Localization of PDGF-B protein in macrophages in all phases of atherogenesis

Hypolipidaemic effects of naringenin, rutin, nicotinic acid and their associations

Atherosclerosis can be defined as being a disease of coronary circulation. The present work evaluates the action of the naringenin, rutin, nicotinic acid, isolated and in association, on the metabolism of lipids. Cholesterol, cholesterol HDL, and triacylglycerols have been dosed after retreat of blood, following the administration of the compounds dissolved in propylene glycol by intraperitoneal route in doses of 5 mg kg-1 body wt. Results evidence that naringenin and nicotinic acid, isolated as well as their association with naringenin and nicotinic acid-rutin, present the largest percentual reduction of cholesterol. On the other hand, the best results for cholesterol-HDL have been obtained with naringenin, while rutin has shown the best triacylglycerols levels.

Endothelial cells regulate the proliferation of monocytes in vitro

Monocytes (MPhis) are among the first cells to accumulate in early atherosclerotic lesions and generally are believed to be incapable of proliferation. However, recent studies indicate that the number of MPhis in atherosclerotic lesion may increase due to induction of local proliferation. Since proliferation of hematopoietic lineage cells is strongly influenced by interaction with neighboring cell types, we examined the ability of vascular endothelial cells (EC), smooth muscle cells or fibroblasts to stimulate MPhi proliferation. In this study, we show that only when seeded at high densities MPhis could proliferate in culture. However, when contact co-cultured with EC, MPhis proliferated at a higher rate (260% on day 6) than those cultured alone or co-cultured with smooth muscle cells or fibroblasts. Endothelial cells could stimulate the proliferation of MPhis even at non-proliferating densities. Only EC that were growth arrested or in lag phase could induce MPhi proliferation, whereas those in the exponential proliferating phase were non-stimulatory. Conditioned medium prepared from EC in growth arrested or lag phase failed to stimulate MPhi proliferation. Similarly physical separation of MPhis from EC also resulted in no proliferation. These results suggest that EC induced MPhi proliferation is contact dependent and no soluble factors are involved in this induction. This EC induced MPhi proliferation may have a profound effect on the rate of progression of atherosclerosis.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Platelet-derived growth factor beta receptor regulates interstitial fluid homeostasis through phosphatidylinositol-3' kinase signaling

Platelet-derived growth factor (PDGF) isoforms lead to mitogenic, survival, and chemotactic responses in a variety of mesenchymal cell types during development and in the adult. We have studied the importance of phosphatidylinositol-3' kinase (PI3K) signaling in these responses by mutating the PI3K-binding sites in the PDGF-beta receptor by gene targeting in embryonic stem cells. Homozygous mutant mice developed normally; however, cells derived from the mutants were less chemotactic and had largely lost their ability to contract collagen gels in response to PDGF. Injection of a mast cell degranulating agent in mice led to a decrease in interstitial fluid pressure resulting in edema formation. In contrast to wild-type mice, mutant mice were unable to normalize the pressure after treatment with PDGF. Taken together, these observations suggest a function for PDGF signaling through PI3K in interstitial fluid homeostasis by modulating the tension between cells and extracellular matrix structures.

[Pathophysiologic significance of growth factors and new therapeutic concepts in cardiovascular disease]

Peptide growth factors such as PDGF, FGF, VEGF, and TGF-beta play a critical role in the pathogenesis of cardiovascular diseases. In addition to their pathophysiological role in atherosclerosis and myocardial remodeling, growth factors also promote beneficial effects such as stimulation of angiogenesis and formation of collateral vessels in ischemic tissue. This review focuses on the mechanisms of action and signal relay cascades of peptide growth factors, and summarizes novel therapeutic approaches in cardiovascular medicine. These approaches include both inhibition of growth factors in order to suppress pathogenic processes, and stimulation of growth factors to promote their beneficial effects.

Interleukin 1beta induces type II-secreted phospholipase A(2) gene in vascular smooth muscle cells by a nuclear factor kappaB and peroxisome proliferator-activated receptor-mediated process

Type II-secreted phospholipase A(2) (type II-sPLA(2)) is expressed in smooth muscle cells during atherosclerosis or in response to interleukin-1beta. The present study shows that the induction of type II-sPLA(2) gene by interleukin-1beta requires activation of the NFkappaB pathway and cytosolic PLA(2)/PPARgamma pathway, which are both necessary to achieve the transcriptional process. Interleukin-1beta induced type II-sPLA(2) gene dose- and time-dependently and increased the binding of NFkappaB to a specific site of type II-sPLA(2) promoter. This effect was abolished by proteinase inhibitors that block the proteasome machinery and NFkappaB nuclear translocation. Type II-sPLA(2) induction was also obtained by free arachidonic acid and was blocked by either AACOCF(3), a specific cytosolic-PLA(2) inhibitor, PD98059, a mitogen-activated protein kinase kinase inhibitor which prevents cytosolic PLA(2) activation, or nordihydroguaiaretic acid, a lipoxygenase inhibitor, but not by the cyclooxygenase inhibitor indomethacin, suggesting a role for a lipoxygenase product. Type II-sPLA(2) induction was obtained after treatment of the cells by 15-deoxy-Delta(12,14)-dehydroprostaglandin J(2), carbaprostacyclin, and 9-hydroxyoctadecadienoic acid, which are ligands of peroxisome proliferator-activated receptor (PPAR) gamma, whereas PPARalpha ligands were ineffective. Interleukin-1beta as well as PPARgamma-ligands stimulated the activity of a reporter gene containing PPARgamma-binding sites in its promoter. Binding of both NFkappaB and PPARgamma to their promoter is required to stimulate the transcriptional process since inhibitors of each class block interleukin-1beta-induced type II-sPLA(2) gene activation. We therefore suggest that NFkappaB and PPARgamma cooperate at the enhanceosome-coactivator level to turn on transcription of the proinflammatory type II-sPLA(2) gene.

Immunohistochemical analysis of platelet-derived growth factor-B expression in myocardial tissues in hypertrophic cardiomyopathy

Intimal and/or medial hyperplasia of intramyocardial small vessels is thought to be one of the causes of myocardial ischemia in hypertrophic cardiomyopathy (HCM). However, the pathogenesis of such vascular lesions in HCM is not yet known. To evaluate the pathogenic role of platelet-derived growth factor (PDGF-B) and basic fibroblast growth factor (b-FGF), which have a potential to induce cellular and molecular changes observed in the vessels in HCM, we examined the expression of these molecules and PDGF receptors in cardiac tissues from six patients with HCM and seven controls using immunohistochemistry. The percentage of PDGF-B positive cells in the myocyte population in HCM was significantly higher than that in controls (52.6 +/- 16.2 (mean +/- SD) vs. 21.6 +/- 9.6, p < 0.01). PDGF-B was also observed in vascular regions in HCM (61.1 +/- 25.5% of arterioles) but not in controls. There were no significant differences in the expression of b-FGF and PDGF receptors in the myocyte and non-myocyte populations and the vascular regions between the HCM and control groups. Our study revealed that the expression of PDGF-B protein was up-regulated in HCM, suggesting the contribution of this molecule to the development of intramyocardial vasculopathy.

Impairment of EDR by a long-term PDGF treatment in organ-cultured rabbit mesenteric artery

Platelet-derived growth factor (PDGF) has been shown to act chronically on blood vessels to regulate not only proliferation but also vascular tone. These effects may be at least partly due to the chronic effect of PDGF on vascular endothelium. To evaluate this possibility, we examined the effects of PDGF on the endothelium-dependent relaxation (EDR) and total RNA for endothelial nitric oxide (NO) synthase (eNOS) using an organ culture system. In rabbit mesenteric arteries cultured in a serum-free medium for 1 wk, amplitude of the substance P-induced EDR did not change, whereas dependency of the EDR on NO (approximately 60.0% vs. 18.9%) and the total amounts of recoverable eNOS mRNA estimated by RT-PCR were increased compared with those in freshly isolated arteries. Culture with PDGF for 1 wk decreased the relaxant effect of substance P and ionomycin (P < 0.01 compared with the arteries without PDGF), NO production estimated by bioassay (P < 0.01), and eNOS mRNA level, whereas the sodium nitroprusside-induced relaxation did not change. These results suggest that PDGF has a chronic effect on vascular endothelium to decrease eNOS mRNA and NO production and to impair NO-dependent EDR.

Expression of platelet-derived growth factor in newly formed cholangiocytes during experimental biliary fibrosis in rats

BACKGROUND/AIMS

Chronic cholestasis stimulates a fibroductular reaction which may progress to secondary biliary fibrosis and cirrhosis. Since platelet-derived growth factor has been indicated as a major fibrogenic factor in chronic liver disease, we analyzed its expression and that of its receptor beta subunit in a rat model of chronic cholestasis.

METHODS

Liver tissue samples collected at 7, 10, 21, and 28 days after induction of cholestasis obtained by bile duct ligation, were analyzed by immunohistochemistry, in situ hybridization and RNase protection assay for the expression of platelet-derived growth factor (PDGF)-B chain and receptor beta subunit. Furthermore, the expression of PDGF-B chain mRNA was analyzed in highly purified cholangiocytes from normal and cholestatic rat liver.

RESULTS

In cholestatic liver, platelet-derived growth factor-BB and B chain mRNA expression increased up to 4 weeks in epithelial cells of proliferating bile ducts, and periductular mesenchymal cells. The increased expression of PDGF-B chain mRNA was confirmed in highly purified cholangiocytes obtained from normal and cholestatic rat liver. The expression of the receptor beta subunit progressively increased after induction of cholestasis and was mainly localized to desmin-positive periductular hepatic stellate cells.

CONCLUSIONS

These data suggest that platelet-derived growth factor-B chain can be synthesized by cholangiocytes during chronic cholestasis. The presence of its receptor on periductular hepatic stellate cells raises the possibility that, in this experimental setting, this cytokine might contribute to fibrogenesis in vivo.

Cytomegalovirus infection and cardiac allograft vasculopathy

There is a wealth of clinical and experimental evidence indicating the interaction of cytomegalovirus (CMV) infection and rejection in cardiac and other solid organ allografts. A plausible explanation for this association comes from data showing that therapy with biologicals, sepsis, and rejection, all lead to the release of TNF-alpha which, upon binding to its receptor, activates NF-kB. TNF-alpha is also able to stimulate the activity of the CMV-IE enhancer/promoter region. CMV infection of several cell lines leads to NF-kB activation. NF-kB binding sites are present in regulatory regions of various cellular and viral genes, including the IE enhancer region of CMV. In a reciprocal situation, CMV infection, most likely via gamma-interferon, leads to upregulation of MHC antigens in the transplant and, thereby, to increased transplant immunogenicity. Thus, a vicious circle is induced. We have investigated in detail the pathobiology of CMV and allograft vasculopathy (chronic rejection) in experimental animals, using aortic and cardiac allografts as well as a trachea model. The results may be summarized as follows: Infection of the recipient with rat CMV results in an early inflammatory response in the aortic and cardiac allograft vascular adventitia and intima (endothelialitis) and in the airway wall of tracheal allografts. This early inflammatory response leads to enhanced intimal thickness in aortic and cardiac allografts and enhanced luminal occlusion of tracheal allografts. Timewise, this coincides with early activation of intragraft inflammatory leukocytes and increased mRNA of various growth factors and cytokines. When the recipients receive gancyclovir, the enhanced intimal response in aortic and cardiac allografts and luminal occlusion in tracheal allografts is entirely abolished. Gancyclovir treatment dramatically reduces the inflammatory response in the allograft, and thereby growth factor synthesis in response to injury. However, gancyclovir does not prevent the expression of IE antigen of CMV, suggested to inactivate tumor suppressor protein p53 predisposing smooth muscle cells to increased growth. Taken together, the effect of CMV infection on cardiac allograft dysfunction is bidirectional and biphasic. The bidirectional nature emerges from the observations that acute CMV infection may accelerate acute rejection, and, on the other hand, acute alloimmune response-associated cytokine response may activate latent CMV infection. The biphasic effect of CMV on allograft dysfunction refers to its early and late detrimental effects, i.e. during the time of acute and chronic rejection. These two effects of CMV on allograft dysfunction emphasize the need for precise diagnosis of CMV infection in transplant recipients and pre-emptive or prophylactic anti-viral therapy. The benefits of this strategy may not be evident during the early post-transplant period, but 5-10 years after transplantation they manifest as better graft survival.

Local neovascularization and cellular composition within vulnerable regions of atherosclerotic plaques of human carotid arteries

An improved immunohistochemical method has been used to assess neovascularization within the vulnerable 'shoulder' regions of atherosclerotic plaques from carotid arteries. A combination of monoclonal antibodies (CD31, CD34, +/- von Willebrand factor) was shown to be far more effective than conventional techniques in demonstrating extensive vascularizations within the 'shoulder' and cap regions of late-stage plaques. Such sites were shown to be microfocal, often appearing as a plexus of both large and small vessels which occupied a significant proportion of the 'shoulder' area. These regions of marked neovascularization were commonly associated with accumulations of macrophages, mast cells, and T-cells, indicative of local inflammatory reactions. The matrix components elastin and collagen type VI showed variable distributions which suggested extensive tissue remodelling, whereas collagen type IV was recognized as a basement membrane protein of most blood vessels, as well as being associated with 'stellate' smooth muscle cells. Evidence of local microvascular damage within the shoulder regions of some specimens was demonstrated by extravascular red blood cells, macrophages containing haemosiderin, and perivascular fibrin deposition. These local haemorrhages derived from microvessels beneath the lining of the arterial lumen are a further indication of how the microfocal vascularization of the plaque 'shoulder' might contribute to further complications of inflammation and plaque destabilization in late-stage disease.

Emphysematous lesions, inflammation, and fibrosis in the lungs of transgenic mice overexpressing platelet-derived growth factor

Because of its expression pattern and its potent effects on mesenchymal cells, platelet-derived growth factor (PDGF) has been implicated as an important factor in epithelial-mesenchymal cell interactions during normal lung development and in the pathogenesis of fibrotic lung disease. To further explore the role of PDGF in these processes, we have developed transgenic mice that express the PDGF-B gene from the lung-specific surfactant protein C (SPC) promoter. Adult SPC-PDGFB transgenic mice exhibited lung pathology characterized by enlarged airspaces, inflammation, and fibrosis. Emphysematous changes frequently occurred throughout the lung, but inflammation and fibrotic lesions were usually confined to focal areas. The severity of this phenotype varied significantly among individual mice within the same SPC-PDGFB transgenic lineage. A pathology similar to that observed in adult mice was noted in lungs from transgenic mice as young as 1 week of age. Neonatal transgenic mice exhibited enlarged saccules and thickened primary septa. Results of these studies indicated that overexpression of PDGF-B induced distinct abnormalities in the developing and adult lung and led to a complex phenotype that encompassed aspects of both emphysema and fibrotic lung disease.

Prevention of cardiac allograft arteriosclerosis by protein tyrosine kinase inhibitor selective for platelet-derived growth factor receptor

BACKGROUND

Increased immunoreactivity of platelet-derived growth factor (PDGF)-AA, -Ralpha, and -Rbeta in intimal cells correlates with the development of cardiac allograft arteriosclerosis, a condition for which there is little or no current therapy. Therefore, we hypothesized that PDGF may have a rate-limiting role in the development of this disease.

METHODS AND RESULTS

The hypothesis was tested in a rat model of heterotopic cardiac and aortic allografts using dark agouti (AG-B4, RT1(a)) donors and Wistar-Furth (AG-B2, RT1(u)) recipients. The recipients received CGP 53716, a selective PDGF-R protein tyrosine kinase inhibitor, 50 mg. kg-1. d-1, or vehicle for 60 days. Cardiac allograft recipients also received background cyclosporin A immunosuppression. Our results demonstrate that CGP 53716 significantly reduced the incidence and intensity of arteriosclerotic lesions in rat cardiac and aortic allograft recipients. When rat coronary smooth muscle cells were stimulated in vitro with PDGF-AA or -BB in the presence of interleukin-1beta or tumor necrosis factor-alpha, CGP 53716 significantly inhibited only AA-ligand-induced but not BB-ligand-induced replication. Concomitantly, in quantitative reverse transcriptase-polymerase chain reaction, interleukin-1beta or tumor necrosis factor-alpha stimulation specifically upregulated the expression of PDGF-Ralpha mRNA but not of other ligand or receptor genes in cultured smooth muscle cells.

CONCLUSIONS

We conclude that a PDGF-AA/Ralpha-dependent cycle is induced in the generation of allograft arteriosclerosis that may be inhibited by blocking of signaling downstream of PDGF-R.

Chimera analysis reveals that fibroblasts and endothelial cells require platelet-derived growth factor receptorbeta expression for participation in reactive connective tissue formation in adults but not during development

The hypothesis that platelet-derived growth factor (PDGF) plays an important role in repair of connective tissue has been difficult to test experimentally, in part because the disruption of any of the PDGF ligand and receptor genes is embryonic lethal. We have developed a method that circumvents the embryonic lethality of the PDGF receptor (R)beta-/- genotype and minimizes the tendency of compensatory processes to mask the phenotype of gene disruption by comparing the behavior of wild-type and PDGFRbeta-/- cells within individual chimeric mice. This quantitative chimera analysis method has revealed that during development PDGFRbeta expression is important for all muscle lineages but not for fibroblast or endothelial lineages. Here we report that fibroblasts and endothelial cells, but not leukocytes, are dependent on PDGFRbeta expression during the formation of new connective tissue in and around sponges implanted under the skin. Even the 50% reduction in PDGFRbeta gene dosage in PDGFRbeta+/- cells reduces fibroblast and endothelial cell participation by 85%. These results demonstrate that the PDGFRbeta/PDGF B-chain system plays an important direct role in driving both fibroblast and endothelial cell participation in connective tissue repair, that cell behavior can be regulated by relatively small changes in PDGFRbeta expression, and that the functions served by PDGF in wound healing are different from the roles served during development.

Angiotensin II activates the proinflammatory transcription factor nuclear factor-kappaB in human monocytes

The renin-angiotensin system may contribute to the pathogenesis of atherosclerosis. A common feature of all stages of atherosclerosis is inflammation of the vessel wall. The transcription factor nuclear factor-kappaB (NF-kappaB) participates in most signaling pathways involved in inflammation. This study therefore examined the effect of angiotensin (ANG) II on NF-kappaB activation in monocytic cells, a major cellular component of human atheroma, by electrophoretic mobility shift assay. ANG II, like TNFalpha, caused rapid activation of NF-kappaB in human mononuclear cells isolated from peripheral blood by Ficoll density gradient. This ANG II effect was blocked by the angiotensin AT1 receptor antagonist losartan. Specificity of ANG II-induced NF-kappaB activation was ascertained by supershift and competition experiments. Moreover, ANG II stimulated NF-kappaB activation in human monocytes, but not in lymphocytes from the same preparation. Together, the data demonstrate the ability of the vasoactive peptide ANG II to activate inflammatory pathways in human monocytes.

The role of alpha and beta platelet-derived growth factor receptor in the vascular response to injury in nonhuman primates

Restenosis remains a significant clinical problem associated with mechanical interventional procedures for arterial revascularization or repair, including coronary angioplasty and stenting. Studies with rodents have established that platelet-derived growth factor (PDGF), a potent chemotactic and mitogenic agent for vascular smooth muscle cells, is a key mediator of lesion formation after vascular injury. To further explore this hypothesis in a more clinically relevant model, neutralizing monoclonal antibodies (mAbs) were used to examine the effect of selective inhibition of alpha or beta PDGF receptor (PDGFR) on neointima formation in nonhuman primates. Carotid arteries were injured by surgical endarterectomy and femoral arteries by balloon catheter dilatation. Immunostaining revealed that both injuries induced cell proliferation and the upregulation of beta PDGFR but not alpha PDGFR. By 7 days after injury, beta PDGFR staining was limited to the luminal region of the media, the small areas of neointima, and the adventitia. Nearly all bromodeoxyuridine-positive cells were found in these regions as well. After 30 days, a concentric neointima that stained strongly for beta PDGFR had formed in the carotid and femoral arteries. Treatment of baboons with anti-beta PDGFR mAb 2A1E2 for 6 days after injury reduced the carotid artery and femoral artery lesion sizes by 37% (P<0.05) and 48% (P<0.005), respectively, when measured at 30 days. Under the same conditions, treatment with anti-alpha PDGFR mAb 2H7C5 had no effect. These findings suggest that PDGF mediates neointima formation through the beta PDGFR, and that antagonism of this pathway may be a promising therapeutic strategy for reducing clinical restenosis.

NGF activates similar intracellular signaling pathways in vascular smooth muscle cells as PDGF-BB but elicits different biological responses

The signaling pathways that regulate smooth muscle cell migration and proliferation are incompletely understood. Smooth muscle cells express at least 3 families of receptor tyrosine kinases that mediate cell migration: platelet-derived growth factor (PDGF) receptors, the trk family of neurotrophin receptors, and insulin-like growth factor 1 receptor. The neurotrophin, nerve growth factor (NGF), and insulin-like growth factor 1 induce the migration but not the proliferation of smooth muscle cells, whereas PDGF-BB stimulates both responses. To determine whether distinct signaling pathways downstream of receptor tyrosine kinases specifically mediate smooth muscle cell migration or proliferation, the ligand-induced activation of different signaling pathways in smooth muscle cells was examined. NGF induces prolonged activation of the Shc/MAP kinase pathway and phospholipase Cgamma compared with PDGF-BB. The activation of phosphatidylinositol-3 kinase, however, was 10-fold greater in response to PDGF-BB compared with NGF. Insulin-like growth factor 1 activates only phosphatidylinositol-3 kinase. Pharmacological inhibitors of phosphatidylinositol-3 kinase, Wortmannin and LY294002, inhibit PDGF-BB and NGF-induced migration, whereas an inhibitor of MAP kinase kinase, PD98059, has no effect. Our results suggest that (1) different receptor tyrosine kinases use similar patterns of activation of signaling pathways to mediate distinct biological outcomes of cell migration and proliferation, (2) NGF activates signaling proteins in smooth muscle cells similar to those activated during NGF-induced neuronal differentiation, and (3) the combinatorial effects of different signaling pathways are important for the regulation of smooth muscle cell migration and proliferation. Further studies using mutant trk receptors will help to define the signal transduction pathways mediating NGF-induced smooth muscle cell migration.

The immediate early gene products of human cytomegalovirus increase vascular smooth muscle cell migration, proliferation, and expression of PDGF beta-receptor

Evidence suggests that human cytomegalovirus (HCMV) infection contributes to the development of atherosclerosis and restenosis. Because smooth muscle cell (SMC) proliferation and migration are crucial events of both processes, and because PDGF beta-receptor modulates SMC migration, we determined whether HCMV infection affects SMC proliferation, migration, and PDGF beta-receptor expression. We employed a SMC model in which HCMV infection leads to expression of only the immediate early (IE) HCMV gene products-HCMV infection of rat SMCs. We found that HCMV infection significantly (i) increased SMC proliferation (from 0.9 x 10(6) +/- 0.024 x 10(6) to 1.4 x 10(6) +/- 0.051 x 10(6) cells/well, p < 0.001); (ii) augmented SMC migration toward PDGF (from 64 +/- 37 to 116 +/- 51 cells/high power field; p < 0.01); and (iii) enhanced PDGF beta-receptor expression in a time-dependent fashion. We conclude that HCMV infection of rat SMCs increases SMC proliferation, migration, and PDGF beta-receptor expression. These findings identify further mechanisms by which CMV may contribute to the development of atherosclerosis and restenosis.

Prevention of neointimal formation by a serine protease inhibitor, FUT-175, after carotid balloon injury in rats

BACKGROUND AND PURPOSE

In vivo and vitro studies revealed the activation of thrombin and the complement system in vascular lesion formation during the process of atherosclerosis, along with pathological proliferation of smooth muscle cells. We examined the effect of the synthetic serine protease inhibitor FUT-175 (developed as a potent inhibitor of thrombin and the complement system) on vascular lesions using balloon dilatation-induced neointimal formation in the carotid artery of rats.

METHODS

Sprague-Dawley (SD) rats underwent balloon dilatation injury of the left carotid artery to induce neointimal formation. Three groups of these rats (n=8, each) were treated with daily intraperitoneal injections of 1 of the following doses of FUT-175: 0.5, 1.0, or 2.0 mg/d in 1 mL of saline for 7 consecutive days. The control group (n=8) was similarly treated with 1 mL of saline for 7 days. The injections were started immediately after balloon injury. Two weeks after the injury, the left carotid arteries were perfusion-fixed, and the areas of the neointimal and medial layer were analyzed under a microscope.

RESULTS

A morphometric analysis revealed that there were significant differences in the intima-media ratio between the 4 groups treated with vehicle (saline) or a low, medium, or high dose of FUT-175 (1.45+/-0.11, 1.08+/-0.06, 0.71+/-0.04, or 0.32+/-0.04, respectively). This suppression was achieved in a dose-dependent manner by the administration of FUT-175 after balloon injury. In the histological study, it was demonstrated that FUT-175 suppresses the production of platelet-derived growth factor (PDGF)-BB in the neointima and the medial smooth muscle cell layer.

CONCLUSIONS

After balloon injury activated proteases that were inhibited by FUT-175 were demonstrated to have an essential role in the development of the pathological thickening of the arterial wall.

PDGFbeta receptor blockade inhibits intimal hyperplasia in the baboon

BACKGROUND

We have evaluated the use of a mouse/human chimeric anti-platelet-derived growth factor-beta receptor antibody in combination with heparin to inhibit intimal hyperplasia in the saphenous artery of the baboon after balloon angioplasty.

METHODS AND RESULTS

The study evaluated lesion development in sequential injuries made 28 days apart. Each animal received control treatment after the first injury and antibody/heparin therapy after the second injury to the contralateral artery. The antibody was administered by bolus intravenous injections (10 mg/kg) on study days 1, 4, 8, 15, and 22 and heparin coadministered by continuous intravenous infusion at a dose of 0.13 mg/kg per hour. Morphometric analysis of tissue sections showed a 53% decrease in intimal area after antibody/heparin treatment (P=0.005), corresponding to a 40% decrease in the intima-to-media ratio (P=0.005). Smooth muscle cell proliferation in the injured wall, measured at both 4 and 29 days after balloon injury, were similar in the control and antibody/heparin-treated animals.

CONCLUSIONS

These data suggest that platelet-derived growth factor plays a key role in the development of intimal lesions at sites of acute vascular injury in the nonhuman primate.

Evidence for distinct signaling properties and biological responses induced by the PDGF receptor alpha and beta subtypes

Platelet-derived growth factor (PDGF) acts as a potent mitogen, chemoattractant and survival factor for mesenchymal cells. In addition to its importance in mammalian development, PDGF plays a critical role in physiological repair mechanisms and in the pathogenesis of various proliferative diseases. The biological effects of PDGF are initiated via two related receptor tyrosine kinases, termed alpha and betaPDGF receptors. Recent observations provide increasing evidence for distinct roles of the two PDGF receptor subtypes in both embryogenesis and disease formation. Moreover, characterization of the signal relay mechanisms indicates, that the alpha and betaPDGF receptors are not identical in their ability to bind intracellular effector molecules. Furthermore, the two PDGF receptors initiate overlapping, yet distinct signal transduction pathways. These differences may account for some of the variabilities in biological responses resulting from activation of these two receptors.

Lipid lowering promotes accumulation of mature smooth muscle cells expressing smooth muscle myosin heavy chain isoforms in rabbit atheroma

Smooth muscle cells (SMCs) in the atherosclerotic intima characteristically differ from those in the arterial media, for example, by reduced expression of SMC differentiation/maturation markers such as smooth muscle myosin heavy chain isoforms (SM1 and SM2). This study tested the hypothesis that lipid lowering promotes maturation of intimal SMCs in 33 rabbits subjected to balloon injury and cholesterol feeding (0.3%) for 4 months (Baseline group, n=15); some of which then were switched to a low-cholesterol diet for 8 months (Low group at 8 months, n=3) or 16 months (Low group at 16 months, n=10). The remaining rabbits continued to consume a high-cholesterol diet for 16 months (High group, n=5). We monitored SMC phenotype by expression of immunoreactive alpha-smooth muscle actin, SM1, and SM2. alpha-Actin is an early marker, and SM1 and SM2 are late markers for SMC differentiation/maturation. Only fully differentiated or mature SMCs express SM2. Data are reported as the percentage of the alpha-actin-positive intimal area occupied by smooth muscle myosin-positive SMCs determined by color image analysis of immunostained sections. Levels of SM1 and SM2, highly expressed by SMCs in the normal aortic media (n=5) decreased in the aortic intima of the Baseline and High groups, indicating a less mature phenotype. In contrast, SM1 and SM2 increased in the Low (16 months) group, indicating that intimal SMCs exhibit a more mature phenotype after lipid lowering. Electron microscopy also showed the presence of mature intimal SMCs with abundant myofilaments. Furthermore, lipid lowering reduced levels of platelet-derived growth factor-B in the arterial intima, a factor known to suppress smooth muscle myosin expression. These data demonstrate that lipid lowering favors accumulation of mature SMCs in the atherosclerotic intima in association with reduced levels of platelet-derived growth factor-B expression. Intimal SMCs in the Low group also displayed reduced expression of matrix metalloproteinases-3 and -9 compared with the Baseline and High groups. These findings shed new light on the effects of lipid lowering at the level of the vascular wall, which may influence the biology of the atheroma.

Platelet-derived growth factor B-chain expression in the rat retina and optic nerve: distribution and changes after transection of the optic nerve

To test the possible involvement of platelet-derived growth factor B-chain (PDGF-B) in anterograde and retrograde degenerations of the CNS neurons, we studied the changes of PDGF-B localization and its mRNA expression in the rat retina and optic nerve (ON) after unilateral ON transection, using immunohistochemistry and in situ hybridization. In the control retinas immunoreactivity for PDGF-B and its mRNA expression were localized in the retinal ganglion cells (RGCs) and the nerve fiber layer. After ON transection PDGF-B immunoreactivity in the nerve fiber layer started to decrease on post-injury day 3 or 4. Atrophic changes in the RGCs started on day 5 just after the decrease of PDGF expression, and thereafter the RGC number decreased. In the longitudinal section of the ON rostral to the transected site, swollen axons showed intense PDGF-B immunoreactivity and macrophages, and some glial cells revealed a significant increase in both immunoreactivity and hybridization signals. Based on these findings, we hypothesized that the decrease in PDGF-B in RGCs after axotomy causes the loss of RGCs, and that increased PDGF-B expression in the ON plays a role in the cascade of tissue reactions following ON transection.

Inhibition of chemotaxis in A7r5 rat smooth muscle cells by a novel panel of inhibitors

1. Arginine-specific ADP-ribosyltransferase (ART) activity has been implicated in white cell chemotaxis. In this study, we examined the capacity of a panel of structurally unrelated inhibitors and pseudosubstrates of ART to inhibit chemotaxis of A7r5 rat vascular smooth muscle cells in response to PDGF-BB. 2. The IC50 values for nicotinamide (12 mM) and novobiocin (165 microM) were similar to those observed for inhibition of chemotaxis by human polymorphonuclear neutrophil leucocytes (PMN), whereas vitamins K3 (IC50=22 microM) and K1 (IC50=95 microM) were less potent than previously described in PMNs. The pseudo-substrates for the enzyme (DEA-BAG, agmatine and arginine-methylester) also inhibited A7r5 chemotaxis, and in addition inhibited cell adhesion at similar concentrations. Vitamin K3 was unique among the inhibitors of ART, in that it also inhibited cell adhesion. 3. A rat ART1 transcript was amplified by rtPCR from rat skeletal muscle, and was noted to share 94% homology with the mouse ART1 cDNA sequence. No such transcript could be detected in A7r5 cells by Northern blot analysis or rtPCR. 4. Evidence for ART activity on the surface of A7r5 cells was investigated using 32P-NAD+ as substrate, and labelled membrane proteins were observed with MWt values of 116, 100, 90 and 70 kDa. Exposure of the labelled proteins to phosphodiesterase yielded 32P-AMP, and hydrolysis with NaOH yielded 32P-NAD+. These results indicated that the labelled proteins were adducts with NAD+, and not the products of ART activity. The absence of ART catalytic activity in A7r5 cells was confirmed in protocols designed to show ADP-ribosylation of agmatine. 5. We conclude that the chemotactic activity of A7r5 cells is independent of ART activity, and the mechanism whereby the novel panel of inhibitors reduced cell migration remains undefined.

Comparison of apolipoprotein and proteoglycan deposits in human coronary atherosclerotic plaques: colocalization of biglycan with apolipoproteins

BACKGROUND

Because the content of specific proteoglycans and apolipoproteins is increased in atherosclerotic plaques and in vitro studies have suggested a role for proteoglycans in mediating plaque apolipoprotein (apo) retention, immunohistochemistry was performed to systematically examine the relative locations of proteoglycans and apolipoproteins in human atherosclerosis.

METHODS AND RESULTS

The spatial relationships of versican, biglycan, and apoE were compared on 68 human coronary artery segments; apoA-I and apoB also were evaluated on an additional 20 segments. Nonatherosclerotic intima contained extensive deposits of versican, whereas deposits of apoE, apoB, and apoA-I were much less prevalent. In contrast, nearly all atherosclerotic segments contained substantial deposits of biglycan, apoE, apoA-I, and apoB. There was a high degree of colocalization of apoE and biglycan deposits. ApoA-I, the major apolipoprotein of HDL, and apoB also were detected in regions with apoE and biglycan deposition. Exceptions to the localization of biglycan with apolipoproteins were found in regions that lacked intact extracellular matrix because of necrosis or dense macrophage accumulation. In vitro studies demonstrated that biglycan binds apoE-containing but not apoE-free HDL and that biglycan also binds LDL.

CONCLUSIONS

These results suggest that biglycan may bind apoE and apoB in atherosclerotic intima. They also raise the possibility that apoE may act as a "bridging" molecule that traps apoA-I-containing HDL in atherosclerotic intima. Taken together, these findings are consistent with the hypothesis that biglycan may contribute to the pathogenesis of atherosclerosis by trapping lipoproteins in the artery wall.

A 340 kDa hyaluronic acid secreted by human vascular smooth muscle cells regulates their proliferation and migration

The formation of atherosclerotic lesions is characterized by invasion of vascular smooth muscle cells (VSMC) into the tunica intima of the arterial wall and subsequently by increased proliferation of VSMC, a process apparently restricted to the intimal layer of blood vessels. Both events are preceded by the pathological overexpression of several growth factors, such as platelet-derived growth factor (PDGF) which is a potent mitogen for VSMC and can induce their chemotaxis. PDGF is generally not expressed in the normal artery but it is upregulated in atherosclerotic lesions. We have previously shown that PDGF-BB specifically stimulates proliferating VSMC to secrete a 340 kDa hyaluronic acid (HA-340). Here, we present evidence regarding the biological functions of this glycan. We observed that HA-340 inhibited the PDGF-induced proliferation of human VSMC in a dose-dependent manner and enhanced the PDGF-dependent invasion of VSMC through a basement membrane barrier. These effects were abolished following treatment of HA-340 with hyaluronidase. The effect of HA-340 on the PDGF-dependent invasion of VSMC coincided with increased secretion of the 72-kDa type IV collagenase by VSMC and was completely blocked by GM6001, a hydroxamic acid inhibitor of matrix metalloproteinases. HA-340 did not exert any chemotactic potency, nor did it affect chemotaxis of VSMC along a PDGF gradient. In human atheromatic aortas, we found that HA-340 is expressed with a negative concentration gradient from the tunica media to the tunica intima and the atheromatic plaque. Our findings suggest that HA-340 may be linked to the pathogenesis of atherosclerosis, by modulating VSMC proliferation and invasion.

Expression of vascular adhesion molecules in saphenous vein coronary bypass grafts

BACKGROUND

Adhesion of blood elements to the endothelium is an important step in the development of vein graft disease. This study examines the expression of vascular adhesion molecules on explanted saphenous vein bypass grafts.

METHODS

Immunocytochemical staining was performed using explanted saphenous vein grafts from 28 patients. Antibodies against the endothelial markers CD31, von Willebrand factor, intercellular adhesion molecule-1, vascular adhesion molecule-1, and E-selectin were used.

RESULTS

Staining for CD31 and von Willebrand factor demonstrated the presence of endothelial cells in the lumen and the vasa vasorum. Expression of intercellular adhesion molecule-1 was variable between grafts, whereas vascular adhesion molecule-1 and E-selectin were almost always absent on the luminal endothelium. In contrast, the endothelium of the vasa vasorum stained positively for intercellular adhesion molecule-1 and vascular adhesion molecule-1, and was also seen on nonendothelial cells within the vessel wall. Expression of these adhesion molecules did not vary with the severity of vein graft disease.

CONCLUSIONS

This study highlights the blood vessels in the adventitia as possible sites for the adhesion and migration of cells into the vessel wall.

New approaches to the management of acute and chronic cardiac allograft rejection

There are still many problems to be faced in the field of heart transplantation. Acute and chronic rejection are still the major medical obstacles. In this review, we describe recent research in this field undertaken in our laboratory. The induced intercellular adhesion molecule-1 (ICAM-1) and MHC class II antigen resulting from rejection can be visualized in vivo by radioimmunoscintigraphy. This non-invasive method is sensitive for detecting early rejection and allows quantitative assessment of rejection. Short-term administration of monoclonal antibodies to ICAM-1 and leukocyte function-associated antigen-1 (LFA-1) results in an indefinite acceptance of cardiac allografts by induction of antigen-specific tolerance, as evidenced by acceptance of the secondary skin allografts. The characteristics and possible mechanisms of this tolerance induction are discussed. Immunohistopathologic features of graft coronary arteriopathy are shown. Adhesion molecules, cytokines, and growth factors are associated with intimal hyperplasia and phenotypic transformation of smooth muscle cells in the allograft coronary arteries. Dramatic reduction in this intimal hyperplasia was demonstrated by antisense gene therapy targeting cyclin-dependent kinase 2 kinase. We hope that these investigations will contribute to the improvement of the management of patients who undergo heart transplantation.

The advanced glycation endproduct pentosidine induces the expression of PDGF-B in human retinal pigment epithelial cells

Advanced glycation endproducts have been implicated in a number of diabetic and aging changes. Some of these effects occur in part through induction of cytokines such as platelet-derived growth factor (PDGF), which is expressed by the retinal pigment epithelium (RPE). In this study, cultures of RPE were evaluated for PDGF expression after treatment with pentosidine, a well characterized advanced glycation endproduct. Northern analysis provided evidence for the increased expression of a 3.7 kb PDGF-B transcript over unstimulated controls in the established ARPE-19 cell line. Western analysis demonstrated increased PDGF-BB protein in conditioned medium compared to controls of ARPE-19 cells. In addition, two different early passage cultures of RPE showed increased PDGF-BB protein after pentosidine treatment compared to unstimulated controls. The enhanced production of PDGF-BB could play a role in the maintenance of the RPE-Bruch's membrane complex and influence changes associated with diabetes and aging.

Tyrosine phosphorylation of platelet derived growth factor beta receptors in coronary artery lesions: implications for vascular remodelling after directional coronary atherectomy and unstable angina pectoris

BACKGROUND

Growth factors such as platelet derived growth factor (PDGF) have been postulated to be important mediators of neointimal proliferation observed in atherosclerotic plaques and restenotic lesions following coronary interventions. Binding of PDGF to its receptor results in intrinsic receptor tyrosine kinase activation and subsequent cellular migration, proliferation, and vascular contraction.

AIMS

To investigate whether the concentration of PDGF beta receptor tyrosine phosphorylation obtained from directional coronary atherectomy (DCA) samples correlate with atherosclerotic plaque burden, the ability of diseased vessels to remodel, coronary risk factors, and clinical events.

METHODS

DCA samples from 59 patients and 15 non-atherosclerotic left internal thoracic arteries (LITA) were analysed for PDGF beta receptor tyrosine phosphorylation content by receptor immunoprecipitation and antiphosphotyrosine western blot. The amount of PDGF beta receptor phosphorylation was analysed in relation to angiographic follow up data and clinical variables.

RESULTS

PDGF beta receptor tyrosine phosphorylation in the 59 DCA samples was greater than in the 15 non-atherosclerotic LITA (mean (SD) 0.84 (0.67) v 0.17 (0.08) over a control standard, p < 0.0001). As evaluated by stepwise regression analysis, incorporation of both PDGF beta receptor tyrosine phosphorylation and immediate gain correlated strongly (adjusted r2 = 0.579) with late loss, although PDGF beta receptor tyramine phosphorylation alone correlated poorly with late loss. Multivariate regression analysis of coronary risk factors and clinical events revealed unstable angina as the most significant correlate of PDGF beta receptor tyrosine phosphorylation (F value 20.009, p < 0.0001).

CONCLUSIONS

PDGF beta receptor tyrosine phosphorylation in atherosclerotic lesions is increased compared with non-atherosclerotic arterial tissues. The association of PDGF beta receptor tyrosine phosphorylation with immediate gain strongly correlates with vascular remodelling. PDGF beta receptor tyrosine phosphorylation correlates with unstable angina pectoris.

Platelet-derived growth factor, intimal hyperplasia, and ischemic complications in giant cell arteritis

OBJECTIVE

To explore whether vasoocclusion in giant cell (temporal) arteritis (GCA) is related to intimal hyperplasia and in situ production of platelet-derived growth factor (PDGF).

METHODS

Temporal artery biopsy specimens from patients with GCA were analyzed for the presence of intimal hyperplasia. Expression of PDGF-A and PDGF-B was assessed by immunohistochemistry and digitized image analysis.

RESULTS

PDGF-A and PDGF-B were widely expressed in inflamed arteries. CD68+ macrophages, smooth muscle cells, and multinucleated giant cells produced PDGF, whereas hyperplastic intimal tissue did not. Arteries with marked luminal narrowing and those with no or minimal luminal narrowing differed in the extent and distribution of PDGF expression. Concentric intimal hyperplasia was associated with the accumulation of PDGF-A- and PDGF-B-producing CD68+ macrophages at the media-intima junction. PDGF+,CD68+ macrophages in close proximity to the internal elastic lamina frequently coproduced matrix metalloproteinase 2. Intimal hyperplasia of the temporal artery correlated with ischemic complications of GCA, such as ocular involvement, jaw claudication, and aortic arch syndrome.

CONCLUSION

Production of PDGF has a role in arterial occlusion in GCA. The excessive fibroproliferative response leading to luminal narrowing can be distinguished from the stenosing process in atherosclerosis and postangioplasty restenosis, suggesting that there are different response patterns to arterial injury. In GCA, macrophages at the media-intima border are the dominant source of PDGF. Since vasoocclusion is associated with a number of serious complications in GCA, inhibition of intimal proliferation should be a major goal of treatment.

17beta-oestradiol enhances release of matrix metalloproteinase-2 from human vascular smooth muscle cells

Vascular remodelling occurs during all stages of atherosclerotic progression. Anti-atherosclerotic drugs may function by restoring regulation of the processes involved in remodelling of the extracellular matrix. A key group of enzymes involved in these processes are the matrix metalloproteinases (MMPs). Oestrogens have been demonstrated to possess anti-atherosclerotic properties at low concentrations while being associated with lesion formation at high concentrations. We examined the effect of 17beta-oestradiol on MMP-2 expression in human coronary artery (CAVSMC) and umbilical artery vascular smooth muscle cells (UAVSMC). MMP-2 expression was measured by chemiluminescent immunoblotting and quantified by laser densitometry. pro-MMP-2 was secreted by VSMCs and increasing levels of 17beta-oestradiol, from physiological through supraphysiological, were associated with significant dose-dependent increases in MMP-2 levels in culture media. This effect was dependent on de novo protein synthesis and could be antagonised by the oestrogen receptor antagonist, tamoxifen, and the specific receptor antagonist ICI 182, 780. 17beta-Oestradiol appears to be a specific stimulator of MMP-2 release from human vascular cells. The concentration dependence of this effect suggests a basis for the differential effects of low and high oestrogen levels on vascular integrity.

Induction of infarct tolerance by platelet-derived growth factor against reversible focal ischemia

Nerve growth factor, brain-derived neurotrophic factor, and other neurotrophic factors have been reported to have neuroprotective effects against global ischemia. To investigate whether the homodimer of platelet-derived growth factor B-chain (PDGF-BB) can protect neurons against focal temporary ischemia, PDGF-BB was administered to the rat brain for a prolonged period prior to, during, and after ischemia, since PDGF-BB protected rat neurons from global ischemia in our previous study. A total of 82 male Sprague-Dawley rats were used. Recombinant PDGF-BB, or saline was administered into the left neocortex via an implanted osmotic pump for 3 days (1.2 microg in total), 7 days (2 microgram or 4 microgram in total), or 14 days (4 microgram in total) pre-ischemia and 2 days post-ischemia. In an additional group, PDGF-BB (4 microgram in total) was administered for 14 days by osmotic pump and focal ischemia was induced after an additional 7-day interval following removal of the pump. Focal temporary ischemia was induced in the left MCA territory by bilateral CCA and MCA occlusion for 2 h. All rats were sacrificed 2 days after ischemia and the volume of cerebral infarct was analyzed using TTC staining. In a separate set of animals, regional cerebral blood flow (rCBF) was monitored by the hydrogen clearance method and laser Doppler flowmetry (LDF) of the neocortex after 14 days of intracerebral administration of PDGF-BB or saline. In the group receiving PDGF-BB (4 microgram in total) for 7 or 14 days pre-ischemia, there was a significant reduction of neocortical infarction compared to that in the control or saline-infused group. The size of cerebral infarct was smallest in the group that received PDGF-BB for 14 days, when ischemia was induced 7 days after removal of the pump. Regarding rCBF measurement, there were no significant differences in groups receiving PDGF-BB or saline infusion for 14 days. The potent neuroprotective effect of PDGF-BB on global ischemia was also demonstrated in the focal ischemia model. However, prolonged intracerebral infusion for 7 to 14 days was necessary to achieve a significant reduction of infarct volume. Neuroprotection was not due to increased collateral flow during ischemia.

Human monocyte-endothelial cell interaction induces platelet-derived growth factor expression

OBJECTIVE

The purpose of this study was to investigate whether the synthesis of platelet-derived growth factor (PDGF), a major mitogen and chemoattractant for vascular smooth muscle cells, was induced by the direct cell-to-cell interaction between human monocytes and umbilical vein endothelial cells (ECs).

METHODS

PDGF protein and mRNA expression were determined by cellular ELISA, immunohistochemical and Northern blot analyses.

RESULTS

Coculture of monocytes and ECs secreted a large amount of PDGF into the supernatant, whereas culture of ECs or monocytes alone induced low levels of PDGF production. In Northern blot analysis, substantial amounts of PDGF-A and -B mRNA were induced by coculture of monocytes with ECs. Immunohistochemistry revealed that PDGF-B chain protein was detectable in both ECs and monocytes. PDGF production by ECs induced by conditioned medium of the coculture was significantly inhibited by Abs against interleukin-1 beta (IL-1 beta) and tumor necrosis factor- alpha (TNF alpha).

CONCLUSIONS

These results indicate that the direct cell-to-cell interaction between human monocytes and ECs induces PDGF synthesis in both types of cells, suggesting that PDGF produced locally by monocyte-EC adhesive interaction plays an important role in the pathogenesis of atherosclerosis by promoting the migration and accumulation of vascular smooth muscle cells.

Induction of PDGF receptor-alpha in rat myofibroblasts during pulmonary fibrogenesis in vivo

Platelet-derived growth factor (PDGF) is a potent mitogen for mesenchymal cells. Induction of the PDGF receptor-alpha (PDGF-R alpha) in vitro enhances PDGF-induced mitogenesis and chemotaxis. Thus we investigated whether the PDGF-R alpha is induced in vivo during pulmonary fibrogenesis using a vanadium pentoxide (V2O5) model of lung injury. PDGF-R alpha mRNA expression was induced 24 h postinstillation. PDGF-R beta mRNA was constitutively expressed and did not increase. Western blotting showed upregulation of PDGF-R alpha protein by 48 h, and immunohistochemical analysis localized PDGF-R alpha primarily in mesenchymal cells residing within fibrotic lesions. Upregulation of PDGF-R alpha in vivo preceded mesenchymal cell hyperplasia (3-7 days) and collagen deposition by day 15. Supernatants from alveolar macrophages treated with V2O5 in vitro released upregulatory activity for PDGF-R alpha on cultured lung myofibroblasts, and this activity was blocked by the interleukin-1-receptor antagonist. These data suggest that interleukin-1 beta-mediated induction of PDGF-R alpha in vivo is important to lung myofibroblast hyperplasia during fibrogenesis.

Functional importance of platelet-derived growth factor (PDGF) receptor extracellular immunoglobulin-like domains. Identification of PDGF binding site and neutralizing monoclonal antibodies

The biological effects of platelet-derived growth factor (PDGF) are mediated by alpha- and beta-PDGF receptors (PDGFR), which have an intracellular tyrosine kinase domain and an extracellular region comprising five immunoglobulin-like domains (D1-D5). Using deletion mutagenesis we mapped the PDGF binding site in each PDGFR to the D2-D3 region. In the case of alpha-PDGFR, 125I-PDGF AA and 125I-PDGF BB bound to the full-length extracellular domain, D1-D5, and D2-D3 with equal affinity (Kd = 0.21-0.42 nM). Identical results were obtained for 125I-PDGF BB binding to beta-PDGFR mutants D1-D5 and D2-D3, establishing that D1, D4, and D5 do not contribute to PDGF binding. Monoclonal antibodies (mAb) directed against individual PDGFR Ig-like domains were used to extend these observations. The anti-D1 mAb 1E10E2 and anti-D5 mAb 2D4G10 had no effect on alpha- or beta-PDGFR function, respectively. In contrast, mAb 2H7C5 and 2A1E2 directed against D2 of the alpha- and beta-receptor, respectively, blocked PDGF binding, receptor autophosphorylation and mitogenic signaling with IC50 values of 0.1-3.0 nM. An anti-D4 mAb 1C7D5 blocked beta-receptor autophosphorylation and signaling without inhibiting PDGF binding consistent with the observation that D4 is essential for PDGFR dimerization (Omura, T., Heldin, C.-H., and Ostman, A. (1997) J. Biol. Chem. 272, 12676-12682). mAbs identified here act as potent PDGFR antagonists that can be used as research tools and potentially as therapeutic agents for the treatment of diseases involving unwanted PDGFR signaling.

Role of membrane-anchored heparin-binding epidermal growth factor-like growth factor and CD9 on macrophages

Heparin-binding epidermal-growth-factor-like growth factor (HB-EGF) is a potent mitogen for smooth-muscle cells (SMCs) belonging to the EGF family. We have previously determined that HB-EGF is expressed in macrophages and SMCs of human atherosclerotic lesions and that its membrane-anchored precursor, proHB-EGF, also has a juxtacrine mitogenic activity which is markedly enhanced by CD9, a surface marker of lymphohaemopoietic cells. Therefore, when both proHB-EGF and CD9 are expressed on macrophages, they may strongly promote the development of atherosclerosis. In the present study we have investigated the changes in proHB-EGF and CD9 in THP-1 cells during differentiation into macrophages and by the addition of oxidized low-density lipoproteins (OxLDL) and assessed juxtacrine growth activity of THP-1 macrophages for human aortic SMCs. HB-EGF and CD9 at both the mRNA and the protein level were up-regulated after differentiation into macrophages, and further expression of HB-EGF was induced by the addition of OxLDL or lysophosphatidylcholine. Juxtacrine induction by formalin-fixed growth was suppressed to control levels by an inhibitor of HB-EGF and was partially decreased by anti-CD9 antibodies. These results suggest that co-expression of proHB-EGF and CD9 on macrophages plays an important role in the development of atherosclerosis by a juxtacrine mechanism.

Calreticulin, a potential vascular regulatory protein, reduces intimal hyperplasia after arterial injury

Both thrombotic and inflammatory responses to arterial injury have been implicated in atherosclerotic plaque growth. Calreticulin is a ubiquitous calcium-binding protein with antithrombotic activity and, in addition, is associated with leukocyte activation. We are investigating calreticulin as a potential vascular regulatory protein. The development of intimal hyperplasia was studied at sites of balloon injury in iliofemoral arteries from 91 rats. Calreticulin was infused directly into the artery immediately before balloon injury, and plaque growth was then assessed at 4 weeks' follow-up. Parallel studies of the effects of each calreticulin domain as well as a related calcium-binding protein, calsequestrin, were examined. The effects of calreticulin on platelet activation, clot formation, and mononuclear cell migration were also studied. When infused before balloon injury in rat iliofemoral arteries, calreticulin, or its high-capacity Ca(2+)-binding C domain, significantly reduces plaque development, whereas calsequestrin, a related calcium-binding protein that lacks the multifunctional nature of calreticulin, does not decrease plaque area (saline: 0.037 +/- 0.007 mm2, calsequestrin: 0.042 +/- 0.021 mm2, calreticulin: 0.003 +/- 0.002 mm2, n = 46, P < .04). The N domain and more specifically the P domain, a low-capacity, high-affinity calcium-binding domain in calreticulin, do not reduce intimal hyperplasia (N + P domain: 0.038 +/- 0.012 mm2, C domain: 0.003 +/- 0.002 mm2, n = 45 rats, P < .0001). Calreticulin reduces macrophage and T cell staining in the arterial wall after injury but has no direct effect on monocyte migration in vitro (percent medial area staining positive for macrophage 24 hours after injury (N + P: 4.06 +/- 1.42, calreticulin: 0.273 +/- 0.02; n = 26, P < .009). Calreticulin does, however, reduce platelet-dependent whole blood clotting time, in vitro (baseline: 78.23 +/- 2.04 seconds, calreticulin: 113.5 +/- 1.95 seconds; n = 5, P < .002). We conclude that calreticulin significantly reduces intimal hyperplasia after arterial injury, potentially acting as a vascular regulatory protein.

Expression and localization of platelet-derived growth factor ligand and receptor protein during acute and chronic rejection of rat cardiac allografts

BACKGROUND

The molecular mechanisms of cardiac allograft vasculopathy (CAV) remain largely unknown. Using rat cardiac allografts, we examined by immunohistochemistry the expression and localization of platelet-derived growth factor ligand (PDGF-AA and -BB) and receptor (R alpha and R beta) proteins during acute and chronic rejection.

METHODS AND RESULTS

In acute rejection, a prominent induction of both PDGF ligand and receptor proteins occurred in the interstitial mononuclear inflammatory cells (P<.05), most of which were ED1-immunoreactive. PDGF-R beta was also induced in the capillary endothelium (P<.01). In cardiac allografts with severe intimal thickening, PDGF-AA expression was localized to the media and intima, whereas PDGF-BB expression was less prominent and was detected mainly in interstitial ED1-immunoreactive inflammatory cells. Double staining revealed that intimal cells expressing PDGF-AA were alpha-smooth muscle actin-positive but also alpha-smooth muscle actin-negative myofibroblast-like cells and to a lesser extent, ED1-immunoreactive cells. Both PDGF-R alpha and -R beta expression occurred in intimal, arterial endothelial, and interstitial mononuclear inflammatory cells. High-dose cyclosporin A (CsA) treatment significantly reduced both PDGF-AA and PDGF-R alpha expression in intimal cells. Furthermore, linear regression analysis revealed that PDGF-AA, PDGF-R alpha, and PDGF-R beta expression in intimal cells and PDGF-BB expression in interstitial mononuclear inflammatory cells correlated with intimal thickening.

CONCLUSIONS

Alloimmune injury induces the expression of PDGF ligands, especially of PDGF-AA, in the graft vasculature and sufficient immunosuppression with CsA suppresses the expression of PDGF and inhibits the development of CAV. PDGF may have a substantial role in the regulation of smooth muscle cell migration and proliferation in an autocrine or paracrine manner during the development of CAV.

Ligation of CD40 activates interleukin 1beta-converting enzyme (caspase-1) activity in vascular smooth muscle and endothelial cells and promotes elaboration of active interleukin 1beta

Inflammation contributes to a variety of arterial diseases including atherosclerosis. Interleukin 1beta (IL-1beta) in its activated mature 17-kDa form may mediate aspects of vascular inflammation. As shown previously, human vascular wall cells, such as smooth muscle cells (SMC), express the IL-1beta precursor upon stimulation and the IL-1beta-converting enzyme (ICE) constitutively but do not produce mature IL-1beta or express ICE activity. How SMC, the most numerous cell type in arteries, may release active IL-1beta has therefore remained a perplexing problem. We report here that stimulation of human vascular SMC and endothelial cells (EC) through CD40 ligand, a mediator recently localized in human atheroma, induced elaboration of the IL-1beta precursor as well as activation of cell-associated ICE. In addition to the constitutively expressed 45- and 30-kDa immunoreactive ICE proteins, vascular cells incubated with recombinant human CD40 ligand (rCD40L) (but not IL-1 or TNF) showed an increase of a 20-kDa immunoreactive ICE protein by Western blot analysis. Furthermore, SMC and EC stimulated through rCD40L processed recombinant human IL-1beta precursor (pIL-1beta), generating a cleavage product of approximately 17 kDa. Appearance of both the 20-kDa immunoreactive ICE protein and pIL-1beta processing activity required at least 6 h of stimulation with 0.3 or 1.0 microg/ml rCD40L, respectively, and was inhibited by pre-incubation of the ligand with an anti-CD40L antibody. Stimulation of vascular SMC and EC through rCD40L resulted in the release of biologically active IL-1beta, indicating processing of the native IL-1beta precursor induced by the ligand. These findings establish a novel mechanism of IL-1beta activation in human vascular cells and, moreover, indicate a new pathway of ICE-activation, which could participate in inflammatory aspects of atherogenesis and other disease states.

Rapid activation of PDGF-A and -B expression at sites of lung injury in asbestos-exposed rats

The development of interstitial pulmonary fibrosis is associated with a variety of inflammatory mediators, including peptide growth factors and cytokines. In the work presented here, we have asked whether or not platelet-derived growth factor (PDGF)-A and -B genes and proteins are expressed in anatomic and temporal patterns consistent with this factor playing a role in the disease process. Using an established rat model of asbestos-induced fibroproliferative lung disease, we demonstrate elevated levels of PDGF-A and -B mRNAs in total lung RNA immediately after a single 5-h exposure to approximately 1,000 fibers/ml of chrysotile asbestos. In situ hybridization revealed the PDGF-A and -B in RNAs primarily in macrophages and bronchiolar-alveolar epithelial cells at sites of initial fiber deposition and lung injury. There was clear evidence of PDGF-A and -B mRNAs in interstitial cells as well. The pattern of in situ hybridization was entirely consistent with the appearance (established by immunohistochemistry) of PDGF-A and -B proteins by 24 h post-exposure in the same cell types. Both mRNAs and proteins remained detectable at the fiber deposition sites for almost 2 wk post-exposures. These findings are consistent with our previous studies showing increased mesenchymal cell proliferation and fibroproliferative lesions that progress at the sites where PDGF-A and -B are expressed. Although it is clear that multiple growth factors are produced simultaneously at sites of initial injury, we suggest that the PDGF isoforms could be playing a central role in the disease process based upon their potent mitogenic effects upon mesenchymal cells.

Anti-VLA-4 antibody reduces intimal hyperplasia in the endarterectomized carotid artery in nonhuman primates

PURPOSE

Recently, very late antigen-4 (VLA-4) has been shown to mediate initial monocyte adhesion and migration to the injured artery. We hypothesized that blocking monocyte adhesion using a specific monoclonal antibody against VLA-4 may reduce intimal hyperplasia.

METHODS

Bilateral carotid endarterectomies were performed in eight adult baboons. Among them, five animals received an intravenous bolus injection of anti-VLA-4 antibody (3 mg/kg) during surgery and again after 2 weeks. Three animals underwent bilateral carotid endarterectomies and served as untreated control subjects. Specimens were harvested at 4 weeks and subjected to morphometric analysis, cell proliferation assay, and immunostaining for macrophages.

RESULTS

All of the endarterectomized arteries were patent except for one in the treated group. The number of macrophages in the intimal tissues was significantly reduced in the treated arteries compared with that in the control vessels (15.78 +/- 3.05 cells/section versus 33.50 +/- 6.13 cells/section; p < 0.001). The cell proliferation rate was significantly lower (p < 0.001) in the treated vessels (2.88% +/- 1.07%) compared with the control vessels (4.89% +/- 0.77%). The intimal area at the endarterectomized sites of carotid arteries was significantly less (p < 0.05) in the group treated with the anti-VLA-4 antibody (1.10 +/- 0.68 mm2) than in the control group (2.00 +/- 0.52 mm2).

CONCLUSION

These data show that blocking monocyte adhesion by use of an anti-VLA-4 antibody significantly reduces the number of intimal macrophages, intimal cell proliferation, and intimal hyperplasia in injured carotid arteries in baboons. This study supports a central role for macrophages in the development of intimal hyperplasia and may suggest a new therapeutic strategy to prevent clinical restenosis.

Aortic endothelial cells regulate proliferation of human monocytes in vitro via a mechanism synergistic with macrophage colony-stimulating factor. Convergence at the cyclin E/p27(Kip1) regulatory checkpoint

Monocyte-derived macrophages (Mphis) are pivotal participants in the pathogenesis of atherosclerosis. Evidence from both animal and human plaques indicates that local proliferation may contribute to accumulation of lesion Mphis, and the major Mphi growth factor, macrophage colony stimulating factor (MCSF), is present in atherosclerotic plaques. However, most in vitro studies have failed to demonstrate that human monocytes/Mphis possess significant proliferative capacity. We now report that, although human monocytes cultured in isolation showed only limited MCSF-induced proliferation, monocytes cocultured with aortic endothelial cells at identical MCSF concentrations underwent enhanced (up to 40-fold) and prolonged (21 d) proliferation. In contrast with monocytes in isolation, this was optimal at low seeding densities, required endothelial cell contact, and could not be reproduced by coculture with smooth muscle cells. Intimal Mphi isolated from human aortas likewise showed endothelial cell contact-dependent, MCSF-induced proliferation. Consistent with a two-signal mechanism governing Mphi proliferation, the cell cycle regulatory protein, cyclin E, was rapidly upregulated by endothelial cell contact in an MCSFindependent fashion, but MCSF was required for successful downregulation of the cell cycle inhibitory protein p27(Kip1) before cell cycling. Thus endothelial cells and MCSF differentially and synergistically regulate two Mphi genes critical for progression through the cell cycle.

The role of Fas/APO 1 and apoptosis in the development of human atherosclerotic lesions

The possibility that Fas/APO 1 is involved in the apoptosis of advanced human coronary atherosclerosis was examined in the present study. Coronary arteries with atherosclerosis were obtained from human hearts with chronic ischemic heart disease at cardiac transplantation. Normal vessels were used as controls. Fas/APO 1 was detected by immunohistochemistry with a monoclonal antibody. Apoptotic cells were stained in situ by terminal deoxynucleotidyl transferase mediated-dUTP nick end labeling (TUNEL) and DNA fragmentation into oligonucleosomes was checked by gel electrophoresis. Bcl-2, an antiapoptotic oncoprotein, was detected by immunohistochemistry and Western blot. Apoptotic cells were present in the neointima in all stages of atherosclerosis, and in intraplaque small vessels. In initial lesions, only a few cells were undergoing apoptosis. By contrast, in advanced lesions, many cells were found to undergo apoptosis. Apoptosis was further confirmed by genomic DNA analysis using gel electrophoresis. Apoptotic cells were either smooth muscle cells or macrophages, but also endothelial and blood borne cells. Fas/APO 1 was present in foam cells. Most of the Fas/APO 1 positive cells were stained for the macrophage marker CD68 and for alpha-smooth muscle actin in serial sections. Several anti-Fas/APO 1 positive foam cells were revealed to undergo apoptosis by double staining. Bcl-2 was detected in Fas/APO 1 expressing plaques. A number of CD3-positive T-lymphocytes were found around foam cells expressing Fas/APO 1. This data suggests that Fas/APO 1 regulated apoptosis is involved in the development of advanced human atherosclerotic lesions and that it probably determines the amount of tissue mass in the diseased vessels.

Platelet-derived growth factor: a key regulator of connective tissue cells in embryogenesis and pathogenesis

Studies of PDGF-A, PDGF-B and PDGF receptor-beta knock-out mice have revealed critical functions for the PDGF-PDGF receptor signaling systems in the ontogeny of connective tissue cells: the mesangial cells of kidney glomeruli and the alveolar smooth muscle cells (SMC) of the lung. The phenotypes of the PDGF mutant mice have also shed light on the identity and functions of these cell types, as well as revealed analogies suggesting that common morphogenetic principles have evolved for use in different organs, involving related growth factors and cell types. Although the lethality of PDGF knock-out mice has not allowed an investigation of the role of PDGF in SMC of the vessel wall, regulation of PDGF and its receptors in adult vessels following injury is consistent with a role for PDGF in the fibroproliferative response in the intima that occurs as part of the pathogenesis of atherosclerosis. PDGF modulation of connective tissue synthesis may thus be critical to connective tissue phenotype and proliferation in both embryogenesis and pathogenesis.