Increased endothelial and vascular smooth muscle cell adhesion on nanostructured titanium and CoCrMo

In the body, vascular cells continuously interact with tissues that possess nanostructured surface features due to the presence of proteins (such as collagen and elastin) embedded in the vascular wall. Despite this fact, vascular stents intended to restore blood flow do not have nanoscale surface features but rather are smooth at the nanoscale. As the first step towards creating the next generation of vascular stent materials, the objective of this in vitro study was to investigate vascular cell (specifically, endothelial, and vascular smooth muscle cell) adhesion on nanostructured compared with conventional commercially pure (cp) Ti and CoCrMo. Nanostructured cp Ti and CoCrMo compacts were created by separately utilizing either constituent cp Ti or CoCrMo nanoparticles as opposed to conventional micron-sized particles. Results of this study showed for the first time increased endothelial and vascular smooth muscle cell adhesion on nanostructured compared with conventional cp Ti and CoCrMo after 4 hours' adhesion. Moreover, compared with their respective conventional counterparts, the ratio of endothelial to vascular smooth muscle cells increased on nanostructured cp Ti and CoCrMo. In addition, endothelial and vascular smooth muscle cells had a better spread morphology on the nanostructured metals compared with conventional metals. Overall, vascular cell adhesion was better on CoCrMo than on cp Ti. Results of surface characterization studies demonstrated similar chemistry but significantly greater root-mean-square (rms) surface roughness as measured by atomic force microscopy (AFM) for nanostructured compared with respective conventional metals. For these reasons, results from the present in vitro study provided evidence that vascular stents composed of nanometer compared with micron-sized metal particles (specifically, either cp Ti or CoCrMo) may invoke cellular responses promising for improved vascular stent applications.     

Role of vascular smooth muscle cell in the inflammation of atherosclerosis

Atherosclerosis is a pathologic process occurring within the artery, in which many cell types, including T cell, macrophages, endothelial cells, and smooth muscle cells, interact, and cause chronic inflammation, in response to various inner- or outer-cellular stimuli. Atherosclerosis is characterized by a complex interaction of inflammation, lipid deposition, vascular smooth muscle cell proliferation, endothelial dysfunction, and extracellular matrix remodeling, which will result in the formation of an intimal plaque. Although the regulation and function of vascular smooth muscle cells are important in the progression of atherosclerosis, the roles of smooth muscle cells in regulating vascular inflammation are rarely focused upon, compared to those of endothelial cells or inflammatory cells. Therefore, in this review, we will discuss here how smooth muscle cells contribute or regulate the inflammatory reaction in the progression of atherosclerosis, especially in the context of the activation of various membrane receptors, and how they may regulate vascular inflammation. [BMB Reports 2014; 47(1): 1-7]     

Vascular wall resident progenitor cells: A review

The vessel wall has usually been thought to be relatively quiescent. But the discovery of progenitor cells in many tissues and in the vasculature itself has led to a reconsideration of the vascular biology. The presence of circulating endothelial and smooth muscle progenitors able to home to the injured vascular wall is a firm acquisition; less known is the notion, coming from embryonic and adult tissue studies, that stem cells able to differentiate into endothelial cells and smooth muscle cells also reside in the arterial wall. Moreover, the existence of a vasculogenic zone has recently been identified in adult human arteries; this niche-like zone is believed to act as a source of progenitors for postnatal vasculogenesis. From the literature it is already apparent that a complex interplay between circulating and resident vascular wall progenitors takes place during embryonal and postnatal life; a structural/functional disarray of these intimate stem cell compartments could hamper appropriate vascular repair, the development of vascular wall disease being the direct clinical consequence in adult life. This review gives an overview of adult large vessel progenitors established in the vascular wall during embryogenesis and their role in the maintenance of wall homeostasis.     

The role of circulating precursors in vascular repair and lesion formation

The accumulation of smooth muscle cells (SMCs) plays a principal role in atherogenesis, post-angioplasty restenosis and transplantation-associated vasculopathy. Therefore, much effort has been expended in targeting the migration and proliferation of medial smooth muscle cells to prevent occlusive vascular remodeling. Recent evidence suggests that bone marrow-derived circulating precursors can also give rise to endothelial cells and smooth muscle cells that contribute to vascular repair, remodeling, and lesion formation under physiological and pathological conditions. This article overviews recent findings on circulating vascular progenitor cells and describes potential therapeutic strategies that target these cells to treat occlusive vascular diseases.     

Increased retinoid signaling in vascular smooth muscle cells by proinflammatory cytokines

Retinoids have been shown to modulate inflammation and the immune response in many cell types including macrophages, endothelial cells, and vascular smooth muscle cells. However, present knowledge of whether inflammatory mediators modulate vitamin A status in these cells is limited. To identify the role of inflammation on retinoid metabolism in vascular smooth muscle cells, the cells were exposed to a combination of proinflammatory cytokines: interleukin-1beta, interferon-gamma, and lipopolysaccharides. Without stimulation with proinflammatory cytokines, vascular smooth muscle cells expressed retinol dehydrogenases-2 and 5 mRNA detected by RT-PCR. Stimulation with the combination of cytokines induced a substantial increase of retinol dehydrogenase-5 mRNA. This was associated with increased production of ligands for retinoic acid receptors, when assayed in a retinoic acid receptor-dependent luciferase reporter system. Our results demonstrate that inflammatory mediators activate the retinoid metabolic pathway in vascular smooth muscle cells, which potentially may modulate the inflammatory response in the vascular wall.     

Endothelial dysfunction as a cellular mechanism for vascular failure

The regulation of vascular tone, vascular permeability, and thromboresistance is essential to maintain blood circulation and therefore tissue environments under physiological conditions. Atherogenic stimuli, including diabetes, dyslipidemia, and oxidative stress, induce vascular dysfunction, leading to atherosclerosis, which is a key pathological basis for cardiovascular diseases such as ischemic heart disease and stroke. We have proposed a novel concept termed "vascular failure" to comprehensively recognize the vascular dysfunction that contributes to the development of cardiovascular diseases. Vascular endothelial cells form the vascular endothelium as a monolayer that covers the vascular lumen and serves as an interface between circulating blood and immune cells. Endothelial cells regulate vascular function in collaboration with smooth muscle cells. Endothelial dysfunction under pathophysiological conditions contributes to the development of vascular dysfunction. Here, we address the barrier function and microtubule function of endothelial cells. Endothelial barrier function, mediated by cell-to-cell junctions between endothelial cells, is regulated by small GTPases and kinases. Microtubule function, regulated by the acetylation of tubulin, a component of the microtubules, is a target of atherogenic stimuli. The elucidation of the molecular mechanisms of endothelial dysfunction as a cellular mechanism for vascular failure could provide novel therapeutic targets of cardiovascular diseases.     

Pannexin channel and connexin hemichannel expression in vascular function and inflammation

Control of blood flow distribution and tissue homeostasis depend on the tight regulation of and coordination between the microvascular network and circulating blood cells. Channels formed by connexins or pannexins that connect the intra- and extracellular compartments allow the release of paracrine signals, such as ATP and prostaglandins, and thus play a central role in achieving fine regulation and coordination of vascular function. This review focuses on vascular connexin hemichannels and pannexin channels. We review their expression pattern within the arterial and venous system with a special emphasis on how post-translational modifications by phosphorylation and S-nitrosylation of these channels modulate their function and contribute to vascular homeostasis. Furthermore, we highlight the contribution of these channels in smooth muscle cells and endothelial cells in the regulation of vasomotor tone as well as how these channels in endothelial cells regulate inflammatory responses such as during ischemic and hypoxic conditions. In addition, this review will touch on recent evidence implicating a role for these proteins in regulating red blood cell and platelet function.     

Effect of glucose concentration on vascular function in aging. Action on calcium fluxes and vasomotricity induced by elastin peptides

Glycemia is a physiological parameter tightly regulated for an optimal energetic supply to the organism, in spite of variable tissular glucose needs. Physiopathological alteration of glycemic regulation leads to dysfunctions of many cell types. For example, diabetes considerably increases morbidity and mortality linked to cardiovascular pathologies and constitute nowadays a serious public health problem. Many in vivo and in vitro studies have investigated the impact of extracellular glucose concentration on smooth muscle and endothelial cells. Glycemia regulates expression and activity of proteins implicated in various processes, such as vasodilation (eNOS), cellular adherence (ICAM-1, VCAM-1), glucose transport (GLUT-1) or free radical generation. Nuclear receptors of the PPAR (peroxisome proliferator-activated receptors) family which are implicated in glucose and lipid metabolism control, seem to have direct vascular actions, in the regulation of cellular functions by extracellular glucose, reinforcing their status of pharmacological targets for preservation and improvement of vascular function. More general processes, such as cellular proliferation and cell death, are also influenced by glucose concentration. Concerning the contractile function, hypoglycemia and hyperglycemia modulate vascular reactivity while acting on the vasoactive substances level and the cellular response to these molecules. In particular they act on variation of ionic channels (K+, Ca2+) activity or by interfering with some signaling pathways (NO). For example, the age-dependant vasodilation and endothelial calcium influx induced by elastin peptide are modulated by extracellular glucose levels. In conclusion, abnormal chronic variations of circulating glucose levels seem to be directly responsible for endothelial and smooth muscle cell dysfunction in the pathogenesis of cardiovascular abnormalities of patients presenting glycemia dysregulations.     

Thrombin and vascular inflammation

Vascular endothelium is a key regulator of homeostasis. In physiological conditions it mediates vascular dilatation, prevents platelet adhesion, and inhibits thrombin generation. However, endothelial dysfunction caused by physical injury of the vascular wall, for example during balloon angioplasty, acute or chronic inflammation, such as in atherothrombosis, creates a proinflammatory environment which supports leukocyte transmigration toward inflammatory sites. At the same time, the dysfunction promotes thrombin generation, fibrin deposition, and coagulation. The serine protease thrombin plays a pivotal role in the coagulation cascade. However, thrombin is not only the key effector of coagulation cascade; it also plays a significant role in inflammatory diseases. It shows an array of effects on endothelial cells, vascular smooth muscle cells, monocytes, and platelets, all of which participate in the vascular pathophysiology such as atherothrombosis. Therefore, thrombin can be considered as an important modulatory molecule of vascular homeostasis. This review summarizes the existing evidence on the role of thrombin in vascular inflammation.     

Thematic review series: The immune system and atherogenesis. Cytokines affecting endothelial and smooth muscle cells in vascular disease

The cellular and extracellular matrix accumulations that comprise the lesions of atherosclerosis are driven by local release of cytokines at sites of predilection for lesion formation, and by the specific attraction and activation of cells expressing receptors for these cytokines. Although cytokines were originally characterized for their potent effects on immune and inflammatory cells, they also promote endothelial cell dysfunction and alter smooth muscle cell (SMC) phenotype and function, which can contribute to or retard vascular pathologies. This review summarizes in vivo studies that have characterized endothelial- and smooth muscle-specific effects of altering cytokine signaling in vascular disease. Although multiple reports have identified cytokines as pivotal players in endothelial and SMC responses in vascular disease, they also have highlighted the need to delineate the critical genes and specific cellular functions regulated by individual cytokine signaling pathways.     

Progenitor cells in vascular repair

PURPOSE OF REVIEW: A common characteristic of all types of vascular disease is endothelial dysfunction/damage followed by an inflammatory response. Although mature endothelial cells can proliferate and replace damaged cells in the vessel wall, recent findings indicate an impact of stem and progenitor cells in repair process. This review aims to briefly summarize the recent findings in stem/progenitor cell research relating to vascular diseases, focusing on the role of stem/progenitor cells in vascular repair. RECENT FINDINGS: It has been demonstrated that endothelial progenitor cells present in the blood have an ability to repair damaged arterial-wall endothelium. These cells may be derived from a variety of sources, including bone marrow, spleen, liver, fat tissues and the adventitia of the arterial wall. In response to cytokine released from damaged vessel wall and adhered platelets, circulating progenitor cells home in on the damaged areas. It was also reported that the adhered progenitor cells can engraft into endothelium and may differentiate into mature endothelial cells. SUMMARY: Vascular progenitor cells derived from different tissues have an ability to repair damaged vessel, in which the local microenvironment of the progenitors plays a crucial role in orchestrating cell homing and differentiation.     

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.     

Arterial wall-determined risk factors to vascular diseases

Many decades of research have led to considerable in-depth understanding of circulating factors that may lead to coronary atherosclerosis. However, not every individual with serious known risk factors such as hypercholesterolemia or cigarette smoking develops atherosclerosis. Differential susceptibility of the arterial wall to circulating atherogenic risk factors, which may be largely controlled by genetic variants, may provide this missing link. Endothelial cells, the lining of the arterial wall, are responsible for the integrity and responses to the circulating environment. Dysfunctional endothelial cells and the subsequent proliferation of vascular smooth muscle cells are the prelude of atherosclerosis and acute coronary syndrome. Yet, there have been no detailed studies exploring the interaction between circulating environmental and arterial wall endogenous risk factors in living human subjects. This deficiency is largely the result of restricted access. Genetic factors almost certainly play a key role in directing how the arterial wall responds to circulating "environmental" factors. This endogenous-exogenous (i.e. the arterial wall-circulating) blood balance is the reflection of nature-nurture or gene-environment interaction. Understanding the interaction fully will require direct access to the arteries, and nonhuman primates can provide an excellent model for such investigations. In the current review, we discuss the importance of arterial wall factors in vascular diseases and present a baboon model for practical studies of arterial wall factors and their interaction with circulating factors. Direct biopsy access to baboon arteries will provide a unique opportunity to explore arterial wall susceptibilities and to evaluate the direct effects of diet or pharmaceutical agents on vascular diseases. The use of baboons from large pedigreed families in these studies will enable the identification of genes that interact with these environmental factors in determining individual risk of atherosclerosis.     

Cellular interplay in pulmonary arterial hypertension: Implications for new therapies

Pulmonary arterial hypertension (PAH) is a complex and multifactorial disease characterized by vascular remodeling, vasoconstriction, inflammation and thrombosis. Although the available therapies have resulted in improvements in morbidity and survival, PAH remains a severe and devastating disease with a poor prognosis and a high mortality, justifying the need of novel therapeutic targets. An increasing number of studies have demonstrated that endothelial cells (ECs), smooth muscle cells (SMCs) and fibroblasts of the pulmonary vessel wall, as well as platelets and inflammatory cells have a role in PAH pathogenesis. This review aims to integrate the interplay among different types of cells, during PAH development and progression, and the impact of current therapies in cellular modulation. The interplay among endothelial cells, smooth muscle cells and fibroblasts present in pulmonary vessels wall, platelets and inflammatory cells is regulated by several mediators produced by these cells, contributing to the pathophysiologic features of PAH. Current therapies are mainly focused in the pulmonary vascular tone and in the endothelial dysfunction. However, once they have not been effective, novel therapies targeting other PAH features, such as inflammation and platelet dysfunction are emerging. Further understanding of the interplay among different vascular cell types involved in PAH development and progression can contribute to find novel therapeutic targets, decreasing PAH mortality and morbidity in the future.     

Pathophysiology of stem cells in restenosis

Recent evidence has shown that vascular function depends not only on cells within the vessels, but is also significantly modulated by circulating cells derived from the bone marrow. A number of studies indicate that an early reendothelialization by circulating endothelial precursors after vascular injury prevents excessive cell proliferation and restenosis. Conversely, other studies concluded that the homing of other cell fractions, consisting mainly of smooth muscle precursors, cause pathological remodelling. Different cell types have been identified and characterized so far as circulating precursors able to participate in vascular repair by homing and differentiating towards endothelial cells or smooth muscle cells. Among these, endothelial precursor cells, smooth muscle progenitor cells, mesenchymal stem cells and others have been described. The origins, the hierarchy, the role and the markers of these different cell populations are still controversial. Nevertheless, different strategies have been developed so far in animal models to induce the mobilization and the recruitment of stem cells to the injury site, based on physical training, hormone injection and application of stem cell-capturing coated stents. It should also be mentioned that the limited data currently available derived from clinical trials provide contrasting results about the effective role of vascular cell precursors in restenosis prevention, thus indicating that conclusions derived from studies in animal models cannot always be directly applied to humans and that caution should be used in the manipulation of circulating progenitor cells for therapeutic strategies.     

Sorting of murine vascular smooth muscle cells during wound healing in the chicken chorioallantoic membrane

The vascular wall is built up of a heterogeneous population of smooth muscle cells, which exhibit not only morphological distinctions but also important differences in the composition of their structural and contractile proteins. "Epithelioid" smooth muscle cells correspond to an intimal-like type and display features associated with immaturity, whereas "spindle-shaped" cells closely resemble the more typical medial smooth muscle population. We have investigated the integration of these two cell types into the vascular architecture of an in vivo wound-healing model. Stably transfected with the beta-galactosidase gene, intima- and media-like cells were injected intravenously into the chicken chorioallantoic membrane, within which superficial foci of granulation tissue had been created by thermal or chemical injury. At 24 to 72 h after injection, cells had honed in on the lesion sites and were observed in juxtaposition to the endothelial lining of the capillaries. They began to deposit laminin, thereby indicating an impending role in the formation of the vascular wall. Intima- and media-like smooth muscle cells did not differ in their capacity to associate with capillaries, and, in so doing, their biochemical lineage characteristics became indistinguishable from one another. However, intima-like cells also penetrated the adventitial and medial layers of arteries. These findings reveal vascular smooth muscle cells to possess an extraordinary degree of plasticity, being able to adapt flexibly to changes in functional demands.     

Lipid transfer between endothelial and smooth muscle cells in coculture

A coculture system was employed to study the interactions between endothelium and vascular smooth muscle cells in arachidonic acid metabolism. Bovine aortic endothelial cells grown on micropore filters impregnated with gelatin and coated with fibronectin are mounted on polystyrene chambers and suspended over confluent smooth muscle cultures. The endothelial basal laminae are oriented toward the underlying smooth muscle, and the two layers are separated by only 1 mm. Each cell layer was assayed individually: apical and basolateral fluid also was collected separately for assay. Fatty acids, including arachidonic acid, are readily transferred between the endothelial and smooth muscle cells in this system. Distribution of the incorporated fatty acids among the lipids of each cell is the same as when the fatty acid is added directly to the culture medium. Arachidonic acid released from endothelial cells is available as a substrate for prostaglandin production by smooth muscle. In addition, fatty acids released from the smooth muscle cells can pass through the endothelium and accumulate in the fluid bathing the endothelial apical surface. These fatty acid interchanges may be involved in cell-cell signaling within the vascular wall, the clearance of lipids from the vascular wall, or the redistribution of arachidonic acid and other polyunsaturated fatty acids between adjacent cell types. Furthermore, the findings suggest that prostaglandin production by smooth muscle cells can occur in response to stimuli that cause arachidonic acid release from endothelial cells.     

Endothelial dysfunction — A major mediator of diabetic vascular disease

The vascular endothelium is a multifunctional organ and is critically involved in modulating vascular tone and structure. Endothelial cells produce a wide range of factors that also regulate cellular adhesion, thromboresistance, smooth muscle cell proliferation, and vessel wall inflammation. Thus, endothelial function is important for the homeostasis of the body and its dysfunction is associated with several pathophysiological conditions, including atherosclerosis, hypertension and diabetes. Patients with diabetes invariably show an impairment of endothelium-dependent vasodilation. Therefore, understanding and treating endothelial dysfunction is a major focus in the prevention of vascular complications associated with all forms of diabetes mellitus. The mechanisms of endothelial dysfunction in diabetes may point to new management strategies for the prevention of cardiovascular disease in diabetes. This review will focus on the mechanisms and therapeutics that specifically target endothelial dysfunction in the context of a diabetic setting. Mechanisms including altered glucose metabolism, impaired insulin signaling, low-grade inflammatory state, and increased reactive oxygen species generation will be discussed. The importance of developing new pharmacological approaches that upregulate endothelium-derived nitric oxide synthesis and target key vascular ROS-producing enzymes will be highlighted and new strategies that might prove clinically relevant in preventing the development and/or retarding the progression of diabetes associated vascular complications.     

Simulated hypogravity stimulates cell spreading and wound healing in cultured human vascular endothelial cells

It is well known that endothelial cells (EC) are highly sensitive to mechanical influences such as hemodynamic conditions or pulsatile stretch. However, it is still unknown, how endothelium responds to the changed gravity. The results of some studies suggest that cellular elements of vascular wall and, particularly, endothelium, may directly participate in development of physiological responces to microgravity. On our suggestion, this is extremely attractive since vascular endothelium is one of the main regulators of vascular tone (via its interaction with vascular smooth muscle cells) and, consequently, can play not last role in maintaining of normal cardiovascular system operation in microgravity. On the other hand, the endothelium itself may be regarded as a widely dispersed organ of approximately 1.5 kg in weight (in the adult human organism). Finally, endothelium is not just a passive barrier between vascular wall and circulating blood but synthesizes, metabolizes, and releases a substances which act on adjacent cell systems or distant cell structures. The main aims of this study were: 1) the development of experimental model, allowing to study functional parameters of human endothelial cells in hypogravity conditions in vitro; 2) the verification of endothelial sensitivity to gravitational micro-environment.