Role of endogenous platelet-derived growth factor in arterial smooth muscle cell migration after balloon catheter injury

KLF13 promotes VSMCs phenotypic dedifferentiation by directly binding to the SM22α promoter

Krüppel-like factor 13 (KLF13), a zinc finger transcription factor, is considered as a potential regulator of cardiomyocyte differentiation and proliferation during heart morphogenesis. However, its precise role in the dedifferentiation of vascular smooth muscle cells (VSMCs) during atherosclerosis and neointimal formation after injury remains poorly understood. In this study, we investigated the relationship between KLF13 and SM22α expression in normal and atherosclerotic plaques by bioanalysis, and observed a significant increase in KLF13 levels in the atherosclerotic plaques of both human patients and ApoE-/- mice. Knockdown of KLF13 was found to ameliorate intimal hyperplasia following carotid artery injury. Furthermore, we discovered that KLF13 directly binds to the SM22α promoter, leading to the phenotypic dedifferentiation of VSMCs. Remarkably, we observed a significant inhibition of platelet-derived growth factor BB-induced VSMCs dedifferentiation, proliferation, and migration when knocked down KLF13 in VSMCs. This inhibitory effect of KLF13 knockdown on VCMC function was, at least in part, mediated by the inactivation of p-AKT signaling in VSMCs. Overall, our findings shed light on a potential therapeutic target for treating atherosclerotic lesions and restenosis after vascular injury.

An integrated approach to simulating the vulnerable atherosclerotic plaque

Analyses of individual atherosclerotic plaques are mostly descriptive, relying, for example, on histological classification by spectral analysis of ultrasound waves or staining and observing particular cellular components. Such passive methods have proved useful for characterizing the structure and vulnerability of plaques but have little quantitative predictive power. Our aim is to introduce and discuss a computational framework to provide insight to clinicians and help them visualize internal plaque dynamics. We use partial differential equations (PDEs) with macrophages, necrotic cells, oxidized lipids, oxygen concentration, and platelet-derived growth factor (PDGF) as primary variables coupled to a biomechanical model to describe vessel growth. The model is deterministic, providing mechanical, morphological, and histological characteristics of an atherosclerotic vessel at any desired future time point. We use our model to create computer-generated animations of a plaque evolution that are in qualitative agreement with published serial ultrasound images and hypothesize possible atherogenic mechanisms. A systems biology model consisting of five differential equations is able to capture the morphology of necrotic cores residing within vulnerable atherosclerotic plaque. In the context of the model, the distribution of oxidized low-density lipoprotein (Ox-LDL) particles, endothelial inflammation, plaque oxygenation (via the presence of vasa vasora), and intimal oxygenation are four important factors that drive changes in core morphology.NEW & NOTEWORTHY In this article, we propose a quantitative framework to describe the evolution of atherosclerotic plaque. We use partial differential equations (PDEs) with macrophages, necrotic cells, oxidized lipids, oxygen concentration, and PDGF as primary variables coupled to a biomechanical model to describe vessel growth. A feature of our method is that it outputs color-coded vessel sections corresponding to regions of the plaque that are necrotic and fibrous, qualitatively similar to images generated by enhanced intravascular ultrasound.

Molecular and Mechanical Mechanisms Regulating Ductus Arteriosus Closure in Preterm Infants

Failure of ductus arteriosus closure after preterm birth is associated with significant morbidities. Ductal closure requires and is regulated by a complex interplay of molecular and mechanical mechanisms with underlying genetic factors. In utero patency of the ductus is maintained by low oxygen tension, high levels of prostaglandins, nitric oxide and carbon monoxide. After birth, ductal closure occurs first by functional closure, followed by anatomical remodeling. High oxygen tension and decreased prostaglandin levels mediated by numerous factors including potassium channels, endothelin-1, isoprostanes lead to the contraction of the ductus. Bradykinin and corticosteroids also induce ductal constriction by attenuating the sensitivity of the ductus to PGE2. Smooth muscle cells of the ductus can sense oxygen through a mitochondrial network by the role of Rho-kinase pathway which ends up with increased intracellular calcium levels and contraction of myosin light chains. Anatomical closure of the ductus is also complex with various mechanisms such as migration and proliferation of smooth muscle cells, extracellular matrix production, endothelial cell proliferation which mediate cushion formation with the interaction of blood cells. Regulation of vessel walls is affected by retinoic acid, TGF-β1, notch signaling, hyaluronan, fibronectin, chondroitin sulfate, elastin, and vascular endothelial cell growth factor (VEGF). Formation of the platelet plug facilitates luminal remodeling by the obstruction of the constricted ductal lumen. Vasa vasorum are more pronounced in the term ductus but are less active in the preterm ductus. More than 100 genes are effective in the prostaglandin pathway or in vascular smooth muscle development and structure may affect the patency of ductus. Hemodynamic changes after birth including fluid load and flow characteristics as well as shear forces within the ductus also stimulate closure. Current pharmacological treatment for the closure of a patent ductus is based on the blockage of the prostaglandin pathway mainly through COX or POX inhibition, albeit with some limitations and side effects. Further research for new agents aiming ductal closure should focus on a clear understanding of vascular biology of the ductus.

Angiotensin-(1-9) prevents vascular remodeling by decreasing vascular smooth muscle cell dedifferentiation through a FoxO1-dependent mechanism

The renin-angiotensin system, one of the main regulators of vascular function, controls vasoconstriction, inflammation and vascular remodeling. Antagonistic actions of the counter-regulatory renin-angiotensin system, which include vasodilation, anti-proliferative, anti-inflammatory and anti-remodeling effects, have also been described. However, little is known about the direct effects of angiotensin-(1-9), a peptide of the counter-regulatory renin-angiotensin system, on vascular smooth muscle cells. Here, we studied the anti-vascular remodeling effects of angiotensin-(1-9), with special focus on the control of vascular smooth muscle cell phenotype. Angiotensin-(1-9) decreased blood pressure and aorta media thickness in spontaneously hypertensive rats. Reduction of media thickness was associated with decreased vascular smooth muscle cell proliferation. In the A7r5 VSMC cell line and in primary cultures of rat aorta smooth muscle cells, angiotensin-(1-9) did not modify basal proliferation. However, angiotensin-(1-9) inhibited proliferation, migration and contractile protein decrease induced by platelet derived growth factor-BB. Moreover, angiotensin-(1-9) reduced Akt and FoxO1 phosphorylation at 30 min, followed by an increase of total FoxO1 protein content. Angiotensin-(1-9) effects were blocked by the AT2R antagonist PD123319, Akt-Myr overexpression and FoxO1 siRNA. These data suggest that angiotensin-(1-9) inhibits vascular smooth muscle cell dedifferentiation by an AT2R/Akt/FoxO1-dependent mechanism.

Hypermethylation of mitochondrial DNA in vascular smooth muscle cells impairs cell contractility

Vascular smooth muscle cell (SMC) from arterial stenotic-occlusive diseases is featured with deficiency in mitochondrial respiration and loss of cell contractility. However, the regulatory mechanism of mitochondrial genes and mitochondrial energy metabolism in SMC remains elusive. Here, we described that DNA methyltransferase 1 (DNMT1) translocated to the mitochondria and catalyzed D-loop methylation of mitochondrial DNA in vascular SMCs in response to platelet-derived growth factor-BB (PDGF-BB). Mitochondrial-specific expression of DNMT1 repressed mitochondrial gene expression, caused functional damage, and reduced SMC contractility. Hypermethylation of mitochondrial D-loop regions were detected in the intima-media layer of mouse carotid arteries subjected to either cessation of blood flow or mechanical endothelial injury, and also in vessel specimens from patients with carotid occlusive diseases. Likewise, the ligated mouse arteries exhibited an enhanced mitochondrial binding of DNMT1, repressed mitochondrial gene expression, defects in mitochondrial respiration, and impaired contractility. The impaired contractility of a ligated vessel could be restored by ex vivo transplantation of DNMT1-deleted mitochondria. In summary, we discovered the function of DNMT1-mediated mitochondrial D-loop methylation in the regulation of mitochondrial gene transcription. Methylation of mitochondrial D-loop in vascular SMCs contributes to impaired mitochondrial function and loss of contractile phenotype in vascular occlusive disease.

The mechanical and pharmacological regulation of glioblastoma cell migration in 3D matrices

The invasion of glioblastoma is a complex process based on the interactions of tumor cells and the extracellular matrix. Tumors that are engineered using biomaterials are more physiologically relevant than a two-dimensional (2D) cell culture system. Matrix metalloproteinases and the plasminogen activator generated by tumor cells regulate a tumor's invasive behavior. In this study, microtumors were fabricated by encapsulating U87 glioma cells in Type I collagen and then glioma cell migration in the collagen hydrogels was investigated. Crosslinking of collagen with 8S-StarPEG increased the hydrogel viscosity and reduced the tumor cell migration speed in the hydrogels. The higher migration speed corresponded to the increased gene expression of MMP-2, MMP-9, urokinase plasminogen activator (uPA), and tissue plasminogen activator (tPA) in glioma cells grown in non-crosslinked collagen hydrogels. Inhibitors of these molecules hindered U87 and A172 cell migration in collagen hydrogels. Aprotinin and tranexamic acid did not inhibit U87 and A172 migration on the culture dish. This study demonstrated the differential effect of pharmacologic molecules on tumor cell motility in either a 2D or three-dimensional culture environment.

Semaphorin-3A protects against neointimal hyperplasia after vascular injury

BACKGROUND

Neointimal hyperplasia is a prominent pathological event during in-stent restenosis. Phenotype switching of vascular smooth muscle cells (VSMCs) from a differentiated/contractile to a dedifferentiated/synthetic phenotype, accompanied by migration and proliferation of VSMCs play an important role in neointimal hyperplasia. However, the molecular mechanisms underlying phenotype switching of VSMCs have yet to be fully understood.

METHODS

The mouse carotid artery ligation model was established to evaluate Sema3A expression and its role during neointimal hyperplasia in vivo. Bioinformatics analysis, chromatin immunoprecipitation (ChIP) assays and promoter-luciferase reporter assays were used to examine regulatory mechanism of Sema3A expression. SiRNA transfection and lentivirus infection were performed to regulate Sema3A expression. EdU assays, Wound-healing scratch experiments and Transwell migration assays were used to assess VSMC proliferation and migration.

FINDINGS

In this study, we found that semaphorin-3A (Sema3A) was significantly downregulated in VSMCs during neointimal hyperplasia after vascular injury in mice and in human atherosclerotic plaques. Meanwhile, Sema3A was transcriptionally downregulated by PDGF-BB via p53 in VSMCs. Furthermore, we found that overexpression of Sema3A inhibited VSMC proliferation and migration, as well as increasing differentiated gene expression. Mechanistically, Sema3A increased the NRP1-plexin-A1 complex and decreased the NRP1-PDGFRβ complex, thus inhibiting phosphorylation of PDGFRβ. Moreover, we found that overexpression of Sema3A suppressed neointimal hyperplasia after vascular injury in vivo.

INTERPRETATION

These results suggest that local delivery of Sema3A may act as a novel therapeutic option to prevent in-stent restenosis.

Smooth muscle cell-driven vascular diseases and molecular mechanisms of VSMC plasticity

Vascular smooth muscle cells (VSMCs) are the major cell type in blood vessels. Unlike many other mature cell types in the adult body, VSMC do not terminally differentiate but retain a remarkable plasticity. Fully differentiated medial VSMCs of mature vessels maintain quiescence and express a range of genes and proteins important for contraction/dilation, which allows them to control systemic and local pressure through the regulation of vascular tone. In response to vascular injury or alterations in local environmental cues, differentiated/contractile VSMCs are capable of switching to a dedifferentiated phenotype characterized by increased proliferation, migration and extracellular matrix synthesis in concert with decreased expression of contractile markers. Imbalanced VSMC plasticity results in maladaptive phenotype alterations that ultimately lead to progression of a variety of VSMC-driven vascular diseases. The nature, extent and consequences of dysregulated VSMC phenotype alterations are diverse, reflecting the numerous environmental cues (e.g. biochemical factors, extracellular matrix components, physical) that prompt VSMC phenotype switching. In spite of decades of efforts to understand cues and processes that normally control VSMC differentiation and their disruption in VSMC-driven disease states, the crucial molecular mechanisms and signalling pathways that shape the VSMC phenotype programme have still not yet been precisely elucidated. In this article we introduce the physiological functions of vascular smooth muscle/VSMCs, outline VSMC-driven cardiovascular diseases and the concept of VSMC phenotype switching, and review molecular mechanisms that play crucial roles in the regulation of VSMC phenotypic plasticity.

Semaphorin-3E attenuates neointimal formation via suppressing VSMCs migration and proliferation

Aims

The migration and proliferation of vascular smooth muscle cells (VSMCs) are crucial events in the neointimal formation, a hallmark of atherosclerosis and restenosis. Semaphorin3E (Sema3E) has been found to be a critical regulator of cell migration and proliferation in many scenarios. However, its role on VSMCs migration and proliferation is unclear. This study aimed to investigate the effect of Sema3E on VSMCs migration, proliferation and neointimal formation, and explore possible mechanisms.

Methods and results

We found that the expression of Sema3E was progressively decreased during neointimal formation in a carotid ligation model. H&E-staining showed lentivirus-mediated overexpression of Sema3E in carotid ligation area attenuated neointimal formation. Immunofluorescence staining showed that the receptor (PlexinD1) of Sema3E was expressed in vascular walls. In cultured mouse VSMCs, Sema3E inhibited VSMCs migration and proliferation via plexinD1 receptor. The inhibitory effect was mediated, at least in part, by inactivating Rap1-AKT signalling pathways in VSMCs. Moreover, we found that PDGFBB down-regulated the expression of Sema3E in VSMCs and Sema3E notably inhibited the expression of PDGFB in endothelial cells. In addition, the number of Sema3E-positive VSMCs was diminished in plaques of atherosclerotic patients. Results from a public GEO microarray database showed a negative correlation between Sema3E and PDGFB transcriptional levels in the human plaques examined.

Conclusion

Our study demonstrates that Sema3E/plexinD1 inhibits proliferation and migration of VSMCs via inactivation of Rap1-AKT signalling pathways. The mutual inhibition between PDGF-BB and Sema3E after vascular injury plays a critical role in the process of neointimal formation.

A biochemical and mechanical model of injury-induced intimal thickening

In this paper, we investigate an axisymmetric model of intimal thickening using hyperelasticity theory. Our model describes the growth of the arterial intima due to cell proliferation which, in turn, is driven by the release of a cytokine such as platelet-derived growth factor (PDGF). With the growth rate tied to both local stress and the local concentration of PDGF, we derive a quadruple free boundary problem with different regions of the vessel wall characterized by different homeostatic stress. We compare our model predictions to rabbit and rodent models of atherosclerosis and find that in order to achieve the growth rates reported in the experiments, growth must be mainly cytokine induced rather than stress induced. Our model is also able to reproduce Glagov remodelling where, as a vessel becomes more diseased, the lumen expands before rapidly contracting.

Smooth muscle cells of human veins show an increased response to injury at valve sites

OBJECTIVE

Venous valves are essential but are prone to injury, thrombosis, and fibrosis. We compared the behavior and gene expression of smooth muscle cells (SMCs) in the valve sinus vs nonvalve sites to elucidate biologic differences associated with vein valves.

METHODS

Tissue explants of fresh human saphenous veins were prepared, and the migration of SMCs from explants of valve sinus vs nonvalve sinus areas was measured. Proliferation and death of SMCs were determined by staining for Ki67 and terminal deoxynucleotidyl transferase dUTP nick end labeling. Proliferation and migration of passaged valve vs nonvalve SMCs were determined by cell counts and using microchemotaxis chambers. Global gene expression in valve vs nonvalve intima-media was determined by RNA sequencing.

RESULTS

Valve SMCs demonstrated greater proliferation in tissue explants compared with nonvalve SMCs (19.3% ± 5.4% vs 6.8% ± 2.0% Ki67-positive nuclei at 4 days, respectively; mean ± standard error of the mean, five veins; P < .05). This was also true for migration (18.2 ± 2.7 vs 7.5 ± 3.0 migrated SMCs/explant at 6 days, respectively; 24 veins, 15 explants/vein; P < .0001). Cell death was not different (39.6% ± 16.1% vs 41.5% ± 16.0% terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells, respectively, at 4 days, five veins). Cultured valve SMCs also proliferated faster than nonvalve SMCs in response to platelet-derived growth factor subunit BB (2.9 ± 0.2-fold vs 2.1 ± 0.2-fold of control, respectively; P < .001; n = 5 pairs of cells). This was also true for migration (6.5 ± 1.2-fold vs 4.4 ± 0.8-fold of control, respectively; P < .001; n = 7 pairs of cells). Blockade of fibroblast growth factor 2 (FGF2) inhibited the increased responses of valve SMCs but had no effect on nonvalve SMCs. Exogenous FGF2 increased migration of valve but not of nonvalve SMCs. Unlike in the isolated, cultured cells, blockade of FGF2 in the tissue explants did not block migration of valve or nonvalve SMCs from the explants. Thirty-seven genes were differentially expressed by valve compared with nonvalve intimal-medial tissue (11 veins). Peptide-mediated inhibition of SEMA3A, one of the differentially expressed genes, increased the number of migrated SMCs of valve but not of nonvalve explants.

CONCLUSIONS

Valve compared with nonvalve SMCs have greater rates of migration and proliferation, which may in part explain the propensity for pathologic lesion formation in valves. Whereas FGF2 mediates these effects in cultured SMCs, the mediators of these stimulatory effects in the valve wall tissue remain unclear but may be among the differentially expressed genes discovered in this study. One of these genes, SEMA3A, mediates a valve-specific inhibitory effect on the injury response of valve SMCs.

Aspirin-triggered resolvin D1 attenuates PDGF-induced vascular smooth muscle cell migration via the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) pathway

BACKGROUND AND OBJECTIVES

Resolvin D1 (RvD1) is a specialized pro-resolving lipid mediator that has been previously shown to attenuate vascular smooth muscle cell (VSMC) migration, a key process in the development of intimal hyperplasia. We sought to investigate the role of the cAMP/PKA pathway in mediating the effects of the aspirin-triggered epimer 17R-RvD1 (AT-RvD1) on VSMC migration.

METHODS

VSMCs were harvested from human saphenous veins. VSMCs were analyzed for intracellular cAMP levels and PKA activity after exposure to AT-RvD1. Platelet-derived growth factor (PDGF)-induced migration and cytoskeletal changes in VSMCs were observed through scratch, Transwell, and cell shape assays in the presence or absence of a PKA inhibitor (Rp-8-Br-cAMP). Further investigation of the pathways involved in AT-RvD1 signaling was performed by measuring Rac1 activity, vasodilator stimulated phosphoprotein (VASP) phosphorylation and paxillin translocation. Finally, we examined the role of RvD1 receptors (GPR32 and ALX/FPR2) in AT-RvD1 induced effects on VSMC migration and PKA activity.

RESULTS

Treatment with AT-RvD1 induced a significant increase in cAMP levels and PKA activity in VSMCs at 5 minutes and 30 minutes, respectively. AT-RvD1 attenuated PDGF-induced VSMC migration and cytoskeletal rearrangements. These effects were attenuated by the PKA inhibitor Rp-8-Br-cAMP, suggesting cAMP/PKA involvement. Treatment of VSMC with AT-RvD1 inhibited PDGF-stimulated Rac1 activity, increased VASP phosphorylation, and attenuated paxillin localization to focal adhesions; these effects were negated by the addition of Rp-8-Br-cAMP. The effects of AT-RvD1 on VSMC migration and PKA activity were attenuated by blocking ALX/FPR2, suggesting an important role of this G-protein coupled receptor.

CONCLUSIONS

Our results suggest that AT-RvD1 attenuates PDGF-induced VSMC migration via ALX/FPR2 and cAMP/PKA. Interference with Rac1, VASP and paxillin function appear to mediate the downstream effects of AT-RvD1 on VSMC migration.

Potential Role of Axonal Chemorepellent Slit2 in Modulating Adventitial Inflammation in a Rat Carotid Artery Balloon Injury Model

Leukocyte infiltration of adventitial and perivascular tissues is an early event in the development of vascular remodeling after injury. We investigated whether Slit/Robo-an axonal chemorepellent system in vertebrate and invertebrate development-is activated during the inflammatory phase that follows endothelial denudation. Using the rat carotid artery model of angioplasty, we conducted a time course analysis of mRNAs encoding Slit ligands (Slit2 and Slit3) and Robo receptors (Robo1, Robo2, and Robo4), as well as proinflammatory cell adhesion molecule (CAM) genes. Adventitial inflammatory cells were counted in immunostained arterial sections. E-selectin, vascular CAM-1, and intercellular CAM-1 were upregulated 2-3 hours after injury, followed by infiltration of neutrophils and monocytes as evidenced by real-time polymerase chain reaction, in situ hybridization, and immunohistochemistry. Slit2, Slit3, and Robo genes exhibited no expression changes at 3 hours; however, they were markedly upregulated 1 day after angioplasty. Intercellular CAM-1 expression was reduced by 50%, and the number of adventitial neutrophils decreased by >75% 1 day after angioplasty. Slit2 has been shown to be a potent chemorepelent of leukocytes, endothelial cells, and smooth muscle cells. Thus, we decided to further investigate the localization of Slit2 in injured vessels. Immunohistochemical stainings revealed the presence of Slit2 within the vessel wall and in the perivascular vasa vasorum of naive and injured arteries. Double immunohistochemical analyses showed that infiltrating monocytes expressed Slit2 in the perivascular and adventitial tissues of injured arteries 1 and 3 days postangioplasty. In addition, recombinant full-length Slit2 and Slit2-N/1118, an N-terminal fragment of Slit2, inhibited stromal cell-derived factor 1-mediated migration of circulating rat peripheral blood mononuclear cells. In summary, adventitial activation of CAM genes and neutrophil infiltration preceded upregulation of Slit/Robo genes. Sli2 expression colocalized with infiltrating inflammatory cells in the adventitial layer. This temporospatial association suggests that leukocyte chemorepellent Slit2 may be involved in halting the adventitial accumulation of inflammatory cells in injured vessels.

A Comparative Study to verify the Efficacy of Preoperative Intravenous Tranexamic Acid in Control of Tonsillectomy Bleeding

Objectives

This study was conducted to assess the efficacy of the drug tranexamic acid administered preoperatively in controlling the bleeding during tonsillectomy intraoperatively.

Materials and methods

A total of 50 patients who underwent tonsillectomy were randomized into two groups. Group I (study group): Intravenous tranexamic acid was given with dose of 10 mg/kg. Group II (control group): Tranexamic acid injection was not given. Intraoperative amount of bleeding was assessed in each case.

Results

The study group had significant reduction in bleeding and the p-value was <0.05, which was statistically significant, when compared to control group. There were no side effects of the drug observed.

Conclusion

Single intravenous dose of tranexamic acid at a dose of 10 mg/kg preoperatively is effective in control of tonsillectomy bleeding.

How to cite this article

Santosh UP, Prashanth KB, Abhilash S. A Comparative Study to verify the Efficacy of Preoperative Intravenous Tranexamic Acid in Control of Tonsillectomy Bleeding. Int J Otorhinolaryngol Clin 2016;8(1):22-25.

Inhibited proliferation of human umbilical artery smooth muscle cells by xanthinol nicotinate

Vascular smooth muscle cell proliferation is a key event in the development of hypertension, instant restenosis and other cardiac disorders. Inhibition of this proliferation could lead to better prevention and treatment of these diseases. This study was designed to investigate the effects and mechanisms of different concentrations of xanthinol nicotinate (XN) on human umbilical artery smooth muscle cell (HUASMC) proliferation in vitro. HUASMCs were cultured by the tissue adherent method, passaged three times, and then identified by immunohistochemistry. HUASMCs were then treated with different concentrations of XN (0, 2.76, 27.6 or 276 µM), and a 3-(4,5-dimethylthiazol-2yl)-2, 5-diphenyltetrazolium bromide (MTT) assay was used to detect the inhibition of HUASMC proliferation. The levels of platelet-derived growth factor receptor (PDGFR) mRNA and protein (PDGFR-β) were detected on the cell membrane of these treated HUASMCs using RT-PCR and Western blot analysis, respectively. After culturing and passaging three times, 90 % of the cultured cells were identified as HUASMCs by immunohistochemistry. HUASMC proliferation was inhibited by XN in a dose-dependent manner (P < 0.05). Furthermore, XN dose-dependently decreased the PDGFR mRNA and PDGFR-β levels on the cell membranes of HUASMCs (P < 0.05). Thus, the results suggest that XN could become a potent therapeutic agent for regulating VSMC-associated vascular disease such as cardiovascular disease and restenosis after angioplasty.

Emergence of a metalloproteinase / phospholipase A2 axis of systemic inflammation

We review select aspects of the biology of matrix metalloproteinases (MMPs) with a focus on the modulation of inflammatory responses by MMP-2. MMP-2 is a zinc- and calcium-dependent endoprotease with substrates including extracellular matrix proteins, vasoactive peptides and chemokines. Humans and mice with MMP-2 deficiency exhibit a predominantly inflammatory phenotype. Recent research shows that MMP-2 deficient mice display elevated activity of a secreted phospholipase A₂ in the heart. Additionally, MMP-2 deficient mice exhibit abnormally high prostaglandin E₂ levels in various organs (i.e., the heart, brain and liver), signs of inflammation and exacerbated lipopolysaccharide-induced fever. We briefly review the biology of sPLA₂ enzymes to propose the existence of a heart-centric MMP-2/sPLA₂ axis of systemic inflammation. Moreover, we postulate that PLA₂ activation is induced by chemokines, whose ability to signal inflammation is regulated in a tissue-specific fashion by MMPs. Thus, genetic and pharmacologically induced MMP-deficiencies can be expected to perturb PLA₂-mediated inflammatory mechanisms.

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.

Antioxidant activity of caffeoyl-prolyl-histidine amide and its effects on PDGF-induced proliferation of vascular smooth muscle cells

Caffeic acid (CA) is one of the antioxidants found in plants, which protects vascular cells against vascular injuries from oxidative stress. In our previous study, caffeoyl-prolyl-histidine amide (CA-L-Pro-L-His-NH2; CA-PH; a CA derivative) was synthesized, which exhibited a strong antioxidant activity with sufficient stability. In this study, we investigated the role of CA-PH in vascular smooth muscle cells (VSMCs) and confirmed the enhanced antioxidant activity of CA-PH compared with that of CA. In in vitro tube assays, CA-PH showed a higher free-radical-scavenging activity and lipid-peroxidation-inhibition activity than those of CA. In VSMCs, CA-PH significantly reduced hydrogen peroxide-induced ROS generation and increased the expression of heme oxygenase-1. Moreover, CA-PH effectively inhibited the platelet-derived growth factor-induced cellular proliferation of VSMCs, which was confirmed by a decrease in the expression of the proliferating cell nuclear antigen and the phosphorylation of Akt.

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.

Implications of autophagy for vascular smooth muscle cell function and plasticity

Vascular smooth muscle cells (VSMCs) are fundamental in regulating blood pressure and distributing oxygen and nutrients to peripheral tissues. They also possess remarkable plasticity, with the capacity to switch to synthetic, macrophage-like, or osteochondrogenic phenotypes when cued by external stimuli. In arterial diseases such as atherosclerosis and restenosis, this plasticity seems to be critical and, depending on the disease context, can be deleterious or beneficial. Therefore, understanding the mechanisms regulating VSMC phenotype and survival is essential for developing new therapies for vascular disease as well as understanding how secondary complications due to surgical interventions develop. In this regard, the cellular process of autophagy is increasingly being recognized as a major player in vascular biology and a critical determinant of VSMC phenotype and survival. Although autophagy was identified in lesional VSMCs in the 1960s, our understanding of the implications of autophagy in arterial diseases and the stimuli promoting its activation in VSMCs is only now being elucidated. In this review, we highlight the evidence for autophagy occurring in VSMCs in vivo, elaborate on the stimuli and processes regulating autophagy, and discuss the current understanding of the role of autophagy in vascular disease.

Mitochondrial fission induced by platelet-derived growth factor regulates vascular smooth muscle cell bioenergetics and cell proliferation

Vascular smooth muscle cells (VSMCs) develop a highly proliferative and synthetic phenotype in arterial diseases. Because such phenotypic changes are likely integrated with the energetic state of the cell, we hypothesized that changes in cellular metabolism regulate VSMC plasticity. VSMCs were exposed to platelet-derived growth factor-BB (PDGF) and changes in mitochondrial morphology, proliferation, contractile protein expression, and mitochondrial metabolism were examined. Exposure of VSMCs to PDGF resulted in mitochondrial fragmentation and a 50% decrease in the abundance of mitofusin 2. Synthetic VSMCs demonstrated a 20% decrease in glucose oxidation, which was accompanied by an increase in fatty acid oxidation. Results of mitochondrial function assays in permeabilized cells showed few changes due to PDGF treatment in mitochondrial respiratory chain capacity and coupling. Treatment of VSMCs with Mdivi-1—an inhibitor of mitochondrial fission—inhibited PDGF-induced mitochondrial fragmentation by 50% and abolished increases in cell proliferation; however, it failed to prevent PDGF-mediated activation of autophagy and removal of contractile proteins. In addition, treatment with Mdivi-1 reversed changes in fatty acid and glucose oxidation associated with the synthetic phenotype. These results suggest that changes in mitochondrial morphology and bioenergetics underlie the hyperproliferative features of the synthetic VSMC phenotype, but do not affect the degradation of contractile proteins. Mitochondrial fragmentation occurring during the transition to the synthetic phenotype could be a therapeutic target for hyperproliferative vascular disorders.

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PDGF promotes mitochondrial fragmentation in vascular smooth muscle cells.

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PDGF increases metabolic reliance on fatty acids.

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Mitochondrial fragmentation regulates proliferation and bioenergetics.

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PDGF-induced bioenergetic and autophagic responses regulate de-differentiation.

Smooth muscle cell hypertrophy, proliferation, migration and apoptosis in pulmonary hypertension

Pulmonary hypertension is a multifactorial disease characterized by sustained elevation of pulmonary vascular resistance (PVR) and pulmonary arterial pressure (PAP). Central to the pathobiology of this disease is the process of vascular remodelling. This process involves structural and functional changes to the normal architecture of the walls of pulmonary arteries (PAs) that lead to increased muscularization of the muscular PAs, muscularization of the peripheral, previously nonmuscular, arteries of the respiratory acinus, formation of neointima, and formation of plexiform lesions. Underlying or contributing to the development of these lesions is hypertrophy, proliferation, migration, and resistance to apoptosis of medial cells and this article is concerned with the cellular and molecular mechanisms of these processes. In the first part of the article we focus on the concept of smooth muscle cell phenotype and the difficulties surrounding the identification and characterization of the cell/cells involved in the remodelling of the vessel media and we review the general mechanisms of cell hypertrophy, proliferation, migration and apoptosis. Then, in the larger part of the article, we review the factors identified thus far to be involved in PH intiation and/or progression and review and discuss their effects on pulmonary artery smooth muscle cells (PASMCs) the predominant cells in the tunica media of PAs.

Identification of a Klf4-dependent upstream repressor region mediating transcriptional regulation of the myocardin gene in human smooth muscle cells

Phenotypic switching of smooth muscle cells (SMCs) plays a central role in the development of vascular diseases such as atherosclerosis and restenosis. However, the factors regulating expression of the human myocardin (Myocd) gene, the master gene regulator of SMC differentiation, have yet to be identified. In this study, we sought to identify the critical factors regulating Myocd expression in human SMCs. Using deletion/genetic reporter analyses, an upstream repressor region (URR) was localised within the Myocd promoter, herein termed PrmM. Bioinformatic analysis revealed three evolutionary conserved Klf4 sites within the URR and disruption of those elements led to substantial increases in PrmM-directed gene expression. Furthermore, ectopic expression established that Klf4 significantly decreased Myocd mRNA levels and PrmM-directed gene expression while electrophoretic mobility shift assays and chromatin immunoprecipitation (ChIP) assays confirmed specific binding of endogenous Klf4, and not Klf5 or Klf2, to the URR of PrmM. Platelet-derived growth factor BB (PDGF-BB), a potent inhibitor of SMC differentiation, reduced Myocd mRNA levels and PrmM-directed gene expression in SMCs. A PDGF-BB-responsive region (PRR) was also identified within PrmM, overlapping with the previously identified URR, where either siRNA knockdown of Klf4 or the combined disruption of the Klf4 elements completely abolished PDGF-BB-mediated repression of PrmM-directed gene expression in SMCs. Moreover, ChIP analysis established that PDGF-BB-induced repression of Myocd gene expression is most likely regulated by enhanced binding of Klf4 and Klf5 to a lesser extent, to the PRR of PrmM. Taken together, these data provide critical insights into the transcriptional regulation of the Myocd gene in vascular SMCs, including during SMC differentiation.

PDGF-mediated autophagy regulates vascular smooth muscle cell phenotype and resistance to oxidative stress

Vascular injury and chronic arterial diseases result in exposure of VSMCs (vascular smooth muscle cells) to increased concentrations of growth factors. The mechanisms by which growth factors trigger VSMC phenotype transitions remain unclear. Because cellular reprogramming initiated by growth factors requires not only the induction of genes involved in cell proliferation, but also the removal of contractile proteins, we hypothesized that autophagy is an essential modulator of VSMC phenotype. Treatment of VSMCs with PDGF (platelet-derived growth factor)-BB resulted in decreased expression of the contractile phenotype markers calponin and α-smooth muscle actin and up-regulation of the synthetic phenotype markers osteopontin and vimentin. Autophagy, as assessed by LC3 (microtubule-associated protein light chain 3 α; also known as MAP1LC3A)-II abundance, LC3 puncta formation and electron microscopy, was activated by PDGF exposure. Inhibition of autophagy with 3-methyladenine, spautin-1 or bafilomycin stabilized the contractile phenotype. In particular, spautin-1 stabilized α-smooth muscle cell actin and calponin in PDGF-treated cells and prevented actin filament disorganization, diminished production of extracellular matrix, and abrogated VSMC hyperproliferation and migration. Treatment of cells with PDGF prevented protein damage and cell death caused by exposure to the lipid peroxidation product 4-hydroxynonenal. The results of the present study demonstrate a distinct form of autophagy induced by PDGF that is essential for attaining the synthetic phenotype and for survival under the conditions of high oxidative stress found to occur in vascular lesions.

Animal models of restenosis

Percutaneous transluminal coronary angioplasty is a widely used technique for recanalizing arteries that are occluded by atherosclerotic plaque, but its usefulness is limited by the occurrence ofrestenosis in a high proportion of patients. The development of new therapies for this currently intractable problem will be facilitated by the use of animal models of restenosis that are predictive of drug efficacy in humans. Two approaches for improving predictivity can be identified. In the first of these, the goal is to maximize the anatomical and procedural resemblance of the model to humans. The second approach seeks to maximize the pathophysiological and molecular biological resemblance of the model to humans. Tangible progress is being made toward the first goal, but lack of understanding of the basic biology of human restenosis is hampering progress toward the second.

Mathematical model of intimal thickening in atherosclerosis: vessel stenosis as a free boundary problem

Atherosclerosis is an inflammatory disease of the artery characterized by an expansion of the intimal region. Intimal thickening is usually attributed to the migration of smooth muscle cells (SMCs) from the surrounding media and proliferation of SMCs already present in the intima. Intimal expansion can give rise to dangerous events such as stenosis (leading to stroke) or plaque rupture (leading to myocardial infarction). In this paper we propose and study a mathematical model of intimal thickening, posed as a free boundary problem. Intimal thickening is driven by damage to the endothelium, resulting in the release of cytokines and migration of SMCs. By coupling a boundary value problem for cytokine concentration to an evolution law for the intimal area, we reduce the problem to a single nonlinear differential equation for the luminal radius. We analyze the steady states, perform a bifurcation analysis and compare model solutions to data from rabbits whose iliac arteries are subject to a balloon pullback injury. In order to obtain a favorable fit, we find that migrating SMCs must enter the intima very slowly compared to cells in dermal wounds. This cell behavior is indicative of a weak inflammatory response which is consistent with atherosclerosis being a chronic inflammatory disease.

Uridine adenosine tetraphosphate (Up4A) is a strong inductor of smooth muscle cell migration via activation of the P2Y2 receptor and cross-communication to the PDGF receptor

The recently discovered dinucleotide uridine adenosine tetraphosphate (Up(4)A) was found in human plasma and characterized as endothelium-derived vasoconstrictive factor (EDCF). A further study revealed a positive correlation between Up(4)A and vascular smooth muscle cell (VSMC) proliferation. Due to the dominant role of migration in the formation of atherosclerotic lesions our aim was to investigate the migration stimulating potential of Up(4)A. Indeed, we found a strong chemoattractant effect of Up(4)A on VSMC by using a modified Boyden chamber. This migration dramatically depends on osteopontin secretion (OPN) revealed by the reduction of the migration signal down to 23% during simultaneous incubation with an OPN-blocking antibody. Due to inhibitory patterns using specific and unspecific purinoreceptor inhibitors, Up(4)A mediates it's migratory signal mainly via the P2Y(2). The signaling behind the receptor was investigated with luminex technique and revealed an activation of the extracellular signal-regulated kinases 1 and 2 (ERK1/2) pathway. By use of the specific PDGF receptor (PDGFR) inhibitor AG1296 and siRNA technique against PDGFR-β we found a strongly reduced migration signal after Up(4)A stimulation in the PDGFR-β knockdown cells compared to control cells. In this study, we present substantiate data that Up(4)A exhibits migration stimulating potential probably involving the signaling cascade of MEK1 and ERK1/2 as well as the matrix protein OPN. We further suggest that the initiation of the migration process occurs predominant through direct activation of the P2Y(2) by Up(4)A and via transactivation of the PDGFR.

Anatomic closure of the premature patent ductus arteriosus: The role of CD14+/CD163+ mononuclear cells and VEGF in neointimal mound formation

Permanent closure of the newborn ductus arteriosus requires the development of neointimal mounds to completely occlude its lumen. VEGF is required for neointimal mound formation. The size of the neointimal mounds (composed of proliferating endothelial and migrating smooth muscle cells) is directly related to the number of VLA4 mononuclear cells that adhere to the ductus lumen after birth. We hypothesized that VEGF plays a crucial role in attracting CD14/CD163 mononuclear cells (expressing VLA4) to the ductus lumen and that CD14/CD163 cell adhesion to the ductus lumen is important for neointimal growth. We used neutralizing antibodies against VEGF and VLA-4 to determine their respective roles in remodeling the ductus of premature newborn baboons. Anti-VEGF treatment blocked CD14/CD163 cell adhesion to the ductus lumen and prevented neointimal growth. Anti-VLA-4 treatment blocked CD14/CD163 cell adhesion to the ductus lumen, decreased the expression of PDGF-B (which promotes smooth muscle migration), and blocked smooth muscle influx into the neointimal subendothelial space (despite the presence of increased VEGF in the ductus wall). We conclude that VEGF is necessary for CD14/CD163 cell adhesion to the ductus lumen and that CD14/CD163 cell adhesion is essential for VEGF-induced expansion of the neointimal subendothelial zone.

Disruption of platelet-derived growth factor-dependent phosphatidylinositol 3-kinase and phospholipase Cγ 1 activity abolishes vascular smooth muscle cell proliferation and migration and attenuates neointima formation in vivo

OBJECTIVES

We tested the hypothesis whether selective blunting of platelet-derived growth factor (PDGF)-dependent vascular smooth muscle cell (VSMC) proliferation and migration is sufficient to prevent neointima formation after vascular injury.

BACKGROUND

To prevent neointima formation and stent thrombosis after coronary interventions, it is essential to inhibit VSMC proliferation and migration without harming endothelial cell function. The role of PDGF-a potent mitogen and chemoattractant for VSMC that does not affect endothelial cells-for neointima formation remains controversial.

METHODS

To decipher the signaling pathways that control PDGF beta receptor (βPDGFR)-driven VSMC proliferation and migration, we characterized 2 panels of chimeric CSF1R/βPDGFR mutants in which the binding sites for βPDGFR-associated signaling molecules (Src, phosphatidylinositol 3-kinase [PI3K], GTPase activating protein of ras, SHP-2, phospholipase Cγ 1 [PLCγ]) were individually mutated. Based on in vitro results, the importance of PDGF-initiated signals for neointima formation was investigated in genetically modified mice.

RESULTS

Our results indicate that the chemotactic response to PDGF requires the activation of Src, PI3K, and PLCγ, whereas PDGF-dependent cell cycle progression is exclusively mediated by PI3K and PLCγ. These 2 signaling molecules contribute to signal relay of the βPDGFR by differentially regulating cyclin D1 and p27(kip1). Blunting of βPDGFR-induced PI3K and PLCγ signaling by a combination mutant (F3) completely abolished the mitogenic and chemotactic response to PDGF. Disruption of PDGF-dependent PI3K and PLCγ signaling in mice expressing the F3 receptor led to a profound reduction of neointima formation after balloon injury.

CONCLUSIONS

Signaling by the activated βPDGFR, particularly through PI3K and PLCγ, is crucial for neointima formation after vascular injury. Disruption of these specific signaling pathways is sufficient to attenuate pathogenic processes such as vascular remodeling in vivo.

Characterization of Pdgfrb-Cre transgenic mice reveals reduction of ROSA26 reporter activity in remodeling arteries

With the intention to modulate gene expression in vascular mural cells of remodeling vessels, we generated and characterized transgenic mouse lines with Cre recombinase under the control of the platelet-derived growth factor receptor-β promoter, referred to as Tg(Pdgfrb-Cre)(35Vli) . Transgenic mice were crossed with the Gt(ROSA)26Sor(tm1Sor) strain and examined for Cre activation by β-galactosidase activity, which was compared with endogenous Pdgfrb expression. In addition, Pdgfrb-Cre mice were used to drive expression of a conditional myc-tagged Cthrc1 transgene. There was good overlap of β-galactosidase activity with endogenous Pdgfrb immunoreactivity. However, dedifferentiation of vascular mural cells induced by carotid artery ligation revealed a dramatic discrepancy between ROSA26 reporter activity and Pdgfrb promoter driven Cre dependent myc-tagged Cthrc1 transgene expression. Our studies demonstrate the capability of the Pdgfrb-Cre mouse to drive conditional transgene expression as a result of prior Cre-mediated recombination in tissues known to express endogenous Pdgfrb. In addition, the study shows that ROSA26 promoter driven reporter mice are not suitable for lineage marking of smooth muscle in remodeling blood vessels.

Syndecan-4 Deficiency Limits Neointimal Formation After Vascular Injury by Regulating Vascular Smooth Muscle Cell Proliferation and Vascular Progenitor Cell Mobilization

Objective—

Syndecan-4 (Syn4) is a heparan sulfate proteoglycan and works as a coreceptor for various growth factors. We examined whether Syn4 could be involved in the development of neointimal formation in vivo.

Methods and Results—

Wild-type (WT) and Syn4-deficient (Syn4 −/− ) mice were subjected to wire-induced femoral artery injury. Syn4 mRNA was upregulated after vascular injury in WT mice. Neointimal formation was attenuated in Syn4 −/− mice, concomitantly with the reduction of Ki67-positive vascular smooth muscle cells (VSMCs). Basic-fibroblast growth factor– or platelet-derived growth factor-BB–induced proliferation, extracellular signal-regulated kinase activation, and expression of cyclin D1 and Bcl-2 were impaired in VSMCs from Syn4 −/− mice. To examine the role of Syn4 in bone marrow (BM)–derived vascular progenitor cells (VPCs) and vascular walls, we generated chimeric mice by replacing the BM cells of WT and Syn4 −/− mice with those of WT or Syn4 −/− mice. Syn4 expressed by both vascular walls and VPCs contributed to the neointimal formation after vascular injury. Although the numbers of VPCs were compatible between WT and Syn4 −/− mice, mobilization of VPCs from BM after vascular injury was defective in Syn4 −/− mice.

Conclusion—

Syn4 deficiency limits neointimal formation after vascular injury by regulating VSMC proliferation and VPC mobilization. Therefore, Syn4 may be a novel therapeutic target for preventing arterial restenosis after angioplasty.

Redox control of vascular smooth muscle migration

Vascular smooth muscle cell migration is important during vascular development and contributes to lesion formation in the adult vasculature. The mechanisms regulating migration of this cell type are therefore of great interest. Recent work has shown that reactive oxygen species (ROS) derived from NADPH oxidases are important mediators of promigratory signaling pathways. ROS regulate the intracellular signals responsible for lamellipodia formation, actin cytoskeleton remodeling, focal adhesion turnover, and contraction of the cell body. In addition, they contribute to matrix remodeling, a critical step to initiate and support vascular smooth muscle cell motility. Despite these recent advances in our understanding of the redox mechanisms that contribute to migration, additional work is needed to evaluate fully the potential of ROS-sensitive molecular signals as therapeutic targets to prevent inappropriate smooth muscle cell migration.

Stent-based release of a selective PDGF-receptor blocker from the bis-indolylmethanon class inhibits restenosis in the rabbit animal model

Long-term success of modern therapies for myocardial ischemia is limited by restenosis, with proliferation and migration of vascular smooth muscle cells (VSMC) as key events. Since findings in recent years indicate, that the Platelet Derived Growth Factor (PDGF) is an important selective factor in mitogenic and motogenic pathways of VSMC, different concepts for reducing restenosis by inhibiting PDGF signaling have been investigated, with local delivery of small receptor kinase inhibitors looking most promising. We tested the stent-based delivery of the PDGF-receptor inhibitor D-65495, a bis(1H-2-indolyl)methanone, in the rabbit iliac artery model of restenosis. New Zealand white rabbits underwent balloon dilation of iliac arteries for implantation of D-65495-coated or non-coated (solvent, either DMSO or 90%THF / 10% DMSO) coronary stents. After 4 weeks stents were removed and neointima formation in medial and proximal/ distal stent sections was histomorphometrically and immunohistochemically analyzed. Arteries with D-65495 eluting stents showed an up to 50% reduced restenosis compared to control stents. Also, the neointimal area was reduced, but there were no significant differences in injury score. Importantly, endothelialization was similar for control stents as well as for D-65495-coated stents, suggesting absence of a general cytostatic effect of the inhibitor. The impact of D-65495 on PDGF-receptor signaling in the vessel wall was indirectly assessed by immunohistochemical staining for activated protein kinase Akt, and PCNA as a proliferation marker and revealed some reduction for the inhibitor-treated vessels. In conclusion, the application of D-65495 caused a significant decrease in neointima formation, further supporting the concept of using locally released PDGF-receptor kinase inhibitors as anti-restenotic agents.

Endothelial and smooth muscle-derived neuropilin-like protein regulates platelet-derived growth factor signaling in human vascular smooth muscle cells by modulating receptor ubiquitination

Endothelial and smooth muscle cell-derived neuropilin-like protein (ESDN) is up-regulated in the neointima of remodeling arteries and modulates vascular smooth muscle cell (VSMC) growth. Platelet-derived growth factor (PDGF) is the prototypic growth factor for VSMCs and plays a key role in vascular remodeling. Here, we sought to further define ESDN function in primary human VSMCs. ESDN down-regulation by RNA interference significantly enhanced PDGF-induced VSMC DNA synthesis and migration. This was associated with increased ERK1/2, Src, and PDGF receptor (PDGFR)beta phosphorylation, without altering total PDGFRbeta expression levels. In binding assays, ESDN down-regulation significantly increased (125)I-PDGF maximum binding (B(max)) to PDGF receptors on VSMCs without altering the binding constant (K(d)), raising the possibility that ESDN regulates PDGFR processing. ESDN down-regulation significantly reduced ligand-induced PDGFRbeta ubiquitination. This was associated with a significant reduction in the expression level of c-Cbl, an E3 ubiquitin ligase that ubiquitinylates PDGFRbeta. Thus, ESDN modulates PDGF signaling in VSMCs via regulation of PDGFR surface levels. The ESDN effect is mediated, at least in part, through effects on PDGFRbeta ubiquitination. ESDN may serve as a target for regulating PDGFRbeta signaling in VSMCs.

Syndecan-1: an inhibitor of arterial smooth muscle cell growth and intimal hyperplasia

OBJECTIVE

Arterial injury induces smooth muscle cell (SMC) proliferation, migration, and intimal accumulation of cells and extracellular matrix. These processes are regulated by the administration of the glycosaminoglycans heparin and heparan sulfate, but little is known about the role of endogenous heparan sulfate proteoglycans in the vessel wall. We investigated the response to carotid injury of syndecan-1-null mice to assess the function of one of a conserved family of transmembrane heparan and chondroitin sulfate proteoglycans.

METHODS AND RESULTS

Syndecan-1-null mice developed a large neointimal lesion after injury, whereas wild-type mice made little or none. This was accompanied by a significant increase in both medial and intimal SMC replication. Cultured syndecan-1-null SMCs showed a significant increase in proliferation in response to PDGF-BB, thrombin, FGF2, EGF, and serum. In response to thrombin, PDGF-BB, and serum syndecan-1-null SMCs expressed more PDGF-B chain message than did wild-type SMCs. Downregulation of PDGF-BB or PDGFRbeta inhibited thrombin-, PDGF-BB-, and serum-induced DNA synthesis in syndecan-1-null SMCs.

CONCLUSIONS

These results suggest the possibility that syndecan-1 may limit intimal thickening in injured arteries by suppressing SMC activation through inhibition of SMC PDGF-B chain expression and PDGFRbeta activation.

Aortic adventitial angiogenesis and lymphangiogenesis promote intimal inflammation and hyperplasia

INTRODUCTION

Adventitial inflammation is known to influence neointimal formation and vascular remodeling. The present study was aimed to clarify the relationship between neointima hyperplasia and adventitial angiogenesis and lymphangiogenesis after balloon-induced aortic endothelial injury.

METHODS

Seventy male Wistar rats were randomly divided into six interventional groups and one control group. The intimal area/medial area ratio (I/M ratio), the adventitial macrophage index, and the number of adventitial microvessels (Ad-MV) and lymphatic vessels (Ad-LV) in the aorta were measured, and the mRNA expressions of VEGF-A, VEGFR-1, VEGF-C, VEGFR-3, PDGF-B, and PDGFR-beta in the aortic wall were quantified by real-time RT-PCR.

RESULTS

Compared with the control group, the I/M ratio, macrophage index, Ad-MV, Ad-LV, and the mRNA expressions of VEGF-A, VEGFR-1, VEGF-C, VEGFR-3, PDGF-B, and PDGFR-beta in interventional groups increased significantly after balloon-induced injury. I/M ratio showed significant correlations with Ad-MV and Ad-LV after balloon intervention. Multiple linear regression analysis indicated that Ad-MV and Ad-LV were independent factors of intimal hyperplasia.

CONCLUSION

Adventitial angiogenesis and lymphangiogenesis are induced by intimal inflammation after balloon injury, and these neogenetic vessels in turn promote intimal inflammation and hyperplasia probably via delivery and activation of inflammatory cells.

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.

Suppression of activation of signal transducer and activator of transcription-5B signaling in the vessel wall reduces balloon injury-induced neointima formation

Previously, we have demonstrated that STAT-5B plays a role in thrombin-induced vascular smooth muscle cell (VSMC) growth and motility. To learn more about the role of STAT-5B in vessel wall remodeling, we examined its involvement in platelet-derived growth factor-BB (PDGF-BB)-stimulated VSMC growth and motility and balloon injury-induced neointima formation. PDGF-BB activated STAT-5B as measured by its tyrosine phosphorylation, DNA binding, and reporter gene activity. PDGF-BB induced cyclin D1 expression, CDK4 activity, and Rb protein phosphorylation, leading to VSMC growth and motility, and these responses were suppressed by the blockade of STAT-5B. Increased cyclin D1 levels, CDK4 activity, and Rb protein phosphorylation were observed in 1-week balloon-injured arteries compared with uninjured arteries, and these responses were also suppressed by adenovirus-mediated expression of dnSTAT-5B. In addition, adenovirus-mediated expression of dnSTAT-5B attenuated balloon injury-induced smooth muscle cell migration from media to intima and their proliferation in intima, resulting in reduced neointima formation. These observations indicate that STAT-5B plays an important role in PDGF-BB-induced VSMC growth and motility in vitro and balloon injury-induced neointima formation in vivo.

Systemic application of anti-ICAM-1 monoclonal antibodies to prevent restenosis in rabbits: an anti-inflammatory strategy

OBJECTIVES

After vascular intervention, cell adhesion molecules such as ICAM-1 and VCAM are fundamental in inflammatory processes. In particular, ICAM-1 expression is strongly associated with macrophage-rich areas in restenotic lesions. Therefore, we hypothesized an anti-restenotic effect by systemic application of anti-ICAM-1 monoclonal antibodies (mAb).

METHODS

Thirty two rabbits underwent balloon angioplasty and stent implantation either in the right or left iliac artery, Animals received either anti-ICAM mAb or saline solution as a control. Animals were sacrificed 7 (n=8) and 14 (n=8) days and tissue was analyzed for basic fibroblast growth factor (bFGF) and transforming growth factor beta (TGF-beta) expression. Sixteen animals were sacrificed 6 months following treatment and tissue was harvested for histomorphometric analysis.

RESULTS

After balloon injury, bFGF significantly increased from 7 to 14 days only in the control group and was significantly higher compared to the anti-ICAM group. At 14 days after stent implantation, controls showed a significant increase of both bFGF and TGF-beta, whereas the anti-ICAM group only showed a significant increase of TGF-beta. Histomorphometric analysis for neointimal growth did not show any differences between control and anti-ICAM groups either after balloon injury or after stent implantation at 6 months.

CONCLUSION

Administration of anti-ICAM-1 mAb following either balloon angioplasty or stent implantation results in a suppression of bFGF in the early phase of restenosis, whereas TGF-beta significantly increases from 7 to 14 days after stent implantation independent of anti-ICAM-1 mAb application. Therefore we conclude that anti-inflammatory strategies are able to interfere with growth factor expression after vascular injury.

Multiple repressor pathways contribute to phenotypic switching of vascular smooth muscle cells

Smooth muscle cell (SMC) differentiation is an essential component of vascular development and these cells perform biosynthetic, proliferative, and contractile roles in the vessel wall. SMCs are not terminally differentiated and possess the ability to modulate their phenotype in response to changing local environmental cues. The focus of this review is to provide an overview of the current state of knowledge of molecular mechanisms involved in controlling phenotypic switching of SMC with particular focus on examination of processes that contribute to the repression of SMC marker genes. We discuss the environmental cues which actively regulate SMC phenotypic switching, such as platelet-derived growth factor-BB, as well as several important regulatory mechanisms required for suppressing expression of SMC-specific/selective marker genes in vivo, including those dependent on conserved G/C-repressive elements, and/or highly conserved degenerate CArG elements found in the promoters of many of these marker genes. Finally, we present evidence indicating that SMC phenotypic switching involves multiple active repressor pathways, including Krüppel-like zinc finger type 4, HERP, and ERK-dependent phosphorylation of Elk-1 that act in a complementary fashion.

Pathological Effects of Pulmonary Vein beta-Radiation in a Swine Model

INTRODUCTION

Atrial fibrillation (AF) may be triggered by ectopic beats originating in sleeves of atrial myocardium entering the pulmonary veins (PVs). PV isolation by means of circumferential ostial or atrial radiofrequency ablation is an effective but also a difficult and long procedure, requiring extensive applications that can have serious potential complications. Our objective was to examine pathological effects of PV beta-radiation, particularly the ability to destroy PV myocardial sleeves without inducing PV stenosis and other unwanted effects, in order to establish its potential feasibility for the treatment of AF.

METHODS AND RESULTS

Ten minipigs were studied. A phosphorus-32 source wire centered within a 2.5-mm diameter balloon catheter (Galileo III Intravascular Radiotherapy System, Guidant, Santa Clara, CA, USA) was used to deliver beta-radiation to the superior wall of the right PV trunk. Pathological analysis was performed either immediately after ablation (2 pigs) or 81 +/- 27 days later (8 pigs). Acute effects of PV beta-radiation consisted of endothelial denudation covered by white thrombus, elastic lamina disruption, and PV sleeve necrosis. Late effects consisted of mild focal neointimal hyperplasia that reduced the PV luminal area by only 1.3 +/- 1.8%, elastic lamina thickening, and PV sleeve fibrosis. Four of these 8 PVs were completely re-endothelized. Lesions were transmural in 6 of 10 radiated PVs and segmental, involving 28 +/- 7% of the right PV perimeter.

CONCLUSION

Intravascular beta-radiation can induce transmural necrosis and fibrosis of PV myocardial sleeves without PV stenosis and other unwanted effects, which supports a potential usefulness of this energy source in the treatment of AF.

Signal transduction to mitochondrial ATP synthase: evidence that PDGF-dependent phosphorylation of the delta-subunit occurs in several cell lines, involves tyrosine, and is modulated by lysophosphatidic acid

Although signal transduction mechanisms originating from receptors on the plasma membrane and targeted to metabolic and other enzymes/proteins localized in the cytoplasm or the nucleus have been extensively studied in animal cells, few such studies have focused on the mitochondrial energy producing machinery, i.e. the electron transport chain and ATP synthase complex (F0F1). Significantly, it was shown in an earlier collaborative study that platelet-derived growth factor (PDGF), which is linked in signal transduction pathways to tyrosine kinase-dependent phosphorylations, regulates the phosphorylation of the mitochondrial ATP synthase delta subunit in cortical neurons (Zhang et. al., 1995. J. Neurochem. 65, 2812-2815). This is a particularly intriguing finding in light of more recent reports demonstrating that ATP synthases are nanomotors with a central rotor, one component of which is the delta subunit. In this report, evidence is provided that the PDGF-dependent phosphorylation of the ATP synthase delta subunit is not confined to neuronal cells but can be demonstrated also in studies with PDGF-treated NIH3T3 and kidney cells. Evidence is provided also that phosphorylation of the ATP synthase delta subunit may involve its single tyrosine residue, and that this phosphorylation is modulated when the cell based assay includes lysophosphatidic acid (LPA), a phospholipid signaling molecules. Finally, results are presented of an analysis which revealed a number of potential tyrosine phosphorylation sites on three other subunits (alpha, beta, and gamma) of the F1 (catalytic) moiety of the mitochondrial ATP synthase, thus making this important complex a most attractive target for future signal transduction studies.

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.

The Effects of Paclitaxel on the Three Phases of Restenosis

PURPOSE

We sought to evaluate the growth-modulating potential of paclitaxel on cultured human arterial smooth muscle cells depending on the administered dose.

MATERIAL AND METHODS

For all experiments human arterial smooth muscle cells (SMCs) were used. SMCs were either cultured for 5 days or for 20 days with paclitaxel (doses: 10(-7) M, 10(-8) M, 10(-9) M). For a total period of 20 days, proliferation kinetics of the SMC were analyzed. To assess the clonogenic activity of the SMC colony-forming assays were performed. Drug- and dose-dependent cell cycle changes were analyzed by flow cytometry. The effect on cell migration was examined in a 2-chamber migration system. The effects of paclitaxel on the synthesis of tenascin were examined via immunofluorescence.

RESULTS

Depending on the dose administered, paclitaxel proved to inhibit SMC proliferation effectively when administered during the total period of 20 days. When incubated for 5 days with doses of paclitaxel ranging between 10(-8) M and 10(-9) M, SMCs showed clear signs of regeneration. When being incubated with 10(-7) M of paclitaxel, however, SMCs reacted with a reduction in cell proliferation, a reduced clonogenic activity, and a drug-induced G2/M phase block. SMC migration was inhibited effectively as well as extracellular matrix formation.

CONCLUSION

Paclitaxel is a potent inhibitor of SMC proliferation, SMC migration, and extracellular matrix formation in vitro, with all three phases of the restenosis process inhibited effectively.