Morphological alterations in endothelial cells from human aorta and umbilical vein induced by forskolin and phorbol 12-myristate 13-acetate: a synergistic action of adenylate cyclase and protein kinase C activators

Local Accumulation of Lymphocytes in the Intima of Human Aorta Is Associated with Giant Multinucleated Endothelial Cells: Possible Explanation for Mosaicism of Atherosclerosis

Distribution of different types of atherosclerotic lesions in the arterial wall is not diffuse, but is characterized by mosaicism. The causes of such distribution remain to be established. At the early stages of atherogenesis, low-density lipoprotein (LDL) particles and immune cells penetrate into the intimal layer of the arterial wall through the endothelium. In adult humans, the luminal surface of the arterial wall is a heterogeneous monolayer of cells with varying morphology including typical endothelial cells (ECs) and multinucleated variant endothelial cells (MVECs). We hypothesized that distribution of MVECs in the endothelial monolayer can be related to the distribution pattern of early atherosclerotic lesions. We obtained en face preparations of intact adult (22–59 years old) aortic wall sections that allowed us to study the endothelial monolayer and the subendothelial layer. We compared the distribution of MVECs in the endothelial monolayer with the localization of early atherosclerotic lesions in the subendothelial layer, which were characterized by lipid accumulation and immune cell recruitment. In primary culture, MVECs demonstrated increased phagocytic activity compared to mononuclear ECs. Moreover, we have shown that unaffected aortic intima contained associates formed as a result of aggregation and/or fusion of LDL particles that are non-randomly distributed. This indicated that MVECs may be involved in the accumulation of LDL in the subendothelial layer through increased transcytosis. Interaction of LDL with subendothelial cells of human aorta in primary culture increased their adhesive properties toward circulating immune cells. Study of unaffected aortic intima revealed non-random distribution of leukocytes in the subendothelial layer and increased localization of CD45+ leukocytes in the subendothelial layer adjacent to MVECs. Together, our observations indicate that MVECs may be responsible for the distribution of atherosclerotic lesions in the arterial wall by participating in LDL internalization and immune cell recruitment.

Prolonged activation of cAMP signaling leads to endothelial barrier disruption via transcriptional repression of RRAS

The increase in cAMP levels in endothelial cells triggers cellular signaling to alter vascular permeability. It is generally considered that cAMP signaling stabilizes the endothelial barrier function and reduces permeability. However, previous studies have only examined the permeability shortly after cAMP elevation and thus have only investigated acute responses. Because cAMP is a key regulator of gene expression, elevated cAMP may have a delayed but profound impact on the endothelial permeability by altering the expression of the genes that are vital for the vessel wall stability. The small guanosine triphosphate hydrolase Ras-related protein (R-Ras) stabilizes VE-cadherin clustering and enhances endothelial barrier function, thereby stabilizing the integrity of blood vessel wall. Here we show that cAMP controls endothelial permeability through RRAS gene regulation. The prolonged cAMP elevation transcriptionally repressed RRAS in endothelial cells via a cAMP response element-binding protein (CREB) 3-dependent mechanism and significantly disrupted the adherens junction. These effects resulted in a marked increase of endothelial permeability that was reversed by R-Ras transduction. Furthermore, cAMP elevation in the endothelium by prostaglandin E2 or phosphodiesterase type 4 inhibition caused plasma leakage from intact microvessels in mouse skin. Our study demonstrated that, contrary to the widely accepted notion, cAMP elevation in endothelial cells ultimately increases vascular permeability, and the cAMP-dependent RRAS repression critically contributes to this effect.-Perrot, C. Y., Sawada, J., Komatsu, M. Prolonged activation of cyclic AMP signaling leads to endothelial barrier disruption via transcriptional repression of RRAS.

p21-Activated Kinase 2 Regulates Endothelial Development and Function through the Bmk1/Erk5 Pathway

p21-activated kinases (Paks) have been shown to regulate cytoskeleton rearrangements, cell proliferation, attachment, and migration in a variety of cellular contexts, including endothelial cells. However, the role of endothelial Pak in embryo development has not been reported, and currently, there is no consensus on the endothelial function of individual Pak isoforms, in particular p21-activated kinase 2 (Pak2), the main Pak isoform expressed in endothelial cells. In this work, we employ genetic and molecular studies that show that Pak2, but not Pak1, is a critical mediator of development and maintenance of endothelial cell function. Endothelial depletion of Pak2 leads to early embryo lethality due to flawed blood vessel formation in the embryo body and yolk sac. In adult endothelial cells, Pak2 depletion leads to severe apoptosis and acute angiogenesis defects, and in adult mice, endothelial Pak2 deletion leads to increased vascular permeability. Furthermore, ubiquitous Pak2 deletion is lethal in adult mice. We show that many of these defects are mediated through a newly unveiled Pak2/Bmk1 pathway. Our results demonstrate that endothelial Pak2 is essential during embryogenesis and also for adult blood vessel maintenance, and they also pinpoint the Bmk1/Erk5 pathway as a critical mediator of endothelial Pak2 signaling.

Role of vitamin C in the function of the vascular endothelium

SIGNIFICANCE

Vitamin C, or ascorbic acid, has long been known to participate in several important functions in the vascular bed in support of endothelial cells. These functions include increasing the synthesis and deposition of type IV collagen in the basement membrane, stimulating endothelial proliferation, inhibiting apoptosis, scavenging radical species, and sparing endothelial cell-derived nitric oxide to help modulate blood flow. Although ascorbate may not be able to reverse inflammatory vascular diseases such as atherosclerosis, it may well play a role in preventing the endothelial dysfunction that is the earliest sign of many such diseases.

RECENT ADVANCES

Beyond simply preventing scurvy, evidence is mounting that ascorbate is required for optimal function of many dioxygenase enzymes in addition to those involved in collagen synthesis. Several of these enzymes regulate the transcription of proteins involved in endothelial function, proliferation, and survival, including hypoxia-inducible factor-1α and histone and DNA demethylases. More recently, ascorbate has been found to acutely tighten the endothelial permeability barrier and, thus, may modulate access of ascorbate and other molecules into tissues and organs.

CRITICAL ISSUES

The issue of the optimal cellular content of ascorbate remains unresolved, but it appears that low millimolar ascorbate concentrations are normal in most animal tissues, in human leukocytes, and probably in the endothelium. Although there may be little benefit of increasing near maximal cellular ascorbate concentrations in normal people, many diseases and conditions have either systemic or localized cellular ascorbate deficiency as a cause for endothelial dysfunction, including early atherosclerosis, sepsis, smoking, and diabetes.

FUTURE DIRECTIONS

A key focus for future studies of ascorbate and the vascular endothelium will likely be to determine the mechanisms and clinical relevance of ascorbate effects on endothelial function, permeability, and survival in diseases that cause endothelial dysfunction.

Glycoproteomic analysis of the secretome of human endothelial cells

Previous proteomics studies have partially unraveled the complexity of endothelial protein secretion but have not investigated glycosylation, a key modification of secreted and membrane proteins for cell communication. In this study, human umbilical vein endothelial cells were kept in serum-free medium before activation by phorbol-12-myristate-13 acetate, a commonly used secretagogue that induces exocytosis of endothelial vesicles. In addition to 123 secreted proteins, the secretome was particularly rich in membrane proteins. Glycopeptides were enriched by zwitterionic hydrophilic interaction liquid chromatography resins and were either treated with PNGase F and H₂¹⁸O or directly analyzed using a recently developed workflow combining higher-energy C-trap dissociation (HCD) with electron-transfer dissociation (ETD) for a hybrid linear ion trap–orbitrap mass spectrometer. After deglycosylation with PNGase F in the presence of H₂¹⁸O, 123 unique peptides displayed ¹⁸O-deamidation of asparagine, corresponding to 86 proteins with a total of 121 glycosylation sites. Direct glycopeptide analysis via HCD-ETD identified 131 glycopeptides from 59 proteins and 118 glycosylation sites, of which 41 were known, 51 were predicted, and 26 were novel. Two methods were compared: alternating HCD-ETD and HCD-product-dependent ETD. The former detected predominantly high-intensity, multiply charged glycopeptides, whereas the latter preferentially selected precursors with complex/hybrid glycans for fragmentation. Validation was performed by means of glycoprotein enrichment and analysis of the input, the flow-through, and the bound fraction. This study represents the most comprehensive characterization of endothelial protein secretion to date and demonstrates the potential of new HCD-ETD workflows for determining the glycosylation status of complex biological samples.

TNF-α and TGF-β synergistically stimulate elongation of human endothelial cells without transdifferentiation to smooth muscle cell phenotype

We earlier reported synergy between tumor necrosis factor-α (TNF-α) and transforming growth factor-β1 (TGF-β1) for apoptosis in human umbilical vein endothelium (HUVEC). Here, we study morphological change by circularity measurement of HUVEC surviving this cytokine induced synergistic apoptosis. Contrasting with reports by others studying bovine endothelium, HUVEC did not change morphology in response to TGF-β1. TNF-α markedly elongated cells (p<0.001) and this further increased with combination of the two cytokines (p<0.001), while elongation was accompanied by increased actin stress fibres. Transdifferentiation of HUVEC to a smooth muscle cell phenotype as reported elsewhere was excluded in the current study.

Membrane and cytoplasmic marker exchange between malignant neoplastic cells and fibroblasts via intermittent contact: increased tumour cell diversity independent of genetic change

We previously demonstrated that human osteosarcoma cells (SAOS-2) induce contact-dependent apoptosis in endothelium, and expected similar apoptosis in human gingival fibroblasts (h-GF) using SAOS-2 alkaline phosphatase (AP) to identify cells. However, h-GF apoptosis did not occur, despite reduction in AP-negative h-GF number (p < 0.01) and enhancement of this by h-GF TNFα pretreatment (p < 0.01). We suggest that TNFα-enhanced transfer of membrane AP from SAOS-2 to h-GF would explain these data. This idea was investigated using fluorescence prelabelled cells and confocal laser scanning microscopy. Co-cultures of membrane-labelled h-GF (marker-DiO) and SAOS-2 (marker-DiD) generated dual-labelled cells, primarily at the expense of single labelled h-GF (p < 0.001), suggesting predominant membrane transfer from SAOS-2 to h-GF. However, opposite directional transfer predominated when membrane labels were reversed; SAOS-2 further expressed green fluorescent protein (GFP) in cytoplasm and nuclei, and h-GF additionally bore nuclear label (Syto59) (p < 0.001). Cytoplasmic exchange was investigated using h-GF prelabelled with cytoplasmic DDAO-SE and nuclear Syto59, co-cultured with SAOS-2 expressing GFP in cytoplasm and nuclei, and predominant cytoplasmic marker transferred from h-GF to SAOS-2 (p < 0.05). Pretreating h-GF with TNFα increased exchange of membrane markers (p < 0.04) but did not affect either cell surface area profile or circularity. Dual-labelled cells had a morphological phenotype differing from SAOS-2 and h-GF (p < 0.001). Time-lapse microscopy revealed extensive migration of SAOS-2 and cell process contact with h-GF, with the appearance of SAOS-2 indulging in 'cellular sipping' from h-GF. Similar exchange of membrane was seen between h-GF and with other cell lines (melanoma MeIRMu, NM39, WMM175, MM200-B12; osteosarcoma U20S; ovarian carcinoma cells PE01, PE04 and COLO316), while cytoplasmic sharing was also seen in all cell lines other than U20S. We suggest that in some neoplasms, cellular sipping may contribute to phenotypic change and the generation of diverse tumour cell populations independent of genetic change, raising the possibility of a role in tumour progression.

Transfer of ascorbic acid across the vascular endothelium: mechanism and self-regulation

To determine how ascorbic acid moves from the bloodstream into tissues, we assessed transfer of the vitamin across the barrier generated by EA.hy926 endothelial cells when these were cultured on semipermeable filter supports. Ascorbate transfer from the luminal to the abluminal compartment was time dependent, inhibited by anion channel blockers and by activation of protein kinase A, but was increased by thrombin. Ascorbate transfer occurred by a paracellular route, since it did not correlate with intracellular ascorbate contents and was not rectified or saturable. Nonetheless, intracellular ascorbate inhibited the transfer of both ascorbate and radiolabeled inulin across the endothelial barrier. The increase in barrier function due to ascorbate was dependent on its intracellular concentration, significant by 15 min of incubation, prevented by the cytoskeletal inhibitor colchicine, associated with F-actin stress fiber formation, and not due to collagen deposition. These results show that ascorbate traverses the endothelial barrier by a paracellular route that is regulated by cell metabolism, ion channels, and ascorbate itself. Since the latter effect occurred over the physiological range of ascorbate plasma concentrations, it could reflect a role for the vitamin in control of endothelial barrier function in vivo.

Heat shock protein 90 inhibitors protect and restore pulmonary endothelial barrier function

Heat shock protein 90 (hsp90) inhibitors inactivate and/or degrade various client proteins, including many involved in inflammation. Increased vascular permeability is a hallmark of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Thus, we tested the hypothesis that hsp90 inhibitors may prevent and/or restore endothelial cell (EC) permeability after injury. Exposure of confluent bovine pulmonary arterial endothelial cell (BPAEC) monolayer to TGF-beta1, thrombin, bacterial lipopolysaccharide (LPS), or vascular endothelial growth factor (VEGF) increased BPAEC permeability, as revealed by decreased transendothelial electrical resistance (TER). Treatment of injured endothelium with hsp90 inhibitors completely restored TER of BPAEC. Similarly, preincubation of BPAEC with hsp90 inhibitors prevented the decline in TER induced by the exposure to thrombin, LPS, VEGF, or TGF-beta1. In addition, hsp90 inhibitors restored the EC barrier function after PMA or nocodazole-induced hyperpermeability. These effects of the hsp90 inhibitors were associated with the restoration of TGF-beta1- or nocodazole-induced decrease in VE-cadherin and beta-catenin expression at EC junctions. The protective effect of hsp90 inhibitors on TGF-beta1-induced hyperpermeability was critically dependent upon preservation of F-actin cytoskeleton and was associated with the inhibition of agonist-induced myosin light chain (MLC) and myosin phosphatase target subunit 1 (MYPT1) phosphorylation, F-actin stress fibers formation, microtubule disassembly, increase in hsp27 phosphorylation, and association of hsp90 with hsp27, but independent of p38MAPK activity. We conclude that hsp90 inhibitors exert barrier protective effects on BPAEC, at least in part, via inhibition of hsp27-mediated, agonist-induced cytoskeletal rearrangement, and therefore may have useful therapeutic value in ALI, ARDS, and other pulmonary inflammatory disease.

Detection of the centriole tyr- or acet-tubulin changes in endothelial cells treated with thrombin using microscopic immunocytochemistry

We used electron microscopic immunocytochemistry to examine the pattern of centriolar staining for tyrosinated or acetylated alpha-tubulin in endothelial cells during short-term incubation with thrombin. Endothelial cells isolated from human aorta (HAEC) and those isolated from umbilical vein (HUVEC) displayed an increase in the intensity of centriolar staining for acet-tubulin within 1 min after thrombin addition. A decrease in the intensity of centriolar staining for tyr-tubulin was detected in HUVEC within 1 min after thrombin addition, while in HAEC centriolar staining for tyr-tubulin became less intense only 5 min later. Mother and daughter centrioles of HUVEC cells displayed different intensity of immunostaining for acet-tubulin and showed no significant variation in the number of subdistal appendages after thrombin addition. Differently, HAEC cells had the same staining pattern of mother and daughter centrioles in both thrombin-untreated and thrombin-treated cultures. A sharp increase in the number of subdistal appendages of mother centriole occurred in HAEC within 5 min of incubation with thrombin. Our findings provided the direct evidence for centrosome involvement in the ligand-mediated signaling events and showed for the first time that ligand-dependent centrosome reorganization includes the centriole per se. Furthermore, based on our observations we would like to propose that MT-nucleating/anchoring properties of the centrosome are subject to rapid regulation by external signals such as thrombin.

Verge: a novel vascular early response gene

Vascular endothelium forms a continuous, semipermeable barrier that regulates the transvascular movement of hormones, macromolecules, and other solutes. Here, we describe a novel immediate early gene that is expressed selectively in vascular endothelial cells, verge (vascular early response gene). Verge protein includes an N-terminal region of approximately 70 amino acids with modest homology (approximately 30% identity) to Apolipoprotein L but is otherwise unique. Verge mRNA and protein are induced selectively in the endothelium of adult vasculature by electrical or chemical seizures. Verge expression appears to be responsive to local tissue conditions, because it is induced in the hemisphere ipsilateral to transient focal cerebral ischemia. In contrast to the transient expression in adult, Verge mRNA and protein are constitutively expressed at high levels in the endothelium of developing tissues (particularly heart) in association with angiogenesis. Verge mRNA is induced in cultured endothelial cells by defined growth factors and hypoxia. Verge protein is dramatically increased by cysteine proteinase inhibitors, suggesting rapid turnover, and is localized to focal regions near the periphery of the cells. Endothelial cell lines that stably express Verge form monolayers that show enhanced permeability in response to activation of protein kinase C by phorbol esters. This response is accompanied by reorganization of the actin cytoskeleton and the formation of paracellular gaps. These studies suggest that Verge functions as a dynamic regulator of endothelial cell signaling and vascular function.

The role of cytoskeleton in cell changes under condition of simulated microgravity

Single cells and cell culture are very good model for estimation of primary effects of gravitational changes. It is suggested that cell cytoskeleton plays a key role in mechanisms of adaptation to mechanical influences including gravitational ones. Our results demonstrated that cultured cells of human vascular endothelium (correction of endotheliun) are highly sensitive to hypogravity (clinorotation) and respond by significant decrease of cell proliferative activity. Simultaneously it was noted that the formation of confluent monolayer appeared early in cultures exposed to simulated microgravity due to accelerated cells spreading. Long-term hypogravity (several hours or days) leads to significant changes of cell cytoskeleton revealed as microfilament thinning and their redistribution within cell. Such changes were observed only in monolayer cells and not in cell suspensions. Gravitational forces as known to be modificators of cell adhesive ability and determine their mobility. Hypogravity environment stimulated endothelial cell migration in culture: 24-48 hrs pre-exposition to hypogravity significantly increased endothelial cell migration resulting in 2-3-fold acceleration of mechanically injured monolayer repair. Obtained results suggest that the effects of hypogravity on cultured human endothelial cells are, possibly, associated with protein kinase C and/or adenylate cyclase activity and are accompanied by noticeable functional cell changes.

Induced cytoskeletal changes in bovine pulmonary artery endothelial cells by resveratrol and the accompanying modified responses to arterial shear stress

BACKGROUND

Atherosclerosis and coronary heart disease (CHD) are significant contributors to morbidity and mortality in developed countries. A noted exception is the low mortality of CHD in France, particularly the southwest region. This phenomenon, commonly referred to as the French paradox, may be associated with high consumption of red wine. We investigate whether the cardioprotective activity of red wine may involve the grape skin-derived polyphenol, resveratrol. We further test the possibility that resveratrol acts by modulating structural and functional changes in endothelial cells lining the blood vessel wall.

RESULTS

Bovine pulmonary artery endothelial cells (BPAEC) were incubated with resveratrol, with and without concurrent exposure to simulated arterial shear stress. Resveratrol significantly affected proliferation and shape of BPAEC; growth was suppressed and cells became elongated, based on morphologic analysis of rhodamine-conjugated phalloidin stained F-actin by confocal microscopy. Using selective signaling inhibitors, we showed that the resveratrol-induced cellular phenotype was dependent on intracellular calcium and tyrosine kinase activities, and assembly of actin microfilaments and microtubules, but was unrelated to PKC activity. Exposure to simulated arterial flow revealed that, whereas controls cells easily detached from the culture support in a time-dependent manner, resulting in total cell loss after a 5 min challenge with simulated arterial flow conditions, a significant percentage of the treated cells remained attached to the cultured plastic coverslips under identical experimental conditions, suggesting that they adhered more strongly to the surface. Western blot analysis shows that whereas cells treated with 25 microM and 100 microM resveratrol had no change in total ERK1/2, treatment did result in an increase in phosphorylated ERK1/2, which probably involved stabilization of the active enzyme. An increase in nitric oxide synthase expression was detected as early as 6 h and persisted for up to 4 days of treatment.

CONCLUSIONS

Results of our studies show that resveratrol interacts with endothelial cells in vitro to elicit morphological and structural changes; the observed changes support the interpretation that resveratrol acts as a cardioprotective agent.

Expression of cyclooxygenase 1 and 2 by human gastric endothelial cells

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase (COX) and cause gastric ulceration. NSAIDs also impair granulation tissue angiogenesis and healing of established gastric ulcers in humans. The mechanism whereby NSAIDs inhibit granulation tissue angiogenesis is unknown but may involve inhibition of either or both COX isoforms (COX-1 and COX-2).

AIMS

To investigate COX expression by human gastric endothelial (HuGE) cells during angiogenesis in vitro.

METHODS

COX-1 and COX-2 expression by HuGE cells was investigated by western blot analysis, indirect immunofluorescence, reverse transcriptase polymerase chain reaction, and measurement of prostaglandin E(2) synthesis. Plating onto basement membrane matrix and stimulation by phorbol ester were used as in vitro models of angiogenesis.

RESULTS

Under normal culture conditions (30% serum), HuGE cells expressed COX-1 and low levels of COX-2. COX-2 expression was induced in HuGE cells in both angiogenesis models. Prostaglandin E(2) production and tubular structure formation by HuGE cells on basement membrane matrix was significantly inhibited by a selective COX-2 inhibitor (NS-398).

CONCLUSION

Angiogenesis by HuGE cells in vitro was associated with induction of functional COX-2 expression. A selective COX-2 inhibitor significantly decreased HuGE cell angiogenesis on basement membrane matrix. Extrapolation of these data to human gastric ulcer angiogenesis in vivo suggests that selective COX-2 inhibitors could delay gastric ulcer healing to the same extent as traditional NSAIDs which are non-selective COX inhibitors.

Role for anions in pulmonary endothelial permeability

beta-Adrenergic stimulation reduces albumin permeation across pulmonary artery endothelial monolayers and induces changes in cell morphology that are mediated by Cl- flux. We tested the hypothesis that anion-mediated changes in endothelial cells result in changes in endothelial permeability. We measured permeation of radiolabeled albumin across bovine pulmonary arterial endothelial monolayers when the extracellular anion was Cl-, Br-, I-, F-, acetate (Ac-), gluconate (G-), and propionate (Pr-). Permeability to albumin (Palbumin) was calculated before and after addition of 0.2 mM of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), which reduces permeability. In Cl-, the Palbumin was 3.05 +/- 0.86 x 10(-6) cm/s and fell by 70% with the addition of IBMX. The initial Palbumin was lowest for Pr- and Ac-. Initial Palbumin was higher in Br-, I-, G-, and F- than in Cl-. A permeability ratio was calculated to examine the IBMX effect. The greatest IBMX effect was seen when Cl- was the extracellular anion, and the order among halide anions was Cl- > Br- > I- > F-. Although the level of extracellular Ca2+ concentration ([Ca2+]o) varied over a wide range in the anion solutions, [Ca2+]o did not systematically affect endothelial permeability in this system. When Cl- was the extracellular anion, varying [Ca2+]o from 0.2 to 2.8 mM caused a change in initial Palbumin but no change in the IBMX effect. The anion channel blockers 4-acetamido-4'-isothiocyanotostilbene-2, 2'-disulfonic acid (0.25 mM) and anthracene-9-carboxylic acid (0.5 mM) significantly altered initial Palbumin and the IBMX effect. The anion transport blockers bumetanide (0.2 mM) and furosemide (1 mM) had no such effects. We conclude that extracellular anions influence bovine pulmonary arterial endothelial permeability and that the pharmacological profile fits better with the activity of anion channels than with other anion transport processes.

Monocyte- and cytokine-induced downregulation of angiotensin-converting enzyme in cultured human and porcine endothelial cells

We investigated the effects of monocytes on endothelial cell (EC) ectoenzyme activity. Coculture of human aortic ECs with human monocytes (2 x 10(5) monocytes per 2-cm2 well) led to a decrease in EC angiotensin-converting enzyme (ACE) activity (64.5 +/- 3.5% of control) but not aminopeptidase N, aminopeptidase P, and 5'-nucleotidase activities. Similar results were obtained using human umbilical vein EC-human monocyte and porcine aortic EC-porcine monocyte cocultures. The decrease in ACE activity was monocyte concentration and coculture time dependent, reaching a maximum of 65% decrease in activity at 120 hours. Monocyte-mediated reduction in ACE activity did not require cell to cell contact, since exposure of ECs to conditioned medium from cocultures (CCCM) or from monocyte cultures (MCM) produced a decrease in ACE activity similar to that observed in EC-monocyte cocultures. Exogenously added tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 alpha, two known secretory products of monocytes, simulated the effects of monocytes on ACE activity. Western blot analysis revealed a decrease in the amount of ACE protein in TNF-alpha-treated and CCCM-treated ECs compared with control ECs. Both TNF-alpha and IL-1 alpha were present in CCCM and MCM but not EC-conditioned medium. Incubation of the cocultures with a mixture of neutralizing antibodies against TNF-alpha and IL-1 totally abolished the monocyte-induced decrease in ACE activity. In conclusion, monocytes decrease ACE activity in cultured ECs through the release of cytokines such as TNF-alpha and IL-1.

Monocyte-induced downregulation of nitric oxide synthase in cultured aortic endothelial cells

Since endothelium-dependent vasodilation is altered in atherosclerosis and enhanced monocyte/endothelial interactions are implicated in early atherosclerosis, we evaluated the effects of monocytes on the endothelial nitric oxide (NO) pathway by estimating release of biologically active NO from cultured endothelial cells and levels of constitutive NO synthase (ecNOS). NO release was estimated in a short-term bioassay using endothelial cell-induced cGMP accumulation in vascular smooth muscle (SM) cells. Exposure of SM cells to porcine aortic endothelial cells (PAECs) and human aortic endothelial cells (HAECs) produced large increases in SM cGMP content; this increase was prevented by NG-nitro-L-arginine methyl ester, the inhibitor of endothelial NOS. Confluent monolayers of PAECs and HAECs cocultured with monocytes also stimulated SM cGMP formation; however, NO release from these cultures was attenuated in a coculture time (2 to 48 hours)- and monocyte concentration (20 to 200 x 10(3) per well)-dependent manner. This effect of monocyte adhesion appeared to be selective for NO release since other biochemical pathways, such as atriopeptin-and isoproterenol-induced cyclic nucleotide accumulation within the endothelial cells, were not altered by monocytes. The effects of adherent monocytes on NO release were mimicked by monocyte-derived cytokines tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 alpha. Furthermore, the conditioned medium of monocytes contained significant quantities of these cytokines. Conditioned medium, as well as monocytes physically separated from the endothelial cells, attenuated NO release, suggesting that soluble factors may mediate the effects of monocytes. An IL-1 beta neutralizing antibody fully prevented the NO dysfunction in response to directly adherent monocytes. Superoxide dismutase, catalase, 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron), and exogenous L-arginine failed to improve NO release, suggesting that oxidant stress-induced inactivation of NO or limited substrate availability were not primarily responsible for the inhibiting effects of monocytes. Western blot analysis revealed reduced quantities of ecNOS in monocyte/endothelium cocultures, as well as in HAECs treated with monocyte-conditioned medium or TNF-alpha. Thus, adhesion of monocytes to endothelial cells and monocyte-derived secretory products downregulate steady state levels of ecNOS, an event associated with attenuated release of biologically active NO. This mechanism may potentially contribute to diminished endothelium-dependent and NO-mediated vasodilation in early atherosclerosis.

Differential activation of protein kinase C isozymes by phorbol ester and collagen in human skin microvascular endothelial cells

Human dermal microvascular endothelial cells participate in activities including inflammation, wound healing, and angiogenesis (neovascularization). Two stages of angiogenesis can be mimicked in vitro by two models of cultured foreskin human dermal microvascular endothelial cells: the differentiation of epithelioid endothelial cells to spindle-shaped mesenchymal-like cells induced by phorbol ester treatment; and the formation of vascular channels induced by exposing the luminal surface of endothelial cell monolayers to type I collagen gels. The mechanisms underlying these two processes, however, are largely unknown. Protein kinase C isozymes, which are activated by phorbol esters, are important mediators in the angiogenic process. In the current work, we identified the protein kinase C isozymes present in human dermal microvascular endothelial cells and determined which of the isozymes are activated in response to phorbol ester or to collagen treatments. Using western blot analysis, we found that microvascular endothelial cells contain at least six protein kinase C isozymes (alpha, beta, delta, epsilon, zeta, eta). Immunocytochemical studies demonstrated that the isozymes are located in distinct cellular compartments and that following treatment with phorbol 12-myristate 13-acetate or with a collagen gel overlay, most isozymes (protein kinase C alpha, beta1, betaII, delta, epsilon, eta) translocated to different parts of the cell. Moreover, for two of these isozymes (betaII and eta), the localization differs after phorbol 12-myristate 13-acetate treatment as compared with collagen treatment. These results demonstrate that agents that mimic two stages in the angiogenic process in vitro initiate diverse changes in the subcellular localization of specific protein kinase C isozymes and suggest a role for different isozymes in this process.

Prostaglandin E2 and monoclonal antibody to lymphocyte function-associated antigen-1 differentially inhibit migration of T lymphocytes across microvascular retinal endothelial cells in rat

Lymphocyte-transendothelial cell migration is a complex event, and although much is known about the receptor-ligand interactions involved, little is understood about the intracellular events which accompany these interactions, or their regulation by inflammatory mediators. In this study we have shown that activation of T lymphocytes increased the proportion of cells migrating across monolayers of cultured retinal microvascular endothelial cells by both lymphocyte function-associated antigen-1 (LFA-1)-dependent and LFA-1-independent mechanisms. In preliminary experiments, it was found that activation of T cells with mitogens such as concanavalin (Con A) increased significantly T-cell migration across the endothelial monolayers. In contrast, activation of the endothelial monolayer with interferon-gamma (IFN-gamma) (96 hr) had no effect on transendothelial migration. Investigation of adhesion molecule requirements for transendothelial migration indicated that LFA-1 was necessary (P < 0.02) but that intracellular adhesion molecule-1 did not appear to be involved. Investigation of the role of prostaglandins in transendothelial migration revealed that, while prostaglandin E2 (PGE2) did not affect adhesion molecule expression on endothelial cells or T cells, treatment of either cell significantly blocked transendothelial migration (P < 0.05). Pretreatment with PGE2 combined with LFA-1 blockade had an additive effect on inhibition of T-cell transendothelial migration, indicating that two independent mechanisms were operative. PGE2 also had a direct inhibitory effect on T-cell adhesion to the endothelium. These results highlight the importance of considering non-adhesion receptor-mediated mechanisms, perhaps involving cytoskeletal and/or motility, in the migration of T cells across endothelial monolayers.

Mechanism of endothelial cell shape change and cytoskeletal remodeling in response to fluid shear stress

Endothelium exposed to fluid shear stress (FSS) undergoes cell shape change, alignment and microfilament network remodeling in the direction of flow by an unknown mechanism. In this study we explore the role of tyrosine kinase (TK) activity, intracellular calcium ([Ca2+]i), mechanosensitive channels and cytoskeleton in the mechanism of cell shape change and actin stress fiber induction in bovine aortic endothelium (BAE). We report that FSS induces beta-actin mRNA in a time- and magnitude-dependent fashion. Treatment with quin2-AM to chelate intracellular calcium release and herbimycin A to inhibit TK activity abolished BAE shape change and actin stress fiber induction by FSS, while inhibition of protein kinase C with chelerythrine had no effect. Altering intermediate filament structure with acrylamide did not affect alignment or F-actin induction by FSS. Examining the role of the BAE cytoskeleton revealed a critical role for microtubules (MT). MT disruption with nocodazole blocked both FSS-induced morphological change and actin stress fiber induction. In contrast, MT hyperpolymerization with taxol attenuated the cell shape change but did not prevent actin stress fiber induction under flow. Mechanosensitive channels were found not to be involved in the FSS-induced shape change. Blocking the shear-activated current (IK.S) with barium and the stretch-activated cation channels (ISA) with gadolinium had no effect on the shear-induced changes in morphology and cytoskeleton. In summary, FSS has a profound effect on endothelial shape and F-actin network by a mechanism which depends on TK activity, intracellular calcium, and an intact microtubule network, but is independent of protein kinase C, intermediate filaments and shear- and stretch-activated mechanosensitive channels.

Antigenic variation in gp120s from molecular clones of HIV-1 LAI

To address the relationship between primary sequence variation in HIV-1 gp120 and its antigenic structure in a simple system, we have measured the binding of human and murine monoclonal antibodies (MAbs) to gp120 from four molecular clones of HIV-1 LAI: HxB2, HxB3, Hx10, and NL4-3. Despite the close relationship between these clones, and their relatively conserved gp120 sequences, there is considerable variation in their antigenic structure, judged by MAb reactivities to the V2, V3, and C4 domains and to discontinuous epitopes. Because of our prior studies of the determinants of MAb binding to HxB2 gp120, we can make reasonable estimates of how sequence variation among the LAI clone gp120s affects their binding of some MAbs; for other MAbs our current knowledge of gp120 structure is too limited to allow such estimates. These results indicate that small variations in primary gp120 amino acid sequence can profoundly affect recognition of this glycoprotein by all five groups of defined anti-gp120 neutralizing antibodies.

Induction of giant endothelial cells in culture by K-252a, a protein kinase inhibitor

K-252a, a protein kinase inhibitor with a wide spectrum of activity, inhibited the serum-stimulated proliferation of cultured bovine carotid endothelial cells dose-dependently, and all the cells became remarkably large, with a diameter of more than 150 microns at K-252a concentrations of 0.3-1 microgram/ml. This effect of the agent was reproducible under the conditions described in this article. When the endothelial cells became abnormally large by K-252a, the surface area of the cell became wider, and the F-actin molecules increased in both number and length. Despite their abnormal size, K-252a-induced giant cells maintained at least three physiological functions characteristic to normal endothelial cells: 1) ability to take up acetylated low density lipoprotein, 2) ability to produce and secrete endothelin and 3) ability to respond via an increase of [Ca2+]i to the stimulation by bradykinin. These observations suggest that K-252a-induced giant cells are useful tools for examining the function of endothelial cells because it is very reproducible and can be produced by an easy treatment.

Regulation of endothelin 1 gene by fluid shear stress is transcriptionally mediated and independent of protein kinase C and cAMP

Fluid shear stress induces a number of morphological and functional changes in vascular endothelium, including a rapid and significant down-regulation of endothelin 1 (ET-1) mRNA and peptide release in bovine aortic endothelial cells. We show here that both the cell alignment and ET-1 down-regulation depend on on-going protein synthesis, and that the latter is the result of a decrease in transcription, as shown by nuclear run-off assay, and not the result of changes in ET-1 mRNA half-life. The treatment of endothelial cells with either phorbol 12-myristate 13-acetate (100 nM) to activate protein kinase C (PKC) or forskolin (10 microM) to stimulate adenylate cyclase sharply decreased ET-1 mRNA. However, the phorbol-induced ET-1 decrease was, unlike the shear-induced down-regulation, independent of active protein synthesis. Physiological shear stress (20 dynes/cm2) did not significantly activate PKC, as assessed by PKC translocation and enzymatic activity assay and failed to increase intracellular cAMP content. Furthermore treatment with calphostin C (1 microM) did not prevent the shear-induced down-regulation of ET-1. DNA transfection experiments suggest that the shear stress-responsive element of the ET-1 gene is contained in the sequence between -2.5 kb and -2.9 kb of the 5'-upstream region. Neither the transcription factor AP-1 binding site nor the GATA-2-factor binding site, necessary for the basal level of transcription of ET-1 gene, is sufficient to confer shear-responsiveness to the reporter gene. These results suggest that shear stress regulates the transcription of the ET-1 gene via an upstream cis element by a distinct mechanism not dependent on the PKC or cAMP pathways.

Modulation of barrier function of bovine aortic and pulmonary artery endothelial cells: dissociation from cytosolic calcium content

1. Barrier function and cytosolic free calcium content [Ca2+]i was measured in monolayers of bovine pulmonary artery endothelial cells (BPAEC) and bovine aortic endothelial cells (BAEC). 2. Thrombin (1 u ml-1) increased albumin transfer across monolayers of BPAEC but not BAEC, yet induced biphasic increases in [Ca2+]i in both endothelial cell types, consisting of a rapid, initial phasic component which decayed to a lower, more sustained plateau phase. 3. 4 beta-Phorbol 12-myristate 13-acetate (PMA; 0.3-3000 nM) increased albumin transfer across monolayers of BPAEC and BAEC, but had no effect on basal levels of [Ca2+]i in either endothelial cell type. 4. Treatment of BPAEC and BAEC with forskolin (30 microM), an activator of adenylate cyclase, had no effect on resting transfer of albumin, but inhibited that stimulated by PMA (600 nM). It also inhibited the thrombin (1 u ml-1)-induced increase in albumin transfer across monolayers of BPAEC, but enhanced the plateau phase of the associated increase in [Ca2+]i. 5. Treatment of BPAEC and BAEC with either atriopeptin II (100 nM), an activator of particulate guanylate cyclase, or 8 bromo cyclic GMP (30 microM) had no effect on resting or PMA (600 nM)-stimulated transfer of albumin. Both agents did, however, inhibit the thrombin (1 u ml-1)-induced increase in albumin transfer across monolayers of BPAEC, but had no effect on the associated increase in [Ca2+]i. 6. These data suggest a dissociation between the ability of agents that increase or decrease albumin transfer and their effects on [Ca2+]i. Consequently, activation of protein kinase C may be the major stimulus for trans-endothelial transfer of macromolecular solutes. Endothelial barrier function is enhanced by elevation of either cyclic AMP or cyclic GMP content. Cyclic AMP appears to act by inhibiting the actions of protein kinase C, while cyclic GMP may act to inhibit a key step proximal to activation of this enzyme.

Endothelium-derived relaxing factor contributes to the regulation of endothelial permeability

To determine whether endothelium-derived relaxing factor (EDRF) contributes to the regulation of endothelial permeability, the transendothelial flux of 14C-sucrose, a marker for the paracellular pathway across endothelial monolayers (Oliver, J. Cell. Physiol. 145:536-548, 1990), was examined in monolayers of bovine aortic endothelial cells grown on collagen-coated filters. The permeability coefficient of 14C-sucrose was significantly decreased by 10(-3) M 8-Bromoguanosine 3',5'-cyclic monophosphate or by 5 x 10(-6) M glyceryl trinitrate, an activator of soluble guanylate cyclase. Depletion of L-arginine from endothelial monolayers increased 14C-sucrose permeability from 3.21 +/- 0.59 to 3.88 +/- 0.50 x 10(-5) cm.sec-1 (mean +/- SEM; n = 6; P < 0.05). The acute administration of 5 x 10(-4) M L-arginine to monolayers depleted of this amino acid decreased 14C-sucrose permeability from 2.91 +/- 0.27 to 2.52 +/- 0.26 x 10(-5) cm.sec-1 (n = 11; P < 0.05). 14C-sucrose permeability was increased by 10(-7) M bradykinin and this effect was enhanced by the presence of each one of the following compounds: 10(-5) M methylene blue, 4 x 10(-6) M oxyhemoglobin, 5 x 10(-4) M NG-methyl-L-arginine or 5 x 10(-4) M N omega-nitro-L-arginine. These results suggest that EDRF contributes to the sealing of the endothelial monolayer and that EDRF released by bradykinin acts as a feedback inhibitor attenuating the increase in endothelial permeability induced by this peptide. Because endothelial cells have the ability to contract and relax and possess guanylate cyclase responsive to nitric oxide, our results suggest that EDRF decreases 14C-sucrose permeability by relaxing endothelial cells, thereby narrowing the width of endothelial junctions.

Role of protein kinase C in the regulation of prostaglandin synthesis in human endothelium

The present study specifically addresses the role of protein kinase C (PKC) activation in human endothelial cell Ca2+ mobilization, a response that is functionally coupled to the production of the potent arachidonate (AA) metabolite, prostacyclin (PGI2). Phorbol 12-myristate 13-acetate (PMA), alpha-thrombin, and sodium fluoride (NaF), a direct G-protein activator, produced a rapid and time-dependent translocation of PKC from the cytosol to the membrane. Activation of PKC by brief pretreatment of human umbilical vein endothelial cell (HUVEC) monolayers with PMA resulted in the inhibition of NaF-induced inositol phosphate increases and attenuation of both alpha-thrombin- and NaF-activated increases in intracellular Ca2+ (Ca2+i). Ca2+ mobilization induced by ionophore A23187 was not affected by PKC preactivation, suggesting PKC-dependent negative feedback inhibition of phosphatidylinositol (PI)-specific phospholipase C (PLC). Agonist-stimulated AA release and PGI2 synthesis in PMA-pretreated cultured human endothelial cells, however, was potentiated, and the enhanced PGI2 synthesis produced by A23187, NaF, and alpha-thrombin was dependent upon the dose of PMA. Treatment of HUVEC monolayers with an intracellular Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid-acetoxymethylester (BAPTA-AM), dramatically reduced alpha-thrombin-, NaF-, and A23187-induced PGI2 synthesis, demonstrating the importance of Ca2+i availability in PGI2 synthesis. BAPTA pretreatment did not inhibit PMA-induced PKC activation, and BAPTA-mediated inhibition of agonist-stimulated PGI2 synthesis was partially attenuated by prior PMA pretreatment. Staurosporine, a potent PKC inhibitor, at concentrations that inhibited PKC-induced phosphorylation of histone-1, augmented both alpha-thrombin- and NaF-induced production of inositol phosphates but markedly inhibited alpha-thrombin-, NaF-, and A23187-induced PGI2 synthesis. The downregulation of PKC activity by prolonged PMA treatment (18 h) produced similar inhibition of PGI2 synthesis by these agonists (approximately 50% inhibition). These studies indicate that the integrated phospholipase A2 and PLC activities are under complex regulation by factors that include both PKC activation and [Ca2+i]. PKC exerts dual effects on prostaglandin synthesis via negative regulation of Gp-coupled PI-specific PLC and positive feedback regulation of AA release and PGI2 synthesis. PKC is thus a critical determinant in the regulation of human endothelial cell prostaglandin synthesis by both receptor-mediated and G-protein-dependent cellular activation.

Serotonin produces a configurational change of cultured smooth muscle cells that is associated with elevation of intracellular cAMP

Early passaged bovine pulmonary artery smooth muscle cells (SMC) respond to serotonin (5-HT) by developing a reversible change in configuration. (Lee et al. J. Cell. Physiol. 138:145, 1989). This configurational change does not occur in pulmonary artery endothelial cells (EC) subjected to 5-HT and is adenosine triphosphate (ATP) dependent, lost with passage of SMC, and inhibited by various agents that block high-affinity 5-HT uptake. We now report a second configurational change (also dendritic formation) of SMC produced by 5-HT only in the presence of isobutylmethylxanthine (IBMX), an inhibitor of phosphodiesterase. This configurational change was also ATP dependent, but unlike the first response, (Lee et al., 1989), it occurred in both first and later passaged SMC and was not inhibited by blockade of 5-HT uptake. Also, unlike the response with 5-HT alone that failed to elevate cAMP, this one was associated with a large elevation of cAMP (eight fold above control values), similar to the response to the beta-agonist isoproterenol, plus IBMX. The second response was not blocked by a variety of 5-HT receptor antagonists but was reproduced by (+/-)-8-hydroxy-DPAT HBr (8-OH-DPAT), a reputed 5-HT1A agonist. The response was not dependent upon Ca2+ and was blocked by 1-2 mM n-phenylanthranilic acid or anthracene-9-carboxylic acid, electrically conductive Cl- channel inhibitors. Hence, 5-HT in the presence of IBMX causes a marked elevation of cAMP of SMC and this elevation in cAMP likely results in a cellular configurational change through a Cl- channel-dependent mechanism similar to that we previously described for EC in the presence of beta-adrenergic agonist stimulation (Ueda et al. Circ. Res. 66:951, 1990). EC do not show a similar response to 5-HT possibly because cAMP is not adequately elevated, even in the presence of IBMX, to enhance Cl- channel activity. We propose that our observations indicate the presence of two sites of action of 5-HT on the smooth muscle cell, one intracellularly and another at a cell surface receptor.

Stellate cells of aortic intima: I. Human and rabbit

Stellate cells hitherto accounted exclusively in the innermost elastic-hyperplastic layer were already reported to inhabit human aortic intima. The present paper shows that most of these cells are situated just beneath the endothelium. Stellate cells also appear in the deendothelialization-induced myointimal thickening of rabbit aorta. In the myointimal thickening these cells were revealed in the direct proximity to the endothelium. A conclusion is available that the previously demonstrated polymorphism of human aortic intimal cells may be reproduced in a simple experimental model, which gives new possibilities for the study of the cellular polymorphism in the vessel wall.

Protein kinase C stimulation enhances the process formation of adult oligodendrocytes and induces proliferation

Oligodendrocytes (OL) isolated from adult pig brains regenerate their processes and form a network of fibers after 14-18 days in vitro (DIV). Stimulation of protein kinase C (Pk-C) by tumour promoters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) produces at day 7 in vitro a similar network after only 20 hr. H-7, an inhibitor of Pk-C, as well as amiloride, which inhibits the subsequent Na+/H+ exchange, reversibly suppress this effect. Activation of the protein kinase A or calmodulin pathway do not result in an increased OL process production. Furthermore, TPA induced proliferation in a subpopulation of OL. We conclude that the stimulation of Pk-C is of utmost importance for OL regeneration.

Norepinephrine and iloprost improve barrier function of human endothelial cell monolayers: role of cAMP

The barrier function of human artery endothelial cells was improved by addition of agents that increase the cellular adenosine 3',5'-cyclic monophosphate (cAMP) concentration. Together with a decrease in the passage rate of peroxidase, an increase in the transendothelial electrical resistance was observed. A direct correlation was found between the relative increases in cellular cAMP concentration and the relative decrease in peroxidase passage after incubation of the cells with forskolin (0.25 and 2.5 microM), the beta-adrenergic agonist isoproterenol (10 microM), and the stable prostacyclin analogue iloprost (10 microM). Norepinephrine (10 microM) reduced the peroxidase passage to a much larger extent (40% reduction) than might be expected on the basis of a small increase of cAMP concentration. This small increase in cAMP (44%) was the result of interactions of norepinephrine with beta-adrenergic receptors, which increase cAMP, and alpha-adrenergic receptors, which decrease cAMP. The relatively strong reduction in permeability (also found in the presence of the alpha-adrenergic antagonist phentolamine) suggests that an additional cAMP-independent mechanism underlaid the barrier-improving effect of norepinephrine. A marked elevation of cAMP by forskolin was accompanied by a disappearance of F-actin and myosin from stress fibers. They were found diffusely spread over the cell, and F-actin in the cell periphery became prominently visible.

Three-dimensional cytoarchitecture of normal and atherosclerotic intima of human aorta

The three-dimensional cytoarchitecture of normal and atherosclerotic intima of human aorta was studied by light microscopy of consecutive en face preparations (Hautchen preparations) and by scanning electron microscopy. In unaffected intima, a three-dimensional network consisting of cells of variable shape and probably origin was demonstrated. Cellular shape changed from predominantly stellate in the luminal regions of the elastic-hyperplastic layer to elongated spindlelike cells in the musculoelastic layer of the intima. In the surface layers of the fatty streak, cellular contacts were severed, and lipid droplets were often seen between cellular processes. Along with stellate and elongated cells, the fatty streak also had a number of round monocytelike cells. Lipid inclusions were usually detected in stellate and ovoid cells. The integrity of the cellular network was preserved at the marginal zone of the atherosclerotic plaque, while at the slopes and in the central part of the plaque, cells practically lost all contact with each other. Giant stellate cells embedded in crude fibrillar connective tissue matrix were often found there. Disintegration of the cellular network during atherosclerosis is suggested to play an important role in the development of various lesions.

Chloride efflux in cyclic AMP-induced configurational change of bovine pulmonary artery endothelial cells

Elevation of cellular cyclic AMP by agents such as isoproterenol plus 3-isobutyl-1-methylxanthine produced rapid and reversible dendritic formation of bovine pulmonary artery endothelial cells in the monolayer. The effect did not occur with exposure of the cells to a variety of other vasoactive agents, calcium ionophore, phorbol ester, or cyclic GMP. The cyclic AMP-induced configurational change was completely inhibited by 2.5 mM N-phenylanthranilic acid or 145 mM sodium gluconate (Cl- channel inhibitors) and was partially inhibited by 2.5 mM 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS), but it was not affected by deprivation of Ca2+ or Na+ ion, 1 mM bumetanide (Cl- cotransport inhibitor), 1 mM amiloride (Na+/H+ exchange inhibitor), 0.1 mM verapamil (Ca2+ channel inhibitor), or 5 mM BaCl2 (K+ channel inhibitor), by change in cellular pH, or by pertussis toxin. Trifluoperazine (calmodulin inhibitor, 50 microM), 1 mM EGTA plus 100 microM 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8, intracellular Ca2+ antagonist), and 5 microM cytochalasin B also produced cellular retraction, but these changes were not blocked by chloride channel inhibition. In the presence of 0.1 mM ouabain plus 0.1 mM bumetanide, 36Cl- uptake was decreased by isoproterenol plus isobutylmethylxanthine while its efflux was enhanced. N-Phenylanthranilic acid inhibited the stimulated efflux. We conclude that cyclic AMP induces a configurational change of endothelial cells that is related to Cl- efflux from the cells; the cellular effects may play a role in vascular function.

Forskolin has biphasic effects on osteoprogenitor cell differentiation in vitro

Cells isolated from fetal rat calvaria (RC) and maintained in vitro in medium containing ascorbic acid and B-glycerophosphate form three-dimensional, mineralized nodules having the histological, immunohistological, and ultrastructural characteristics of woven bone. We have studied the effects of forskolin (FSK), a diterpene that activates adenylate cyclase, in this system. While 10(-7)-10(-5) M FSK significantly stimulated cAMP levels in RC cells, lower concentrations did not. cAMP levels with 10(-5) M FSK reached a maximum by 30 min at 37 degrees C and returned to basal level in 2-3 hr. Changes in cAMP levels correlated with changes in cellular shape: cells treated with 10(-5) M FSK assumed a stellate morphology, lost microfilament bundles, and reduced their substrate adhesiveness, while cells treated with 10(-9) M were not affected. Exponential growth and saturation densities of FSK-treated cultures were similar to untreated cultures, indicating that FSK was neither toxic nor stimulatory to the population. The effect on bone nodule formation of FSK present continuously depended on concentration: 10(-5) M FSK significantly inhibited the number of nodules formed, while 10(-9) M FSK significantly stimulated bone nodule formation. Single short treatments with either 10(-5) M or 10(-9) M FSK had no effect on nodule formation, but repeated short duration treatments (1 hr every 2 days for 21 days) gave results similar to continuous exposure. These results indicate that intermittent elevations in intracellular cAMP have an inhibitory effect on bone formation. In addition, our work indicates that low concentrations of FSK stimulate differentiation of osteoprogenitor cells possibly through a non-cAMP-dependent process.

Passage of low density lipoproteins through monolayers of human arterial endothelial cells. Effects of vasoactive substances in an in vitro model

The endothelium controls the influx of lipoproteins into the arterial wall, a process that may be disturbed in arteriosclerotic blood vessels. We have used an in vitro model to investigate the characteristics of the passage of low density lipoproteins (LDL) through monolayers of human arterial endothelial cells. Umbilical artery, aorta, or carotid artery endothelial cells were cultured on polycarbonate filters and formed a tight monolayer in which the cells were connected by tight junctions. Passage of 125I-LDL through these monolayers proceeded linearly over a 24-hour period. It was threefold lower through monolayers of aorta or carotid artery cells than through monolayers of umbilical artery cells. The LDL passage process did not show saturation with LDL concentrations up to 800 micrograms/ml LDL-protein (i.e., 1.6 nmol/ml apolipoprotein B) between 2 and 4 hours after addition. However, during the first 30 to 60 minutes after addition of high concentrations of LDL, a reduction of the passage rate of both LDL and peroxidase, resulting in an apparent saturation of the passage process, was observed. The passage rate of the negatively charged acetylated LDL was twofold lower than that of native LDL. Addition of histamine to the endothelial monolayer resulted in a large, but transient, increase in permeability paralleled by a decrease in electrical resistance. The effects of histamine were mediated via an H1 receptor. Thrombin and Ca++ ionophore also induced an increase in permeability of the monolayer, while bradykinin did not. The effects of histamine and thrombin were paralleled by a rapid and marked increase in cytoplasmatic Ca++ concentration of the endothelial cells, while bradykinin induced only a small increase. Although the cyclic adenosine 5'-monophosphate-elevating agent, forskolin, markedly decreased the basal rate of LDL passage through the endothelial cell monolayers, it did not change the relative increase in permeability induced by histamine. Thus, histamine induces small, but significant, increases in the permeability of tight endothelial cell monolayers.

Mechano-chemical control of human endothelium orientation and size

Human umbilical vein endothelial cells (EC) were grown on elastic silicone membranes subjected to cyclic stretch, simulating arterial wall motion. Stretching conditions (20% amplitude, 52 cycle/min) stimulated stress fiber formation and their orientation transversely to the strain direction. Cell bodies aligned along the same axis after the actin cytoskeleton. EC orientation response was inhibited by the adenylate cyclase activator, forskolin (10(-5) M), which caused stress fiber disassembly and the redistribution of F-actin to the cortical cytoplasm. Preoriented EC depleted of stress fibers by forskolin treatment retained their aligned state. Thus, stress fibers are essential for the process of EC orientation induced by repeated strain, but not for the maintenance of EC orientation. The monolayer formed by EC grown to confluence in conditions of intermittent strain consisted of uniform elongated cells and was resistant to deformation. In contrast, the monolayer assembled in stationary conditions was less compliant and exposed local denudations on initiation of stretching. When stretched in the presence of 10(-5) M forskolin it rapidly (3-4 h) reestablished integrity but gained a heterogeneous appearance since denuded areas were covered by giant cells. The protective effect of forskolin was because of the stimulation of EC spreading. This feature of forskolin was demonstrated while studying its action on EC spreading and repair of a scratched EC monolayer in conventional culture. Thus mechanical deformation and adenylate cyclase activity may be important factors in the control of endothelium morphology in human arteries.

Identification and regulation of 1,25-dihydroxyvitamin D3 receptor activity and biosynthesis of 1,25-dihydroxyvitamin D3. Studies in cultured bovine aortic endothelial cells and human dermal capillaries

Because 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) has been shown to play roles in both proliferation and differentiation of novel target cells, the potential expression of 1,25(OH)2D3 receptor (VDR) activity was investigated in cultured bovine aortic endothelial cells (BAEC). Receptor binding assays performed on nuclear extracts of BAEC revealed a single class of specific, high-affinity VDR that displayed a 4.5-fold increase in maximal ligand binding (Nmax) in rapidly proliferating BAEC compared with confluent, density-arrested cells. When confluent BAEC were incubated with activators of protein kinase C (PKC), Nmax increased 2.5-fold within 6-24 h and this upregulation was prevented by sphingosine, an inhibitor of PKC, as well as by actinomycin D or cycloheximide. Immunohistochemical visualization using a specific MAb disclosed nuclear localized VDR in venular and capillary endothelial cells of human skin biopsies, documenting the expression of VDR, in vivo, and validating the BAEC model. Finally, additional experiments indicated that BAEC formed the 1,25(OH)2D3 hormonal metabolite from 25(OH)D3 substrate, in vitro, and growth curves of BAEC maintained in the presence of 10(-8) M 1,25(OH)2D3 showed a 36% decrease in saturation density. These data provide evidence for the presence of a vitamin D microendocrine system in endothelial cells, consisting of the VDR and a 1 alpha-hydroxylase enzyme capable of producing 1,25(OH)2D3. That both components of this system are coordinately regulated, and that BAEC respond to the 1,25(OH)2D3 hormone by modulating growth kinetics, suggests the existence of a vitamin D autocrine loop in endothelium that may play a role in the development and/or functions of this pathophysiologically significant cell population.

Role of cyclic adenosine monophosphate in the induction of endothelial barrier properties

Cyclic adenosine monophosphate (AMP) has numerous important effects on cell structure and function, but its role in endothelial cells is unclear. Since cyclic AMP has been shown to affect transmembrane transport, cell growth and morphology, cellular adhesion, and cytoskeletal organization, it may be an important determinant of endothelial barrier properties. To test this we exposed bovine pulmonary artery endothelial cell monolayers to substances known to increase cyclic AMP and measured their effect on endothelial permeability to albumin and endothelial cell cyclic AMP concentrations. Cholera toxin (CT), a stimulant of the guanine nucleotide binding subunit of adenylate cyclase, led to a concentration-dependent 2-6-fold increase in cyclic AMP which was associated with a 3-10-fold reduction in albumin transfer across endothelial monolayers. The effect was not specific to albumin as similar barrier-enhancing effects were also noted with an unrelated macromolecule, fluorescein isothiocyanate (FITC)-dextran (MW 70,000). Barrier enhancement with cyclic AMP elevation was also observed with forskolin, a stimulant of the catalytic subunit of adenylate cyclase. The temporal pattern of barrier enhancement seen with these agents paralleled their effects on increasing cyclic AMP, and the barrier enhancement could be reproduced by incubation with either dibutyryl cyclic AMP or Sp-cAMPS, cyclic AMP-dependent protein kinase agonists. Furthermore, the forskolin effect on barrier enhancement was partially reversed with Rp-cAMPS, an antagonist of cyclic AMP-dependent protein kinase. Since endothelial actin polymerization may be an important determinant of endothelial barrier function, we sought to determine whether the cyclic AMP-induced effects were associated with increases in the polymerized actin pool (F-actin). Both cholera toxin and forskolin led to apparent endothelial cell spreading and quantitative increases in endothelial cell F-actin fluorescence. In conclusion, increased endothelial cell cyclic adenine nucleotide activity was an important determinant of endothelial barrier function in vitro. The barrier enhancement was associated with increased endothelial apposition and increases in F-actin, suggesting that influences on cytoskeletal assembly may be involved in this process.

Induction of an activation antigen on human endothelial cells in vitro

This study describes the expression characteristics of a cell membrane protein recognized by a monoclonal antibody ENA1, which was obtained by immunizing mice with human umbilical vein endothelial (HUVE) cells cultured with a mixture of interleukin 1 and tumor necrosis factor-alpha. The expression of this ENA1 antigen could also be induced by lipopolysaccharide and phorbol esters. Expression was only demonstrated on HUVE cells and human umbilical arterial endothelial cells, pretreated with one or with a mixture of these reagents. No expression was detected on human fibroblasts, renal epithelial cells or on mesothelial cells derived from omental tissue, either pretreated or not with the aforementioned inducers of the antigen. Furthermore, no reactivity was observed with either polymorphonuclear cells, peripheral blood lymphocytes or the monocytic cell line U937. Time course experiments revealed that the expression of the ENA1 antigen was time dependent. Maximal expression on HUVE cells was observed after 5 h of incubation with activator, after which a decline in expression occurred. Induction of expression could be completely blocked by the mRNA synthesis inhibitor actinomycin D and the protein synthesis inhibitor cycloheximide, indicating that de novo synthesis occurs. Other pharmacological reagents tested had no effect on the induction of ENA1 expression. The putative role of the newly described antigen is discussed in relation to the current knowledge of molecules involved in adhesion of immune cells in inflammatory processes.

Phorbol 12-myristate 13-acetate prevents isoproterenol-induced morphological change in cultured vascular smooth muscle cells

The effect of phorbol 12-myristate 13-acetate (PMA) on isoproterenol (ISO)- and dibutyryl cAMP (dBcAMP)-induced morphological change and cytoskeletal reorganization was studied in cultured vascular smooth muscle cells (VSMC) using the fluorescence staining of actin and microtubules. The treatment of VSMC with 1.0 microM of ISO or with 1.0 mM of dBcAMP for 90 min induced the disruption of actin-containing stress fibers followed by cytoplasmic arborization. The addition of 100 or 10 nM of PMA prevented both the destruction of actin fibers and cell arborization induced either by ISO or by dBcAMP. However, PMA rather enhanced cAMP production stimulated by ISO. 1-Oleoyl-2-acetyl-sn-glycerol (100 micrograms/ml) mimicked this inhibitory effect of PMA whereas 4 alpha-phorbol 12,13-didecanoate (100 nM) failed to block the arborization. These results indicated that the inhibition of arborization by PMA was mediated through the activation of protein kinase C. Colchicine at 5.0 microM also had an inhibitory effect on ISO- and dBcAMP-induced cell arborization. However, immunofluorescence studies revealed that colchicine but not PMA elicited the reorganization of microtubules, suggesting that the effect of PMA was mediated through a mechanism different from that of colchicine. These observations indicated that the morphology of VSMC was regulated through the alteration of cytoskeletal organization induced by cAMP-mediated and by protein kinase C-dependent systems.

Growth-dependent subcellular redistribution of protein kinase C in cultured porcine aortic endothelial cells

We have previously observed major differences in the phosphorylation of membrane proteins in sparse, proliferating versus confluent, quiescent pig aortic endothelial cells (EC) (Kazlauskas and DiCorleto, 1987). In the present study we examined whether EC growth state can influence the activity of a specific phosphorylating enzyme, protein kinase C (PKC) in cytosolic and membrane fractions of pig aortic EC. Levels of PKC were measured using two methods: 1) Ca2+ and phospholipid-dependent phosphorylation of exogenous histones using gamma-labeled [32P]ATP, and 2) [3H]phorbol-12,13-dibutyrate (PDBu) binding activity. The total amount of PKC activity in the quiescent versus proliferating cells was similar but the percentage of PKC activity in the membrane fraction correlated with the proliferative index of the cells: confluent, quiescent cultures exhibited a majority of PKC activity in the cytosolic fraction (67%), whereas sparse, proliferating cultures contained principally membrane-bound PKC (70%). We also examined the role of PKC in the mitogenic response of pig aortic EC to fetal calf serum. Following serum stimulation of sparse, serum-deprived pig aortic EC, PKC activity redistributed from the cytosolic to the membrane fraction in a rapid process that correlated with subsequent DNA synthesis. A potent activator of PKC, 12-O-tetradecanoylphorbol-13-acetate (TPA), induced a minimal mitogenic response in pig aortic EC when added alone but acted synergistically with low concentrations of fetal calf serum to greatly stimulate DNA synthesis. Furthermore, pig aortic EC treated with TPA for 24 h to down-regulate PKC exhibited only 25% of the serum-stimulated mitogenic activity of control cultures. These results suggest a role for PKC activation and translocation in the proliferation of pig aortic EC.

Endothelial cell contraction increases Candida adherence to exposed extracellular matrix

Bovine vascular endothelial cells treated with EDTA, urea, or thrombin underwent a marked, reversible contraction resulting in exposure of the subendothelial extracellular matrix (ECM). Candida yeasts adhered more to contracted monolayers than to confluent monolayers (P less than 0.01) by preferentially adhering to the ECM. Two strains of Candida albicans and one strain of Candida tropicalis bound avidly to exposed ECM, but Pseudomonas aeruginosa did not. However, treatment of endothelium with forskolin, which induces cell shape changes without exposure of the ECM, did not cause an increase in adherence.