Response of vascular mesenchymal stem/progenitor cells to hyperlipidemia

Hyperlipidemia is a risk factor for atherosclerosis that is characterized by lipid accumulation, inflammatory cell infiltration, and smooth muscle cell proliferation. It is well known that hyperlipidemia is a stimulator for endothelial dysfunction and smooth muscle cell migration during vascular disease development. Recently, it was found that vessel wall contains a variable number of mesenchymal stem cells (MSCs) that are quiescent in physiological conditions, but can be activated by a variety of stimuli, e.g., increased lipid level or hyperlipidemia. Vascular MSCs displayed characteristics of stem cells which can differentiate into several types of cells, e.g., smooth muscle cells, adipocytic, chondrocytic, and osteocytic lineages. In vitro, lipid loading can induce MSC migration and chemokines secretion. After MSC migration into the intima, they play an essential role in inflammatory response and cell accumulation during the initiation and progression of atherosclerosis. In addition, MSC transplantation has been explored as a therapeutic approach to treat atherosclerosis in animal models. In this review, we aim to summarize current progress in characterizing the identity of vascular MSCs and to discuss the mechanisms involved in the response of vascular stem/progenitor cells to lipid loading, as well as to explore therapeutic strategies for vascular diseases and shed new light on regenerative medicine.     

Cell–cell junctional mechanotransduction in endothelial remodeling

The vasculature is one of the most dynamic tissues that encounter numerous mechanical cues derived from pulsatile blood flow, blood pressure, activity of smooth muscle cells in the vessel wall, and transmigration of immune cells. The inner layer of blood and lymphatic vessels is covered by the endothelium, a monolayer of cells which separates blood from tissue, an important function that it fulfills even under the dynamic circumstances of the vascular microenvironment. In addition, remodeling of the endothelial barrier during angiogenesis and trafficking of immune cells is achieved by specific modulation of cell–cell adhesion structures between the endothelial cells. In recent years, there have been many new discoveries in the field of cellular mechanotransduction which controls the formation and destabilization of the vascular barrier. Force-induced adaptation at endothelial cell–cell adhesion structures is a crucial node in these processes that challenge the vascular barrier. One of the key examples of a force-induced molecular event is the recruitment of vinculin to the VE-cadherin complex upon pulling forces at cell–cell junctions. Here, we highlight recent advances in the current understanding of mechanotransduction responses at, and derived from, endothelial cell–cell junctions. We further discuss their importance for vascular barrier function and remodeling in development, inflammation, and vascular disease.     

Endothelial signaling and the molecular basis of arteriovenous malformation

Arteriovenous malformations occur when abnormalities of vascular patterning result in the flow of blood from arteries to veins without an intervening capillary bed. Recent work has revealed the importance of the Notch and TGF-β signaling pathways in vascular patterning. Specifically, Notch signaling has an increasingly apparent role in arterial specification and suppression of branching, whereas TGF-β is implicated in vascular smooth muscle development and remodeling under angiogenic stimuli. These physiologic roles, consequently, have implicated both pathways in the pathogenesis of arteriovenous malformation. In this review, we summarize the studies of endothelial signaling that contribute to arteriovenous malformation and the roles of genes implicated in their pathogenesis. We further discuss how endothelial signaling may contribute to vascular smooth muscle development and how knowledge of signaling pathways may provide us targets for medical therapy in these vascular lesions.     

Length-tension dependence in vascular smooth muscle: Possible participation of endothelin

The results of experiments with isolated strips of rat portal vein, and of ‘sandwich’ experiments involving strips of the portal vein or aorta, revealed the involvement of endothelin in the development of myogenic reactions of the vascular smooth muscle, observed on distension of the vascular wall. Released by the endothelial cells, endothelin is capable of stimulating the contraction of these muscles.     

Embryonic origins of human vascular smooth muscle cells: implications for in vitro modeling and clinical application

Vascular smooth muscle cells (SMCs) arise from multiple origins during development, raising the possibility that differences in embryological origins between SMCs could contribute to site-specific localization of vascular diseases. In this review, we first examine the developmental pathways and embryological origins of vascular SMCs and then discuss in vitro strategies for deriving SMCs from human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). We then review in detail the potential for vascular disease modeling using iPSC-derived SMCs and consider the pathological implications of heterogeneous embryonic origins. Finally, we touch upon the role of human ESC-derived SMCs in therapeutic revascularization and the challenges remaining before regenerative medicine using ESC- or iPSC-derived cells comes of age.     

The potency of heparin-like activity of glycosaminoglycans released by human endothelial cells in culture

Glycosaminoglycans isolated from culture medium conditioned by human endothelial cells showed heparin-like anti-thrombin III cofactor activity measured by Xa inhibition. Their activity was relatively weak, 0.1% of the potency of heparin, but was approximately 5-fold more potent than that of glycosaminoglycans derived from vascular smooth muscle cells.     

The potency of heparin-like activity of glycosaminoglycans released by human endothelial cells in culture

Summary Glycosaminoglycans isolated from culture medium conditioned by human endothelial cells showed heparin-like antithrombin III cofactor activity measured by Xa inhibition. Their activity was relatively weak, 0.1% of the potency of heparin, but was approximately 5-fold more potent than that of glycosaminoglycans derived from vascular smooth muscle cells.     

Flow signaling and atherosclerosis

Atherosclerosis rarely develops in the region of arteries exposed to undisturbed flow (u-flow, unidirectional flow). Instead, atherogenesis occurs in the area exposed to disturbed flow (d-flow, multidirectional flow). Based on these general pathohistological observations, u-flow is considered to be athero-protective, while d-flow is atherogenic. The fact that u-flow and d-flow induce such clearly different biological responses in the wall of large arteries indicates that these two types of flow activate each distinct intracellular signaling cascade in vascular endothelial cells (ECs), which are directly exposed to blood flow. The ability of ECs to differentially respond to the two types of flow provides an opportunity to identify molecular events that lead to endothelial dysfunction and atherosclerosis. In this review, we will focus on various molecular events, which are differentially regulated by these two flow types. We will discuss how various kinases, ER stress, inflammasome, SUMOylation, and DNA methylation play roles in the differential flow response, endothelial dysfunction, and atherosclerosis. We will also discuss the interplay among the molecular events and how they coordinately regulate flow-dependent signaling and cellular responses. It is hoped that clear understanding of the way how the two flow types beget each unique phenotype in ECs will lead us to possible points of intervention against endothelial dysfunction and cardiovascular diseases.     

Endothelial membrane reorganization during leukocyte extravasation

Leukocyte trafficking from the bloodstream to inflamed tissues across the endothelial barrier is an essential response in innate immunity. Leukocyte adhesion, locomotion, and diapedesis induce signaling in endothelial cells and this is accompanied by a profound reorganization of the endothelial cell surfaces that is only starting to be unveiled. Here we review the current knowledge on the leukocyte-mediated alterations of endothelial membrane dynamics and their role in promoting leukocyte extravasation. The formation of protein- and lipid-mediated cell adhesion nanodomains at the endothelial apical surface, the extension of micrometric apical membrane docking structures, which are derived from microvilli and embrace adhered leukocytes, as well as the vesicle-trafficking pathways that are required for efficient leukocyte diapedesis, are discussed. The coordination between these different endothelial membrane-remodeling events probably provides the road map for transmigrating leukocytes to find exit points in the vessel wall, in a context of severe mechanical and inflammatory stress. A better understanding of how vascular endothelial cells respond to immune cell adhesion should enable new therapeutic strategies to be developed that can abrogate uncontrolled leukocyte extravasation in inflammatory diseases.     

Vascular stem/progenitor cells: functions and signaling pathways

Vascular stem/progenitor cells (VSCs) are an important source of all types of vascular cells needed to build, maintain, repair, and remodel blood vessels. VSCs, therefore, play critical roles in the development, normal physiology, and pathophysiology of numerous diseases. There are four major types of VSCs, including endothelial progenitor cells (EPCs), smooth muscle progenitor cells (SMPCs), pericytes, and mesenchymal stem cells (MSCs). VSCs can be found in bone marrow, circulating blood, vessel walls, and other extravascular tissues. During the past two decades, considerable progress has been achieved in the understanding of the derivation, surface markers, and differentiation of VSCs. Yet, the mechanisms regulating their functions and maintenance under normal and pathological conditions, such as in eye diseases, remain to be further elucidated. Owing to the essential roles of blood vessels in human tissues and organs, understanding the functional properties and the underlying molecular basis of VSCs is of critical importance for both basic and translational research.     

LOX-1 in atherosclerosis: biological functions and pharmacological modifiers

Lectin-like oxidized LDL (oxLDL) receptor-1 (LOX-1, also known as OLR-1), is a class E scavenger receptor that mediates the uptake of oxLDL by vascular cells. LOX-1 is involved in endothelial dysfunction, monocyte adhesion, the proliferation, migration, and apoptosis of smooth muscle cells, foam cell formation, platelet activation, as well as plaque instability; all of these events are critical in the pathogenesis of atherosclerosis. These LOX-1-dependent biological processes contribute to plaque instability and the ultimate clinical sequelae of plaque rupture and life-threatening tissue ischemia. Administration of anti-LOX-1 antibodies inhibits atherosclerosis by decreasing these cellular events. Over the past decade, multiple drugs including naturally occurring antioxidants, statins, antiinflammatory agents, antihypertensive and antihyperglycemic drugs have been demonstrated to inhibit vascular LOX-1 expression and activity. Therefore, LOX-1 represents an attractive therapeutic target for the treatment of human atherosclerotic diseases. This review aims to integrate the current understanding of LOX-1 signaling, regulation of LOX-1 by vasculoprotective drugs, and the importance of LOX-1 in the pathogenesis of atherosclerosis.     

RhoA/Rho-kinase and vascular diseases: what is the link?

RhoA/Rho-kinase pathway plays an important role in many pathological conditions. RhoA participates in the regulation of smooth muscle tone and activates many downstream kinases. The best characterized are the serine/threonine kinase isoforms (Rho-kinase or ROCK), ROCKα/ROCK2 and ROCKβ/ROCK1. ROCK is necessary for diverse functions such as local blood flow, arterial/pulmonary blood pressure, airway resistance and intestinal peristalsis. ROCK activation permits actin/myosin interactions and smooth muscle cells contraction by maintaining the activity of myosin light-chain kinase, independently of the free cytosolic calcium level. The sensitization of smooth muscle myofilaments to calcium has been implicated in many pathological states, such as hypertension, diabetes, heart attack, stroke, pulmonary hypertension, erectile dysfunction, and cancer. The focus of this review is on the involvement of RhoA/Rho-kinase in diseases. We will briefly describe the ROCK isoforms and the role of RhoA/Rho-kinase in the vasculature, before exploring the most recent findings regarding this pathway and various diseases.     

An eicosanoid-centric view of atherothrombotic risk factors

Cardiovascular disease is the foremost cause of morbidity and mortality in the Western world. Atherosclerosis followed by thrombosis (atherothrombosis) is the pathological process underlying most myocardial, cerebral, and peripheral vascular events. Atherothrombosis is a complex and heterogeneous inflammatory process that involves interactions between many cell types (including vascular smooth muscle cells, endothelial cells, macrophages, and platelets) and processes (including migration, proliferation, and activation). Despite a wealth of knowledge from many recent studies using knockout mouse and human genetic studies (GWAS and candidate approach) identifying genes and proteins directly involved in these processes, traditional cardiovascular risk factors (hyperlipidemia, hypertension, smoking, diabetes mellitus, sex, and age) remain the most useful predictor of disease. Eicosanoids (20 carbon polyunsaturated fatty acid derivatives of arachidonic acid and other essential fatty acids) are emerging as important regulators of cardiovascular disease processes. Drugs indirectly modulating these signals, including COX-1/COX-2 inhibitors, have proven to play major roles in the atherothrombotic process. However, the complexity of their roles and regulation by opposing eicosanoid signaling, have contributed to the lack of therapies directed at the eicosanoid receptors themselves. This is likely to change, as our understanding of the structure, signaling, and function of the eicosanoid receptors improves. Indeed, a major advance is emerging from the characterization of dysfunctional naturally occurring mutations of the eicosanoid receptors. In light of the proven and continuing importance of risk factors, we have elected to focus on the relationship between eicosanoids and cardiovascular risk factors.     

The mesenchymoangioblast,mesodermal precursor for mesenchymal and endothelial cells

Mesenchymoangioblast (MB) is the earliest precursor for endothelial and mesenchymal cells originating from APLNR⁺PDGFRα⁺KDR⁺ mesoderm in human pluripotent stem cell cultures. MBs are identified based on their capacity to form FGF2-dependent compact spheroid colonies in a serum-free semisolid medium. MBs colonies are composed of PDGFRβ⁺CD271⁺EMCN⁺DLK1⁺CD73^? primitive mesenchymal cells which are generated through endothelial/angioblastic intermediates (cores) formed during first 3–4 days of clonogenic cultures. MB-derived primitive mesenchymal cells have potential to differentiate into mesenchymal stromal/stem cells (MSCs), pericytes, and smooth muscle cells. In this review, we summarize the specification and developmental potential of MBs, emphasize features that distinguish MBs from other mesenchymal progenitors described in the literature and discuss the value of these findings for identifying molecular pathways leading to MSC and vasculogenic cell specification, and developing cellular therapies using MB-derived progeny.     

Regulatory circuits controlling vascular cell calcification

Vascular calcification is a common feature of chronic kidney disease, cardiovascular disease, and aging. Such abnormal calcium deposition occurs in medial and/or intimal layers of blood vessels as well as in cardiac valves. Once considered a passive and inconsequential finding, the presence of calcium deposits in the vasculature is widely accepted as a predictor of increased morbidity and mortality. Recognition of the importance of vascular calcification in health is driving research into mechanisms that govern its development, progression, and regression. Diverse, but highly interconnected factors, have been implicated, including disturbances in lipid metabolism, oxidative stress, inflammatory cytokines, and mineral and hormonal balances, which can lead to formation of osteoblast-like cells in the artery wall. A tight balance of procalcific and anticalcific regulators dictates the extent of disease. In this review, we focus on the main regulatory circuits modulating vascular cell calcification.     

Effects of polysorbates and Cremophor EL on vascular responses in rat aorta

The effects of Tween 20, Tween 80, and Cremophor EL, surface active agents which are used for dispersion of water-insoluble substances, on vascular responsiveness were investigated using rat aortic rings. In high concentrations all these agents produced persistent contractions in aortic rings independent of the presence of endothelium. These contractions were not influenced by inhibitors of known endogenous contractile mediators. Incubation with these agents caused a concentration-dependent inhibition of the endothelium-dependent relaxant responses to acetylcholine in intact precontracted aortic rings. Endothelium-independent relaxations produced by sodium nitroprusside were not inhibited, but rather potentiated in the presence of Tween 80 (10^–1 ml/l). On the other hand, Tween 80 inhibited the contractile effects of 5-hydroxytryptamine, phenylephrine, and bradykinin significantly. The data suggests that these substances affect both endothelial cells and vascular smooth muscle.     

“Jnking” atherosclerosis

Numerous studies in animal models established a key role of the C-jun N-terminal kinase (JNK) family (JNK1, JNK2 and JNK3) in numerous pathological conditions, including cancer, cardiac hypertrophy and failure, neurodegenerative disorders, diabetes, arthritis and asthma. A possible function of JNK in atherosclerosis remained uncertain since conclusions have mainly been based on in vitro studies investigating endothelial cell activation, T-effector cell differentiation and proliferation of vascular smooth muscle cells, all of which represent crucial cellular processes involved in atherosclerosis. However, recent experiments demonstrated that macrophage-restricted deletion of JNK2 was sufficient to efficiently reduce atherosclerosis in mice. Furthermore, it has been shown that JNK2 specifically promotes scavenger receptor A-mediated foam cell formation, an essential step during early atherogenesis, which occurs when vascular macrophages internalize modified lipoproteins. Thus, specific inhibition of JNK2 activity may emerge as a novel and promising therapeutic approach to attenuate atheroma formation in the future. In this review, we discuss JNK-dependent cellular and molecular mechanisms underlying atherosclerosis. Received 9 June 2005; received after revision 18 July 2005; accepted 18 July 2005     

Sphingosine 1-phosphate induces differentiation of adipose tissue-derived mesenchymal stem cells towards smooth muscle cells

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid which regulates multiple biological parameters in a number of cell types, including stem cells. Here we report, for the first time, that S1P dose-dependently stimulates differentiation of adipose tissue-derived mesenchymal stem cells (ASMC) towards smooth muscle cells. Indeed, S1P not only induced the expression of smooth muscle cell-specific proteins such as α-smooth muscle actin (αSMA) and transgelin, but also profoundly affected ASMC morphology by enhancing cytoskeletal F-actin assembly, which incorporated αSMA. More importantly, S1P challenge was responsible for the functional appearance of Ca²⁺ currents, characteristic of differentiated excitable cells such as smooth muscle cells. By employing various agonists and antagonists to inhibit S1P receptor subtypes, S1P₂ turned out to be critical for the pro-differentiating effect of S1P, while S1P₃ appeared to play a secondary role. This study individuates an important role of S1P in AMSC which can be exploited to favour vascular regeneration. Received 06 March 2009; accepted 17 March 2009