Differential effect of experimental hypertension and hypercholesterolemia on adventitial remodeling

Apoptosis signal-regulating kinase 1 inhibition in in vivo and in vitro models of pulmonary hypertension

Pulmonary arterial hypertension, group 1 of the pulmonary hypertension disease family, involves pulmonary vascular remodelling, right ventricular dysfunction and cardiac failure. Oxidative stress, through activation of mitogen-activated protein kinases is implicated in these changes. Inhibition of apoptosis signal-regulating kinase 1, an apical mitogen-activated protein kinase, prevented pulmonary arterial hypertension developing in rodent models. Here, we investigate apoptosis signal-regulating kinase 1 in pulmonary arterial hypertension by examining the impact that its inhibition has on the molecular and cellular signalling in established disease. Apoptosis signal-regulating kinase 1 inhibition was investigated in in vivo pulmonary arterial hypertension and in vitro pulmonary hypertension models. In the in vivo model, male Sprague Dawley rats received a single subcutaneous injection of Sugen SU5416 (20 mg/kg) prior to two weeks of hypobaric hypoxia (380 mmHg) followed by three weeks normoxia (Sugen/hypoxic), then animals were either maintained for three weeks on control chow or one containing apoptosis signal-regulating kinase 1 inhibitor (100 mg/kg/day). Cardiovascular measurements were carried out. In the in vitro model, primary cultures of rat pulmonary artery fibroblasts and rat pulmonary artery smooth muscle cells were maintained in hypoxia (5% O₂) and investigated for proliferation, migration and molecular signalling in the presence or absence of apoptosis signal-regulating kinase 1 inhibitor. Sugen/hypoxic animals displayed significant pulmonary arterial hypertension compared to normoxic controls at eight weeks. Apoptosis signal-regulating kinase 1 inhibitor decreased right ventricular systolic pressure to control levels and reduced muscularised vessels in lung tissue. Apoptosis signal-regulating kinase 1 inhibition was found to prevent hypoxia-induced proliferation, migration and cytokine release in rat pulmonary artery fibroblasts and also prevented rat pulmonary artery fibroblast-induced rat pulmonary artery smooth muscle cell migration and proliferation. Apoptosis signal-regulating kinase 1 inhibition reversed pulmonary arterial hypertension in the Sugen/hypoxic rat model. These effects may be a result of intrinsic changes in the signalling of adventitial fibroblast.

Why Should Growth Hormone (GH) Be Considered a Promising Therapeutic Agent for Arteriogenesis? Insights from the GHAS Trial

Despite the important role that the growth hormone (GH)/IGF-I axis plays in vascular homeostasis, these kind of growth factors barely appear in articles addressing the neovascularization process. Currently, the vascular endothelium is considered as an authentic gland of internal secretion due to the wide variety of released factors and functions with local effects, including the paracrine/autocrine production of GH or IGF-I, for which the endothelium has specific receptors. In this comprehensive review, the evidence involving these proangiogenic hormones in arteriogenesis dealing with the arterial occlusion and making of them a potential therapy is described. All the elements that trigger the local and systemic production of GH/IGF-I, as well as their possible roles both in physiological and pathological conditions are analyzed. All of the evidence is combined with important data from the GHAS trial, in which GH or a placebo were administrated to patients suffering from critical limb ischemia with no option for revascularization. We postulate that GH, alone or in combination, should be considered as a promising therapeutic agent for helping in the approach of ischemic disease.

Carotid Extra-Media Thickness in Children: Relationships With Cardiometabolic Risk Factors and Endothelial Function

Background: Emerging evidence suggests that structural adventitial modifications and perivascular adipose tissue (PAT) may have a role in early atherogenesis. In a cohort of children and adolescents, we explored (1) the association of carotid extra-media thickness (cEMT), an ultrasound measure whose main determinants are arterial adventitia and PAT, with obesity and its cardiometabolic complications; and (2) the interplay between cEMT and endothelial function. Methods: The study participants included 286 youths (age, 6-16 years; 154 boys, and 132 girls). Anthropometric and laboratory parameters, liver ultrasound, vascular structure measures [cEMT and carotid intima-media thickness (cIMT)], endothelial function [brachial artery flow-mediated dilation (FMD)] were obtained in all subjects. Non-alcoholic fatty liver disease (NAFLD) was diagnosed in the presence of hepatic fat on ultrasonography, in the absence of other causes of liver disease. Diagnosis of metabolic syndrome (MetS) was established on the basis of three or more of the following cardiovascular disease (CVD) risk variables: abdominal obesity, high triglycerides, low high-density lipoprotein cholesterol, elevated blood pressure (BP), and impaired fasting glucose. Results: cEMT demonstrated significant associations with body-mass index (BMI) and waist circumference (WC), BP, insulin resistance, NAFLD, and inflammation. No association was found between cEMT and lipid values, and between cEMT and MetS. A stepwise multivariate linear regression analysis indicated that WC (β coefficient, 0.35; P < 0.0001) was the only determinant of cEMT, independently of other major cardiometabolic risk factors. Further adjustment for cIMT did not significantly alter this association. FMD was correlated to age, Tanner stage, total and abdominal obesity, BP, NAFLD, and cEMT. The association between FMD and cEMT was independent of age, sex, Tanner stage, WC, and BMI (β coefficient, -0.14; P = 0.027). After controlling for CVD risk factors and basal brachial artery diameter, cEMT remained associated with FMD (β coefficient, -0.11; P = 0.049). Conclusions: In youths, cEMT is associated with abdominal fat, a well-established body fat depot with important implications for cardiovascular diseases. Furthermore, cEMT is related to FMD, suggesting that arterial adventitia and PAT may be involved in the early changes in endothelial function.

Hot topics in the mechanisms of pulmonary arterial hypertension disease: cancer-like pathobiology, the role of the adventitia, systemic involvement, and right ventricular failure

In order to intervene appropriately and develop disease-modifying therapeutics for pulmonary arterial hypertension, it is crucial to understand the mechanisms of disease pathogenesis and progression. We herein discuss four topics of disease mechanisms that are currently highly debated, yet still unsolved, in the field of pulmonary arterial hypertension. Is pulmonary arterial hypertension a cancer-like disease? Does the adventitia play an important role in the initiation of pulmonary vascular remodeling? Is pulmonary arterial hypertension a systemic disease? Does capillary loss drive right ventricular failure? While pulmonary arterial hypertension does not replicate all features of cancer, anti-proliferative cancer therapeutics might still be beneficial in pulmonary arterial hypertension if monitored for safety and tolerability. It was recognized that the adventitia as a cell-rich compartment is important in the disease pathogenesis of pulmonary arterial hypertension and should be a therapeutic target, albeit the data are inconclusive as to whether the adventitia is involved in the initiation of neointima formation. There was agreement that systemic diseases can lead to pulmonary arterial hypertension and that pulmonary arterial hypertension can have systemic effects related to the advanced lung pathology, yet there was less agreement on whether idiopathic pulmonary arterial hypertension is a systemic disease per se. Despite acknowledging the limitations of exactly assessing vascular density in the right ventricle, it was recognized that the failing right ventricle may show inadequate vascular adaptation resulting in inadequate delivery of oxygen and other metabolites. Although the debate was not meant to result in a definite resolution of the specific arguments, it sparked ideas about how we might resolve the discrepancies by improving our disease modeling (rodent models, large-animal studies, studies of human cells, tissues, and organs) as well as standardization of the models. Novel experimental approaches, such as lineage tracing and better three-dimensional imaging of experimental as well as human lung and heart tissues, might unravel how different cells contribute to the disease pathology.

Elastic Fibers and Large Artery Mechanics in Animal Models of Development and Disease

Development of a closed circulatory system requires that large arteries adapt to the mechanical demands of high, pulsatile pressure. Elastin and collagen uniquely address these design criteria in the low and high stress regimes, resulting in a nonlinear mechanical response. Elastin is the core component of elastic fibers, which provide the artery wall with energy storage and recoil. The integrity of the elastic fiber network is affected by component insufficiency or disorganization, leading to an array of vascular pathologies and compromised mechanical behavior. In this review, we discuss how elastic fibers are formed and how they adapt in development and disease. We discuss elastic fiber contributions to arterial mechanical behavior and remodeling. We primarily present data from mouse models with elastic fiber deficiencies, but suggest that alternate small animal models may have unique experimental advantages and the potential to provide new insights. Advanced ultrastructural and biomechanical data are constantly being used to update computational models of arterial mechanics. We discuss the progression from early phenomenological models to microstructurally motivated strain energy functions for both collagen and elastic fiber networks. Although many current models individually account for arterial adaptation, complex geometries, and fluid-solid interactions (FSIs), future models will need to include an even greater number of factors and interactions in the complex system. Among these factors, we identify the need to revisit the role of time dependence and axial growth and remodeling in large artery mechanics, especially in cardiovascular diseases that affect the mechanical integrity of the elastic fibers.

Vasa Vasorum Angiogenesis: Key Player in the Initiation and Progression of Atherosclerosis and Potential Target for the Treatment of Cardiovascular Disease

Plaque microvascularization and increased endothelial permeability are key players in the development of atherosclerosis, from the initial stages of plaque formation to the occurrence of acute cardiovascular events. First, endothelial dysfunction and increased permeability facilitate the entry of diverse inflammation-triggering molecules and particles such as low-density lipoproteins into the artery wall from the arterial lumen and vasa vasorum (VV). Recognition of entering particles by resident phagocytes in the vessel wall triggers a maladaptive inflammatory response that initiates the process of local plaque formation. The recruitment and accumulation of inflammatory cells and the subsequent release of several cytokines, especially from resident macrophages, stimulate the expansion of existing VV and the formation of new highly permeable microvessels. This, in turn, exacerbates the deposition of pro-inflammatory particles and results in the recruitment of even more inflammatory cells. The progressive accumulation of leukocytes in the intima, which trigger proliferation of smooth muscle cells in the media, results in vessel wall thickening and hypoxia, which further stimulates neoangiogenesis of VV. Ultimately, this highly inflammatory environment damages the fragile plaque microvasculature leading to intraplaque hemorrhage, plaque instability, and eventually, acute cardiovascular events. This review will focus on the pivotal roles of endothelial permeability, neoangiogenesis, and plaque microvascularization by VV during plaque initiation, progression, and rupture. Special emphasis will be given to the underlying molecular mechanisms and potential therapeutic strategies to selectively target these processes.

Adventitial Activation in the Pathogenesis of Injury-Induced Arterial Remodeling: Potential Implications in Transplant Vasculopathy

Transplant vasculopathy is one of the major causes of chronic rejection after solid organ transplantation. The pathogenic mechanisms of transplant vasculopathy are still poorly understood. Herein, we summarize current evidence suggesting that activation of the tunica adventitia may be involved in the pathogenesis of transplant vasculopathy. Adventitia is an early responder to various vascular injuries and plays an integral role in eliciting vascular inflammation and remodeling. Accumulation of macrophages in the adventitia promotes the development of vascular remodeling by releasing a variety of paracrine factors that have profound impacts on vascular mural cells. Targeting adventitial macrophages has been shown to be effective for repressing transplantation-induced arterial remodeling in animal models. Adventitia also fosters angiogenesis, and neovascularization of the adventitial layer may facilitate the transport of inflammatory cells through the arterial wall. Further investigations are warranted to clarify whether inhibiting adventitial oxidative stress and/or adventitial neovascularization are better strategies for preventing transplant vasculopathy.

The association of obesity and obesity-related conditions with carotid extra-medial thickness in children and adolescents

BACKGROUND

Carotid extra-medial thickness (EMT) and carotid intima-media thickness (cIMT) provide information concerning vascular changes.

OBJECTIVES

In this study, we aimed to evaluate the association between carotid EMT and obesity and its metabolic complications in children.

METHODS

The study included 38 obese subjects and 30 age-matched and sex-matched healthy controls aged between 7 and 17 years. For all subjects, complete blood count, fasting blood glucose, serum insulin, aspartate aminotransferase, alanine aminotransferase, HDL cholesterol, total cholesterol and triglyceride levels were measured. The carotid EMT and cIMT were measured by an expert radiologist in all patients.

RESULTS

Body mass index (BMI) (28.8 ± 3 vs. 18.1 ± 2.2, p < 0.001), total cholesterol (167.9 ± 34.8 mg dL^-1 vs. 150.5 ± 28.1 mg dL^-1 , p = 0.029), homeostatic model assessment of insulin resistance (HOMA-IR) (4.3 vs. 1.7, p < 0.001), cIMT (0.51 ± 0.08 mm vs. 0.45 ± 0.06 mm, p < 0.001) and carotid EMT (0.74 ± 0.11 mm vs. 0.64 ± 0.1 mm, p < 0.001) were significantly higher in obese subjects than in controls, while HDL cholesterol (41.6 ± 6.5 mg dL^-1 vs. 49.5 ± 7.5 mg dL^-1 , p < 0.001) was lower in obesity group. Among the obese subjects, the HOMA-IR values (4.7 vs. 3.6, p = 0.027), cIMT (0.54 ± 0.07 mm vs. 0.49 ± 0.07 mm, p = 0.039) and carotid EMT (0.79 ± 0.1 mm vs. 0.7 ± 0.1 mm, p = 0.013) were significantly higher in post-pubertal children compared with prepubertal children. BMI, cut-off values of HOMA-IR and cIMT were significantly associated with increased carotid EMT (p < 0.001, p = 0.023 and p < 0.001, respectively). The only independent risk factor affecting carotid EMT was BMI (p < 0.001).

CONCLUSION

We have found that carotid EMT is associated with cIMT, obesity and insulin resistance and the assessment of carotid EMT may provide additional information concerning early vascular disease.

Elk-1-mediated 15-lipoxygenase expression is required for hypoxia-induced pulmonary vascular adventitial fibroblast dynamics

AIM

15-Lipoxygenase (15-LO) is an important factor in the pathogenesis of pulmonary artery hypertension (PAH). However, the role of 15-LO in the adventitia of the pulmonary arterial wall is unclear. The aim of this study was to explore the role of 15-LO in the modulation of pulmonary adventitial fibroblast (PAF) dynamics.

METHODS

Rats were exposed to normoxic or hypoxic (fraction of inspired O₂  = 0.12) treatments for 7 days. PAF proliferation and cell cycle alterations were measured by MTT assay, cell immunofluorescence, flow cytometry and Western blot analysis. The 15-LO promoter was analysed by luciferase reporter and ChIP assays.

RESULTS

Our results showed that hypoxia induced 15-LO expression in PAFs both in vivo and in vitro. In addition, hypoxia stimulated JNK phosphorylation in PAFs. Blocking 15-LO or JNK suppressed 15-LO-induced PAF proliferation and cell cycle alterations. The inhibition of p27^kipl by gene silencing attenuated 15-LO-induced PAF proliferation and cell cycle alterations. Furthermore, JNK inhibition or Elk-1 knockdown suppressed hypoxia-induced 15-LO expression in PAFs. Luciferase reporter and ChIP assays revealed that the 15-LO promoter contains Elk-1-binding sites and also that Elk-1 increased the hypoxia-induced activity of the 15-LO promoter.

CONCLUSION

These results suggest that hypoxia promotes changes in the cellular dynamics of PAFs by inducing 15-LO expression, which leads to vascular adventitial remodelling. The modulation of p27^kipl expression by 15-LO enhances PAF proliferation and cell cycle alterations. Furthermore, the JNK-dependent increase in Elk-1 signalling is required for hypoxia-induced 15-LO expression in PAFs.

Carotid extramedial thickness is associated with local arterial stiffness in children

OBJECTIVES

Experimental evidence suggests that structural changes to the arterial adventitia may be a key vascular determinant of early arterial stiffening, although this has not been directly studied. Accordingly, we hypothesized that in young children, in whom this relationship would not be altered by atheroma, carotid extramedial thickness (EMT), a measure that incorporates the thickness of the arterial adventitia, perivascular tissues and the internal jugular venous wall, would be associated with localized arterial stiffness of the same arterial region.

METHODS

We studied 248 healthy prepubescent children (aged 8 years). Carotid diameter and carotid EMT were measured by high-resolution ultrasound. Carotid blood pressure was derived from brachial blood pressure and carotid tonometry. Three measures of localized arterial stiffness (β stiffness index, distensibility coefficient and incremental modulus of elasticity) were calculated for the common carotid artery. Results were adjusted for heart rate and DBP, two important hemodynamic determinants of arterial stiffness.

RESULTS

Carotid EMT was associated with all three measures of arterial stiffness (β stiffness index: standardized β = 0.121, P = 0.03; distensibility coefficient: standardized β = -0.121, P = 0.05; incremental modulus of elasticity: standardized β = 0.140, P = 0.02). These associations remained significant after adjustment for potential confounders such as sex, height, waist circumference, BMI and body surface area.

CONCLUSION

Carotid EMT is associated with the stiffness of the same arterial segment in children, suggesting that the arterial adventitia may be involved in early changes in arterial stiffness during childhood.

Hypercholesterolemia and Hypertension: Two Sides of the Same Coin

The aim of this review article is to summarize the current knowledge about mechanisms that connect blood pressure regulation and hypercholesterolemia, the mutual interaction between hypertension and hypercholesterolemia, and their influence on atherosclerosis development. Our research shows that at least one-third of the population of Western Europe has hypertension and hypercholesterolemia. Several biohumoral mechanisms could explain the relationship between hypertension and hypercholesterolemia and the association between these risk factors and accelerated atherosclerosis. The most investigated mechanisms are the renin-angiotensin-aldosterone system, oxidative stress, endothelial dysfunction, and increased production of endothelin-1. Arterial hypertension is frequently observed in combination with hypercholesterolemia, and this is related to accelerated atherosclerosis. Understanding the mechanisms behind this relationship could help explain the benefits of therapy that simultaneously reduce blood pressure and cholesterol levels.

NADPH oxidase p47phox siRNA attenuates adventitial fibroblasts proliferation and migration in apoE(-/-) mouse

BACKGROUND

Reactive oxide species (ROS) derived from NADPH oxidases is involved in atherosclerosis. However, as a key component of NADPH oxidase, how p47phox regulates NADPH oxidases activity, ROS production and adventitial fibroblasts (AFs) function remains unclear.

METHODS

p47phox in aortic arteries of apoE(-/-) mice fed with hyperlipid diet was detected by immunohistochemistry. NADPH oxidase activity, superoxide anion (O2(-)) generation and p47phox expression were analyzed in primary AFs treated by diphenyleneiodonium (DPI). The proliferation and migration of AFs were also analyzed.

RESULTS

p47phox expression was low in the aortic adventitia but high in the site of intimal injury with continuous hyperlipidic diet. Compared to AFs from wild-type mice, AFs derived from apoE(-/-) mice exhibited elevated NADPH oxidase activity, O2(-) production and higher mRNA and protein levels of p47phox, correlated with increased capability of proliferation and migration. DPI inhibited NADPH oxidase activity and AFs proliferation and migration in a dose-dependent manner. In addition, siRNA mediated knockdown of p47phox attenuated the proliferation and migration of AFs derived from apoE(-/-) mice.

CONCLUSION

p47phox plays a critical role in the regulation of adventitial fibroblast proliferation and migration and may be a new therapeutic target for neointimal hyperplasia.

Interleukin-2/Anti-Interleukin-2 Immune Complex Expands Regulatory T Cells and Reduces Angiotensin II-Induced Aortic Stiffening

Adaptive immune function is implicated in the pathogenesis of vascular disease. Inhibition of T-lymphocyte function has been shown to reduce hypertension, target-organ damage, and vascular stiffness. To study the role of immune inhibitory cells, CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs), on vascular stiffness, we stimulated the proliferation of Treg lymphocytes in vivo using a novel cytokine immune complex of Interleukin-2 (IL-2) and anti-IL-2 monoclonal antibody clone JES6-1 (mAbCD25). Three-month-old male C57BL/6J mice were treated with IL-2/mAbCD25 concomitantly with continuous infusion of angiotensin type 1 receptor agonist, [Val(5)]angiotensin II. Our results indicate that the IL-2/mAbCD25 complex effectively induced Treg phenotype expansion by 5-fold in the spleens with minimal effects on total CD4(+) and CD8(+) T-lymphocyte numbers. The IL-2/mAbCD25 complex inhibited angiotensin II-mediated aortic collagen remodeling and the resulting stiffening, analyzed with in vivo pulse wave velocity and effective Young's modulus. Furthermore, the IL-2/mAbCD25 complex suppressed angiotensin II-mediated Th17 responses in the lymphoid organs and reduced gene expression of IL-17 as well as T cell and macrophage infiltrates in the aortic tissue. This study provides data that support the protective roles of Tregs in vascular stiffening and highlights the use of the IL-2/mAbCD25 complex as a new potential therapy in angiotensin II-related vascular diseases.

The Relationship between Vascular Function and the Autonomic Nervous System

Endothelial dysfunction and autonomic nervous system dysfunction are both risk factors for atherosclerosis. There is evidence demonstrating that there is a close interrelationship between these two systems. In hypertension, endothelial dysfunction affects the pathologic process through autonomic nervous pathways, and the pathophysiological process of autonomic neuropathy in diabetes mellitus is closely related with vascular function. However, detailed mechanisms of this interrelationship have not been clearly explained. In this review, we summarize findings concerning the interrelationship between vascular function and the autonomic nervous system from both experimental and clinical studies. The clarification of this interrelationship may provide more comprehensive risk stratification and a new effective therapeutic strategy against atherosclerosis.

Natural history of mesenchymal stem cells, from vessel walls to culture vessels

Mesenchymal stem/stromal cells (MSCs) can regenerate tissues by direct differentiation or indirectly by stimulating angiogenesis, limiting inflammation, and recruiting tissue-specific progenitor cells. MSCs emerge and multiply in long-term cultures of total cells from the bone marrow or multiple other organs. Such a derivation in vitro is simple and convenient, hence popular, but has long precluded understanding of the native identity, tissue distribution, frequency, and natural role of MSCs, which have been defined and validated exclusively in terms of surface marker expression and developmental potential in culture into bone, cartilage, and fat. Such simple, widely accepted criteria uniformly typify MSCs, even though some differences in potential exist, depending on tissue sources. Combined immunohistochemistry, flow cytometry, and cell culture have allowed tracking the artifactual cultured mesenchymal stem/stromal cells back to perivascular anatomical regions. Presently, both pericytes enveloping microvessels and adventitial cells surrounding larger arteries and veins have been described as possible MSC forerunners. While such a vascular association would explain why MSCs have been isolated from virtually all tissues tested, the origin of the MSCs grown from umbilical cord blood remains unknown. In fact, most aspects of the biology of perivascular MSCs are still obscure, from the emergence of these cells in the embryo to the molecular control of their activity in adult tissues. Such dark areas have not compromised intents to use these cells in clinical settings though, in which purified perivascular cells already exhibit decisive advantages over conventional MSCs, including purity, thorough characterization and, principally, total independence from in vitro culture. A growing body of experimental data is currently paving the way to the medical usage of autologous sorted perivascular cells for indications in which MSCs have been previously contemplated or actually used, such as bone regeneration and cardiovascular tissue repair.

Adventitial fibroblasts from apoE(-/-) mice exhibit the characteristics of transdifferentiation into myofibroblasts

Adventitial fibroblasts (AFs) are the main cell type in the adventitia, however, their role in atherosclerosis remains unclear. We have investigate the role of AFs in atherosclerotic lesion formation by comparing the characteristics of AFs from apoE(-/-) to C57BL/6 mice. A minority of AFs from apoE(-/-) mice expressed α-SM-actin, but no α-SM-actin-positive cells were found in AFs from C57BL/6 mice. The content of total collagens, and the mRNA levels of collagen I and collagen III in AFs of apoE(-/-) mice, were higher than in C57BL/6 mice. AFs from apoE(-/-) mice proliferate and migrate faster, and synthesized more TGF-β(1) , MCP-1, and PDGF-b AFs from apoE(-/-) mice have the characteristics of transdifferentiation into myofibroblasts, including enhanced proliferation and migration, along with synthesis of collagens and cytokines compared to AFs from C57BL/6 mice. The histological and functional characteristics of AFs may contribute to early atherosclerotic lesion formation.

Reactive oxygen species in pulmonary vascular remodeling

The pathogenesis of pulmonary hypertension is a complex multifactorial process that involves the remodeling of pulmonary arteries. This remodeling process encompasses concentric medial thickening of small arterioles, neomuscularization of previously nonmuscular capillary-like vessels, and structural wall changes in larger pulmonary arteries. The pulmonary arterial muscularization is characterized by vascular smooth muscle cell hyperplasia and hypertrophy. In addition, in uncontrolled pulmonary hypertension, the clonal expansion of apoptosis-resistant endothelial cells leads to the formation of plexiform lesions. Based upon a large number of studies in animal models, the three major stimuli that drive the vascular remodeling process are inflammation, shear stress, and hypoxia. Although, the precise mechanisms by which these stimuli impair pulmonary vascular function and structure are unknown, reactive oxygen species (ROS)-mediated oxidative damage appears to play an important role. ROS are highly reactive due to their unpaired valence shell electron. Oxidative damage occurs when the production of ROS exceeds the quenching capacity of the antioxidant mechanisms of the cell. ROS can be produced from complexes in the cell membrane (nicotinamide adenine dinucleotide phosphate-oxidase), cellular organelles (peroxisomes and mitochondria), and in the cytoplasm (xanthine oxidase). Furthermore, low levels of tetrahydrobiopterin (BH4) and L-arginine the rate limiting cofactor and substrate for endothelial nitric oxide synthase (eNOS), can cause the uncoupling of eNOS, resulting in decreased NO production and increased ROS production. This review will focus on the ROS generation systems, scavenger antioxidants, and oxidative stress associated alterations in vascular remodeling in pulmonary hypertension.

Opposite associations of plasma homoarginine and ornithine with arginine in healthy children and adolescents

Homoarginine, a non-proteinogenic amino acid, is formed when lysine replaces ornithine in reactions catalyzed by hepatic urea cycle enzymes or lysine substitutes for glycine as a substrate of renal arginine:glycine amidinotransferase. Decreased circulating homoarginine and elevated ornithine, a downstream product of arginase, predict adverse cardiovascular outcome. Our aim was to investigate correlates of plasma homoarginine and ornithine and their relations with carotid vascular structure in 40 healthy children and adolescents aged 3–18 years without coexistent diseases or subclinical carotid atherosclerosis. Homoarginine, ornithine, arginine, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) were measured by liquid chromatography-tandem mass spectrometry with stable isotope-labeled internal standards. Intima-media thickness (IMT) and extra-medial thickness (EMT) of common carotid arteries were estimated by B-mode ultrasound. Homoarginine correlated with arginine (r = 0.43, p = 0.005), age (r = 0.42, p = 0.007) and, weakly, with an increased arginine-to-ornithine ratio, a putative measure of lower arginase activity (r = 0.31, p = 0.048). Ornithine correlated inversely with arginine (r = −0.64, p < 0.001). IMT, EMT or their sum were unrelated to any of the biochemical parameters (p > 0.12). Thus, opposite associations of plasma homoarginine and ornithine with arginine may partially result from possible involvement of arginase, an enzyme controlling homoarginine degradation and ornithine synthesis from arginine. Age-dependency of homoarginine levels can reflect developmental changes in homoarginine metabolism. However, neither homoarginine nor ornithine appears to be associated with carotid vascular structure in healthy children and adolescents.

The adventitia: Essential role in pulmonary vascular remodeling

A rapidly emerging concept is that the vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and comprises a variety of cells including fibroblasts, immunomodulatory cells, resident progenitor cells, vasa vasorum endothelial cells, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to then influence tone and structure of the vessel wall. Experimental data indicate that the adventitial fibroblast, the most abundant cellular constituent of adventitia, is a critical regulator of vascular wall function. In response to vascular stresses such as overdistension, hypoxia, or infection, the adventitial fibroblast is activated and undergoes phenotypic changes that include proliferation, differentiation, and production of extracellular matrix proteins and adhesion molecules, release of reactive oxygen species, chemokines, cytokines, growth factors, and metalloproteinases that, collectively, affect medial smooth muscle cell tone and growth directly and that stimulate recruitment and retention of circulating inflammatory and progenitor cells to the vessel wall. Resident dendritic cells also participate in "sensing" vascular stress and actively communicate with fibroblasts and progenitor cells to simulate repair processes that involve expansion of the vasa vasorum, which acts as a conduit for further delivery of inflammatory/progenitor cells. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of pulmonary vascular wall function and structure from the "outside in."

Expression and significance of α-SMA and PCNA in the vascular adventitia of balloon-injured rat aorta

The aim of this study was to investigate changes in the expression of α-smooth muscle actin (α-SMA) and proliferating cell nuclear antigen (PCNA) in the vascular adventitia of balloon-injured rat aortas in the second and sixth postoperative weeks. A total of 32 rats were divided into a control group and a balloon-injured group. The rats underwent vascular morphometric analysis and adventitial cell counting, as well as immunohistochemical staining of α-SMA and PCNA in postoperative weeks 2 and 6 for observation of the expression of each immune parameter in the vascular adventitia and calculation of the number of PCNA-positive nuclei and the PCNA labeling index (PCNALI) in the vascular adventitia. The area and thickness of the adventitia, the number of nuclei and the PCNALI of the vascular adventitia were significantly increased in the injured group compared with the control group (P<0.05), while the external elastic lamina area (EELA), internal elastic lamina area (IELA) and lumen area (LA) were significantly decreased (P<0.05) in the second week. The area and thickness of the adventitia, the number of nuclei and the PCNALI of the vascular adventitia were significantly increased in the injured group compared with the control group (P<0.05), while the EELA, IELA and LA were significantly reduced (P<0.05) in the sixth week, and were significantly lower than those in the injured group in the second week (P<0.05). The positive expression levels of α-SMA and PCNA in the vascular adventitia were significantly reduced compared with those in the second week after injury. The vascular adventitial cells underwent proliferation and phenotypic switching and participated in vascular remodeling and vascular restenosis following balloon-induced injury. The vascular contractile remodeling in the injured group was more evident in the sixth week than in the second week, followed by a more aggravated vascular stenosis. Consequently, the vascular remodeling was one of the causes of vascular restenosis.

From Skeleton to Cytoskeleton

Rationale:

The expression of osteocalcin is augmented in human atherosclerotic lesions. How osteocalcin triggers vascular pathogenesis and remodeling is unclear.

Objective:

To investigate whether osteocalcin promotes transformation of adventitial fibroblast to myofibroblasts and the molecular mechanism involved.

Methods and Results:

Immunohistochemistry indicated that osteocalcin was expressed in the neointima of renal arteries from diabetic patients. Western blotting and wound-healing assay showed that osteocalcin induced fibroblast transformation and migration, which were attenuated by blockers of the renin-angiotensin system and protein kinase Cδ (PKCδ), toll-like receptor 4 (TLR4) neutralizing antibody, and antagonist and inhibitors of free radical production and cyclooxygenase-2. Small interfering RNA silencing of TLR4 and PKCδ abolished fibroblast transformation. Angiotensin II level in the conditioned medium from the osteocalcin-treated fibroblasts was found elevated using enzyme immunoassay. Culturing of fibroblasts in conditioned medium collected from differentiated osteoblasts promoted fibroblast transformation. The expression of fibronectin, TLR4, and cyclooxygenase-2 is augmented in human mesenteric arteries after 5-day in vitro exposure to osteocalcin.

Conclusions:

Osteocalcin transforms adventitial fibroblasts to myofibroblasts through stimulating angiotensin II release and subsequent activation of PKCδ/TLR4/reactive oxygen species/cyclooxygenase-2 signaling cascade. This study reveals that the skeletal hormone osteocalcin cross-talks with vascular system and contributes to vascular remodeling.

Cardiac micro-computed tomography imaging of the aging coronary vasculature

BACKGROUND

Alterations at the level of the coronary circulation with aging may play an important role in the evolution of age-associated changes in left ventricular (LV) fibrosis and function. However these age-associated changes in the coronary vasculature remain poorly defined primarily due to the lack of high resolution imaging technologies. The current study was designed to utilize cardiac micro-computed tomography (micro-CT) technology as a novel imaging strategy, to define the 3-dimensional coronary circulation in the young and aged heart and its relationship to LV fibrosis and function.

METHODS AND RESULTS

Young (2 months old; n=10) and aged (20 months old; n=10) Fischer rats underwent cardiac micro-CT imaging as well as echocardiography, blood pressure, and fibrosis analysis. Importantly, when indexed to LV mass, which increased with age, the total and intramyocardial vessel volumes were lower, whereas the epicardial vessel volume, with and without indexing to LV mass, was significantly higher in the aged hearts compared with the young hearts. Moreover, the aged hearts had a significantly lower percentage of intramyocardial vessel volume and a significantly higher percentage of epicardial vessel volume, when normalized to the total vessel volume, compared with the young hearts. Further, the aged hearts had significant LV fibrosis and mild LV dysfunction compared with the young hearts.

CONCLUSIONS

This micro-CT imaging study reports the reduction in normalized intramyocardial vessel volume within the aged heart, in association with increased epicardial vessel volume, in the setting of increased LV fibrosis, and mild LV dysfunction.

Carotid extra-medial thickness in childhood: early life effects on the arterial adventitia

OBJECTIVE

Structural modification of the arterial adventitia may be an early event in atherosclerosis. Carotid extra-medial thickness is a new measure of arterial adventitial thickness. We examined the association of cardiovascular risk factors with extra-medial thickness, in childhood.

METHODS

Carotid extra-medial thickness was assessed by high-resolution ultrasound in 389 non-diabetic children aged 8-years. A non-fasting blood sample was collected from 314 participants. Associations of gender, age, lipoproteins, blood pressure, BMI z-score, waist:height ratio and parental history of early vascular disease, with extra-medial thickness were examined.

RESULTS

Carotid extra-medial thickness was lower in girls (r=-.163, P=.001) and directly associated with systolic (r=.128, P=.009), diastolic blood pressure (r=.130, P=.009), and height (r=.170, P=.0006). These associations remained after adjustment for carotid intima-media thickness. In multivariable analysis including carotid intima-media thickness, only gender and height were significantly associated with carotid extra-medial thickness. In gender-stratified analysis, the strongest associations with extra-medial thickness were BMI z-score (r=.181, P=.01), height (r=.210, P=.003) and diastolic blood pressure (r=.167, P=.02) for boys; and systolic blood pressure (r=.153, P=.03) and parental history of premature cardiovascular disease (r=.139, P=.05) for girls. The association of BMI z-score with extra-medial thickness differed by gender (P-interaction=.04).

CONCLUSIONS

Carotid extra-medial thickness is independently associated with gender and height in childhood. Extra-medial thickness may provide important information concerning early arterial health, particularly related to the arterial adventitia.

Myofibroblast-mediated adventitial remodeling: an underestimated player in arterial pathology

The arterial adventitia has been long considered an essentially supportive tissue; however, more and more data suggest that it plays a major role in the modulation of the vascular tone by complex interactions with structures located within intima and media. The purpose of this review is to summarize these data and to describe the mechanisms involved in adventitia/media and adventitia/intima cross-talk. In response to a plethora of stimuli, the adventitia undergoes remodeling processes, resulting in positive (adaptive) remodeling, negative (constrictive) remodeling, or both. The differentiation of the adventitial fibroblast into myofibroblast (MF), a key player of wound healing and fibrosis development, is a hallmark of negative remodeling; this can lead to vessel stenosis and thus contribute to major cardiovascular diseases. The mechanisms of fibroblast-to-MF differentiation and the role of the MF in adventitial remodeling are highlighted herein.

The vascular adventitia: its role in the arterial injury response

The belief that the adventitia serves only a structural purpose has changed over the last decade. Studies have begun to elucidate the role the adventitia plays in the arterial response to injury. The adventitial fibroblast plays an integral part in the development of neointimal hyperplasia. Adiponectin, an adipokine produced from periadventitial adipose tissue, exhibits numerous vasoprotective properties. Stem cells arise, in part, from the adventitia, and stem cell recruitment into the adventitia from the vasa vasorum has been shown to be important in the development of neointimal hyperplasia. The exact role the vasa vasorum plays in neointimal growth is poorly understood and different studies endorse conflicting viewpoints. Thus, understanding the nuances of adventitial pathophysiology will allow us to better appreciate the mechanisms behind the pathology of neointimal hyperplasia. This review will summarize recent findings on the active role the adventitia plays toward the development of neointimal hyperplasia.

Simvastatin preserves diastolic function in experimental hypercholesterolemia independently of its lipid lowering effect

OBJECTIVE

Isolated diastolic dysfunction is present in 40% of heart failure patients. It has been attributed to myocardial fibrosis and related to cardiovascular risk factor exposure. We hypothesized that simvastatin will improve these dynamics in experimental hypercholesterolemia (HC).

METHODS

Three groups of pigs were studied after 12 weeks of normal (N) diet, HC diet, or HC diet with simvastatin (80 mg/day) treatment. Cardiac function was assessed by electron beam computed tomography (EBCT) and percentage of myocardium occupied by microvessels (myocardial vascular fraction) was calculated by micro-CT. Collagen content was determined by Sirius red staining and confirmed by a quantitative, hydroxyoproline-based assay.

RESULTS

Compared with N, LDL serum concentration was higher in HC and HC+simvastatin (1.0±0.1 vs. 7.9±1.7 and 9.6±1.2 mmol/L, p<0.05 for both). Cardiac early diastolic filling was reduced in HC compared with N (102.4±11.3 vs. 151.1±12.1 mL/s; p<0.05) but restored in HC+simvastatin (176.8±21.3 mL/s, p<0.05 vs. HC). Compared with N, myocardial vascular fraction was higher in HC but not in HC+simvastatin (1.98±0.84 vs. 4.48±0.31 and 2.95±0.95%; p<0.05 for HC vs. N). Myocardial collagen content was higher in HC than in HC+simvastatin and N (4.72±1.03 vs. 1.62±0.12 and 1.21±0.24% area staining; p<0.05 for HC vs. N), which was attributable mainly to an increase in collagen III (2.90±0.48 vs. 1.62±0.12 and 1.21±0.24% area staining; p<0.05 for HC vs. N).

CONCLUSIONS

Simvastatin is able to prevent diastolic dysfunction in experimental HC independent of its lipid lowering effect. This beneficial effect is, at least partially, due to a decrease in myocardial fibrosis and angiogenesis.

Carotid intima-media and adventitial thickening: comparison of new and established ultrasound and magnetic resonance imaging techniques

OBJECTIVE

Carotid intima-media thickness is a well established non-invasive surrogate marker of cardiovascular disease, however there is evidence that structural modification of the arterial adventitia also accompanies cardiovascular risk factors and might be involved causally in atherosclerosis. We sought to determine the relative contributions of the intima-media and adventitia to variation in ultrasound and magnetic resonance derived measures of carotid wall thickness.

METHODS

Carotid ultrasound and magnetic resonance imaging were undertaken in 20 participants. Carotid intima-media thickness, carotid extra-media thickness (which incorporates the arterial adventitia) and total wall thickness (a combined near-wall intima-media thickness and carotid extra-media thickness) using high-resolution ultrasound, and wall thickness using magnetic resonance imaging, were obtained.

RESULTS

All ultrasound-derived measures of the arterial wall thickness were highly correlated with wall thickness by magnetic resonance imaging (all P<0.001); as expected the total wall thickness by ultrasound measure was most tightly correlated (correlation coefficient=0.814, P<0.0001). In multivariable models, there was evidence that both carotid intima-media thickness and carotid extra-media thickness contributed independently to the variance in wall thickness by magnetic resonance imaging, especially for the most severe focal thickening. Measures of carotid wall thickness that incorporated all three layers of the arterial wall were more closely correlated with the number of cardiovascular risk factors than carotid intima-media thickness alone.

CONCLUSIONS

These results indicate that the arterial adventitia is an important contributor to the wall thickness measure derived by magnetic resonance imaging, and that carotid extra-media thickness likely provides additional information concerning arterial structure than that obtained from carotid intima-media thickness alone.

Somatic cell plasticity and Niemann-Pick type C2 protein: fibroblast activation

A growing body of evidence points toward activated fibroblasts, also known as myofibroblasts, as one of the leading mediators in several major human pathologies including proliferative fibrotic disorders, invasive tumor growth, rheumatoid arthritis, and atherosclerosis. Niemann-Pick Type C2 (NPC2) protein has been recently identified as a product of the second gene in NPC disease. It encodes ubiquitous, highly conserved, secretory protein with the poorly defined function. Here we show that NPC2 deficiency in human fibroblasts confers their activation. The activation phenomenon was not limited to fibroblasts as it was also observed in aortic smooth muscle cells upon silencing NPC2 gene by siRNA. More importantly, activated synovial fibroblasts isolated from patients with rheumatoid arthritis were also identified as NPC2-deficient at both the NPC2 mRNA and protein levels. The molecular mechanism responsible for activation of NPC2-null cells was shown to be a sustained phosphorylation of ERK 1/2 mitogen-activated protein kinase (MAPK), which fulfills both the sufficient and necessary fibroblast activation criteria. All of these findings highlight a novel mechanism where NPC2 by negatively regulating ERK 1/2 MAPK phosphorylation may efficiently suppress development of maladaptive tissue remodeling and inflammation.

Perivascular ancestors of adult multipotent stem cells

Independent studies by numerous investigators have shown that it is possible to harvest multipotent progenitor cells from diverse dissociated and cultured fetal, perinatal, and principally adult developed tissues. Despite the increasingly recognized medical value of these progenitor cells, the archetype of which remains the mesenchymal stem cell, this indirect extraction method has precluded the understanding of their native identity, tissue distribution, and frequency. Consistent with other researchers, we have hypothesized that blood vessels in virtually all organs harbor ubiquitous stem cells. We have identified, marked, and sorted to homogeneity by flow cytometry endothelial and perivascular cells in a large selection of human fetal, perinatal, and adult organs. Perivascular cells, including pericytes in the smallest blood vessels and adventitial cells around larger ones, natively express mesenchymal stem cell markers and produce in culture a long-lasting progeny of multilineage mesodermal progenitor cells. Herein, we review results from our and other laboratories that suggest a perivascular origin for mesenchymal stem cells and other adult progenitor cells. Recent experiments illustrate the therapeutic potential of human pericytes to regenerate skeletal muscle and promote functional recovery in the diseased heart and kidney.

Prevention of vasa vasorum neovascularization attenuates early neointima formation in experimental hypercholesterolemia

Vasa vasorum (VV) neovascularization is a key feature of early atherosclerosis and adds substantial endothelial exchange-surface to the coronary vessel wall. Thus, it is conceivable that VV neovascularization favors the entry of pro-inflammatory and pro-atherosclerotic blood components into the coronary vessel wall. We sought to investigate the effects of Thalidomide (Th), a potent anti-angiogenic drug on vasa vasorum (VV) neovascularization, vessel wall inflammation, and neointima formation in early experimental atherosclerosis. Female domestic swine, 3 months old, were fed normal (N, n = 12) or high-cholesterol diet (HC, n = 12) for 3 months. In each group six pigs were randomized to 200 mg Thalidomide daily for the diet period (N + Th, HC + Th). LADs were scanned with micro-CT (20 microm cubic voxel size) to determine VV spatial density (#/mm2). Fresh-frozen coronary tissue was used for western blotting (VEGF, TNF-alpha, LOX-1, Ikappabetaalpha and Gro-alpha) and electrophoretic mobility shift assay (EMSA, NFkappabeta). Treatment with Thalidomide preserved VV spatial density [2.7 +/- 0.3 (N), 6.4 +/- 0.7 (HC), 3.5 +/- 0.8 (HC + Th); p = ns HC + Th vs. N] and inhibited the expression of VEGF, TNF-alpha and LOX-1, but not NFkappabeta activity in the coronary vessel wall. Immunofluorescence analyses revealed co-localization of vWF but not SMA and NFkappabeta, TNF-alpha as well as VEGF in HC and HC + Th coronaries. Intima-media thickness was significantly inhibited in HC + Th compared to HC. Serum levels of hs-CRP and TNF-alpha did not differ among the groups. Our study supports a role of VV neovascularization in the development of and a therapeutic potential for anti-angiogenic intervention in early atherosclerosis.

Phase-contrast MRI-based elastography technique detects early hypertensive changes in ex vivo porcine aortic wall

PURPOSE

To measure the elastic properties of ex vivo porcine aortas in control and hypertensive groups using a phase contrast magnetic resonance imaging (MRI)-based elastography technique.

MATERIALS AND METHODS

Female domestic pigs were randomized to a normal control group (N; n=5) or a renovascular hypertension group (HT; n=5) for the duration of 3 months. Mean arterial pressure was significantly higher in the hypertension group than in the control group (173+/-12 vs. 115+/-11 mmHg, P

RESULTS

The Young's modulus-wall thickness product, a reflection of vascular stiffness, was significantly higher in the hypertension group than in the control group (0.571+/-0.080 vs. 0.419+/-0.026, P<0.05). Histological analysis and staining confirmed increased intima-media thickness and collagen content in the hypertensive aorta, while elastin staining showed no difference.

CONCLUSION

The current study shows that MR elastography offers a method to study the physiologic changes in the arterial wall secondary to early hypertension.

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Key Words

• mri
• elastography
• aorta

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MESH Headings

• Animals
• Aorta, Abdominal/pathology
• Aorta, Abdominal/ultrastructure
• Blood Pressure
• Body Weight
• Cholesterol/blood
• Disease Models, Animal
• Elasticity Imaging Techniques/methods
• Female
• Hypertension/diagnosis
• Magnetic Resonance Imaging/methods
• Microscopy, Phase-Contrast
• Swine

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Grants

• R37 EB001981 NIBIB NIH HHS
• DK73608 NIDDK NIH HHS
• R01 EB001981-08 NIBIB NIH HHS
• R01 DK073608 NIDDK NIH HHS
• R01 EB001981 NIBIB NIH HHS
• EB001981 NIBIB NIH HHS

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Affiliation(s)

David A Woodrum Radiology Department, Mayo Clinic, Rochester, Minnesota 55905, USA.
Joerg Herrmann
Amir Lerman
Anthony J Romano
Lilach O Lerman
Richard L Ehman

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Hypertension and Hypercholesterolemia Differentially Affect the Function and Structure of Pig Carotid Artery

The purpose of this work was to compare the effects of hypertension and hypercholesterolemia on carotid endothelial function, structure, and vasa vasorum density. Seventeen pigs were randomized to a 12-week normal diet without (n=5), or with renovascular hypertension (HT; n=6), or to a high cholesterol diet (HC; n=6). Carotid arteries were studied by organ chambers (endothelial function) and microcomputed tomography (vasa vasorum), and tissue was processed for Sirius red staining and immunoblotting (vascular endothelium growth factor, endostatin, matrix metalloproteinase-9, and matrix metalloproteinase-2). HC and HT showed reduced vasodilation to acetylcholine as compared with controls, but HT also had a lower response to sodium nitroprusside. In addition, HT showed a higher content of organized collagen fibers and increased intima-media thickness. Vasa vasorum density was increased in HC but not in HT. Both HT and HC showed a proangiogenetic biochemical milieu (higher vascular endothelium growth factor, matrix metalloproteinases, and lower endostatin), but this was more pronounced in HC. Both hypertension and hypercholesterolemia induce endothelial dysfunction in the carotid artery. However, hypertension is also associated with greater fibrosis and vascular wall thickening, which might impair endothelium-independent vasorelaxation and vasa vasorum growth. Hypercholesterolemia is, in turn, associated with vasa vasorum neovascularization. These data suggest that carotid atherosclerosis can evolve through different mechanisms in relation to different risk factors.

Frontiers in nephrology: early atherosclerosis--a view beyond the lumen

Endothelial dysfunction is an established clinical marker of early coronary artery disease and has been shown to be associated with increased cardiovascular morbidity and mortality. New concepts now extend the view of endothelial dysfunction beyond the traditional involvement of the coronary arterial endothelium alone. Recent research indicates that the coronary vessel wall, especially the vasa vasorum, as well as bone marrow-derived endothelial progenitor cells may be subject to proatherosclerotic changes, even before the development of angiographically evident endothelial dysfunction; therefore, "microvascular endothelial dysfunction," which is composed of dysfunction of the vasa vasorum's endothelium as well as "microcellular endothelial dysfunction," reflecting impaired mobilization and function of endothelial progenitor cells, may precede "macrovascular endothelial dysfunction." Vasa vasorum neovascularization, with endothelial leakage and dysfunction increasing influx of proinflammatory and proatherogenic cellular and noncellular substances into the vessel wall, is proposed as one feature of this new concept. In addition, the role of bone marrow-derived endothelial progenitor cells is discussed as are the potential impact of impaired progenitor cell mobilization, release from the marrow, and function in acute and stable coronary artery disease. Finally, potential future therapies are proposed, focusing on interventions that may prevent or diminish the development of the microvascular and microcellular endothelial dysfunction.

Chronic proteasome inhibition contributes to coronary atherosclerosis

The proteasome is responsible for the degradation of oxidized proteins, and proteasome inhibition has been shown to generate oxidative stress in vitro. Atherosclerosis is thought to be initiated as a consequence of increased endogenous oxidative stress. The current study was designed to assess whether chronic proteasome inhibition is associated with early coronary atherosclerosis. Female pigs, 3 months of age, were randomized to a normal (N) or high-cholesterol (HC) diet (2% cholesterol, 15% lard) without or with twice weekly subcutaneous injections of the proteasome inhibitor (PSI) MLN-273 (0.08 mg/kg, N+PSI and HC+PSI) for a period of 12 weeks (n=5 per group). Coronary vasorelaxation to bradykinin (10(-10.5) to 10(-6.5) mol/L) and sodium nitroprusside (10(-9) to 10(-5) mol/L) was assessed by in vitro organ chamber experiments, intima-media ratio by morphometric analysis of Elastica-van Gieson-stained slides, and intima superoxide production by dihydroethidium fluorescence. Vasorelaxation to 10(-6.5) mol/L bradykinin was reduced in HC compared with N (69+/-7 versus 90+/-2%, P<0.05) and further reduced in N+PSI and HC+PSI (57+/-6 and 48+/-13%, P<0.05 versus N and HC for each). Compared with N (0.03+/-0.01), intima-media ratio was higher in N+PSI (0.09+/-0.04, P<0.01) and HC+PSI (0.15+/-0.06, P<0.05). Compared with N (0.6+/-0.9% of intima area), dihydroethidium fluorescence was higher in HC, N+PSI, and HC+PSI (8.9+/-1.6, 6.0+/-3.5, and 7.2+/-3.9% of intima area, P<0.05 for all). Thus, chronic proteasome inhibition is associated with increased coronary artery oxidative stress and early atherosclerosis. These findings support the significance of the proteasome and related protein quality control for vascular biology and pathology.

Transient middle cerebral artery occlusion causes different structural, mechanical, and myogenic alterations in normotensive and hypertensive rats

Transient focal cerebral ischemia in the rat alters vessel properties, and spontaneously hypertensive rats (SHR) show a poorer outcome after ischemia. In the present study we examined the role of hypertension on vessel properties after ischemia-reperfusion. The right middle cerebral artery (MCA) was occluded (90 min) and reperfused (24 h) in SHR (n = 12) and Wistar-Kyoto rats (WKY; n = 11). Sham-operated rats (SHR, n = 10; WKY, n = 10) were used as controls. The structural, mechanical, and myogenic properties of the MCA were assessed by pressure myography. Nuclei distribution and elastin content and organization were analyzed by confocal microscopy. Infarct volume was larger in SHR than in WKY rats. Ischemia-reperfusion induced adventitial hypertrophy associated with an increase in the total number of adventitial cells. In addition, fenestrae area and arterial distensibility increased and myogenic tone decreased in the MCA of WKY rats after ischemia-reperfusion. Hypertension per se induced hypertrophic inward remodeling. Ischemia-reperfusion decreased the cross-sectional area of the MCA in SHR, without significant changes in distensibility, despite an increase in fenestrae area. In addition, MCA myogenic properties were not altered after ischemia-reperfusion in SHR. Our results indicate that in normotensive rats, MCA develops a compensatory mechanism (i.e., enhanced distensibility and decreased myogenic tone) that counteracts the effect of ischemia-reperfusion and ensures correct cerebral irrigation. These compensatory mechanisms are lost in hypertension, thereby explaining, at least in part, the greater infarct volume observed in SHR.

Topological determinants and consequences of adventitial responses to arterial wall injury

Arteries are composed of 3 concentric tissue layers which exhibit different structures and properties. Because arterial injury is generally initiated at the interface with circulating blood, most studies performed to unravel the mechanisms involved in injury-induced arterial responses have focused on the innermost layer (intima) rather than on the outermost adventitial layer. In the present review, we focus on the involvement of the adventitia in response to various types of arterial injury leading to vascular remodeling. Physiologically, soluble vascular mediators are centrifugally conveyed by mass transport toward the adventitia. Moreover, in pathological conditions, neomediators and antigens can be generated within the arterial wall, whose outward conveyance triggers different patterns of local adventitial response. Adventitial angiogenesis, immunoinflammation, and fibrosis sequentially interact and their net balance defines the participation of the adventitial response in arterial pathology. In the present review we discuss 4 pathological entities in which the adventitial response to arterial wall injury participates in arterial wall remodeling. Hence, the adventitial adaptive immune response predominates in chronic rejection. Inflammatory phagocytic cell recruitment and initiation of a shift from innate to adaptive immunity characterize the adventitial response to products of proteolysis in abdominal aortic aneurysm. Adventitial sprouting of neovessels, leading to intraplaque hemorrhages, predominates in atherothrombosis. Adventitial fibrosis characterizes the response to mechanical stress and is responsible for the constrictive remodeling of arterial segments and initiating interstitial fibrosis in perivascular tissues. These adventitial events, therefore, have an impact not only on the vessel wall biology but also on the surrounding tissue.

Renal artery stenosis and accelerated atherosclerosis: which comes first?

Renal artery stenosis (RAS) is usually observed in hypertensive patients with extensive atherosclerosis. There is some evidence that in these patients the atherosclerotic process and the consequent target-organ damage is more severe than in hypertensive patients without RAS. In this review we will entertain the hypothesis that some of the humoral factors that are activated by RAS may contribute to accelerate the progression of atherosclerosis. Several studies identified RAS as a predictor of cardiovascular events in high-risk patients, although in most cases the contribution of blood pressure per se to the progression of vascular lesions could not be determined. As a result of experimental RAS, hypertension and increased oxidative stress are stimuli for atherosclerosis as well as cardiac and renal damage. In the presence of RAS, the renin-angiotensin system is stimulated, and it has been shown that angiotensin II exerts proinflammatory, pro-oxidant and procoagulant activities in experimental models and humans. The potential contribution of reactive oxygen species to the prohypertensive and proatherosclerotic effects of RAS is supported by evidence that nicotinamide adenine dinucleotide phosphate, reduced form oxidase is specifically stimulated by angiotensin II, an activity not shared by epinephrine. Moreover, angiotensin II triggers the release of aldosterone, endothelin 1, thromboxane A2 and other derivatives of the arachidonic acid metabolism, all of which can further and independently aggravate cardiovascular damage. Epidemiological and experimental evidence so far available suggests that accelerated atherosclerosis can be both the cause and the consequence of RAS.

Adventitial fibroblasts are activated in the early stages of atherosclerosis in the apolipoprotein E knockout mouse

The role of the adventitia in vascular function and vascular lesion formation has been largely ignored. This study observed the activation of the adventitia and specifically the fibroblasts in the development of atherosclerosis in the apoE(-/-) mouse. The results showed a gradual increase in expression of collagen types I and III after 2, 4, and 8 weeks of hyperlipidic diet. The earliest expression of monocyte chemoattractant protein-1 (MCP-1) protein and mRNA was detected in the adventitial fibroblast before the formation of intimal lesions. Proliferation, too, was first found in the adventitial fibroblasts. We hypothesize that the adventitial fibroblast is activated in the early stage of atherosclerosis. Adventitial inflammation may be an early event in the development of atherosclerotic lesions.

Activation of adventitial fibroblasts contributes to the early development of atherosclerosis: A novel hypothesis that complements the “Response-to-Injury Hypothesis” and the “Inflammation Hypothesis”

The role of the adventitia in vascular function and vascular lesion formation has been largely ignored. This article introduces the hypothesis that the activation of the adventitia, specifically the fibroblasts, contributes to the formation of intimal atherosclerotic lesions. The evidence for this hypothesis includes: (a) the early proliferative changes seen in fibroblasts found in the adventitia; (b) the increase and the alteration of extracellular matrix deposition in the adventitia; (c) fibroblast differentiation into myofibroblasts and migration into the intima; and (d) fibroblast synthesis and release of cytokines that have potent effects on neighboring smooth muscle and endothelial cells prior to intimal lesion formation. In conclusion, the activation of adventitial fibroblasts is a key regulator of vascular function and structure from the "outside-in" and contributes to the development of atherosclerotic lesions. The outer location of the adventitia makes it a suitable location for drug delivery and gene therapy aimed at preventing and treating atherosclerosis.

Role of the adventitia in pulmonary vascular remodeling

An increasing volume of experimental data indicates that the adventitial fibroblast, in both the pulmonary and systemic circulations, is a critical regulator of vascular wall function in health and disease. A rapidly emerging concept is that the vascular adventitia acts as biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. In response to stress or injury, resident adventitial cells can be activated and reprogrammed to exhibit different functional and structural behaviors. In fact, under certain conditions, the adventitial compartment may be considered the principal injury-sensing tissue of the vessel wall. In response to vascular stresses such as overdistension and hypoxia, the adventitial fibroblast is activated and undergoes phenotypic changes, which include proliferation, differentiation, upregulation of contractile and extracellular matrix proteins, and release of factors that directly affect medial smooth muscle cell tone and growth and that stimulate recruitment of inflammatory and progenitor cells to the vessel wall. Each of these changes in fibroblast phenotype modulates either directly or indirectly changes in overall vascular function and structure. The purpose of this review is to present the current evidence demonstrating that the adventitial fibroblast acts as a key regulator of pulmonary vascular function and structure from the "outside-in."

Adventitial dysfunction: an evolutionary model for understanding atherosclerosis

Endothelial and smooth muscle dysfunctions are widely implicated in the pathogenesis of atherosclerosis. Modern mechanical and pharmacologic treatments aim to remodel abnormalities of the vessel intima and media. We hypothesize that adventitial dysfunction comprises the dominant source of atherosclerosis by originating many endothelial and smooth muscle abnormalities. The autonomic nervous system innervates the adventitia, and autonomic dysfunction induces many end-organ dysfunctions including inflammation and thrombosis. The link between diabetes and atherosclerosis may operate through adventitial autonomic neuropathy. Smoking may promote atherosclerosis by inducing adventitial autonomic dysfunction related to nicotine-mediated compensatory upregulation of sympathetic bias independent of endothelial injury induced by purported tobacco toxins. While hypertension is thought to cause atherosclerosis, the two conditions may instead represent independent consequences of autonomic dysfunction. The link between aging and atherosclerosis may operate through adventitial dysfunction induced by autonomic dysregulations. Exercise may ameliorate atherosclerosis by restoring adventitial autonomic function, thereby normalizing adventitial regulation of medial and intimal biology. Feed-forward adventitial vascular baroreceptor and chemoreceptor dysregulation may further exacerbate atherosclerosis as intimal plaque interferes with these sensors. Since penetrating external physical injury likely represented a dominant selective force during evolution, the adventitia may be preferentially equipped with sensors and response systems for vessel trauma. The convergent response of adrenergia, inflammation, and coagulation, which is adaptive for physical trauma, may be maladaptive today when different stressors trigger the cascade. Endoluminal therapies including atherectomy, angioplasty, and stent deployment involve balloon expansion that traumatizes all layers of the vessel wall. These interventions may paradoxically reinitiate the cascade of atherogenesis that begins with adventitial dysfunction and leads to restenosis. Methods to reduce adventitial trauma, a maladaptive trigger of adventitial dysfunction, may reduce the risk of restenosis. We envision novel mechanical and biopharmaceutical solutions that target the adventitia to prevent or treat atherosclerosis including novel drug delivery strategies, exo-stents that wrap vessels, and neuromodulation of vessels.