ERK1/2-dependent contractile protein expression in vascular smooth muscle cells

Mineralocorticoid receptor antagonism attenuates arteriovenous fistula stenosis by modulating the phenotype of vascular smooth muscle cells

BACKGROUND

Fistula stenosis is a primary contributor to arteriovenous fistula (AVF) failure in maintenance hemodialysis patients. Emerging data indicated excessive fibrotic remodeling was the primarily contributor to fistula stenosis during AVF remodeling. The mineralocorticoid receptor (MR) has been implicated in vascular remodeling across various cardiovascular pathologies. However, its role in AVF remodeling, particularly concerning fibrotic remodeling, remains elusive.

METHODS

MR expression and the phenotypes of vascular smooth muscle cells (VSMC) were assessed in dysfunctional AVF. The effects of MR on VSMC phenotypic switching were examined in vitro, and the protective effects of MR antagonists on AVF outcome were evaluated in a rat AVF model.

RESULTS

Dysfunctional fistula exhibited significant medial fibrosis and extracellular matrix deposition, alongside markedly increased MR activity. In the dysfunctional fistula vessels, VSMC displayed reduced expression of the contractile marker SMMHC and features characteristic of a synthetic phenotype, including increased osteopontin expression and heightened proliferation. In vitro studies with cultured VSMC revealed that MR overactivity induced by aldosterone led to phenotypic switching from contractile to synthetic state, concomitant with EGFR-ERK1/2 pathway overactivation. These effects were largely abolished by the MR antagonist finerenone. Knockdown of EGFR expression abrogated ERK1/2 phosphorylation and inhibited the VSMC phenotypic switching. Conversely, ectopic overexpression of EGFR in VSMC diminished the protective effect of finerenone. In rat AVF models, pharmacologic targeting of MR with finerenone significantly improved AVF outcomes, characterized by increased luminal diameters and flow volume, reduced medial fibrosis, and inhibited VSMC phenotypic switching. These beneficial outcomes were likely attributable to a restrained activity of the EGFR-ERK1/2 pathway in VSMC.

CONCLUSIONS

Our study demonstrated that therapeutic targeting of MR may improve AVF outcome by modulating VSMC phenotypic switching. These findings offer promising avenues for further clinical investigations aimed at optimizing AVF outcomes in the hemodialysis population.

MEK inhibitors: a promising targeted therapy for cardiovascular disease

Cardiovascular disease (CVD) represents the leading cause of mortality and disability all over the world. Identifying new targeted therapeutic approaches has become a priority of biomedical research to improve patient outcomes and quality of life. The RAS-RAF-MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase) pathway is gaining growing interest as a potential signaling cascade implicated in the pathogenesis of CVD. This pathway is pivotal in regulating cellular processes like proliferation, growth, migration, differentiation, and survival, which are vital in maintaining cardiovascular homeostasis. In addition, ERK signaling is involved in controlling angiogenesis, vascular tone, myocardial contractility, and oxidative stress. Dysregulation of this signaling cascade has been linked to cell dysfunction and vascular and cardiac pathological remodeling, which contribute to the onset and progression of CVD. Recent and ongoing research has provided insights into potential therapeutic interventions targeting the RAS-RAF-MEK-ERK pathway to improve cardiovascular pathologies. Preclinical studies have demonstrated the efficacy of targeted therapy with MEK inhibitors (MEKI) in attenuating ERK activation and mitigating CVD progression in animal models. In this article, we first describe how ERK signaling contributes to preserving cardiovascular health. We then summarize current knowledge of the roles played by ERK in the development and progression of cardiac and vascular disorders, including atherosclerosis, myocardial infarction, cardiac hypertrophy, heart failure, and aortic aneurysm. We finally report novel therapeutic strategies for these CVDs encompassing MEKI and discuss advantages, challenges, and future developments for MEKI therapeutics.

Phospholipase C-β3 is dispensable for vascular constriction but indispensable for vascular hyperplasia

Angiotensin II (AngII) induces the contraction and proliferation of vascular smooth muscle cells (VSMCs). AngII activates phospholipase C-β (PLC-β), thereby inducing Ca2+ mobilization as well as the production of reactive oxygen species (ROS). Since contraction is a unique property of contractile VSMCs, signaling cascades related to the proliferation of VSMCs may differ. However, the specific molecular mechanism that controls the contraction or proliferation of VSMCs remains unclear. AngII-induced ROS production, migration, and proliferation were suppressed by inhibiting PLC-β3, inositol trisphosphate (IP3) receptor, and NOX or by silencing PLC-β3 or NOX1 but not by NOX4. However, pharmacological inhibition or silencing of PLC-β3 or NOX did not affect AngII-induced VSMC contraction. Furthermore, the AngII-dependent constriction of mesenteric arteries isolated from PLC-β3∆SMC, NOX1-/-, NOX4-/- and normal control mice was similar. AngII-induced VSMC contraction and mesenteric artery constriction were blocked by inhibiting the L-type calcium channel Rho-associated kinase 2 (ROCK2) or myosin light chain kinase (MLCK). The activation of ROCK2 and MLCK was significantly induced in PLC-β3∆SMC mice, whereas the depletion of Ca2+ in the extracellular medium suppressed the AngII-induced activation of ROCK2, MLCK, and vasoconstriction. AngII-induced hypertension was significantly induced in NOX1-/- and PLC-β3∆SMC mice, whereas LCCA ligation-induced neointima formation was significantly suppressed in NOX1-/- and PLC-β3∆SMC mice. These results suggest that PLC-β3 is essential for vascular hyperplasia through NOX1-mediated ROS production but is nonessential for vascular constriction or blood pressure regulation.

The Role of PKC-MAPK Signalling Pathways in the Development of Hyperglycemia-Induced Cardiovascular Complications

Cardiovascular disease is the most common cause of death among diabetic patients worldwide. Hence, cardiovascular wellbeing in diabetic patients requires utmost importance in disease management. Recent studies have demonstrated that protein kinase C activation plays a vital role in the development of cardiovascular complications via its activation of mitogen-activated protein kinase (MAPK) cascades, also known as PKC-MAPK pathways. In fact, persistent hyperglycaemia in diabetic conditions contribute to preserved PKC activation mediated by excessive production of diacylglycerol (DAG) and oxidative stress. PKC-MAPK pathways are involved in several cellular responses, including enhancing oxidative stress and activating signalling pathways that lead to uncontrolled cardiac and vascular remodelling and their subsequent dysfunction. In this review, we discuss the recent discovery on the role of PKC-MAPK pathways, the mechanisms involved in the development and progression of diabetic cardiovascular complications, and their potential as therapeutic targets for cardiovascular management in diabetic patients.

Downregulation of the transcriptional co-activator PCAF inhibits the proliferation and migration of vascular smooth muscle cells and attenuates NF-κB-mediated inflammatory responses

P300/CBP-associated factor (PCAF) regulates vascular inflammation. This study was to explore the effect of PCAF on the proliferation and migrationof vascular smooth muscle cells (VSMCs) and neointimal hyperplasia in balloon-injured rat carotid artery. Downregulation of PCAF remarkably suppressed VSMCs proliferation and migration induced by lipopolysaccharide, and also significantly inhibit the nuclear translocation of nuclear factor-kappaB p65. Meanwhile, downregulation of PCAF inhibited the mRNA expression of tumor necrosis factor-α and interleukin-6, and also the levels in culture supernatants. Moreover, downregulation of PCAF profoundly reduced the intima area and the ratio of intima area to media area in balloon-injured rat carotid artery. In addition, the expression of PCNA and NF-κB p65 in intima were decreased by downregulation of PCAF. These results highlight that PCAF may be a potential target for prevention and treatment of neointimal hyperplasia and restenosis after angioplasty.

Transforming growth factor-β downregulates sGC subunit expression in pulmonary artery smooth muscle cells via MEK and ERK signaling

TGFβ activation during newborn lung injury decreases the expression of pulmonary artery smooth muscle cell (PASMC)-soluble guanylate cyclase (sGC), a critical mediator of nitric oxide signaling. Using a rat PASMC line (CS54 cells), we determined how TGFβ downregulates sGC expression. We found that TGFβ decreases sGC expression through stimulating its type I receptor; TGFβ type I receptor (TGFβR1) inhibitors prevented TGFβ-1-mediated decrease in sGCα1 subunit mRNA levels in the cells. However, TGFβR1-Smad mechanisms do not regulate sGC; effective knockdown of Smad2 and Smad3 expression and function did not protect sGCα1 mRNA levels during TGFβ-1 exposure. A targeted small-molecule kinase inhibitor screen suggested that MEK signaling regulates sGC expression in TGFβ-stimulated PASMC. TGFβ activates PASMC MEK/ERK signaling; CS54 cell treatment with TGFβ-1 increased MEK and ERK phosphorylation in a biphasic, time- and dose-dependent manner. Moreover, MEK/ERK activity appears to be required for TGFβ-mediated sGC expression inhibition in PASMC; MEK and ERK inhibitors protected sGCα1 mRNA expression in TGFβ-1-treated CS54 cells. Nuclear ERK activity is sufficient for sGC regulation; heterologous expression of a nucleus-retained, constitutively active ERK2-MEK1 fusion protein decreased CS54 cell sGCα1 mRNA levels. The in vivo relevance of this TGFβ-MEK/ERK-sGC downregulation pathway is suggested by the detection of ERK activation and sGCα1 protein expression downregulation in TGFβ-associated mouse pup hyperoxic lung injury, and the determination that ERK decreases sGCα1 protein expression in TGFβ-1-treated primary PASMC obtained from mouse pups. These studies identify MEK/ERK signaling as an important pathway by which TGFβ regulates sGC expression in PASMC.

Curcumin enhances vascular contractility via induction of myocardin in mouse smooth muscle cells

A variety of cardiovascular diseases is accompanied by the loss of vascular contractility. This study sought to investigate the effects of curcumin, a natural polyphenolic compound present in turmeric, on mouse vascular contractility and the underlying mechanisms. After mice were administered curcumin (100 mg·kg-1·d-1, ig) for 6 weeks, the contractile responses of the thoracic aorta to KCl and phenylephrine were significantly enhanced compared with the control group. Furthermore, the contractility of vascular smooth muscle (SM) was significantly enhanced after incubation in curcumin (25 μmol/L) for 4 days, which was accompanied by upregulated expression of SM marker contractile proteins SM22α and SM α-actin. In cultured vascular smooth muscle cells (VSMCs), curcumin (10, 25, 50 μmol/L) significantly increased the expression of myocardin, a "master regulator" of SM gene expression. Curcumin treatment also significantly increased the levels of caveolin-1 in VSMCs. We found that as a result of the upregulation of caveolin-1, curcumin blocked the activation of notch1 and thereby abolished Notch1-inhibited myocardin expression. Knockdown of caveolin-1 or activation of Notch1 signaling with Jagged1 (2 μg/mL) diminished these effects of curcumin in VSMCs. These findings suggest that curcumin induces the expression of myocardin in mouse smooth muscle cells via a variety of mechanisms, including caveolin-1-mediated inhibition of notch1 activation and Notch1-mediated repression of myocardin expression. This may represent a novel pathway, through which curcumin protects blood vessels via the beneficial regulation of SM contractility.

Pravastatin attenuates the action of the ETS domain-containing protein ELK1 to prevent atherosclerosis in apolipoprotein E-knockout mice via modulation of extracellular signal-regulated kinase 1/2 signal pathway

Oxidative stress plays an important role in atherosclerosis, a vascular disease with high morbidity and mortality. The ETS domain-containing protein ELK1 is an oxidative stress-sensitive factor modulated by the extracellular signal-regulated kinase (ERK) 1/2 pathway. However, the role of ELK1 in the prevention of atherosclerosis by pravastatin remains unclear. In the present study, male apolipoprotein E-knockout (apoE^-/- ) mice fed a diet containing 1.25% cholesterol (w/w) were divided into two groups, one treated with pravastatin (80 mg/kg, 2-2.4 mg/mouse per day) for 8 weeks and the other not. Male C57BL/6J mice fed with a normal diet were used as a control group. Human umbilical vein endothelial cells (HUVEC) were cultured and treated with pravastatin (10 μmol/L) for 18 hours before testing for the presence or absence of 100 μmol/L H₂ O₂ (24 hours). Examination of pathological sections from mice aortas revealed that pravastatin treatment almost prevented atherosclerotic plaque formation. Pravastatin also inhibited increases in serum and aortic levels of oxidized low-density lipoprotein and aortic malondialdehyde levels and decreases in aortic reduced glutathione, and the activities of superoxide dismutase, catalase and glutathione peroxidase. H₂ O₂ -induced increases in reactive oxygen species in HUVECs were reversed by pravastatin by 48%. Pravastatin blocked the phosphorylation of ELK1 and ERK1/2 proteins and reduced mRNA levels of early growth response 1, a known atherogenic transcription factor upregulated by the ROS/ERK/ELK1 pathway, in mice. In conclusion, pravastatin attenuates the action of ELK1 induced by oxidative stress to prevent atherosclerosis, which is dependent partly on modulation of ERK1/2 signalling.

Tungstate-targeting of BKαβ1 channels tunes ERK phosphorylation and cell proliferation in human vascular smooth muscle

Despite the substantial knowledge on the antidiabetic, antiobesity and antihypertensive actions of tungstate, information on its primary target/s is scarce. Tungstate activates both the ERK1/2 pathway and the vascular voltage- and Ca²⁺-dependent large-conductance BKαβ₁ potassium channel, which modulates vascular smooth muscle cell (VSMC) proliferation and function, respectively. Here, we have assessed the possible involvement of BKαβ₁ channels in the tungstate-induced ERK phosphorylation and its relevance for VSMC proliferation. Western blot analysis in HEK cell lines showed that expression of vascular BKαβ₁ channels potentiates the tungstate-induced ERK1/2 phosphorylation in a G_i/o protein-dependent manner. Tungstate activated BKαβ₁ channels upstream of G proteins as channel activation was not altered by the inhibition of G proteins with GDPβS or pertussis toxin. Moreover, analysis of G_i/o protein activation measuring the FRET among heterologously expressed G_i protein subunits suggested that tungstate-targeting of BKαβ₁ channels promotes G protein activation. Single channel recordings on VSMCs from wild-type and β₁-knockout mice indicated that the presence of the regulatory β₁ subunit was essential for the tungstate-mediated activation of BK channels in VSMCs. Moreover, the specific BK channel blocker iberiotoxin lowered tungstate-induced ERK phosphorylation by 55% and partially reverted (by 51%) the tungstate-produced reduction of platelet-derived growth factor (PDGF)-induced proliferation in human VSMCs. Our observations indicate that tungstate-targeting of BKαβ₁ channels promotes activation of PTX-sensitive G_i proteins to enhance the tungstate-induced phosphorylation of ERK, and inhibits PDGF-stimulated cell proliferation in human vascular smooth muscle.

Phenotypic modulation of smooth muscle cells by chemical and mechanical cues of electrospun tecophilic/gelatin nanofibers

The ability of mature smooth muscle cells (SMCs) to modulate their phenotype in response to environmental cues is a critical issue related to vascular diseases. A tissue engineered vascular graft shall promote the contractile phenotype of vascular SMCs. To this aim, Tecophilic/gelatin (TP/gel) was electrospun at different weight ratios of TP/gelatin (100:0, 70:30, 50:50, 30:70), leading to differences in biochemical and mechanical properties of the nanofibers which in turn influenced the phenotype of SMCs. Results indicated that both the substrate with higher ligand density and lower stiffness could enhance SMC contractility and reduce cell proliferation. However, observing the highest SMCs contractility on electrospun TP(70)/gel(30) among the composite scaffolds demonstrated stiffness as the most critical parameter. Due to conflicting effects of softness versus minor fraction of gelatin (reduced ligand density) within TP(70)/gel(30) fibers, a relatively high proliferation of SMCs was still observed on TP(70)/gel(30) scaffold. The surface of TP(70)/gel(30) scaffold was further modified through physical adsorption of gelatin molecules so as to increase the ligand density on its surface, whereby a functional vascular construct that promotes the contractile behavior of SMCs with low cell proliferation was developed.

Angiotensin II reduces cardiac AdipoR1 expression through AT1 receptor/ROS/ERK1/2/c-Myc pathway

Adiponectin, an abundant adipose tissue-derived protein, exerts protective effect against cardiovascular disease. Adiponectin receptors (AdipoR1 and AdipoR2) mediate the beneficial effects of adiponectin on the cardiovascular system. However, the alteration of AdipoRs in cardiac remodeling is not fully elucidated. Here, we investigated the effect of angiotensin II (AngII) on cardiac AdipoRs expression and explored the possible molecular mechanism. AngII infusion into rats induced cardiac hypertrophy, reduced AdipoR1 but not AdipoR2 expression, and attenuated the phosphorylations of adenosine monophosphate-activated protein kinase and acetyl coenzyme A carboxylase, and those effects were all reversed by losartan, an AngII type 1 (AT1) receptor blocker. AngII reduced expression of AdipoR1 mRNA and protein in cultured neonatal rat cardiomyocytes, which was abolished by losartan, but not by PD123319, an AT2 receptor antagonist. The antioxidants including reactive oxygen species (ROS) scavenger NAC, NADPH oxidase inhibitor apocynin, Nox2 inhibitor peptide gp91 ds-tat, and mitochondrial electron transport chain complex I inhibitor rotenone attenuated AngII-induced production of ROS and phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. AngII-reduced AdipoR1 expression was reversed by pretreatment with NAC, apocynin, gp91 ds-tat, rotenone, and an ERK1/2 inhibitor PD98059. Chromatin immunoprecipitation assay demonstrated that AngII provoked the recruitment of c-Myc onto the promoter region of AdipoR1, which was attenuated by PD98059. Moreover, AngII-induced DNA binding activity of c-Myc was inhibited by losartan, NAC, apocynin, gp91 ds-tat, rotenone, and PD98059. c-Myc small interfering RNA abolished the inhibitory effect of AngII on AdipoR1 expression. Our results suggest that AngII inhibits cardiac AdipoR1 expression in vivo and in vitro and AT1 receptor/ROS/ERK1/2/c-Myc pathway is required for the downregulation of AdipoR1 induced by AngII.

Arrestins 2 and 3 differentially regulate ETA and P2Y2 receptor-mediated cell signaling and migration in arterial smooth muscle

Overstimulation of endothelin type A (ET(A)) and nucleotide (P2Y) Gα(q)-coupled receptors in vascular smooth muscle causes vasoconstriction, hypertension, and, eventually, hypertrophy and vascular occlusion. G protein-coupled receptor kinases (GRKs) and arrestin proteins are sequentially recruited by agonist-occupied Gα(q)-coupled receptors to terminate phospholipase C signaling, preventing prolonged/inappropriate contractile signaling. However, these proteins also play roles in the regulation of several mitogen-activated protein kinase (MAPK) signaling cascades known to be essential for vascular remodeling. Here we investigated whether different arrestin isoforms regulate endothelin and nucleotide receptor MAPK signaling in rat aortic smooth muscle cells (ASMCs). When intracellular Ca(2+) levels were assessed in isolated ASMCs loaded with Ca(2+)-sensitive dyes, P2Y(2) and ET(A) receptor desensitization was attenuated by selective small-interfering (si)RNA-mediated depletion of G protein-coupled receptor kinase 2 (GRK2). Using similar siRNA techniques, knockdown of arrestin2 prevented P2Y(2) receptor desensitization and enhanced and prolonged p38 and ERK MAPK signals, while arrestin3 depletion was ineffective. Conversely, arrestin3 knockdown prevented ET(A) receptor desensitization and attenuated ET1-stimulated p38 and ERK signals, while arrestin2 depletion had no effect. Using Transwell assays to assess agonist-stimulated ASMC migration, we found that UTP-stimulated migration was markedly attenuated following arrestin2 depletion, while ET1-stimulated migration was attenuated following knockdown of either arrestin. These data highlight a differential arrestin-dependent regulation of ET(A) and P2Y(2) receptor-stimulated MAPK signaling. GRK2 and arrestin expression are essential for agonist-stimulated ASMC migration, which, as a key process in vascular remodeling, highlights the potential roles of GRK2 and arrestin proteins in the progression of vascular disease.

Functional characterization of human coronary artery smooth muscle cells under cyclic mechanical strain in a degradable polyurethane scaffold

There are few synthetic elastomeric biomaterials that simultaneously provide the required biological conditioning and the ability to translate biomechanical stimuli to vascular smooth muscle cells (VSMCs). Biomechanical stresses are important physiological elements that regulate VSMC function, and polyurethane elastomers are a class of materials capable of facilitating the translation of stress induced biomechanics. In this study, human coronary artery smooth muscle cells (hCASMCs), which were seeded into a porous degradable polar/hydrophobic/ionic (D-PHI) polyurethane scaffold, were subjected to uniaxial cyclic mechanical strain (CMS) over a span of four weeks using a customized bioreactor. The distribution, proliferation and contractile protein expression of hCASMCs in the scaffold were then analyzed and compared to those grown under static conditions. Four weeks of CMS, applied to the elastomeric scaffold, resulted in statistically greater DNA mass, more cell area coverage and a better distribution of cells deeper within the scaffold construct. Furthermore, CMS samples demonstrated improved tensile mechanical properties following four weeks of culture, suggesting the generation of more extracellular matrix within the polyurethane constructs. The expression of smooth muscle α-actin, calponin and smooth muscle myosin heavy chain and the absence of Ki-67+ cells in both static and CMS cultures, throughout the 4 weeks, suggest that hCASMCs retained their contractile character on these biomaterials. The study highlights the importance of implementing physiologically-relevant biomechanical stimuli in the development of synthetic elastomeric tissue engineering scaffolds.

A critical role for chloride channel-3 (CIC-3) in smooth muscle cell activation and neointima formation

OBJECTIVE

We have shown that the chloride-proton antiporter chloride channel-3 (ClC-3) is required for endosome-dependent signaling by the Nox1 NADPH oxidase in SMCs. In this study, we tested the hypothesis that ClC-3 is necessary for proliferation of smooth muscle cells (SMCs) and contributes to neointimal hyperplasia following vascular injury.

METHODS AND RESULTS

Studies were performed in SMCs isolated from the aorta of ClC-3-null and littermate control (wild-type [WT]) mice. Thrombin and tumor necrosis factor-α (TNF-α) each caused activation of both mitogen activated protein kinase extracellular signal-regulated kinases 1 and 2 and the matrix-degrading enzyme matrix metalloproteinase-9 and cell proliferation of WT SMCs. Whereas responses to thrombin were preserved in ClC-3-null SMCs, the responses to TNF-α were markedly impaired. These defects normalized following gene transfer of ClC-3. Carotid injury increased vascular ClC-3 expression, and compared with WT mice, ClC-3-null mice exhibited a reduction in neointimal area of the carotid artery 28 days after injury.

CONCLUSIONS

ClC-3 is necessary for the activation of SMCs by TNF-α but not thrombin. Deficiency of ClC-3 markedly reduces neointimal hyperplasia following vascular injury. In view of our previous findings, this observation is consistent with a role for ClC-3 in endosomal Nox1-dependent signaling. These findings identify ClC-3 as a novel target for the prevention of inflammatory and proliferative vascular diseases.

Characterization of anandamide-stimulated cannabinoid receptor signaling in human ULTR myometrial smooth muscle cells

Accumulating evidence highlights the importance of the endocannabinoid anandamide (AEA) as a key mediator in reproductive physiology. Current data suggest potential roles for AEA in gametogenesis, fertilization, and parturition. AEA exerts its actions through two G protein-coupled receptors, termed cannabinoid receptor 1 (CB1), and 2 (CB2), and the ligand-gated transient receptor potential vanilloid receptor type 1 (TRPV1) ion channel. At present, the cellular mechanism(s) and consequences of AEA signaling in reproductive tissues, especially the myometrium, are poorly understood. Here, we examine the expression of CB1, CB2, and TRPV1 in the human myometrial smooth muscle cell-line (ULTR) and characterize intracellular signaling after stimulation with AEA. Radioligand binding analysis revealed a total CB receptor expression of 76 +/- 24 fmol/mg protein, with both quantitative PCR and competition binding studies indicating a negligible CB2 component. AEA caused Galpha(i/o)-dependent inhibition of adenylate cyclase to reduce intracellular cAMP levels. In addition, AEA caused a 2.5- to 3.5-fold increase in ERK activation, which was ablated by inhibition of Galpha(i/o), phosphoinositide-3-kinase and Src-kinase activities, but not by inhibition of Ca(2+)/calmodulin-dependent protein kinase or protein kinase C activities. TRPV1 channel activation with capsaicin failed to activate ERK. Consistent with these findings, the selective agonists, arachidonyl-2-chloroethylamide (CB1) and L759656 (CB2), and selective antagonists AM251 (CB1) and JTE907 (CB2), provided pharmacological evidence that the ERK signaling pathway is activated through endogenously expressed CB1. These findings provide an insight into myometrial AEA signaling, highlighting a potential role for endocannabinoids in the regulation of gene expression in myometrial smooth muscle cells.

The transactivated epidermal growth factor receptor recruits Pyk2 to regulate Src kinase activity

G protein-coupled receptors such as proteinase-activated receptor 1 induce phosphorylation of mitogen-activated protein kinases through multiple pathways including transactivation of receptor tyrosine kinases. In vascular smooth muscle cells, both matrix-metalloproteinase-dependent extracellular shedding of membrane-bound epidermal growth factor (EGF) receptor ligands and activation of the nonreceptor tyrosine kinases Pyk2 and Src contributed to the thrombin-induced ERK1/2 phosphorylation. Surprisingly, disruption of the HB-EGF-mediated extracellular mode of EGF receptor transactivation also prevented the phosphorylation of the nonreceptor tyrosine kinases Pyk2 and Src, locating these kinases downstream of the transactivated EGF receptor. The ionomycin-induced Pyk2 phosphorylation was partially sensitive to AG1478, heparin, or the matrix-metalloproteinase inhibitor BB2116, and the ionomycin-induced EGF receptor phosphorylation was almost completely blocked by these inhibitors of extracellular transactivation. Coimmunoprecipitation experiments revealed that, upon thrombin stimulation, a signaling complex consisting of Pyk2 and Src assembles at the EGF receptor. Reconstitution of the signaling molecules in HEK293 or vascular smooth muscle cells and subsequent determination of the EGF-induced Src kinase activity applying fluorescent sensor proteins demonstrated that a Ca(2+)-independent mode of Pyk2 activation is critical for the activation of Src downstream of the EGF receptor.

Requirement of an intermediate gene expression for biphasic ERK1/2 activation in thrombin-stimulated vascular smooth muscle cells

The expression of contractile proteins in vascular smooth muscle cells is controlled by still poorly defined mechanisms. A thrombin-inducible expression of smooth muscle-specific alpha-actin and myosin heavy chain requires transactivation of the epidermal growth factor (EGF) receptor and a biphasic activation of ERK1/2. Here we demonstrate that the sustained second phase of ERK1/2 phosphorylation requires de novo RNA and protein synthesis. Depolymerization of the actin cytoskeleton by cytochalasin D or disruption of transit between the endoplasmic reticulum and the Golgi apparatus by brefeldin A prevented the second phase of ERK1/2 phosphorylation. We thus conclude that synthesis and trafficking of a plasma membrane-resident protein may be critical intermediates. Analysis of the expression of protease-activated receptor 1, heparin-binding EGF (HB-EGF), and the EGF receptor revealed that pro-HB-EGF is significantly up-regulated upon thrombin stimulation. The kinetic of HB-EGF expression closely matched that of the second phase of ERK1/2 phosphorylation. Because inhibition of matrix metalloproteases or of the EGF receptor strongly attenuated the late phase of ERK1/2 phosphorylation, the second phase of ERK1/2 activation is primarily relayed by shedding of EGF receptor ligands. The small interfering RNA-mediated knockdown of HB-EGF expression confirmed an important role of HB-EGF expression in triggering the second phase of ERK1/2 activation. Confocal imaging of a yellow fluorescent protein-tagged HB-EGF construct demonstrates the rapid plasma membrane integration of the newly synthesized protein. These data imply that the hormonal control of contractile protein expression relies on an intermediate HB-EGF expression to sustain the signaling strength within the Ras/Raf/MEK/ERK cascade.

ERK1/2 signaling pathway modulates the airway smooth muscle cell phenotype in the rat model of chronic asthma

BACKGROUND

It has been demonstrated that the phenotypic modulation of airway smooth muscle cells (ASMCs) is important to the pathogenesis of airway remodeling in chronic asthma. The extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway is one of the most important transduction pathways involved in the process of asthma; however, its role in the phenotypic transition of ASMCs remains unclear.

OBJECTIVES

To examine the role of ERK1/2 in the phenotypic modulation of ASMCs in the rat model of chronic asthma.

METHODS

Bronchial smooth muscle strips were cultured in vitro in the presence of the ERK1/2 agonist epidermal growth factor or/and the MEK inhibitor PD98059. The phenotype of ASMCs was determined by observing these cells under an electron microscope and analyzing expression of phenotypic markers (smooth muscle alpha-actin for the contractile phenotype and osteopontin for the synthetic) by using Western blot and reverse-transcriptase polymerase chain reaction, respectively.

RESULTS

The phenotype of the ASMCs from the chronic asthmatic rats changed from the contractile type to the synthetic type with synthetic organelles abundantly gathered around the nucleus and altered expression of phenotypic markers. ERK1/2 was strongly expressed in the ASMCs of the chronic asthmatic rats and its activation by epidermal growth factor excessively promoted the synthetic function of ASMCs; the MEK inhibitor PD98059, however, reversed this phenotypic change in the ASMCs.

CONCLUSIONS

Our results reveal a key role of the ERK1/2 signaling pathway in the phenotypic modulation of ASMCs in chronic asthmatic rats, indicating that specific inhibition of ERK1/2 in ASMCs may be therapeutically valuable in the control of airway remodeling in chronic asthma.

Influence of thrombin concentration on the mechanical and morphological properties of cell-seeded fibrin hydrogels

Fibrin is a biopolymer that has been used in a variety of biomaterial, cell delivery and tissue engineering applications. The enzyme thrombin catalyzes the formation of fibrin microfibrils, which form a three-dimensional mesh in which cells can be directly embedded at the time of gel formation. In this study, fibrin hydrogels containing vascular smooth muscle cells were created using varying concentrations of thrombin. Over 7 days in culture, all gels decreased in volume as the fibrin matrix compacted, and the degree of gel compaction increased as thrombin concentration decreased. The material modulus and ultimate tensile stress of the gels also increased with decreasing thrombin concentration. Addition of thrombin to similar constructs made using collagen Type I did not show an effect on gel compaction or mechanical properties, suggesting that these effects were a result of thrombin's action on fibrin polymerization, and not cellular functions. Cell proliferation in fibrin hydrogels was not significantly affected by thrombin addition. Matrix examination using scanning electron microscopy showed increasing fibrin fiber diameters as thrombin concentration decreased. Confocal microscopic imaging of the actin cytoskeleton showed that cell morphology on two-dimensional substrates of fibrin showed marked changes, with higher thrombin concentrations producing cells with longer cellular projections. However, these morphological changes were not as apparent in cells embedded in three-dimensional (3-D) matrices, in which cells exhibited a similar morphology independent of thrombin concentration. These results relate features of the matrix and cellular components of 3-D fibrin constructs to mechanical properties, and contribute to the understanding of structure-function relationships in cell-seeded, 3-D protein hydrogels.

Mitogenic modulation of Ca2+ -activated K+ channels in proliferating A7r5 vascular smooth muscle cells

Modulation of Ca(2+)-activated K(+) channels (K(Ca)) has been implicated in the control of proliferation in vascular smooth muscle cells (VSMC) and other cell types. In the present study, we investigated the underlying signal transduction mechanisms leading to mitogen-induced alterations in the expression pattern of intermediate-conductance K(Ca) in VSMC. Regulation of expression of IK(Ca)/rK(Ca)3.1 and BK(Ca)/rK(Ca)1.1 in A7r5 cells, a cell line derived from rat aortic VSMC, was investigated by patch-clamp technique, quantitative RT-PCR, immunoblotting procedures, and siRNA strategy.PDGF stimulation for 2 and 48 h induced an 11- and 3.5-fold increase in rK(Ca)3.1 transcript levels resulting in a four- and seven-fold increase in IK(Ca) currents after 4 and 48 h, respectively. Upregulation of rK(Ca)3.1 transcript levels and channel function required phosphorylation of extracellular signal-regulated kinases (ERK1/2) and Ca(2+) mobilization, but not activation of p38-MAP kinase, c-Jun NH(2)-terminal kinase, protein kinase C, calcium-calmodulin kinase II and Src kinases. In contrast to rK(Ca)3.1, mRNA expression and functions of BK(Ca)/rK(Ca)1.1 were decreased by half following mitogenic stimulation. Downregulation of rK(Ca)1.1 did not require ERK1/2 phosphorylation or Ca(2+) mobilization. In an in vitro-proliferation assay, knockdown of rK(Ca)3.1 expression by siRNA completely abolished functional IK(Ca) channels and mitogenesis. Mitogen-induced upregulation of rK(Ca)3.1 expression is mediated via activation of the Raf/MEK- and ERK-signaling cascade in a Ca(2+)-dependent manner. Upregulation of rK(Ca)3.1 promotes VSMC proliferation and may thus represent a pharmacological target in cardiovascular disease states characterized by abnormal cell proliferation.

N-Terminal Proteolysis of the Endothelin B Receptor Abolishes Its Ability to Induce EGF Receptor Transactivation and Contractile Protein Expression in Vascular Smooth Muscle Cells

OBJECTIVE

The extracellular N terminus of the endothelin B (ETB) receptor is cleaved by a metalloprotease in an agonist-dependent manner, but the physiological role of this N-terminal proteolysis is not known. In this study, we aimed to determine the functional role of the ETB receptor and of its N-terminal cleavage in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

VSMCs expressing either the full-length ETB receptor or an N-terminally truncated ETB receptor (corresponding to the N-terminally cleaved receptor) were analyzed for ligand-induced mitogen-activated protein kinase activation and expression of contractile proteins. In VSMCs expressing the full-length ETB receptor, IRL1620 (an ETB-selective agonist) induced a biphasic extracellular signal-regulated kinase 1/2 (ERK1/2) activation and increased expression of contractile proteins (smooth muscle myosin-1 [SM-1]/SM-2, SM22alpha, and alpha-actin). Interestingly, the second phase of ERK1/2 activation required metalloprotease activity, epidermal growth factor (EGF) receptor transactivation, and predominantly activation of Gi proteins. In contrast, in VSMCs expressing N-terminally truncated ETB receptors, IRL1620 did not elicit EGF transactivation and failed to increase contractile protein expression.

CONCLUSIONS

This study is the first to show that stimulation of full-length ETB receptors promotes expression of contractile proteins and may thus participate in the differentiation of VSMCs.

Mechanical, biochemical, and extracellular matrix effects on vascular smooth muscle cell phenotype

The vascular smooth muscle cell (VSMC) is surrounded by a complex extracellular matrix that provides and modulates a variety of biochemical and mechanical cues that guide cell function. Conventional two-dimensional monolayer culture systems recreate only a portion of the cellular environment, and therefore there is increasing interest in developing more physiologically relevant three-dimensional culture systems. This review brings together recent studies on how mechanical, biochemical, and extracellular matrix stimulation can be applied to study VSMC function and how the combination of these factors leads to changes in phenotype. Particular emphasis is placed on in vitro experimental studies in which multiple stimuli are combined, especially in three-dimensional culture systems and in vascular tissue engineering applications. These studies have provided new insight into how VSMC phenotype is controlled, and they have underscored the interdependence of biochemical and mechanical signaling. Future improvements in creating more complex in vitro culture environments will lead to a better understanding of VSMC biology, new treatments for vascular disease, as well as improved blood vessel substitutes.

Molecular Determinants of Vascular Smooth Muscle Cell Diversity

Although the primary role of vascular smooth muscle cells (SMCs) is contraction, they exhibit extensive phenotypic diversity and plasticity during normal development, during repair of vascular injury, and in disease states. Results of recent studies indicate that there are unique as well as common transcriptional regulatory mechanisms that control expression of various SMC marker genes in distinct SMC subtypes, and that these mechanisms are complex and dynamic even at the single cell level. This article will review recent progress in our understanding of the transcriptional regulatory mechanisms involved in controlling expression of SMC marker genes with a particular focus on examination of processes that contribute to the phenotypic diversity of SMCs. In addition, because of considerable controversy in the literature regarding the relationship between phenotypically modulated SMCs and myofibroblasts, we will briefly consider both similarities and differences in regulation of gene expression between these cell types.

The mTOR/p70 S6K1 pathway regulates vascular smooth muscle cell differentiation

Vascular smooth muscle cells (VSMC) in mature, normal blood vessels exhibit a differentiated, quiescent, contractile morphology, but injury induces a phenotypic modulation toward a proliferative, dedifferentiated, migratory phenotype with upregulated extracellular matrix protein synthesis (synthetic phenotype), which contributes to intimal hyperplasia. The mTOR (the mammalian target of rapamycin) pathway inhibitor rapamycin inhibits intimal hyperplasia in animal models and in human clinical trials. We report that rapamycin treatment induces differentiation in cultured synthetic phenotype VSMC from multiple species. VSMC treated with rapamycin assumed a contractile morphology, quantitatively reflected by a 67% decrease in cell area. Total protein and collagen synthesis were also inhibited by rapamycin. Rapamycin induced expression of the VSMC differentiation marker contractile proteins smooth muscle (SM) α-actin, calponin, and SM myosin heavy chain (SM-MHC), as observed by immunoblotting and immunohistochemistry. Notably, we detected a striking rapamycin induction of calponin and SM-MHC mRNA, suggesting a role for mTOR in transcriptional control of VSMC gene expression. Rapamycin also induced expression of the cyclin-dependent kinase inhibitors p21cipand p27kip, consistent with cell cycle withdrawal. Rapamycin inhibits mTOR, a signaling protein that regulates protein synthesis effectors, including p70 S6K1. Overexpression of p70 S6K1 inhibited rapamycin-induced contractile protein and p21cipexpression, suggesting that this kinase opposes VSMC differentiation. In conclusion, we report that regulation of VSMC differentiation is a novel function of the rapamycin-sensitive mTOR signaling pathway.

ROS during the acute phase of Ang II hypertension participates in cardiovascular MAPK activation but not vasoconstriction

The relations among hypertensive response, oxidative stress, and mitogen-activated protein kinase (MAPK) in cardiovascular tissues have not been fully established. We investigated the involvement of reactive oxygen species on changes in the hemodynamics and cardiovascular MAPKs activities induced by acutely administered angiotensin II (Ang II) in conscious normotensive rats with or without treatment with a superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (tempol). Intravenous infusion of a pressor dose of Ang II rapidly increased mean arterial blood pressure (MBP) by 53+/-5 mm Hg. After a 30-minute treatment with Ang II, phosphorylated MAPKs (ERK1/2, JNK, p38) as well as thiobarbital reactive substances (T-BARS) were increased in the aorta and cardiac left ventricle. Tempol had no significant effect on the elevation of MBP elicited by Ang II; however, it dose-dependently suppressed the augmented phosphorylation of cardiovascular MAPKs and increased T-BARS levels in plasma and tissues induced by Ang II. An acutely administered pressor dose of phenylephrine, an alpha-adrenoceptor agonist, also showed tempol-sensitive cardiovascular MAPK activation and tempol-insensitive blood pressure elevation. These in vivo data indicate that acute administration of Ang II or phenylephrine provoked an increase in oxidative stress in the cardiovascular tissues leading to the activation of MAPKs, whether it was mediated by pressure overload or the direct action of these vasoconstrictors, and that oxidative stress might not have a major contribution to the acute hypertensive responses elicited by the vasoconstrictors.