Effect of platelet factors on migration of cultured bovine aortic endothelial and smooth muscle cells

Role of cimetidine in the prevention of intimal hyperplasia in rat carotid artery

In vitro studies have revealed that histamine increases smooth muscle cell proliferation and migration, an effect abolished by the H2 antagonist cimetidine. This study examined the effect of cimetidine on intimal hyperplasia in vivo. Thirty male Wistar rats underwent endothelial denudation of the left carotid artery; 15 received cimetidine 350 mg per kg per day for four weeks and 15 received vehicle only. Four weeks after injury the left carotid arteries were perfusion fixed and harvested. Morphometric analysis revealed that there was no significant difference between the intima:media ratio of rats treated with cimetidine (median (interquartile range (i.q.r.)) 1.69 (0.59)) and those treated with vehicle (median (i.q.r.) 1.59 (0.59), P = 0.28). Similarly, the percentage luminal reduction was not significantly different between the groups (median (i.q.r.) 54.7 (19.9) per cent and 45.8 (13.4) per cent respectively, P = 0.30). It is concluded that treatment with cimetidine does not reduce the formation of intimal hyperplasia in rat carotid arteries de-endothelialized with a balloon catheter.

Nitric oxide inhibits angiotensin II-induced migration of rat aortic smooth muscle cell. Role of cyclic-nucleotides and angiotensin1 receptors

Nitric oxide (NO) and angiotensin II (AII) can effect vascular smooth muscle cell (SMC) proliferation. However, the effects of such agents on SMC migration, an equally important phenomenon with regard to vascular pathophysiology, have received little attention. The objectives of the present study were: (a) to determine whether NO inhibits AII-induced migration of vascular SMCs; (b) to investigate the mechanism of the interaction of NO and AII on SMC migration; and (c) to evaluate the AII receptor subtype that mediates AII-induced SMC migration. Migration of rat SMCs was evaluated using a modified Boydens Chamber (transwell inserts with gelatin-coated polycarbonate membranes, 8 microns pore size). AII stimulated SMC migration in a concentration-dependent manner, and this effect was inhibited by sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP). In the presence of L-arginine, but not D-arginine, IL-1 beta, an inducer of inducible NO synthase, also inhibited AII-induced SMC migration, and this effect was prevented by the NO-synthase inhibitor, N-nitro-L-arginine methyl ester. The effects of NO donors on AII-induced SMC migration were mimicked by 8-bromo-cGMP. Also, the antimigratory effects of SNAP were partially inhibited by LY83583 (an inhibitor of soluble guanylyl cyclase) and by KT5823 (an inhibitor of cGMP-dependent protein kinase). Although 8-bromo-cAMP (cAMP) also mimicked the antimigratory effects of NO donors, the antimigratory effects of SNAP were not altered by 2',5'-dideoxyadenosine (an inhibitor of adenyl cyclase) or by (R)-p-adenosine-3',5'-cyclic phosphorothioate (an inhibitor of the cAMP-dependent protein kinase). Low concentrations of the subtype AT1-receptor antagonist CGP 48933, but not the subtype AT2-receptor antagonist CGP 42112, blocked AII-induced SMC migration. These findings indicate that (a) NO inhibits AII-induced migration of vascular SMCs; (b) the antimigratory effect of NO is mediated in part via a cGMP-dependent mechanism; and (c) AII stimulates SMC migration via an AT1 receptor.

Platelet attachment stimulates endothelial cell regeneration after arterial injury

BACKGROUND

Arterial injury is associated with endothelial disruption and attachment of platelets to an exposed subintimal layer. A variety of factors released by platelets may affect the ability of endothelial cells bordering an injury to regenerate. In this study an organ culture model of arterial injury was used to investigate the relationship between attachment of platelets to a superficial arterial injury and endothelial regeneration.

METHODS

A defined superficial endothelial injury was made in whole vessel wall explants of rabbit thoracic aorta. Injured explants were treated with either fresh whole platelets, the supernatant of platelets aggregated by collagen, or basic fibroblast growth factor. Four days after injury and treatment, the average distance of endothelial regeneration was determined.

RESULTS

A dramatic increase in the rate of endothelial cell regeneration was observed when injured vessels were exposed to fresh whole platelets (p = 0.003). This increase in regeneration was comparable to that observed with fibroblast growth factor. No increase in the regenerative rate was found after exposure of explants to the supernatant of aggregated platelets (p = 0.69).

CONCLUSIONS

Platelets stimulate endothelial regeneration at a rate equal to that observed with the potent endothelial mitogen basic fibroblast growth factor. Because this effect was not demonstrated with the supernatant of aggregated platelets, endothelial regeneration may be dependent on attachment of the platelets to the area of injury.

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

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

Platelet-induced vascular smooth muscle cell proliferation is modulated by the growth amplification factors serotonin and adenosine diphosphate

BACKGROUND

Platelet-mediated mechanisms have been implicated in intimal lesion formation following vascular injury. Although the participation of peptide growth factors has been suspected in this process, little has been known about the possible mitogenic role of other platelet factors that are released at sites of vascular injury.

METHODS AND RESULTS

We tested the hypothesis that platelet products, which are not peptide growth factors, are important modulators of the platelet-induced smooth muscle cell (SMC) proliferative response by acting as growth amplification factors. In these studies, cell proliferation was assessed by [3H]thymidine incorporation, flow cytometry, and direct cell counting. We examined the potential mitogenicity of several platelet products, including serotonin, ADP, norepinephrine, histamine, platelet-activating factor, the thromboxane A2 mimetic U46619, and bradykinin. Of the platelet products tested, serotonin and ADP induced a synergistic response with peptide growth factors. This synergy was greatest at low growth-factor concentrations. Addition of nonaggregated platelets to quiescent SMC cultures strongly stimulated cell proliferation. Since the addition of suramin to platelet-treated cultures markedly inhibited SMC proliferation, peptide growth factors are most likely the primary mitogens mediating this response. However, platelet-induced proliferation was also markedly reduced by the serotonin antagonists ketanserin and LY53857 (44%), and by the ADP antagonist apyrase (35%).

CONCLUSIONS

Therefore, serotonin and ADP contribute significantly, in synergy with peptide growth factors, to the platelet-induced SMC proliferative response. We propose that in vivo serotonin and ADP act as amplification factors for SMC proliferation at sites of vascular injury.

Growth factor modulation of injury-reactive ependymal cell proliferation and migration

Injury-reactive ependymal cells from regenerating axolotl spinal cord can be maintained in their mesenchymal outgrowth phase in culture (O'Hara et al., 1992). To address the ability of specific growth factors in stimulating or maintaining migration and proliferation, mesenchymal ependymal cell cultures derived from injured axolotl spinal cord at 2 weeks post-lesioning were used to determine the potential effects of epidermal growth factor, platelet-derived growth factor and transforming growth factor-beta 1. In our cultures, medium containing epidermal growth factor alone or in combination with the other growth factors permitted significant migration and proliferation from ependymal explants. Platelet-derived growth factor alone was shown to have a small positive effect on ependymal cell migration and no effect on proliferation. Transforming growth factor-beta 1 alone did not support cell migration and was found to be inhibitory towards cellular proliferation. Lastly, medium containing platelet-derived growth factor and transforming growth factor-beta 1, but not epidermal growth factor, caused ependymal cell explants to break apart and migrate on the dish as cords. Migration and proliferation of injury-reactive ependymal cells was shown to be dependent on epidermal growth factor in vitro. These results suggest that epidermal growth factor may be a critical component in vivo during the initiation of ependymal migration and proliferation following transection of the axolotl spinal cord. The reorganization of cultured ependymal cells in response to the combination of platelet-derived growth factor and transforming growth factor-beta shows that ependymal organization can be modulated by growth factors. This suggests that the progressive changes observed during regeneration may be under the control of growth factors.

Alpha 1 adrenergic receptor-induced c-fos gene expression in rat aorta and cultured vascular smooth muscle cells

While growth of blood vessels is important in hypertension, relatively little is known about the contribution of catecholamines. Using isolated rat aorta and cultured smooth muscle cells, we examined adrenergic stimulation of gene expression. Phenylephrine, a selective alpha 1 adrenergic receptor agonist, caused a rapid and transient increase in c-fos mRNA accumulation which was inhibited by prazosin, an alpha 1 receptor antagonist. Similarly, phenylephrine stimulated c-jun and c-myc mRNA accumulation. Chloroethyl-clonidine, a compound which irreversibly blocks alpha 1B receptors, completely blocked the phenylephrine-induced increase in c-fos mRNA. RNase protection experiments demonstrated that rat aorta prominently expressed mRNA for alpha 1B and alpha 1A/D receptors. Phenylephrine-induced c-fos mRNA was partially inhibited by H-7, a protein kinase C inhibitor, and by nifedipine, a Ca2+ channel blocker; these two compounds together had additive effects. In situ hybridization showed that expression of c-fos mRNA induced by phenylephrine was localized to aorta's medial layer. These results suggest that alpha 1 receptor-induced increase in c-fos mRNA in aorta is mediated by a chloroethyl-clonidine-sensitive receptor subtype signaling via increasing intracellular Ca2+ concentrations and activating protein kinase C.

Autocrine control of wound repair by insulin-like growth factor I in cultured endothelial cells

The repair process of the vascular endothelium is modulated by growth factors from both endogenous (within the vessel wall) and exogenous (blood borne) sources. We utilized a tissue culture model of endothelial wounding to gain further insight into the potential autocrine control of proliferation during wound repair. Cultured porcine aortic endothelial monolayers were mechanically wounded by passing a 7-mm sterile glass rod over the surface of the culture. Proliferation at the wound edge was quantified using [3H]thymidine autoradiography. In wounded cultures incubated in media supplemented with 10% fetal calf serum, 81 +/- 2% of the nuclei at the wound edge were labeled. When the cultures were incubated in serum-free media, proliferation at the wound edge was only slightly diminished with 65 +/- 3% (P < 0.05) of the cells labeled. These findings raise the possibility that there is a significant contribution from autocrine growth factors to endothelial wound repair. To evaluate the potential role of insulin-like growth factor I (IGF-I) in the wound repair process, we used a radioimmunoassay to measure IGF-I secretion. Wounded cultures exhibited a 187 +/- 58% increase in IGF-I production when compared with nonwounded cultures (P < 0.05). To determine the extent to which endogenous IGF-I mediates the proliferative response of endothelial cell monolayers to wounding, wounded cultures were incubated with inactivating concentrations of IGF-I antibody. When IGF-I antibody was present in the culture media, only 26 +/- 3% of the nuclei at the wound edge were labeled with [3H]thymidine (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosapentaenoic acid abolishes the proatherogenic effects of cholesterol: effects on migration of bovine smooth muscle and endothelial cells in vitro

It is well known that vascular endothelial cell (EC) migration plays a major role in regeneration of the injured endothelium and also that smooth muscle cell (SMC) migration is the important step for atheromatous plaque formation. In the present study, we investigated the effects of cholesterol and eicosapentaenoic acid (EPA) on bovine carotid artery EC and SMC migration using the modified Boyden chamber technique. The migration activity of the cholesterol-enriched ECs loaded with cholesterol-rich liposomes was significantly suppressed, whereas that of the cholesterol-enriched SMCs was enhanced. Next, we examined the effects of EPA pretreatment on the migration of both cell types. When ECs and SMCs were treated with EPA (5 micrograms/ml) for 2 days, the EPA content increased from 0.55 +/- 0.04% to 11.72 +/- 0.19% and 1.22 +/- 0.09% to 9.69 +/- 0.07% in cellular phospholipids, respectively. Although pretreatment of the ECs with EPA caused a significant increase in serum-induced cell migration, pretreatment of SMCs had no effect. If both cell types were concomitantly pretreated with EPA and cholesterol-rich liposomes, EPA abolished the effects of cholesterol on the migration of both cell types, but did not affect the content of cholesterol in both cells. These data indicate the possibility that EPA counteracts the atherogenic effect of cholesterol on EC and SMC migration.

Inhibitory effects of antisense oligodeoxynucleotides targeting c-myc mRNA on smooth muscle cell proliferation and migration

Smooth muscle cell (SMC) proliferation and migration play pivotal roles in restenosis following angioplasty. c-myc is an immediate early response gene induced by various mitogens, and several lines of evidence derived from experiments using transformed or hematopoietic cell lines, or transgenic mice, suggest its protein product plays a role in numerous signaling transduction pathways, including those modulating cell division. We therefore reasoned that a strategy employing oligodeoxynucleotides (ODNs) complementary to c-myc mRNA (antisense ODNs) might be potent inhibitors of SMC proliferation and, perhaps, of SMC migration. To evaluate this concept, we tested several antisense ODNs targeted to c-myc mRNA (15- or 18-mer ODNs complementary to different c-myc mRNA sequences) by introducing them individually into the medium of cultured rat aortic SMCs. Phosphoroamidate-modified ODNs were employed to retard degradation. Antisense ODNs inhibited, in a concentration-dependent manner, SMC proliferation and SMC migration. Maximal inhibitory effect was 50% for proliferation and > 90% for migration. These effects were associated with decreased SMC expression of c-myc-encoded protein by Western immunoblotting and immunocytochemical staining. ODNs with the same nucleotides but a scrambled sequence caused no effect. These results indicate that the c-myc gene product is involved in the signal transduction pathways mediating SMC proliferation and migration in the in vitro model we employed. The results also suggest a potential role of antisense strategies designed to inhibit c-myc expression for the prevention of coronary restenosis.

Photoinhibition of smooth muscle cell migration: potential therapy for restenosis

Evidence from animal, autopsy, and atherectomy studies demonstrates that migration and proliferation of smooth muscle cells of medial origin result in neointima formation and decreased luminal cross-sectional area. The purpose of this study was to evaluate whether low energy light irradiation can inhibit smooth muscle cell migration and therefore potentially reduce the degree of neointima formation and the incidence of restenosis. The migration kinetics of bovine aortic smooth muscle cell monolayers were examined using a fence assay. The effect on smooth muscle cell migration of irradiation with monochromatic light at wave-lengths ranging from 400 to 700 nm was compared to the migration of cells irradiated with broadband white light or maintained in the dark. Wavelength specific photoinhibition of smooth muscle cell migration was observed; 594-600 nm light reproducibly inhibited migration by 12-29% (P < 0.05). Migration rate was significantly reduced following daily radiant exposures of 1.0 J/cm2 as well as following a single radiant exposure of 0.09 or 0.9 J/cm2. The decrease in migration was not associated with any change in cell proliferation or [3H] thymidine incorporation. We conclude that 594-600 nm light inhibits smooth muscle cell migration in vitro and may potentially be used in vivo to decrease fibrointimal thickening following arterial injury. This application of photoinhibition may be useful in retarding restenosis following angioplasty.

Transforming growth factor-beta: signal transduction via protein kinase C in cultured embryonic vascular smooth muscle cells

Transforming growth factor-beta (TGF-beta), an ubiquitous regulatory peptide, has diverse effects on the differentiation and behavior of vascular smooth muscle cells (VSMC). However, the molecular mechanism through which TGF-alpha exerts its effects remains obscure. We investigated the phosphoinositide/protein kinase C [PKC] signaling pathway in the action of TGF-beta on cultured embryonic avian VSMC of differing lineage: a) thoracic aorta, derived from the neural crest; and b) abdominal aorta, derived from mesenchyme. The second messenger responsible for activation of PKC is sn-1,2-diacylglycerol [DAG]; TGF-beta increased the mass amounts of DAG in the membranes of neural crest-derived VSMC concurrent with translocation of PKC from the soluble to the membrane fraction, but TGF-beta had no effect on the DAG or PKC of mesenchyme-derived VSMC. TGF-beta potentiated the growth of platelet-derived growth factor (PDGF)-treated, neural crest-derived VSMC; but abolished PDGF-induced growth of mesenchymal cells. It is concluded that molecular and functional responses of VSMC to TGF-beta are heterogeneous and are functions of the embryonic lineage of the VSMC.

Influence of mitomycin C on endothelial monolayer regeneration in vitro

This study examines the effect of Mitomycin C, a fungal toxin which inhibits DNA synthesis, on the regeneration of partially denuded large vessel endothelium in vitro. Monolayers of bovine pulmonary artery endothelial cells were treated with Mitomycin C prior to or immediately following partial denudation and were incubated in the continuing presence of Mitomycin C; the effects of this treatment on monolayer repair, cell proliferation, and other aspects of endothelial phenotype were monitored. Cell proliferation, DNA, RNA, and protein synthesis were all reduced in a dose dependent manner in treated cultures. Incubation with Mitomycin C for 48 h or longer resulted in reduced cell spreading, and rounding up and loss of cells from both intact and partially denuded cultures. Effects were less severe with lower doses and shorter incubation times. However, significant reductions in monolayer regeneration occurred within 8 h of incubation, sufficiently early to suggest that Mitomycin C may affect aspects of the regeneration process independent of cell proliferation. Polarization/spreading of cells at the denudation edge was monitored by fluorescence staining for golgi with C5-DMB-ceramide, and for centrioles with antibodies to tubulin. Centrioles and golgi rapidly reoriented to a location at the putative leading edge of control cultures. Mitomycin C treatment had no effect on centriole reorientation, but caused a significant delay in golgi localization. These results suggest that Mitomycin C inhibits endothelial monolayer regeneration by mechanisms independent of cell proliferation and DNA synthesis, perhaps by interfering with cell spreading or translocation at the wound edge.

Differential modulation of vascular cell integrin and extracellular matrix expression in vitro by TGF-beta 1 correlates with reciprocal effects on cell migration

In vitro, BAEC and BASMC migratory phenotypes are known to be reciprocally modulated by both soluble factors and extracellular matrix proteins. In addition, integrin matrix receptors mediate endothelial and smooth muscle cell attachment and migration. To further elucidate these phenomena, we studied the effects of TGF-beta 1 on integrin expression by vascular BASMC and BAEC in tissue culture. TGF-beta 1 upregulated mRNA levels and surface pools of BASMC beta 3 integrin classes without modulating beta 1 integrin mRNA levels or expression of beta 1 integrin organization. In contrast to its effects on BASMC, TGF-beta 1 increased BAEC mRNA levels and surface expression of beta 1 and beta 3 integrins without altering their organization. Conversely, extracellular matrix components (fibronectin, laminin, and fibrinogen) organized cell surface integrins in both BASMC and BAEC without affecting the size of their cell surface pools. These data are consistent with the hypothesis that SMC and EC behavior in neointimal lesions may be modulated, in part, through a coordination of soluble factor and extracellular matrix protein regulation of integrin surface expression and organization.

Inhibition of platelet accumulation by beta 1-adrenoceptor blockade in the thoracic aorta of rabbits subjected to experimental sympathetic activation

Arterial platelet adhesion is an initiating event in the thrombo-embolic complications of atherosclerosis and may also accelerate the development rate of atherosclerotic lesions. Psychosocial stress has been shown to accelerate atherogenesis in animals, an effect probably mediated via beta-adrenoceptor activation. In view of the postulated roles of platelets and beta-adrenoceptor activation in atherosclerosis development, we decided to test whether beta blockade affects arterial platelet accumulation. We studied the accumulation of radioactivity from 111In-labelled platelets on the wall of the thoracic aorta of rabbits as a measure of platelet accumulation. During the exposure to the labelled platelets, the animals were also exposed to 3 hours of chloralose anesthesia. This is a reproducible model of experimental sympathetic activation, including beta-adrenoceptor activation, which we used to amplify possible effects of beta-blockade on platelet-vessel wall interaction. The effectiveness of the anesthesia in increasing sympathetic activity was verified by significant rises in mean arterial blood pressure (from 77 to 88 mmHg), heart rate (190 to 290 bpm), and plasma levels of norepinephrine (1.0 to 3.3 nM) and epinephrine (0.13 to 0.83 nM). In chloralose anesthetized rabbits, approximately 30 x 10(-9)% of the injected 111In accumulated in each square millimeter of intima at unbranched thoracic aorta. Platelet accumulation was significantly higher at arterial branching points, 70% higher at intercostal artery bifurcations, and 150% higher at coronary artery bifurcations than in unbranched aortic intima. Pretreatment with metoprolol in a dose resulting in "therapeutic" plasma levels significantly reduced platelet accumulation by 48% in unbranched aorta, 65% at intercostal, and 53% at coronary artery bifurcations.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta 1 is a heparin-binding protein: identification of putative heparin-binding regions and isolation of heparins with varying affinity for TGF-beta 1

Previous studies indicated that a major factor in heparin's ability to suppress the proliferation of vascular smooth muscle cells is an interaction with transforming growth factor-beta 1 (TGF-beta 1). Heparin appeared to bind directly to TGF-beta 1 and to prevent the association of TGF-beta 1 with alpha 2-macroglobulin (alpha 2-M). The present studies indicate that 20-70% of iodinated TGF-beta 1 binds to heparin-Sepharose and the retained fraction is eluted with approximately 0.37 M NaCl. Native, unlabelled platelet TGF-beta 1, however, is completely retained by heparin-Sepharose and eluted with 0.9-1.2 M NaCl. Using synthetic peptides, the regions of TGF-beta 1 that might be involved in the binding of heparin and other polyanions were examined. Sequence analysis of TGF-beta 1 indicated three regions with a high concentration of basic residues. Two of these regions had the basic residues arranged in a pattern homologous to reported consensus heparin-binding regions of other proteins. The third constituted a structurally novel pattern of basic residues. Synthetic peptides homologous to these three regions, but not to other regions of TGF-beta 1, were found to bind to heparin-Sepharose and were eluted with 0.15 M-0.30 M NaCl. Only two of these regions were capable of blocking the binding of heparin to 125I-TGF-beta. Immobilization of these peptides, followed by affinity purification of heparin, indicated that one peptide was capable of isolating subspecies of heparin with high and low affinity for authentic TGF-beta 1. The ability of TGF-beta 1 to bind to heparin or related proteoglycans under physiological conditions may be useful in understanding the biology of this pluripotent growth and metabolic signal. Conversely, a subspecies of heparin molecules with high affinity for TGF-beta 1 may be a factor in some of the diverse biological actions of heparin.

Human enterocyte (Caco-2) migration is modulated in vitro by extracellular matrix composition and epidermal growth factor

The modulation of enterocyte sheet migration was studied using Caco-2 cells, a well-differentiated human colonic cell line. Although Caco-2 cells attached and spread equivalently over collagen types I, III, IV, and V and laminin, migration over laminin was significantly slower than migration over the collagen types. Fibronectin was a poor substrate for attachment, spreading, and migration. Epidermal growth factor (EGF) stimulated migration over laminin but did not alter Caco-2 migration over collagen or fibronectin. This effect was independent of cell proliferation, which was stimulated equivalently on both laminin and collagen I. Expression and organization of cell surface receptors for matrix (integrins) were studied using antibodies specific for beta and alpha integrin subunits. Integrin surface expression was assessed by immunoprecipitation of surface 125iodinated control and EGF-treated cells. Beta 1 surface pools did not change substantially in any condition studied. Alpha 1 subunit pools were decreased after EGF treatment on collagen I but alpha 1 pools increased after EGF treatment on laminin. Surface pools of alpha 2 subunits were increased following EGF treatment whether cells were cultured on laminin or collagen I. However, traditional immunofluorescent and laser confocal imaging demonstrated substantial differences in the character of alpha 2 subunit organization between collagen and laminin in the migrating cell front. Furthermore, a functional antibody to the alpha 2 subunit inhibited EGF stimulation of migration over laminin without substantial effects on basal migration over laminin or collagen I. Thus, EGF appears to exert a matrix-specific effect on enterocyte migration by modulation of integrin expression and organization.

Modulation of vascular cell behavior by transforming growth factors beta

The vascular cell responses to the type 1, 2, and 3 isoforms of transforming growth factor-beta (TGF-beta 1, TGF-beta 2, TGF-beta 3) were studied using bovine aortic endothelial (BAECs) and smooth muscle cells (BASMC3) as well as rat epididymal fat pad microvascular endothelia (RFCs). Three distinct bioassays indicated that TGF-beta elicits results that do not differ significantly from those of the TGF-beta 1 isoform in all three cell populations. These assays are: inhibition of proliferation, cell migration, and neovascularization. By contrast the cellular responses to TGF-beta 1 and TGF-beta 3 differed from those to TGF-beta 2. Three distinct receptor assays revealed the presence of type I and type II TGF-beta 1 cell surface binding proteins on BAECs, BASMCs, and RFCs. Experimentation to decipher cell surface binding by the different isoforms revealed that iodinated TGF-beta 1 bound to the surface of all three vascular cell types can be competed off in similar fashion by either TGF-beta 1 or TGF-beta 3; however, competition with TGF-beta 2 produced unique binding profiles dependent on the cell type examined. The ratios of type I to type II TGF-beta receptors in these three vascular cell types vary from 1:1 in BAECs to 1.5:1 in RFCs to 3:1 in BASMCs and can be correlated with the differences noted in cellular responses to TGF-beta 1 and TGF-beta 2 in proliferation, migration, and in vitro angiogenic assays.(ABSTRACT TRUNCATED AT 250 WORDS)

Visualization of histamine binding to nuclei

The binding of histamine to cultured microvascular endothelial cells and glycol methacrylate embedded ovarian tissue sections has been localized using fluorescein-albumin-histamine conjugate. Histamine conjugate was bound to the plasma membranes and nuclei of luteal, endothelial, and ovarian stromal cells. An apparent increase in the binding of histamine to nuclei was observed in the presence of cimetidine but the plasma membrane staining was still evident. Unlike cimetidine, pyrilamine completely inhibited the binding of histamine to the plasma membrane. Instead, in the presence of pyrilamine, histamine bound exclusively to the nuclei of endothelial, germinal epithelial, granulosa, and stromal cells. However, the nuclei of terminally differentiated luteal cells and oocytes were not labeled. The functional significance of these nuclear histamine binding sites remains to be determined.

Autocrine angiotensin system regulation of bovine aortic endothelial cell migration and plasminogen activator involves modulation of proto-oncogene pp60c-src expression

Rapid endothelial cell migration and inhibition of thrombosis are critical for the resolution of denudation injuries to the vessel wall. Inhibition of the endothelial cell autocrine angiotensin system, with either the angiotensin-converting enzyme inhibitor lisinopril or the angiotensin II receptor antagonist sar1, ile8-angiotensin II, leads to increased endothelial cell migration and urokinase-like plasminogen activator (u-PA) activity (Bell, L., and J. A. Madri. 1990. Am. J. Pathol. 137:7-12). Inhibition of the autocrine angiotensin system with the converting-enzyme inhibitor or the receptor antagonist also leads to increased expression of the proto-oncogene c-src: pp60c-src mRNA increased 7-11-fold, c-src protein 3-fold, and c-src kinase activity 2-3-fold. Endothelial cell expression of c-src was constitutively elevated after stable infection with a retroviral vector containing the c-src coding sequence. Constitutively increased c-src kinase activity reconstituted the increases in migration and u-PA observed with angiotensin system interruption. Antisera to bovine u-PA blocked the increase in migration associated with increased c-src expression. These data suggest that increases in endothelial cell migration and plasminogen activator after angiotensin system inhibition are at least partially pp60c-src mediated. Elevated c-src expression with angiotensin system inhibition may act to enhance intimal wound closure and to reduce luminal thrombogenicity in vivo.

Experimental models of coronary artery restenosis

The study of potentially effective drug therapies and mechanical devices for the prevention of restenosis after percutaneous coronary revascularization has relied heavily on the use of experimental animal models. To date, greater than 50 experimental studies have been reported and have suggested that at least nine different classes of pharmacologic agents inhibit the intimal proliferative response to arterial injury. However, no pharmacologic intervention has yet been shown to reproducibly reduce the incidence of restenosis after coronary balloon angioplasty in humans. To identify the reasons for the apparent nonspecificity of the animal models and to determine which model should most reliably predict the efficacy of individual therapies in humans, the distinguishing characteristics of the experimental models were compared. Particular attention was paid to the size and morphologic structure of the treated artery, the susceptibility of the species to spontaneous and diet-induced arterial disease, the nature of the stimulus to intimal proliferation and several practical and logistic considerations. Finally, the reported efficacies of specific drug therapies in the respective animal models and in humans were compared. This review suggests that significant interspecies and occasionally intraspecies differences do exist among the respective animal models, particularly in the extent and composition of the neointimal thickening.(ABSTRACT TRUNCATED AT 250 WORDS)

5-HT2 receptor mRNA is overexpressed in cultured rat aortic smooth muscle cells relative to normal aorta

Proliferation of smooth muscle cells in arteries is associated with contractile hypersensitivity to serotonin (5-HT). A possible explanation is that smooth muscle cells express increased numbers of phospholipase C (PLC)-coupled 5-HT receptors (5-HTR), which could mediate contractile and mitogenic signals via phosphatidylinositol turnover. To test this hypothesis, we performed a molecular characterization of 5-HTR subtypes in normal aorta and passaged rat aortic smooth muscle cells (RASM) in culture. Northern blot analysis revealed that growth-arrested cultured cells expressed 5-HT2R mRNA at 50-fold greater levels than aorta. 5-HT1CR mRNA was not detected in either case. 5-HT stimulated intracellular Ca2+ mobilization (fivefold peak increase) and c-fos mRNA induction (10-fold peak increase); both responses were strongly inhibited by selective 5-HT2R antagonists. Specific agonists for the 5-HT1AR, 5-HT1BR, and 5-HT1DR failed to induce c-fos mRNA. Although 5-HT (10 microM) increased [3H]thymidine incorporation (28% relative to 10% calf serum), it was a weak mitogen for cultured RASM based on cell counts. Thus there is high level expression of 5-HT2R mRNA by cultured RASM relative to aorta, and the 5-HT2R appears to be the only 5-HTR subtype mediating early growth signals in these cells. These data suggest that, following arterial injury in vivo, smooth muscle cells may overexpress the 5-HT2R, resulting in 5-HT contractile hypersensitivity and increased responsiveness to other growth factors.

Production of transforming growth factor beta 1 during repair of arterial injury

Repair of arterial injury produced by balloon angioplasty leads to the formation of a neointima and a narrowing of the vascular lumen. In this study, we examined the possibility that smooth muscle cells (SMC) in injured rat carotid arteries are stimulated to produce type-1 transforming growth factor-beta (TGF-beta 1) during neointima formation in vivo. Levels of TGF-beta 1 transcripts (2.4 kb) were significantly increased within 6 h after carotid injury and reached a maximum (five to sevenfold) by 24 h. Regenerating left carotids had sustained increases in TGF-beta 1 mRNA levels (about fivefold) over the next 2 wk, during which time a substantial neointimal thickening was formed. No changes in basal TGF-beta 1 mRNA levels were found in contralateral uninjured carotids at any of the times examined. Immunohistochemical studies showed that a large majority of neointimal SMC were stained for TGF-beta 1 protein in an intracellular pattern, consistent with active TGF-beta 1 synthesis in this tissue. Neointima formation and TGF-beta 1 immunoreactivity were correlated with increases in fibronectin, collagen alpha 2(I), and collagen alpha 1(III) gene expression. Infusion of purified, recombinant TGF-beta 1 into rats with a preexisting neointima produced a significant stimulation of carotid neointimal SMC DNA synthesis. These results suggest that TGF-beta 1 plays an important role as an endogenous growth regulatory factor produced by neointimal SMC themselves during progressive neointimal thickening after balloon angioplasty.

Pharmacologic roles of heparin and glucocorticoids to prevent restenosis after coronary angioplasty

Restenosis after successful percutaneous transluminal coronary angioplasty is the major clinical problem limiting the long-term efficacy of this treatment for coronary atherosclerosis. Recent advances in the understanding of the biology of restenosis indicate that intimal hyperplasia of smooth muscle cells is the predominant cause for restenosis. Therefore, therapeutic agents that inhibit vascular smooth muscle cell proliferation should be candidate drugs to prevent restenosis. Heparin has documented antiproliferative effects on smooth muscle cells, and the availability of low molecular weight heparins that lack anticoagulant properties makes them ideal agents. Glucocorticoids have wide effects on inflammatory and wound healing events and inhibit smooth muscle cell growth in culture and in animal models of arterial injury. Recent laboratory data suggest that combination therapy with both low molecular weight heparin and hydrocortisone may be a powerful treatment regimen to limit restenosis.

Induction of cell cycle-dependent genes during cell cycle progression of arterial smooth muscle cells in culture

Serum stimulation of arterial smooth muscle cells in culture induces a progression through the cell cycle and cell proliferation. Most genes previously described as cell cycle-dependent in various cell types also demonstrate a cell cycle-dependent expression in arterial smooth muscle cells. As in other cell types, these genes can be classified into three groups according to their mode of expression: "immediate early" genes (c-fos, c-myc, ...), "delayed early" genes (2F1, ...), and "late-G1" genes (proliferating cell nuclear antigen, thymidine kinase, . . .). In addition to these previously described genes, three genes isolated from a cDNA library of stimulated smooth muscle cells have been demonstrated to be cell cycle-dependent: A21, the rat JE gene, and L51 can be classified as "immediate early" genes, while M11 represents a new member of the "delayed early" gene family.

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

Vessel walls are comprised of several different cell populations residing in and on complex extracellular matrices. Each of the vascular cell types has diverse and sometimes unique functions and morphologies, and each has roles in repair processes following injury. Large vessel endothelial cells are known to respond to denudation injury by sheet migration and proliferation. This is in contrast to the migration through soft tissues with tube formation and subsequent lumen formation exhibited by microvascular endothelial cells in response to injury. Vascular smooth muscle cells of larger vessels respond to injury by migration from the arterial media into the intima, proliferation, and matrix biosynthesis, ultimately causing intimal thickening. Both these cell types exhibit "dysfunctional" phenotypes during their responses to injury. Microvascular cell responses to injury, while extremely variable, are less well documented. Specifically, responses to injury by microvascular endothelial vascular cells appear to be modulated, in part, by the composition and organization of the surrounding matrix as well as by the various soluble factors and cytokines found at sites of injury, suggesting that the extracellular matrix and soluble factors modulate each other's effects on local vascular cell populations following injury.

Vascular cell responses to TGF-beta 3 mimic those of TGF-beta 1 in vitro

The vascular cell responses to the type 3 isoform of transforming growth factor-beta (TGF-beta 3) were studied using bovine aortic endothelial (BAECs) and smooth muscle cells (BASMCs) as well as rat epididymal fat pad microvascular endothelia (RFCs). Four distinct bioassays indicated that TGF-beta 3 elicits results that do not differ significantly from those of the TGF-beta 1 isoform in all three cell populations. Inhibition of proliferation by TGF-beta 3 at a 5-day time point ranged from 85% on BAECs, to 55% and 53% on RFCs and BASMCs, respectively. The effects of TGF-beta 3 and TGF-beta 1 on cell migration were also found to be similar; migration of large vessel endothelial cells was inhibited 35%, while migration of smooth muscle cells was enhanced 30%. TGF-beta 1 and TGF-beta 3 also had equivalent effects on neovascularization while a 10-fold higher concentration of TGF-beta 2 was required to elicit a similar response. Experimentation to decipher cell surface binding by the different isoforms revealed that iodinated TGF-beta 1 bound to the surface of all three vascular cell types can be competed off in similar fashion by either TGF-beta 1 or TGF-beta 3; however, competition with TGF-beta 2 produced unique binding profiles dependent upon the cell type examined. In summary, both the TGF-beta 1 and TGF-beta 3 isoforms of the transforming growth factor-beta family evoke comparable responses in proliferation, migration, angiogenic and cell surface binding assays using three distinct vascular cell types, while the biofunctions of TGF-beta 2 on these cells are distinct.

Smooth muscle cell growth factors

While the roles of the platelet-derived growth factors (PDGFs) in vascular smooth muscle cells (SMCs) continue to be elucidated, these cells, especially in their activated 'synthetic' state, have also been found to express, and proliferate in response to, many of the other families of polypeptide growth factors, such as the fibroblast growth factors. Other stimulators of DNA synthesis, and particularly of SMC hypertrophy, include the vasoconstrictor hormones such as angiotensin II, as well as physical forces, especially stretch or tension. For many of these ligands, multiple receptors have been identified and their means of signal transduction are being characterized rapidly. Regulatory regions of these genes are being identified as are transcription factors. Complex post-transcriptional regulation has also been shown by the findings that some growth factors are phosphorylated, or translocated to the nucleus or the extracellular matrix. Inhibitors have also been identified. These include some prostaglandins, calcium antagonists, agonists that activate guanylate and adenylate cyclases, inhibitors of angiotensin-converting enzyme, interferon gamma, and heparin. Future studies are likely to show that tyrosine phosphatases and recessive oncogenes also regulate growth. The existence of so many autocrine/paracrine mitogens--together with some experimental data--suggests some redundancy in the system as well as some additive effects. Redundancy may limit the efficacy of antibodies to a single growth factor to block cell proliferation. Their evolutionary conservation implies some unique roles for each growth factor but these have not been apparent from in vitro studies to date. Further insights are apt to come from the increasing recognition that growth factors have other effects--on cell attachment, migration, survival, production of extracellular matrix, thrombosis, vaso-constriction, regulation of cytokine synthesis, and inhibition of growth. Many of these effects may prove to be context-dependent, as with the case of growth inhibition by transforming growth factor-beta. Studies in monolayer cultures may not obtain the same results as studies using cocultures of endothelial and smooth muscle cells, or 3-dimensional matrix cultures, organ cultures, or in the intact animal. In vivo descriptive studies of growth factors expressed in vascular embryogenesis, hypertension, atherosclerosis, acute balloon injury and thrombosis are being supplemented by interventions such as infusions with growth factors, antibodies, and toxin conjugates. These studies, and studies using transgenic mice and homologous recombination, should yield information as to mechanisms and may also suggest new therapies.