Migrating endothelial cells are distinctly hyperglycosylated and express specific migration-associated cell surface glycoproteins

Protein glycosylation in cardiovascular health and disease

Protein glycosylation, which involves the attachment of carbohydrates to proteins, is one of the most abundant protein co-translational and post-translational modifications. Advances in technology have substantially increased our knowledge of the biosynthetic pathways involved in protein glycosylation, as well as how changes in glycosylation can affect cell function. In addition, our understanding of the role of protein glycosylation in disease processes is growing, particularly in the context of immune system function, infectious diseases, neurodegeneration and cancer. Several decades ago, cell surface glycoproteins were found to have an important role in regulating ion transport across the cardiac sarcolemma. However, with very few exceptions, our understanding of how changes in protein glycosylation influence cardiovascular (patho)physiology remains remarkably limited. Therefore, in this Review, we aim to provide an overview of N-linked and O-linked protein glycosylation, including intracellular O-linked N-acetylglucosamine protein modification. We discuss our current understanding of how all forms of protein glycosylation contribute to normal cardiovascular function and their roles in cardiovascular disease. Finally, we highlight potential gaps in our knowledge about the effects of protein glycosylation on the heart and vascular system, highlighting areas for future research.

Docetaxel and Doxorubicin Codelivery by Nanocarriers for Synergistic Treatment of Prostate Cancer

Combination chemotherapy has been proven to be an efficient strategy for the treatment of prostate cancer (PCA). However, the pharmacokinetic distinction between the relevant drugs is an insurmountable barrier to the realization of their synergistic use against cancer. To overcome the disadvantages of combination chemotherapy in the treatment of PCA, targeted nanoparticles (NPs), which can codeliver docetaxel (DOC) and doxorubicin (DOX) at optimal synergistic proportions, have been designed. In this study, the DOC and DOX codelivery nanoparticles (DDC NPs) were constructed by hyaluronic acid (HA) and cationic amphipathic starch (CSaSt) through a self-assembly process. Human PCA cell lines (PC-3, DU-145, and LNCap) and mouse models were then used for evaluation in vitro and in vivo, respectively, of delivery and antitumor effects. The DDC NPs were spherical with rough surfaces, and the size and zeta potential were 68.4 ± 7.1 nm and -22.8 ± 2.2 mV, respectively. The encapsulation efficiencies of DOC and DOX in the NPs were 96.1 ± 2.3% and 91.4 ± 3.7%, respectively, while the total drug loading was 9.1 ± 1.7%. Moreover, the ratio of DOC to DOX in the DDC NPs was approximately 1:400, which aligned with the optimal synergistic proportions of the drugs. The DDC NPs exhibited excellent loading capacities, performed sustained and enzymatic release, and were stable in PBS, medium, and serum. After investigations in vitro, the DDC NPs were as effective as the dual drug combination in terms of cytotoxicity, antimigration, and apoptosis. Internalization results indicated that the DDC NPs could effectively deliver and fully release the payloads into PCA cells, and the process was mediated by the ligand-receptor interaction of HA with the CD44 protein. Low toxicity in vivo was confirmed by acute toxicity and hemolytic assays. The distribution in vivo showed that DDC NPs could enhance the accumulation of drugs in tumors and decrease nonspecific accumulation in normal organs. More importantly, DDC NPs significantly promoted the curative effect of the DOC and DOX combination in the PCA cell xenograft mouse model, indicating that the drugs with NPs did indeed act synergistically. This study suggests that the DDC NPs possess noteworthy potential as prospects for the development of PCA clinical chemotherapy.

NEU1 sialidase regulates the sialylation state of CD31 and disrupts CD31-driven capillary-like tube formation in human lung microvascular endothelia

The highly sialylated vascular endothelial surface undergoes changes in sialylation upon adopting the migratory/angiogenic phenotype. We recently established endothelial cell (EC) expression of NEU1 sialidase (Cross, A. S., Hyun, S. W., Miranda-Ribera, A., Feng, C., Liu, A., Nguyen, C., Zhang, L., Luzina, I. G., Atamas, S. P., Twaddell, W. S., Guang, W., Lillehoj, E. P., Puché, A. C., Huang, W., Wang, L. X., Passaniti, A., and Goldblum, S. E. (2012) NEU1 and NEU3 sialidase activity expressed in human lung microvascular endothelia. NEU1 restrains endothelial cell migration whereas NEU3 does not. J. Biol. Chem. 287, 15966-15980). We asked whether NEU1 might regulate EC capillary-like tube formation on a Matrigel substrate. In human pulmonary microvascular ECs (HPMECs), prior silencing of NEU1 did not alter tube formation. Infection of HPMECs with increasing multiplicities of infection of an adenovirus encoding for catalytically active WT NEU1 dose-dependently impaired tube formation, whereas overexpression of either a catalytically dead NEU1 mutant, NEU1-G68V, or another human sialidase, NEU3, did not. NEU1 overexpression also diminished EC adhesion to the Matrigel substrate and restrained EC migration in a wounding assay. In HPMECs, the adhesion molecule, CD31, also known as platelet endothelial cell adhesion molecule-1, was sialylated via α2,6-linkages, as shown by Sambucus nigra agglutinin lectin blotting. NEU1 overexpression increased CD31 binding to Arachis hypogaea or peanut agglutinin lectin, indicating CD31 desialylation. In the postconfluent state, when CD31 ectodomains are homophilically engaged, NEU1 was recruited to and desialylated CD31. In postconfluent ECs, CD31 was desialylated compared with subconfluent cells, and prior NEU1 silencing completely protected against CD31 desialylation. Prior CD31 silencing and the use of CD31-null ECs each abrogated the NEU1 inhibitory effect on EC tube formation. Sialyltransferase 6 GAL-I overexpression increased α2,6-linked CD31 sialylation and dose-dependently counteracted NEU1-mediated inhibition of EC tube formation. These combined data indicate that catalytically active NEU1 inhibits in vitro angiogenesis through desialylation of its substrate, CD31.

Endothelial heterogeneity and adhesion molecules N-glycosylation: implications in leukocyte trafficking in inflammation

Inflammation is a major contributing element to a host of diseases with the interaction between leukocytes and the endothelium being key in this process. Much is understood about the nature of the adhesion molecule proteins expressed on any given leukocyte and endothelial cell that modulates adhesive interactions. Although it is appreciated that these proteins are heavily glycosylated, relatively little is known about the roles of these posttranslational modifications and whether they are regulated, and if so how during inflammation. Herein, we suggest that a paucity in this understanding is one major reason for the lack of successful therapies to date for modulating leukocyte-endothelial interactions in human inflammatory disease and discuss developing paradigms of (i) how endothelial adhesion molecule glycosylation (with a focus on N-glycosylation) maybe a critical element in understanding endothelial heterogeneity between different vascular beds and species, (ii) how adhesion molecule N-glycosylation may be under distinct, and as yet, unknown modes of regulation during inflammatory stress to affect the inflammatory response in a vascular bed- and disease-specific manner (analogous to a "zip code" for inflammation) and finally (iii) to underscore the concept that a fuller appreciation of the role of adhesion molecule glycoforms is needed to provide foundations for disease and tissue-specific targeting of inflammation.

NEU1 and NEU3 sialidase activity expressed in human lung microvascular endothelia: NEU1 restrains endothelial cell migration, whereas NEU3 does not

The microvascular endothelial surface expresses multiple molecules whose sialylation state regulates multiple aspects of endothelial function. To better regulate these sialoproteins, we asked whether endothelial cells (ECs) might express one or more catalytically active sialidases. Human lung microvascular EC lysates contained heat-labile sialidase activity for a fluorogenic substrate, 2'-(4-methylumbelliferyl)-α-D-N-acetylneuraminic acid (4-MU-NANA), that was dose-dependently inhibited by the competitive sialidase inhibitor, 2,3-dehydro-2-deoxy-N-acetylneuraminic acid but not its negative control. The EC lysates also contained sialidase activity for a ganglioside mixture. Using real time RT-PCR to detect mRNAs for the four known mammalian sialidases, NEU1, -2, -3, and -4, NEU1 mRNA was expressed at levels 2700-fold higher that those found for NEU2, -3, or -4. Western analyses indicated NEU1 and -3 protein expression. Using confocal microscopy and flow cytometry, NEU1 was immunolocalized to both the plasma membrane and the perinuclear region. NEU3 was detected both in the cytosol and nucleus. Prior siRNA-mediated knockdown of NEU1 and NEU3 each decreased EC sialidase activity for 4-MU-NANA by >65 and >17%, respectively, and for the ganglioside mixture by 0 and 40%, respectively. NEU1 overexpression in ECs reduced their migration into a wound by >40%, whereas NEU3 overexpression did not. Immunohistochemical studies of normal human tissues immunolocalized NEU1 and NEU3 proteins to both pulmonary and extrapulmonary vascular endothelia. These combined data indicate that human lung microvascular ECs as well as other endothelia express catalytically active NEU1 and NEU3. NEU1 restrains EC migration, whereas NEU3 does not.

Ricinus communis agglutinin I leads to rapid down-regulation of VEGFR-2 and endothelial cell apoptosis in tumor blood vessels

Ricinus communis agglutinin I (RCA I), a galactose-binding lectin from castor beans, binds to endothelial cells at sites of plasma leakage, but little is known about the amount and functional consequences of binding to tumor endothelial cells. We addressed this issue by examining the effects of RCA I on blood vessels of spontaneous pancreatic islet-cell tumors in RIP-Tag2 transgenic mice. After intravenous injection, RCA I bound strongly to tumor vessels but not to normal blood vessels. At 6 minutes, RCA I fluorescence of tumor vessels was largely diffuse, but over the next hour, brightly fluorescent dots appeared as the lectin was internalized by endothelial cells. RCA I injection led to a dose- and time-dependent decrease in vascular endothelial growth factor receptor-2 (VEGFR-2) immunoreactivity in tumor endothelial cells, with 95% loss over 6 hours. By comparison, VEGFR-3, CD31, and CD105 had decreases in the range of 21% to 33%. Loss of VEGFR-2 was followed by increased activated caspase-3 in tumor vessels. Prior inhibition of VEGF signaling by AG-028262 decreased RCA I binding and internalization into tumor vessels. These findings indicate RCA I preferentially binds to and is internalized by tumor endothelial cells, which leads to VEGFR-2 down-regulation, endothelial cell apoptosis, and tumor vessel regression. Together, the results illustrate the selective impact of RCA I on VEGF signaling in tumor blood vessels.

Concanavalin A, but not glycated albumin, increases subendothelial deposition of von Willebrand factor in vitro

Diabetes is associated with augmentation of prothrombogenic von Willebrand factor (vWF) content in plasma. Earlier, the author and colleagues have shown that high glucose and insulin do not appreciably influence deposition of vWF into the subendothelial extracellular matrix (SECM) produced by cultured human umbilical vein endothelial cells (HUVECs). In the present work, the author used this model to test the effects of nonenzymatically glycated albumin (Glyc-HSA) and two lectins, concanavalin A (ConA) and wheat germ agglutinin (WGA), on vWF deposition into the SECM. First-passage HUVECs were seeded into gelatin-coated 96-well plates and cultured for 6 to 7 days. HSA or Glyc-HSA (at concentrations 25, 50, and 100 microg/mL), and WGA or ConA (4, 8, and 16 microg/mL) were added 3 h after seeding. Cell viability was tested by the MTT method. To determine vWF contents in the SECM, HUVECs were detached by treatment with NH4OH and the residual material was used as a solid phase in an enzyme-linked immunosorbent assay (ELISA)-like assay with primary (anti-vWF) and secondary (peroxidase-conjugated) antibodies. Addition of Glyc-HSA did not essentially influence VWF contents in the SECM (A490 was 0.226 versus 0.268 at 0 and 100 microg/mL, respectively; p > .05, n = 16). Cultivation in the presence of WGA led to the deterioration of cell viability, which was accompanied by a significant decrease of vWF in the SECM (0.248 versus 0.128 at 0 and 16 microg/mL, respectively; p < .001, n = 16). ConA did not influence viability of HUVECs, but this lectin at all concentrations consistently increased the deposition of vWF (up to 164% relative to control, p <.001; n = 16). These data indicate that endothelial carbohydrate determinants and corresponding ligands (namely, mannose-specific lectins) may be involved in the regulation of production and deposition of vWF.

Fetomaternal glycosylation of early placentation events in the African elephant Loxodonta africana

During implantation in the African elephant (Loxodonta africana), fetal trophoblast displaces the surface uterine epithelium and superficially penetrates the uterine glands. This limited invasion is followed by the upgrowth of blunt fingers of endometrial stroma, covered with trophoblast and containing capillaries that subsequently vascularize the growing placenta. We have used lectin histochemistry to compare the glycosylation of maternal endothelial cells in the endometrium with those growing within the trophoblastic processes of a 2 g embryo (approximately 125 days' gestation), and also examine changes in the endometrial glands associated with trophoblastic invasion. Maternal vessels at the apices of the trophoblast-covered stromal upgrowths showed increased expression of terminal N-acetyl galactosamine, N-acetyl glucosamine oligomers, some sialic acids, and tri/tetra-antennate non-bisected complex N-linked glycan, as indicated by increased lectin staining. The areas of increased staining were also more resistant to neuraminidase digestion. Invaded glands had distended walls composed of flattened epithelial cells, some of which showed heavy lectin staining suggestive of intracellular glycan accumulation. The vascular changes suggest that new maternal capillary growth is accompanied by alterations in surface glycosylation. This may be the result of increased glycosyl transferase activity associated with cell proliferation and may also indicate the expression of significantly increased anti-adhesive molecules preventing blood stasis and egress of maternal immunocompetent cells into the fetal compartment.

Selective binding of lectins to embryonic chicken vasculature

Chicken embryos are an excellent model system for studies related to vascular morphogenesis. Development in ovo allows manipulations otherwise difficult in mammals, and the use of chicken-quail chimeras offers an additional advantage to this experimental system. Furthermore, the chicken chorioallantoic membrane has been extensively used for in vivo assays of angiogenesis. Surprisingly, few markers are available for a comprehensive visualization of the vasculature. Here we report the use of lectins for identification of embryonic chicken blood vessels. Nine lectins were evaluated using intravascular perfusion and directly on sections. Our results indicate that Lens culinaris agglutinin, concanavalin A, and wheat germ agglutinin can be used effectively for visualization of vessels of early chicken embryos (E2.5-E4). At later developmental stages, Lens culinaris agglutinin is a better choice because it displays equal affinity for the endothelia of arteries, veins, and capillaries. The findings presented here expand our understanding of lectin specificity in the endothelium of avian species and provide information as to the use of these reagents to obtain comprehensive labeling of the embryonic and chorioallantoic membrane vasculature.

Morphological characteristics of the microvasculature in healing myocardial infarcts

Myocardial infarction (MI) is associated with an angiogenic response, critical for healing and cardiac repair. Using a canine model of myocardial ischemia and reperfusion, we examined the structural characteristics of the evolving microvasculature in healing MI. After 7 days of reperfusion, the infarcted territory was rich in capillaries and contained enlarged, pericyte-poor "mother vessels" and endothelial bridges. During scar maturation arteriolar density in the infarct increased, and a higher percentage of microvessels acquired a pericyte coat (60.4 +/- 6.94% after 28 days of reperfusion vs 30.17 +/- 3.65% after 7 days of reperfusion; p<0.05). The microvascular endothelium in the early stages of healing showed intense CD31/PECAM-1 and CD146/Mel-CAM immunoreactivity but weak staining with the Griffonia simplicifolia lectin I (GS-I). In contrast, after 28 days of reperfusion, most infarct microvessels demonstrated significant lectin binding. Our findings suggest that the infarct microvasculature undergoes a transition from an early phase of intense angiogenic activity to a maturation stage associated with pericyte recruitment and formation of a muscular coat. In addition, in the endothelium of infarct microvessels CD31 and CD146 expression appears to precede that of the specific sugar groups that bind the GS-I lectin. Understanding of the mechanisms underlying the formation and remodeling of the microvasculature after MI may be important in designing therapeutic interventions to optimize cardiac repair.

Pharmacological aspects of targeting cancer gene therapy to endothelial cells

Targeting cancer gene therapy to endothelial cells seems to be a rational approach, because (a) a clear correlation exists between proliferation of tumor vessels and tumor growth and malignancy, (b) differences of cell membrane structures between tumor endothelial cells and normal endothelial cells exist which could be used for targeting of vectors and (c) tumor endothelial cells are accessible to vector vehicles in spite of the peculiarities of the transvascular and interstitial blood flow in tumors. Based on the knowledge on the pharmacokinetics of macromolecules it can be concluded that vectors targeting tumor endothelial cells should own a long blood residence time after intravascular application. This precondition seems to be fulfilled best by vectors exhibiting a slight anionic charge. A long blood residence time would allow the formation of a high amount of complexes between tumor endothelial cells and vector particles. Such high amount of complexes should enable a high transfection rate of tumor endothelial cells. In view of their pharmacokinetic behavior nonviral vectors seem to be more suitable for in vivo targeting tumor endothelial cells than viral vectors. Specific binding of nonviral vectors to tumor endothelial cells should be enhanced by multifunctional ligands and the transduction efficiency should be improved by cationic carriers. Effector genes should encode proteins potent enough to induce reactions which eliminate the tumor tissue. To be effective to that degree such proteins should induce self-amplifying antitumor reactions. Examples for proteins which have the potential to induce such self-amplifying tumor reactions are proteins endowed with antiangiogenic and antiproliferative activity, enzymes which convert prodrugs into drugs and possibly also proteins which induce embolization of tumor vessels. The pharmacological data for such examples are discussed in detail.

Individual cell motility studied by time-lapse video recording: influence of experimental conditions

BACKGROUND

Eukaryotic cell motility plays a key role during development, wound healing, and tumour invasion. Computer-assisted image analysis now makes it a realistic task to quantify individual cell motility of a large number of cells. However, the influence of culture conditions before and during measurements has not been investigated systematically.

METHODS

We have evaluated intraassay and interassay variations in determinations of cellular speed of fibroblastoid L929 cells and investigated the effects of a series of physical and biological parameters on the motile behavior of this cell line. Cellular morphology and organization of filamentous actin were assessed by means of phase-contrast and confocal laser scanning microscopy and compared to the corresponding motility data.

RESULTS

Cell dissociation procedure, seeding density, time of cultivation, and substrate concentration were shown to affect cellular speed significantly. pH and temperature of the medium most profoundly influenced cell motility and morphology. Thus, the mean cell speed was 40% lower at pH 7.25 than at pH 7.6; at 29 degrees C, it was approximately four times lower than at 39 degrees C.

CONCLUSION

Of the parameters evaluated, cell motility was most strongly affected by changes in pH and temperature. In general, changes in cell speed were accompanied by alterations in cell morphology and organization of filamentous actin, although no consistent phenotypic characteristics could be demonstrated for cells exhibiting high cell speed.

Regulation of cdk2 activity in endothelial cells that are inhibited from growth by cell contact

Endothelial cells (ECs) are quiescent in normal blood vessels but undergo rapid bursts of proliferation after vascular injury and during angiogenesis. Here we show that the activity of cyclin-dependent kinase-2 (cdk2), a key regulator of the G1 and S phases of the cell cycle, is expressed at high levels in proliferating ECs but at low levels in ECs that are contact-inhibited for growth. Despite these differences in kinase activity, the protein levels of cdk2 and 1 of its activating subunits, cyclin E, are not modulated by these different growth conditions. The cdk inhibitor p27 is highly expressed in contact-inhibited but not proliferating ECs, whereas the level of cyclin A protein is preferentially expressed in proliferating ECs. p27 protein was detected in immunoprecipitable complexes with cdk2 or cyclin E in cultures that were contact-inhibited for growth. The functional significance of the p27 induction was indicated by the detection of a heat-stable cdk2 inhibitory activity that was induced by endothelial cell-cell contact and could be immunodepleted with anti-p27 antibodies. In a confluent EC monolayer, cdk2 kinase activity was activated by a scraping injury that led to cell migration and proliferation. The injury-induced activation of cdk2 coincided with the downregulation of p27 and the induction of cyclin A. These data demonstrate that p27 is induced in confluent cultures of ECs. They also indicate that both p27 induction and cyclin A downregulation contribute to the inhibition of cdk2 and cell proliferation by cell-cell contact in ECs.

Sialic acid and crystal binding

BACKGROUND

We studied the role of cell surface sialic acid in the adherence of calcium oxalate monohydrate (COM) crystals to Madin-Darby canine kidney (MDCK) cells.

METHODS

Studies were performed with undifferentiated (crystal-binding) cells in subconfluent cultures and maturated (noncrystal-binding) cells in confluent cultures. Lectins were used to study the emergence and abundance of oligosaccharides at the cell surface during epithelial development. The effect of neuraminidase treatment on crystal binding was studied with [14C]COM crystals, and the enzyme-induced release of cell surface-associated sialic acid molecules was monitored by labeling the cells metabolically with [3H]glucosamine.

RESULTS

Binding studies with lectins derived from Maackia Amurensis II (MALII) and Sambucus Nigra (SNA) demonstrated that the cells expressed terminal sialic acids attached to penultimate galactose through alpha 2,3 and alpha 2,6 bonds at different stages of epithelial development. Neuraminidase treatment strongly reduced the affinity of the cell surface for COM crystals in subconfluent cultures. Nevertheless, neuraminidase cleaved more sialic acids from cells in confluent cultures than from those in subconfluent cultures. Peanut agglutinin (PNA), which binds only to sialylated terminal galactose units, adhered to developing but not to maturated cells, unless the latter were pretreated with neuraminidase. Both results indicate that the surface of maturated MDCK cells is more heavily sialylated than that of undifferentiated cells. Free sialic acid molecules showed little or no affinity for COM crystals and did not affect the adherence of the crystals to undifferentiated cells.

CONCLUSIONS

There are at least two models that may explain these results. First, sialic acids are presented at the surface of immature cells in an orientation that specifically matches crystal surface characteristics favoring crystal-cell interactions. Second, sialic acid molecules are not directly associated with the crystals, but may be involved in the exposure of another crystal binding molecule at the cell surface.

Class A scavenger receptors and the phagocytosis of apoptotic cells

Apoptotic cells are rarely seen in situ because of rapid clearance by phagocytes. A number of receptors have been implicated in the recognition and ingestion of dying cells. Class A scavenger receptors (SRs) are multi-domained membrane glycoproteins that can endocytose modified lipoproteins and bind a wide range of ligands. There is growing evidence that they contribute to several biological processes. We present data that suggest class A SRs are involved in the phagocytosis of apoptotic cells.

Recognizing death: the phagocytosis of apoptotic cells

Although apoptotic cell death is widespread, dying cells are rarely seen in situ because of their rapid clearance by neighbouring phagocytes. Phagocytic recognition of apoptotic cells is less well understood than the death programme itself, but an increasing number of recent studies are highlighting its importance. This review discusses the nature of the receptors that have been implicated in apoptotic cell phagocytosis, the mechanisms of uptake and the immunological consequences of apoptotic cell ingestion.

Endothelial cells differentially express functional CXC-chemokine receptor-4 (CXCR-4/fusin) under the control of autocrine activity and exogenous cytokines

Analysis of endothelial cell (EC) chemokine receptor expression by RT-PCR revealed that EC essentially do not express CC-chemokine receptors whereas they express all known CXC-chemokine receptors. Endotheliotropic functions of ligands for CXCR-1, CXCR-2, and CXCR-3 have previously been described. We have consequently performed a detailed analysis of endothelial CXCR-4 expression. CXCR-4 is constitutively expressed by quiescent, resting EC. Cytokine stimulation revealed that bFGF upregulates endothelial CXCR-4 expression, whereas TNF alpha downregulates endothelial CXCR-4 expression. Expression of CXCR-4 mRNA as well as protein is also upregulated in autocrine activated, migrating bovine aortic endothelial cells (BAEC). Furthermore, migrating BAEC preferentially present CXCR-4 on the cell surface as evidenced by cytochemistry and FACS analysis. Lastly, the monospecific CXCR-4 ligand SDF-1 was found to act as a potent inducer of EC chemotaxis. In summary, the data indicate that the CXCR-4/SDF-1 receptor ligand interaction may be an important regulator of activated endothelial cell functions as they occur during vascular remodeling and angiogenesis.

Cell-associated activation of latent transforming growth factor-beta by calpain

Transforming growth factor-beta (TGF-beta) is normally secreted in a latent form, and plasmin-mediated proteolytic cleavage of latency-associated peptide (LAP), a component of latent TGF-beta complex that makes the complex inactive, activates latent TGF-beta. In the present study, we investigated the possible involvement of calpain, one of the cysteine proteases, in the activation of latent TGF-beta. When recombinant latent TGF-beta was incubated with calpain (1-10 u/ml) in a test tube, calpain cleaved LAP and released mature TGF-beta from the latent complex. When calpain was applied to cultured bovine capillary endothelial (BCE) cells, a low concentration of calpain (0.05-0.1 u/ml) inhibited the migration and proliferation of the cells, and these inhibitory effects were abrogated by anti-TGF-beta antibody as well as by calpain inhibitor peptide, but not by alpha2-antiplasmin, a specific inhibitor of plasmin. Active TGF-beta was detected in the conditioned medium of BCE cells collected in the presence of calpain. Chemical cross-linking of (125)I-calpain to BCE cells followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that calpain bound to the cell surface through chondroitinase ABC-sensitive proteoglycan. In addition, treatment of the BCE cells with chondroitinase ABC abrogated the inhibitory effect of calpain on the migration of these cells. Our data thus suggest that calpain is able to activate latent TGF-beta through a mechanism independent of plasmin. This activation is efficient in the presence of cells, and calpain binds to the cell surface via proteoglycan and activates latent TGF-beta, which is targeted to the same surface.

Basic fibroblast growth factor (bFGF) regulates the expression of the CC chemokine monocyte chemoattractant protein-1 (MCP-1) in autocrine-activated endothelial cells

The CC chemokine monocyte chemoattractant protein (MCP)-1 is induced by inflammatory cytokines and acts as a potent regulator of monocyte trafficking. Monocytes adhere preferentially to migrating endothelial cells in vitro and to endothelial cells at the migration front in vivo after aortic balloon denudation injury. Based on these findings, we analyzed MCP-1 expression in migrating and resting bovine aortic endothelial (BAE) cells and identified prominently upregulated levels of MCP-1 expression in migrating BAE cells. Stimulation of resting BAE cells with 5 ng/mL bFGF resulted in a fourfold induction of MCP-1 mRNA expression. The time course of bFGF-induced MCP-1 mRNA expression indicated a rapid and direct stimulation of MCP-1 expression that was detectable 30 minutes after stimulation. Levels of basal MCP-1 expression, as well as upregulated levels of MCP-1 in migrating BAE cells, were downregulated by addition of a neutralizing anti-bFGF monoclonal antibody (1.0 microgram/mL). Digestion of conditioned media of resting BAE cells with collagenase led to a dose-dependent induction of MCP-1 expression in resting BAE cells, which was inhibited > 50% by addition of neutralizing anti-bFGF antibody. Confirmation of the Northern blot experiments by ELISA-based quantitation of MCP-1 protein levels identified threefold to sixfold higher levels of MCP-1 in the supernatants of bFGF-stimulated BAE cells than in unstimulated resting BAE cells. Finally, analysis of MCP-1 expression by in situ hybridization carried out on en face preparations of aortas demonstrated that MCP-1 expression is dramatically upregulated in regenerating endothelial cells in vivo after balloon denudation. Though not establishing a direct causal relation between the preferential adhesion of monocytes to migrating endothelial cells, these findings strongly suggest that autocrine-activated endothelial cell-derived MCP-1 may play a critical role in recruiting monocytes. They furthermore support the concept that bFGF acts as an autocrine regulator of endothelial cell activity and may imply an involvement of bFGF as a mediator of inflammatory cell trafficking.

Glycosylation differences between a cystic fibrosis and rescued airway cell line are not CFTR dependent

Altered glycosylation of mucus and membrane glycoconjugates could explain reported differences in binding of bacterial pathogens to cystic fibrosis (CF) versus normal tissue. However, because bacteria can alter cell surface glycoconjugates, it is not possible to assess the role of cystic fibrosis transmembrane conductance regulators (CFTR) in glycosylation in these studies. To address this issue, we have developed quantitative lectin binding assays to compare cell surface glycosylation in well-matched immortalized CF cells and rescued cell lines. The CF airway bronchial epithelial cell line IB3-1 consistently bound more peanut agglutinin (PNA) than its clonal derivative S9, which stably expresses functional wild-type CFTR. Pretreatment with neuraminidase increased PNA binding and abolished the difference between the two cell lines. However, infection of the IB3-1 cells with a replication-deficient recombinant adenovirus encoding CFTR restored CFTR function but did not alter PNA binding to cells. In contrast, treatment with the weak base ammonium chloride increased PNA binding to both cell lines as expected. Our data show that even clonally related CF and rescued cells can exhibit significant differences in carbohydrate processing. Although the differences that we found are consistent with the proposed role for CFTR in modulating intraorganellar pH, our data strongly suggest that they are CFTR independent. These studies add a cautionary note to the interpretation of differences in glycosylation between CF and normal primary tissues and immortalized cells.

Interendothelial junctions: structure, signalling and functional roles

Endothelial cell-cell adhesive junctions are formed by transmembrane adhesive proteins linked to a complex cytoskeletal network. These structures are important not only for maintaining adhesion between endothelial cells and, as a consequence, for the control of vascular permeability, but also for intracellular signalling properties. The establishment of intercellular junctions might affect the endothelial functional phenotype by the downregulation or upregulation of endothelial-specific activities.

CD44-related chondroitin sulfate proteoglycan, a cell surface receptor implicated with tumor cell invasion, mediates endothelial cell migration on fibrinogen and invasion into a fibrin matrix

Microvascular endothelial cell invasion into the fibrin provisional matrix is an integral component of angiogenesis during wound repair. Cell surface receptors which interact with extracellular matrix proteins participate in cell migration and invasion. Malignant cells use CD44-related chondroitin sulfate proteoglycan (CSPG) as a matrix receptor to mediate migration and invasion. In this study, we examine whether cell surface CSPG can mediate similar events in nonmalignant wound microvascular endothelial cells or whether use of CSPG for migration and invasion is a property largely restricted to malignant cells. After inhibiting CSPG synthesis with p-nitrophenyl beta-d xylopyranoside (beta-d xyloside), wound microvascular endothelial cells were capable of attaching and spreading on the surface of a fibrin gel; however, their ability to invade the fibrin matrix was virtually eliminated. To begin to examine the mechanism by which endothelial cells use CSPG to invade fibrin matrices, cell adhesion and migration on fibrinogen was examined. Endothelial cell adhesion and migration on fibrinogen were inhibited by both beta-d xyloside and after cleavage of chondroitin sulfate from the core protein by chondroitinase ABC. We have determined that wound microvascular endothelial cells express the majority of their proteoglycan as CSPG and that the CSPG core protein is immunologically related to CD44. PCR studies show that these cells express both the "standard" (CD44H) isoform and an isoform containing the variably spliced exon V3. In addition, anti-CD44 antibody blocks endothelial cell migration on fibrinogen. Affinity chromatography studies reveal that partially purified microvascular endothelial cell CSPG binds fibrinogen. These findings suggest that CD44-related CSPG, a molecule implicated in the invasive behavior of tumor cells, is capable of binding fibrinogen/fibrin, thereby mediating endothelial cell migration and invasion into the fibrin provisional matrix during wound repair.

Contraction of fibrillar type I collagen by endothelial cells: a study in vitro

The formation of microvascular sprouts during angiogenesis requires that endothelial cells move through an extracellular matrix. Endothelial cells that migrate in vitro generate forces of traction that compress (i.e., contract) and reorganize vicinial extracellular matrix, a process that might be important for angiogenic invasion and morphogenesis in vivo. To study potential relationships between traction and angiogenesis, we have measured the contraction of fibrillar type I collagen gels by endothelial cells in vitro. We found that the capacity of bovine aortic endothelial (BAE) cells to remodel type I collagen was similar to that of human dermal fibroblasts--a cell type that generates high levels of traction. Contraction of collagen by BAE cells was stimulated by fetal bovine serum, human plasma-derived serum, bovine serum albumin, and the angiogenic factors phorbol myristate acetate and basic fibroblast growth factor (bFGF). In contrast, fibronectin and immunoglobulin from bovine serum, several nonserum proteins, and polyvinyl pyrrolidone (a nonproteinaceous substitute for albumin in artificial plasma) were not stimulatory. Contraction of collagen by BAE cells was diminished by an inhibitor of metalloproteinases (1,10-phenanthroline) at concentrations that were not obviously cytotoxic. Zymography of proteins secreted by BAE cells that had contracted collagen gels revealed matrix metalloproteinase 2. Subconfluent BAE cells that were migratory and proliferating were more effective contractors of collagen than were quiescent, confluent cells of the same strain. Moreover, bovine capillary endothelial cells contracted collagen gels to a greater degree than was seen with BAE cells. Collectively, our observations indicate that traction-driven reorganization of fibrillar type I collagen by endothelial cells is sensitive to different mediators, some of which, e.g., bFGF, are known regulators of angiogenesis in vivo.

Anti-adhesive glycosylation of fibronectin-like molecules in human placental matrix-type fibrinoid

Recently, fibrinoid of the human placenta has been described as being composed of two main types differing in origin and chemical composition. Fibrin-type fibrinoid is mostly a blood clot product. Matrix-type fibrinoid was defined as the extracellular matrix secreted by extravillous trophoblast cells. The structure and composition of matrix-type fibrinoid was addressed in this study, focusing on fibronectins as one major constituent. A panel of antibodies directed against different fibronectin isoforms generated by different mRNA splicing, as well as antibodies recognizing oncofetal carbohydrate epitopes, were used on cryostat, paraffin and Lowicryl sections of placental tissue from different stages of pregnancy. The oncofetal carbohydrate epitopes studied comprised the blood group precursor antigens i and I. We identified the blood group-related antigen i as an additional marker for matrix-type fibrinoid. The antigen was detected on a glycoprotein that was also recognized by the fibronectin antibodies in western blots. Immunohistochemically this i-glycosylated oncofetal fibronectin-like molecule of about 55 kDa is expressed only by the invasive phenotype of extravillous trophoblast. Long chain carbohydrate moieties with a structure fulfilling the criteria for i reactivity on human placental fibronectin are known to have antiadhesive properties and to enhance resistance of the protein chain to proteolysis. These properties underline the functional relevance of glycosylation of fibronectins in matrix-type fibrinoid and suggest matrix-type fibrinoid is a typical matrix of invasive cells. In contrast, the more mature blood group precursor I could be detected after sialidase pretreatment of sections. This antigen was expressed by villous, non-invasive trophoblast.

Ovarian angiogenesis. Phenotypic characterization of endothelial cells in a physiological model of blood vessel growth and regression

Angiogenesis occurs during embryogenesis and is a down-regulated process in the healthy adult that is almost exclusively linked to pathological conditions such as tumor growth, wound healing, and inflammation. Physiological angiogenic processes in the adult are restricted to the female reproductive system where they occur cyclically during the ovarian and uterine cycle as well as during pregnancy. By systematically analyzing the phenotypic changes of endothelial cells during bovine corpus luteum (CL) formation and regression, we have established a physiological model of blood vessel growth and regression. Quantitation of vessel density, percentage of vessels with lumen, and ratio of Bandeiraea simplicifolia-I to von Willebrand Factor-positive endothelial cells were established as parameters of angiogenesis. Sprouting endothelial cells invade the growing CL and continue to grow throughout the first third of the ovarian cycle. Thereafter the mature CL is characterized by a dense network of vessels with gradually decreasing vessel density. During luteolysis and for several weeks thereafter (regressing and residual CL) all newly formed vessels regress, which is accompanied by gradual foreshortening and rounding of endothelial cells and subsequent detachment. Based on histochemical detection of nucleosomal fragmentation products physiological blood vessel regression in the cyclic CL does not appear to involve endothelial cell apoptosis. Lectin histochemical analysis revealed a distinct alteration of endothelial cell glycoconjugate expression during ovarian angiogenesis comparable with the distinct pattern of hyperglycosylation of cultured migrating endothelial cells (up-regulation of binding sites for Lycopersicon esculentum lectin, wheat germ agglutinin, neuraminidase-treated peanut agglutinin, and Ricinus communis agglutinin-I on sprouting ECs). Northern blot analysis of glycosyltransferases during the different stages of angiogenesis revealed an up-regulation of beta-galactoside alpha 2,6-sialyltransferase and alpha 1,3-galactosyltransferase mRNA expression during the angiogenic stages of CL formation. These data establish the ovarian angiogenesis model as a suitable experimental system to study the functional and phenotypic properties of endothelial cells in sprouting and regressing blood vessels and provide additional evidence for the importance of endothelial cell surface glycoconjugates during angiogenesis.

Differences in binding of platelet factor 4 to vascular endothelium in vivo and endothelial cells in vitro

The binding of fluorescein-labelled recombinant human platelet factor 4 (rhPF4) to the vasculature of the hamster cheek pouch in vivo was compared with that to cultured endothelial cells (EC) from human umbilical veins (HUVEC) and arteries (HUAEC) and from human aorta (HAEC). In vivo data: systemically injected rhPF4 rapidly disappeared from plasma in a biphasic pattern (t1/2 = 2 and 41 min). High intensity non-uniform binding of rhPF4 occurred at short specific sites along both arterioles and venules. The length of the intense sites was 76 +/- 46 microns and their frequency was 10 +/- 4 per cm2 cheek pouch. Heparin was injected at 4 and 9 min, but not 30 min, post-rhPF4 displaced most of the high intensity labelling indicating internalization with time. Neither pretreatment with more than 50-fold excess of unlabelled rhPF4 nor histamine- or LTB4-induced vascular macromolecular leakage changed the frequency of short intense sites. In vitro data: uniform time-dependent intense binding of rhPF4 occurred in a similar fashion in subconfluent HUVEC, HUAEC and HAEC. All cell types showed nuclear staining, demonstrating internalization. When heparin was given to EC prior to rhPF4, binding was delayed in time but not blocked. In conclusion, rhPF4 does not bind uniformly with high intensity along pre- and post-capillary vessels of the hamster cheek pouch in vivo as predicted by the rhPF4-labelling of subconfluent (migrating/proliferating) human EC in vitro. The short infrequent sites of intense rhPF4-labeling in vivo may represent regions of endothelial cell migration/proliferation similar to subconfluent EC in culture.

Differentiation of endothelial cells: analysis of the constitutive and activated endothelial cell phenotypes

Endothelial cells line the inside of all blood vessels, forming a structurally and functionally heterogeneous population of cells. Their complexity and diversity has long been recognized, yet very little is known about the molecules and regulatory mechanisms that mediate the heterogeneity of different endothelial cell populations. The constitutive organ- and microenvironment-specific phenotype of endothelial cells controls internal body compartmentation, regulating the trafficking of circulating cells to distinct vascular beds. In contrast, surface molecules associated with the activated cytokine-inducible endothelial phenotype play a critical role in pathological conditions including inflammation, tumor angiogenesis, and wound healing. Differentiation of the endothelial cell phenotypes appears to follow similar mechanisms to the differentiation of hematopoietic cells, with the exception that endothelial cells maintain transdifferentiating competence. The present review offers a scheme of endothelial cell differentiation and discusses the possible applications of differentially expressed endothelial cell molecules as targets for directed therapeutic intervention.

A new model of vasculogenesis and angiogenesis in vitro as compared with vascular growth in the avian area vasculosa

In cultures of dissociated quail epiblast the basic constituents of the vascular system, blood cells and endothelial cells can be induced by basic fibroblast growth factor (Flamme and Risau, Development, 116: 435-439, 1992). As we show here, in those cultures three types of vascular plexus differentiate spontaneously under different culture conditions: At the 3rd day a vascular plexus appears in situ closely resembling the vascular plexus of the quail area opaca vasculosa (vasculogenesis). Vascular sprouts are formed, extending long filopodia at their tips. Such filopodia are shown to build the first intervascular bridges in the growing vascular plexus of the area vasculosa at embryonic day 3. Connections of filopodia turn out to be precursors of new capillaries interconnecting pre-existing blood vessels (angiogenesis). Two further types of in vitro capillary plexus differentiate in long term endothelial cell cultures derived from induced angioblasts. Whereas one closely resembles so-called angiogenesis in vitro, the third type comprises mainly multinucleated giant endothelial cells lining loop like capillaries and represents a differentiation of aging endothelial cell culture. Thus, the present in vitro model is an approach to the sequence of angioblast induction, vasculogenesis, and angiogenesis.