Actin expression in smooth muscle cells of rat aortic intimal thickening, human atheromatous plaque, and cultured rat aortic media

Local infusion of the nitric oxide donor Sin-1 after angioplasty. Effects on intimal hyperplasia in porcine coronary arteries

PURPOSE

To investigate the development of intimal hyperplasia in response to percutaneous transluminal coronary angioplasty (PTCA) followed by local delivery of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1).

MATERIAL AND METHODS

Overdilation PTCA was performed in coronary arteries in 20 healthy pigs. One of the dilated segments was additionally treated with local delivery of SIN-1 for 10 min. Segments distal to the treated part of the arteries served as controls. Arteries were radiographically depicted and analyzed after 1 and 8 weeks for actin, myosin and intermediate filaments (IF), nitric oxide synthetase (NOS) and histological evaluation.

RESULTS

Segments treated with PTCA+SIN-1 showed a significantly (p=0.03) larger luminal diameter compared with PTCA only treated segments. The luminal loss after SIN-1 was not significant compared with the diameter prior to treatment. Endothelial NOS content was significantly lower in the PTCA+SIN-1 group compared with the PTCA group after 1 (p=0.03) and 8 weeks (p=0.013). IF/actin ratio after 1 week was significantly increased in PTCA-treated segments compared with untreated controls (p=0.004), and compared with PTCA+SIN-1-treated segments (p=0.004).

CONCLUSION

PTCA-induced intimal hyperplasia was potently inhibited by local delivery of the NO donor SIN-1. Momentary events at the time of injury play a significant role in the development of intimal hyperplasia and long-lasting down-regulation of the endothelial NOS expression after SIN-1 exposure is suggested. The IF/actin ratio can be useful as an early marker of intimal hyperplasia.

Functional P2Y2 nucleotide receptors mediate uridine 5'-triphosphate-induced intimal hyperplasia in collared rabbit carotid arteries

BACKGROUND

Extracellular uridine 5'-triphosphate (UTP) induces mitogenic activation of smooth muscle cells (SMCs) through binding to P2Y2 nucleotide receptors. P2Y2 receptor mRNA is upregulated in intimal lesions of rat aorta, but it is unclear how this G-protein-coupled receptor contributes to development of intimal hyperplasia.

METHODS AND RESULTS

This study used a silicone collar placed around rabbit carotid arteries to induce vascular injury and intimal thickening. Collar placement caused rapid upregulation of P2Y2 receptor mRNA in medial SMCs before appearance of neointima. Fura-2 digital imaging of single SMCs was used to measure changes in myoplasmic calcium concentration (Ca(m)) in response to P2Y receptor agonists. In contrast to UDP, activation by UTP or adenosine 5'-triphosphate (ATP) greatly increased Ca(m), which indicates upregulation of functional P2Y2 receptors at which UTP and ATP are equipotent agonists. The number of responsive cells was significantly greater for freshly dispersed SMCs from collared arteries than for controls. Perivascular infusion of UTP (100 micromol/L) within the collar significantly enhanced neointimal development. Intimas that resulted from UTP exposure were infiltrated by macrophages. Moreover, increased expression of osteopontin occurred in response to in situ application of UTP. ATP or UTP also stimulated osteopontin expression in cultured SMCs in a dose-dependent manner. Furthermore, P2Y2 antisense oligonucleotide inhibited osteopontin expression induced by UTP.

CONCLUSIONS

These findings indicate for the first time a role for the UTP/ATP receptor, P2Y2, in development of intimal hyperplasia associated with atherosclerosis and restenosis.

Changes in gene expression in atherosclerotic plaques analyzed using DNA array

A better understanding of atherogenesis at the level of gene expression could lead to the identification of new therapeutic strategies for vascular diseases. With DNA array technology, it is possible to identify multiple, simultaneous changes in gene expression in small tissue samples from atherosclerotic arteries. We analyzed gene expression in normal arteries and in immunohistologically characterized human advanced atherosclerotic lesions using an array of 18376 cDNA fragments. The array method was first validated by detecting a group of genes (n=17) that were already known to be connected to atherogenesis. These genes included e.g. Apolipoprotein E, CD68, TIMP and phospholipase D. Next we detected 75 differentially expressed genes that were previously not connected to atherogenesis. A subgroup of genes involved in cell signaling and proliferation was selected for further analyzes with in situ hybridization and RT-PCR which confirmed array results by showing induction in advanced lesions of Janus kinase 1 (JAK-1) which is an important signaling molecule in activated macrophages; VEGF receptor-2 which mediates angiogenic and vasculoprotective effects of VEGF; and an unknown gene, which mapped on chromosome 19. It is concluded that DNA array technology enables fast screening of gene expression in small samples of atherosclerotic lesions. The technique will be useful for the identification of new factors, such as JAK-1 and VEGF receptor-2, which may play an important role in atherogenesis.

Cell volume and rate of proliferation, but not protein expression pattern, distinguish pup/intimal smooth muscle cells from subcultured adult smooth muscle cells

Smooth muscle cells from neonatal rats and from injured blood vessels grow with a characteristic cobblestone morphology that distinguishes them from adult smooth muscle cells. This has led to the proposition that there are two distinct types of smooth muscle cells with different proliferative capacity. Here we systematically compare the properties of subcultured adult smooth muscle cells in culture and clonal lines of cobblestone smooth muscle cells from both neonatal rats and injured vessels. The cobblestone smooth muscle cells have a significantly smaller average cell volume, estimated using two different flow cytometry measurements. However, the two types of smooth muscle cells have indistinguishable protein expression patterns when the levels of more than 20 different proteins (including cytoskeletal proteins, matrix proteins, cytokines, cytokine receptors, adhesion molecules and enzymes) are measured by quantitative immunofluorescence. Furthermore, in contrast to previous observations, we demonstrate that both types of smooth muscle cells secrete a powerful mitogenic activity. The higher cell density achieved by the cobblestone smooth muscle cells in culture was responsible for the earlier reports that this mitogenic activity was secreted only by cobblestone smooth muscle cells. We conclude that many of the differences seen between cobblestone smooth muscle cells and adult smooth muscle cells in vitro (proliferation rate, morphology, protein expression pattern, secretion of mitogenic activity) could be attributable to a stable difference in the median cell volume of the cultures.

Targeted overexpression of IGF-I in smooth muscle cells of transgenic mice enhances neointimal formation through increased proliferation and cell migration after intraarterial injury

The response of arterial smooth muscle cells to injury is governed by a complex series of events. Significant among them is the paracrine production of peptide growth factors. To determine the impact of local IGF-I gene expression on vascular injury, the left carotid arteries of SMP8-IGF-I mice (in which IGF-I is selectively overexpressed in smooth muscle cells by means of a smooth muscle alpha-actin promoter) and wild-type controls were injured mechanically with an epon resin probe. After 7 and 14 d, a progressive increase in medial area was seen in both SMP8-IGF-I and wild-type mice, but they were not significantly different from each other. However, by 14 d there was a more than 4-fold increase in neointimal area in transgenic vs. wild-type. The intima/media ratios were also strikingly increased at 14 d in the IGF-I-overexpressing animals. The mitotic index, determined in animals injected daily with bromodeoxyuridine for 3 d before death, was markedly elevated in both the media and neointima 7 d after injury in SMP8-IGF-I mice, but the effect had subsided by 14 d. Despite a higher rate of cell division, the relative increase in medial area was less in the SMP8-IGF-I mice than in wild-type mice at both 7 and 14 d, consistent with a stimulation of cell migration to the neointima. The experiments reported here provide compelling evidence that paracrine expression of IGF-I is a powerful stimulus for smooth muscle cell proliferation and migration in vivo.

Phenotypic heterogeneity influences apoptotic susceptibility to retinoic acid and cis-platinum of rat arterial smooth muscle cells in vitro: Implications for the evolution of experimental intimal thickening

Rat aortic smooth muscle cells (SMCs) cultured from intimal thickening 15 days after endothelial injury (IT-15), unlike those of normal media, show a monolayered, epithelioid phenotype and high levels of cellular retinol binding protein-1 (CRBP). Epithelioid clones obtained from the normal media suggest a "mosaicism" of arterial SMCs. Intimal cell homeostasis from the balance of proliferation and apoptosis is critical for the progression of vascular lesions. All-trans retinoic acid (tRA) reduced [(3)H]thymidine incorporation and G(1)-->S phase progression of IT-15 and epithelioid clone but not of normal media and IT 60 days after injury (IT-60) SMCs. Hoechst staining, flow cytometry, and ligation-mediated polymerase chain reaction showed an increased susceptibility of IT-15 and epithelioid clone to tRA and cis-diaminedichloroplatinum II (CDDP)-induced apoptosis and cytotoxicity compared with normal media and IT-60 cells. The latter retained an increased susceptibility to tRA-induced apoptosis compared with normal media SMCs. tRA-induced apoptosis associated with an increased ratio of bax to bcl-2 by bax overexpression and cleavage of caspase-3. Anti-CRBP but not anti-IgG antibody prevented tRA-induced apoptosis and changes in related signaling molecules but not CDDP effects. Our findings support the relevant role of phenotypic heterogeneity in the determining proliferative as well as apoptotic behavior of arterial SMCs.

Functional specificity of actin isoforms

Actin, one of the main proteins of muscle and cytoskeleton, exists as a variety of highly conserved isoforms whose distribution in vertebrates is tissue-specific. Synthesis of specific actin isoforms is accompanied by their subcellular compartmentalization, with both processes being regulated by factors of cell proliferation and differentiation. Actin isoforms cannot substitute for each other, and the high-level synthesis of exogenous actins leads to alterations in cell organization and morphology. This indicates that the highly conserved actins are functionally specialized for the tissues in which they predominate. The first goal of this review is to analyze the data on the polymerizability of actin isoforms to show that cytoskeleton isoactins form less stable polymers than skeletal muscle actin. This difference correlates with the dynamics of actin microfilaments versus the stability of myofibrillar systems. The three-dimensional actin structure as well as progress in the analysis of conformational changes in both the actin monomer and the filament allows us to view the data on the structure and polymerization of isoactins in terms of structure-function relationships within the actin molecule. Most of the amino acid substitutions that distinguish actin isoforms are located apart from actin-actin contact sites in the polymer. We suggest that these substitutions can modulate the ability of actin monomers to form more or less stable polymers by long-range (allosteric) regulation of the contact sites.

Homeobox protein Hex induces SMemb/nonmuscle myosin heavy chain-B gene expression through the cAMP-responsive element

Recent studies have shown that the homeobox gene Hex plays an important role in inducing differentiation of vascular endothelial cells. In this study, we examined the expression of Hex in vascular smooth muscle cells (VSMCs) in vitro and in vivo. Immunohistochemistry showed a marked induction of Hex protein in neointimal VSMCs after balloon injury in rat aorta. Western and reverse transcriptase-polymerase chain reaction analyses demonstrated that Hex was abundantly expressed in cultured VSMCs, whereas it was undetectable in other cell types or in normal aorta. The expression pattern of Hex was similar to that of SMemb/NMHC-B, a nonmuscle isoform of myosin heavy chain that we have previously reported to be a molecular marker of dedifferentiated VSMCs. We next examined the role of Hex in SMemb gene transcription. Promoter analysis demonstrated that the sequence identical to consensus cAMP-responsive element (CRE) located at -481 of the SMemb promoter was critical for Hex responsiveness. Mutant Hex expression vector, which lacks the homeodomain, failed to stimulate SMemb gene transcription, suggesting the requirement of the homeodomain for its transactivation. Elecrophoretic mobility shift assay showed that Hex binds to a consensus binding sequence for homeobox proteins, but not to CRE. Cotransfection of protein kinase A expression vector increased the ability of Hex to stimulate SMemb promoter activity in a CRE-dependent manner. Overexpression of CRE binding protein (CREB), but not Mut-CREB which contains mutation at Ser133, strongly activated Hex-induced SMemb promoter activity. These results suggest that Hex mediates transcriptional induction of the SMemb/NMHC-B gene via its homeodomain, and Hex can function as a transcriptional modulator of CRE-dependent transcription in VSMCs.

The smooth muscle gamma-actin gene promoter is a molecular target for the mouse bagpipe homologue, mNkx3-1, and serum response factor

An evolutionarily conserved vertebrate homologue of the Drosophila NK-3 homeodomain gene bagpipe, Nkx3-1, is expressed in vascular and visceral mesoderm-derived muscle tissues and may influence smooth muscle cell differentiation. Nkx3-1 was evaluated for mediating smooth muscle gamma-actin (SMGA) gene activity, a specific marker of smooth muscle differentiation. Expression of mNkx3-1 in heterologous CV-1 fibroblasts was unable to elicit SMGA promoter activity but required the coexpression of serum response factor (SRF) to activate robust SMGA transcription. A novel complex element containing a juxtaposed Nkx-binding site (NKE) and an SRF-binding element (SRE) in the proximal promoter region was found to be necessary for the Nkx3-1/SRF coactivation of SMGA transcription. Furthermore, Nkx3-1 and SRF associate through protein-protein interactions and the homeodomain region of Nkx3-1 facilitated SRF binding to the complex NKE.SRE. Mutagenesis of Nkx3-1 revealed an inhibitory domain within its C-terminal segment. In addition, mNkx3-1/SRF cooperative activity required an intact Nkx3-1 homeodomain along with the MADS box of SRF, which contains DNA binding and dimerization structural domains, and the contiguous C-terminal SRF activation domain. Thus, SMGA is a novel target for Nkx3-1, and the activity of Nkx3-1 on the SMGA promoter is dependent upon SRF.

Effects of extracellular matrix on phenotype modulation and MAPK transduction of rat aortic smooth muscle cells in vitro

The transition of arterial smooth muscle cells (SMCs) from a contractile to a synthetic phenotype may play an essential role in the formation of atherosclerotic and restenotic lesions. This process includes a prominent structural reorganization and allows cells to acquire the ability to migrate, proliferate, and secrete extracellular matrix components. According to Western blotting analysis and immunohistochemical and morphological observations, laminin not only retains SMCs in a contractile state but also possibly stimulates cells to transform a synthetic to a contractile phenotype at an early stage, mediated by P38 MAPK signal transduction. However, fibronectin promotes SMCs to transform from a contractile to a synthetic phenotype, mediated by the ERK MAPK signal pathway. The localization of smooth muscle alpha -actin, myosin heavy chain isoform SM2, and vimentin in explant-isolated rat SMCs was affected by a substrate of fibronectin and laminin and also by ERK MAP kinase inhibitor (PD098059) and P38 MAPK inhibitor (SB203580). Furthermore, vimentin may play a much more important role in differentiation than desmin in phenotype modulation in rat aortic smooth muscle cells.

Photodynamic therapy induces apoptosis in intimal hyperplastic arteries

Photodynamic therapy (PDT) generates free radicals through the absorption of light by photosensitizers. PDT shows promise in the treatment of intimal hyperplasia, which contributes to restenosis, by completely eradicating cells in the vessel wall. This study investigates the mechanisms of PDT-induced cell death. PDT, using the photosensitizer chloroaluminum-sulfonated phthalocyanine (1 mg/kg) and laser light (lambda = 675 nm) 100 J/cm(2) was administered to rat carotid arteries after balloon injury-induced intimal hyperplasia. Apoptosis was determined by cell morphology with light microscopy and transmission electron microscopy, DNA cleavage by terminal dUTP nick-end labeling staining, and nucleosomal fragmentation (ladder pattern) by DNA agarose gel electrophoresis. Four hours after PDT, apoptosis was observed in vascular cells, as evidenced by terminal dUTP nick-end labeling staining and transmission electron microscopy. Within 24 hours no cells were present in the neointima and media. Immunofluorescence using an alpha-smooth muscle cell actin antibody confirmed the disappearance of all neointimal and medial cells within 24 hours. No inflammatory cell infiltrate was observed during this time frame. Apoptosis was sharply confined to the PDT treatment field. These data demonstrate that vascular PDT induces apoptosis as a mechanism of rapid, complete, and precise cell eradication in the artery wall. These findings and the lack of inflammatory reaction provide the basis for understanding and developing PDT for a successful clinical application in the treatment of hyperplastic conditions such as restenosis.

Induction of smooth muscle alpha-actin in vascular smooth muscle cells by arginine vasopressin is mediated by c-Jun amino-terminal kinases and p38 mitogen-activated protein kinase

Exposure of vascular smooth muscle cells to arginine vasopressin (AVP) increases smooth muscle alpha-actin (SM-alpha-actin) expression through activation of the SM- alpha-actin promoter. The goal of this study was to determine the role of the mitogen-activated protein kinase (MAP kinase) family in regulation of SM-alpha-actin expression. AVP activated all three MAP kinase family members: ERKs, JNKs, and p38 MAP kinase. Inhibition of JNKs or p38 decreased AVP-stimulated SM-alpha-actin promoter activity, whereas inhibition of ERKs had no effect. A 150-base pair region of the promoter containing two CArG boxes was sufficient to mediate regulation by vasoconstrictors. Mutations in either CArG box decreased AVP-stimulated promoter activity. Electrophoretic mobility shift assays using oligonucleotides corresponding to either CArG box resulted in a complex of similar mobility whose intensity was increased by AVP. Antibodies against serum response factor (SRF) completely super-shifted this complex, indicating that SRF binds to both CArG boxes. Overexpression of SRF increased basal promoter activity, but activity was still stimulated by AVP. AVP stimulation rapidly increased SRF phosphorylation. These data indicate that both JNKs and p38 participate in regulation of SM- alpha-actin expression. SRF, which binds to two critical CArG boxes in the promoter, represents a potential target of these kinases.

Temporal events underlying arterial remodeling after chronic flow reduction in mice: correlation of structural changes with a deficit in basal nitric oxide synthesis

To define the cellular events of vascular remodeling in mice, we measured blood flow and analyzed the morphology of remodeled vessels at defined points after a flow-reducing remodeling stimulus for 3, 7, 14, and 35 days. Acute ligation of the left external carotid artery reduced blood flow in the left common carotid artery (LC) compared with sham and contralateral right common carotid arteries (RCs). In morphometric analyses, the decrease in diameter in LCs was reversible by vasodilator perfusion 3 days after ligation, whereas ligation for 7 days or greater resulted in a permanent diameter reduction. Coincident with structural remodeling at day 7 was an increase in cell death in remodeled LCs. Functionally, rings from remodeled LCs contracted to prostaglandin F(2alpha) and relaxed to acetylcholine in a manner identical to that of control arteries. However, remodeled LCs were hypersensitive to the nitrovasodilator sodium nitroprusside (at day 7) and exhibited a marked reduction in basal NO synthesis at 7 and 14 days after ligation. The impairment of endothelial NO synthase function was likely due to post-translational mechanisms, given that endothelial NO synthase mRNA and protein levels did not change in remodeled LCs. These data define the ontogeny of flow-triggered luminal remodeling in adult mice and suggest that endothelial dysfunction occurs during reorganization of the vessel wall.

Local paclitaxel delivery for the prevention of restenosis: biological effects and efficacy in vivo

OBJECTIVE

The aim of this study was to evaluate the potential of paclitaxel to prevent restenosis in vivo.

BACKGROUND

Paclitaxel (Taxol) is a microtubule-stabilizing compound with potent antitumor activity. It influences the cytoskeleton equilibrium by increasing the assembly of altered microtubules, thereby inducing cellular modifications that result in reduced proliferation, migration and signal transduction.

METHODS

Before the in vivo study, delivery efficiency was determined with radiolabeled paclitaxel in porcine hearts. After induction of a defined plaque in the right carotid arteries of 76 New Zealand rabbits by electrical stimulation, 27 animals underwent balloon dilation and subsequent local paclitaxel delivery (10 ml, 10 micromol/liter) with a double-balloon catheter. Twenty-nine animals served as control with angioplasty only, 10 animals underwent local delivery of vehicle only (0.9% NaCl solution) and 10 animals were solely electrostimulated. Vessels were excised one, four, and eight weeks after intervention.

RESULTS

The extent of stenosis in paclitaxel-treated animals was significantly reduced compared with balloon-dilated control animals (p = 0.0012, one, four and eight weeks after intervention: 14.6%, 24.6% and 20.5%, vs. 24.9%, 33.8% and 43.1%, respectively). Marked vessel enlargement compared with balloon-dilated control animals could be observed (p = 0.0001, total vessel area after one, four and eight weeks: paclitaxel group: 1.983, 1.700 and 1.602 mm2, control: 1.071, 1.338 and 1.206 mm2, respectively). Tubulin staining and electron microscopy revealed changes in microtubule assembly, which were limited to the intimal area. Vasocontractile function after paclitaxel treatment showed major impairment.

CONCLUSIONS

Local delivery of paclitaxel resulted in reduced neointimal stenosis and enlargement in vessel size. Both these effects contribute to a preservation of vessel shape and are likely to be caused by a structural alteration of the cytoskeleton.

The extracellular matrix dynamically regulates smooth muscle cell responsiveness to PDGF

Focal accumulation of smooth muscle (SMC) within the arterial intima contributes to the formation of lesions of atherosclerosis. Platelet-derived growth factor (PDGF) is a potent stimulant of SMC migration and proliferation in culture that may play a role in the accumulation of SMC in atherogenesis. SMCs normally reside in the media of the artery wall surrounded by extracellular matrix (ECM), including type I collagen. In atherogenesis, the ECM is degraded, new ECM components, such as fibronectin, are synthesized and assembled, and these alterations in ECM components are associated with changes in SMC phenotype. To model the changes in ECM in normal and diseased arteries, we have analyzed SMCs cultured on different forms of type I collagen. Our studies demonstrate that integrin-mediated signals from various forms of type I collagen lead to specific and rapid modulation of the integrin signaling complex, including cytoskeletal connections, and of the responsiveness of SMC to PDGF stimulation.

Osteopontin expression in spontaneously developed neointima in fowl (Gallus gallus)

Fowl show spontaneous elevation of blood pressure and neointimal plaque formation in the abdominal aorta at young ages. A similar neointima can be induced by a balloon-catheter-induced endothelium injury to the fowl aorta. Both spontaneously developed and injury-induced vascular lesions exhibit subendothelial hyperplasia consisting of neointimal cells with a synthetic phenotype and abundant extracellular matrix. The role of the extracellular matrix in the formation of neointima is not known. In this study, we investigated whether osteopontin, an adhesive glycoprotein present in the extracellular matrix, is expressed in aortic smooth muscle tissue of the fowl abdominal aorta, in spontaneously developed neointimal plaques and in the aortic smooth muscle underlying neointimal plaques. Crude protein extracted from isolated aortic smooth muscle tissues and neointimal plaques was fractionated by SDS-polyacrylamide gel electrophoresis and analyzed by immunoblotting with rabbit anti-fowl osteopontin (provided by Dr L. C. Gerstenfeld, Boston University) or anti-α smooth muscle actin antibodies. The anti-fowl osteopontin antibody predominantly recognized a 66–70 kDa protein band in neointimal plaques that co-migrated with the osteopontin phosphoprotein from chick bone. In contrast, intact aortic smooth muscle and the smooth muscle underlying neointimal plaques equally expressed three proteins (66–70 kDa, approximately 50 kDa and approximately 43 kDa) recognized by the anti-osteopontin antibody. Anti-α smooth muscle actin antibody recognized a 43 kDa protein band, and the expression of α smooth muscle actin was higher in aortic smooth muscle than in neointimal plaques. Osteopontin mRNA expression was examined using reverse transcription-polymerase chain reaction (RT-PCR) of total RNA from vascular tissues with specific primers constructed on the basis of the reported fowl osteopontin nucleotide sequence. The PCR products from intact aortic smooth muscle and neointimal plaques correspond to the product from recombinant plasmid cDNA (a gift from Dr L. C. Gerstenfeld) transcribed in vitro. These results suggest that osteopontin is synthesized in intact aortic smooth muscle and neointimal plaques in fowl and that unmetabolized approximately 66 kDa osteopontin protein is a predominant form in the neointima, indicating that osteopontin protein may be actively synthesized in the neointima.

Role of endothelial cell denudation and smooth muscle cell dedifferentiation in neointimal formation of human vein grafts after coronary artery bypass grafting: therapeutic implications

OBJECTIVE

To provide better insights into the genesis of neointimal thickening in human vein grafts early after surgery.

DESIGN

Retrospective study.

SETTING

Tertiary referral centre.

SUBJECTS

18 distal anastomotic sites of patent grafts, obtained at necropsy from eight patients who died over differing periods (ranging from two days to nine months) after the procedure.

MAIN OUTCOME MEASURES

Immunohistochemical evaluation of smooth muscle cell phenotype modulation in relation to proliferative activity.

RESULTS

The earliest changes are characterised by loss of surface lining endothelial cells and insudation of blood corpuscular elements admixed with fibrin-platelet thrombus. At sites of injury vimentin positive and actin negative spindle shaped cells appear in the intima, while the related pre-existent media shows focal absence of actin positive smooth muscle cells. Proliferative activity colocalises at these sites. With time distinct neointimal thickening occurs, associated with disappearance of proliferative activity and a phenotypic shift of the smooth muscle cells.

CONCLUSIONS

The observation that luminal endothelial cell denudation, with insudation of the intima with blood elements, occurs in the very early stages suggests that these phenomena are responsible for the observed dedifferentiation of pre-existent smooth muscle cells, known to be a prerequisite for cell proliferation and the evolution of intimal thickening. It is likely, therefore, that platelet released growth factors play a pivotal role, which thus may provide a target for preventive pharmacological intervention.

Effects of partial bladder outlet obstruction and its relief on types I and III collagen and detrusor contractility in the rat

Bladder outlet obstruction induces a rapid hypertrophy characterized by increased bladder mass and collagen deposition. An increase in collagen is likely to reduce the contractility and compliance of bladder wall. This study was undertaken to investigate the effects of partial bladder outlet obstruction and its relief on types I and III collagen, and the relationship between detrusor contractility and collagen types. A total of 40 female rats was used for experiment and divided into one control, one obstruction, and three recovery groups. The contractility to field stimulation was recorded; total collagen and collagen concentration were quantified. The localization of types I and III collagen and the expression of pro-alpha1(I) and alpha1(III) collagen mRNA were determined by immunohistochemical staining and Northern blot hybridization, respectively. Contractile response to field stimulation was reduced after obstruction and recovered following relief. The total amount of collagen increased after obstruction and decreased after relief; however, collagen concentration decreased after obstruction and increased following relief. Contractility correlated negatively with total collagen but positively with collagen concentration. The protein deposition of types I and III collagen was localized in lamina propria and muscle bundles in all groups. The expression of types I and III collagen gene was up regulated after obstruction, but down regulated after relief. Negative correlation between contractility and gene expressions of collagen types was significant. These data suggest that the change in localization and quantity of collagen types leads to morphologic changes of bladder and can have an impact on the contractility of detrusor. Neurourol. Urodynam. 19:29-42, 2000.

Characterization of an E-box-dependent cis element in the smooth muscle alpha-actin promoter

Identification of the regulators of smooth muscle specific gene expression is critical for understanding smooth muscle cell (SMC) differentiation and the alterations in SMC phenotype seen in vascular diseases. Previous studies have identified that a 2-bp mutation in a conserved cis-acting element (TGTTTATC) in the promoter of the chicken smooth muscle (SM) alpha-actin gene abolished nuclear factor binding and decreased transcriptional activity of a 271-bp SM alpha-actin promoter fragment when transfected into rat aortic SMC. However, the promoter region containing this conserved sequence has negative cis regulatory activity when studied in homologous systems. The goal of the present studies was to further characterize the transcriptional activity of the rat SM alpha-actin promoter region between -224 and -236 that is conserved across mammals. DNAse I analysis and electrophoretic mobility shift assays demonstrated that SMC nuclear proteins bound an extended sequence (TGTTTATCCCCATAA). Transient transfection experiments of wild-type and mutant rat SM alpha-actin promoter-luciferase constructs into rat aortic SMC revealed that promoter activity was enhanced by mutations of specific nucleotides in the TGTTTATCCCCA region. Interestingly, the TGTTTATCCCCA element in the rat SM alpha-actin promoter is centered between 2 canonical E-boxes. Mutations of the flanking E-boxes abolished the enhancement in promoter activity seen with mutation of the TGTTTATCCCCA element alone. Thus studies provide evidence for a regulatory cassette in the rat SM alpha-actin promoter that regulates gene expression via combinatorial interactions between 2 E-boxes and a newly described TGTTTATCCCCA element.

Upstream stimulatory factor 1 regulates osteopontin expression in smooth muscle cells

Vascular smooth muscle cells (SMCs) undergo a dramatic phenotypic transition in response to injury and ex vivo culture that includes enhanced proliferation, migration, matrix deposition, and alterations in gene expression. Osteopontin is a good marker for the injury-induced SMC phenotypic state in vivo and in vitro. To identify transcription factors that might control the regulation of osteopontin expression, we investigated cultured vascular SMCs that express high and low levels of osteopontin. Using nuclear run-on assays, mRNA stability studies, and deletion analysis, we demonstrate that regulation of osteopontin steady-state mRNA levels in SMCs occurs at the transcriptional level. Transient transfection and gel-shift analyses of osteopontin promoter indicated that a region between -123 and +66 was involved in the expression of osteopontin. Supershift EMSAs identified the bHLH-leucine zipper transcription factor upstream stimulatory factor-1 (USF1) as the protein binding to this sequence. Finally, we show that USF1 protein is induced in vivo within 24 h of balloon angioplasty of rat carotids coordinately with osteopontin induction. These data suggest that USF1 governs expression of osteopontin in cultured vascular SMCs and might contribute to initial osteopontin expression observed post carotid injury and in vascular pathologies in vivo.

Matrix metalloproteinase can facilitate the heparanase-induced promotion of phenotype change in vascular smooth muscle cells

Previous studies from this laboratory have shown that degradation of heparan sulphate proteoglycan by both living macrophages and macrophage lysosomal heparanase induces phenotypic change of vascular smooth muscle cells (SMC) from a high volume fraction of myofilaments (V(v)myo) to a low V(v)myo [Campbell et al. Exp Cell Res 1992; 200: 156-167]. The aim of this study was to determine whether matrix metalloproteinase (MMP) activity is also involved in the induction of SMC phenotypic change by macrophages. A specific inhibitor of MMPs (BB94) was able to block macrophage-induced SMC phenotypic change and subsequent DNA synthesis in freshly dispersed SMC seeded in primary culture at confluent density. The inhibitor did not block these SMC changes when SMC were seeded at low density without macrophages nor did it block heparanase activity directly. We also determined whether heparanase and MMP activities are upregulated together in vivo. Artery homogenates were analysed in a heparanase enzyme assay and for MMPs using zymograms. Increased heparanase activity was observed 3-14 days following balloon catheter injury of rabbit carotid arteries, and returned to control levels 6 weeks after injury. Active MMP2 was induced with heparanase after injury. MMP9 induction was also apparent 6 h after injury. Immunohistology on sections of these arteries showed the presence of MMPI1, 2, 3 and 9 with these MMPs being strongly induced in the intima 7 days after balloon catheter injury. Both heparanase and MMP activities were also present in human end-stage complex lesions from coronary arteries, carotid endarterectomies and abdominal aortic aneurysms. Because MMPs and heparanase are expressed at the same time, it is possible that MMPs facilitate heparanase activity in promotion of phenotypic modulation of SMC in vivo during neointimal thickening following injury and in atherosclerotic lesions.

Targeted expression of SV40 large T-antigen to visceral smooth muscle induces proliferation of contractile smooth muscle cells and results in megacolon

Many pathological conditions result from the proliferation and de-differentiation of smooth muscle cells leading to impaired contractility of the muscle. Here we show that targeted expression of SV40 large T-antigen to visceral smooth muscle cells in vivo results in increased smooth muscle cell proliferation without de-differentiation or decreased contractility. These data suggest that the de-differentiation and proliferation of smooth muscle cells, seen in many pathological states, may be independently regulated. In the T-antigen transgenic mice the increased smooth muscle cell proliferation results in thickening of the distal colon. Consequently the distal colon becomes hyper-contractile and impedes the flow of digesta through the colon resulting in enlargement of the colon oral to the obstruction. These transgenic mice thus represent a novel model of megacolon that results from increased smooth muscle cell proliferation rather than altered neuronal innervation.

Smooth muscle differentiation in human vein wall at valvular level: comparison with nonvalvular wall and correlation with venous function

The aim of this study was to evaluate local differences in smooth muscle differentiation in venous valves of patients suffering from chronic venous insufficiency, in relation to functional hemodynamic parameters measured by echo Doppler. These functional parameters did not correlate with smooth muscle differentiation at the valvular site. These results failed to support an initiating role of valvular structure in the development of chronic venous insufficiency. However, this work stresses differences in cellular differentiation of valve wall and nonvalvular smooth muscle cells in culture, and we found histologic differences in the structure of endovein and media (connective tissue relative content) between valvular and nonvalvular venous wall. The presence of smooth muscle cells in the valve cusp was demonstrated by smooth muscle alpha-actin-specific labeling and was observed to be restricted to one side of the valve cusp.

Enhanced neointimal growth in cultured rabbit aorta following in vivo balloon angioplasty

We have used in vivo balloon catheterization in combination with in vitro organ culture to develop a model system for vascular neointima formation. A Fogarty balloon catheter was used to deendothelialize and rupture the internal elastic lamina of aortae in adult rabbits. After three d of recovery, aortae were harvested, divided into segments, and placed into organ culture. We obtained a daily index of cell proliferation in cultured vessels using [3H]thymidine incorporation into DNA. Also, segments were collected and processed for routine histology or immunohistochemistry. Aortic segments that had undergone ballooning 3 d before harvest and then cultured exhibited diffuse neointimal growth after several d in vitro, whereas those from sham-operated (nonballooned) rabbits showed generally only a single endothelial cell layer that is characteristic of normal intima. Aortae that were harvested, balloon-damaged in vitro, and then cultured exhibited no neointimal growth. The neointima that developed in cultured segments from in vivo ballooned rabbits was primarily of smooth muscle cell origin as determined by positive immunostaining for alpha-smooth muscle actin. The intima:media thickness ratios were significantly higher in aortic segments from ballooned rabbits at harvest and after 4 or 7 d in culture compared with those from nonballooned rabbits. Also, the [3H]thymidine index was higher in the in vivo ballooned aorta compared to non-ballooned or in vitro ballooned vessel. We conclude that ballooning in vivo followed by exposure to blood-borne elements produces an enhanced proliferative response in cultured vessels that is distinct from other in vitro models of neointimal growth.

Control of vascular smooth muscle cell growth in fowl

In adult domestic fowl, angiotensin (ANG) receptors are present in the vascular smooth muscles (VSM) and in the endothelium, mediating vasorelaxation via endothelium-derived relaxing factor/cGMP. ANG II-induced relaxation is minor in chicks and becomes more marked as they mature but diminishes in adult birds, whereas ANG II neither relaxes nor contracts endothelium-denuded aortae from mature chickens. The present study examines in cultured fowl aortic SM cells whether (1) ANG II stimulates or inhibits VSM cell growth and, if so, whether this growth-stimulatory or -inhibitory effect changes with maturation/aging, and (2) S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide donor, and cGMP attenuate the basal or stimulated VSM cell growth. [Asp1, Val5]ANG II (native fowl ANG II, 10(-6) M) markedly increased (increase from vehicle control, 226.5%; P < 0.01) [3H]thymidine (Thd) incorporation into DNA of quiescent VSM cells (first subculture) from 6-week-old chicks. This growth-stimulating effect was reduced with age (41.4, 29.6, and 3.2% at 9, 19, and 43 weeks of age, respectively). In contrast, platelet-derived growth factor (PDGF, 20 ng/ml) increased [3H]Thd incorporation similarly in chicks, pullets, and hens. Furthermore, ANG II significantly (45.9%, P < 0.01) attenuated the growth-promoting effect of fetal calf serum in cultured VSM cells from 6-week-old chicks. This inhibitory effect also decreased in older birds. ANG II showed neither a growth-stimulatory nor -inhibitory effect in cultured neointimal cells. SNAP attenuated dose dependently (20-60 microM) the basal and PDGF-induced VSM cell growth, whereas cGMP inhibited basal growth only at a high dose (100 microM). These results indicate that in fowl VSM cells, ANG II is mitogenic and antimitogenic in chicks but not in mature birds, suggesting that phenotypic modulation occurs in the ANG receptors/signaling mechanism with maturation/age or in neointimal cells, whereas the mitogenic mechanism via PDGF remains in both young and mature birds.

Two MCAT elements of the SM alpha-actin promoter function differentially in SM vs. non-SM cells

Transcriptional activity of the smooth muscle (SM) alpha-actin gene is differentially regulated in SM vs. non-SM cells. Contained within the rat SM alpha-actin promoter are two MCAT motifs, binding sites for transcription enhancer factor 1 (TEF-1) transcriptional factors implicated in the regulation of many muscle-specific genes. Transfections of SM alpha-actin promoter-CAT constructs containing wild-type or mutagenized MCAT elements were performed to evaluate their functional significance. Mutation of the MCAT elements resulted in increased transcriptional activity in SM cells, whereas these mutations either had no effect or decreased activity in L6 myotubes or endothelial cells. High-resolution gel shift assays resolved several complexes of different mobilities that were formed between MCAT oligonucleotides and nuclear extracts from the different cell types, although no single band was unique to SM. Western blot analysis of nuclear extracts with polyclonal antibodies to conserved domains of the TEF-1 gene family revealed multiple reactive bands, some that were similar and others that differed between SM and non-SM. Supershift assays with a polyclonal antibody to the TEF-related protein family demonstrated that TEF-1 or TEF-1-related proteins were contained in the shifted complexes. Results suggest that the MCAT elements may contribute to cell type-specific regulation of the SM alpha-actin gene. However, it remains to be determined whether the differential transcriptional activity of MCAT elements in SM vs. non-SM is due to differences in expression of TEF-1 or TEF-1-related proteins or to unique (cell type specific) combinatorial interactions of the MCAT elements with other cis-elements and trans-factors.

Phenotype modulation in primary cultures of aortic smooth muscle cells from streptozotocin-diabetic rats

Diabetes mellitus is a major risk factor for atherosclerosis. In atherosclerotic lesions, arterial smooth muscle cells (SMC) change from a contractile to a synthetic phenotype characterized by active proliferation. A similar phenotype modulation occurs in vitro when isolated arterial SMC are grown in culture and is characterized by both changes in cell morphology and a typical switch in actin isoform expression. In this study, we examined the influence of streptozotocin (STZ)-induced diabetes on the differentiation state and the phenotype modulation of cultured rat aortic SMC. We used transmission electron microscopy to study the fine structure of STZ-diabetic and non-diabetic SMC in primary culture and immunological methods for the determination of the proportions of alpha-smooth muscle actin (alpha-SM) and nonmuscle beta-actin (beta-NM) isoforms. Cultured STZ-diabetic SMC exhibited a large cytoplasmic volume, rich in rough endoplasmic reticulum, when compared with cultured non-diabetic SMC. alpha-SM, organized in stress fibers, was less homogeneously and abundantly distributed and by contrast, beta-NM was more abundant in STZ-diabetic than in non-diabetic SMC. Cytofluorimetric analyses demonstrated that the alpha-SM content was reduced in freshly STZ-diabetic SMC. Furthermore, during logarithmic growth of cultured SMC, the decrease of alpha-SM was more important in STZ-diabetic than in non-diabetic SMC. Immunoblotting of actin isoforms confirmed that expression of beta-NM was more important in STZ-diabetic than in non-diabetic SMC even in freshly isolated cells. The results suggest that SMC from STZ-diabetic rats express a more dedifferentiated state and undergo a more rapid phenotypic modulation in primary cultures than SMC from non-diabetic rats. Therefore, diabetes could induce changes in the phenotype of arterial SMC which might be associated with the onset or progression of the atherogenic process.

Restenosis in human vein bypass grafts

The restenosis rate in vein bypass grafts is higher than in native coronary arteries, and both the cascade of regulatory factors and the vessel reaction may be altered. In this study, vein bypass atherectomy specimens were classified as primary (n = 10) or restenotic (n = 12). Immunohistochemistry with 11 primary antibodies showed low levels of proliferation in both tissues and similar amounts of extracellular matrix components in both primary and restenotic specimens at the time points at which tissue was removed for clinical reasons. Inflammation appeared increased in restenotic specimens. Using in situ hybridization, transforming growth factor-beta1 messenger RNA was detected in both primary and restenotic tissue, with a trend to higher expression in restenosis (8.4 +/- 5.3 vs. 9.4 +/- 7.4 grains/nucleus) and further increased expression in multiple compared with single restenoses (15.1 +/- 6.1 vs. 5.6 +/- 5.1 grains/nucleus, P < 0.05). Hence, there were no great differences in cell proliferation or extracellular matrix formation between primary and restenosis vein graft tissue, in contrast to previously described findings in arterial tissue. This suggests that primary vein graft tissue is already in a chronic 'restenosis-like' state and subsequent injury creates minimal additional upregulation.

Altered expression of alpha-actin, smooth muscle myosin heavy chain-1 and calponin in cultured smooth muscle cells by oxidized low density lipoproteins

The expression of the contractile proteins, alpha-actin, smooth muscle myosin heavy chain-1 (SM1) and calponin present in smooth muscle cells (SMC) in the presence of oxidized low density lipoproteins (oxLDL) was investigated in two different cell cultures: the mouse smooth muscle cell line SVSC and rat smooth muscle cells (RSMC). Exposure of the cells to 187 microg protein/ml oxLDL for 24 h reduced the expression of all three contractile proteins in both cell cultures when compared to cells incubated in the presence of native LDL. This investigation of the response of SMC contractile proteins to oxLDL may provide further insights into the mechanisms by which oxidatively modified LDL is atherogenic and suggests that oxLDL may contribute to the regulation of the expression of the genes responsible for the synthesis of smooth muscle cell contractile proteins.

Changes in cultured arterial smooth muscle cells isolated from chicks upon cholesterol feeding

We have developed cultures of smooth muscle cells (SMC) isolated from arterial hypercholesterolemic chicks (cholesterol-SMC). These cultures are suitable for the study at the molecular level of the changes in arterial SMC induced by a cholesterol diet. By using a strong dose of cholesterol (5%) for 10 d, we obtained very proliferative SMC which became foam cells after 30 d in culture. On the other hand, SMC cultures isolated from control-fed chicks had a lower growth rate than the SMC ones under the same culture conditions. DNA synthesis was fourfold greater in cholesterol-SMC than in control-SMC cultures. Intracellular cholesterol concentrations were the same in both cholesterol and control SMC during the first 14 d of culture but afterward increased in differing ways: after 20 d of culture the cholesterol-SMC increased their cholesterol content to double the control. We give here the results obtained from transmission electron microscopy, lipid analysis, proliferation studies, DNA, RNA and protein synthesis, and then discuss their implications.

Overexpression of P2Y2 purinoceptor in intimal lesions of the rat aorta

Extracellular nucleotides, particularly ATP, are involved in the modulation of arterial vasomotricity via P2 purinoceptors present on smooth muscle and endothelial cells. These nucleotides could also be implicated in the smooth muscle cell hyperplasia observed in intimal lesions. In this study, we tried to define the potential role of the P2Y2 (P2u) purinoceptor by studying its expression in normal and balloon-injured rat aortas. The cloning of a rat P2Y2 cDNA from a rat smooth muscle cell cDNA library made it possible to study P2Y2 expression both by Northern blot and in situ hybridization. Northern blot experiments indicated that P2Y2 mRNA was present in rat medial aortic smooth muscle and in cultured rat aortic smooth muscle cells. In situ hybridization indicated that P2Y2 mRNA was present in endothelial cells of the intima and in some smooth muscle cells scattered throughout the media of adult rat aortas, while almost all medial smooth muscle cells of rat embryo aorta expressed this receptor. In contrast with adult aortic media, the majority of neointimal smooth muscle cells found in aortic intimal lesions either 8 or 20 days after balloon injury were positive for P2Y2 mRNA. Moreover, a subpopulation of neointimal cells localized at the luminal surface could be identified by a higher P2Y2 expression than the underlying neointimal smooth muscle cells. These data showing a strong expression of the P2Y2 purinoceptor in the neointima of injured arteries suggest that extracellular nucleotides may be involved, via this receptor, in the intimal hyperplasia and/or chronic constriction observed at the lesion site, and consequently in the restenotic process.

Sequence of cDNAs encoding components of vascular actin single-stranded DNA-binding factor 2 establish identity to Puralpha and Purbeta

Transcriptional repression of the mouse vascular smooth muscle alpha-actin gene in fibroblasts and myoblasts is mediated, in part, by the interaction of two single-stranded DNA binding activities with opposite strands of an essential transcription enhancer factor-1 recognition element (Sun, S., Stoflet, E. S., Cogan, J. G., Strauch, A. R., and Getz, M. J. (1995) Mol. Cell. Biol. 15, 2429-2436). One of these activities, previously designated vascular actin single-stranded DNA-binding factor 2 includes two distinct polypeptides (p44 and p46) which specifically interact with the purine-rich strand of both the enhancer and a related element in a protein coding exon of the gene (Kelm, R. J., Jr., Sun, S., Strauch, A. R., and Getz, M. J. (1996) J. Biol. Chem. 271, 24278-24285). Expression screening of a mouse lung cDNA library with a vascular actin single-stranded DNA-binding factor 2 recognition element has now resulted in the isolation of two distinct cDNA clones that encode p46 and p44. One of these proteins is identical to Puralpha, a retinoblastoma-binding protein previously implicated in both transcriptional activation and DNA replication. The other is a related family member, presumably Purbeta. Comparative band shift and Southwestern blot analyses conducted with cellular p46, p44, and cloned Pur proteins synthesized in vitro and in vivo, establish identity of p46 with Puralpha and p44 with Purbeta. This study implicates Puralpha and/or Purbeta in the control of vascular smooth muscle alpha-actin gene transcription.

Effects of protein kinase C alpha overexpression on A7r5 smooth muscle cell proliferation and differentiation

Smooth muscle cell differentiation and proliferation are increasingly seen to be intimately tied to the etiology of atherosclerosis and hypertension. To determine the role of PKC alpha in the regulation of smooth muscle cell differentiation and proliferation, the rat embryonic smooth muscle cell line A7r5 was transfected with an expression vector containing the full-length PKC alpha cDNA. Neomycin-resistant clones which exhibited increased PKC alpha levels compared to wild-type cells were selected. The A7r5 cells overexpressing PKC alpha had altered morphology and decreased growth rates compared to wild-type cells and cells transfected only with the neomycin resistance gene. Electrophoretic mobility shift assays showed that nuclear extracts from overexpressing clones gave a different pattern of protein-DNA binding to an AP-1 consensus oligonucleotide compared to wild-type cells. In contrast to the growth characteristics of these clones, their levels of cell differentiation marker proteins such as vinculin and desmin were not affected by PKC alpha overexpression. Moreover, the smooth muscle-specific differentiation marker alpha-actin was markedly reduced, while beta-actin levels were found to remain unchanged. Northern blot analysis confirmed that alpha-actin downregulation occurred at the RNA level. Western blot analysis revealed that A7r5 cells have five different PKC isoforms and that these isoform protein levels were not changed by PKC alpha overexpression. These findings suggest that PKC alpha regulates growth and differentiation of A7r5 smooth muscle cells and that these changes might result from altered expression/function of AP-1 transcription factors.

Responsiveness to growth factors in aortic vascular smooth muscle cells from rats with cirrhosis

Hemodynamic changes in cirrhosis may be associated with alterations in aortic vascular smooth muscle cell (AVSMC) function. The present study compared the proliferative response to serum and growth factors in cirrhotic and control AVSMC. Serum from cirrhotic rats, cirrhotic cell lysates, and the conditioned medium of cultured cirrhotic AVSMC induced an increase in [3H]thymidine incorporation in control but not in cirrhotic AVSMC. Platelet-derived growth factor-beta (PDGF-BB) induced a greater increase in [3H]thymidine incorporation in cirrhotic than in control cells. [3H]thymidine incorporation induced by cirrhotic conditioned medium was blocked by anti-PDGF antibody. Immunoblot studies showed that the anti-PDGF antibody recognized a 30-kDa protein in the conditioned medium of cirrhotic AVSMC culture, a protein corresponding to PDGF. Binding studies of PDGF-BB indicated a twofold increase in receptor density in cirrhotic AVSMC with no alteration in affinity for PDGF-BB. We conclude that an increased responsiveness of cirrhotic AVSMC to the PDGF could contribute to alterations in AVSMC and muscle cell tone that may play a role in the hemodynamic changes in cirrhosis.

Hypertrophy and prolonged DNA synthesis in smooth muscle cells characterize pulmonary arterial wall thickening after monocrotaline pyrrole administration to rats

Monocrotaline pyrrole (MCTP) is a highly reactive pneumotoxic metabolite of the pyrrolizidine alkaloid plant toxin monocrotaline. When administered to rats, it causes a delayed and progressive lung injury, vascular remodeling, and pulmonary hypertension. Structural remodeling consists of endothelial cell swelling followed by increased thickness of the vascular media in small pulmonary arteries and muscularization of normally nonmuscular arteries. Experiments were performed to characterize DNA synthesis and cell proliferation in vascular smooth muscle cells (VSMCs) after MCTP and to determine their relationship to changes in the thickness of the arterial medial layer of pulmonary resistance vessels. Male Sprague-Dawley rats were treated with MCTP (3.5 mg/kg, intravenously) or its vehicle (dimethylformamide). To label cells actively synthesizing DNA, rats were given the thymidine analog, bromodeoxyuridine (BrdU), 3 times by intraperitoneal injection during the 24 hr preceding euthanasia. Using immunohistochemistry, BrdU incorporation was quantified as a ratio of labeled nuclei to total nuclei. Within 5 days after MCTP administration, the thickness of the medial smooth muscle layer in arteries 60-250 microm in diameter was increased, prior to evidence of right heart hypertrophy. BrdU incorporation by VSMCs in pulmonary arteries was not different in vehicle- and MCTP-treated rats for the first 48 hr after treatment. However, MCTP caused a significant increase in DNA synthesis in VSMC on days 3-8 in arteries up to 250 microm in diameter. Although increased DNA synthesis precedes cell proliferation, the relative number of medial VSMCs did not increase over 8 days, suggesting that hypertrophy alone was responsible for the increased thickness of the arterial media. These results demonstrate that MCTP causes thickening of the media of pulmonary vessels through VSMC hypertrophy and that the prolonged DNA synthesis that accompanies VSMC hypertrophy is not followed by proliferation.

Human immunodeficiency virus-associated vasculopathy in transgenic mice

There is substantial clinical evidence for the development of vascular disorders in human immunodeficiency virus (HIV)-infected individuals, particularly in the form of vasculitis. Transgenic mice carrying a replication-defective HIV-1 provirus with selective deletion of the gag, pol, and env genes developed extensive vasculopathy. Restricted expression of HIV nonstructural genes in smooth muscle cells was accompanied by the migration and proliferation of these cells in blood vessels of all sizes and at different body sites. The frequent infiltration observed in the hypertrophic vessel walls occurred predominantly in the adventitia and was composed of primarily T cells and occasionally plasma cells. The intimal thickening generated significant luminal narrowing in some vessels, and the restricted blood flow led to ischemia in the affected tissues. Interestingly, the endothelium did not appear to support HIV gene expression or be involved in the pathological process. This transgenic model provides an opportunity to dissect the mechanism underlying HIV-associated vasculopathy.

TGF-beta 1 reverses PDGF-stimulated migration of human aortic smooth muscle cells in vitro

Platelet-derived growth factor (PDGF) and transforming growth factor beta-1(TGF-beta 1) were tested separately or together for the ability to stimulate migration of human aortic vascular smooth muscle cells (VSMC). PDGF (10 ng/ml) stimulated migration of VSMC over a 48-h period. TGF-beta 1 (10 ng/ml) had no effect on migration during the same period. VSMC exposed simultaneously to both TGF-beta 1 and PDGF exhibited diminished migration (50%) when compared to cells treated only with PDGF. Cells that migrated in the presence of PDGF possessed short actin cables that extended from cellular processes at the leading edge of migrating cells; focal adhesions containing the alpha v beta 3/beta 5 integrins localised to the same region. Cells grown in the presence of TGF-beta 1 exhibited long, intensely stained actin filaments that spanned the entire length of the cell and were similar to untreated control VSMC. Focal adhesions containing alpha v beta 3/beta 5 distributed evenly on the basal surface in both TGF-beta 1-treated cells and control cultures. Cellular responses to PDGF were mitigated when TGF-beta 1 was present in the culture medium. VSMC grown in the presence of both PDGF and TGF-beta 1 exhibited elongated actin filaments that were similar to nonmotile TGF-beta 1-treated cultures. Concomitant exposure of VSMC to PDGF and TGF-beta 1 resulted in focal adhesions that distributed evenly on the lower cell surface. This study suggests that TGF-beta 1 can partially reverse the stimulatory effect of PDGF on VSMC migration in vitro by modifying the actin cytoskeleton and the distribution of the alpha v beta3/beta 5 integrins.

Differentiation of smooth muscle cells in human blood vessels as defined by smoothelin, a novel marker for the contractile phenotype

Smoothelin is a constituent of the cytoskeleton specific for smooth muscle cells (SMCs) in a broad range of species. It has been postulated that smoothelin represents a marker of highly differentiated, contractile SMCs. Here, we present data on the presence of smoothelin in the human vascular system that support this hypothesis. For this purpose, smoothelin distribution was studied (1) during vasculogenesis of the placenta, (2) in normal adult blood vessels, and (3) in atherosclerotic lesions. Smoothelin was first observed in placental tissue at approximately week 10 to 11 of gestation. In full-term placenta, it was found in the SMCs of vessels in the large stem villi and in the chorionic plate. Furthermore, it was present in the fetal arteries of smaller stem villi, but it was not found in the veins. In adult blood vessels, a small population of aortic (approximately 10%) and large muscular artery (approximately 30% to 50%) SMCs was positive for smoothelin. In general, smoothelin and desmin were coexpressed in the same SMCs, but expression of desmin appeared to be less abundant. However, the majority of SMCs in these blood vessels were smoothelin- and desmin negative but expressed vimentin, whereas alpha-smooth muscle actin (alpha-SMA) was present in all SMCs. The SMCs in the media of small muscular arteries were positive for smoothelin and desmin (> 95%), whereas the vimentin-positive SMC type was scarce. Smoothelin was absent in capillaries, pericytic venules, and small veins but was occasionally observed in the SMCs of large veins. Thus, the distribution of smoothelin in the SMCs of the vascular system appears to be limited to blood vessels that are capable of pulsatile contraction. In atherosclerotic femoral arteries, smoothelin-positive cells were detected in the media, the atheromatous plaque, and the intimal thickening. Smoothelin-positive cells were present primarily at the luminal portion of advanced lesions. The presence of a considerable number of such smoothelin-positive cells at that location may indicate that these plaques are no longer expanding.

Differential expression of nonmuscle myosin II isoforms in human atherosclerotic plaque

Intimal proliferation and functional changes involving vascular smooth muscle cells are key events in the development of atherosclerosis, including restenosis after percutaneous transluminal angioplasty. Nonmuscle myosin (NMM) is required for cytokinesis and has been shown in cultures of vascular smooth muscle cells to undergo changes of isoform expression depending on the stage of proliferation and differentiation. The purpose of this study was to examine the differential expression of the two most recently identified nonmuscle myosin heavy chain isoform II (NMMHC-II) isoforms A and B in atherosclerotic plaque. Primary atherosclerotic and restenotic atherectomy specimens and non-atherosclerotic controls, were analyzed by Western Blot analysis, immunohistochemistry and in situ hybridization. Nonmuscle myosin heavy chain isoform IIA (NMMHC-IIA) was equally expressed in all types of tissue specimens both at the protein and mRNA levels. In contrast, NMMHC-IIB protein was found in restenotic specimens and normal artery but was at very low levels in primary atherosclerotic plaque. By in situ hybridization NMMHC-IIB mRNA levels were significantly greater in restenotic versus primary atherosclerotic lesions. NMMHC-IIB expression is associated with vascular restenosis but is downregulated in stable atherosclerotic lesions, whereas NMMHC-IIA is expressed in both. These results indicate that these new myosin isoforms have different functions and should be regarded separately with respect to smooth muscle proliferation and restenosis. They should prove to be useful molecular markers for the study of atherosclerosis and restenosis.

Vascular myofibroblasts. Lessons from coronary repair and remodeling

Recent findings demonstrate that adventitial fibroblasts (i.e., nonmuscle cells) are endowed with several characteristics previously attributed to medial SM cells. The response of the coronary artery to balloon angioplasty is associated with the activation of adventitial cells in a porcine model. They appear to be the most reactive in the arterial wall, as reflected by the extent of proliferation and the synthesis of collagen. Differentiation of adventitial cells, which acquire alpha-SM actin, illustrates the formation of vascular myofibroblasts, a ubiquitous cellular mechanism of tissue repair. Myofibroblasts are involved in remodeling of the adventitia and may contribute to the formation of the neointima after balloon-induced coronary injury. These findings suggest that at least some synthetic SM-like cells present in intimal lesions may originate from medial or adventitial nonmuscle cells. Myofibroblasts also appear to play a role in other cardiovascular abnormalities (e.g., vein graft remodeling), which raises the possibility of targeted therapies.

Enhanced proliferation and migration and altered cytoskeletal proteins in early passage smooth muscle cells from young and old rat aortic explants

Smooth muscle cell (SMC) proliferation, migration, and cytoskeletal protein expression were studied in cultured cells obtained from the aortic explants of young (6-month) and old (30-month) Fischer 344XNB rats. Second-passage SMC were cultured on coverslips, and cytoskeletal fibers were examined by immunofluorescence microscopy using antibodies specific for smooth muscle myosin, alpha-smooth muscle actin, vimentin, desmin, and tubulin. The cytoskeletal fiber density was quantified as fluorescence intensity by confocal microscopy. The proliferation of SMC was analyzed from the growth curve of cells grown in culture from 0 to 14 days, and a Boyden chamber assay was used to quantify the SMC migration rate. The diameter of fresh SMC digested enzymatically from old rat aortae was 52.4% larger than that of the cells from young animals (20.0 +/- 3 microm vs 13.1 +/- 2 microm, P < 0.05). In SMC cultured from old animals, the intensities of smooth muscle myosin, alpha-smooth muscle actin, and vimentin decreased by 59.6, 41.2, and 54.8%, respectively; desmin and tubulin increased by 46.1 and 65.1% (all P < 0.001). Compared to SMC isolated from young rat aortae, the number of SMC cultured (second passage) from the old rat aorta was increased by 48.4, 27.2, and 26.9%, respectively, at Days 3, 7, and 14 in culture (P < 0.05, P < 0.01, and P < 0.001). The migration rate of SMC cultured from old rats was 59.3% higher than that of the cells obtained from young rats. These data show that alterations of the SMC cytoskeleton occur concomitantly with changes in SMC proliferation and migration rate during aging, suggesting that the age-associated changes in cytoskeletal proteins may play a role in remodeling of the aortic wall during aging.

Inflammatory cytokines cause coronary arteriosclerosis-like changes and alterations in the smooth-muscle phenotypes in pigs

We recently developed a porcine model in which chronic, local treatment with interleukin-1 beta (IL-1 beta) causes coronary arteriosclerosis-like changes and hyperconstrictive responses. This study was designed to examine whether or not other major inflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 alpha (IL-1 alpha) might also cause similar coronary responses and whether those responses are associated with alterations in the smooth-muscle phenotypes. A segment of the porcine coronary artery was aseptically wrapped with cotton mesh, absorbing IL-1 beta, TNF-alpha, and IL-1 alpha. Two weeks after the operation, coronary arteriography showed the development of mild stenotic lesions at the cytokine-treated sites, where hyperconstrictive responses were repeatedly induced by intracoronary serotonin or histamine. Histologically mild intimal thickening was noted at those cytokine-treated sites. Immunostaining and immunoblotting demonstrated that all three myosin heavy chain isoforms, SM1, SM2 (smooth-muscle type), and SMemb (nonmuscle type), were noted in the normal coronary segments, whereas in the segments treated with inflammatory cytokines, SM1 and SM2 were markedly reduced, and only SMemb was noted. These results indicate that inflammatory cytokines all have a similar ability to induce coronary arteriosclerosis-like changes and hyperconstrictive responses, which are associated with alterations in smooth-muscle phenotypes toward dedifferentiation.

Regional variability in the time course of TGF-beta 1 expression, cellular proliferation and extracellular matrix expansion following arterial injury

Transforming growth factor-beta 1 (TGF-beta 1) has been variably associated with the regulation of cellular proliferation and extracellular matrix expansion after arterial injury. We tested these associations in vivo in the rat carotid injury model. At 0, 3, 7, 14 and 28 days following arterial balloon injury, regional expression of TGF-beta 1 mRNA was assessed using in situ hybridization and the results compared to measures of cellular proliferation and extracellular matrix expansion. Both the TGF-beta 1 concentration measured in culture media of explanted carotid arteries and the quantitative in situ hybridization signal for TGF-beta 1 arterial media and neointima were maximal at 14 days after balloon injury. However, medial cellular proliferation was maximal at 3 days whereas neointimal proliferation was maximal at 14 days and significantly greater than medial proliferation. Neointimal cell density declined significantly between 7 and 14 days, indicating the expansion of extracellular matrix; however, medial cell density was unchanged between 3 and 28 days after balloon injury. Thus, differences in the regional arterial wall relationships between the time course of cellular proliferation, extracellular matrix expansion and the level of TGF-beta 1 expression demonstrate in vivo variability in the response to TGF-beta 1.

Hybridization of biotinylated oligo(dT) for eukaryotic mRNA quantitation

Quantitation of mRNA content in samples of total cellular RNA is required for the analysis of Northern blot hybridization to estimate the relative level of specific gene expression. Commonly used methods based on UV absorbance and dye staining measure only total RNA, and mRNA normalization by probing for mRNA levels of housekeeping genes, such as beta-actin and glyceraldehyde-3-phosphate dehydrogenase, assumes a constant level of their expression, which, in fact, may vary as a function of cell proliferation and differentiation. We describe here a nonradioactive, slot-blotting method for quantifying eukaryotic mRNA levels using a biotinylated oligo(dT) probe, which hybridizes directly to the 3'-polyadenylated sequence of eukaryotic mRNAs. The method provides a more accurate estimation of mRNA content in total RNA samples and should be applicable for quantitative Northern analysis.

Comparative effects of basic fibroblast growth factor and vascular endothelial growth factor on coronary collateral development and the arterial response to injury

BACKGROUND

We have shown that the angiogenic peptides basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) enhance canine coronary collateral development when administered for > or = 4 weeks. bFGF, a pluripotent mitogen of mesodermally derived cells, could theoretically exacerbate neointimal smooth muscle cell hyperplasia, a fundamental component of atherosclerosis. VEGF, an endothelial cell-specific mitogen and vascular permeability factor, could have deleterious effects related to vascular hyperpermeability. The present investigation had two aims: (1) to ascertain whether brief (7-day) systemic arterial treatment with bFGF or VEGF would improve myocardial collateral perfusion and (2) to determine whether these peptides induce neointimal accumulation in vivo.

METHODS AND RESULTS

Dogs were subjected to ameroid-induced occlusion of the left circumflex coronary artery and randomized to bFGF 1.74 mg (n = 9), VEGF 0.72 mg (n = 9), or saline (n = 10) as a daily left atrial bolus (days 10 to 16). Additional dogs were randomized to VEGF 0.72 mg (n = 6) or saline (n = 5); however, treatment was delayed by 1 week. Coincident with the institution of treatment, all dogs underwent balloon denudation injury of the iliofemoral artery. bFGF markedly increased maximal collateral flow but did not exacerbate neointimal accumulation. VEGF had no discernible effect on maximal collateral flow, but it exacerbated neointimal thickening after vascular injury.

CONCLUSIONS

Short-term treatment with bFGF enhanced collateral development without increasing neointimal accumulation at sites of vascular injury. Although VEGF did not increase collateral development as administered in this study, it significantly exacerbated neointimal accumulation. These data provide support for the clinical investigation of bFGF in selected patients with ischemic heart disease.