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Plaque angiogenesis and its relation to inflammation and atherosclerotic plaque destabilization

de Vries, Margreet R.; Quax, Paul H.A.

doi: 10.1097/MOL.0000000000000339

Purpose of review The review discusses the recent literature on plaque angiogenesis and its relation to inflammation and plaque destabilization. Furthermore, it discusses how plaque angiogenesis can be used to monitor atherosclerosis and serve as a therapeutic target.

Recent findings Histopathologic studies have shown a clear relationship between plaque angiogenesis, intraplaque hemorrhage (IPH), plaque vulnerability, and cardiovascular events. Hypoxia is a main driver of plaque angiogenesis and the mechanism behind angiogenesis is only partly known. IPH, as the result of immature neovessels, is associated with increased influx of inflammatory cells in the plaques. Experimental models displaying certain features of human atherosclerosis such as plaque angiogenesis or IPH are developed and can contribute to unraveling the mechanism behind plaque vulnerability. New imaging techniques are established, with which plaque angiogenesis and vulnerability can be detected. Furthermore, antiangiogenic therapies in atherosclerosis gain much attention.

Summary Plaque angiogenesis, IPH, and inflammation contribute to plaque vulnerability. Histopathologic and imaging studies together with specific experimental studies have provided insights in plaque angiogenesis and plaque vulnerability. However, more extensive knowledge on the underlying mechanism is required for establishing new therapies for patients at risk.

Department of Surgery, Einthoven Laboratory for Experimental Vascular Medicine, Leiden University Medical Center, Leiden, The Netherlands

Correspondence to Margreet R. de Vries, PhD, Department of Surgery, Einthoven Laboratory for Experimental Vascular Medicine, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands. Tel: +31 715264859;. e-mail:

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0, where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially.

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The majority of acute cardiovascular events in patients is caused by occlusive thrombosis because of rupture or erosion of an atherosclerotic plaque [1]. Plaques that are most at risk are characterized by large necrotic cores with a thin fibrous cap [1,2▪▪]. A high-inflammatory content with increased protease activity critically determines the risk of rupture [3]. Hypoxia in atherosclerotic plaques is now widely recognized, because of the use of specific probes in imaging studies [4]. Plaque angiogenesis is a physiological response to facilitate the increased oxygen demand in the plaque but can have adverse effects by facilitating intraplaque hemorrhage (IPH) and influx of inflammatory mediators (Fig. 1a). IPH as a result of immature plaque neovessels is clearly associated with subsequent ischemic events [5–8]. Inflammatory cell, endothelial cell, and pericyte interactions can provide insight in the biological mechanisms of plaque angiogenesis. In this review, we focus on plaque angiogenesis, the relation with inflammatory mediators, and the subsequent effects of IPH on plaque instability, both in experimental models and in humans. We will further discuss options to target plaque angiogenesis, for imaging and therapeutic purposes.



Box 1

Box 1

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Nourishment and oxygenation of arteries is to a certain extent possible by diffusion from the luminal blood. Larger arteries (vessel size >0.5 mm) need vasa vasorum, a specialized microvascular network, to meet these demands [9]. Atherosclerotic lesion formation increases the vessel wall thickness resulting in regional limited oxygen exchange. Vascular cells respond to hypoxic conditions with changes in cell metabolism, angiogenesis, apoptosis, and inflammatory responses comparable to cells in tumors [10▪]. Local hypoxic regions and hypoxic cells in atherosclerotic lesions are demonstrated in humans and experimental models [11–14]. Increased oxygen consumption by high metabolic active cells such as macrophages further depletes the oxygen availability, creating a hypoxic environment in the atherosclerotic lesion [13]. In macrophages, hypoxia not only affects the metabolism [15,16▪] and lipid uptake [17], but also results in an increased inflammatory response characterized by increased IL-1β and caspase-1 activation [18]. Hypoxia also augments the thrombogenic potential of atherosclerotic plaques via upregulation of tissue factor [19▪]. The importance of hypoxia in enhancing atherosclerosis and plaque destabilization is excellently reviewed in this journal by Marsch et al. [4]. These authors also observed that hypoxia replacement therapy in mice affected efferocytosis resulting in reduced atherosclerosis [20].

Adaptation to the hypoxic environment is directed by the oxygen-sensitive transcription factor hypoxia-inducible factor (HIF)-1. HIF-1 consists of a heterodimer of the rapidly modified and degraded HIF1-α and the constant available HIF-1β. Prolyl hydroxylase domain-containing protein 2 is essential for degrading HIF-1-α and blockade of prolyl hydroxylase domain-containing protein 2 improves angiogenic responses [21]. HIF-1 induces transcription of hypoxia responsive genes such as fibroblast growth factor, cytokines, angiopoietins (ANG), and in particular vascular endothelial growth factor (VEGF) [22]. The role of HIF-1 in atherosclerosis is not univocal. Silencing of HIF-1-α in macrophages reduces proinflammatory factors and increases macrophage apoptosis [16▪]. Hyperlipidemia impairs angiogenesis in a HIF-1β and NF-κB-dependent manner [23,24]. HIF-1α inhibition abrogates the macrophage-dependent proangiogenic effect of oxidized LDL in an in-vivo angiogenesis assay [25]. Specific knockdown of HIF1-α in endothelial cells reduces atherosclerosis via reduced monocyte recruitment [26], whereas knockdown in antigen presenting cells results in aggravation of atherosclerosis via T-cell polarization [27].

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As early as 1936, small blood vessels entering an atherosclerotic plaque were described by the pathologist Paterson [28]. The pathological effect of plaque angiogenesis by facilitating inflammatory influx and IPH is well established [29–31]. A direct relationship of plaque angiogenesis and hypoxia was shown by Sluimer et al. [12]. Plaque angiogenesis is frequently associated with shoulder regions and gradually increases with lesion progression [31]. The majority of the neovessels in the plaque originate from adventitial vasa vasorum [29,32]. Pathophysiological studies have reported increased vasa vasorum densities in vulnerable lesions [9,32] as well as in aortic aneurysms [33]. There is experimental evidence that sprouting of vasa vasorum precedes lesion formation [34] and is more associated with adventitial inflammation and perivascular fat [30,35] and less with hypoxia. It is therefore proposed that vasa vasorum hyperplasia and plaque angiogenesis are based on two different mechanisms [9,36].

To initiate vessel sprouting, endothelial cells switch from a quiescent state to a highly migratory and proliferative state (Fig. 1b). This switch is codetermined by the metabolic status of the endothelial cells [37]. VEGF-A, the most prominent VEGF, is highly upregulated in various cell types in atherosclerotic plaques and enhances atherosclerosis [38]. VEGFR2 is the main receptor for VEGF-A, because of its strong tyrosine kinase activity. VEGF-bound VEGFR2 becomes internalized, under the influence of the urokinase plasminogen activator receptor, and continues to signal from the endosomal compartments in endothelial cells [39]. Vessel wall enveloping pericytes detach in response to ANG-2 and liberate themselves from the basement membrane by proteolytic degradation. Plasma proteins leak into the extracellular space and create an environment into which endothelial cells can migrate in response to integrin signaling. Leading tip cells and the following stalk cells form a tube-like structure under the control of VEGF receptors, neutroplins, and NOTCH ligands [40].

For a vessel to become functional it has to become mature and perfused, otherwise it will regress. Fusion of sprouting neovessels, which is necessary to form a vascular network, is controlled by macrophages [41,42]. Basement membranes and pericytes stabilize the endothelial tubes and help in regulating the capillary diameter and vessel permeability [43▪]. ANG-1 and NOTCH stimulate basement membrane deposition [44,45]. Together with platelet-derived growth factor-B and transforming growth factor-β these factors attract pericytes and stimulate them to envelope the nascent blood vessels [44,46]. Akt signaling in endothelial cells is crucial for the interaction with pericytes [47]. Defective pericyte coverage or pericyte loss leads to abnormal capillary function [48] and consequently to leaky blood vessels. ANG and their receptor Tie-2 are essential for the maintenance of pericyte and endothelial cell integrity with a stabilizing role for ANG-1 and a destabilizing role for ANG-2. In atherosclerotic lesions with a high neovessel density, the local balance between ANG-1 and ANG-2 is in favor of ANG-2 [49]. Furthermore, inhibition of ANG-2 in mice reduces early atherosclerosis plaque development [27].

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Neovessels in vulnerable plaques appear abnormal with an excess in disorganized vessels that are enlarged and facilitate extravasation of erythrocytes [50,51]. A profound relationship between IPH and cardiovascular outcome is well established [7,52]. Plaque angiogenesis and IPH are also associated with an increased risk for secondary events [52]. Histopathologic analysis of IPH is based on extravasated erythrocytes and intramural fibrin around immature neovessels (Fig. 1c). Older hemorrhages can be identified by residual iron or glycophorin [29]. Neovessel leakages enrich plaques with blood-borne components such as erythrocytes, inflammatory cells, lipoproteins, and plasma constituents affecting pathological processes such as cholesterol retention, oxidative and proteolytic activities. Membranes of circulating cells and especially erythrocytes contain significant amounts of free cholesterol, which contribute to lipid accumulation in the plaque and can trigger inflammatory responses [29]. Hemoglobin and iron released from erythrocytes are pro-oxidant and capable of causing lipid oxidation and tissue damage [53]. Hemoglobin can trigger an atheroprotective macrophage subset, which has antioxidant and foam-cell protective effects [54–56]. IPH is, however, considered proatherosclerotic, as most macrophages associated with IPH have significant protease activity especially from excreted matrix metalloproteases (MMPs) [57]. Furthermore, intramural fibrin deposits are cleared by fibrinolytic factors, such as tPA, uPA, and plasmin, triggering a proinflammatory, proatherosclerotic response [58].

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Inflammatory cells such as macrophages and mast cells are found in the local presence of plaque neovessels [41,58]. These cells are rich sources of cytokines, growth factors, and MMPs, and can influence both plaque stability and plaque angiogenesis [41,59▪]. Inflammatory cells can leak from immature neovessels, but active attraction of these cells via release of specific mediators such as complement factors and TLR ligands also occurs [60▪,61,62]. Furthermore, immature neovessels are known for their active extravasation of leukocytes [62]. The mechanisms involved in trafficking of leukocytes across the endothelium are well studied and involve integrin and adhesion molecule interactions [63,64]. Inflammatory mediators are released by inflammatory cells, neovessel associated endothelial cells, and pericytes. These cell types also respond to the same inflammatory mediators resulting in crosstalk and intertwined responses enhancing their (adverse) effects (Fig. 1d).

Various subsets of macrophages have different roles in atherosclerosis [56,65]. M1 macrophages display a proinflammatory role, including proinflammatory cytokine secretion and phagocytosis, enhancing plaque vulnerability. Whereas, repair-associated M2-like macrophages are linked to neovessels and promote angiogenesis, in part by elevated VEGF secretion [66,67▪]. Endothelial progenitor cells of monocytic origin are mobilized by VEGF and contribute to plaque angiogenesis [41].

A clear relationship between cardiovascular events and plaque neovessel-associated mast cells is established [58]. Mast cells contain and excrete numerous factors, such as tryptase, chymase complement factors, and TLRs, that can influence angiogenesis and plaque vulnerability [59▪,68]. In a murine vein graft model in which plaque angiogenesis prominently occurs [69], complement factor 5a [70] and TLR4 analogue radioprotective 105 [71] influence plaque stability, including IPH, in a mast cell-dependent way.

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Complex atherosclerotic lesions with plaque rupture and subsequent thrombosis are rare in experimental animals [72,73]. Especially, plaque neovessels are seldom observed. However, various mouse models of plaque rupture and especially IPH have been described [74,75▪]. Moulton et al. [76] were the first to show a reduction of atherosclerotic lesion formation in apolipoprotein E deficient (ApoE−/−) mice after treatment with the angiogenesis inhibitors endostatin, TNP-470, and angiostatin [77]. Hartwig et al. [75▪] performed a comparative study on models for vulnerable plaques and found that hypercholesterolemic mice with a shear stress modifier device best replicated human-like lesions with IPH. In ApoE−/− mice with a mutation in the fibrillin-1 gene, highly unstable plaques with plaque angiogenesis and plaque rupture were observed. This model was further associated with myocardial infarction, stroke, and sudden death [78▪▪]. Stress enhanced the phenotype, whereas treatment with atorvastatin prevented mortality and morbidity [79,80]. Human atherosclerotic lesions in saphenous vein bypass grafts are vulnerable and have a higher risk to disrupt than native atherosclerotic lesions [2▪▪,81,82]. Atherosclerotic lesions in vein grafts in hypercholesterolemic mice demonstrate plaque angiogenesis and IPH (Fig. 2) [69]. Moreover, dissections and erosion are frequently observed. Disruption of these lesions could be prevented by inhibiting protease activity by overexpressing tissue inhibitor of MMP-1 [69]. Experimental models that completely resemble human lesions will likely never occur, especially taken into account that human lesions develop over decades and animal atherosclerotic plaques in months. However, specific features of vulnerable lesions can be studied in animal models. Especially, mice carrying the fibrilin-1 mutation and the vein graft model are very suitable to study plaque rupture and plaque angiogenesis.



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The lymphatic system forms a blind-ended network from the extracellular space to the blood circulation and consists of lymphatic vessels, lymph nodes, and associated lymph organs [83,84]. The lymphatic system actively regulates tissue fluid homeostasis, absorption of gastrointestional lipids [85], and trafficking of cells and antigens to lymph nodes [86]. VEGF-C, VEGFR-3, and lymphatic vessel endothelial hyaluron receptor 1 (LYVE1) are involved in lymph angiogenesis and maturation of the lymphatic system [84]. Lymphoid-homing chemokines CCL21, CCL19, and plasmalemma vesicle-associated protein expressed by lymphatic endothelial cells actively guide CCR7 expressing leukocytes or antigen-presenting cells to the lymph nodes [87]. CCR7 deficient mice on an atherosclerotic background showed retention of lymphocytes and exacerbated atherosclerosis [88]. Interestingly, in aged APOE−/− mice adventitial lymphatic lymphatic vessel endothelial hyaluron receptor 1 + vessels seem to regress, which coincides with increased levels of VEGFR-2, which could trap VEGF-C [89]. Upon chronic inflammation, tertiary lymphoid organs (TLOs) can emerge on the adventitial side of plaques [90]. These TLOs contain, in contrast to secondary lymph nodes, high densities of regulatory T cells [90] and B cells [91], and seem to be associated with atherosclerosis protection [92▪]. These intriguing findings bring new insights in the dynamic role of the adventitial lymphatic system in atherosclerosis.

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In-vivo imaging technology now offers opportunities to identify vulnerable atherosclerotic lesions in patients by analysis of major plaque components, aiming at prevention of acute events. Computerized tomographic angiography, MRI, (intravascular) ultrasound imaging, and optical coherence tomography can identify thin-cap plaques, calcification, and outward remodeling. Various established techniques and new approaches are extensively reviewed [93,94,95▪▪,96]. Contrast agents, tracers, and targeted imaging probes can enhance the resolution and/or specificity of the imaging strategy [97–100]. Especially, (18)[F]-fluorodeoxyglucose PET imaging has emerged as a promising imaging strategy, because of recognition of plaque glycolysis, plaque inflammation, and hypoxia, all major stimuli for plaque angiogenesis and vulnerability [16▪,101]. A more specific approach to image plaque angiogenesis is the use of endothelial-specific targeting. Several specific probes have been shown to be successful in experimental models [102–104]. These novel imaging techniques can be used to perform functional imaging and in-vivo microscopy of plaque components in greater detail than ever before, allowing longitudinal analyses and investigation of the efficacy of antiatherosclerotic strategies.

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Plaque angiogenesis is a physiological process in which the associated proinflammatory and proatherosclerotic effects are detrimental for plaque vulnerability. Plaque angiogenesis is therefore considered a potential therapeutic target comparable to tumor angiogenesis [105]. Antiangiogenic therapies are effective in experimental atherosclerosis [76,77], whereas inhibition of VEGF increased atherosclerosis [106]. Unfortunately, antiangiogenesis strategies showed minor survival benefits in cancer patients, even increased hypoxia and tumor progression was observed [10▪]. Antiangiogenic strategies to improve vessel maturation are a potential alternative [10▪,107,108▪▪], including targeting pericytes [43▪,109]. This seems an elegant strategy, but there are still many unresolved issues that need to be clarified.

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It is well established that intraplaque angiogenesis and IPH are crucial processes for plaque instability, however, the pathophysiology of these processes are not yet resolved. The increased knowledge of plaque angiogenesis as well as the improved animal models in which plaque angiogenesis can be studied, and the potential of antiangiogenic approaches in the tumor field, suggest that antiangiogenic treatments in atherosclerosis will be defined in the near future.

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Financial support and sponsorship

The work was supported by a grant from the European union, Horizon 2020 MSCA joint doctoral project, MOGLYNET (project 675527).

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Conflicts of interest

There are no conflicts of interest.

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Papers of particular interest, published within the annual period of review, have been highlighted as:

  • ▪ of special interest
  • ▪▪ of outstanding interest
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1. Bentzon JF, Otsuka F, Virmani R, Falk E. Mechanisms of plaque formation and rupture. Circ Res 2014; 114:1852–1866.
2▪▪. Yahagi K, Kolodgie FD, Otsuka F, et al. Pathophysiology of native coronary, vein graft, and in-stent atherosclerosis. Nat Rev Cardiol 2015; 13:79–98.

An update on the pathophysiology of native atherosclerosis and a thorough description of vein graft and in stent atherosclerosis. They observed that atherosclerotic lesions, which are formed after a surgical intervention are often found vulnerable.

3. Hansson GK, Libby P, Tabas I. Inflammation and plaque vulnerability. J Intern Med 2015; 278:483–493.
4. Marsch E, Sluimer JC, Daemen MJ. Hypoxia in atherosclerosis and inflammation. Curr Opin Lipidol 2013; 24:393–400.
5. Kolodgie FD, Gold HK, Burke AP, et al. Intraplaque hemorrhage and progression of coronary atheroma. N Engl J Med 2003; 349:2316–2325.
6. Michel JB, Virmani R, Arbustini E, Pasterkamp G. Intraplaque haemorrhages as the trigger of plaque vulnerability. Eur Heart J 2011; 32:1977–1985.
7. Teng Z, Sadat U, Brown AJ, Gillard JH. Plaque hemorrhage in carotid artery disease: pathogenesis, clinical and biomechanical considerations. J Biomech 2014; 47:847–858.
8. Vrijenhoek JE, Den Ruijter HM, De Borst GJ, et al. Sex is associated with the presence of atherosclerotic plaque hemorrhage and modifies the relation between plaque hemorrhage and cardiovascular outcome. Stroke 2013; 44:3318–3323.
9. Mulligan-Kehoe MJ, Simons M. Vasa vasorum in normal and diseased arteries. Circulation 2014; 129:2557–2566.
10▪. Jain RK. Antiangiogenesis strategies revisited: from starving tumors to alleviating hypoxia. Cancer Cell 2014; 26:605–622.

Excellent review on the latest antiangiogenic strategies, which are based on stabilizing vascular beds to facilitate the delivery of cytostatic agents.

11. Bjornheden T, Levin M, Evaldsson M, Wiklund O. Evidence of hypoxic areas within the arterial wall in vivo. Arterioscler Thromb Vasc Biol 1999; 19:870–876.
12. Sluimer JC, Gasc JM, van Wanroij JL, et al. Hypoxia, hypoxia-inducible transcription factor, and macrophages in human atherosclerotic plaques are correlated with intraplaque angiogenesis. J Am Coll Cardiol 2008; 51:1258–1265.
13. Parathath S, Mick SL, Feig JE, et al. Hypoxia is present in murine atherosclerotic plaques and has multiple adverse effects on macrophage lipid metabolism. Circ Res 2011; 109:1141–1152.
14. van der Valk FM, Sluimer JC, Voo SA, et al. In vivo imaging of hypoxia in atherosclerotic plaques in humans. JACC Cardiovasc Imaging 2015; 8:1340–1341.
15. Yamashita A, Zhao Y, Matsuura Y, et al. Increased metabolite levels of glycolysis and pentose phosphate pathway in rabbit atherosclerotic arteries and hypoxic macrophage. PLoS One 2014; 9:e86426.
16▪. Tawakol A, Singh P, Mojena M, et al. HIF-1α and PFKFB3 mediate a tight relationship between proinflammatory activation and anerobic metabolism in atherosclerotic macrophages. Arterioscler Thromb Vasc Biol 2015; 35:1463–1471.

Hypoxia potentiates proinflammatory activity and glycolysis in macrophages in a HIF-1α-dependent manner.

17. Crucet M, Wust SJ, Spielmann P, et al. Hypoxia enhances lipid uptake in macrophages: role of the scavenger receptors Lox1, SRA, and CD36. Atherosclerosis 2013; 229:110–117.
18. Folco EJ, Sukhova GK, Quillard T, Libby P. Moderate hypoxia potentiates interleukin-1β production in activated human macrophages. Circ Res 2014; 115:875–883.
19▪. Matsuura Y, Yamashita A, Iwakiri T, et al. Vascular wall hypoxia promotes arterial thrombus formation via augmentation of vascular thrombogenicity. Thromb Haemost 2015; 114:158–172.

Shows the effect of hypoxia on prothrombotic factor upregulation in arterial thrombus formation.

20. Marsch E, Theelen TL, Demandt JA, et al. Reversal of hypoxia in murine atherosclerosis prevents necrotic core expansion by enhancing efferocytosis. Arterioscler Thromb Vasc Biol 2014; 34:2545–2553.
21. Lijkwan MA, Hellingman AA, Bos EJ, et al. Short hairpin RNA gene silencing of prolyl hydroxylase-2 with a minicircle vector improves neovascularization of hindlimb ischemia. Hum Gene Ther 2014; 25:41–49.
22. Deng W, Feng X, Li X, et al. Hypoxia-inducible factor 1 in autoimmune diseases. Cell Immunol 2016; 303:7–15.
23. van Weel V, de Vries M, Voshol PJ, et al. Hypercholesterolemia reduces collateral artery growth more dominantly than hyperglycemia or insulin resistance in mice. Arterioscler Thromb Vasc Biol 2006; 26:1383–1390.
24. Yao G, Zhang Q, Doeppner TR, et al. LDL suppresses angiogenesis through disruption of the HIF pathway via NF-kappaB inhibition which is reversed by the proteasome inhibitor BSc2118. Oncotarget 2015; 6:30251–30262.
25. Hutter R, Speidl WS, Valdiviezo C, et al. Macrophages transmit potent proangiogenic effects of oxLDL in vitro and in vivo involving HIF-1α activation: a novel aspect of angiogenesis in atherosclerosis. J Cardiovasc Transl Res 2013; 6:558–569.
26. Akhtar S, Hartmann P, Karshovska E, et al. Endothelial hypoxia-inducible factor-1α promotes atherosclerosis and monocyte recruitment by upregulating microRNA-19a. Hypertension 2015; 66:1220–1226.
27. Chaudhari SM, Sluimer JC, Koch M, et al. Deficiency of HIF1α in antigen-presenting cells aggravates atherosclerosis and type 1 T-helper cell responses in mice. Arterioscler Thromb Vasc Biol 2015; 35:2316–2325.
28. Paterson JC. Vascularization and hemorrhage of the intima of arteriosclerotic coronary arteries. Arch Path 1936; 22:313.
29. Virmani R, Kolodgie FD, Burke AP, et al. Atherosclerotic plaque progression and vulnerability to rupture: angiogenesis as a source of intraplaque hemorrhage. Arterioscler Thromb Vasc Biol 2005; 25:2054–2061.
30. van Hinsbergh VW, Eringa EC, Daemen MJ. Neovascularization of the atherosclerotic plaque: interplay between atherosclerotic lesion, adventitia-derived microvessels and perivascular fat. Curr Opin Lipidol 2015; 26:405–411.
31. Sluimer JC, Daemen MJ. Novel concepts in atherogenesis: angiogenesis and hypoxia in atherosclerosis. J Pathol 2009; 218:7–29.
32. Xu J, Lu X, Shi GP. Vasa vasorum in atherosclerosis and clinical significance. Int J Mol Sci 2015; 16:11574–11608.
33. Kessler K, Borges LF, Ho-Tin-Noe B, et al. Angiogenesis and remodelling in human thoracic aortic aneurysms. Cardiovasc Res 2014; 104:147–159.
34. Herrmann J, Lerman LO, Rodriguez-Porcel M, et al. Coronary vasa vasorum neovascularization precedes epicardial endothelial dysfunction in experimental hypercholesterolemia. Cardiovasc Res 2001; 51:762–766.
35. Manka D, Chatterjee TK, Stoll LL, et al. Transplanted perivascular adipose tissue accelerates injury-induced neointimal hyperplasia: role of monocyte chemoattractant protein-1. Arterioscler Thromb Vasc Biol 2014; 34:1723–1730.
36. Fleiner M, Kummer M, Mirlacher M, et al. Arterial neovascularization and inflammation in vulnerable patients: early and late signs of symptomatic atherosclerosis. Circulation 2004; 110:2843–2850.
37. Eelen G, de Zeeuw P, Simons M, Carmeliet P. Endothelial cell metabolism in normal and diseased vasculature. Circ Res 2015; 116:1231–1244.
38. Celletti FL, Waugh JM, Amabile PG, et al. Vascular endothelial growth factor enhances atherosclerotic plaque progression. Nat Med 2001; 7:425–429.
39. Herkenne S, Paques C, Nivelles O, et al. The interaction of uPAR with VEGFR2 promotes VEGF-induced angiogenesis. Sci Signal 2015; 8:ra117.
40. Carmeliet P, Jain RK. Molecular mechanisms and clinical applications of angiogenesis. Nature 2011; 473:298–307.
41. Jaipersad AS, Lip GY, Silverman S, Shantsila E. The role of monocytes in angiogenesis and atherosclerosis. J Am Coll Cardiol 2014; 63:1–11.
42. Fantin A, Vieira JM, Gestri G, et al. Tissue macrophages act as cellular chaperones for vascular anastomosis downstream of VEGF-mediated endothelial tip cell induction. Blood 2010; 116:829–840.
43▪. Stapor PC, Sweat RS, Dashti DC, et al. Pericyte dynamics during angiogenesis: new insights from new identities. J Vasc Res 2014; 51:163–174.

Review on the role of pericytes in angiogenesis, the phenotypes of pericytes and possible therapeutic strategies.

44. Stratman AN, Malotte KM, Mahan RD, et al. Pericyte recruitment during vasculogenic tube assembly stimulates endothelial basement membrane matrix formation. Blood 2009; 114:5091–5101.
45. Tattersall IW, Du J, Cong Z, et al. In vitro modeling of endothelial interaction with macrophages and pericytes demonstrates Notch signaling function in the vascular microenvironment. Angiogenesis 2016; 19:201–215.
46. van Dijk CG, Nieuweboer FE, Pei JY, et al. The complex mural cell: pericyte function in health and disease. Int J Cardiol 2015; 190:75–89.
47. Kerr BA, West XZ, Kim YW, et al. Stability and function of adult vasculature is sustained by Akt/Jagged1 signalling axis in endothelium. Nat Commun 2016; 7:10960.
48. Hellstrom M, Gerhardt H, Kalen M, et al. Lack of pericytes leads to endothelial hyperplasia and abnormal vascular morphogenesis. J Cell Biol 2001; 153:543–553.
49. Post S, Peeters W, Busser E, et al. Balance between angiopoietin-1 and angiopoietin-2 is in favor of angiopoietin-2 in atherosclerotic plaques with high microvessel density. J Vasc Res 2008; 45:244–250.
50. Sluimer JC, Kolodgie FD, Bijnens AP, et al. Thin-walled microvessels in human coronary atherosclerotic plaques show incomplete endothelial junctions relevance of compromised structural integrity for intraplaque microvascular leakage. J Am Coll Cardiol 2009; 53:1517–1527.
51. Dunmore BJ, McCarthy MJ, Naylor AR, Brindle NP. Carotid plaque instability and ischemic symptoms are linked to immaturity of microvessels within plaques. J Vasc Surg 2007; 45:155–159.
52. Hellings WE, Peeters W, Moll FL, et al. Composition of carotid atherosclerotic plaque is associated with cardiovascular outcome: a prognostic study. Circulation 2010; 121:1941–1950.
53. Habib A, Finn AV. The role of iron metabolism as a mediator of macrophage inflammation and lipid handling in atherosclerosis. Front Pharmacol 2014; 5:195.
54. Boyle JJ, Harrington HA, Piper E, et al. Coronary intraplaque hemorrhage evokes a novel atheroprotective macrophage phenotype. Am J Pathol 2009; 174:1097–1108.
55. Finn AV, Nakano M, Polavarapu R, et al. Hemoglobin directs macrophage differentiation and prevents foam cell formation in human atherosclerotic plaques. J Am Coll Cardiol 2012; 59:166–177.
56. Boyle JJ. Heme and haemoglobin direct macrophage Mhem phenotype and counter foam cell formation in areas of intraplaque haemorrhage. Curr Opin Lipidol 2012; 23:453–461.
57. Newby AC. Proteinases and plaque rupture: unblocking the road to translation. Curr Opin Lipidol 2014; 25:358–366.
58. Willems S, Vink A, Bot I, et al. Mast cells in human carotid atherosclerotic plaques are associated with intraplaque microvessel density and the occurrence of future cardiovascular events. Eur Heart J 2013; 34:3699–3706.
59▪. Shi GP, Bot I, Kovanen PT. Mast cells in human and experimental cardiometabolic diseases. Nat Rev Cardiol 2015; 12:643–658.

Complete review on the role of mast cells in cardiovascular diseases.

60▪. Aplin AC, Ligresti G, Fogel E, et al. Regulation of angiogenesis, mural cell recruitment and adventitial macrophage behavior by Toll-like receptors. Angiogenesis 2014; 17:147–161.

Delineates the role of various Toll-like receptors in experimental aortic explants.

61. Langer HF, Chung KJ, Orlova VV, et al. Complement-mediated inhibition of neovascularization reveals a point of convergence between innate immunity and angiogenesis. Blood 2010; 116:4395–4403.
62. Stark K, Eckart A, Haidari S, et al. Capillary and arteriolar pericytes attract innate leukocytes exiting through venules and ‘instruct’ them with pattern-recognition and motility programs. Nat Immunol 2013; 14:41–51.
63. Vestweber D. How leukocytes cross the vascular endothelium. Nat Rev Immunol 2015; 15:692–704.
64. Gerhardt T, Ley K. Monocyte trafficking across the vessel wall. Cardiovasc Res 2015; 107:321–330.
65. Tabas I, Bornfeldt KE. Macrophage phenotype and function in different stages of atherosclerosis. Circ Res 2016; 118:653–667.
66. Jetten N, Verbruggen S, Gijbels MJ, et al. Anti-inflammatory M2, but not pro-inflammatory M1 macrophages promote angiogenesis in vivo. Angiogenesis 2014; 17:109–118.
67▪. Barbay V, Houssari M, Mekki M, et al. Role of M2-like macrophage recruitment during angiogenic growth factor therapy. Angiogenesis 2015; 18:191–200.

A decisive role for M2-like macrophages in angiogenesis in various experimental models is shown.

68. de Souza Junior DA, Santana AC, da Silva EZ, et al. The role of mast cell specific chymases and tryptases in tumor angiogenesis. Biomed Res Int 2015; 2015:142359.
69. de Vries MR, Niessen HW, Lowik CW, et al. Plaque rupture complications in murine atherosclerotic vein grafts can be prevented by TIMP-1 overexpression. PLoS One 2012; 7:e47134.
70. de Vries MR, Wezel A, Schepers A, et al. Complement factor C5a as mast cell activator mediates vascular remodelling in vein graft disease. Cardiovasc Res 2013; 97:311–320.
71. Wezel A, de Vries MR, Maassen JM, et al. Deficiency of the TLR4 analogue RP105 aggravates vein graft disease by inducing a pro-inflammatory response. Sci Rep 2016; 6:24248.
72. Silvestre-Roig C, de Winther MP, Weber C, et al. Atherosclerotic plaque destabilization: mechanisms, models, and therapeutic strategies. Circ Res 2014; 114:214–226.
73. van der Heiden K, Hoogendoorn A, Daemen MJ, Gijsen FJ. Animal models for plaque rupture: a biomechanical assessment. Thromb Haemost 2016; 115:501–508.
74. Matoba T, Sato K, Egashira K. Mouse models of plaque rupture. Curr Opin Lipidol 2013; 24:419–425.
75▪. Hartwig H, Silvestre-Roig C, Hendrikse J, et al. Atherosclerotic plaque destabilization in mice: a comparative study. PLoS One 2015; 10:e0141019.

A comparison between three different mouse models of atherosclerotic plaque destabilization, including IPH.

76. Moulton KS, Heller E, Konerding MA, et al. Angiogenesis inhibitors endostatin or TNP-470 reduce intimal neovascularization and plaque growth in apolipoprotein E-deficient mice. Circulation 1999; 99:1726–1732.
77. Moulton KS, Vakili K, Zurakowski D, et al. Inhibition of plaque neovascularization reduces macrophage accumulation and progression of advanced atherosclerosis. Proc Natl Acad Sci U S A 2003; 100:4736–4741.
78▪▪. Van der Donckt C, Van Herck JL, Schrijvers DM, et al. Elastin fragmentation in atherosclerotic mice leads to intraplaque neovascularization, plaque rupture, myocardial infarction, stroke, and sudden death. Eur Heart J 2015; 36:1049–1058.

A description of the fibrilin-1 mutant mouse crossbred on an ApoE−/− background; probably the best mouse model for plaque vulnerability at this moment. Together with [77,78▪▪], in which strategies are described that target plaque vulnerability in this particular model.

79. Roth L, Rombouts M, Schrijvers DM, et al. Chronic intermittent mental stress promotes atherosclerotic plaque vulnerability, myocardial infarction and sudden death in mice. Atherosclerosis 2015; 242:288–294.
80. Roth L, Rombouts M, Schrijvers DM, et al. Cholesterol-independent effects of atorvastatin prevent cardiovascular morbidity and mortality in a mouse model of atherosclerotic plaque rupture. Vascul Pharmacol 2016; 80:50–58.
81. Yazdani SK, Farb A, Nakano M, et al. Pathology of drug-eluting versus bare-metal stents in saphenous vein bypass graft lesions. JACC Cardiovasc Interv 2012; 5:666–674.
82. de Vries MR, Simons KH, Jukema JW, et al. Vein graft failure: from pathophysiology to clinical outcomes. Nat Rev Cardiol 2016; doi: 10.1038/nrcardio.2016.76. [Epub ahead of print].
83. Kutkut I, Meens MJ, McKee TA, et al. Lymphatic vessels: an emerging actor in atherosclerotic plaque development. Eur J Clin Invest 2015; 45:100–108.
84. Yang Y, Oliver G. Development of the mammalian lymphatic vasculature. J Clin Invest 2014; 124:888–897.
85. Vuorio T, Nurmi H, Moulton K, et al. Lymphatic vessel insufficiency in hypercholesterolemic mice alters lipoprotein levels and promotes atherogenesis. Arterioscler Thromb Vasc Biol 2014; 34:1162–1170.
86. Aspelund A, Robciuc MR, Karaman S, et al. Lymphatic system in cardiovascular medicine. Circ Res 2016; 118:515–530.
87. Rantakari P, Auvinen K, Jappinen N, et al. The endothelial protein PLVAP in lymphatics controls the entry of lymphocytes and antigens into lymph nodes. Nat Immunol 2015; 16:386–396.
88. Wan W, Lionakis MS, Liu Q, et al. Genetic deletion of chemokine receptor Ccr7 exacerbates atherogenesis in ApoE-deficient mice. Cardiovasc Res 2013; 97:580–588.
89. Taher M, Nakao S, Zandi S, et al. Phenotypic transformation of intimal and adventitial lymphatics in atherosclerosis: a regulatory role for soluble VEGF receptor 2. FASEB J 2016; 30:2490–2499.
90. Mohanta SK, Yin C, Peng L, et al. Artery tertiary lymphoid organs contribute to innate and adaptive immune responses in advanced mouse atherosclerosis. Circ Res 2014; 114:1772–1787.
91. Srikakulapu P, Hu D, Yin C, et al. Artery tertiary lymphoid organs control multilayered territorialized atherosclerosis B-cell responses in aged ApoE−/−mice. Arterioscler Thromb Vasc Biol 2016; 36:1174–1185.
92▪. Hu D, Mohanta SK, Yin C, et al. Artery tertiary lymphoid organs control aorta immunity and protect against atherosclerosis via vascular smooth muscle cell lymphotoxin β receptors. Immunity 2015; 42:1100–1115.

An elegant study, in which a role is shown for artery TLOs in controlling the immune response in aged atherosclerotic mice.

93. Magnoni M, Ammirati E, Camici PG. Noninvasive molecular imaging of vulnerable atherosclerotic plaques. J Cardiol 2015; 65:261–269.
94. Alonso A, Artemis D, Hennerici MG. Molecular imaging of carotid plaque vulnerability. Cerebrovasc Dis 2015; 39:5–12.
95▪▪. Tarkin JM, Dweck MR, Evans NR, et al. Imaging atherosclerosis. Circ Res 2016; 118:750–769.

Up to date overview on atherosclerosis imaging technologies.

96. Bourantas CV, Jaffer FA, Gijsen FJ, et al. Hybrid intravascular imaging: recent advances, technical considerations, and current applications in the study of plaque pathophysiology. Eur Heart J 2016; [Epub ahead of print].
97. Calcagno C, Lobatto ME, Dyvorne H, et al. Three-dimensional dynamic contrast-enhanced MRI for the accurate, extensive quantification of microvascular permeability in atherosclerotic plaques. NMR Biomed 2015; 28:1304–1314.
98. Alie N, Eldib M, Fayad ZA, et al. Inflammation, atherosclerosis, and coronary artery disease: PET/CT for the evaluation of atherosclerosis and inflammation. Clin Med Insights Cardiol 2014; 8:13–21.
99. Yoo JS, Lee J, Jung JH, et al. SPECT/CT imaging of high-risk atherosclerotic plaques using integrin-binding RGD dimer peptides. Sci Rep 2015; 5:11752.
100. Kim S, Lee MW, Kim TS, et al. Intracoronary dual-modal optical coherence tomography-near-infrared fluorescence structural-molecular imaging with a clinical dose of indocyanine green for the assessment of high-risk plaques and stent-associated inflammation in a beating coronary artery. Eur Heart J 2016; [Epub ahead of print].
101. Taqueti VR, Di Carli MF, Jerosch-Herold M, et al. Increased microvascularization and vessel permeability associate with active inflammation in human atheromata. Circ Cardiovasc Imaging 2014; 7:920–929.
102. Zhang R, Pan D, Cai X, et al. alphaVbeta3-targeted copper nanoparticles incorporating an Sn 2 lipase-labile fumagillin prodrug for photoacoustic neovascular imaging and treatment. Theranostics 2015; 5:124–133.
103. Wang K, Pan D, Schmieder AH, et al. Atherosclerotic neovasculature MR imaging with mixed manganese-gadolinium nanocolloids in hyperlipidemic rabbits. Nanomedicine 2015; 11:569–578.
104. Belliere J, Martinez de Lizarrondo S, Choudhury RP, et al. Unmasking silent endothelial activation in the cardiovascular system using molecular magnetic resonance imaging. Theranostics 2015; 5:1187–1202.
105. Jain RK, Finn AV, Kolodgie FD, et al. Antiangiogenic therapy for normalization of atherosclerotic plaque vasculature: a potential strategy for plaque stabilization. Nat Clin Pract Cardiovasc Med 2007; 4:491–502.
106. Winnik S, Lohmann C, Siciliani G, et al. Systemic VEGF inhibition accelerates experimental atherosclerosis and disrupts endothelial homeostasis: implications for cardiovascular safety. Int J Cardiol 2013; 168:2453–2461.
107. Heist RS, Duda DG, Sahani DV, et al. Improved tumor vascularization after anti-VEGF therapy with carboplatin and nab-paclitaxel associates with survival in lung cancer. Proc Natl Acad Sci U S A 2015; 112:1547–1552.
108▪▪. Peterson TE, Kirkpatrick ND, Huang Y, et al. Dual inhibition of Ang-2 and VEGF receptors normalizes tumor vasculature and prolongs survival in glioblastoma by altering macrophages. Proc Natl Acad Sci U S A 2016; 113:4470–4475.

Elegant strategy to normalize tumor vascular beds as well as the inflammatory response by alteration of macrophages.

109. Kelly-Goss MR, Sweat RS, Stapor PC, et al. Targeting pericytes for angiogenic therapies. Microcirculation 2014; 21:345–357.

angiogenesis; atherosclerosis; inflammation; intraplaque hemorrhage; neovessel maturation

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