Autocrine activities of basic fibroblast growth factor: regulation of endothelial cell movement, plasminogen activator synthesis, and DNA synthesis

Inhibition of the migration, attachment, spreading, growth and collagen synthesis of human gingival fibroblasts by arecoline, a major areca alkaloid, in vitro

Because betel quid (BQ) chewing has been linked to a higher prevalence of periodontal diseases, the pathobiological effects of arecoline, a main alkaloid found in areca nut, were investigated in cultured human gingival fibroblasts. At concentrations higher than 0.4 mM, arecoline inhibits cell attachment, cell spreading and cell migration in a dose-dependent manner. These inhibitory effects were associated with intracellular depletion of glutathione (GSH). At concentrations of 0.4 mM and 1 mM, arecoline depleted about 26% and 45% of GSH after 2 h incubation. Exposure of cells to arecoline at concentrations lower than 0.4 mM for 2 h showed no significant decrease in either cell viability or intracellular GSH. However, incubation of cells for 24 h in 1 mM are colined decreased the cell numbers to only 35% of those in the untreated control. Arecoline also decreased cell growth and collagen synthesis in a dose-dependent manner. Because of repeated and long-term exposure to arecoline, BQ chewers could be more susceptible to periodontal damage and less responsive to new attachment procedures.

FGF-1-dependent proliferative and migratory responses are impaired in senescent human umbilical vein endothelial cells and correlate with the inability to signal tyrosine phosphorylation of fibroblast growth factor receptor-1 substrates

Senescent cells do not proliferate in response to exogenous growth factors, yet the number and affinity of growth factor receptors on the cell surface appear to be similar to presenescent cell populations. To determine whether a defect in receptor signaling exists, we analyzed human umbilical vein endothelial cells (HUVEC) since HUVEC growth is absolutely dependent upon the presence of FGF. We report that in both presenescent and senescent HUVEC populations, FGF-1 induces the expression of cell cycle-specific genes, suggesting that functional FGF receptor (FGFR) may exist on the surface of these cells. However, the tyrosine phosphorylation of FGFR-1 substrates, Src and cortactin, is impaired in senescent HUVEC, and only the presenescent cell populations exhibit a FGF-1-dependent Src tyrosine kinase activity. Moreover, we demonstrate that senescent HUVEC are unable to migrate in response to FGF-1, and these data correlate with an altered organization of focal adhesion sites. These data suggest that the induction of gene expression is insufficient to promote a proliferative or migratory phenotype in senescent HUVEC and that the attenuation of the FGFR-1 signal transduction pathway may be involved in the inability of senescent HUVEC to proliferate and/or migrate.

Isolation and characterization of microvascular endothelial cells from chicken fat pads

Microvascular endothelial cells from abdominal fat pads of 6-wk-old broiler chickens were isolated to provide an in vitro system to study their physiological functions. The isolation procedure produced clumps of 10-30 cells, which attached to culture vessels in 4 h and attained confluency in 2 wk. At confluency, cells had a cobblestone appearance but were not contact inhibited and detached from the bottom of the culture vessel 2 wk after reaching confluency. The cells internalized acetylated low density lipoproteins, a characteristic of endothelial cells. This property was used to obtain pure endothelial cell cultures using the cell sorter. When cultured over Matrigel, a reconstituted matrix, the cells aligned themselves into chordlike structures and formed branching microvessels. Cells plated on type I collagen-coated culture flasks occasionally formed chordlike structures and proliferated at a faster rate than cells plated on Matrigel. Cells cultured on laminin-coated plates were slender and had long cytoplasmic extensions; however, cells cultured on uncoated plastic had fibroblastic morphology. These properties are similar to those described for microvessel endothelial cells isolated from tissues of other species.

Protein kinase C mediates up-regulation of urokinase and its receptor in the migrating keratinocytes of wounded cultures, but urokinase is not required for movement across a substratum in vitro

Both in cell culture and in vivo, keratinocytes that are migrating in response to a wound express enhanced levels of both urokinase-type plasminogen activator (uPA) and the uPA cell surface receptor (uPA-R). To explore the mechanism of this up-regulation, keratinocyte cultures were treated proir to wounding with a variety of metabolic and growth factor inhibitors in order to evaluate their effect on uPA and uPA-R expression. Actinomycin D and cycloheximide inhibited the up-regulation of both uPA and uPA-R, as determined by immunohistochemistry, indicating that RNA and protein syntheses are required for their induction in migrating keratinocytes. Neither removal of protein growth factors from the medium nor addition of inhibitory antibodies to a number of growth factors depressed uPA or uPA-R induction; these findings suggest that a variety of exogenous or endogenous growth factors [i.e., basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), amphiregulin, and tumor necrosis factor-alpha (TNF-alpha) do not have a critical role in the induction of uPA or uPA-R. In contrast, when protein kinase C (PKC) was either down-regulated with bryostatin 5 or inhibited with Ro31-8220 or staurosporine, the expression of both uPA and uPA-R was greatly decreased in migrating keratinocytes. Furthermore, pharmacologic activation of PKC enhanced uPA levels in non-wounded cultures. These data suggest that the enhanced expression of uPA and uPA-R in migrating keratinocytes is mediated by selective activation of PKC in these cells, perhaps secondary to alterations in the cytoskeleton induced by wounding. To test the requirement for uPA during keratinocyte migration in vitro, the extent of migration was quantified in the presence and absence of a variety of inhibitors in the wounded culture model. Migration was not altered by actinomycin D, cycloheximide, any of the above growth factor inhibitors, anti-uPA antibodies, a variety of inhibitors of uPA or plasmin enzymatic activity, or exogenous uPA. The independence of keratinocyte migration in vitro from uPA was further suggested by experiments which combined the phagokinetic assay of migration and the zymographic assay for pericellular uPA activity; no relationship was observed between pericellular uPA activity and the motility of individual cells.

Mitogenesis, cell migration, and loss of focal adhesions induced by tenascin-C interacting with its cell surface receptor, annexin II

In a previous study we demonstrated that the alternatively spliced region of tenascin-C, TNfnA-D, bound with high affinity to a cell surface receptor, annexin II. In the present study we demonstrate three changes in cellular activity that are produced by adding intact tenascin-C or TNfnA-D to cells, and we show that all three activities are blocked by antibodies against annexin II. 1) TNfnA-D added to confluent endothelial cells induced loss of focal adhesions. 2) TNfnA-D produced a mitogenic response of confluent, growth-arrested endothelial cells in 1% serum. TNfnA-D stimulated mitogenesis only when it was added to cells before or during exposure to other mitogens, such as basic fibroblast growth factor or serum. Thus the effect of TNfnA-D seems to be to facilitate the subsequent response to growth factors. 3) TNfnA-D enhanced cell migration in a cell culture wound assay. Antibodies to annexin II blocked all three cellular responses to TNfnA-D. These data show that annexin II receptors on endothelial cells mediate several cell regulatory functions attributed to tenascin-C, potentially through modulation of intracellular signalling pathways.

Potential role of bFGF and retinoic acid in the regeneration of chicken cochlear hair cells

Messenger RNAs (mRNA) of several growth factor receptors and relate genes were examined with reverse transcriptase polymerase chain reaction (RT-PCR) in normal and noise-damaged chicken basilar papillae (BP). Analysis of the amplification products indicated the presence of mRNAs for epidermal growth factor receptor (EGFR), fibroblast factor receptor (FGFR), insulin-like growth factor receptor (IGFR), insulin receptor (IR), retinoic acid receptor beta (RAR beta), retinoic acid receptor gamma (RXR gamma), and basic fibroblast growth factor (BFGF) in both normal and noise-damaged BP. The RT-PCR products generated were characterized by size and sequencing analysis to confirm the identities of the target molecules. The subcellular localization of the mature protein analogs for EGFR, FGFR, IGFR, RAR beta, and BFGF were identified using fluorescence immunocytochemistry and confocal laser scanning microscopy. These experiments indicated that EGFR is present in the stereociliary bundles in the hair cells, IGFR is not present in the cells of the BP, BFGF localizes in the nuclei of supporting cells in the BP, but not hair cells or hyaline cells, and that RAR beta localizes in the perinuclear regions of hair cells. The subcellular distributions of these proteins were consistent in both noise-damaged and control BP. FGFR, in contrast, changed its distribution in the tissue after noise damage. In normal BP, FGFR is concentrated in the stereocilia of hair cells. However, in damaged regions of noise-exposed chick cochleae, FGFR is heavily expressed in the expanded apical regions of the supporting cells. These findings suggest that BFGF and retinoic acid may potentially play a role in the mechanisms which regulate the regeneration of chicken cochlear hair cells.

Regulation of lysyl oxidase by basic fibroblast growth factor in osteoblastic MC3T3-E1 cells

Lysyl oxidase catalyzes the final known enzymatic step required for collagen and elastin cross-linking. A cross-linked collagenous extracellular matrix is required for bone formation. This study investigated whether lysyl oxidase, like its type I collagen substrate, is down-regulated by basic fibroblast growth factor (bFGF) in osteoblastic MC3T3-E1 cells and determined the degree of post-transcriptional control. Steady-state lysyl oxidase mRNA levels decreased to 30% of control after 24 h of treatment with 1 and 10 nm bFGF. This regulation was time-dependent. COL1A1 mRNA levels declined to less than 10% of control after 24 h of bFGF treatment. Media lysyl oxidase activity decreased consistent with steady-state mRNA changes in cultures that were refed after 24 h of growth factor treatment. Interestingly, treatment of MC3T3-E1 cells with 0.01-0.1 nm bFGF for 24 h and treatment with 1 nm bFGF for up to 12 h resulted in a modest stimulation of lysyl oxidase gene expression and enzyme activity. At least 50% of the down-regulation of lysyl oxidase was shown to be posttranscriptional. New protein synthesis was not required for the down-regulation by bFGF, but cycloheximide did increase constitutive lysyl oxidase mRNA levels 2.5-fold. We conclude that lysyl oxidase and COL1A1 are regulated similarly by bFGF in these osteoblastic cells, consistent with the in vivo effects of this growth factor on bone collagen metabolism.

The roles of integrins and extracellular matrix proteins in the insulin-like growth factor I-stimulated chemotaxis of human breast cancer cells

The effects of insulin-like growth factor I (IGF-I) on the migration of two human breast cancer cell lines, MCF-7 and MDA-231, were examined using a modified Boyden chamber. 10 ng/ml was the optimal IGF-I concentration for stimulation of migration. The majority of IGF-I-stimulated migration in both cell types was due to chemotaxis. MCF-7 cells failed to migrate on membranes coated with gelatin or fibronectin and migrated only in small numbers on laminin. In contrast, when vitronectin- or type IV collagen-coated membranes were used, the MCF-7 cells migrated in large numbers specifically in response to IGF-I but not to 10% fetal calf serum, epidermal growth factor, fibroblast growth factor, or platelet derived growth factor-BB. An IGF-I receptor-blocking antibody inhibited IGF-I-stimulated migration in both cell types. In addition, a blocking antibody to the alpha v beta 5 integrin (a vitronectin receptor) inhibited migration of MCF-7 cells in response to IGF-I through vitronectin but not through type IV collagen. Similarly, blocking antibodies specific for alpha 2 and beta 1 integrins significantly inhibited migration of both cell types through type IV collagen-coated membranes but not through vitronectin-coated membranes. We conclude that: 1) IGF-I stimulates migration of these two cell types through the IGF-I receptor; 2) interaction of vitronectin with the alpha v beta 5 integrin or collagen with the alpha 2 beta 1 integrin is necessary for the complete IGF-I response in MCF-7 cells, and 3) because migration represents an in vitro model for metastatic spread, integrins, extracellular matrix proteins, and IGF-I may play coordinated roles in the metastasis of breast cancer in vivo.

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

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

Heparin-binding epidermal growth factor-like growth factor: p91 activation induction of plasminogen activator/inhibitor, and tubular morphogenesis in human microvascular endothelial cells

Epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) stimulates cell migration, proliferation and the formation of tube-like structures of human microvascular endothelial cells in culture. Heparin-binding EGF-like growth factor(HB-EGF), which shows 35% homology with EGF/TGF-alpha, is a member of the EGF family, and it is ubiquitous in many tissues and organs. We examined whether or not HB-EGF induced angiogenic responses in human microvascular endothelial cells. HB-EGF inhibited the binding of (125) I-EGF to the EGF receptor and induced autophosphorylation of the receptor on endothelial cells. Exogenous HB-EGF induced the loss of more than 70% of the EGF receptor from the cell surface within 30 min, with similar kinetics to that of EGF. The level of c-fos mRNA markedly increased at 30 min in response to HB-EGF as well as EGF. A gel shift assay demonstrated the activation of the transcription factor p91 by HB-EGF and EGF. This factor directly interacts with EGF receptor and mediates the activation of c-fos gene promoter. HB-EGF enhanced the mRNA expression of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) mRNA. However, the enhancement of t-PA and PAI-1 by HB-EGF was less than that by EGF. Heparitinase/chlorate, which digests the heparan sulfate proteoglycan of the endothelial cell surface, restored both t-PA and PAI-1 mRNA levels in response to HB-EGF in a manner similar to that by EGF. HB-EGF at 10 ng/ml developed tube-like structures in type I collagen gel at similar levels to that of EGF at 10 ng/ml, suggesting that HB-EGF is also a potent angiogenic factor in the model system for angiogenesis. The tubulogenesis activity of HB-EGF is discussed in relation to the expression of the t-PA and PAI-1 genes.

Basic fibroblast growth factor controls the expression and molecular structure of heparan sulfate in corneal endothelial cells

Cultured bovine corneal endothelial cells express 5-8 ng basic fibroblast growth factor (bFGF)/mg cell protein and distribute it between the intracellular and pericellular compartment. Confluent cultures retain approximately 80% of the total bFGF intracellularly, whereas 20% is present in the pericellular (trypsin-releasable) compartment. No bFGF can be detected in the culture medium. The presence of 1-2 ng/ml medium of endogenous or exogenous (human recombinant) bFGF is sufficient to support cell growth. Simultaneously, cells incorporate [35S]sulfate and [3H]glucosamine into the sulfated proteoglycans associated with the cell layer at a rate that is three times higher than in the absence of bFGF. The enhanced proteoglycan synthesis is accompanied by a shift in proteoglycan distribution. In control cells, cell-associated heparan sulfate accounts for about 30% of the total glycosaminoglycans, whereas under the influence of bFGF the amount of heparan sulfate increases to approximately 60%. At the same time, the molecular structure of the heparan sulfate molecule undergoes bFGF-specific changes as indicated by the [35S]oligosaccharide pattern generated by heparitinase I degradation. The proportion of [35S]oligosaccharides with greater than six monosaccharides decreases on account of disaccharides and tetrasaccharides under the influence of bFGF. Pretreatment of bFGF with neutralizing antibodies against bFGF abolishes its biological activity. The results suggest a bFGF-dependent change in the rate of synthesis and structural features of the membrane-associated heparan sulfate in corneal endothelial cells. The modification of the heparan sulfate structure could influence its bFGF-binding and antiproliferative activity.

Control of endothelial cell gene expression by flow

The vessel wall is constantly subjected to, and affected by, the stresses resulting from the hemodynamic stimuli of transmural pressure and flow. At the interface between blood and the vessel wall, the endothelial cell plays a crucial role in controlling vessel structure and function in response to changes in hemodynamic conditions. Using bovine aortic endothelium monolayers, we show that fluid shear stress causes simultaneous differential regulation of endothelial-derived products. We also report that the downregulation of endothelin-1 mRNA by flow is a reversible process, and through the use of uncharged dextran supplementation demonstrate it to be shear stress- rather than shear rate-dependent. Recent work on the effect of fluid shear stress on endothelial cell gene expression of a number of potent endothelial products is reviewed, including vasoactive substances, autocrine and paracrine growth factors, thrombosis/fibrinolysis modulators, chemotactic factors, surface receptors and immediate-early genes. The encountered patterns of gene expression responses are classified into three categories: a transient increase with return to baseline (type I), a sustained increase (type II) and a biphasic response consisting of an early transient increase of varying extent followed by a pronounced and sustained decrease (type III). The importance of the dynamic character of the flow stimulus and the magnitude dependence of the response are presented. Potential molecular mechanisms of shear-induced gene regulation, including putative shear stress response elements (SSRE), are discussed. These results suggest exquisite modulation of endothelial cell phenotype by local fluid shear stress and may offer insight into the mechanism of flow-dependent vascular remodeling and the observed propensity of atherosclerosis formation around bifurcations and areas of low shear stress.

Possible participation of autocrine and paracrine vascular endothelial growth factors in hypoxia-induced proliferation of endothelial cells and pericytes

Hypoxia is the principal factor that causes angiogenesis. These experiments were conducted to explore how it induces the proliferation of vascular cells, a key step in angiogenesis. Human umbilical vein endothelial cells and bovine retinal pericytes were grown in controlled atmosphere culture chambers containing various concentrations of oxygen. The numbers of both endothelial cells and pericytes increased significantly under hypoxic conditions; the O2 concentrations that achieved maximal growth promotion were 10% for endothelial cells and 2.5% for pericytes. Quantitative reverse transcription-polymerase chain reaction analysis revealed that mRNAs coding for the secretory forms of vascular endothelial growth factor (VEGF), a mitogen specific to endothelial cells, were present in both endothelial cells and pericytes and that their levels increased significantly in the two cell types as the atmospheric O2 concentration decreased. The two genes for VEGF receptors, kinase insert domain-containing receptor (kdr) and fms-like tyrosine kinase 1 (flt1), were found to be constitutively expressed in endothelial cells, and their relative mRNA levels were ranked in that order. On the other hand, only flt1 mRNA was detected in pericytes under hypoxic conditions. Furthermore, most antisense oligodeoxyribonucleotides complementary to VEGF mRNAs efficiently inhibited DNA synthesis in endothelial cells cultured under hypoxic conditions. These results indicate that autocrine and paracrine VEGFs may take part in the hypoxia-induced proliferation of endothelial cells.

Angiogenesis

The formation of new blood vessels, angiogenesis, is a complex process which is central to normal development and homeostasis. However, uncontrolled angiogenesis plays a critical role in both inflammatory and neoplastic disorders. Our understanding of angiogenesis has expanded greatly over the past two decades due to the development of in vivo and in vitro models to study this important process. A variety of cytokines and growth factors have been shown to induce new blood vessel formation in vivo, and in vitro studies have been able to define whether agents have direct or indirect effects upon vascular endothelial cells. Our improved understanding of the mechanisms which regulate angiogenesis has now created important opportunities for the development of new therapies for the treatment of inflammatory and neoplastic skin disease.

Detection of candidates for cancer cell motility inhibitory protein in the Dunning adenocarcinoma model

The more differentiated components of a primary tumor may produce substances that reduce the growth rate and metastatic potential of more aggressive components. In the Dunning R-3327 prostatic adenocarcinoma model, cancer cell motility is required for metastatic potential. Medium conditioned by the non-motile, non-metastatic G subline contains proteins of molecular weight 50-100 kDa that inhibited the motility of the highly motile, highly metastatic MAT-LyLu subline. G subline-conditioned medium was separated by DEAE-cellulose chromatography using a linear gradient of 0-0.5 M NaCl in 100 mM Tris at pH 8.3. The motility inhibitory activity of G-conditioned medium was localized to column fractions 51-70 that contained 18% of the applied protein and only 6.5% of the proteins secreted by the G cells. Analysis of pooled fractions 51-60 and 61-70 by two-dimensional gel electrophoresis identified five protein families, with a total of 12 charged proteins of molecular weights approximating 66, 54, 50, 41 and 34 kDa, that were not present or present in reduced quantities in column fractions that did not inhibit motility. Isolation and identification of motility inhibitory protein may prove it the first substance discovered that is produced by a more differentiated component of a neoplasm that directly inhibits a metastasis-associated property.

Intervention in diabetic vascular disease by modulation of growth factors

Several growth factors have been implicated in the derangements of cellular metabolism and proliferation that occur in diabetes, eg. kidney mesangial expansion, retinal neovascular formation, and acceleration of atherosclerosis in large vessels. These phenomena contribute to the development and progression of diabetic microvascular and macrovascular disease. Pharmacological interventions aimed at reducing growth factor alterations, among other actions in diabetic vasculopathy, include a multitude of classes of drugs, such as angiotensin-converting enzyme (ACE) inhibitors, calcium antagonists, lipid-lowering drugs, and somatostatin analogs. New potential interventions, ie, antisense oligonucleotide local delivery, are being applied in growth factor research and may prove beneficial in diabetic macrovascular disease.

A cellular automaton model for the proliferation of migrating contact-inhibited cells

A cellular automaton is used to develop a model describing the proliferation dynamics of populations of migrating, contact-inhibited cells. Simulations are carried out on two-dimensional networks of computational sites that are finite-state automata. The discrete model incorporates all the essential features of the cell locomotion and division processes, including the complicated dynamic phenomena occurring when cells collide. In addition, model parameters can be evaluated by using data from long-term tracking and analysis of cell locomotion. Simulation results are analyzed to determine how the competing processes of contact inhibition and cell migration affect the proliferation rates. The relation between cell density and contact inhibition is probed by following the temporal evolution of the population-average speed of locomotion. Our results show that the seeding cell density, the population-average speed of locomotion, and the spatial distribution of the seed cells are crucial parameters in determining the temporal evolution of cell proliferation rates. The model successfully predicts the effect of cell motility on the growth of isolated megacolonies of keratinocytes, and simulation results agree very well with experimental data. Model predictions also agree well with experimentally measured proliferation rates of bovine pulmonary artery endothelial cells (BPAE) cultured in the presence of a growth factor (bFGF) that up-regulates cell motility.

Intracellular signaling pathways required for rat vascular smooth muscle cell migration. Interactions between basic fibroblast growth factor and platelet-derived growth factor

Intracellular signaling pathways activated by both PDGF and basic fibroblast growth factor (bFGF) have been implicated in the migration of vascular smooth muscle cells (VSMC), a key step in the pathogenesis of many vascular diseases. We demonstrate here that, while bFGF is a weak chemoattractant for VSMCs, it is required for the PDGF-directed migration of VSMCs and the activation of calcium/calmodulin-dependent protein kinase II (CamKinase II), an intracellular event that we have previously shown to be important in the regulation of VSMC migration. Neutralizing antibodies to bFGF caused a dramatic reduction in the size of the intracellular calcium transient normally seen after PDGF stimulation and inhibited both PDGF-directed VSMC migration and CamKinase II activation. Partially restoring the calcium transient with ionomycin restored migration and CamKinase II activation as did the forced expression of a mutant CamKinase II that had been "locked" in the active state by site-directed mutagenesis. These results suggest that bFGF links PDGF receptor stimulation to changes in intracellular calcium and CamKinase II activation, reinforcing the central role played by CamKinase II in regulating VSMC migration.

Inhibition by cardiac natriuretic peptides of rat vascular endothelial cell migration

Vascular endothelial cell migration is proposed to be an important process in the initiation and progression of atherosclerosis. We designed the present study to examine the effects of atrial and brain natriuretic peptides on fetal calf serum-stimulated migration of cultured rat aortic endothelial cells using Boyden's chamber method. Fetal calf serum clearly stimulated migration in a concentration- and time-dependent manner. Rat atrial natriuretic peptide-(1-28) and rat brain natriuretic peptide-45, which are the major circulating forms of atrial and brain natriuretic peptides in rats, inhibited fetal calf serum-stimulated migration in a concentration-dependent manner between 10(-10) and 10(-6) mol/L. Such inhibition by these natriuretic peptides was paralleled by an increase in the cellular level of cGMP. The addition of a cGMP analogue 8-bromo-cGMP, significantly inhibited fetal calf serum-stimulated migration in a concentration-dependent manner between 10(-7) and 10(-3) mol/L. Rat atrial natriuretic peptide-(5-25) was much less effective than atrial natriuretic peptide-(1-28) or rat brain natriuretic peptide-45 with respect to inhibiting migration and increasing cGMP levels. These results indicate that atrial and brain natriuretic peptides inhibit fetal calf serum-stimulated vascular endothelial cell migration, probably through a cGMP-dependent 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.

Modulation of cell migration and vessel formation by vascular endothelial growth factor and basic fibroblast growth factor in cultured embryonic heart

Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) stimulate endothelial cell proliferation, migration, and vascular tube formation. We tested the hypotheses that these growth factors stimulate (1) cell migration and (2) assembly into cord-like structures in embryonic rat heart explants cultured on collagen gels. Atrial and ventricular explants from rat embryos at 12 (E12, avascular) and 14 (E14, early vascularization stage) days of gestation were cultured on a collagen substrate. Western blot analysis of the explants indicated that endogenous VEGF was present in both atria and ventricles during incubation. Addition of bFGF to E12 explants markedly increased cell migration, whereas VEGF had no significant effect. In E14 explants neither growth factor influenced cell migration. Cotreatment with VEGF and bFGF did not have a synergistic effect on the migration distance of cells from either E12 or E14 embryonic hearts. However, VEGF stimulated the appearance of cord-like structures in E14, but not E12, explants. Transmission electron microscopy analysis showed that these cord-like structures consist of elongated cells, some of which aggregate into clusters, or form tube-like structures, similar to capillaries. Serial sections of monolayers revealed that tube formation occurs beneath the surface of collagen gel. We conclude that in this model system VEGF and bFGF play distinct roles, at specific time points, in coronary vascular tube formation in the developing heart.

Vasculotropin/vascular endothelial growth factor is an autocrine growth factor for human retinal pigment epithelial cells cultured in vitro

Vasculotropin (VAS), also called vascular endothelial growth factor (VEGF) or vascular permeability factor, is a secreted growth factor whose target cell specificity has been reported as restricted to vascular endothelium. Its effects are mediated by at least two distinct membrane-spanning tyrosine kinase receptors, KDR and flt-1; the expression of which also seems restricted to vascular endothelium. We describe here that cultured human retinal pigment epithelial (HRPE) cells express both KDR and flt-1 receptors, bind VAS/VEGF on two high affinity sites (apparent Kd of 9 and 210 pM corresponding to 940 and 18,800 sites per cell) and proliferate or migrate upon recombinant VAS/VEGF addition. HRPE cells also express the mRNA corresponding to the 121 and 165 amino acid forms of VAS/VEGF. HRPE cells release in their own culture medium and store in their extracellular matrix self-mitogenic and chemoattractant factors indistinguishable from 121 and 165 VAS/VEGF isoforms. The autocrine role of VAS/VEGF was confirmed by the inhibition of these bioactivities by neutralizing specific anti-VAS/VEGF antibodies.

Reduced contact-inhibition and substratum adhesion in epithelial cells expressing GlcNAc-transferase V

Malignant transformation of fibroblast and epithelial cells is accompanied by increased beta 1-6 N-acetylglucosaminyltransferase V (GlcNAc-TV) activity, a Golgi N-linked oligosaccharide processing enzyme. Herein, we report that expression of GlcNAc-TV in Mv1Lu cells, an immortalized lung epithelial cell line results in loss of contact-inhibition of cell growth, an effect that was blocked by swainsonine, an inhibitor of Golgi processing enzyme alpha-mannosidase II. In serum-deprived and high density monolayer cultures, the GlcNAc-TV transfectants formed foci, maintained microfilaments characteristic of proliferating cells, and also experienced accelerated cell death by apoptosis. Injection of the GlcNAc-TV transfectants into nude mice produced a 50% incidence of benign tumors, and progressively growing tumors in 2:12 mice with a latency of 6 mo, while no growth was observed in mice injected with control cells. In short term adhesion assays, the GlcNAc-TV expressing cells were less adhesive on surfaces coated with fibronectin and collagen type IV, but no changes were observed in levels of cell surface alpha 5 beta 1 or alpha v beta 3 integrins. The larger apparent molecular weights of the LAMP-2 glycoprotein and integrin glycoproteins alpha 5, alpha v and beta 1 in the transfected cells indicates that their oligosaccharide chains are substrates for GlcNAc-TV. The results suggest that beta 1-6GlcNAc branching of N-linked oligosaccharides contributes directly to relaxed growth controls and reduce substratum adhesion in premalignant epithelial cells.

Characterization of endothelial cell locomotion using a Markov chain model

A Markov chain model was developed to characterize the two-dimensional locomotion of bovine pulmonary artery endothelial (BPAE) cells cultured with or without basic fibroblast growth factor (bFGF). This model provides a detailed description of the migration process by computing the following locomotory parameters: (i) the speed of cell locomotion; (ii) the expected duration of cell movement in any given direction; (iii) the probability distribution of turn angles that will decide the next direction of cell movement; (iv) the frequency of cell stops; and (v) the duration of cell stops. Eight directional states and a stationary state were used in our Markov analysis. From cell trajectory data, the transition probabilities among the various states and the waiting times for the directional and the stationary states were computed. The steady-state probabilities were also calculated to obtain the ultimate direction of cell motion and, thus, determine whether cell motion was random. Our results showed how the addition of bFGF enhanced the locomotory capability of BPAE cells. Cells cultured with 30 ng/mL bFGF had lower probability of moving to the stationary state than those cultured without bFGF. In addition, cells cultured with 30 ng/mL bFGF remained in the stationary state for shorter periods of time than cells cultured without bFGF. In both these cases, however, the transition probabilities from the stationary state to any directional state were uniformly distributed and were not affected by the presence of bFGF.

Significance of angiogenesis in tumour progression and metastasis

Angiogenesis is defined as a vascular neoformation usually of capillary origin. This phenomenon is important during development and under several physiological and or pathological conditions. In recent years, progress has been made to understand this phenomenon at the molecular level. This includes the identification of potent angiogenic factors, the appreciation of the role of proteases, the importance of the extracellular matrix, and the emerging characterisation of signal transduction pathways in endothelial cells. Two important participants in angiogenesis are molecules from the fibroblast growth factor (FGF) and the transforming growth factor-beta (TGF-beta) family. In our laboratory, we have extensively studied the roles and mechanisms of action of the major FGF prototype, FGF-2 and of the TGF-beta member, TGF-beta 1. Different isoforms of FGF-2 have been previously described, a high molecular weight (HMW) form associated with the nucleus and 18 kDa bFGF that is cytoplasmic. These two forms of FGF-2 also exhibit different functions when expressed endogenously. TGF-beta is formed from a latent complex by plasmin-dependent and plasmin-independent pathways. With the exception of macrophages, the plasmin-dependent pathway requires coculture conditions, urokinase, and the concentration of TGF-beta on the cell surface by the mannose-6-phosphate receptor and transglutaminase. Other important angiogenic modulators include vascular endothelial growth factor (VEGF) and angiostatin. The nature of the tumour angiogenesis factor is not yet known with certainty, but several identified and not yet identified angiogenic factors may act in concert. It is hoped that an angiostatic treatment for cancer will be derived from these molecular studies.

Regulation of basic fibroblast growth factor (bFGF) gene and protein expression following its release from sublethally injured endothelial cells

Basic fibroblast growth factor (bFGF; FGF-2) lacks a signal sequence and thus is not secreted by classical pathways. It has been speculated that one mode of bFGF release may be injury, either sublethal or lethal; and, transient disruption of the plasma membrane has been shown to release bFGF [Muthukrihnan et al. (1991): J Cell Physiol 148:1-16]. This observation has led to the concept of bFGF as a "wound hormone," involved in tissue integrity and repair. Findings of elevated bFGF following injury in vivo support this concept. Using an in vitro model, we have examined the regulation of bFGF gene expression following its release by sublethal injury. Analysis of bFGF protein by ELISA revealed that scraping subconfluent bovine aortic EC (BAE) released up to 80% of their bFGF. Following scraping, there was a 4- to 10-fold increase in the steady state level of bFGF mRNA, which reached a maximum at 2-3 h. There was a parallel increase in protein so that by 6 h after the scrape-induced release, bFGF levels were restored to those measured prior to scraping. Since bFGF has been reported to induce its own expression, we hypothesized that the released bFGF might be responsible for the increase in bFGF mRNA. However, inclusion of neutralizing antibodies against bFGF had a negligible effect on the scrape-induced increase in bFGF mRNA levels. Because of the important role of transforming growth factor type-beta 1 (TGF-beta 1), the plasminogen/plasminogen activator system, and thrombin in wound healing, we investigated their potential contributions to the increase in bFGF expression. Addition of anti-TGF-beta 1 antibodies, plasminogen activator inhibitor-1 (PAI-1), or the thrombin inhibitory combination of heparin and anti-thrombin III (AT III) to the cells at the time of scraping blocked about 50% of the increase in bFGF mRNA; the effects of these agents were not additive. The suppression of bFGF mRNA was associated with a proportional reduction in bFGF protein. Inclusion of the antagonists for 2 h at the time of scraping led to reduced cell proliferation, suggesting that cell-associated bFGF may be required for recovery and growth. Finally, studies to characterize the molecular mechanisms underlying the increased bFGF mRNA following sublethal injury revealed an increase in the transcriptional activation of bFGF gene. These results indicate that in spite of the fact that bFGF is not a secreted protein, levels of bFGF in the cell are tightly regulated. Furthermore, these findings suggest a role for bFGF in recovery from cell injury.

Insulin does not disrupt actin microfilaments, microtubules, and in vitro aortic endothelial wound repair

In the face of small denuding injuries, the endothelium undergoes a process of rapid repair involving actin microfilaments, microtubules, and centrosomes to reestablish an intact monolayer. Failure to maintain an intact endothelial monolayer is an important factor in the pathogenesis of the atherosclerotic plaque. It was hypothesized that increased susceptibility to atherosclerosis in diabetes mellitus may be, in part, due to delayed reendothelialization following endothelial injury. To test this, the effects of high insulin concentrations on the reendothelialization of small wounds were examined using an in vitro porcine aortic endothelial cell wound model. Elevated concentrations of insulin did not disrupt the confluent endothelial monolayer or alter endothelial cell shape. Insulin also did not induce detectable alterations in the distribution of microtubules and microfilaments in the confluent monolayer. High insulin did not reduce the extent of reendothelialization of a linear wound made in the confluent monolayer. Centrosomal reorientation was similar to that of control wounded cultures as was the reorganization of the microfilaments and microtubules. The data suggest that the atherogenic effects of hyperinsulinemia are not due to disruption of endothelial repair.

Modulation of coronary collateral angiogenesis: a canine model of neovascularization induced by chronic ischemia

Coronary collateral development in response to chronic myocardial ischemia is modulated by the integrated release of a variety of growth factors. Protamine, a specific inhibitor of angiogenesis in vitro and in vivo, may attenuate coronary collateral development. The purpose of this investigation was to characterize a model of canine coronary collateral development and to ascertain the effects of protamine on collateral perfusion in response to chronic myocardial ischemia. Ischemia-induced coronary collateral enhancement in response to daily, repetitive, 2-minute left anterior descending (LAD) coronary artery occlusions over 22 consecutive days was demonstrated in control (saline treated) dogs by time dependent, significant (p < 0.05) increases in collateral blood flow to ischemic myocardium. Concomitant with increases in collateral perfusion, myocardial contractile function during LAD occlusion was progressively normalized, and percent coronary flow repayment was reduced successively. These indicators of collateral development were attenuated significantly by administration of subcutaneous protamine. The present findings demonstrate that a model of brief, repetitive, coronary artery occlusion in chronically instrumented dogs sensitively elicits extensive enhancement of the coronary collateral circulation in response to chronic myocardial ischemia. In contrast, protamine attenuates coronary collateral development through its actions as an inhibitor of angiogenesis.

Effects of fibrin on the angiogenesis in vitro of bovine endothelial cells in collagen gel

The effect of fibrin on angiogenesis in vitro was investigated using an experimental model of tube formation by bovine capillary endothelial cells (BCEs) in type I collagen gel. One milligram per milliliter of fibrin added into type I collagen gel significantly increased the length of the tubular structures formed by BCEs in the gel by about 180% compared with type I collagen only. The facilitating effect of fibrin on tube formation by BCEs was inhibited by either anti-basic fibroblast growth factor (bFGF) IgG (25 micrograms/ml) or anti-urokinase type plasminogen activator (uPA) IgG (10 micrograms/ml) added to the gel and culture medium, but not by anti-tissue type plasminogen activator (uPA) IgG (10 micrograms/ml) added to the gel and culture medium, but not by anti-tissue type plasminogen activator (10 micrograms/ml) or non-immune IgG. The Arg-Gly-Asp (RGD) containing peptides (100 micrograms/ml) added to the culture medium also suppressed tube formation by BCEs in fibrin-containing type I collagen gel, but not in type I collagen gel. These results suggest that the increased release of bFGF and uPA by BCEs therefore plays a role in the angiogenic effect of fibrin in vitro, and the angiogenic effect of fibrin is mediated by the RGD sequence in fibrin, probably via the function of integrin receptor of the BCEs.

The urokinase/urokinase-receptor system and cancer invasion

u-PA binds with high affinity to its specific GPI-anchored receptor on the cell surface. The binding has at least two important consequences: (1) it enhances the rate of plasminogen activation on the cell surface; and (2) it focuses the u-PA proteolytic activity at the leading front of migrating cells. Several recent findings suggest that surface-bound u-PA is essential for the invasive ability of tumour cells, even if a picture is emerging indicating a concerted action with other proteases, like collagenases and cathepsin B (Kobayashi et al, 1992; Ossowski, 1992; Schmitt et al, 1992; (Danø et al, 1994). In some tumours, e.g. colon, breast and skin cancer, in situ hybridization studies have given an insight into the u-PA/u-PAR tumour biology showing a complex interplay between stromal and cancer cells Danø et al, 1994). u-PA, u-PAR, and PAI-1 tumour content are now well established prognostic factor in breast cancer. This body of knowledge could be used for theurapeutic purposes. For example, a large study with 671 patients has allowed the identification of node-negative patients which, according to their u-PA levels, would need adjuvant therapy (Foekens et al, 1992). Many other tumours, especially colorectal cancer, expect a direct clinical evaluation of u-PA, u-PAR and serpins as prognostic factors.

Basic fibroblast growth factor is a signal for the initiation of centrosome redistribution to the front of migrating endothelial cells at the edge of an in vitro wound

Rapid, efficient repair of the endothelium following focal endothelial wounding and denudation is regulated by a complex series of cellular processes. Directed cell migration, an early essential event in repair, is thought to be initiated by centrosome redistribution toward the front of the cell prior to the onset of migration. As such, centrosomal polarity may be an important regulatory event in directed endothelial cell migration. Little is known about the regulation of this process. To study this further, in vitro wounds were created down the middle of confluent porcine aortic endothelial monolayers by mechanical denudation. Conditioned media collected 1 hour after wounding contained basic fibroblast growth factor (bFGF). Antibodies directed against bFGF added to the cultures at the time of wounding significantly inhibited cell migration and transiently inhibited centrosome redistribution. When transcription was transiently inhibited with actinomycin D, present at 1 hour before and for 1 hour after wounding, the cells moved more slowly (5.2 +/- 2.8 versus 22.7 +/- 5.7 microns/h for control), taking five times longer for the wound to close. Throughout this period, centrosomes did not reorient to the front of the cells. When either recombinant bFGF or conditioned medium collected from control cultures at 1 hour after wounding was added 23 hours after actinomycin D was washed out (at which time RNA synthesis returned to control levels), the centrosomes redistributed to the front of the cells, and cells migrated at a rapid rate (17.2 +/- 4.2 microns/h), similar to control. However, the recombinant bFGF or conditioned media had no effect when added immediately after actinomycin D was removed, ie, when RNA synthesis was still inhibited.(ABSTRACT TRUNCATED AT 250 WORDS)

Cells transfected with the basic fibroblast growth factor gene fused to a signal sequence are invasive in vitro and in situ in the brain

Invasiveness is a critical event in the development of malignancy in brain tumors. A potential molecular mediator is basic fibroblast growth factor (bFGF). NIH-3T3 cells transfected with the bFGF gene fused with a signal peptide sequence (signal peptide bFGF) acquire an invasive phenotype as measured by in vitro assays of invasion including: 1) the formation of branching networks on Matrigel; 2) invasiveness in a chemoinvasion assay; 3) migration in a cell spreading assay; 4) detection of an Mr 92,000 gelatinase; and 5) local invasion into the surrounding neuropil after injection in the athymic mouse brain. By contrast, cells transfected with only the native bFGF gene (wild-type bFGF): 1) formed discrete cell clusters on Matrigel; 2) were less invasive and migratory in vitro; 3) released minimal Mr 92,000 collagenase; and 4) in vivo formed a pseudocapsule that separated the tumor cells from the neuropil. Quantitation of bFGF in the conditioned serum-free medium of the cell lines by enzyme-linked immunosorbent assay demonstrated that the signal peptide-bFGF cell clone secreted bFGF. These findings suggest a role for bFGF-mediated pathways and collagenase as molecular determinants of invasiveness in the brain.

Inhibition of basic fibroblast growth factor and vasculotropin biological activities on cultured cells by almitrine

Autonomous cell growth may result from interactions of cellular growth factors with their receptors leading to the establishment of external or internal autocrine loops which can induce tumor formation. Tumor progression above a small volume also requires an increase in blood supply. This is achieved by the release from the tumor of angiogenic growth factors which diffuse toward preexisting capillaries. The search for compounds interfering with growth factors and their receptors represents a field of investigation of increasing importance. In this report we show that almitrine interferes with the binding of basic fibroblast growth factor and vasculotropin/vascular endothelial growth factor to their receptors present on vascular endothelial cells, smooth muscle cells or retinal pigment epithelium. This molecule inhibits reversibly serum and basic growth factors stimulated cell growth and motility without affecting epidermal growth factor-stimulated proliferation.

A rapid, high capacity assay for basic fibroblast growth factor binding

A rapid, high capacity assay for the binding of basic fibroblast growth factor has been developed. Rat lung tissue was selected as the optimum source of membranes and 2M sodium chloride used to remove endogenous growth factor. The assay has been adapted to the Millipore Multi-Screen system so that it can be run in 96-well format with a volume of 300 microliters. The assay has been validated through the demonstration of inhibition by standard inhibitors such as suramin and protamine sulfate. The assay has proven useful for the screening of random compounds as well as the more detailed examination of suspected inhibitors. By running compounds in the presence and absence of a mid-range concentration of unlabeled bFGF, an estimate of the proportion of the inhibition due to high affinity binding can be obtained. Suramin and protamine sulfate show no selectivity and inhibit high affinity binding and overall binding with similar potencies. Another inhibitor, dimercaptothiadiazole, is more potent against high affinity binding.

Growth factor regulation of proliferation in primary cultures of small intestinal epithelium

Although the intestinal epithelium is one of the most rapidly renewing tissues, little is known about the major growth factors that control the rate of cell replacement and migration. Recently, a primary culture model has been described for the developing rat small intestinal epithelium, which permits epithelial growth while maintaining interactions with associated stromal cells, thereby possessing several contextual advantages over established cell lines (Evans et al., 1992). We have used this model to begin to determine the factors that may be involved in controlling intestinal epithelial cell proliferation. Under the conditions examined, no single growth factor promoted exclusive proliferation of epithelial cells; stromal cell proliferation was also apparent. The most potent stimulators of epithelial proliferation were insulin and insulin-like growth factor 1 (IGF-1). These factors also appeared to inhibit migration of the epithelial cells. 5-10 ng/ml EGF, 5-20 ng/ml TGF alpha, and 10-20 ng/ml PDGF also slightly increased epithelial cell numbers. Cell proliferation was inhibited by 0.1 ng/ml TGF beta-1. In Dulbecco's modified Eagle's medium (DMEM) containing 0.25 IU/ml insulin, glucose levels of 2-3 g/liter permitted epithelial growth with limited expansion of the stromal cell population. Higher levels of glucose further stimulated the nonepithelial cell types. Transferrin was also a potent stimulator of both cell types.

Muscle regeneration following injury can be modified in vivo by immune neutralization of basic fibroblast growth factor, transforming growth factor beta 1 or insulin-like growth factor I

Previous in vitro studies pointed out the role played by several growth factors (basic fibroblast growth factor or bFGF, transforming growth factor beta-1 or TGF beta 1, insulin-like growth factor-I or IGF-I) on the proliferation, the differentiation and the fusion of myogenic precursor cells. We attempted to modify the muscle regeneration which follows the denervation-devascularization of extensor digitorum longus in mice, by acting on the growth factors which are possibly involved in this process. The injection of neutralizing antibodies against either bFGF or IGF-I into the muscle at the time of lesion reduced the number and diameter of regenerating myofibres, suggesting a delay in proliferation and/or fusion of activated satellite cells. The neutralization of TGF beta 1 led to an increased number of small regenerating myofibres, which would be due to the promoting effects of the remaining growth factors (i.e. bFGF and IGF-I) on myoblast proliferation. These contrasted results strongly suggest that the growth factors regulate in vivo muscle regeneration and would be accessible tools for future therapy of muscular disorders.

Astrogliosis in culture. IV. Effects of basic fibroblast growth factor

Previous studies have shown that the mechanical wounding of 3-week-old cultured rat astrocytes results in cell proliferation and hypertrophy resembling astrocyte responses to a brain injury in vivo. We now report the effects of basic fibroblast growth factor (bFGF) and an anti-bFGF antibody on astrocyte morphology, proliferation, and migration following in vitro wounding of confluent secondary cultures. Addition of bFGF (20 ng/ml) to wounded cultures induced morphological changes characteristic of differentiation in wounded and nonwounded areas of the culture. Combined treatment with bFGF and an anti-bFGF antibody (100 micrograms/ml) prevented this effect. Astrocyte proliferation along the edges of a scratch wound was at maximum 24 hr after wounding in cells growing in Eagle's minimum essential medium (EMEM) containing 10% serum. Low serum concentration and treatment with dibutyryl cyclic adenosine monophosphate (dbc-AMP) reduced injury-associated astrocyte proliferation. Addition of bFGF to cultures in EMEM with serum increased astrocyte proliferation at 18 and 24 hr after wounding. This effect was reduced considerably by treatment of cultures with bFGF in combination with an anti-bFGF antibody. The combined treatment and the antibody alone reduced cell division to a level lower than in control cultures. Twenty-four hr following wounding, astrocytes along the edges of the wound exhibited extension of thick, flat processes into the wound area. At 3 and 5 days after wounding, a bodily migration of astrocytes into the wounded area was observed. Addition of bFGF significantly increased astrocyte migration 1 day after wounding, with maximum effect on day 3 and no subsequent increase on day 5. A combination of bFGF and anti-bFGF antibody as well as the antibody alone reduced astrocyte migration to a level lower than in controls. Immunohistochemical localization and isoform pattern of bFGF in astrocytes did not change with dbc-AMP treatment or wounding. We conclude that mechanically wounded confluent astrocytes respond to bFGF added to the culture medium by enhancing cell division, differentiation, and migration. In addition, the results of the antibody treatment also suggest a role for endogenous bFGF in astrocyte proliferation and migration elicited by wounding in vitro. These results support the notion that in vivo, both bFGF released by injury and endogenous bFGF synthesized by astrocytes, contribute to the cellular responses that lead to astrogliosis.

Expression of basic fibroblast growth factor and its receptors in human fetal microglia cells

The presence of basic fibroblast growth factor (bFGF) and FGF receptors was investigated in microglia cells derived from human fetal brain long-term cultures. Production of bFGF was suggested through the capability of microglial extracts to stimulate plasminogen activator (PA) synthesis in endothelial cells. The identity of PA-stimulating activity with bFGF was confirmed by its high affinity for heparin and its cross-reactivity with polyclonal antibodies to human recombinant bFGF. These antibodies recognized a cell-associated M(r) 18,000 protein as well as trace amounts of the M(r) 24,000 bFGF isoform in Western blot. All microglial cells showed bFGF immunoreactivity in the cytoplasm and, sometimes, in the nucleus. Scatchard plot analysis of 125I-bFGF binding data revealed the presence of low affinity heparansulphate proteoglycans (380,000 +/- 60,000 sites/cell; Kd = 730 +/- 200 nM) and of high affinity tyrosine-kinase receptors (10,300 + 2500 sites/cell; Kd = 30 +/- 9 pM). Immunocytochemistry confirmed the presence of FGF receptor (1/flg) on the cell surface of some, but not all microglial cells, with prevalent association to ameboid microglia. Transcripts for FGF receptors 1, 2, 3 and 4 were found in microglia by Northern blot analysis. Co-expression of bFGF and its receptors in human fetal microglia suggests an autocrine role of bFGF in these cells.

Expression of tissue-type plasminogen activator and its inhibitor couples with development of capillary network by human microvascular endothelial cells on Matrigel

Human omental microvascular endothelial (HOME) cells seeded on Matrigel begin to migrate within 1 h, forming honeycomb-like structures and capillary-like networks within 18 h. Cross-sections of the capillary networks show them to be tube-like structures. Northern blot analysis showed that tissue-type plasminogen activator (t-PA) mRNA synthesis increased from the initial state at 0 h after seeding on Matrigel, reaching a steady state after 4 h. This elevated cellular t-PA mRNA level decreased markedly at 24 h. In contrast, the cellular plasminogen activator inhibitor-1 (PAI-1) mRNA level demonstrated biphasic curves during the 24 h after seeding on Matrigel: the PAI-1 mRNA level was increased eightfold initially at 4 h over that at 0 h, then declined, and again secondarily increased to greater than tenfold at 18 h. Cellular levels of both 72 kD type IV collagenase and tissue inhibitor of metalloproteinase (TIMP-2) mRNA were increased only a slightly within 2-4 h. These elevated mRNA levels were maintained for 18 h, while the TIMP-1 mRNA level increased up to 18 h, reaching around three times the level at 0 h. However, on collagen-coated dishes, cellular levels of t-PA, PAI-1, 72 kD type IV collagenase, TIMP-1, and TIMP-2 mRNA were not greatly changed during incubation for 24 h. On Matrigel, the cellular t-PA mRNA level at 18 h after seeding was greatly increased when treated with specific anti-transforming growth factor-beta (TGF-beta) antibody. In contrast, both PAI-1 and TIMP-1 mRNA levels at 18 h were reduced in the presence of anti-TGF-beta antibody. Development of the capillary network on Matrigel was inhibited in the presence of anti-t-PA antibody. Epidermal growth factor (EGF) enhanced t-PA gene expression and TGF-beta inhibited its expression in HOME cells cultured on collagen-coated dishes. On the other hand, TGF-beta enhanced cellular expression of the PAI-1 gene. The formation of a capillary network by HOME cells on Matrigel appears to be balanced by angiogenic EGF and anti-angiogenic TGF-beta through modulation of PA activity.

Melanocyte mitogens induce both melanocyte chemokinesis and chemotaxis

It is believed that during repigmentation of vitiligo, inactive melanocytes in the outer root sheath of the hair follicle become activated, proliferate, and migrate into the depigmented skin. However, the mechanisms controlling melanocyte migration remain to be elucidated. In this study, we investigated the effects of well-described melanocyte growth factors on melanocyte migration. Using time-lapse photography, we demonstrated that melanocyte chemokinetic movement was induced by basic fibroblast growth factor, stem cell factor, and endothelin-1, with the greatest effect noted using 100 nM endothelin-1. Similar results were reported previously with leukotriene C4. When surrounded by these stimuli, melanocytes moved in a random, nonlinear fashion and showed no desensitization at the concentrations studied. In Boyden chamber checkerboard analysis, basic fibroblast growth factor, leukotriene C4 and endothelin-1 were chemotactic. They produced directional migration and showed desensitization at higher concentrations. The greatest effect again was seen with 100 nM endothelin-1. Stem cell factor showed no effect in this assay system at the concentrations tested. The four melanocyte mitogens--leukotriene C4, endothelin-1, basic fibroblast growth factor, and stem cell factor--stimulate melanocyte migration, and this migration may be either chemokinetic (activated random movement) or chemotactic (requiring a gradient, directional, and showing desensitization), depending on the conditions used. We believe that these factors may be effective in stimulating vitiligo repigmentation by inducing proliferation and migration of hair-follicle outer-root-sheath melanocytes into the depigmented epidermis.

Inhibitory effect of lead on the proliferation of cultured vascular endothelial cells

We investigated the effect of lead nitrate (0.5, 1.0, 2.0 or 5.0 microM) on the proliferation of cultured bovine aortic endothelial cells. After exposure to lead, the number of cells and the incorporation of [3H]thymidine into the acid-insoluble fraction of the cells were reduced in parallel in a concentration-dependent manner. Histologically, lead treatment resulted in a decrease in the cell number accompanied by a change in the cell shape from polygonal to spindle; however, no degenerative change was observed except in 5.0 microM lead-treated cells. Furthermore, stimulation of [3H]thymidine incorporation by either basic or acidic fibroblast growth factor was significantly reduced by lead. However, the leakage of lactate dehydrogenase into the medium from the cells, a marker of nonspecific cell damage, was not changed by lead. From these results, it was revealed that lead inhibits the proliferation of cultured vascular endothelial cells without nonspecific cell damage. Although lead does not destroy the monolayer of endothelial cells, the metal may exhibit its noxious effect in the repair process of the vascular endothelium.

Angiogenesis: models and modulators

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