Altered expression of vascular endothelial growth factor and its receptors in normal saphenous vein and in arterialized and stenotic vein grafts

The role of extracellular vesicles in neointima formation post vascular injury

Pathological neointimal growth can develop in patients as a result of vascular injury following percutaneous coronary intervention and coronary artery bypass grafting using autologous saphenous vein, leading to arterial or vein graft occlusion. Neointima formation driven by intimal hyperplasia occurs as a result of a complex interplay between molecular and cellular processes involving different cell types including endothelial cells, vascular smooth muscle cells and various inflammatory cells. Therefore, understanding the intercellular communication mechanisms underlying this process remains of fundamental importance in order to develop therapeutic strategies to preserve endothelial integrity and vascular health post coronary interventions. Extracellular vesicles (EVs), including microvesicles and exosomes, are membrane-bound particles secreted by cells which mediate intercellular signalling in physiological and pathophysiological states, however their role in neointima formation is not fully understood. The purification and characterization techniques currently used in the field are associated with many limitations which significantly hinder the ability to comprehensively study the role of specific EV types and make direct functional comparisons between EV subpopulations. In this review, the current knowledge focusing on EV signalling in neointima formation post vascular injury is discussed.

Preventing treatment failures in coronary artery disease: what can we learn from the biology of in-stent restenosis, vein graft failure, and internal thoracic arteries?

Coronary artery disease (CAD) remains one of the most important causes of morbidity and mortality worldwide, and the availability of percutaneous or surgical revascularization procedures significantly improves survival. However, both strategies are daunted by complications which limit long-term effectiveness. In-stent restenosis (ISR) is a major drawback for intracoronary stenting, while graft failure is the limiting factor for coronary artery bypass graft surgery (CABG), especially using veins. Conversely, internal thoracic artery (ITA) is known to maintain long-term patency in CABG. Understanding the biology and pathophysiology of ISR and vein graft failure (VGF) and mechanisms behind ITA resistance to failure is crucial to combat these complications in CAD treatment. This review intends to provide an overview of the biological mechanisms underlying stent and VGF and of the potential therapeutic strategy to prevent these complications. Interestingly, despite being different modalities of revascularization, mechanisms of failure of stent and saphenous vein grafts are very similar from the biological standpoint.

The Role of Immunomodulation in Vein Graft Remodeling and Failure

Obstructive arterial disease is a major cause of morbidity and mortality in the developed world. Venous bypass graft surgery is one of the most frequently used revascularization strategies despite its considerable short and long time failure rate. Due to vessel wall remodeling, inflammation, intimal hyperplasia, and accelerated atherosclerosis, vein grafts may (ultimately) fail to revascularize tissues downstream to occlusive atherosclerotic lesions. In the past decades, little has changed in the prevention of vein graft failure (VGF) although new insights in the role of innate and adaptive immunity in VGF have emerged. In this review, we discuss the pathophysiological mechanisms underlying the development of VGF, emphasizing the role of immune response and associated factors related to VG remodeling and failure. Moreover, we discuss potential therapeutic options that can improve patency based on data from both preclinical studies and the latest clinical trials. This review contributes to the insights in the role of immunomodulation in vein graft failure in humans. We describe the effects of immune cells and related factors in early (thrombosis), intermediate (inward remodeling and intimal hyperplasia), and late (intimal hyperplasia and accelerated atherosclerosis) failure based on both preclinical (mouse) models and clinical data.

Inflammation in Vein Graft Disease

Bypass surgery is one of the most frequently used strategies to revascularize tissues downstream occlusive atherosclerotic lesions. For venous bypass surgery the great saphenous vein is the most commonly used vessel. Unfortunately, graft efficacy is low due to the development of vascular inflammation, intimal hyperplasia and accelerated atherosclerosis. Moreover, failure of grafts leads to significant adverse outcomes and even mortality. The last couple of decades not much has changed in the treatment of vein graft disease (VGD). However, insight is the cellular and molecular mechanisms of VGD has increased. In this review, we discuss the latest insights on VGD and the role of inflammation in this. We discuss vein graft pathophysiology including hemodynamic changes, the role of vessel wall constitutions and vascular remodeling. We show that profound systemic and local inflammatory responses, including inflammation of the perivascular fat, involve both the innate and adaptive immune system.

Pathogenesis of Varicose Veins and Implications for Clinical Management

Varicose veins (VVs) classically result from venous hypertension owing to incompetence of the major communications between the superficial and deep veins of the lower extremity. In a significant number of patients, there is no demonstrable truncal saphenous reflux and varicosities are the result of isolated perforating and nonsaphenous vein incompetence. The clinical and histologic features of VVs are the result of disruption of the normal architectural structure of the venous wall as a consequence of remodeling of the extracellular matrix (ECM) in response to increased venous distention and altered hemodynamic shear stress. Although a number of genes, growth factors, proteases, and their inhibitors known to modulate the ECM have been implicated in the pathogenesis of VVs, their etiology remains unknown. The complex variations in venous anatomy in patients with VVs require detailed vein mapping to determine the source and drainage locations of reflux if the rates of residual and recurrent varicosities are to be reduced. The distinct pathogenic mechanisms involved in the development of VVs have important implications for the management of VVs that include a wide spectrum of treatment modalities ranging from reassurance, alternative medicines, conservative management or compression therapy, and surgical or endovascular therapy.

Vein graft failure: from pathophysiology to clinical outcomes

Occlusive arterial disease is a leading cause of morbidity and mortality worldwide. Aside from balloon angioplasty, bypass graft surgery is the most commonly performed revascularization technique for occlusive arterial disease. Coronary artery bypass graft surgery is performed in patients with left main coronary artery disease and three-vessel coronary disease, whereas peripheral artery bypass graft surgery is used to treat patients with late-stage peripheral artery occlusive disease. The great saphenous veins are commonly used conduits for surgical revascularization; however, they are associated with a high failure rate. Therefore, preservation of vein graft patency is essential for long-term surgical success. With the exception of 'no-touch' techniques and lipid-lowering and antiplatelet (aspirin) therapy, no intervention has hitherto unequivocally proven to be clinically effective in preventing vein graft failure. In this Review, we describe both preclinical and clinical studies evaluating the pathophysiology underlying vein graft failure, and the latest therapeutic options to improve patency for both coronary and peripheral grafts.

Neuropilin 1 expression in human aortas, coronaries and the main bypass grafts

OBJECTIVES

Development of intimal hyperplasia (IH) is the main pathology underlying graft failure following coronary artery bypass graft surgeries for ischaemic heart diseases, especially for great saphenous vein grafts which have a lower patency rate than internal mammary arteries. Neuropilin 1 (NRP1), which is a co-receptor for vascular endothelial growth factor found in vascular endothelial and smooth muscle cells, affects the development of IH. We examined the difference in NRP1 expression and distribution in human coronaries, aortas, mammary arteries and saphenous veins to detect a possible relation to their susceptibility to IH.

METHODS

Ninety-five human vascular segments obtained from 40 patients were used for the comparison of NRP1 expression between different groups of blood vessels by western blot and real-time PCR. Additionally, staining scores were generated by computerized analysis of the microscopic images obtained after immunofluorescence and immunohistochemical staining to compare NRP1 expression patterns in endothelium, smooth muscles and adventitia in each vessel type.

RESULTS

NRP1 expression in the aorta (2.03 ± 1.44) was more than twice as high as mammary artery expression (0.85 ± 0.75; n = 16, P = 0.0004); NRP1 of the latter (0.99 ± 0.91) was more than 30% greater than that of the corresponding saphenous vein (0.73 ± 0.69; n = 20, P = 0.0085). In adventitia, NRP1 receptor staining of the saphenous vein was higher (22.96 ± 8.73) than in the mammary artery (15.83 ± 7.13; n = 7, P = 0.049). Variations in NRP1 protein levels were accompanied by parallel variations in its mRNA levels (n = 15, P = 0.34).

CONCLUSIONS

Autologous saphenous vein grafts, unlike internal mammary artery grafts, have lower NRP1 expression and abundant adventitial distribution of NRP1 within their walls; this may correlate with higher susceptibility to IH development.

Pathophysiology of aortocoronary saphenous vein bypass graft disease

Aortocoronary saphenous vein bypass grafting relieves anginal pain in patients with coronary artery disease. However, its effectiveness is limited due to graft failure; the 10-year patency rate is 50%-60%. Early, 1-year and late graft failure may be due to thrombosis, fibrointimal hyperplasia and atherosclerosis, respectively. There is general agreement that vein graft atherosclerosis differs from arterial lesions in terms of temporal and histological changes. Vein graft atherosclerosis is more rapid, with diffuse concentric changes and a less noticeable fibrous cap, making venous plaques more vulnerable to rupture and subsequent thrombus formation. Despite progress in understanding the pathophysiology, some aspects of vein graft atherosclerosis need to be clarified. This review focuses on the pathophysiologic aspects of this widespread, costly and disabling disease, with emphasis on late graft occlusion and distinctions between arterial and venous atherosclerosis in terms of histology, pathophysiology and risk factors.

Current Advances in the Pathogenesis of Varicose Veins

Varicose veins have a wide prevalence and are characterized by their tortuous, dilated, and serpentine appearance. This pattern is the result of disruption of the normal arrangement of the extracellular matrix (ECM) and smooth muscle cells (SMC) in veins. Valvular incompetence and the effect of increased hydrostatic pressure have been implicated in the pathogenesis of varicose veins. Alterations in the ECM and varied expression of metalloproteinases and their inhibitors can effect changes in venous wall remodeling. Gene expression and specific candidate markers have been identified in varicose veins. Differential gene transcription may influence the adaptive response of the venous wall to stimuli and the remodeling of the ECM that leads to the development of varicose veins.

Neuron Restrictive Silencer Factor NRSF/REST Is a Transcriptional Repressor of Neuropilin-1 and Diminishes the Ability of Semaphorin 3A to Inhibit Keratinocyte Migration

Neuropilin-1 (NRP1) is expressed by endothelial cells and neurons and serves as a receptor for both vascular endothelial growth factor (VEGF), an angiogenesis factor, and semaphorin 3A (Sema3A), a mediator of axonal guidance. We show here that NRP1 is also expressed in keratinocytes in vitro and in vivo. However, nothing has been reported about the regulation or function of keratinocyte NRP1. Using NRP1 promoter constructs in HaCaT cells, a keratinocyte cell line, we could demonstrate that a neuron restrictive silencer element (NRSE) was implicated in transcriptional repression of the NRP1 gene. Electrophoretic mobility shift assays demonstrated that the neuron restrictive silencer factor (NRSF) binds to NRSE. Overexpression of NRSF in HaCaT cells decreased NRP1 RNA and protein, whereas a dominant negative NRSF increased NRP1. Furthermore, the histone deacetylase inhibitor trichostatin A, an inhibitor of NRSF silencing activity, also increased NRP1 levels. NRP2 expression was not affected. Epidermal growth factor (EGF) and heparin-binding EGF-like growth factor (HB-EGF) strongly up-regulated NRP1 expression, concomitant with down-regulation of NRSF. Other keratinocyte mitogens such as keratinocyte growth factor (KGF) had no effect. To address function, HaCaT cells were exposed to two NRP1 ligands, VEGF165 and Sema3A. Neither had an effect on proliferation, whereas Sema3A, but not VEGF165, inhibited cell migration. Down-regulation of NRP1 by NRSF overexpression reduced Sema3A activity. It was concluded that NRSF is a transcription factor that silences NRP1 expression and thereby diminishes the Sema3A mediated inhibition of HaCaT keratinocyte migration.

Direct chemotactic action of angiopoietin-1 on mesenchymal cells in the presence of VEGF

Angiopoietin-1 (Ang1) and its receptor, Tie2, play an important role in angiogenesis and vessel maturation. We previously reported that overexpression of Ang1 in MCF7 xenograft tumors facilitated vessel stabilization by mural cells, and that cultured SMC express Tie2. Here, we investigated whether Ang1 directly acts as a chemoattractant on mural cells or their precursors. In a Matrigel plug assay, neither Ang1 nor VEGF alone induced angiogenesis but together stimulated infiltration of non-endothelial cells that were CD31-negative, vimentin-positive and also positive for VEGFR-1 and Tie2. While negative for smooth muscle actin, reactivity for desmin suggests that the cells are mural cell precursors. VEGF treatment of cultured smooth muscle cells (SMC) upregulated Tie2 and allowed for Ang1-mediated phosphorylation of Tie2 and the AKT serine-threonine kinase. The combination of Ang1 and VEGF stimulated SMC migration in a Boyden chamber-type assay. In the presence of VEGF, Tie2 is upregulated on mural cells, allowing for a migratory response to Ang1. These findings support the view that Ang1, in concert with VEGF, can act directly on mural cells or their precursors to facilitate their recruitment to new blood vessels. This action may play an important role in vascular stabilization.