Patterns of kinase activation induced by injury in the murine femoral artery

Silencing of FOS-like antigen 1 represses restenosis via the ERK/AP-1 pathway in type 2 diabetic mice

Restenosis is a major limiting factor for a successful outcome in type 2 diabetes (T2D) patients undergoing percutaneous coronary intervention (PCI). The aim of this study is to explore the role and regulatory mechanism of FOS-like antigen 1 (FOSL1) in restenosis in T2D. A T2D with restenosis mouse model was established by the combination of high-fat diet and streptozotocin injection and by wire-injury. High glucose (HG)-treated vascular smooth muscle cells (VSMCs) were used to mimic T2D in vitro. The results of quantitative real time PCR and western blotting demonstrated that the expression of FOSL1 was increased not only in T2D mice or HG-induced VSMCs, but also in T2D mice that underwent wire-injury. HE staining revealed that FOSL1 knockdown significantly reduced the intimal/media ratio of T2D mice after wire-injury. Silencing of FOSL1 reversed the promoting effects of HG treatment on viability, migration and inflammation reactions, and the inhibiting effect on the apoptosis of VSMCs. Inhibition of ERK/AP-1 pathway obtained similar patterns in HG-induced VSMCs. The activation of ERK/AP-1 pathway reversed the influence of FOSL1 knockdown on HG-induced VSMCs. Our findings indicate that silencing of FOSL1 may suppress restenosis via regulation of the ERK/AP-1 pathway in T2D mice, pointing out a potential therapeutic target to prevent restenosis in T2D.

Clinical factors that influence the cellular responses of saphenous veins used for arterial bypass

OBJECTIVE

When an autogenous vein is harvested and used for arterial bypass, it suffers physical and biologic injuries that may set in motion the cellular processes that lead to wall thickening, fibrosis, stenosis, and ultimately graft failure. Whereas the injurious effects of surgical preparation of the vein conduit have been extensively studied, little is known about the influence of the clinical environment of the donor leg from which the vein is obtained.

METHODS

We studied the cellular responses of fresh saphenous vein samples obtained before implantation in 46 patients undergoing elective lower extremity bypass surgery. Using an ex vivo model of response to injury, we quantified the outgrowth of cells from explants of the adventitial and medial layers of the vein. We correlated this cellular outgrowth with the clinical characteristics of the patients, including the Wound, Ischemia, and foot Infection classification of the donor leg for ischemia, wounds, and infection as well as smoking and diabetes.

RESULTS

Cellular outgrowth was significantly faster and more robust from the adventitial layer than from the medial layer. The factors of leg ischemia (P < .001), smoking (P = .042), and leg infection (P = .045) were associated with impaired overall outgrowth from the adventitial tissue on multivariable analysis. Only ischemia (P = .046) was associated with impaired outgrowth of smooth muscle cells (SMCs) from the medial tissue. Co-culture of adventitial cells and SMCs propagated from vein explants revealed that adventitial cells significantly inhibited the growth of SMCs, whereas SMCs promoted the growth of adventitial cells. The AA genotype of the -838C>A p27 polymorphism (previously associated with superior graft patency) enhanced these effects, whereas the factor of smoking attenuated adventitial cell inhibition of SMC growth. Comparing gene expression, the cells cultured from the media overexpress Kyoto Encyclopedia of Genes and Genomes pathways associated with inflammation and infection, whereas those from the adventitia overexpress gene families associated with development and stem/progenitor cell maintenance.

CONCLUSIONS

The adverse clinical environment of the leg may influence the biologic behavior of the cells in the vein wall, especially the adventitial cells. Chronic ischemia was the most significant factor that retards adventitial cell outgrowth. The cells arising from the vein adventitia may be key players in determining a healthy adaptive or a pathologic response to the injuries associated with vein grafting.

Smooth muscle cell-specific Tgfbr1 deficiency attenuates neointimal hyperplasia but promotes an undesired vascular phenotype for injured arteries

Neointimal hyperplasia (NIH) and inward wall remodeling cause arterial restenosis and failure of bypass vein grafts. Previous studies from our group suggest that transforming growth factor (TGF) β promotes these pathologies via regulating cell kinetics at the early stage and matrix metabolism at the late stage. Although these temporal TGFβ effects may result from its signaling in different cell groups, the responsible cell type has not been identified. In the current study, we evaluated the effect of smooth muscle cell (SMC)‐specific TGFβ signaling through its type I receptor TGFBR1 on NIH and wall remodeling of the injured femoral arteries (FAs). An inducible Cre/loxP system was employed to delete SMC Tgfbr1 (Tgfbr1^iko). Mice not carrying the Cre allele (Tgfbr1^f/f) served as controls. The injured FAs were evaluated on d3, d7, and d28 postoperatively. Tgfbr1^iko attenuated NIH by 92%, but had insignificant influence on arterial caliber when compared with Tgfbr1^f/f controls on d28. This attenuation correlated with greater cellularity and reduced collagen content. Compared with Tgfbr1^f/fFAs, however, Tgfbr1^ikoFAs exhibited persistent neointimal cell proliferation and cell apoptosis, with both events at a greater rate on d28. Tgfbr1^ikoFAs additionally contained fewer SMCs and more inflammatory infiltrates in the neointima and displayed a thicker adventitia than did Tgfbr1^f/fFAs. More MMP9 proteins were detected in the adventitia of Tgfbr1^ikoFAs than in that of Tgfbr1^f/f controls. Our results suggest that disruption of SMC Tgfbr1 inhibits arterial NIH in the short term, but the overall vascular phenotype may not favor long‐term performance of the injured arteries.

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.

Gingerol Inhibits Serum-Induced Vascular Smooth Muscle Cell Proliferation and Injury-Induced Neointimal Hyperplasia by Suppressing p38 MAPK Activation

Purpose:

Gingerol inhibits growth of cancerous cells; however, its role in vascular smooth muscle cell (VSMC) proliferation is not known. The present study investigated the effect of gingerol on VSMC proliferation in cell culture and during neointima formation after balloon injury.

Method and Results:

Rat VSMCs or carotid arteries were harvested at 15 minutes, 30 minutes, 1, 6, 12, and 24 hours of fetal bovine serum (FBS; 10%) stimulation or balloon injury, respectively. Gingerol prevented FBS (10%)-induced proliferation of VSMCs in a dose-dependent manner (50 μmol/L-400 μmol/L). The FBS-induced proliferating cell nuclear antigen (PCNA) upregulation and p27Kip1 downregulation were also attenuated in gingerol (200 μmol/L) pretreated cells. Fetal bovine serum-induced p38 mitogen-activated protein kinase (MAPK) activation, PCNA upregulation, and p27Kip1 downregulation were abrogated in gingerol (200 μmol/L) and p38 MAPK inhibitor (SB203580, 10 μmol/L) pretreated cells. Balloon injury induced time-dependent p38 MAPK activation in the carotid artery. Pretreatment with gingerol (200 μmol/L) significantly attenuated injury-induced p38 MAPK activation, PCNA upregulation, and p27Kip1 downregulation. After 14 days of balloon injury, intimal thickening, neointimal proliferation, and endothelial dysfunction were significantly prevented in gingerol pretreated arteries. In isolated organ bath studies, gingerol (30 nmol/L-300 μmol/L) inhibited phenylephrine-induced contractions and induced dose-dependent relaxation of rat thoracic aortic rings in a partially endothelium-dependent manner.

Conclusion:

Gingerol prevented FBS-induced VSMC proliferation and balloon injury-induced neointima formation by regulating p38 MAPK. Vasodilator effect of gingerol observed in the thoracic aorta was partially endothelium dependent. Gingerol is thus proposed as an attractive agent for modulating VSMC proliferation, vascular reactivity, and progression of vascular proliferative diseases.

Involvement of interleukin-1 receptor-associated kinase-1 in vascular smooth muscle cell proliferation and neointimal formation after rat carotid injury

OBJECTIVE

Reduced frequency of atherosclerotic plaques is observed in interleukin-1 receptor-associated kinase-1 (IRAK1)-deficient mice; however, the underlying mechanism is not clear. Therefore, this study investigate the role of IRAK1 in vascular smooth muscle cell proliferation and neointimal hyperplasia.

APPROACH AND RESULTS

Stimulation of rat primary vascular smooth muscle cells with fetal bovine serum (10%) or platelet-derived growth factor-BB (20 ng/mL) for 15 minutes to 24 hours induced a time-dependent increase in IRAK1 and extracellular signal-regulated kinase (ERK) activation, proliferating cell nuclear antigen upregulation and p27Kip1 downregulation as assessed by Western blotting. Inhibitors of ERK pathway (U0126, 10 μmol/L), IRAK (IRAK1/4, 3 μmol/L), protein kinase C (PKC; Ro-31-8220, 1 μmol/L), siRNA of toll-like receptor-4 (200 nmol/L), and PKC-ε (200 nmol/L) significantly attenuated these changes. Platelet-derived growth factor induced endogenous IRAK-ERK-PKC-ε association in a toll-like receptor-4 and PKC-ε-dependent manner. A time-dependent increase in IRAK1 and ERK activation was observed after 15 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, and 24 hours of carotid balloon injury in rats. Balloon injury induced endogenous IRAK-ERK-PKC-ε interaction. Perivascular application of IRAK1/4 inhibitor (100 μmol/L), U0126 (100 μmol/L), and IRAK1 siRNA (220 and 360 nmol/L) in pluronic gel abrogated balloon injury-induced ERK phosphorylation, activation, and p27Kip1 downregulation. Hematoxylin and eosin staining and immunohistochemistry of proliferating cell nuclear antigen and smooth muscle actin demonstrated that balloon injury-induced intimal thickening and neointimal vascular smooth muscle cell proliferation were significantly abrogated in the presence of IRAK1/4 inhibitor, IRAK1 siRNA, and U0126.

CONCLUSIONS

IRAK1 mediates vascular smooth muscle cell proliferation and neointimal hyperplasia by regulating PKC-ε-IRAK1-ERK axis.

Requirement of JNK1 for endothelial cell injury in atherogenesis

Objective

The c-Jun N-terminal kinase (JNK) family regulates fundamental physiological processes including apoptosis and metabolism. Although JNK2 is known to promote foam cell formation during atherosclerosis, the potential role of JNK1 is uncertain. We examined the potential influence of JNK1 and its negative regulator, MAP kinase phosphatase-1 (MKP-1), on endothelial cell (EC) injury and early lesion formation using hypercholesterolemic LDLR^−/− mice.

Methods and results

To assess the function of JNK1 in early atherogenesis, we measured EC apoptosis and lesion formation in LDLR^−/− or LDLR^−/−/JNK1^−/− mice exposed to a high fat diet for 6 weeks. En face staining using antibodies that recognise active, cleaved caspase-3 (apoptosis) or using Sudan IV (lipid deposition) revealed that genetic deletion of JNK1 reduced EC apoptosis and lesion formation in hypercholesterolemic mice. By contrast, although EC apoptosis was enhanced in LDLR^−/−/MKP-1^−/− mice compared to LDLR^−/− mice, lesion formation was unaltered.

Conclusion

We conclude that JNK1 is required for EC apoptosis and lipid deposition during early atherogenesis. Thus pharmacological inhibitors of JNK may reduce atherosclerosis by preventing EC injury as well as by influencing foam cell formation.

•

We studied the role of JNK1 MAP kinase in atherosclerosis.

•

JNK1 was required for endothelial cell apoptosis and lesion formation.

•

An interaction between flow, JNK1 activity and endothelial injury was detected.

•

Targeting of JNK1 may have clinical utility to prevent atherosclerosis.

Effect of metabolic syndrome on the response to arterial injury

BACKGROUND

Metabolic syndrome is now an epidemic in the United States population. Intimal hyperplasia remains the principal lesion in the development of restenosis after vessel wall injury. The aim of this study is to characterize the changes induced in wall morphology in the developing intimal hyperplasia within a murine model in the presence of diabetes (type 1) and metabolic syndrome.

METHODS

Control (wild type B6), Non Obese Diabetic, and metabolic syndrome (RCS-10) mice were used. The murine femoral wire injury model was used in which a micro wire is passed through a branch of the femoral and used to denude the common femoral and iliac arteries. Specimens were perfusion fixed and sections were stained with hematoxylin and eosin and Movat stains such that dimensional and compositional morphometry could be performed using an ImagePro system. Additional stains for proliferation and apoptosis were used.

RESULTS

In control mice, the injured femoral arteries develop intimal hyperplasia, which is maximal at 28 d and remains stable to day 56. Sham-operated vessels do not produce such a response. In diabetic mice, the intimal response increased 5-fold with a 2-fold increase in proteoglycan deposition, whereas in the metabolic syndrome mice there was a 6-fold increase in the intimal response and a similar increase in proteoglycan deposition. Collagen deposition was different with a 22-fold increase over control in collagen deposition in diabetes and a 100-fold increase over control in collagen deposition in metabolic syndrome as compared with the control injury mice. Maximal vascular smooth muscle cell (VSMC) proliferation was decreased in both diabetes and metabolic syndrome compared with controls, whereas early cell apoptosis in both diabetes and metabolic syndrome was sustained over a longer period of time compared with wild-type mice.

CONCLUSIONS

These data demonstrate that development of intimal hyperplasia is markedly different in diabetes and metabolic syndrome compared with controls, with an increase in collagen deposition, a reduction in VSMC proliferation, and an increase in early VSMC apoptosis. These findings suggest that preventative strategies against restenosis must be tailored for the diabetic and metabolic syndrome patients.

Essential role of Pin1 via STAT3 signalling and mitochondria-dependent pathways in restenosis in type 2 diabetes

Type 2 diabetes (T2D) is associated with accelerated restenosis rates after angioplasty. We have previously proved that Pin1 played an important role in vascular smooth muscle cell (VSMC) cycle and apoptosis. But neither the role of Pin1 in restenosis by T2D, nor the molecular mechanism of Pin1 in these processes has been elucidated. A mouse model of T2D was generated by the combination of high-fat diet (HFD) and streptozotocin (STZ) injections. Both Immunohistochemistry and Western blot revealed that Pin1 expression was up-regulated in the arterial wall in T2D mice and in VSMCs in culture conditions mimicking T2D. Next, increased activity of Pin1 was observed in neointimal hyperplasia after arterial injury in T2D mice. Further analysis confirmed that 10% serum of T2D mice and Pin1-forced expression stimulated proliferation, inhibited apoptosis, enhanced cell cycle progression and migration of VSMCs, whereas Pin1 knockdown resulted in the converse effects. We demonstrated that STAT3 signalling and mitochondria-dependent pathways played critical roles in the involvement of Pin1 in cell cycle regulation and apoptosis of VSMCs in T2D. In addition, VEGF expression was stimulated by Pin1, which unveiled part of the mechanism of Pin1 in regulating VSMC migration in T2D. Finally, the administration of juglone via pluronic gel onto injured common femoral artery resulted in a significant inhibition of the neointima/media ratio. Our findings demonstrated the vital effect of Pin1 on the VSMC proliferation, cell cycle progression, apoptosis and migration that underlie neointima formation in T2D and implicated Pin1 as a potential therapeutic target to prevent restenosis in T2D.

Transforming growth factor-β increases vascular smooth muscle cell proliferation through the Smad3 and extracellular signal-regulated kinase mitogen-activated protein kinases pathways

INTRODUCTION

We have previously demonstrated that transforming growth factor-β (TGF-β) in the presence of elevated levels of Smad3, its primary signaling protein, stimulates rat vascular smooth muscle cell (VSMC) proliferation and intimal hyperplasia. The mechanism is partly through the nuclear exportation of phosphorylated cyclin-dependent kinase inhibitor p27. The objective of this study is to clarify the downstream pathways through which Smad3 produces its proliferative effect. Specifically, we evaluated the role of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) in TGF-β-induced VSMC proliferation.

METHODS

Cultured rat aortic VSMCs were incubated with TGF-β at varying concentrations and times, and phosphorylated ERK was measured by Western blotting. Smad3 was enhanced in VSMCs using an adenovirus expressing Smad3 or inhibited with small interfering RNA (siRNA). For in vivo experiments, male Sprague-Dawley rats underwent carotid balloon injury, followed by intraluminal infection with an adenovirus expressing Smad3. Arteries were harvested at 3 days and subjected to immunohistochemistry for Smad3, phospho-ERK MAPK, and proliferating cell nuclear antigen.

RESULTS

In cultured VSMCs, TGF-β induced activation and phosphorylation of ERK MAPK in a time-dependent and concentration-dependent manner. Overexpression of the signaling protein Smad3 enhanced TGF-β-induced activation of ERK MAPK, whereas inhibition of Smad3 with a siRNA blocked ERK MAPK phosphorylation in response to TGF-β. These data suggest that Smad3 acts as a signaling intermediate between TGF-β and ERK MAPK. Inhibition of ERK MAPK activation with PD98059 completely blocked the ability of TGF-β/Smad3 to stimulate VSMC proliferation, demonstrating the importance of ERK MAPK in this pathway. Immunoprecipitation of phospho-ERK MAPK and blotting with Smad3 revealed a physical association, suggesting that activation of ERK MAPK by Smad3 requires a direct interaction. In an in vivo rat carotid injury model, overexpression of Smad3 resulted in an increase in phosphorylated ERK MAPK as well as increased VSMC proliferation as measured by proliferating cell nuclear antigen.

CONCLUSIONS

Our findings demonstrate a mechanism through which TGF-β stimulates VSMC proliferation. Although TGF-β has been traditionally identified as an inhibitor of proliferation, our data suggest that TGF-β enhances VSMC proliferation through a Smad3/ERK MAPK signaling pathway. These findings at least partly explain the mechanism by which TGF-β enhances intimal hyperplasia. Knowledge of this pathway provides potential novel targets that may be used to prevent restenosis.

Gαq G proteins modulate MMP-9 gelatinase during remodeling of the murine femoral artery

BACKGROUND

Vessels heal after injury and G protein-coupled receptors are involved in the vascular smooth muscle cell proliferation required to form intimal hyperplasia. We have previously identified the role of Gαq in vascular smooth muscle cell proliferation in vitro. This study now examines the role of Gαq in the developing intimal hyperplasia in a murine model and the impact of disruption of Gαq signaling on intimal hyperplasia development.

METHODS

We employed a murine femoral wire injury model in which a micro-wire is passed through a branch of the femoral artery and used to denude the common femoral artery. We perfusion-fixed specimens and stained sections with hematoxylin-eosin and Movat's stains such that morphometric analysis could be performed using an Image-Pro system. We also harvested additional specimens of femoral artery and snap-froze them for Western blotting or zymography, to allow for the study of G protein expression and both protease expression and activity. We used contralateral vessels as controls. We immersed additional vessels in pluronic gel containing the chemical Gαq G protein inhibitors GP-2A, siRNA to Gαq or adenovirus containing mutant inactive Gαq.

RESULTS

Gαq expression increased in a time-dependent manner after femoral artery injury. Sham-operated vessels did not produce such a response. Inhibition of Gαq reduced cell proliferation without affecting cell migration. Interruption of Gαq signaling also inhibited the development of intimal hyperplasia. Inhibition of Gαq did not alter peak urinary-type plasminogen activator activity and expression, but did increase early plasminogen activator inhibitor-1 activity and expression. Inhibition of Gαq reduced peak metalloproteinase (MMP)-9 activity at Day 3 but did not influence peak MMP-2 activity at Day 7. Protein expression for MMP-9 was also decreased, but that of MMP-2 was not affected. There were no changes in the expression or the activity of the respective inhibitors for MMP-9 and MMP-2, and tissue inhibitor of metalloproteinases-1 and -2.

CONCLUSIONS

These data demonstrate that femoral wire injury in the mouse is associated with a time-dependent increase in Gαq expression. Inhibition of Gαq alters cell proliferation and is associated with decreased MMP-9 expression and activity.

Role for Gβγ G-proteins in protease regulation during remodeling of the murine femoral artery

BACKGROUND

Intimal hyperplasia remains the principal lesion in the development of restenosis after vessel wall injury. G-protein coupled receptors are involved in smooth muscle cell proliferation but the role of Gβγ in arterial intimal hyperplasia has not been well defined. The aim of this study is to characterize the expression of Gβγ G-proteins in the developing intimal hyperplasia in a murine model and the impact of disruption of Gβγ signaling on intimal hyperplasia development.

METHODS

The murine femoral wire injury model was employed. Specimens were perfusion-fixed and sections were stained with H&E and Movat's stains such that morphometry could be performed using an Image-Pro system. Additional specimens of femoral artery were also harvested and snap frozen for Western blotting for the Gβγ expression and for Western blotting and zymography to allow for the study of gelatinase and plasminogen activator expression and activation. Contralateral vessels were used as controls. Additional vessels were immersed in pluronic gel containing an adenovirus with the Gβγ inhibitor βARK(CT).

RESULTS

The injured femoral arteries developed intimal hyperplasia, while sham vessels did not produce such a response. Cell proliferation peaked at 3-5 d and cell migration at 7 d after injury. There was a marked time-dependent increase in Gβγ over the 28 d following injury. Inhibition of Gβγ with βARK(CT) inhibited cell proliferation, cell migration and the development of intimal hyperplasia. Inhibition of Gβγ decreased peak uPA activity and expression without increasing early PAI-1 activity and expression. Inhibition of Gβγ reduced peak MMP-2 activity at d 1 but not at d 7 and also reduced peak MMP-9 activity at d 3. Protein expression for both MMP-2 and MMP-9 was also transiently decreased. There were no changes in TIMP-1 and TIMP-2 expression and activity.

CONCLUSIONS

These data demonstrate a time-dependent increase in Gβγ G-protein expression following wire injury in the mouse. Inhibition of Gβγ alters cell proliferation and migration with associated changes in MMP-2, MMP-9, and uPA expression and activity.

Disturbed blood flow induces RelA expression via c-Jun N-terminal kinase 1: a novel mode of NF-κB regulation that promotes arterial inflammation

RATIONALE

The nuclear factor (NF)-κB pathway is involved in arterial inflammation. Although the signaling pathways that regulate transcriptional activation of NF-κB are defined, the mechanisms that regulate the expression levels of NF-κB transcription factors are uncertain.

OBJECTIVE

We studied the signaling mechanisms that regulate RelA NF-κB subunit expression in endothelial cells (ECs) and their role in arterial inflammation.

METHODS AND RESULTS

Gene silencing and chromatin immunoprecipitation revealed that RelA expression was positively regulated by c-Jun N-terminal kinase (JNK) and the downstream transcription factor ATF2 in ECs. We concluded that this pathway promotes focal arterial inflammation as genetic deletion of JNK1 reduced NF-κB expression and macrophage accumulation at an atherosusceptible site. We hypothesized that JNK signaling to NF-κB may be controlled by mechanical forces because atherosusceptibility is associated with exposure to disturbed blood flow. This was assessed by positron emission tomography imaging of carotid arteries modified with a constrictive cuff, a method that was developed to study the effects of disturbed flow on vascular physiology in vivo. This approach coupled to en face staining revealed that disturbed flow elevates NF-κB expression and inflammation in murine carotid arteries via JNK1.

CONCLUSIONS

We demonstrate that disturbed blood flow promotes arterial inflammation by inducing NF-κB expression in endothelial cells via JNK-ATF2 signaling. Thus, our findings illuminate a novel form of JNK-NF-κB crosstalk that may determine the focal nature of arterial inflammation and atherosclerosis.

Signaling pathways regulating vascular smooth muscle cell differentiation

Vascular smooth muscle cell (VSMC) differentiation is an essential component of vascular development. These cells perform biosynthetic, proliferative, and contractile roles in the vessel wall. VSMCs are not terminally differentiated and are able to modulate their phenotype in response to changing local environmental cues. There is clear evidence that alterations in the differentiated state of the VSMC play a critical role in the pathogenesis of atherosclerosis and intimal hyperplasia, as well as in a variety of other major human diseases, including hypertension, asthma, atherosclerosis and vascular aneurysms. 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 VSMCs, with particular focus on examination of the signaling pathways that regulate this process.

Patterns of gelatinase activation induced by injury in the murine femoral artery

BACKGROUND

Intimal hyperplasia remains the principal lesion in the development of restenosis after vessel wall injury. Modulation of the extracellular matrix by proteases is a pivotal component of the response to injury. The aim of this study is to characterize the changes in gelatinase (MMP-2/TIMP-2 and MMP-9/TIMP-1) systems in a murine model.

METHODS

The murine femoral wire injury model was used in which a microwire is passed through a branch of the femoral and used to denude the common femoral artery. Pluronic gel was used to apply a proteass inhibitor (GM6001) to the exterior of the vessels. Specimens were perfusion-fixed and sections were stained with hematoxylin and eosin and Movat's stain such that morphometry could be performed by using an ImagePro system. Additional specimens of femoral artery were also harvested and snap frozen for Western blotting and zymography to allow for the study of gelatinase expression and activation. Contralateral vessels were used as controls.

RESULTS

MMP-2 activity increased significantly at day 1, peaked again at day 7, and then showed a continual decline in activity to day 56. MMP-9 activity peaked early at day 3 and declined thereafter. Protein expression for both MMP-2 and MMP-9 increased significantly after injury and both were maximal at day 14. There was an initial decrease in TIMP-1 and TIMP-2 expression and activity after injury until day 5. Both expression and activation gradually increased thereafter to level out by day 21 and correlated well with the early increases in MMP-2 and MMP-9 activity and their subsequent decline. Local application of protease inhibitor (GM6001) within a pluronic gel decreased cell proliferation, and at 14 d there was a decrease in intimal hyperplasia.

CONCLUSIONS

These data demonstrate that femoral wire injury in the mouse is associated with a time-dependent increase in gelatinase activity. Cell proliferation is associated with increased MMP-2/MMP-9 activity and decreased TIMP-2/TIMP-1 activity, whereas migration is associated with increased in MMP-2 activity. Modulation of proteases and their inhibitors control the vessels' response to injury.