Expression of platelet derived growth factor B chain and beta receptor in human coronary arteries after percutaneous transluminal coronary angioplasty: an immunohistochemical study

Deletion of smooth muscle ZFP36 promotes neointimal hyperplasia in mice

Platelet-derived growth factor (PDGF-BB) released from the injured intima induces the proliferation and migration of vascular smooth muscle cells (VSMCs), which is the key mechanism of neointimal hyperplasia. Zinc finger 36 (ZFP36), a widespread RNA-binding protein, is important for pathological processes in many diseases. In this study we investigated the role of ZFP36 in VSMCs proliferation, migration and neointimal hyperplasia in mice. We generated smooth muscle-specific Zfp36 knockout (Zfp36SMKO) mice, and established restenosis mouse models by ligation of left carotid artery in Zfp36SMKO mice. We showed that the expression levels of ZFP36 were significantly decreased in human atherosclerotic coronary arteries and murine injured carotid arteries compared with controls. Compared to control Zfp36fl/fl mice, Zfp36SMKO mice displayed accelerated neointimal hyperplasia. In cultured mouse VSMCs, PDGF-BB (20 ng/mL) significantly downregulated ZFP36 expression through KLF4 binding site in Zfp36 promoter. We revealed that ZFP36 could bind to the mRNA of cell migration-inducing protein (CEMIP) and promoted its degradation in VSMCs, thereby reducing the expression of CEMIP protein. Knockdown of Cemip inhibited VSMCs proliferation and migration induced by Zfp36 knockout, thereby suppressing neointimal hyperplasia in Zfp36SMKO mice. We conclude that vascular smooth muscle ZFP36 has a protective effect against neointimal hyperplasia by reducing CEMIP expression. ZFP36 is downregulated by vascular injury and PDGF-BB treatment, which promotes VSMCs proliferation and migration and neointima formation. The results suggest that targeting ZFP36 may represent a novel therapeutic strategy for preventing or treating neointimal hyperplasia and related cardiovascular diseases.

Inhibition of p90RSK Ameliorates PDGF-BB-Mediated Phenotypic Change of Vascular Smooth Muscle Cell and Subsequent Hyperplasia of Neointima

Platelet-derived growth factor type BB (PDGF-BB) regulates vascular smooth muscle cell (VSMC) migration and proliferation, which play critical roles in the development of vascular conditions. p90 ribosomal S6 kinase (p90RSK) can regulate various cellular processes through many different target substrates in several cell types, but the regulatory function of p90RSK on PDGF-BB-mediated cell migration and proliferation and subsequent vascular neointima formation has not yet been extensively examined. In this study, we investigated whether p90RSK inhibition protects VSMCs against PDGF-BB-induced cellular phenotypic changes and the molecular mechanisms underlying the effect of p90RSK inhibition on neointimal hyperplasia in vivo. Pretreatment of cultured primary rat VSMCs with FMK or BI-D1870, which are specific inhibitors of p90RSK, suppressed PDGF-BB-induced phenotypic changes, including migration, proliferation, and extracellular matrix accumulation, in VSMCs. Additionally, FMK and BI-D1870 repressed the PDGF-BB-induced upregulation of cyclin D1 and cyclin-dependent kinase-4 expression. Furthermore, p90RSK inhibition hindered the inhibitory effect of PDGF-BB on Cdk inhibitor p27 expression, indicating that p90RSK may induce VSMC proliferation by regulating the G0/G1 phase. Notably, treatment with FMK resulted in attenuation of neointima development in ligated carotid arteries in mice. The findings imply that p90RSK inhibition mitigates the phenotypic switch and neointimal hyperplasia induced by PDGF-BB.

The rich pharmacological activities of Magnolia officinalis and secondary effects based on significant intestinal contributions

ETHNOPHARMACOLOGICAL RELEVANCE

Magnolia officinalis Cortex (M. officinalis) is a traditional herbal drug widely used in Asian countries. Depending on its multiple biological activities, M. officinalis is used to regulate gastrointestinal (GI) motility, relieve cough and asthma, prevent cardiovascular and cerebrovascular diseases, and treat depression and anxiety.

AIM OF THE REVIEW

We aimed to review the abundant form of pharmacodynamics activity and potential mechanisms of action of M. officinalis and the characteristics of the internal processes of the main components. The potential mechanisms of local and distance actions of M. officinalis based on GI tract was provided, and it was used to reveal the interconnections between traditional use, phytochemistry, and pharmacology.

MATERIALS AND METHODS

Published literatures about M. officinalis and its main components were collected from several scientific databases, including PubMed, Elsevier, ScienceDirect, Google Scholar and Web of Science etc. RESULTS: M. officinalis was shown multiple effects including effects on digestive system, respiratory system, central system, which is consistent with traditional applications, as well as some other activities such as cardiovascular system, anticancer, anti-inflammatory and antioxidant effects and so on. The mechanisms of these activities are abundant. Its chief ingredients such as magnolol and honokiol can be metabolized into active metabolites in vivo, which can increase water solubility and bioavailability and exert pharmacological activity in the whole body. In the GI tract, M. officinalis and its main ingredient can regulate GI hormones and substance metabolism, protect the intestinal barrier and affect the gut microbiota (GM). These actions are effective to improve local discomfort and some distal symptoms such as depression, asthma, or metabolic disorders.

CONCLUSIONS

Although M. officinalis has rich pharmacological effects, the GI tract makes great contributions to it. The GI tract is not only an important place for absorption and metabolism but also a key site to help M. officinalis exert local and distal efficacy. Pharmacodynamical studies on the efficacies of distal tissues based on the contributions of the GI tract hold great potential for understanding the benefits of M. officinalis and providing new ideas for the treatment of important diseases.

Preventive Effect and Mechanism of Crossostephium chinense Extract on Balloon Angioplasty-Induced Neointimal Hyperplasia

Balloon angioplasty-induced neointimal hyperplasia remains a clinical problem that must be resolved. The bioactivities of the Crossostephium chinense extract (CCE) have demonstrated potential in preventing the progression of restenosis. The present study evaluated whether CCE can suppress balloon angioplasty-induced neointima formation and elucidated its possible pharmacological mechanisms. A rat model of carotid arterial balloon angioplasty was established to evaluate the inhibitory effect of CCEs on neointimal hyperplasia. Two cell lines, A10 vascular smooth muscle cells (VSMCs) and RAW264.7 macrophages, were used to investigate the potential regulatory activities and pharmacological mechanisms of CCEs in cell proliferation and migration and in inflammation. Our in vitro results indicated that CCE3, the ethanolic extract of C. chinense, exerted the strongest growth inhibitory and antimigratory effects on VSMCs. CCE3 blocked the activation of focal adhesion kinase, platelet-derived growth factor receptor-β (PDGFRB), and its downstream molecules (AKT and mTOR) and reduced the expression of matrix metalloproteinase-2. In addition, our findings revealed that CCE3 significantly increased the expression of miRNA-132, an inhibitory regulator of inflammation and restenosis, and suppressed the expression of inflammation-related molecules (inducible nitric oxide synthase, cyclooxygenase-2, interleukin- (IL-) 1β, and IL-6). Our in vivo study results indicated that balloon injury-induced neointimal hyperplasia was inhibited by CCE3. CCE3 could reduce neointima formation in balloon-injured arteries, and this effect may be partially attributed to the CCE3-induced suppression of PDGFRB-mediated downstream pathways and inflammation-related molecules.

Imatinib improves insulin resistance and inhibits injury-induced neointimal hyperplasia in high fat diet-fed mice

Imatinib, a PDGF receptor tyrosine kinase inhibitor, has been shown to suppress intimal hyperplasia in different animal models under normal metabolic milieu, diabetic, and/or hypercholesterolemic conditions. However, the impact of imatinib treatment on injury-induced neointimal hyperplasia has not yet been investigated in the setting of insulin resistance without frank diabetes. Using a mouse model of high fat diet (HFD)-induced insulin resistance and guidewire-induced arterial injury, the present study demonstrates that intraperitoneal administration of imatinib (25 mg/kg/day) for ~3 weeks resulted in a marked attenuation of neointimal hyperplasia (intima/media ratio) by ~78% (n = 6-9 per group; P < 0.05). Imatinib treatment also led to significant improvements in key metabolic parameters. In particular, imatinib improved insulin resistance and glucose tolerance, as revealed by complete inhibition of HFD-induced increase in HOMA-IR index and AUC_IPGTT, respectively. In addition, imatinib treatment led to diminutions in HFD-induced increases in plasma total cholesterol and triglycerides by ~73% and ~59%, respectively. Furthermore, imatinib decreased HFD-induced increase in visceral fat accumulation by ~51% (as determined by epididymal white adipose tissue weight). Importantly, imatinib treatment in HFD-fed mice enhanced plasma levels of high-molecular-weight adiponectin by ~2-fold without affecting total adiponectin. However, there were no significant changes in mean arterial pressure in insulin-resistant state or after imatinib exposure, as measured by tail-cuff method. Together, the present findings suggest that targeting PDGF receptor tyrosine kinase using imatinib may provide a realistic treatment option to prevent injury-induced neointimal hyperplasia and diet-induced insulin resistance in obesity.

Oxidative stress-induced cellular senescence desensitizes cell growth and migration of vascular smooth muscle cells through down-regulation of platelet-derived growth factor receptor-beta

The relationship between aging and restenosis are unclear. The purposes of this study were to investigate the possible pathological role and mechanism of aging on formation of restenosis. Our data indicated that cell proliferation and migration of the oxidative stress-induced senescent vascular smooth muscle cells were obviously desensitized to stimulation by platelet-derived growth factor (PDGF)-BB, which may have been caused by suppression of promoter activity, transcription, translation, and activation levels of PDGF receptor (PDGFR)-β. The analyzed data obtained from the binding array of transcription factors (TFs) showed that binding levels of eighteen TFs on the PDGFR-β promoter region (-523 to -1) were significantly lower in senescent cells compared to those of non-senescent cells. Among these TFs, the bioinformatics prediction suggested that the putative binding sites of ten TFs were found in this promoter region. Of these, transcriptional levels of seven TFs were markedly reduced in senescent cells. The clinical data showed that the proportion of restenosis was relatively lower in the older group than that in the younger group. Our study results suggested that a PDGFR-β-mediated pathway was suppressed in aging cells, and our clinical data showed that age and the vascular status were slightly negatively correlated in overall participants.

LncRNA MALAT1 regulates smooth muscle cell phenotype switch via activation of autophagy

Vascular smooth muscle cells (VSMCs), switching from a differentiated to a proliferative phenotype, contribute to various vascular diseases. However, the role of long noncoding RNA metastasis-associated lung adenocarcinoma transcript 1 MALAT1 in the phenotype switching of VSMCs remains unclear. Here, we report that the knockdown of MALAT1 promotes the transformation of smooth muscle cells from a proliferative phenotype to a differentiated phenotype. MALAT1 knockdown inhibited cellular proliferation and migration, leading to significant cell cycle arrest in the G2 phase. MALAT1 was downregulated in bone morphogenetic protein-7 (BMP-7)-induced cellular differentiation, while MALAT1 was upregulated in platelet-derived growth factor-BB (PDGF-BB)-induced cellular proliferation. PDGF induced the transformation of smooth muscle cells into a proliferative phenotype accompanied by an increase in autophagy. The downregulation of MALAT1 attenuated PDGF-BB-induced proliferation and migration by inhibiting autophagy. MALAT1 could act as a competing endogenous RNA (ceRNA) to regulate autophagy-related 7 (ATG7) gene expression by sponging miR142-3p. The present study reveals a novel mechanism by which MALAT1 promotes the transformation of smooth muscle cells from contraction to synthetic phenotypes.

The effects of low-molecular-weight heparin on lung and pulmonary artery injuries in acute pulmonary embolism rat model via platelet-derived growth factor-β

Objective

To evaluate the effects of anticoagulant agent (low-molecular-weight heparin, LMWH) on the pulmonary artery intima hyperplasia of rats with acute pulmonary embolism (APE) by assaying platelet-derived growth factor-β (PDGF-β).

Methods

A total of 90 Sprague-Dawley rats were randomly assigned into the sham, APE, and LMWH groups with 30 rats in each group. The APE rat models were established by injecting autologous blood clots via external jugular veins. In each group, six mice were sacrificed at the 1st day (D1), 4th day (D4), 7th day (D7), 14th day (D14), and 28th (D28) subsequent to the induction of APE to collect the lungs. Right ventricle pressure (RVP) and mean pulmonary arterial pressure (mPAP) were measured. Western blot and RT-PCR analyses were used to assess PDGF-β expression at various time points. In addition, changes in lung pathology were evaluated using hematoxylin and eosin (H&E) staining and electron microscope.

Results

The overall success rate of establishing APE rat models was 85.7% (60/70). There was no difference in mPAP between the sham group and the APE group at the D1, D4, D7, and D14. However, at the D28, mPAP in the APE group was significantly higher than that in the sham group. There was no difference among the three groups regarding RVP. PDGF-β expression were decreased in the LMWH group at all time points compared with the sham and APE groups (P < 0.01). Furthermore, pulmonary embolism, alveolar wall necrosis and hemorrhage, and inflammation were significantly attenuated in the LMWH group compared with the sham and APE groups subsequent to the induction of APE.

Conclusion

LMWH attenuates lung and pulmonary artery injuries and improves prognosis. Decreased PDGF-β in the lungs may be the important factor in the effects observed.

Transplantation of EPCs overexpressing PDGFR-β promotes vascular repair in the early phase after vascular injury

BACKGROUND

Endothelial progenitor cells (EPCs) play important roles in the regeneration of the vascular endothelial cells (ECs). Platelet-derived growth factor receptor (PDGFR)-β is known to contribute to proliferation, migration, and angiogenesis of EPCs, this study aims to investigate effects of transplantation of EPCs overexpressing PDGFR-β on vascular regeneration.

METHODS

We transplanted genetically modified EPCs overexpressing PDGFR-β into a mouse model with carotid artery injury. After 3 days of EPCs transplantation, the enhanced green fluorescent protein (EGFP)-expressing cells were found at the injury site and the lining of the lumen by laser scanning confocal microscope (LSCM). At 4, 7, and 14 days of the carotid artery injury, reendothelialization was evaluated by Evans Blue staining. Neointima formation was evaluated at day 14 with hematoxylin and eosin (HE) staining by calculating the neointimal area, medial area, and neointimal/media (NI/M) ratio. Intimal cell apoptosis was evaluated using TUNEL assay. Then we tested whether PDGF-BB-induced VSMC migration and PDGF-BB's function in reducing VSMC apoptosis can be attenuated by EPCs overexpressing PDGFR-β in a transwell co-culture system.

RESULTS

Our results showed that EPCs overexpressing PDGFR-β accelerates reendothelialization and mitigates neointimal formation at 14 days after injury. Moreover, we found that there is great possibility that EPCs overexpressing PDGFR-β enhanc VSMC apoptosis and suppress VSMC migration by competitive consumption of PDGF-BB in the early phase after carotid artery injury in mice.

CONCLUSIONS

We report the first in vivo and in vitro evidence that transplantation of genetically modified EPC can have a combined effect of both amplifying the reendothelialization capacity of EPCs and inhibiting neointima formation so as to facilitate better inhibition of adverse remodeling after vascular injury.

Alkaloid rich fraction from Nelumbo nucifera targets VSMC proliferation and migration to suppress restenosis in balloon-injured rat carotid artery

AIMS

Restenosis- an adverse consequence following angioplasty, and atherosclerosis are characterized by abnormal vascular smooth muscle cell (VSMC) proliferation and migration leading to neo-intima formation. In the present study, we investigated the inhibitory effects of alkaloid rich fraction (ARF) from Nelumbo nucifera and isolated compound neferine on platelet-derived growth factor (PDGF-BB) induced VSMC proliferation and migration in vitro and neo-intima formation in a rat carotid artery injury model.

METHODS

PDGF-BB induced VSMC proliferation and migration was assessed using colorimetric assay and modified Boyden chamber method respectively. Gene expression of cell cycle associated molecules was determined by reverse transcription-polymerase chain reaction (RT-PCR). The signaling molecules such as PDGF-Rβ, extracellular regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK), P38, metalloproteinase (MMP)-9 and nuclear factor-kappa B (NF-κB) were determined by western blot analysis. Stress fiber formation was evaluated using immunofluorescence microscopy. The rat carotid artery balloon injury model was performed to assess the effect of ARF on neo-intima formation.

RESULTS

ARF possessed the strongest anti-oxidant activities. The anti-proliferative activity of both ARF and neferine was due to suppression of cyclin D1, cyclin E and cyclin-dependent kinase (Cdk) gene expression. Moreover, ARF and neferine inhibited PDGF-Rβ, ERK1/2, JNK and P38 activations and NF-κB translocation. Also, ARF and neferine inhibited VSMC migration by inhibiting MMP-9 activity without affecting cytoskeleton remodeling. In a rat carotid artery injury model, ARF inhibited neo-intima formation.

CONCLUSION

Our results indicate that ARF targets VSMC proliferation and migration to attenuate neo-intima formation by inhibition of PDGF-Rβ mediated signaling.

Smooth Muscle Cell-targeted RNA Aptamer Inhibits Neointimal Formation

Inhibition of vascular smooth muscle cell (VSMC) proliferation by drug eluting stents has markedly reduced intimal hyperplasia and subsequent in-stent restenosis. However, the effects of antiproliferative drugs on endothelial cells (EC) contribute to delayed re-endothelialization and late stent thrombosis. Cell-targeted therapies to inhibit VSMC remodeling while maintaining EC health are necessary to allow vascular healing while preventing restenosis. We describe an RNA aptamer (Apt 14) that functions as a smart drug by preferentially targeting VSMCs as compared to ECs and other myocytes. Furthermore, Apt 14 inhibits phosphatidylinositol 3-kinase/protein kinase-B (PI3K/Akt) and VSMC migration in response to multiple agonists by a mechanism that involves inhibition of platelet-derived growth factor receptor (PDGFR)-β phosphorylation. In a murine model of carotid injury, treatment of vessels with Apt 14 reduces neointimal formation to levels similar to those observed with paclitaxel. Importantly, we confirm that Apt 14 cross-reacts with rodent and human VSMCs, exhibits a half-life of ~300 hours in human serum, and does not elicit immune activation of human peripheral blood mononuclear cells. We describe a VSMC-targeted RNA aptamer that blocks cell migration and inhibits intimal formation. These findings provide the foundation for the translation of cell-targeted RNA therapeutics to vascular disease.

Vascular Protective Effect of an Ethanol Extract of Camellia japonica Fruit: Endothelium-Dependent Relaxation of Coronary Artery and Reduction of Smooth Muscle Cell Migration

Camellia japonica is a popular garden plant in Asia and widely used as cosmetic sources and traditional medicine. However, the possibility that C. japonica affects cardiovascular system remains unclear. The aim of the present study was to evaluate vascular effects of an extract of C. japonica. Vascular reactivity was assessed in organ baths using porcine coronary arteries and inhibition of proliferation and migration were assessed using human vascular smooth muscle cells (VSMCs). All four different parts, leaf, stem, flower, and fruits, caused concentration-dependent relaxations and C. japonica fruit (CJF) extract showed the strongest vasorelaxation and its effect was endothelium dependent. Relaxations to CJF were markedly reduced by inhibitor of endothelial nitric oxide synthase (eNOS) and inhibitor of PI3-kinase, but not affected by inhibitor of cyclooxygenase and endothelium-derived hyperpolarizing factor-mediated response. CJF induced activated a time- and concentration-dependent phosphorylation of eNOS in endothelial cells. Altogether, these studies have demonstrated that CJF is a potent endothelium-dependent vasodilator and this effect was involved in, at least in part, PI3K-eNOS-NO pathway. Moreover, CJF attenuated TNF-α induced proliferation and PDGF-BB induced migration of VSMCs. The present findings indicate that CJF could be a valuable candidate of herbal medicine for cardiovascular diseases associated with endothelial dysfunction and atherosclerosis.

Terminalia chebula Fructus Inhibits Migration and Proliferation of Vascular Smooth Muscle Cells and Production of Inflammatory Mediators in RAW 264.7

Pathogenesis of atherosclerosis and neointima formation after angioplasty involves vascular smooth muscle cells (VSMCs) migration and proliferation followed by inflammatory responses mediated by recruited macrophages in the neointima. Terminalia chebula is widely used traditional medicine in Asia for its beneficial effects against cancer, diabetes, and bacterial infection. The study was designed to determine whether Terminalia chebula fructus water extract (TFW) suppresses VSMC migration and proliferation and inflammatory mediators production in macrophage (RAW 264.7). Our results showed that TFW possessed strong antioxidative effects in 1,1-diphenyl-2-picryl hydrazyl (DPPH) scavenging and lipid peroxidation assays. In addition, TFW reduced nitric oxide (NO) production, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) expression in RAW 264.7 cells. Also, TFW inhibited platelet-derived growth factor (PDGF-BB) induced VSMC migration as determined by wound healing and Boyden chamber assays. The antimigratory effect of TFW was due to its inhibitory effect on metalloproteinase-9 (MMP-9) expression, focal adhesion kinase (FAK) activation, and Rho-family of small GTPases (Cdc42 and RhoA) expression in VSMCs. Furthermore, TFW suppressed PDGF-BB induced VSMC proliferation by downregulation of mitogen activated protein kinases (MAPKs) signaling molecules. These results suggest that TFW could be a beneficial resource in the prevention of atherosclerosis.

Expression of platelet-derived growth factor in the vascular walls of patients with lower extremity arterial occlusive disease

The aim of the present study was to quantitatively analyze the expression of platelet-derived growth factor (PDGF)-A and PDGF-B in the vascular walls of patients with lower extremity arterial occlusive disease (LEAOD). The expression levels of PDGF-A and PDGF-B in the lower extremity arteries of 19 LEAOD patients (case group) and three healthy subjects (control group) was determined using quantitative polymerase chain reaction. Intergroup comparisons revealed that the relative mRNA expression levels were higher in the case group, as compared with the control group, for PDGF-A (34.38±5.80 vs. 21.94±1.05; P<0.05) and PDGF-B (33.95±5.92 vs. 24.15±3.12; P<0.05). In addition, the expression of PDGF-A revealed a positive linear correlation with the expression of PDGF-B (P<0.05). Therefore, the expression levels of PDGF-A and PDGF-B were found to be higher in the vascular walls of LEAOD patients, while the expression of PDGF-A was found to correlate with the expression of PDGF-B. A significant increase in the expression levlels of PDGF-A and PDGF-B were observed in the vascular walls of patients with LEAOD, and the expression of PDGF-A was associated with the expression of PDGF-B.

Vascular injury and repair: a potential target for cell therapies

ABSTRACT 

Whether due to atherosclerotic disease or mechanical intervention, vascular injury is a frequently encountered pathology in cardiovascular medicine. The past decade has seen growing interest in the role of circulating endothelial progenitor cells in vessel recovery postinjury. Despite this, the definition, origin and potential role of endothelial progenitor cells in vascular regeneration remains highly controversial. While animal work has shown early promise, evidence of a therapeutic role for endothelial progenitor cells in humans remains elusive. To date, clinical trials involving direct cell administration, growth factor therapy and endothelial cell capture stents have largely been disappointing, although this may in part reflect limitations in study design. This article will outline the pathophysiological mechanisms of vascular injury with an emphasis on endothelial progenitor cell biology and the potential therapeutic role of this exciting new field.

Magnolol attenuates neointima formation by inducing cell cycle arrest via inhibition of ERK1/2 and NF-kappaB activation in vascular smooth muscle cells

BACKGROUND

Endovascular injury induces switching of contractile phenotype of vascular smooth muscle cells (VSMCs) to synthetic phenotype, thereby causing proliferation of VSMCs leading to intimal thickening. The purpose of this study was to assess the effect of magnolol on the proliferation of VSMCs in vitro and neointima formation in vivo, as well as the related cell signaling mechanisms.

METHODS

Tumor necrosis factor alpha (TNF-alpha) induced proliferation ofVSMCs was assessed using colorimetric assay. Cell cycle progression and mRNA expression of cell cycle associated molecules were determined by flow cytometry and reverse transcription polymerase chain reaction (RT-PCR) respectively. The signaling molecules such as ERK1/2,JNK, P38 and NF-kappaB were determined by Western blot analysis. In addition, rat carotid artery balloon injury model was performed to assess the effect of magnolol on neointima formation in vivo.

RESULTS

Oral administration of magnolol significantly inhibited intimal area and intimal/medial ratio (I/M). Our in vitro assays revealed magnolol dose dependently induced cell cycle arrest at G0/G1. Also, magnolol inhibited mRNA and protein expression of cyclin D1, cyclin E, CDK4 and CDK2 in vitro and in vivo. The cell cycle arrest was associated with inhibition of ERK1/2 phosphorylation and NF-kappaB translocation.

CONCLUSION

Magnolol suppressed proliferation of VSMCs in vitro and attenuated neointima formation in vivo by inducing cell cycle arrest at G0/G1 through modulation of cyclin D1, cyclin E, CDK4 and CDK2 expression.

GENERAL SIGNIFICANCE

Thus, the results suggest that magnolol could be a potential therapeutic candidate for the prevention of restenosis and atherosclerosis.

Ribozyme-mediated gene knock down strategy to dissect the consequences of PDGF stimulation in vascular smooth muscle cells

Background

Vascular Smooth Muscle Cells (VSMCs), due to their plasticity and ability to shift from a physiological contractile-quiescent phenotype to a pathological proliferating-activated status, play a central role in the onset and progression of atherosclerosis and cardiovascular diseases. PDGF-BB, among a series of cytokines and growth factors, has been identified as the critical factor in this phenotypic switch. In order to obtain new insights on the molecular effects triggered by PDGF-BB, a hammerhead ribozyme targeting the membrane receptor PDGFR-β was applied to inhibit PDGF pathway in porcine VSMCs.

Findings

Ribozymes, loaded on a cationic polymer-based vehicle, were delivered into cultured VSMCs. A significant impairment of the activation mechanisms triggered by PDGF-BB was demonstrated since cell migration decreased after treatments. In order to functionally validate the effects of PDGFR-β partial knock down we focused on the phosphorylation status of two proteins, protein disulfide isomerase-A3 (PDI-A3) and heat shock protein-60 (HSP-60), previously identified as indicative of VSMC phenotypic switch after PDGF-BB stimulation. Interestingly, while PDI-A3 phosphorylation was counteracted by the ribozyme administration indicating that PDI-A3 is a factor downstream the receptor signalling cascade, the HSP-60 phosphorylation status was greatly increased by the ribozyme administration.

Conclusion

These contradictory observations suggested that PDGF-BB might trigger different parallel pathways that could be modulated by alternative isoforms of the receptors for the growth factor. In conclusion the knock down strategy here described enables to discriminate between two tightly intermingled pathways. Moreover it opens new attractive perspectives in functional investigations where combined gene knock down and proteomic technologies would allow the identification of key factors and pathways involved in VSMC-linked pathological disorders.

Plasma BDNF and PDGF-AA levels are associated with high TCD velocity and stroke in children with sickle cell anemia

Sickle cell anemia (SCA) associated cerebrovascular disease includes vascular remodeling, abnormal cerebral blood flow (CBF) and infarction. We studied the relationships between plasma brain derived neurotropic factor (BDNF), platelet derived growth factors (PDGF-AA and -AB/BB) and high trans-cranial Doppler (TCD) velocity, an indication of CBF velocity. Baseline plasma samples from 39 children (19 SCA with abnormal/high TCD [SATCD], 13 SCA with normal TCD [SNTCD] and 7 healthy non-SCA), were assayed for BDNF, PDGF-AA and -AB/BB plus 11 other cytokines. The sensitivity, specificity and usefulness of these biomarkers for stroke prediction was investigated. All subject groups were of similar age and gender distribution. Mean BDNF was significantly higher among SATCD than SNTCD (p=0.004) as was mean PDGF-AA (p=0.001). Similarly, mean PDGF-AA was higher among SCA subjects who developed stroke than those who did not (p=0.012). Elevated BDNF and PDGF-AA were good predictors of the presence of abnormally high CBF velocity and were both associated with severity of anemia. Elevated PDGF-AA predicted risk for stroke development. Stroke incidence and high TCD velocity were associated with elevated BDNF and PDGF-AA. These findings suggest a role for BDNF and PDGF-AA in the patho-physiological mechanism of cerebrovascular disease in SCA.

Imatinib mesylate for the treatment of pulmonary arterial hypertension

INTRODUCTION

Despite recent advances, pulmonary arterial hypertension (PAH) remains a devastating disease which harbors a poor prognosis. Novel therapeutic approaches directly targeting pulmonary vascular remodeling are warranted.

AREAS COVERED

This review delineates the current limitations in the management of PAH and focuses on a novel, anti-proliferative therapeutic concept. It will help readers understand the mechanisms of receptor tyrosine kinase signaling, with a special focus on platelet-derived growth factor (PDGF) receptors and their role in the pathobiology of PAH. Furthermore, it provides a comprehensive summary regarding the rationale, efficacy and safety of the tyrosine kinase inhibitor imatinib mesylate , which potently inhibits the PDGF receptor, as an additional treatment option in PAH.

EXPERT OPINION

PDGF is a potent mitogen for pulmonary vascular smooth muscle cells and represents an important mediator of pulmonary vascular remodeling. Imatinib mesylate, a compound that inhibits the Bcr-Abl kinase and was developed for the treatment of chronic myeloid leukemia, also targets PDGF receptors. Both experimental and clinical data indicate that it reverses the vascular remodeling process even when it is fully established. Results from Phase II and III clinical trials suggest potent and prolonged efficacy in patients with severe PAH (i.e., pulmonary vascular resistance > 800 dynes*s*cm(-5)). Future studies should evaluate the long-term clinical efficacy and safety of imatinib, including patients with less impaired hemodynamics. Based on the current knowledge, this compound is likely to become an additional treatment option for patients with PAH and has the potential to at least partially correct the pathology of the disease.

Tenascin-C enhances crosstalk signaling of integrin αvβ3/PDGFR-β complex by SRC recruitment promoting PDGF-induced proliferation and migration in smooth muscle cells

Migration and proliferation of smooth muscle cells (SMCs) are key events during neointimal formation in pathological conditions of vessels. Tenascin-C (TNC) is upregulated in the developing neointima of lesions. We evaluated the effects of TNC on responses of SMCs against platelet-derived growth factor (PDGF) stimulation. TNC coated on substrate promoted PDGF-BB-induced proliferation and migration of rat SMC cell line A10 in BrdU incorporation and transwell assays, respectively. Immunoblotting showed that TNC substrate enhanced autophosphorylation of PDGFR-β after PDGF-BB stimulation. Integrin αvβ3 is known to be a receptor for TNC in SMCs. In immunofluorescence and immunoblot of integrin αv subunit, clustering of αv-positive focal adhesions and upregulated αv expression were observed in the cells on TNC substrate. Immunoprecipitation using anti-integrin αvβ3 antibody demonstrated that PDGFR-β and integrin αvβ3 were co-precipitated and that the relative amount of PDGFR-β after the stimulation was increased by TNC treatment. TNC also promoted phosphorylation of focal adhesion kinase (FAK) at tyrosine (Y) 397 and Y925. The phosphorylated FAK was localized at focal adhesions in immunofluorescence. Phosphorylated SRC at Y418 was also seen at focal adhesions. Immunoprecipitation with αv antibody showed increased SRC association with the integrin signaling complex in the cells on TNC after PDGF treatment. In the cells on TNC substrate, crosstalk signaling between integrin αvβ3 and PDGFR-β could be amplified by SRC and FAK recruited to focal adhesions, followed by enhanced proliferation and migration of A10 cells by PDGF-BB.

PDGF-induced vascular smooth muscle cell proliferation is associated with dysregulation of insulin receptor substrates

In vascular smooth muscle cells (VSMCs), platelet-derived growth factor (PDGF) plays a major role in inducing phenotypic switching from contractile to proliferative state. Importantly, VSMC phenotypic switching is also determined by the phosphorylation state/expression levels of insulin receptor substrate (IRS), an intermediary signaling component that is shared by insulin and IGF-I. To date, the roles of PDGF-induced key proliferative signaling components including Akt, p70S6kinase, and ERK1/2 on the serine phosphorylation/expression of IRS-1 and IRS-2 isoforms remain unclear in VSMCs. We hypothesize that PDGF-induced VSMC proliferation is associated with dysregulation of insulin receptor substrates. Using human aortic VSMCs, we demonstrate that prolonged PDGF treatment led to sustained increases in the phosphorylation of protein kinases such as Akt, p70S6kinase, and ERK1/2, which mediate VSMC proliferation. In addition, PDGF enhanced IRS-1/IRS-2 serine phosphorylation and downregulated IRS-2 expression in a time- and concentration-dependent manner. Notably, phosphoinositide 3-kinase (PI 3-kinase) inhibitor (PI-103) and mammalian target of rapamycin inhibitor (rapamycin), which abolished PDGF-induced Akt and p70S6kinase phosphorylation, respectively, blocked PDGF-induced IRS-1 serine phosphorylation and IRS-2 downregulation. In contrast, MEK1/ERK inhibitor (U0126) failed to block PDGF-induced IRS-1 serine phosphorylation and IRS-2 downregulation. PDGF-induced IRS-2 downregulation was prevented by lactacystin, an inhibitor of proteasomal degradation. Functionally, PDGF-mediated IRS-1/IRS-2 dysregulation resulted in the attenuation of insulin-induced IRS-1/IRS-2-associated PI 3-kinase activity. Pharmacological inhibition of PDGF receptor tyrosine kinase with imatinib prevented IRS-1/IRS-2 dysregulation and restored insulin receptor signaling. In conclusion, strategies to inhibit PDGF receptors would not only inhibit neointimal growth but may provide new therapeutic options to prevent dysregulated insulin receptor signaling in VSMCs in nondiabetic and diabetic states.

Vascular smooth-muscle-cell activation: proteomics point of view

Vascular smooth-muscle cells (VSMCs) are the main component of the artery medial layer. Thanks to their great plasticity, when stimulated by external inputs, VSMCs react by changing morphology and functions and activating new signaling pathways while switching others off. In this way, they are able to increase the cell proliferation, migration, and synthetic capacity significantly in response to vascular injury assuming a more dedifferentiated state. In different states of differentiation, VSMCs are characterized by various repertories of activated pathways and differentially expressed proteins. In this context, great interest is addressed to proteomics technology, in particular to differential proteomics. In recent years, many authors have investigated proteomics in order to identify the molecular factors putatively involved in VSMC phenotypic modulation, focusing on metabolic networks linking the differentially expressed proteins. Some of the identified proteins may be markers of pathology and become useful tools of diagnosis. These proteins could also represent appropriately validated targets and be useful either for prevention, if related to early events of atherosclerosis, or for treatment, if specific of the acute, mid, and late phases of the pathology. RNA-dependent gene silencing, obtained against the putative targets with high selective and specific molecular tools, might be able to reverse a pathological drift and be suitable candidates for innovative therapeutic approaches.

Urokinase activates macrophage PON2 gene transcription via the PI3K/ROS/MEK/SREBP-2 signalling cascade mediated by the PDGFR-beta

AIMS

We have recently shown that urokinase plasminogen activator (uPA) increases oxidative stress (OS), cholesterol biosynthesis, and paraoxonase 2 (PON2) expression in macrophages via binding to its receptor, the uPAR. Since PON2 is regulated by both OS and cholesterol content, we hypothesized that uPA elicits a cascade of signal transduction events shared by NADPH oxidase and cholesterol biosynthesis that culminates in PON2 gene expression. Here, we investigated the signalling pathway that leads to the expression of PON2 in macrophages in response to uPA.

METHODS AND RESULTS

The increase in macrophage PON2 mRNA levels in response to uPA was shown to depend on PON2 gene promoter activation and mRNA transcription. LDL abolished these effects, suggesting a possible role for a transcription factor involved in cellular cholesterogenesis. Indeed, uPA upregulated PON2 expression in a sterol regulatory binding protein-2 (SREBP-2)-dependent manner, since blocking SREBP-2 maturation by 4-(2-aminoethyl)-benzenesulfonyl fluoride abolished uPA-stimulation of PON2, whereas inhibition of SREBP-2 catabolism by N-acetyl-leucyl-norleucinal had an opposite effect. The upstream signalling mechanisms include uPA activation of extracellular signal-regulated kinases (ERK1/2), which was dependent on NADPH oxidase and phosphatidylinositol 3-kinase activation, and these latter effects were mediated by the tyrosine kinase activity of the platelet-derived growth factor receptor-beta.

CONCLUSION

These findings provide a framework linking interactions among cellular signalling pathways associated with reactive oxygen species production, macrophage cholesterol biosynthesis, and cellular PON2 expression in vascular pathophysiology.

PDGF-C and -D and their receptors PDGFR-alpha and PDGFR-beta in atherosclerotic human arteries

BACKGROUND

Platelet derived growth factors (PDGFs) are mitogens for fibroblasts and smooth muscle cells. This growth factor family contains four members PDGF-A, PDGF-B, PDGF-C and PDGF-D. Biology of recently discovered PDGF-C and PDGF-D is not well-established. Here we studied the expression of PDGF-C and PDGF-D and their receptors PDGFR-alpha and PDGFR-beta in normal and atherosclerotic human arteries.

MATERIALS AND METHODS

Human arterial samples from amputations and autopsies were classified according to the atherosclerotic stage and the expression of PDGF-C and PDGF-D proteins and their receptors was studied by immunohistochemistry. In situ hybridization and reverse transcriptase-PCR were used to study mRNA expression.

RESULTS

Both growth factors were expressed in medial smooth muscle cells (SMCs) in normal arteries and atherosclerotic lesions. However, clear differences were found in the expression profiles in endothelium: PDGF-C was strongly expressed in endothelial cells in both normal arteries and lesions whereas PDGF-D was only weakly expressed in endothelium. PDGF-C expression was very prominent in lesion macrophages. PDGF-D was expressed throughout the artery wall in lesions. PDGFR-alpha expression was strong in endothelium and in lesion macrophage-rich areas, whereas PDGFR-beta was mostly expressed in SMCs.

CONCLUSIONS

Our results suggest that PDGF-C may play an important role in endothelium in normal and atherosclerotic arteries and in macrophages in lesions. PDGF-D was expressed in all types of lesions with the same intensity and thus differs from the expression of PDGF-C.

Sp1-dependent activation of KLF4 is required for PDGF-BB-induced phenotypic modulation of smooth muscle

There is clear evidence that the phenotypic modulation of smooth muscle cells (SMCs) contributes to the pathophysiology of vascular disease. Phenotypic modulation refers to the unique ability of SMCs to alter their phenotype in response to extracellular stimuli and is hallmarked by the loss of SMC marker gene expression. The transcription factor Krüppel-like factor 4 (KLF4) is a known powerful negative regulator of SMC marker gene expression that works, in part, by decreasing the expression of the serum response factor (SRF) myocardin. KLF4 is not expressed in healthy adult SMCs but is increased in SMCs in response to vascular injury in vivo or PDGF-BB treatment in vitro. The aim of the present study was to determine the molecular mechanisms that regulate the expression of KLF4 in phenotypically modulated SMCs. The results demonstrated that the transcription factor stimulating protein-1 (Sp1) regulated the expression of KLF4 in SMCs. The KLF4 promoter contains three consensus Sp1 binding sites. Using a series of truncated KLF4 promoters, we showed that only fragments containing these Sp1 sites could be activated by PDGF-BB. In addition, overexpression of Sp1 alone was sufficient to increase the activity of the KLF4 promoter. Moreover, inhibiting Sp1 expression with small-interfering RNA attenuated the effects of PDGF-BB on KLF4 expression. Mutation of the three Sp1 sites within the KLF4 promoter abolished both baseline and PDGF-BB-induced activity. Finally, the results demonstrated enhanced Sp1 binding to the KLF4 promoter in SMCs treated with PDGF-BB in vitro and following vascular injury in vivo. Taken together, the results suggest a novel role for Sp1 in increasing the expression of KLF4 in phenotypically modulated SMCs.

Differential effects of red and white wines on inhibition of the platelet-derived growth factor receptor: impact of the mash fermentation

AIMS

Moderate wine consumption is associated with a significant reduction of cardiovascular mortality. The molecular basis of this phenomenon remains unknown. Platelet-derived growth factor (PDGF) is an important contributor to atherogenesis. We investigated the effects of selected red and white wines on PDGF receptor (PDGFR) signalling in rat and human vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

All red wines concentration dependently inhibited the ligand-induced tyrosine phosphorylation of the PDGFR, downstream signalling events such as mitogen activated protein (MAP) kinase activation (Erk 1/2) and induction of immediate early genes (Egr-1, c-fos), and PDGF-induced cellular responses, whereas all white wines had no effect. At concentrations achieved after wine consumption in humans, all red wines completely abolished PDGF-dependent VSMC proliferation and migration. Red wines also inhibited PDGFR phosphorylation in vascular tissue, and in human coronary smooth muscle cells. Quantitative analyses of all tested wines and of samples collected at various time points (Days 0-16) of the 'mash fermentation', which is only performed for red wine, revealed that flavonoids of the catechin family, which potently inhibit PDGFR signalling, are extracted from grape seeds and skins during this process and therefore accumulate specifically in red wine. The accumulation of flavonoids correlated with the inhibitory potency of red wines on PDGFR signalling. Furthermore, this procedure could be imitated by incubation of wines with shredded grape seeds, and flavonoid-enriched white wine inhibited the PDGFR as potently as red wines.

CONCLUSION

Only red wines abrogate a critical pathogenic mechanism during atherogenesis, PDGFR signalling, in VSMCs. This effect is mediated by non-alcoholic constituents, which accumulate during the mash fermentation. Our findings offer a molecular explanation for the vasoprotective effects particularly of red wine. Therefore, future epidemiological studies should consider differential protective effects of red and white wine in vivo.

C-reactive protein and vein graft disease: evidence for a direct effect on smooth muscle cell phenotype via modulation of PDGF receptor-beta

Plasma C-reactive protein (CRP) concentration is a biomarker of systemic atherosclerosis and may also be associated with vein graft disease. It remains unclear whether CRP is also an important modulator of biological events in the vessel wall. We hypothesized that CRP influences vein graft healing by stimulating smooth muscle cells (SMCs) to undergo a phenotypic switch. Distribution of CRP was examined by immunohistochemistry in prebypass human saphenous veins (HSVs, n = 21) and failing vein grafts (n = 18, 25-4,400 days postoperatively). Quiescent HSV SMCs were stimulated with human CRP (5-50 microg/ml). SMC migration was assessed in modified Boyden chambers with platelet-derived growth factor (PDGF)-BB (5-10 ng/ml) as the chemoattractant. SMC viability and proliferation were assessed by trypan blue exclusion and reduction of Alamar Blue substrate, respectively. Expression of PDGF ligand and receptor (PDGFR) genes was examined at RNA and protein levels after 24-72 h of CRP exposure. CRP staining was present in 13 of 18 diseased vein grafts, where it localized to the deep media and adventitia, but it was minimally detectable in most prebypass veins. SMCs pretreated with CRP demonstrated a dose-dependent increase in migration to PDGF-BB (P = 0.02), which was inhibited by a PDGF-neutralizing antibody. SMCs treated with CRP showed a dose-dependent increase in PDGFRbeta expression and phosphorylation after 24-48 h. Exogenous CRP had no effect on SMC viability or proliferation. These data suggest that CRP is detectable within the wall of most diseased vein grafts, where it may exert local effects. Clinically relevant levels of CRP can stimulate SMC migration by a mechanism that may involve upregulation and activation of PDGFRbeta.

Induction of vascular atrophy as a novel approach to treating restenosis. A review

Regardless of the type of arterial reconstruction, luminal narrowing (stenosis or restenosis) develops in approximately one third of the vessels. In the past, the focus of research has been on the mechanisms of stenosis (intimal hyperplasia, pathologic remodeling) and pharmacologic approaches to prevention. An alternative approach is to induce intimal atrophy after luminal narrowing has developed, thus limiting treatment to only those patients that develop a problem. This approach to treat established disease by reducing wall mass through induction of cell death and extracellular matrix removal would be particularly useful for treating stenosis in synthetic bypass grafts or stented vessels, in which intimal hyperplasia is the primary mechanism of stenosis. This approach may be applicable as well to other vascular proliferative disorders, such as pulmonary hypertension and chronic transplant arteriopathy. Proof of principle has been shown in experiments with antibodies to platelet-derived growth factor (PDGF) receptors that cause neointimal regression in baboon polytetrafluoroethylene (PTFE) grafts and with angiotensin-converting enzyme inhibitors that induce medial atrophy in hypertensive arteries. Possible molecular targets could include PDGF receptors, A20, and BMP4. Further studies are needed to determine the utility of such a therapeutic approach to vascular disease.

Cellular, molecular and immunological mechanisms in the pathophysiology of vein graft intimal hyperplasia

Coronary artery disease, leading to myocardial infarction and ischaemia, affects millions of persons and is one of the leading causes of morbidity and mortality worldwide. Invasive techniques such as coronary artery bypass grafting are used to alleviate the sequelae of arterial occlusion. Unfortunately, restenosis or occlusion of the grafted conduit occurs over a time frame of months to years with a gradual reduction in patency, especially in vein grafts. The events leading to intimal hyperplasia (IH) formation involve numerous cellular and molecular components. Various cellular elements of the vessel wall are involved as are leucocyte-endothelial interactions that trigger the coagulation cascade leading to localized thrombus formation. Subsequent phenotypic modification of the medial smooth muscle cells and their intimal migration is the basis of the lesion formation that is thought to be propagated by an immune-mediated reaction. Despite intense scrutiny, the pathophysiology of IH remains an enigma. Although several growth factors, cytokines and numerous other biomolecules have been implicated and their relationship to prohyperplasia pathways such as the phosphatidyl-inositol 3-kinase (PI3K)-Akt pathway has been established, many pieces of the puzzle are still missing. An in-depth understanding of early vein graft adaptation and progression is necessary to improve the long-term prognosis and develop more effective therapeutic measures. In this review, we have critically evaluated and summarized the literature to elucidate and interlink the numerous established and emerging factors that play a key role in the development of IH leading to vein graft restenosis.

PDGF and cardiovascular disease

Platelet-derived growth factor (PDGF) was identified in a search for serum factors that stimulate smooth muscle cell (SMC) proliferation. During the development of lesions of atherosclerosis that can ultimately lead to vessel occlusion, SMC are stimulated by inflammatory factors to migrate from their normal location in the media. They accumulate within the forming lesion where they contribute to lesion expansion by proliferation and deposition of extracellular matrix. Different genetic manipulations in vascular cells combined with various inhibitory strategies have provided strong evidence for PDGF playing a prominent role in the migration of SMC into the neointima following acute injury and in atherosclerosis. Other activities of PDGF identified in vivo suggest additional functions for PDGF in the pathogenesis of cardiovascular disease.

Adenovirus-Encoded Hammerhead Ribozyme to PDGF A-Chain mRNA Inhibits Neointima Formation after Arterial Injury

To develop a strategy for gene therapy of restenosis following coronary angioplasty, we examined the effects of a recombinant adenovirus vector encoding a hammerhead ribozyme specific for rat platelet-derived growth factor (PDGF) A-chain mRNA (Ad. Ribozyme) and a control recombinant adenovirus vector encoding the Escherichia coli LacZ gene (Ad.LacZ) on neointima formation in rat carotid artery after balloon injury. Ad. Ribozyme (10(8) PFU/ml) markedly reduced the increased expression of PDGF A-chain mRNA and protein. Ad. Ribozyme significantly decreased the intima/media ratio (68%) of the injured artery, whereas Ad.LacZ had no effect on the intima/media ratio. Most carotid arteries developed thrombi by 14 days after balloon injury, whereas Ad. Ribozyme completely inhibited thrombus formation. Expression of thromboxane A2 (TXA2) receptor mRNA was significantly increased after balloon injury. Ad. Ribozyme significantly decreased the levels of TXA2 receptor. Expression of prostaglandin I2 (PGI2) synthase mRNA was significantly decreased after balloon injury. Ad. Ribozyme significantly increased levels of PGI2 synthase mRNA after balloon injury. The observation that adenovirus-encoded ribozyme to PDGF A-chain inhibits neointima formation may serve as a novel strategy to prevent restenosis after coronary angioplasty. Inhibition of growth factors by genetic approaches may yield new insights into the mechanisms underlying responses to vascular injury and lead to new therapeutic applications.

Molecular and cellular basis of restenosis after percutaneous coronary intervention: the intertwining roles of platelets, leukocytes, and the coagulation-fibrinolysis system

The major limitation of percutaneous coronary intervention (PCI) is restenosis. Restenosis is considered to be an overreaction of the natural healing process after traumatic balloon dilatation. An elaborate web of cellular and molecular responses, including the interaction of platelets, leukocytes, and the coagulation-fibrinolysis system, as well as the secretion of various growth factors and pro-inflammatory cytokines, contributes to neointimal hyperplasia and the development of restenosis. Moreover, platelet and neutrophil activation after stenting appears to be different from that after balloon angioplasty alone. Pharmacotherapy targeting the cell-to-cell interaction between platelets and neutrophils may potentially offer an effective treatment strategy against restenosis after PCI.

Molecular regulation of vascular smooth muscle cell differentiation in development and disease

The focus of this review is to provide an overview of the current state of knowledge of molecular mechanisms/processes that control differentiation of vascular smooth muscle cells (SMC) during normal development and maturation of the vasculature, as well as how these mechanisms/processes are altered in vascular injury or disease. A major challenge in understanding differentiation of the vascular SMC is that this cell can exhibit a wide range of different phenotypes at different stages of development, and even in adult organisms the cell is not terminally differentiated. Indeed, the SMC is capable of major changes in its phenotype in response to changes in local environmental cues including growth factors/inhibitors, mechanical influences, cell-cell and cell-matrix interactions, and various inflammatory mediators. There has been much progress in recent years to identify mechanisms that control expression of the repertoire of genes that are specific or selective for the vascular SMC and required for its differentiated function. One of the most exciting recent discoveries was the identification of the serum response factor (SRF) coactivator gene myocardin that appears to be required for expression of many SMC differentiation marker genes, and for initial differentiation of SMC during development. However, it is critical to recognize that overall control of SMC differentiation/maturation, and regulation of its responses to changing environmental cues, is extremely complex and involves the cooperative interaction of many factors and signaling pathways that are just beginning to be understood. There is also relatively recent evidence that circulating stem cell populations can give rise to smooth muscle-like cells in association with vascular injury and atherosclerotic lesion development, although the exact role and properties of these cells remain to be clearly elucidated. The goal of this review is to summarize the current state of our knowledge in this area and to attempt to identify some of the key unresolved challenges and questions that require further study.

Increase of PTP levels in vascular injury and in cultured aortic smooth muscle cells treated with specific growth factors

Migration and proliferation of vascular smooth muscle cells are key events in injury-induced neointima formation. Several growth factors and ANG II are thought to be involved in neointima formation. A recent report indicated that vascular injury is associated with increased mRNA levels of protein tyrosine phosphatase (PTP)-1B (PTP-1B). In the present study, we tested the following hypotheses: 1) rat carotid artery injury induces the expression of PTP-1B, Src homology-2 domain phosphatase (SHP-2), and PTP-proline, glutamate, serine, and threonine sequence (PEST) protein; and 2) polypeptide growth factors as well as ANG II increase the levels of tyrosine phosphatases in cultured rat aortic smooth muscle cells. We found that vascular injury induced by balloon catheter increases the protein levels of aforementioned phosphatases and that these effects occur in a PTP specific, as well as temporally and regionally specific, manner. Moreover, treatment of cultured primary rat aortic smooth muscle cells with PDGF or bFGF, but not with IGF1, EGF, or ANG II, increases PTP-1B, SHP-2, and PTP-PEST protein levels. These results suggest that increased PDGF and bFGF levels, occurring after vascular injury, may induce expression of several PTPs.

Arterial injury repair in nonhuman primates-the role of PDGF receptor-beta

BACKGROUND

This study documents the time course of the response to injury of the saphenous artery in baboons and the role of the platelet-derived growth factor-beta. Fundamental differences with the well-characterized rat arterial injury model have been found.

MATERIALS AND METHODS

Thirty-eight baboons received a unilateral balloon injury to the saphenous artery and were treated with a chimeric blocking antibody to PDGFR-beta or vehicle control for 7, 14, or 28 days. The arteries were evaluated morphologically and for cell proliferation.

RESULTS

Both medial and intimal smooth muscle cell proliferation were elevated 7 days after injury and were back close to baseline at 14 days. Unlike the rat, blockade of PDGFR-beta inhibited medial proliferation over 80% at 7 and 14 days, while intimal proliferation was only inhibited at 14 days (>95%). Also, unlike the rat, the baboon arterial media, as well as the intima, increased in size by 14 days after injury. Blockade of PDGFR-beta completely inhibited both intimal and medial growth at 14 days, but there was less of an effect on intimal growth at 28 days.

CONCLUSION

Blockade of PDGFR-beta may be a clinical approach to inhibit intimal hyperplasia in humans, but this study raises concerns about the long-term efficacy of this treatment.

Stent-induced restenosis in the swine coronary artery is inhibited by a platelet-derived growth factor receptor tyrosine kinase inhibitor, TKI963

Activities of vascular smooth muscle cells (SMCs) such as proliferation, migration, and matrix production contribute to restenosis following clinical interventions of angioplasty and stent placement. Because activation of platelet-derived growth factor (PDGF)-receptor tyrosine kinase (PDGFr-TK) influences these processes and promotes restenosis, TKI963, an inhibitor of the PDGFr-TK was discovered, and its efficacy was evaluated in blocking stent-induced restenosis as analyzed by intravascular ultrasound (IVUS). TKI963, a low-molecular-weight compound, inhibited the cell-free PDGFbetar-TK with a K(i) value of 56 +/- 14 nM. TKI963 also inhibited PDGF-dependent events in human aortic SMCs (e.g., in situ PDGFr autophosphorylation, mitogenesis, chemotaxis, and collagen production with median inhibitory concentration values of approximately 300 nM) without affecting the activity of a series of membrane receptor tyrosine kinases and intracellular serine/threonine kinases. In vivo, stent-induced restenosis in the swine coronary artery was reduced by oral administration of TKI963 (1.25, 2.5, and 5 mg/kg BID, for 28 days). Late lumen cross-sectional area (CSA) loss, plaque CSA growth, and plaque volume in the stent determined by IVUS were dose-relatedly decreased (33-62% at 1.25 mg/kg BID to 66-92% at 5 mg/kg BID, depending on the parameter) compared with controls. TKI963 treatment of </=1 week following stent placement had no effect on the prevention of restenosis. TKI963, a selective, orally bioavailable inhibitor of the PDGFr-TK, dose-relatedly reduced stent-induced restenosis and did so by inhibiting PDGF-dependent activities that occur as late events following stent placement.

Inhibition of the PDGF receptor by red wine flavonoids provides a molecular explanation for the "French paradox"

The mortality rate from coronary artery disease (CAD) in France is approximately 50% compared to other European countries and the United States ("French paradox"). Epidemiological studies indicate an inverse relationship between moderate wine consumption and CAD mortality. Here, we demonstrate that preincubation of vascular smooth muscle cells (VSMCs) with red wine, but not white wine, inhibits ligand binding and the subsequent tyrosine phosphorylation of the platelet-derived growth factor beta receptor (betaPDGFR), which plays a critical role in the pathogenesis of atherosclerosis. As a consequence, red wine abrogates the ligand-induced recruitment of betaPDGFR-associated signaling molecules (RasGAP, SHP-2, PI3K, PLCgamma), PDGF-dependent downstream events such as Erk activation and induction of immediate early genes, and VSMC proliferation and migration. Wine analysis revealed flavonoids of the catechin family as major constituents of red wine, and these were identified as potent inhibitors of betaPDGFR signaling. Importantly, the concentrations of red wine/catechins shown to inhibit the PDGFR in vitro correlate with the serum levels after red wine consumption in humans. We conclude that nonalcoholic constituents of red wine, which accumulate during the "mash fermentation," inhibit betaPDGFR activation and PDGF-dependent cellular responses in VSMCs. Therefore, catechin-mediated inhibition of betaPDGFR signaling offers a molecular explanation for the "French paradox."

Tyrosine kinases regulate intracellular calcium during alpha(2)-adrenergic contraction in rat aorta

We have demonstrated enhanced contractile sensitivity to the alpha(2)-adrenoreceptor (alpha(2)-AR) agonist UK-14304 in arteries from rats made hypertensive with chronic nitric oxide synthase (NOS) inhibition (LHR) compared with arteries from normotensive rats (NR); additionally, this contraction requires Ca(2+) entry. We hypothesized that tyrosine kinases augment alpha(2)-AR contraction in LHR arteries by increasing Ca(2+). The tyrosine kinase inhibitor tyrphostin 23 significantly attenuated UK-14304 contraction of denuded thoracic aortic rings from NR and LHR. However, tyrphostin 23 did not alter UK-14304 contraction in ionomycin-permeabilized aorta, which indicates that tyrosine kinases regulate intracellular Ca(2+) concentration. The Src family inhibitor PP1 and the epidermal growth factor receptor kinase inhibitor AG-1478 did not alter alpha(2)-AR contraction, whereas the mitogen-activated protein kinase extracellular signal-regulated kinase kinase inhibitor PD-98059 attenuated the contraction. Contraction to CaCl(2) in ionomycin-permeabilized LHR rings was greater than in NR rings. UK-14304 augmented CaCl(2) contraction in ionomycin-permeabilized rings from both groups but to a greater extent in LHR aorta. Together, these data suggest that alpha(2)-AR stimulates contraction via two pathways. One, which is enhanced with NOS inhibition hypertension, activates Ca(2+) sensitivity and is independent of tyrosine kinases. The other is tyrosine kinase dependent and regulates intracellular Ca(2+) concentration.

Local arterial responses to 32P beta-emitting stents

PURPOSE

32P beta-emitting stents reduce neointimal growth in rabbit iliac arteries for at least 12 months after deployment but are associated with incomplete healing. The aim of this study was to quantitate arterial cellularity, with emphasis on the inflammatory response following radioactive stenting.

METHODS

32P beta-emitting stents were placed in rabbit iliac arteries and analyzed at 3 months (6 and 24 microCi), and 6 and 12 months (6, 24, and 48 microCi). Arterial cellular proliferation and cell densities of smooth muscle cells (SMC), mononuclear cells (macrophages and lymphocytes), and neutrophils (PMN) were determined.

RESULTS

Total intimal cell density was greatest in control stents at all three time points, composed mostly of SMCs. SMC density associated with radioactive stents increased from 3 to 12 months but was significantly less than control nonradioactive stents. There was a 4-fold increase in cellular proliferation in the 24 and 48 microCi group vs. control stents. In the media, SMC density of radioactive stent groups was significantly reduced vs. control stents at all three time points, for all three activities. At 3, 6 and 12 months, there was a dose-dependent increase in intimal inflammatory cell density, which consisted mostly of macrophages. For 6-microCi stents inflammation peaked at 3 months and decreased thereafter. Inflammation for 24-microCi stents peaked at 6 months and then decreased at 12 months. Inflammation associated with 48-microCi stents remained high at 6 and 12 months. Focal atherosclerotic change was seen in 11% of stents in the 24-microCi group, and 37% and 50% in the 48-microCi group at 6 and 12 months, respectively.

CONCLUSION

Intimal SMC density remains suppressed out to 12 months after placement of 32P beta-emitting stents. However, inflammation and cell proliferation remain increased and may potentially result in greater neointimal formation over time.

Functional blockade of platelet-derived growth factor receptor-beta but not of receptor-alpha prevents vascular smooth muscle cell accumulation in fibrous cap lesions in apolipoprotein E-deficient mice

BACKGROUND

The vascular smooth muscle cell (VSMC) is the central cell component involved in the fibroproliferative response in atherogenesis. As the lesion advances, VSMCs migrate from the media into the subendothelial space, thereby forming fibrous plaque lesions. Platelet-derived growth factor (PDGF) has been known to be a potent chemoattractant and mitogen for SMCs, but the pathophysiological role of the 2 PDGF receptors, receptor-alpha (PDGFR-alpha) and receptor-beta (PDGFR-beta) in atherogenesis is poorly understood. To clarify this problem, we prepared antagonistic rat monoclonal antibodies, APA5 and APB5, against murine PDGFR-alpha and PDGFR-beta, respectively.

METHODS AND RESULTS

Apolipoprotein E-deficient mice were fed a high-fat diet containing 0.3% cholesterol from 6 weeks of age and subjected to injection with 1 mg/d IP of either antibody from 12 to 18 weeks every other day. In the mice injected with APB5, the aortic atherosclerotic lesion size and the number of intimal VSMCs were reduced by 67% and 80%, respectively, compared with the control mice injected with irrelevant rat IgG. In contrast, the mice that received APA5 showed only minimal reduction of lesion size, and a large number of VSMCs were observed in the intima. In the intima of advanced lesions, APB5 immunolabeled VSMCs, whereas APA5 could detect VSMCs mainly in the media.

CONCLUSIONS

These results indicate that PDGFR-beta plays a significant role in formation of fibrous atherosclerotic lesions and that regulation of the signal transduction through PDGFR-beta could affect atherogenesis in mice.

Weekly dosing with the platelet-derived growth factor receptor tyrosine kinase inhibitor SU9518 significantly inhibits arterial stenosis

The platelet-derived growth factor (PDGF) ligands and their receptors have been implicated as critical regulators of the formation of arterial lesions after tissue injury. SU9518 (3[5-(5-bromo-2-oxo-1,2-dihydroindol-3-ylidenemethyl)-2,4-dimethyl-1H-pyrrol-3-yl]propionic acid) is a novel synthetic indolinone that potently and selectively inhibits the cellular PDGF receptor kinase and PDGF receptor-induced cell proliferation. Inhibition of PDGF receptor phosphorylation in cell-based assays occurs within 5 minutes after drug exposure and persists for >6 hours after drug removal. The pharmacokinetics indicate plasma levels that exceeded the effective concentration required to inhibit the PDGF receptor in cells for up to 8 hours or 7 days after a single oral or subcutaneous administration, respectively. In the rat balloon arterial injury-induced stenosis model, once-daily oral or once-weekly subcutaneous administration of SU9518 reduced intimal thickening of the carotid artery (ratio of neointimal to medial area, 1.94+/-0.38 versus 1.03+/-0.29 [P<0.01] 2.21+/-0.32 versus 1.34+/-0.45 [P<0.01], respectively). These studies provide the rationale to evaluate PDGF receptor tyrosine kinase inhibitors, including inhibitors related to the indolinone, SU9518, for the treatment of arterial restenosis.

Involvement of platelet-derived growth factor in disease: development of specific antagonists

Platelet-derived growth factor (PDGF) is a family of dimeric isoforms that stimulates, e.g., growth, chemotaxis and cell shape changes of various connective tissue cell types and certain other cells. The cellular effects of PDGF isoforms are exerted through binding to two structurally related tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation. This enables a number of SH2 domain containing signal transduction molecules to bind to the receptors, thereby initiating various signaling pathways. PDGF isoforms have important roles during the embryonic development, particularly in the formation of connective tissue in various organs. In the adult, PDGF stimulates wound healing. Overactivity of PDGF has been implicated in certain disorders, including fibrotic conditions, atherosclerosis, and malignancies. Different kinds of PDGF antagonists are currently being developed and evaluated in different animal disease models, as well as in clinical trials.