Migration of vascular endothelial cells in monolayers under hypoxic exposure

Human Placental Mesenchymal Stem Cells-Exosomes Alleviate Endothelial Barrier Dysfunction via Cytoskeletal Remodeling through hsa-miR-148a-3p/ROCK1 Pathway

Background

Endothelial barrier disruption of human pulmonary vascular endothelial cells (HPVECs) is an important pathogenic factor for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Mesenchymal stem cells-exosome (MSCs-Exo) represents an ideal carrier for cell-free therapy. The therapeutic implication and underlying mechanism of human placental MSCs-Exo (HPMSCs-Exo) in ALI/ARDS need to be further explored.

Materials and Methods

HPMSCs-Exo was extracted from HPMSCs and characterized. Then, the therapeutic effects of exosomes were evaluated in ALI mice and HPVECs. RNA-sequencing was applied to reveal the miRNA profile of HPMSCs-Exo and differentially expressed genes (DEGs) in HPMSCs-Exo-pretreated HPVECs. The targets of miRNAs were predicted by bioinformatics methods and correlated to DEGs. Finally, the role of hsa-miR-148a-3p/ROCK1 pathway in HPVECs has been further discussed.

Results

The results showed that HPMSCs-Exo could downregulate Rho-associated coiled-coil-containing protein kinase 1 (ROCK1), upregulate the expression of zonula occludens-1 (ZO-1) and F-actin, promote HPVECs migration and tube formation, reduce cytoskeletal disorders and cell permeability, and thus improve ALI/ARDS. RNA-sequencing revealed the DEGs were mainly enriched in cell junction, angiogenesis, inflammation, and energy metabolism. HPMSCs-Exo contains multiple miRNAs which are associated with cytoskeletal function; the expression abundance of hsa-miR-148a-3p is the highest. Bioinformatic analysis identified ROCK1 as a target of hsa-miR-148a-3p. The overexpression of hsa-miR-148a-3p in HPMSCs-Exo promoted the migration and tube formation of HPVECs and reduced ROCK1 expression. However, the overexpression of ROCK1 on HPVECs reduced the therapeutic effect of HPMSCs-Exo.

Conclusions

HPMSCs-Exo represents a protective regimen against endothelial barrier disruption of HPVECs in ALI/ARDS, and the hsa-miR-148a-3p/ROCK1 pathway plays an important role in this therapeutics implication.

Hypoxia suppresses glucose-induced increases in collective cell migration in vascular endothelial cell monolayers

Blood glucose levels fluctuate during daily life, and the oxygen concentration is low compared to the atmosphere. Vascular endothelial cells (ECs) maintain vascular homeostasis by sensing changes in glucose and oxygen concentrations, resulting in collective migration. However, the behaviors of ECs in response to high-glucose and hypoxic environments and the underlying mechanisms remain unclear. In this study, we investigated the collective migration of ECs simultaneously stimulated by changes in glucose and oxygen concentrations. Cell migration in EC monolayer formed inside the media channels of microfluidic devices was observed while varying the glucose and oxygen concentrations. The cell migration increased with increasing glucose concentration under normoxic condition but decreased under hypoxic condition, even in the presence of high glucose levels. In addition, inhibition of mitochondrial function reduced the cell migration regardless of glucose and oxygen concentrations. Thus, oxygen had a greater impact on cell migration than glucose, and aerobic energy production in mitochondria plays an important mechanistic role. These results provide new insights regarding vascular homeostasis relative to glucose and oxygen concentration changes.

Evaluation of the effects of glucose and oxygen on the vascular endothelial cell migration

Glucose is essential as the main energy source for living organisms. However, excessive elevation of blood sugar levels can lead to diabetes and serious complications such as arteriosclerosis. Even though blood sugar levels as well as hypoxia associated with hyperglycemia are known to be closely related to diabetes complications, the responses of vascular endothelial cells to glucose and oxygen have not been fully investigated. In this study, using a microfluidic device that can control the oxygen concentration, we observed the behavior of vascular endothelial cell monolayers while simultaneously controlling glucose and oxygen levels. Results showed that the cell migration speed was increased by high-glucose exposure in an oxygen-rich environment, but was decreased in a hypoxic environment regardless of glucose condition. The expression of vascular endothelial-cadherin at the cell periphery, which plays a role in cell-cell adhesion, was increased by hypoxic exposure, but was largely independent of glucose condition. This suggested that cell-cell adhesion is less involved in the increase in migration caused by high glucose. Furthermore, stabilization and nuclear translocation of hypoxia-inducible factor-1α, which is involved in cellular hypoxia sensing, increased 5 h after exposure to high glucose, but decreased 3 days after the exposure. This indicated that intracellular hypoxia was generated by increased oxygen consumption in mitochondria just after the high-glucose exposure, but it was moderated within 3 days.

Microfluidic platform for the reproduction of hypoxic vascular microenvironments

Vascular endothelial cells (ECs) respond to mechanical stimuli caused by blood flow to maintain vascular homeostasis. Although the oxygen level in vascular microenvironment is lower than the atmospheric one, the cellular dynamics of ECs under hypoxic and flow exposure are not fully understood. Here, we describe a microfluidic platform for the reproduction hypoxic vascular microenvironments. Simultaneous application of hypoxic stress and fluid shear stress to the cultured cells was achieved by integrating a microfluidic device and a flow channel that adjusted the initial oxygen concentration in a cell culture medium. An EC monolayer was then formed on the media channel in the device, and the ECs were observed after exposure to hypoxic and flow conditions. The migration velocity of the ECs immediately increased after flow exposure, especially in the direction opposite to the flow direction, and gradually decreased, resulting in the lowest value under the hypoxic and flow exposure condition. The ECs after 6-h simultaneous exposure to hypoxic stress and fluid shear stress were generally aligned and elongated in the flow direction, with enhanced VE-cadherin expression and actin filament assembly. Thus, the developed microfluidic platform is useful for investigating the dynamics of ECs in vascular microenvironments.

Dissolved oxygen gradient on three dimensionally printed microfluidic platform for studying its effect on fish at three levels: cell, embryo, and larva

A simple and low-cost dissolved oxygen gradient platform of three dimensionally (3D) printed microfluidic chip was developed for cultivating cells, embryos, and larvae of fish. "Christmas tree" structure channel networks generated a dissolved oxygen gradient out of two fluids fed to the device. Polydimethylsiloxane (PDMS) membrane with high biocompatibility was used as the substrate for cell culture in the 3D-printed microfluidic chip, which made the cell analysis easy. The embryos and larvae of fish could be cultured directly in the chip, and their development can be observed in real time with a microscope. Using zebrafish as a model, we assessed the effect of different dissolved oxygen on its cells, embryos, and larvae. Hypoxia induced production of reactive oxygen species (ROS) in zebrafish cells, embryos, and larvae, eventually leading to cell apoptosis and developmental impairment. Hypoxia also increased nitric oxide content in zebrafish cells, which might be a defensive strategy to overcome the adverse effect of hypoxia in fish cells. This is the first platform that could comprehensively investigate the effects of different dissolved oxygen on fish at the cell, embryo, and larva levels, which has great potential in studying the responses of aquatic organisms under different oxygen concentrations.

Regulation of cells of the arterial wall by hypoxia and its role in the development of atherosclerosis

The cell's response to hypoxia depends on stabilization of the hypoxia-inducible factor 1 complex and transactivation of nuclear factor kappa-B (NF-κB). HIF target gene transcription in cells resident to atherosclerotic lesions adjoins a complex interplay of cytokines and mediators of inflammation affecting cholesterol uptake, migration, and inflammation. Maladaptive activation of the HIF-pathway and transactivation of nuclear factor kappa-B causes monocytes to invade early atherosclerotic lesions, maintaining inflammation and aggravating a low-oxygen environment. Meanwhile HIF-dependent upregulation of the ATP-binding cassette transporter ABCA1 causes attenuation of cholesterol efflux and ultimately macrophages becoming foam cells. Hypoxia facilitates neovascularization by upregulation of vascular endothelial growth factor (VEGF) secreted by endothelial cells and vascular smooth muscle cells lining the arterial wall destabilizing the plaque. HIF-knockout animal models and inhibitor studies were able to show beneficial effects on atherogenesis by counteracting the HIF-pathway in the cell wall. In this review the authors elaborate on the up-to-date literature on regulation of cells of the arterial wall through activation of HIF-1α and its effect on atherosclerotic plaque formation.

Mechanical regulation of the early stages of angiogenesis

Favouring or thwarting the development of a vascular network is essential in fields as diverse as oncology, cardiovascular disease or tissue engineering. As a result, understanding and controlling angiogenesis has become a major scientific challenge. Mechanical factors play a fundamental role in angiogenesis and can potentially be exploited for optimizing the architecture of the resulting vascular network. Largely focusing on in vitro systems but also supported by some in vivo evidence, the aim of this Highlight Review is dual. First, we describe the current knowledge with particular focus on the effects of fluid and solid mechanical stimuli on the early stages of the angiogenic process, most notably the destabilization of existing vessels and the initiation and elongation of new vessels. Second, we explore inherent difficulties in the field and propose future perspectives on the use of in vitro and physics-based modelling to overcome these difficulties.

Endothelial Cell Differentiation and Hemogenic Specification

Formation of the vasculature is a critical step within the developing embryo and its disruption causes early embryonic lethality. This complex process is driven by a cascade of signaling events that controls differentiation of mesodermal progenitors into primordial endothelial cells and their further specification into distinct subtypes (arterial, venous, hemogenic) that are needed to generate a blood circulatory network. Hemogenic endothelial cells give rise to hematopoietic stem and progenitor cells that generate all blood cells in the body during embryogenesis and postnatally. We focus our discussion on the regulation of endothelial cell differentiation, and subsequent hemogenic specification, and highlight many of the signaling pathways involved in these processes, which are conserved across vertebrates. Gaining a better understanding of the regulation of these processes will yield insights needed to optimize the treatment of vascular and hematopoietic disease and generate human stem cell-derived vascular and hematopoietic cells for tissue engineering and regenerative medicine.

A Review of Functional Analysis of Endothelial Cells in Flow Chambers

The vascular endothelial cells constitute the innermost layer. The cells are exposed to mechanical stress by the flow, causing them to express their functions. To elucidate the functions, methods involving seeding endothelial cells as a layer in a chamber were studied. The chambers are known as parallel plate, T-chamber, step, cone plate, and stretch. The stimulated functions or signals from endothelial cells by flows are extensively connected to other outer layers of arteries or organs. The coculture layer was developed in a chamber to investigate the interaction between smooth muscle cells in the middle layer of the blood vessel wall in vascular physiology and pathology. Additionally, the microfabrication technology used to create a chamber for a microfluidic device involves both mechanical and chemical stimulation of cells to show their dynamics in in vivo microenvironments. The purpose of this study is to summarize the blood flow (flow inducing) for the functions connecting to endothelial cells and blood vessels, and to find directions for future chamber and device developments for further understanding and application of vascular functions. The relationship between chamber design flow, cell layers, and microfluidics was studied.

Recent research advances of the biomimetic tumor microenvironment and regulatory factors on microfluidic devices: A systematic review

Tumor microenvironment is a multicomponent system consisting of tumor cells, noncancer cells, extracellular matrix, and signaling molecules, which hosts tumor cells with integrated biophysical and biochemical elements. Because of its critical involvement in tumor genesis, invasion, metastasis, and resistance, the tumor microenvironment is emerging as a hot topic of tumor biology and a prospective therapeutic target. Unfortunately, the complex of microenvironment modeling in vitro is technically challenging and does not effectively generalize the local tumor tissue milieu. Recently, significant advances in microfluidic technologies have provided us with an approach to imitate physiological systems that can be utilized to mimic the characterization of tumor responses with pathophysiological relevance in vitro. In this review, we highlight the recent progress and innovations in microfluidic technology that facilitates the tumor microenvironment study. We also discuss the progress and future perspective of microfluidic bionic approaches with high efficiency for the study of tumor microenvironment and the challenges encountered in cancer research, drug discovery, and personalized therapy.

Oxygen control: the often overlooked but essential piece to create better in vitro systems

Variations in oxygen levels play key roles in numerous physiological and pathological processes, but are often not properly controlled in in vitro models, introducing a significant bias in experimental outcomes. Recent developments in microfluidic technology have introduced a paradigm shift by providing new opportunities to better mimic physiological and pathological conditions, which is achieved by both regulating and monitoring oxygen levels at the micrometre scale in miniaturized devices. In this review, we first introduce the nature and relevance of oxygen-dependent pathways in both physiological and pathological contexts. Subsequently, we discuss strategies to control oxygen in microfluidic devices, distinguishing between engineering approaches that operate at the device level during its fabrication and chemical approaches that involve the active perfusion of fluids oxygenated at a precise level or supplemented with oxygen-producing or oxygen-scavenging materials. In addition, we discuss readout approaches for monitoring oxygen levels at the cellular and tissue levels, focusing on electrochemical and optical detection schemes for high-resolution measurements directly on-chip. An overview of different applications in which microfluidic devices have been utilized to answer biological research questions is then provided. In the final section, we provide our vision for further technological refinements of oxygen-controlling devices and discuss how these devices can be employed to generate new fundamental insights regarding key scientific problems that call for emulating oxygen levels as encountered in vivo. We conclude by making the case that ultimately emulating physiological or pathological oxygen levels should become a standard feature in all in vitro cell, tissue, and organ models.

Bioprinted microvasculature: progressing from structure to function

Three-dimensional (3D) bioprinting seeks to unlock the rapid generation of complex tissue constructs, but long-standing challenges with efficientin vitromicrovascularization must be solved before this can become a reality. Microvasculature is particularly challenging to biofabricate due to the presence of a hollow lumen, a hierarchically branched network topology, and a complex signaling milieu. All of these characteristics are required for proper microvascular-and, thus, tissue-function. While several techniques have been developed to address distinct portions of this microvascularization challenge, no single approach is capable of simultaneously recreating all three microvascular characteristics. In this review, we present a three-part framework that proposes integration of existing techniques to generate mature microvascular constructs. First, extrusion-based 3D bioprinting creates a mesoscale foundation of hollow, endothelialized channels. Second, biochemical and biophysical cues induce endothelial sprouting to create a capillary-mimetic network. Third, the construct is conditioned to enhance network maturity. Across all three of these stages, we highlight the potential for extrusion-based bioprinting to become a central technique for engineering hierarchical microvasculature. We envision that the successful biofabrication of functionally engineered microvasculature will address a critical need in tissue engineering, and propel further advances in regenerative medicine andex vivohuman tissue modeling.

P21-activated kinase regulates oxygen-dependent migration of vascular endothelial cells in monolayers

The collective migration of vascular endothelial cells plays important roles in homeostasis and angiogenesis. Oxygen tension in vivo is a key factor affecting the cellular dynamics. We previously reported hypoxic conditions promote the internalization of vascular endothelial (VE)-cadherin and increase the collective migration of vascular endothelial cells. However, the mechanism through which cells regulate collective migration as affected by oxygen tension is not fully understood. Here, we investigated oxygen-dependent collective migration, focusing on intracellular protein p21-activated kinase (PAK) and hypoxia-inducing factor (HIF)-1α. The results indicate that the oxygen-dependent variation of the migration speed of vascular endothelial cells is mediated by the regulation of VE-cadherin through the PAK pathway, as well as other mechanisms via HIF-1α, especially under extreme hypoxic conditions.

The pro-migration and anti-apoptosis effects of HMGA2 in HUVECs stimulated by hypoxia

High-mobility group AT-hook2 (HMGA2), serving as an architectural transcription factor, participates in plenty of biological processes. Our study is aimed at illustrating the effect of HMGA2 on hypoxia-induced HUVEC injury and the underlying mechanism. To induce hypoxia-related cell injury, HUVECs were exposed to hypoxic condition for 12-24 h. Molecular expression was determined by Western blot analysis, real-time PCR and immunofluorescence staining. Cell migration was monitored by wound healing assay and Transwell chamber assay. Cell proliferation and apoptosis were measured by MTT assay kits and TUNEL staining. In this study, we discovered that HMGA2 was upregulated in hypoxia-induced HUVECs. Overexpression of HMGA2 promoted cell migration, decreased the apoptosis ratio in response to hypoxia stimulation, while HMGA2 knockdown inhibited cell migration and accelerated apoptosis in HUVECs under hypoxic condition. Mechanistically, we found that HMGA2 induced increased expression of HIF-1α,VEGF, eNOS and AKT. eNOS knockdown significantly reduced HMGA2-mediated pro-migration effects, and AKT knockdown strikingly counteracted HMGA2-mediated anti-apoptotic effect. Hence, our data indicated that HMGA2 promoted cell migration by regulating HIF-1α/VGEF/eNOS signaling and prevented cell apoptosis by activating HIF-1α/VGEF/AKT signaling in HUVECs.

Hypoxia, partial EMT and collective migration: Emerging culprits in metastasis

Epithelial-mesenchymal transition (EMT) is a cellular biological process involved in migration of primary cancer cells to secondary sites facilitating metastasis. Besides, EMT also confers properties such as stemness, drug resistance and immune evasion which can aid a successful colonization at the distant site. EMT is not a binary process; recent evidence suggests that cells in partial EMT or hybrid E/M phenotype(s) can have enhanced stemness and drug resistance as compared to those undergoing a complete EMT. Moreover, partial EMT enables collective migration of cells as clusters of circulating tumor cells or emboli, further endorsing that cells in hybrid E/M phenotypes may be the 'fittest' for metastasis. Here, we review mechanisms and implications of hybrid E/M phenotypes, including their reported association with hypoxia. Hypoxia-driven activation of HIF-1α can drive EMT. In addition, cyclic hypoxia, as compared to acute or chronic hypoxia, shows the highest levels of active HIF-1α and can augment cancer aggressiveness to a greater extent, including enriching for a partial EMT phenotype. We also discuss how metastasis is influenced by hypoxia, partial EMT and collective cell migration, and call for a better understanding of interconnections among these mechanisms. We discuss the known regulators of hypoxia, hybrid EMT and collective cell migration and highlight the gaps which needs to be filled for connecting these three axes which will increase our understanding of dynamics of metastasis and help control it more effectively.

Oxygen homeostasis and cardiovascular disease: A role for HIF?

Hypoxia, the decline of tissue oxygen stress, plays a role in mediating cellular processes. Cardiovascular disease, relatively widespread with increased mortality, is closely correlated with oxygen homeostasis regulation. Besides, hypoxia-inducible factor-1(HIF-1) is reported to be a crucial component in regulating systemic hypoxia-induced physiological and pathological modifications like oxidative stress, damage, angiogenesis, vascular remodeling, inflammatory reaction, and metabolic remodeling. In addition, HIF1 controls the movement, proliferation, apoptosis, differentiation and activity of numerous core cells, such as cardiomyocytes, endothelial cells (ECs), smooth muscle cells (SMCs), and macrophages. Here we review the molecular regulation of HIF-1 in cardiovascular diseases, intended to improve therapeutic approaches for clinical diagnoses. Better knowledge of the oxygen balance control and the signal mechanisms involved is important to advance the development of hypoxia-related diseases.

Automated platform for cell selection and separation based on four-dimensional motility and matrix degradation

Motility and invasion are key steps in the metastatic cascade, enabling cells to move through normal tissue borders into the surrounding stroma. Most available in vitro assays track cell motility or cell invasion but lack the ability to measure both simultaneously and then separate single cells with unique behaviors. In this work, we developed a cell-separation platform capable of tracking cell movement (chemokinesis) and invasion through an extracellular matrix in space and time. The platform utilized a collagen scaffold with embedded tumor cells overlaid onto a microraft array. Confocal microscopy enabled high resolution (0.4 × 0.4 × 3.5 µm voxel) monitoring of cell movement within the scaffolds. Two pancreatic cancer cell lines with known differing invasiveness were characterized on this platform, with median motilities of 14 ± 6 μm and 10 ± 4 μm over 48 h. Within the same cell line, cells demonstrated highly variable motility, with XYZ movement ranging from 144 μm to 2 μm over 24 h. The ten lowest and highest motility cells, with median movements of 33 ± 11 μm and 3 ± 1 μm, respectively, were separated and sub-cultured. After 6 weeks of culture, the cell populations were assayed on a Transwell invasion assay and 227 ± 56 cells were invasive in the high motility population while only 48 ± 10 cells were invasive in the low motility population, indicating that the resulting offspring possessed a motility phenotype reflective of the parental cells. This work demonstrates the feasibility of sorting single cells based on complex phenotypes along with the capability to further probe those cells and explore biological phenomena.

Metabolic Switching of Tumor Cells under Hypoxic Conditions in a Tumor-on-a-chip Model

Hypoxia switches the metabolism of tumor cells and induces drug resistance. Currently, no therapeutic exists that effectively and specifically targets hypoxic cells in tumors. Development of such therapeutics critically depends on the availability of in vitro models that accurately recapitulate hypoxia as found in the tumor microenvironment. Here, we report on the design and validation of an easy-to-fabricate tumor-on-a-chip microfluidic platform that robustly emulates the hypoxic tumor microenvironment. The tumor-on-a-chip model consists of a central chamber for 3D tumor cell culture and two side channels for medium perfusion. The microfluidic device is fabricated from polydimethylsiloxane (PDMS), and oxygen diffusion in the device is blocked by an embedded sheet of polymethyl methacrylate (PMMA). Hypoxia was confirmed using oxygen-sensitive probes and the effect on the 3D tumor cell culture investigated by a pH-sensitive dual-labeled fluorescent dextran and a fluorescently labeled glucose analogue. In contrast to control devices without PMMA, PMMA-containing devices gave rise to decreases in oxygen and pH levels as well as an increased consumption of glucose after two days of culture, indicating a rapid metabolic switch of the tumor cells under hypoxic conditions towards increased glycolysis. This platform will open new avenues for testing anti-cancer therapies targeting hypoxic areas.

Early-Stage Dynamics in Vascular Endothelial Cells Exposed to Hydrostatic Pressure

Blood pressure is an important factor both in maintaining body homeostasis and in its disruption. Vascular endothelial cells (ECs) are exposed to varying degrees of blood pressure and therefore play an important role in these physiological and pathological events. However, the effect of blood pressure on EC functions remains to be elucidated. In particular, we do not know how ECs sense and respond to changes in hydrostatic pressure even though the hydrostatic pressure is known to affect the EC functions. Here, we hypothesized that the cellular responses, leading to the reported pressure effects, occur at an early stage of pressure exposure and observed the early-stage dynamics in ECs to elucidate mechanisms through which ECs sense and respond to hydrostatic pressure. We found that exposure to hydrostatic pressure causes an early actomyosin-mediated contraction of ECs without a change in cell morphology. This response could be caused by water efflux from the ECs following exposure to hydrostatic pressure. Although only a limited study, these findings do explain a part of the mechanism through which ECs sense and respond to hydrostatic pressure.