Endothelial cells line the inside of all blood vessels, forming a structurally and functionally heterogenous population of cells. Their complexity and diversity has long been recognized, yet very little is known about the molecules and regulatory mechanisms that mediate the heterogeneity of different endothelial cell populations. The constitutive organ‐ and microenvironment‐specific phenotype of endothelial cells controls internal body compartmentation, regulating the trafficking of circulating cells to distinct vascular beds. In contrast, surface molecules associated (...) with the activated cytokine‐inducible endothelial phenotype play a critical role in pathological conditions including inflammation, tumor angiogenesis, and wound healing. Differentiation of the endothelial cell phenotypes appears to follow similar mechanisms to the differentiation of hematopoietic cells, with the exception that endothelial cells maintain transdifferentiating competence. The present review offers a scheme of endothelial cell differentially expressed endothelial cell molecules as targets for directed therapeutic intervention. (shrink)

Endothelial cells in culture have, in the past, been a valuable but capricious tool to test hypotheses on the role of components of the blood vessel wall in such functions as blood pressure homeostasis, hemostasis, permeability, transport of macromolecules and the processing of circulating biologically active substances. Now techniques are becoming available for raising long‐term, large‐scale cultures that can be maintained reproducibly and without loss of phenotypic characteristics. The outlook for establishing endothelial cell factories invites speculation on (...) some far‐reaching possibilities, such as endothelial cell banks that could be used for seeding autogenous cells on vascular prostheses, artificial kidney tubing, heart valves, or corneas, or for virus production, or for synthesis by endothelial cells of products at present beyond the reach of bacterial cells. (shrink)

Segmentation of the medical image plays a significant role when it comes to diagnosis using computer aided system. This article focuses on the human corneal endothelium’s health, which is one of the filed research interests, especially in the human cornea. Various pathological environments fasten the extermination of the endothelial cells, which in turn decreases the cell density in an abnormal manner. Dead cells worsen the hexagonal design. The mutilated endothelial cells can no longer revive back (...) and that gives room for neighbouring cells to migrate and expand so that they can fill in the space. The latter results in cell elongation that is unpredictable as well as increase in size and thinning. Cell density and shape are therefore considered major parameters when it comes to explaining the health condition attributed to corneal endothelium. In this study, medical feature extraction was obtained depending on the segmentation of the endothelial cell boundary, and the task of segmentation of such objects especially the thin, transparent, and unclear cell boundary is considered challenging due to the nature of the image capture during endothelium layer examination by ophthalmologists using confocal or specular microscopy. The resulting image suffers from various issues that affect the quality of the image. Low quality is due to non-uniformity of illumination and the presence of a lot of noise and artefacts resulting from high amounts of distortion, and most of these limitations are present because of the nature of the imaging modality. Usually, images contain certain kind of noise and also continuous shadow. Furthermore, the cells are separated by poor border, thereby leading to great difficulty in the segmentation of the images. The irregular shape of cell and also the contrast of such images seem to be low as they possess blurry boundaries with diverse objects existing in addition to the lack of homogeneity. The main aim of the study is to propose and develop a totally automatic, robust, and real-time model for the segmentation of endothelial cells of the human cornea obtained by in vivo microscopy and computation of different clinical features of endothelial cells. To achieve the aim of this study a new scheme of image enhancement was proposed such as the Contrast-Limited Adaptive Histogram Equalisation technique to enhance contrast. After that, a new image denoising technique called Wavelet Transform Filter and Butterworth Bandpass for Segmentation is used. Subsequently, brightness level correction is applied by using the moving average filter and the CLAHE to reduce the effects of the non-uniform image lighting produced as a result of the previous step. The main aim of this article is the segmentation of endothelial cells, which involves precise detection of the endothelial contours. So a new segmentation model was proposed such that the shape of the cells will be extracted, and the contours were highlighted. This stage is followed by clinical feature extraction and uses the features for diagnosis. In this stage, several relevant clinical features such as pleomorphism mean cell perimeter, mean cell density, mean cell area, and polymegathism are extracted. The role of these clinical features is crucial for the early detection of corneal pathologies as well as the evaluation of the health of the corneal endothelium layer. The findings of this study were promising. (shrink)

Pericytes, like vascular smooth muscle cells, are perivascular cells closely associated with blood vessels throughout the body. Pericytes are necessary for vascular development and homeostasis, with particularly critical roles in the brain, where they are involved in regulating cerebral blood flow and establishing the blood-brain barrier. A role for pericytes during neurovascular disease pathogenesis is less clear—while some studies associate decreased pericyte coverage with select neurovascular diseases, others suggest increased pericyte infiltration in response to hypoxia or traumatic brain (...) injury. Here, we used an endothelial loss-of-function Recombination signal binding protein for immunoglobulin kappa J region (Rbpj)/Notch mediated mouse model of brain arteriovenous malformation (AVM) to investigate effects on pericytes during neurovascular disease pathogenesis. We tested the hypothesis that pericyte expansion, via morphological changes, and Platelet-derived growth factor B/Platelet-derived growth factor receptor β (Pdgf-B/Pdgfrβ)-dependent endothelial cell-pericyte communication are affected, during the pathogenesis of Rbpj mediated brain AVM in mice. Our data show that pericyte coverage of vascular endothelium expanded pathologically, to maintain coverage of vascular abnormalities in brain and retina, following endothelial deletion of Rbpj. In Rbpj-mutant brain, pericyte expansion was likely attributed to cytoplasmic process extension and not to increased pericyte proliferation. Despite expanding overall area of vessel coverage, pericytes from Rbpj-mutant brains showed decreased expression of Pdgfrβ, Neural (N)-cadherin, and cluster of differentiation (CD)146, as compared to controls, which likely affected Pdgf-B/Pdgfrβ-dependent communication and appositional associations between endothelial cells and pericytes in Rbpj-mutant brain microvessels. By contrast, and perhaps by compensatory mechanism, endothelial cells showed increased expression of N-cadherin. Our data identify cellular and molecular effects on brain pericytes, following endothelial deletion of Rbpj, and suggest pericytes as potential therapeutic targets for Rbpj/Notch related brain AVM. (shrink)

Polyclonal antibodies raised against the human erythrocyte nucleoside transporter were used to investigate the distribution of the nucleoside transporters in the placenta. Immunoblots of brush-border membranes isolated from the human syncytiotrophoblast revealed a cross-reactive species that co-migrated with the erythrocyte nucleoside transporter as a broad band of apparent M 55,000. In contrast, no labelling was detected in basal membranes containing a similar number of equilibrative nucleoside transporters as assessed by nitrobenzylthioinosine -binding. The absence of cross-reactive epitopes in basal membranes and (...) their presence in brush-border membranes was confirmed by confocal immunofluorescence microscopy. The results suggest that at least two isoforms of the NBMPR-sensitive nucleoside transporter are present in the human placenta. The lumenal surfaces of fetal capillaries, small placental vessels and umbilical vein ware also strongly labelled by the antibody, a finding that suggests that the high fetal-placental adenosine uptake previously reported is due to endothelial transporters. (shrink)

Angiogenesis is central to both the growth and metastasis of solid tumours. Anti‐angiogenic strategies result in blood vessel regression accompanied by tumour cell apoptosis. Radiotherapy and many chemotherapeutic agents kill tumours by inducing apoptotic cell death. We propose that, in addition to its role as an angiogenic factor, vascular endothelial growth factor (VEGF) can act as a survival factor for tumour cells protecting them from apoptosis. Thus anti‐angiogenics, in particular those directed against VEGF, have multiple anti‐tumour effects. We (...) suggest that anti‐VEGF strategies prevent vessel growth and block a tumour cell survival factor, VEGF, rendering tumour cells more sensitive to chemotherapy and radiotherapy. In addition, as chemotherapy and radiotherapy have been shown to increase VEGF expression, anti‐VEGF strategies may overcome therapy‐ induced tumour cell resistance. BioEssays 24:280–283, 2002. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/bies.10043. (shrink)

The establishment of distinct cellular identities was pivotal during the evolution of Metazoa, enabling the emergence of an array of specialized tissues with different functions. In most animals including vertebrates, cell specialization occurs in response to a combination of intrinsic (e.g., cellular ontogeny) and extrinsic (e.g., local environment) factors that drive the acquisition of unique characteristics at the single‐cell level. The first functional organ system to form in vertebrates is the cardiovascular system, which is lined by a network of (...) class='Hi'>endothelial cells whose organ‐specific characteristics have long been recognized. Recent genetic analyses at the single‐cell level have revealed that heterogeneity exists not only at the organ level but also between neighboring endothelial cells. Thus, how endothelial heterogeneity is established has become a key question in vascular biology. Drawing upon evidence from multiple organ systems, here we will discuss the role that lineage history may play in establishing endothelial heterogeneity. (shrink)

Lymphangiogenesis is an important developmental process that is critical to regulation of fluid homeostasis, immune surveillance and response as well as pathogenesis of a number of diseases, among them cancer, inflammation, and heart failure. Specification, formation, and maturation of lymphatic blood vessels involves an interplay between a series of events orchestrated by various transcription factors that determine expression of key genes involved in lymphangiogenesis. These are traditionally thought to be under control of several key growth factors including vascular growth factor‐C (...) (VEGF‐C) and fibroblast growth factors (FGFs). Recent insights into VEGF and FGF signaling point to their role in control of endothelial metabolic processes such as glycolysis and fatty acid oxidation that, in turn, play a major role in regulation of lymphangiogenesis. These advances have significantly increased our understanding of lymphatic biology and opened new therapeutic vistas. Here we review our current understanding of metabolic controls in the lymphatic vasculature. (shrink)

Adenosine transport in cultured human umbilical vein endothelial cells (HUVEC) was characterized and shown to be mediated by a single facilitated diffusion mechanism. Initial rates of adenosine influx at 22 degrees C were saturable [apparent Michaelis constant, 69 +/- 10 mu M; maximum velocity (V-max), 600 +/- 70 pmol.10(6) cells(-1).s(-1)] and inhibited by nitrobenzylthioinosine (NBMPR). Formycin B had an unusually high affinity [inhibitory constant K-i), 18 +/- 4.3 mu M], whereas inosine had a low affinity (K-i, 440 (...) +/- 68 mu M) and nucleobases were without effect on adenosine influx. The number of transporters (1.2 x 10(6) sites/cell) was estimated by NBMPR equilibrium binding (apparent dissociation constant, 0.11 +/- 0.01 nM; maximum binding, 2.0 +/- 0.15 pmol/10(6) cells). In addition, we compared these endothelial cells with those obtained from cords from pregnancies complicated by diabetes (HUVEC-D), since embriopathy may occur in these conditions. HUVEC-D exhibited a 2.3-fold reduction in both the V-max for adenosine influx and the maximum number of NBMPR binding sites (260 +/- 40 pmol.10(6) cells(-1).s(-1) and 0.86 +/- 0.08 pmol/10(6) cells, respectively). However, the turnover number for each nucleoside transporter in normal and diabetic HUVEC was similar (approximate to 300 adenosine molecules/s). Adenosine metabolism at 10 mu M in HUVEC-D was modified compared with normal cells. Intracellular phosphorylation (> 90%) was the predominant pathway in normal HUVEC, whereas in HUVEC-D, substantial levels of adenine and adenosine were detected. The present results demonstrate therefore the downregulation of the NBMPR-sensitive nucleoside transporter and changes in adenosine metabolism in HUVEC from diabetic pregnancies. (shrink)

Brain arteriovenous malformations (bAVMs) are abnormal vessels that are prone to rupture, causing life-threatening intracranial bleeding. The mechanism of bAVM formation is poorly understood. Nevertheless, animal studies revealed that gene mutation in endothelial cells (ECs) and angiogenic stimulation are necessary for bAVM initiation. Evidence collected through analyzing bAVM specimens of human and mouse models indicate that cells other than ECs also are involved in bAVM pathogenesis. Both human and mouse bAVMs vessels showed lower mural cell-coverage, suggesting a (...) role of pericytes and vascular smooth muscle cells (vSMCs) in bAVM pathogenesis. Perivascular astrocytes also are important in maintaining cerebral vascular function and take part in bAVM development. Furthermore, higher inflammatory cytokines in bAVM tissue and blood demonstrate the contribution of inflammatory cells in bAVM progression, and rupture. The goal of this paper is to provide our current understanding of the roles of different cellular loci in bAVM pathogenesis. (shrink)

Traction forces developed by most cell types play a significant role in the spatial organisation of biological tissues. However, due to the complexity of cell-extracellular matrix interactions, these forces are quantitatively difficult to estimate without explicitly considering cell properties and extracellular mechanical matrix responses. Recent experimental devices elaborated for measuring cell traction on extracellular matrix use cell deposits on a piece of gel placed between one fixed and one moving holder. We formulate here a mathematical model describing the dynamic behaviour (...) of the cell-gel medium in such devices. This model is based on a mechanical force balance quantification of the gel visco-elastic response to the traction forces exerted by the diffusing cells. Thus, we theoretically analyzed and simulated the displacement of the free moving boundary of the system under various conditions for cells and gel concentrations. This modelis then used as the theoretical basis of an experimental device where endothelial cells are seeded on a rectangular biogel of fibrin cast between two floating holders, one fixed and the other linked to a force sensor. From a comparison of displacement of the gel moving boundary simulated by the model and the experimental data recorded from the moving holder displacement, the magnitude of the traction forces exerted by the endothelial cell on the fibrin gel was estimated for different experimental situations. Different analytical expressions for the cell traction term are proposed and the corresponding force quantifications are compared to the traction force measurements reported for various kind of cells with the use of similar or different experimental devices. (shrink)

While the control of cell migration by biochemical and biophysical factors is largely documented, a precise quantification of cell migration parameters in different experimental contexts is still questionable. Indeed, these phenomenological parameters can be evaluated from data obtained either at the cell population level or at the individual cell level. However, the range within which both characterizations of cell migration are equivalent remains unclear. We analyse here to which extent both sources of data could be integrated within a unified description (...) of cell migration by considering the motility of the endothelial cell line EAhy926. Using time-lapse video-microscopy and associated analysis of digital image time series, we quantified EAhy926 random motility coefficient, migration speed and trajectory persistence time in two different migration assays: the in vitro wound healing assay, and the cell-populated agarose drop assay. In order to analyse the agreement between independent quantifications of cell motility based either on individual cell analysis or cell population dynamic analysis, a theoretical multi-agents cellular model was developed and discussed as a possible theoretical framework able to unify these multi-scale data. Model simulations especially reveal the potential bias induced by cell proliferation and cell-cell adhesion when cell migration parameters are estimated from the extensively used in vitro wound healing assay. (shrink)

The vertebrate heart comprises a variety of cell types, the majority of which are cardiomyocytes, smooth muscle and endothelial cells. Their origin is still an intriguing research topic and the question is whether these cells derive from a common or from multiple distinct progenitor cell(s). Three recent publications not only suggest the existence of a single progenitor cell that can give rise to cardiovascular lineages but additionally uncovered, at least in part, the molecular identity of such a (...) multipotent precursor cell.1-3 These findings constitute major progress in the quest for stem-cell therapies for cardiac diseases. BioEssays 29:422–426, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

Protein‐carbohydrate interactions have been found to be important in many steps in lymphocyte recirculation and inflammatory responses. A family of carbohydrate‐binding proteins or lectins, termed selectins, has been discovered and shown to be involved directly in these processes. The three known selectins, termed L‐, E‐ and P‐selectins, have domains homologous to other Ca2+‐dependent (C‐type) lectins. L‐selectin is expressed constitutively on lymphocytes, E‐selectin is expressed by activated endothelial cells, and P‐selectin is expressed by activated platelets and endothelial (...) class='Hi'>cells. Here, we review the nature of the carbohydrate determinants in tissues recognized by these selectins. The expression of specific sialylated, fucosylated and sulfated carbohydrates in activated endothelium and high endothelial venules promotes interactions with L‐selectin on leukocyte surfaces. In contrast, E‐ and P‐selectins recognize specific carbohydrate determinants related to sialyl Lex antigen on neutrophil and monocyte surfaces. The discovery of the selectins has generated excitemient among glycoconjugate researchers that other carbohydrate‐binding proteins and their cognate ligands will be found to function in regulating many types of cellular interactions. (shrink)

The behavior of somatic stem cells is regulated by their niche. Interaction between hematopoietic stem cells (HSCs) and their niches are a representative model to understand stem cell‐niche interplay. Here, we provide an overview of crosstalk between HSCs and their niches in bone marrow and extramedullary organs following the life journey of HSCs from emergence, development, maturation until aging. We highlight the unique differences of HSC niches in different life stages within various organs focusing on recent literature to (...) propose new speculations and hypotheses. (shrink)

Osteoporosis (OP) is a bone disease which affects a number of post‐menopausal females and puts many at risk for fractures. A large number of patients are taking bisphosphonates (BPs) to treat their OP and a rare complication is the development of atypical femoral fractures (AFF). No real explanations for the mechanisms underlying the basis for development of where AFF develop while on BPs has emerged. The present hypothesis will discuss the possibility that part of the risk for an AFF is (...) a secondary effect of BPs on a subset of vascular cells in a genetically at‐risk population, leading to localized deregulation of the endothelial cell (EC)‐bone cell‐matrix units in nutrient channels/canals of the femur and increased risk for AFF. This concept of targeting ECs is consistent with location of AFF in the femur, the bilateral risk for occurrence of AFF, and the requirement for long term exposure to the drugs. (shrink)

Reorganization of cell organelle‐deprived host red blood cells by the apicomplexan malaria parasite Plasmodium falciparum enables their cytoadherence to endothelial cells that line the microvasculature. This increases the time red blood cells infected with mature developmental stages remain within selected organs such as the brain to avoid the spleen passage, which can lead to severe complications and cumulate in patient death. The Maurer's clefts are a novel secretory organelle of parasite origin established by the parasite in (...) the cytoplasm of the host red blood cell in order to facilitate the establishment of cytoadherence by conducting the trafficking of immunovariant adhesins to the host cell surface. Another important function of the organelle is the sorting of other proteins the parasite traffics into its host cell. Although the organelle is of high importance for the pathology of malaria, additional putative functions, structure, and genesis remain shrouded in mystery more than a century after its discovery. In this review, we highlight our current knowledge about the Maurer's clefts and other novel secretory organelles established within the host cell cytoplasm by human‐pathogenic malaria parasites and other parasites that reside within human red blood cells. (shrink)

Uncoupling proteins (UCPs) regulate mitochondrial function, and thus cellular metabolism. Angiotensin‐converting enzyme (ACE) is the central component of endocrine and local tissue renin–angiotensin systems (RAS), which also regulate diverse aspects of whole‐body metabolism and mitochondrial function (partly through altering mitochondrial UCP expression). We show that ACE expression also appears to be regulated by mitochondrial UCPs. In genetic analysis of two unrelated populations (healthy young UK men and Scandinavian diabetic patients) serum ACE (sACE) activity was significantly higher amongst UCP3‐55C (rather than (...) T) and UCP2 I (rather than D) allele carriers. RNA interference against UCP2 in human umbilical vein endothelial cells reduced UCP2 mRNA sixfold (P < 0·01) whilst increasing ACE expression within a physiological range (<1·8‐fold at 48 h; P < 0·01). Our findings suggest novel hypotheses. Firstly, cellular feedback regulation may occur between UCPs and ACE. Secondly, cellular UCP regulation of sACE suggests a novel means of crosstalk between (and mutual regulation of) cellular and endocrine metabolism. This might partly explain the reduced risk of developing diabetes and metabolic syndrome with RAS antagonists and offer insight into the origins of cardiovascular disease in which UCPs and ACE both play a role. (shrink)

Endothelial cells, when cultured on gelled basement membrane matrix exert forces of tension through which they deform the matrix and at the same time they aggregate into clusters. The cells eventually form a network of cord-like structures connecting cell aggregates. In this network, almost all of the matrix has been pulled underneath the cell cords and cell clusters. This phenomenon has been proposed as a possible model for the growth and development of planar vascular systems in vitro. (...) Our hypothesis is that the matrix is reorganized and the cellular networks form as a result of traction forces exerted by the cells on the matrix and the latter's elasticity. We construct and analyze a mathematical model based on this hypothesis and examine conditions necessary for the formation of the pattern. We show cell migration is not necessary for pattern formation and that isotropic, strain-stimulated traction is sufficient to form the observed patterns. (shrink)

Both blood vessels and nerves are guided to their target. Vascular endothelial growth factor (VEGF)A is a key signal in the induction of vessel growth (a process termed angiogenesis). Though initial studies, now a decade ago, indicated that VEGF is an endothelial cell‐specific factor, more recent findings revealed that VEGF also has direct effects on neural cells. Genetic studies showed that mice with reduced VEGF levels develop adult‐onset motor neuron degeneration, reminiscent of the human neurodegenerative disorder amyotrophic (...) lateral sclerosis (ALS). Additional genetic studies confirmed that VEGF is a modifier of motor neuron degeneration in humans and in SOD1G93A mice—a model of ALS. Reduced VEGF levels may promote motor neuron degeneration by limiting neural tissue perfusion and VEGF‐dependent neuroprotection. VEGF also affects neuron death after acute spinal cord or cerebral ischemia, and has also been implicated in other neurological disorders such as diabetic and ischemic neuropathy, nerve regeneration, Parkinson's disease, Alzheimer's disease and multiple sclerosis. These findings have raised growing interest in assessing the therapeutic potential of VEGF for neurodegenerative disorders. BioEssays 26:943–954, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

In heart, the propagation of electrical activity is mediated by intercellular channels, referred to as junctional channels, aggregated into gap junctions and localised between myocytes. These channels consist of structurally related transmembrane proteins, the connexins, three of which (CX43, CX40 and CX45) have been shown to be associated with the myocytes of mammalian heart; a fourth, CX37, was detected exclusively in endothelial cells. In this paper, we review the recent data dealing with the topographical heterogeneity of expression of (...) these connexins in the different cardiac tissues and the unique conductance properties of the channels they form, and attempt to assess the role played by each connexin and the consequences of their multiplicity in the propagation of action potentials. (shrink)

Microvascular development is determined by the interplay between tissue cells and microvascular endothelial cells. Because the pancreatic islet is an organ composed mainly of endothelial and endocrine cells, it represents a good model tissue for studying microvascular development in the context of a tissue. In this review, we will describe the special morphology of islet capillaries and its role in the physiologic function of islets: secretion of insulin in response to blood glucose levels. We will (...) speculate on how islet‐secreted VEGF‐A generates a permeable endothelium that allows insulin to pass quickly into the blood stream. In addition, we speculate on how endothelial cells might form a capillary lumen within the islets. At the end, we look at the islet microvasculature from a medical point of view, thus describing its critical role during type I diabetes and islet transplantation. BioEssays 26:1069–1075, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

A tree‐like hierarchical branching structure is present in many biological systems, such as the kidney, lung, mammary gland, and blood vessels. Most of these organs form through branching morphogenesis, where outward growth results in smaller and smaller branches. However, the blood vasculature is unique in that it exists as two trees (arterial and venous) connected at their tips. Obtaining this organization might therefore require unique developmental mechanisms. As reviewed here, recent data indicate that arterial trees often form in reverse order. (...) Accordingly, initial arterial endothelial cell differentiation occurs outside of arterial vessels. These pre‐artery cells then build trees by following a migratory path from smaller into larger arteries, a process guided by the forces imparted by blood flow. Thus, in comparison to other branched organs, arteries can obtain their structure through inward growth and coalescence. Here, new information on the underlying mechanisms is discussed, and how defects can lead to pathologies, such as hypoplastic arteries and arteriovenous malformations. -/- . (shrink)

David KC Cooper,1 David Ayares21Thomas E Starzl Transplantation Institute, University of Pittsburgh Medical Center, Pittsburgh, PA, USA; 2Revivicor, Blacksburg, VA, USA: The transplantation of organs and cells from pigs into humans could overcome the critical and continuing problem of the lack of availability of deceased human organs and cells for clinical transplantation. Developments in the genetic engineering of pigs have enabled considerable progress to be made in the experimental laboratory in overcoming the immune barriers to successful xenotransplantation. With (...) regard to pig organ xenotransplantation, antibody- and cell-mediated rejection have largely been overcome, and the current major barrier is the development of coagulation dysregulation. This is believed to be due to a combination of immune activation of the vascular endothelial cells of the graft and molecular incompatibilities between the pig and primate coagulation–anticoagulation systems. Pigs with new genetic modifications specifically directed to this problem are now becoming available. With regard to less complex tissues, such as islets, neuronal cells, and corneas, the remaining barriers are less problematic, and graft survival in nonhuman primate models extends for >1 year in all three cases. In planning the initial clinical trials, consideration will be concentrated on the risk–benefit ratio, based to a large extent on the results of preclinical studies in nonhuman primates. If the benefit to the patient is anticipated to be high, eg, insulin-independent control of glycemia, and the potential risks low, eg, minimal risk of transfer of a porcine infectious agent, then a clinical trial would be justified.Keywords: infection, pigs, genetically-engineered, xenotransplantation, islets, xenotransplantation, organs. (shrink)

In heart, the propagation of electrical activity is mediated by intercellular channels, referred to as junctional channels, aggregated into gap junctions and localised between myocytes. These channels consist of structurally related transmembrane proteins, the connexins, three of which (CX43, CX40 and CX45) have been shown to be associated with the myocytes of mammalian heart; a fourth, CX37, was detected exclusively in endothelial cells. In this paper, we review the recent data dealing with the topographical heterogeneity of expression of (...) these connexins in the different cardiac tissues and the unique conductance properties of the channels they form, and attempt to assess the role played by each connexin and the consequences of their multiplicity in the propagation of action potentials. (shrink)

Cancers have a formidable capacity to develop resistance to a large and diverse array of chemical, biologic, and physical anti‐neoplastic agents. This can be largely traced to the instability of the tumor cell genome, and the resultant ability of tumor cell populations to generate phenotypic variants rapidly. It is therefore argued that anti‐cancer strategies should be directed at eliminating those genetically stable normal diploid cells that are required for the progressive growth of tumors. Micro‐vascular endothelial cells comprising (...) the tumor vasculature represent such a normal cell target. Moreover, specificity for tumor associated vasculature by anti‐cancer agents may be achieved by virtue of the fact that many of the endothelial cells that comprise these blood vessels are in an immature, cycling, and ‘activated’ state, in contrast to the endothelial cells associated with normal tissue and organ blood vessels. (shrink)

Plasminogen activator inhibitor‐1 (PAI‐1) is a physiological inhibitor of urokinase (uPA), a serine protease known to promote cell migration and invasion. Intuitively, increased levels of PAI‐1 should be beneficial in downregulating uPA activity, particularly in cancer. By contrast, in vivo, increased levels of PAI‐1 are associated with a poor prognosis in breast cancer. This phenomenon is termed the “PAI‐1 paradox”. Many factors are responsible for the upregulation of PAI‐1 in the tumor microenvironment. We hypothesize that there is a breast cancer (...) predisposition to a more aggressive stage when PAI‐1 is upregulated as a consequence of Metabolic Syndrome (MetS). MetS exerts a detrimental effect on the breast tumor microenvironment that supports cancer invasion. People with MetS have an increased risk of coronary heart disease, stroke, peripheral vascular disease and hyperinsulinemia. Recently, MetS has also been identified as a risk factor for breast cancer. We hypothesize the existence of the “PAI‐1 cycle”. Sustained by MetS, adipocytokines alter PAI‐1 expression to promote angiogenesis, tumor‐cell migration and procoagulant microparticle formation from endothelial cells, which generates thrombin and further propagates PAI‐1 synthesis. All of these factors culminate in a chemotherapy‐resistant breast tumor microenvironment. The PAI‐1 cycle may partly explain the PAI‐1 paradox. In this hypothesis paper, we will discuss further how MetS upregulates PAI‐1 and how an increased level of PAI‐1 can be linked to a poor prognosis. BioEssays 29:1029–1038, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

The cardiovascular system has the life‐providing task of delivering oxygen and any flaw in this system can be life‐threatening. This has encouraged extensive studies to elucidate the mechanisms behind cardiovascular development/homeostasis. The zebrafish has emerged as a formidable tool to speed up this quest, as illustrated in a recent issue of Nature Genetics.1 Baculovirus IAP repeat c2 (BIRC2), also termed cellular inhibitor of apoptosis (cIAP)‐1, was found to specifically prevent endothelial cells (ECs, lining the inside of vessels) from (...) going into suicide mode (‘apoptosis’) and so preserve vessel integrity. Here, we summarize the factors determining vascular integrity and elaborate on the suitability of the zebrafish to study this phenomenon. BioEssays 30:418–422, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

Although the generation of reactive oxygen species is an activity normally associated with phagocytic leucocytes, mammalian spermatozoa were, in fact, the first cell type in which this activity was described. In recent years it has become apparent that spermatozoa are not the only nonphagocytic cells to exhibit a capacity for reactive oxygen species production, because this activity has been detected in a wide variety of different cells including fibroblasts, mesangial cells, oocytes, Leyding cells endothelial (...) class='Hi'>cells, thryroid cells, adipocytes, tumour cell and platelets. Since the capacity to generate reactive oxygen species is apparently so widespread, the risk‐benefit equation for these potentially pernicious molecules becomes a matter of intese interest. In the case of human spermatozoa, the risk of manufacturing reactive oxygen metabolites is considerable because these cells are particularly vulnerable to lipid peroxidation. Indeed, there is now good evidence to indicate that oxygen radicals are involved in the initiation of peroxidative damage to the sperm plasma membrane, seen in many cases of male infertility. This risk is off‐set by recent data suggesting that superoxide anions and hydrogen peroxide also participate in the induction of key biological events such as hyperactiavated motility and the acrosome reaction. Thus, human spermatozoa appear to use reactive oxygen species for a physiological purpose and have the difficult task of ensuring the balanced generation of these potentially harmful, but biologically important, modulators of cellular function. (shrink)

Despite the recent discovery that thalidomide causes limb defects by targeting highly angiogenic, immature blood vessels, several challenges still remain and new ones have arisen. These include understanding the drug's species specificity, determining molecular target(s) in the endothelial cell, shedding light on the molecular basis of phocomelia and producing a form of the drug that is clinically effective without having side effects. Now that the trigger of thalidomide‐induced teratogenesis has been uncovered, a framework is proposed, incorporating and uniting previous (...) models of thalidomide action, explaining how thalidomide causes not just limb defects, but also all the other defects it induces. (shrink)

The establishment of a functional vascular system requires multiple complex steps throughout embryogenesis, from endothelial cell (EC) specification to vascular patterning into venous and arterial hierarchies. Following the initial assembly of ECs into a network of cord‐like structures, vascular expansion and remodeling occur rapidly through morphogenetic events including vessel sprouting, fusion, and pruning. In addition, vascular morphogenesis encompasses the process of lumen formation, critical for the transformation of cords into perfusable vascular tubes. Studies in mouse, zebrafish, frog, and human (...) endothelial cells have begun to outline the cellular and molecular requirements underlying lumen formation. Although the lumen can be generated through diverse mechanisms, the coordinated participation of multiple conserved molecules including transcription factors, small GTPases, and adhesion and polarity proteins remains a fundamental principle, leading us closer to a more thorough understanding of this complex event. (shrink)

Insulin is well known for its essential role in carbohydrate metabolism: insulin deficiency results in the development of diabetes mellitus. It has been known for many years that people with diabetes mellitus are predisposed to develop thrombotic diseases including myocardial infarction. It was thought that the thrombus formation was the consequence of impaired carbohydrate metabolism. In recent years, it has become apparent that insulin is capable of ameliorating several pathophysiological events, leading to the inhibition and dissolution of the formed thrombus (...) in the system. These insulin‐induced events include inhibition of platelet aggregation by prompting the synthesis of NO in platelet and prostacyclin in endothelial cells. Furthermore, insulin upregulates prostacyclin receptors and downregulates α2 adrenergic receptor in platelets, thereby amplifying the inhibition of platelet aggregation. Insulin also releases tissue plasminogen activator, a potent thrombolytic enzyme, from the platelet membrane which dissolves the formed thrombus leading to the resumption of normal blood circulation. In effect, insulin could be an essential tool in the control of thrombotic disorders. BioEssays 26:91–98, 2004. © 2003 Wiley Periodicals, Inc. (shrink)

Atherosclerosis is the major cause of death in the industrialised world. Though much work on the pathogenesis of atherosclerosis points to 'oxidised' low density lipoprotein (LDL) as a key aetiological feature in the generation of the atherosclerotic plaque, the nature of this 'oxidised' LDL in vivo remains an enigma. We argue here that glycated LDL shows many of the characteristics attributed to 'oxidised LDL' and may be the source of the latter in vivo. These include the increased uptake and impaired (...) degradation of glycated LDL by macrophages and the stimulation of transendothelial chemotaxis of monocytes, cytokine secretion and platelet aggregation. We hypothesise that the covalent binding of glycated LDL to the endothelial cell wall may result in the formation of the early atherosclerotic lesion of the fatty streak and that apolipoprotein E may mediate the physiological clearance of glycated moieties. The proposed role of glycation in the pathogenesis of atherosclerosis would explain its high incidence among diabetics and the contentious epidemiological and experimental correlations between dietary sugar and atherosclerosis. (shrink)

In order to accomplish the transition from avascular to vascular growth, solid tumours secrete a diffusible substance known as tumour angiogenesis factor (TAF) into the surrounding tissue. Endothelial cells which form the lining of neighbouring blood vessels respond to this chemotactic stimulus in a well-ordered sequence of events comprising, at minimum, of a degradation of their basement membrane, migration and proliferation. Capillary sprouts are formed which migrate towards the tumour eventually penetrating it and permitting vascular growth to take (...) place. It is during this stage of growth that the insidious process of invasion of surrounding tissues can and does take place. A model mechanism for angiogenesis is presented which includes the diffusion of the TAF into the surrounding host tissue and the response of the endothelial cells to the chemotactic stimulus. Numerical simulations of the model are shown to compare very well with experimental observations. The subsequent vascular growth of the tumour is discussed with regard to a classical reaction-diffusion pre-pattern model. (shrink)

The formation of blood vessels within the vascular system entails a variety of cellular processes, including proliferation, migration and differentiation. In many cases, these diverse processes need to be finely coordinated among neighbouring endothelial cells in order to establish a functional vascular network. For instance, during angiogenic sprouting specialized endothelial tip cells follow guidance cues and migrate extensively into avascular tissues while trailing stalk cells must stay connected to the patent blood vessel. The vascular (...) class='Hi'>endothelial growth factor (VEGF) and Notch signalling pathways have emerged as the major players in governing these different cellular behaviours. In particular, recent work indicates an important role for Notch signalling in determining how an endothelial cell responds to VEGF. In this review, we provide an overview of these biochemically distinct pathways and discuss how they may interact during endothelial cell differentiation and angiogenesis. BioEssays 30:303–313, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

Angiogenesis, the generation of new blood vessels from pre‐existing vessels, is an integral component of wound healing, responses to inflammation and other physiologic processes. It is also an essential part of tumor growth; in the absence of new vessel formation, tumors cannot expand beyond a small volume. Although much is known about angiogenesis and its regulation, there is no overall theory that describes or explains this process. It is here suggested that the intracrine hypothesis, which ascribes to certain extracellular signaling (...) peptides (whether hormones, growth factors, DNA‐binding proteins or enzymes) a role in both intracellular biology and extracellular signaling, can contribute to a more general understanding of angiogenesis. Intracrine factors participate in angiogenesis in the following ways: (1) they can act within the cells that synthesized them (type I intracrine action), (2) they can be secreted and then taken up by their cell of synthesis to act intracellularly (type II intracrine action ), or (3) they can be secreted and internalized by a distant target cell (type III intracrine action). The parallels between the intracrine growth factor mechanisms cancer cells employ in stimulating their own growth and the mechanisms operative in endothelial cell proliferation during angiogenesis (“intracrine reciprocity”) are discussed. Collectively, these explorations lead to testable hypotheses regarding the regulation of normal and pathological angiogenesis, and point to similarities between tumor‐induced angiogenesis and tissue differentiation. BioEssays 28: 943–953, 2006. © 2006 Wiley periodicals, Inc. (shrink)

Vascular Endothelial Growth Factor (VEGF) is the most potent and ubiquitous vascular growth factor known to date. Yet, prior to its description as a secreted mitogen for endothelial cells, it was identified as a vascular permeability factor. These seemingly disparate avenues of discovery highlight VEGF's ability to control many distinct aspects of endothelial cell behaviour, including proliferation, migration, specialisation and survival. The versatility of VEGF as a patterning molecule is likely linked to its association with various (...) signalling receptor complexes, but also its expression in several isoforms with a differential affinity for heparan sulfate proteoglycans in the extracellular matrix. In contrast to the absolute requirement for all known VEGF receptors, the presence of only a single VEGF isoform is sufficient for vascular development. However, the isoforms serve as exquisite tools for the fine patterning of growing vessel networks during embryogenesis and in postnatal life. BioEssays 25:1052–1060, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

The blood‐brain barrier (BBB) is a complex structure formed by vascular endothelial cells, which serve to stabilize the homeostasic processes that are essential for neural functioning. The barrier relies on tight junctions between neighboring endothelial cells and a highly restricted passage of blood‐borne components through the endothelial lining. Selective transport mechanisms guarantee the essential import and export of metabolites through the BBB into and out of the neural microenvironment. The dual functions of barrier and carrier (...) depend on distinct proteins, some of which have been characterized in detail. (shrink)

Cell–extracellular matrix interactions are important in the process of tumor cell invasion and metastasis. In particular, the interactions of tumor cells with basement membranes of tissue epithelial, as well as vascular endothelial, cells are likely to represent key steps in the metastatic process. The interactions between cells and the connective tissue matrix are mediated by a large family of cell surface receptors, the integrins, which represent multiple receptors the integrins, which represent multiple receptors for extracellular matrix (...) and basement membrane components. Here, I review recent progress in elucidating the roles of integrins in tumor cell invasion. Altered expression of this large family of receptors on invasive tumor cells, as compared with non‐invasive cells, may represent a fundamental step in the progressive expression of the invasive phenotype. (shrink)

Angiogenesis is a complex morphogenetic process regulated by growth factors, but also by the force balance between endothelial cells traction stresses and extracellular matrix viscoelastic resistance. Studies conducted with in vitro angiogenesis assays demonstrated that decreasing ECM stiffness triggers an angiogenic switch that promotes organization of EC into tubular cords or pseudo-capillaries. Thus, mechano-sensitivity of EC with regard to proteases secretion, and notably matrix metalloproteinases, should likely play a pivotal role in this switching mechanism. While most studies analysing (...) strain regulation of MMPs used cell cultured on stretched membranes, this work focuses on MMP expression during self-assembly of EC into capillary-like structures within fibrin gels, i.e. on conditions that mimics more closely the in vivo cellular mechanical microenvironment. The activity of MMP-2 and MMP-9, two MMPs that have a pivotal role in capillaries formation, has been monitored in pace with the progressive elongation of EAhy926 cells that takes place during the emergence of cellular cords. We found an increase of the zymogen proMMP-2 that correlates with the initial stages of EC cords formation. However, MMP-2 was not detected. ProMMP-9 secretion decreased, with levels of MMP-9 kept at a rather low value. In order to analyse more precisely the observed differences of EAhy926 response on fibrin and plastic substrates, we proposed a theoretical model of the mechano-regulation of proMMP-2 activation in the presence of type 2 tissue inhibitor of MMPs. Using association/dissociation rates experimentally reported for this enzymatic network, the model adequately describes the synergism of proMMP-2 and TIMP-2 strain activation during pseudo-capillary morphogenesis. All together, these results provide a first step toward a systems biology approach of angiogenesis mechano-regulation by cell-generated extracellular stresses and strains. (shrink)

Vascular development entails multiple cell‐fate decisions to specify a diverse array of vascular structures. Notch proteins are signaling receptors that regulate cell‐fate determination in a variety of cell types. The finding that Notch genes are robustly expressed in the vasculature suggests roles for Notch in guiding endothelial and associated mural cells through the myriad of cell‐fate decisions needed to form the vasculature. In fact, mice with defects in genes encoding Notch, Notch ligands, and components of the Notch signaling (...) cascade invariably display vascular defects. Human Notch genes are linked to Alagille's Syndrome, a developmental disorder with vascular defects, and CADASIL, a cerebral arteriopathy. Studies in zebrafish, mice and humans indicate that Notch works in conjunction with other angiogenic pathways to pattern and stabilize the vasculature. Here, we will focus on established functions for Notch in vascular remodeling and arterial/venous specification and more speculative roles in vascular homeostasis and organ‐specific angiogenesis. BioEssays 26:225–234, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

Protein ubiquitination constitutes a post‐translational modification mediated by ubiquitin ligases whereby ubiquitinated substrates are degraded through the proteasomal or lysosomal pathways, or acquire novel molecular functions according to their “ubiquitin codes.” Dysfunction of the ubiquitination process in cells causes various diseases such as cancers along with neurodegenerative, auto‐immune/inflammatory, and metabolic diseases. KCTD10 functions as a substrate recognition receptor for cullin‐3 (CUL3), a scaffold protein in RING‐type ubiquitin ligase complexes. Recently, studies by ourselves and others have identified new substrates that (...) are ubiquitinated by the CUL3/KCTD10 ubiquitin ligase complex. Moreover, the type of polyubiquitination (e.g., K27‐, K48‐, or K63‐chain) of various substrates (e.g., RhoB, CEP97, EIF3D, and TRIF) mediated by KCTD10 underlies its divergent roles in endothelial barrier formation, primary cilium formation, plasma membrane dynamics, cell proliferation, and immune response. Here, the physiological functions of KCTD10 are summarized and potential mechanisms are proposed. (shrink)

Thrombospondin (TSP‐1) is a large glycoprotein secreted by platelets and synthesized by many cell types, including endothelial and tumor cells. Although controversy exists about the biological function of TSP‐1, the following observations suggest that TSP‐1 may potentiate tumor progression. (1) Tumor metastases in mice are promoted by TSP‐1 and inhibited by anti‐TSP‐1 antibodies. (2) TSP‐1 promotes tumor cell adhesion, migration and invasion. (3) TSP‐1 promotes angiogenesis in the rat aorta model. (4) TSP‐1 up‐regulates the plasminogen activator system through (...) a mechanism involving the activation of TGF‐β1. (5) Human tumors express increased levels of the CSVTCG‐specific TSP‐1 receptor. (6) Tumor stroma is enriched in TSP‐1. (7) Cancer patients have high blood levels of TSP‐1. (8) Poor patient survival correlates with a higher expression of the CSVTCG‐specific TSP‐1 receptor on tumor cells. In this paper we discuss the evidence that TSP‐1 promotes tumor progression and present a hypothetical scheme for its mechanism of action. (shrink)

Angiogenesis plays an essential role in tumor growth, invasion and metastasis. After initial pessimism about the usefulness of the antiangiogenic therapeutic approach for cancer, interest has increased in the development of antiangiogenic compounds after the first clinical approval of an antiangiogenic therapy. The anti‐vascular endothelial growth factor (VEGF) antibody bevacizumab has recently been approved for use in combination with chemotherapy for the treatment of metastatic colorectal and non‐small cell lung cancer patients. However, no survival benefit has been demonstrated in (...) anti‐VEGF monotherapy trials, probably due to the high complexity of tumor angiogenesis regulation. Experimental and clinical data, including the approval of the multitargeted drugs sunitinib and sorafenib, indicate that exciting results, including tumor regression, can be expected from the combined targeting of different pathways in the tumor angiogenesis scenario. Several obstacles, including the high cost of new molecular targeted drugs make this therapeutic approach difficult. BioEssays 29:1159–1168, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

Among emotions, surprise has been extensively studied in psychology. In linguistics, surprise, like other emotions, has mainly been studied through the syntactic patterns involving surprise lexemes. However, little has been done so far to correlate the reaction of surprise investigated in psychological approaches and the effects of surprise on language. This cross-disciplinary volume aims to bridge the gap between emotion, cognition and language by bringing together nine contributions on surprise from different backgrounds - psychology, human-agent interaction, linguistics. Using different methods (...) at different levels of analysis, all contributors concur in defining surprise as a cognitive operation and as a component of emotion rather than as a pure emotion. Surprise results from expectations not being met and is therefore related to epistemicity. Linguistically, there does not exist an unequivocal marker of surprise. Surprise may be either described by surprise lexemes, which are often associated with figurative language, or it may be expressed by grammatical and syntactic constructions. Originally published as a special issue of Review of Cognitive Linguistics 13:2 (2015). (shrink)