Effects of soluble factors and extracellular matrix components on vascular cell behavior in vitro and in vivo: models of de-endothelialization and repair

Novel Hypoxia-Inducible Factor 1α (HIF-1α) Inhibitors for Angiogenesis-Related Ocular Diseases: Discovery of a Novel Scaffold via Ring-Truncation Strategy

Ocular diseases featuring pathologic neovascularization are the leading cause of blindness, and anti-VEGF agents have been conventionally used to treat these diseases. Recently, regulating factors upstream of VEGF, such as HIF-1α, have emerged as a desirable therapeutic approach because the use of anti-VEGF agents is currently being reconsidered due to the VEGF action as a trophic factor. Here, we report a novel scaffold discovered through the complete structure-activity relationship of ring-truncated deguelin analogs in HIF-1α inhibition. Interestingly, analog 6i possessing a 2-fluorobenzene moiety instead of a dimethoxybenzene moiety exhibited excellent HIF-1α inhibitory activity, with an IC₅₀ value of 100 nM. In particular, the further ring-truncated analog 34f, which showed enhanced HIF-1α inhibitory activity compared to analog 2 previously reported by us, inhibited in vitro angiogenesis and effectively suppressed hypoxia-mediated retinal neovascularization. Importantly, the heteroatom-substituted benzene ring as a key structural feature of analog 34f was identified as a novel scaffold for HIF-1α inhibitors that can be used in lieu of a chromene ring.

An Accessible Organotypic Microvessel Model Using iPSC-Derived Endothelium

While organotypic approaches promise increased relevance through the inclusion of increased complexity (e.g., 3D extracellular microenvironment, structure/function relationships, presence of multiple cell types), cell source is often overlooked. Induced pluripotent stem cell (iPSC)-derived cells are potentially more physiologically relevant than cell lines, while also being less variable than primary cells, and recent advances have made them commercially available at costs similar to cell lines. Here, the use of induced pluripotent stem cell-derived endothelium for the generation of a functional microvessel model is demonstrated. High precision structural and microenvironmental control afforded by the design approach synergizes with the advantages of iPSC to produce microvessels for modeling endothelial biology in vitro. iPSC microvessels show endothelial characteristics, exhibit barrier function, secrete angiogenic and inflammatory mediators, and respond to changes in the extracellular microenvironment by altering vessel phenotype. Importantly, when deployed in the investigation of neutrophils during innate immune recruitment, the presence of the iPSC endothelial vessel facilitates neutrophil extravasation and migration toward a chemotactic source. Relevant cell sources, such as iPSC, combine with organotypic models to open the way for improved and increasingly accessible in vitro tissue, disease, and patient-specific models.

Influence of extracellular matrix proteins and substratum topography on corneal epithelial cell alignment and migration

The basement membrane (BM) of the corneal epithelium presents biophysical cues in the form of topography and compliance that can impact the phenotype and behaviors of cells and their nuclei through modulation of cytoskeletal dynamics. In addition, it is also well known that the intrinsic biochemical attributes of BMs can modulate cell behaviors. In this study, the influence of the combination of exogenous coating of extracellular matrix proteins (ECM) (fibronectin-collagen [FNC]) with substratum topography was investigated on cytoskeletal architecture as well as alignment and migration of immortalized corneal epithelial cells. In the absence of FNC coating, a significantly greater percentage of cells aligned parallel with the long axis of the underlying anisotropically ordered topographic features; however, their ability to migrate was impaired. Additionally, changes in the surface area, elongation, and orientation of cytoskeletal elements were differentially influenced by the presence or absence of FNC. These results suggest that the effects of topographic cues on cells are modulated by the presence of surface-associated ECM proteins. These findings have relevance to experiments using cell cultureware with biomimetic biophysical attributes as well as the integration of biophysical cues in tissue-engineering strategies and the development of improved prosthetics.

Endothelial cell microparticles act as centers of matrix metalloproteinsase-2 (MMP-2) activation and vascular matrix remodeling

Endothelial cell (EC)-derived microparticles (MPs) are small membrane vesicles associated with various vascular pathologies. Here, we investigated the role of MPs in matrix remodeling by analyzing their interactions with the extracellular matrix. MPs were shown to bind preferentially to surfaces coated with matrix molecules, and MPs bound fibronectin via integrin α(V) . MPs isolated from EC-conditioned medium (Sup) were significantly enriched for matrix-altering proteases, including matrix metalloproteinases (MMPs). MPs lacked the MMP inhibitors TIMP-1 and TIMP-2 found in the Sup and, while Sup strongly inhibited MMP activities but MPs did not. In fact, MPs were shown to bind and activate both endogenous and exogenous proMMP-2. Taken together, these results indicate that MPs interact with extracellular matrices, where they localize and activate MMP-2 to modify the surrounding matrix molecules. These findings provide insights into the cellular mechanisms of vascular matrix remodeling and identify new targets of vascular pathologies.

The control of endothelial cell adhesion and migration by shear stress and matrix-substrate anchorage

Endothelial cells constitute the natural inner lining of blood vessels and possess anti-thrombogenic properties. This characteristic is frequently used by seeding endothelial cells on vascular prostheses. As the type of anchorage of adhesion ligands to materials surfaces is known to determine the mechanical balance of adherent cells, we investigated herein the behaviour of endothelial cells under physiological shear stress conditions. The adhesion ligand fibronectin was anchored to polymer surfaces of four physicochemical characteristics exhibiting covalent and non-covalent attachment as well as high and low hydrophobicity. The in situ analysis combined with cell tracking of shear stress-induced effects on cultured isolated cells and monolayers under venous (0.5 dyn/cm(2)) and arterial (12 dyn/cm(2)) shear stress over a time period of 24 h revealed distinct differences in their morphological and migratory features. Most pronounced, unidirectional and bimodal migration patterns of endothelial cells in or against flow direction were found in dependence on the type of substrate-matrix anchorage. Combined by an immunofluorescent analysis of the actin cytoskeleton, cell-cell junctions, cell-matrix adhesions, and matrix reorganization these results revealed a distinct balance of laminar shear stress, cell-cell contacts and substrate-matrix anchorage in affecting endothelial cell fate under flow conditions. This analysis underlines the importance of materials surface parameters as well as primary and secondary adhesion ligand anchorage in the context of artificial blood vessels for future therapeutic devices.

Differential effects of matrix and growth factors on endothelial and fibroblast motility: application of a modified cell migration assay

Cell migration is crucial in virtually every biological process and strongly depends on the nature of the surrounding matrix. An assay that enables real-time studies on the effects of defined matrix components and growth factors on cell migration is not available. We have set up a novel, quantitative migration assay, which enables unharmed cells to migrate along a defined matrix. Here, we used this so-called barrier-assay to define the contribution of fibronectin (FN) and Collagen-I (Col-I) to vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and lysophosphatidic acid (LPA)-induced cell migration of endothelial cells (EC) and fibroblasts. In EC, both FN and Col-I stimulated migration, but FN-induced motility was random, while net movement was inhibited. Addition of bFGF and VEGF overcame the effect of FN, with VEGF causing directional movement. In contrast, in 3T3 fibroblasts, FN stimulated motility and this effect was enhanced by bFGF. This motility was more efficient and morphologically completely different compared to LPA stimulation. Strikingly, directional migration of EC was not paralleled by higher amounts of stable microtubules (MT) or an increased reorientation of the microtubule-organizing centre (MTOC). For EC, the FN effect appeared concentration dependent; high FN was able to induce migration, while for fibroblasts both low and high concentrations of FN induced motility. Besides showing distinct responses of the different cells to the same factors, these results address contradictive reports on FN and show that the interplay between matrix components and growth factors determines both pattern and regulation of cell migration. J. Cell. Biochem. 99: 1536-1552, 2006. (c) 2006 Wiley-Liss, Inc.

Inhibition of Human Pulmonary Artery Smooth Muscle Cell Proliferation and Migration by Sabiporide, a New Specific NHE-1 Inhibitor

Abnormal growth of vascular smooth muscle cells is seen in various pathological conditions such as hypertension, atherosclerosis, and restenosis. Na/H exchanger (NHE) activation appears to play a permissive role in vascular smooth muscle cell proliferation and vascular remodeling. The present study investigated the effect of a new specific NHE-1 inhibitor, sabiporide, on human pulmonary artery smooth muscle cell proliferation and migration. Concentrations of sabiporide as low as 20 micromol/L in the culture medium containing growth factors inhibited cell proliferation, as measured by cell counting, and also inhibited the rate of DNA synthesis, as examined by measuring BrdU incorporation into DNA. Cell growth inhibition was not caused by cell death, as demonstrated by the measurement of intracellular lactate dehydrogenase release and by the reversibility of inhibition upon washing. By fluorescent-activated cell sorting analysis, we are the first to demonstrate that NHE-1 inhibition arrests the cell cycle progression at G0/G1 phase, suggesting that NHE activation plays a permissive role in entrance of cells into the cell cycle. Sabiporide also concentration-dependently inhibited human pulmonary artery smooth muscle cell migration. The present study showed that sabiporide inhibits vascular smooth muscle cell proliferation and migration by blocking the cell cycle progression at G0/G1 phase.

Cellular, molecular and immunological mechanisms in the pathophysiology of vein graft intimal hyperplasia

Coronary artery disease, leading to myocardial infarction and ischaemia, affects millions of persons and is one of the leading causes of morbidity and mortality worldwide. Invasive techniques such as coronary artery bypass grafting are used to alleviate the sequelae of arterial occlusion. Unfortunately, restenosis or occlusion of the grafted conduit occurs over a time frame of months to years with a gradual reduction in patency, especially in vein grafts. The events leading to intimal hyperplasia (IH) formation involve numerous cellular and molecular components. Various cellular elements of the vessel wall are involved as are leucocyte-endothelial interactions that trigger the coagulation cascade leading to localized thrombus formation. Subsequent phenotypic modification of the medial smooth muscle cells and their intimal migration is the basis of the lesion formation that is thought to be propagated by an immune-mediated reaction. Despite intense scrutiny, the pathophysiology of IH remains an enigma. Although several growth factors, cytokines and numerous other biomolecules have been implicated and their relationship to prohyperplasia pathways such as the phosphatidyl-inositol 3-kinase (PI3K)-Akt pathway has been established, many pieces of the puzzle are still missing. An in-depth understanding of early vein graft adaptation and progression is necessary to improve the long-term prognosis and develop more effective therapeutic measures. In this review, we have critically evaluated and summarized the literature to elucidate and interlink the numerous established and emerging factors that play a key role in the development of IH leading to vein graft restenosis.

Transdifferentiation of Endothelial and Renal Tubular Epithelial Cells into Myofibroblast-Like Cells under in vitro Conditions: A Morphological Analysis

Renal fibrosis is a hallmark of progressive kidney disease and is characterized by an accumulation of extracellular-matrix-synthesizing cells in the glomerulus and tubulointerstitium. This population of myofibroblast-like cells (MFLC) is heterogeneous. It has been experimentally shown, for example, that tubular epithelial cells could change their phenotype into MFLC under certain circumstances, a process called epithelial-mesenchymal transdifferentiation. However, MFLC may also originate from other sources. Therefore, we examined whether endothelial cells (EDC) are able to transdifferentiate into MFLC in vitro. We compared potential differences between syngeneic tubular epithelial cells (EPC) and EDC during transdifferentiation into MFLC using bovine and porcine EDC isolated from pulmonary arteries, and glomerular capillaries. Renal tubular EPC were prepared from bovine renal cortical tissue by collagenase digestion and isolation from homogeneous cell monolayers. Bovine renal tubular EPC stained positive for cytokeratin. Furthermore, tubular EPC selectively incorporated labeled bovine serum albumin, a typical property of differentiated renal tubular cells. EDC were characterized by the absence of epithelial markers (e.g. cytokeratin), but stained positive for vWF. The transdifferentiation of EDC into MFLC occurs sequentially in two steps: First, by a rapid reversible transformation in postconfluent or clonal cultures without the need of cytokine stimulation and second, by a prolonged secondary step in the presence of the transformation-accelerating cytokines and the absence of adherently growing EDC. Thus, EDC that are able to sprout can also irreversibly transdifferentiate into MFLC. On the other hand, prolonged incubation of EPC in the presence of cytokines such as transforming growth factor-beta1 and tumor necrosis factor-alpha leads only to a very small number of MFLC without the ability to further proliferate. Our in vitro data suggest that EDC can more easily transdifferentiate into MFLC than syngeneic renal tubular EPC.

The role of inflammation in vascular injury and repair

Inflammation plays a critical role in the vascular response to injury. In particular, mechanical injury using techniques such as balloon angioplasty and stenting results in complex inflammatory reactions which influence proliferation of vessel wall constituents such as endothelial cells, smooth muscle cells, and extracellular matrix proteins. Inflammatory cells are recruited to the injured vessel wall initially as a reparative mechanism; however, these same inflammatory processes are also pivotal in the development of restenotic lesions. Leukocytes serve as the primary inflammatory cells but we now know that platelets produce a number of important inflammatory mediators. This review describes the mechanisms that regulate endothelial cell migration, smooth muscle cell activation, and extracellular matrix protein production, all of which are key components in the inflammatory response to vascular injury.

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.

PDGF receptor-alpha deficiency in glomerular mesangial cells of tenascin-C knockout mice

Tenascin-C (TNC) knockout (TNKO) mice showed reduced proliferation of mesangial cells and abnormal restoration after habu-snake venom (HSV)-induced glomerulonephritis. In this study, we examined the relationship of TNC and platelet-derived growth factor receptor (PDGFR) in glomerular mesangial cells. TNC and PDGFR-alpha and -beta transcriptions were up-regulated in wild type (WT) mice after HSV injection, but in TNKO mice PDGFR-alpha transcription was not up-regulated. Immunohistochemistry showed that PDGFR-alpha was found in mesangial areas of colocalized alpha-smooth muscle actin, but in TNKO mice it was not detectable. In vitro studies showed that the expressions of PDGFR-alpha and -beta mRNA and protein in cultured glomerular mesangial cells (GMC) of TNKO mice were lower than those in WT GMC. These results suggest that failures of both TNC and PDGFR-alpha are a candidate for abnormal restoration of TNKO mice.

Can molecular mechanisms of biological processes be extracted from expression profiles? Case study: endothelial contribution to tumor-induced angiogenesis

Whereas the genome contains all potential developmental programs, expression profiles permit the determination of genes that are actively transcribed under defined physiological conditions. In this article, the idea of extracting biological mechanisms from expression data is tested. Molecular processes of the endothelial contribution to angiogenesis are derived from recently published expression profiles. The analysis reveals the sensitivity limits of experimental detection of transcriptional changes and how sequence-analytic techniques can help to identify the function of genes in question. We conclude that the transcripts (http://mendel.imp.univie.ac.at/SEQUENCES/TEMS/) found to be up-regulated in angiogenesis are involved in extracellular matrix remodeling, cellular migration, adhesion, cell-cell communication rather than in angiogenesis initiation or integrative control. Comparison with tissue-specific patterns of EST occurrence shows that, indeed, the presumptive tumor-specific endothelial markers are more generally expressed by cell types involved in migration and matrix remodeling processes. This exemplary study demonstrates how bioinformatics approaches can be helpful in deriving mechanistic information from diverse sources of experimental data.

Adenovirus-mediated gene transfer of a secreted transforming growth factor-beta type II receptor inhibits luminal loss and constrictive remodeling after coronary angioplasty and enhances adventitial collagen deposition

BACKGROUND

Extracellular matrix (ECM) remodeling is central to the development of restenosis after coronary angioplasty (PTCA). As a regulator of ECM deposition by vascular cells, substantial evidence implicates transforming growth factor-beta1 (TGF-beta1) in the pathogenesis of restenosis. We investigated the effects of intracoronary expression of a transgenic antagonist of TGF-beta1 on luminal loss after PTCA.

METHODS AND RESULTS

Porcine coronary arteries were randomized to receive a recombinant adenovirus expressing a secreted form of TGF-beta type II receptor (Ad5-RIIs), an adenovirus expressing beta-galactosidase (Ad5-lacZ), or vehicle only by intramural injection at the site of PTCA. Computerized morphometry 28 days after angioplasty revealed a greater minimum luminal area in Ad5-RIIs-injected arteries (1.71+/-0.12 mm(2)) than in the Ad5-lacZ (1.33+/-0.13 mm(2)) or vehicle-only (1.08+/-0.17 mm(2); P=0.010 by ANOVA) groups. This was accompanied by greater areas within the internal (P=0.013) and external (P=0.031) elastic laminae in Ad5-RIIs-treated vessels. Adventitial collagen content at the site of injury was increased in the Ad5-RIIs group, in contrast to decreases in the Ad5-lacZ and vehicle-only groups (P=0.004).

CONCLUSIONS

Adenovirus-mediated antagonism of TGF-beta1 at the site of PTCA reduces luminal loss after PTCA by inhibiting constrictive remodeling. Antagonism of TGF-beta1 stimulates the formation of a dense collagenous adventitia, which prevents constrictive remodeling by acting as an external scaffold. These findings demonstrate the potential of gene therapy-mediated antagonism of TGF-beta1 as prophylactic therapy for restenosis.

Vascular graft endothelialization: comparative analysis of canine and human endothelial cell migration on natural biomaterials

Canines are typically used as the standard preclinical model to gauge the success of vascular graft materials. However, canines spontaneously re-endothelialize vascular grafts, whereas humans do not, even after years. This raises questions of why there are differences in vascular healing between humans and other species and whether the canine is the appropriate preclinical model. In the present study we evaluated human and canine endothelial cell (EC) migration on the novel cross-linked collagen biomaterial PhotoFix(TM) pericardium. We compared in vitro migration of these cells on PhotoFix alone and on PhotoFix adsorbed with various growth factors (aFGF and bFGF) and adhesion proteins (fibronectin, collagen IV, vitronectin, and laminin). We also compared human and canine ECs in terms of their morphologies and prostacyclin production. We found that human umbilical vein ECs (HUVECs) and canine ECs (CECs) migrated well on PhotoFix, suggesting that this biomaterial may be a good vascular graft candidate. Both cell types responded similarly to different growth factors and adhesive proteins, but HUVEC migration was consistently higher than that for CECs. This suggested that human in vivo graft re-endothelialization is likely not hindered by poor endothelial migration but is hindered by other cellular or graft properties.

The effects of HIV infection on endothelial function

Endothelial dysfunction and/or injury is pivotal to the development of cardiovascular and inflammatory pathology. Endothelial dysfunction and/or injury has been described in Human Immunodeficiency Virus (HIV) infection. Elaboration of circulating markers of endothelial activation, such as soluble adhesion molecules and procoagulant proteins, occurs in HIV infection. Certain endothelial cells, such as those lining liver sinusoids, human umbilical vein endothelial cells, bone marrow stromal endothelial cells or brain microvascular endothelial cells, have been shown to be variably permissive for HIV infection. Entry of virus into endothelial cells may occur via CD4 antigen or galactosyl-ceramide receptors. Other mechanisms of entry including chemokine receptors have been proposed. Nevertheless, endothelial activation may also occur in HIV infection either by cytokines secreted in response to mononuclear or adventitial cell activation by virus or else by the effects of the secreted HIV-associated proteins, gp 120 (envelope glycoprotein) and Tat (transactivator of viral replication) on endothelium. Enhanced adhesiveness of endothelial cells, endothelial cell proliferation and apoptosis as well as activation of cytokine secretion have all been demonstrated. Synergy between select inflammatory cytokines and viral proteins in inducing endothelial injury has been shown. In HIV infection, dysfunctional or injured endothelial cells potentiate tissue injury, inflammation and remodeling, and accelerate the development of cardiovascular disease.

Developmental expression of vascular endothelial growth factor (VEGF) receptors and VEGF binding in ovine placenta and fetal membranes

The receptor tyrosine kinases, kinase-insert domain-containing receptor (KDR) and fms-like tyrosine kinase (Flt-1), and their ligand vascular endothelial growth factor (VEGF) are essential for the development and maintenance of placental vascular function during pregnancy. To further understand the role of VEGF in mediating angiogenesis and vascular permeability during development, the cellular localization of KDR and Flt-1 mRNA and protein, and the distribution of(125)I-VEGF binding sites in placenta, chorion and amnion of ovine fetuses were examined at three different gestational ages. In placentae at 62, 103 and 142 days, the predominant site of KDR mRNA and protein, and VEGF binding was the maternal vascular endothelium. In addition, a specific, although weak, signal for KDR mRNA was found in the maternal epithelium. At 103 and 142 days but not 62 days gestation, KDR mRNA and protein as well as VEGF binding sites were abundantly present in the endothelium of villous blood vessels. In the fetal membranes at 62, 103 and 142 days gestation, KDR mRNA and protein were expressed in the amniotic epithelium and intramembranous blood vessel endothelium, where binding of(125)I-VEGF was strong. There was no KDR mRNA or VEGF binding in the chorionic cytotrophoblast. Flt-1 expression was not detectable in placentae or fetal membranes at the three ages studied. In summary, the results demonstrated that VEGF receptors are present in the maternal and fetal vasculatures of the ovine placenta. This expression is consistent with a capillary growth-promoting function of KDR and its ligand VEGF. Further, the presence of KDR and VEGF binding sites in ovine fetal membranes suggests a role for VEGF in promoting intramembranous vascularity and permeability throughout gestation.

The effect of minocycline on the metabolism of androgens by human oral periosteal fibroblasts and its inhibition by finasteride

The antimicrobial minocycline has matrix-stimulatory effects on connective tissue and bone. The aim here was to study the effect of minocycline on 5alpha reduction of androgen substrates to 5alpha-dihydrotestosterone (DHT) in periosteal fibroblasts and the influence of the antiandrogen finasteride on this conversion. Confluent cultures of periosteal fibroblasts established from oral periosteum isolated from the bone surface were incubated in duplicate in multiwell dishes with two androgen substrates, [(14)C]-testosterone/[(14)C]-4-androstenedione, in the presence or absence of serial concentrations of minocycline or the antiandrogen finasteride or the two in combination for 24 h. The metabolites formed were solvent-extracted with ethyl acetate, separated by thin-layer chromatography and quantified using a radioisotope scanner. Both androgen substrates were metabolized to DHT and 4-androstenedione or testosterone. Minocycline stimulated the synthesis of DHT from these substrates by 75-83% at 20-30 microg/ml (n=4; p<0.01). Finasteride inhibited the 5alpha-reductase activity of these substrates by 3-5-fold at 1 microg/ml and 40-80% at 0.01 and 0.1 microg/ml (n=4; p<0.01), with little change in 17beta-hydroxysteroid dehydrogenase activity. Minocycline and finasteride in combination showed an intermediate response with one substrate. As finasteride inhibits the type 2, 5alpha-reductase isoenzyme associated with anabolic functions, these findings demonstrate target-tissue androgen metabolic activity in periosteal fibroblasts at baseline and in response to minocycline. This has implications for the reparatory potential of the diseased periodontium during adjunctive treatment with minocycline.

Implications of minocycline, platelet-derived growth factor, and transforming growth factor-beta on inflammatory repair potential in the periodontium

BACKGROUND

Semisynthetic tetracyclines used in the adjunctive treatment of inflammatory periodontal disease enhance collagen expression in induced periodontal lesions of rats. Polypeptide growth factors regulate key cellular events in tissue repair. The physiologically active androgen 5 alpha-dihydrotestosterone (DHT) stimulates bone and connective tissue turnover. It was relevant to study the effects of transforming growth factor beta (TGF-beta)/platelet-derived growth factor (PDGF) and minocycline alone and in combination on the formation of biologically effective androgens which can influence repair.

METHODS

Confluent monolayer cultures of human gingival fibroblasts of the fifth through the ninth passage were incubated in Eagle's minimum essential medium, with 14C-testosterone/14C-4-androstenedione in the presence or absence of optimal concentrations of TGF-beta/PDGF/minocycline (M), alone and in combination. At the end of a 24-hour incubation period, the medium was analyzed for steroid metabolites and quantified using a radioisotope scanner.

RESULTS

The androgen substrates 14C-testosterone (14C-T) and 14C-4-androstenedione (14C-4-A) were metabolized to DHT and 4-androstenedione/testosterone respectively. There were significant increases in the formation of DHT from 14C-T in response to M, TGF-beta, and PDGF, alone and in combination (13 to 48%), compared with controls (n = 4; P<0.01). The yields of 4-androstenedione were also greater in response to these agents (31%; 3-fold). When 14C-4-A was used as substrate, there were 21 to 80% increases in the formation of DHT in response to these agents alone and in combination (n = 4; P<0.01).

CONCLUSIONS

The biologically effective androgen metabolites formed in response to minocycline, TGF-beta, and PDGF can contribute to reparatory events in the inflamed periodontium. Judicious, adjunctive usage of the chemically-modified tetracyclines in the treatment of periodontal diseases can obviate the risk of microbial resistance, with potential applications of their anti-inflammatory and proanabolic effects in regenerative technology.

Fibronectin and collagen I matrixes promote calcification of vascular cells in vitro, whereas collagen IV matrix is inhibitory

Vascular calcification is a frequent component of atherosclerosis, yet the pathological mechanisms that regulate its formation are poorly understood. Calcification of the vessel wall may represent a process by which cells that normally exhibit a smooth muscle phenotype differentiate into cells that exhibit an osteoblast-like phenotype. One of the determinants of cellular phenotype is extracellular matrix; thus, we undertook the current study to evaluate the influence of extracellular matrix on calcification of vascular cells in vitro. Cell lines derived from bovine aortic media were divided into 1 of 3 groups: those that did not mineralize, those that mineralized slowly, or those that mineralized rapidly. When slowly mineralizing cells were plated onto matrix produced by rapidly mineralizing cells, the time required for mineralization decreased from 33+/-3.0 days to 7.8+/-1.3 days. Matrix produced by rapidly mineralizing cells was found to contain 3 times the amount of collagen I and fibronectin but 70% less collagen IV than nonmineralizing clones. When slowly mineralizing cells were cultured on purified collagen I or fibronectin, mineralized nodule formation, calcium incorporation, von Kossa staining, and alkaline phosphatase activity increased. In contrast, culturing slowly mineralizing cells on purified collagen IV inhibited these mineralization parameters. Furthermore, blocking antibodies to alpha5 integrins significantly inhibited the fibronectin-mediated increases in alkaline phosphatase activity, indicating that integrin-based signaling may be involved. These data suggest that matrix composition can regulate development of arterial calcification and that a subpopulation of vascular cells preferentially produces positively regulating matrix components.

Time-course for in vitro development of basement membrane, gap junctions, and repair by adult endothelial cells seeded on precoated ePTFE

OBJECTIVES

To establish some functional characteristics after in vitro endothelialisation of precoated ePTFE grafts.

MATERIALS AND METHODS

Saphenous vein endothelial cells were confluently seeded on human serum-precoated ePTFE. Collagen I-precoated ePTFE served as control. Time-courses for development of laminin, collagen IV and connexin43 was followed-up with immunofluorescence. Endothelial migration and proliferation was studied with cresyl violet staining and tritiated thymidine-labelling.

RESULTS

Six hours post-seeding, basement membrane components were visualised subendothelially as thin fibrils. After 24 h, there was a distinct fibril network, which did not seem to be further enhanced. Connexin43 was detected 6 h post-seeding, and the number of intercellular connections appeared to be similar up to day 7. The time-courses were similar on serum- and collagen I-precoated ePTFE. Endothelialisation of a 4 mm wide gap showed migrating fronts largely composed of proliferating cells. The process was completed within 10 days on collagen I-precoated ePTFE, and 15 days on serum-precoated ePTFE.

CONCLUSIONS

These findings suggest human endothelial cells, seeded on precoated ePTFE, maintain some differentiated functions seen in vivo. This is of importance for cell retention, functionality and endothelial repair of in vitro endothelialised ePTFE-grafts after implantation in man.

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.

The expression of collagen I and XII mRNAs in Porphyromonas gingivalis-induced periodontitis in rats: the effect of doxycycline and chemically modified tetracycline

Tissue remodeling is a dynamic state in which a balance is achieved between the proteolytic breakdown and synthesis of the extracellular matrix. Type I collagen is a major component of the gingival connective tissue (GCT) and the periodontal ligament (PDL) throughout development, while type XII collagen has been found in the mature forms of these tissues. The purpose of this study was to investigate the effects of periodontitis on the expression of type I and XII collagen and subsequently to investigate the effects of doxycycline (DOXY) and chemically modified non-antimicrobial tetracycline (CMT-1) on the expression of these molecules in this model. Adult barrier-raised male Sprague-Dawley rats were inoculated with Porphyromonas gingivalis obtained from humans to create the experimental periodontitis. The animals with the P. gingivalis-induced periodontitis were then split into the following groups: Group A served as infected untreated controls (PGI group); group B was treated with doxycycline (DOXY group); and group C was treated with chemically modified tetracycline-1 (CMT-1 group). Group D contained uninfected animals that served as uninfected controls (NIC group). The expression of type I and XII collagen mRNAs was examined by in situ hybridization in each group, with the co-expression of these molecules representing mature and functional gingival connective tissue. In the NIC group, cells hybridized with digoxygenine-labeled cDNA probes encoding rat alpha2(I) or alpha1(XII) collagens were found distributed uniformly throughout the periodontal connective tissue. The PGI group showed little hybridization in the areas of infection, while both the DOXY and CMT-1 groups showed co-expression of the alpha2(I) and alpha1(XII) probes in the GCT and coronal part of the PDL. This study demonstrates that doxycycline and CMT-1 moderate or reduce the inhibitory effects of periodontal infection on the expression of type I and type XII collagen mRNAs. These results suggest that doxycycline and a form of non-antimicrobial tetracycline, chemically modified tetracycline-1, can reduce periodontal destruction by reversing the inhibitory effect of periodontal infection on collagen synthesis.

Extracellular matrix heparan sulfate modulates endothelial cell susceptibility to Staphylococcus aureus

The ability of extracellular matrix heparan sulfate to alter the susceptibility of human endothelial cells to S. aureus was investigated. Endothelial cells grown on extracellular matrix synthesized by S. aureus-infected endothelial cells were more susceptible to subsequent staphylococcal infection than endothelial cells grown on the extracellular matrix synthesized by untreated endothelial cells. Endothelial cells were more susceptible to S. aureus infection when 1) grown on heparitinase-treated extracellular matrix that removed heparan sulfate chains, 2) grown on extracellular matrix produced by chlorate-treated endothelial cells that reduced sulfation in the matrix heparan sulfate proteoglycans, 3) grown on heparan sulfate purified from extracellular matrix elaborated by infected endothelial cells, and 4) endothelial cells were chlorate-treated and therefore expressed desulfated cellular heparan sulfate proteoglycans. Extracellular matrix produced by S. aureus-infected endothelial cells contained heparan sulfate proteoglycans with reduced sulfation. The altered extracellular matrix with reduced sulfated heparan sulfate proteoglycans signalled the uninfected endothelial cells to produce under sulfated cellular heparan sulfate proteoglycans that increased S. aureus adherence to the endothelial cells.

Photodynamic therapy inactivates extracellular matrix-basic fibroblast growth factor: insights to its effect on the vascular wall

PURPOSE

Photodynamic therapy (PDT), the light activation of photosensitizer dyes for the production of oxygen and other free radical moieties without the generation of heat, has been shown to inhibit the development of experimentally induced intimal hyperplasia. The host response to PDT, a form of vascular injury that results in complete vascular wall cell eradication, is devoid of inflammation and proliferation and promotes favorable vascular wall healing. These effects do not result in intimal hyperplasia and are suggestive of PDT-induced changes in the extracellular matrix (ECM). As a model to better understand the biologic consequences of PDT on the vascular wall matrix proteins, the effect of PDT was studied on the powerful matrix-resident mitogen basic fibroblast factor (bFGF) in vitro.

METHODS

PDT (5 to 200 J/cm2, 100 mW/cm2, 675 nm) was used with the photosensitizer chloroaluminum sulfonated phthalocyanine (5 micrograms/ml) to inactivate bFGF in vitro while 100 J/cm2 of irradiation was administered 24 hours after 5 mg/ml of the photosensitizer was used in vivo. PDT was used on bFGF in solution and on endothelial cell-derived ECM. Enzyme-linked immunosorbent assay was used to quantitate bFGF in solution after PDT treatment or after extraction from the ECM by collagenase and heparin. Functional activity of matrix-associated bFGF was assessed by smooth muscle cell mitogenesis by 3H-thymidine incorporation. To demonstrate the in vivo relevance of these observations, immunohistochemical analysis of PDT-treated rat carotid arteries was undertaken.

RESULTS

PDT eliminated detectable levels of bFGF in solution. PDT of ECM significantly reduced matrix-bound bFGF (1.0 +/- 0.6 vs 27.5 +/- 1.3 pg/ml; p < 0.0001). This reduction in bFGF after PDT of the ECM was associated with a decrease in vascular smooth muscle cell mitogenesis (52.4% +/- 4.6%; p < 0.0001) when plated on PDT-treated matrix compared with nontreated matrix. Quantitative replenishment of exogenous bFGF to PDT-treated matrix restored proliferation to baseline levels. PDT of rat carotid arteries demonstrated a loss of bFGF staining compared with control nontreated arteries.

CONCLUSIONS

PDT inactivation of matrix-resident bFGF and possibly other bioactive molecules can provide a mechanism by which PDT suppresses smooth muscle cell proliferation in the vessel wall. This free radical-mediated alteration of matrix may contribute to favorable vascular healing when PDT is used for the inhibition of injury-induced intimal hyperplasia.

Endothelial cell effect on smooth muscle cell collagen synthesis

Extracellular matrix (ECM) constitutes the bulk of mature intimal hyperplastic lesions. To determine if endothelial cells (ECs) inhibit smooth muscle cell (SMC) collagen synthesis, bovine aortic SMCs were cultured on plastic semipermeable membranes either alone or opposite ECs. SMCs were pulsed with 4 microCi/ml [3H]proline for 3 days and collagen synthesis was measured as trichloroacetic acid-precipitable counts in conditioned media and in cell lysate fractions. Each was standardized to SMC DNA (cpm/microgram DNA). EC effect on SMC gene expression of type I collagen was studied using Northern analysis. To determine whether TGF-beta 1 activation is involved in collagen synthesis regulation, parallel studies were performed in the presence of a neutralizing antibody to TGF-beta 1 (25 micrograms/ml) or aprotinin (a plasmin inhibitor, 200 micrograms/ml). SMCs cocultured with ECs were either untreated or treated with 5 ng/ml TGF-beta 1. The effect of culture substrate on EC-SMC interaction was studied by repeating experiments on type I collagen (CI), matrigel (MG), fibronectin (FN), and type IV collagen (CIV).

RESULTS

Compared to SMCs cultured alone, ECs inhibited SMC collagen synthesis by 40 +/- 5% (P < 0.01) and gene expression of type I collagen by 60 +/- 4% (P < 0.01). The addition of neutralizing TGF-beta 1 Ab or aprotinin to SMCs cultured alone had no effect on collagen synthesis. Collagen synthesis in SMCs cultured alone on MG was reduced by 49% and by 16% on CIV when compared to SMCs cultured on plastic (plastic: 100 +/- 12% vs MG: 51 +/- 15% vs CIV: 84 +/- 18%, P = 0.10). Collagen synthesis was increased in SMCs cultured alone on FN (195 +/- 14% vs plastic: 100 +/- 12, P < 0.001) and CI (207 +/- 17 vs plastic: 100 +/- 12, P < 0.001). ECs decreased SMC collagen synthesis by 18 +/- 4% when cocultured on CI (P < 0.05) and by 22 +/- 2% when cocultured on MG (P < 0.05). FN prevented EC inhibition of SMC collagen synthesis.

CONCLUSIONS

ECs inhibit SMC collagen synthesis and downregulate SMC type I collagen gene expression. TGF-beta 1 does not appear to be involved in this process. Culture substrate composition can affect SMC collagen synthesis and EC modulation of this process.

Activation of a 66-kilodalton human endothelial cell matrix metalloprotease by Streptococcus pyogenes extracellular cysteine protease

Human umbilical vein endothelial cells (HUVECs) were used to gain insight into the molecular mechanism whereby the major extracellular protease from group A streptococci damages host tissue. HUVECs exposed to streptococcal cysteine protease (SCP) for various times exhibited cytopathic effect and cell detachment from the culture vessel. Gelatin substrate zymography showed that a time- and concentration-dependent increase in the level of activity of an approximately 66-kDa gelatinase occurred in culture medium taken from cells exposed to enzymatically active SCP. This gelatinase comigrated in gelatin zymograms with the activated form of purified recombinant matrix metalloprotease 2 (MMP-2) and had type IV collagenase activity. In contrast, medium taken from cells exposed to inactivated (boiled) SCP and cells exposed to SCP inhibited by treatment with N-benzyloxycarbonyl-leucyl-valyl-glycine diazomethyl ketone lacked the 66-kDa gelatinase. Appearance of the 66-kDa gelatinase activity was also prevented by 1,10-phenanthroline, a zinc chelator and MMP inhibitor. Inasmuch as proteolytically active SCP is required for the emergence of this gelatinase and MMP activation occurs by proteolytic processing, the 66-kDa gelatinase may be a proteolytic cleavage product of a latent MMP expressed extracellularly by HUVECs. Direct SCP treatment of culture supernatant taken from HUVECs not exposed to SCP also produced the 66-kDa gelatinase. The data show that SCP activates an MMP produced by human endothelial cells, a process that may contribute to endothelial cell damage, tissue destruction, and hemodynamic derangement observed in some patients with severe, invasive group A streptococcal infection.

Curcumin inhibits the proliferation and cell cycle progression of human umbilical vein endothelial cell

We have studied the effect of curcumin (diferuloylmethane), a major component of the food flavor turmeric, on the proliferation and cell cycle progression of human umbilical vein endothelial cells (HUVEC). Curcumin inhibited the DNA synthesis of HUVEC as revealed by [3H]thymidine incorporation in a dose-dependent manner without significantly affecting the viability of the cells. The growth of HUVEC stimulated with fibroblast growth factor (FGF) and endothelial growth supplement (ECGS) was also inhibited by curcumin. Addition of curcumin to HUVEC resulted in an accumulation of > 46% of the cells in early S-phase, as determined by the FACS analysis. Pulse labeling studies with [3H]thymidine demonstrated that curcumin affected cells that were actively undergoing DNA synthesis. The de-novo synthesis of thymidine depends on thymidine kinase (TK) enzyme. Curcumin caused a significant loss of TK activity, which may be one of the possible mechanism(s) for the inhibition of DNA synthesis activity of HUVEC by curcumin. These studies have revealed a unique mode of action of curcumin whereby it effectively blocked the cell cycle progression during S-phase by inhibiting the activity of TK enzyme. The migration, proliferation and differentiation of HUVEC leads to angiogenesis, which facilitates the tumor initiation and promotion. Since curcumin inhibited the proliferation of HUVEC, it could turn out to be a very useful compound for the development of novel anti-cancer therapy.

Expression of angiogenesis factors and selected vascular wall matrix proteins in intracranial saccular aneurysms

OBJECTIVE

Little is known about the biological mechanisms associated with the genesis, growth, and rupture of intracranial saccular aneurysms. It is postulated that the vascular wall pathological response of aneurysmal disease is associated with abnormal angiogenesis factor expression.

METHODS

We have examined the expression and distribution of immunoreactivity to angiogenesis growth factors (vascular endothelial growth factor and basic fibroblast growth factor) and selected vascular wall matrix proteins (fibronectin, Type IV collagen, and alpha smooth muscle actin) in the walls of human intracranial aneurysms from surgical biopsy or autopsy specimens. Double antibody immunohistochemical stains were performed in contiguous fixed sections from three control circle of Willis arteries, five berry aneurysms, four giant aneurysms, and one mycotic aneurysm (three unruptured and seven ruptured lesions).

RESULTS

The aneurysmal wall exhibited diffuse disorganized expression of matrix proteins as compared to their organization in control vessels. There was strong patchy expression of vascular endothelial growth factor within the walls of all aneurysms, including marked staining of capillaries and small vessels within the thickened walls of giant lesions. The expression of basic fibroblast growth factor was more diffuse and occurred around the fibrocytes and myocytes within the disrupted media of 9 of 10 aneurysms.

CONCLUSIONS

These results confirm the gross architectural molecular disruption in the walls of intracranial aneurysms and illustrate an apparent biological response involving angiogenesis factors. Further research should elucidate the time course and possible causal relationships of these changes to aneurysm growth and rupture with the aim of possible therapeutic manipulation.

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.

Identification of the extracellular matrix binding sites for insulin-like growth factor-binding protein 5

Fibroblast extracellular matrix (ECM) contains two forms of insulin-like growth factor-binding proteins (IGFBPs), IGFBP-3 and IGFBP-5. These studies were undertaken to identify the regions within IGFBP-5 that mediate its binding to fibroblast ECM. Synthetic peptides were prepared that were homologous with two regions of basic amino acids within IGFBP-5 (Arg201-Arg218 and Ala131-Thr141). Increasing concentrations of both peptides competed with IGFBP-5 for binding to ECM but the Arg201-Arg218 peptide was more potent. Mutagenesis was used to define the effect of substituting for these basic residues on ECM binding. Substitution for two peptide B residues K134A and R136A reduced binding by 40%. Substitution of a single basic residue within the peptide A region (K211N) reduced binding to ECM by 49%. Substitution for K211N, K134A, and R136A reduced binding by 52%. More extensive substitutions in the peptide A region, e.g. K211N,R214A,K217A,R218N, resulted in a greater (e.g. 88%) decrease. The positional location of basic residues appeared to be more important than the total number of substitutions since the mutant K202N,K206A,R207A had a 79% reduction in ECM binding. Two basic regions of IGFBP-5 contribute to its binding to ECM, but the region containing amino acids 201-218 has a greater contribution. ECM binding is mediated by charged residues and acts to stabilize IGFBP-5 by protecting it from proteolysis.

Differential modulation of vascular endothelial and smooth muscle cell function by photodynamic therapy of extracellular matrix: novel insights into radical-mediated prevention of intimal hyperplasia

PURPOSE

Photodynamic therapy (PDT) has been demonstrated to inhibit experimental intimal hyperplasia and to lead to expedient reendothelialization but negligible repopulation of the vessel media. The mechanism that underlies the differential ingrowth of cells into PDT-treated vessel segments is not understood. Because the extracellular matrix (ECM) is known to modulate specific cell functions, this study was designed to determine whether PDT of isolated ECM affects the function of endothelial cells (ECs) and smooth muscle cells (SMCs).

METHODS

PDT of bovine aortic EC-ECM was performed with chloroaluminum sulfonated phthalocyanine and 675-nm laser light. Control specimens included untreated ECM, ECM-free plates, and ECM exposed to either light or photosensitizer only. Cell function was characterized by attachment, proliferation, and migration of ECs or SMCs that were plated onto identically treated matrixes.

RESULTS

SMC attachment (86% +/- 0.4% vs 95% +/- 0.4%), proliferation (46% +/- 0.5% vs 100% +/- 1.4%), and migration (40% +/- 1.0% vs 100% +/- 0.9%) were significantly inhibited after PDT of ECM when compared with untreated ECM (all p < 0.001). In contrast, PDT of ECM significantly enhanced EC proliferation (129% +/- 6.2% vs 100% +/- 6.2%; p < 0.03) and migration (118% +/- 2% vs 100% +/- 0.8; p < 0.01), but did not affect attachment.

CONCLUSIONS

This report establishes PDT-induced changes in the ECM with a result of inhibition of SMCs and stimulation of EC functions. It provides insight into how PDT-treated arteries can develop favorable EC repopulation without SMC-derived intimal hyperplasia. These findings may help provide a better understanding of the interactions between cells and their immediate environment in vascular remodeling.

Cooperative effect of TNFalpha, bFGF, and VEGF on the formation of tubular structures of human microvascular endothelial cells in a fibrin matrix. Role of urokinase activity

In angiogenesis associated with tissue repair and disease, fibrin and inflammatory mediators are often involved. We have used three-dimensional fibrin matrices to investigate the humoral requirements of human microvascular endothelial cells (hMVEC) to form capillary-like tubular structures. bFGF and VEGF165 were unable to induce tubular structures by themselves. Simultaneous addition of one or both of these factors with TNFalpha induced outgrowth of tubules, the effect being the strongest when bFGF, VEGF165, and TNFalpha were added simultaneously. Exogenously added u-PA, but not its nonproteolytic amino-terminal fragment, could replace TNFalpha, suggesting that TNFalpha-induced u-PA synthesis was involved. Soluble u-PA receptor (u-PAR) or antibodies that inhibited u-PA activity prevented the formation of tubular structures by 59-99%. epsilon-ACA and trasylol which inhibit the formation and activity of plasmin reduced the extent of tube formation by 71-95%. TNFalpha or u-PA did not induce tubular structures without additional growth factors. bFGF and VEGF165 enhanced of the u-PAR by 72 and 46%, but TNFalpha itself also increased u-PAR in hMVEC by 30%. Induction of mitogenesis was not the major contribution of bFGF and VEGF165 because the cell number did not change significantly in the presence of TNFalpha, and tyrphostin A47, which inhibited mitosis completely, reduced the formation of tubular structures only by 28-36%. These data show that induction of cell-bound u-PA activity by the cytokine TNFalpha is required in addition to the angiogenic factors VEGF165 and/or bFGF to induce in vitro formation of capillary-like structures by hMVEC in fibrin matrices. These data may provide insight in the mechanism of angiogenesis as occurs in pathological conditions.

Human endothelial cell growth and coagulant function varies with respect to interfacial properties of polymeric substrates

The in vitro coagulant function of human aortic endothelial cells (HAECs) was investigated when grown on a series of polymer surfaces that ranged from hydrophobic to hydrophilic. The polymer interface materials were prepared by radiofrequency plasma polymerization from hexamethyl-disilazane, gamma-butyrolactone, and N-vinyl-2-pyrrolidone and deposited onto tissue culture Permanox. The three plasma polymers were noncytotoxic. When precoated with fibronectin (FN), HAECs on all four polymer surfaces were similar with respect to cell proliferation and coagulant function. Without FN precoating, cell proliferation and spreading increased with increasing surface hydrophilicity. Normalized production of tissue-type plasminogen activator increased with increasing hydrophilicity of the polymers during early incubation times, as did tissue plasminogen activator/plasminogen activator inhibitor-1 ratios. In comparison, normalized von Willebrand factor release decreased on the more hydrophilic surfaces. Thus, both endothelial cell growth and some coagulant/fibrinolytic functions are improved with increasing substrate hydrophilicity.

Effect of Guglielmi detachable coils on experimental carotid artery aneurysms in primates

BACKGROUND AND PURPOSE

Clinical experience has established that intravascularly placed metal coils can be a useful treatment for cerebral vascular aneurysms. However, the mechanism by which the coils induce occlusion of the aneurysm is unclear. Appropriate use of this promising treatment modality requires basic understanding of the occlusive process. We used an animal model system of experimentally induced carotid aneurysms to investigate the initial events induced by Guglielmi detachable coils (GDCs), as well as the subsequent vascular changes induced by the coils over time.

METHODS

We induced 23 aneurysms in the carotid arteries of 16 Japanese monkeys. Nineteen aneurysms were then occluded with GDCs placed via endovascular surgery; 4 aneurysms served as controls. We then used gross and microscopic pathological examination, angiography, and scanning electron microscopy to assess the effects of the GDC.

RESULTS

In the first few hours after placement of the GDC in the experimental aneurysms, we observed leukocyte attachment and deposition of fibrinlike materials and other proteins. By 4 days after coil placement, leukocytes and fibroblasts were observed in the thrombus. By 2 weeks after coil placement, there was evidence of an endothelial-like covering of the coils. At 3 months after coil placement, we observed development of an arterial media in the occluded aneurysms.

CONCLUSIONS

The GDCs initiated a cellular response within several hours of aneurysm occlusion. By 2 weeks after coil placement, endothelialization was proceeding, and by 3 months after occlusion, remodeling of the aneurysm had progressed to produce a media-like structure in the former aneurysm.

Plasminogen activators augment endothelial cell organization in vitro by two distinct pathways

Endothelial cell differentiation into capillary structures is a complex process that requires the concerted effects of several extracellular matrix proteases, including plasminogen activators. Here, the role of tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) was evaluated in an in vitro model of endothelial morphogenesis involving organization of human umbilical vein endothelial cells into tubular structures when they are cultured on the basement membrane preparation, Matrigel. Both uPA and tPA were detected in HUVEC cultures on Matrigel, and inhibitors of plasminogen activators or of serine proteases decreased the extent of the tube network formed by the cells. The decrease resulting from serine protease inhibitors was additive to that from matrix metalloproteinase inhibitors which have previously been shown to decrease tube formation in this model, suggesting that the two classes of proteases modulate tube formation by distinct mechanisms. Plasminogen activator inhibitor (PAI)-1 decreased tube formation by 50% when added up to 4.5 h after the initiation of an 18 h assay and caused 25% inhibition when added 9.5 h after culture initiation, indicating that the effects of plasminogen activators are not limited to an early event in the differentiation process. Steady-state expression of mRNA for uPA increased during the first several hours of culture on Matrigel, further supporting a role for PA activity throughout the process of tube formation. These findings suggested that PAs may affect multiple events during tube-forming activity. A fucosylated peptide comprising the amino-terminal domain of uPA that binds to the uPA receptor (uPAR) but lacking proteolytic activity enhanced tube formation. In contrast, a defucosylated form of the same peptide had no effect. Since fucosylation of this fragment has been shown to be essential in other models of cell stimulation by uPA-uPAR interaction, these data support the hypothesis that uPA enhances endothelial morphogenesis both through proteolytic activity and via uPAR occupancy. Plasminogen activators could facilitate angiogenesis in vivo.

Chronic congestive heart failure is associated with a phenotypic shift of intramyocardial endothelial cells

BACKGROUND

There is evidence that patients with chronic congestive heart failure have endothelial cell-related abnormalities of the peripheral circulation and the coronary microvasculature. For that reason, we have studied the phenotypic expression of endothelial cells in hearts of patients with congestive heart failure.

METHODS AND RESULTS

We studied cardiac explants (n = 19) and autopsy hearts (n = 5) of patients with chronic congestive heart failure caused by either a dilated cardiomyopathy (n = 12) or ischemic heart disease (n = 12) and compared them with normal hearts (n = 12). The antigenic expression obtained with several endothelial cell markers (factor VIII-related antigen, EN-4, Ulex europaeus agglutinin-1 (UEA-1), PAL-E, endoglin, and endothelin) and adhesion molecules (intercellular adhesion molecule [ICAM], vascular cell adhesion molecule [VCAM], or E-selectin) was compared by use of immunohistochemical techniques. On the basis of the initial findings, the number of PAL-E- and EN-4-positive vessels was counted. The incidence of PAL-E-positive vessels per area was quantified and related to the percentage of heart muscle cells and the total number of vessels per area. In control hearts, endothelial cells rarely were positive for PAL-E. In hearts of patients with ischemic cardiomyopathies, there was distinct staining with this marker. Hearts of patients with dilated cardiomyopathies showed a marked increase in the number of PAL-E-positive endothelial cells. Vessels with a muscular media were PAL-E-negative. Two-sample analysis revealed a statistically significant difference between hearts with dilated cardiomyopathies and ischemic cardiomyopathies (P < .01), between hearts with dilated cardiomyopathies and control hearts (P < .01), and between hearts with ischemic cardiomyopathies and control hearts (P < .01). Endoglin and ICAM were positive but nondiscriminating. Endothelin, VCAM, and E-selectin were negative.

CONCLUSIONS

A phenotypic shift in endothelial antigen expression of the coronary microvasculature occurs in both ischemic hearts and hearts with dilated cardiomyopathies, as revealed by PAL-E, compared with control hearts. The change may relate to compensatory mechanisms in long-standing chronic heart failure.

Phenotypic modulation of smooth muscle cells during the formation of neointimal thickenings in the rat carotid artery after balloon injury: an electron-microscopic and stereological study

The formation of neointimal thickenings in the rat carotid artery after balloon injury was studied by a combination of electron-microscopic and stereological methods. All smooth muscle cells in the normal media had a contractile phenotype, the cytoplasm being dominated by myofilaments. Seven days after endothelial denudation, the smooth muscle cells in the innermost part of the media had assumed a synthetic phenotype by loss of myofilaments and formation of a large endoplasmic reticulum and Golgi complex. These cells moved through fine openings in the internal elastic lamina and gave rise to a growing neointima by proliferation and secretion of extracellular matrix components. Fourteen days after the operation, the neointima had almost reached its final size, and mitoses were no longer noted. Nevertheless, the cells maintained a synthetic phenotype with prominent secretory organelles, although myofilaments had started to become more abundant again. They were surrounded by an extracellular matrix made up of collagen fibrils and coalescing patches of elastin. Thirty-five days after the operation, an endothelial cell layer had reformed and covered most of the luminal vessel surface. In parallel, the smooth muscle cells in the neointima had returned to a contractile phenotype with a cytoplasm dominated by myofilaments. These findings provide a morphological basis for further analysis of the cellular and molecular interactions involved in the formation of neointimal thickenings after endothelial injury, and for the search for agents interfering with this process.

Human dermal microvascular endothelial cells produce matrix metalloproteinases in response to angiogenic factors and migration

Matrix metalloproteinases (MMPs) are a family of inducible enzymes that degrade extracellular matrix components, allowing cells to traverse connective tissue structures efficiently. Specific tissue inhibitors (TIMPs) function as physiologic inhibitors of MMP activity. Because neovascularization may require various proteinases, we characterized the profile of metalloenzyme production by microvascular endothelial cells (MEC) and the modulation of expression by phorbol esters (PMA) and by the physiologically relevant cytokines tumor necrosis factor-alpha (TNF-alpha), basic fibroblast growth factor, and interferon-gamma. MMP expression by MEC and large-vessel human umbilical vein endothelial cells (HUVEC) was determined by enzyme-linked immunosorbent assay, immunoprecipitation, Northern hybridization, and transfection assays. Constitutive expression of MMPs by endothelial cells was low. PMA stimulated the production of collagenase, stromelysin, 92-kDa gelatinase, and TIMP-1 in both endothelial cell types. TIMP-2 was constitutively expressed by MEC and HUVEC, but was down-regulated by PMA. TNF-alpha induced an endothelial-cell-specific up-regulation of collagenase with a concomitant inhibition of PMA-induced TIMP-1 up-regulation, a response that is distinct from that of fibroblasts. Interferon-gamma up-regulated TIMP-1 production by MEC and blocked PMA and TNF-induced up-regulation of collagenase. Northern hybridization assays showed pretranslational control of PMA-, basic fibroblast growth factor-, and TNF-alpha-induced MMP expression. Collagenase-promoter CAT constructs containing 2.28 kb of the 5' region of the collagenase gene demonstrated transcriptional regulation. The potential physiologic relevance of such regulation was shown in an in vitro migration assay. MEC were stimulated to migrate by wounding and exposure to TNF-alpha. Collagenase mRNA was prominently expressed by the migrating cells, as shown by in situ hybridization. In sum, MEC have a unique profile of MMP expression and regulation compared with other cell types, which may be important for wound healing and angiogenesis, particularly during the early phase of migration.

Quantitative and qualitative characterization of apolipoprotein B containing lipoproteins produced by the visceral rat yolk sac in two different in vitro systems: organ culture and isolated epithelial cells in suspension culture

Tissue pieces as well as isolated epithelial cells taken from visceral rat yolk sacs at the 18th day of gestation were able to synthesize and to secrete apo B containing lipoproteins floating in the density ranges of VLDL, IDL and LDL. In all three density classes only the high molecular weight apo B was detectable. VLDL secreted from yolk sac tissue or isolated epithelial cells lacked apo E and apo C. Studies with cycloheximide revealed that about 77% of the particles was delivered from a pool of preformed lipoproteins. Evidence was given that also de novo-synthesis of apo B containing lipoproteins took place in the tissue segments and the isolated epithelial cells. Most of apo B mass (90%) and of apo B radioactivity (60%) secreted by the tissue pieces of the visceral yolk sac floated in the density range 1.020-1.064 g/ml, the remainder being found in the d < or = 1.020 g/ml fraction. In contrast, only 40% of apo B mass and 45% of apo B radioactivity delivered from isolated epithelial cells belonged to the d = 1.020-1.064 g/ml fraction. LDL released from yolk sacs and isolated epithelial cells contained more triacylglycerols (41% vs. 25%) and had a larger mean diameter (24 nm vs. 21.8 nm) than those obtained from fetal rat serum, whereas the comparatively small VLDL produced in vitro (mean diameter = 34 nm) contained less triacylglycerols (46% vs. 60.5%) and more protein (20% vs. 10.2%) in comparison with fetal serum VLDL (mean diameter = 42.3 nm). Incubation experiments with [125I]VLDL led to the conclusion that the lipase secreted by yolk sac tissue into the medium could not be responsible for the conversion of VLDL into LDL, thus supporting our view of a direct LDL secretion by visceral rat yolk sacs.

Estrogen promotes angiogenic activity in human umbilical vein endothelial cells in vitro and in a murine model

BACKGROUND

Angiogenesis is a critical event in wound healing, tumor growth, and the inflammatory vasculitides. Since women have a higher incidence of many vasculitic diseases, we examined the effects of female sex steroids, particularly estradiol, on human umbilical vein endothelial cell (HUVEC) behavior in vitro and on angiogenesis in vivo.

METHODS AND RESULTS

HUVECs were grown in estrogen-free medium before each assay. Exogenous 17 beta-estradiol (1 to 5 nmol/L) increased cell attachment to laminin, types I and IV collagen, and fibronectin, as well as to tissue culture plastic. After a confluent monolayer of cells was "wounded" by scraping, estradiol-treated (10(-8) mol/L) cells migrated into the wound three times faster than untreated cells. Cell proliferation on plastic and on laminin increased threefold to fivefold, respectively, in the presence of estradiol. Estradiol also enhanced the ability of HUVECs to organize into tubular networks when plated on a reconstituted basement membrane, Matrigel. Estradiol effects on both the "wounding" assay and tube formation were blocked by the specific estrogen receptor antagonist ICI 182,780. Ovariectomy markedly decreased in vivo vascularization of Matrigel plugs coinjected with basic fibroblast growth factor in mice. With estrogen replacement, angiogenesis was increased to the levels observed in nonovariectomized mice.

CONCLUSIONS

These studies demonstrate that, in vitro and in vivo, estradiol enhances endothelial cell activities important in neovascularization and suggest a promoting influence of estrogens on angiogenesis.