Mechanisms of monocyte recruitment in vascular repair after injury

Harnessing the potential of monocytes/macrophages to regenerate tissue-engineered vascular grafts

Cell-free tissue-engineered vascular grafts provide a promising alternative to treat cardiovascular disease, but timely endothelialization is essential for ensuring patency and proper functioning post-implantation. Recent studies from our lab showed that blood cells like monocytes (MCs) and macrophages (Mϕ) may contribute directly to cellularization and regeneration of bioengineered arteries in small and large animal models. While MCs and Mϕ are leucocytes that are part of the innate immune response, they share common developmental origins with endothelial cells (ECs) and are known to play crucial roles during vessel formation (angiogenesis) and vessel repair after inflammation/injury. They are highly plastic cells that polarize into pro-inflammatory and anti-inflammatory phenotypes upon exposure to cytokines and differentiate into other cell types, including EC-like cells, in the presence of appropriate chemical and mechanical stimuli. This review focuses on the developmental origins of MCs and ECs; the role of MCs and Mϕ in vessel repair/regeneration during inflammation/injury; and the role of chemical signalling and mechanical forces in Mϕ inflammation that mediates vascular graft regeneration. We postulate that comprehensive understanding of these mechanisms will better inform the development of strategies to coax MCs/Mϕ into endothelializing the lumen and regenerate the smooth muscle layers of cell-free bioengineered arteries and veins that are designed to treat cardiovascular diseases and perhaps the native vasculature as well.

Metabolic reprogramming of immune cells by mitochondrial division inhibitor-1 to prevent post-vascular injury neointimal hyperplasia

BACKGROUND AND AIMS

New treatments are needed to prevent neointimal hyperplasia that contributes to post-angioplasty and stent restenosis in patients with coronary artery disease (CAD) and peripheral arterial disease (PAD). We investigated whether modulating mitochondrial function using mitochondrial division inhibitor-1 (Mdivi-1) could reduce post-vascular injury neointimal hyperplasia by metabolic reprogramming of macrophages from a pro-inflammatory to anti-inflammatory phenotype.

METHODS AND RESULTS

In vivo Mdivi-1 treatment of Apoe-/- mice fed a high-fat diet and subjected to carotid-wire injury decreased neointimal hyperplasia by 68%, reduced numbers of plaque vascular smooth muscle cells and pro-inflammatory M1-like macrophages, and decreased plaque inflammation, endothelial activation, and apoptosis, when compared to control. Mdivi-1 treatment of human THP-1 macrophages shifted polarization from a pro-inflammatory M1-like to an anti-inflammatory M2-like phenotype, reduced monocyte chemotaxis and migration to CCL2 and macrophage colony stimulating factor (M-CSF) and decreased secretion of pro-inflammatory mediators. Finally, treatment of pro-inflammatory M1-type-macrophages with Mdivi-1 metabolically reprogrammed them to an anti-inflammatory M2-like phenotype by inhibiting oxidative phosphorylation and attenuating the increase in succinate levels and correcting the decreased levels of arginine and citrulline.

CONCLUSIONS

We report that treatment with Mdivi-1 inhibits post-vascular injury neointimal hyperplasia by metabolic reprogramming macrophages towards an anti-inflammatory phenotype thereby highlighting the therapeutic potential of Mdivi-1 for preventing neointimal hyperplasia and restenosis following angioplasty and stenting in CAD and PAD patients.

Differential Role for Activating FcγRIII in Neointima Formation After Arterial Injury and Diet-Induced Chronic Atherosclerosis in Apolipoprotein E-Deficient Mice

Atherogenesis and arterial remodeling following mechanical injury are driven by inflammation and mononuclear cell infiltration. The binding of immune complexes (ICs) to immunoglobulin (Ig)-Fc gamma receptors (FcγRs) on most innate and adaptive immune cells induces a variety of inflammatory responses that promote atherogenesis. Here, we studied the role of FcγRIII in neointima formation after arterial injury in atherosclerosis-prone mice and compared the outcome and mechanism to that of FcγRIII in diet-induced “chronic” atherosclerosis. FcγrIII^–/–/Apoe^–/– and control Apoe^–/– mice were subjected to wire-induced endothelial denudation of the carotid artery while on high-fat diet (HFD). FcγrIII deficiency mitigated neointimal plaque formation and lesional macrophage accumulation, and enhanced neointimal vascular smooth muscle cell (VSMC) numbers. This went along with a reduced expression of tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1/CCL2), and vascular cell adhesion molecule-1 (VCAM-1) in the neointimal lesions. Interestingly, in a chronic model of diet-induced atherosclerosis, we unraveled a dichotomic role of FcγRIII in an early versus advanced stage of the disease. While FcγrIII deficiency conferred atheroprotection in the early stage, it promoted atherosclerosis in advanced stages. To this end, FcγrIII deficiency attenuated pro-inflammatory responses in early atherosclerosis but promoted these events in advanced stages. Analysis of the mechanism(s) underlying the athero-promoting effect of FcγrIII deficiency in late-stage atherosclerosis revealed increased serum levels of anti-oxidized-LDL immunoglobulins IgG2c and IgG2b. This was paralleled by enhanced lesional accumulation of IgGs without affecting levels of complement-activated products C5a or C5ar1, FcγRII, and FcγRIV. Moreover, FcγrIII-deficient macrophages expressed more FcγrII, Tnf-α, and Il-1β mRNA when exposed to IgG1 or oxLDL-IgG1 ICs in vitro, and peripheral CD4+ and CD8+ T-cell levels were altered. Collectively, our data suggest that deficiency of activating FcγRIII limits neointima formation after arterial injury in atherosclerosis-prone mice as well as early stage chronic atherosclerosis, but augments late-stage atherosclerosis suggesting a dual role of FcγRIII in atherogenic inflammation.

Near-infrared -triggered release of tirofiban from nanocarriers for the inhibition of platelet integrin αIIbβ3 to decrease early-stage neointima formation

Platelets play an important role in the early stage of arterial remodeling after injury. Integrin GPIIb/IIIα (αIIbβ3) regulates platelet activation in the inside-out and outside-in signaling pathways. The use of tirofiban, an integrin αIIbβ3 inhibitor, in clinical therapy is limited by its short in vivo circulation time. Herein, a controlled drug-release system was formulated using CuS@mSiO2-PEG core-shell nanoparticles as near-infrared-triggered nanocarriers to release tirofiban on demand. The nanocarriers possessed good colloidal stability and very high loading efficiency for the integrin αIIbβ3 inhibitor (14.5 wt% for tirofiban). Local application of αIIbβ3 antagonist-tirofiban on an injured arterial wall inhibited platelet activation, which was accelerated by laser irradiation. Ex vivo platelet-promoted monocyte transmigration trans-well assays revealed decreased monocyte transmigration after platelet activation was inhibited by tirofiban. Two weeks after the wire-induced injury, the intimal area and cellular content were analyzed. The neointimal area was decreased in ApoE-/- mice with CuS@mSiO2-PEG/tirofiban and laser irradiation-promoted tirofiban release, which had limited the neointima formation. The lesions showed a decreased content of macrophages and smooth muscle cells compared with ApoE-/- mice without tirofiban inhibition. Therefore, the action of platelet-integrin αIIbβ3 in neointima formation after vascular injury was successfully inhibited in vivo through the controlled release of tirofiban using a near-infrared-triggered nanocarrier, leading to the decrease of early-stage neointima formation. This study also emphasizes the role of platelets in vascular remodeling and provides a new target, namely integrin αIIbβ3, for the inhibition of neointimal hyperplasia during vascular inflammation.

The role of monocyte subpopulations in vascular injury following partial and transient depletion

The innate immunity system plays a critical role in vascular repair and restenosis development. Liposomes encapsulating bisphosphonates (LipBPs), but not free BPs, suppress neointima formation following vascular injury mediated in part by monocytes. The objective of this study was to elucidate the role of monocyte subpopulations on vascular healing following LipBP treatment. The potency- and dose-dependent treatment effect of clodronate (CLOD) and alendronate (ALN) liposomes on restenosis inhibition, total monocyte depletion, and monocytes subpopulation was studied. Rats subjected to carotid injury were treated by a single IV injection of LipBPs at the time of injury. Low- and high-dose LipALN treatment (3 and 10 mg/kg, respectively) resulted in a dose-dependent effect on restenosis development after 30 days. Both doses of LipALN resulted in a dose-dependent inhibition of restenosis, but only high dose of LipALN depleted monocytes (-60.1 ± 4.4%, 48 h post injury). Although LipCLOD treatment (at an equivalent potency to 3 mg/kg alendronate) significantly reduced monocyte levels (72.1 ± 6%), no restenosis inhibition was observed. The major finding of this study is the correlation found between monocyte subclasses and restenosis inhibition. Non-classical monocyte (NCM) levels were found higher in LipALN-treated rats, but lower in LipCLOD-treated rats, 24 h after injury and treatment. We suggest that the inhibition of circulating monocyte subpopulations is the predominant mechanism by which LipBPs prevent restenosis. The effect of LipBP treatment on the monocyte subpopulation correlates with the dose and potency of LipBPs.

CRISPR/Cas9-mediated gene knockout reveals a guardian role of NF-κB/RelA in maintaining the homeostasis of human vascular cells

Vascular cell functionality is critical to blood vessel homeostasis. Constitutive NF-κB activation in vascular cells results in chronic vascular inflammation, leading to various cardiovascular diseases. However, how NF-κB regulates human blood vessel homeostasis remains largely elusive. Here, using CRISPR/Cas9-mediated gene editing, we generated RelA knockout human embryonic stem cells (hESCs) and differentiated them into various vascular cell derivatives to study how NF-κB modulates human vascular cells under basal and inflammatory conditions. Multi-dimensional phenotypic assessments and transcriptomic analyses revealed that RelA deficiency affected vascular cells via modulating inflammation, survival, vasculogenesis, cell differentiation and extracellular matrix organization in a cell type-specific manner under basal condition, and that RelA protected vascular cells against apoptosis and modulated vascular inflammatory response upon tumor necrosis factor α (TNFα) stimulation. Lastly, further evaluation of gene expression patterns in IκBα knockout vascular cells demonstrated that IκBα acted largely independent of RelA signaling. Taken together, our data reveal a protective role of NF-κB/RelA in modulating human blood vessel homeostasis and map the human vascular transcriptomic landscapes for the discovery of novel therapeutic targets.

Endothelial extracellular vesicles modulate the macrophage phenotype: Potential implications in atherosclerosis

Endothelial cells (ECs) and macrophages engage in tight and specific interactions that play critical roles in cardiovascular homeostasis and the pathogenesis of atherosclerosis. Extracellular vesicles (EVs) are circular membrane fragments released from the endosomal compartment as exosomes or shed from the surfaces of the membranes of most cell types. Increasing evidence indicates that EVs play a pivotal role in cell-to-cell communication. However, the contribution of EVs, as determine by oxidized low-density lipoprotein (ox-LDL)-exposed and/or Kruppel-like factor 2 (KLF2)-transduced ECs in the interaction between vascular ECs and monocytes/macrophages, which is a key event in atherosclerotic plaque development, has remained elusive. This study demonstrates the characteristic impact of EVs from ox-LDL-treated and/or KLF2-transduced ECs on the monocyte/macrophage phenotype in vitro and in vivo.Q-PCR showed that both the atherosclerosis inducer ox-LDL and atheroprotective factor KLF2 regulated inflammation-associated microRNA-155 (miR-155) expression in human umbilical vein endothelial cells (HUVECs). Moreover, coculture, immunofluorescence and flow cytometry revealed that miR-155 was enriched in ox-LDL-induced ECs-EVs and subsequently transferred to human monocytic THP1 cells, in which these vesicles enhance monocyte activation by shifting the monocytes/macrophages balance from anti-inflammatory M2 macrophages towards proinflammatory M1 macrophages; EVs from KLF2-expressing ECs suppressed monocyte activation by enhancing immunomodulatory responses and diminishing proinflammatory responses, which indicate the potent anti-inflammatory activities of these cells. Furthermore, oil red staining showed that atherosclerotic lesions were reduced in mice that received EVs from KLF2-transduced ECs with decreased proinflammatory M1 macrophages and increased anti-inflammatory M2 macrophages, and this effect is at least partly due to the decreased expression of inflammation-associated miR-155, confirming our in vitro findings. In summary, this study provides novel insights into the pathophysiological effects of altered EV secretion and/or microRNA content and their influence on modulating monocyte activation depending on the environment surrounding EVs-releasing ECs.

Platelet CD40 Mediates Leukocyte Recruitment and Neointima Formation after Arterial Denudation Injury in Atherosclerosis-Prone Mice

The role of platelets in the development of thrombosis and abrupt closure after angioplasty is well recognized. However, the direct impact of platelets on neointima formation after arterial injury remains undetermined. Herein, we show that neointima formation after carotid artery wire injury reduces markedly in CD40-/- apolipoprotein E-deficient (apoE-/-) mice but only slightly in CD40 ligand-/-apoE-/- mice, compared with apoE-/- mice. Wild-type and CD40-deficient platelets were isolated from blood of apoE-/- and CD40-/-apoE-/- mice, respectively. The i.v. injection of thrombin-activated platelets into CD40-/-apoE-/- mice was performed every 5 days, starting at 2 days before wire injury. Injection of wild-type platelets promoted neointima formation, which was associated with increased inflammation by stimulating leukocyte recruitment via up-regulation of circulating platelet surface P-selectin expression and the formation of platelet-leukocyte aggregates. It was also associated with further promoting the luminal deposition of platelet-derived regulated on activation normal T cell expressed and secreted/chemokine (C-C motif) ligand 5 and expression of monocyte chemoattractant protein-1 and vascular cell adhesion molecule 1 in wire-injured carotid arteries. Remarkably, all these inflammatory actions by activated platelets were abrogated by lack of CD40 on injected platelets. Moreover, injection of wild-type platelets inhibited endothelial recovery in wire-injured carotid arteries, but this effect was also abrogated by lack of CD40 on injected platelets. Results suggest that platelet CD40 plays a pivotal role in neointima formation after arterial injury and might represent an attractive target to prevent restenosis after vascular interventions.

Inhibition of activated factor X by rivaroxaban attenuates neointima formation after wire-mediated vascular injury

Accumulating evidence suggests that activated factor X (FXa), a key coagulation factor, plays an important role in the development of vascular inflammation through activation of many cell types. Here, we investigated whether pharmacological blockade of FXa attenuates neointima formation after wire-mediated vascular injury. Transluminal femoral artery injury was induced in C57BL/6 mice by inserting a straight wire. Rivaroxaban (5mg/kg/day), a direct FXa inhibitor, was administered from one week before surgery until killed. At four weeks after surgery, rivaroxaban significantly attenuated neointima formation in the injured arteries compared with control (P<0.01). Plasma lipid levels and blood pressure were similar between the rivaroxaban-treated group and non-treated group. Quantitative RT-PCR analyses demonstrated that rivaroxaban reduced the expression of inflammatory molecules (e.g., IL-1β and TNF-α) in injured arteries at seven days after surgery (P<0.05, respectively). In vitro experiments using mouse peritoneal macrophages demonstrated that FXa increased the expression of inflammatory molecules (e.g., IL-1β and TNF-α), which was blocked in the presence of rivaroxaban (P<0.05). Also, in vitro experiments using rat vascular smooth muscle cells (VSMC) demonstrated that FXa promoted both proliferation and migration of this cell type (P<0.05), which were blocked in the presence of rivaroxaban. Inhibition of FXa by rivaroxaban attenuates neointima formation after wire-mediated vascular injury through inhibition of inflammatory activation of macrophages and VSMC.

Deficiency of MAPK-activated protein kinase 2 (MK2) prevents adverse remodelling and promotes endothelial healing after arterial injury

Maladaptive remodelling of the arterial wall after mechanical injury (e. g. angioplasty) is characterised by inflammation, neointima formation and media hypertrophy, resulting in narrowing of the affected artery. Moreover, mechanical injury of the arterial wall causes loss of the vessel protecting endothelial cell monolayer. Mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MK2), a major downstream target of p38 MAPK, regulates inflammation, cell migration and proliferation, essential processes for vascular remodelling and reendothelialisation. Therefore, we investigated the role of MK2 in remodelling and reendothelialisation after arterial injury in genetically modified mice in vivo. Hypercholesterolaemic low-densitylipoprotein- receptor-deficient mice (ldlr-/- ) were subjected to wire injury of the common carotid artery. MK2-deficiency (ldlr-/-/mk2-/- ) nearly completely prevented neointima formation, media hypertrophy, and lumen loss after injury. This was accompanied by reduced proliferation and migration of MK2-deficient smooth muscle cells. In addition, MK2-deficiency severely reduced monocyte adhesion to the arterial wall (day 3 after injury, intravital microscopy), which may be attributed to reduced expression of the chemokine ligands CCL2 and CCL5. In line, MK2-deficiency significantly reduced the content of monocytes, neutrophiles and lymphocytes of the arterial wall (day 7 after injury, flow cytometry). In conclusion, in a model of endothelial injury (electric injury), MK2-deficiency strongly increased proliferation of endothelial cells and improved reendothelialisation of the arterial wall after injury. Deficiency of MK2 prevents adverse remodelling and promotes endothelial healing of the arterial wall after injury, suggesting that MK2-inhibition is a very attractive intervention to prevent restenosis after percutaneous therapeutic angioplasty.

Inhibition of p110δ PI3K prevents inflammatory response and restenosis after artery injury

Inflammatory cells play key roles in restenosis upon vascular surgical procedures such as bypass grafts, angioplasty and stent deployment but the molecular mechanisms by which these cells affect restenosis remain unclear. The p110δ isoform of phosphoinositide 3-kinase (PI3K) is mainly expressed in white blood cells. Here, we have investigated whether p110δ PI3K is involved in the pathogenesis of restenosis in a mouse model of carotid injury, which mimics the damage following arterial grafts. We used mice in which p110δ kinase activity has been disabled by a knockin (KI) point mutation in its ATP-binding site (p110δD910A/D910A PI3K mice). Wild-type (WT) and p110δD910A/D910A mice were subjected to longitudinal carotid injury. At 14 and 30 days after carotid injury, mice with inactive p110δ showed strongly decreased infiltration of inflammatory cells (including T lymphocytes and macrophages) and vascular smooth muscle cells (VSMCs), compared with WT mice. Likewise, PI-3065, a p110δ-selective PI3K inhibitor, almost completely prevented restenosis after artery injury. Our data showed that p110δ PI3K plays a main role in promoting neointimal thickening and inflammatory processes during vascular stenosis, with its inhibition providing significant reduction in restenosis following carotid injury. p110δ-selective inhibitors, recently approved for the treatment of human B-cell malignancies, therefore, present a new therapeutic opportunity to prevent the restenosis upon artery injury.

P-Selectin and ICAM-1 synergy in mediating THP-1 monocyte adhesion in hemodynamic flow is length dependent

The tightly orchestrated recruitment of monocytes, whose progeny are critical to the progression and resolution of various physiological and pathophysiological processes, is implicated in the time course, severity, and resolution of pathology. Using a microfluidic-based cell adhesion assay integrating spatiotemporal analyses and micropatterning of adhesive proteins, we interrogated the effects of adhesive molecule presentation length, which varies in vivo with disease and stage, on THP-1 monocyte cell rolling versus firm adhesion mediated by P-selectin and/or ICAM-1 in hemodynamic flow. Our results indicate that co-presentation of P-selectin and ICAM-1 substantially decreases the length of adhesive substrate required to sustain adhesion in flow and that P-selectin functions synergistically with ICAM-1 to substantially enhance THP-1 firm adhesion. This synergy was found to furthermore correlate with diminished cell rolling velocities and length-enhanced secondary cell capture. Our results suggest pathophysiological ramifications for local remodeling of the inflamed microvascular microenvironment in directing the efficiency of monocyte trafficking.

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.

Global Gene Expression Patterns and Somatic Mutations in Sporadic Intracranial Aneurysms

BACKGROUND

High-throughput sequencing technologies can expand our understanding of the pathologic basis of intracranial aneurysms (IAs). Our study was aimed to decipher the gene expression signature and genetic factors associated with IAs.

METHODS

We determined the gene expression levels of 3 cases of IAs by RNA sequencing. Bioinformatics analysis was conducted to identify the differentially expressed genes (DEGs) and uncover their biological function. In addition, whole genome sequencing was performed on an additional 6 cases of IAs to detect the potential somatic alterations in DEGs.

RESULTS

Compared with the normal arterial tissue, 1709 genes were differentially expressed in IAs arterial tissue. The most significantly up-regulated gene and down-regulated gene, H19 and HIST1H3J, may be essential for tumorigenesis of IAs. Hub protein of IKBKG in protein-protein interaction network was probably involved in the inflammation process in aneurysms. Another 2 hub proteins, ACTB and MKI67IP, as well as up-regulated genes, might be abnormally activated in aneurysms and involved in the pathogenesis of IAs. Further whole genome sequencing and filtering yielded 4 candidate somatic single nucleotide variants including MUC3B, and BLM may be involved in the pathogenesis of IAs. Even though, our results do not support the hypothesis of somatic mutations occurred in the DEGs.

CONCLUSIONS

Two-dimensional genomic data from transcriptome and whole genome sequencing indicated that no somatic mutations occurred in DEGs. In addition, 3 DEGs (IKBKG, ACTB, and MKI67IP) and 2 mutant genes (MUC3B and BLM) were essential in IAs.

Novel Association of miR-451 with the Incidence of TEVG Stenosis in a Murine Model

The development of a tissue-engineered vascular graft (TEVG) holds great promise for advancing the field of cardiac surgery. Despite the successful translation of this technology, previous reports identify the primary mode of graft failure as stenosis secondary to intimal hyperplasia. MicroRNAs (miRNAs) regulate gene expression by interfering with mRNA function and recent research has suggested miRNA as a potential therapeutic target. The role of miRNAs in TEVGs during neotissue formation is currently unknown. In this study, we investigated if miRNAs regulate the inhibition of graft stenosis. Biodegradable PGA-P(LA/CL) scaffolds were implanted as inferior vena cava interposition grafts in a murine model (n = 14). Mice were sacrificed 14 days following implantation and TEVGs were harvested for histological analysis and miRNA profiling using Affymetrix miRNA arrays. Graft diameters were measured histologically, and the largest grafts (patent group) and smallest grafts (stenosed group) were profiled (n = 4 for each group). Cell population in each graft was analyzed with immunohistochemistry using antismooth muscle actin (SMA) and antimacrophage (F4/80) antibodies. The graft diameter was significantly greater in the patent group (0.63 ± 0.06 mm) than in the stenosed group (0.17 ± 0.06 mm) (p < 0.01). Cell proliferation was significantly greater in the stenosed grafts than in patent grafts (p < 0.01: SMA [187 ± 11 vs. 77 ± 8 cells] vs. p = 0.025: F4/80 [245 ± 23 vs. 187 ± 11 cells]). MiRNA array of 1416 genes showed that in stenosed grafts, mir-451, mir-338, and mir-466 were downregulated and mir-154 was upregulated. Mir-451 exhibited the greatest difference in expression between stenosed and patent grafts by -3.1-fold. Significant negative correlation was found between the expression of mir-451 and cell proliferation (SMA: r = -0.86, p = 0.003; F4/80: r = -0.89, p = 0.001). Our data, along with previous evidence that mir-451 regulates tumor suppressor genes, suggest that downregulation of mir-451 promotes acute proliferation of macrophages and smooth muscle cells, thereby inducing TEVG stenosis. Adequate expression of mir-451 may be critical for improving TEVG patency.

The Function of Rho-Associated Kinases ROCK1 and ROCK2 in the Pathogenesis of Cardiovascular Disease

Rho-associated kinases ROCK1 and ROCK2 are serine/threonine kinases that are downstream targets of the small GTPases RhoA, RhoB, and RhoC. ROCKs are involved in diverse cellular activities including actin cytoskeleton organization, cell adhesion and motility, proliferation and apoptosis, remodeling of the extracellular matrix and smooth muscle cell contraction. The role of ROCK1 and ROCK2 has long been considered to be similar; however, it is now clear that they do not always have the same functions. Moreover, depending on their subcellular localization, activation, and other environmental factors, ROCK signaling can have different effects on cellular function. With respect to the heart, findings in isoform-specific knockout mice argue for a role of ROCK1 and ROCK2 in the pathogenesis of cardiac fibrosis and cardiac hypertrophy, respectively. Increased ROCK activity could play a pivotal role in processes leading to cardiovascular diseases such as hypertension, pulmonary hypertension, angina pectoris, vasospastic angina, heart failure, and stroke, and thus ROCK activity is a potential new biomarker for heart disease. Pharmacological ROCK inhibition reduces the enhanced ROCK activity in patients, accompanied with a measurable improvement in medical condition. In this review, we focus on recent findings regarding ROCK signaling in the pathogenesis of cardiovascular disease, with a special focus on differences between ROCK1 and ROCK2 function.

Immunomodulation by lipid emulsions in pulmonary inflammation: a randomized controlled trial

INTRODUCTION

Acute respiratory distress syndrome (ARDS) is a major cause of mortality in intensive care units. As there is rising evidence about immuno-modulatory effects of lipid emulsions required for parenteral nutrition of ARDS patients, we sought to investigate whether infusion of conventional soybean oil (SO)-based or fish oil (FO)-based lipid emulsions rich in either n-6 or n-3 fatty acids, respectively, may influence subsequent pulmonary inflammation.

METHODS

In a randomized controlled, single-blinded pilot study, forty-two volunteers received SO, FO, or normal saline for two days. Thereafter, volunteers inhaled pre-defined doses of lipopolysaccharide (LPS) followed by bronchoalveolar lavage (BAL) 8 or 24 h later. In the murine model of LPS-induced lung injury a possible involvement of resolvin E1 (RvE1) receptor ChemR23 was investigated. Wild-type and ChemR23 knockout mice were infused with both lipid emulsions and challenged with LPS intratracheally.

RESULTS

In volunteers receiving lipid emulsions, the fatty acid profile in the plasma and in isolated neutrophils and monocytes was significantly changed. Adhesion of isolated monocytes to endothelial cells was enhanced after infusion of SO and reduced by FO, however, no difference of infusion on an array of surface adhesion molecules was detected. In neutrophils and monocytes, LPS-elicited generation of pro-inflammatory cytokines increased in the SO and decreased in the FO group. LPS inhalation in volunteers evoked an increase in neutrophils in BAL fluids, which decreased faster in the FO group. While TNF-α in the BAL was increased in the SO group, IL-8 decreased faster in the FO group. In the murine model of lung injury, effects of FO similar to the volunteer group observed in wild-type mice were abrogated in ChemR23 knockout mice.

CONCLUSIONS

After infusion of conventional lipid emulsions, leukocytes exhibited increased adhesive and pro-inflammatory features. In contrast, FO-based lipid emulsions reduced monocyte adhesion, decreased pro-inflammatory cytokines, and neutrophil recruitment into the alveolar space possibly mediated by ChemR23-signaling. Lipid emulsions thus exert differential effects in human volunteers and mice in vivo.

TRIAL REGISTRATION

DRKS00006131 at the German Clinical Trial Registry, 2014/05/14.

Biopsy-induced inflammatory conditions improve endometrial receptivity: the mechanism of action

A decade ago, we first reported that endometrial biopsy significantly improves the success of pregnancy in IVF patients with recurrent implantation failure, an observation that was later confirmed by others. Recently, we have demonstrated that this treatment elevated the levels of endometrial pro-inflammatory cytokines and increased the abundance of macrophages (Mac) and dendritic cells (DCs). We therefore hypothesised that the biopsy-related successful pregnancy is secondary to an inflammatory response, and aimed at deciphering its mechanism of action. Supporting our hypothesis, we found that the pro-inflammatory TNFα stimulated primary endometrial stromal cells to express cytokines that attracted monocytes and induced their differentiation into DCs. These monocyte-derived DCs stimulated endometrial epithelial cells to express the adhesive molecule SPP1 (osteopontin (OPN)) and its receptors ITGB3 and CD44, whereas MUC16, which interferes with adhesion, was downregulated. Other implantation-associated genes, such as CHST2, CCL4 (MIP1B) and GROA, were upregulated by monocyte-derived Mac. These findings suggest that uterine receptivity is mediated by the expression of molecules associated with inflammation. Such an inflammatory milieu is not generated in some IVF patients with recurrent implantation failure in the absence of local injury provoked by the biopsy treatment.

Monocyte chemoattractant protein 1-mediated migration of mesenchymal stem cells is a source of intimal hyperplasia

OBJECTIVE

Intimal hyperplasia is considered to be a healing response and is a major cause of vessel narrowing after injury, where migration of vascular progenitor cells contributes to pathological events, including transplant arteriosclerosis.

APPROACH AND RESULTS

In this study, we used a rat aortic-allograft model to identify the predominant cell types associated with transplant arteriosclerosis and to identify factors important in their recruitment into the graft. Transplantation of labeled adventitial tissues allowed us to identify the adventitia as a major source of cells migrating to the intima. RNA microarrays revealed a potential role for monocyte chemoattractant protein 1 (MCP-1), stromal cell-derived factor 1, regulated on activation, normal T cell expressed and secreted, and interferon-inducible protein 10 in the induced vasculopathy. MCP-1 induced migration of adventitial fibroblast cells. CCR2, the receptor for MCP-1, was coexpressed with CD90, CD44, NG2, or sca-1 on mesenchymal stem cells. In vivo experiments using MCP-1-deficient and CCR2-deficient mice confirmed an important role of MCP-1 in the formation of intimal hyperplasia in a mouse model of vascular injury.

CONCLUSIONS

The adventitia is a potentially important cellular source that contributes to intimal hyperplasia, and MCP-1 is a potent chemokine for the recruitment of adventitial vascular progenitor cells to intimal lesions.

Pathogenic arterial remodeling: the good and bad of microRNAs

A number of cardiovascular diseases, such as restenosis, aneurysm, and atherosclerosis, lead to vascular remodeling associated with complex adaptive reactions of different cell populations. These reactions include growth of smooth muscle cells, proliferation of endothelial cells, and the inflammatory response of macrophages. MicroRNAs (miRNAs), a class of short RNAs, play key roles in various biological processes and in the development of human disease by post-transcriptional regulation of gene expression. Here, we review the molecular mechanisms of a subset of miRNAs involved in vascular remodeling, including miR-143/145, miR-221/222, miR-126, miR-21, and miR-155. Some of these miRNAs, such as miR-143/145 and miR-126, have been shown to be protective during vascular remodeling, whereas others, such as miR-21, may promote the cellular response that leads to neointima formation. The increasing knowledge regarding the roles of miRNAs in vascular remodeling opens novel avenues for the treatment of various cardiovascular diseases. However, more in vivo studies on the functional roles of these miRNAs are required in the future.

Targeted anti-inflammatory systemic therapy for restenosis: the Biorest Liposomal Alendronate with Stenting sTudy (BLAST)-a double blind, randomized clinical trial

BACKGROUND

Activation of systemic innate immunity is critical in the chain of events leading to restenosis. LABR-312 is a novel compound that transiently modulates circulating monocytes, reducing accumulation of these cells at vascular injury sites and around stent struts. The purpose of the study was to examine the safety and efficacy of a single intravenous bolus of LABR-312 in reducing restenosis in patients treated for coronary narrowing. Patient response was examined in light of differential inflammatory states as evidenced by baseline circulating monocyte levels, diabetes mellitus, and acute coronary syndrome.

METHODS

BLAST is a Phase II prospective, randomized, multicenter, double-blind, placebo-controlled trial that assessed the safety and efficacy of LABR-312. Patients were randomized to receive LABR-312 at 2 dose levels or placebo as an intravenous infusion during percutaneous coronary intervention and bare metal stent implantation. The primary end point was mean angiographic in-stent late loss at 6 months.

RESULTS

Patients (N = 225) were enrolled at 12 centers. There were no safety concerns associated with the study drug. For the overall cohort, there were no differences between the groups in the primary efficacy end point (in-stent late loss of 0.86 ± 0.60 mm, 0.83 ± 0.57 mm, and 0.81 ± 0.68 mm for the placebo, low-dose, and high-dose group, respectively; P = not significant for all comparisons). In the prespecified subgroups of patients with a baseline proinflammatory state, patients with diabetes mellitus, and patients with high baseline monocyte count, there was a significant treatment effect.

CONCLUSIONS

Intravenous administration of LABR-312 to patients undergoing percutaneous coronary intervention is safe and effectively modulates monocyte behavior. The average late loss did not differ between the treatment and placebo groups. However, in the inflammatory patient group with baseline monocyte count higher than the median value, there was a significant reduction in late loss with LABR-312.

An assay to quantify chemotactic properties of degradation products from extracellular matrix

The endogenous chemotaxis of cells toward sites of tissue injury and/or biomaterial implantation is an important component of the host response. Implanted biomaterials capable of recruiting host stem/progenitor cells to a site of interest may obviate challenges associated with cell transplantation. An assay for the identification and quantification of chemotaxis induced by surgically placed biologic scaffolds composed of extracellular matrix is described herein.

Platelet IκB kinase-β deficiency increases mouse arterial neointima formation via delayed glycoprotein Ibα shedding

OBJECTIVE

On the luminal surface of injured arteries, platelet activation and leukocyte-platelet interactions are critical for the initiation and progression of arterial restenosis. The transcription factor nuclear factor-κB is a critical molecule in platelet activation. Here, we investigated the role of the platelet nuclear factor-κB pathway in forming arterial neointima after arterial injury.

METHODS AND RESULTS

We performed carotid artery wire injuries in low-density lipoprotein receptor-deficient (LDLR(-/-)) mice with a platelet-specific deletion of IκB kinase-β (IKKβ) (IKKβ(fl/fl)/PF4(cre)/LDLR(-/-)) and in control mice (IKKβ(fl/fl)/LDLR(-/-)). The size of the arterial neointima was 61% larger in the IKKβ(fl/fl)/PF4(cre)/LDLR(-/-) mice compared with the littermate control IKKβ(fl/fl)/LDLR(-/-) mice. Compared with the control mice, the IKKβ(fl/fl)/PF4(cre)/LDLR(-/-) mice exhibited more leukocyte adhesion at the injured area. The extent of glycoprotein Ibα shedding after platelet activation was compromised in the IKKβ-deficient platelets. This effect was associated with a low level of the active form of A Disintegrin And Metalloproteinase 17, the key enzyme involved in mediating glycoprotein Ibα shedding in activated IKKβ-deficient platelets.

CONCLUSIONS

Platelet IKKβ deficiency increases the formation of injury-induced arterial neointima formation. Thus, nuclear factor-κB-related inhibitors should be carefully evaluated for use in patients after an arterial intervention.

Evaluation of the potentials of autologous blood injection for healing in diabetic foot ulcers

Healing is a complex multifactorial process, hence it is not easy to be studied accurately. In this paper we tried to demonstrate the potentials of application of autologous blood by injection into the raw areas and ulcers of three diabetic patients using their blood as an alternative to synthesized and cultured stem cells or growth factors. It was found that a natural easily obtained blood can be used to enrich the media of the wound. Also it was applicable in relation to its cost-effectiveness as well as availability. The healing process was accelerated in the injected side more than the non-injected one.

Smooth muscle-specific expression of calcium-independent phospholipase A2β (iPLA2β) participates in the initiation and early progression of vascular inflammation and neointima formation

Whether group VIA phospholipase A(2) (iPLA(2)β) is involved in vascular inflammation and neointima formation is largely unknown. Here, we report that iPLA(2)β expression increases in the vascular tunica media upon carotid artery ligation and that neointima formation is suppressed by genetic deletion of iPLA(2)β or by inhibiting its activity or expression via perivascular delivery of bromoenol lactone or of antisense oligonucleotides, respectively. To investigate whether smooth muscle-specific iPLA(2)β is involved in neointima formation, we generated transgenic mice in which iPLA(2)β is expressed specifically in smooth muscle cells and demonstrate that smooth muscle-specific expression of iPLA(2)β exacerbates ligation-induced neointima formation and enhanced both production of proinflammatory cytokines and vascular infiltration by macrophages. With cultured vascular smooth muscle cell, angiotensin II, arachidonic acid, and TNF-α markedly induce increased expression of IL-6 and TNF-α mRNAs, all of which were suppressed by inhibiting iPLA(2)β activity or expression with bromoenol lactone, antisense oligonucleotides, and genetic deletion, respectively. Similar suppression also results from genetic deletion of 12/15-lipoxygenase or inhibiting its activity with nordihydroguaiaretic acid or luteolin. Expression of iPLA(2)β protein in cultured vascular smooth muscle cells was found to depend on the phenotypic state and to rise upon incubation with TNF-α. Our studies thus illustrate that smooth muscle cell-specific iPLA(2)β participates in the initiation and early progression of vascular inflammation and neointima formation and suggest that iPLA(2)β may represent a novel therapeutic target for preventing cardiovascular diseases.

The role of microRNAs in arterial remodelling

Adaptive alterations of the vessel wall architecture, called vascular remodelling, can be found in arterial hypertension, during the formation of aneurysms, in restenosis after vascular interventions, and in atherosclerosis. MicroRNAs (miR) critically affect the main cellular players in arterial remodelling and may either promote or inhibit the structural changes in the vessel wall. They regulate the phenotype of smooth muscle cells (SMCs) and control the inflammatory response in endothelial cells and macrophages. In SMCs, different sets of miRs induce either a synthetic or contractile phenotype, respectively. The conversion into a synthetic SMC phenotype is a crucial event in arterial remodelling. Therefore, reprogramming of the SMC phenotype by miR targeting can modulate the remodelling process. Furthermore, the effects of stimuli that induce remodelling, such as shear stress, angiotensin II, oxidised low-density lipoprotein, or apoptosis, on endothelial cells are mediated by miRs. The endothelial cell-specific miR-126, for example, is transferred in microvesicles from apoptotic endothelial cells and plays a protective role in atherogenesis. The inflammatory response of the innate immune system, especially through macrophages, promotes arterial remodelling. miR-155 induces the expression of inflammatory cytokines, whereas miR-146a and miR-147 are involved in the resolution phase of inflammation. However, in vivo data on the role of miRs in vascular remodelling are still scarce, which are required to test the therapeutic potential of the available, highly effective miR inhibitors.

The vascular repair process after injury of the carotid artery is regulated by IL-1RI and MyD88 signalling

AIM

The aim of this study was to determine whether innate immune signalling influences the vascular repair process in response to mechanical injury of arteries in mice.

METHODS AND RESULTS

A non-obstructive collar was introduced around the carotid artery of MyD88-deficient mice, and neointima formation was compared with that observed in MyD88-competent mice. MyD88-deficient mice are characterized by impaired signal transduction from interleukin (IL)-1/IL-18 receptors and most Toll-like receptors (TLRs). The vascular response to injury was severely impaired in MyD88-deficient mice as neointima formation was not different from sham-operated mice, whereas MyD88-competent mice displayed robust neointima formation. Furthermore, infiltration of CD68-positive leucocytes was dependent on MyD88. During the early response to injury, 3 days after collar placement, a transient increase in the expression of TLR4 on vascular smooth muscle cells was observed. To determine the relative importance of IL-1 receptor and TLR4 activation in the vascular response to injury, mice were injected with blocking antibodies to these receptors prior to the collar placement. Neointima formation was reduced by 80% in mice administered IL-1RI blocking antibodies compared with mice given a control antibody, whereas administration of TLR4 blocking antibodies was without effect.

CONCLUSION

These results show that inhibition of MyD88- or IL-1 receptor signalling reduces neointima formation in response to vascular injury and could offer therapeutic options for reducing clinical complications of excessive smooth muscle cell proliferation, such as that observed in in-stent restenosis.

VCAM-1 siRNA reduces neointimal formation after surgical mechanical injury of the rat carotid artery

OBJECTIVE

Restenosis is one of several complications following carotid endarterectomy (CEA). The pathogenesis of restenosis may be related to postsurgery inflammation and leukocyte recruitment mediated by cellular adhesion molecules. In this study, we examine the role of vascular cell adhesion molecule-1 (VCAM-1) in carotid neointimal hyperplasia following carotid surgical mechanical de-endothelialization (CSMDE) in a rat model of CEA.

METHODS

The inhibition of siRNA on VCAM-1 protein expression was determined by using the methods of immunostaining and Western blot. Ultrasound imaging and morphometric analysis were applied to measure the degree of CSMDE-induced carotid artery neointimal hyperplasia of rats.

RESULTS

We found that a lentivirus-based construct expressing a small interfering RNA (siRNA) against VCAM-1 could effectively (P < .05, n = 10 per group) reduce VCAM-1 protein expression in the carotid arteries of rats undergoing CSMDE (CSMDE+RNAi: 135.0 +/- 27.6%) when compared that of CSMDE with scrambled siRNA (CSMDE+CON: 182.7 +/- 36.4%). Doppler ultrasonography revealed that CSMDE+RNAi was accompanied by a significant reduction in the extent of stenosis demonstrated by increased blood velocity (665.85 +/- 48.37 mm/s) and linear diameter (0.59 +/- 0.77 mm) compared to CSMDE+CON (46.72 +/- 28.67 mm/s with undetectable linear diameter, P < .05, n = 10 per group). In addition, morphometric analysis of hematoxylin and eosin (HE)-stained sections indicated that the intima (innermost layer of media at lesion site)/media area ratio (I/M) was significantly increased (P < .05, n = 10 per group) both in the CSMDE (3.99 +/- 0.65) and CSMDE+CON (4.33 +/- 0.59) groups compared with the SHAM group (0.35 +/- 0.13). However, CSMDE+RNAi resulted in a significant (P < .05, n = 10 per group) decrease in the I/M ratio (1.79 +/- 0.43) compared to CSMDE+CON, whereas there were no significant differences in the total arterial area and medial areas among the groups.

CONCLUSION

These results suggest that perivascular events mediated by VCAM-1 are likely to play an important role in the pathogenesis of carotid artery neointimal hyperplasia in rats after CSMDE.

Delayed wound healing in elderly people

Our ability to heal wounds deteriorates with age, leading in many cases to a complete lack of repair and development of a chronic wound. Moreover, as the elderly population continues to grow the prevalence of non-healing chronic wounds is escalating. Cutaneous wound repair occurs through a combination of overlapping phases, including an initial inflammatory response, a proliferative phase and a final remodelling phase. In elderly subjects the inflammatory response is delayed, macrophage and fibroblast function compromised, angiogenesis reduced and re-epithelialization inhibited. Whilst a large body of historic research describes the defective processes that lead to delayed healing, only recently have the molecular mechanisms by which these defects arise begun to be elucidated. Current therapies available for treatment of chronic wounds in elderly people are surprisingly limited and generally ineffective. Thus there is an urgent need to develop new therapeutic strategies based on these recent molecular and cellular insights.

Macrophage migration inhibitory factor: a noncanonical chemokine important in atherosclerosis

In the recent years, atherogenesis has increasingly been linked to inflammatory processes in the injured vessel wall. Recruitment and arrest of monocytes, T cells, and neutrophils via the concerted actions of multiple chemokines and their chemokine receptors have been the subject of intense research and are being appreciated as key events underlying atherosclerotic lesion formation and progression. The evolutionary conserved cytokine macrophage migration inhibitory factor (MIF) exhibits prominent proinflammatory and proatherogenic functions, and the latest findings on its chemotactic and chemokine-like properties imply MIF as a crucial drug target for the treatment of inflammatory diseases. In this review, the role of MIF in atherosclerosis and injury-induced neointima formation is discussed. We place an emphasis on its proinflammatory and chemokine-like functions in the context of underlying extra- and intracellular signaling mechanisms. These findings clearly distinguish MIF from other cytokines in atherosclerosis and justify the intensive search for inhibitors targeting MIF in the treatment of inflammatory diseases, including advanced atherosclerosis.

Interplay of CCR2 signaling and local shear force determines vein graft neointimal hyperplasia in vivo

Leukocytes play a central role in vein graft neointimal hyperplasia, which is significantly augmented under low shear conditions. The current concept is that shear force regulates leukocyte adhesion predominately through up-regulation of chemokines and growth factors within the graft wall. Using rabbit and murine vein graft models, we demonstrate that CC chemokine receptor 2/monocyte chemoattractant protein-1 mediated monocyte recruitment and a low shear environment act synergistically to augment neointimal hyperplasia development and removal of either of the conditions leads to a significant reduction in neointimal thickening. We propose a novel concept that the shear stress response element phenotypically stems from the complex interplay of the biological and physical microenvironments.

Importance of junctional adhesion molecule-C for neointimal hyperplasia and monocyte recruitment in atherosclerosis-prone mice-brief report

OBJECTIVE

Although junctional adhesion molecule (JAM)-C has been implicated in the control of inflammatory leukocyte recruitment, its role in neointima formation after arterial injury has not been elucidated.

METHODS AND RESULTS

In apolipoprotein E-deficient (Apoe(-/-)) mice fed an atherogenic diet, antibody blockade of JAM-C significantly reduced neointimal hyperplasia after wire injury of carotid arteries without altering medial area and decreased neointimal macrophage but not smooth muscle cell (SMC) content. An increased expression of JAM-C was detected in colocalization with luminal SMCs 1 day after injury and neointimal SMCs after 3 weeks. Blocking JAM-C inhibited monocytic cell arrest and leukocyte adhesion to carotid arteries perfused ex vivo and in vivo. Furthermore, monocyte adhesion to activated coronary artery SMCs under flow conditions in vitro was diminished by blocking JAM-C.

CONCLUSIONS

Our data provide the first evidence for a crucial role of JAM-C in accelerated lesion formation and leukocyte recruitment in atherosclerosis-prone mice.

Macrophage migration inhibitory factor in cardiovascular disease

The highly conserved and archetypical yet atypical cytokine macrophage migration inhibitory factor (MIF) fulfills pleiotropic immune functions in many acute and chronic inflammatory diseases. Recent evidence has emerged from both expression and functional studies to implicate MIF in various aspects of cardiovascular disease. The present review is aimed at providing a synopsis of the involvement of MIF in the inflammatory pathogenesis of atherosclerosis and its consequences, namely unstable plaque formation, remodeling after arterial injury, aneurysm formation, myocardial infarction, or ischemia-reperfusion injury. In addition, other forms of myocardial dysfunction and inflammation and the role of MIF in angiogenesis are reviewed. The functional data are reconciled with recent progress in the identification of heptahelical (CXC chemokine) receptors for MIF, its prototypic role as their noncanonical ligand, and its signal transduction profile operative in atherogenic and inflammatory recruitment of mononuclear cells and in the oxidative damage and apoptosis of cardiomyocytes. Its unique features and functions clearly distinguish MIF from other cytokines implicated in atherogenesis and make it a prime target for achieving therapeutic regression of atherosclerosis. The potential of targeting or exploiting MIF for therapeutic strategies or as a diagnostic marker in the management of cardiovascular diseases or disorders is scrutinized.

Nitric oxide-releasing/generating polymers for the development of implantable chemical sensors with enhanced biocompatibility

The development of reliable in vivo chemical sensors for real-time clinical monitoring of blood gases, electrolytes, glucose, etc. in critically ill and diabetic patients remains a great challenge owing to inherent biocompatibility problems that can cause errant analytical results upon sensor implantation (e.g., cell adhesion, thrombosis, inflammation). Nitric oxide (NO) is a well-known inhibitor of platelet activation and adhesion, and also a potent inhibitor of smooth muscle cell proliferation. In addition, NO mediates inflammatory response and promotes angiogenesis. Polymers that release or generate NO at their surfaces have been shown to exhibit greatly enhanced thromboresistance in vivo when in contact with flowing blood, as well as reduce inflammatory response when placed subcutaneously, and thus have the potential to improve the biocompatibility of implanted chemical sensors. Locally elevated NO levels at the surface of implanted devices can be achieved by using polymers that incorporate NO donor species that can decompose and release NO spontaneously when in contact with physiological fluids, or NO-generating polymers that possess an immobilized catalyst that decompose endogenous S-nitrosothiols to generate NO in situ. The potential use of such NO-releasing/generating materials for preparing in vivo sensors implanted either intravascularly or subcutaneously, is examined in this review.

Chemokine-like functions of MIF in atherosclerosis

The cytokine macrophage migration inhibitory factor (MIF) is a unique pro-inflammatory regulator of many acute and chronic inflammatory diseases. In the pathogenesis of atherosclerosis, chronic inflammation of the arterial wall characterized by chemokine-mediated influx of leukocytes plays a central role. The contribution of MIF to atherosclerotic vascular disease has come into focus of many studies in recent years. MIF is highly expressed in macrophages and endothelial cells of different types of atherosclerotic plaques, and functional studies established the contribution of MIF to lesion progression and plaque inflammation. This proatherogenic effect may partly be explained by the finding that MIF regulates inflammatory cell recruitment to lesion areas. Similar to chemokines, MIF induces integrin-dependent arrest and transmigration of monocytes and T cells. These chemokine-like functions are mediated through interaction of MIF with the chemokine receptors CXCR2 and CXCR4 as a non-canonical ligand. In atherogenic monocyte recruitment, MIF-induced monocyte adhesion involves CD74 and CXCR2, which form a signaling receptor complex. In addition to lesion progression, MIF has been implicated in plaque destabilization, since MIF is predominantly expressed in vulnerable plaques and can induce collagen-degrading matrix metalloproteinases. The latter could be a relevant mechanism in atherosclerotic abdominal aneurysm formation, where MIF expression is correlated with aneurysmal expansion. In summary, MIF has been identified as an important regulator of atherosclerotic vascular disease with exceptional chemokine-like functions. Detailed analysis of the interaction of MIF with its receptors could provide valuable information for drug development for the anti-inflammatory treatment of established and unstable atherosclerosis.

Nuclear translocation of p65 NF-kappaB is sufficient for VCAM-1, but not ICAM-1, expression in TNF-stimulated smooth muscle cells: Differential requirement for PARP-1 expression and interaction

Although nuclear translocation of NF-kappaB and subsequent binding to promoters of ICAM-1 and VCAM-1 have been shown to be decisive for their expression, a number of discrepancies in the expression patterns of these adhesion molecules have been reported in both cell culture systems and disease settings, including atherosclerosis, asthma, and autoimmune diseases. Here we show that while p65 NF-kappaB nuclear translocation in TNF-treated smooth muscle cells (SMCs) was sufficient for the expression of VCAM-1, expression of ICAM-1 showed a critical requirement for PARP-1. I-kappaBalpha phosphorylation and subsequent degradation were virtually identical in both TNF-treated wild-type and PARP-1-/- SMCs. VCAM-1 expression in TNF-treated PARP-1-/- SMCs was completely inhibited by the NF-kappaB inhibitor, pyrrolidine dithiocarbamate, confirming that VCAM-1 expression was indeed NF-kappaB-dependent. The expression of both VCAM-1 and ICAM-1 was associated with a transient interaction between PARP-1 and p65 NF-kappaB when examined in the fibroblastic cell line, COS-7, and in the airway epithelial cell line, A549. Such interactions were confirmed using florescence resonance energy transfer analysis. Protein acetylation activity, mediated by p300/CBP, was required for both VCAM-1 and ICAM-1 expression in TNF-treated SMCs; however, the interaction of PARP-1 with p300/CBP was dispensable for VCAM-1 expression. These findings indicate that p65 NF-kappaB nuclear translocation may be sufficient for certain genes (e.g., VCAM-1) while insufficient for others (e.g., ICAM-1), thus providing a novel insight into the role of NF-kappaB in driving target gene expression. Furthermore, the data suggest a differential requirement for PARP-1 expression in inflammatory processes.

Regulation of endothelial cell proliferation by primary monocytes

OBJECTIVE

Endothelial cell-monocyte cross talk is essential for vascular repair. Monocytes colocalize with endothelial cells forming a complex set of interactions distinct from the growth promoting cytokines secreted by differentiated macrophages. In the present work we examined the growth regulation and in vitro wound repair early after binding of monocytes to endothelial cells.

METHODS AND RESULTS

After direct contact with primary unactivated monocytes, endothelial cells enter S-phase through a mechanism mediated in part by contact-dependent activation of endothelial Met as demonstrated by siRNA silencing of Met, neutralizing antibodies for hepatocyte growth factor and Met as well as by specific inhibition of Met by the Met kinase inhibitor SU11274. Monocytes robustly promote endothelial cell proliferation and migration into a wounded endothelial monolayer. Monocyte-induced endothelial cell proliferation is accompanied by prolonged extracellular signal-regulated kinase (ERK) activation and is inhibited by the specific ERK inhibitor PD98059. The contact-mediated effect of monocytes is specific to endothelial cells and does not occur with vascular smooth muscle cells. Interestingly, although Flk1 is activated by monocytes, the proliferative effect of monocytes reported here is minimally mediated by Flk1 signaling.

CONCLUSIONS

These results suggest that the early interaction between endothelial cells and monocytes is critical for the regulation of endothelial cell proliferation. This complex regulation is mediated in part by contact-dependent Met and ERK phosphorylation. These findings add to a broader set of leukocyte-endothelial contact mediated signals that together regulate endothelial function in health and disease.

Expression of HIF-1alpha in injured arteries controls SDF-1alpha mediated neointima formation in apolipoprotein E deficient mice

OBJECTIVE

Hypoxia-inducible factor (HIF)-1alpha is the regulatory subunit of a transcriptional complex, which controls the recruitment of multipotent progenitor cells and tissue repair in ischemic tissue by inducing stromal cell-derived factor (SDF)-1alpha expression. Because HIF-1alpha can be activated under normoxic conditions in smooth muscle cells (SMCs) by platelet products, we investigated the role of HIF-1alpha in SDF-1alpha-mediated neointima formation after vascular injury.

METHODS AND RESULTS

Wire-induced injury of the left carotid artery was performed in apolipoprotein E-deficient mice. HIF-1alpha expression was increased in the media as early as 1 day after injury, predominantly in SMCs. Nuclear translocation of HIF-1alpha and colocalization with SDF-1alpha was detected in neointimal cells after 2 weeks. HIF-1alpha mRNA expression was induced at 6 hours after injury as determined by real-time RT-PCR. Inhibition of HIF-1alpha expression by local application of HIF-1alpha-siRNA reduced the neointimal area by 49% and significantly decreased the neointimal SMCs content compared with control-siRNA. HIF-1alpha and SDF-1alpha expression were clearly diminished in neointimal cells of HIF-1alpha-siRNA treated arteries.

CONCLUSIONS

HIF-1alpha expression is directly involved in neointimal formation after vascular injury and mediates the upregulation of SDF-1alpha, which may affect the stem cell-based repair of injured arteries.

Cost-effectiveness of antiplatelet therapy for secondary stroke prevention

Antiplatelet therapy is recommended over anticoagulants for the secondary prevention of vascular death in patients with noncardioembolic ischemic stroke or transient ischemic attack based upon the 2006 American Heart Association/American Stroke Association guidelines for the prevention of stroke and the National Stroke Association guidelines for the management of transient ischemic attack. Aspirin is commonly used as a cornerstone antiplatelet agent considering its mild but definite prevention benefit and low costs. Other antiplatelet strategies that are currently recommended include extended-release dipyridamole plus low-dose aspirin (Aggrenox((R)), Asasantin((R))) and clopidogrel. In this brief review, we evaluate the cost-effectiveness of antiplatelet agents for secondary stroke prevention to better understand the socioeconomical value of the recommended agents.

Temporal evolution of gene expression in rat carotid artery following balloon angioplasty

The success of vascular intervention including angioplasty, stenting, and arterial bypass remains limited by negative remodeling resulted in lumen restenosis. This study was to characterize the global transcription profile reflecting concurrent events along arterial remodeling and neointima formation in a rat carotid artery balloon-injury model. Expression profiling of injured and control common carotid arteries on days 4, 7, 14 post-injury that mark the major pathohistological progression stages of neointimal formation were recorded on high-density oligonucleotide arrays. A subset of genes from microarray-based data was further studied using quantitative real time RT-PCR and in situ hybridization with sequential arterial samples from days 1 to 28 post-injury. The gene-encoded proteins were validated with Western blot. Besides temporal induction of a large cluster of genes over-represented by cell proliferation and macromolecule metabolism gene ontology categories, a fast-evolving inflammation could be demonstrated by the induction of Tgfb and other anti-inflammatory genes (e.g., C1qtnf3 (C1q and tumor necrosis factor related protein 3 (predicted))) and a shift from type 1 to 2 helper T cell response. The most significant signature of the induced neointimal profile is enrichment of genes functionally related to angiogenesis and extracellular matrix (ECM) remodeling (e.g., Spp1 (secreted phosphoprotein 1), CD44 (CD44 antigen), and Cxcl12 (chemokine (C-X-C motif) ligand 12 (stromal cell-derived factor 1)). Some of the genes represent stress-responsive mesenchymal stromal cell cytokines. This study highlighted mesenchymal stromal cell cytokines-driven inflammatory extracellular matrix remodeling, as target processes for potential clinical therapeutic intervention.