Roles of PAD4 and NETosis in Experimental Atherosclerosis and Arterial Injury: Implications for Superficial Erosion
TL;DR: Results indicate that PAD4 from bone marrow-derived cells and NETs do not influence chronic experimental atherogenesis, but participate causally in acute thrombotic complications of intimal lesions that recapitulate features of superficial erosion.
Abstract: Rationale: Neutrophils likely contribute to the thrombotic complications of human atheromata. In particular, neutrophil extracellular traps (NETs) could exacerbate local inflammation and amplify and propagate arterial intimal injury and thrombosis. Peptidyl arginine deiminase 4 (PAD4) participates in NET formation, but understanding of this enzyme9s role in atherothrombosis remains scant. Objective: This study tested the hypothesis that PAD4 and NETs influence experimental atherogenesis and in processes implicated in superficial erosion, a form of plaque complication we previously associated with NETs. Methods and Results: Bone marrow chimeric Ldlr deficient mice reconstituted with either wild type or Pad4 deficient cells underwent studies that assessed atheroma formation or procedures designed to probe mechanisms related to superficial erosion. PAD4 deficiency neither retarded fatty streak formation nor reduced plaque size or inflammation in bone marrow chimeric mice that consumed an atherogenic diet. In contrast, either PAD4 deficiency in bone marrow-derived cells, or administration of DNaseI to disrupt NETs, decreased the extent of arterial intimal injury in mice with arterial lesions tailored to recapitulate characteristics of human atheroma complicated by erosion. Conclusions: These results indicate that PAD4 from bone marrow-derived cells and NETs do not influence chronic experimental atherogenesis, but participate causally in acute thrombotic complications of intimal lesions that recapitulate features of superficial erosion.
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TL;DR: Soehnlein et al. as discussed by the authors consider a gamut of attractive possibilities for modifying inflammation in atherosclerosis, including targeting pivotal inflammatory pathways such as the inflammasomes, inhibiting cytokines, manipulating adaptive immunity and promoting pro-resolution mechanisms.
Abstract: Atherosclerosis, a dominant and growing cause of death and disability worldwide, involves inflammation from its inception to the emergence of complications. Targeting inflammatory pathways could therefore provide a promising new avenue to prevent and treat atherosclerosis. Indeed, clinical studies have now demonstrated unequivocally that modulation of inflammation can forestall the clinical complications of atherosclerosis. This progress pinpoints the need for preclinical investigations to refine strategies for combatting inflammation in the human disease. In this Review, we consider a gamut of attractive possibilities for modifying inflammation in atherosclerosis, including targeting pivotal inflammatory pathways such as the inflammasomes, inhibiting cytokines, manipulating adaptive immunity and promoting pro-resolution mechanisms. Along with lifestyle measures, pharmacological interventions to mute inflammation could complement traditional targets, such as lipids and hypertension, to make new inroads into the management of atherosclerotic risk. The contribution of inflammation to atherosclerosis is substantial, and is just beginning to be understood. In this Review, Soehnlein and Libby discuss how inflammation promotes atherosclerosis and its consequences, and how such processes could be targeted therapeutically. The potential pitfalls of targeting immune processes — namely the increased potential for infections — are also discussed, along with ways to modulate cardiovascular therapies in time and space to make them more effective.
287 citations
TL;DR: The mechanisms that underlie superficial erosion, a cause of coronary thrombosis distinct from plaque rupture, have garnered recent interest as mentioned in this paper, and a substantial shift in the mechanisms of the complications of atherosclerosis has been proposed.
Abstract: The mechanisms that underlie superficial erosion, a cause of coronary thrombosis distinct from plaque rupture, have garnered recent interest. In an era of improved control of traditional risk factors, such as LDL (low-density lipoprotein), plaque erosion may assume greater clinical importance. Plaques complicated by erosion tend to be matrix-rich, lipid-poor, and usually lack prominent macrophage collections, unlike plaques that rupture, which characteristically have thin fibrous caps, large lipid pools, and abundant foam cells. Thrombi that complicate superficial erosion seem more platelet-rich than the fibrinous clots precipitated by plaque rupture. The pathogenesis of plaque rupture probably does not pertain to superficial erosion, a process heretofore little understood mechanistically. We review here data that support a substantial shift in the mechanisms of the thrombotic complications of atherosclerosis. We further consider pathophysiologic processes recently implicated in the mechanisms of erosion. Multiple processes likely predispose plaques to superficial erosion, including experiencing disturbed flow, basement membrane breakdown, endothelial cell death, and detachment potentiated by innate immune activation mediated through pattern-recognition receptors and endothelial-to-mesenchymal transition. Monocytes/macrophages predominate in the pathogenesis of plaque rupture and consequent thrombosis, but polymorphonuclear leukocytes likely promote endothelial damage during superficial erosion. The formation of neutrophil extracellular traps probably perpetuates and propagates intimal injury and potentiates thrombosis due to superficial erosion. These considerations have profound clinical implications. Acute coronary syndromes because of erosion may not require immediate invasive therapy. Understanding the biological bases of erosion points to novel therapies for acute coronary syndrome caused by erosion. Future research should probe further the mechanisms of superficial erosion, and develop point-of-care tests to distinguish acute coronary syndromes provoked by erosion versus rupture that may direct more precision management. Future clinical investigations should evaluate intervening on the targets that have emerged from experimental studies and the management strategies that they inform.
230 citations
Ludwig Maximilian University of Munich1, Maastricht University2, University of California, San Francisco3, University of Grenoble4, Centro Nacional de Investigaciones Cardiovasculares5, University of Hamburg6, Scripps Research Institute7, Technische Universität München8, Karolinska Institutet9, Max Planck Society10
TL;DR: This work demonstrates that extracellular histone H4-mediated membrane lysis of smooth muscle cells (SMCs) triggers arterial tissue damage and inflammation, and identifies a form of cell death found at the core of chronic vascular disease that is instigated by leukocytes and can be targeted therapeutically.
Abstract: The perpetuation of inflammation is an important pathophysiological contributor to the global medical burden. Chronic inflammation is promoted by non-programmed cell death; however, how inflammation is instigated, its cellular and molecular mediators, and its therapeutic value are poorly defined. Here we use mouse models of atherosclerosis-a major underlying cause of mortality worldwide-to demonstrate that extracellular histone H4-mediated membrane lysis of smooth muscle cells (SMCs) triggers arterial tissue damage and inflammation. We show that activated lesional SMCs attract neutrophils, triggering the ejection of neutrophil extracellular traps that contain nuclear proteins. Among them, histone H4 binds to and lyses SMCs, leading to the destabilization of plaques; conversely, the neutralization of histone H4 prevents cell death of SMCs and stabilizes atherosclerotic lesions. Our data identify a form of cell death found at the core of chronic vascular disease that is instigated by leukocytes and can be targeted therapeutically.
224 citations
TL;DR: The influence of traditional and novel cardiovascular risk factors on neutrophil production and function is discussed and the current knowledge of the contribution of neutrophils to the different stages of atherosclerosis, including atherogenesis, plaque destabilization and plaque erosion is appraised.
Abstract: Neutrophils have traditionally been viewed as bystanders or biomarkers of cardiovascular disease. However, studies in the past decade have demonstrated the important functions of neutrophils during cardiovascular inflammation and repair. In this Review, we discuss the influence of traditional and novel cardiovascular risk factors on neutrophil production and function. We then appraise the current knowledge of the contribution of neutrophils to the different stages of atherosclerosis, including atherogenesis, plaque destabilization and plaque erosion. In the context of cardiovascular complications of atherosclerosis, we highlight the dichotomous role of neutrophils in pathogenic and repair processes in stroke, heart failure, myocardial infarction and neointima formation. Finally, we emphasize how detailed knowledge of neutrophil functions in cardiovascular homeostasis and disease can be used to generate therapeutic strategies to target neutrophil numbers, functional status and effector mechanisms.
216 citations
TL;DR: In this paper, the synergy between inflammation and thrombosis is discussed, and the huge potential of anti-inflammatory strategies to target cardiovascular pathologies is highlighted, with the aim of covering therapeutic gaps in cardiovascular diseases.
Abstract: Thrombosis is the most feared complication of cardiovascular diseases and a main cause of death worldwide, making it a major health-care challenge. Platelets and the coagulation cascade are effectively targeted by antithrombotic approaches, which carry an inherent risk of bleeding. Moreover, antithrombotics cannot completely prevent thrombotic events, implicating a therapeutic gap due to a third, not yet adequately addressed mechanism, namely inflammation. In this Review, we discuss how the synergy between inflammation and thrombosis drives thrombotic diseases. We focus on the huge potential of anti-inflammatory strategies to target cardiovascular pathologies. Findings in the past decade have uncovered a sophisticated connection between innate immunity, platelet activation and coagulation, termed immunothrombosis. Immunothrombosis is an important host defence mechanism to limit systemic spreading of pathogens through the bloodstream. However, the aberrant activation of immunothrombosis in cardiovascular diseases causes myocardial infarction, stroke and venous thromboembolism. The clinical relevance of aberrant immunothrombosis, referred to as thromboinflammation, is supported by the increased risk of cardiovascular events in patients with inflammatory diseases but also during infections, including in COVID-19. Clinical trials in the past 4 years have confirmed the anti-ischaemic effects of anti-inflammatory strategies, backing the concept of a prothrombotic function of inflammation. Targeting inflammation to prevent thrombosis leaves haemostasis mainly unaffected, circumventing the risk of bleeding associated with current approaches. Considering the growing number of anti-inflammatory therapies, it is crucial to appreciate their potential in covering therapeutic gaps in cardiovascular diseases.
208 citations
References
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TL;DR: It is described that, upon activation, neutrophils release granule proteins and chromatin that together form extracellular fibers that bind Gram-positive and -negative bacteria, which degrade virulence factors and kill bacteria.
Abstract: Neutrophils engulf and kill bacteria when their antimicrobial granules fuse with the phagosome. Here, we describe that, upon activation, neutrophils release granule proteins and chromatin that together form extracellular fibers that bind Gram-positive and -negative bacteria. These neutrophil extracellular traps (NETs) degrade virulence factors and kill bacteria. NETs are abundant in vivo in experimental dysentery and spontaneous human appendicitis, two examples of acute inflammation. NETs appear to be a form of innate response that binds microorganisms, prevents them from spreading, and ensures a high local concentration of antimicrobial agents to degrade virulence factors and kill bacteria.
7,554 citations
TL;DR: Mechanisms of atherosclerotic plaque initiation and progression; how plaques suddenly precipitate life-threatening thrombi; and the concepts of plaque burden, activity, and vulnerability are discussed.
Abstract: Atherosclerosis causes clinical disease through luminal narrowing or by precipitating thrombi that obstruct blood flow to the heart (coronary heart disease), brain (ischemic stroke), or lower extremities (peripheral vascular disease). The most common of these manifestations is coronary heart disease, including stable angina pectoris and the acute coronary syndromes. Atherosclerosis is a lipoprotein-driven disease that leads to plaque formation at specific sites of the arterial tree through intimal inflammation, necrosis, fibrosis, and calcification. After decades of indolent progression, such plaques may suddenly cause life-threatening coronary thrombosis presenting as an acute coronary syndrome. Most often, the culprit morphology is plaque rupture with exposure of highly thrombogenic, red cell-rich necrotic core material. The permissive structural requirement for this to occur is an extremely thin fibrous cap, and thus, ruptures occur mainly among lesions defined as thin-cap fibroatheromas. Also common are thrombi forming on lesions without rupture (plaque erosion), most often on pathological intimal thickening or fibroatheromas. However, the mechanisms involved in plaque erosion remain largely unknown, although coronary spasm is suspected. The calcified nodule has been suggested as a rare cause of coronary thrombosis in highly calcified and tortious arteries in older individuals. To characterize the severity and prognosis of plaques, several terms are used. Plaque burden denotes the extent of disease, whereas plaque activity is an ambiguous term, which may refer to one of several processes that characterize progression. Plaque vulnerability describes the short-term risk of precipitating symptomatic thrombosis. In this review, we discuss mechanisms of atherosclerotic plaque initiation and progression; how plaques suddenly precipitate life-threatening thrombi; and the concepts of plaque burden, activity, and vulnerability.
1,369 citations
TL;DR: It is found that citrullination decreased the bacterial killing activity of histones and nucleosomes, which suggests that PAD4 mainly plays a role in chromatin decondensation to form NETs instead of increasing histone-mediated bacterial killing.
Abstract: Neutrophils trap and kill bacteria by forming highly decondensed chromatin structures, termed neutrophil extracellular traps (NETs) We previously reported that histone hypercitrullination catalyzed by peptidylarginine deiminase 4 (PAD4) correlates with chromatin decondensation during NET formation However, the role of PAD4 in NET-mediated bacterial trapping and killing has not been tested Here, we use PAD4 knockout mice to show that PAD4 is essential for NET-mediated antibacterial function Unlike PAD4+/+ neutrophils, PAD4−/− neutrophils cannot form NETs after stimulation with chemokines or incubation with bacteria, and are deficient in bacterial killing by NETs In a mouse infectious disease model of necrotizing fasciitis, PAD4−/− mice are more susceptible to bacterial infection than PAD4+/+ mice due to a lack of NET formation Moreover, we found that citrullination decreased the bacterial killing activity of histones and nucleosomes, which suggests that PAD4 mainly plays a role in chromatin decondensation to form NETs instead of increasing histone-mediated bacterial killing Our results define a role for histone hypercitrullination in innate immunity during bacterial infection
1,117 citations
TL;DR: An important role is shown for neutrophils in lupus pathogenesis, whereby neutrophil activated by anti-self antibodies release NETs, which contain antimicrobial peptides complexed with self-DNA and can entrap bacteria, enabling them to be killed.
Abstract: Systemic lupus erythematosus (SLE) is a severe and incurable autoimmune disease characterized by chronic activation of plasmacytoid dendritic cells (pDCs) and production of autoantibodies against nuclear self-antigens by hyperreactive B cells. Neutrophils are also implicated in disease pathogenesis; however, the mechanisms involved are unknown. Here, we identified in the sera of SLE patients immunogenic complexes composed of neutrophil-derived antimicrobial peptides and self-DNA. These complexes were produced by activated neutrophils in the form of web-like structures known as neutrophil extracellular traps (NETs) and efficiently triggered innate pDC activation via Toll-like receptor 9 (TLR9). SLE patients were found to develop autoantibodies to both the self-DNA and antimicrobial peptides in NETs, indicating that these complexes could also serve as autoantigens to trigger B cell activation. Circulating neutrophils from SLE patients released more NETs than those from healthy donors; this was further stimulated by the antimicrobial autoantibodies, suggesting a mechanism for the chronic release of immunogenic complexes in SLE. Our data establish a link between neutrophils, pDC activation, and autoimmunity in SLE, providing new potential targets for the treatment of this devastating disease.
1,104 citations
Medical University of South Carolina1, University of Massachusetts Medical School2, Johns Hopkins University3, University of Washington4, University of Texas Health Science Center at San Antonio5, Baylor College of Medicine6, University of Pittsburgh7, Columbia University8, University of Texas Southwestern Medical Center9, Pennsylvania State University10, Cystic Fibrosis Foundation11, Dartmouth College12
TL;DR: New guidelines are provided for the appropriate application of drug therapies used in the maintenance of pulmonary function to improve and extend the lives of all individuals with cystic fibrosis.
Abstract: The natural history of cystic fibrosis lung disease is one of chronic progression with intermittent episodes of acute worsening of symptoms frequently called acute pulmonary exacerbations These exacerbations typically warrant medical intervention. It is important that appropriate therapies are recommended on the basis of available evidence of efficacy and safety. The Cystic Fibrosis Foundation therefore established a committee to define the key questions related to pulmonary exacerbations, review the clinical evidence using an evidence-based methodology, and provide recommendations to clinicians. It is hoped that these guidelines will be helpful to clinicians in the treatment of individuals with cystic fibrosis.
1,016 citations