Synthetic microvessels

Leveraging avidin-biotin interaction to quantify permeability property of microvessels-on-a-chip networks

Microvessels-on-a-chip have enabled in vitro studies to closely simulate in vivo microvessel environment. However, assessing microvessel permeability, a functional measure of microvascular exchange, has not been attainable in nonpermeable microfluidic platforms. This study developed a new approach that enables permeability coefficients (P_s) to be quantified in microvessels developed in nonpermeable chip platforms by integrating avidin-biotin technology. Microvessels were developed on biotinylated fibronectin-coated microfluidic channels. Solute transport was assessed by perfusing microvessels with fluorescence-labeled avidin. Avidin molecules that crossed endothelium were captured by substrate biotin and recorded with real-time confocal images. The P_s was derived from the rate of avidin-biotin accumulation at the substrate relative to solute concentration difference across microvessel wall. Avidin tracers with different physiochemical properties were used to characterize the barrier properties of the microvessel wall. The measured baseline P_s and inflammatory mediator-induced increases in P_s and endothelial cell (EC) [Ca²⁺]_i resembled those observed in intact microvessels. Importantly, the spatial accumulation of avidin-biotin at substrate defines the transport pathways. Glycocalyx layer is well formed on endothelium and its degradation increased transcellular transport without affecting EC junctions. This study demonstrated that in vitro microvessels developed in this simply designed microfluidics structurally possess in vivo-like glycocalyx layer and EC junctions and functionally recapitulate basal barrier properties and stimuli-induced responses observed in intact microvessels. This new approach overcomes the limitations of nonpermeable microfluidics and provides an easily executed highly reproducible in vitro microvessel model with in vivo microvessel functionality, suitable for a wide range of applications in blood and vascular research and drug development.NEW & NOTEWORTHY Our study developed a novel method that allows permeability coefficient to be measured in microvessels developed in nonpermeable microfluidic platforms using avidin-biotin technology. It overcomes the major limitation of nonpermeable microfluidic system and provides a simply designed easily executed and highly reproducible in vitro microvessel model with permeability accessibility. This model with in vivo-like endothelial junctions, glycocalyx, and permeability properties advances microfluidics in microvascular research, suitable for a wide range of biomedical and clinical applications.

Effects of Acute Low-Frequency Pulsed Electromagnetic Field Therapy on Aerobic Performance during a Preseason Training Camp: A Pilot Study

Bio-electromagnetic-energy-regulation (BEMER) therapy is a technology using a low-frequency pulsed electromagnetic field (PEMF) in a biorhythmic format. BEMER has been shown to optimize recovery and decrease fatigue by increasing blood flow in microvessels. Our aim was to determine its effects during preseason training in endurance athletes. A total of 14 male cross-country runners (19.07 ± 0.92 y.o.) were placed in either the intervention (PEMF; n = 8) or control (CON; n = 6) group using a covariate-based, constrained randomization. Participants completed six running sessions at altitudes ranging from 881.83 (±135.98 m) to 1027.0 (±223.44 m) above sea level. PEMF group used BEMER therapy before and after each training session, totaling 12 times. There were no significant changes in absolute or relative VO2Peak, ventilation or maximum respiration rate for either the PEMF or CON group (p > 0.05). There was a significant effect of time for absolute and relative ventilatory threshold (VT), and maximum heart rate, heart rate at VT and respiration rate at VT. This study was the first of its kind to study PEMF technology in combination with elevated preseason training. Results indicate some evidence for the use of PEMF therapy during short-term training camps to improve VT.

Rapid Internalization and Nuclear Translocation of CCL5 and CXCL4 in Endothelial Cells

The chemokines CCL5 and CXCL4 are deposited by platelets onto endothelial cells, inducing monocyte arrest. Here, the fate of CCL5 and CXCL4 after endothelial deposition was investigated. Human umbilical vein endothelial cells (HUVECs) and EA.hy926 cells were incubated with CCL5 or CXCL4 for up to 120 min, and chemokine uptake was analyzed by microscopy and by ELISA. Intracellular calcium signaling was visualized upon chemokine treatment, and monocyte arrest was evaluated under laminar flow. Whereas CXCL4 remained partly on the cell surface, all of the CCL5 was internalized into endothelial cells. Endocytosis of CCL5 and CXCL4 was shown as a rapid and active process that primarily depended on dynamin, clathrin, and G protein-coupled receptors (GPCRs), but not on surface proteoglycans. Intracellular calcium signals were increased after chemokine treatment. Confocal microscopy and ELISA measurements in cell organelle fractions indicated that both chemokines accumulated in the nucleus. Internalization did not affect leukocyte arrest, as pretreatment of chemokines and subsequent washing did not alter monocyte adhesion to endothelial cells. Endothelial cells rapidly and actively internalize CCL5 and CXCL4 by clathrin and dynamin-dependent endocytosis, where the chemokines appear to be directed to the nucleus. These findings expand our knowledge of how chemokines attract leukocytes to sites of inflammation.

Variability of von Willebrand factor-related parameters in endothelial colony forming cells

Essentials Endothelial colony forming cells (ECFCs) are a powerful tool to study vascular diseases ex vivo. Separate ECFC lines show variations in morphology and von Willebrand factor-related parameters. Maximum cell density is correlated with von Willebrand factor expression in ECFCs. Variations in ECFC lines are dependent on the age and mesenchymal state of the cells. ABSTRACT: Background Endothelial colony forming cells (ECFCs) are cultured endothelial cells derived from peripheral blood. ECFCs are a powerful tool to study pathophysiological mechanisms underlying vascular diseases, including von Willebrand disease. In prior research, however, large variations between ECFC lines were observed in, among others, von Willebrand factor (VWF) expression. Objective Understand the relation between phenotypic characteristics and VWF-related parameters of healthy control ECFCs. Methods ECFC lines (n = 16) derived from six donors were studied at maximum cell density. Secreted and intracellular VWF antigen were measured by ELISA. The angiogenic capacity of ECFCs was investigated by the Matrigel tube formation assay. Differences in expression of genes involved in angiogenesis, aging, and endothelial to mesenchymal transition (EndoMT) were measured by quantitative PCR. Results Different ECFC lines show variable morphologies and cell density at maximum confluency and cell lines with a low maximum cell density show a mixed and more mesenchymal phenotype. We identified a significant positive correlation between maximum cell density and VWF production, both at protein and mRNA level. Also, significant correlations were observed between maximum cell density and several angiogenic, aging and EndoMT parameters. Conclusions We observed variations in morphology, maximum cell density, VWF production, and angiogenic potential between healthy control ECFCs. These variations seem to be attributable to differences in aging and EndoMT. Because variations correlate with cell density, we believe that ECFCs maintain a powerful tool to study vascular diseases. It is however important to compare cell lines with the same characteristics and perform experiments at maximum cell density.

Engineered Microvessels for the Study of Human Disease

The microvasculature is an extensive, heterogeneous, and complex system that plays a critical role in human physiology and disease. It nourishes almost all living human cells and maintains a local microenvironment that is vital for tissue and organ function. Operating under a state of continuous flow, with an intricate architecture despite its small caliber, and subject to a multitude of biophysical and biochemical stimuli, the microvasculature can be a complex subject to study in the laboratory setting. Engineered microvessels provide an ideal platform that recapitulates essential elements of in vivo physiology and allows study of the microvasculature in a precise and reproducible way. Here, we review relevant structural and functional vascular biology, discuss different methods to engineer microvessels, and explore the applications of this exciting tool for the study of human disease.

Fabrication of a reticular poly(lactide-co-glycolide) cylindrical scaffold for the in vitro development of microvascular networks

The microvascular network is a simple but critical system that is responsible for a range of important biological mechanisms in the bodies of all animals. The ability to generate a functional microvessel not only makes it possible to engineer vital tissue of considerable size but also serves as a platform for biomedical studies. However, most of the current methods for generating microvessel networks in vitro use rectangular channels which cannot represent real vessels in vivo and have dead zones at their corners, hence hindering the circulation of culture medium. We propose a scaffold-wrapping method which enables fabrication of a customized microvascular network in vitro in a more biomimetic way. By integrating microelectromechanical techniques with thermal reflow, we designed and fabricated a microscale hemi-cylindrical photoresist template. A replica mold of polydimethylsiloxane, produced by casting, was then used to generate cylindrical scaffolds with biodegradable poly(lactide-co-glycolide) (PLGA). Human umbilical vein endothelial cells were seeded on both sides of the PLGA scaffold and cultured using a traditional approach. The expression of endothelial cell marker CD31 and intercellular junction vascular endothelial cadherin on the cultured cell demonstrated the potential of generating a microvascular network with a degradable cylindrical scaffold. Our method allows cells to be cultured on a scaffold using a conventional culture approach and monitors cell conditions continuously. We hope our cell-covered scaffold can serve as a framework for building large tissues or can be used as the core of a vascular chip for in vitro circulation studies.

Vascular cognitive impairment: Modeling a critical neurologic disease in vitro and in vivo

BACKGROUND

Vascular contributions to cognitive impairment and dementia (VCID) is a complex form of dementia, combining aspects of vascular disease and other forms of dementia, such as Alzheimer's disease. VCID encompasses a wide spectrum of cerebrovascular-driven cognitive impairment, from mild cognitive impairment to fully developed dementia. This disease state is further complicated by metabolic disorders, such as type 2 diabetes and hypertension, and lifestyle factors, like obesity and high fat diets.

SCOPE OF REVIEW

This manuscript is meant to both define VCID and review the in vitro and in vivo models of the disease state. This includes in vitro models of the neurovascular unit, models of chronic cerebral hypoperfusion, animals with NOTCH3 mutations as a model of small vessel disease, large animals with cerebral amyloid angiopathy (CAA), and animal models of mixed dementia.

MAJOR CONCLUSIONS

Synthetic microvessels are a promising technique to study the neurovascular unit and canines, despite the cost, are an excellent model to study CAA. While there are several good models of individual aspects of VCID, the heterogeneity of the disease states prevents them from being a model of all aspects of the disease. Therefore, VCID needs to be further defined into disease states that exist within this umbrella term. This includes specific guidelines for stroke counts and stroke locations and further categorization of overlapping cerebrovascular and AD pathologies that contribute to dementia. This will allow for better models and a more thorough understanding of how vascular disease contributes to dementia.

GENERAL SIGNIFICANCE

VCID is the second most common form of dementia and is expected to increase in coming years. The heterogeneity of VCID makes it difficult to study, but without better definitions and models, VCID presents a major public health problem for our aging population. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia, edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

High-density lipoprotein modulates thrombosis by preventing von Willebrand factor self-association and subsequent platelet adhesion

The ability of von Willebrand factor (VWF) to initiate platelet adhesion depends on the number of monomers in individual VWF multimers and on the self-association of individual VWF multimers into larger structures. VWF self-association is accelerated by shear stress. We observed that VWF self-association occurs during adsorption of VWF onto surfaces, assembly of secreted VWF into hyperadhesive VWF strings on the endothelial surface, and incorporation of fluid-phase VWF into VWF fibers. VWF adsorption under static conditions increased with increased VWF purity and was prevented by a component of plasma. We identified that component as high-density lipoprotein (HDL) and its major apolipoprotein ApoA-I. HDL and ApoA-I also prevented VWF on the endothelium from self-associating into longer strands and inhibited the attachment of fluid-phase VWF onto vessel wall strands. Platelet adhesion to VWF fibers was reduced in proportion to the reduction in self-associated VWF. In a mouse model of thrombotic microangiopathy, HDL also largely prevented the thrombocytopenia induced by injection of high doses of human VWF. Finally, a potential role for ApoA-I in microvascular occlusion associated with thrombotic thrombocytopenic purpura and sepsis was revealed by the inverse relationship between the concentration of ApoA-I and that of hyperadhesive VWF. These results suggest that interference with VWF self-association would be a new approach to treating thrombotic disorders.

BCL-2 is dispensable for thrombopoiesis and platelet survival

Navitoclax (ABT-263), an inhibitor of the pro-survival BCL-2 family proteins BCL-2, BCL-XL and BCL-W, has shown clinical efficacy in certain BCL-2-dependent haematological cancers, but causes dose-limiting thrombocytopaenia. The latter effect is caused by Navitoclax directly inducing the apoptotic death of platelets, which are dependent on BCL-XL for survival. Recently, ABT-199, a selective BCL-2 antagonist, was developed. It has shown promising anti-leukaemia activity in patients whilst sparing platelets, suggesting that the megakaryocyte lineage does not require BCL-2. In order to elucidate the role of BCL-2 in megakaryocyte and platelet survival, we generated mice with a lineage-specific deletion of Bcl2, alone or in combination with loss of Mcl1 or Bclx. Platelet production and platelet survival were analysed. Additionally, we made use of BH3 mimetics that selectively inhibit BCL-2 or BCL-XL. We show that the deletion of BCL-2, on its own or in concert with MCL-1, does not affect platelet production or platelet lifespan. Thrombocytopaenia in Bclx-deficient mice was not affected by additional genetic loss or pharmacological inhibition of BCL-2. Thus, BCL-2 is dispensable for thrombopoiesis and platelet survival in mice.