Regulation of VEGFR Signalling in Lymphatic Vascular Development and Disease: An Update

The importance of lymphatic vessels in a myriad of human diseases is rapidly gaining recognition; lymphatic vessel dysfunction is a feature of disorders including congenital lymphatic anomalies, primary lymphoedema and obesity, while improved lymphatic vessel function increases the efficacy of immunotherapy for cancer and neurological disease and promotes cardiac repair following myocardial infarction. Understanding how the growth and function of lymphatic vessels is precisely regulated therefore stands to inform the development of novel therapeutics applicable to a wide range of human diseases. Lymphatic vascular development is initiated during embryogenesis following establishment of the major blood vessels and the onset of blood flow. Lymphatic endothelial progenitor cells arise from a combination of venous and non-venous sources to generate the initial lymphatic vascular structures in the vertebrate embryo, which are then further ramified and remodelled to elaborate an extensive lymphatic vascular network. Signalling mediated via vascular endothelial growth factor (VEGF) family members and vascular endothelial growth factor receptor (VEGFR) tyrosine kinases is crucial for development of both the blood and lymphatic vascular networks, though distinct components are utilised to different degrees in each vascular compartment. Although much is known about the regulation of VEGFA/VEGFR2 signalling in the blood vasculature, less is understood regarding the mechanisms by which VEGFC/VEGFD/VEGFR3 signalling is regulated during lymphatic vascular development. This review will focus on recent advances in our understanding of the cellular and molecular mechanisms regulating VEGFA-, VEGFC- and VEGFD-mediated signalling via VEGFRs which are important for driving the construction of lymphatic vessels during development and disease.     

Induction of Angiogenesis and Vasculogenesis in Cell-Embedded Biomaterials

The central role of prevascularization of engineered tissue grafts in postimplantational survival and integration is becoming increasingly appreciated. An in-depth understanding of the regulating factors and intricacies of generation of three-dimensional vascular networks in vitro will facilitate effective fabrication of clinically relevant vascularized tissues. In this review we aim to examine the influence of different biomaterials on vasculogenesis and angiogenesis, with particular focus on the impact of various matrix properties, such as composition, stiffness and geometry, on the resulting vasculature. Additionally, the contribution of externally applied mechanical forces, mimicking blood flow patterns, to tissue vascularization efforts is reviewed. We present here pivotal studies focusing on the influence of mechanical forces, such as shear stress and stretching tension, on vascular network formation in biomaterial-based scaffolds. Comprehensive understanding of the key factors dictating the patterns and functionality of engineered vasculature will facilitate more efficient fabrication of viable tissue grafts, with a broad range of medical applications.     

Relationship between Blood Vessels and Migration of Neuroblasts in the Olfactory Neurogenic Region of the Rodent Brain

Neural precursors originating in the subventricular zone (SVZ), the largest neurogenic region of the adult brain, migrate several millimeters along a restricted migratory pathway, the rostral migratory stream (RMS), toward the olfactory bulb (OB), where they differentiate into interneurons and integrate into the local neuronal circuits. Migration of SVZ-derived neuroblasts in the adult brain differs in many aspects from that in the embryonic period. Unlike in that period, postnatally-generated neuroblasts in the SVZ are able to divide during migration along the RMS, as well as they migrate independently of radial glia. The homophilic mode of migration, i.e., using each other to move, is typical for neuroblast movement in the RMS. In addition, it has recently been demonstrated that specifically-arranged blood vessels navigate SVZ-derived neuroblasts to the OB and provide signals which promote migration. Here we review the development of vasculature in the presumptive neurogenic region of the rodent brain during the embryonic period as well as the development of the vascular scaffold guiding neuroblast migration in the postnatal period, and the significance of blood vessel reorganization during the early postnatal period for proper migration of RMS neuroblasts in adulthood.     

Remodelling and pathology development associated with aneurysmal ascending aortic tissues

The human ascending aorta (AA) is exposed to very high shear and pressure stresses exerted by the blood flow ejected from the left ventricle outflow tract. This vessel has a unique structural behaviour which adequately redistributes the energy captured from the blood flow ejection to sustain a more continuous blood flow through the entire vascular system. Unfortunately, this vessel is prone to a pathological dilation process involving significant structural changes that can lead to fundamental modification of its mechanical behaviour and functions. Genetic and/or environmental factors have been implicated in the disease process. It is believed that in particular the forces created by blood flow (hemodynamics) can be a stimulus for vessel remodelling. For patients suffering from this deadly condition, surgical replacement or repair is the best solution to increase life expectancy. However, the replacement materials available as a treatment have a significant impact on the blood flow, the biomechanics of the aortic arch, and the entire vascular system. In this review we summarise the current understanding of the pathogenesis mechanisms involved in the dilation of the AA from a mechanical and biochemical point of view. We will also underline the needs for better replacement materials in surgical repair to improve graft patency.     

Linear viscoelasticity and stress growth in blood

This note complements a previous publication where we used first order kinetics to describe biofluid behavior, especially blood, in the cases of simple shear flow, hysteresis and yield stress. Here, we extend the model and consider the viscoelastic properties of blood. Specifically, we look at small amplitude oscillatory flow and stress growth. Successful comparisons of model predictions with blood data are produced.     

The Epidermal Growth Factor Receptor and Its Ligands in Cardiovascular Disease

The epidermal growth factor receptor (EGFR) family and its ligands serve as a switchboard for the regulation of multiple cellular processes. While it is clear that EGFR activity is essential for normal cardiac development, its function in the vasculature and its role in cardiovascular disease are only beginning to be elucidated. In the blood vessel, endothelial cells and smooth muscle cells are both a source and a target of EGF-like ligands. Activation of EGFR has been implicated in blood pressure regulation, endothelial dysfunction, neointimal hyperplasia, atherogenesis, and cardiac remodeling. Furthermore, increased circulating EGF-like ligands may mediate accelerated vascular disease associated with chronic inflammation. Although EGFR inhibitors are currently being used clinically for the treatment of cancer, additional studies are necessary to determine whether abrogation of EGFR signaling is a potential strategy for the treatment of cardiovascular disease.     

Intramuscular Exposure to a Lethal Dose of Ricin Toxin Leads to Endothelial Glycocalyx Shedding and Microvascular Flow Abnormality in Mice and Swine

Ricin toxin isolated from the castor bean (Ricinus communis) is one of the most potent and lethal molecules known. While the pathophysiology and clinical consequences of ricin poisoning by the parenteral route, i.e., intramuscular penetration, have been described recently in various animal models, the preceding mechanism underlying the clinical manifestations of systemic ricin poisoning has not been completely defined. Here, we show that following intramuscular administration, ricin bound preferentially to the vasculature in both mice and swine, leading to coagulopathy and widespread hemorrhages. Increased levels of circulating VEGF and decreased expression of vascular VE-cadherin caused blood vessel impairment, thereby promoting hyperpermeability in various organs. Elevated levels of soluble heparan sulfate, hyaluronic acid and syndecan-1 were measured in blood samples following ricin intoxication, indicating that the vascular glycocalyx of both mice and swine underwent extensive damage. Finally, by using side-stream dark field intravital microscopy imaging, we determined that ricin poisoning leads to microvasculature malfunctioning, as manifested by aberrant blood flow and a significant decrease in the number of diffused microvessels. These findings, which suggest that glycocalyx shedding and microcirculation dysfunction play a major role in the pathology of systemic ricin poisoning, may serve for the formulation of specifically tailored therapies for treating parenteral ricin intoxication.     

Tumor Vessels Fuel the Fire in Glioblastoma

Glioblastoma, a subset of aggressive brain tumors, deploy several means to increase blood vessel supply dedicated to the tumor mass. This includes typical program borrowed from embryonic development, such as vasculogenesis and sprouting angiogenesis, as well as unconventional processes, including co-option, vascular mimicry, and transdifferentiation, in which tumor cells are pro-actively engaged. However, these neo-generated vascular networks are morphologically and functionally abnormal, suggesting that the vascularization processes are rather inefficient in the tumor ecosystem. In this review, we reiterate the specificities of each neovascularization modality in glioblastoma, and, how they can be hampered mechanistically in the perspective of anti-cancer therapies.     

Nitric Oxide and Reactive Oxygen Species in the Pathogenesis of Preeclampsia

Preeclampsia (PE) is characterized by disturbed extravillous trophoblast migration toward uterine spiral arteries leading to increased uteroplacental vascular resistance and by vascular dysfunction resulting in reduced systemic vasodilatory properties. Its pathogenesis is mediated by an altered bioavailability of nitric oxide (NO) and tissue damage caused by increased levels of reactive oxygen species (ROS). Furthermore, superoxide (O₂⁻) rapidly inactivates NO and forms peroxynitrite (ONOO⁻). It is known that ONOO⁻ accumulates in the placental tissues and injures the placental function in PE. In addition, ROS could stimulate platelet adhesion and aggregation leading to intravascular coagulopathy. ROS-induced coagulopathy causes placental infarction and impairs the uteroplacental blood flow in PE. The disorders could lead to the reduction of oxygen and nutrients required for normal fetal development resulting in fetal growth restriction. On the other hand, several antioxidants scavenge ROS and protect tissues against oxidative damage. Placental antioxidants including catalase, superoxide dismutase (SOD), and glutathione peroxidase (GPx) protect the vasculature from ROS and maintain the vascular function. However, placental ischemia in PE decreases the antioxidant activity resulting in further elevated oxidative stress, which leads to the appearance of the pathological conditions of PE including hypertension and proteinuria. Oxidative stress is defined as an imbalance between ROS and antioxidant activity. This review provides new insights about roles of oxidative stress in the pathophysiology of PE.     

Pulsatile flows in stenosed blood vessels

The pulsatile blood flows in solid blood vessels are investigated numerically in order to understand some physiological phenomena in arteries. For the geometry of the blood vessels, one-point stenosed and periodically stenosed blood vessels are considered. Taking advantage of axisymmetry in the problem, the stream function-vorticity formulation is used for the governing equations of the fluid flows. All the computations are performed by using the ADI scheme of the finite difference method on the numerically generated boundary-fitted orthogonal curvilinear coordinate systems. The flow fields are found to be dramatically different depending on the Strouhal number. When the Strouhal number is 0(1) or larger, the flow field is quite dynamic in the sense that the vortices formed during the previous period survive and exert residual stress on the blood vessel wall. On the other hand, when the Strouhal number is as small as 0(10^-2), the flow fields are found to be in the quasi-steady state. The computation results suggest that the deterioration of endothelial cells may occur due to strong local flow fields near the stenosis and that the probability of platelet attachment to the blood vessel wall is higher in the region behind the stenosis. From the results for the periodically stenosed vessel, the so-called steady streaming phenomenon is confirmed. The steady streaming effect in a wavy channel is expected to increase the heat and mass transfer rate without making the flow turbulent.     

Dissection of the Regulatory Elements of the Complex Expression Pattern of Puckered,a Dual-Specificity JNK Phosphatase

For developmental processes, we know most of the gene networks controlling specific cell responses. We still have to determine how these networks cooperate and how signals become integrated. The JNK pathway is one of the key elements modulating cellular responses during development. Yet, we still know little about how the core components of the pathway interact with additional regulators or how this network modulates cellular responses in the whole organism in homeostasis or during tissue morphogenesis. We have performed a promoter analysis, searching for potential regulatory sequences of puckered (puc) and identified different specific enhancers directing gene expression in different tissues and at different developmental times. Remarkably, some of these domains respond to the JNK activity, but not all. Altogether, these analyses show that puc expression regulation is very complex and that JNK activities participate in non-previously known processes during the development of Drosophila.     

Adhesion of blood platelets under flow to wettability gradient polyethylene surfaces made in a shielded gas plasma

Adhesion and activation of platelets are important steps in the thrombosis of blood after contact with a biomaterial surface and are governed, in part, by the wettability of the surface. Since most implanted devices are in contact with blood under flow conditions, it is important to study the effect of wettability of device surfaces on the behavior of platelets also under flow. To this end, wettability gradient polyethylene surfaces were prepared through glow discharge with partial shielding over a length of 5 cm, with advancing water contact angles varying from 95 to 45 degrees and a contact angle hysteresis of 30 degrees. The role of blood flow on the adhesion of platelets was examined by incubating these gradient surfaces in anticoagulated, whole human blood under static conditions or in blood under a flow of 10 or 40 ml/min through a 3 mm diameter circuit or for 5 or 15 min with either the hydrophobic or hydrophilic end upstream. Generally, more platelets adhered on the hydrophilic end of the wettability gradient than on the hydrophobic end, although the increment along the wettability gradient was dependent on both the flow conditions and direction. More platelets adhered under a flow of 10 ml/min than under static conditions, due to higher mass transport. Especially when the hydrophilic end was upstream, there was a more pronounced adhesion. This can be explained in terms of immediate platelet activation by shear stress imposed at the upstream end. During flow of 40 ml/min, platelet adhesion on an upstream hydrophilic end was less than on a downstream hydrophilic end. We conclude that platelets detach from the hydrophilic end at high shear stress due to the spherical form of adhered platelets. Platelets on the hydrophobic end could withstand detachment by strong, flat shaped platelet-material contact.     

Surface modification of biomaterials by photochemical immobilization and photograft polymerization to improve hemocompatibility

Thrombus formation and blood coagulation are serious problems associated with blood contacting products, such as catheters, vascular grafts, artificial hearts, and heart valves. Recent progresses and strategies to improve the hemocompatibility of biomaterials by surface modification using photochemical immobilization and photograft polymerization are reviewed in this paper. Three approaches to modify biomaterial surfaces for improving the hemocompatibility, i.e., bioinert surfaces, immobilization of anticoagulative substances and biomimetic surfaces, are introduced. The biomimetic amphiphilic phosphorylcholine and Arg-Gly-Asp (RGD) sequence are the most effective and most often employed biomolecules and peptide sequence for improving hemocompatibility of material surfaces. The RGD sequence can enhance adhesion and growth of endothelial cells (ECs) on material surfaces and increase the retention of ECs under flow shear stress conditions. This surface modification is a promising strategy for biomaterials especially for cardiovascular grafts and functional tissue engineered blood vessels.     

Surface modification of biomaterials by photochemical immobilization and photograft polymerization to improve hemocompatibility

Thrombus formation and blood coagulation are serious problems associated with blood contacting products, such as catheters, vascular grafts, artificial hearts, and heart valves. Recent progresses and strategies to improve the hemocompatibility of biomaterials by surface modification using photochemical immobilization and photograft polymerization are reviewed in this paper. Three approaches to modify biomaterial surfaces for improving the hemocompatibility, i.e., bioinert surfaces, immobilization of anticoagulative substances and biomimetic surfaces, are introduced. The biomimetic amphiphilic phosphorylcholine and Arg-Gly-Asp (RGD) sequence are the most effective and most often employed biomolecules and peptide sequence for improving hemocompatibility of material surfaces. The RGD sequence can enhance adhesion and growth of endothelial cells (ECs) on material surfaces and increase the retention of ECs under flow shear stress conditions. This surface modification is a promising strategy for biomaterials especially for cardiovascular grafts and functional tissue engineered blood vessels.     

A concentrated suspension model for the couette rheology of blood

A simple “cell” method for concentrated suspensions has been used to construct a model for the rheological behavioi of blood. The model includes the physical pioperties of the suspending medium, red cell membrane and red cell fluid content. Predictions of the gross viscosity of red cell suspensions are found to agree very well with experiment in the cases of hardened red cells (or normal red cells at very low shear rate) and of normal red cells in the asyniptotic limit of high shear rates. The behavior at intermediate shear rates requires a knowledge of the visco-plastic properties of the membrane and a number of membrane models are investigated. Of particular interest is a plastic membrane which employs a membrane yield stress obtained from other experiments and whose results are qualitatively in agreement with the viscometric data at these intermediate shear rates.     

Ultrastructural Analysis of Nanogold-Labeled Cell Surface Microvilli in Liquid by Atmospheric Scanning Electron Microscopy and Their Relevance in Cell Adhesion

The adhesion of leukocytes circulating in the blood to vascular endothelium is critical for their trafficking in the vasculature, and CD44 is an important cell surface receptor for rolling adhesion. In this study, we demonstrate the correlative observation of CD44 distribution at the lymphocyte cell surface in liquid by fluorescence optical microscopy and immuno-electron microscopy using an atmospheric scanning electron microscope (ASEM). The ultrastructure of the cell surface was clearly imaged by ASEM using positively charged Nanogold particles. ASEM analysis demonstrated microvilli projections around the cell surface and the localization of CD44 on the microvilli. Treatment of cells with cytochalasin D resulted in a loss of the microvilli projections and concomitantly abrogated CD44-mediated adhesion to its ligand hyaluronan. These results suggest the functional relevance of microvilli in CD44-mediated rolling adhesion under shear flow.     

The MEK5/ERK5 Pathway in Health and Disease

The MEK5/ERK5 mitogen-activated protein kinases (MAPK) cascade is a unique signaling module activated by both mitogens and stress stimuli, including cytokines, fluid shear stress, high osmolarity, and oxidative stress. Physiologically, it is mainly known as a mechanoreceptive pathway in the endothelium, where it transduces the various vasoprotective effects of laminar blood flow. However, it also maintains integrity in other tissues exposed to mechanical stress, including bone, cartilage, and muscle, where it exerts a key function as a survival and differentiation pathway. Beyond its diverse physiological roles, the MEK5/ERK5 pathway has also been implicated in various diseases, including cancer, where it has recently emerged as a major escape route, sustaining tumor cell survival and proliferation under drug stress. In addition, MEK5/ERK5 dysfunction may foster cardiovascular diseases such as atherosclerosis. Here, we highlight the importance of the MEK5/ERK5 pathway in health and disease, focusing on its role as a protective cascade in mechanical stress-exposed healthy tissues and its function as a therapy resistance pathway in cancers. We discuss the perspective of targeting this cascade for cancer treatment and weigh its chances and potential risks when considering its emerging role as a protective stress response pathway.     

聚乳酸-聚乙醇酸-聚乙二醇膜片与血管平滑肌细胞相容性研究

目的探讨生物可降解材料聚乳酸-聚乙醇酸-聚乙二醇(PLGA-PEG)与血管平滑肌的细胞相容性,为可降解血管支架材料的研究提供依据。方法采用体外培养的兔血管平滑肌细胞种植在PLGA-PEG膜片上,用相差显微镜观察细胞的生长情况,每天计数,绘制细胞生长曲线,用MTT法测定细胞增殖指数,流式细胞仪检测细胞周期分布。结果兔血管平滑肌细胞在PLGA-PEG膜片上生长良好,与对照组差异无显著意义;MTT法检测细胞增殖指数,与对照组差异无显著意义;流式细胞仪检测细胞周期显示对细胞增殖活性无明显影响。结论PLGA-PEG与兔血管平滑肌细胞具有良好的细胞相容性,可以用于可降解血管支架的制备。