (4 hours after wounding) did not reduce subsequent wound repair (60 +/- 1.3 hours). This study supports our hypothesis that centrosome redistribution is essential for efficient wound repair and suggests that redistribution is regulated by transcription of essential gene(s) that is induced immediately after wounding by an unknown short-lived signal. Two possible signals are the loss of cell contact and/or a soluble substance released from the cells at the time of wounding. When the signal is unable to induce transcription, dysfunctional repair occurs by a very slow centrosome-independent process.

Centrosome reorientation in regenerating endothelial monolayers requires bFGF

Monolayers of endothelial cells respond to physical denudation with a characteristic sequence of lamellipodia extrusion, cell migration, and cell proliferation. Basic fibroblast growth factor (bFGF) has been implicated as a necessary component of this process: addition of exogenous bFGF enhances monolayer regeneration both in vitro and in vivo, and monolayer regeneration can be inhibited in vitro by treatment with neutralizing antibodies raised against bFGF. Centrosome reorientation from a random location to one preferentially situated between the nucleus and the denudation edge has been postulated as a mechanism essential for cell polarization and subsequent migration. This present study examined the effects of a polyclonal antibody to bFGF and suramin on monolayer regeneration, actin microfilament staining, and centrosome orientation at the wound edge of partially denuded bovine large vessel endothelial monolayers. Treatment with anti-bFGF or suramin abolished monolayer repair in these cultures. Cells at the denudation edge showed altered actin staining patterns and reduced lamellipodia extrusion, and there was complete inhibition of centrosome reorientation in treated cultures. Monolayer repair and centrosome reorientation could be restored by addition of exogenous bFGF in antibody but not suramin treated cultures. Recent evidence suggests that preferential centrosome location in migrating cells may be a consequence of lamellipodia protrusion and cell spreading, rather than an indication of cell polarization. However, these results indicate that agents which interfere with bFGF availability prevent endothelial monolayer regeneration via mechanisms involving cell spreading and/or centrosome reorientation.

Pathophysiological mechanisms for restenosis following coronary angioplasty: possible preventive alternatives

Restenosis after successful percutaneous transluminal coronary angioplasty (PTCA) remains an unsolved medical problem. The search for the underlying pathophysiological mechanisms have identified intimal proliferation of smooth muscle cells (SMC) to be the prevailing cause of late restenosis, with endothelial cells (EC) and platelets being important participators in the process. According to the most accepted present theory, SMC would be stimulated to migrate and proliferate shortly after the angioplasty by the release of growth factors from injured EC and accumulated platelets. However, clinical trials of agents interfering with these mechanisms have not significantly diminished the rate of restenosis, which suggest both that our knowledge of the process is incomplete, and that new ways of administering the agents may be required.

Influence of mitomycin C on endothelial monolayer regeneration in vitro

This study examines the effect of Mitomycin C, a fungal toxin which inhibits DNA synthesis, on the regeneration of partially denuded large vessel endothelium in vitro. Monolayers of bovine pulmonary artery endothelial cells were treated with Mitomycin C prior to or immediately following partial denudation and were incubated in the continuing presence of Mitomycin C; the effects of this treatment on monolayer repair, cell proliferation, and other aspects of endothelial phenotype were monitored. Cell proliferation, DNA, RNA, and protein synthesis were all reduced in a dose dependent manner in treated cultures. Incubation with Mitomycin C for 48 h or longer resulted in reduced cell spreading, and rounding up and loss of cells from both intact and partially denuded cultures. Effects were less severe with lower doses and shorter incubation times. However, significant reductions in monolayer regeneration occurred within 8 h of incubation, sufficiently early to suggest that Mitomycin C may affect aspects of the regeneration process independent of cell proliferation. Polarization/spreading of cells at the denudation edge was monitored by fluorescence staining for golgi with C5-DMB-ceramide, and for centrioles with antibodies to tubulin. Centrioles and golgi rapidly reoriented to a location at the putative leading edge of control cultures. Mitomycin C treatment had no effect on centriole reorientation, but caused a significant delay in golgi localization. These results suggest that Mitomycin C inhibits endothelial monolayer regeneration by mechanisms independent of cell proliferation and DNA synthesis, perhaps by interfering with cell spreading or translocation at the wound edge.