Transcriptional control of deformation-induced preproendothelin-1 gene expression in endothelial cells

Arterial wall stress controls NFAT5 activity in vascular smooth muscle cells

Background

Nuclear factor of activated T‐cells 5 (NFAT5) has recently been described to control the phenotype of vascular smooth muscle cells (VSMCs). Although an increase in wall stress or stretch (eg, elicited by hypertension) is a prototypic determinant of VSMC activation, the impact of this biomechanical force on the activity of NFAT5 is unknown. This study intended to reveal the function of NFAT5 and to explore potential signal transduction pathways leading to its activation in stretch‐stimulated VSMCs.

Methods and Results

Human arterial VSMCs were exposed to biomechanical stretch and subjected to immunofluorescence and protein‐biochemical analyses. Stretch promoted the translocation of NFAT5 to the nucleus within 24 hours. While the protein abundance of NFAT5 was regulated through activation of c‐Jun N‐terminal kinase under these conditions, its translocation required prior activation of palmitoyltransferases. DNA microarray and ChiP analyses identified the matrix molecule tenascin‐C as a prominent transcriptional target of NFAT5 under these conditions that stimulates migration of VSMCs. Analyses of isolated mouse femoral arteries exposed to hypertensive perfusion conditions verified that NFAT5 translocation to the nucleus is followed by an increase in tenascin‐C abundance in the vessel wall.

Conclusions

Collectively, our data suggest that biomechanical stretch is sufficient to activate NFAT5 both in native and cultured VSMCs where it regulates the expression of tenascin‐C. This may contribute to an improved migratory activity of VSMCs and thus promote maladaptive vascular remodeling processes such as hypertension‐induced arterial stiffening.

High glucose-induced increased expression of endothelin-1 in human endothelial cells is mediated by activated CCAAT/enhancer-binding proteins

High glucose-induced endothelial dysfunction is partially mediated by the down-stream pathophysiological effects triggered by increased expression of endothelin-1 (ET-1). The molecular control mechanisms of ET-1 synthesis are yet to be discovered. Members of the CCAAT/enhancer-binding proteins (C/EBP) family are important regulators of key metabolic processes, cellular differentiation and proinflammatory genes. In this study, we aimed at elucidating the role of C/EBP in mediating the high glucose effect on ET-1 expression in human endothelial cells (EC). Human umbilical vein cells (EAhy926) and primary cultures of human aortic EC were exposed to high levels of glucose (16.5-25 mM). Real-time PCR, Western blot, enzyme-linked immunosorbent assay, ET-1 promoter-luciferase reporter analysis, and chromatin immunoprecipitation assays were employed to investigate ET-1 regulation. High glucose activated C/EBPα, C/EBPβ, and C/EBPδ in a dose-dependent manner. It also promoted significant increases in ET-1 gene and peptide expression. Chemical inhibition of JNK, p38MAPK and ERK1/2 diminished significantly the high glucose-induced nuclear translocation of C/EBP and ET-1 expression. Silencing of C/EBPα, C/EBPβ or C/EBPδ greatly reduced the high glucose-induced upregulation of ET-1 mRNA, pre-pro-ET-1, and ET-1 secretion. The expression of various C/EBP isoforms was selectively downregulated by siRNA-mediated gene silencing. In silico analysis indicated the existence of typical C/EBP elements within human ET-1 gene promoter. Transient overexpression of C/EBPα, C/EBPβ or C/EBPδ upregulated the luciferase level controlled by the ET-1 gene promoter. The direct interaction of C/EBPα, C/EBPβ or C/EBPδ proteins with the ET-1 promoter in high glucose-exposed EC was confirmed by chromatin immunoprecipitation assay. High glucose-induced ET-1 expression is mediated through multiple mechanisms. We present evidence that members of the C/EBP proinflammatory transcription factors are important regulators of ET-1 in high glucose-exposed human endothelial cells. High glucose-induced activation of C/EBP-related signaling pathways may induce excessive ET-1 synthesis, thus promoting vasoconstriction and dysfunction of the vascular wall cells in diabetes.

Hypertension impairs myocardin function: a novel mechanism facilitating arterial remodelling

AIMS

Hypertension evokes detrimental changes in the arterial vessel wall that facilitate stiffening and thus lead to a further rise in mean blood pressure, eventually causing heart failure. The underlying pathophysiological remodelling process is elicited by an increase in wall stress (WS) and is strictly dependent on the activation of vascular smooth muscle cells (SMC). However, it remains unclear as to why these cells fail to maintain their contractile and quiescent phenotype in a hypertensive environment.

METHODS AND RESULTS

In this context, we reveal that the knockdown of myocardin--a pivotal transcriptional determinant of the contractile SMC phenotype--is sufficient to induce SMC proliferation. In line with this observation, immunofluorescence analysis of the media of remodelling arteries from hypertensive mice demonstrated a significant decrease in the abundance of myocardin and an increase in SMC proliferation. Subsequent analyses of isolated perfused mouse arteries and human cultured SMCs exposed to cyclic stretch (i.e. mimicking one component of WS) suggested that this biomechanical force facilitates serine phosphorylation of myocardin. Furthermore, this biomechanical stimulus promotes rapid translocation of myocardin from the nucleus to the cytoplasm, inhibits its mRNA expression, and causes proteasomal degradation of the cytoplasmic protein.

CONCLUSIONS

Collectively, these findings suggest that hypertension negates the activity of myocardin in SMCs on multiple levels, hence eliminating a crucial determinant of SMC quiescence. This mechanism may control the initial switch from the contractile towards the synthetic SMC phenotype during hypertension and may offer an interesting novel approach to prevent cardiovascular disease.

Toxicological insight from AP-1 silencing study on proliferation, migration, and dedifferentiation of rat vascular smooth muscle cell

There has an effective way to prevent intimal hyperplasia on vascular smooth muscle cell (VSMC) proliferation in grafted veins. The activator protein-1 (AP-1) transcription factor plays an important role in cardiovascular generation and angioplasty. Once activated, AP-1 binds its specific DNA sequence to promote the proliferation of VSMC, differentiation, and migration. The objectives of this study were to determine toxicological effects of AP-1 silencing study on proliferation, migration, and dedifferentiation of rat vascular smooth muscle cell. To suppress the expression of AP-1 gene, AP-1 siRNA was used to interfere post-transcription in rat primary VSMCs. To observe the expression of SM α-actin and downstream genes of AP-1, the activity of cell matrix metal proteinases and the migration ability of VSMC was examined by a modified Boyden chamber assay. Effects of AP-1 siRNA on proliferation and differentiation in rat VSMCs were evaluated by cell cycle analysis, DNA synthesis, MTT-test, and immunofluorescence. The results showed that the level of SM α-actin protein expression was increased. AP-1 siRNA also significantly decreased the MTT extinction value, DNA synthesis, PCNA expression, and the cell migration velocity when compared to the control group. AP-1 siRNA also clearly arrested cell cycle of VSM at the G0/G1 phase. Zymographic and Western blotting analyses showed that AP-1 siRNA suppressed serum-induced MMP-2 expression. These data suggest that the AP-1 siRNA was able to effectively inhibit the proliferation, migration, and dedifferentiation of smooth muscle cells. Thus, AP-1 siRNA provides a novel method to prevent intimal hyperplasia in blood vessel angioplasty.

Upregulation of glutathione peroxidase offsets stretch-induced proatherogenic gene expression in human endothelial cells

OBJECTIVE

Localization of atherosclerotic plaques typically correlates with areas of biomechanical strain where shear stress is decreased while stretch, thought to promote atherogenesis through enhanced oxidative stress, is increased.

METHODS AND RESULTS

In human cultured endothelial cells, nitric oxide synthase expression was exclusively shear stress-dependent whereas expression of glutathione peroxidase-1 (GPx-1), but not that of Cu(2+)/Zn(2+)-superoxide dismutase or Mn(2+)-superoxide dismutase, was upregulated solely in response to cyclic stretch. GPx-1 expression was also enhanced in isolated mouse arteries perfused at high pressure. Combined pharmacological and decoy oligodeoxynucleotide blockade revealed that activation of p38 MAP kinase followed by nuclear translocation of CCAAT/enhancer binding protein plays a pivotal role in stretch-induced GPx-1 expression in human endothelial cells. Antisense oligodeoxynucleotide knockdown of GPx-1 reinforced both their capacity to generate hydrogen peroxide and the transient stretch-induced expression of CD40, monocyte chemoatractant protein-1, and vascular cell adhesion molecule-1. Consequently, THP-1 monocyte adhesion to the GPx-1-depleted cells was augmented.

CONCLUSIONS

Stretch-induced proatherosclerotic gene expression in human endothelial cells seems to be hydrogen peroxide-mediated. The concomitant rise in GPx-1 expression, but not that of other antioxidant enzymes, may comprise an adaptive mechanism through which the cells maintain their antiatherosclerotic properties in spite of a decreased bioavailability of nitric oxide.

Stretch-Induced Activation of the Transcription Factor Activator Protein-1 Controls Monocyte Chemoattractant Protein-1 Expression During Arteriogenesis

Cerebral, coronary, and peripheral artery diseases combined represent the most frequent cause of death in developed nations. The underlying progressive occlusion of large conductance arteries can partially be compensated for by transformation of preexisting collateral arterioles to small artery bypasses, a process referred to as arteriogenesis. Because biomechanical forces have been implicated in the initiation of arteriogenesis, we have investigated the mechanosensitive expression of a pivotal proarteriogenic molecule, monocyte chemoattractant protein (MCP)-1, which governs the recruitment of circulating monocytes to the wall of the remodeling collateral arterioles. Using a new ear artery ligation model and the classic hindlimb ischemia model in mice, we noted that MCP-1 expression is significantly increased in collateral arterioles undergoing arteriogenesis already 24 hours after its onset. By mimicking proarteriogenic perfusion conditions in small mouse arteries, we observed that MCP-1 expression is predominantly upregulated in the smooth muscle cells, which solely sense changes in circumferential wall tension or stretch. Subsequent analyses of cultured endothelial and smooth muscle cells confirmed that cyclic stretch but not shear stress upregulates MCP-1 expression in these cells. Blockade of the mechanosensitive transcription factor activator protein-1 by using a specific decoy oligodeoxynucleotide abolished this stretch-induced MCP-1 expression. Likewise, topical administration of the decoy oligodeoxynucleotide to the mouse ear abrogated arteriogenesis through downregulation of MCP-1 expression and monocyte recruitment. Collectively, these findings point toward a stretch-induced activator protein-1–mediated rise in MCP-1 expression in vascular smooth muscle cells as a critical determinant for the initiation of arteriogenesis.

The epithelial membrane protein 1 is a novel tight junction protein of the blood-brain barrier

In the central nervous system, a constant microenvironment required for neuronal cell activity is maintained by the blood-brain barrier (BBB). The BBB is formed by the brain microvascular endothelial cells (BMEC), which are sealed by tight junctions (TJ). To identify genes that are differentially expressed in BMEC compared with peripheral endothelial cells, we constructed a subtractive cDNA library from porcine BMEC (pBMEC) and aortic endothelial cells (AOEC). Screening the library for differentially expressed genes yielded 26 BMEC-specific transcripts, such as solute carrier family 35 member F2 (SLC35F2), ADP-ribosylation factor-like 5B (ARL5B), TSC22 domain family member 1 (TSC22D1), integral membrane protein 2A (ITM2A), and epithelial membrane protein 1 (EMP1). In this study, we show that EMP1 transcript is enriched in pBMEC compared with brain tissue and that EMP1 protein colocalizes with the TJ protein occludin in mouse BMEC by coimmunoprecipitation and in rat brain vessels by immunohistochemistry. Epithelial membrane protein 1 expression was transiently induced in laser-capture microdissected rat brain vessels after a 20-min global cerebral ischemia, in parallel with the loss of occludin immunoreactivity. The study identifies EMP1 as a novel TJ-associated protein of the BBB and suggests its potential role in the regulation of the BBB function in cerebral ischemia.

Signal transducer and activator of transcription 1 decoy oligodeoxynucleotide suppression of contact hypersensitivity

BACKGROUND

Cytokines play a pivotal role in allergy development through activating signaling mechanisms, such as the Janus kinase/signal transducer and activator of transcription (STAT) pathway, which controls the expression of numerous proinflammatory genes.

OBJECTIVE

In comparison with 2 different corticosteroids and a calcineurin inhibitor, the efficacy of a STAT1 decoy oligodeoxynucleotide (dODN)-containing ointment on hapten-induced contact hypersensitivity was examined in 3 different animal models.

METHODS

After sensitization, the test compounds were administered before hapten challenge, after hapten challenge, or both to different sites of the animal skin. Subsequent erythema and edema formation was scored macroscopically, microscopically, or by a shift in ear weight. Biopsy specimens were taken and processed for histopathology, immunohistochemistry, and real-time PCR analyses.

RESULTS

Treatment with the STAT1 dODN but not the corresponding control ODN markedly improved the clinical signs of inflammation in all 3 animal models in a dose-related manner. In guinea pig skin this was accompanied by a distinct decrease in leukocyte infiltration into the dermis after 24 hours. In addition, expression of CD40, IFN-gamma, IL-1beta, IL-8, IL-12, and TNF-alpha was strongly attenuated. The dODN was equally effective in the domestic pig model when administered therapeutically, and its preventive effect in the mouse model lasted for more than 48 hours.

CONCLUSIONS

Altogether, treatment with the dODN proved to be at least as effective as treatment with the reference compounds.

Effect of AP-1 decoy using hemagglutinating virus of Japan-liposome on the intimal hyperplasia of the autogenous vein graft in mongrel dogs

Intimal hyperplasia is the leading cause of late vein graft failure. Smooth muscle cell proliferation and migration is the underlying mechanism. Pharmacological approaches to prolong vein graft patency have produced limited results. AP-1 proteins play a role in the expression of many genes involved in cellular proliferation and cell cycle progression. Previously we reported inhibition of vascular smooth muscle cell migration, proliferation, and intimal hyperplasia in the balloon-injured rat carotid artery using an AP-1 decoy with HVJ-liposomes. In this report, we evaluated the effect of the AP-1 decoy on intimal hyperplasia in a large animal model. The jugular vein was transfected with hemagglutinating virus of Japan-liposomes containing the AP-1 decoy or scrambled oligonucleotides. An interposition graft was performed with the pretreated jugular vein between the transected femoral arteries. The graft was harvested at 16 weeks after the procedure. The intimal area was compared: the intimal area of the AP-1 decoy-treated versus control group was 47.3 +/- 15.2 versus 102.3 +/- 15.9 (P < .05), respectively. In conclusion, AP-1 decoy using HVJ-liposomes effectively prevented intimal hyperplasia of an autogenous vein graft in mongrel dogs.

Inverse regulation of preproendothelin-1 and endothelin-converting enzyme-1beta genes in cardiac cells by mechanical load

Mechanical stretch and para- and/or autocrine factors, including endothelin-1, induce hypertrophy of cardiac myocytes and proliferation of fibroblasts. To investigate the effect of mechanical load on endothelin-1 production and endothelin system gene expression in neonatal rat ventricular myocytes and fibroblasts, we exposed cells to cyclic mechanical stretch in vitro (0.5 Hz, 10-25% elongation, from 1 min to 24 h). Endothelin-1 peptide levels were measured from culture media of myocytes and fibroblasts and human umbilical vein endothelial cells (positive control) by specific radioimmunoassay. Preproendothelin-1 promoter activity was measured via transfection of reporter plasmids and mRNA levels with Northern blot analysis or quantitative RT-PCR. Activity of extracellular signal-regulated kinase was quantified with specific kinase assay. We found that stretching of myocytes activated preproendothelin-1 gene expression, including promoter activation, transient mRNA level increases, and augmented endothelin-1 secretion. In contrast, preproendothelin-1 gene expression was inhibited in stretched fibroblasts. Endothelin-converting enzyme-1beta mRNA levels elevated in stretched fibroblasts but decreased in stretched myocytes. Endothelin receptor type A mRNA levels declined in stretched myocytes, whereas levels were below detection in fibroblasts. Stretch activated extracellular signal-regulated kinase in myocytes, and when the kinase activity was pharmacologically inhibited, the preproendothelin-1 induction was suppressed. Transient overexpression of mitogen-activated ERK-activating kinase-1 induced preproendothelin-1 promoter in myocytes. In summary, mechanical stretch distinctly regulates endothelin system gene expression in cardiac myocytes and fibroblasts. The inhibition of the endothelin system may affect cardiac mechanotransduction and therefore provides an approach in treatment of load-induced cardiac pathology.

Effect of temporary tracheal occlusion on the endothelin system in experimental cases of diaphragmatic hernia

Previously, the authors have shown that tracheal occlusion (TO) partially reverses the onset of congenital diaphragmatic hernia (CDH)-induced pulmonary hypertension (PH) and abnormal pulmonary vascular development whereas release of the occlusion (TR) abolishes these clinical benefits. As a consequence of their mitogenic and vasoactive properties, the authors hypothesize that the expression of endothelin (ET)-1 and ET receptor (ETA) genes is increased in lungs of CDH lambs, and that this increase is abolished partially in CDH + TO but not in CDH + TO + TR. A surgical left-sided CDH was created in fetal lambs at 80 days of gestation (gd), followed by TO at 108 gd, and by TR at 129 gd. Four groups were compared: CDH, CDH + TO, CDH + TO + TR, and nonoperated controls (C). Assessment of mRNA expression by Northern blot showed significantly lower ET-1 and ETA levels in the CDH group than in the CDH + TO +/- TR groups (P < .05). Endothelin protein expression levels were lower in CDH +/- TO +/- TR groups when compared with controls for airways and vessels (P < .05) with the exception of endothelial cells. In contrast, ETA protein expression levels were higher in CDH +/- TO +/- TR groups compared with controls for airways and blood vessels smooth muscles (P < .05). These results suggest that involvement of the endothelin system in the pulmonary hypertension associated with CDH is limited. However, the endothelin system appears to be modulated during development.

Nitric oxide decreases endothelin-1 secretion through the activation of soluble guanylate cyclase

The use of exogenous nitric oxide (NO) has been shown to alter the regulation of other endothelially derived mediators of vascular tone, such as endothelin-1 (ET-1). However, the interaction between NO and ET-1 appears to be complex and remains incompletely understood. One of the major actions of NO is the activation of soluble guanylate cyclase (sGC) with the subsequent generation of cGMP. Therefore, we undertook this study to test the hypothesis that NO regulates ET-1 production via the activation of the sGC/cGMP pathway. The results obtained indicated that the exposure of primary cultures of 4-wk-old ovine pulmonary arterial endothelial cells (4-wk PAECs) to the long-acting NO donor DETA NONOate induced both a dose- and time-dependent decrease in secreted ET-1. This decrease in ET-1 secretion occurred in the absence of changes in endothelin-converting enzyme-1 or sGC expression but in conjunction with a decrease in prepro-ET-1 mRNA. The changes in ET-1 release were inversely proportional to the cellular cGMP content. Furthermore, the NO-independent activator of sGC, YC-1, or treatment with a cGMP analog also produced significant decreases in ET-1 secretion. Conversely, pretreatment with the sGC inhibitor ODQ blocked the NO-induced decrease in ET-1. Therefore, we conclude that exposure of 4-wk PAECs to exogenous NO decreases secreted ET-1 resulting from the activation of sGC and increased cGMP generation.

Mechanical stress triggers selective release of fibrotic mediators from bronchial epithelium

Transforming growth factor-beta (TGF-beta) and endothelin (ET) are found in elevated amounts in the airways of individuals with asthma. The cellular source of these peptides and their role in mediating the airway fibrosis of chronic asthma are unknown. In response to mechanical stresses similar to those occurring in vivo during airway constriction, bronchial epithelial cells increase the steady-state level of mRNA for both ET-1 and ET-2, followed by increased release of ET protein. Mechanical stress also enhances release of TGF-beta2 from a preformed cell-associated pool. TGF-beta2 and ET act individually and, more importantly, synergistically to promote fibrotic protein synthesis in reporter fibroblasts. To confirm the role of these intermediates in stress-induced fibrosis, conditioned medium from mechanically stressed bronchial epithelial cells was shown to elicit fibrotic protein synthesis in reporter fibroblasts; this effect was significantly inhibited by combined treatment with ET receptor antagonists and a neutralizing antibody to TGF-beta2. These data are consistent with a primary pathogenic role for mechanical stress-induced release of both TGF-beta2 and ET in the subepithelial fibrosis that characterizes chronic asthma.

PPAR-alpha ligands inhibit H2O2-mediated activation of transforming growth factor-beta1 in human mesangial cells

Transforming growth factor-beta1 (TGF-beta1) mediates the development of glomerulosclerosis by stimulating mesangial cell production of extracellular matrix (ECM) proteins. TGF-beta1 and several ECM genes are regulated by promoter O-tetradecanoylphorbol 13-acetate-responsive elements (TREs) that are transactivated by the activator protein-1 (AP-1) transcription factor complex. AP-1-TRE interactions are regulated by redox changes. Recently, peroxisome proliferator-activated receptors (PPARs) were shown to negatively regulate several transcription factor families. In these studies, we postulated that PPAR-alpha could antagonize TGF-beta1 expression by cultured human mesangial cells (HMC). A TGF-beta1 luciferase expression plasmid was transduced into HMC via recombinant deficient adenoviral vectors. The TGF-beta1 promoter activity increased twofold (209%) following 18-h treatments with H(2)O(2) (1,000 micro M). Using RT-PCR, we demonstrated that HMC possess PPAR-alpha RNA, and PPAR-alpha protein was identified by immunohistochemistry. Pretreatment of cells with the PPAR-alpha ligands WY14643 (100-500 micro M) or clofibrate (100-500 micro M) dose-dependently inhibited oxidant-mediated induction of TGF-beta1. This inhibition occurred without affecting the H(2)O(2)-mediated activation of the mitogen-activated protein kinase (MAPK) pathways extracellular regulated kinase, p38 MAPK, or Jun N-terminal kinase, which are responsible for the regulation of AP-1 phosphorylation. These studies are the first to identify PPAR-alpha expression by HMC. The results of these studies suggest that TGF-beta1 expression mediated by oxidant stress may be suppressible by PPAR-alpha activation.

Inhibitory effects of novel AP-1 decoy oligodeoxynucleotides on vascular smooth muscle cell proliferation in vitro and neointimal formation in vivo

Excessive proliferation of vascular smooth muscle cells (VSMCs) and neointimal formation are critical steps in the pathogenesis of atherosclerosis and restenosis after percutaneous transluminal angioplasty. In this study, we investigated the hypothesis that the activator protein-1 (AP-1) plays an important role in neointimal formation after vascular injury. A circular dumbbell AP-1 decoy oligodeoxynucleotide (CDODN) was developed as a novel therapeutic strategy for restenosis after angioplasty. This CDODN was more stable than the conventional phosphorothioate linear decoy ODN (PSODN) and maintained structural integrity on exposure to exonuclease III or serum. Transfection with AP-1 decoy ODNs strongly inhibited VSMC proliferation and migration, as well as glucose- and serum-induced expression of PCNA and cyclin A genes. Administration of AP-1 decoy ODNs in vivo using the hemagglutinating virus of Japan (HVJ)-liposome method virtually abolished neointimal formation after balloon injury to the rat carotid artery. Compared with PSODN, CDODN was more effective in inhibiting the proliferation of VSMCs in vitro and neointimal formation in vivo. Our results collectively indicate that AP-1 activation is crucial for the mediation of VSMC proliferation in response to vascular injury. Moreover, the use of stable CDODN specific for AP-1 activity in combination with the highly effective HVJ-liposome method provides a novel potential therapeutic strategy for the prevention of restenosis after angioplasty in humans.

CCAAT/enhancer-binding protein decoy oligodeoxynucleotide inhibition of macrophage-rich vascular lesion formation in hypercholesterolemic rabbits

Many cytokine genes, including those encoding acute-phase proteins and immunoglobulins, share binding sites for the CCAAT/enhancer-binding protein (C/EBP) in their 5'-flanking regions, and C/EBP-related transcription factors regulate cell proliferation during terminal differentiation. Therefore, C/EBP represents an attractive target for inhibiting restenosis after balloon angioplasty. In a rabbit model of restenosis that combines balloon injury of the carotid artery with cholesterol-mediated chronic inflammation, a decoy oligodeoxynucleotide (ODN) capable of neutralizing C/EBP was administered to the site of injury for 30 minutes. Electrophoretic mobility shift analysis confirmed that C/EBP activity in decoy ODN-treated segments was virtually absent after 2 days. Morphometric analysis after 28 days revealed significant reduction (up to 50%) of neointimal formation and intravascular inflammation in decoy ODN-treated segments compared with mutant control ODN or vehicle-treated segments. In addition, de novo synthesis of endothelin-1 and the number of proliferating cell nuclear antigen-positive smooth muscle cells in the vessel wall were markedly attenuated at day 3. These findings suggest that decoy ODN-based neutralization of C/EBP may be a feasible and effective method to limit restenosis after angioplasty brought about, at least in part, by inhibiting the de novo synthesis of endothelin-1.

Atorvastatin inhibition of cytokine-inducible nitric oxide synthase expression in native endothelial cells in situ

Animal experimental studies have demonstrated that inducible nitric oxide synthase (iNOS) expression correlates with neointima formation and is prevented by HMG-CoA reductase inhibitors (statins). In the present study we have investigated the underlying mechanism of action of these drugs in isolated segments of the rat aorta. Western blot analysis and immunohistochemistry revealed that tumour necrosis factor alpha (TNFalpha) plus interferon-gamma (IFNgamma) synergistically induce iNOS gene expression in the endothelium but not in the smooth muscle of these segments while constitutive endothelial NO synthase (eNOS) abundance was markedly reduced. Pre-treatment with 1 - 10 microM atorvastatin, cerivastatin or pravastatin decreased TNFalpha plus IFNgamma stimulated iNOS expression in the endothelium irrespective of the presence of the HMG-CoA reductase product mevalonate (400 microM). Electrophoretic mobility shift assay experiments confirmed that the combination of TNFalpha plus IFNgamma causes activation of the transcription factors STAT-1 and NF-kappaB in native endothelial cells. Neutralization of these transcription factors by employing the corresponding decoy oligonucleotides confirmed their involvement in TNFalpha plus IFNgamma stimulated iNOS expression. Translocation of both transcription factors was attenuated by atorvastatin, and this effect was insensitive to exogenous mevalonate. The present findings thus demonstrate a specific HMG-CoA reductase-independent inhibitory effect of statins, namely atorvastatin, on cytokine-stimulated transcription factor activation in native endothelial cells in situ and the subsequent expression of a gene product implicated in vascular inflammation. This effect may be therapeutically relevant and in addition provide an explanation for the reported rapid onset of action of these drugs in humans.

Decoy oligodeoxynucleotide against activator protein-1 reduces neointimal proliferation after coronary angioplasty in hypercholesterolemic minipigs

OBJECTIVES

We sought to demonstrate, in an appropriate animal model, that co-medication with a transcription factor-blocking agent limits restenosis after percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Enhanced synthesis in the vessel wall of endothelin-1 (ET-1), a powerful co-mitogen for vascular smooth muscle cells, appears to be one mechanism that promotes restenosis after PTCA. Deformation-induced expression of prepro-ET-1 is governed by the transcription factor, activator protein-1 (AP-1).

METHODS

An anti-AP-1 decoy oligodeoxynucleotide (dODN) strategy was devised in which the dODN-containing solution (20 nmol) was administered locally through a Dispatch catheter into the coronary arteries of hypercholesterolemic minipigs at the time of PTCA (AVE-GFX stent).

RESULTS

Treatment with an AP-1 dODN, mimicking the consensus binding site of the transcription factor, significantly reduced neointimal formation in the coronary arteries of hypercholesterolemic minipigs (n = 10 to 12), compared with vehicle-treated coronary arteries, after four weeks of follow-up (neointimal area 2.64 +/- 0.33 vs. 4.81 +/- 1.04 mm(2) [mean +/- SEM]; p < 0.05). This effect was maintained after eight weeks (neointimal area 2.04 +/- 0.22 mm(2); n = 3) and correlated with a reduction in both nuclear translocation of AP-1 and ET-1 synthesis in the vessel wall 48 h after PTCA (n = 4). In contrast, an AP-1 mutant dODN, to which the transcription factor does not bind, showed no effect on neointimal formation at either time point (n = 3 to 7). Moreover, a consensus dODN directed against CCAAT/enhancer binding protein (C/EBP), another deformation-sensitive transcription factor, did not significantly affect neointimal formation after four weeks (n = 3).

CONCLUSIONS

These findings demonstrate the feasibility, efficacy and specificity of the anti-AP-1 dODN approach to the treatment of restenosis, which principally but not exclusively targets deformation-induced ET-1 synthesis in the vessel wall. Provided that these findings can be extrapolated to the situation of patients with coronary artery disease, the observed extent of the inhibitory effect of the AP-1 dODN treatment suggests that this co-medication may greatly reduce the incidence of in-stent restenosis.

Deformation-induced endothelin B receptor-mediated smooth muscle cell apoptosis is matrix-dependent

To maintain normal blood flow, pressure overload in both arteries and veins requires a structural adaptation of the vessel wall (remodelling) that involves smooth muscle cell (SMC) hypertrophy and/or hyperplasia. Due to its potent vasoconstrictor and growth-promoting effects, endothelin-1 (ET-1) is a likely candidate to initiate and/or promote remodelling in blood vessels exposed to a chronic increase in blood pressure. To test this hypothesis, isolated segments of the rabbit carotid artery and jugular vein were perfused at different levels of intraluminal pressure. In both types of segments, pressure overload (160 and 20 mmHg, respectively) resulted in an increase in endothelial prepro-ET-1 and SMC endothelin B receptor (ETB-R) expression. Moreover, in pressurised segments from the carotid artery an ETB-R antagonist-sensitive increase in SMC apoptosis in the media was observed, while in the vein medial SMC started to proliferate. Isolated SMC from these rabbit blood vessels as well as from the aorta and vena cava of the rat, when cultured on a collagen or laminin matrix, uniformly revealed an ETB-R-mediated increase in apoptosis upon exposure to mechanical deformation plus exogenous ET-1 (10 nmol/L). However, when grown on a fibronectin matrix, the cultured SMC did not respond with an increase in apoptosis under otherwise identical experimental conditions. These findings suggest that deformation-induced activation of the endothelin system in the vessel wall not only plays a crucial role in remodelling, but that the structural components of the vessel wall, in particular the cell-matrix interaction, determine how SMC respond phenotypically to these changes in gene expression.

Decoy oligodeoxynucleotide characterization of transcription factors controlling endothelin-B receptor expression in vascular smooth muscle cells

Endothelin-1 is not only a powerful vasoconstrictor but also a potent mitogen for vascular smooth muscle cells (SMC), acting through both the endothelin-A and endothelin-B receptor (ET(B)-R). Although vascular SMC are known to express the ET(B)-R, its transcriptional regulation has not been studied thus far. Here we demonstrate that the potent inhibitor of nuclear factor kappaB activation, pyrrolidine dithiocarbamate (PDTC; 30-100 microM), induces de novo ET(B)-R expression in rat aortic and mesenteric cultured SMC. Electrophoretic mobility shift analyses revealed that besides inhibition of nuclear factor kappaB, PDTC enhances activator protein-1 (AP-1), CCAAT/enhancer-binding protein (C/EBP), and GATA-2 activity in these cells. Preincubation of PDTC-stimulated cells with appropriate decoy oligodeoxynucleotides confirmed the involvement of these three transcription factors, namely that of AP-1, in ET(B)-R expression. The stimulatory effect of PDTC on ET(B)-R expression was also confirmed functionally by monitoring an enhanced ET-1-induced apoptosis in PDTC-treated cells that was sensitive to the ET(B)-R antagonist, BQ788. Taken together, these findings demonstrate that C/EBP, GATA-2, and in particular AP-1 can control ET(B)-R expression in vascular SMC. They further support the notion that ET(B)-R expression in these cells may play an important role in cardiovascular complications, such as restenosis following angioplasty that in the early phase is characterized by prominent SMC apoptosis.