Self-DNA (eg, released from dying cells or in neutrophil extracellular traps) and an increased expression of the antimicrobial peptide Cramp/LL37 in atherosclerotic lesions may thus stimulate a pDC-driven pathway of autoimmune activation and the generation of anti-double-stranded-DNA antibodies, critically aggravating atherosclerosis lesion formation. These key factors may thus represent novel therapeutic targets.

Immune mechanisms are known to control the pathogenesis of atherosclerosis. However, the exact role of DCs, which are essential for priming of immune responses, remains elusive. We have shown here that the DC-derived chemokine CCL17 is present in advanced human and mouse atherosclerosis and that CCL17 + DCs accumulate in atherosclerotic lesions. In atherosclerosis-prone mice, Ccl17 deficiency entailed a reduction of atherosclerosis, which was dependent on Tregs. Expression of CCL17 by DCs limited the expansion of Tregs by restricting their maintenance and precipitated atherosclerosis in a mechanism conferred by T cells. Conversely, a blocking antibody specific for CCL17 expanded Tregs and reduced atheroprogression. Our data identify DC-derived CCL17 as a central regulator of Treg homeostasis, implicate DCs and their effector functions in atherogenesis, and suggest that CCL17 might be a target for vascular therapy.

Key Points• NET formation is required for neutrophil recruitment during sterile inflammation.• Platelet-induced NET formation requires stimulation of neutrophils by platelet chemokines and outside-in signaling via the integrin Mac-1.There is emerging evidence that neutrophil extracellular traps (NETs) play important roles in inflammatory processes. Here we report that neutrophils have to be simultaneously activated by integrin-mediated outside-in-and G-protein-coupled receptor (GPCR) signaling to induce NET formation in acute lung injury (ALI), which is associated with a high mortality rate in critically ill patients. NETs consist of decondensed chromatin decorated with granular and cytosolic proteins and they can trap extracellular pathogens. The prerequisite for NET formation is the activation of neutrophils and the release of their DNA. In a neutrophil-and platelet-dependent mouse model of ventilator-induced lung injury (VILI), NETs were found in the lung microvasculature, and circulating NET components increased in the plasma. In this model, blocking integrin-mediated outside-in or either GPCR-signaling or heteromerization of platelet chemokines decreased NET formation and lung injury. Targeting NET components by DNAse1 application or neutrophil elastase-deficient mice protected mice from ALI, whereas DNase1 2/2 /Trap1 m/m mice had an aggravated ALI, suggesting that NETs directly influence the severity of ALI. These data suggest that NETs form in the lungs during VILI, contribute to the disease process, and thus may be a promising new direction for the treatment of ALI. (Blood. 2014; 123(16):2573-2584

The chemokine receptor CXCR4 and its ligand CXCL12 play an important homeostatic function by mediating the homing of progenitor cells in the bone marrow and regulating their mobilization into peripheral tissues upon injury or stress. Although the CXCL12/CXCR4 interaction has long been regarded as a monogamous relation, the identification of the pro-inflammatory chemokine macrophage migration inhibitory factor (MIF) as an important second ligand for CXCR4, and of CXCR7 as an alternative receptor for CXCL12, has undermined this interpretation and has considerably complicated the understanding of CXCL12/CXCR4 signaling and associated biological functions. This review aims to provide insight into the current concept of the CXCL12/CXCR4 axis in myocardial infarction (MI) and its underlying pathologies such as atherosclerosis and injury-induced vascular restenosis. It will discuss main findings from in vitro studies, animal experiments and large-scale genome-wide association studies. The importance of the CXCL12/CXCR4 axis in progenitor cell homing and mobilization will be addressed, as will be the function of CXCR4 in different cell types involved in atherosclerosis. Finally, a potential translation of current knowledge on CXCR4 into future therapeutical application will be discussed.

Neutrophil extracellular traps expelled from suicidal neutrophils comprise a complex structure of nuclear chromatin and proteins of nuclear, granular, and cytosolic origin. These net-like structures have also been detected in atherosclerotic lesions and arterial thrombi in humans and mice. Functionally, neutrophil extracellular traps have been shown to induce activation of endothelial cells, antigen-presenting cells, and platelets, resulting in a proinflammatory immune response. Overall, this suggests that they are not only present in plaques and thrombi but also they may play a causative role in triggering atherosclerotic plaque formation and arterial thrombosis. This review will focus on current findings of the involvement of neutrophil extracellular traps in atherogenesis and atherothrombosis.

We used a novel approach of cytostatically induced leucocyte depletion and subsequent reconstitution with leucocytes deprived of classical (inflammatory/Gr1hi) or non-classical (resident/Gr1lo) monocytes to dissect their differential role in atheroprogression under high-fat diet (HFD). Apolipoprotein E-deficient (Apoe−/−) mice lacking classical but not non-classical monocytes displayed reduced lesion size and macrophage and apoptotic cell content. Conversely, HFD induced a selective expansion of classical monocytes in blood and bone marrow. Increased CXCL1 levels accompanied by higher expression of its receptor CXCR2 on classical monocytes and inhibition of monocytosis by CXCL1-neutralization indicated a preferential role for the CXCL1/CXCR2 axis in mobilizing classical monocytes during hypercholesterolemia. Studies correlating circulating and lesional classical monocytes in gene-deficient Apoe−/− mice, adoptive transfer of gene-deficient cells and pharmacological modulation during intravital microscopy of the carotid artery revealed a crucial function of CCR1 and CCR5 but not CCR2 or CX3CR1 in classical monocyte recruitment to atherosclerotic vessels. Collectively, these data establish the impact of classical monocytes on atheroprogression, identify a sequential role of CXCL1 in their mobilization and CCR1/CCR5 in their recruitment.

Methods and Results: Compared to Apoe؊/؊ mice, Cramp ؊/؊ Apoe ؊/؊ mice exhibit reduced lesion sizes with lower macrophage numbers. In atherosclerotic aortas, we could detect CRAMP specifically in neutrophils, but not in monocytes or macrophages. By use of intravital microscopy, CRAMP was found to be deposited by activated neutrophils on inflamed endothelium of large arteries. In this location cathelicidins promote adhesion of classical monocytes and neutrophils, but not nonclassical monocytes in a formyl-peptide receptor-dependent manner. Key Words: atherosclerosis Ⅲ monocyte recruitment Ⅲ neutrophil A therosclerosis is a chronic inflammation of the arterial vessel wall with relatively well-defined roles for leukocytes such as macrophages and lymphocytes. 1,2 Recent studies, however, have revealed that neutrophils infiltrate atherosclerotic lesions at various time points, 3-5 and depletion studies provide evidence for a proatherogenic role of neutrophils. 5,6 Nevertheless, mechanistic insights into how neutrophils promote early atherosclerotic lesion formation remain elusive. Neutrophils contain granules with more than 300 different proteins that undergo limited exocytosis on neutrophil extravasation. 7 Some of these proteins are able to activate and recruit immune cells and thus have been coined alarmins. 8 Cathelicidins (CRAMP in mouse, LL37 in humans) residing in neutrophil secondary granules were shown to potently activate and recruit monocytes and macrophages, 9,10 thus fulfilling alarmin criteria. Because cathelicidins were identified in atherosclerotic lesions, 11 we investigated their role in a mouse model of atherosclerosis. Conclusions: Editorial, see p 1036 In This Issue, see p 1035 MethodsDetailed Methods are provided in the Online Supplement. Plaque StudiesCramp Ϫ/Ϫ mice 12 were crossed with Apoe Ϫ/Ϫ mice. Atherosclerotic lesion size as well as lesional neutrophil and macrophage content were assessed by histology and immunohistochemistry. Intravital MicroscopyLeukocyte adhesion to the carotid artery was studied by intravital fluorescence microscopy as described previously. 5 ResultsTo investigate the role of CRAMP in early atherosclerotic lesion formation, we fed Apoe Ϫ/Ϫ and CrampOriginal received January 29, 2012; revision received February 15, 2012; accepted February 27, 2012. In January 2012, the average time from submission to first decision for all original research papers submitted to Circulation Research was 13.88 days.Brief UltraRapid Communications are designed to be a format for manuscripts that are of outstanding interest to the readership, report definitive observations, but have a relatively narrow scope.

Rationale: Atheroprogression is a consequence of nonresolved inflammation, and currently a comprehensive overview of the mechanisms preventing resolution is missing. However, in acute inflammation, resolution is known to be orchestrated by a switch from inflammatory to resolving lipid mediators. Therefore, we hypothesized that lesional lipid mediator imbalance favors atheroprogression. Objective: To understand the lipid mediator balance during atheroprogression and to establish an interventional strategy based on the delivery of resolving lipid mediators. Methods and Results: Aortic lipid mediator profiling of aortas from Apoe −/− mice fed a high-fat diet for 4 weeks, 8 weeks, or 4 months revealed an expansion of inflammatory lipid mediators, Leukotriene B4 and Prostaglandin E2, and a concomitant decrease of resolving lipid mediators, Resolvin D2 (RvD2) and Maresin 1 (MaR1), during advanced atherosclerosis. Functionally, aortic Leukotriene B4 and Prostaglandin E2 levels correlated with traits of plaque instability, whereas RvD2 and MaR1 levels correlated with the signs of plaque stability. In a therapeutic context, repetitive RvD2 and MaR1 delivery prevented atheroprogression as characterized by halted expansion of the necrotic core and accumulation of macrophages along with increased fibrous cap thickness and smooth muscle cell numbers. Mechanistically, RvD2 and MaR1 induced a shift in macrophage profile toward a reparative phenotype, which secondarily stimulated collagen synthesis in smooth muscle cells. Conclusions: We present evidence for the imbalance between inflammatory and resolving lipid mediators during atheroprogression. Delivery of RvD2 and MaR1 successfully prevented atheroprogression, suggesting that resolving lipid mediators potentially represent an innovative strategy to resolve arterial inflammation.