Secondary Logo

Mechanisms of erosion of atherosclerotic plaques

Quillard, Thibaut; Franck, Grégory; Mawson, Thomas; Folco, Eduardo; Libby, Peter

doi: 10.1097/MOL.0000000000000440
ATHEROSCLEROSIS: CELL BIOLOGY AND LIPOPROTEINS: Edited by Mohamad Navab and Andrew Newby
Free
Editor's Choice

Purpose of review The present review explores the mechanisms of superficial intimal erosion, a common cause of thrombotic complications of atherosclerosis.

Recent findings Human coronary artery atheroma that give rise to thrombosis because of erosion differ diametrically from those associated with fibrous cap rupture. Eroded lesions characteristically contain few inflammatory cells, abundant extracellular matrix, and neutrophil extracellular traps (NETs). Innate immune mechanisms such as engagement of Toll-like receptor 2 (TLR2) on cultured endothelial cells can impair their viability, attachment, and ability to recover a wound. Hyaluronan fragments may serve as endogenous TLR2 ligands. Mouse experiments demonstrate that flow disturbance in arteries with neointimas tailored to resemble features of human eroded plaques disturbs endothelial cell barrier function, impairs endothelial cell viability, recruits neutrophils, and provokes endothelial cells desquamation, NET formation, and thrombosis in a TLR2-dependent manner.

Summary Mechanisms of erosion have received much less attention than those that provoke plaque rupture. Intensive statin treatment changes the characteristic of plaques that render them less susceptible to rupture. Thus, erosion may contribute importantly to the current residual burden of risk. Understanding the mechanisms of erosion may inform the development and deployment of novel therapies to combat the remaining atherothrombotic risk in the statin era.

Division of Cardiovascular Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA

Correspondence to Peter Libby, MD, Brigham and Women's Hospital, Harvard Medical School, 77 Ave Louis Pasteur, NRB-741-G, Boston, MA 02115, USA. Tel: +1 617 525 4383; fax:+617 525 4400; e-mail: plibby@bwh.harvard.edu

Back to Top | Article Outline

TWO MAJOR MECHANISMS OF THE ACUTE THROMBOTIC COMPLICATIONS OF ATHEROSCLEROSIS

The acute coronary syndromes (ACS) persist as a leading cause of morbidity, mortality, and loss of quality life years. The epidemic of atherothrombosis today affects not only developed countries, but also those with emerging economies. Successes in acute care have markedly reduced in-hospital and short-term mortality in patients with ACS. Yet, many ACS survivors develop ischemic cardiomyopathy and the clinical syndrome of heart failure, a major limitation of quality of life, cause of mortality, and a burden to healthcare systems. Despite our very effective revascularization, lifestyle measures including cardiac rehabilitation programs, successful pharmacologic treatments including aspirin and other potent antiplatelet agents, β-adrenergic blocking drugs, and a variety of avenues to lower LDL levels, the residual burden of disease remains unacceptably high [1].

Much work on the mechanisms of ACS over the last several decades has focused on the so-called ‘vulnerable plaque’. These lesions have characteristically large lipid pools, many macrophages and other inflammatory leukocytes, thin fibrous caps depleted of interstitial collagen, and few arterial smooth muscle cells (Fig. 1, right). Research has made considerable inroads into understanding the pathophysiologic basis of development of such thin-capped atheromatous lesions [3]. Overexpression of collagenases and reduced collagen synthesis signaled by inflammatory mediators can impair the biomechanical integrity of the plaque's fibrous cap. Pro-inflammatory cytokines can also augment the expression of the potent procoagulant tissue factor that triggers thrombosis in plaques that undergo rupture of the fibrous cap. Experimental and human studies have shown that lipid-lowering therapies can limit inflammation, reduce lipid accumulation, and reinforce the fibrous skeleton of plaques, changes that would render them less likely to rupture.

FIGURE 1

FIGURE 1

We have therefore hypothesized that some of the residual burden of risk in an era of extreme lipid lowering may result from superficial erosion, a mechanism of thrombotic complications of atherosclerotic plaques generally relegated to minority status as a cause of ACS. The lesions associated with superficial erosion in humans exhibit a morphology quite distinct from the thin-capped atheromata associated with plaque rupture. In stark contrast with ruptured plaques, they contain abundant smooth muscle cells and extracellular matrix (ECM), and exhibit scarce lipid and macrophage/foam cell accumulation (Fig. 1, left). Intravascular imaging using optical coherence tomography (OCT) readily identifies culprit lesions of ACS that have ruptured [4]. Many nonruptured plaques that cause ACS may have provoked thrombus formation because of superficial erosion. OCT imaging indicates that up to one-third of ACS in the current era result from erosion rather than rupture [4,5].

We have argued that because of the increasing success of our LDL-lowering therapies we are currently witnessing a rise in the proportion of ACS caused by erosion. We further propose that this pathway to coronary thrombosis may persist in the current era of effective LDL-lowering therapy, as the relatively lipid-poor substrate may respond less well to such treatment than lipid-rich, thin-capped atheromatous plaques. Although we have achieved considerable mastery over the pathophysiology and prevention of the classical ‘vulnerable’ plaque, we have very little understanding of the pathophysiology and treatment of lesions prone to develop erosion. Hence, we need to understand better the mechanisms that underlie superficial erosion, a mechanism of thrombotic complications of plaques that appears on the rise in the era of effective LDL lowering.

Box 1

Box 1

Back to Top | Article Outline

EMERGING CONCEPTS OF THE MECHANISMS OF PLAQUE EROSION: ROLES FOR DISTURBED FLOW AND TOLL-LIKE RECEPTOR 2

Recent work has focused on the innate immune receptor toll-like receptor 2 (TLR2) as a contributor to altered endothelial function that can predispose to superficial erosion [6,7]. Observations on cultured human endothelial cells and on atherosclerotic mice support overexpression of TLR2 in regions of disturbed flow [8,9]. Endothelial cells in human atherosclerotic arteries distal to stenoses, regions that experience disturbed flow, show increased indices of cell death by apoptosis [10]. We therefore hypothesized that TLR2 engagement could predispose towards endothelial cell desquamation, a likely trigger to thrombosis in eroded lesions. Increased TLR2 expression in regions of disturbed flow might lead to an increased activation of the receptor. Studies in atherosclerotic mice have furnished evidence that TLR2 actively contributes to experimental atherosclerosis [8,9]. Administration of Pam3CSK4 – a synthetic TLR2/TLR1 agonist – substantially increased atherosclerotic burden in LDLR−/− atherosclerotic mice. Mice with double deficiency of LDLR and TLR2, either globally or restricted to bone marrow-derived cells, did not show increased lesion size in response to TLR2 agonism. The atherogenic role of TLR2 seems therefore to depend on its direct action in cells of nonbone marrow origin [8]. Using ApoE−/− atherosclerotic mice, other groups found that TLR2 activation by exogenous ligands increases atherosclerotic plaque size and neointima formation in femoral arteries, notably through promoting reactive oxygen species (ROS) production and smooth muscle cell migration in an interleukin (IL)-6-dependent manner [11–15].

Related to its ability to form heterodimers with other TLR family members, numerous exogenous and endogenous ligands can trigger TLR2 activation [16]. TLR2 ligation to lipoproteins (i.e. oxLDL) with the scavenger receptor CD36, and high-mobility group box 1 protein (HMGB1) contributes to foam cell formation and inflammation, supporting its participation in atherogenesis [17–21].

TLR2 activation may derive from other endogenous ligands. Of particular interest in this context, TLR2 can bind low-molecular weight hyaluronic acid [22] via direct association with CD44 [23] or with versican [24], two major components of ECM typically found in eroded lesions [25]. Our recent work, and others’, showed that TLR2 agonists, lipoteichoic acid, or Pam3CSK4 suffice to promote a low-level, smoldering activation and dysfunction of endothelial cells with increased expression of E-Selectin and VCAM-1, endoplasmic reticulum stress, ROS production, and ultimately apoptosis. Treatment with hyaluronic acid, either in soluble form or coated on the culture dish, led to comparable results [6,26,27]. This observation further supports the involvement of hyaluronan as a disease-relevant endogenous TLR2 agonist. Combination of disturbed flow that associates with increased endothelial TLR2 expression and lesions with high glycosaminoglycan content might therefore set the stage for endothelial cells dysfunction and ultimately erosion.

Back to Top | Article Outline

A SPECIAL ROLE FOR GRANULOCYTES AND NEUTROPHIL EXTRACELLULAR TRAPS IN SUPERFICIAL EROSION?

Macrophages have traditionally commanded considerable attention as contributors to atherogenesis, because of their fundamental roles in every aspect of plaque formation, development, and rupture. Yet, other phagocytic and innate immune cells may also contribute to atherogenesis (e.g. mast cells, eosinophils, and notably neutrophils) [28]. Our recent findings point to a particular place for polymorphonuclear leukocytes in propagating intimal injury in the context of superficial erosion.

Neutrophils furnish the first line of defence against pathogens and use an assortment of granular proteins, proteases, and ROS to attack microorganisms and amplify locally innate and adaptive immune responses. Neutrophils can also entrap infectious agents through the formation of neutrophil extracellular traps (NETs). NETs consist of web-like structures derived from decondensed chromatin with histones, antimicrobials, and proteins that capture and promote pathogen death. NET formation (NETosis) results from a controlled death program like apoptosis or necroptosis, even if in some rare cases netotic anucleate neutrophils remain motile and able to kill bacteria through phagocytosis and degranulation [29].

In addition to clearing microorganisms, neutrophils may also participate in the pathophysiology of cancer, autoimmunity, and chronic inflammatory diseases. Neutrophils can localize in complicated atherosclerotic lesions [6,29–31]. In apoE−/− mice, increased presence of NETs associated with higher expression of IFNα. Inhibition of NET formation by peptidyl-arginine deiminase 4 (PAD4) blockade reduced lesion size after 11 weeks of treatment and a high-fat diet (HFD), although the inhibitor used may lack specificity [32]. Warnatsch et al. also reported that cholesterol crystals induced NETosis in vitro. NETosis occurred after 8 weeks on a HFD in cholesterol-rich areas of experimental atheromata, and depended on ROS, as diphenylene iodonium – an inhibitor of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase or an inhibitor of the neutrophil-specific proteases neutrophil elastase (NEi) and proteinase 3 (PR3) – blocked this process. NET blockade using Apoe−/− mice lacking both neutrophil elastase and PR3 (Apoe−/−Elane−/−Prtn3−/−) or DNase injections (6 weeks) reduced lesions size in Apoe−/−Elane−/−Prtn3−/− animals after 8 weeks but not after 4 weeks of high-fat diet feeding [33]. In contrast, others reported a similar protective effect in Apoe−/−Elane−/−Prtn3−/− mice, but only in early stages of the disease [34]. In this latter study, DNase treatment for 4 weeks was insufficient to attenuate atherogenesis. This point, discussed by Döring et al.[35] raises questions on the precise mechanisms implicated in the detrimental role of neutrophils on plaque progression, either via NETosis, or/and specific neutrophil proteases that affect inflammatory cytokines production and maturation.

Previous reports implied a direct role for neutrophils in superficial erosion and in endothelial desquamation. Ferrante et al.[36] showed that systemic myeloperoxidase (MPO) levels – a heme protein most abundantly expressed in azurophilic granules in neutrophils – rose significantly in patients with eroded plaques compared with patients presenting with ruptured plaque, as determined by OCT. In vitro, ROS derived from MPO release can promote endothelial cell apoptosis, [37] and MPO-containing neutrophil microparticles damage vascular endothelial cells and disrupt the endothelial barrier [38]. MPO can generate locally hypochlorous acid (HOCl), a potent pro-oxidant that can propagate damage in regions of arteries where granulocytes congregate. Activated endothelial cells can induce NETosis and reciprocally neutrophil and NETs directly induce endothelial dysfunction and damage of endothelial cells [39,40]. In Lupus erythematosis, NETosis associates with activation of endothelial MMP-2, impairment of endothelium-dependent vasorelaxation, and apoptosis [41,42].

In typical erosion-type lesions exposed to disturbed flow and rich in hyaluronic acid and versican, TLR2 activation can lead to endothelial cell stress, as stated previously. TLR2 ligation induces the production of IL-8, a chemokine that promotes neutrophil recruitment and adhesion [27]. TLR2 can also interact with NETs and influence cytokine production, including IL-17 that further drives neutrophil chemotaxis [33]. Such molecular interactions may sustain granulocyte recruitment, compensating for their short lifespan in tissue [43].

TLR2 activation impairs the ability of neighboring endothelial cells to repair breaches in the endothelial monolayer [6]. Co-incubation of endothelial cells with TLR2 agonists and with neutrophils also promotes endothelial cell death in vitro[6]. Such treatment further favors endothelial desquamation by inducing the nonfibrillar collagenases MMP2 and MMP9, capable of degrading components of the basement membrane to which endothelial cells attach.

To test the relevance of this hypothesis to human disease, we analyzed the association between TLR2 expression, luminal neutrophils, and NETs, and apoptotic endothelials in human endarterectomy specimens. We colocalized apoptotic endothelial cells with TLR2, neutrophils, and markers of NETosis in lesions complicated by superficial erosion, but not in plaques with characteristics considered ‘rupture-prone’ (Fig. 2) [6]. ‘Stable’ lesions that exhibit little endothelial cell apoptosis express similar levels of TLR2 as do erosion-type lesions, but harbor few neutrophils. In contrast, typical ruptured lesions that contain far lower levels of putative endogenous agonists for TLR2 (e.g. hyaluronic acid, versican) contain similar neutrophil numbers, but lower TLR2 expression [6].

FIGURE 2

FIGURE 2

NETs also directly promote thrombosis through multiple mechanisms. Extracellular nucleic acids in NETs bind circulating platelets, coagulation factors, and VWF, acting as a solid-state reactor for the coagulation cascade and providing a scaffold for developing thrombi [44–46]. Neutrophil proteinases and extracellular histones activate platelets and accelerate thrombin formation [47,48]. In addition, histones, elastase, and MPO-generated HOCl each induce endothelial tissue factor production [37,49–51]. Supporting these in vitro studies, clinical data implicate NETs in coronary disease, venous thrombosis, and other thrombotic conditions [52–55]. Thrombi retrieved from the culprit arteries of patients with ACS show higher levels of NET markers. NETs isolated from culprit artery blood contain tissue factor. Furthermore, culprit arteries have higher blood levels of markers of NETs than nonculprit arteries [56]. A separate study of patients with STEMI showed that a higher burden of NETs within thrombi correlated with greater infarct size and delayed resolution of ST-segment elevation [57]. Collectively, these data indicate that the elevated levels of NETs observed at the intimal surface of eroded lesions may contribute causally to erosion-associated coronary thrombosis.

Back to Top | Article Outline

EXTENDING IN-VITRO STUDIES OF MECHANISMS OF SUPERFICIAL EROSION IN VIVO

Our in-vitro studies described above implicated disturbed flow, neutrophils, hyaluronan, and TLR2 ligation in endothelial damage, which we conjectured contribute to superficial erosion. Our recent study tested in mice the involvement of these factors in superficial intimal injury in vivo[7]. We crafted intimal lesions in mouse carotid arteries that resemble the substrate of human eroded plaques by having high ECM content, but scant macrophages, intimal lesions, and lipid. This preparation used electrical injury to the adventitia, followed by 4 weeks of healing to form a neointima and allow re-endothelialization of the intimal surface. After this period of healing, we produced flow perturbation by means of periadventitial cuff. This intervention promoted downstream endothelial activation, neutrophil accumulation, death of endothelial cells, and their eventual desquamation. Mural thrombosis ensued. Inhibition of neutrophil function by two independent methods mitigated this endothelial damage and detachment. Administration of TLR2 agonists activated luminal endothelial cells, whereas TLR2 deficiency reduced intimal neutrophil content in zones of locally disturbed flow, and protected endothelial cells from injury and limited local thrombus formation. We do not affirm that this in vivo preparation represents a ‘model’ for superficial erosion, rather a tool to study under controlled experimental circumstances mechanisms that may pertain to plaque erosion in humans [58].

Bone marrow chimera experiments pointed to intrinsic vascular cells rather than leukocytes as the responders to TLR2 agonism. TLR2 localized mainly on the basal aspect of endothelial cells, strategically positioned to respond to intimal hyaluronate, a potential endogenous TLR2 ligand. These results in mice and parallel observations on human atheromata provided in vivo support for the notion that flow disturbance, neutrophils, and TLR2 signaling participate in the pathogenesis of superficial erosion.

Back to Top | Article Outline

EROSION MECHANISMS LIKELY INVOLVE MULTIPLE ‘HITS’

Given this ensemble of findings, we have proposed that sequential ‘hits’ promote endothelial cells desquamation and ultimately plaque erosion and thrombosis (Fig. 3). For example, TLR2 activation initially leads to chronic low-level endothelial activation and eventually neutrophil recruitment that jeopardizes intimal integrity by sloughing of endothelial cells. Then the tempo of mischief picks up, and from a low-level smoldering process, in a second, much more rapid phase, thrombosis ensues. NETs can amplify and propagate endothelial damage, widen the area of intimal damage, and potentiate local thrombosis. If the thrombus persists and grows to obstruct flow, the situation can cross the clinical threshold to produce ischemia, cause symptoms, and myocardial damage: an ACS.

FIGURE 3

FIGURE 3

Back to Top | Article Outline

CLINICAL IMPLICATIONS OF SUPERFICIAL EROSION

As noted above, we are beginning to unravel pathophysiologic pathways relevant to arterial thrombosis provoked by superficial erosion. This effort has merit not only from a basic science perspective, but may also provide a foundation for clinical advances. The triage and therapeutic pathways for patients with ACS depend on the clinical assessment, a surface electrocardiogram, and biomarkers of myocardial injury. None of these tools provides insight into the pathophysiologic mechanism of the ACS: erosion versus plaque rupture. Yet, the optimum management strategy for these two very different substrates for coronary artery thrombosis might very well vary considerably. OCT data suggest that the type of thrombus in erosion differs from that provoked by plaque rupture. Intimal erosion may give rise to platelet-rich, white thrombi, whereas clots that complicate plaque rupture have a more fibrin-rich ‘red’ character [59]. Thus, intensive antiplatelet therapy might benefit particularly ACS caused by superficial erosion.

Indeed, a pilot clinical trial, EROSION, used OCT to gauge the resolution of coronary thrombi in patients with ST-segment elevation myocardial infarction (STEMI)-associated culprit lesions with the findings of superficial erosion versus rupture [60]. The patients did not receive coronary artery stent deployment, the current standard of care for STEMI, but received intensive antiplatelet treatment. The study was not powered for events, but showed that most of the subjects had substantial resolution of the intra-coronary thrombosis after 30 days. Although this pilot study has many limitations, it does illustrate the enticing concept that we might tailor the treatment of ACS depending on the underlying mechanism that precipitated the thrombotic event. Performing OCT, an invasive procedure, will not prove practical for triage of ACS patients on a routine basis.

If we were to develop biomarkers based on pathophysiologic insights derived from mechanistic studies such as those described in this review that could distinguish ACS because of erosion from those arising from rupture it could revolutionize the triage and management of patients presenting with ACS. Such an advancement would represent a step towards a more personalized approach, and illustrate the value of translation of basic science insights to clinical practice.

Back to Top | Article Outline

Acknowledgements

None.

Back to Top | Article Outline

Financial support and sponsorship

This work was supported by grants from the National Heart, Lung and Blood institute (NIH-R01HL080472) by the Leducq Foundation (Paris, France) and from the RRM charitable fund. G.F. was supported by the Harold M. English Fellowship Fund from Harvard Medical School (Boston, USA), the Fondation Bettencourt Schueller (Neuilly-sur-Seine, France), and the Philippe Foundation (New York, USA and Paris, France). T.M. received support from by the Sarnoff Cardiovascular Research Foundation (Great Falls, USA).

Back to Top | Article Outline

Conflicts of interest

There are no conflicts of interest.

Back to Top | Article Outline

REFERENCES

1. Jernberg T, Hasvold P, Henriksson M, et al. Cardiovascular risk in postmyocardial infarction patients: nationwide real world data demonstrate the importance of a long-term perspective. Eur Heart J 2015; 36:1163–1170.
2. Libby P. Superficial erosion and the precision management of acute coronary syndromes: not one-size-fitsall. Eur Heart J 2017; 38:801–803.
3. Libby P. Mechanisms of acute coronary syndromes and their implications for therapy. New Engl J Med 2013; 368:2004–2013.
4. Jia H, Abtahian F, Aguirre AD, et al. In vivo diagnosis of plaque erosion and calcified nodule in patients with acute coronary syndrome by intravascular optical coherence tomography. J Am Coll Cardiol 2013; 62:1748–1758.
5. Pasterkamp G, den Ruijter HM, Libby P. Temporal shifts in clinical presentation and underlying mechanisms of atherosclerotic disease. Nat Rev Cardiol 2016; 14:21–29.
6. Quillard T, Araujo HA, Franck G, et al. TLR2 and neutrophils potentiate endothelial stress, apoptosis and detachment: implications for superficial erosion. Eur Heart J 2015; 36:1394–1404.
7. Franck G, Mawson T, Sausen G, et al. Flow perturbation mediates neutrophil recruitment and potentiates endothelial injury via TLR2 in mice - implications for superficial erosion. Circ Res 2017; 121:31–42.
8. Mullick AE, Tobias PS, Curtiss LK. Modulation of atherosclerosis in mice by Toll-like receptor 2. J Clin Invest 2005; 115:3149–3156.
9. Mullick AE, Tobias PS, Curtiss LK. Toll-like receptors and atherosclerosis: key contributors in disease and health? Immunol Res 2006; 34:193–209.
10. Tricot O, Mallat Z, Heymes C, et al. Relation between endothelial cell apoptosis and blood flow direction in human atherosclerotic plaques. Circulation 2000; 101:2450–2453.
11. Wang XX, Lv XX, Wang JP, et al. Blocking TLR2 activity diminishes and stabilizes advanced atherosclerotic lesions in apolipoprotein E-deficient mice. Acta Pharma Sin 2013; 34:1025–1035.
12. Lee GL, Chang YW, Wu JY, et al. TLR 2 induces vascular smooth muscle cell migration through cAMP response element-binding protein-mediated interleukin-6 production. Arterioscler Thromb Vasc Biol 2012; 32:2751–2760.
13. Shishido T, Nozaki N, Takahashi H, et al. Central role of endogenous Toll-like receptor-2 activation in regulating inflammation, reactive oxygen species production, and subsequent neointimal formation after vascular injury. Biochem Biophys Res Commun 2006; 345:1446–1453.
14. Liu X, Ukai T, Yumoto H, et al. Toll-like receptor 2 plays a critical role in the progression of atherosclerosis that is independent of dietary lipids. Atherosclerosis 2008; 196:146–154.
15. Schoneveld AH, Oude Nijhuis MM, van Middelaar B, et al. Toll-like receptor 2 stimulation induces intimal hyperplasia and atherosclerotic lesion development. Cardiovasc Res 2005; 66:162–169.
16. Oliveira-Nascimento L, Massari P, Wetzler LM. The role of TLR2 in infection and immunity. Front Immunol 2012; 3:79.
17. Chavez-Sanchez L, Garza-Reyes MG, Espinosa-Luna JE, et al. The role of TLR2, TLR4 and CD36 in macrophage activation and foam cell formation in response to oxLDL in humans. Hum Immunol 2014; 75:322–329.
18. Chukkapalli SS, Velsko IM, Rivera-Kweh MF, et al. Global TLR2 and 4 deficiency in mice impacts bone resorption, inflammatory markers and atherosclerosis to polymicrobial infection. Mol Oral Microbiol 2017; 32:211–225.
19. Huang B, Park DW, Baek SH. TRIF is a regulator of TLR2-induced foam cell formation. Mol Med Rep 2016; 14:3329–3335.
20. Inoue K, Kawahara K, Biswas KK, et al. HMGB1 expression by activated vascular smooth muscle cells in advanced human atherosclerosis plaques. Cardiovasc Pathol 2007; 16:136–143.
21. Messmer D, Yang H, Telusma G, et al. High mobility group box protein 1: an endogenous signal for dendritic cell maturation and Th1 polarization. J Immunol 2004; 173:307–313.
22. Dusio GF, Cardani D, Zanobbio L, et al. Stimulation of TLRs by LMW-HA induces self-defense mechanisms in vaginal epithelium. Immunol Cell Biol 2011; 89:630–639.
23. Abe T, Fukuhara T, Wen X, et al. CD44 participates in IP-10 induction in cells in which hepatitis C virus RNA is replicating, through an interaction with Toll-like receptor 2 and hyaluronan. J Virol 2012; 86:6159–6170.
24. Wang W, Xu GL, Jia WD, et al. Ligation of TLR2 by versican: a link between inflammation and metastasis. Arch Med Res 2009; 40:321–323.
25. Wang W, Xu GL, Jia WD, et al. Differential accumulation of proteoglycans and hyaluronan in culprit lesions: insights into plaque erosion. Arterioscler Thromb Vasc Biol 2002; 22:1642–1648.
26. Favre J, Musette P, Douin-Echinard V, et al. Toll-like receptors 2-deficient mice are protected against postischemic coronary endothelial dysfunction. Arterioscler Thromb Vasc Biol 2007; 27:1064–1071.
27. Shin HS, Xu F, Bagchi A, et al. Bacterial lipoprotein TLR2 agonists broadly modulate endothelial function and coagulation pathways in vitro and in vivo. J Immunol 2011; 186:1119–1130.
28. Doring Y, Drechsler M, Soehnlein O, Weber C. Neutrophils in atherosclerosis: from mice to man. Arterioscler Thromb Vasc Biol 2015; 35:288–295.
29. Yipp BG, Petri B, Salina D, et al. Infection-induced NETosis is a dynamic process involving neutrophil multitasking in vivo. Nat Med 2012; 18:1386–1393.
30. Megens RT, Vijayan S, Lievens D, et al. Presence of luminal neutrophil extracellular traps in atherosclerosis. Thromb Haemost 2012; 107:597–598.
31. Naruko T, Ueda M, Haze K, et al. Neutrophil infiltration of culprit lesions in acute coronary syndromes. Circulation 2002; 106:2894–2900.
32. Knight JS, Luo W, O’Dell AA, et al. Peptidylarginine deiminase inhibition reduces vascular damage and modulates innate immune responses in murine models of atherosclerosis. Circ Res 2014; 114:947–956.
33. Warnatsch A, Ioannou M, Wang Q, Papayannopoulos V. Neutrophil extracellular traps license macrophages for cytokine production in atherosclerosis. Science 2015; 349:316–320.
34. Soehnlein O, Ortega-Gomez A, Doring Y, Weber C. Neutrophil-macrophage interplay in atherosclerosis: protease-mediated cytokine processing versus NET release. Thromb Haemost 2015; 114:866–867.
35. Doring Y, Soehnlein O, Weber C. Neutrophil extracellular traps in atherosclerosis and atherothrombosis. Circ Res 2017; 120:736–743.
36. Ferrante G, Nakano M, Prati F, et al. High levels of systemic myeloperoxidase are associated with coronary plaque erosion in patients with acute coronary syndromes: a clinicopathological study. Circulation 2010; 122:2505–2513.
37. Sugiyama S, Kugiyama K, Aikawa M, et al. Hypochlorous acid, a macrophage product, induces endothelial apoptosis and tissue factor expression: involvement of myeloperoxidase-mediated oxidant in plaque erosion and thrombogenesis. Arterioscler Thromb Vasc Biol 2004; 24:1309–1314.
38. Pitanga TN, de Aragao Franca L, Rocha VC, et al. Neutrophil-derived microparticles induce myeloperoxidase-mediated damage of vascular endothelial cells. BMC Cell Biol 2014; 15:21.
39. Dorweiler B, Torzewski M, Dahm M, et al. Subendothelial infiltration of neutrophil granulocytes and liberation of matrix-destabilizing enzymes in an experimental model of human neo-intima. Thromb Haemost 2008; 99:373–381.
40. Gupta AK, Joshi MB, Philippova M, et al. Activated endothelial cells induce neutrophil extracellular traps and are susceptible to NETosis-mediated cell death. Febs Lett 2010; 584:3193–3197.
41. Carmona-Rivera C, Zhao W, Yalavarthi S, Kaplan MJ. Neutrophil extracellular traps induce endothelial dysfunction in systemic lupus erythematosus through the activation of matrix metalloproteinase-2. Ann Rheum Dis 2015; 74:1417–1424.
42. Villanueva E, Yalavarthi S, Berthier CC, et al. Netting neutrophils induce endothelial damage, infiltrate tissues, and expose immunostimulatory molecules in systemic lupus erythematosus. J Immunol 2011; 187:538–552.
43. Dancey JT, Deubelbeiss KA, Harker LA, Finch CA. Neutrophil kinetics in man. J Clin Invest 1976; 58:705–715.
44. Fuchs TA, Brill A, Duerschmied D, et al. Extracellular DNA traps promote thrombosis. Proc Natl Acad Sci U S A 2010; 107:15880–15885.
45. von Bruhl ML, Stark K, Steinhart A, et al. Monocytes, neutrophils, and platelets cooperate to initiate and propagate venous thrombosis in mice in vivo. J Exp Med 2012; 209:819–835.
46. McDonald B, Davis RP, Kim SJ, et al. Platelets and neutrophil extracellular traps collaborate to promote intravascular coagulation during sepsis in mice. Blood 2017; 129:1357–1367.
47. Massberg S, Brand K, Gruner S, et al. A critical role of platelet adhesion in the initiation of atherosclerotic lesion formation. J Exp Med 2002; 196:887–896.
48. Gould TJ, Vu TT, Swystun LL, et al. Neutrophil extracellular traps promote thrombin generation through platelet-dependent and platelet-independent mechanisms. Arterioscler Thromb Vasc Biol 2014; 34:1977–1984.
49. Yang X, Li L, Liu J, et al. Extracellular histones induce tissue factor expression in vascular endothelial cells via TLR and activation of NF-kappaB and AP-1. Thromb Res 2016; 137:211–218.
50. Haubitz M, Gerlach M, Kruse HJ, Brunkhorst R. Endothelial tissue factor stimulation by proteinase 3 and elastase. Clin Exp Immunol 2001; 126:584–588.
51. Kim JE, Yoo HJ, Gu JY, Kim HK. Histones induce the procoagulant phenotype of endothelial cells through tissue factor up-regulation and thrombomodulin down-regulation. PLoS One 2016; 11:e0156763.
52. Borissoff JI, Joosen IA, Versteylen MO, et al. Elevated levels of circulating DNA and chromatin are independently associated with severe coronary atherosclerosis and a prothrombotic state. Arterioscler Thromb Vasc Biol 2013; 33:2032–2040.
53. Fuchs TA, Brill A, Wagner DD. Neutrophil extracellular trap (NET) impact on deep vein thrombosis. Arterioscler Thromb Vasc Biol 2012; 32:1777–1783.
54. Martinod K, Wagner DD. Thrombosis: tangled up in NETs. Blood 2014; 123:2768–2776.
55. Kambas K, Chrysanthopoulou A, Vassilopoulos D, et al. Tissue factor expression in neutrophil extracellular traps and neutrophil derived microparticles in antineutrophil cytoplasmic antibody associated vasculitis may promote thromboinflammation and the thrombophilic state associated with the disease. Ann Rheum Dis 2014; 73:1854–1863.
56. Stakos DA, Kambas K, Konstantinidis T, et al. Expression of functional tissue factor by neutrophil extracellular traps in culprit artery of acute myocardial infarction. Eur Heart J 2015; 36:1405–1414.
57. Mangold A, Alias S, Scherz T, et al. Coronary neutrophil extracellular trap burden and deoxyribonuclease activity in ST-elevation acute coronary syndrome are predictors of ST-segment resolution and infarct size. Circ Res 2015; 116:1182–1192.
58. Libby P, Pasterkamp G. Requiem for the ’vulnerable plaque’. Eur Heart J 2015; 36:2984–2987.
59. Libby P. Seeing and sampling the surface of the atherosclerotic plaque: red or white can make blue. Arterioscler Thromb Vasc Biol 2016; 36:2275–2277.
60. Jia H, Dai J, Hou J, et al. Effective antithrombotic therapy without stenting: intravascular optical coherence tomography-based management in plaque erosion (the EROSION study). Eur Heart J 2017; 38:792–800.
Keywords:

acute coronary syndromes; glycosaminoglycans; intimal hyperplasia; lipid lowering therapy

Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.