Distinct patterns of expression of fibroblast growth factors and their receptors in human atheroma and nonatherosclerotic arteries. Association of acidic FGF with plaque microvessels and macrophages

Induction of macrophage VEGF in response to oxidized LDL and VEGF accumulation in human atherosclerotic lesions

The interaction between macrophages and oxidatively modified low density lipoprotein (Ox-LDL) appears to play a central role in the development of atherosclerosis, not only through foam cell formation but also via the induction of numerous cytokines and growth factors. The current study demonstrated that Ox-LDL upregulated vascular endothelial growth factor (VEGF) mRNA expression in RAW 264 cells, a monocytic cell line, in a time- and concentration-dependent manner and that Ox-LDL stimulated VEGF protein secretion from the cells. Lysophosphatidylcholine, a component of Ox-LDL, also enhanced VEGF mRNA expression in RAW 264 cells and VEGF secretion from RAW 264 cells, with a maximal effect at a concentration of 10 micromol/L lysophosphatidylcholine. Immunohistochemical studies showed that human early atherosclerotic lesions exhibited intense VEGF immunoreactivity in subendothelial macrophage-rich regions of the thickened intima. In atherosclerotic plaques, VEGF staining was also observed in foam cell-rich regions adjacent to the lipid core or the neovascularized basal regions of plaque consisting predominantly of smooth muscle cells. High-power-field observation revealed that VEGF was localized in the extracellular space as well as at the macrophage cell surface. These observations suggest the possible involvement of Ox-LDL in the development of human atherosclerosis through VEGF induction in macrophages.

A functional fibroblast growth factor-1 immunoglobulin fusion protein

Proteins of the fibroblast growth factor (FGF) family play diverse roles in embryonic development, angiogenesis, and wound healing. The most well studied targets of FGF activity typically are cells of mesodermal and neuroectodermal origin; in addition, expression of FGF-1 (acidic FGF) is increased at several sites of chronic immunologic injury, and recent studies show that FGF-1 also may interact with cells of the immune system. In some human T cells, FGF-1 can induce signals necessary for production of interleukin-2, a key cytokine required for T cell proliferation. To better characterize the interaction of FGF-1 with FGF receptors on T cells, a fusion protein was constructed containing a portion of the constant region of human IgG1 (Fc) at the amino terminus of FGF-1. The Fc-FGF-1 fusion protein retained FGF function as determined by stimulation of tyrosine phosphorylation and DNA synthesis in NIH 3T3 cells. Binding of the intact fusion protein to FGF receptor 1 (FGFR1) on T cells was demonstrated by immunoprecipitation of the receptor bound to Fc-FGF-1 and by flow cytometry showing binding of fusion protein to T cells expressing FGFR1. This functional Fc-FGF-1 protein should prove useful in identifying FGFR-expressing cells.

A human gene encodes a putative G protein-coupled receptor highly expressed in the central nervous system

The mammalian bombesin (Bn)-like neuropeptide receptors gastrin-releasing peptide receptor (GRP-R) and neuromedin B receptor (NMB-R) transduce a variety of physiological signals that regulate secretion, growth, muscle contraction, chemotaxis and neuromodulation. We have used reverse transcription-polymerase chain reaction (PCR) to isolate a cDNA from human brain mRNA, GPCR/CNS, that encodes a putative G protein-coupled receptor (GPCR) based upon the presence of the paradigmatic seven heptahelical transmembrane domains in its predicted amino acid sequence. Analysis of the deduced protein sequence of GPCR/CNS reveals this putative receptor to be 98% identical to the deduced amino acid sequence of a recently reported gene product and minimally identical (approximately 23%) to both murine GRP-R and human endothelin-B (ET-B) receptor. Our deduced protein sequence differs at 12 positions, scattered throughout the open reading frame, relative to the original sequence. A 3.7 kb GPCR/CNS mRNA species is expressed in vivo in a tissue-specific manner, with highest levels detected in brain and spinal cord, lower levels found in testis, placenta and liver, but no detectable expression observed in any other tissue. Analysis of GPCR/CNS genomic clones reveals that the human gene contains one intron that is about 21 kb in length that divides the coding region into two exons and maps to human chromosome 7q31. No specific binding is observed with either a newly identified ligand (DTyr6, beta Ala11, Phe13, Nle14]Bn-(6-14)) having high affinity for all Bn receptor subtypes or Bn after GPCR/CNS is stably expressed in fibroblasts. No elevation in inositol trisphosphate is observed after the application of micromolar levels of either DPhe6, beta Ala11, Phe13, Nle14]Bn-(6-14) or Bn, a concentration of agonist known to activate all four known Bn receptor subtypes. When GPCR/CNS is expressed in Xenopus oocytes, no activation of the calcium-dependent chloride channel is detected despite the addition of micromolar levels of Bn peptide agonists. We conclude that the natural ligand for this receptor is none of the known naturally occurring Bn-like peptides and the true agonist for GPCR/CNS remains to be elucidated.

Differential expression of the keratinocyte growth factor (KGF) and KGF receptor genes in human vascular smooth muscle cells and arteries

Keratinocyte growth factor (KGF) is a secreted member of the fibroblast growth factor (FGF) family of heparin-binding proteins. Studies reported to date indicate that it functions primarily as an important paracrine mediator of epithelial cell growth and differentiation. KGF appears to act via binding to a specific FGF receptor-2 isoform generated by an alternative splicing mechanism. To determine whether KGF may play a role in vascular smooth muscle cell (SMC) biology, we investigated KGF and KGF receptor gene expression in human SMC cultured in vitro as well as in several human nonatherosclerotic artery and atheroma specimens. KGF mRNA but not KGF receptor mRNA was expressed by SMCs, as determined by Northern blot hybridization analysis or reverse transcription-polymerase chain reaction assays, respectively. Additional experiments demonstrated that 1) human SMCs produce and secrete mitogenically active KGF and that 2) the cytokine interleukin-1 increases KGF mRNA and protein levels in human SMCs. We also found that KGF transcripts but not KGF receptor transcripts were expressed in control and atherosclerotic human arteries. Taken together, these results indicate that KGF is unlikely to be involved in SMC growth regulation unless it can function intracellularly or interact with a presently unidentified KGF receptor.

Basic fibroblast growth factor (bFGF) regulates the expression of the CC chemokine monocyte chemoattractant protein-1 (MCP-1) in autocrine-activated endothelial cells

The CC chemokine monocyte chemoattractant protein (MCP)-1 is induced by inflammatory cytokines and acts as a potent regulator of monocyte trafficking. Monocytes adhere preferentially to migrating endothelial cells in vitro and to endothelial cells at the migration front in vivo after aortic balloon denudation injury. Based on these findings, we analyzed MCP-1 expression in migrating and resting bovine aortic endothelial (BAE) cells and identified prominently upregulated levels of MCP-1 expression in migrating BAE cells. Stimulation of resting BAE cells with 5 ng/mL bFGF resulted in a fourfold induction of MCP-1 mRNA expression. The time course of bFGF-induced MCP-1 mRNA expression indicated a rapid and direct stimulation of MCP-1 expression that was detectable 30 minutes after stimulation. Levels of basal MCP-1 expression, as well as upregulated levels of MCP-1 in migrating BAE cells, were downregulated by addition of a neutralizing anti-bFGF monoclonal antibody (1.0 microgram/mL). Digestion of conditioned media of resting BAE cells with collagenase led to a dose-dependent induction of MCP-1 expression in resting BAE cells, which was inhibited > 50% by addition of neutralizing anti-bFGF antibody. Confirmation of the Northern blot experiments by ELISA-based quantitation of MCP-1 protein levels identified threefold to sixfold higher levels of MCP-1 in the supernatants of bFGF-stimulated BAE cells than in unstimulated resting BAE cells. Finally, analysis of MCP-1 expression by in situ hybridization carried out on en face preparations of aortas demonstrated that MCP-1 expression is dramatically upregulated in regenerating endothelial cells in vivo after balloon denudation. Though not establishing a direct causal relation between the preferential adhesion of monocytes to migrating endothelial cells, these findings strongly suggest that autocrine-activated endothelial cell-derived MCP-1 may play a critical role in recruiting monocytes. They furthermore support the concept that bFGF acts as an autocrine regulator of endothelial cell activity and may imply an involvement of bFGF as a mediator of inflammatory cell trafficking.

Reciprocal relation between VEGF and NO in the regulation of endothelial integrity

Balloon angioplasty disrupts the protective endothelial lining of the arterial wall, rendering arteries susceptible to thrombosis and intimal thickening. We show here that vascular endothelial growth factor (VEGF), an endothelial cell mitogen, is upregulated in medial smooth muscle cells of the arterial wall in response to balloon injury. Both protein kinase C (PKC) and tyrosine kinase pp60src mediate augmented VEGF expression. In contrast, nitric oxide (NO) donors inhibit PKC-induced VEGF upregulation by interfering with binding of the transcription factor activator protein-1 (AP-1) to the VEGF promoter. Inhibition of VEGF promoter activation suggests that NO secreted by a restored endothelium functions as the negative feedback mechanism that downregulates VEGF expression to basal levels. Administration of a neutralizing VEGF antibody impaired reendothelialization following balloon injury performed in vivo. These findings establish a reciprocal relation between VEGF and NO in the endogenous regulation of endothelial integrity following arterial injury.

FGF-1-induced platelet-derived growth factor-A chain gene expression in endothelial cells involves transcriptional activation by early growth response factor-1

Fibroblast growth factor-1 (FGF-1), a prototype member of the heparin-binding growth factor family, is a potent mitogen for vascular endothelial cells and a variety of other cell types. FGF-1 can induce the expression of the platelet-derived growth factor-A chain (PDGF-A) gene in endothelial cells; however, the underlying transcriptional mechanisms are not known. We used serial 5' deletion and transient transfection analysis of the human PDGF-A promoter to demonstrate that a 16-bp element, located 55 to 71 bp upstream of the transcriptional start site, is required for FGF-1-inducible promoter-dependent expression. This region contains nucleotide recognition elements for the early growth response gene product, early growth response factor-1 (Egr-1), and the related zinc-finger transcription factor, Sp1. Reverse-transcription polymerase chain reaction revealed that FGF-1 induced Egr-1 mRNA expression within 30 minutes. Electrophoretic mobility shift, supershift, and Western blot analysis demonstrated that Egr-1 protein accumulated in the nuclei of endothelial cells exposed to the growth factor, whereas levels of Sp1 did not change. Egr-1 bound to the FGF-1 response element in the proximal PDGF-A promoter in a specific and time-dependent manner. These findings indicate that Egr-1 plays a key regulatory role in FGF-1-inducible endothelial PDGF-A expression and implicate this transcription factor in pathological settings in which these mitogens are both expressed.

Fibroblast growth factor-1 induction of delayed-early mRNA expression in NIH 3T3 cells is prolonged by heparin addition

Fibroblast growth factor (FGF)-1, also known as acidic FGF, is a multifunctional heparin-binding protein that is mitogenic for a wide variety of cell types cultured in vitro and a potent angiogenic agent in vivo. These cellular responses are mediated via high-affinity binding to a family of four membrane-spanning tyrosine kinase receptors. FGF-1-stimulated mitogenesis is potentiated by heparin, a sulfated glycosaminoglycan. In this study, we examined the effect of exogenous heparin on FGF-1-inducible gene expression in murine NIH 3T3 cells using both wild-type FGF-1 and FGF-1/glu132, an FGF-1 mutant with a reduced apparent affinity for heparin. The induction levels and temporal expression kinetics of two immediate-early response mRNAs (early growth response gene-1, thrombospondin-1) as well as two delayed-early response mRNAs (proliferin, ornithine decarboxylase) were monitored by Northern blot hybridization analysis. We found that although FGF-1 alone can promote the initial induction of these four mRNAs, heparin coaddition is necessary for prolonged delayed-early mRNA expression. This heparin effect occurs when cells are stimulated with wild-type FGF-1 but not with FGF-1/glu132. Furthermore, FGF-1 and heparin must be added together at the initial time of mitogen stimulation and they must remain present in the cell culture medium for a minimum period of 8 h to promote sustained delayed-early mRNA expression. These findings are consistent with the proposal that heparin promotes a long-term FGF-1:FGFR interaction which is required for sustained delayed-early gene expression and a full mitogenic response.

Inhibitory effects of hypercholesterolemia and ox-LDL on angiogenesis-like endothelial growth in rabbit aortic explants. Essential role of basic fibroblast growth factor

Hypercholesterolemic (HC) rabbits exhibit suppressed compensatory vascular growth after restriction of arterial supply. However, neovascularization is commonly found in atheromas containing inflammatory cells. We used an in vitro model to determine the effects of hypercholesterolemia on angiogenesis in the absence or presence of inflammatory cells. HC rabbit aortic explants (1 mm2) with or without (n = 90 each) lesion-forming inflammatory cells were cultured in a collagen matrix with serum-free medium. Explant-derived endothelial cell growth was organized into capillary-like microtubes (CLM) that could be videomicroscopically quantified. CLM growth from lesion-free HC explants was significantly reduced to 13 +/- 4% of the value in explants (n = 90) from normocholesterolemic (NC, n = 15) rabbits (P < .001). In contrast, in lesion-containing HC explants, the matrix was invaded by foam cells, and CLM growth was not inhibited. Immunoassayable basic fibroblast growth factor (bFGF, in pg/mL) in the culture medium was significantly lower in lesion-free HC (< 5) than NC explants (11 +/- 2, P < .01) or HC explants with lesions (14 +/- 3). In addition, CLM growth was reduced in NC explants incubated with oxidized LDL (ox-LDL, 50-100 micrograms/mL). Exogenous bFGF (10 ng/mL) reversed the inhibitory effects of hypercholesterolemia and ox-LDL, whereas bFGF-neutralizing antibody (10 micrograms/mL) abolished CLM growth in all groups. In cultured rabbit aortic endothelial cells, ox-LDL reduced DNA synthesis, but this inhibition was reversed by bFGF. We conclude that hypercholesterolemia and ox-LDL inhibit angiogenesis like endothelial growth because of a suppressed availability of endogenous bFGF. Retained responsiveness to exogenous bFGF suggests that inducing bFGF expression at targeted sites may improve collateral growth in hyperlipidemic arterial disease.

Serum basic fibroblast growth factor levels in patients with ischemic heart disease

BACKGROUND

Being a potent promoter of endothelial and smooth muscle cell proliferation, basic fibroblast growth factor (bFGF) is presumed to play a key role in coronary collateral development and atherogenesis.

PURPOSE

To characterize serum bFGF levels in patients with ischemic heart disease.

METHODS

The study population consisted of patients with angina (n=33) and after uncomplicated myocardial infarction (n=12). The number of significantly stenosed (> or = 50%) vessels and angiographic coronary collateral score were noted. Blood was drawn immediately prior to elective coronary angiography in study patients for bFGF levels. Twenty healthy, age-matched subjects served as control for serum bFGF.

RESULTS

Serum bFGF levels were undetectable in all 20 control subjects, but were detectable in 15/33 (45%) patients with angina and 3/12 (25%) post-infarction patients, respectively (P=0.002). Serum bFGF levels were detectable in 13/23 (57%) patients with 0- or 1-vessel disease, as compared with 5/22 (23%) patients with 2- or 3-vessel disease (P<0.05). Detectable serum bFGF levels were not in correlation with coronary collateral score (P=1).

CONCLUSIONS

Serum levels of bFGF are elevated in patients with ischemic heart disease, particularly in those with minimal coronary artery disease. We postulate that detectable serum bFGF levels reflect active atherogenesis rather than myocardial collateral development.

Immunolocalization of acidic fibroblast growth factor and receptors in the tubulointerstitial compartment of chronically rejected human renal allografts

Tubular damage and loss associated with interstitial inflammation and fibrosis may be the most important determinants in chronic renal allograft rejection. To elucidate potential pathophysiologic mechanisms associated with tubulointerstitial lesions, we examined the expression of a fibrogenic cytokine, acidic fibroblast growth factor (FGF-1) and its high-affinity receptors, in both relevant renal transplant controls (n=5) and tissue from patients (n=19) who underwent nephrectomy after graft loss, secondary to chronic rejection. In situ hybridization and immunohistochemical analyses demonstrated minimal expression of FGF-1 mRNA and protein in the tubulointerstitial compartment of the normal human kidney. In contrast, tubulointerstitial lesions in kidney allografts experiencing chronic rejection demonstrated the exaggerated appearance of both FGF-1 protein and mRNA in resident inflammatory and tubular epithelial cells. Patterns of staining were consistent throughout tubular compartments and did not appear to be localized to any particular region. The tubulointerstitium in kidneys with findings of chronic rejection also exhibited increased immunodetection of proliferating cell nuclear antigen in the tubular epithelium, inflammatory cell infiltrate, and neovascular structures. The enhanced appearance of FGF-1 and readily detectable fibroblast growth factor receptors suggests that this polypeptide mitogen may serve as an important mediator of growth and repair responses, associated with development of angiogenesis and tubulointerstitial lesions during chronic rejection of human renal allografts.

Oxidized LDL mediates the release of fibroblast growth factor-1

Fibroblast growth factor-1 (FGF-1) and lipoproteins play an important role in atherogenesis. In the present study, we explored a possible mechanism by which abnormal lipid metabolism could be linked to the proliferative aspects of the disease. We tested oxidized LDL (oxLDL) as a possible pathophysiological mediator of the release of FGF-1, using FGF-1-transfected mouse NIH 3T3 cells and FGF-1-transfected rabbit smooth muscle cells, and compared it with the release caused by elevated temperature. Immunoblot analysis showed that oxLDL induced the release of FGF-1 in a concentration-dependent manner from 10 to 100 micrograms/mL. The effect correlated with the extent of oxidative modification of LDL and was maximal within 4 hours of exposure of cells to oxLDL. In contrast to the temperature stress-induced FGF-1 secretion pathway, FGF-1 released in response to oxLDL (1) appeared in the conditioned medium as a monomer, (2) appeared independently of the presence of either actinomycin D or cycloheximide, and (3) was neither enhanced nor inhibited by brefeldin A. We did not detect cell loss, significant morphological changes, changes in growth characteristics, or other indications of lethal toxicity in oxLDL-treated cells. Although the level of lactate dehydrogenase activity was elevated after oxLDL exposure, the calculations showed that > 90% of the FGF-1 was released by viable cells. We propose that oxLDL-induced FGF-1 release is mediated by sublethal and apparently transient changes in cell membrane permeability. In the environment of an atherosclerotic lesion, oxLDL-induced FGF-1 release may be among the mediators of endothelial and smooth muscle cell proliferation.

Increased expression of angiogenic growth factors in age-related maculopathy

AIMS/BACKGROUND

The late stages of age-related maculopathy (ARM), especially neovascular macular degeneration (ARMD), can severely affect central vision and are the main cause of blindness in the elderly in the Western world. It has been shown that angiogenic growth factors are present in neovascular membranes in ARMD. However, it is not known if angiogenic growth factors play a role in the onset of neovascularisation.

METHODS

In order to elucidate the involvement of angiogenic growth factors in the initiation of neovascularisation in early stages of ARM, the expression patterns of VEGF, TGF-beta, b-FGF, and PDGF-AA on 18 human maculae with ARM, and on 11 control specimens were investigated immunohistochemically.

RESULTS

A significantly increased expression of VEGF (p = 0.00001) and TGF-beta (p = 0.019) was found in the retinal pigment epithelium (RPE) of maculae with ARM compared with control maculae. Furthermore, an increased expression of VEGF and PDGF was found in the outer nuclear layer of maculae with ARM.

CONCLUSION

These results demonstrate an increased expression of VEGF in the RPE, and in the outer nuclear layer in maculae with ARM, that could be involved in the pathogenesis of neovascular macular degeneration. Furthermore, enhanced TGF-beta expression in the RPE cells of maculae with early stages of ARM was shown.

The broad spectrum of cytokine gene expression by myoid cells from the human marrow microenvironment

Nontransformed stromal colony-derived cell lines (CDCLs) consist of a pure stromal cell population that differentiates following a vascular smooth muscle cell repertoire, and whose in vivo counterpart is that of myoid cells found in adult and fetal human bone marrow cords. We studied the cytokine expression by reverse-transcriptase polymerase chain reaction (RT-PCR) from pooled fast-growing clones from 10 different bone marrow samples. RT-PCR indicated that 30 cytokines (out of 42 studied) were expressed by CDCLs (20 after medium renewal and hydrocortisone renewal, three after addition of interleukin I beta (IL-1 beta) and seven in only part of the CDCL layers examined). The cytokines expressed comprised mediators known to be involved in the maintenance of early and late hematopoiesis (IL-1 alpha and IL-beta, IL-6, IL-7, IL-8, IL-11 and IL-13; colony-stimulating factors, thrombopoietin, erythropoietin, stem cell factor, fit 3-ligand, hepatocyte cell growth factor, tumor necrosis factor alpha, leukemia inhibitory factor, transforming growth factors beta 1 and beta 3; and macrophage inflammatory protein 1 alpha), angiogenic factors (fibroblast growth factors 1 and 2, vascular endothelial growth factor) and mediators whose usual target (and source) is the connective tissue-forming cells (platelet-derived growth factor A, epidermal growth factor, transforming growth factors alpha and beta 2, oncostatin M and insulin-like growth factor 1), or neuronal cells (nerve growth factor). The cytokines not expressed were lymphokines (IL-2, IL-3, IL-4, IL-5, IL-9, IL-10, and IL-12 and interferon gamma) or mediators synthesized by macrophages (inhibin, activin, platelet-derived growth factor B, and IL-1 receptor antagonist). This study complements the description of the phenotype of the myoid cells, confirming that these cells are the marrow connective tissue-forming cells; moreover, this work suggests that stromal control of hematopoiesis is multifactorial and that myoid cells are involved in the control of marrow angiogenesis and innervation.

Localization of heparin-binding epidermal growth factor-like growth factor in human coronary arteries. Possible roles of HB-EGF in the formation of coronary atherosclerosis

BACKGROUND

Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) is a newly identified member of the EGF family. Our previous in vitro studies showed that HB-EGF is a potent mitogen and chemoattractant for vascular smooth muscle cells (SMCs), suggesting the role of HB-EGF in the pathogenesis of atherosclerosis. The purposes of the present study were to investigate the localization of HB-EGF in both normal and atherosclerotic human coronary arteries and to elucidate the possible roles of this growth factor in the formation of atherosclerotic lesions.

METHODS AND RESULTS

The immunohistochemical localization of HB-EGF, SMCs, macrophages, and EGF receptors (EGFRs) was examined in human coronary arteries obtained at autopsy. The medial SMCs of coronary arteries in neonates, infants, and children consistently synthesized HB-EGF protein. In normal adults, however, the relative number of HB-EGF-positive medial SMCs decreased gradually with age after about 30 years of age. In nonatherosclerotic coronary arteries with diffuse intimal thickening, SMCs of the intima, especially those located in the area of the medial side of the intima, were strongly positive for HB-EGF protein. In atherosclerotic plaques of coronary arteries with eccentric intimal thickening, both SMCs and macrophages in and around the core lesions, in addition to the intimal and medial SMCs located adjacent to the plaque, produced HB-EGF protein. A strong immunostaining of EGFRs was observed in these SMCs, suggesting a close association of HB-EGF and EGFR expression.

CONCLUSIONS

These data suggest that HB-EGF might play important roles in the migration of SMCs from the media to the intima, the proliferation of intimal SMCs, and the interaction between SMCs and macrophages in the process of coronary atherogenesis.

Postnatal regulation of fibroblast growth factor ligand and receptor gene expression in rat thoracic aorta

Fibroblast growth factor (FGF)-1 and FGF-2 are potent angiogenic factors and vascular smooth muscle cell (SMC) mitogens in vivo. They function via binding to a family of structurally related cell surface receptors that possess intrinsic tyrosine kinase activity. Several studies have indicated that increased FGF and/or FGF receptor (FGFR) expression may correlate with adult SMC proliferation in vivo. In this study, we used Northern blot hybridization and reverse transcription-polymerase chain reaction assays to compare the FGF and FGFR mRNA levels in newborn rat aorta, where SMCs have a high replication index, to those in adult rat aorta, where SMCs are relatively quiescent. We found that FGF-2 and FGFR-2 mRNA expression was elevated 8.2- and 5.6-fold, respectively, in adult aorta. Increased FGF-2 protein expression in the adult aorta was confirmed by Western blot analysis. We also examined FGF and FGFR mRNA expression levels in SMC cultures derived from newborn or adult rat aorta. FGF-1 transcripts were more abundant in newborn SMCs whereas FGF-2 and FGFR-1 mRNA expression was higher in adult SMCs. Furthermore, FGF-1 and FGF-2 mRNA expression levels were altered by cell culture density and by serum treatment. We conclude that elevated FGF ligand and receptor expression does not always correlate with a high SMC proliferative index, that FGF-1 or FGF-2 may not be the primary mitogens responsible for newborn SMC growth in vivo, and that FGF-1 and FGF-2 may serve nonmitogenic functions within the mature, adult vessel wall.

Increased accumulation of tissue ACE in human atherosclerotic coronary artery disease

BACKGROUND

Angiotensin may play a pathophysiological role in experimental and human cardiovascular disease. Clinical studies have shown that ACE inhibitors reduce mortality, recurrent myocardial infarction, and ischemic events in patients with left ventricular dysfunction. Animal studies suggest that tissue ACE, particularly within blood vessels, may be an important target.

METHODS AND RESULTS

To study tissue ACE in human coronary artery disease and to identify potential mechanisms of ACE inhibitor action, we examined ACE expression immunohistochemically in nonatherosclerotic and diseased human coronary arteries. In nonatherosclerotic arteries, ACE immunoreactivity was found in luminal and adventitial vasa vasorum endothelium. In early- and intermediate-stage atherosclerotic lesions, ACE was detected prominently in regions of fat-laden macrophages and in association with T lymphocytes. In advanced lesions, ACE immunoreactivity was also localized to the endothelium of the microvasculature throughout the plaques. Immunoreactive angiotensin II was also detected in these areas. ACE expression in macrophages was further examined by in vitro experiments with a monocytoid cell line. ACE activity was induced threefold after differentiation of the cells into macrophages and was further increased after stimulation with acetylated LDL.

CONCLUSIONS

These observations demonstrate that significant sources of tissue ACE in human atherosclerotic plaques are regions of inflammatory cells, especially areas of clustered macrophages as well as microvessel endothelial cells. These results suggest that ACE accumulation within the plaque may contribute to an increased production of local angiotensin that may participate in the pathobiology of coronary artery disease. Plaque ACE probably is an important target of drug action.

Cloning and characterization of a novel upstream untranslated exon of the mouse Fgf-1 gene

Fibroblast growth factor 1 (FGF-1 or aFGF), is the prototype member of the heparin-binding growth factors which are capable of angiogenesis in vivo. FGF-1 has been implicated in atherosclerosis, cancer, wound repair and inflammatory autoimmune diseases. As part of an effort to understand the role of FGF-1 in the etiopathogenesis of inflammation and cancer, we have undertaken steps to isolate and characterize the mouse Fgf-1 gene. Southern blotting and sequence analysis displayed considerable conservation within the coding and upstream untranslated regions of Fgf-1 in human, mouse, hamster, rat and bovine. By using primers derived from the 5'-untranslated exon of a rat prostate-specific Fgf-1 cDNA, a 220-bp product was amplified from mouse genomic DNA via PCR. Sequence analysis of this amplicon showed that there was 80% similarity with the corresponding region of the rat FGF-cDNA sequence. Primers designed from this amplicon and the Fgf-1 coding region were used to isolate multiple overlapping genomic clones spanning the entire mouse Fgf-1 gene. Sequencing analysis of the genomic sequence upstream from this novel 5'-untranslated exon did not reveal typical TATA, CCAAT sequences. It appears that the occurrence of multiple untranslated exons for FGF-1 is a highly conserved theme for this gene across species.

Cloning and characterization of the mouse Fgf-1 gene

Fibroblast growth factor 1 (FGF-1 or aFGF), is a mitogen for a variety of mesoderm- and neuroectoderm-derived cells, as well as an angiogenic factor in vivo. It has been implicated in angiogenic diseases including atherosclerosis, cancer and inflammatory autoimmune diseases. As part of an effort to understand the role of FGF-1 in the pathobiology of inflammation, we have isolated and characterized the mouse Fgf-1 gene. Southern blot analysis of mouse genomic DNA using the mouse Fgf-1 cDNA as a probe revealed that mouse FGF-1 is encoded by a single copy gene. Comparison of the available mouse Fgf-1 cDNA sequence with newly obtained genomic sequence allowed us to establish the exon/intron boundaries. The mouse Fgf-1 coding region is comprised of three protein coding exons, which we determined to be separated by an 11.4-kb and a 4.9-kb intron. The elucidation of the mouse Fgf-1 coding region revealed great similarity between the mouse and human Fgf-1 gene structure.

Elevated levels of basic fibroblast growth factor in patients with limb ischemia

Basic fibroblast growth factor (bFGF), a prototypic member of a family of heparin-binding growth factors, is angiogenic both in vitro and in vivo. Increased levels and activity of bFGF have been documented in a variety of diseases, including tumors. We sought to determine whether bFGF might be similarly elevated in patients with clinical evidence of limb ischemia. Serum was obtained at the time of percutaneous revascularization from patients with symptomatic peripheral vascular disease (46 procedures were performed on 40 patients). An enzyme-linked immunoassay specific for bFGF was used (limit of detection, 1 pg/ml; range in normal subjects, 0 to 5 pg/ml). Among the 40 patients (28 men, 12 women, mean age 70 years) studied, elevated circulating bFGF (> or = 10 pg/ml) was detected in 36 samples (78%); levels ranged from 10 to 310 pg/ml (mean +/- SEM = 62 +/- 12). In 16 (89%) of 18 patients with both rest pain and nonhealing ischemic ulcers, serum bFGF levels were elevated up to 30 times normal values. In conclusion, circulating levels of bFGF are elevated in patients with vascular insufficiency and may reflect a physiologic response to limb ischemia.

Neovascularization in human coronary atherosclerotic lesions

Neovessels within human coronary atherosclerotic lesions are frequently observed, but their pathophysiological significance is still subject to debate. Also, the origin of these vessels and their pathways in the arterial wall are not well-known. In this study, we describe the transmural pathway and the frequency of neovessels both in vivo and in autopsy cases. Atherosclerotic coronary arteries were obtained during autopsy in 10 subjects without previous cardiovascular symptoms. In 25 patients undergoing percutaneous intervention for either stable or unstable angina, plaque fragments were retrieved by directional coronary atherectomy. In the autopsy study, at least one coronary artery in each case showed some degree of neointimal proliferation, characterized by smooth muscle cells in a dense extracellular matrix. A neovascularization process was seen in 17.5% of the 40 samples analyzed. In 2 cases, the transmural pathway of the neovessels could be tracked: serial sections revealed the emergence of an arteriole from the adventitia of the coronary artery, its transmedial course as a capillary, and its opening into the coronary arterial lumen. In symptomatic patients who underwent atherectomy, neovessels were found in 1 of 9 patients with stable angina (11%) and in 8 of 16 patients with unstable angina (50%, P < 0.05). Mostly, the neovessels appeared as capillaries cut in their short axis. In 2 cases, however, the capillary was seen in its longitudinal axis, and its pathway could be traced through the atherosclerotic lesion to its opening in the coronary lumen, as in the autopsy study. Therefore, neovessels frequently develop in the atherothrombotic plaque, both in asymptomatic and anginal patients. In the latter group, the proliferation of neovessels is more frequent in acute coronary syndromes. These findings have several implications, in particular for percutaneous coronary angioplasty and related procedures, such as local drug delivery.

Expression of Fas and anti-Fas-mediated apoptosis in human hepatocellular carcinoma cell lines

BACKGROUND/AIMS

Fas transduces apoptotic signals upon cross-linking with the Fas ligand, which is experimentally replaced by anti-Fas antibodies. Because little is known about Fas expression and function in hepatocellular carcinoma, these issues are addressed in the current article.

METHODS

We examined Fas expressions at protein and mRNA levels, and susceptibility to anti-Fas-mediated apoptosis, on six hepatocellular carcinoma cell lines.

RESULTS

Two cell lines constitutively expressed high levels of Fas both on their cell surface and in their cytoplasm, whereas the other four cell lines expressed Fas mainly in their cytoplasm. Fas mRNA of normal size was detected in all cell lines in reverse transcriptase-polymerase chain reaction analyses. Although a Fas mRNA variant, suggesting a soluble Fas molecule, was detected in the two cell lines expressing high levels of Fas, its amount was very small compared to that of normal-sized Fas transcript. Anti-Fas dose-dependently induced apoptosis exclusively in the two cell lines which constitutively express high levels of cell surface Fas. However, after preincubation with interferon-gamma, one cell line with low surface Fas expression became anti-Fas sensitive equivalent to the two cell lines expressing surface Fas at high levels. Studies of two clonally related cell lines showed that dedifferentiated clones had lower Fas expression and resistance to anti-Fas, suggesting deterioration of Fas system after clonal cell dedifferentiation.

CONCLUSIONS

These findings suggest sensitivity to anti-Fas is virtually relevant to cell surface Fas, but not to cytoplasmic Fas expression. However, its expression level does not correlate to sensitivity to anti-Fas.

Immunolocalization of FGF-1 and receptors in human renal allograft vasculopathy associated with chronic rejection

Despite recognition of chronic vasculo-occlusive disease in solid organ transplantation, the exact pathophysiologic events resulting in neointima formation remain to be elucidated. Since acidic fibroblast growth factor (FGF-1) is an established modulator of vascular cell function, we examined the expression of this growth factor and its high affinity receptors in both relevant renal transplant controls (n = 5) and tissue from patients (n = 19) who underwent nephrectomy following graft loss secondary to chronic rejection. In situ hybridization and immunohistochemical studies demonstrated minimal vascular expression and distribution of FGF-1 and FGF high affinity receptors in the normal human kidney. In contrast, vascular lesions in kidney allografts experiencing chronic rejection demonstrated the exaggerated appearance of FGF-1 ligand and receptors. Immunoreactive FGF-1 readily was detected in medial smooth muscle cells and focal areas of intimal hyperplasia, particularly in association with the presence of inflammatory infiltrate. Enhanced staining for FGF-1 mRNA primarily was associated with the appearance of resident inflammatory cells. Medial smooth muscle cells of hyperplastic vascular structures demonstrated the greatest immunoappearance of FGF receptors-however, diffuse immunostaining also was observed in areas of intimal hyperplasia. The enhanced appearance of both FGF-1 and FGF receptors in the vascular wall suggests that this polypeptide mitogen may serve as an important mediator of growth responses associated with neointima development and angiogenesis during chronic rejection of human renal allografts.

Thrombin potently stimulates cytokine production in human vascular smooth muscle cells but not in mononuclear phagocytes

Thrombosis frequently occurs during atherogenesis and in response to vascular injury. Accumulating evidence supports a role for inflammation in the same situation. The present study therefore sought links between thrombosis and inflammation by determining whether thrombin, which is present in active form at sites of thrombosis, can elicit inflammatory functions of human monocytes and vascular smooth muscle cells (SMCs), two major constituents of advanced atheroma. Human alpha-thrombin (EC50, approximately equal to 500 pmol/L) potently induced interleukin (IL)-6 release from SMCs. The tethered-ligand thrombin receptor appeared to mediate this effect. Furthermore, alpha-thrombin also rapidly increased levels of mRNA encoding IL-6 and monocyte chemotactic protein-1 (MCP-1) in SMCs. In contrast, only alpha-thrombin concentrations of > or = 100 nmol/L could stimulate release of IL-6 or tumor necrosis factor-alpha (TNF alpha) in peripheral blood monocytes or monocyte-derived macrophages. Lipid loading of macrophages did not augment thrombin responsiveness. Likewise, only alpha-thrombin concentrations of > or = 100 nmol/L increased levels of IL-6, IL-1 beta, MCP-1, or TNF alpha mRNA in monocytes. Differential responses of SMCs and monocytes to thrombin extended to early agonist-mediated increases in [Ca2+]i. SMCs and endothelial cells, but not monocytes, contained abundant mRNA encoding the thrombin receptor and displayed cell surface thrombin receptor expression detected with a novel monoclonal antibody. Thus, the level of thrombin receptors appeared to account for the differential thrombin susceptibility of SMCs and monocytes. These data suggest that SMCs may be more sensitive than monocytes/macrophages to thrombin activation in human atheroma. Cytokines produced by thrombin-activated SMCs may contribute to ongoing inflammation in atheroma complicated by thrombosis or subjected to angioplasty.

Heparin-binding epidermal growth factor-like growth factor regulates fibroblast growth factor-2 expression in aortic smooth muscle cells

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a vascular smooth muscle cell (SMC) mitogen and chemotactic factor that is expressed by endothelial cells, SMCs, monocytes/macrophages, and T lymphocytes. Both the membrane-anchored HB-EGF precursor and the secreted mature HB-EGF protein are biologically active; thus, HB-EGF may stimulate SMC growth via autocrine, paracrine, and juxtacrine mechanisms. In the present study, we report that HB-EGF treatment of serum-starved at aortic SMCs can induce fibroblast growth factor (FGF)-2 (basic FGF) gene expression but not FGF-1 (acidic FGF) gene expression. Increased FGF-2 mRNA expression is first detectable at 1 hour after HB-EGF addition, and maximal FGF-2 mRNA levels, corresponding to an approximately 46-fold level of induction, are present at 4 hours. The effect of HB-EGF on FGF-2 mRNA levels appears to be mediated primarily by a transcriptional mechanism and requires de novo synthesized proteins. HB-EGF induction of FGF-2 mRNA levels can be inhibited by treating cells with the anti-inflammatory glucocorticoid dexamethasone or the glycosaminoglycan heparin. Finally, Western blot analyses indicate that HB-EGF-treated SMCs also produce an increased amount of FGF-2 protein. These results indicate that HB-EGF expressed at sites of vascular injury or inflammation in vivo may upregulate FGF-2 production by SMCs.

Immunolocalization of FGF-1 and receptors in glomerular lesions associated with chronic human renal allograft rejection

Glomerular lesions are considered one of the more detrimental pathologic changes associated with chronic rejection of renal allografts. To elucidate potential pathophysiologic mechanisms associated with transplant glomerulopathy, we examined the expression of acidic fibroblast growth factor (FGF-1) and its high-affinity receptors (FGFR) in both relevant renal transplant controls (n=5) and tissue from patients (n=19) who underwent nephrectomy following graft loss secondary to chronic rejection. In situ immunohistochemical analyses demonstrated minimal staining and distribution of FGFR and FGF-1, which was localized to the mesangial matrix in glomeruli from normal human kidneys. In situ hybridization failed to detect the presence of FGF-1 mRNA in control tissue. In contrast, each stage of the developing glomerular lesion associated with chronic rejection demonstrated the exaggerated appearance of FGF-1 protein in visceral and parietal epithelial cells. Intense staining for FGF-1 protein did not correlate with the increased appearance of FGF-1 mRNA, which was restricted to circulating inflammatory cells. Glomeruli in kidneys with findings of chronic rejection also exhibited increased immunodetection of both FGFR and PCNA in mesangial and epithelial cells. Immunogold labeling of chronically rejected visceral epithelial cells revealed both cytoplasmic and nuclear/localization of FGF-1, thereby establishing mitogenic potential of the growth factor. The enhanced appearance of both biologically active FGF-1 and FGFR suggests that this polypeptide may serve as an important mediator of growth responses associated with glomerular lesion development during chronic rejection.

Identification of a murine TEF-1-related gene expressed after mitogenic stimulation of quiescent fibroblasts and during myogenic differentiation

Fibroblast growth factor (FGF)-1 binding to cell surface receptors stimulates an intracellular signaling pathway that ultimately promotes the transcriptional activation of specific genes. We have used a mRNA differential display method to identify FGF-1-inducible genes in mouse NIH 3T3 fibroblasts. Here, we report that one of these genes, FGF-regulated (FR)-19, is predicted to encode a member of the transcriptional enhancer factor (TEF)-1 family of structurally related DNA-binding proteins. Specifically, the deduced FR-19 amino acid sequence has approximately89, 77, and 68% overall identity to chicken TEF-1A, mouse TEF-1, and mouse embryonic TEA domain-containing factor, respectively. Gel mobility shift experiments indicate that FR-19, like TEF-1, can bind the GT-IIC motif found in the SV40 enhancer. The FR-19 gene maps in the distal region of mouse chromosome 6, and analysis of several FR-19 cDNA clones indicates that at least two FR-19 isoforms may be expressed from this locus. FGF-1 induction of FR-19 mRNA expression in mouse fibroblasts is first detectable at 4 h after FGF-1 addition and is dependent on de novo RNA and protein synthesis. FGF-2, calf serum, platelet-derived growth factor-BB, and phorbol 12-myristate 13-acetate can also induce FR-19 mRNA levels. We have also found that FR-19 mRNA expression increases during mouse C2C12 myoblast differentiation in vitro. The FR-19 gene is expressed in vivo in a tissue-specific manner, with a relatively high level detected in lung. These results indicate that increased expression of a TEF-1-related protein may be important for both mitogen-stimulated fibroblast proliferation and skeletal muscle cell differentiation.

Serum-starvation induces the extracellular appearance of FGF-1

Autocrine/paracrine stimulation of cell growth by members of the fibroblast growth factor (FGF) family of polypeptides is dependent upon extracellular interactions with specific high affinity receptors at the cell surface. Acidic FGF (FGF-1) lacks a classical signal sequence for secretion, suggesting that intrinsic levels of this mitogen may not stimulate cell growth and utilizes a non-classical pathway to gain access to the extracellular compartment. To evaluate the biological potential of intracellular FGF-1 more rigorously, human cDNA sequences for the growth factor were introduced into primary murine embryonic fibroblasts using retrovirally mediated gene transfer. Heparin affinity, Western analysis, mitogenic assays, in situ immunohistochemical techniques, induction of tyrosine phosphorylation and antibody inhibition studies were used to demonstrate functionality of the FGF-1 transgene in this experimental model. Under normal culture conditions, cells constitutively expressing intracellular FGF-1 exhibited a slight growth advantage. In contrast, when maintained in reduced serum, these cells adopted a transformed phenotype and demonstrated an enhanced growth potential, induction of FGF-specific phosphotyrosyl proteins and the nuclear association of the growth factor. Analysis of the conditioned media from these stressed cells indicated that serum starvation induces the secretion of FGF-1 as latent high molecular mass complexes requiring reducing agents to activate its full biological potential.

Induction of human endothelial cell growth by mildly oxidized low density lipoprotein

The aim of the present study was to examine whether endothelial growth could be modulated by mildly oxidized low density lipoprotein. When human endothelial cells were cultured in the presence of mildly oxidized low density lipoprotein (1 microgram/ml), a significant induction of endothelial cell growth was observed, whereas native low or high density lipoprotein were ineffective. Further, treatment of endothelial cells with mildly oxidized low density lipoprotein modulated the expression of cytokines and growth factors which may be relevant in atherogenesis. Endothelial cells chronically exposed to mildly oxidized low density lipoprotein underwent a more rapid onset of cellular senescence. Since senescence is associated with endothelial dysfunction, the novel finding showing that mildly oxidized low density lipoprotein induces endothelial cell growth may be relevant in the development and evolution of the atherosclerotic lesions.

Increased ferritin gene expression in atherosclerotic lesions

To identify genes potentially implicated in atherogenesis, a cDNA library was constructed from human atherosclerotic aorta and differentially screened with 32P-labeled-cDNAs prepared from human normal and atherosclerotic aortas. Two cDNA clones exhibiting higher hybridization to the 32P-labeled cDNAs from atherosclerotic vessels were isolated and identified to be genes encoding L-ferritin and H-ferritin, respectively. Northern blot analysis confirmed that the expression of both ferritin genes was notably higher in human and rabbit atherosclerotic aortas than in their normal counterparts. A time-course study illustrated that both L- and H-ferritin mRNAs were markedly increased in aortas of rabbits after feeding with a high cholesterol diet for 6 wk, which was also the time period after which the formation of lesions became evident. In situ hybridization revealed that both L- and H-ferritin mRNAs were induced in endothelial cells and macrophages of human early lesions. The signals were also detected in the smooth muscle cells of advanced lesions. Immunostaining further identified the presence of ferritin protein in atherosclerotic lesions. On the other hand, Prussian blue stain revealed the presence of iron deposits in advanced lesions but not in early human or rabbit lesions. Further experiments with cultured human monocytic THP-1 cells and aortic smooth muscle cells demonstrated that ferritin mRNAs were subjected to up-regulation by treatment with IL-1 or TNF, while TGF, PDGF, and oxidized LDL did not affect the expression of either ferritin gene in both cell lines. Collectively, these results clearly demonstrate that ferritin genes are susceptible to induction in the course of plaque formation.

Vascular remodelling and molecular biology: new concepts and therapeutic possibilities

1. Over the past decade major advances in molecular cell biology have greatly increased our understanding of the way in which many growth factor genes are expressed and regulated. This knowledge is currently being translated into investigations of the cardiovascular system. 2. Two growth factor families appear to play particularly important roles, the fibroblast growth factors and the transforming growth factors-beta. These are multifunctional growth factors capable of remodelling the vasculature through their effects on cell migration, proliferation and matrix formation. 3. An understanding of their regulation, properties and nature of their receptors is providing novel insights into the physiology and pathobiology of the vasculature. It is also providing highly specific targets for future therapy.

Fibroblast growth factor receptor-1 expression is associated with neointimal formation in vitro

Neointimal formation was studied in a porcine aortic organ culture model that exhibits intimal smooth muscle cell accumulation after a brief time in culture. This in vitro model is dependent upon an intact endothelium, as removal of the endothelium at the time of harvesting results in the failure to develop a neointima. We previously showed that conditioned media from intact cultures induce neointimal formation in denuded aortic explants, and we speculated that basic fibroblast growth factor was the endothelial-derived factor in conditioned media promoting neointimal formation. However, the concentration of basic fibroblast growth factor in conditioned media from both intact and denuded explants, measured by an enzyme-linked immunosorbent assay, was not significantly different and, in fact, steadily decreased over the first 7 days of culture. Furthermore, the amount and intensity of immunoreactive basic fibroblast growth factor in tissue sections, also similar in both groups, decreased over the same time course. Nonetheless, exogenous basic fibroblast growth factor (1 ng/ml) induced neointimal formation in intact explants but was unable to do so in denuded explants. Western blot analysis of intimal lysates prepared from both intact and denuded explants showed a time-dependent increase in fibroblast growth factor receptor-1 expression over the first 7 days of culture, with higher levels seen in intimal lysates from intact explants at each time point examined. Immunoreactive fibroblast growth factor receptor-1 was detected in both endothelial cells and intimal smooth muscle cells of intact explant sections. These data indicate that, in the presence of the endothelium, neointimal formation may in part be mediated by upregulation of fibroblast growth factor receptor-1 in the intimal cells of porcine aortic explants.

Neovascular expression of E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 in human atherosclerosis and their relation to intimal leukocyte content

BACKGROUND

Leukocyte recruitment is an early event in atherogenesis, and the leukocyte adhesion molecules E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) recently have been detected in human atherosclerosis. However, no previous study has evaluated either the distribution of these three molecules at different sites within the arterial intima or their relation to plaque leukocyte content.

METHODS AND RESULTS

Immunohistochemistry was performed on 99 coronary artery segments (34 controls and 65 with atherosclerotic plaque) to identify E-selectin, ICAM-1, VCAM-1, macrophages, smooth muscle cells, and T lymphocytes. For each segment, the presence or absence of adhesion molecule was determined at the arterial lumen, on intimal neovasculature, and on intimal nonendothelial cells. Each segment was scored for intimal macrophage and T-lymphocyte densities on a semiquantitative scale of 0 to 3. In atherosclerotic plaques, the prevalences of E-selectin, ICAM-1, and VCAM-1 on plaque neovasculature were twofold higher than their prevalences on arterial luminal endothelium. E-selectin was the only adhesion molecule for which expression on arterial luminal endothelial cells was more prevalent in plaques than in control segments. Increased plaque intimal macrophage density was associated with expression of VCAM-1 on neovasculature (P < .01) and on nonendothelial cells (P < .01). Increased plaque intimal T-lymphocyte density was associated with the presence of both ICAM-1 and VCAM-1 on neovasculature (both P < .01) and on nonendothelial cells (both P < .01).

CONCLUSIONS

In atherosclerotic plaques, the expression of all three leukocyte adhesion molecules was more prevalent on intimal neovasculature than on arterial luminal endothelium. Further, the presence on neovasculature and nonendothelial cells of VCAM-1 and ICAM-1 was strongly associated with increased intimal leukocyte accumulation. These findings suggest that leukocyte recruitment through and/or activation of intimal neovasculature may play important roles in the pathogenesis of human atherosclerosis.

Stimulation of proliferation of a human osteosarcoma cell line by exogenous acidic fibroblast growth factor requires both activation of receptor tyrosine kinase and growth factor internalization

U2OS Dr1 cells, originating from a human osteosarcoma, are resistant to the intracellular action of diphtheria toxin but contain toxin receptors on their surfaces. These cells do not have detectable amounts of fibroblast growth factor receptors. When these cells were transfected with fibroblast growth factor receptor 4, the addition of acidic fibroblast growth factor to the medium induced tyrosine phosphorylation, DNA synthesis, and cell proliferation. A considerable fraction of the cell-associated growth factor was found in the nuclear fraction. When the growth factor was fused to the diphtheria toxin A fragment, it was still bound to the growth factor receptor and induced tyrosine phosphorylation but did not induce DNA synthesis or cell proliferation, nor was any fusion protein recovered in the nuclear fraction. On the other hand, when the fusion protein was associated with the diphtheria toxin B fragment to allow translocation to the cytosol by the toxin pathway, the fusion protein was targeted to the nucleus and stimulated both DNA synthesis and cell proliferation. In untransfected cells containing toxin receptors but not fibroblast growth factor receptors, the fusion protein was translocated to the cytosol and targeted to the nucleus, but in this case, it stimulated only DNA synthesis. These data indicate that the following two signals are required to stimulate cell proliferation in transfected U2OS Dr1 cells: the tyrosine kinase signal from the activated fibroblast growth factor receptor and translocation of the growth factor into the cell.

Proliferating arterial smooth muscle cells after balloon injury express TNF-alpha but not interleukin-1 or basic fibroblast growth factor

We have recently reported that balloon withdrawal injury to rabbit abdominal aortas induces sustained activation indicated by the expression of certain adhesion molecules such as vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in regenerating endothelial cells and/or proliferating smooth muscle cells (SMCs). Local cytokine signaling may contribute to ongoing modulation of cellular functions and proliferation of intimal SMCs after acute vascular injury. We therefore studied the expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta), proinflammatory and SMC growth-promoting cytokines, and basic fibroblast growth factor (bFGF) in SMCs of rabbit aorta at 2 (n = 4), 5 (n = 4), and 10 days (n = 6) after balloon injury. All animals were given bromodeoxyuridine (BrdU, 10 mg/kg per day) continuously to label proliferating SMCs. Frozen cross sections of injured vessels at each time point after balloon injury were examined by immunoperoxidase staining with monoclonal antibodies. As early as 2 days after injury, before intimal thickening begins, foci of medial SMCs expressed TNF-alpha, but not all TNF-alpha-positive medial SMCs had incorporated BrdU, suggesting that TNF-alpha expression by medial SMCs may precede their proliferation. At 5 days, TNF-alpha-bearing and BrdU-labeled medial SMCs increased in number. At 10 days after injury, when uniform intimal thickening occurred, almost all neointimal SMCs and foci of medial SMCs labeled with BrdU. Most of the BrdU-positive (proliferating) SMCs expressed immunoreactive TNF-alpha. Reverse transcription polymerase chain reaction showed increased TNF-alpha mRNA at 10 days after ballooning in the injured portion of the aorta. In contrast, regions of SMC proliferation showed inconsistent IL-1 beta expression, and bFGF, abundant in normal rabbit arteries, was not detected in areas of SMC replication. These data indicate that replication of arterial SMCs after balloon injury occurs in regions of TNF-alpha but not IL-1 beta expression and correlates inversely with the presence of bFGF. These results indicate that SMC-derived TNF-alpha serves as a marker of modulated SMC phenotype after acute vascular injury and may contribute to local cellular activation and proliferation of SMCs at sites of arterial injury.

Immunological mechanisms in atherosclerosis

Immunological mechanisms seem to be potent modulators of the atherosclerotic process. The presence of substantial numbers of T-lymphocytes in the lesion and local and circulating autoantibodies to plaque components suggests that a specific immune response is operating. Focal expression of adhesion molecules and local secretion of chemoattractants could mediate the recruitment of inflammatory cells to the lesion. Local cytokine and growth factor networks may operate later, controlling cell migration and proliferation. Although it is still important to realize the complexity of these mechanisms, the ongoing characterization of the molecular mechanisms in atherogenesis may lead to new strategies for intervention with the disease process.

Intervention in diabetic vascular disease by modulation of growth factors

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

Active proliferation of different cell types, including lymphocytes, in human atherosclerotic plaques

Cell proliferation, an important mechanism of atherosclerotic plaque growth, occurs among smooth muscle, inflammatory cell, and other cell types. We have identified different topographical patterns of cell proliferation in human carotid plaques, based on cell type. Cell proliferation was determined with an antibody to the proliferating cell nuclear antigen (PCNA), combined with cell type-specific antibodies. Despite low levels of overall proliferative activity, the intima displayed more proliferative activity than the underlying media (1.61 +/- 0.35% in intima versus 0.05 +/- 0.03% in media; P < 0.01). The preponderant proliferative cell type in the intima was the monocyte/macrophage (46.0% of PCNA-positive cells), with a minority being smooth muscle alpha-actin-positive (9.7%), microvascular endothelial (14.3%), and T cells (13.1%). Smooth muscle cells were the dominant proliferating cell type in the media (44.4% of PCNA-positive cells versus 20% endothelial cells, 13.0% monocyte/macrophages, and 14.3% T cells). Within the plaque, foam-cell-rich regions mostly displayed proliferation among macrophages (66.5%), whereas in vascularized fields PCNA positivity was almost equally shared by endothelial cells (23.8%), monocyte/macrophages (26.3%), smooth muscle alpha-actin-positive cells (14.0%), and to a lesser extent, T cells (8.2%). Logistic and linear regression analyses also demonstrated that location in foam-cell-rich regions was a significant predictor of proliferation only among monocyte/macrophages, whereas location in vascularized regions was a good predictor of PCNA positivity among both inflammatory and noninflammatory cells. These different patterns of cell type proliferation suggest possibly different distributions of putative responsible growth regulatory factors in human atherosclerosis.

Induction of angiogenesis by smooth muscle cell-derived factor: possible role in neovascularization in atherosclerotic plaque

The development of atherosclerotic plaque is associated with neovascularization in the thickened intima and media of vascular walls. Neovascularization may have a role in the progression of atherosclerotic plaque as well as in the development of intraplaque hemorrhage. However, the mechanism and stimulus for neovascularization in atherosclerotic plaque are unknown. We postulated that smooth muscle cells (SMCs), a major cellular component in the vascular wall, might contribute to the induction of neovascularization in atherosclerotic plaque through the secretion of an angiogenic factor. We observed that endothelial cells (ECs) cultured on collagen gel with SMC-conditioned medium became spindle shaped, invaded the underlying collagen gel, and organized a capillary-like branching cord structure in the collagen gel. The conditioned medium also stimulated EC proliferation and increased the EC-associated plasminogen activator activity. The angiogenic factor in SMC-conditioned medium was retained in a heparin-Sepharose column and eluted with 0.9 M NaCl. Neutralizing anti-vascular endothelial growth factor (VEGF) antibody attenuated the angiogenic activity in the conditioned medium, including the induction of morphologic changes in ECs, mitogenic activity, and increased plasminogen activator activity associated with ECs. Immunoblotting analysis confirmed the secretion of VEGF from SMCs. These observations indicate that SMC may be responsible for the neovascularization in atherosclerotic plaque through the secretion of VEGF.

Neurotrophin and neurotrophin receptors in vascular smooth muscle cells. Regulation of expression in response to injury

The neurotrophins, a family of related polypeptide growth factors including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-3 and NT-4/5 promote the survival and differentiation of distinctive sets of embryonic neurons. Here we define a new functional role for neurotrophins, as autocrine or local paracrine mediators of vascular smooth muscle cell migration. We have identified neurotrophins, and their cognate receptors, the trk tyrosine kinases, in human and rat vascular smooth muscle cells in vivo. In vitro, cultured human smooth muscle cells express BDNF; NT-3; and trk A, B, and C. Similarly, rat smooth muscle cells expressed all three trk receptors as well as all four neurotrophins. Moreover, NGF induces cultured human smooth muscle cell migration at subnanomolar concentrations. In the rat aortic balloon deendothelialization model of vascular injury, the expression of NGF, BNDF, and their receptors trk A and trk B increased dramatically in the area of injury within 3 days and persisted during the formation of the neointima. In human coronary atherosclerotic lesions, BDNF, NT-3, and NT-4/5, and the trk B and trk C receptors could be demonstrated in smooth muscle cells. These findings suggest that neurotrophins play an important role in regulating the response of vascular smooth muscle cells to injury.

Basic fibroblast growth factor upregulates the expression of vascular endothelial growth factor in vascular smooth muscle cells. Synergistic interaction with hypoxia

BACKGROUND

Vascular endothelial growth factor (VEGF) is a hypoxia-inducible direct angiogenic factor. Upregulation of VEGF is thought to mediate many of the angiogenic effects of growth factors that are not direct endothelial cell mitogens. Like VEGF, basic fibroblast growth factor (bFGF) is considered to induce angiogenesis by a direct effect on endothelial cells. This study investigated the possibility that bFGF may also act indirectly by regulating VEGF expression in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Incubation of confluent and quiescent cultures of rabbit VSMCs with bFGF caused a time- and concentration-dependent increase in steady-state levels of VEGF mRNA, as analyzed by Northern blot hybridization. Exposure of VSMCs to a threshold hypoxic stimulus (2.5% O2) caused a modest increase in VEGF mRNA levels. However, the combination of 2.5% O2 with bFGF had a marked synergistic effect. This effect was specific for VEGF as hypoxia did not enhance bFGF-induced expression of the proto-oncogene c-myc. Synergistic upregulation of VEGF mRNA expression also was observed between hypoxia and TGF-beta 1.

CONCLUSIONS

These results suggest that bFGF may promote angiogenesis both by a direct effect on endothelial cells and also indirectly by the upregulation of VEGF in VSMCs. The synergy demonstrated between hypoxia and either bFGF or TGF-beta 1 suggests that multiple diverse stimuli may interact via the upregulation of VEGF expression in VSMCs to amplify the angiogenic response.

Functional characterization of the brain-specific FGF-1 promoter, FGF-1.B

Expression of alternatively spliced human FGF-1 (or aFGF) transcripts is regulated in a tissue-specific manner via multiple promoters. To identify the cis-regulatory elements in the brain-specific FGF-1.B promoter, we constructed a series of promoter deletions fused to the luciferase reporter gene and transfected into an FGF-1.B positive glioblastoma cell line, U1240MG, and a 1.B negative cell line, U1242MG. Results of transient transfections indicate three elements that are involved in the positive regulation of FGF-1.B expression. The core promoter is located in a 40-base pair region (between -92 and -49), and two regulatory regions (RR-1 and RR-2) are located within the 540-base pair region 5' to the major transcription start site (defined as +1). Electrophoretic mobility shift assays and footprinting analysis have identified sequence-specific binding sites in RR-1 and RR-2. Mutants of RR-2 abolished binding to nuclear proteins and showed diminished luciferase reporter activity. The effects seen are specific for the U1240MG cell line, supporting a role for RR-2 in the tissue-specific regulation of FGF-1.B. Southwestern analysis using an oligonucleotide probe derived from RR-2 (nucleotides -489 to -467) further identified a 37-kDa protein that is present in nuclear extracts from U1240MG and brain but not from U1242MG.

Tissue endothelin-1 immunoreactivity in the active coronary atherosclerotic plaque. A clue to the mechanism of increased vasoreactivity of the culprit lesion in unstable angina

BACKGROUND

The pathomorphological substrate of complicated coronary atherosclerotic lesions underlying unstable angina is characterized by a localized chronic inflammatory process. Functionally, coronary lesions associated with unstable angina demonstrate an enhanced vasoreactivity. Endothelin-1 is a potent vasoconstrictor peptide produced not only by endothelial cells but also by macrophages and polymorphonuclear leukocytes, the cell types characteristic of inflammation.

METHODS AND RESULTS

By use of immunohistochemical techniques, we examined the presence of endothelin-1 in coronary atherosclerotic plaque tissue obtained by directional coronary atherectomy of primary lesions from 50 consecutive patients. The tissue specimens of 43 of 50 patients (86%) demonstrated endothelin-1-like immunoreactivity. Endothelin-1-like immunoreactivity preferentially localized to macrophage-rich areas, to hypercellular regions rich in microvessels, and to plaque areas with evidence of prior hemorrhage. Double-immunolabeling revealed that both macrophages (HAM56 positive) and intimal smooth muscle cells (alpha-actin positive) demonstrated cytoplasmic immunostaining for endothelin-1. Semiquantitative analysis of endothelin-1-like immunostaining revealed significantly (P < .005) higher staining grades in active (1.86 +/- 0.15, n = 40) compared with nonactive lesions (0.78 +/- 0.35, n = 10): endothelin-1 staining grades were significantly (P < .001) lower in patients with stable angina (0.69 +/- 0.19, n = 13) than in patients with crescendo angina (1.82 +/- 0.30, n = 11), with angina at rest (2.08 +/- 0.21, n = 12), or with angina after myocardial infarction (2.0 +/- 0.26, n = 14).

CONCLUSIONS

Endothelin-1 immunostaining of atherosclerotic tissue localizes predominantly with plaque components indicative of chronic inflammatory processes. The increased tissue endothelin-1-like immunoreactivity in active coronary atherosclerotic lesions may provide a clue to the mechanisms of increased vasoreactivity of the culprit lesion in acute ischemic syndromes, which is the clinical substrate of the active coronary atherosclerotic plaque.

Human fibroblast growth factor 1 gene expression in vascular smooth muscle cells is modulated via an alternate promoter in response to serum and phorbol ester

We have previously isolated the human FGF-1 gene in order to elucidate the molecular basis of its gene expression. The gene spans over 100 kbp and encodes multiple transcripts expressed in a tissue- and cell-specific manner. Two variants of FGF-1 mRNA (designated FGF-1.A and 1.B), which differ in their 5' untranslated region, were identified in our laboratory. Recently, two novel variants of FGF-1 mRNA (designated FGF-1.C and 1.D) have been isolated. In this study we used RNase protection assays to demonstrate expression of FGF-1.D mRNA in human fibroblasts and vascular smooth muscle cells and to show that promoter 1D has multiple transcription start sites. A single-strand nuclease-sensitive region has also been identified in the promoter 1D region that may have implications in chromatin conformation and transcriptional regulation of this promoter. Using Northern blot hybridization analyses, a previous study demonstrated a significant increase of FGF-1 mRNA levels in cultured saphenous vein smooth muscle cells in response to serum and phorbol ester. Here we confirm these results by RNase protection analysis and show that FGF-1.C mRNA is significantly increased in response to these stimuli. RNase protection assays indicate that promoter 1C has one major start site. The phorbol ester effect suggests that a protein kinase C-dependent signalling pathway may be involved in this phenomenon. Our results point to a dual promoter usage of the FGF-1 gene in vascular smooth muscle cells. Thus, normal growing cells primarily utilize promoter 1D. In contrast, quiescent cells, when exposed to serum or phorbol ester, utilize a different FGF-1 promoter, namely promoter 1C. Overall, these phenomena suggest mechanisms for increased production of FGF-1 that may play a role in inflammatory settings, wound healing, tissue repair, and neovascularization events and processes via autocrine and paracrine mechanisms. Our findings suggest that different FGF-1 promoters may respond to different physiological conditions and stimuli, in reference to the cell type or tissue milieu, resulting in ultimate production of the FGF-1 protein.

Nitric oxide mediates cytotoxicity and basic fibroblast growth factor release in cultured vascular smooth muscle cells. A possible mechanism of neovascularization in atherosclerotic plaques

To define the pathophysiological role of nitric oxide (NO) released from vascular smooth muscle cells (VSMC), we examined whether NO released from VSMC induces cytotoxicity in VSMC themselves and adjacent endothelial cells (EC) using a coculture system. Prolonged incubation with interleukin-1 (IL-1) induced large amounts of NO release and cytotoxicity in VSMC. NG-Monomethyl-L-arginine, an inhibitor of NO synthesis, inhibited both NO release and cytotoxicity induced by IL-1. In contrast, DNA synthesis in cocultured EC was not inhibited but rather stimulated by prolonged incubation with IL-1 or sodium nitroprusside (SNP), a NO donor. However, IL-1 and SNP did not stimulate but inhibited DNA synthesis in EC alone. On the other hand, conditioned medium from VSMC incubated for a long period with IL-1 or SNP stimulated DNA synthesis in EC alone. Furthermore, the concentration of basic fibroblast growth factor in the conditioned medium was increased and correlated with the degree of cytotoxicity in VSMC. These results indicate that NO released from VSMC induces VSMC death, which results in release of basic fibroblast growth factor, which then stimulates adjacent EC proliferation. Thus, NO released from VSMC may participate in the mechanism of neovascularization in atherosclerotic plaques.