Endothelial Cell Shape Change Research Articles

Alterations in human endothelial cell morphology, proliferation and function by a macrophage-derived factor

Changes in endothelial cell (EC) morphology occur at sites of physiological lymphocyte traffic and in areas of chronic inflammation. Previous studies have shown that EC shape changes also occur in vitro following exposure of EC monolayers to peripheral blood mononuclear cell (PBMC)-derived conditioned media (CM). In the present study, quantitative image analysis is used to define the cell of origin of the elongating factor(s), to examine changes in EC proliferation and function accompanying PBMC-induced human EC elongation and to identify the active PBMC-derived products responsible for this elongation. By separating mononuclear cells into subpopulations (macrophages, B cells and T cells) and adding conditioned media derived from these subpopulations to cultured ECs, the macrophage (M phi) is shown to be the primary cell of origin of the elongating factor(s). Furthermore, EC elongation is accompanied by both a dose-dependent decrease in cellular proliferation and an increase in prostacyclin production. These findings suggest that PBMC-induced changes in EC morphology may be associated with a shift from a proliferative state to a more secretory phase of the EC cycle. Finally, using recombinant factors it is shown that TNF alpha acting in combination with IL-1 may be the active PBMC-derived products which contribute to EC elongation.

Fluid shear stress differentially modulates expression of genes encoding basic fibroblast growth factor and platelet-derived growth factor B chain in vascular endothelium.

Fluid shear stress has been shown to be an important regulator of vascular structure and function through its effect on the endothelial cell. We have explored the effect of shear stress on the expression of the heparin-binding growth factors platelet-derived growth factor B chain (PDGF-B) and basic fibroblast growth factor (bFGF) in bovine aortic endothelial cells using a purpose-built cone-plate viscometer. Using morphometric analysis, we have mimicked the endothelial cell shape changes encountered in vivo in response to shear stress and correlated these with changes in gene expression. Steady laminar shear stress of 15 and 36 dyn/cm2 both resulted in endothelial cell shape change, but the higher shear stress induced greater and more uniform alignment in the direction of flow and nuclear protrusion after 24 h. Steady laminar shear stress of both 15 and 36 dyn/cm2 induced a significant 3.9- and 4.2-fold decrease, respectively, in PDGF-B mRNA at 9 h. In contrast, steady laminar shear of 15 dyn/cm2 induced a mild and transient 1.5-fold increase in bFGF mRNA while shear of 36 dyn/cm2 induced a significant 4.8-fold increase at 6 h of shear which remained at 2.9-fold at 9 h. Pulsatile and turbulent shear stress showed the same effect as steady laminar shear stress (all at 15 dyn/cm2 time-average magnitude) on PDGF-B and bFGF mRNA content. Cyclic stretch (20% strain, 20/min) of cells grown on silicone substrate did not significantly affect either PDGF-B or bFGF mRNA levels. These results suggest that expression of each peptide growth factor gene is differentially regulated by fluid shear stress in the vascular endothelial cell. These results may have implications on vascular structure and function in response to hemodynamic forces and present a model for the study of transduction of mechanical stimuli into altered gene expression.

Histamine, actin-gelsolin binding, and polyphosphoinositides in human umbilical vein endothelial cells.

Histamine activates inositol phospholipid metabolism, increases calcium, and causes a change in shape of human umbilical vein endothelial (HUVE) cells. Changes in endothelial cell shape are determined, in part, by changes in the actin cytoskeleton. Gelsolin is an actin-binding protein with the potential to alter the actin cytoskeleton in response to changes in cell calcium and/or changes in polyphosphoinositides. Therefore, we examined the interactions of actin and gelsolin in HUVE cells in which inositol phospholipid metabolism was activated with histamine. In HUVE cells exposed to histamine we estimated actin-gelsolin binding by quantitating actin and gelsolin, immunoprecipitated with anti-gelsolin Sepharose. We estimated the relative amount of filamentous actin in the histamine-exposed HUVE cells by quantitating the amount of actin that was Triton soluble. We also measured the amount of phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) in the HUVE cells before and after exposure to histamine. We found that histamine decreased the amount of actin that was immunoprecipitated with gelsolin, decreased the fraction of cell actin that was Triton soluble, and increased PIP and PIP2. These results demonstrate that histamine promotes actin filament formation in HUVE cells and that histamine-mediated changes in actin-gelsolin binding in these cells are better predicted by changes in polyphosphoinositides than by increases in cell calcium.

Electrical method for detection of endothelial cell shape change in real time: assessment of endothelial barrier function.

We have developed an electrical method to study endothelial cell shape changes in real time in order to examine the mechanisms of alterations in the endothelial barrier function. Endothelial shape changes were quantified by using a monolayer of endothelial cells grown on a small (10(-3) cm2) evaporated gold electrode and measuring the changes in electrical impedance. Bovine pulmonary microvessel endothelial cells and bovine pulmonary artery endothelial cells were used to study the effects of alpha-thrombin on cell-shape dynamics by the impedance measurement. alpha-Thrombin produced a dose-dependent decrease in impedance that occurred within 0.5 min in both cell types, indicative of retraction of endothelial cells and widening of interendothelial junctions because of "rounding up" of the cells. The alpha-thrombin-induced decrease in impedance persisted for approximately 2 hr, after which the value recovered to basal levels. Pretreatment of endothelial cells with the protein kinase C inhibitor, calphostin C, or with 8-bromoadenosine 3',5'-cyclic monophosphate prevented the decreased impedance, suggesting that the endothelial cell change is modulated by activation of second-messenger pathways. The alpha-thrombin-induced decrease in impedance was in agreement with the previously observed increases in transendothelial albumin permeability and evidence of formation of intercellular gaps after alpha-thrombin challenge. The impedance measurement may be a valuable in vitro method for the assessment of mechanisms of decreased endothelial barrier function occurring with inflammatory mediators. Since the rapidly occurring changes in endothelial cell shape in response to mediators such as thrombin are mediated activation of second-messenger pathways, the ability to monitor endothelial cell dynamics in real time may provide insights into the signal-transduction events mediating the increased endothelial permeability.

Physiological fluid shear stress causes downregulation of endothelin-1 mRNA in bovine aortic endothelium.

We report here that the level of endothelin-1 (ET-1) mRNA from bovine aortic endothelial cells grown in vitro is rapidly (within 1 h of exposure) and significantly (fivefold) decreased in response to fluid shear stress of physiological magnitude. The downregulation of ET-1 mRNA occurs in a dose-dependent manner that exhibits saturation above 15 dyn/cm2. The decrease is complete prior to detectable changes in endothelial cell shape and is maintained throughout and following alignment in the direction of blood flow. Peptide levels of ET-1 secreted into the media are also reduced in response to fluid shear stress. Cyclical stretch experiments demonstrated no changes in ET-1 mRNA, while increasing media viscosity with dextran showed that the downregulation is a specific response to shear stress and not to fluid velocity. Although both pulsatile and turbulent shear stress of equal time-average magnitude elicited the same decrease in ET-1 mRNA as steady laminar shear (15 dyn/cm2), low-frequency reversing shear stress did not result in any change. These results show that the magnitude as well as the dynamic character of fluid shear stress can modulate expression of ET-1 in vascular endothelium.

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<h3>ABSTRACT</h3> The formation of vascular tubes is driven by extensive changes in endothelial cell (EC) shape. Here, we have identified a novel role of the actin-binding protein, Marcksl1, in modulating the mechanical properties of EC cortex to regulate cell shape and vessel structure during angiogenesis. Increasing and depleting Marcksl1 expression level <i>in vivo</i> resulted in an increase and decrease, respectively, in EC size and the diameter of microvessels. Furthermore, endothelial overexpression of Marcksl1 induced ectopic blebbing on both apical and basal membranes, during and after lumen formation, that is suppressed by reduced blood flow. High resolution imaging revealed that Marcksl1 promotes the formation of linear actin bundles and decreases actin density at the EC cortex. Our findings demonstrate that a balanced network of linear and branched actin at the EC cortex is essential in conferring cortical integrity to resist the deforming forces of blood flow to regulate vessel structure.

Modification by some antagonists of the shape changes of venous endothelial cells in response to inflammatory agentsin vitro

Endothelial cells lining guinea pig inferior venae cavae change shape when exposed to histamine, bradykinin, A23187 or platelet-activating factor (PAF) in vitro. Pre-treatment of the endothelium with isoprenaline or quin 2 significantly reduced the shape changes produced in response to histamine, bradykinin and A23187, but not those to PAF. Since both isoprenaline and quin 2 may reduce the concentration of cytoplasmic Ca++, the former by raising cyclic AMP (cAMP) levels and the latter by acting as a Ca++ buffer, the results provide further evidence for the involvement of Ca++ in the responses of large vein endothelial cells to inflammatory agents in vitro. The effects of pre-treating the endothelium with the histamine receptor-blockers mepyramine (H1) or cimetidine (H2), or the bradykinin receptor-blockers des-arg9[leu8] bradykinin (B1) or des-arg[Hyp3, Thi5,8,D-Phe7] bradykinin (B2) suggest that the response to histamine is both H1 and H2 receptor-mediated, while the response to bradykinin is only B2 receptor-mediated.

Effects of PAF and PAF antagonists on the shape of venous endothelial cellsin vitro

Three platelet-activating factor (PAF) antagonists were tested for their ability to prevent or reduce PAF-induced shape changes of large vein endothelial cells in vitro. BN52021 had a significant protective action at concentrations of 1 microM and 0.1 microM, but at 100 microM had a damaging effect of its own. CV3988 (0.1 microM and 1 microM) and L652,731 (20 microM) did not reduce the responses to PAF, and at higher concentrations (CV3988 10 microM and 100 microM, L652,731 100 microM) both compounds alone caused significant changes of shape. BN52021 (0.1 microM) was also effective against leukotriene (LT) C4, at 1 microM against bradykinin and LTE4, and at 10 microM against LTD4 and the calcium ionophore A23187. BN52021 (10 microM) was ineffective against shape changes induced by histamine, prostaglandin (PG) E2 and lysophosphatidylcholine (LPC). Neither indomethacin (100 microM) nor verapamil (20 microM) altered the response to PAF. Using electron spin resonance (ESR) spectrometry it was shown that the damaging effects of LPC and CV3988 may be due partly to their detergent properties. It is suggested that the mechanism by which PAF alters the shape of large vein endothelial cells is primarily receptor mediated.

Mechanism of endothelial cell shape change in oxidant injury

Changes in endothelial cell morphology induced by neutrophil-generated hydrogen peroxide (H 2O 2) may account for the capillary leak of the adult respiratory distress syndrome (ARDS). The relationship of H 2O 2 effects on the concentration of intracellular Ca 2+([Ca 2+] i) and ATP to changes in microfilaments and microtubules, important determinants of cell shape, was examined. Bovine pulmonary artery endothelial cells were injured over a 2-hr time course with a range of H 2O 2 doses (0–20 m M). The higher concentrations of H 2O 2 consistently produced contraction and rounding of >50–75% of cells by 1–2 hr. The range of 1–20 m M H 2O 2 produced rapid, significant reductions in endothelial ATP levels over the time course of injury. Although there were significant increases in mean endothelial [Ca 2+] i in response to 5, 10, and 20 m M H 2O 2, 1 m MH 2O 2 did not affect the [Ca 2+] i. Fluorescence microscopy revealed that microfilament disruption occurred as ATP levels fell and preceded depolymerization of microtubules which developed after [Ca 2+] 1 approached 1 × 10 −6 M. H 2O 2 at 1 m M injury caused microfilament disruption but did not depolymerize microtubules. Microfilament disruption occurred without oxidant exposure, when ATP levels were reduced by glucose depletion and mitochondrial inhibition with oligomycin (650 n M). If a Ca 2+ ionophore, ionomycin (5 μ M), was then added, [Ca 2+] i rose to > 1 × 10 −6 M, microtubules fragmented and depolymerized, and cell contraction and rounding very similar to that induced by H 2O 2 occurred. These results suggest that endothelial cell dysfunction and capillary leak in ARDS may be due to H 2O 2-mediated changes in cellular ATP and [Ca 2+] i.

The effects of TMB-8 on the shape changes of vascular endothelial cells resulting from exposure to various inflammatory agents

Pre-treatment of the endothelial cells lining the guinea pig inferior vena cava with 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8) (10 microM) in vitro significantly reduced the shape changes resulting from subsequent exposure to platelet activating factor (PAF) (0.1 microM), calcium ionophore A23187 (10 microM), histamine (300 microM), bradykinin (2 microM), prostaglandin E2 (PGE2) (30 microM), or leukotrienes (LT) C4, D4 or E4 (1 microM). Since TMB-8 is an intracellular calcium antagonist, this provides evidence to support the suggestion that these inflammatory agents increase the concentration of intracellular calcium which brings about a contraction of the actin-myosin complex resulting in endothelial cell shape changes, and the formation of interendothelial cell gaps.

The effects of indomethacin and verapamil on the shape changes of vascular endothelial cells resulting from exposure to various inflammatory agents.

Histamine (300 microM), bradykinin (2 microM), prostaglandin E2 (PGE2) (30 microM), or the leukotrienes (LT) C4 and E4 (1 microM) but not D4 (1 microM) applied in vitro have been shown to change the shape of endothelial cells lining the guinea pig isolated thoracic inferior vena cava. All caused the formation of inter-endothelial cell gaps. Pre-treatment with either indomethacin (100 microM) or verapamil (20 microM) reduced the effects of these compounds. It is suggested that indomethacin and verapamil act by reducing the amount of intracellular calcium available for the shortening of contractile protein filaments within endothelial cells.

Corneal endothelial polymegathism after the extended wear of rigid gas-permeable contact lenses.

To determine if there are any corneal endothelial cell size and shape changes in subjects wearing rigid gas-permeable contact lenses for cosmetic extended wear, six unadapted lens wearers were fitted using four different lens materials. Each subject wore one lens extended-wear and the other daily-wear for 3 months. Before lens wear and after 3 months, noncontact endothelial photographs were taken. Cell tracings were analyzed by a digitizing computer. This study showed significant endothelial polymegathism, an increase in maximum cell area to minimum cell area, and a significant decrease in percent frequency of hexagonal cells in the extended-wear eyes. There existed in these subjects a significant correlation between changes in cell size (polymegathism) and cell shape (pleomorphism).

Quantitative studies of human monokine-induced endothelial cell elongation.

Leucocyte-endothelial cell interactions are important in the inflammatory response. In this study, the effect of peripheral blood mononuclear cell (PBMC) products on endothelial cell (EC) shape was examined and quantified. PBMC were obtained from normal donors by Ficoll-Hypaque separation of heparinized whole blood and cultured for 72 hr in media containing 10% fetal calf serum with and without concanavalin A (Con A). Media conditioned by PBMC or control, nonconditioned media were then added to preconfluent, first passage EC cultures derived from human umbilical veins. Conditioned media from Con A-stimulated PBMC resulted in a dose-dependent, marked elongation and whorling of cultured EC. The minimum effective concentration found to elicit a response was 1.25%, with a maximum response occurring at 10%. Quantitative morphometric analyses of treated EC indicated that the elongation was highly significant (p less than 0.001) when compared to EC incubated with control, nonconditioned media. In addition, EC elongation was accompanied by a highly significant (p less than 0.001) increase in cell area. Although less dramatic, conditioned media from unstimulated PBMC also elicited a similar, significant dose-dependent change in EC shape. Significant changes in EC shape were evident within 6 hr and continued over the time course of the experiment (40 h). Cell shape changes were partially reversible at 18 h after removal of the PBMC-conditioned media and replacement with control, nonconditioned media. The change in EC morphology induced by a PBMC-derived factor(s) suggests a mechanism by which activated leucocytes may modulate cellular traffic at the blood-vessel wall interface.

Cationic neutrophil proteins increase transendothelial albumin movement.

Neutrophils play a role in the development of pulmonary edema in many models of the adult respiratory distress syndrome, but the mechanism of their action is not completely understood. We asked whether two neutrophil secretory products, human neutrophil cationic protein (NCP) and human neutrophil elastase (HNE), would nonenzymatically alter the movement of albumin across a cultured endothelial monolayer. Both enzymes were inactivated by heating before use. HNE was additionally enzymatically inactivated with a chloromethylketone oligopeptide (CMK) inhibitor and with alpha 1-proteinase inhibitor (alpha 1-PI). Heated NCP, heated HNE, and CMK-complexed HNE all increased transendothelial albumin transfer. The cation protamine also increased albumin transfer across the endothelium and this increase was blocked by heparin. Alpha 1-PI and fetal bovine serum also prevented the cationic proteins from increasing albumin transfer. Using the release of lactate dehydrogenase as a marker of cytotoxicity, heated HNE was toxic to endothelial cells, heated NCP had only minimal toxicity, and protamine had no toxicity. Changes in endothelial cell shape with gap formation was seen after exposure to both heated HNE and heated NCP. Both the cytotoxicity associated with heated HNE and the cell shape changes associated with heated NCP and heated HNE could be blocked by heparin. These results suggest that in addition to neutrophil proteases and reactive O2 molecules, neutrophil-derived cationic proteins can directly and nonenzymatically contribute to edema formation during acute inflammation.

Thrombin-induced increase in albumin permeability across the endothelium.

We studied the effect of thrombin on albumin permeability across the endothelial monolayer in vitro. Bovine pulmonary artery endothelial cells were grown on micropore membranes. Morphologic analysis confirmed the presence of a confluent monolayer with interendothelial junctions. Albumin permeability was measured by the clearance of 125I-albumin across the endothelial monolayer. The control 125I-albumin clearance was 0.273 +/- 0.02 microliter/min. The native enzyme, alpha-thrombin (10(-6) to 10(-10) M), added to the luminal side of the endothelium produced concentration-dependent increases in albumin clearance (maximum clearance of 0.586 +/- 0.08 microliter/min at 10(-6) M). Gamma (gamma) thrombin (10(-6) M and 10(-8) M), which lacks the fibrinogen recognition site, also produced a concentration-dependent increase in albumin clearance similar to that observed with alpha-thrombin. Moreover, the two proteolytically inactive forms of the native enzyme, i-Pr2 P-alpha-thrombin and D-Phe-Pro-Arg-CH2-alpha-thrombin, increased the 125I-albumin clearance (0.610 +/- 0.09 microliter/min and 0.609 +/- 0.02 microliter/min for i-Pr2 P-alpha-thrombin and D-Phe-Pro-Arg-CH2-alpha-thrombin at 10(-6) M, respectively). Since the modified forms of thrombin lack the fibrinogen recognition and active serine protease sites, the results indicate that neither site is required for increased albumin permeability. The increase in albumin clearance with alpha-thrombin was not secondary to endothelial cell lysis because lactate dehydrogenase concentration in the medium following thrombin was not significantly different from baseline values. There was also no morphological evidence of cell lysis. Moreover, the increase in 125I-albumin clearance induced by alpha-thrombin was reversible by washing thrombin from the endothelium. The basis for the increased albumin permeability following the addition of alpha-thrombin appears to be a reversible change in endothelial cell shape with formation of intercellular gaps.

Reversible Oxidant-Induced Increases in Albumin Transfer Across Cultured Endothelium: Alterations in Cell Shape and Calcium Homeostasis

To determine whether reactive oxygen molecules could directly and reversibly increase the transfer of albumin across an endothelial barrier, we measured albumin transfer across monolayers of endothelium cultured on micropore filters before and after exposure to xanthine and xanthine oxidase. Xanthine and xanthine oxidase increased endothelial albumin transfer in a dose-dependent fashion. Parallel phase contrast and fluorescence microscopy demonstrated retraction of adjacent cells from one another and disruption of the actin filaments. The oxidant-induced increases in albumin transfer and changes in cell shape were reversed by removing xanthine oxidase and then incubating the monolayers for 3 1/2 hours in tissue culture media enriched with fetal bovine serum. However, incubation in tissue culture media without serum resulted in progressive injury and cell death. Hence, the brief exposure to oxidants initiated a progressive injury process that was reversed by incubation in serum. Because intracellular and extracellular calcium are important determinants of cell shape, and because some oxidized membrane lipids act as calcium ionophores, we asked whether oxidants altered endothelial calcium homeostasis. Xanthine-xanthine oxidase increased release of 45Ca++ from preloaded cells. The calcium antagonist lanthanum chloride prevented xanthine-xanthine oxidase increases in endothelial albumin transfer and prevented the changes in cell shape; chelation of extracellular calcium inhibited lysis of endothelium by xanthine-xanthine oxidase; and the calcium ionophore A23187 increased endothelial albumin transfer and mimicked the oxidant-induced changes in cell shape. Lanthanum chloride inhibited these effects of A23187. These data suggest that oxygen radicals can reversibly increase endothelial permeability to macromolecules, that this is associated with reversible changes in endothelial cell shape and actin filaments, and that the changes in cell shape are related to oxidant-induced changes in endothelial calcium homeostasis.

Reversible oxidant-induced increases in albumin transfer across cultured endothelium: alterations in cell shape and calcium homeostasis

To determine whether reactive oxygen molecules could directly and reversibly increase the transfer of albumin across an endothelial barrier, we measured albumin transfer across monolayers of endothelium cultured on micropore filters before and after exposure to xanthine and xanthine oxidase. Xanthine and xanthine oxidase increased endothelial albumin transfer in a dose-dependent fashion. Parallel phase contrast and fluorescence microscopy demonstrated retraction of adjacent cells from one another and disruption of the actin filaments. The oxidant- induced increases in albumin transfer and changes in cell shape were reversed by removing xanthine oxidase and then incubating the monolayers for 3 1/2 hours in tissue culture media enriched with fetal bovine serum. However, incubation in tissue culture media without serum resulted in progressive injury and cell death. Hence, the brief exposure to oxidants initiated a progressive injury process that was reversed by incubation in serum. Because intracellular and extracellular calcium are important determinants of cell shape, and because some oxidized membrane lipids act as calcium ionophores, we asked whether oxidants altered endothelial calcium homeostasis. Xanthine-xanthine oxidase increased release of 45Ca++ from preloaded cells. The calcium antagonist lanthanum chloride prevented xanthine- xanthine oxidase increases in endothelial albumin transfer and prevented the changes in cell shape; chelation of extracellular calcium inhibited lysis of endothelium by xanthine-xanthine oxidase; and the calcium ionophore A23187 increased endothelial albumin transfer and mimicked the oxidant-induced changes in cell shape. Lanthanum chloride inhibited these effects of A23187. These data suggest that oxygen radicals can reversibly increase endothelial permeability to macromolecules, that this is associated with reversible changes in endothelial cell shape and actin filaments, and that the changes in cell shape are related to oxidant-induced changes in endothelial calcium homeostasis.

The effect of thrombin on fibronectin in cultured human endothelial cells

Cultures of human endothelial cells (EC) incubated for periods up to 24 h with highly purified thrombin (2 NIH u/ml) contained considerably less cell-associated fibronectin fibrils than corresponding controls. The loss of fibronectin fibrils was evident after 4 h and was accompanied by a 2–3 fold increase in the concentration of fibronectin in the incubation medium. Hirudin inhibited the effects of thrombin. Thrombin also induced characteristic shape changes of EC. These shape changes were reversible within a 4–6 h period and could not be reinvoked by new additions of thrombin. Thus, structural refractoriness to thrombin coincided temporally with a period when EC-associated fibronectin fibrils were markedly reduced.