Spatiotemporal segregation of endothelial cell integrin and nonintegrin extracellular matrix-binding proteins during adhesion events

Oxidative stress enhanced the transforming growth factor-β2-induced epithelial-mesenchymal transition through chemokine ligand 1 on ARPE-19 cell

Fibroblast-like transformation of retinal pigment epithelial (RPE) cells is a pathological feature of proliferative vitreoretinopathy (PVR) that may cause blindness. The effect of oxidative stress alone or together with transforming growth factor-beta 2 (TGF-β2) on epithelial-mesenchymal transformation (EMT) is not fully understood in RPE. TGF-β2 induced the upregulation EMT markers including α-smooth muscle actin (α-SMA), Snail, and Slug and downregulation of E-cadherin (E-cad) in ARPE-19 cells. Hydrogen peroxide (H₂O₂) not only upregulated α-SMA but also enhanced the effect of TGF-β2 on the expression of Snail and Slug. The CXCL family of cytokines could be the mediators of EMT induced by H₂O₂ and TGF-β2. H₂O₂ induced CXCL1, that upregulated α-SMA and fibronectin. Both SB225002, an inhibitor of CXCR2, and antioxidant N-acetylcysteine suppressed the TGF-β2-induced EMT in ARPE-19 cells. Taken together, the results suggest that oxidative stress enhanced TGF-β2-induced EMT through the possible autocrine effect of CXCL1 on CXCR2 in ARPE-19 cells.

Looking into laminin receptor: critical discussion regarding the non-integrin 37/67-kDa laminin receptor/RPSA protein

The 37/67-kDa laminin receptor (LAMR/RPSA) was originally identified as a 67-kDa binding protein for laminin, an extracellular matrix glycoprotein that provides cellular adhesion to the basement membrane. LAMR has evolutionary origins, however, as a 37-kDa RPS2 family ribosomal component. Expressed in all domains of life, RPS2 proteins have been shown to have remarkably diverse physiological roles that vary across species. Contributing to laminin binding, ribosome biogenesis, cytoskeletal organization, and nuclear functions, this protein governs critical cellular processes including growth, survival, migration, protein synthesis, development, and differentiation. Unsurprisingly given its purview, LAMR has been associated with metastatic cancer, neurodegenerative disease and developmental abnormalities. Functioning in a receptor capacity, this protein also confers susceptibility to bacterial and viral infection. LAMR is clearly a molecule of consequence in human disease, directly mediating pathological events that make it a prime target for therapeutic interventions. Despite decades of research, there are still a large number of open questions regarding the cellular biology of LAMR, the nature of its ability to bind laminin, the function of its intrinsically disordered C-terminal region and its conversion from 37 to 67 kDa. This review attempts to convey an in-depth description of the complexity surrounding this multifaceted protein across functional, structural and pathological aspects.

MT-MMPS as Regulators of Vessel Stability Associated with Angiogenesis

The development of vascular system depends on the coordinated activity of a number of distinct families of molecules including growth factors and their receptors, cell adhesion molecules, extracellular matrix (ECM) molecules, and proteolytic enzymes. Matrix metalloproteases (MMPs) are a family of ECM degrading enzymes required for both physiological and pathological angiogenesis. Increasing evidence, point to a direct role of membrane type-MMPs (MT-MMPs) in vascular system stabilization, maturation, and leakage. Our understanding of the nature of MT-MMP interaction with extracellular and cell surface molecules and their multiple roles in vessel walls and perivascular stroma may provide new insights into mechanisms underlying vascular cell–ECM interactions and cell fate decisions in pathological conditions. Regulation of vascular leakage by MT-MMP interactions with the ECM could also lead to novel targeting opportunities for drug delivery in tumor. This review will shed lights on the emerging roles of MT1-MMP and MT4-MMP in vascular system alterations associated with cancer progression.

Modulation of in vitro attachment, proliferation and osteogenic differentiation of rat bone-marrow-derived stem cells using different molecular mass chitosans and their blends with gelatin

We systematically investigated the behaviors of rat bone-marrow-derived stem cells (MSCs) on films prepared from high-molecular-mass chitosan (CH), low-molecular-mass chitooligosaccharide (COS) and their blends with gelatin (G) at various weight blending ratios. On the first day after seeding, the spreading areas of MSCs attached on the blended G/CH and G/COS films were larger than those attached on pure gelatin and COS films. Round-shaped MSCs on pure CH film were observed. The number of proliferated MSCs was also dominant in the case of blended films, at some certain blending ratios which correlated to suitably positive charge of the blended films obtained from zeta potential measurement. Among pure materials, attachment and proliferation of MSCs on COS film were comparable to those on gelatin film while CH film was toxic. The difference in toxicity of CH and COS was also confirmed by Annexin V-FITC/PI apoptosis test. After a 7-day culture under osteogenic induction, the blended films were also found to be more preferable materials for in vitro osteogenic differentiation of MSCs, as confirmed by alkaline phosphatase (ALP) activities, calcium contents and Von Kossa staining. It was proved from this study that attachment, proliferation and osteogenic differentiation of MSCs strongly depended on molecular mass of CHs and the ratio of their blends with gelatin.

Cell culture models of higher complexity in tissue engineering and regenerative medicine

Cell culture techniques have tended to be used in biomaterial research as a screening method prior to embarking on specific in vivo experimentation. This presentation aims at showing that it is possible to develop more sophisticated in vitro systems using primary human cells in co-culture with other cell types and biomaterials in a three-dimensional setting. While the predictive value of such systems is still not proven these models can be employed to unravel the complexity of biological systems in order to understand molecular mechanisms of cell-cell and cell-material interactions. The brief overview is under the headings of basic principles of relevant culture systems, the study of inflammation and the healing response, scenarios for specific biomaterial applications and future directions. How human endothelial cells can be usefully incorporated into more complex cell culture models is presented as an example of how relevant questions in tissue engineering and regenerative medicine can be addressed. The central tenet of this paper is that it is possible to refine in vitro methodology using cells of human origin to establish relevant assay systems that more closely simulate the cellular and molecular microenvironment encountered in a specific situation of regeneration using biomaterials.

Epithelial-derived fibronectin expression, signaling, and function in intestinal inflammation

Fibronectin (FN) is a multifunctional extracellular matrix protein that plays an important role in cell proliferation, adhesion, and migration. FN expression or its role in colitis is not known. The goal of this study is to characterize FN expression, regulation, and role during intestinal inflammation. Wild-type and transgenic mice expressing luciferase under the control of the human FN promoter, given water or 3% dextran sodium sulfate, were used as animal models of colitis. The Caco2-BBE model intestinal epithelial cell line was used for in vitro studies. FN protein is abundantly expressed by surface epithelial cells in the normal colon. Immunohistochemistry and luciferase assay in mice expressing the FN promoter linked to luciferase demonstrated that FN synthesis was up-regulated during colitis, during both the acute phase and the healing phase. In vitro experiments demonstrated that FN increased the expression of the FN integrin receptor alpha5beta1 in a dose- and time-dependent manner. FN also induced the expression and activation of NF-kappaB. Further, FN potentiated Caco2-BBE cell attachment and wound healing, which was inhibited by RGD peptide as well as NF-kappaB inhibitors MG-132 and 1-pyrrolidinecarbodithioic acid, ammonium salt. In conclusion, FN is abundantly expressed and synthesized by colonic epithelial cells. FN is transcriptionally up-regulated in epithelial cells during both the dextran sodium sulfate-induced colitic and the recovery phase. FN enhances cell attachment and wound healing, which is dependent on binding to the integrin receptor and the NF-kappaB signaling. Together our data show that epithelial-derived FN potentiates cell attachment and wound healing through epithelial-matrix interactions and that FN expression may have important implications for maintaining normal epithelial integrity as well as regulating epithelial response to injury during colitis.

The extracellular matrix and blood vessel formation: not just a scaffold

The extracellular matrix plays a number of important roles, among them providing structural support and information to cellular structures such as blood vessels imbedded within it. As more complex organisms have evolved, the matrix ability to direct signalling towards the vasculature and remodel in response to signalling from the vasculature has assumed progressively greater importance. This review will focus on the molecules of the extracellular matrix, specifically relating to vessel formation and their ability to signal to the surrounding cells to initiate or terminate processes involved in blood vessel formation.

Adhesion Receptors Mediate Efficient Non-viral Gene Delivery

For a variety of reasons, including production limitations, potential unanticipated side effects, and an immunological response upon repeated systemic administration, virus-based vectors are as yet not ideal gene delivery vehicles, justifying further research into alternatives. Unlike viral vectors, non-viral vectors pose minimal health risks, but to meet therapeutic requirements their efficacy needs major improvement. This goal may be accomplished by better defining the mechanism of non-viral gene delivery and exploiting specific cellular properties. Here we demonstrate that transfection of epithelial cells with lipoplexes is almost exclusively mediated by the beta1 integrin cell surface receptor. More important, we show that in general, adhesion receptors can be exploited by lipoplexes to gain access to cells, including difficult-to-transfect primary neural stem cells and suspension cells, thereby leading to productive transfection. We propose that adhesion receptors serve as "natural" receptors for lipoplexes. As no natural cellular receptors for lipoplexes have previously been identified, our results are an important step forward in understanding the mechanisms of non-viral gene delivery. Moreover, the finding that adhesion receptors mediate efficient non-viral gene delivery paves the way for the optimization of (standard) transfection procedures as well as ex vivo gene therapy protocols using non-viral vectors.

Neuropilin-1 regulates attachment in human endothelial cells independently of vascular endothelial growth factor receptor-2

Neuropilin-1 (NRP-1) is a type 1 membrane protein that binds the axon guidance factors belonging to the class-3 semaforin family. In endothelial cells, NRP-1 serves as a co-receptor for vascular endothelial growth factor (VEGF) and regulates VEGF receptor 2 (VEGFR-2)-dependent angiogenesis. Although gene-targeting studies documenting embryonic lethality in NRP-1 null mice have demonstrated a critical role for NRP-1 in vascular development, the activities of NRP-1 in mature endothelial cells have been incompletely defined. Using RNA interference-mediated silencing of NRP-1 or VEGFR-2 in primary human endothelial cells, we confirm that NRP-1 modulates VEGFR-2 signaling-dependent mitogenic functions of VEGF. Importantly, we now show that NRP-1 regulates endothelial cell adhesion to extracellular matrix proteins independently of VEGFR-2. Based on its dual role as an enhancer of VEGF activity and a mediator of endothelial cell adhesiveness described here, NRP-1 emerges as a promising molecular target for the development of antiangiogenic drugs.

A role for Tbx5 in proepicardial cell migration during cardiogenesis

Transcriptional regulatory cascades during epicardial and coronary vascular development from proepicardial progenitor cells remain to be defined. We have used immunohistochemistry of human embryonic tissues to demonstrate that the TBX5 transcription factor is expressed not only in the myocardium, but also throughout the embryonic epicardium and coronary vasculature. TBX5 is not expressed in other human fetal vascular beds. Furthermore, immunohistochemical analyses of human embryonic tissues reveals that unlike their epicardial counterparts, delaminating epicardial-derived cells do not express TBX5 as they migrate through the subepicardium before undergoing epithelial-mesenchymal transformation required for coronary vasculogenesis. In the chick, Tbx5 is expressed in the embryonic proepicardial organ (PEO), which is composed of the epicardial and coronary vascular progenitor cells. Retrovirus-mediated overexpression of human TBX5 inhibits cell incorporation of infected proepicardial cells into the nascent chick epicardium and coronary vasculature. TBX5 overexpression as well as antisense-mediated knockdown of chick Tbx5 produce a cell-autonomous defect in the PEO that prevents proepicardial cell migration. Thus, both increasing and decreasing Tbx5 dosage impairs development of the proepicardium. Culture of explanted PEOs demonstrates that untreated chick proepicardial cells downregulate Tbx5 expression during cell migration. Therefore, we propose that Tbx5 participates in regulation of proepicardial cell migration, a critical event in the establishment of the epicardium and coronary vasculature.

Gamma radiation inhibits fibroblast-mediated collagen gel retraction

Radiation exposure is known to impair healing in irradiated areas. Fibroblasts play a major role in the production and modification of extracellular matrix in wound repair. Since one important aspect of wound repair is the contraction of the wound, this study investigated the effects of radiation on the ability of fibroblasts to mediate collagen gel contraction in an in vitro model of wound retraction. After irradiation, the cells were detached and suspended in a solution of rat tail tendon collagen. Radiation exposure decreased retraction, and this effect was dose dependent. In order to define the mechanism of reduced gel retraction, we investigated alpha2beta1 cell surface integrin and fibronectin, which are thought to mediate contraction, and prostaglandin E2 (PGE2), which is known to inhibit this process. PGE2 release increased dose responsively following radiation. The cyclooxygenase inhibitor indomethacin could partially restore the contractile activity of irradiated fibroblasts. Fibronectin production in gel culture showed a significant decrease. In contrast, there was no decrease in alpha2beta1 integrin expression in radiated cells. In conclusion, radiation decreases fibroblast-mediated gel contraction. Increased PGE2 production and decreased fibronectin production by irradiated fibroblasts may contribute to this effect and may be in part responsible for poor healing of radiated tissue.

A stable matrix for generation of tissue-engineered nonthrombogenic vascular grafts

The potential of freeze-dried fibrin glue (FG) in combination with growth factor (GF) and gelatin (GEL) is evaluated for use as a matrix for endothelialization of artificial vascular grafts made of polytetrafluoroethylene (PTFE, Teflon) and polyethyleneterephthalate (Dacron). Improved adhesion and proliferation of human umbilical vein endothelial cells are demonstrated on different substrates coated with the FG-GF/FG-GF-GEL mixture, compared with the respective bare surfaces. The strength of adhesion of endothelial cells on the coated matrices was found to be adequate to resist shear stress when monolayers were exposed to forces of flow in an in vitro parallel plate flow chamber. The monolayers maintained physiological nonthrombogenic character as evidenced by in vitro platelet adhesion and response to agonist measurements. Nitric oxide synthesis by cells grown on the study matrices was also found to be normal. Thus, the matrix composition and the coating technique, as presented here, can be easily applied to generate tissue-engineered biomaterials with a nonthrombogenic endothelial cell monolayer for cardiovascular implants. The freeze-drying of the coated matrix ensures prolonged stability and thus the materials can be stored in a ready-to-use state for endothelial cell sodding or seeding.

Vascular endothelial cells that express dystroglycan are involved in angiogenesis

We have earlier shown that dystroglycan (DG) is a lamininbinding protein and as such is a cell adhesion molecule. DG is a heterodimer of α andβ DG subunits. β-dystroglycan (βDG) is the membrane spanning subunit, whereas the α subunit is bound to the extracellular domain ofβDG. To study physiological function of the protein, we expressed full-length DG (FL-DG) and the cytoplasmic domain of βDG(ΔβDG) in bovine aortic endothelial cells (BAE) and examined their effects on cell adhesion, migration, proliferation and tube formation. FL-DG enhanced adhesion of BAE to laminin-1, whereas ΔβDG inhibited it. Cell migration was inhibited by overexpressing ΔβDG in these cells,although it was not affected by FL-DG overexpression. In a proliferation assay, FL-DG decreased the growth rate, and it also caused cells to extensively spread. ΔβDG caused opposite effects; it increased the growth rate and reduced the cell surface area. In a tube formation assay on Matrigel, FL-DG caused an obvious inhibition, whereas ΔβDG accelerated tube formation. These results suggest a potential role of endothelial dystroglycan in the control of angiogenesis. Anti-βDG immunohistochemistry indicated increased expression of DG in vascular endothelial cells within malignant tumors. By contrast, the antibody failed to stain endothelial cells in normal tissues. In cultured BAE, the level ofβDG was low in serum-deprived quiescent cells and was upregulated in proliferating cells. Our results suggest that the expression of DG in endothelial cells is under a dynamic regulation and may play a role in angiogenesis.

Dynamic platelet accumulation at the site of the occluded middle cerebral artery and in downstream microvessels is associated with loss of microvascular integrity after embolic middle cerebral artery occlusion

Information is lacking regarding dynamic platelet accumulation at the site of the occluded middle cerebral artery (MCA) and the relationship between platelet aggregation in downstream cerebral microvessels and loss of perfusion and vascular integrity of these microvessels. In the present study, we employed a model of embolic MCA occlusion in the rat to simultaneously measure temporal and spatial profiles of platelet accumulation at the site of the embolus occluding the MCA and within downstream cerebral microvessels. We also measured the integrity of microvessels and matrix metalloproteinase (MMP) activity in ischemic brain. Rats (n=36) were subjected to embolic MCA occlusion. Immunohistochemistry was used to detect microvascular integrity, plasminogen activator inhibitor 1 (PAI-1) and the deposition of fibrin. SDS-PAGE zymography was used to measure MMP2 and MMP9 activities. Accumulation of platelets and increases in PAI-1 immunoreactivity at the site of the embolus occluding the MCA were detected 1 h (n=7) and 4 h (n=7) after ischemia, respectively, and numbers of GPIIb/IIIa immunoreactive downstream cerebral microvessels increased significantly (209+/-59; n=7; P<0.05) 4 h after ischemia, suggesting dynamic platelet aggregation. A significant (n=7; P<0.01) diffuse loss of type IV collagen immunoreactivity in microvessels was temporally associated with platelet GPIIb/IIIa immunoreactivity within the vessels. Triple immunostaining revealed that microvessels containing platelet aggregates exhibited loss of type IV collagen immunoreactivity and both intra- and extra-vascular fibrin deposition, suggesting that intravascular platelet aggregation is associated with decreases in the integrity of the microvascular basal lamina and blood-brain barrier leakage. A significant increase (P<0.05) in MMP9 was detected at 4 h (n=3) and 24 h (n=3) after ischemia but levels of MMP2 were not significantly changed in ischemic brain. Our data suggest that dynamic platelet aggregation in ischemic brain may contribute to time-dependent resistance to fibrinolysis. In addition, platelet deposition and increased MMP9 coincided with degradation of type IV collagen and loss of vascular integrity. These data suggest an important role for post-occlusive distal platelet deposition in the pathophysiology of stroke.

Engineering of vascular ingrowth matrices: are protein domains an alternative to peptides?

Anastomotic intimal hyperplasia and surface thrombogenicity are the main reasons for the high failure rate of prosthetic small-diameter vascular grafts. While anastomotic intimal hyperplasia is a multifactorial event, ongoing surface thrombogenicity is primarily caused by the lack of an endothelium, even after years of clinical implantation. After decades of poorly performing synthetic artery-grafts, tissue engineering has emerged as a promising approach to generate biologically functional bio-synthetic hybrid grafts mimicking native arteries regarding the presence of an endothelial lining on the blood surface. "In vitro endothelialization" represented the first generation of such tissue-engineered vascular grafts, utilising cell culture techniques for the creation of a confluent autologous endothelium on ePTFE grafts. The clinical long-term results with this method in almost 200 patients are highly encouraging, showing patencies equal to vein grafts. Since "in vitro endothelialization" requires cell culture facilities, it will always be confined to large centres. Therefore, research of the 1990s turned to the development of spontaneously endothelializing implants, to make tissue-engineered grafts amenable to the entire vascular-surgical community. Apart from scaffold designs allowing transmural ingrowth, biological signalling through a facilitating ingrowth matrix holds a key to spontaneous endothelialization. In biological signalling, the increasingly deeper understanding of bio-active molecules and the discovery of domains and peptide sequences during the 1980s created the expectation in the 1990s that peptide signalling may be all that is needed. This present review highlights the possible problems associated with such a reductionist approach. Using the fibronectin molecule, we demonstrated that domains may be more suitable modules in tissue engineering than peptide sequences.

Adhesion of cultured bovine aortic endothelial cells to laminin-1 mediated by dystroglycan

Expression of dystroglycan (DG) by cultured bovine aortic endothelial (BAE) cells was confirmed by cDNA cloning from a BAE cDNA library, Northern blotting of mRNA, Western blotting of membrane proteins, and double immunostaining with antibodies against betaDG and platelet endothelial cell adhesion molecule-1. Immunocytochemical analysis revealed localization of DG in multiple plaques on the basal side of resting cells. This patchy distribution was obscured in migrating cells, in which the most prominent staining was observed in the trailing edge anchoring the cells to the substratum. Biotin-labeled laminin-1 overlay assay of dissociated BAE membrane proteins indicated the interaction of laminin-1 with alphaDG. The laminin alpha5 globular domain fragment expressed in bacteria and labeled with biotin could also bind alphaDG on the membrane blot, and the unlabeled fragment disrupted the binding of biotin-laminin-1 to alphaDG. The interaction of biotin-laminin-1 with alphaDG was inhibited by soluble alphaDG contained in the conditioned medium from DG cDNA-transfected BAE cells and by a series of glycosaminoglycans (heparin, dextran sulfate, and fucoidan). Soluble alphaDG in the conditioned medium inhibited the adhesion of BAE cells to laminin-1-coated dishes, whereas it had no effect on their adhesion to fibronectin. All three glycosaminoglycans that disrupted the biotin-laminin-1 binding to alphaDG inhibited BAE cell adhesion to laminin-1, whereas they failed to inhibit the adhesion to fibronectin. These results indicate a role of DG as a non-integrin laminin receptor involved in vascular endothelial cell adhesion to the extracellular matrix.

Alterative expression of the collagenase and adhesion molecules in the highly metastatic clones of human colonic cancer cell lines

Human colonic carcinoma cell lines, KM12C, KM12SM and KM12L4, were previously established and their in vivo metastatic potentials have been well evaluated. The highly metastatic cell lines KM12SM and KM12L4 were derived from the parental low metastatic cell line KM12C in vivo. To evaluate the metastatic behavior of these cell lines in vitro, we examined colony formation on monolayers of the pulmonary arterial endothelial (CPAE) cells. On day 4, the highly metastatic cell lines showed an approximately 2-fold increase in number of colonies on CPAE cell monolayers relative to the parental KM12C cell line. To investigate what evidence is correlated with their metastatic and invasive abilities, Northern blot analysis and flow cytometry were performed in all cell lines. According to the results of Northern blot analysis, the levels of matrix metalloproteinase (MMP)-2 and c-met mRNA expression were increased in highly metastatic cell lines as compared with the parental cell line. We also examined the cell-surface expression of several adhesion molecules by flow cytometry. The levels of expression of sialyl Lewisa antigen (sLe(a)) in KM12SM and KM12L4 were twice higher than that in KM12C. However, the levels of expression of E-cadherin in KM12SM and KM12L4 were decreased to half that in KM12C. The alterative expression of the collagenase and adhesion molecules might contribute to their metastatic/invasive abilities of these cell lines both in vivo and in vitro.

Resistance of freshly adherent endothelial cells to detachment by shear stress is matrix and time dependent

PURPOSE

The placement of endothelial cells on the surfaces of arteries immediately after vascular interventions has the potential to limit restenosis by inhibiting intimal thickening and by stimulating arterial enlargement. Because such re-endothelialization is dependent on rapid formation of strong endothelial cell-matrix interactions, experiments were performed to identify the extracellular matrix that provided endothelial cells with the greatest resistance to detachment by a shear stress in the least amount of time.

MATERIALS AND METHODS

Rabbit microvascular endothelial cells were plated onto glass slides coated with collagen, laminin, vitronectin, or fibronectin. After allowing 5-45 minutes for cell adhesion, each slide was placed in a parallel plate chamber, and the number of cells present before and after exposure of the cells to shear stresses (1-25 dynes/cm2) were counted.

RESULTS

Endothelial cell retention to the matrix-coated slides was time and matrix dependent. The percentages of endothelial cells retained after adhesion times of 5, 15, 30, and 45 minutes followed by exposure to 15 dynes/cm2 were 9%, 20%, 32%*, and 38%* for collagen; 7%, 20%, 36%*, and 49%* for laminin; 35%, 47%, 62%, and 76%* for vitronectin; and 64%, 58%, 71%, and 78% for fibronectin, respectively (*P < .05 versus 5 minutes adhesion). Similar results were obtained for lower and higher shear stresses, indicating that cell retention was independent of shear stress above 1 dyne/cm2.

CONCLUSIONS

The resistance of freshly adherent endothelial cells to detachment by shear stress is matrix- (fibronectin approximately equal to vitronectin > laminin approximately equal to COL) and time-dependent. Fibronectin provided the greatest cell retention in the least amount of time.

Using avidin-mediated binding to enhance initial endothelial cell attachment and spreading

Binding between the protein avidin and the vitamin biotin was used as an extrinsic, high affinity receptor-ligand system to augment the intrinsic integrin-dependent cellular adhesion mechanism. Glass substrates were coupled with avidin receptors through an adsorbed film of biotinylated bovine serum albumin (b-BSA). The avidin-treated slides then were seeded with biotinylated bovine aortic endothelial cells (BAEC). A 3:1 ratio of BSA:b-BSA provided the best results in terms of specific cellular attachment, growth, and spreading. Control surfaces consisted of bare glass or glass with adsorbed BSA. Attachment of unmodified BAEC to glass decreased in the presence of anti-beta 1 integrin antibody. Adhesion of biotinylated BAEC to avidin-treated slides was not affected by anti-beta 1 integrin antibody, consistent with integrin-independent avidin-mediated adhesion. The initial rate of cell spreading was greatest for avidin-biotin-mediated adhesion (80.0 +/- 25.6 microns2/h), followed by integrin-dependent cellular adhesion on plain glass (35.7 +/- 7.7 microns2/h) and, finally, by adhesion on BSA-coated protein surfaces (10.2 +/- 0.3 microns2/h). Biotinylated and unmodified BAEC, cultured for 1 h in serum-containing media, were subjected to laminar flow in a variable-height flow chamber that provided a range of shear stresses from 0.2 to 75 dynes/cm2. The critical shear stress required to detach 50% of the cells in serum-containing media increased from 4.6 +/- 0.8 dynes/cm2 for integrin-dependent adhesion to 12.6 +/- 1.2 dynes/cm2 for avidin-biotin-mediated adhesion. Avidin-mediated attachment for biotinylated BAEC increased initial cellular spreading rates and strength of attachment (i.e., at 1 h) by a factor of two and three, respectively. These results support the hypothesis that integrin-mediated cell attachment and spreading can be enhanced using high affinity integrin-independent binding.

Further characterization of a new in vitro angiogenesis model under serum free culture conditions; suppression of endothelial cell differentiation by serum

We studied the regulation of the extracellular matrix in the recently established murine vascular endothelial cell clones, F-2 or F-2C. F-2 cells constitutively show a cobblestone growth pattern under serum supplemented culture conditions, whereas F-2C cells undergo spontaneous histodifferentiation to form tubular structures in chemically defined media. We reported that the tubulogenesis induced by F-2C might relate to the heavy deposition of a 'basement membrane analog' as a subendothelial matrix (SEM). We further characterized the regulation of extracellular matrix (ECM) metabolism in these cell clones, in terms of gelatinase expression, ECM degradation and the effects of serum. F-2C cells in culture medium containing 1% serum did not undergo tubulogenesis but presented cobblestone growth. Zymography analysis showed that both F-2 and F-2C cells express two gelatinase (72 and 92 kDa). However, F-2 cells mainly expressed the former and faintly the latter, whereas F-2C mainly expressed the latter. Proteolysis studies showed that the spent media conditioned by F-2C cells partially cleaved type IV collagen and completely degraded type V collagen. The cleavage of type V collagen was suppressed by the addition of serum, whereas that of type IV collagen was not. The proteolysis of laminin and fibronectin by the conditioned medium was not observed. Serum-supplemented F-2 or F-2C cultures markedly suppressed SEM deposition. These results indicated that F-2C cells under serum free culture conditions not only present a simple and useful in vitro model with which to study the dynamic processes of proteolysis and ECM metabolism during the sequential phases of angiogenesis, but is also useful for analyzing the serum effects on angiogenesis (AG).

Coculture conditions alter endothelial modulation of TGF-beta 1 activation and smooth muscle growth morphology

We examined whether endothelial cells (ECs) inhibit smooth muscle cell (SMC) transforming growth factor-beta 1 (TGF-beta 1) activation in bilayer coculture. Western analysis showed that SMCs cocultured with ECs as a bilayer had lower amounts of active TGF-beta 1 protein compared with SMCs cultured alone and SMCs cocultured with ECs as a monolayer. EC inhibition of TGF-beta 1 activation could be blocked with plasminogen activator inhibitor-1 (PAI-1) antibody. Similarly, SMC hill-and-valley growth, a marker for TGF-beta 1 activity, was present in SMCs cultured alone and SMCs cocultured with ECs as a monolayer but was absent in SMCs cocultured as a bilayer. SMCs cocultured with ECs as a bilayer migrated at a greater rate than SMCs cultured either alone or cocultured as a monolayer. The EC effect on SMC migration was inhibited by the addition of 5 ng/ml TGF-beta 1. ECs had no effect on SMC RNA levels of TGF-beta 1. PAI-1 levels were increased in ECs and ECs cocultured with SMCs compared with SMCs cultured alone. ECs inhibit TGF-beta 1 activation in bilayer coculture. This appears to be mediated through an increase in EC PAI-1 release. Alterations in coculture conditions, in particular the degree of EC-SMC cell contact, have profound effects on this process.

Un-cross-linked fibrin substrates inhibit keratinocyte spreading and replication: correction with fibronectin and factor XIII cross-linking

Wound repair is characterized by the presence of a fibrin-rich matrix, but the effect of fibrin on re-epithelialization remains unclear. In this study, we determined the effects of different fibrin matrices on cultured human neonatal keratinocytes. Using purified fibrinogen and fibrin gels generated by the enzymatic action of thrombin, batroxobin (it leads to retention of fibrinopeptide B), or Agkistrodon contortrix thrombin-like enzyme (ACTE; it leads to retention of fibrinopeptide A), we determined the effect of each of these matrices on keratinocyte morphology, attachment, spreading, and replication as compared to tissue culture plastic. Morphologically, keratinocytes seeded on fibrin surfaces were more rounded and formed three-dimensional structures. Specific cell attachment, as measured at either 37 degrees C or 4 degrees C, was not altered on the different fibrin substrates (P > .05) but was increased on fibrinogen and factor XIII cross-linked fibrin (P < .01). However, keratinocytes seeded on fibrin, regardless of the presence or absence of fibrinopeptides A or B, showed a marked decrease (up to 71%) in cell numbers by days 5 (P = .0357) and 10 (P = .0114). Keratinocyte spreading was decreased by 78.8% (P = .0006), 80.3% (P = .0001), and 89.2% (P = .0001) on thrombin-, batroxobin-, and ACTE-generated fibrin, respectively, but not on fibrinogen-coated dishes. However, either the addition of fibronectin or cross-linking of fibrin with factor XIII allowed full keratinocyte spreading to occur (P = .0002 and P = .0013, respectively). We conclude that fibrin inhibits keratinocyte spreading in the absence of other matrix or plasma proteins or cross-linking by factor XIII.

In vitro angiogenesis is modulated by the mechanical properties of fibrin gels and is related to alpha(v)beta3 integrin localization

This study deals with the role of the mechanical properties of matrices in in vitro angiogenesis. The ability of rigid fibrinogen matrices with fibrin gels to promote capillarylike structures was compared. The role of the mechanical properties of the fibrin gels was assessed by varying concentration of the fibrin gels. When the concentration of fibrin gels was decreased from 2 mg/ml to 0.5 mg/ml, the capillarylike network increased. On rigid fibrinogen matrices, capillarylike structures were not formed. The extent of the capillarylike network formed on fibrin gels having the lowest concentration depended on the number of cells seeded. The dynamic analysis of capillarylike network formation permitted a direct visualization of a progressive stretching of the 0.5 mg/ml fibrin gels. This stretching was not observed when fibrin concentration increases. This analysis shows that 10 h after seeding, a prearrangement of cells into ringlike structures was observed. These ringlike structures grew in size. Between 16 and 24 h after seeding, the capillarylike structures were formed at the junction of two ringlike structures. Analysis of the alpha(v)beta3 integrin localization demonstrates that cell adhesion to fibrinogen is mediated through the alpha(v)beta3 integrin localized into adhesion plaques. Conversely, cell adhesion to fibrin shows a diffuse and dot-contact distribution. We suggest that the balance of the stresses between the tractions exerted by the cells and the resistance of the fibrin gels triggers an angiogenic signal into the intracellular compartment. This signal could be associated with modification in the alpha(v)beta3 integrin distribution.

Inhibition of angiogenesis in vitro and in vivo: comparison of the relative activities of triflavin, an Arg-Gly-Asp-containing peptide and anti-alpha(v)beta3 integrin monoclonal antibody

Disintegrin which contains the amino acid sequence Arg-Gly-Asp (RGD), has been implicated as a recognition site in interactions between extracellular matrix (ECM) and cell membrane receptors. Triflavin, a 7.5 kDa cysteine-rich polypeptide purified from Trimeresurus flavoviridis snake venom, belongs to a family of disintegrins. Integrin alpha(v)beta3 has recently been identified as a marker of angiogenic blood vessels and therefore anti-alpha(v)beta3 mAb may significantly inhibit angiogenesis. Therefore, this study was designed to compare the relative activity of triflavin and anti-alpha(v)beta3 mAb in human umbilical vein endothelial cell (HUVEC) adhesion and migration in vitro, and on angiogenesis induced by TNF(alpha) in chicken chorioallantoic membrane (CAM). In this study, it was shown that triflavin (0.1 to 0.4 microM) dose-dependently inhibited the adhesion of HUVECs to ECMs (i.e., vitronectin, fibronectin, laminin and collagen type IV). At a concentration of 10 microM, anti-alpha(v)beta3 mAb almost completely inhibited the adhesion of cells to vitronectin, had a moderate inhibitory effect on fibronectin and laminin, but only a slight inhibitory effect on collagen type IV. On the other hand, vitronectin and fibronectin promote a significantly greater extent of cell adhesion and migration than laminin or collagen type IV over a wide range of concentrations (5 to 15 microg/ml). In cell migration studies, triflavin (0.4 microM) inhibited more markedly vitronectin- and fibronectin-mediated migration than that mediated by laminin- and collagen type IV. Comparison of the relative effectiveness of triflavin with anti-alpha(v)beta3 mAb, showed that triflavin was at least twenty to thirty times more potent than anti-alpha(v)beta3 mAb at inhibiting cell adhesion and migration. Furthermore, we used TNF(alpha) as an inducer of angiogenesis in the CAM assay. Close examination of the effects of triflavin and anti-alpha(v)beta3 mAb on TNF(alpha)-induced angiogenesis revealed the presence of discontinuous and disrupted blood vessels. However, anti-alpha(v)beta3 mAb showed a significant effect only at a higher concentration (10 microM). These results suggest that the inhibition of angiogenesis may have been due to interference with the adhesion and migration of endothelial cells to ECMs. The results also indicate that triflavin has a more powerful inhibitory effect than anti-alpha(v)beta3 mAb on angiogenesis, suggesting that triflavin could theoretically be used as a reasonable therapeutic adjuvant for therapy or prevention of angiogenesis-induced diseases.

Involvement of endothelial PECAM-1/CD31 in angiogenesis

The adhesive interactions of endothelial cells with each other and the adhesion receptors that mediate these interactions are probably of fundamental importance to the process of angiogenesis. We therefore studied the effect of inhibiting the function of the endothelial cell-cell adhesion molecule, PECAM-1/ CD31, in rat and murine models of angiogenesis. A polyclonal antibody to human PECAM-1, which cross-reacts with rat PECAM-1, was found to block in vitro tube formation by rat capillary endothelial cells and cytokine-induced rat corneal neovascularization. In mice, two monoclonal antibodies against murine PECAM-1 prevented vessel growth into subcutaneously implanted gels supplemented with basic fibroblast growth factor (bFGF). Taken together these findings provide evidence that PECAM-1 is involved in angiogenesis and suggest that the interactions of endothelial cell-cell adhesion molecules are important in the formation of new vessels.

Fibroblasts spread on immobilized fibrin monomer by mobilizing a beta1-class integrin, together with a vitronectin receptor alphavbeta3 on their surface

Human and murine fibroblasts were found to spread far more avidly on fibrin monomer monolayers than on immobilized fibrinogen, indicating that removal of fibrinopeptides by thrombin is a prerequisite for the fibrin-mediated augmentation of cell spreading. In fact, cell spreading was not efficiently augmented on monolayers of a thrombin-treated dysfibrinogen lacking the release of fibrinopeptide A due to an Aalpha Arg-16 --> Cys substitution. Since a synthetic Arg-Gly-Asp (RGD)-containing peptide inhibited the fibrin-mediated cell spreading, subsequent dissociation of the carboxyl-terminal globular domain of the Aalpha-chains appears to render the RGD segments accessible to the cell-surface integrins. In support of this, fibrin-augmented cell spreading was inhibited by an antibody recognizing a 12-kDa peptide segment with gamma Met-89 at its amino terminus, which is located in close association with the RGD segment at Aalpha 95-97 in the helical coiled-coil interdomainal connector. The fibrin-mediated augmentation of cell spreading was inhibited not only by an antibody against human vitronectin receptor (LM 609) but also by an antibody against the beta1 subunit of integrin (mAb13), suggesting that the beta1-class integrin together with a vitronectin receptor, alphavbeta3, is mobilized onto the surface of fibroblasts upon contact with the fibrin monomer monolayer.

Enhancement of migration by protein kinase Calpha and inhibition of proliferation and cell cycle progression by protein kinase Cdelta in capillary endothelial cells

Activation of protein kinase C (PKC) induces angiogenesis, migration, and proliferation of endothelial cells (EC), but can also prevent growth factor-induced EC proliferation. To determine whether these disparate effects are mediated by substrates of individual PKC isoenzymes, PKCalpha and PKCdelta were overexpressed in rat microvascular EC. Basal and stimulated migration were enhanced in PKCalpha EC compared with either PKCdelta or control EC. Serum-induced growth of PKCdelta EC was decreased, while that of PKCalpha cells was similar to control EC. Phorbol ester markedly inhibited PKCdelta EC growth but enhanced growth of PKCalpha and control EC. To determine possible causes for this altered proliferation, the effect of PKCdelta on adhesion, mitogen-activated protein kinase activity, and cell cycle progression was measured. Adherence of PKCdelta EC to vitronectin was significantly enhanced. Serum-induced extracellular signal-regulated kinase-2 activity was increased equally in both PKCalpha and PKCdelta EC above that of control, while extracellular signal-regulated kinase-1 activity was similar in all EC. Cell cycle analysis suggested that PKCdelta EC entered S phase inappropriately and were delayed in passage through S phase. Thus, PKCalpha may mediate some proangiogenic effects of PKC activation; conversely, PKCdelta may direct antiangiogenic aspects of overall PKC activation, including slowing of the cell cycle progression.

Heparin-binding domain of fibrin mediates its binding to endothelial cells

Spreading of human umbilical vein endothelial cells (ECs) on fibrin requires thrombin cleavage of fibrinopeptide B (FPB) and subsequent exposure of the new beta 15-42 N-terminus. To further understand the interactions between ECs and fibrin beta 15-42 sequences, binding of fibrin(ogen) to EC monolayers was measured with polyclonal anti-fibrinogen (FBG) in parallel with monoclonal anti-FBG (18C6, beta 1-21; J88B, gamma 63-78) and anti-fibrin (T2G1, beta 15-21) antibodies in an indirect enzyme-linked immunosorbent assay. To accomplish this, large, soluble fragments of fibrin were prepared by cyanogen bromide (CNBr) cleavage (fibrin-CNBr); CNBr-cleaved FBG (FBG-CNBr) served as the control ligand. N-terminal fibrin-CNBr bound to EC monolayers and cells in suspension in a dose-dependent and saturable manner. By contrast, FBG-CNBr bound only 50% as well to EC monolayers, with no significant binding of intact FBG, C-terminal FBG plasmic fragment D, or N-terminal plasmic fragment E, which lacks beta 1-53. ECs bound the peptide beta 15-42-bovine serum albumin (BSA) conjugate but neither a scrambled beta 15-42 peptide conjugate nor conjugates of beta 24-42, beta 18-27, or beta 18-31. Binding of fibrin-CNBr was inhibited 54% by the beta 15-42-BSA conjugate and 17% by the B beta 1-42-BSA conjugate but not by free beta 15-42 peptide or RGDS-cell binding peptide. Binding of fibrin-CNBr was inhibited > 95% by heparin in a concentration-dependent manner; the same concentrations of heparin inhibited binding of beta 15-42-BSA by > 75% but not the dose-dependent binding of fibronection to ECs. These data suggest that in their native conformation, FBG B beta 15-42 sequences are unavailable for binding to ECs and that thrombin-induced exposure of beta 15-42 is required for binding by a heparin-dependent, RGD-independent mechanism at the new N-terminus of fibrin.

An in vitro invasion model for human renal cell carcinoma cell lines mimicking their metastatic abilities

We developed a modified in vitro invasion assay system using monolayers of vascular endothelial cells. A type I collagen gel was formed in plastic dishes, and overlaid with type IV collagen. Calf pulmonary arterial endothelial (CPAE) cells were seeded onto these plates, and incubated until they reached confluence. Five human renal cell carcinoma cell lines with various metastatic potentials in vivo were then seeded on the monolayer CPAE cells, and their colony formation and invasion activities were examined for 9 days. At day 4, the highly metastatic cell lines increased the number of colony foci on monolayer CPAE cells several fold higher than their poorly metastatic counterpart. The horizontal spreading patterns were also different between poorly and highly metastatic cell lines. On day 9, the number of carcinoma foci that penetrated the monolayer of CPAE cells and type IV collagen sheets into type I collagen gels in highly metastatic cell lines greatly increased as compared with that of poorly metastatic cell lines. Our in vitro invasion assay using monolayer CPAE cells would be useful to evaluate protease activities and colony formation during invasion.

Expression of the 14 kDa galactose-binding protein, galectin-1, on human tubular epithelial cells

By reverse phase PCR and Northern blotting, RNA of the 14 kDa galactose-binding protein (galectin-1) could be identified in primary cultures of human tubular epithelial cells. To assess protein synthesis and the possible function of galectin-1 on TEC, the cellular proteins were biosyntheticically labeled with [34S]-methionine and absorbed to immobilized laminin. Multiple radiolabeled proteins were eluted, a strong band in the area of 14 kDa was seen, coinciding with the galectin-1 band as identified by Western blotting. Surface expression of galectin-1 was seen by cytofluorometry with two different polyclonal antibodies to galectin-1. These data are in line with the finding that tubular epithelial cells adhere to laminin, partly in a Ca(2+)-independent manner.

Role of plasminogen activator inhibitor in the reciprocal regulation of bovine aortic endothelial and smooth muscle cell migration by TGF-beta 1

Vascular endothelial and smooth muscle cells exhibit reciprocal migratory responses after transforming growth factor (TGF)-beta 1 treatment. Endothelial cells exhibit a decreased migratory rate and smooth muscle cells exhibit an increased migratory rate. Previous studies have demonstrated increases in extracellular matrix and integrin synthesis and expression in response to TGF-beta 1. In this report, we illustrate the roles of plasminogen activator inhibitor in modulating the migratory rates in these two cell types. Endothelial cells appear to require a proteolytic phenotype for rapid migration, whereas vascular smooth muscle cells appear to require an anti-proteolytic phenotype. Modulation of proteinase/anti-proteinase activity ratios was accomplished via TGF-beta 1 induction, addition of exogenous plasminogen activator inhibitor, addition of anti-catalytic antibodies directed against urokinase plasminogen activator, overexpression of plasminogen activator inhibitor utilizing stable transfectants, and the use of vitronectin as a substratum. The reciprocal migratory behaviors exhibited by these two vascular cell types in response to TGF-beta 1 is discussed in the context that these two vascular cell types utilize distinct adhesive and signaling pathways in their interactions with extracellular matrix components and responsiveness to proteolytic activity.

Matrix-specific effect of endothelial control of smooth muscle cell migration

PURPOSE

Smooth muscle cell (SMC) migration is a critical element in the development of intimal hyperplasia. The effect of endothelial cells (ECs) on SMC migration and the modulation of this cell-to-cell interaction by extracellular matrix is not well understood.

METHODS

To examine this relationship SMCs and ECs were cocultured on opposite sides of a semipermeable membrane and were compared with SMCs cultured alone. To assess migration SMCs were plated at confluent density into the center of the membrane with a steel fence. After the fence was removed, SMCs were treated for 2 hours with mitomycin C (20 micrograms/ml) to assess migration independent of proliferation. Cell migration was measured with morphometry. Experiments were performed on plastic and membranes coated with fibronectin or type I collagen (n > or = 8/group). Cell adhesiveness was quantitated by cell attachment and spreading assays.

RESULTS

ECs stimulated SMC migration by 187% when compared with SMCs cultured alone on plastic and by 160% when cultured on fibronectin (p < 0.01). Type I collagen stimulated migration of SMCs cultured alone and prevented EC stimulated migration in cocultured SMCs (p < 0.01). Cell adhesiveness was significantly increased in cocultured SMCs compared with SMCs cultured alone regardless of whether cells were cultured on plastic (EC/SMC, 13.5 +/- 0.6 SMCs/high power field vs SMC, 8.9 +/- 0.5, p < 0.01), fibronectin (16.3 +/- 0.8 vs 12.3 +/- 0.7, p < 0.01) or type I collagen (15.5 +/- 1.0 vs 12.4 +/- 0.6, p < 0.01). ECs increased SMC cell spreading on plastic and fibronectin when compared with SMCs cultured alone. No difference in SMC cell spreading was seen in the presence or absence of ECs when cells were cultured on type I collagen. EC-SMC contact was not required; EC-conditioned media alone increased SMC migration by 75% when compared with SMCs cultured alone. Our data suggest that ECs increase SMC migration by a diffusable molecule that may also alter SMC adhesion molecule expression. Extracellular matrix composition can attenuate these effects.

CDw49b/CD29 integrin complex mediates the differentiation of human endothelial cells into capillary-like structures in vitro

We have investigated different beta-1 integrins (CDw49/CD29) on human umbilical vein endothelial cells (HUVEC) with regard to their roles in modifying the morphological structure of these cells on/in matrigel. The inhibition of matrigel-induced capillary formation by antibodies against subunits of beta-1 integrins was examined quantitatively using a digital analyzer. Antibodies to CDw49b and CD29 (common beta chain) caused a marked inhibition of capillary formation (up to 70%) in a dose-dependent manner, whereas antibodies to CDw49d, CDw49e and CDw49f were less inhibitory. We also examined the appearance of HUVEC cultured in matrigel. HUVEC suspended in matrigel for 24 h formed extended cell processes which connected, resulting in the formation of a capillary network. In contrast, fibroblasts cultured in matrigel showed only bipolar extensions without cell-cell contact. After 48 h in culture in matrigel, some HUVEC showed the capillary-unit of a lumen encircled by EC which may mimic the basic putative unit in the formation of capillaries. However, HUVEC pretreated with antibodies to CDw49b and CD29 failed to form significant processes and a hollow lumen. These phenomena may illustrate the importance of endothelial cell-basement membrane matrix interaction (through integrins, especially CDw49b/CD29 complex) occurring during differentiation of endothelial cells in angiogenesis.

Ligation of endothelial alpha v beta 3 integrin increases capillary hydraulic conductivity of rat lung

Complement-mediated pulmonary edema results from increases in lung capillary hydraulic conductivity (Lp), possibly by receptor-mediated mechanisms. We considered the Lp effects of vitronectin and the vitronectin-containing complement complex SC5b-9, which ligate the integrin alpha v beta 3. Vitronectin, SC5b-9, and SC5b-9-enriched zymosan-activated serum all rapidly increased Lp, as determined by the split-drop technique in single lung capillaries of rat lung. The Lp increases were inhibited by a monospecific (LM609) and a polyclonal (R838) antibody against the alpha v beta 3 integrin but not by an irrelevant monoclonal antibody isotype matched with LM609, by a monoclonal antibody against the alpha v beta 5 integrin, or by preimmune rabbit serum. Vitronectin monomers failed to increase Lp. The tyrosine kinase blockers genistein and methyl 2,5-dihydroxycinnamate caused significant concentration-dependent inhibitions of Lp increases due to vitronectin and zymosan-activated serum. By contrast, the protein kinase C blocker calphostin C had no major effect. We conclude that (1) multivalent ligation of the luminally located alpha v beta 3 integrin of lung capillary endothelium increases transcapillary liquid flux, and (2) the dominant signal transduction pathway for this effect occurs through tyrosine kinase activation.

Migration of bovine aortic smooth muscle cells after wounding injury. The role of hyaluronan and RHAMM

The migration of smooth muscle cells is a critical event in the pathogenesis of vascular diseases. We have investigated the role of hyaluronan (HA) and the hyaluronan receptor RHAMM in the migration of adult bovine aortic smooth muscle cells (BASMC). Cultured BASMC migrated from the leading edge of a single scratch wound with increased velocity between 1 and 24 h. Polyclonal anti-RHAMM antisera that block HA binding with this receptor abolished smooth muscle cell migration following injury. HA stimulated the random locomotion of BASMC and its association with the cell monolayer increased following wounding injury. Immunoblot analysis of wounded monolayers demonstrated a novel RHAMM protein isoform that appeared within one hour after injury. At the time of increased cell motility after wounding, FACS analysis demonstrated an increase in the membrane localization in approximately 25% of the cell population. Confocal microscopy of injured monolayers confirmed that membrane expression of this receptor was limited to cells at the wound edge. Collectively, these data demonstrate that RHAMM is necessary for the migration of smooth muscle cells and that expression and distribution of this receptor is tightly regulated following wounding of BASMC monolayers.

Angiogenesis: models and modulators

Angiogenesis in vivo is distinguished by four stages: subsequent to the transduction of signals to differentiate, stage 1 is defined as an altered proteolytic balance of the cell allowing it to digest through the surrounding matrix. These committed cells then proliferate (stage 2), and migrate (stage 3) to form aligned cords of cells. The final stage is the development of vessel patency (stage 4), generated by a coalescing of intracellular vacuoles. Subsequently, these structures anastamose and the initial flow of blood through the new vessel completes the process. We present and discuss how the available models most closely represent phases of in vivo angiogenesis. The enhancement of angiogenesis by hyaluronic acid fragments, transforming growth factor beta, tumor necrosis factor alpha, angiogenin, okadaic acid, fibroblast growth factor, interleukin 8, vascular endothelial growth factor, haptoglobin, and gangliosides, and the inhibition of the process by hyaluronic acid, estrogen metabolites, genestein, heparin, cyclosporin A, placental RNase inhibitor, steroids, collagen synthesis inhibitors, thrombospondin, fumagellin, and protamine are also discussed.

Integrin-mediated adhesive properties of uroepithelial cells are inhibited by treatment with bacterial toxins

Gram-negative bacteria are a dominant cause of urinary tract infection, and their ability to produce toxins is an important virulence attribute. Cellular mechanisms triggered by the production of toxins in the lower urinary tract have not been completely defined. Ureteral epithelial cells (UT; A. Elgavish, Infect. Immun. 61: 3304-3312, 1993) have served as an in vitro model to explore the possibility that bacterial toxins act on UT by affecting integrin-mediated adhesive properties. The effect of treatment with lipopolysaccharides (LPS) from three strains of the gram-negative Escherichia coli [055:B5 (LPS-1), 0111:B4 (LPS-4), and 0127:B8 (LPS-5)] and lipoteichoic acids from two gram-positive bacteria, Streptococcus faecalis (LT-2) and Bacillus subtilis (LT-3), were examined. LPS-5 inhibited markedly UT attachment to collagen and fibronectin. LPS-4 had no effect, whereas LPS-1 inhibited UT attachment to collagen but not to fibronectin. The fact that LPS-5 and LT-2 inhibited an Arg-Gly-Asp sequence-sensitive component of UT attachment to fibronectin is consistent with the possibility that these toxins acted via a mechanism involving typical fibronectin receptors. UT spreading was inhibited markedly by LPS-1, LT-2, and LT-3, whereas LPS-4 and LPS-5 had no effect. Because clustering of integrins is a crucial step in integrin-mediated signal transduction, the possibility that toxins inhibited spreading by affecting clustering was tested. Treatment with LT-2, which inhibited spreading dramatically, abolished completely a UT cell population containing more than five to eight beta 1- or beta 4-subunit-containing integrin clusters.(ABSTRACT TRUNCATED AT 250 WORDS)

Integrin overexpression induced by high glucose and by human diabetes: potential pathway to cell dysfunction in diabetic microangiopathy

The nature of the process leading to the acellular nonperfused capillaries of diabetic microangiopathy remains unknown. Because these capillaries manifest thickened basement membranes, we asked whether the process causing deposition of excess extracellular matrix in diabetes modifies cell-matrix interactions in a direction that would compromise cell renewal. In 44 individual isolates of human umbilical vein endothelial cells we observed that high glucose concentrations (30 mM) induce coordinate increases in the levels of mRNAs encoding fibronectin and the fibronectin-specific integrin receptor alpha 5 beta 1 as well as in the cognate proteins. Expression of the integrin subunit alpha 3, component of the alpha 3 beta 1 polyspecific receptor for fibronectin, laminin, and collagen, was also up-regulated by high glucose. Overexpression of integrins correlated with increased cell attachment to exogenous fibronectin and laminin as well as to complex matrix. Moreover, cells exhibited firmer steady-state adhesion to their own matrix. To correlate these in vitro observations with events in human diabetic retinopathy we measured integrin levels in retinal trypsin digests prepared from 10 patients with 8.2 +/- 1.6 (mean +/- SE) years of diabetes and 10 age- and sex-matched nondiabetic controls. Microvessels of diabetic patients showed increased immunostaining for beta 1 integrin (P = 0.025) when compared with control microvessels. These data show that high glucose and diabetes increase integrin expression and thus alter the interaction of vascular endothelial cells with their basement membranes in the direction of firmer cell-matrix adhesion. This could compromise the migration and replication critical to the reendothelialization process and contribute to microvascular occlusion.

Basic fibroblast growth factor modulates integrin expression in microvascular endothelial cells

During angiogenesis capillary endothelial cells undergo a coordinated set of modifications in their interactions with extracellular matrix components. In this study we have investigated the effect of the prototypical angiogenic factor basic fibroblast growth factor (bFGF) on the expression and function of several integrins in microvascular endothelial cells. Immunoprecipitation experiments with antibodies to individual subunits indicated that microvascular cells express at their surface several integrins. These include the alpha 1 beta 1, alpha 2 beta 1, and alpha 3 beta 1 laminin/collagen receptors; the alpha 6 beta 1 laminin receptor; the alpha 5 beta 1 and alpha v beta 1 fibronectin receptors; the alpha 6 beta 4 basement membrane receptor; and the alpha v beta 3 and alpha v beta 5 vitronectin receptors. Treatment with bFGF caused a significant increase in the surface expression of the alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, alpha 6 beta 1, alpha 6 beta 4, and alpha v beta 5 integrins. In contrast, the level of expression of the alpha 1 beta 1 and alpha v beta 3 integrins was decreased in bFGF-treated cells. Immunoprecipitation of metabolically labeled cells indicated that bFGF increases the biosynthesis of the alpha 3, alpha 5, alpha 6, beta 4, and beta 5 subunits and decreases the production of the alpha v and beta 3 subunits. These results suggest that bFGF modulates integrin expression by altering the biosynthesis of individual alpha or beta subunits. In accordance with the upregulation of several integrins observed in bFGF-treated cells, these cells adhered better to fibronectin, laminin, vitronectin, and type I collagen than did untreated cells. The largest differences in beta 1 integrin expression occurred approximately 72 h after exposure to bFGF, at a time when the expression of the endothelial cell-to-cell adhesion molecule endoCAM was also significantly upregulated. In contrast, a shorter exposure to bFGF (24-48 h) was required for the maximal induction of plasminogen activator production in the same cells. Taken together, these results show that bFGF causes significant changes in the level of expression and function of several integrins in microvascular endothelial cells.

Maximal migration of human smooth muscle cells on fibronectin and type IV collagen occurs at an intermediate attachment strength

Although a biphasic dependence of cell migration speed on cell-substratum adhesiveness has been predicted theoretically, experimental data directly demonstrating a relationship between these two phenomena have been lacking. To determine whether an optimal strength of cell-substratum adhesive interactions exists for cell migration, we measured quantitatively both the initial attachment strength and migration speed of human smooth muscle cells (HSMCs) on a range of surface concentrations of fibronectin (Fn) and type IV collagen (CnIV). Initial attachment strength was measured in order to characterize short time-scale cell-substratum interactions, which may be representative of dynamic interactions involved in cell migration. The critical fluid shear stress for cell detachment, determined in a radial-flow detachment assay, increased linearly with the surface concentrations of adsorbed Fn and CnIV. The detachment stress required for cells on Fn, 3.6 +/- 0.2 x 10(-3) mu dynes/absorbed molecule, was much greater than that on CnIV, 5.0 +/- 1.4 x 10(-5) mu dynes/absorbed molecule. Time-lapse videomicroscopy of individual cell movement paths showed that the migration behavior of HSMCs on these substrates varied with the absorbed concentration of each matrix protein, exhibiting biphasic dependence. Cell speed reached a maximum at intermediate concentrations of both proteins, with optimal concentrations for migration at 1 x 10(3) molecules/micron2 and 1 x 10(4) molecules/micron2 on Fn and CnIV, respectively. These optimal protein concentrations represent optimal initial attachment strengths corresponding to detachment shear stresses of 3.8 mu dyne/micron2 on Fn and 1.5 mu dyne/micron2 on CnIV. Thus, while the optimal absorbed protein concentrations for migration on Fn and CnIV differed by an order of magnitude, the optimal initial attachment strengths for migration on these two proteins were very similar. Further, the same minimum strength of initial attachment, corresponding to a detachment shear stress of approximately 1 mu dyne/micron2, was required for movement on either protein. These results suggest that initial cell-substratum attachment strength is a central variable governing cell migration speed, able to correlate observations of motility on substrata differing in adhesiveness. They also demonstrate that migration speed depends in biphasic manner on attachment strength, with maximal migration at an intermediate level of cell-substratum adhesiveness.

Adhesion molecules and their role in cancer metastasis

This article describes various adhesion molecules and reviews evidence to support a mechanistic role for adhesion molecules in the process of cancer metastasis. A variety of evidence supports the involvement of specific adhesion molecules in metastasis. 1. For example, some cancer cells metastasize to specific organs, irrespective of the first organ encountered by the circulating cancer cells. This ability to colonize a specific organ has been correlated with the preferential adhesion of the cancer cells to endothelial cells derived from the target organ. This suggests that cancer cell/endothelial cell adhesion is involved in cancer cell metastasis and that adhesion molecules are expressed on the endothelium in an organ-specific manner. 2. Further, inclusion of peptides that inhibit cell adhesion, such as the YIGSR- or RGD-containing peptides, is capable of inhibiting experimental metastasis. 3. Metastasis can be enhanced by acute or chronic inflammation of target vessels, or by treatment of animals with inflammatory cytokines, such as interleukin-1. In vitro, cancer cell/endothelial cell adhesion can be enhanced by pretreating the endothelial cell monolayer with cytokines, such as interleukin-1 or tumor necrosis factor-alpha. This suggests that, in addition to organ-specific adhesion molecules, a population of inducible endothelial adhesion molecules is involved and is relevant to metastasis. 4. Further support for this model is found in the comparison to leukocyte/endothelial adhesion during leukocyte trafficking. Convincing evidence exists, both in vivo and in vitro, to demonstrate an absolute requirement for leukocyte/endothelial adhesion before leukocyte extravasation can occur. The relevance of this comparison to metastasis is reinforced by the observation that some of the adhesion molecules involved in leukocyte/endothelial adhesion are also implicated in cancer cell/endothelial adhesion. The involvement of adhesion molecules suggests a potential therapy for metastasis based on interrupting adhesive interactions that would augment other treatments for primary tumors.

Fibronectin expression correlates with U937 cell adhesion to migrating bovine aortic endothelial cells in vitro

A blood vessel's response to denudation injury will determine its final luminal diameter as well as its function. The synthesis, deposition, and remodeling of extracellular matrix components and migration by vascular endothelial cells are major factors in determining luminal diameter, cellular proliferative and migratory responses, and mononuclear cell adhesion at sites of injury. Previously, we have shown that after in vivo and in vitro denudation injury, endothelial cell migration is dramatically influenced by the amount of fibronectin synthesized and deposited by the responding endothelial cell population. The aim of this study was to elucidate the roles of fibronectin in modulating mononuclear cell adhesion to the endothelial cell population during in vitro migration. In this report we demonstrate that U937 cell binding to the migrating fronts of endothelial cell monolayers is modulated by the amount of fibronectin synthesized and deposited by the endothelial cells. Agents which increase fibronectin deposition, such as transforming growth factor-beta 1, elicit greater U937 cell adhesion. Manipulations that decrease fibronectin deposition, such as transfection and overexpression of pp60c-src proto-oncogene in endothelial cells, reduce U937 cell adhesion. These results suggest that changes in endothelial cell extracellular matrix synthesis and deposition modulate, in part, the adhesive properties of the vessel wall after injury. In turn, the intensity and duration of mononuclear cell adhesion at sites of vessel wall injury determines, in part, the vessel wall response.

Fibronectin promotes the elongation of microvessels during angiogenesis in vitro

Fibronectin is a component of the extracellular matrix of developing microvessels whose role in angiogenesis is poorly understood. This study evaluated the effect of plasma fibronectin on angiogenesis in serum-free collagen gel culture of rat aorta. Aortic explants embedded in collagen gels generated microvascular outgrowths. Fibronectin incorporated in the collagen gel promoted a selective dose-dependent elongation of the newly formed microvessels without stimulating vascular proliferation. The fibronectin-treated microvessels were longer due to a proportional increase in the number of microvascular cells. However, fibronectin had no effect on microvascular DNA synthesis and mitotic activity. Fibronectin stimulated microvascular length also in cultures in which mitotic activity was suppressed and angiogenesis was markedly reduced by pretreating the aortic explants with mitomycin C. The synthetic peptide Gly-Arg-Gly-Asp-Ser (GRGDS), which competes for the binding of fibronectin to its cell receptors and inhibits the adhesion of endothelial cells to substrates, arrested the elongation of developing microvessels causing regression and inhibition of angiogenesis. Conversely, Gly-Arg-Gly-Glu-Ser (GRGES), which lacks the RGD sequence, had no inhibitory effect. These data support the hypothesis that fibronectin promotes angiogenesis and suggest that developing microvessels elongate in response to fibronectin as a result of an adhesion-dependent migratory recruitment of endothelial cells that does not require increased cell proliferation.

Migration of bovine bronchial epithelial cells to extracellular matrix components

Migration of epithelial cells is an important feature of wound healing. Components of extracellular matrix stimulate migration of other cells, and we hypothesized that basement membrane components, laminin and type IV collagen, stimulate migration of bovine bronchial epithelial cells (BBEC). BBEC cultured for 3 days were used in migration assays using the blindwell chamber technique. BBEC migrated in a concentration-dependent manner to laminin, type IV collagen, and fibronectin. "Checkerboard" analysis demonstrated that the migration was directional for each of the components studied. We also evaluated the stimulatory activity of fibronectin fragments. A fragment containing the RGDS peptide was stimulatory of migration while other fragments were much less so, suggesting a role for RGDS-sensitive, integrin-mediated mechanisms. In order to evaluate whether bound or soluble matrix components were required to direct cell migration, we performed haptotaxis assays with precoated filters in the migration chambers. Fibronectin-precoated filters demonstrated significant stimulation of migration, suggesting that some of the migration in our original assays with fibronectin present in the lower chambers could be termed haptotactic. laminin- and type IV collagen-precoated filters were less active. When insulin was used as a chemoattractant, the fibronectin-precoated filters were more facilitatory of migration than the other matrix coatings. In summary, BBEC can chemotactically migrate to extracellular matrix components. Thus, the composition of the provisional matrix that forms at sites of epithelial injury may play an important role in the repair processes that occur after injury to the bronchial epithelium.

Comparison of gene expression of extracellular matrix molecules in brain microvascular endothelial cells and astrocytes

By use of random-primed cDNA probes the expression of extracellular matrix molecules in cerebral microvascular endothelial cells (cEC) and in astrocytes from mouse brain was examined. Two phenotypically different batches of cloned cEC were used. Expression of major adhesive ECM molecules, constituting the endothelial basement membrane (i.e., fibronectin, laminin A, B and collagen IV) and of other attachment factors, such as SPARC (osteonectin), tenascin and thrombospondin 1, was examined. We have demonstrated that cEC of different morphology display variations in the expression of fibronectin (FN), thrombospondin 1 (TSP1) and collagen IV (C IV). Astrocytes were shown to contain FN, TSP1, TN and SPARC mRNA. Unexpectedly, SPARC mRNA could not be detected in any of the capillary endothelial cells examined. Therefore, we suggest that astrocytes are likely to be involved in endothelial differentiation and function in the central nervous system via ECM molecule secretion.

Basic FGF and TGF-beta differentially modulate integrin expression of human microvascular endothelial cells

Basic fibroblast growth factor (bFGF) and transforming growth factor-beta (TGF-beta) are known to alter the migratory and proliferative capacity of endothelial cells in vitro and to stimulate angiogenesis in vivo. One mechanism by which these cytokines induce their effects may be through the regulation of integrin adhesion receptor expression and activity. We examined the ability of these growth factors to modulate the expression of specific integrins in human microvascular endothelial cells (MEC). Immunoprecipitation of metabolically labeled MEC showed that bFGF upregulated the biosynthesis of alpha 2, alpha 5, beta 1, and beta 3. bFGF induced an increase in the levels of mRNA for alpha 2 and beta 1. TGF-beta increased synthesis of alpha 2, alpha 5, and beta 1. These results suggest that bFGF and TGF-beta selectively alter integrin profiles and influence interactions of MEC with the extracellular matrix during neovascularization. In particular, the upregulation of the collagen/laminin receptor, alpha 2 beta 1, by bFGF may provide activated endothelial cells with an enhanced capacity to migrate through both their underlying basement membrane and the interstitial matrix.