The synthesis of subendothelial matrix by bovine aortic endothelial cells in culture

A protocol for isolation and culture of human umbilical vein endothelial cells

We describe a protocol for easy isolation and culture of human umbilical vein endothelial cells (HUVECs) to supply every researcher with a method that can be applied in cell biology laboratories with minimum equipment. Endothelial cells (ECs) are isolated from umbilical vein vascular wall by a collagenase treatment, then seeded on fibronectin-coated plates and cultured in a medium with Earles' salts and fetal calf serum (FCS), but without growth factor supplementation, for 7 days in a 37 degrees C-5% CO2 incubator. Cell confluency can be monitored by phase-contrast microscopy; ECs can be characterized using cell surface or intracellular markers and checked for contamination. Various protocols can be applied to HUVECs, from simple harvesting to a particular solubilization of proteins for proteomic analysis.

Decrease in culture temperature releases monolayer endothelial cell sheets together with deposited fibronectin matrix from temperature-responsive culture surfaces

Bovine aortic endothelial cells were cultured on surfaces grafted with a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm), in the presence of serum. Cells adhered, spread, proliferated, and reached confluency as observed on ungrafted tissue culture polystyrene dishes. A decrease in culture temperature released cells only from the grafted surfaces without enzymatic or ethylenediaminetetraacetic acid treatment. Upon lowering temperature, the culture surfaces changed from hydrophobic to hydrophilic owing to the hydration of grafted PIPAAm and thus weakened the cell attachment to the dishes. Released cells maintained cell-cell junctions composing monolayer cell sheets. Immunoblotting and immunofluorescence microscopy revealed that fibronectin (FN) was deposited and accumulated on the grafted surfaces during the culture. Furthermore, the deposited FN matrix adhering to cell sheets was also recovered from temperature-responsive surfaces by low-temperature treatment, while trypsin treatment destroyed the matrix. The recovery of FN by low-temperature treatment was as high as by physical scraping with a rubber blade. Temperature-responsive surfaces can provide a novel method to use cultured confluent cell sheets for tissue engineering, and also to elucidate structure and function of deposited extracellular matrix during cell culture.

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.

Interaction of prostate epithelial cells from benign and malignant tumor tissue with bone-marrow stroma

BACKGROUND

Metastases of prostate cancer form selectively within the skeleton. To understand this metastatic spread, we studied the ability of prostate epithelial cells to grow and proliferate within the bone marrow, using primary coculture.

METHODS

Prostate epithelia and fibroblasts were prepared from men with benign prostatic hyperplasia (n = 13) and cancer of the prostate (n = 10). Confluent cultures of bone-marrow stroma or fibroblast controls were prepared in 96-well plates, and identical plates were treated with detergent to expose the extracellular matrix of the cells. Epithelial cells were seeded onto either cells or matrix, and their growth characteristics were determined by counting increases in colony size and number over time. Further experiments evaluated the effects on epithelial growth when cells were exposed to media conditioned by these stroma, using an MTT assay.

RESULTS

Results showed that for epithelial cells derived from malignant (or benign) tissue, the median value of the total area of colonies formed on bone-marrow stroma was 2.1 (benign, 2.6) mm2, in contrast to 0.3 (benign, 0.4) mm2 or 0.25 (benign, 0) mm2 when these cells were cocultured with fibroblasts from benign or malignant prostates, respectively. Statistics indicated that growth was significantly greater on bone-marrow stroma than on control stroma (P < 0.005). However, no significant stimulation of epithelial cell growth was seen when these epithelial cells were cultured on extracellular matrix from bone-marrow stroma or when exposed to bone-marrow stroma-conditioned media in comparison to fibroblast controls. No statistical differences were found between the formation of colonies from malignant tissue in comparison to benign.

CONCLUSIONS

This system allows the investigation of bone-marrow stroma colonization by primary prostate epithelial cells, and could be developed for the study of metastasis.

Evidence that tenascin and thrombospondin-1 modulate sprouting of endothelial cells

Cultured endothelial cells undergo a reversible transition from a resting (cobblestone) phenotype to an angiogenic (sprouting) phenotype. This transition mimics the early events of angiogenesis. We have previously reported that the addition of exogenous xylosides inhibits endothelial cel sprouting and modifies the extracellular matrix (ECM) synthesised by the cells. We have now investigated whether endothelial sprouting is mediated by the nature of the extracellular matrix in contact with the cells. Accordingly, cell-free matrices deposited by bovine aortic endothelial cells (BAEC) were isolated. These matrices were produced under conditions in which the formation of the sprouting phenotype was permitted (controls) or inhibited (by the addition of exogenous xylosides). BAEC were then plated on these matrices and grown under conditions which promote sprouting. Sprouting proceeded normally on control matrices, whereas it was inhibited when the cells were grown on matrices deposited in the presence of xylosides. The composition of the permissive and inhibitory matrices was then analysed. Inhibitory matrices contained reduced levels of tenascin and increased levels of thrombospondin-1 by comparison to the permissive matrices. In contrast, no differences were detected in the relative levels of laminin. The roles of tenascin and thrombospondin-1 in endothelial sprouting were confirmed using specific antibodies. Immunolocalisation studies revealed the presence of both proteins in sprouting cells. Antibodies to tenascin inhibited the formation of sprouting cells on permissive matrices and on gelatin-coated dishes without affecting cell growth. Tenascin synthesis was increased when sprouting cells were present in the cultures. Antibodies to thrombospondin-1 stimulated sprouting on inhibitory matrices. These results suggest that the transition from a resting to a sprouting phenotype is promoted by tenascin and inhibited by thrombospondin-1.

Glial extracellular matrix modulates gamma-glutamyl transpeptidase activity in cultured bovine brain capillary and bovine aortic endothelial cells

Glial extracellular matrix (ECM) elevated gamma-glutamyl transpeptidase (gamma-GTP) activity in cultured bovine brain capillary and aortic endothelial cells (BBCEC, BAEC). In particular, the ECM of glial cells cultured with the conditioned medium of BAEC (BAEC CM) dramatically elevated gamma-GTP activity in BBCEC and BAEC. The ECM of glial cells cultured with BBCEC CM also had a marked effect. The ECM of 3T3 cells cultured with BAEC CM, and the ECM of glial cells cultured with 3T3 CM had no effect. Glial CM had no effect on gamma-GTP activity in BBCEC and BAEC. These findings indicate that gamma-GTP activity in endothelial cells (EC) is modulated by glial ECM, and that the factor of ECM that affects gamma-GTP activity in EC arises from the interaction between glial cells and EC.

Morphological differentiation of endothelial cells co-cultured with astrocytes on type-I or type-IV collagen

In this study bovine aortic endothelial cells were co-cultured with astrocytes from fetal Wistar Kyoto rats. Endothelial cells growing on type-I collagen, co-cultured with astrocytes, showed various stages of development. Although some cells appeared to be mature, horseradish peroxidase penetrated within 1 min of incubation through the intercellular junctions of these endothelial elements maintained on type-I collagen. In contrast, endothelial cells on type-IV collagen, co-cultured with astrocytes, were well developed; their intercellular junctions were well established, and plasmalemmal vesicles reduced in number. As a result, horseradish peroxidase was unable to penetrate through the endothelial cells grown on type-IV collagen and co-cultured with astrocytes because of the reduced extent of the junctional and vesicular transport. These findings reveal that (1) type-IV collagen is essential for the differentiation of endothelial cells, (2) endothelial cell-astrocyte interactions occur during co-culture, and (3) endothelial permeability depends on astrocyte-produced factors, in addition to type-IV collagen.

T cell adhesion to extracellular matrix molecules secreted by endothelial cells cultured on a substrate of type IV collagen

T cell emigrating from the bloodstream into lymphoid organs or sites of inflammation in the connective tissue must adhere to, and traverse, the subendothelial basement membrane (BM). The goal of the current investigation was to develop a method to study the adhesion of T cells to endothelial cell (EC)-derived extracellular matrix (ECM) as a model for the interaction of T cells with the subendothelial BM in vivo. To be certain that we were truly measuring T cell adhesion to ECM molecules secreted by the EC, it was necessary to culture the EC on a substrate to which T cells could not attach. Non-tissue culture-treated microtiter plate wells which had been coated with type IV collagen (tIVC), a major constituent of BM in vivo, were found to be suitable for this purpose since EC, but very few T cells, adhered to such wells. After incubating the EC on a substrate of tIVC in non-treated wells for a period of 48 h, the EC were gently removed from their underlying ECM and T cell adhesion to that ECM was examined. Using this system, it was observed that approximately 15-40% of human peripheral blood T cells specifically adhered to ECM molecules produced by the EC. This method should be useful as a model for the interactions of T cells and other leukocytes with the vascular BM in vivo.

Thrombospondin gene expression by endothelial cells in culture is modulated by cell proliferation, cell shape and the substratum

Endothelial cells plated on the surface of a two-dimensional substratum (gelatin-coated dishes, dishes coated with native type I collagen or collagen gels) form a cobblestone monolayer at confluence, whereas cells plated within a three-dimensional gel matrix elongate into a sprouting morphology and self-associate into tube-like structures. In this study, we have compared the synthesis of thrombospondin by quiescent endothelial cells displaying (a) the same morphological phenotype (cobblestone) on different substrata (gelatin and collagen) and (b) different morphological phenotypes (cobblestone and sprouting) on the same substratum (collagen). We demonstrate that thrombospondin is a major biosynthetic product of confluent, quiescent cells cultured on dishes coated with either gelatin or collagen, and that the synthesis of this protein is markedly decreased when cells are plated on or in three-dimensional collagen gels. Moreover, we demonstrate that cells plated in gel (sprouting) secrete less thrombospondin than do cells plated on the gel surface (cobblestone). The regulation of thrombospondin synthesis is reversible and occurs at the level of transcription, as steady-state mRNA levels for thrombospondin decrease in a manner comparable with the levels of protein secreted by these cells. We also show that mRNA levels for laminin B2 chains are increased when cells are cultured on and in collagen gels compared with on gelatin-coated dishes, suggesting that the syntheses of thrombospondin and laminin are regulated by different mechanisms. When cells are cultured on gelatin- or collagen-coated dishes, thrombospondin gene expression is directly proportional to the proliferative state of the cultures. By contrast, the synthesis of thrombospondin by cells cultured on collagen gels remains at equally low levels whether they are labelled when they are sparse and rapidly proliferating or when they are confluent and quiescent. Fibronectin synthesis was found to increase with increasing confluency of the cells plated on all three substrata. These results demonstrate that thrombospondin gene expression is modulated by cell shape, cell proliferation and the nature of the substratum used for cell culture.

The effect of a native collagen gel substratum on the synthesis of collagen by bovine brain capillary endothelial cells

Cultured capillary endothelial cells, derived from bovine brain, and maintained on a plastic substratum synthesized predominantly interstitial collagens of which approximately 75 per cent were secreted into the medium. When grown on a native hydrated collagen type I gel, although no marked alteration in the 'collagen synthetic pattern' was observed, the overall level of collagen synthesis was increased by approximately 100 per cent. More dramatic, however, was the alteration in the distribution of these molecules between medium and cell layer. Interstitial collagens produced by cells grown on collagen gels were almost exclusively associated with the cell layer or collagenous gel. These studies, thus, demonstrate that an extracellular matrix may exert a considerable influence on the cellular synthetic activities and possibly cellular polarity of capillary endothelial cells.

Inhibition of endothelial cell morphogenetic interactions in vitro by alpha- and beta-xylosides

Bovine aortic endothelial cells retain the ability to undergo histiotypic morphogenetic interactions in vitro as evidenced by a) the reversible expression of a sprouting cell phenotype and b) the patterned self-association of these sprouting cells into three-dimensional meshworks and tubule-like structures. These morphogenetic events are inhibited by xylosides in a dose-dependent manner. Two types of beta-xylosides (p-nitrophenyl-beta-D-xylopyranoside and 4-methylumbelliferyl-beta-D-xylopyranoside) and one alpha-xyloside (p-nitrophenyl-alpha-D-xylopyranoside) were tested. beta-xylosides are well characterized acceptors of glycosaminoglycan chains, whereas alpha-xylosides do not function in this capacity and have been extensively used as negative controls when studying the effects of beta-xylosides. Both alpha- and beta-xylosides inhibited endothelial morphogenetic interactions. This inhibition was slowly reversed during the 6- to 7-d period following removal of the xyloside. Inhibition of morphogenetic interactions by xylosides occurred at concentrations (0.5 to 2.0 mM) that had no demonstrable effects on cell proliferation, migration, or adhesion to 2-D plastic or collagen substrata. The xylosides seemed to inhibit cell spreading on a 3-D environment, they also inhibited the incorporation of [3H]-proline and Na2 35SO4 into the extracellular matrix deposited by the cells, suggesting that the inhibition of morphogenesis may be related to the inhibition of matrix deposition. Endothelial morphogenetic interactions were not inhibited by the extracellular matrix or by the conditioned medium produced by cells cultured in the presence of xylosides.

Comparative assessment of cell/substratum static adhesion using an in vitro organ culture method and computerized analysis system

The trypsin sensitivity of chick embryo cellular layers cultivated by an in vitro organ culture method toward different biomaterials has been analysed. Monolayer cells grown on to tested samples were enzymatically dissociated in 5 min - 1 h. Cumulative cell numbers, expressed as the percentage of the totally detached cell number, were plotted versus time, thus permitting the calculation of the function. The mathematical treatment by a computerized system of this function represents the trypsin sensitivity. This value modulated by the migration cell number is the static adhesion modulated index (SAMI). The trypsin sensitivity expressed according to this index allowed the establishment of an abacus wherein several zones, A, B, C and D, define cell adhesion behaviour on different biomaterials. Scanning electron microscopy analysis performed on dissociation steps showed the selective activity of trypsin on cells toward different substrata, revealing the role of an extracellular matrix and cytoskeleton in the adhesion behaviour.

Characteristics of lung pericytes in culture including their growth inhibition by endothelial substrate

Pericytes and endothelial cells from the same sample of adult rat lung have been separately established in culture by use of selective growth media. The endothelial cells are positive and the pericytes negative for angiotensin-converting enzyme activity and tissue plasminogen activator. Morphologically in culture, the pericytes are similar to pericytes from bovine retina and other sites and show positive immunofluorescence to both human platelet (non-muscle) myosin and smooth muscle myosin. In this respect they resemble smooth muscle cells grown from the rat main pulmonary artery, but lack the myofilaments and dense bodies characteristic of muscle cells. Lung endothelial cells and fibroblasts are positive only for platelet myosin. Pericytes in culture demonstrate an unusual growth response to endothelial substrate, obtained by removing confluent endothelial monolayers with nonionic detergent or alkali. When plated onto this material at low density, pericyte growth is inhibited. By contrast, the substrate stimulates the growth of endothelial cells and has no effect on smooth muscle cells. Initial attachment of endothelial cells and pericytes to the substrate is similar.

Importance of vitamin C in maintenance of the normal amnion: an experimental study

Collagenous matrix in amnion accounts for most of the dry weight of the tissue and provides its mechanical strength and resistance to rupture. Cell and organ culture techniques have been utilized to study the influence of vitamin C upon the synthesis and deposition of extracellular matrix by cells of normal amnion at term. The cultures have been examined using light and electron microscopy and metabolic labelling. These studies show that both epithelial cells and fibroblasts of the deeper stromal layer are active in the production of fibrillar matrix at this time. Matrix deposition by epithelial cells in culture increases several-fold when the vitamin C concentration in the supernatant medium is increased from zero to 50 micrograms/ml, and, at the latter concentration, a continuous anastomosing fibrillar collagenous meshwork appears beneath the cells. This study thus provides new evidence that an adequate dietary supply of vitamin C is probably needed to maintain the strength of the chorioamnion.

Extracellular matrix proteoglycans and cell-substratum adhesion of human endothelial cells: the effect of methyl beta-D-xylopyranoside

The influence of methyl beta-D-xylopyranoside on human endothelial cell proteoglycans isolated from the medium and extracellular matrix was investigated. Confluent cultures of human endothelial cells incorporate significant amounts of heparan sulfate (78%), chondroitin sulfate (10%), and dermatan sulfate (12%) into the extracellular matrix. Chondroitin sulfate (35%) and dermatan sulfate (37%) were the major glycosaminoglycans present in the medium. In the presence of methyl beta-D-xylopyranoside, incorporation of labeled proteoglycans into extracellular matrix was diminished by approximately 70%. Heparan sulfate comprised the major proteoglycan present in extracellular matrix (89%) in cells grown in the presence of methyl beta-D-xylopyranoside. In contrast to the incorporation of proteoglycan into extracellular matrix, methyl beta-D-xylopyranoside stimulated the secretion of labeled glycosaminoglycan chains into the medium 2.5-fold. In the presence of methyl beta-D-xylopyranoside, secretion of chondroitin sulfate into the medium was markedly stimulated, with a slight increase in secretion of heparan sulfate. Chondroitin sulfate (62%) and heparan sulfate (34%) were the major labeled glycosaminoglycans present in medium from methyl beta-D-xylopyranoside-treated cultures. The effect of methyl beta-D-xylopyranoside on cell adhesion and detachment was investigated. Cell detachment from extracellular matrix depleted of proteoglycan was significantly faster than detachment from normal matrix. Conversely, human endothelial cells adhered faster to normal matrix than to matrix depleted of proteoglycan.

The isolation and culture of endothelial cells and pericytes from the bovine retinal microvasculature: a comparative study with large vessel vascular cells

Endothelial cells (BREC) and pericytes (BRP) were isolated from the bovine retinal microvasculature. These cells were first identified by morphological criteria and by their differential staining for Factor VIII related antigen. BREC and BRP responded differently to a number of experimental parameters in vitro; for example, the plating efficiency of BREC was enhanced by the use of a gelatin substratum and medium conditioned by either endothelial cells or pericytes; oxygen tension had no effect. In contrast, the plating efficiency of BRP was only enhanced by low oxygen tension. Conditioned media also stimulated the proliferation of BREC, but not that of BRP. The saturation density reached by BREC was dependent on the initial plating density while BRP plated at different initial densities reached the same final density. The in vitro behavior of the retinal microvascular cells was also compared to that of large vessel (aorta) endothelial cells (BAEC) and smooth muscle cells (SMC). Aortic and retinal endothelial cells showed similar morphology and behavior. When initially plated as a homogeneous cell suspension within a collagen matrix, both BREC and BAEC self-associated to form three-dimensional meshworks; this morphogenesis was accomplished by cell migration and did not involve cell proliferation. By contrast, BRP and SMC divided and remained homogeneously distributed when plated within a collagen gel matrix. BRP and SMC did, however, behave differently when plated on the surface of a collagen gel; SMC migrated extensively into the gel while BRP remained confined to the gel surface. BRP grown on any substratum began to retract upon themselves shortly after confluence, producing characteristic nodules interconnected by cellular strands. BRP and SMC were able to contract a collagen gel substratum, while retinal and aortic endothelial cells were unable to do so. These results provide new means for the in vitro characterization of endothelial cells, smooth muscle cells and pericytes.

The biosynthesis of extracellular-matrix components by bovine retinal endothelial cells displaying distinctive morphological phenotypes

Previous studies have indicated that the morphology and behaviour of bovine retinal microvessel endothelial cells are influenced by culture conditions in vitro. Data are presented here concerning the biosynthesis of matrix macromolecules by bovine retinal endothelial cells cultured under conditions in which the cells display either the 'cobblestone' or the 'sprouting' phenotype. Newly synthesized matrix proteins were identified by their characteristic electrophoretic mobilities, immunoprecipitation with specific antibodies, susceptibilities to enzymic digestions and chromatographic behaviour. Type IV procollagen was the major collagenous species synthesized by early-passage cells forming a 'cobblestone' monolayer. In contrast, cells displaying the 'sprouting' morphology switched to the predominant synthesis of interstitial fibrillar collagens (types I and III). Fibronectin was synthesized by retinal endothelial cells under all the experimental conditions studied. A non-collagenous glycoprotein of Mr approx. 47,000 was also a major biosynthetic product of these cells. The synthesis of thrombospondin was very much dependent on the nature of the substratum on which the cells were cultured. This glycoprotein was synthesized in large amounts by 'cobblestone' endothelial cells cultured on gelatin-coated dishes, whereas its synthesis was markedly decreased by culturing the cells on collagen gels, and the protein appeared to be absent when the cells were plated within collagen gels ('sprouting' cells). Late-passage retinal cells synthesized predominantly type I procollagen, variable amounts of type III procollagen and only traces of type IV procollagen, irrespective of whether the cells displayed a 'cobblestone' or 'sprouting' morphology.

The interaction of melanoma cells with fibroblasts and endothelial cells in three-dimensional macromolecular matrices: a model for tumour cell invasion

Comparative quantitative data are presented concerning the adhesion, proliferation and invasive behaviour of RPMI-3460 melanoma cells on (1) plain collagen gels, (2) monolayer cultures of fibroblasts and endothelial cells growing on the gel surface, and (3) the exposed endothelial and fibroblast extracellular matrices (ECMs). Both types of ECMs enhanced melanoma cell adhesion and proliferation (compared with plain gels) and had marked, but distinctive, effects on melanoma morphology. The thickness and composition of the ECMs was altered by treatment of the matrices with enzymes (trypsin, elastase and chondroitinase ABC) or by using ECMs produced by endothelial cells at various times after confluence. Variations in the thickness and composition of the ECMs had no effect on the behaviour of melanoma cells growing on these matrices; our results suggest that the glycoproteins and glycosaminoglycan ECM constituents removed by digestion with the enzymes do not play an important role in melanoma cell attachment, proliferation and migration. Melanoma cells plated on the surface of a plain collagen gel rapidly migrated down into the collagen matrix, with approximately 30% of the cells found within the gel after 6 days of incubation. Fibroblast and endothelial ECMs significantly and distinctively inhibited melanoma invasion into the underlying collagen gel. The extensive invasion of melanoma cells into the gel was not accompanied by hydrolysis of the collagen fibres. Conversely, fibroblast and endothelial ECMs, which acted as effective barriers, were extensively hydrolysed by the melanoma cells. The possible use of ECMs deposited on collagen in the study of melanoma local invasion (on fibroblast ECMs) and extravasation (on endothelial ECMs) is discussed.