Macrophage Accumulation In Plaques Research Articles

The Role of the Association Between Serum C-Reactive Protein Levels and Coronary Plaque Macrophage Accumulation in Predicting Clinical Events - Results from the CLIMA Registry.

The present investigation aims to study the interaction between systemic and intra-plaque inflammation in predicting cardiac events. We investigated C-reactive protein (CRP) levels as well as plaque inflammation with optical coherence tomography (OCT)-detected macrophages in the CLIMA study. 689 patients had admission CRP serum values reported, and high CRP values were defined as ≥ 2mg/dl. The main study endpoint was a composite of cardiac death, myocardial infarction, and/or target vessel revascularization at 1-year follow-up. At multivariate Cox regression analysis, a large (hazard ratio [HR] 2.27, 95% confidence interval [CI] 1.2-4.3; p = 0.013) and superficial (HR 2.78, 95%CI 1.5-5.1; p = 0.001) macrophage arc was predicted of the main composite endpoint in patients with high CRP levels. Patients with large/superficial macrophage accumulation and low CRP levels were not at higher risk of adverse events. The presence of high CRP levels and large/superficial macrophage accumulation at OCT analysis identified patients at higher risk of clinical events.

Pharmacological Targeting of the CCL2/CCR2 Axis for Atheroprotection: A Meta-Analysis of Preclinical Studies.

The CCL2 (CC-chemokine ligand 2)/CCR2 (CC-chemokine receptor 2) axis governs monocyte recruitment to atherosclerotic lesions. Genetic and epidemiological studies show strong associations of CCL2 levels with atherosclerotic disease. Still, experimental studies testing pharmacological inhibition of CCL2 or CCR2 in atheroprone mice apply widely different approaches and report variable results, thus halting clinical translation. We systematically searched the literature for studies employing pharmacological CCL2/CCR2 blockade in atheroprone mice and meta-analyzed their effects on lesion size and morphology. In a meta-analysis of 14 studies testing 11 different agents, CCL2/CCR2 blockade attenuated atherosclerotic lesion size in the aortic root or arch (g=-0.75 [-1.17 to -0.32], P=6×10-4; N=171/171 mice in experimental/control group), the carotid (g=-2.39 [-4.23 to -0.55], P=0.01; N=24/25), and the femoral artery (g=-2.38 [-3.50 to -1.26], P=3×10-5; N=10/10). Furthermore, CCL2/CCR2 inhibition reduced intralesional macrophage accumulation and increased smooth muscle cell content and collagen deposition. The effects of CCL2/CCR2 inhibition on lesion size correlated with reductions in plaque macrophage accumulation, in accord with a prominent role of CCL2/CCR2 signaling in monocyte recruitment. Subgroup analyses showed comparable efficacy of different CCL2- and CCR2-inhibitors in reducing lesion size and intralesional macrophages. The quality assessment revealed high risk of detection bias due to lack of blinding during outcome assessment, as well as evidence of attrition and reporting bias. Preclinical evidence suggests that pharmacological targeting of CCL2 or CCR2 might lower atherosclerotic lesion burden, but the majority of existing studies suffer major quality issues that highlight the need for additional high-quality research.

STING, a cytosolic DNA sensor, plays a critical role in atherogenesis: a link between innate immunity and chronic inflammation caused by lifestyle-related diseases.

Lifestyle-related diseases promote atherosclerosis, a chronic inflammatory disease; however, the molecular mechanism remains largely unknown. Endogenous DNA fragments released under over-nutrient condition provoke sterile inflammation through the recognition by DNA sensors. Here, we investigated the role of stimulator of interferon genes (STING), a cytosolic DNA sensor, in atherogenesis. Apolipoprotein E-deficient (Apoe-/-) mice fed a western-type diet (WTD), a hypercholesterolaemic mouse model, showed higher STING expression and markers for DNA damage such as γH2AX, p53, and single-stranded DNA (ssDNA) accumulation in macrophages in the aorta compared with wild-type (WT) mice. The level of cGAMP, a STING agonist, in the aorta was higher in Apoe-/- mice. Genetic deletion of Sting in Apoe-/- mice reduced atherosclerotic lesions in the aortic arch, lipid, and macrophage accumulation in plaques, and inflammatory molecule expression in the aorta compared with the control. Pharmacological blockade of STING using a specific inhibitor, C-176, ameliorated atherogenesis in Apoe-/- mice. In contrast, bone marrow-specific STING expression in Apoe-/- mice stimulated atherogenesis. Expression or deletion of STING did not affect metabolic parameters and blood pressure. In vitro studies revealed that STING activation by cGAMP or mitochondrial DNA accelerated inflammatory molecule expression (e.g. TNF-α or IFN-β) in mouse and human macrophages. Activation of nuclear factor-κB and TANK binding kinase 1 was involved in STING-associated vascular inflammation and macrophage activation. Furthermore, human atherosclerotic lesions in the carotid arteries expressed STING and cGAMP. Stimulator of interferon genes stimulates pro-inflammatory activation of macrophages, leading to the development of atherosclerosis. Stimulator of interferon genes signalling may serve as a potential therapeutic target for atherosclerosis.

Lactucopicrin Inhibits Cytoplasmic Dynein-Mediated NF-κB Activation in Inflammated Macrophages and Alleviates Atherogenesis in Apolipoprotein E-Deficient Mice.

Nuclear factor-κB (NF-κB) activation in macrophages aggravates atherosclerosis. Dietary plant secondary metabolites including sesquiterpene lactone lactucopicrin target multiple organs. This study is focused on the impact of lactucopicrin on NF-κB activation in inflammed macrophages and atherogenesis in a mouse model of atherosclerosis. In LPS-stimulated mouse bone marrow-derived macrophages, lactucopicrin inhibits NF-κB activation, and concomitantly represses the expression of IL-1β, IL-6, and tumor necrosis factor-alpha. This effect is not due to modulation of the inhibitor of NF-κB kinases (IKK) α/β/γ and NF-κB inhibitor α, and NF-κB/p65 DNA binding activity. Instead, the lactucopicrin effect is reliant on the inhibition of cytoplasmic dynein-mediated p65 transportation, a prerequisite step for p65 nuclear translocation. In high-fat diet-fed apolipoprotein E-deficient mice, lactucopicrin consumption dose-dependently reduces plaque area, inhibits plaque macrophage accumulation, attenuates plaque macrophage NF-κB activation, and reduces both plaque and serum inflammatory burden. However, lactucopicrin consumption does not affect the levels of serum lipids and anti-inflammatory cytokines (IL-4, IL-10, and transforming growth factor beta). Dietary lactucopicrin inhibits atherogenesis in mice likely by its anti-inflammatory property. These findings suggest that dietary supplementation with lactucopicrin is a promising strategy to inhibit atherosclerotic cardiovascular disease.

Monocytes, Macrophages, and Metabolic Disease in Atherosclerosis

Atherosclerotic cardiovascular disease (CVD) is a lipid-driven chronic inflammatory disease, in which macrophages are responsible for taking up these lipids and driving disease progression. Over the years, we and others have uncovered key pathways that regulate macrophage number/function and identified how metabolic disorders such as diabetes and obesity, which are common risk factors for CVD, exacerbate these pathways. This ultimately accelerates the progression of atherosclerosis and hinders atherosclerotic regression. In this review, we discuss the different types of macrophages, from monocyte-derived macrophages, local macrophage proliferation, to macrophage-like vascular smooth muscle cells, that contribute to atherosclerosis as well as myeloid-derived suppressor cells that may have anti-atherogenic effects. We will also discuss how diabetes and obesity influence plaque macrophage accumulation and monocyte production (myelopoiesis) to promote atherogenesis as well as an exciting therapeutic target, S100A8/A9, which mediates myelopoiesis in response to both diabetes and obesity, shown to be effective in reducing atherosclerosis in pre-clinical models of diabetes.

Abstract 17163: Nox4 Deletion Attenuates Age-Associated Vascular Inflammation and Atherosclerosis Burden in Hyperlipidemic Mice by Modulating Macrophage Phenotype

Introduction: Increased vascular reactive oxygen species (ROS) levels and chronic inflammation are hallmarks of vascular aging. We previously reported that expression of NOX4 NADPH oxidase increases with age in mouse and human arteries and correlates with inflammatory cytokine secretion and atherosclerotic lesion progression. Hypothesis: To determine whether NOX4 promotes atherosclerosis in aging, we assessed vascular inflammation and atherosclerosis burden in Nox4 -/- / Apoe -/- and Apoe -/- mice. Results: Aortic atherosclerotic lesion area was not different between 5-month old (young) Nox4 -/- / Apoe -/- and Apoe -/- mice fed a Western diet for 3 months. Lesion area increased significantly in 16-month old (aged) compared with young mice but was 51% lower in Nox 4 -/- / Apoe -/- versus Apoe -/- mice (n=12, P <0.0001). Immunofluorescence analysis of aorta transverse sections showed 30% lower ROS levels and significantly reduced expression of inflammatory cytokines - CCL2 and IL6 - in atherosclerotic lesions of aged Nox4 -/- / Apoe -/- versus Apoe -/- mice. Flow cytometry analysis of atherosclerotic aortas showed significantly higher number of CD11b + macrophages in the lesions of aged Apoe -/- versus Nox4 -/- /Apoe -/- mice. However, the number of M1 pro-inflammatory macrophages (CD38 + ) was not different, whereas percentage of M2 macrophages (Egr2 + ) was significantly higher in aged Nox4 -/- Apoe -/- versus Apoe -/- mice (46% vs. 33%, respectively). In addition, Nox4 deletion increased the ratio of M2/M1 macrophages in the atherosclerotic aortas from aged Apoe -/- mice (0.56 and 0.43 in Nox 4 -/- / Apoe -/- and Apoe -/- , respectively). Macrophages isolated from Nox4 -/- mice showed lower number of M1 cells after IFNγ+LPS treatment and higher number of M2 cells after IL4 treatment versus macrophages from the wild-type. Furthermore, wild-type macrophages showed significantly higher secreted IL1β levels after IFNγ+LPS treatment versus macrophages from Nox4 -/- mice. Conclusions: These data suggest that increased vascular NOX4 levels in aged Apoe -/- mice promote a proinflammatory environment, enhancing plaque macrophage accumulation and skewing polarization to M1 phenotype resulting in inflammasome activation and atherosclerotic lesion expansion.

Abstract 413: CD11c/CD18 Affinity Modulates Monocyte Inflammatory in Primary and Recurrent Myocardial Infarction

Several studies address the role of CD11c + monocytes in the exacerbation of atherosclerosis through the maintenance of macrophages, notably foam cells, however this cell type remains elusive in the context of human atherosclerosis. Intermediate monocytes (CD14+CD16+, Mon2) have a high degree of potential participation in atherosclerosis through the upregulation of membrane β2-integrin CD11c/CD18 expression that functionally orchestrates their recruitment to VCAM-1 activating VLA-4 leading to focal clustering and shear resistant arrest. Both Mon2 frequency and CD11c expression remain critical factors associated with the extent of coronary artery disease (CAD) related to persistent inflammation, plaque growth and destabilization, myocardial infarction and morbidity. Understanding dynamic alteration of Mon2 CD11c and its function in promoting macrophage accumulation in plaques that exacerbate and progress atherosclerotic disease progression toward myocardial infarction remains undetermined. In this study, we investigated the activation status of circulating Mon2 in patients experiencing non-ST myocardial infarction (NSTEMI) compared to those undergoing angiography in the cardiac clinic. Mon2 activation status and CD11c function was gauged using flow cytometry and real-time microfluidics using an Artery-on-a-Chip (A-Chip) device. Circulating Mon2 upregulated CD11c receptors to the greatest extent in patients experiencing myocardial infarct that increase with recurrence and lead to enhanced CD11c dependent capture on VCAM-1 relative to patients being treated in the cardiac clinic. Arrest on VCAM-1 under shear flow resulted in time-dependent phenotypic alteration including the loss of CD16 over 45 min and was dependent on atherosclerotic disease but independent of NSTEMI and involved CD11c outside-in signaling. A shift from a high to low affinity state of CD11c triggered the translocation of several activation and differentiation markers such as NfKB, and upregulation of MMP-9 associated with an M1 phenotype. CD11c receptor number and subsequent signaling provides a potential target for intervention of atherogenesis by altering Mon2 differentiation potential and inflammatory capacity.

Cardiovascular Immunotherapy and the Role of Imaging.

Despite significant advances in prevention and treatment, cardiovascular diseases (CVDs) remain the most common cause of death in the United States.1–3 In part, and compared with treatment developments in oncology, this is because of the lack of current generation CVD precision therapies.4–6 Most CVDs are caused by atherosclerosis, a disease process that causes thickening of the arterial wall because of inflammation and lipid accumulation, resulting in plaque formation.7,8 Macrophage dynamics plays a central role in atherosclerosis progression, vessel wall destabilization, and—as has been recently discovered—plaque aggravation because of myocardial infarction.9–11 Therefore, and despite current standardized treatments, ≈25% of patients who had myocardial infarction or stroke will experience secondary major adverse cardiovascular events, often more harmful than the primary event.12–14 To break this vicious cycle, innovative and tailored therapeutic strategies are needed. Various targeted immunotherapies that showed anticancer potential in in vitro screens also displayed in vivo potential in mouse models. Such proof-of-concept studies in validated syngeneic mouse tumor models not only provide information on in vivo efficacy but also disclose the targeted immunotherapies’ underlying mechanism of action and safety profile. However, immunotherapies’ high costs and the identification of amendable patients compromise clinical translation.15,16 Continued and focused efforts are needed to understand patient responsiveness and reduce high dropout rates in trials. A parallel effort focused on the development of novel imaging tools that can guide patient selection may offer a potential solution. Positron emission tomography (PET) can be used to trace immunotherapies. So-called immunoPET uses antibodies, developed for cancer treatment, that selectively recognize a specific epitope on target cells. The antibodies are labeled with radioactive isotopes, such as zirconium-89 or iodine-124, with relatively long decay half-lives of 3.27 and 4.18 days, respectively, to …

Abstract 162: Resident Aortic Intimal Mononuclear Phagocytes (MNPs) in the Promotion of Atherosclerosis

Atherosclerosis is an underlying cause of cardiovascular disease (CVD) and a leading cause of morbidity and mortality worldwide. Atherosclerosis promotes CVD through plaque formation, restricted blood flow, and thrombotic events. Macrophage accumulation in plaques, their uptake of cholesterol, and subsequent local death drive disease progression, however, there is growing appreciation for more diverse roles of myeloid cells during disease progression. Here, we focused on characterization of so-called vascular dendritic cells (DCs), which we refer to as aortic mononuclear phagocytes (MNP), that reside under the endothelium in plaque-prone areas. Using en face whole-mount confocal microscopy of aortas, we confirm a uniform resident CD11c+ CX3CR1+ MHCII+ MNP population, even in C57/BL6 mice resistant to atherosclerosis. We find aortic MNPs require M-CSF and Flt3 signaling for survival, but are independent of CCR2 and GM-CSF receptor signaling, making them a distinct myeloid population. They express macrophage-restricted genes LysM and CD64, but not dendritic cell specific genes zBTB46 or L-myc. Lineage-tracing analysis using CD115creER and Flt3cre reporter mice indicate that aortic MNPs likely differentiate from definitive hematopoiesis and not early yolk sac progenitors. Parabiosis experiments show that aortic MNPs are self-maintained independent of blood-born progenitors, failing to exchange with blood progenitors for up to 5 months. Aortic MNPs are different from either typical DCs or macrophages and instead appear to blend distinguishing features of each, more closely resembling macrophages. Using our characterization data, we hope to develop an inducible cell-tracking and a cell-depletion model to differentiate the function of aortic MNPs during the progression of atherosclerosis. Overall, we anticipate these functional analyses will reveal, for the first time, the role of resident aortic MNPs in atherosclerosis.

Platelet Transcriptional Profiling and Atherothrombosis

Platelets participate in events that immediately precede acute myocardial infarction. Because platelets lack nuclear DNA but retain megakaryocyte-derived mRNAs, the platelet transcriptome provides a novel window on gene expression preceding acute coronary events. We profiled platelet mRNA from patients with acute ST-segment–elevation myocardial infarction (STEMI, n=16) or stable coronary artery disease (n=44). The platelet transcriptomes were analyzed and single-gene models constructed to identify candidate genes with differential expression. We validated one candidate gene product by performing a prospective, nested case-control study (n=255 case-control pairs) among apparently healthy women to assess the risk of future cardiovascular events (nonfatal MI, nonfatal stroke, and cardiovascular death) associated with baseline plasma levels of the candidate protein. Platelets isolated from STEMI and coronary artery disease patients contained 54 differentially expressed transcripts. The strongest discriminators of STEMI in the microarrays were CD69 (odds ratio 6.2, P<0.001) and myeloid-related protein-14 (MRP-14 also known as S100A8/A9; odds ratio 3.3, P=0.002). In the validation study, the risk of a first cardiovascular event increased with each increasing quartile of MRP-8/14 (P trend <0.001) such that women with the highest levels had a 3.8-fold increase in risk of any vascular event (P<0.001). We evaluated vascular inflammation in wild-type and MRP-14-deficient (MRP-14-/-) mice that lack MRP-8/14 complexes with experimental arterial injury, vasculitis, or atherosclerosis. After femoral artery wire injury, MRP-14-/- mice had significant reductions in leukocyte accumulation, cellular proliferation, and neointimal formation compared with wild-type mice. In a cytokine-induced local Shwartzman-like reaction that produces thrombohemorrhagic vasculitis, MRP-14-/- mice had significant reductions in neutrophil accumulation, lesion severity, and hemorrhagic area. In response to high-fat feeding, mice doubly deficient in apolipoprotein E and MRP-8/14 complexes had attenuation in atherosclerotic lesion area and in macrophage accumulation in plaques compared with mice deficient in apolipoprotein E alone. These findings indicate that MRP-8/14 broadly regulates vascular inflammation and contributes to the biological response to vascular injury by promoting leukocyte recruitment. However, a causal role for MRP-14 in thrombosis has not been established and a viable molecular mechanism remains unknown. Here we show that time to thrombotic occlusion was prolonged markedly in MRP-14-/- mice. We observed that MRP-14 and MRP-8/14 are expressed in, and secreted by platelets, and that thrombus formation is reduced in whole blood from MRP-14-/-mice. Infusion of WT platelets or purified MRP-14 (or MRP-8/14) into MRP-14-/- mice shortened the carotid artery occlusion time, indicating that platelet-derived MRP-14 directly regulates thrombosis. Thus, a new pathway of inflammation and thrombosis involving MRP-14 is identified. MRP-14 represents a novel target for treating atherothrombotic disorders, including myocardial infarction and stroke. Disclosures:Simon:Cordis/J&J: Consultancy; Janssen/J&J: Consultancy; Medtronic Vascular: Consultancy; Merck: Consultancy; Medtronic Foundation: Research Funding.

Neuroimmune Guidance Cue Semaphorin 3E Is Expressed in Atherosclerotic Plaques and Regulates Macrophage Retention

The persistence of myeloid-derived cells in the artery wall is a characteristic of advanced atherosclerotic plaques. However, the mechanisms by which these cells are retained are poorly understood. Semaphorins, a class of neuronal guidance molecules, play a critical role in vascular patterning and development, and recent studies suggest that they may also have immunomodulatory functions. The present study evaluates the expression of Semaphorin 3E (Sema3E) in settings relevant to atherosclerosis and its contribution to macrophage accumulation in plaques. Immunofluorescence staining of Sema3E, and its receptor PlexinD1, demonstrated their expression in macrophages of advanced atherosclerotic lesions of Apoe(-/-) mice. Notably, in 2 different mouse models of atherosclerosis regression, Sema3E mRNA was highly downregulated in plaque macrophages, coincident with a reduction in plaque macrophage content and an enrichment in markers of reparative M2 macrophages. In vitro, Sema3E mRNA was highly expressed in inflammatory M1 macrophages and in macrophages treated with physiological drivers of plaque progression and inflammation, such as oxidized low-density lipoprotein and hypoxia. To explore mechanistically how Sema3E affects macrophage behavior, we treated macrophages with recombinant protein in the presence/absence of chemokines, including CCL19, a chemokine implicated in the egress of macrophages from atherosclerotic plaques. Sema3E blocked actin polymerization and macrophage migration stimulated by the chemokines, suggesting that it may immobilize these cells in the plaque. Sema3E is upregulated in macrophages of advanced plaques, is dynamically regulated by multiple atherosclerosis-relevant factors, and acts as a negative regulator of macrophage migration, which may promote macrophage retention and chronic inflammation in vivo.

High-Resolution Magnetic Resonance Imaging Enhanced With Superparamagnetic Nanoparticles Measures Macrophage Burden in Atherosclerosis

Macrophages contribute to the progression and acute complications of atherosclerosis. Macrophage imaging may serve as a biomarker to identify subclinical inflamed lesions, to predict future risk, and to aid in the assessment of novel therapies. To test the hypothesis that nanoparticle-enhanced, high-resolution magnetic resonance imaging (MRI) can measure plaque macrophage accumulation, we used 3-T MRI with a macrophage-targeted superparamagnetic nanoparticle preparation (monocrystalline iron oxide nanoparticles-47 [MION-47]) in cholesterol-fed New Zealand White rabbits 6 months after balloon injury. In vivo MRI visualized thickened abdominal aortas on both T1- and T2-weighted spin-echo images (T1 spin echo, 20 axial slices per animal; T2 spin echo, 28 slices per animal). Seventy-two hours after MION-47 injection, aortas exhibited lower T2 signal intensity compared with before contrast imaging (signal intensity ratio, aortic wall/muscle: before, 1.44 ± 0.26 versus after, 0.95 ± 0.22; 164 slices; P<0.01), whereas T1 spin echo images showed no significant change. MRI on ex vivo specimens provided similar results. Histological studies colocalized iron accumulation with immunoreactive macrophages in atheromata. The magnitude of signal intensity reduction on T2 spin echo in vivo images further correlated with macrophage areas in situ (150 slices; r=0.73). Treatment with rosuvastatin for 3 months yielded diminished macrophage content (P<0.05) and reversed T2 signal intensity changes (P<0.005). Signal changes in rosuvastatin-treated rabbits correlated with reduced macrophage burden (r=0.73). In vitro validation studies showed concentration-dependent MION-47 uptake by human primary macrophages. The magnitude of T2 signal intensity reduction in high-resolution MRI after administration of superparamagnetic phagocytosable nanoparticles can assess macrophage burden in atheromata, providing a clinically translatable tool to identify inflamed plaques and to monitor therapy-mediated changes in plaque inflammation.

Hypercoagulability Inhibits Monocyte Transendothelial Migration Through Protease-Activated Receptor-1-, Phospholipase-Cβ-, Phosphoinositide 3-Kinase-, and Nitric Oxide-Dependent Signaling in Monocytes and Promotes Plaque Stability

Clinical studies failed to provide clear evidence for a proatherogenic role of hypercoagulability. This is in contrast to the well-established detrimental role of hypercoagulability and thrombin during acute atherosclerotic complications. These seemingly opposing data suggest that hypercoagulability might exert both proatherogenic and antiatherogenic effects. We therefore investigated whether hypercoagulability mediates a beneficial effect during de novo atherogenesis. De novo atherogenesis was evaluated in 2 mouse models with hyperlipidemia and genetically imposed hypercoagulability (TM(Pro/Pro)ApoE(-/-) and FVL(Q/Q)ApoE(-/-) mice). In both mouse models, hypercoagulability resulted in larger plaques, but vascular stenosis was not enhanced secondary to positive vascular remodeling. Importantly, plaque stability was increased in hypercoagulable mice with less necrotic cores, more extracellular matrix, more smooth muscle cells, and fewer macrophages. Long-term anticoagulation reversed these changes. The reduced frequency of intraplaque macrophages in hypercoagulable mice is explained by an inhibitory role of thrombin and protease-activated receptor-1 on monocyte transendothelial migration in vitro. This is dependent on phospholipase-Cbeta, phosphoinositide 3-kinase, and nitric oxide signaling in monocytes but not in endothelial cells. Here, we show a new function of the coagulation system, averting stenosis and plaque destabilization during de novo atherogenesis. The in vivo and in vitro data establish that thrombin-induced signaling via protease-activated receptor-1, phospholipase-Cbeta, phosphoinositide 3-kinase, and nitric oxide in monocytes impairs monocyte transendothelial migration. This likely accounts for the reduced macrophage accumulation in plaques of hypercoagulable mice. Thus, in contrast to their role in unstable plaques or after vascular injury, hypercoagulability and thrombin convey a protective effect during de novo atherogenesis.

Myeloid-Related Protein-8/14 Is Critical for the Biological Response to Vascular Injury

Myeloid-related protein (MRP)-8 (S100A8) and MRP-14 (S100A9) are members of the S100 family of calcium-modulated proteins that regulate myeloid cell function and control inflammation, in part, through activation of Toll-like receptor-4 and the receptor for advanced glycation end products. A transcriptional profiling approach in patients with acute coronary syndromes identified MRP-14 as a novel predictor of myocardial infarction. Further studies demonstrated that elevated plasma levels of MRP-8/14 heterodimer predict increased risk of first and recurrent cardiovascular events. Beyond its serving as a risk marker, whether MRP-8/14 participates directly in vascular inflammation and disease remains unclear. We evaluated vascular inflammation in wild-type and MRP-14-deficient (MRP-14(-/-)) mice that lack MRP-8/14 complexes with experimental arterial injury, vasculitis, or atherosclerosis. After femoral artery wire injury, MRP-14(-/-) mice had significant reductions in leukocyte accumulation, cellular proliferation, and neointimal formation compared with wild-type mice. In a cytokine-induced local Shwartzman-like reaction that produces thrombohemorrhagic vasculitis, MRP-14(-/-) mice had significant reductions in neutrophil accumulation, lesion severity, and hemorrhagic area. In response to high-fat feeding, mice doubly deficient in apolipoprotein E and MRP-8/14 complexes had attenuation in atherosclerotic lesion area and in macrophage accumulation in plaques compared with mice deficient in apolipoprotein E alone. This study demonstrates that MRP-8/14 broadly regulates vascular inflammation and contributes to the biological response to vascular injury by promoting leukocyte recruitment.

Abstract 3373: MRP-8/14 is Critical for the Biological Response to Vascular Injury

Background : MRP-8 (S100A8) and MRP-14 (S100A9) are members of the S100-family of calcium-modulated proteins that regulate myeloid cell function and control inflammation, in part, through activation of toll-like receptor-4 and RAGE. Using a transcriptional profiling approach in patients with acute coronary syndromes, we made the novel discovery that MRP-14 is associated with atherothrombosis, and demonstrated that elevated plasma levels of MRP-8/14 heterodimer predict increased risk of first and recurrent cardiovascular events. Despite functioning as a pro-inflammatory mediator, the role of MRP-8/14 in vascular inflammation and disease are unknown. Methods and Results : We evaluated vascular inflammation in wild-type (WT) and MRP-14-deficient (MRP-14 −/− ) mice that lack MRP-8/14 complexes with experimental arterial injury, vasculitis, or atherosclerosis. After femoral artery wire injury, MRP-14 −/− mice had a 33% reduction in leukocyte accumulation ( P =.0004) and a 72% reduction in cellular proliferation ( P =0.001) in the arterial wall followed by a 45% reduction in neointima formation ( P =0.004) compared to WT mice. In a cytokine-induced local Schwartzman-like reaction that produces thrombohemorrhagic vasculitis, MRP-14 −/− mice had a 59% reduction in lesion severity ( P &lt;0.0001), an 82% smaller hemorrhagic area ( P =0.015), and a 45% decline in neutrophil accumulation ( P =0.013). Finally, in response to high-fat feeding, mice doubly deficient in ApoE and MRP-8/14 complexes had attenuation in atherosclerotic lesion area by 34% ( P =0.023) and a 60% decrease in macrophage accumulation in plaques ( P =0.021) compared to mice deficient in ApoE alone. Conclusions: This study demonstrates that MRP-8/14 broadly regulates vascular inflammation and contributes to the biological response to vascular injury. Targeting MRP-8/14 may provide a novel therapeutic approach to modulate diverse forms of vascular injury, including restenosis, vasculitis, and atherosclerosis.