Intimal hyperplasia in murine models

The innate immune sensor STING accelerates neointima formation via NF-κB signaling pathway

Vascular smooth muscle cells (VSMCs) proliferation, migration, and phenotypic switching are considered crucial events in the progression of neointima formation. Stimulator of interferon genes (STING), an innate immune sensor of cyclic dinucleotides against pathogens, in neointima formation remains obscure. Here, we observed a significant increase in STING expression on the neointima of injured vessels and mouse aortic VSMCs induced by PDGF-BB. In vivo, global knockout of STING (Sting-/-) attenuated neointima formation after vascular injury. In vitro data showed that STING deficiency significantly alleviated PDGF-BB-induced proliferation and migration in VSMCs. Furthermore, these contractile marker genes were upregulated in Sting-/- VSMCs. Overexpression of STING promoted proliferation, migration, and phenotypic switching in VSMCs. Mechanistically, STING-NF-κB signaling was involved in this process. The pharmacological inhibition of STING induced by C-176 partially prevented neointima formation due to suppression of VSMCs proliferation. Taken together, STING-NF-κB axis significantly promoted proliferation, migration, and phenotypic switching of VSMCs, which may be a novel therapeutic approach to combat vascular proliferative diseases.

The mitochondrial regulation of smooth muscle cell proliferation in type 2 diabetes

Background

Type 2 diabetes (T2D) is associated with a strongly increased risk for restenosis after angioplasty driven by proliferation of vascular smooth muscle cells (VSMCs). Here, we sought to determine whether and how mitochondrial dysfunction in T2D drives VSMC proliferation with a focus on ROS and intracellular [Ca 2+ ] that both drive cell proliferation, occur in T2D and are regulated by mitochondrial activity.

Methods

Using a diet-induced mouse model of T2D, the inhibition of the mitochondrial Ca 2+ /calmodulin-dependent kinase II (mtCaMKII), a regulator of Ca 2+ entry via the mitochondrial Ca 2+ uniporter selectively in VSMCs, we performed in vivo phenotyping after mechanical injury and established the mechanisms of excessive proliferation in cultured VSMCs.

Results

In T2D, the inhibition of mtCaMKII reduced both neointima formation after mechanical injury and the proliferation of cultured VSMCs. VSMCs from T2D mice displayed accelerated proliferation, reduced mitochondrial Ca 2+ entry and membrane potential with elevated baseline [Ca 2+ ] cyto compared to cells from normoglycemic mice. Accelerated proliferation after PDGF treatment was driven by activation of Erk1/2 and its upstream regulators. Hyperactivation of Erk1/2 was Ca 2+ -dependent rather than mitochondrial ROS-driven Ca 2+ -dependent and included the activation of CaMKII in the cytosol. The inhibition of mtCaMKII exaggerated the Ca 2+ imbalance by lowering mitochondrial Ca 2+ entry and increasing baseline [Ca 2+ ] cyto , further enhancing baseline Erk1/2 activation. With inhibition of mtCaMKII, PDGF treatment had no additional effect on cell proliferation. Inhibition of activated CaMKII in the cytosol decreased excessive Erk1/2 activation and reduced VSMC proliferation.

Conclusions

Collectively, our results provide evidence for the molecular mechanisms of enhanced VSMC proliferation after mechanical injury by mitochondrial Ca 2+ entry in T2D.

Sophocarpine Alleviates Injury-Induced Intima Hyperplasia of Carotid Arteries by Suppressing Inflammation in a Rat Model

INTRODUCTION

Balloon angioplasty is a commonly applied procedure for treating atherosclerotic vascular diseases. However, the maintenance of long-term lumen patency is relatively difficult due to the occurrence of restenosis. Previous research has shown that the occurrence of vascular wall inflammation is associated with higher rates of restenosis. Sophocarpine (SPC) can exert various therapeutic effects such as anti-oxidation, anti-inflammation, anti-tumor, antivirus and immune regulation. This study aimed to investigate whether SPC can alleviate intimal hyperplasia following balloon injury in a rat carotid artery model.

METHODS

Twenty Sprague-Dawley rats were randomly assigned to four groups: (i) control, (ii) balloon injury, (iii) balloon injury followed by saline injection, and (iv) balloon injury followed by SPC administration. Each group contained five rats. A high-pressure balloon of 3 mm × 20 mm was placed in the carotid artery. The balloon was inflated to a pressure of 8 atmospheres to carry out rat carotid artery balloon injury model. The areas of neointimal and media were determined by Verhoeff_Van Gieson staining, and the intima-to-media (I:M) ratios were subsequently evaluated. After that, the protein levels of IL-6, IL-1β, MCP-1, NF-κB, TNF-α, VCAM-1, ICAM-1 and eNOS were measured.

RESULTS

The ratio of I:M was remarkably higher in the balloon injury group than in the control group (p < 0.01). SPC could significantly decrease the ratio of I:M compared with the balloon injury group (p < 0.01). Besides, the protein levels of IL-6, IL-1β, MCP-1, NF-κB, TNF-α, ICAM-1 and VCAM-1 were increased in rat carotid arteries exposed to balloon injury (p < 0.01), and treatment with SPC could attenuate these effects (p < 0.05). Furthermore, balloon injury inhibited the protein expression of eNOS (p < 0.01), and SPC could elevate its level (p < 0.05).

CONCLUSIONS

SPC could alleviate an intimal hyperplasia in balloon-injured carotid artery, and the mechanisms underlying this protective effect might be due to its inhibitory potency against inflammation signals. Our study also implies the potential applicability of SPC in treating restenosis after balloon angioplasty.

Translocator protein imaging with 18F-FEDAC-positron emission tomography in rabbit atherosclerosis and its presence in human coronary vulnerable plaques

BACKGROUND AND AIMS

This study aimed to investigate whether N-benzyl-N-methyl-2-[7,8-dihydro-7-(2-[18F]fluoroethyl)-8-oxo-2-phenyl-9H-purin-9-yl]acetamide (18F-FEDAC), a probe for translocator protein (TSPO), can visualize atherosclerotic lesions in rabbits and whether TSPO is localized in human coronary plaques.

METHODS

18F-FEDAC-PET of a rabbit model of atherosclerosis induced by a 0.5% cholesterol diet and balloon injury of the left carotid artery (n = 7) was performed eight weeks after the injury. The autoradiography intensity of 18F-FEDAC in carotid artery tissue sections was measured, and TSPO expression was evaluated immunohistochemically. TSPO expression was examined in human coronary arteries obtained from autopsy cases (n = 16), and in human coronary plaques (n = 12) aspirated from patients with acute myocardial infarction (AMI).

RESULTS

18F-FEDAC-PET visualized the atherosclerotic lesions in rabbits as high-uptake areas, and the standard uptake value was higher in injured arteries (0.574 ± 0.24) than in uninjured arteries (0.277 ± 0.13, p < 0.05) or myocardium (0.189 ± 0.07, p < 0.05). Immunostaining showed more macrophages and more TSPO expression in atherosclerotic lesions than in uninjured arteries. TSPO was localized in macrophages, and arterial autoradiography intensity was positively correlated with macrophage concentration (r = 0.64) and TSPO (r = 0.67). TSPO expression in human coronary arteries was higher in AMI cases than in non-cardiac death, or in the vulnerable plaques than in early or stable lesions, respectively. TSPO was localized in macrophages in all aspirated coronary plaques with thrombi.

CONCLUSIONS

18F-FEDAC-PET can visualize atherosclerotic lesions, and TSPO-expression may be a marker of high-risk coronary plaques.

Endothelial Progenitor Cells Modulate the Phenotype of Smooth Muscle Cells and Increase Their Neointimal Accumulation Following Vascular Injury

BACKGROUND

 Smooth muscle cells (SMCs) are the main driver of neointima formation and restenosis following vascular injury. In animal models, endothelial progenitor cells (EPCs) accelerate endothelial regeneration and reduce neointima formation after arterial injury; however, EPC-capture stents do not reduce target vessel failure compared with conventional stents. Here we examined the influence of EPCs on features of SMCs pivotal for their impact on injury-induced neointima formation including proliferation, migration, and phenotype switch.

METHODS AND RESULTS

 EPCs, their conditioned medium, and EPC-derived microparticles induced proliferation of SMCs while limiting their apoptosis. In transwell membrane experiments and scratch assays, EPCs stimulated migration of SMCs and accelerated their recovery from scratch-induced injury. Treatment of SMCs with an EPC-derived conditioned medium or microparticles triggered transformation of SMCs toward a synthetic phenotype. However, co-cultivation of EPCs and SMCs enabling direct cell-cell contacts preserved their original phenotype and protected from the transformative effect of SMC cholesterol loading. Adhesion of EPCs to SMCs was stimulated by SMC injury and reduced by blocking CXCR2 and CCR5. Interaction of EPCs with SMCs modulated their secretory products and synergistically increased the release of selected chemokines. Following carotid wire injury in athymic mice, injection of EPCs resulted not only in reduced neointima formation but also in altered cellular composition of the neointima with augmented accumulation of SMCs.

CONCLUSION

 EPCs stimulate proliferation and migration of SMCs and increase their neointimal accumulation following vascular injury. Furthermore, EPCs context-dependently modify the SMC phenotype with protection from the transformative effect of cholesterol when a direct cell-cell contact is established.

Particulate matter air pollutants and cardiovascular disease: Strategies for intervention

Air pollution is consistently linked with elevations in cardiovascular disease (CVD) and CVD-related mortality. Particulate matter (PM) is a critical factor in air pollution-associated CVD. PM forms in the air during the combustion of fuels as solid particles and liquid droplets and the sources of airborne PM range from dust and dirt to soot and smoke. The health impacts of PM inhalation are well documented. In the US, where CVD is already the leading cause of death, it is estimated that PM2.5 (PM < 2.5 μm in size) is responsible for nearly 200,000 premature deaths annually. Despite the public health data, definitive mechanisms underlying PM-associated CVD are elusive. However, evidence to-date implicates mechanisms involving oxidative stress, inflammation, metabolic dysfunction and dyslipidemia, contributing to vascular dysfunction and atherosclerosis, along with autonomic dysfunction and hypertension. For the benefit of susceptible individuals and individuals who live in areas where PM levels exceed the National Ambient Air Quality Standard, interventional strategies for mitigating PM-associated CVD are necessary. This review will highlight current state of knowledge with respect to mechanisms for PM-dependent CVD. Based upon these mechanisms, strategies for intervention will be outlined. Citing data from animal models and human subjects, these highlighted strategies include: 1) antioxidants, such as vitamins E and C, carnosine, sulforaphane and resveratrol, to reduce oxidative stress and systemic inflammation; 2) omega-3 fatty acids, to inhibit inflammation and autonomic dysfunction; 3) statins, to decrease cholesterol accumulation and inflammation; 4) melatonin, to regulate the immune-pineal axis and 5) metformin, to address PM-associated metabolic dysfunction. Each of these will be discussed with respect to its potential role in limiting PM-associated CVD.

MEF2 (Myocyte Enhancer Factor 2) Is Essential for Endothelial Homeostasis and the Atheroprotective Gene Expression Program

OBJECTIVE

Atherosclerosis predominantly forms in regions of oscillatory shear stress while regions of laminar shear stress are protected. This protection is partly through the endothelium in laminar flow regions expressing an anti-inflammatory and antithrombotic gene expression program. Several molecular pathways transmitting these distinct flow patterns to the endothelium have been defined. Our objective is to define the role of the MEF2 (myocyte enhancer factor 2) family of transcription factors in promoting an atheroprotective endothelium. Approach and Results: Here, we show through endothelial-specific deletion of the 3 MEF2 factors in the endothelium, Mef2a, -c, and -d, that MEF2 is a critical regulator of vascular homeostasis. MEF2 deficiency results in systemic inflammation, hemorrhage, thrombocytopenia, leukocytosis, and rapid lethality. Transcriptome analysis reveals that MEF2 is required for normal regulation of 3 pathways implicated in determining the flow responsiveness of the endothelium. Specifically, MEF2 is required for expression of Klf2 and Klf4, 2 partially redundant factors essential for promoting an anti-inflammatory and antithrombotic endothelium. This critical requirement results in phenotypic similarities between endothelial-specific deletions of Mef2a/c/d and Klf2/4. In addition, MEF2 regulates the expression of Notch family genes, Notch1, Dll1, and Jag1, which also promote an atheroprotective endothelium. In contrast to these atheroprotective pathways, MEF2 deficiency upregulates an atherosclerosis promoting pathway through increasing the amount of TAZ (transcriptional coactivator with PDZ-binding motif).

CONCLUSIONS

Our results implicate MEF2 as a critical upstream regulator of several transcription factors responsible for gene expression programs that affect development of atherosclerosis and promote an anti-inflammatory and antithrombotic endothelium. Graphic Abstract: A graphic abstract is available for this article.

OCT4 regulated neointimal formation in injured mouse arteries by matrix metalloproteinase 2-mediated smooth muscle cells proliferation and migration

The excessive proliferation and migration of vascular smooth muscle cells (VSMCs) play vital roles in neointimal hyperplasia and vascular restenosis. In the present study, we aimed to investigate the function and mechanism of octamer-binding transcription factor 4 (OCT4, a key transcription factor for maintaining stem cells in de-differentiated state) on neointima formation in response to vascular injury. Quantitative reverse-transcription polymerase chain reaction and western blot results displayed a significant increase of OCT4 levels in injured carotid arteries. Immunohistochemistry and immunofluorescence assays confirmed that the increased OCT4 expression was primarily localized in α-SMA-positive VSMCs from neointima, and colocalized with PCNA in the nuclei of VSMCs. Adenovirus-mediated OCT4 overexpression in injured carotid arteries exacerbated intimal thickening, while OCT4 knockdown significantly inhibited intimal thickening. In-vitro experiments confirmed that the increased OCT4 expression in VMSCs could be induced by platelet-derived growth factor-BB (PDGF-BB) in a time-dependent manner. Overexpression of OCT4 greatly promoted VSMCs proliferation and migration, while OCT4 knockdown significantly retarded the PDGF-BB-induced excessive proliferation and migration of VSMCs. Bioinformatics analysis, dual-luciferase reporter assay, and chromatin immunoprecipitation assay confirmed that OCT4 could upregulate matrix metalloproteinases 2 (MMP2) expression through promoting its transcription. Moreover, knockdown of MMP2 significantly attenuated OCT4-mediated VSMCs proliferation and migration. These results indicated that OCT4 facilitated neointimal formation in response to vascular injury by MMP2-mediated VSMCs proliferation and migration, and targeting OCT4 in VSMCs might be a novel therapeutic strategy for vascular restenosis.

miRNA 146b-5p protects against atherosclerosis by inhibiting vascular smooth muscle cell proliferation and migration

Aim: To explore the potentially important role of miRNA 146b-5p (miR-146b) during the development of atherosclerosis. Materials & methods: Proliferation, migration and luciferase assays and mouse models were used to determine the functions of miR-146b. Results: miR-146b was identified as substantially upregulated in the aortic plaques of ApoE-/- mice as well as in response to inflammatory cytokines. Overexpression of miR-146b repressed proliferation and migration of vascular smooth muscle cells by downregulating Bag1 and Mmp16, respectively. Adeno-associated virus-mediated miR-146b overexpression inhibited neointima formation after carotid injury and suppressed atherosclerotic plaque formation in western diet-induced ApoE-/- mice. Conclusion: miR-146b is a novel regulator of vascular smooth muscle cell function induced by inflammatory response, specifically in neointima formation, and offers a novel therapeutic strategy for treating atherosclerosis.

The Development of the Ascending Aortic Wall in Tricuspid and Bicuspid Aortic Valve: A Process from Maturation to Degeneration

Background: Patients with a bicuspid aortic valve (BAV) have an increased risk for aortic dilation and dissection. In this study, we provide a histological stratification of the developing aorta in the tricuspid aortic valve (TAV) and the BAV populations as a reference for future studies on aortopathy and related syndromes. Methods: Non-dilated TAV and BAV ascending aortic wall samples were collected, including 60 TAV (embryonic–70 years) and 32 BAV specimens (fetal–72 years, categorized in eight age groups. Results: In TAV, intimal development starts in the neonatal phase. After birth, the thickness of the medial layer increases significantly by increase of elastic lamellae up to and including the “young child” phase stabilizing afterwards. The BAV shows already prenatal intimal thickening becoming significantly thinner after birth subsequently stabilizing. In BAV, increase in elastic lamellae is seen between the young child and the adolescent phases, stabilizing afterwards. Conclusions: Vascular development in TAV is described in three phases: maturation, stabilization, and degeneration. For BAV, the development can be described in two phases: maturation (already prenatally) and degeneration. After birth, the development of the aorta is characterized by degeneration, leading to weakening of the ascending aortic wall and increasing the risk of aortopathy.

CD36 Enhances Vascular Smooth Muscle Cell Proliferation and Development of Neointimal Hyperplasia

Objective- Dysregulated proliferation of vascular smooth muscle cells (VSMC) plays an essential role in neointimal hyperplasia. CD36 functions critically in atherogenesis and thrombosis. We hypothesize that CD36 regulates VSMC proliferation and contributes to the development of obstructive vascular diseases. Approach and Results- We found by immunofluorescent staining that CD36 was highly expressed in human vessels with obstructive diseases. Using guidewire-induced carotid artery injury and shear stress-induced intima thickening models, we compared neointimal hyperplasia in Apoe^-/-, Cd36^-/- /Apoe^-/-, and CD36 specifically deleted in VSMC (VSMC ^cd36-/-) mice. CD36 deficiency, either global or VSMC-specific, dramatically reduced injury-induced neointimal thickening. Correspondingly, carotid artery blood flow was significantly increased in Cd36^-/- /Apoe^-/- compared with Apoe^-/- mice. In cultured VSMCs from thoracic aorta of wild-type and Cd36^-/- mice, we found that loss of CD36 significantly decreased serum-stimulated proliferation and increased cell populations in S phase, suggesting that CD36 is necessary for VSMC S/G2-M-phase transition. Treatment of VSMCs with a TSR (thrombospondin type 1 repeat) peptide significantly increased wild-type, but not Cd36^-/- VSMC proliferation. TSR or serum treatment significantly increased cyclin A expression in wild-type, but not in Cd36^-/- VSMCs. STAT3 (signal transducer and activator of transcription), which reportedly enhances both VSMC differentiation and maturation, was higher in Cd36^-/- VSMCs. CD36 deficiency significantly decreased expression of Col1A1 (type 1 collagen A1 chain) and TGF-β1 (transforming growth factor beta 1), and increased expression of contractile proteins, including calponin 1 and smooth muscle α actin, and dramatically increased cell contraction. Conclusions- CD36 promotes VSMC proliferation via upregulation of cyclin A expression that contributes to the development of neointimal hyperplasia, collagen deposition, and obstructive vascular diseases.

ApoER2 (Apolipoprotein E Receptor-2) Deficiency Accelerates Smooth Muscle Cell Senescence via Cytokinesis Impairment and Promotes Fibrotic Neointima After Vascular Injury

OBJECTIVE

Genome-wide studies showed that mutation in apoER2 (apolipoprotein E receptor-2) is additive with ε4 polymorphism in the APOE gene on cardiovascular disease risk in humans. ApoE or apoER2 deficiency also accelerates atherosclerosis lesion necrosis in hypercholesterolemic mice and promotes neointima formation after vascular injury. This study tests the hypothesis that apoE and apoER2 modulate vascular occlusive diseases through distinct mechanisms. Approach and Results: Carotid endothelial denudation induced robust neointima formation in both apoE-/- and apoER2-deficient Lrp8-/- mice. The intima in apoE-/- mice was rich in smooth muscle cells, but the intima in Lrp8-/- mice was cell-poor and rich in extracellular matrix. Vascular smooth muscle cells isolated from apoE-/- mice were hyperplastic whereas Lrp8-/- smooth muscle cells showed reduced proliferation but responded robustly to TGF (transforming growth factor)-β-induced fibronectin synthesis indicative of a senescence-associated secretory phenotype, which was confirmed by increased β-galactosidase activity, p16INK4a immunofluorescence, and number of multinucleated cells. Western blot analysis of cell cycle-associated proteins showed that apoER2 deficiency promotes cell cycle arrest at the metaphase/anaphase. Coimmunoprecipitation experiments revealed that apoER2 interacts with the catalytic subunit of protein phosphatase 2A. In the absence of apoER2, PP2A-C (protein phosphatase 2A catalytic subunit) failed to interact with CDC20 (cell-division cycle protein 20) thus resulting in inactive anaphase-promoting complex and impaired cell cycle exit.

CONCLUSIONS

This study showed that apoER2 participates in APC (anaphase-promoting complex)/CDC20 complex formation during mitosis, and its absence impedes cytokinesis abscission thereby accelerating premature cell senescence and vascular disease. This mechanism is distinct from apoE deficiency, which causes smooth muscle cell hyperplasia to accelerate vascular disease.

Tumor Necrosis Factor Receptor-Associated Factor 5 Promotes Arterial Neointima Formation through Smooth Muscle Cell Proliferation

Tumor necrosis factor (TNF) receptor-associated factors (TRAFs) are cytoplasmic adaptor proteins of the TNF/interleukin (IL)-1/Toll-like receptor superfamily. Ligands of this family such as TNFα, CD40L, and IL-1β promote chronic inflammatory processes such as atherosclerosis and restenosis, the latter being a common adverse reaction after vascular interventions. We previously reported overexpression of TRAF5 in murine and human atheromata and TRAF5-dependent proinflammatory functions in vitro. However, the role of TRAF5 in restenosis remains unsettled. To evaluate whether TRAF5 affects neointima formation, TRAF5-/-LDLR-/- and TRAF5+/+LDLR-/- mice consuming a high cholesterol diet (HCD) received wire-induced injury of the carotid artery. After 28 days, TRAF5-deficient mice showed a 45% decrease in neointimal area formation compared with TRAF5-compentent mice. Furthermore, neointimal vascular smooth muscle cells (vSMC) and macrophages decreased whereas collagen increased in TRAF5-deficient mice. Mechanistically, the latter expressed lower transcript levels of the matrix metalloproteinases 2 and 9, both instrumental in extracellular matrix degradation and vSMC mobilization. Additionally, TRAF5-specific siRNA interference rendered murine vSMC less proliferative upon CD40L stimulation. In accordance with these findings, fewer vSMC isolated from TRAF5-deficient aortas were in a proliferative state as assessed by Ki67 and cyclin B1 expression. In conclusion, TRAF5 deficiency mitigates neointima formation in mice, likely through a TRAF5-dependent decrease in vSMC proliferation.

A vascular smooth muscle cell X-box binding protein 1 and transglutaminase 2 regulatory circuit limits neointimal hyperplasia

Neointimal hyperplasia, stimulated by injury and certain vascular diseases, promotes artery obstruction and tissue ischemia. In vascular smooth muscle cell (VSMCs), multiple modulators of protein handling machinery regulate intimal hyperplasia. These include elements of the VSMC unfolded protein response to endoplasmic reticulum stress (UPRER), and transglutaminase 2 (TG2), which catalyzes post-translational protein modification. Previous results for deficiency of UPRER-specific mediator XBP1, and of TG2, have been significant, but in multiple instances contradictory, for effects on cultured VSMC function, and, using multiple models, for neointimal hyperplasia in vivo. Here, we engineered VSMC-specific deficiency of XBP1, and studied cultured VSMCs, and neointimal hyperplasia in response to carotid artery ligation in vivo. Intimal area almost doubled in Xbp1fl/fl SM22α-CRE+ mice 21 days post-ligation. Cultured murine Xbp1 deficient VSMCs migrated more in response to platelet derived growth factor (PDGF) than control VSMCs, and had an increased level of inositol-requiring enzyme 1α (Ire1α), a PDGF receptor-binding UPRER transmembrane endonuclease whose substrates include XBP1. Cultured XBP1-deficient VSMCs demonstrated decreased levels of TG2 protein, in association with increased TG2 polyubiquitination, but with increased TG transamidation catalytic activity. Moreover, IRE1α, and TG2-specific transamidation cross-links were increased in carotid artery neointima in Xbp1fl/fl SM22α-CRE+ mice. Cultured TG2-deficient VSMCs had decreased XBP1 associated with increased IRE1α, and increased migration in response to PDGF. Neointimal hyperplasia also was significantly increased in Tgm2fl/fl SM22α-CRE+ mice at 21 days after carotid ligation. In conclusion, a VSMC regulatory circuit between XBP1 and TG2 limits neointimal hyperplasia in response to carotid ligation.

Sphingosine-1-phosphate receptor 1 regulates neointimal growth in a humanized model for restenosis

OBJECTIVE

The main objective of this study was to define a role of sphingosine-1-phosphate receptor 1 (S1PR1) in the arterial injury response of a human artery. The hypotheses were tested that injury induces an expansion of S1PR1-positive cells and that these cells accumulate toward the lumen because they follow the sphingosine-1-phosphate gradient from arterial wall tissue (low) to plasma (high).

METHODS

A humanized rat model was used in which denuded human internal mammary artery (IMA) was implanted into the position of the abdominal aorta of immunosuppressed Rowett nude rats. This injury model is characterized by medial as well as intimal hyperplasia, whereby intimal cells are of human origin. At 7, 14, and 28 days after implantation, grafts were harvested and processed for fluorescent immunostaining for S1PR1 and smooth muscle α-actin. Nuclei were stained with 4',6-diamidine-2'-phenylindole dihydrochloride. Using digitally reconstructed, complete cross sections of grafts, intimal and medial areas were measured, whereby the medial area had virtually been divided into an outer (toward adventitia) and inner (toward lumen) layer. The fraction of S1PR1-positive cells was determined in each layer by counting S1PR1-positive and S1PR1-negative cells.

RESULTS

The fraction of S1PR1-postive cells in naive IMA is 58.9% ± 6.0% (mean ± standard deviation). At day 28 after implantation, 81.6% ± 4.4% of medial cells were scored S1PR1 positive (P < .01). At day 14, the ratio between S1PR1-positive and S1PR1-negative cells was significantly higher in the lumen-oriented inner layer (9.3 ± 2.1 vs 6.0 ± 1.0; P < .01). Cells appearing in the intima at day 7 and day 14 were almost all S1PR1 positive. At day 28, however, about one-third of intimal cells were scored S1PR1 negative.

CONCLUSIONS

From these data, we conclude that denudation of IMA specifically induces the expansion of S1PR1-positive cells. Based on the nonrandom distribution of S1PR1-positive cells, we consider the possibility that much like lymphocytes, S1PR1-positive smooth muscle cells also use S1PR1 to recognize the sphingosine-1-phosphate gradient from tissue (low) to plasma (high) and so migrate out of the media toward the intima of the injured IMA.

CaMKII (Ca2+/Calmodulin-Dependent Kinase II) in Mitochondria of Smooth Muscle Cells Controls Mitochondrial Mobility, Migration, and Neointima Formation

OBJECTIVE

The main objective of this study is to define the mechanisms by which mitochondria control vascular smooth muscle cell (VSMC) migration and impact neointimal hyperplasia.

APPROACH AND RESULTS

The multifunctional CaMKII (Ca²⁺/calmodulin-dependent kinase II) in the mitochondrial matrix of VSMC drove a feed-forward circuit with the mitochondrial Ca²⁺ uniporter (MCU) to promote matrix Ca²⁺ influx. MCU was necessary for the activation of mitochondrial CaMKII (mtCaMKII), whereas mtCaMKII phosphorylated MCU at the regulatory site S92 that promotes Ca²⁺ entry. mtCaMKII was necessary and sufficient for platelet-derived growth factor-induced mitochondrial Ca²⁺ uptake. This effect was dependent on MCU. mtCaMKII and MCU inhibition abrogated VSMC migration and mitochondrial translocation to the leading edge. Overexpression of wild-type MCU, but not MCU S92A, mutant in MCU^-/- VSMC rescued migration and mitochondrial mobility. Inhibition of microtubule, but not of actin assembly, blocked mitochondrial mobility. The outer mitochondrial membrane GTPase Miro-1 promotes mitochondrial mobility via microtubule transport but arrests it in subcellular domains of high Ca²⁺ concentrations. In Miro-1^-/- VSMC, mitochondrial mobility and VSMC migration were abolished, and overexpression of mtCaMKII or a CaMKII inhibitory peptide in mitochondria (mtCaMKIIN) had no effect. Consistently, inhibition of mtCaMKII increased and prolonged cytosolic Ca²⁺ transients. mtCaMKII inhibition diminished phosphorylation of focal adhesion kinase and myosin light chain, leading to reduced focal adhesion turnover and cytoskeletal remodeling. In a transgenic model of selective mitochondrial CaMKII inhibition in VSMC, neointimal hyperplasia was significantly reduced after vascular injury.

CONCLUSIONS

These findings identify mitochondrial CaMKII as a key regulator of mitochondrial Ca²⁺ uptake via MCU, thereby controlling mitochondrial translocation and VSMC migration after vascular injury.

Periadventitial local drug delivery to target restenosis

The adventitia functions as a dynamic compartment for cell trafficking into and out of the artery wall, and communicates with medial and intimal cells. The resident cells in the tunica adventitia play an integral role in the regulation of vessel wall structure, repair, tone, and remodeling. Following injury to the vascular wall, adventitial fibroblasts are activated, which proliferate and differentiate into migratory myofibroblasts, and initiate inflammation through the secretion of soluble factors such as chemokines, cytokines, and adhesion molecules. The secreted factors subsequently promote leukocyte recruitment and extravasation into the media and intima. The adventitia generates reactive oxygen species and growth factors that participate in cell proliferation, migration, and hypertrophy, resulting in intimal thickening. The adventitial vasa vasorum undergoes neovascularization and serves as a port of entry for the delivery of inflammatory cells and resident stem/progenitor cells into the intima, and thus facilitates vascular remodeling. This review highlights the contribution of multilineage cells in the adventitia along with de-differentiated smooth muscle-like cells to the formation of neointimal hyperplasia, and discusses the potential of periadventitial local drug delivery for the prevention of vascular restenosis.

IFN-γ aggravates neointimal hyperplasia by inducing endoplasmic reticulum stress and apoptosis in macrophages by promoting ubiquitin-dependent liver X receptor-α degradation

Neointimal hyperplasia is the main cause of restenosis after percutaneous coronary interventions (PCIs). Both IFN-γ and macrophages play nonredundant roles in the pathogenesis of vascular intimal hyperplasia; however, the underlying mechanisms remain elusive and must be further investigated. In mouse peritoneal macrophages, IFN-γ significantly accelerated degradation and up-regulated polyubiquitination of liver X receptor (LXR)-α. Signal transducer and activator of transcription 1 (STAT1) inhibitor, fludarabine, and PIAS1 knockdown reduced ubiquitination and increased the expression of LXR-α in IFN-γ-treated macrophages. IFN-γ also increased the expression of endoplasmic reticulum (ER) stress-related proteins, including p-PERK, p-eIIF2α, and CCAAT-enhancer-binding protein homologous protein (CHOP), as well as apoptosis of macrophages. Treatment with ER stress inhibitor, 4-phenylbutyric acid (4-PBA), and LXR agonist, T0901317 (T0), alleviated IFN-γ-induced apoptosis in macrophages. Neointimal hyperplasia was significant after carotid ligation for 4 wk in ApoE^-/- mice. IFN-γ mAb, T0, and 4-PBA treatment not only significantly attenuated neointimal hyperplasia but also decreased CD68⁺TUNEL⁺ double-positive macrophages in the hyperplastic neointima. Moreover, after 4-PBA or T0 administration, the number of CD68⁺p-eIIF2α⁺ and CD68⁺CHOP⁺ double-positive cells in neointimal was also apparently decreased. Taken together, these results defined an unexpected role of IFN-γ and LXR-α in the development of neointimal hyperplasia. The PIAS1/STAT1-dependent LXR-α degradation induced by IFN-γ promoted ER stress and apoptosis in macrophages, which leads to aggravated neointimal hyperplasia. LXR agonist efficiently improved neointimal hyperplasia, which may be a promising new strategy to ameliorate restenosis and vascular remodeling after PCI.-Zhao, Q., Zhou, D., You, H., Lou, B., Zhang, Y., Tian, Y., Guo, N., Chen, X., Liu, Y., Wu, Y., Yuan, Z., Zhou, J. IFN-γ aggravates neointimal hyperplasia by inducing endoplasmic reticulum stress and apoptosis in macrophages by promoting ubiquitin-dependent liver X receptor-α degradation.

Endothelial Myocyte Enhancer Factor 2c Inhibits Migration of Smooth Muscle Cells Through Fenestrations in the Internal Elastic Lamina

OBJECTIVE

Laminar flow activates myocyte enhancer factor 2 (MEF2) transcription factors in vitro to induce expression of atheroprotective genes in the endothelium. Here we sought to establish the role of Mef2c in the vascular endothelium in vivo.

APPROACH AND RESULTS

To study endothelial Mef2c, we generated endothelial-specific deletion of Mef2c using Tie2-Cre or Cdh5-Cre-ER^T2 and examined aortas and carotid arteries by en face immunofluorescence. We observed enhanced actin stress fiber formation in the Mef2c-deleted thoracic aortic endothelium (laminar flow region), similar to those observed in normal aortic inner curvature (disturbed flow region). Furthermore, Mef2c deletion resulted in the de novo formation of subendothelial intimal cells expressing markers of differentiated smooth muscle in the thoracic aortas and carotids. Lineage tracing showed that these cells were not of endothelial origin. To define early events in intimal development, we induced endothelial deletion of Mef2c and examined aortas at 4 and 12 weeks postinduction. The number of intimal cell clusters increased from 4 to 12 weeks, but the number of cells within a cluster peaked at 2 cells in both cases, suggesting ongoing migration but minimal proliferation. Moreover, we identified cells extending from the media through fenestrations in the internal elastic lamina into the intima, indicating transfenestral smooth muscle migration. Similar transfenestral migration was observed in wild-type carotid arteries ligated to induce neointimal formation.

CONCLUSIONS

These results indicate that endothelial Mef2c regulates the endothelial actin cytoskeleton and inhibits smooth muscle cell migration into the intima.

Evaluation of synthetic vascular grafts in a mouse carotid grafting model

Current animal models for the evaluation of synthetic grafts are lacking many of the molecular tools and transgenic studies available to other branches of biology. A mouse model of vascular grafting would allow for the study of molecular mechanisms of graft failure, including in the context of clinically relevant disease states. In this study, we comprehensively characterise a sutureless grafting model which facilitates the evaluation of synthetic grafts in the mouse carotid artery. Using conduits electrospun from polycaprolactone (PCL) we show the gradual development of a significant neointima within 28 days, found to be greatest at the anastomoses. Histological analysis showed temporal increases in smooth muscle cell and collagen content within the neointima, demonstrating its maturation. Endothelialisation of the PCL grafts, assessed by scanning electron microscopy (SEM) analysis and CD31 staining, was near complete within 28 days, together replicating two critical aspects of graft performance. To further demonstrate the potential of this mouse model, we used longitudinal non-invasive tracking of bone-marrow mononuclear cells from a transgenic mouse strain with a dual reporter construct encoding both luciferase and green fluorescent protein (GFP). This enabled characterisation of mononuclear cell homing and engraftment to PCL using bioluminescence imaging and histological staining over time (7, 14 and 28 days). We observed peak luminescence at 7 days post-graft implantation that persisted until sacrifice at 28 days. Collectively, we have established and characterised a high-throughput model of grafting that allows for the evaluation of key clinical drivers of graft performance.

New Insights in the Pathophysiology of Antiphospholipid Syndrome

The antiphospholipid syndrome (APS) is an autoimmune disorder characterized by an elevated risk for arterial and venous thrombosis and pregnancy-related morbidity. Since the discovery of the disease in 1980s, numerous studies in cell culture systems, in animal models, and in patient populations have been reported, leading to a deeper understanding of the pathogenesis of APS. These studies have determined that circulating autoantibodies, collectively called antiphospholipid antibodies (aPL), the majority of which recognize cell surface proteins attached to the plasma membrane phospholipids, play a causal role in the development of the disease. The binding of aPL to the cell surface antigens triggers interaction of the complex with transmembrane receptors to initiate intracellular signaling in critical cell types, including platelets, monocytes, endothelial cells, and trophoblasts. Subsequent alteration of various cell functions results in inflammation, thrombus formation, and pregnancy complications. Apolipoprotein E receptor 2 (apoER2), a lipoprotein receptor family member, has been implicated as a mediator for aPL actions in platelets and endothelial cells. Nitric oxide (NO) is a signaling molecule known to exert potent antithrombotic, anti-inflammatory, and anti-atherogenic effects. NO insufficiency and oxidative stress have been linked to APS pathogenesis. This review will focus on the recent findings on how apoER2 and dysregulation of NO production contribute to aPL-mediated pathologies in APS.

The Ratio of Diameters Between the Target Artery and the Bypass Modifies Hemodynamic Parameters Related to Intimal Hyperplasia in the Distal End-to-Side Anastomosis

Hemodynamics in the distal end-to-side anastomosis is related to early development of intimal hyperplasia and bypass failure. In this study we investigated the effect of diameter ratios between the target artery and the bypass at three different angles of the connection. The pulsatile flow field was visualized using particle image velocimetry in transparent models with three different angles of the connection (25°, 45°, 60°) and the diameter ratio between the bypass and the target artery was 4.6 mm : 6 mm, 6 mm : 6 mm, and 7.5 mm : 6 mm. Six parameters including location and oscillation of the stagnation point, local energy dissipation, wall shear stress (WSS), oscillatory shear index, spatial and temporal gradient of WSS and their distribution in the target artery were calculated from the flow field. In the wider bypass, the stagnation point oscillated in a greater range and was located more proximal to the anastomosis. Energy dissipation was minimal in a wider bypass with a more acute angle. The maximum WSS values were tree times greater in a narrow bypass and concentrated in a smaller circular region at the floor of the anastomosis. The oscillatory shear index increased with wider bypass and more acute angle. The maximum of spatial gradient of WSS concentrated around the floor and toe of the anastomosis and decreased with more acute angle and wider bypass, the temporal gradient of WSS was stretched more towards the side wall. Greater bypass to target vessel ratio and more acute anastomosis angle promote hemodynamics known to reduce formation of intimal hyperplasia.

Increased Intimal Hyperplasia After Vascular Injury in Male Androgen Receptor-Deficient Mice

Intimal hyperplasia is a vascular pathological process involved in the pathogenesis of atherosclerosis. Data suggest that T, the most important sex steroid hormone in males, protects men from atherosclerotic cardiovascular disease. T mainly acts via the androgen receptor (AR), and in this study we evaluated formation of intimal hyperplasia in male AR knockout (ARKO) mice using a vascular injury model. Two weeks after ligation of the carotid artery, male ARKO mice showed increased intimal area and intimal thickness compared with controls. After endothelial denudation by an in vivo scraping injury, there was no difference in the reendothelialization in ARKO compared with control mice. Ex vivo, we observed increased outgrowth of vascular smooth muscle cells from ARKO compared with control aortic tissue explants; the number of outgrown cells was almost doubled in ARKO. In vitro, stimulation of human aortic vascular smooth muscle cells with a physiological T concentration inhibited both migration and proliferation of the cells. Analyzing the expression of central regulators of cell proliferation and migration, we found that mRNA and protein levels of p27 were lower in uninjured arteries from ARKO mice and that T replacement to castrated male mice increased p27 mRNA in an AR-dependent manner. In conclusion, AR deficiency in male mice increases intimal hyperplasia in response to vascular injury, potentially related to the effects of androgens/AR to inhibit proliferation and migration of smooth muscle cells.

ApoE knockout and knockin mice: the history of their contribution to the understanding of atherogenesis

ApoE is a multifunctional protein that is expressed by many cell types that influences many aspects of cardiovascular physiology. In humans, there are three major allelic variants that differentially influence lipoprotein metabolism and risk for the development of atherosclerosis. Apoe-deficient mice and human apoE isoform knockin mice, as well as hypomorphic Apoe mice, have significantly contributed to our understanding of the role of apoE in lipoprotein metabolism, monocyte/macrophage biology, and atherosclerosis. This brief history of these mouse models will highlight their contribution to the understanding of the role of apoE in these processes. These Apoe(-/-) mice have also been extensively utilized as an atherosensitive platform upon which to assess the impact of modulator genes on the development and regression of atherosclerosis.

Cuff-Induced Neointimal Formation in Mouse Models

Ischemic heart failure caused by atherosclerosis is a major cause of death worldwide. Although remarkable technological advances have been made in the treatment of coronary heart disease, there is as yet no treatment that can sufficiently suppress the progression of atherosclerosis, including neointimal thickening. Therefore, a precise understanding of the mechanism of neointimal hyperplasia will provide the development of new technologies. Both ApoE-KO and LDLR-KO mice have been employed to generate other relevant mouse models of cardiovascular disease through breeding strategies. Although these mice are effective tools for the investigation of atherosclerosis, development of a progressive atherosclerotic lesion takes a long time, resulting in increase of both the costs and the space needed for the research. Thus, it is necessary to develop simpler tools that would allow easy evaluation of atherosclerosis in mouse models. In this review, we discuss our experience in generating mouse models of cuff-induced injury of the femoral artery and attempt to provide a better understanding of cuff-induced neointimal formation.

HMGB1-Driven Inflammation and Intimal Hyperplasia After Arterial Injury Involves Cell-Specific Actions Mediated by TLR4

OBJECTIVE

Endoluminal vascular interventions such as angioplasty initiate a sterile inflammatory response resulting from local tissue damage. This response drives the development of intimal hyperplasia (IH) that, in turn, can lead to arterial occlusion. We hypothesized that the ubiquitous nuclear protein and damage-associated molecular pattern molecule, high-mobility group box 1 (HMGB1), is one of the endogenous mediators that activates processes leading to IH after endoluminal injury to the arterial wall. The aim of this study is to investigate whether approaches that reduce the levels of HMGB1 or inhibit its activity suppresses IH after arterial injury.

APPROACH AND RESULTS

Here, we show that HMGB1 regulates IH in a mouse carotid wire injury model. Induced genetic deletion or neutralization of HMGB1 prevents IH, monocyte recruitment, and smooth muscle cell growth factor production after endoluminal carotid artery injury. A specific inhibitor of HMGB1 myeloid differentiation factor 2-toll-like receptor 4 (TLR4) interaction, P5779, also significantly inhibits IH. HMGB1 deletion is mimicked in this model by global deletion of TLR4 and partially replicated by myeloid-specific deletion of TLR4 but not TLR2 or receptor for advanced glycation endproducts deletion. The specific HMGB1 isoform known to activate TLR4 signaling (disulfide HMGB1) stimulates smooth muscle cell to migrate and produce monocyte chemotactic protein 1/CCL2) via TLR4. Macrophages produce smooth muscle cell mitogens in response to disulfide HMGB1 also in a TLR4/myeloid differentiation primary response gene (88)/Trif-dependent manner.

CONCLUSIONS

These findings place HMGB1 and its receptor, TLR4 as critical regulators of the events that drive the inflammation leading to IH after endoluminal arterial injury and identify this pathway as a possible therapeutic target to limit IH to attenuate damage-associated molecular pattern molecule-mediated vascular inflammatory responses.

Impact of eNOS-Dependent Oxidative Stress on Endothelial Function and Neointima Formation

AIMS

Vascular oxidative stress generated by endothelial NO synthase (eNOS) was observed in experimental and clinical cardiovascular disease, but its relative importance for vascular pathologies is unclear. We investigated the impact of eNOS-dependent vascular oxidative stress on endothelial function and on neointimal hyperplasia.

RESULTS

A dimer-destabilized mutant of bovine eNOS where cysteine 101 was replaced by alanine was cloned and introduced into an eNOS-deficient mouse strain (eNOS-KO) in an endothelial-specific manner. Destabilization of mutant eNOS in cells and eNOS-KO was confirmed by the reduced dimer/monomer ratio. Purified mutant eNOS and transfected cells generated less citrulline and NO, respectively, while superoxide generation was enhanced. In eNOS-KO, introduction of mutant eNOS caused a 2.3-3.7-fold increase in superoxide and peroxynitrite formation in the aorta and myocardium. This was completely blunted by an NOS inhibitor. Nevertheless, expression of mutant eNOS in eNOS-KO completely restored maximal aortic endothelium-dependent relaxation to acetylcholine. Neointimal hyperplasia induced by carotid binding was much larger in eNOS-KO than in mutant eNOS-KO and C57BL/6, while the latter strains showed comparable hyperplasia. Likewise, vascular remodeling was blunted in eNOS-KO only.

INNOVATION

Our results provide the first in vivo evidence that eNOS-dependent oxidative stress is unlikely to be an initial cause of impaired endothelium-dependent vasodilation and/or a pathologic factor promoting intimal hyperplasia. These findings highlight the importance of other sources of vascular oxidative stress in cardiovascular disease.

CONCLUSION

eNOS-dependent oxidative stress is unlikely to induce functional vascular damage as long as concomitant generation of NO is preserved. This underlines the importance of current and new therapeutic strategies in improving endothelial NO generation.

Hepatic Overexpression of Soluble Urokinase Receptor (uPAR) Suppresses Diet-Induced Atherosclerosis in Low-Density Lipoprotein Receptor-Deficient (LDLR-/-) Mice

Objective

Atherosclerosis, a chronic inflammatory disease, arises from metabolic disorders and is driven by inappropriate recruitment and proliferation of monocytes / macrophages and vascular smooth-muscle-cells. The receptor for the urokinase-type plasminogen activator (uPAR, Plaur) regulates the proteolytic activation of plasminogen. It is also a coactivator of integrins and facilitates leukocyte-endothelial interactions and vascular smooth-muscle-cell migration. The role of uPAR in atherogenesis remains elusive.

Methods and Results

We generated C57Bl6/J low-density lipoprotein receptor (LDL) and uPAR double knockout (uPAR^-/-/LDLR^-/-) mice to test the role of uPAR in two distinct atherosclerosis models. In LDLR^-/- mice, hepatic overexpression following hydrodynamic transfection of soluble uPAR that competes with endogenous membrane-bound uPAR was performed as an interventional strategy. Aortic root atherosclerotic lesions induced by feeding a high-fat diet were smaller and comprised less macrophages and vascular smooth-muscle-cells in double knockout mice and animals overexpressing soluble uPAR when compared to controls. In contrast, lesion size, lipid-, macrophage-, and vascular smooth muscle cell content of guide-wire-induced intima lesions in the carotid artery were not affected by uPAR deficiency. Adhesion of uPAR^-/--macrophages to TNFα-stimulated endothelial cells was decreased in vitro accompanied by reduced VCAM-1 expression on primary endothelial cells. Hepatic overexpression of soluble full-length murine uPAR in LDLR^-/- mice led to a reduction of diet-induced atherosclerotic lesion formation and monocyte recruitment into plaques. Ex vivo incubation with soluble uPAR protein also inhibited adhesion of macrophages to TNFα-stimulated endothelial cells in vitro.

Conclusion

uPAR-deficiency as well as competitive soluble uPAR reduced diet-promoted but not guide-wire induced atherosclerotic lesions in mice by preventing monocyte recruitment and vascular smooth-muscle-cell infiltration. Soluble uPAR may represent a therapeutic tool for the modulation of hyperlipidemia-associated atherosclerotic lesion formation.

The Activation Function-1 of Estrogen Receptor Alpha Prevents Arterial Neointima Development Through a Direct Effect on Smooth Muscle Cells

RATIONALE

17β-Estradiol (E2) exerts numerous beneficial effects in vascular disease. It regulates gene transcription through nuclear estrogen receptor α (ERα) via 2 activation functions, AF1 and AF2, and can also activate membrane ERα. The role of E2 on the endothelium relies on membrane ERα activation, but the molecular mechanisms of its action on vascular smooth muscle cells (VSMCs) are not fully understood.

OBJECTIVE

The aim of this study was to determine which cellular target and which ERα subfunction are involved in the preventive action of E2 on neointimal hyperplasia.

METHODS AND RESULTS

To trigger neointimal hyperplasia of VSMC, we used a mouse model of femoral arterial injury. Cre-Lox models were used to distinguish between the endothelial- and the VSMC-specific actions of E2. The molecular mechanisms underlying the role of E2 were further characterized using both selective ERα agonists and transgenic mice in which the ERαAF1 function had been specifically invalidated. We found that (1) the selective inactivation of ERα in VSMC abrogates the neointimal hyperplasia protection induced by E2, whereas inactivation of endothelial and hematopoietic ERα has no effect; (2) the selective activation of membrane ERα does not prevent neointimal hyperplasia; and (3) ERαAF1 is necessary and sufficient to inhibit postinjury VSMC proliferation.

CONCLUSIONS

Altogether, ERαAF1-mediated nuclear action is both necessary and sufficient to inhibit postinjury arterial VSMC proliferation, whereas membrane ERα largely regulates the endothelial functions of E2. This highlights the exquisite cell/tissue-specific actions of the ERα subfunctions and helps to delineate the spectrum of action of selective ER modulators.

PDZK1 prevents neointima formation via suppression of breakpoint cluster region kinase in vascular smooth muscle

Scavenger receptor class B, type I (SR-BI) and its adaptor protein PDZK1 mediate responses to HDL cholesterol in endothelium. Whether the receptor-adaptor protein tandem serves functions in other vascular cell types is unknown. The current work determined the roles of SR-BI and PDZK1 in vascular smooth muscle (VSM). To evaluate possible VSM functions of SR-BI and PDZK1 in vivo, neointima formation was assessed 21 days post-ligation in the carotid arteries of wild-type, SR-BI-/- or PDZK1-/- mice. Whereas neointima development was negligible in wild-type and SR-BI-/-, there was marked neointima formation in PDZK1-/- mice. PDZK1 expression was demonstrated in primary mouse VSM cells, and compared to wild-type cells, PDZK1-/- VSM displayed exaggerated proliferation and migration in response to platelet derived growth factor (PDGF). Tandem affinity purification-mass spectrometry revealed that PDZK1 interacts with breakpoint cluster region kinase (Bcr), which contains a C-terminal PDZ binding sequence and is known to enhance responses to PDGF in VSM. PDZK1 interaction with Bcr in VSM was demonstrated by pull-down and by coimmunoprecipitation, and the augmented proliferative response to PDGF in PDZK1-/- VSM was abrogated by Bcr depletion. Furthermore, compared with wild-type Bcr overexpression, the introduction of a Bcr mutant incapable of PDZK1 binding into VSM cells yielded an exaggerated proliferative response to PDGF. Thus, PDZK1 has novel SR-BI-independent function in VSM that affords protection from neointima formation, and this involves PDZK1 suppression of VSM cell proliferation via an inhibitory interaction with Bcr.

A murine model of arterial restenosis: technical aspects of femoral wire injury

Cardiovascular disease caused by atherosclerosis is the leading cause of death in the developed world. Narrowing of the vessel lumen, due to atherosclerotic plaque development or the rupturing of established plaques, interrupts normal blood flow leading to various morbidities such as myocardial infarction and stroke. In the clinic endovascular procedures such as angioplasty are commonly performed to reopen the lumen. However, these treatments inevitably damage the vessel wall as well as the vascular endothelium, triggering an excessive healing response and the development of a neointimal plaque that extends into the lumen causing vessel restenosis (re-narrowing). Restenosis remains a major cause of failure of endovascular treatments for atherosclerosis. Thus, preclinical animal models of restenosis are vitally important for investigating the pathophysiological mechanisms as well as translational approaches to vascular interventions. Among several murine experimental models, femoral artery wire injury is widely accepted as the most suitable for studies of post-angioplasty restenosis because it closely resembles the angioplasty procedure that injures both endothelium and vessel wall. However, many researchers have difficulty utilizing this model due to its high degree of technical difficulty. This is primarily because a metal wire needs to be inserted into the femoral artery, which is approximately three times thinner than the wire, to generate sufficient injury to induce prominent neointima. Here, we describe the essential surgical details to effectively overcome the major technical difficulties of this model. By following the presented procedures, performing the mouse femoral artery wire injury becomes easier. Once familiarized, the whole procedure can be completed within 20 min.

Thrombin Receptor Protease-Activated Receptor 4 Is a Key Regulator of Exaggerated Intimal Thickening in Diabetes Mellitus

Background—

Diabetes mellitus predisposes to thrombotic and proliferative vascular remodeling, to which thrombin contributes via activation of protease-activated receptor (PAR) 1. However, the use of PAR-1 inhibitors to suppress remodeling may be limited by severe bleeding. We recently reported upregulation of an additional thrombin receptor, PAR-4, in human vascular smooth muscle cells exposed to high glucose and have now examined PAR-4 as a novel mediator linking hyperglycemia, hypercoagulation, and vascular remodeling in diabetes mellitus.

Methods and Results—

PAR-4 expression was increased in carotid atherectomies and saphenous vein specimens from diabetic versus nondiabetic patients and in aorta and carotid arteries from streptozotocin-diabetic versus nondiabetic C57BL/6 mice. Vascular PAR-1 mRNA was not increased in diabetic mice. Ligated carotid arteries from diabetic mice developed more extensive neointimal hyperplasia and showed greater proliferation than arteries from nondiabetic mice. The augmented remodeling response was absent in diabetic mice deficient in PAR-4. At the cellular level, PAR-4 expression was controlled via the mRNA stabilizing actions of human antigen R, which accounted for the stimulatory actions of high glucose, angiotensin II, and H 2 O 2 on PAR-4 expression, whereas cicaprost via protein kinase A activation counteracted this effect.

Conclusions—

PAR-4 appears to play a hitherto unsuspected role in diabetic vasculopathy. The development of PAR-4 inhibitors might serve to limit mainly proliferative processes in restenosis-prone diabetic patients, particularly those patients in whom severe bleeding attributed to selective PAR-1 blockade or complete thrombin inhibition must be avoided or those who do not require anticoagulation.

Left main disease progression following left branch vessel percutaneous intervention in patients who are referred for coronary artery bypass grafting

BACKGROUND AND AIM OF THE STUDY

We studied patients presenting for coronary artery bypass grafting (CABG) with significant left main coronary artery disease (LMD) despite previously documented minimal or no LMD at percutaneous coronary intervention (PCI) for left-sided branch coronary artery disease.

METHODS

Patients undergoing CABG for LMD with previous PCI were separated into fast or slow stenosis progression using percent change in LMD from first PCI to CABG divided by time (progression velocity). Outcomes and Kaplan-Meier survival were compared between the two groups.

RESULTS

Between September 1997 and June 2010, 4837 patients underwent CABG with 1235 of them having previous PCI of which 118 had LMD and previous left-sided branch PCI. Using median progression velocity fast and slow progression groups were identified (0.53 ± 0.18 and 4.5 ± 4.8%/month, p < 0.001). Mean follow-up was 4.9 ± 3.6 years and 6.9 ± 3.9 years, respectively. Fast progression patients were younger (p = 0.042), with higher baseline LMD at PCI (16.4% vs. 9% stenosis, p = 0.025), and a mean of 2.5 years to LMD compared to 10.6 years for the slow group (p < 0.001). There was no difference between the groups in number or type of PCI and number or type of vessel intervened. Kaplan-Meier survival was similar at one, three, and five years.

CONCLUSIONS

Fast LMD progression patients were younger and made up 4.7% (59/1235) of patients undergoing CABG with a history of PCI. Rapid progression was not related to number, type of PCI, or branch vessel intervened.

Antiphospholipid antibodies attenuate endothelial repair and promote neointima formation in mice

Background

Antiphospholipid syndrome patients have antiphospholipid antibodies (aPLs) that promote thrombosis, and they have increased cardiovascular disease risk. Although the basis for the thrombosis has been well delineated, it is not known why antiphospholipid syndrome patients also have an increased prevalence of nonthrombotic vascular occlusion. The aims of this work were to determine if aPLs directly promote medial hypertrophy or neointima formation in mice and to identify the underlying mechanisms.

Methods and Results

Medial hypertrophy and neointima formation invoked by carotid artery endothelial denudation were evaluated in mice administered normal human IgG or aPLs. While aPLs had no effect on medial hypertrophy, they caused exaggerated neointima development. This was related to an aPL‐induced impairment in reendothelialization post denudation, and scratch assays in cell culture revealed that there are direct effects of aPLs on endothelium that retard cell migration. Further experiments showed that aPL antagonism of endothelial migration and repair is mediated by antibody recognition of β2‐glycoprotein I, apolipoprotein E receptor 2, and a decline in bioavailable NO. Consistent with these mechanisms, the adverse impacts of aPLs on reendothelialization and neointima formation were fully prevented by the NO donor molsidomine.

Conclusions

APLs blunt endothelial repair, and there is related aPL‐induced exaggeration in neointima formation after endothelial injury in mice. The initiating process entails NO deficiency mediated by β2‐glycoprotein I recognition by aPLs and apolipoprotein E receptor 2. The modulation of endothelial apolipoprotein E receptor 2 function or NO bioavailability may represent new interventions to prevent the nonthrombotic vascular occlusion and resulting cardiovascular disorders that afflict antiphospholipid syndrome patients.

Genetic variants of ApoE and ApoER2 differentially modulate endothelial function

It is poorly understood why there is greater cardiovascular disease risk associated with the apolipoprotein E4 (apoE) allele vs. apoE3, and also greater risk with the LRP8/apolipoprotein E receptor 2 (ApoER2) variant ApoER2-R952Q. Little is known about the function of the apoE-ApoER2 tandem outside of the central nervous system. We now report that in endothelial cells apoE3 binding to ApoER2 stimulates endothelial NO synthase (eNOS) and endothelial cell migration, and it also attenuates monocyte-endothelial cell adhesion. However, apoE4 does not stimulate eNOS or endothelial cell migration or dampen cell adhesion, and alternatively it selectively antagonizes apoE3/ApoER2 actions. The contrasting endothelial actions of apoE4 vs. apoE3 require the N-terminal to C-terminal interaction in apoE4 that distinguishes it structurally from apoE3. Reconstitution experiments further reveal that ApoER2-R952Q is a loss-of-function variant of the receptor in endothelium. Carotid artery reendothelialization is decreased in ApoER2(-/-) mice, and whereas adenoviral-driven apoE3 expression in wild-type mice has no effect, apoE4 impairs reendothelialization. Moreover, in a model of neointima formation invoked by carotid artery endothelial denudation, ApoER2(-/-) mice display exaggerated neointima development. Thus, the apoE3/ApoER2 tandem promotes endothelial NO production, endothelial repair, and endothelial anti-inflammatory properties, and it prevents neointima formation. In contrast, apoE4 and ApoER2-R952Q display dominant-negative action and loss of function, respectively. Thus, genetic variants of apoE and ApoER2 impact cardiovascular health by differentially modulating endothelial function.

LincRNA-p21 regulates neointima formation, vascular smooth muscle cell proliferation, apoptosis, and atherosclerosis by enhancing p53 activity

BACKGROUND

Long noncoding RNAs (lncRNAs) have recently been implicated in many biological processes and diseases. Atherosclerosis is a major risk factor for cardiovascular disease. However, the functional role of lncRNAs in atherosclerosis is largely unknown.

METHODS AND RESULTS

We identified lincRNA-p21 as a key regulator of cell proliferation and apoptosis during atherosclerosis. The expression of lincRNA-p21 was dramatically downregulated in atherosclerotic plaques of ApoE(-/-) mice, an animal model for atherosclerosis. Through loss- and gain-of-function approaches, we showed that lincRNA-p21 represses cell proliferation and induces apoptosis in vascular smooth muscle cells and mouse mononuclear macrophage cells in vitro. Moreover, we found that inhibition of lincRNA-p21 results in neointimal hyperplasia in vivo in a carotid artery injury model. Genome-wide analysis revealed that lincRNA-p21 inhibition dysregulated many p53 targets. Furthermore, lincRNA-p21, a transcriptional target of p53, feeds back to enhance p53 transcriptional activity, at least in part, via binding to mouse double minute 2 (MDM2), an E3 ubiquitin-protein ligase. The association of lincRNA-p21 and MDM2 releases MDM2 repression of p53, enabling p53 to interact with p300 and to bind to the promoters/enhancers of its target genes. Finally, we show that lincRNA-p21 expression is decreased in patients with coronary artery disease.

CONCLUSIONS

Our studies identify lincRNA-p21 as a novel regulator of cell proliferation and apoptosis and suggest that this lncRNA could serve as a therapeutic target to treat atherosclerosis and related cardiovascular disorders.

Expression of sarco (endo) plasmic reticulum calcium ATPase (SERCA) system in normal mouse cardiovascular tissues, heart failure and atherosclerosis

The sarco(endo)plasmic reticulum Ca(2+)ATPases (SERCA) system, a key regulator of calcium cycling and signaling, is composed of several isoforms. We aimed to characterize the expression of SERCA isoforms in mouse cardiovascular tissues and their modulation in cardiovascular pathologies (heart failure and/or atherosclerosis). Five isoforms (SERCA2a, 2b, 3a, 3b and 3c) were detected in the mouse heart and thoracic aorta. Absolute mRNA quantification revealed SERCA2a as the dominant isoform in the heart (~99%). Both SERCA2 isoforms co-localized in cardiomyocytes (CM) longitudinal sarcoplasmic reticulum (SR), SERCA3b was located at the junctional SR. In the aorta, SERCA2a accounted for ~91% of total SERCA and SERCA2b for ~5%. Among SERCA3, SERCA3b was the most expressed (~3.3%), mainly found in vascular smooth muscle cells (VSMC), along with SERCA2a and 2b. In failing CM, SERCA2a was down-regulated by 2-fold and re-localized from longitudinal to junctional SR. A strong down-regulation of SERCA2a was also observed in atherosclerotic vessels containing mainly synthetic VSMCs. The proportion of both SERCA2b and SERCA3b increased to 9.5% and 8.3%, respectively.

IN CONCLUSION

1) SERCA2a is the major isoform in both cardiac and vascular myocytes; 2) the expression of SERCA2a mRNA is ~30 fold higher in the heart compared to vascular tissues; and 3) nearly half the amount of SERCA2a mRNA is measured in both failing cardiomyocytes and synthetic VSMCs compared to healthy tissues, with a relocation of SERCA2a in failing cardiomyocytes. Thus, SERCA2a is the principal regulator of excitation-contraction coupling in both CMs and contractile VSMCs.

DJ-1 protein regulates CD3+ T cell migration via overexpression of CXCR4 receptor

OBJECTIVE

DJ-1-a multifunctional protein responding to oxidative stress-is a possible regulator of the inflammatory response that plays an important role in atherosclerosis. Stromal cell-derived factor (SDF)-1 and its receptor, chemokine receptor type 4 (CXCR4), have been implicated in the recruitment of inflammatory cells during atherosclerosis. Here we investigated the hypothesis that DJ-1 protein might participate in CD3+ T cell functions in response to SDF-1 and contribute to the pathogenesis of atherosclerosis.

METHODS AND RESULTS

SDF-1 stimulated migration in mouse CD3+ T cells in a dose-dependent manner. SDF-1 also elevated the phosphorylation level of extracellular-regulated kinase (ERK) 1/2 in CD3+ T cells. These SDF-1-induced responses were greater in CD3+ T cells from DJ-1 gene knockout (DJ-1(-/-)) mice than in those from wild type (DJ-1(+/+)) mice and were abolished by treatment with WZ811 and PD98059, inhibitors of CXCR4 and ERK1/2, respectively. Flow cytometry revealed that expression of the CXCR4 receptor was greater in CD3+ T cells from DJ-1(-/-) mice than in those from the controls. Moreover, expression of the CD3 protein was observed in the neointimal plaque from carotid artery-ligated mice and was stronger in DJ-1(-/-) mice compared with controls. The CD3+ T cell subsets, Th1 and Th17, showed increased production of interferon-γ and interleukin-17 in DJ-1(-/-) compared with DJ-1(+/+) mice.

CONCLUSION

DJ-1 protein is involved in the SDF-1-induced CD3+ T cell migration via overexpression of the CXCR4 receptor, and that DJ-1 acts as an inhibitory regulator in vascular remodeling such as neointima formation.

Resveratrol promotes endothelial cell wound healing under laminar shear stress through an estrogen receptor-α-dependent pathway

Restenosis is an adverse outcome of angioplasty, characterized by vascular smooth muscle cell (VSMC) hyperplasia. However, therapies targeting VSMC proliferation delay re-endothelialization, increasing the risk of thrombosis. Resveratrol (RESV) inhibits restenosis and promotes re-endothelialization after arterial injury, but in vitro studies assessing RESV-mediated effects on endothelial cell growth contradict these findings. We thus hypothesized that fluid shear stress, mimicking physiological blood flow, would recapitulate RESV-dependent endothelial cell wound healing. Since RESV is an estrogen receptor (ER) agonist, we tested whether RESV promotes re-endothelialization through an ER-α-dependent mechanism. Mice fed a high-fat diet or a diet supplemented with RESV were subjected to carotid artery injury. At 7 days after injury, RESV significantly accelerated re-endothelialization compared with vehicle. In vitro wound healing assays demonstrated that RESV exhibits cell-type selectivity, inhibiting VSMC, but not endothelial cell growth. Under laminar shear stress (LSS), RESV dramatically enhanced endothelial cell wound healing and increased both the activation of extracellular signal-regulated kinase (ERK) and endothelial cell proliferation. Under LSS, small interfering RNA against ER-α, but not endothelial nitric oxide synthase, abolished RESV-induced ERK activation, endothelial cell proliferation, and wound healing. Thus these studies suggest that the EC phenotype induced by LSS better models the prohealing effects of RESV and that RESV and LSS interact to promote an ER-α-dependent mitogenic effect in endothelial cells.

Critical role of 5-lipoxygenase and heme oxygenase-1 in wound healing

Lipid mediators derived from 5-lipoxygenase (5-LO) metabolism can activate both pro- and anti-inflammatory pathways, but their role in wound healing remains largely unexplored. In this study we show that 5-LO knockout (5-LO(-/-)) mice exhibited faster wound healing than wild-type (WT) animals, and exhibited upregulation of heme oxygenase-1 (HO-1). Furthermore, HO-1 inhibition in 5-LO(-/-) mice abolished the beneficial effect observed. Despite the fact that 5-LO(-/-) mice exhibited faster healing, in in vitro assays both migration and proliferation of human dermal fibroblasts (HDFs) were inhibited by the 5-LO pharmacologic inhibitor AA861. No changes were observed in the expression of fibronectin, transforming growth factor (I and III), and α-smooth muscle actin (α-SMA). Interestingly, AA861 treatment significantly decreased ROS formation by stimulated fibroblasts. Similar to 5-LO(-/-) mice, induction of HO-1, but not superoxide dismutase-2 (SOD-2), was also observed in response to 5-LO (AA861) or 5-LO activating protein (MK886) inhibitors. HO-1 induction was independent of nuclear factor (erythroid derived-2) like2 (Nrf-2), cyclooxygenase 2 (COX-2) products, or lipoxin action. Taken together, our results show that 5-LO disruption improves wound healing and alters fibroblast function by an antioxidant mechanism based on HO-1 induction. Overexpression of HO-1 in wounds may facilitate early wound resolution.

Role of hemodynamic forces in the ex vivo arterialization of human saphenous veins

BACKGROUND

Human saphenous vein grafts are one of the salvage bypass conduits when endovascular procedures are not feasible or fail. Understanding the remodeling process that venous grafts undergo during exposure to arterial conditions is crucial to improve their patency, which is often compromised by intimal hyperplasia. The precise role of hemodynamic forces such as shear stress and arterial pressure in this remodeling is not fully characterized. The aim of this study was to determine the involvement of arterial shear stress and pressure on vein wall remodeling and to unravel the underlying molecular mechanisms.

METHODS

An ex vivo vein support system was modified for chronic (up to 1 week), pulsatile perfusion of human saphenous veins under controlled conditions that permitted the separate control of arterial shear stress and different arterial pressure (7 mm Hg or 70 mm Hg).

RESULTS

Veins perfused for 7 days under high pressure (70 mm Hg) underwent significant development of a neointima compared with veins exposed to low pressure (7 mm Hg). These structural changes were associated with altered expression of several molecular markers. Exposure to an arterial shear stress under low pressure increased the expression of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of metalloproteinase (TIMP)-1 at the transcript, protein, and activity levels. This increase was enhanced by high pressure, which also increased TIMP-2 protein expression despite decreased levels of the cognate transcript. In contrast, the expression of plasminogen activator inhibitor-1 increased with shear stress but was not modified by pressure. Levels of the venous marker Eph-B4 were decreased under arterial shear stress, and levels of the arterial marker Ephrin-B2 were downregulated under high-pressure conditions.

CONCLUSIONS

This model is a valuable tool to identify the role of hemodynamic forces and to decipher the molecular mechanisms leading to failure of human saphenous vein grafts. Under ex vivo conditions, arterial perfusion is sufficient to activate the remodeling of human veins, a change that is associated with the loss of specific vein markers. Elevation of pressure generates intimal hyperplasia, even though veins do not acquire arterial markers.

CLINICAL RELEVANCE

The pathological remodeling of the venous wall, which leads to stenosis and ultimately graft failure, is the main limiting factor of human saphenous vein graft bypass. This remodeling is due to the hemodynamic adaptation of the vein to the arterial environment and cannot be prevented by conventional therapy. To develop a more targeted therapy, a better understanding of the molecular mechanisms involved in intimal hyperplasia is essential, which requires the development of ex vivo models of chronic perfusion of human veins.

Regression of atherosclerosis in apolipoprotein E-deficient mice by lentivirus-mediated gene silencing of lipoprotein-associated phospholipase A2

Overexpression of lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) is implicated in atherosclerosis. We tested the hypothesis that lentivirus-mediated Lp-PLA(2) silencing could inhibit atherosclerosis in apolipoprotein E-deficient mice. Sixty eight apolipoprotein E-deficient mice were fed a high-fat diet and a constrictive collar was placed around the left carotid artery to induce plaque formation. The mice were randomly divided into control, negative control (NC) and RNA interference (RNAi) groups. Lp-PLA(2) RNAi or scrambled NC lentivirus viral suspensions were constructed and transfected into the carotid plaques 8 weeks after surgery; the control group was administered saline. The carotid plaques were assessed 7 weeks later using hematoxylin and eosin, Masson's trichrome and oil red O staining; plasma and lesion inflammatory gene expression were examined using ELISAs and real-time PCR. Seven weeks after transfection, the serum concentration and plaque mRNA expression of Lp-PLA(2) was significantly lower in the RNAi group, and lead to reduced local and systemic inflammatory gene expression. Lp-PLA(2) RNAi also ameliorated plaque progression, reduced the plaque lipid content and increased the plaque collagen content. The effects of Lp-PLA(2) RNAi were independent of serum lipoprotein levels, as the triglyceride and total cholesterol levels of the control, NC and RNAi groups were not significantly different. These findings support the hypothesis that lentivirus-mediated Lp-PLA(2) gene silencing has therapeutic potential to inhibit atherosclerosis and increase plaque stability, without altering the plasma lipoprotein profile.

Expression of endothelial lipase correlates with the size of neointima in a murine model of vascular remodeling

AIM

Endothelial lipase (EL) regulates plasma high-density lipoprotein-cholesterol (HDL-C) levels by promoting HDL catabolism. However, it remains unknown whether the inhibition of EL has beneficial effects on the genesis of vascular diseases. Here, we investigated the role of EL on vascular remodeling in mice.

METHODS

Vascular remodeling was developed by ligation of the left common carotid artery and neointimal lesions were histologically compared between EL-knockout (ELKO), EL-transgenic (ELTg), and wild-type (WT) mice. HDL was isolated from these mice, and effects of the HDL on cell growth and Erk activation were evaluated in vitro using cultured vascular smooth muscle cells.

RESULTS

Plasma HDL-C levels were 62% higher in ELKO and 13% lower in ELTg than in WT mice, after the carotid ligation. The size of neointimal lesion was significantly larger in ELTg and smaller in ELKO than in WT mice. Vascular expression of adhesion molecules was lower in ELKO and higher in ELTg compared with WT mice. Moreover, oxidative stress was attenuated in ELKO mice. HDL isolated from ELKO, ELTg, and WT mice inhibited expression of intercellular adhesion molecule-1, angiotensin II-induced activation of Erk, and growth of cultured vascular smooth muscle cells, whereas EL expression itself did not affect cell migration or growth.

CONCLUSION

EL expression modulates vascular remodeling as well as plasma HDL-C levels. EL inactivation may increase HDL particles that can inhibit smooth muscle cell growth and migration.

Thymidine phosphorylase inhibits vascular smooth muscle cell proliferation via upregulation of STAT3

Dysregulated growth and motility of vascular smooth muscle cells (VSMC) play important role in obstructive vascular diseases. We previously reported that gene transfer of thymidine phosphorylase (TP) into rat VSMC inhibits cell proliferation and attenuates balloon injury induced neointimal hyperplasia; however, the mechanism remains unclear. The current study identified a signaling pathway that mediates effect of TP inhibited VSMC proliferation with a TP activity-dependent manner. Rat VSMC overexpressing human TP gene (C2) or control empty vector (PC) were used. Serum stimulation induced constitutive STAT3 phosphorylation at tyrosine705 in C2 cell but not in PC, which was independent of JAK2 signaling pathway. Inhibition of Src family kinases activity inhibited STAT3 phosphorylation in C2 cells. Lyn activity was higher in C2 cell than in PC. SiRNA based gene knockdown of Lyn significantly decreased serum induced STAT3 phosphorylation in C2 and dramatically increased proliferation of this cell, suggesting that Lyn plays a pivotal role in TP inhibited VSMC proliferation. Unphosphorylated STAT3 (U-STAT3) expression was significantly increased in C2 cells, which may be due to the increased STAT3 transcription. Gene transfection of mouse wild-type or Y705F mutant STAT3 into PC cell or mouse primary cultured VSMC significantly reduced proliferation of these cells, suggesting that overexpression of U-STAT3 inhibits VSMC proliferation. We conclude that Lyn mediates TP induced STAT3 activation, which subsequently contributes to upregulate expression of U-STAT3. The U-STAT3 plays a critical role in inhibiting VSMC proliferation.

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

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

Sphingosine-1-phosphate receptor 3 promotes neointimal hyperplasia in mouse iliac-femoral arteries

OBJECTIVE

The objective of this study was to define a role for sphingosine-1-phosphate receptor 3 (S1PR3) in intimal hyperplasia.

METHODS AND RESULTS

A denudation model of the iliac-femoral artery in wild-type and S1PR3-null mice was used to define a role for S1PR3 in the arterial injury response because we found in humans and mice that expression of S1PR3 was higher in these arteries compared with carotid arteries. At 28 days after surgery, wild-type arteries formed significantly larger lesions than S1PR3-null arteries. Bromodeoxyuridine labeling experiments demonstrated that on injury, wild-type arteries exhibited higher medial as well as intimal proliferation than S1PR3-null arteries. Because S1PR3 expression in vitro was low, we expressed S1PR3 in S1PR3-null smooth muscle cells (SMCs) using retroviral-mediated gene transfer to study the effects of S1PR3 on cell functions and signaling. SMCs expressing S1PR3, but not vector-transfected controls, responded to sphingosine-1-phosphate stimulation with activation of Rac, Erk, and Akt. SMCs expressing S1PR3 also migrated more.

CONCLUSIONS

In humans and mice, S1PR3 expression was higher in iliac-femoral arteries compared with carotid arteries. S1PR3 promoted neointimal hyperplasia on denudation of iliac-femoral arteries in mice, likely by stimulating cell migration and proliferation through activation of signaling pathways involving Erk, Akt, and Rac.

Redox regulation of cell migration and adhesion

Reactive oxygen species (ROS), particularly hydrogen peroxide, and the proteins that regulate them play important roles in the migration and adhesion of cells. Stimulation of cell surface receptors with growth factors and chemoattractants generates ROS, which relay signals from the cell surface to key signaling proteins inside the cell. ROS act within cells to promote migration and also in nonmigrating cells to influence the behavior of migrating cells. Hydrogen peroxide has also been suggested to act as a chemoattractant in its own right, drawing immune cells to wounds. We discuss recent progress made towards understanding how organisms use ROS, and to what degree they depend on them, during the related processes of cell migration and adhesion.

Specificity protein-1 as a critical regulator of human cystathionine gamma-lyase in smooth muscle cells

Cystathionine γ-lyase (CSE) is the major enzyme in vascular smooth muscle cells (SMCs) that catalyzes the endogenous production of H(2)S. Phenotypic switching of SMCs is affected by endogenous H(2)S level and alterations of this switching may result in vascular disorders. To date, the mechanisms underlying the alteration of CSE expression and H(2)S production in vascular proliferative diseases have been unclear. In the present study, we found that serum deprivation induced SMC differentiation marker gene expressions and increased CSE expression and H(2)S production in cultured human aorta SMCs (HASMCs). Carotid artery ligation in mice resulted in enhanced neointima formation and down-regulation of CSE expression, suggesting an important role of CSE in SMC differentiation. Transient transfection of HASMCs with human CSE (hCSE) promoter/luciferase reporter revealed that the region between -226 to +140 base pair contains the core promoter for the hCSE gene. Deletion and mutation analysis demonstrated that two specificity protein-1 (Sp1) consensus binding sites were present in the core promoter region of the hCSE gene. Incubation of HASMCs with Sp1 binding inhibitor mithramycin inhibited CSE mRNA expression in a dose-dependent manner. Overexpression of Sp1 alone was sufficient to increase the activity of the hCSE core promoter and CSE protein expression. Chromatin immunoprecipitation assay showed that the binding of Sp1 to the hCSE promoter was increased in differentiated HASMCs compared with that in proliferated HASMCs. Exogenously applied H(2)S at 100 μM stimulated SMC differentiation, which was reversed by p38 MAPK inhibitor SB203580. These results suggest that transcript factor Sp1 is a critical regulator of the hCSE expression during SMC differentiation, and CSE/H(2)S system is essential for maintenance of SMC phenotype.