Cell-extracellular matrix interactions in morphogenesis: an in vitro approach

Extracellular Vesicles' Role in Angiogenesis and Altering Angiogenic Signaling

Angiogenesis, the process of new blood vessels formation from existing vasculature, plays a vital role in development, wound healing, and various pathophysiological conditions. In recent years, extracellular vesicles (EVs) have emerged as crucial mediators in intercellular communication and have gained significant attention for their role in modulating angiogenic processes. This review explores the multifaceted role of EVs in angiogenesis and their capacity to modulate angiogenic signaling pathways. Through comprehensive analysis of a vast body of literature, this review highlights the potential of utilizing EVs as therapeutic tools to modulate angiogenesis for both physiological and pathological purposes. A good understanding of these concepts holds promise for the development of novel therapeutic interventions targeting angiogenesis-related disorders.

Molecular mediators of angiogenesis

Angiogenesis, or the formation of new blood vessels from the preexisting vasculature, is a key component in numerous physiologic and pathologic responses and has broad impact in many medical and surgical specialties. In this review, we discuss the key cellular steps that lead to the neovascularization of tissues and highlight the main molecular mechanisms and mediators in this process. We include discussions on proteolytic enzymes, cell-matrix interactions, and pertinent cell signaling pathways and end with a survey of the mechanisms that lead to the stabilization and maturation of neovasculatures.

Lymphangiogenesis and lymphatic remodeling induced by filarial parasites: implications for pathogenesis

Even in the absence of an adaptive immune system in murine models, lymphatic dilatation and dysfunction occur in filarial infections, although severe irreversible lymphedema and elephantiasis appears to require an intact adaptive immune response in human infections. To address how filarial parasites and their antigens influence the lymphatics directly, human lymphatic endothelial cells were exposed to filarial antigens, live parasites, or infected patient serum. Live filarial parasites or filarial antigens induced both significant LEC proliferation and differentiation into tube-like structures in vitro. Moreover, serum from patently infected (microfilaria positive) patients and those with longstanding chronic lymphatic obstruction induced significantly increased LEC proliferation compared to sera from uninfected individuals. Differentiation of LEC into tube-like networks was found to be associated with significantly increased levels of matrix metalloproteases and inhibition of their TIMP inhibitors (Tissue inhibitors of matrix metalloproteases). Comparison of global gene expression induced by live parasites in LEC to parasite-unexposed LEC demonstrated that filarial parasites altered the expression of those genes involved in cellular organization and development as well as those associated with junction adherence pathways that in turn decreased trans-endothelial transport as assessed by FITC-Dextran. The data suggest that filarial parasites directly induce lymphangiogenesis and lymphatic differentiation and provide insight into the mechanisms underlying the pathology seen in lymphatic filariasis.

The nematode parasites Brugia malayi and Wuchereria bancrofti are the major organisms responsible for lymphatic filariasis. Lymphatic filariasis is characterized by the dysfunction of the lymphatics that can lead to severe (and often) irreversible lymphedema and elephantiasis. Current advances in distinguishing blood vascular from lymphatic endothelial cells have allowed the direct study of the interaction between live filarial parasites and their lymphatic niche. In the quest towards understanding parasite-lymphatic endothelium interactions, we observed that the filarial antigens have a specific but differential stimulatory capacity towards the lymphatics and cause them to differentiate into tube-like vascular networks in vitro that resemble the formation of collateral lymphatics in vivo. This was a lymphatic-specific phenomenon, as the filarial parasites or antigen did not exhibit similar effects on the human umbilical vein endothelial cells. The differentiation of the lymphatic endothelial monolayers into vascular networks was not dependent on typical markers of lymphangiogenesis but rather involves the matrix metalloproteases and their inhibitors that suggest lymphatic matrix remodeling rather than rendering of the lymphatics hyper-permeable as has been postulated previously.

Distinct Patterns of Microvascular Endothelial Cell Morphology Are Determined by Extracellular Matrix Composition

Endothelial interactions with the extracellular matrix (ECM) play important roles in angiogenesis but whether specific ECM signals can determine specific cellular morphologies is unclear. The authors compared in vitro ECM-induced morphological responses of the phenotypically distinct human placental microvascular endothelial cells (HPMECs) with large vessel endothelial cells (HUVECs). HPMECs showed distinct patterns of reorganization in response to collagen-I or collagen-IV (monolayer disruption, sprouting, migration) and Matrigel or laminin-A (intussusception, cord formation, tubulogenesis), and an intermediate response to fibrin; whereas HUVECs responded similarly to collagen-1 and Matrigel (elongation, lattice formation, vacuolation) and showed little response to fibrin. Although the extent of collagen and Matrigel responses of HPMECs were increased by serum, acidic or basic fibroblast growth factor (aFGF, bFGF), or vascular endothelial growth factor (VEGF), and varied with matrix protein concentration, the basic patterns were matrix specific, and were independent of fibronectin. The collagen responses correlated with disruption of adherens and tight junctions and the formation of filopodial protrusions. Matrigel responses were associated with up-regulated junctional localization of VE-cadherin, and tubulogenesis developed mainly through paracellular remodeling rather than intracellular vacuolation. Overall, these findings suggest that distinct ECM interactions stimulate specific morphological responses. These signals may regulate morphological behaviour in the angiogenesis cycle, switching endothelial cells between migratory and vasculogenic phenotypes.

Effect of lead on tube formation by cultured human vascular endothelial cells

The effect of lead acetate (Pb) on the growth of and tube formation by cultured human umbilical vascular endothelial cells (HUVEC) was examined. HUVEC were collected by enzymatic digestion with collagenase. The number of viable cells of HUVEC was negligibly affected by cultivation with Pb at concentrations of 1-100 microM, but was slightly reduced by cultivation at 500 microM. Tube formation was studied by culturing the cells on a gelled basement membrane matrix (Matrigel). Treatment of HUVEC with 0.1-50.0 microM Pb for 24 h inhibited tube formation dose-dependently. The length of tube formation decreased time-dependently with 1.0 microM Pb. These findings suggest that Pb inhibits the formation of a capillary network by HUVEC, and that Pb could be injurious to endothelial cell function.

Methylmercury-injury effect on tube formation by cultured human vascular endothelial cells

The effect of methylmercury chloride (MeHg) on growth and tube formation by cultured human umbilical vein endothelial cells (HUVECs) was investigated. HUVECs were collected by enzymatic digestion with collagenase. Precultivation of HUVECs with MeHg at concentrations of 1.0-50.0 mumol/L exerted negligible effects on the viable cell number, while the viable cell number was slightly reduced at 100 mumol/L and fell to zero at concentrations exceeding 500.0 mumol/L MeHg. The viable cell number was depressed in a concentration-dependent manner. Tube formation was studied by culturing the cells on gelled basement membrane matrix (Matrigel). Treatment of HUVECs with 0.1-5.0 mumol/L MeHg for 24 h inhibited tube formation dose-dependently. Fetal bovine serum (FBS) increased tube formation in a dose-dependent manner, with half-maximum stimulation of tube formation at approximately 3.4% FBS. The length of tube formation decreased time-dependently at concentrations of 0.1 and 1.0 mumol/L MeHg. Pretreatment of Matrigel with 1 mumol/L MeHg before the cell seeding reduced the tube formation by HUVECs. These results suggest that the growth and tube formation by HUVECs is susceptible to MeHg cytotoxicity, and that MeHg could be injurious to endothelial cell function.

A line of rat ovarian surface epithelium provides a continuous source of complex extracellular matrix

A spontaneously immortalized, yet non-tumorigenic rat ovarian surface epithelial (ROSE 199) cell line, deposits large amounts of extracellular matrix (ECM) in response to crowding. The characteristics and components of ROSE 199-derived cell-free ECM were compared after three different preparative techniques: treatment with 20 mM ammonium hydroxide, with 1% sodium deoxycholate, or by repeated freeze-thaws. The ECMs were analyzed by histochemistry, immunofluorescence, electron microscopy, and Western immunoblotting. Components of ROSE 199 ECM included laminin, fibronectin, and collagen types I and III. Even though ROSE 199 is an epithelial cell line, striated collagen fibers formed a major part of its matrix. Thus, ROSE 199 matrix consists of both basement membrane and stromal matrix components. This matrix supported the adhesion, spreading, and growth of several cell types without altering their morphology or growth pattern, and enhanced the attachment of some cell types that spread on plastic only with difficulty. Immunofluorescence, electron microscopy, and dry weight determinations indicated that a greater proportion of matrix was retained in preparations obtained by ammonium hydroxide or freeze thaw techniques than after sodium deoxycholate treatment. Ammonium hydroxide and freeze-thaw treated matrices were also superior to sodium deoxycholate preparations as evidenced by enhanced initial cellular adhesion and spreading compared to cells plated on plastic. Residual nuclear material did not seem to affect the biological activity of this matrix. ROSE 199 extracellular matrix provides a novel, complex substratum for cell culture and for studies of matrix functions and synthesis.

Characterization of a gamma-glutamyl transpeptidase positive subpopulation of endothelial cells in a spontaneous tube-forming clone of rat cerebral resistance-vessel endothelium

A spontaneous tube-forming clone of rat cerebral resistance-vessel endothelium was characterized in long-term serial culture. In this study, a clone, RV-150 ECT, of cerebral resistance vessel endothelial cells in long-term culture has been shown to have a subpopulation of gamma-GTP positive cells that are present in all cultures regardless of confluency status or tube-forming stages. In pre-confluent and confluent cultures, the gamma-GTP positive cells are few in number, stain weakly, and are randomly distributed in the monolayers. In monolayer post-confluent cultures, gamma-GTP positive cells increase in number, stain strongly, and begin to show signs of non-random distributions. In early post-confluent cultures that have become a mixture of monolayer and multilayer cells, there is a further increase in gamma-GTP positive cells which begin to form distinct groupings. In mid post-confluent cultures, the multilayered areas of the culture have begun clustering to form clear multicellular aggregates. The gamma-GTP positive cells at this stage are reduced in number and are predominantly associated with the cell clusters. In late post-confluent cultures, the multicellular clusters develop clear cell cords between/among the clusters. At this stage the gamma-GTP positive cells are associated exclusively with cell clusters. With cord development, the gamma-GTP positive cells are associated with both clusters and cords, and are reduced in number apparently because of selective degeneration of these cells. The results of this study demonstrate that a phenotypically distinct subpopulation of endothelial cells exhibits characteristic features of the blood-brain barrier, namely gamma-GTP. The ability of these cells to express this property in long-term serial culture suggests that this may represent a useful in vitro model to study the growth and differentiation of blood-brain barrier vessels.

Role of laminin in endothelial cell recognition and differentiation

The vascular endothelium normally is maintained in a quiescent state, but under certain conditions it is induced to undergo marked changes in behavior and form new vascular structures. A complex interaction among various growth and differentiation factors and the extracellular milieu regulates this behavior. One series of signals affecting endothelial behavior is provided by laminin, a major structural protein of basement membrane. These signals have been studied using Matrigel, a reconstituted basement membrane preparation from the murine Englebreth-Holm-Swarm sarcoma, in an in vitro assay of endothelial cell differentiation. Three biologically-active sequences from the laminin molecule have been evaluated. Synthetic peptides that include the sequences -RGD-, -YIGSR-, and -SIKVAV- mediate, respectively, cell binding to Matrigel, alterations in cell morphology, and induction of migration and collagenase activity. Preliminary data indicate that observations made with this system may be relevant to endothelial function in vivo. Endothelial cell differentiation on Matrigel may thus be a useful in vitro model for the study of certain steps in angiogenesis.

Interaction of endothelial cells with a laminin A chain peptide (SIKVAV) in vitro and induction of angiogenic behavior in vivo

Endothelial cells are known to bind to laminin, and two peptides derived from the laminin A (CTFALRGDNP) and B1 (CDPGYIGSR) chains block the capillary-like tube formation on a laminin-rich basement membrane matrix, Matrigel. In the present study, we have used various in vitro and in vivo assays to investigate the angiogenic-biologic effects of a third active site in the laminin A chain, CSRARKQAASIKVAVSADR (designated PA22-2) on endothelial cells. The SIKVAV-containing peptide was as active as the YIGSR-containing peptide for endothelial cell attachment but was less active than either the RGD-containing peptide or intact laminin. Endothelial cells seeded on this peptide appeared fibroblastic with many extended processes, unlike the normal cobblestone morphology observed on tissue culture plastic. In addition, in contrast to normal tube formation on Matrigel, short irregular structures formed, some of which penetrated the matrix and sprouting was more apparent. Analysis of endothelial cell conditioned media of cells cultured in the presence of this peptide indicated degradation of the Matrigel and zymograms demonstrated active collagenase IV (gelatinase) at 68 and 62 Kd. A murine in vivo angiogenesis assay and the chick yolk sac/chorioallantoic membrane assays with the peptide demonstrated increased endothelial cell mobilization, capillary branching, and vessel formation. These data suggest that the -SIKVAV-site may play an important role in initiating branching and formation of new capillaries from the parent vessels, a behavior that is observed in vivo in response to tumor growth or in the normal vascular response to injury.

Protein kinase C regulates endothelial cell tube formation on basement membrane matrix, Matrigel

Human umbilical vein endothelial cells differentiate within 12 h to form capillary-like networks of tube structures when the cells are plated on Matrigel, a mixture of basement membrane proteins. Nothing is known about the intracellular signaling events involved in this differentiation. As a first step to define the process, we investigated the possible role of protein kinase C activation by beta-phorbol 12-myristate 13-acetate (PMA) in regulating the formation of the tube structures. In this model, PMA increased tube formation several-fold in a dose-dependent manner with half-maximum stimulation of tube formation at approximately 5 nM PMA. In the absence of serum, essentially little or no tubes were formed on Matrigel unless PMA was added to the medium. Only active phorbol analogs increased tube formation, while the protein kinase C inhibitor, H-7, blocked tube formation. The protein kinase C activators and inhibitors were effective only when added at or just after plating of the cells and did not affect already formed tubes. This study suggests that protein kinase C is involved in the early events of in vitro endothelial cell tube formation on Matrigel.

Intracellular mechanisms involved in basement membrane induced blood vessel differentiation in vitro

The extracellular matrix, particularly basement membranes, plays an important role in angiogenesis (blood vessel formation). Previous work has demonstrated that a basement membranelike substrate (Matrigel) induces human umbilical vein endothelial cells to rapidly form vessel-like tubes (Kubota, et al., 1988; Grant et al., 1989b); however, the precise mechanism of tube formation is unclear. Using this in vitro model, we have investigated morphologic changes occurring during tube formation and the cytoskeletal and protein synthesis requirements of this process. Electron microscopy showed that endothelial cells attach to the Matrigel surface, align, and form cylindrical structures that contain a lumen and polarized cytoplasmic organelles. The cytoskeleton is reorganized into bundles of actin filaments oriented along the axis of the tubes and is located at the periphery of the cells. The addition of colchicine or cytochalasin D blocked tube formation, indicating that both microfilaments and microtubules are involved in this process. Cycloheximide blocked tube formation by 100%, indicating that the process also required protein synthesis. In particular, collagen synthesis seems to be required for tube formation because cis-hydroxyproline inhibited tube formation, whereas either the presence of ascorbic acid or the addition of exogenous collagen IV to the Matrigel increased tube formation. Our results indicate that endothelial cell attachment to Matrigel induces the reorganization of the cytoskeleton and elicits the synthesis of specific proteins required for the differentiated phenotype of the cells.

Extracellular matrix influences hormone and protein production by human chorionic villi

Increasing evidence confirms that the extracellular matrix greatly influences cell behaviour and function. Collagen and fibrin are in contact with trophoblast throughout pregnancy. To investigate whether these two matrices influence hormone production by the trophoblast, explants from first-trimester chorionic villi were cultured for up to 30 days either a) in medium with agitation, b) embedded in type-I collagen (three-dimensional gels), or c) embedded in fibrin (three-dimensional gels). The supernatant culture medium was changed every 48 h and tested by radioimmunoassay for hCG, progesterone and pregnancy-associated plasma protein A. In addition, after 3, 7, 15, and 30 days of culture villi were fixed and studied by light and electron microscopy. Embedding in the extracellular matrix showed higher and longer-lasting production rates of all measured products and superior structural preservation as compared to cultures with agitation. Collagen matrix proved to be superior to fibrin. As established by several tests, this difference was neither due to thrombin used to polymerize fibrinogen, nor to differences in the diffusion rates through the two different matrices used. We conclude that extracellular matrix, particularly collagen, influences the synthesis of trophoblastic products. Embedding of the villous explants in three-dimensional gels constitutes a new method for long-term cultures of chorionic villi.

Two different laminin domains mediate the differentiation of human endothelial cells into capillary-like structures in vitro

Endothelial cells, both microvascular as well as large vessel, undergo differentiation slowly in culture under most conditions. When endothelial cells are cultured on Matrigel, a solid gel of basement membrane proteins, they rapidly align and form hollow tube-like structures. We show here that tube formation is a multi-step process induced by laminin. An RGD-containing sequence in the A chain of laminin through an integrin receptor on the endothelial cell induces their attachment to the protein while a YIGSR site in the B1 chain induces cell-cell interactions and the resulting tube formation. We also show that the laminin-derived synthetic peptide YIGSR contains sufficient information to induce single endothelial cells to form ring-like structures surrounding a hollow lumen, the basic putative unit in the formation of capillaries.

The expression of transthyretin mRNA in the developing rat brain

Specific cDNA and oligonucleotide probes were used to study the appearance of transthyretin mRNA in developing rat brain using Northern gel analysis, cytoplasmic dot hybridization, and in situ hybridization. Transthyretin mRNA in embryonic rat brain was found to be confined to the epithelial layer of the choroid plexus primordia appearing first in the fourth ventricle, followed by appearance in the lateral ventricles, and subsequently in the third ventricle. Transthyretin mRNA was localized in these cells from early stages of neuroepithelium differentiation, showing that it is a sensitive marker for the differentiation of the choroid plexus within the fetal brain.

Effects of ageing and long-term subcultivation on collagen lattice contraction and intra-lattice proliferation in three rat cell types

Many cells can contract a hydrated collagen lattice when seeded within one, reorganizing the collagen fibrils into a compact structure by tractional forces exerted during cell movement and translocation. The effects of ageing on this tractional-motility property of cells was examined for three cell types from adult Fischer 344 male rats: skin fibroblasts, aortic smooth muscle cells, and dedifferentiated chondrocytes. All cell types at low population doubling levels (PDL less than 10) contracted collagen lattices, though with different proficiencies (smooth muscle cells greater than dedifferentiated chondrocytes greater than skin fibroblasts). There was no significant difference in contraction ability of cell isolates of the same type obtained from 4-month and 24-30-month animals. Cells that had been subcultivated extensively (PDLs of 50-110) retained contractional ability. The cell types proliferated within lattices to varying extents, and there was no correlation between a cell type's extent of proliferation in a lattice and its proliferation in monolayer culture. That lattice contraction ability is preserved intact with ageing in three cell types suggests that the tractional forces exerted by cells on a collagen matrix in vitro may have a significant role in adult life in vivo.

Effects of retinoic acid on the growth and morphology of hamster tracheal epithelial cells in primary culture

Hamster tracheal epithelial cells were grown in primary culture on a collagen gel substrate in hormone-supplemented serum-free Ham's F12 medium with 10(-8) M retinoic acid (RA+), or without retinoic acid (RA-). On days 1 and 2, the colonies were composed of large (secretory) cells and lesser numbers of small (basal) cells; ciliated cells were rare. At these times, cell number, thymidine incorporation, and total labelling indices (small and large cells, combined) were similar in RA+ and RA- cultures, but the large cells became flat in RA- medium on day 2. On days 3-5, thymidine incorporation and total labelling indices were less in RA- than RA+ cultures, and on days 4-6, cell numbers were decreased in RA- cultures. On day 3, the large cells of the RA- colonies had flattened further and clusters of small basal cells had formed. On day 4, the RA+ colonies were composed of densely-packed cuboidal secretory cells, small basal cells were inconspicuous; the total labelling index was about 27%. The RA- colonies were composed of large flat secretory cells and numerous small basal cells which were clustered in groups; the total labelling index was about 7%. Since large and small cells could be discriminated by size in RA- colonies, a labelling index was generated based on cell size. On days 2, 3 and 4, the labelling index of the small basal cells in the RA- colonies was 44%, 43% and 24% respectively, whereas the labelling index of the large secretory cells fell rapidly over the same period (56%, 14% and 2%). On days 5 and 6, the cuboidal secretory cells in the RA+ cultures had differentiated further and the cells were stratified focally. Some new ciliated cells had formed on day 6. In RA- cultures, mucous granules were not observed in the large flat cells and ciliated cells were not seen. The total labelling indices were 11% and 0.35% in RA+ cultures, and 0.5% and 0.25% in RA- cultures on days 5 and 6, respectively. The study shows that the target cell for vitamin A in the hamster tracheal epithelium is the secretory (mucous) cell. When retinoic acid was deficient, the secretory cells flattened and their capacity to divide was greatly diminished. Since the basal cells continued to replicate when the secretory cells did not, the population density of the basal cells increased disproportionally, which could be interpreted erroneously as a "basal cell hyperplasia".(ABSTRACT TRUNCATED AT 400 WORDS)

Use of extracellular matrix components for cell culture

Extracellular matrix components when used as a substratum in vitro can greatly influence cell behavior. The response observed is dependent on the type of cell and matrix used. Cells in vitro usually respond best to the matrix components with which they are normally in contact in vivo. More differentiated phenotypes are observed and cells generally survive longer on such matrices. In some cases, the presence of such matrices allows cells to be cultured in the absence of serum and growth factors. As more investigators try the matrices and matrix components described, as well as new components and combinations of them, it is anticipated that improvement in the culture of many cells can be expected.