Role of JNK, p38, and ERK in platelet-derived growth factor-induced vascular proliferation, migration, and gene expression

Pericytes, mesenchymal stem cells and their contributions to tissue repair

Regenerative medicine using mesenchymal stem cells for the purposes of tissue repair has garnered considerable public attention due to the potential of returning tissues and organs to a normal, healthy state after injury or damage has occurred. To achieve this, progenitor cells such as pericytes and bone marrow-derived mesenchymal stem cells can be delivered exogenously, mobilised and recruited from within the body or transplanted in the form organs and tissues grown in the laboratory from stem cells. In this review, we summarise the recent evidence supporting the use of endogenously mobilised stem cell populations to enhance tissue repair along with the use of mesenchymal stem cells and pericytes in the development of engineered tissues. Finally, we conclude with an overview of currently available therapeutic options to manipulate endogenous stem cells to promote tissue repair.

The matricellular protein Cyr61 is a key mediator of platelet-derived growth factor-induced cell migration

Platelet-derived growth factor (PDGF), a potent chemoattractant, induces cell migration via the MAPK and PI3K/Akt pathways. However, the downstream mediators are still elusive. In particular, the role of extracellular mediators is largely unknown. In this study, we identified the matricellular protein Cyr61, which is de novo synthesized in response to PDGF stimulation, as the key downstream mediator of the ERK and JNK pathways, independent of the p38 MAPK and AKT pathways, and, thereby, it mediates PDGF-induced smooth muscle cell migration but not proliferation. Our results revealed that, when Cyr61 was newly synthesized by PDGF, it was promptly translocated to the extracellular matrix and physically interacted with the plasma membrane integrins α6β1 and αvβ3. We further demonstrate that Cyr61 and integrins are integral components of the PDGF signaling pathway via an "outside-in" signaling route to activate intracellular focal adhesion kinase (FAK), leading to cell migration. Therefore, this study provides the first evidence that the PDGF-induced endogenous extracellular matrix component Cyr61 is a key mediator in modulating cell migration by connecting intracellular PDGF-ERK and JNK signals with integrin/FAK signaling. Therefore, extracellular Cyr61 convergence with growth factor signaling and integrin/FAK signaling is a new concept of growth factor-induced cell migration. The discovered signaling pathway may represent an important therapeutic target in growth factor-mediated cell migration/invasion-related vascular diseases and tumorigenesis.

EPO gene expression promotes proliferation, migration and invasion via the p38MAPK/AP-1/MMP-9 pathway by p21WAF1 expression in vascular smooth muscle cells

The use of recombinant human erythropoietin (rHuEpo) can lead to hypertrophy and hyperplasia, and has induced the proliferation of vascular smooth muscle cells (VSMCs). The effect of the EPO gene in the migration and invasion of VSMCs remains unclear. In this study, overexpression of the EPO gene increased the DNA synthesis and phosphorylation of ERK1/2 and p38MAPK in VSMCs. In addition, EPO gene expression induced the migration and invasion of VSMCs via the expression of MMP-9 by the activation of NF-κB and AP-1 binding. A blockade of p38MAPK by specific p38MAPK inhibitor SB203580 led to a suppression of the increased DNA synthesis, migration, and invasion of VSMCs that was induced by the EPO gene. SB203580 treatment blocked the increased expression of MMP-9 through the binding activity of AP-1. Transfection of the EPO gene with VSMCs was associated with the up-regulation of cyclin D1/CDK4, cyclin E/CDK2, and p21WAF1, and with the down-regulation of p27KIP1. The specific suppression of p21WAF1 expression by siRNA rescued the enhancement of DNA synthesis via the phosphorylation of p38MAPK and the increase in migration and invasion through AP-1-mediated MMP-9 expression in EPO gene transfectants. These novel findings demonstrate that p21WAF1 regulates the proliferation, migration and invasion of VSMC induced by EPO gene.

Nobiletin Inhibits PDGF-BB-induced vascular smooth muscle cell proliferation and migration and attenuates neointimal hyperplasia in a rat carotid artery injury model

Preclinical Research The abnormal migration and proliferation of vascular smooth muscle cells (VSMCs) plays a pivotal role in the development of neointimal hyperplasia after vascular injury. Nobiletin, a citrus bioflavonoid, exhibits anti-inflammatory and anti-oxidative activities. The present study evalutaed whether nobiletin could inhibit platelet-derived growth factor (PDGF)-BB- stimulated VSMC proliferation and migration and decrease neointimal hyperplasia in a rat carotid artery injury model. Cultured VSMCs from rat thoracic aortas were treated with nobiletin before being stimulated with 20 ng/ml PDGF-BB, and rats were subjected to carotid artery injury. Nobiletin inhibited PDGF-BB-induced VSMC proliferation and migration, attenuated reactive oxygen species (ROS) production and reduced phosphorylation of ERK1/2 and the expression of nuclear NF-κB p65 in PDGF-BB-stimulated VSMCs. Nobiletin decreased the intima area and the ratio of neointima to media in balloon-injured rat carotid arteries. Serum levels of TNF-α and IL-6 in nobiletin-treated rats were decreased. These results indicated that nobiletin could be a potential protective agent for the prevention and treatment of restenosis after angioplasty.

Piperine inhibits platelet-derived growth factor-BB-induced proliferation and migration in vascular smooth muscle cells

The proliferation and migration of vascular smooth muscle cells (VSMCs) in blood vessels are important in the pathogenesis of vascular disorders such as atherosclerosis and restenosis. Piperine, a major component of black pepper, has antioxidant, anticancer, and anti-inflammatory activity. However, the antiatherosclerotic effects of piperine have not been investigated. In this study, the effects of piperine on platelet-derived growth factor (PDGF)-BB-induced proliferation and migration of VSMCs were investigated. The antiproliferative effects of piperine were determined using MTT assays, cell counting, real-time polymerase chain reaction, and western blots. Our results showed that piperine significantly attenuated the proliferation of VSMCs by increasing the expression of p27(kip1), regulating the mRNA expression of cell cycle enzymes (cyclin D, cyclin E, and PCNA), and decreasing the phosphorylation of extracellular signal-regulated kinase (ERK)1/2 in a noncytotoxic concentration-dependent manner (30-100 μM). Moreover, we examined the effects of piperine on the migration of PDGF-BB-stimulated VSMCs, as determined by the Boyden chamber assay, H2DCFDA staining, and western blots. Our results showed that 100 μM piperine decreased cell migration, the production of reactive oxygen species (ROS), and phosphorylation of the p38 mitogen-activated protein kinase (MAPK). Taken together, our results suggest that piperine inhibits PDGF-BB-induced proliferation and the migration of VSMCs by inducing cell cycle arrest and suppressing MAPK phosphorylation and ROS. These findings suggest that piperine may be beneficial for the treatment of vascular-related disorders and diseases.

Rho/ROCK signal cascade mediates asymmetric dimethylarginine-induced vascular smooth muscle cells migration and phenotype change

Asymmetric dimethylarginine (ADMA) induces vascular smooth muscle cells (VSMCs) migration. VSMC phenotype change is a prerequisite of migration. RhoA and Rho-kinase (ROCK) mediate migration of VSMCs. We hypothesize that ADMA induces VSMC migration via the activation of Rho/ROCK signal pathway and due to VSMCs phenotype change. ADMA activates Rho/ROCK signal pathway that interpreted by the elevation of RhoA activity and phosphorylation level of a ROCK substrate. Pretreatment with ROCK inhibitor, Y27632 completely reverses the induction of ADMA on ROCK and in turn inhibits ADMA-induced VSMCs migration. When the Rho/ROCK signal pathway has been blocked by pretreatment with Y27632, the induction of ERK signal pathway by ADMA is completely abrogated. Elimination of ADMA via overexpression of dimethylarginine dimethylaminohydrolase 2 (DDAH2) and L-arginine both blocks the effects of ADMA on the activation of Rho/ROCK and extra cellular signal-regulated kinase (ERK) in VSMCs. The expression of differentiated phenotype relative proteins was reduced and the actin cytoskeleton was disassembled by ADMA, which were blocked by Y27632, further interpreting that ADMA inducing VSMCs migration via Rho/ROCK signal pathway is due to its effect on the VSMCs phenotype change. Our present study may help to provide novel insights into the therapy and prevention of atherosclerosis.

Isorhynchophylline protects against pulmonary arterial hypertension and suppresses PASMCs proliferation

Increased pulmonary arterial smooth muscle cells (PASMCs) proliferation is a key pathophysiological component of pulmonary vascular remodeling in pulmonary arterial hypertension (PAH). Isorhynchophylline (IRN) is a tetracyclic oxindole alkaloid isolated from the Chinese herbal medicine Uncaria rhynchophylla. It has long been used clinically for treatment of cardiovascular and cerebrovascular diseases. However, very little is known about whether IRN can influence the development of PAH. Here we examined the effect of IRN on monocrotaline (MCT) induced PAH in rats. Our data demonstrated that IRN prevented MCT induced PAH in rats, as assessed by right ventricular (RV) pressure, the weight ratio of RV to (left ventricular+septum) and RV hypertrophy. IRN significantly attenuated the percentage of fully muscularized small arterioles, the medial wall thickness, and the expression of smooth muscle α-actin (α-SMA) and proliferating cell nuclear antigen (PCNA). In vitro studies, IRN concentration-dependently inhibited the platelet-derived growth factor (PDGF)-BB-induced proliferation of PASMCs. Fluorescence-activated cell-sorting analysis showed that IRN caused G0/G1 phase cell cycle arrest. IRN-induced growth inhibition was associated with downregulation of Cyclin D1 and CDK6 as well as an increase in p27Kip1 levels in PDGF-BB-stimulated PASMCs. Moreover, IRN negatively modulated PDGF-BB-induced phosphorylation of PDGF-Rβ, ERK1/2, Akt/GSK3β, and signal transducers and activators of transcription 3 (STAT3). These results demonstrate that IRN could inhibit PASMCs proliferation and attenuate pulmonary vascular remodeling after MCT induction. These beneficial effects were at least through the inhibition of PDGF-Rβ phosphorylation and its downstream signaling pathways. Therefore, IRN might be a potential candidate for the treatment of PAH.

Systemic sclerosis immunoglobulin induces growth and a pro-fibrotic state in vascular smooth muscle cells through the epidermal growth factor receptor

OBJECTIVE

It has been suggested that autoantibodies in systemic sclerosis (SSc) may induce the differentiation of cultured fibroblasts into myofibroblasts through platelet-derived growth factor receptor (PDGFR) activation. The present study aims to characterize the effects of SSc IgG on vascular smooth muscle cells (VSMCs) and to determine if stimulatory autoantibodies directed to the PDGFR can be detected, and whether they induce a profibrotic response in primary cultured VSMCs.

METHODS

Cultured VSMCs were exposed to IgG fractions purified from SSc-patient or control sera. VSMC responses were then analyzed for ERK1/2 and Akt phosphorylation, PDGFR immunoprecipitation, cellular proliferation, protein synthesis, and pro-fibrotic changes in mRNA expression.

RESULTS

Stimulatory activity in IgG fractions was more prevalent and intense in the SSc samples. SSc IgG immunoprecipitated the PDGFR with greater avidity than control IgG. Interestingly, activation of downstream signaling events (e.g. Akt, ERK1/2) was independent of PDGFR activity, but required functional EGFR. We also detected increased protein synthesis in response to SSc IgG (p<0.001) and pro-fibrotic changes in gene expression (Tgfb1 +200%; Tgfb2 -23%; p<0.001)) in VSMCs treated with SSc IgG.

CONCLUSION

When compared to control IgG, SSc IgG have a higher stimulation index in VSMCs. Although SSc IgG interact with the PDGFR, the observed remodeling signaling events occur through the EGFR in VSMC. Our data thus favour a model of transactivation of the EGFR by SSc-derived PDGFR autoantibodies and suggest the use of EGFR inhibitors in future target identification studies in the field of SSc.

Decorin mimic regulates platelet-derived growth factor and interferon-γ stimulation of vascular smooth muscle cells

Following balloon injury, smooth muscle cells (SMCs) serve as targets for many of the pro-inflammatory and pro-fibrotic factors, including platelet-derived growth factor (PDGF) and interferon-γ (IFN-γ) released from activated inflammatory cells and platelets. Previously, our lab designed a mimic of the proteoglycan decorin, termed DS-SILY20, that suppressed vascular SMC proliferation, migration, and protein synthesis in vitro, and injured vessels treated with DS-SILY20 demonstrated reduced hyperplasia in vivo. Here we characterize the effects of DS-SILY20 on modulating PDGF and IFN-γ stimulation in both proliferative and quiescent human SMCs to further evaluate the potential impact of DS-SILY20-SMC interaction on restenosis. Nanomolar dissociation constants were observed between DS-SILY20 and both PDGF and IFN-γ. PDGF significantly increased migration, proliferation, and protein and cytokine expression, as well as increased ERK-1/2 and p38 MAPK phosphorylation in both quiescent and proliferative cultures. However, DS-SILY20 inhibited these increases, presumably through sequestration of the PDGF. Consistent with the complex responses seen with IFN-γ in SMC physiology in the literature, the response of SMC cultures to IFN-γ was variable and complex. However, where increased activity was seen with IFN-γ, DS-SILY20 attenuated this activity. Overall, the results suggest that DS-SILY20 would be an ideal alternative to traditional therapeutics used and may be an effective therapy for the prevention of intimal hyperplasia after balloon angioplasty.

The LIM-only protein FHL2 reduces vascular lesion formation involving inhibition of proliferation and migration of smooth muscle cells

The LIM-only protein FHL2, also known as DRAL or SLIM3, has a function in fine-tuning multiple physiological processes. FHL2 is expressed in the vessel wall in smooth muscle cells (SMCs) and endothelial cells and conflicting data have been reported on the regulatory function of FHL2 in SMC phenotype transition. At present the function of FHL2 in SMCs in vascular injury is unknown. Therefore, we studied the role of FHL2 in SMC-rich lesion formation. In response to carotid artery ligation FHL2-deficient (FHL2-KO) mice showed accelerated lesion formation with enhanced Ki67 expression compared with wild-type (WT)-mice. Consistent with these findings, cultured SMCs from FHL2-KO mice showed increased proliferation through enhanced phosphorylation of extracellular-regulated kinase-1/2 (ERK1/2) and induction of CyclinD1 expression. Overexpression of FHL2 in SMCs inhibited CyclinD1 expression and CyclinD1-knockdown blocked the enhanced proliferation of FHL2-KO SMCs. We also observed increased CyclinD1 promoter activity in FHL2-KO SMCs, which was reduced upon ERK1/2 inhibition. Furthermore, FHL2-KO SMCs showed enhanced migration compared with WT SMCs. In conclusion, FHL2 deficiency in mice results in exacerbated SMC-rich lesion formation involving increased proliferation and migration of SMCs via enhanced activation of the ERK1/2-CyclinD1 signaling pathway.

Resveratrol inhibits phenotype modulation by platelet derived growth factor-bb in rat aortic smooth muscle cells

Dedifferentiated vascular smooth muscle cells (VSMCs) are phenotypically modulated from the contractile state to the active synthetic state in the vessel wall. In this study, we investigated the effects of resveratrol on phenotype modulation by dedifferentiation and the intracellular signal transduction pathways of platelet derived growth factor-bb (PDGF-bb) in rat aortic vascular smooth muscle cells (RAOSMCs). Treatment of RAOSMCs with resveratrol showed dose-dependent inhibition of PDGF-bb-stimulated proliferation. Resveratrol treatment inhibited this phenotype change and disassembly of actin filaments and maintained the expression of contractile phenotype-related proteins such as calponin and smooth muscle actin-alpha in comparison with only PDGF-bb stimulated RAOSMC. Although PDGF stimulation elicited strong and detectable Akt and mTOR phosphorylations lasting for several hours, Akt activation was much weaker when PDGF was used with resveratrol. In contrast, resveratrol only slightly inhibited phosphorylations of 42/44 MAPK and p38 MAPK. In conclusion, RAOSMC dedifferentiation, phenotype, and proliferation rate were inhibited by resveratrol via interruption of the balance of Akt, 42/44MAPK, and p38MAPK pathway activation stimulated by PDGF-bb.

Anti-atherosclerotic effects of Polygonum aviculare L. ethanol extract in ApoE knock-out mice fed a Western diet mediated via the MAPK pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Polygonum aviculare L. has been used in traditional Korean medicine to treat obesity and symptoms associated with hypertension. The effectiveness or mechanism of Polygonum aviculare L. ethanol extract (PAE) on atherosclerosis disease has not been examined experimentally. This study investigated the protective effect of PAE in atherosclerotic mice.

MATERIALS AND METHODS

ApoE KO mice were fed a Western diet (WD) alone or with PAE or a statin for 12 weeks, followed by analysis of bodyweight, serum lipid levels, and blood pressure. Staining of the aorta and adipose tissue, expression levels of adhesion molecules, and the MAPK pathway were also examined. Cell viability, NF-κB activity, and protein levels of adhesion molecules were assessed in vitro.

RESULTS

ApoE KO mice fed PAE (50 and 100 mg/kg) or statin (10 mg/kg) gained less body weight, and has less adipose tissue and lower serum lipid levels and blood pressures than the WD group. Aorta ICAM-1, VCAM-1, and NF-κB levels were decreased by PAE in a dose-dependent manner, consistent with the in vitro observations. PAE and statin decreased atherosclerotic plaque and adipocyte size versus the WD group. Furthermore, PAE decreased phosphorylation of MAPK pathway components in the aorta of PAE-treated mice, suggesting that PAE's anti-atherosclerotic effects are mediated via a MAPK pathway-dependent mechanism.

CONCLUSIONS

PAE may protect against the development of atherosclerotic disease. The beneficial effects are associated with lowering bodyweight, serum lipids, blood pressure, adhesion molecular protein levels, atherosclerotic plaque, and adipocyte size, involving the MAPK pathway.

Mitogenesis of vascular smooth muscle cell stimulated by platelet-derived growth factor-bb is inhibited by blocking of intracellular signaling by epigallocatechin-3-O-gallate

Epigallocatechin gallate (EGCG) is known to exhibit antioxidant, antiproliferative, and antithrombogenic effects and reduce the risk of cardiovascular diseases. Key events in the development of cardiovascular disease are hypertrophy and hyperplasia according to vascular smooth muscle cell proliferation. In this study, we investigated whether EGCG can interfere with PDGF-bb stimulated proliferation, cell cycle distribution, and the gelatinolytic activity of MMP and signal transduction pathways on RAOSMC when it was treated in two different ways-cotreatment with PDGF-bb and pretreatment of EGCG before addition of PDGF-bb. Both cotreated and pretreated EGCG significantly inhibited PDGF-bb induced proliferation, cell cycle progression of the G0/G1 phase, and the gelatinolytic activity of MMP-2/9 on RAOSMC. Also, EGCG blocked PDGF receptor-β (PDGFR-β) phosphorylation on PDGF-bb stimulated RAOSMC under pretreatment with cells as well as cotreatment with PDGF-bb. The downstream signal transduction pathways of PDGFR-β, including p42/44 MAPK, p38 MAPK, and Akt phosphorylation, were also inhibited by EGCG in a pattern similar to PDGFR-β phosphorylation. These findings suggest that EGCG can inhibit PDGF-bb stimulated mitogenesis by indirectly and directly interrupting PDGF-bb signals and blocking the signaling pathway via PDGFR-β phosphorylation. Furthermore, EGCG may be used for treatment and prevention of cardiovascular disease through blocking of PDGF-bb signaling.

Crucial role of ROCK2 in vascular smooth muscle cells for hypoxia-induced pulmonary hypertension in mice

OBJECTIVE

Rho/Rho-kinase (ROCK) pathway in vascular smooth muscle cells (VSMCs) plays an important role in the pathogenesis of cardiovascular diseases, including pulmonary arterial hypertension (PAH). Rho-kinase has 2 isoforms, ROCK1 and ROCK2, with different functions in different cells; ROCK1 for circulating inflammatory cells and ROCK2 for the vasculature. In the present study, we aimed to examine whether ROCK2 in VSMC is involved in the pathogenesis of PAH.

APPROACH AND RESULTS

In patients with PAH, the expression of ROCK2 was increased in pulmonary arterial media and primary pulmonary arterial smooth muscle cells when compared with controls. To investigate the role of ROCK2 in VSMC, we generated VSMC-specific heterozygous ROCK2-deficient (ROCK2(+/-)) mice and VSMC-specific ROCK2-overexpressing transgenic (ROCK2-Tg) mice. The extent of hypoxia-induced pulmonary hypertension was reduced in ROCK2(+/-) mice and was enhanced in ROCK2-Tg mice compared with respective littermates. The protein expression of ROCK activity and phosphorylated extracellular signal-regulated kinase and the number of Ki67-positive proliferating cells in the lung were reduced in ROCK2(+/-) mice and were increased in ROCK2-Tg mice compared with respective littermates. In cultured mouse aortic VSMC, migration and proliferation activities were reduced in ROCK2(+/-) mice, and migration activity was increased in ROCK2-Tg mice compared with respective littermates. In addition, in primary pulmonary arterial smooth muscle cells from a patient with PAH, ROCK2 was required for migration and proliferation through ROCK and extracellular signal-regulated kinase activation.

CONCLUSIONS

ROCK2 in VSMC contributes to the pathogenesis of PAH.

Anti-Proliferative Effect of an Aqueous Extract of Prunella vulgaris in Vascular Smooth Muscle Cells

The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial walls is an important pathogenic factor of vascular disorders such as diabetic atherosclerosis. We have reported the anti-inflammatory effect of an aqueous extract from Prunella vulgaris (APV) in vascular endothelial cell. In the present study, APV exhibited inhibitory effects on high glucose-stimulated VSMC proliferation, migration, and invasion activities, inducing G₁ cell cycle arrest with downregulation of cyclins and CDKs and upregulation of the CKIs, p21^waf1/cip1 and p27^kip1. Furthermore, APV dose dependently suppressed the high glucose-induced matrix metalloproteinase activity. High glucose-induced phosphorylation of ERK, p38 MAPK, was decreased by the pretreatment of APV. NF-κB activation by high glucose was attenuated by APV, as an antioxidant. APV attenuated the high glucose-induced decrease of nuclear factor E2-related factor-2 (Nrf2) translocation and heme oxygenase-1 (HO-1) expression. Intracellular cGMP level was also increased by APV treatment. These results demonstrate that APV may inhibit VSMC proliferation via downregulating ROS/NF-κB /ERK/p38 MAPK pathways. In addition, APV has a beneficial effect by the interaction of Nrf2-mediated NO/cGMP with HO-1, suggesting that Prunella vulgaris may be useful in preventing diabetic atherosclerosis.

Expression and proliferation profiles of PKC, JNK and p38MAPK in physiologically stretched human bladder smooth muscle cells

OBJECTIVE

To determine protein kinase C (PKC), c-Jun NH2-Terminal Kinase (JNK) and P38 mitogen-activated protein kinases (p38MAPK) expression levels and effects of their respective inhibitors on proliferation of human bladder smooth muscle cells (HBSMCs) when physiologically stretched in vitro.

MATERIALS AND METHODS

HBSMCs were grown on silicone membrane and stretch was applied under varying conditions; (equibiaxial elongation: 2.5%, 5%, 10%, 15%, 20%, 25%), (frequency: 0.05, 0.1, 0.2, 0.5, 1Hz). Optimal physiological stretch was established by assessing proliferation with 5-Bromo-2-deoxyuridine (BrdU) assay and flow cytometry. PKC, JNK and p38 expression levels were analyzed by Western blot. Specificity was maintained by employing specific inhibitors; (GF109203X for PKC, SP600125 for JNK and SB203580 for p38MAPK), in some experiments.

RESULTS

Optimum proliferation was observed at 5% equibiaxial stretch (BrdU: 0.837±0.026 (control) to 1.462±0.023)%, (P<0.05) and apoptotic cell death rate decreased from 16.4±0.21% (control) to 4.5±0.13% (P<0.05) applied at 0.1Hz. Expression of PKC was upregulated with slight increase in JNK and no change in p38MAPK after application of stretch. Inhibition had effects on proliferation (1.075±0.024, P<0.05 GF109203X); (1.418±0.021, P>0.05 SP600125) and (1.461±0.01, P>0.05 SB203580). These findings show that mechanical stretch can promote magnitude-dependent proliferative modulation through PKC and possibly JNK but not via p38MAPK in hBSMCs.

Cortistatin inhibits migration and proliferation of human vascular smooth muscle cells and decreases neointimal formation on carotid artery ligation

RATIONALE

Proliferation and migration of smooth muscle cells (SMCs) are key steps for the progression of atherosclerosis and restenosis. Cortistatin is a multifunctional neuropeptide belonging to the somatostatin family that exerts unique functions in the nervous and immune systems. Cortistatin is elevated in plasma of patients experiencing coronary heart disease and attenuates vascular calcification.

OBJECTIVE

To investigate the occurrence of vascular cortistatin and its effects on the proliferation and migration of SMCs in vitro and in vivo and to delimitate the receptors and signal transduction pathways governing its actions.

METHODS AND RESULTS

SMCs from mouse carotid and human aortic arteries and from human atherosclerotic plaques highly expressed cortistatin. Cortistatin expression positively correlated with the progression of arterial intima hyperplasia. Cortistatin inhibited platelet-derived growth factor-stimulated proliferation of human aortic SMCs via binding to somatostatin receptors (sst2 and sst5) and ghrelin receptor, induction of cAMP and p38-mitogen-activated protein kinase, and inhibition of Akt activity. Moreover, cortistatin impaired lamellipodia formation and migration of human aortic SMCs toward platelet-derived growth factor by inhibiting, in a ghrelin-receptor-dependent manner, Rac1 activation and cytosolic calcium increases. These effects on SMC proliferation and migration correlated with an inhibitory action of cortistatin on the neointimal formation in 2 models of carotid arterial ligation. Endogenous cortistatin seems to play a critical role in regulating SMC function because cortistatin-deficient mice developed higher neointimal hyperplasic lesions than wild-type mice.

CONCLUSIONS

Cortistatin emerges as a natural endogenous regulator of SMCs under pathological conditions and an attractive candidate for the pharmacological management of vascular diseases that course with neointimal lesion formation.

Integrative pathway dissection of molecular mechanisms of moxLDL-induced vascular smooth muscle phenotype transformation

Background

Atherosclerosis (AT) is a chronic inflammatory disease characterized by the accumulation of inflammatory cells, lipoproteins and fibrous tissue in the walls of arteries. AT is the primary cause of heart attacks and stroke and is the leading cause of death in Western countries. To date, the pathogenesis of AT is not well-defined. Studies have shown that the dedifferentiation of contractile and quiescent vascular smooth muscle cells (SMC) to the proliferative, migratory and synthetic phenotype in the intima is pivotal for the onset and progression of AT. To further delineate the mechanisms underlying the pathogenesis of AT, we analyzed the early molecular pathways and networks involved in the SMC phenotype transformation.

Methods

Quiescent human coronary artery SMCs were treated with minimally-oxidized LDL (moxLDL), for 3 hours and 21 hours, respectively. Transcriptomic data was generated for both time-points using microarrays and was subjected to pathway analysis using Gene Set Enrichment Analysis, GeneMANIA and Ingenuity software tools. Gene expression heat maps and pathways enriched in differentially expressed genes were compared to identify functional biological themes to elucidate early and late molecular mechanisms of moxLDL-induced SMC dedifferentiation.

Results

Differentially expressed genes were found to be enriched in cholesterol biosynthesis, inflammatory cytokines, chemokines, growth factors, cell cycle control and myogenic contraction themes. These pathways are consistent with inflammatory responses, cell proliferation, migration and ECM production, which are characteristic of SMC dedifferentiation. Furthermore, up-regulation of cholesterol synthesis and dysregulation of cholesterol metabolism was observed in moxLDL-induced SMC. These observations are consistent with the accumulation of cholesterol and oxidized cholesterol esters, which induce proinflammatory reactions during atherogenesis. Our data implicate for the first time IL12, IFN-α, HGF, CSF3, and VEGF signaling in SMC phenotype transformation. GPCR signaling, HBP1 (repressor of cyclin D1 and CDKN1B), and ID2 and ZEB1 transcriptional regulators were also found to have important roles in SMC dedifferentiation. Several microRNAs were observed to regulate the SMC phenotype transformation via an interaction with IFN-γ pathway. Also, several “nexus” genes in complex networks, including components of the multi-subunit enzyme complex involved in the terminal stages of cholesterol synthesis, microRNAs (miR-203, miR-511, miR-590-3p, miR-346*/miR- 1207-5p/miR-4763-3p), GPCR proteins (GPR1, GPR64, GPRC5A, GPR171, GPR176, GPR32, GPR25, GPR124) and signal transduction pathways, were found to be regulated.

Conclusions

The systems biology analysis of the in vitro model of moxLDL-induced VSMC phenotype transformation was associated with the regulation of several genes not previously implicated in SMC phenotype transformation. The identification of these potential candidate genes enable hypothesis generation and in vivo functional experimentation (such as gain and loss-of-function studies) to establish causality with the process of SMC phenotype transformation and atherogenesis.

Aldosterone-induced osteopontin expression in vascular smooth muscle cells involves MR, ERK, and p38 MAPK

Osteopontin (OPN) is known to be one of the cytokines that is involved in the vascular inflammation caused by aldosterone (Ald). Previous reports have shown that Ald increases OPN expression, and the mechanisms for this remain to be clarified. In this study, we investigated how Ald increases OPN expression in the vascular smooth muscle cells (VSMCs) of rats. Ald increased OPN expression time dependently as well as dose dependently. This increase was diminished by spironolactone, a mineralocorticoid receptor (MR) antagonist. PD98059, an inhibitor of p42/44 MAPK pathway, and SB203580, an inhibitor of p38 MAPK pathway, suppressed Ald-induced OPN expression and secretion in VSMCs. VSMCs migration stimulated by aldosterone required OPN expression. In conclusion, these data suggest that Ald-induced OPN expression in VSMC is mediated by MR and signaling cascades involving ERK and p38 MAPK. These molecules may represent therapeutic targets for the prevention of pathological vascular remodeling.

Vinpocetine suppresses pathological vascular remodeling by inhibiting vascular smooth muscle cell proliferation and migration

Abnormal vascular smooth muscle cell (SMC) activation is associated with various vascular disorders such as atherosclerosis, in-stent restenosis, vein graft disease, and transplantation-associated vasculopathy. Vinpocetine, a derivative of the alkaloid vincamine, has long been used as a cerebral blood flow enhancer for treating cognitive impairment. However, its role in pathological vascular remodeling remains unexplored. Herein, we show that systemic administration of vinpocetine significantly reduced neointimal formation in carotid arteries after ligation injury. Vinpocetine also markedly decreased spontaneous remodeling of human saphenous vein explants in ex vivo culture. In cultured SMCs, vinpocetine dose-dependently suppressed cell proliferation and caused G1-phase cell cycle arrest, which is associated with a decrease in cyclin D1 and an increase in p27Kip1 levels. In addition, vinpocetine dose-dependently inhibited platelet-derived growth factor (PDGF)-stimulated SMC migration as determined by the two-dimensional migration assays and three-dimensional aortic medial explant invasive assay. Moreover, vinpocetine significantly reduced PDGF-induced type I collagen and fibronectin expression. It is noteworthy that PDGF-stimulated phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2), but not protein kinase B, was specifically inhibited by vinpocetine. Vinpocetine powerfully attenuated intracellular reactive oxidative species (ROS) production, which largely mediates the inhibitory effects of vinpocetine on ERK1/2 activation and SMC growth. Taken together, our results reveal a novel function of vinpocetine in attenuating neointimal hyperplasia and pathological vascular remodeling, at least partially through suppressing ROS production and ERK1/2 activation in SMCs. Given the safety profile of vinpocetine, this study provides insight into the therapeutic potential of vinpocetine in proliferative vascular disorders.

Function of Ahnak protein in aortic smooth muscle cell migration through Rac activation

AIMS

Ahnak protein acts as a scaffold protein networking phospholipase C-γ and protein kinase C-α, which subsequently stimulate an extracellular signal-regulated kinase (Erk) pathway. In mouse aortic smooth muscle cells (ASMCs), the activation of the signalling cascade ultimately promotes the cell migration through an unknown mechanism. We aimed to dissect the Ahnak-mediated cell signalling network involved in the migration of ASMCs.

METHODS AND RESULTS

Migration of ASMCs from wild-type mice was significantly increased by platelet-derived growth factor (PDGF) stimulation in transwell chamber and wound-healing assays, whereas migration of ASMCs from Ahnak knockout mice was reduced. Consistently, stimulation of wild-type ASMCs with PDGF resulted in Rac activation-mediated lamellipodial protrusion in migrating cells. In contrast, Ahnak knockout ASMCs displayed lower activation of Rac in response to PDGF and slow lamellipodial protrusion rate and cell migration. Ahnak signalling complex was analysed by immunoprecipitation with antibody to p21-activated protein kinase (PAK). Ahnak protein was shown to function as the signalling scaffold interacting with the multiple protein complex of Erk, PAK, and p21-activated kinase-interacting exchange factor β. The proposed role of Ahnak in cell migration was examined using a restenosis model in which the carotid arteries of mice were subjected to post-ligation injury. We show neointimal formation and SMC migration after ligation injury in Ahnak knockout mice were significantly retarded compared with wild-type mice.

CONCLUSION

Ahnak protein plays an important scaffolding function connecting Erk and Rac activation in PDGF-dependent migration of ASMC.

Tunicamycin inhibits PDGF-BB-induced proliferation and migration of vascular smooth muscle cells through induction of HO-1

The abnormal proliferation and migration of vascular smooth muscle cell (VSMC), which is triggered by various external stimuli, contributes importantly to the pathogenesis of atherosclerosis and restenosis. Recent studies indicate that the endoplasmic reticulum (ER) stress is intensively involved in the pathophysiological changes of VSMCs by various stimuli. However, the direct effects of ER stress on VSMC proliferation and migration remain unknown. In this study, we found that pretreatment with tunicamycin (Tm), an ER stress inducer, significantly inhibited platelet-derived growth factor (PDGF)-BB-induced VSMC proliferation and migration in a dose-dependent manner without causing significant apoptosis. Tm stimulated the expression of the antioxidant gene heme oxygenase-1 (HO-1) both at the transcriptional and translational levels, while reducing phosphorylation and activation of mitogen-activated protein (MAP) kinases. The negative regulative effects of Tm were associated with a decrease in cyclins and cyclin-dependent kinases (CDKs) activation. More importantly, HO-1 siRNA partially abolished the beneficial effects of Tm on VSMCs. These results indicate that Tm-induced ER stress provides protection against the abnormal VSMC activation by PDGF-BB, which may be mediated by the induction of HO-1 and blockade of cell cycle reentry.

TGF-β and Smad3 modulate PI3K/Akt signaling pathway in vascular smooth muscle cells

Transforming growth factor-β (TGF-β) is upregulated at the time of arterial injury; however, the mechanism through which TGF-β enhances the development of intimal hyperplasia is not clear. Recent studies from our laboratory suggest that in the presence of elevated levels of Smad3, TGF-β stimulates smooth muscle cell (SMC) proliferation. This is a novel phenomenon in that TGF-β has traditionally been known as a potent inhibitor of cellular proliferation. In these studies we explore the signaling pathways through which TGF-β mediates its proliferative effect in vascular SMCs. We found that TGF-β phosphorylates and activates Akt in a time-dependent manner, and this effect is significantly enhanced by overexpression of Smad3. Furthermore, both chemical and molecular inhibition of Smad3 can reverse the effect of TGF-β on Akt. Although we found numerous signaling pathways that might function as intermediates between Smad3 and Akt, p38 appeared the most promising. Overexpression of Smad3 enhanced p38 phosphorylation and inhibition of p38 with a chemical inhibitor or a small interfering RNA blocked TGF-β-induced Akt phosphorylation. Moreover, TGF-β/Smad3 enhancement of SMC proliferation was blocked by inhibition of p38. Phosphorylation of Akt by TGF-β/Smad3 was not dependent on gene expression or protein synthesis, and immunoprecipitation studies revealed a physical association among p38, Akt, and Smad3 suggesting that activation requires a direct protein-protein interaction. Our findings were confirmed in vivo where overexpression of Smad3 in a rat carotid injury model led to enhancement of p-p38, p-Akt, as well as SMC proliferation. Furthermore, inhibition of p38 in vivo led to decreased Akt phosphorylation and SMC proliferation. In summary, our studies reveal a novel pathway whereby TGF-β/Smad3 stimulates SMC proliferation through p38 and Akt. These findings provide a potential mechanism for the substantial effect of TGF-β on intimal hyperplasia and suggest new targets for chemical or molecular prevention of vascular restenosis.

Upregulation of thrombospondin-1 expression by leptin in vascular smooth muscle cells via JAK2- and MAPK-dependent pathways

Hyperleptinemia, characteristic of diabetes and a hallmark feature of human obesity, contributes to the increased risk of atherosclerotic complications. However, molecular mechanisms mediating leptin-induced atherogenesis and gene expression in vascular cells remain incompletely understood. Accumulating evidence documents a critical role of a potent antiangiogenic and proatherogenic matricellular protein, thrombospondin-1 (TSP-1), in atherosclerosis. Although previous studies reported elevated TSP-1 levels in both diabetic and obese patients and rodent models, there is no direct information on TSP-1 expression in vascular cells in response to leptin. In the present study, we show that leptin upregulates TSP-1 expression in cultured human aortic smooth muscle cells (HASMC) in vitro, and this increase occurs at the level of transcription, revealed by mRNA stability and TSP-1 promoter-reporter assays. Utilizing specific pharmacological inhibitors and siRNA approaches, we demonstrate that upregulation of TSP-1 expression by leptin is mediated by JAK2/ERK/JNK-dependent mechanisms. Furthermore, we report that while ERK and JNK are required for both the constitutive and leptin-induced expression of TSP-1, JAK-2 appears to be specifically involved in leptin-mediated TSP-1 upregulation. Finally, we found that increased HASMC migration and proliferation in response to leptin is significantly inhibited by a TSP-1 blocking antibody, thereby revealing the physiological significance of leptin-TSP-1 crosstalk. Taken together, these findings demonstrate, for the first time, that leptin has a direct regulatory effect on TSP-1 expression in HASMCs, underscoring a novel role of TSP-1 in hyperleptinemia-induced atherosclerotic complications.

3,3'Diindolylmethane suppresses vascular smooth muscle cell phenotypic modulation and inhibits neointima formation after carotid injury

BACKGROUND

3,3'Diindolylmethane (DIM), a natural phytochemical, has shown inhibitory effects on the growth and migration of a variety of cancer cells; however, whether DIM has similar effects on vascular smooth muscle cells (VSMCs) remains unknown. The purpose of this study was to assess the effects of DIM on the proliferation and migration of cultured VSMCs and neointima formation in a carotid injury model, as well as the related cell signaling mechanisms.

METHODOLOGY/PRINCIPAL FINDINGS

DIM dose-dependently inhibited the platelet-derived growth factor (PDGF)-BB-induced proliferation of VSMCs without cell cytotoxicity. This inhibition was caused by a G0/G1 phase cell cycle arrest demonstrated by fluorescence-activated cell-sorting analysis. We also showed that DIM-induced growth inhibition was associated with the inhibition of the expression of cyclin D1 and cyclin-dependent kinase (CDK) 4/6 as well as an increase in p27(Kip1) levels in PDGF-stimulated VSMCs. Moreover, DIM was also found to modulate migration of VSMCs and smooth muscle-specific contractile marker expression. Mechanistically, DIM negatively modulated PDGF-BB-induced phosphorylation of PDGF-recptorβ (PDGF-Rβ) and the activities of downstream signaling molecules including Akt/glycogen synthase kinase(GSK)3β, extracellular signal-regulated kinase1/2 (ERK1/2), and signal transducers and activators of transcription 3 (STAT3). Our in vivo studies using a mouse carotid arterial injury model revealed that treatment with 150 mg/kg DIM resulted in significant reduction of the neointima/media ratio and proliferating cell nuclear antigen (PCNA)-positive cells, without affecting apoptosis of vascular cells and reendothelialization. Infiltration of inflammatory cells was also inhibited by DIM administration.

CONCLUSION

These results demonstrate that DIM can suppress the phenotypic modulation of VSMCs and neointima hyperplasia after vascular injury. These beneficial effects on VSMCs were at least partly mediated by the inhibition of PDGF-Rβ and the activities of downstream signaling pathways. The results suggest that DIM has the potential to be a candidate for the prevention of restenosis.

The effect of endothelial progenitor cells on angiotensin II-induced proliferation of cultured rat vascular smooth muscle cells

Previous studies have demonstrated that endothelial progenitor cells (EPCs) could delay the progress of vascular remodeling in blood vessel-proliferating diseases. The proliferation of vascular smooth muscle cells (VSMCs) is a pivotal factor in cardiovascular diseases. In this study, we investigated whether EPCs could inhibit the Angiotensin II (Ang II)-induced proliferation of VSMCs. The effect of early EPC-conditioned medium (E-EPC-CM), late EPCs-CM (L-EPC-CM), and HUVEC-CM on Ang II-induced proliferation of VSMCs was assessed by BrdU incorporation, total protein content, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, and flow cytometry. Reverse transcriptase-polymerase chain reaction and Western blot were performed to analyze the effect of different CMs on Ang II-induced phosphorylations of ERK, JNK, p38, and NF-κB subunit p65 and the expressions of c-myc and c-fos. E-EPC-CM, L-EPC-CM, and HUVEC-CM significantly inhibited the Ang II-induced DNA synthesis, total protein expression, cell survival, and cell cycle progress of VSMCs. Furthermore, E-EPC-CM significantly inhibited the Ang II-induced phosphorylation of ERK, JNK, p38, and p65 (nuclear translocation of p65) and the expressions of c-myc and c-fos. Taken together, these data suggested that EPCs may delay the progress of vascular remodeling in blood vessel-proliferating diseases by inhibiting Ang II-induced proliferation of VSMCs through inactivating MAPKs and NF-κB signaling pathways and by reducing the expressions of c-myc and c-fos.

Salvianolic acid A inhibits PDGF-BB induced vascular smooth muscle cell migration and proliferation while does not constrain endothelial cell proliferation and nitric oxide biosynthesis

Proliferation and migration of vascular smooth muscle cells (VSMCs) are critical events in the initiation and development of restenosis upon percutaneous transluminal coronary angioplasty (PTCA). Polyphenols have been suggested to ameliorate post-angioplasty restenosis. Salvianolic A (SalA) is one of the most abundant polyphenols extracted from salvia. In this study, we investigated the effect of salvianolic A (SalA) on the migration and proliferation of VSMCs. We found a preferential interaction of SalA with cellular systems that rely on the PDGF signal, but not on the EGF and bFGF signal. SalA inhibits PDGF-BB induced VSMC proliferation and migration in the concentration range from 0.01 to 0.1 μM. The inhibition of SalA on VSMC proliferation is associated with cell cycle arrest. We also found that SalA inhibits the PDGFRβ-ERK1/2 signaling cascade activated by PDGF-BB in VSMCs. In addition, SalA does not influence the proliferation of endothelial cells, the synthesis of NO and eNOS protein expression. Our results suggest that SalA inhibits migration and proliferation of VSMCs induced by PDGF-BB via the inhibition of the PDGFRβ-ERK1/2 cascade, but that it does not constrain endothelial cell proliferation and nitric oxide biosynthesis. Thus, the present study suggests a novel adjunct pharmacological strategy to prevent angioplasty-related restenosis.

p38 mitogen-activated protein kinase (MAPK) promotes cholesterol ester accumulation in macrophages through inhibition of macroautophagy

p38 MAPK has been strongly implicated in the development of atherosclerosis, but its role in cholesterol ester accumulation in macrophages and formation of foam cells, an early step in the development of atherosclerosis, has not been investigated. We addressed this issue and made some brand new observations. First, elevated intracellular cholesterol level induced by the exposure to LDL-activated p38 MAPK and activation of p38 MAPK with anisomycin increased the ratio of cholesterol esters over free cholesterol, whereas inhibition of p38 MAPK with SB203580 or siRNA reduced the LDL loading-induced intracellular accumulation of free cholesterol and cholesterol esters in macrophages. Second, exposure to LDL cholesterol inhibited autophagy in macrophages, and inhibition of autophagy with 3-methyladenine increased intracellular accumulation of cholesterol (free cholesterol and cholesterol esters), whereas activation of autophagy with rapamycin decreased intracellular accumulation of free cholesterol and cholesterol esters induced by the exposure to LDL cholesterol. Third, LDL cholesterol loading-induced inhibition of autophagy was prevented by blockade of p38 MAPK with SB203580 or siRNA. Neutral cholesterol ester hydrolase was co-localized with autophagosomes. Finally, LDL cholesterol loading and p38 activation suppressed expression of the key autophagy gene, ulk1, in macrophages. Together, our results provide brand new insight about cholesterol ester accumulation in macrophages and foam cell formation.

JNK/stress-activated protein kinase associated protein 1 is required for early development of telencephalic commissures in embryonic brains

We previously reported that mice lacking JSAP1 (jsap1-/-) were lethal and the brain of jsap1-/- at E18.5 exhibited multiple types of developmental defects, which included impaired axon projection of the corpus callosum and anterior commissures. In the current study, we examined whether the early telencephalic commissures were formed abnormally from the beginning of initial development or whether they arose normally, but have been progressively lost their maintenance in the absence of JSAP1. The early corpus callosum in the brain of jsap1+/+ at E15.5-E16.5 was found to cross the midline with forming a distinct U-shaped tract, whereas the early axonal tract in jsap1-/- appeared to cross the midline in a diffuse manner, but the lately arriving axons did not cross the midline. In the brain of jsap1-/- at E17.5, the axon terminals of lately arriving collaterals remained within each hemisphere, forming an early Probst's bundle-like shape. The early anterior commissure in the brain of jsap1+/+ at E14.5-E15.5 crossed the midline, whereas the anterior commissure in jsap1-/- developed, but was deviated from their normal path before approaching the midline. The axon tracts of the corpus callosum and anterior commissure in the brain of jsap1-/- at E16.5-E17.5 expressed phosphorylated forms of FAK and JNK, however, their expression levels in the axonal tracts were reduced compared to the respective controls in jsap1+/+. Considering the known scaffolding function of JSAP1 for the FAK and JNK pathways, these results suggest that JSAP1 is required for the pathfinding of the developing telencephalic commissures in the early brains.

Pharmacotherapy to improve outcomes in vascular access surgery: a review of current treatment strategies

BACKGROUND

Renal failure is a major cause of morbidity in western Europe, with rising prevalence. Vascular access complications are the leading cause of morbidity among patients on haemodialysis. Considering the health care burden of vascular access failure, there is limited research dedicated to the topic.

METHODS

Randomised control trials of medications aimed at improving vascular access patency were identified using a medline search between January 1950 and January 2011.

RESULTS

Thirteen randomised trials were identified, investigating antiplatelets, anticoagulants and fish oil in preserving vascular access patency. Outcomes are presented and reviewed in conjunction with the underlying pathophysiological mechanisms of failure of vascular access.

DISCUSSION

Vascular access failure is a complex process. Most clinical trials so far have involved medications primarily aimed at preventing thrombosis. Other contributing pathways such as neointimal hyperplasia have not been investigated clinically. Improved outcomes may be seen by linking future therapies to these pathways.

ROCK1 induces ERK nuclear translocation in PDGF-BB-stimulated migration of rat vascular smooth muscle cells

It has been known that Rho-associated protein kinase (ROCK) signaling regulates the migration of vascular smooth muscle cells (VSMCs). However, the isoform-specific roles of ROCK and its underlying mechanism in VSMC migration are not well understood. The current study thus aimed to investigate the roles of ROCK1/2 and their relationship to the MAPK signaling pathway in platelet-derived growth factor (PDGF)-induced rat aorta VSMC migration by manipulating ROCK gene expression. The results revealed that ROCK1 small interfering ribonucleic acid (siRNA) rather than ROCK2 siRNA decreased PDGF-BB-generated VSMC migration, and upregulation of ROCK1 expression via transfection of constructed pEGFP-C1/ROCK1 plasmid further increased the migration of PDGF-BB-treated VSMCs. In PDGF-treated VSMCs, ROCK1 siRNA did not affect the phosphorylation levels of ERK and p38 in the cytoplasm, but decreased the level of ERK phosphorylation in the nucleus. These findings demonstrate that activated ROCK1 can promote VSMC migration through facilitating phosphorylation and nuclear translocation of ERK protein.

Thrombin induced connective tissue growth factor expression in rat vascular smooth muscle cells via the PAR-1/JNK/AP-1 pathway

AIM

To investigate the signaling pathways involved in thrombin-induced connective tissue growth factor (CTGF) expression in rat vascular smooth muscle cells (VSMCs).

METHODS

Experiments were preformed on primary rat aortic smooth muscle cells (RASMCs) and a rat VSMC line (A10). CTGF protein levels were measured using Western blotting. Luciferase reporter genes and dominant negative mutants (DNs) were used to investigate the signaling pathways mediating the induction of CTGF expression by thrombin.

RESULTS

Thrombin (0.3-3.0 U/mL) caused a concentration- and time-dependent increase in CTGF expression in both RASMCs and A10 cells. Pretreating A10 cells with the protease-activated receptor 1 (PAR-1) antagonist SCH79797 (0.1 μmol/L) significantly blocked thrombin-induced CTGF expression, while the PAR-4 antagonist tcY-NH(2) (30 μmol/L) had no effect. The PAR-1 agonist SFLLRN-NH(2) (300 μmol/L) induced CTGF expression, while the PAR-4 agonist GYPGQV-NH(2) (300 μmol/L) had no effect. Thrombin (1 U/mL) caused time-dependent phosphorylation of c-Jun N-terminal kinase (JNK). Pretreating with the JNK inhibitor SP600125 (3-30 μmol/L) or transfection with DNs of JNK1/2 significantly attenuated thrombin-induced CTGF expression. Thrombin (0.3-3.0 U/mL) increased activator protein-1 (AP-1)-luciferase activity, which was inhibited by the JNK inhibitor SP600125. The AP-1 inhibitor curcumin (1-10 μmol/L) concentration-dependently attenuated thrombin-induced CTGF expression.

CONCLUSION

Thrombin acts on PAR-1 to activate the JNK signaling pathway, which in turn initiates AP-1 activation and ultimately induces CTGF expression in VSMCs.

Nox1 transactivation of epidermal growth factor receptor promotes N-cadherin shedding and smooth muscle cell migration

AIMS

In atherosclerosis and restenosis, vascular smooth muscle cells (SMCs) migrate into the subendothelial space and proliferate, contributing to neointimal formation. The goal of this study was to define the signalling pathway by which Nox1 NAPDH oxidase mediates SMC migration.

METHODS AND RESULTS

SMCs were cultured from thoracic aorta from Nox1(-/y) (Nox1 knockout, KO) and wild-type (WT) mice. In response to thrombin, WT but not Nox1 KO SMCs generated increased levels of reactive oxygen species (ROS). Deficiency of Nox1 prevented thrombin-induced phosphorylation of Src and the subsequent transactivation of the epidermal growth factor receptor (EGFR) at multiple tyrosine residues. Next, activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and matrix metalloproteinase-9 (MMP-9) by thrombin was inhibited by the EGFR inhibitor AG1478 and in Nox1 KO SMCs. Thrombin-induced shedding of N-cadherin from the plasma membrane was dependent on the presence of Nox1 and was blocked by AG1478 and an inhibitor of metalloproteinases. Migration of SMCs to thrombin was impaired in the Nox1 KO SMCs and was restored by expression of Nox1. Finally, treatment of WT SMCs with AG1478 abrogated Nox1-dependent SMC migration.

CONCLUSIONS

The Nox1 NADPH oxidase signals through EGFR to activate MMP-9 and promote the shedding of N-cadherin, thereby contributing to SMC migration.

Platonin inhibited PDGF-BB-induced proliferation of rat vascular smooth muscle cells via JNK1/2-dependent signaling

AIM

To examine the inhibitory actions of the immunoregulator platonin against proliferation of rat vascular smooth muscle cells (VSMCs).

METHODS

VSMCs were prepared from the thoracic aortas of male Wistar rats. Cell proliferation was examined using MTT assays. Cell cycles were analyzed using flow cytometry. c-Jun N-terminal kinase (JNK)1/2, extracellular signal-regulated kinase (ERK)1/2, AKT, and c-Jun phosphorylation or p27 expression were detected using immunoblotting.

RESULTS

Pretreatment with platonin (1-5 μmol/L) significantly suppressed VSMC proliferation stimulated by PDGF-BB (10 ng/mL) or 10% fetal bovine serum (FBS), and arrested cell cycle progression in the S and G(2)/M phases. The same concentrations of platonin significantly inhibited the phosphorylation of JNK1/2 but not ERK1/2 or AKT in VSMCs stimulated by PDGF-BB. Furthermore, platonin also attenuated c-Jun phosphorylation and markedly reversed the down-regulation of p27 expression after PDGF-BB stimulation.

CONCLUSION

Platonin inhibited VSMC proliferation, possibly via inhibiting phosphorylation of JNK1/2 and c-Jun, and reversal of p27 down-regulation, thereby leading to cell cycle arrest at the S and G(2)/M phases. Thus, platonin may represent a novel approach for lowering the risk of abnormal VSMC proliferation and related vascular diseases.

Tangeretin, a citrus flavonoid, inhibits PGDF-BB-induced proliferation and migration of aortic smooth muscle cells by blocking AKT activation

Tangeretin, a natural polymethoxylated flavone concentrated in the peel of citrus fruits, is known to have antiproliferative, antiinvasive, antimetastatic and antioxidant activities. However, the effect of tangeretin on vascular smooth muscle cells (VSMCs) is unknown. This study examined the effect of tangeretin on platelet-derived growth factor (PDGF)-BB-induced proliferation and migration of rat aortic smooth muscle cells (RASMCs) as well as its underlying mechanisms. Tangeretin significantly inhibited proliferation, DNA synthesis and migration of PDGF-BB-stimulated RASMCs without inducing cell death. Treatment with tangeretin-induced cell-cycle arrest in the G₀/G₁ phase was associated with down-regulation of cyclin D1 and cyclin E in addition to up-regulation of p27(kip1). We also showed that tangeretin inhibited PDGF-BB-induced phosphorylation of AKT, while it had no effect on the phosphorylation of phospholipase Cγ (PLCγ), PDGF receptor β-chain (PDGF-Rβ) and extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases (MAPKs). An in vitro kinase assay revealed that tangeretin inhibited AKT activity in a dose-dependent manner. Moreover, treatment of LY294002, a phosphoinositide 3-kinase (PI3K) inhibitor, had similar effects than that of tangeretin on the expression of p27(kip1) and cyclin D1, as well as cell migration in PDFG-BB-stimulated RASMCs. Taken together, these findings suggest that tangeretin could suppress PDGF-BB-induced proliferation and migration of RASMCs through the suppression of PI3K/AKT signaling pathway, and may be a potential candidate for preventing or treating vascular diseases, such as atherosclerosis and restenosis.

Ectopic overexpression of haem oxygenase-1 protects kidneys from carboplatin-mediated apoptosis

BACKGROUND AND PURPOSE

We previously reported that the activation of the nuclear factor of activated T-lymphocyte-3 (NFAT3) by carboplatin leads to renal apoptosis as a result of oxidative stress, which is reversed by N-acetylcysteine. Herein, we extend our previous work to provide evidence of the molecular mechanisms of haem oxygenase (HO)-1 in protecting against injury.

EXPERIMENTAL APPROACH

Protective mechanisms of HO-1 in carboplatin-mediated renal apoptosis were examined in C57BL/6 mice and rat renal tubular cells (RTC) with HO-1 induction or inactivation/knockdown.

KEY RESULTS

The HO-1, induced by cobalt protoporphyrin, protected against carboplatin-induced renal injury in vivo. This protection was decreased by an inhibitor of HO-1 action, tin protoporphyrin. In cultures of RTC, carboplatin-induced apoptosis was similarly affected by HO-1 overexpression or knockdown. Carboplatin-mediated NFAT3 activation and apoptosis involve activation of the signalling kinases, extracellular signal regulated kinase, Jun N-terminal kinase and protein kinase C, and such activation was reversed in cells overexpressing HO-1. Both products of the HO-1 reaction, CO and bilirubin, inhibited (by 30-40%) NFAT3 activation and production of the pro-apoptotic proteins Bcl-XS/Bax. Additionally, the activation of NFκB was markedly decreased by HO-1 induction.

CONCLUSION AND IMPLICATIONS

HO-1 and its reaction products show anti-apoptotic effects in carboplatin-mediated renal injury. A novel functional NFAT3 binding site identified in the rat HO-1 promoter region was involved in producing a 1.5-fold to 2.5-fold increase in HO-1 induction by carboplatin. Nevertheless, only HO-1 overexpression and activation prior to the carboplatin challenge provided protection against carboplatin-induced injury.

p38 MAPK activation is required for esculetin-induced inhibition of vascular smooth muscle cells proliferation

The phenolic compound esculetin is known to inhibit the proliferation of vascular smooth muscle cells (VSMC). However, the signaling pathway by which esculetin mediates its molecular effects in VSMC remains to be identified. The present results suggest an unexpected role of the p38 MAPK signaling pathway in esculetin-induced inhibition of VSMC growth. Treatment of VSMC with esculetin resulted in significant growth inhibition and G1-phase cell-cycle arrest, which was followed by down-regulation of cyclins and cyclin-dependent kinase (CDK) expression. This G1-phase cell-cycle arrest was due to up-regulation of p21WAF1 expression. In addition, esculetin treatment activated p38 MAPK and ERK1/2. Pretreatment with SB203580, which is a p38 MAPK specific inhibitor, or expression of the dominant negative p38 MAPK (DN p38 MAPK) gene blocked esculetin-induced p38 MAPK activation and p21WAF1 expression. Finally, both the growth inhibition and the down-regulation of CDKs induced by esculetin were suppressed by either SB203580 or the DN p38 MAPK mutant gene. In conclusion, these results demonstrate that activation of p38 MAPK contributes to esculetin-induced p21WAF1 expression in VSMC by decreasing both the cyclin D1/CDK4 and cyclin E/CDK2 complexes. These novel results regarding the molecular mechanism of esculetin action suggest new preventive and therapeutic treatments for atherosclerosis.

Caffeic acid phenethyl ester inhibits PDGF-induced proliferation of vascular smooth muscle cells via activation of p38 MAPK, HIF-1α, and heme oxygenase-1

Hyperproliferation of vascular smooth muscle cells (VSMCs) is critically involved in the onset of atherosclerosis and restenosis. Although caffeic acid phenethyl ester (CAPE, 1), one of the main constituents of honeybee propolis, has been shown to exert a beneficial effect in models of vascular injury in vivo, detailed mechanistic investigations in vascular cells are scarce. This study has examined the antiproliferative activity of 1 in platelet-derived growth factor (PDGF)-stimulated primary rat aortic VSMCs and aimed to shed light on underlying molecular mechanisms. Compound 1 inhibited the proliferation of VSMCs upon exposure to PDGF in a dose-dependent manner by interfering with cell cycle progression from the G0/1- to the S-phase. Enhanced phosphorylation of p38 mitogen-activated protein kinase (MAPK) as well as stabilization of hypoxia-inducible factor (HIF)-1α and subsequent induction of heme oxygenase-1 (HO-1) could be identified as molecular events contributing to the observed growth arrest in PDGF-activated VSMCs upon exposure to 1.

Pharmacology in health food: metabolism of quercetin in vivo and its protective effect against arteriosclerosis

Quercetin, a member of the bioflavonoids family, has been proposed to have anti-atherogenic, anti-inflammatory, and anti-hypertensive properties leading to the beneficial effects against cardiovascular diseases. It was recently demonstrated that quercetin 3-O-β-D-glucuronide (Q3GA) is one of the major quercetin conjugates in human plasma, in which the aglycone could not be detected. Although most of the in vitro pharmacological studies have been carried out using only the quercetin aglycone form, experiments using Q3GA would be important to discover the preventive mechanisms of cardiovascular diseases by quercetin in vivo. Therefore we examined the effects of the chemically synthesized Q3GA, as an in vivo form, on vascular smooth muscle cell (VSMC) disorders related to the progression of arteriosclerosis. Platelet-derived growth factor-induced cell migration and proliferation were inhibited by Q3GA in VSMCs. Q3GA attenuated angiotensin II-induced VSMC hypertrophy via its inhibitory effect on JNK and the AP-1 signaling pathway. Q3GA scavenged 1,1-diphenyl-2-picrylhydrazyl radical measured by the electron paramagnetic resonance method. In addition, immunohistochemical studies with monoclonal antibody 14A2 targeting the Q3GA demonstrated that the positive staining specifically accumulates in human atherosclerotic lesions, but not in the normal aorta. These findings suggest Q3GA would be an active metabolite of quercetin in plasma and may have preventative effects on arteriosclerosis relevant to VSMC disorders.