Endothelial cell-to-cell junctions: molecular organization and role in vascular homeostasis

Simulated Microgravity Increases the Permeability of HUVEC Monolayer through Up-Regulation of Rap1GAP and Decreased Rap2 Activation

Space microgravity condition has great physiological influence on astronauts’ health. The interaction of endothelial cells, which control vascular permeability and immune responses, is sensitive to mechanical stress. However, whether microgravity has significant effects on the physiological function of the endothelium has not been investigated. In order to address such a question, a clinostat-based culture model with a HUVEC monolayer being inside the culture vessel under the simulated microgravity (SMG) was established. The transmittance of FITC-tagged dextran was used to estimate the change of integrity of the adherens junction of the HUVEC monolayer. Firstly, we found that the permeability of the HUVEC monolayer was largely increased after SMG treatment. To elucidate the mechanism of the increased permeability of the HUVEC monolayer under SMG, the levels of total expression and activated protein levels of Rap1 and Rap2 in HUVEC cells, which regulate the adherens junction of endothelial cells, were detected by WB and GST pull-down after SMG. As the activation of both Rap1 and Rap2 was significantly decreased under SMG, the expression of Rap1GEF1 (C3G) and Rap1GAP in HUVECs, which regulate the activation of them, was further determined. The results indicate that both C3G and Rap1GAP showed a time-dependent increase with the expression of Rap1GAP being dominant at 48 h after SMG. The down-regulation of the expression of junctional proteins, VE-cadherin and β-catenin, in HUVEC cells was also confirmed by WB and immunofluorescence after SMG. To clarify whether up-regulation of Rap1GAP is necessary for the increased permeability of the HUVEC monolayer after SMG, the expression of Rap1GAP was knocked down by Rap1GAP-shRNA, and the change of permeability of the HUVEC monolayer was detected. The results indicate that knock-down of Rap1GAP reduced SMG-induced leaking of the HUVEC monolayer in a time-dependent manner. In total, our results indicate that the Rap1GAP-Rap signal axis was necessary for the increased permeability of the HUVEC monolayer along with the down-regulation of junctional molecules including VE-cadherin and β-catenin.

High content Image Analysis to study phenotypic heterogeneity in endothelial cell monolayers

Endothelial cells (EC) are heterogeneous across and within tissues, reflecting distinct, specialised functions. EC heterogeneity has been proposed to underpin EC plasticity independently from vessel microenvironments. However, heterogeneity driven by contact-dependent or short-range cell-cell crosstalk cannot be evaluated with single cell transcriptomic approaches as spatial and contextual information is lost. Nonetheless, quantification of EC heterogeneity and understanding of its molecular drivers is key to developing novel therapeutics for cancer, cardiovascular diseases and for revascularisation in regenerative medicine. Here, we developed an EC profiling tool (ECPT) to examine individual cells within intact monolayers. We used ECPT to characterise different phenotypes in arterial, venous and microvascular EC populations. In line with other studies, we measured heterogeneity in terms of cell cycle, proliferation, and junction organisation. ECPT uncovered a previously under-appreciated single-cell heterogeneity in NOTCH activation. We correlated cell proliferation with different NOTCH activation states at the single cell and population levels. The positional and relational information extracted with our novel approach is key to elucidating the molecular mechanisms underpinning EC heterogeneity.

Bioglass promotes wound healing by inhibiting endothelial cell pyroptosis through regulation of the connexin 43/reactive oxygen species (ROS) signaling pathway

Bioactive glass (BG) has recently shown great promise in soft tissue repair, especially in wound healing; however, the underlying mechanism remains unclear. Pyroptosis is a novel type of programmed cell death that is involved in various traumatic injury diseases. Here, we hypothesized that BG may promote wound healing through suppression of pyroptosis. To test this scenario, we investigated the possible effect of BG on pyroptosis in wound healing both in vivo and in vitro. This study showed that BG can accelerate wound closure, granulation formation, collagen deposition, and angiogenesis. Moreover, western blot analysis and immunofluorescence staining revealed that BG inhibited the expression of pyroptosis-related proteins in vivo and in vitro. In addition, while BG regulated the expression of connexin43 (Cx43), it inhibited reactive oxygen species (ROS) production. Cx43 activation and inhibition experiments further indicate that BG inhibited pyroptosis in endothelial cells by decreasing Cx43 expression and ROS levels. Taken together, these studies suggest that BG promotes wound healing by inhibiting pyroptosis via Cx43/ROS signaling pathway.

Endothelial barrier dysfunction induced by anthracene and its nitrated or oxygenated derivatives at environmentally relevant levels

Polycyclic aromatic hydrocarbons (PAHs) are epidemiologically associated with cardiovascular diseases characterized by early key events involving in the disruption of endothelial barrier function. Whether PAHs can induce adverse cardiovascular outcome by directly destabilizing endothelial barrier function remains elusive. Herein, we investigated the effect of anthracene (ANT), 9-nitroanthracene (9-NANT), and 9,10-anthraquinone (9,10-AQ) on vascular endothelial barrier functions in human umbilical vein endothelial cells (HUVECs). The integrity of endothelial barrier in HUVECs was disturbed with a 1.15-1.42 fold increase in fluorescein leakage, and 21.8%-58.3% downregulated transendothelial electrical resistance. ANT, 9-NANT and 9,10-AQ promoted paracellular gap formation as revealed by transmission electron microscope. The disrupted cell junctions after 24 h exposure to ANT, 9-NANT and 9,10-AQ at 0.01 μM were indicated by the downregulated mRNA expression of vascular endothelial cadherin (VE-cadherin), zona occludens-1 (ZO-1) and occludin by 33.2%-71.4%, 19.1%-21.0%, and 31.9% respectively, and the downregulated protein expression of ZO-1 and occludin, and by the internalization of VE-cadherin. We demonstrated that ANT and its derivatives at environmentally relevant concentrations induced endothelial barrier dysfunction via the disruption of cell junctions, providing essential in vitro evidence on the association with their adverse cardiovascular outcomes.

Sphingolipid Metabolism and Signaling in Endothelial Cell Functions

The endothelium, inner layer of blood vessels, constitutes a metabolically active paracrine, endocrine, and autocrine organ, able to sense the neighboring environment and exert a variety of biological functions important to preserve the health of vasculature, tissues, and organs. Sphingolipids are both fundamental structural components of the eukaryotic membranes and signaling molecules regulating a variety of biological functions. Ceramide and sphingosine-1-phosphate (S1P), bioactive sphingolipids, have emerged as important regulators of cardiovascular functions in health and disease. In this review we discuss recent insights into the role of ceramide and S1P biosynthesis and signaling in regulating endothelial cell functions, in health and diseases. We also highlight advances into the mechanisms regulating serine palmitoyltransferase, the first and rate-limiting enzyme of de novo sphingolipid biosynthesis, with an emphasis on its inhibitors, ORMDL and NOGO-B. Understanding the molecular mechanisms regulating the sphingolipid de novo biosynthesis may provide the foundation for therapeutic modulation of this pathway in a variety of conditions, including cardiovascular diseases, associated with derangement of this pathway.

Pineapple Leaf Phenols Attenuate DSS-Induced Colitis in Mice and Inhibit Inflammatory Damage by Targeting the NF-κB Pathway

Colitis is not fully curable, although currently, some treatment options are being adopted. In this study, we investigated the effects of pineapple leaf phenols (PLPs), natural phenol products from pineapple leaves, on DSS-induced colitis in mice. The results showed that PLPs dramatically decreased the inflammatory response by inhibiting NF-κB activation and the secretion of pro-inflammatory factors. Moreover, PLPs provided protection against DSS-induced acute colitis by maintaining epithelial integrity. Caffeic and P-coumaric acids had similar effects and could be the active components responsible for PLPs’ effect on colitis. These results indicate that the oral administration of PLPs might be considered as a therapeutic strategy in the treatment of patients with colitis. However, further research on clinical applications and the exact effect of PLPs on colitis is required.

Do Periodontal Pathogens or Associated Virulence Factors Have a Deleterious Effect on the Blood-Brain Barrier, Contributing to Alzheimer's Disease?

The central nervous system (CNS) is protected by a highly selective barrier, the blood-brain barrier (BBB), that regulates the exchange and homeostasis of bloodborne molecules, excluding xenobiotics. This barrier forms the first line of defense by prohibiting pathogens from crossing to the CNS. Aging and chronic exposure of the BBB to pathogens renders it permeable, and this may give rise to pathology in the CNS such as Alzheimer's disease (AD). Researchers have linked pathogens associated with periodontitis to neuroinflammation and AD-like pathology in vivo and in vitro. Although the presence of periodontitis-associated bacteria has been linked to AD in several clinical studies as DNA and virulence factors were confirmed in brain samples of human AD subjects, the mechanism by which the bacteria traverse to the brain and potentially influences neuropathology is unknown. In this review, we present current knowledge about the association between periodontitis and AD, the mechanism whereby periodontal pathogens might provoke neuroinflammation and how periodontal pathogens could affect the BBB. We suggest future studies, with emphasis on the use of human in vitro models of cells associated with the BBB to unravel the pathway of entry for these bacteria to the CNS and to reveal the molecular and cellular pathways involved in initiating the AD-like pathology. In conclusion, evidence demonstrate that bacteria associated with periodontitis and their virulence factors are capable of inflecting damage to the BBB and have a role in giving rise to pathology similar to that found in AD.

Drug Delivery Challenges in Brain Disorders across the Blood-Brain Barrier: Novel Methods and Future Considerations for Improved Therapy

Due to the physiological and structural properties of the blood-brain barrier (BBB), the delivery of drugs to the brain poses a unique challenge in patients with central nervous system (CNS) disorders. Several strategies have been investigated to circumvent the barrier for CNS therapeutics such as in epilepsy, stroke, brain cancer and traumatic brain injury. In this review, we summarize current and novel routes of drug interventions, discuss pharmacokinetics and pharmacodynamics at the neurovascular interface, and propose additional factors that may influence drug delivery. At present, both technological and mechanistic tools are devised to assist in overcoming the BBB for more efficient and improved drug bioavailability in the treatment of clinically devastating brain disorders.

The natural product vioprolide A exerts anti-inflammatory actions through inhibition of its cellular target NOP14 and downregulation of importin-dependent NF-ĸB p65 nuclear translocation

Chronic inflammation is characterized by persisting leukocyte infiltration of the affected tissue, which is enabled by activated endothelial cells (ECs). Chronic inflammatory diseases remain a major pharmacotherapeutic challenge, and thus the search for novel drugs and drug targets is an ongoing demand. We have identified the natural product vioprolide A (vioA) to exert anti-inflammatory actions in vivo and in ECs in vitro through inhibition of its cellular target nucleolar protein 14 (NOP14). VioA attenuated the infiltration of microglia and macrophages during laser-induced murine choroidal neovascularization and the leukocyte trafficking through the vascular endothelium in the murine cremaster muscle. Mechanistic studies revealed that vioA downregulates EC adhesion molecules and the tumor necrosis factor receptor (TNFR) 1 by decreasing the de novo protein synthesis in ECs. Most importantly, we found that inhibition of importin-dependent NF-ĸB p65 nuclear translocation is a crucial part of the action of vioA leading to reduced NF-ĸB promotor activity and inflammatory gene expression. Knockdown experiments revealed a causal link between the cellular target NOP14 and the anti-inflammatory action of vioA, classifying the natural product as unique drug lead for anti-inflammatory therapeutics.

Salidroside protects against ventilation-induced lung injury by inhibiting the expression of matrix metalloproteinase-9

CONTEXT

Salidroside, a compound extracted from Rhodiola rosea L. (Crassulaceae), possesses many beneficial pathological effects.

OBJECTIVE

To explore the effect of salidroside on ventilator-induced lung endothelial dysfunction in vivo and in vitro.

MATERIALS AND METHODS

In vivo, male ICR mice were divided into sham, ventilation, salidroside, and ventilation plus salidroside groups. The mice were ventilated for 4 h, salidroside (50 mg/kg) was administrated intraperitoneally before ventilation, dexamethasone (Dex) (5 mg/kg) was used as a positive control. In vitro, mouse lung vascular endothelial cells (MLVECs) were treated with salidroside, MMP-9 siRNA, and BAY11-7082 (10 μM), and then exposed to cyclic stretch for 4 h. Afterward, lung tissues and MLVECs were collected for further analysis.

RESULTS

Salidroside pre-treatment significantly reversed the expression of vascular endothelial cadherin (VE-cadherin) and zonula occluden-1 (ZO-1) proteins in cyclic stretch-treated MLVECs (0.46 ± 0.09 vs. 0.80 ± 0.14, 0.49 ± 0.05 vs. 0.88 ± 0.08) and ventilated lung tissues (0.56 ± 0.06 vs. 0.83 ± 0.46, 0.49 ± 0.08 vs. 0.80 ± 0.12). The results further indicated that salidroside inhibited the expression of matrix metalloproteinase-9 (MMP-9), whereas knockdown of its expression restored the expression levels of VE-cadherin (0.37 ± 0.08 vs. 0.85 ± 0.74) and ZO-1 (0.48 ± 0.08 vs. 0.81 ± 0.11) in stretched MLVECs. Meanwhile, salidroside inhibited the NF-κB signalling pathway and alleviated lung injury.

CONCLUSIONS

Salidroside protected against stretch-induced endothelial barrier function, improving lung injury after ventilation. Thus, salidroside may be a promising therapeutic agent for patients with MV-induced lung injury.

3D hydrogel models of the neurovascular unit to investigate blood-brain barrier dysfunction

The neurovascular unit (NVU), consisting of neurons, glial cells, vascular cells (endothelial cells, pericytes and vascular smooth muscle cells (VSMCs)) together with the surrounding extracellular matrix (ECM), is an important interface between the peripheral blood and the brain parenchyma. Disruption of the NVU impacts on blood-brain barrier (BBB) regulation and underlies the development and pathology of multiple neurological disorders, including stroke and Alzheimer's disease (AD). The ability to differentiate induced pluripotent stem cells (iPSCs) into the different cell types of the NVU and incorporate them into physical models provides a reverse engineering approach to generate human NVU models to study BBB function. To recapitulate the in vivo situation such NVU models must also incorporate the ECM to provide a 3D environment with appropriate mechanical and biochemical cues for the cells of the NVU. In this review, we provide an overview of the cells of the NVU and the surrounding ECM, before discussing the characteristics (stiffness, functionality and porosity) required of hydrogels to mimic the ECM when incorporated into in vitro NVU models. We summarise the approaches available to measure BBB functionality and present the techniques in use to develop robust and translatable models of the NVU, including transwell models, hydrogel models, 3D-bioprinting, microfluidic models and organoids. The incorporation of iPSCs either without or with disease-specific genetic mutations into these NVU models provides a platform in which to study normal and disease mechanisms, test BBB permeability to drugs, screen for new therapeutic targets and drugs or to design cell-based therapies.

Nectin stabilization at adherens junctions is counteracted by Rab5a-dependent endocytosis

Cell-cell junctions undergo constant remodeling, which is crucial for the control of vascular integrity. Indeed, transport of junctional components such as cadherins is understood in increasing depth. However, little is known about the respective pathways regulating localization of nectin at cell-cell junctions. Here, we performed an siRNA-based screen of vesicle regulators of the RabGTPase family, leading to the identification of a novel role for Rab5a in the endocytosis nectin-2 at adherens junctions of primary human endothelial cells (HUVEC). Confocal microscopy experiments revealed disordered nectin-2 localization at adherens junctions upon Rab5a depletion. In addition, internalized nectin-2 was shown to prominently localize to Rab5a-positive vesicles in both fixed and living cells. As shown previously, nectin-2 stabilization at junctions is achieved via drebrin-dependent coupling to the subcortical actin cytoskeleton. Consistently, depletion of drebrin in this study leads to enhanced internalization of nectin-2 from junctions. Strikingly, simultaneous silencing of Rab5a and drebrin restored the junctional localization of nectin-2, pointing to Rab5a as counteracting the drebrin-dependent stabilization of nectin-2 at adherens junctions. This mechanism could be further validated by transendothelial resistance measurements. Collectively, our results identify Rab5a as a key player in the endocytosis of nectin-2 and thus in the regulation of adherens junction integrity in primary human endothelial cells.

The Role of lncRNAs in Regulating the Intestinal Mucosal Mechanical Barrier

lncRNA is a transcript that is more than 200 bp in length. Currently, evidence has shown that lncRNA is of great significance in cell activity, involved in epigenetics, gene transcription, chromatin regulation, etc. The existence of an intestinal mucosal mechanical barrier hinders the invasion of pathogenic bacteria and toxins, maintaining the stability of the intestinal environment. Serious destruction or dysfunction of the mechanical barrier often leads to intestinal diseases. This review first summarizes the ability of lncRNAs to regulate the intestinal mucosal mechanical barrier. We then discussed how lncRNAs participate in various intestinal diseases by regulating the intestinal mucosal mechanical barrier. Finally, we envision its potential as a new marker for diagnosing and treating intestinal inflammatory diseases.

Reversibly Modulating the Blood-Brain Barrier by Laser Stimulation of Molecular-Targeted Nanoparticles

The blood-brain barrier (BBB) is highly selective and acts as the interface between the central nervous system and circulation. While the BBB is critical for maintaining brain homeostasis, it represents a formidable challenge for drug delivery. Here we synthesized gold nanoparticles (AuNPs) for targeting the tight junction specifically and demonstrated that transcranial picosecond laser stimulation of these AuNPs post intravenous injection increases the BBB permeability. The BBB permeability change can be graded by laser intensity, is entirely reversible, and involves increased paracellular diffusion. BBB modulation does not lead to significant disruption in the spontaneous vasomotion or the structure of the neurovascular unit. This strategy allows the entry of immunoglobulins and viral gene therapy vectors, as well as cargo-laden liposomes. We anticipate this nanotechnology to be useful for tissue regions that are accessible to light or fiberoptic application and to open new avenues for drug screening and therapeutic interventions in the central nervous system.

Identification of novel biomarkers for intracerebral hemorrhage via long noncoding RNA-associated competing endogenous RNA network

Intracerebral hemorrhage (ICH) is a leading cause of death and disability worldwide. This study aimed to examine the involvement of long non-coding RNAs (lncRNAs), a group of non-coding transcripts, in ICH as potential biomarkers. An expression profile of patients with ICH using four contralateral grey matter controls (GM) and four contralateral white matter controls (WM) was downloaded from the Gene Expression Omnibus (GEO) database. Co-expressed lncRNAs and mRNAs were selected to create competing endogenous RNA (ceRNA) networks. Key lncRNAs were identified in ceRNA networks, which were validated through Real-time qPCR (RT-qPCR) with peripheral blood samples from patients with ICH. A total of 49 differentially expressed lncRNAs were discovered in different brain regions. The ceRNA network in GM included 9 lncRNAs, 40 mRNAs, and 20 microRNAs (miRNAs), while the one in WM covered 6 lncRNAs, 25 mRNAs, and 14 miRNAs. Six hub lncRNAs were observed and RT-qPCR results showed that LY86-AS1, DLX6-AS1, RRN3P2, and CRNDE were down-regulated, while HCP5 and MIAT were up-regulated in patients with ICH. Receiver Operating Characteristic (ROC) assessments demonstrated the diagnostic value of these lncRNAs. Our findings highlight the potential roles of lncRNA in ICH pathogenesis. Moreover, the hub lncRNAs discovered here might become novel biomarkers and promising targets for ICH drug development.

Chinese Herbal Preparation SaiLuoTong Alleviates Brain Ischemia via Nrf2 Antioxidation Pathway-Dependent Cerebral Microvascular Protection

Stroke is one of the most devastating diseases worldwide. The Chinese herbal preparation SaiLuoTong (SLT) capsule showed outstanding therapeutic effects on stroke and its sequelae. The aim of this study was to further elucidate its therapeutic mechanism. We duplicated a permanent cerebral ischemia model in rats by MCAO and used SLT (33 and 16.5 mg/kg) to intervene. The results showed SLT dose dependently decreased infarction volumes, relieved neuron degeneration and loss, and ameliorated neurological functions, and the dose of 33 mg/kg had statistical significance (compared with the model group, p < 0.05); SLT of 33 mg/kg also significantly inhibited the elevation in brain water content and the loss in claudin-1 and occludin expressions; additionally, it significantly increased nucleus translocation of Nrf2, elevated the expression of HO-1, and raised the activity of SOD and content of GSH (compared with the model group, p < 0.05 or 0.01). These results testified SLT’s anti-brain ischemia effect and hint this effect may be related to the protection of brain microvascular endothelial cells (BMECs) that is dependent on the Nrf2 pathway. To further testify, we cultured hCMEC/D3 cells, duplicated OGD/R model to simulate ischemia, and used SLT (3.125, 6.25, and 12.5 mg/L) to treat. SLT dose dependently and significantly inhibited the drop in cell viabilities, and activated the Nrf2 pathway by facilitating Nrf2 nucleus translocation, and increasing HO-1 expression, SOD activity, and GSH content (compared with the model group, p < 0.05 or 0.01); last, the anti-OGD/R effects of SLT, including raising cell viabilities, inhibiting the elevation in dextran permeability, and preserving expressions of claudin-1 and occludin, were all abolished by Nrf2 siRNA interference. The in vitro experiment undoubtedly confirmed the direct protective effect of SLT on BMECs and the obligatory role of the Nrf2 pathway in it. Collectively, data of this study suggest that SLT’s therapeutic effect on brain ischemia is related to its Nrf2-dependent BMECs protection.

Microtubules as Major Regulators of Endothelial Function: Implication for Lung Injury

Endothelial dysfunction has been attributed as one of the major complications in COVID-19 patients, a global pandemic that has already caused over 4 million deaths worldwide. The dysfunction of endothelial barrier is characterized by an increase in endothelial permeability and inflammatory responses, and has even broader implications in the pathogenesis of acute respiratory syndromes such as ARDS, sepsis and chronic illnesses represented by pulmonary arterial hypertension and interstitial lung disease. The structural integrity of endothelial barrier is maintained by cytoskeleton elements, cell-substrate focal adhesion and adhesive cell junctions. Agonist-mediated changes in endothelial permeability are directly associated with reorganization of actomyosin cytoskeleton leading to cell contraction and opening of intercellular gaps or enhancement of cortical actin cytoskeleton associated with strengthening of endothelial barrier. The role of actin cytoskeleton remodeling in endothelial barrier regulation has taken the central stage, but the impact of microtubules in this process remains less explored and under-appreciated. This review will summarize the current knowledge on the crosstalk between microtubules dynamics and actin cytoskeleton remodeling, describe the signaling mechanisms mediating this crosstalk, discuss epigenetic regulation of microtubules stability and its nexus with endothelial barrier maintenance, and overview a role of microtubules in targeted delivery of signaling molecules regulating endothelial permeability and inflammation.

Rho GTPase signalling networks in cancer cell transendothelial migration

Rho GTPases are small signalling G-proteins that are central regulators of cytoskeleton dynamics, and thereby regulate many cellular processes, including the shape, adhesion and migration of cells. As such, Rho GTPases are also essential for the invasive behaviour of cancer cells, and thus involved in several steps of the metastatic cascade, including the extravasation of cancer cells. Extravasation, the process by which cancer cells leave the circulation by transmigrating through the endothelium that lines capillary walls, is an essential step for metastasis towards distant organs. During extravasation, Rho GTPase signalling networks not only regulate the transmigration of cancer cells but also regulate the interactions between cancer and endothelial cells and are involved in the disruption of the endothelial barrier function, ultimately allowing cancer cells to extravasate into the underlying tissue and potentially form metastases. Thus, targeting Rho GTPase signalling networks in cancer may be an effective approach to inhibit extravasation and metastasis. In this review, the complex process of cancer cell extravasation will be discussed in detail. Additionally, the roles and regulation of Rho GTPase signalling networks during cancer cell extravasation will be discussed, both from a cancer cell and endothelial cell point of view.

A Framework of Paracellular Transport via Nanoparticles-Induced Endothelial Leakiness

Nanomaterial-induced endothelial leakiness (NanoEL) is an interfacial phenomenon denoting the paracellular transport of nanoparticles that is pertinent to nanotoxicology, nanomedicine and biomedical engineering. While the NanoEL phenomenon is complementary to the enhanced permeability and retention effect in terms of their common applicability to delineating the permeability and behavior of nanoparticles in tumoral environments, these two effects significantly differ in scope, origin, and manifestation. In the current study, the descriptors are fully examined of the NanoEL phenomenon elicited by generic citrate-coated gold nanoparticles (AuNPs) of changing size and concentration, from microscopic gap formation and actin reorganization down to molecular signaling pathways and nanoscale interactions of AuNPs with VE-cadherin and its intra/extracellular cofactors. Employing synergistic in silico methodologies, for the first time the molecular and statistical mechanics of cadherin pair disruption, especially in response to AuNPs of the smallest size and highest concentration are revealed. This study marks a major advancement toward establishing a comprehensive NanoEL framework for complementing the understanding of the transcytotic pathway and for guiding the design and application of future nanomedicines harnessing the myriad functions of the mammalian vasculature.

Therapeutic antibodies - natural and pathological barriers and strategies to overcome them

Antibody-based therapeutics have become a major class of therapeutics with over 120 recombinant antibodies approved or under review in the EU or US. This therapeutic class has experienced a remarkable expansion with an expected acceleration in 2021-2022 due to the extraordinary global response to SARS-CoV2 pandemic and the public disclosure of over a hundred anti-SARS-CoV2 antibodies. Mainly delivered intravenously, alternative delivery routes have emerged to improve antibody therapeutic index and patient comfort. A major hurdle for antibody delivery and efficacy as well as the development of alternative administration routes, is to understand the different natural and pathological barriers that antibodies face as soon as they enter the body up to the moment they bind to their target antigen. In this review, we discuss the well-known and more under-investigated extracellular and cellular barriers faced by antibodies. We also discuss some of the strategies developed in the recent years to overcome these barriers and increase antibody delivery to its site of action. A better understanding of the biological barriers that antibodies have to face will allow the optimization of antibody delivery near its target. This opens the way to the development of improved therapy with less systemic side effects and increased patients' adherence to the treatment.

HIF-Overexpression and Pro-Inflammatory Priming in Human Mesenchymal Stromal Cells Improves the Healing Properties of Extracellular Vesicles in Experimental Crohn's Disease

Extracellular vesicles (EVs) derived from mesenchymal stromal cells (MSCs) have therapeutic potential in the treatment of several immune disorders, including ulcerative colitis, owing to their regenerative and immunosuppressive properties. We recently showed that MSCs engineered to overexpress hypoxia-inducible factor 1-alpha and telomerase (MSC-T-HIF) and conditioned with pro-inflammatory stimuli release EVs (EV_MSC-T-HIF^C) with potent immunomodulatory activity. We tested the efficacy of EV_MSC-T-HIF^C to repolarize M1 macrophages (Mφ1) to M2-like macrophages (Mφ2-like) by analyzing surface markers and cytokines and performing functional assays in co-culture, including efferocytosis and T-cell proliferation. We also studied the capacity of EV_MSC-T-HIF^C to dampen the inflammatory response of activated endothelium and modulate fibrosis. Finally, we tested the therapeutic capacity of EV_MSC-T-HIF^C in an acute colitis model. EV_MSC-T-HIF^c induced the repolarization of monocytes from Mφ1 to an Mφ2-like phenotype, which was accompanied by reduced inflammatory cytokine release. EV_MSC-T-HIF^c-treated Mφ1 had similar effects of immunosuppression on activated peripheral blood mononuclear cells (PBMC) as Mφ2, and reduced the adhesion of PBMCs to activated endothelium. EV_MSC-T-HIF^c also prevented myofibroblast differentiation of TGF-β-treated fibroblasts. Finally, administration of EV_MSC-T-HIF^c promoted healing in a TNBS-induced mouse colitis model in terms of preserving colon length and intestinal mucosa architecture and altering the ratio of Mφ1/ Mφ2 infiltration. In conclusion, EV_MSC-T-HIF^C have effective anti-inflammatory properties, making them potential therapeutic agents in cell free-based therapies for the treatment of Crohn’s disease and likely other immune-mediated inflammatory diseases.

EVL is a novel focal adhesion protein involved in the regulation of cytoskeletal dynamics and vascular permeability

Increases in lung vascular permeability is a cardinal feature of inflammatory disease and represents an imbalance in vascular contractile forces and barrier-restorative forces, with both forces highly dependent upon the actin cytoskeleton. The current study investigates the role of Ena-VASP-like (EVL), a member of the Ena-VASP family known to regulate the actin cytoskeleton, in regulating vascular permeability responses and lung endothelial cell barrier integrity. Utilizing changes in transendothelial electricial resistance (TEER) to measure endothelial cell barrier responses, we demonstrate that EVL expression regulates endothelial cell responses to both sphingosine-1-phospate (S1P), a vascular barrier-enhancing agonist, and to thrombin, a barrier-disrupting stimulus. Total internal reflection fluorescence demonstrates that EVL is present in endothelial cell focal adhesions and impacts focal adhesion size, distribution, and the number of focal adhesions generated in response to S1P and thrombin challenge, with the focal adhesion kinase (FAK) a key contributor in S1P-stimulated EVL-transduced endothelial cell but a limited role in thrombin-induced focal adhesion rearrangements. In summary, these data indicate that EVL is a focal adhesion protein intimately involved in regulation of cytoskeletal responses to endothelial cell barrier-altering stimuli.

Keywords: cytoskeleton, vascular barrier, sphingosine-1-phosphate, thrombin, focal adhesion kinase (FAK), Ena-VASP like protein (EVL), cytoskeletal regulatory protein

The Use of Tissue Engineering to Fabricate Perfusable 3D Brain Microvessels in vitro

Tissue engineering of the blood-brain barrier (BBB) in vitro has been rapidly expanding to address the challenges of mimicking the native structure and function of the BBB. Most of these models utilize 2D conventional microfluidic techniques. However, 3D microvascular models offer the potential to more closely recapitulate the cytoarchitecture and multicellular arrangement of in vivo microvasculature, and also can recreate branching and network topologies of the vascular bed. In this perspective, we discuss current 3D brain microvessel modeling techniques including templating, printing, and self-assembling capillary networks. Furthermore, we address the use of biological matrices and fluid dynamics. Finally, key challenges are identified along with future directions that will improve development of next generation of brain microvasculature models.

Design considerations for engineering 3D models to study vascular pathologies in vitro

Many cardiovascular diseases (CVD) are driven by pathological remodelling of blood vessels, which can lead to aneurysms, myocardial infarction, ischaemia and strokes. Aberrant remodelling is driven by changes in vascular cell behaviours combined with degradation, modification, or abnormal deposition of extracellular matrix (ECM) proteins. The underlying mechanisms that drive the pathological remodelling of blood vessels are multifaceted and disease specific; however, unravelling them may be key to developing therapies. Reductionist models of blood vessels created in vitro that combine cells with biomaterial scaffolds may serve as useful analogues to study vascular disease progression in a controlled environment. This review presents the main considerations for developing such in vitro models. We discuss how the design of blood vessel models impacts experimental readouts, with a particular focus on the maintenance of normal cellular phenotypes, strategies that mimic normal cell-ECM interactions, and approaches that foster intercellular communication between vascular cell types. We also highlight how choice of biomaterials, cellular arrangements and the inclusion of mechanical stimulation using fluidic devices together impact the ability of blood vessel models to mimic in vivo conditions. In the future, by combining advances in materials science, cell biology, fluidics and modelling, it may be possible to create blood vessel models that are patient-specific and can be used to develop and test therapies. STATEMENT OF SIGNIFICANCE: Simplified models of blood vessels created in vitro are powerful tools for studying cardiovascular diseases and understanding the mechanisms driving their progression. Here, we highlight the key structural and cellular components of effective models and discuss how including mechanical stimuli allows researchers to mimic native vessel behaviour in health and disease. We discuss the primary methods used to form blood vessel models and their limitations and conclude with an outlook on how blood vessel models that incorporate patient-specific cells and flows can be used in the future for personalised disease modelling.

The Disruption of the Endothelial Barrier Contributes to Acute Lung Injury Induced by Coxsackievirus A2 Infection in Mice

Sporadic occurrences and outbreaks of hand, foot, and mouth disease (HFMD) caused by Coxsackievirus A2 (CVA2) have frequently reported worldwide recently, which pose a great challenge to public health. Epidemiological studies have suggested that the main cause of death in critical patients is pulmonary edema. However, the pathogenesis of this underlying comorbidity remains unclear. In this study, we utilized the 5-day-old BALB/c mouse model of lethal CVA2 infection to evaluate lung damage. We found that the permeability of lung microvascular was significantly increased after CVA2 infection. We also observed the direct infection and apoptosis of lung endothelial cells as well as the destruction of tight junctions between endothelial cells. CVA2 infection led to the degradation of tight junction proteins (e.g., ZO-1, claudin-5, and occludin). The gene transcription levels of von Willebrand factor (vWF), endothelin (ET), thrombomodulin (THBD), granular membrane protein 140 (GMP140), and intercellular cell adhesion molecule-1 (ICAM-1) related to endothelial dysfunction were all significantly increased. Additionally, CVA2 infection induced the increased expression of inflammatory cytokines (IL-6, IL-1β, and MCP-1) and the activation of p38 mitogen-activated protein kinase (MAPK). In conclusion, the disruption of the endothelial barrier contributes to acute lung injury induced by CVA2 infection; targeting p38-MAPK signaling may provide a therapeutic approach for pulmonary edema in critical infections of HFMD.

Beneficial Effects of Transplanted Human Bone Marrow Endothelial Progenitors on Functional and Cellular Components of Blood-Spinal Cord Barrier in ALS Mice

Convincing evidence of blood-spinal cord barrier (BSCB) alterations has been demonstrated in amyotrophic lateral sclerosis (ALS) and barrier repair is imperative to prevent motor neuron dysfunction. We showed benefits of human bone marrow-derived CD34+ cells (hBM34+) and endothelial progenitor cells (hBM-EPCs) intravenous transplantation into symptomatic G93A SOD1 mutant mice on barrier reparative processes. These gains likely occurred by replacement of damaged endothelial cells, prolonging motor neuron survival. However, additional investigations are needed to confirm the effects of administered cells on integrity of the microvascular endothelium. The aim of this study was to determine tight junction protein levels, capillary pericyte coverage, microvascular basement membrane, and endothelial filamentous actin (F-actin) status in spinal cord capillaries of G93A SOD1 mutant mice treated with human bone marrow-derived stem cells. Tight junction proteins were detected in the spinal cords of cell-treated versus non-treated mice via Western blotting at four weeks after transplant. Capillary pericyte, basement membrane laminin, and endothelial F-actin magnitudes were determined in cervical/lumbar spinal cord tissues in ALS mice, including controls, by immunohistochemistry and fluorescent staining. Results showed that cell-treated versus media-treated ALS mice substantially increased tight junction protein levels, capillary pericyte coverage, basement membrane laminin immunoexpressions, and endothelial cytoskeletal F-actin fluorescent expressions. The greatest benefits were detected in mice receiving hBM-EPCs versus hBM34+ cells. These study results support treatment with a specific cell type derived from human bone marrow toward BSCB repair in ALS. Thus, hBM-EPCs may be advanced for clinical applications as a cell-specific approach for ALS therapy through restored barrier integrity.

Variable fluid flow regimes alter human brain microvascular endothelial cell-cell junctions and cytoskeletal structure

The human brain microvasculature is constantly exposed to variable fluid flow regimes and their influence on the endothelium depends in part on the synchronous cooperative behavior between cell-cell junctions and the cytoskeleton. In this study, we exposed human cerebral microvascular endothelial cells to a low laminar flow (1 dyne⋅cm^-2 ), high laminar flow (10 dyne⋅cm^-2 ), low oscillatory flow (±1 dyne⋅cm^-2 ), or high oscillatory flow (±10 dyne⋅cm^-2 ) for 24 hr. After this time, endothelial cell-cell junction and cytoskeletal structural response was characterized through observation of zonula occludens-1 (ZO-1), claudin-5, junctional adhesion molecule-A (JAM-A), vascular endothelial cadherin (VE-Cad), and F-actin. In addition, we also characterized cell morphology through measurement of cell area and cell eccentricity. Our results revealed the greatest change in junctional structure reorganization for ZO-1 and JAM-A to be observed under low laminar flow conditions while claudin-5 exhibited the greatest change in structural reorganization under both low and high laminar flow conditions. However, VE-Cad displayed the greatest structural response under a high laminar flow, reflecting the unique responses each cell-cell junction protein had to each fluid flow regime. In addition, cell area and cell eccentricity displayed most significant changes under the high laminar flow and low oscillatory flow, respectively. We believe this study will be useful to the field of cell mechanics and mechanobiology.

Therapeutic targets and nanomaterial-based therapies for mitigation of secondary injury after spinal cord injury

Spinal cord injury (SCI) and the resulting neurological trauma commonly result in complete or incomplete neurological dysfunction and there are few effective treatments for primary SCI. However, the following secondary SCI, including the changes of microvasculature, inflammatory response and oxidative stress around the injury site, may provide promising therapeutic targets. The advances of nanomaterials hold promise for delivering therapeutics to alleviate secondary SCI and promote functional recovery. In this review, we highlight recent achievements of nanomaterial-based therapy, specifically targeting blood-spinal cord barrier disruption, mitigation of the inflammatory response and lightening of oxidative stress after spinal cord injury.

Endothelial barrier function is co-regulated at vessel bifurcations by fluid forces and sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid mediator of endothelial barrier function. Prior studies have implicated mechanical stimulation due to intravascular laminar shear stress in co-regulating S1P signaling in endothelial cells (ECs). Yet, vascular networks in vivo consist of vessel bifurcations, and this geometry generates hemodynamic forces at the bifurcation point distinct from laminar shear stress. However, the role of these forces at vessel bifurcations in regulating S1P-dependent endothelial barrier function is not known. In this study, we implemented a microfluidic platform that recapitulates the flow dynamics of vessel bifurcations with in situ quantification of the permeability of microvessel analogues. Co-application of S1P with impinging bifurcated fluid flow, which is characterized by approximately zero shear stress and 38 dyn•cm-2 stagnation pressure at the vessel bifurcation point, promotes vessel stabilization. Similarly, co-treatment of S1P with 3 dyn•cm-2 laminar shear stress is also protective of endothelial barrier function. Moreover, it is shown that vessel stabilization due to bifurcated fluid flow and laminar shear stress is dependent on S1P receptor 1 or 2 signaling. Collectively, these findings demonstrate the endothelium-protective function of fluid forces at vessel bifurcations and their involvement in coordinating S1P-dependent regulation of vessel permeability.

Strategies to Attenuate Myocardial Infarction and No-Reflow Through Preservation of Vascular Integrity by Pigment Epithelium-Derived Factor

The phenomenon of no-reflow seriously limits the therapeutic value of coronary recanalization and leads to poor prognosis. Recent studies have demonstrated the potential role of pigment epithelium-derived factor (PEDF) in stabilizing endothelial cell junction, reducing vascular permeability and maintaining a quiescent vasculature. In this study, intramyocardial gene delivery was performed 5 days before the acute myocardial infarction/recanalization experiment in male rats. Positron emission tomography perfusion imaging with ¹³N-NH₃ indicated PEDF to promote microvascular reperfusion significantly 4 h postcoronary occlusion. PEDF was observed to maintain the stability of endothelial adherens junctions (AJs), thus preventing the occurrence of no-reflow. PEDF reduced the hypoxia-induced vascular endothelial (VE)-cadherin endocytosis through PEDF/LR/Src/VE-cadherin S665 axis in vitro, which was remarkably observed to maintain endothelial AJs. Generally, PEDF might function as a relevant target for therapeutic vasculoprotection by way of regulating the phosphorylation level of VE-cadherin according to our data, thus being crucial for preventing no-reflow.

Circular Ribonucleic Acid circFTO Promotes Angiogenesis and Impairs Blood-Retinal Barrier Via Targeting the miR-128-3p/Thioredoxin Interacting Protein Axis in Diabetic Retinopathy

Background: Increasing attention has been attracted by the role of circular RNAs (circRNAs) in ocular diseases. Previous study has revealed that circ_0005941 (also known as circFTO, an alpha-ketoglutarate-dependent dioxygenase) was upregulated in the vitreous humor of diabetic retinopathy (DR), while its underlying mechanism in DR remains unknown. Methods: Retinal vascular endothelial cells (RVECs) treated with high glucose (HG) were used to establish the DR cell model. The in vivo assays were conducted using streptozotocin-induced diabetic mice. The circular structure and stability of circFTO were identified by Sanger sequencing and RNase R treatment. RT-qPCR analysis was used to detect the RNA expression. The levels of the mRNA-encoded protein thioredoxin-interacting protein (TXNIP) or angiogenesis-associated proteins (VEGFA, PDGF, and ANG2) and blood-retinal barrier (BRB)-related proteins (ZO-1, Occludin, and Claudin-5) were measured by Western blot. The viability of RVECs was measured using CCK-8 assays. The angiogenesis of RVECs was assessed using tube formation assays in vitro. Endothelial permeability assays were conducted to examine the function of the BRB. The binding between genes was explored using RNA pulldown and luciferase reporter assays. Results: CircFTO was upregulated in HG-treated RVECs. CircFTO deficiency reversed the HG-induced increase in the viability and angiogenesis of RVECs and alleviated HG-mediated impairment of the BRB. MiR-128-3p bound with circFTO and was downregulated in HG-treated RVECs. TXNIP was a downstream target gene of miR-128-3p. TXNIP was highly expressed in the DR cell model. Rescue assays revealed that circFTO promoted angiogenesis and impaired the blood-retinal barrier by upregulating TXNIP. In the DR mouse model, circFTO silencing inhibited angiogenesis and promoted BRB recovery in vivo. Conclusion: CircFTO promotes angiogenesis and impairs the blood-retinal barrier in vitro and in vivo by binding with miR-128-3p to upregulate TXNIP in DR.

A designer cell culture insert with a nanofibrous membrane toward engineering an epithelial tissue model validated by cellular nanomechanics

Engineered platforms for culturing cells of the skin and other epithelial tissues are useful for the regeneration and development of in vitro tissue models used in drug screening. Recapitulating the biomechanical behavior of the cells is one of the important hallmarks of successful tissue generation on these platforms. The biomechanical behavior of cells profoundly affects the physiological functions of the generated tissue. In this work, a designer nanofibrous cell culture insert (NCCI) device was developed, consisting of a free-hanging polymeric nanofibrous membrane. The free-hanging nanofibrous membrane has a well-tailored architecture, stiffness, and topography to better mimic the extracellular matrix of any soft tissue than conventional, flat tissue culture polystyrene (TCPS) surfaces. Human keratinocytes (HaCaT cells) cultured on the designer NCCIs exhibited a 3D tissue-like phenotype compared to the cells cultured on TCPS. Furthermore, the biomechanical characterization by bio-atomic force microscopy (Bio-AFM) revealed a markedly altered cellular morphology and stiffness of the cellular cytoplasm, nucleus, and cell-cell junctions. The nuclear and cytoplasmic moduli were reduced, while the stiffness of the cellular junctions was enhanced on the NCCI compared to cells on TCPS, which are indicative of the fluidic state and migratory phenotype on the NCCI. These observations were corroborated by immunostaining, which revealed enhanced cell-cell contact along with a higher expression of junction proteins and enhanced migration in a wound-healing assay. Taken together, these results underscore the role of the novel designer NCCI device as an in vitro platform for epithelial cells with several potential applications, including drug testing, disease modeling, and tissue regeneration.

Platelet-derived growth factor B restores vascular barrier integrity and diminishes permeability in ovarian hyperstimulation syndrome

Although advances in the prediction and management of ovarian hyperstimulation syndrome (OHSS) have been introduced, complete prevention is not yet possible. Previously, we and other authors have shown that vascular endothelial growth factor, angiopoietins (ANGPTs) and sphingosine-1-phosphate are involved in OHSS etiology. In addition, we have demonstrated that ovarian protein levels of platelet-derived growth factor (PDGF) ligands -B and -D decrease in an OHSS rat model, whilst PDGFR-β and ANGPT2 remain unchanged. In the present work, we investigated the role of PDGF-B in OHSS by evaluating ligand protein levels in follicular fluid (FF) from women at risk of developing OHSS and by using an immature rat model of OHSS. We demonstrated that PDGF-B and PDGF-D are lower in FF from women at risk of developing OHSS compared to control patients (P < 0.05). In the OHSS rat model, PDGF-B (0.5 µg/ovary) administration decreased ovarian weight (P < 0.05), reduced serum progesterone (P < 0.05) and lowered the percentage of cysts (P < 0.05), compared to untreated OHSS rats, but had no effect on the proportion of follicles or corpora lutea (CL). PDGF-B treatment also restored the expression of steroidogenic acute regulatory protein (P < 0.05) and P450 cholesterol side-chain cleavage enzyme (P < 0.01) to control levels. In addition, PDGF-B increased the peri-endothelial cell area in CL and cystic structures, and reduced vascular permeability compared to untreated OHSS ovaries. Lastly, PDGF-B increased the levels of junction proteins claudin-5 (P < 0.05), occludin (P < 0.05) and β-catenin (P < 0.05), while boosting the extracellular deposition of collagen IV surrounding the ovarian vasculature (PP < 0.01), compared to OHSS alone. In conclusion, our findings indicate that PDGF-B could be another crucial mediator in the onset and development of OHSS, which may lead to the development of novel prediction markers and therapeutic strategies.

Directed movement toward, translocation along, penetration into and exit from vascular networks by breast cancer cells in 3D

We developed a computer-assisted platform using laser scanning confocal microscopy to 3D reconstruct in real-time interactions between metastatic breast cancer cells and human umbilical vein endothelial cells (HUVECs). We demonstrate that MB-231 cancer cells migrate toward HUVEC networks, facilitated by filopodia, migrate along the network surfaces, penetrate into and migrate within the HUVEC networks, exit and continue migrating along network surfaces. The system is highly amenable to 3D reconstruction and computational analyses, and assessments of the effects of potential anti-metastasis monoclonal antibodies and other drugs. We demonstrate that an anti-RHAMM antibody blocks filopodium formation and all of the behaviors that we found take place between MB-231 cells and HUVEC networks.

Fermitin family homolog 2 (Kindlin-2) affects vascularization during the wound healing process by regulating the Wnt/β-catenin signaling pathway in vascular endothelial cells

Kindlin-2 is a member of the FERM-containing cytoskeletal protein family that regulates cell–matrix interactions. Previous studies have shown that Kindlin-2 recruits focal adhesion proteins and regulates integration by binding to the focal adhesion region of the integrin β-segment. Although Kindlin-2 has been reported to be involved in various skin diseases and many kinds of tumors, its role in the skin wound healing process remains unclear. The aim of the present study was to investigate the role of Kindlin-2 in the regulation of wound healing. The effects of Kindlin-2 on wound healing were studied by a wound healing model, kindlin-2 (±) mice. The effects of Kindlin-2 on cell migration, cellular tube formation, and cell adhesion and spreading were evaluated in human umbilical vein endothelial cells (HUVECs) with downregulated Kindlin-2 expression. We found that the expression of kindlin-2 was elevated in wound healing tissues and that interfering with the expression of Kindlin-2 delayed the wound healing process and reduced neovascularization. We found that the wound healing of kindlin-2 (±) mice was delayed, with a decreased number of new blood vessels. Furthermore, depletion of Kindlin-2 impaired HUVEC spreading, migration and tube formation. Intriguingly, we found that kindlin-2 binds to β-catenin in the Wnt/β-catenin signaling pathway and cooperates with β-catenin to enter the nucleus from the cytoplasm, activating the downstream Wnt/β-catenin signaling pathway. Taken together, these results help to elucidate the mechanism of Kindlin-2 in the regulation of the wound healing process and provide a theoretical basis for further study of wound healing and abnormal healing.

Development of Novel Therapeutics Targeting the Blood-Brain Barrier: From Barrier to Carrier

The blood-brain barrier (BBB) is a highly specialized neurovascular unit, initially described as an intact barrier to prevent toxins, pathogens, and potentially harmful substances from entering the brain. An intact BBB is also critical for the maintenance of normal neuronal function. In cerebral vascular diseases and neurological disorders, the BBB can be disrupted, contributing to disease progression. While restoration of BBB integrity serves as a robust biomarker of better clinical outcomes, the restrictive nature of the intact BBB presents a major hurdle for delivery of therapeutics into the brain. Recent studies show that the BBB is actively engaged in crosstalk between neuronal and the circulatory systems, which defines another important role of the BBB: as an interfacing conduit that mediates communication between two sides of the BBB. This role has been subject to extensive investigation for brain-targeted drug delivery and shows promising results. The dual roles of the BBB make it a unique target for drug development. Here, recent developments and novel strategies to target the BBB for therapeutic purposes are reviewed, from both barrier and carrier perspectives.

HSPA12A improves endothelial integrity to attenuate lung injury during endotoxemia through activating ERKs and Akt-dependent signaling

Acute lung injury (ALI) is a critical manifestation of sepsis/septic shock. Disruption of endothelial barrier function is critical for ALI pathogenesis; however, the regulation of endothelial barrier integrity remains largely unclear. Heat shock protein A12A (HSPA12A) is an atypical member of HSP70 family. We have recently demonstrated that hepatocyte HSPA12A attenuated the bacteria endotoxin (lipopolysaccharide, LPS)-induced liver injury. However, the role of HSPA12A in endothelial barrier function and ALI is unknown. Here in this study, HSPA12A showed upregulation in lungs of mice during bacteria endotoxin (lipopolysaccharide, LPS)-induced lung injury in vivo and in primary human umbilical vein endothelial cells (HUVECs) during LPS-induced barrier disruption in vitro. Knockout of HSPA12A in mice exacerbated LPS-induced ALI. Intriguingly, overexpression of HSPA12A in HUVECs attenuated the LPS-induced endothelial hyperpermeability. In line with this, HSPA12A overexpression increased VE-cadherin and decreased VEGF expression following LPS treatment in HUVECs. Also, knockout of HSPA12A enhanced the LPS-evoked pulmonary endothelial cell apoptosis in mice whereas overexpression of HSPA12A inhibited the LPS-induced death of HUVECs. The levels of ERKs and Akt phosphorylation in HUVECs were promoted by HSPA12A overexpression when cells exposed to LPS. Importantly, inhibition of either ERKs or Akt diminished the HSPA12A-induced protection from LPS-induced endothelial hyperpermeability and death. Taken together, these findings indicated that HSPA12A is a novel regulator of endothelial barrier function through both ERKs and Akt-mediated signaling. HSPA12A might represent a viable strategy for the pulmonary protection against endotoxemia challenge.

Secretome and Tunneling Nanotubes: A Multilevel Network for Long Range Intercellular Communication between Endothelial Cells and Distant Cells

As a cellular interface between the blood and tissues, the endothelial cell (EC) monolayer is involved in the control of key functions including vascular tone, permeability and homeostasis, leucocyte trafficking and hemostasis. EC regulatory functions require long-distance communications between ECs, circulating hematopoietic cells and other vascular cells for efficient adjusting thrombosis, angiogenesis, inflammation, infection and immunity. This intercellular crosstalk operates through the extracellular space and is orchestrated in part by the secretory pathway and the exocytosis of Weibel Palade Bodies (WPBs), secretory granules and extracellular vesicles (EVs). WPBs and secretory granules allow both immediate release and regulated exocytosis of messengers such as cytokines, chemokines, extracellular membrane proteins, coagulation or growth factors. The ectodomain shedding of transmembrane protein further provide the release of both receptor and ligands with key regulatory activities on target cells. Thin tubular membranous channels termed tunneling nanotubes (TNTs) may also connect EC with distant cells. EVs, in particular exosomes, and TNTs may contain and transfer different biomolecules (e.g., signaling mediators, proteins, lipids, and microRNAs) or pathogens and have emerged as a major triggers of horizontal intercellular transfer of information.

Effects of cannabinoid (CBD) on blood brain barrier permeability after brain injury in rats

Cannabidiol is a natural herbal medicine known to protect the brain from traumatic brain injury (TBI). Here, a TBI rat model was established, with cannabidiol administered intraperitoneally at doses of 5, 10, or 20 mg/kg, 30 min before surgery and 6 h after surgery until sacrifice. Brain water content, body weight, and modified neurological severity scores were determined, and enzyme-linked immunosorbent assay, immunofluorescence staining, hematoxylin and eosin staining, Nissl staining, Evans-blue dye extravasation, and western blotting were performed. Results showed that cannabidiol decreased the number of aquaporin-4-positive and glial fibrillary acidic protein-positive cells. Cannabidiol also significantly reduced the protein levels of proinflammatory cytokines (TNF-α and IL-1β) and significantly increased the expression of tight junction proteins (claudin-5 and occludin). Moreover, cannabidiol administration significantly mitigated water content in the brain after TBI and blood-brain barrier disruption and ameliorated the neurological deficit score after TBI. Cannabidiol administration improved the integrity and permeability of the blood-brain barrier and reduced edema in the brain after TBI.

Trends in liposomal nanocarrier strategies for the oral delivery of biologics

The number of approved macromolecular drugs such as peptides, proteins and antibodies steadily increases. Since drugs with high molecular weight are commonly not suitable for oral delivery, research on carrier strategies enabling oral administration is of vital interest. In past decades, nanocarriers, in particular liposomes, have been exhaustively investigated as oral drug-delivery platform. Despite their successful application as parenteral delivery vehicles, liposomes have up to date not succeeded for oral administration. However, a plenitude of approaches aiming to increase the oral bioavailability of macromolecular drugs administered by liposomal formulations has been published. Here, we summarize the strategies published in the last 10 years (vaccine strategies excluded) with a main focus on strategies proven efficient in animal models.

Involvement of noncoding RNA in blood-brain barrier integrity in central nervous system disease

Given the important role of the blood-brain barrier (BBB) in the central nervous system (CNS), increasing studies have been carried out to determine how the structural and functional integrity of the BBB impacts the pathogenesis of CNS diseases such as stroke, traumatic brain injuries (TBIs), and gliomas. Emerging studies have revealed that noncoding RNAs (ncRNAs) help to maintain the integrity and permeability of the BBB, thereby mediating CNS homeostasis. This review summarizes recent studies that focus on the effects of ncRNAs on the BBB in CNS diseases, including regulating the biological processes of inflammation, necrosis, and apoptosis of cells, affecting the translational dysfunction of proteins and regulating tight junctions (TJs). A comprehensive and detailed understanding of the interaction between ncRNAs and the BBB will lay a solid foundation for the development of early diagnostic methods and effective treatments for CNS diseases.

Proteomic and Biological Analysis of an In Vitro Human Endothelial System in Response to Drug Anaphylaxis

Anaphylaxis is a life-threatening systemic hypersensitivity reaction. During anaphylaxis, mediator release by effector cells causes endothelial barrier breakdown, increasing vascular permeability and leakage of fluids, which may lead to tissue edema. Although endothelial cells (ECs) are key players in this context, scant attention has been paid to the molecular analysis of the vascular system, and further analyses of this cell type are necessary, especially in humans. The protein expression pattern of human microvascular ECs was analyzed in response to sera from anaphylactic patients (EC-anaphylaxis) and sera from non-allergic subjects (EC-control) after 2 hours of contact. Firstly, a differential quantitative proteomic analysis of the protein extracts was performed by mass spectrometry using an isobaric labeling method. Second, the coordinated behavior of the identified proteins was analyzed using systems biology analysis (SBA). The proteome of the EC-anaphylaxis system showed 7,707 proteins, of which 1,069 were found to be significantly altered between the EC-control and EC-anaphylaxis groups (p-value < 0.05). Among them, a subproteome of 47 proteins presented a high rate of change (|ΔZq| ≥ 3). This panel offers an endothelial snapshot of the anaphylactic reaction. Those proteins with the highest individual changes in abundance were hemoglobin subunits and structural support proteins. The interacting network analysis of this altered subproteome revealed that the coagulation and complement systems are the main biological processes altered in the EC-anaphylactic system. The comprehensive SBA resulted in 5,512 functional subcategories (biological processes), 57 of which were significantly altered between EC-control and EC-anaphylaxis. The complement system, once again, was observed as the main process altered in the EC system created with serum from anaphylactic patients. Findings of the current study further our understanding of the underlying pathophysiological mechanisms operating in anaphylactic reactions. New target proteins and relevant signaling pathways operating in the in vitro endothelial-serum system have been identified. Interestingly, our results offer a protein overview of the micro-EC-anaphylaxis environment. The relevance of the coagulation, fibrinolytic, contact and complement systems in human anaphylaxis is described. Additionally, the untargeted high-throughput analysis used here is a novel approach that reveals new pathways in the study of the endothelial niche in anaphylaxis.

Baicalin Protects Vascular Tight Junctions in Piglets During Glaesserella parasuis Infection

Glaesserella parasuis (G. parasuis) can cause Glässer's disease and severely affect swine industry worldwide. This study is an attempt to address the issue of the capability of G. parasuis to damage the vascular barrier and the effects of baicalin on vascular tight junctions (TJ) in order to investigate the interactions between the pathogen and the porcine vascular endothelium. Piglets were challenged with G. parasuis and treated with or without baicalin. The expressions of vascular TJ genes were examined using RT-PCR. The distribution patterns of TJ proteins were detected by immunofluorescence. The involved signaling pathways were determined by Western blot assays on related proteins. G. parasuis can downregulate TJ expression and disrupt the distribution of TJ proteins. Baicalin can alleviate the downregulation of vascular TJ mRNA, maintain the distribution, and prevent the abnormalities of TJ. These results provide ample evidence that baicalin has the capacity to protect vascular TJ damaged by G. parasuis through inhibiting PKC and MLCK/MLC pathway activation. As a result, baicalin is a promising candidate for application as a natural agent for the prevention and control of G. parasuis infection.

Mechanical Fingerprint of Senescence in Endothelial Cells

Endothelial senescence entails alterations of the healthy cell phenotype, which accumulate over time and contribute to cardiovascular disease. Mechanical aspects regulating cell adhesion, force generation, and the response to flow contribute to the senescence-associated drift; however, they remain largely unexplored. Here, we exploit force microscopy to resolve variations of the cell anchoring to the substrate and the tractions generated upon aging in the nanonewton (nN) range. Senescent endothelial cells display a multifold increase in the levels of basal adhesion and force generation supported by mature and strong focal adhesions. The enhanced mechanical interaction with the substrate yields static endothelial monolayers that polarize in response to flow but fail the process of coordinated cell shape remodeling and reorientation. The emerging picture indicates that senescence reinforces the local cell interaction with the substrate and may therefore prevent endothelial denudation; however, it compromises the ability to functionally adapt to the local hemodynamic conditions.

Regulation of angiogenesis by microRNAs in cancer

MicroRNAs (miRs) are endogenous, small, non‑coding RNA molecules with ~22 nucleotides, and are involved in regulating the expression of multiple genes and controlling cellular functions. miRs serve key roles in angiogenesis by regulating the proliferation, differentiation, apoptosis and migration of endothelial cells. Regulation of angiogenesis is essential for several physiological and pathological processes, particularly for tumor development and progression. Therefore, it is important to investigate the roles served by miRs in angiogenesis as this may aid in discovering novel strategies for treating tumors via modulating angiogenesis. In this review, miRNA biogenesis, regulation and functions are described with new information and corresponding references. In particular, the latest advances in the role of various miRs and their target genes involved in tumor angiogenesis were updated. Next, different signaling pathways by which miRNAs could be regulated in different types of tumor progression were addressed. Furthermore, the potential clinical value of miRs as biomarkers for diagnosing and monitoring the response to therapy, as well as their ability to regulate tumor angiogenesis and the mechanism underlying this regulation, were investigated.

Resveratrol and endothelial function: A literature review

Endothelial dysfunction is a major contributing factor to diseases such as atherosclerosis, diabetes mellitus, obesity, hypertension, acute lung injury, preeclampsia, among others. Resveratrol (RSV) is a naturally occurring bioactive polyphenol found in grapes and red wine. According to experimental studies, RSV modulates several events involved in endothelial dysfunction such as impaired vasorelaxation, eNOS uncoupling, leukocyte adhesion, endothelial senescence, and endothelial mesenchymal transition. The endothelial protective effects of RSV are found to be mediated by numerous molecular targets (e.g. Silent Information Regulator 1 (SIRT1), 5' AMP-activated protein kinase (AMPK), endothelial nitric oxide synthase (eNOS), nuclear factor-erythroid-derived 2-related factor-2 (Nrf2), peroxisome proliferator-activated receptor (PPAR), Krüppel-like factor-2 (KLF2), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB)). Herein, we present an updated review addressing pharmacological effects and molecular targets of RSV in maintaining endothelial function, and the potential of this phytochemical for endothelial dysfunction-associated disorders.

Role of Intermediate Filaments in Blood-Brain Barrier in Health and Disease

The blood–brain barrier (BBB) is a highly selective cellular monolayer unique to the microvasculature of the central nervous system (CNS), and it mediates the communication of the CNS with the rest of the body by regulating the passage of molecules into the CNS microenvironment. Limitation of passage of substances through the BBB is mainly due to tight junctions (TJ) and adherens junctions (AJ) between brain microvascular endothelial cells. The importance of actin filaments and microtubules in establishing and maintaining TJs and AJs has been indicated; however, recent studies have shown that intermediate filaments are also important in the formation and function of cell–cell junctions. The most common intermediate filament protein in endothelial cells is vimentin. Vimentin plays a role in blood–brain barrier permeability in both cell–cell and cell–matrix interactions by affecting the actin and microtubule reorganization and by binding directly to VE-cadherin or integrin proteins. The BBB permeability increases due to the formation of stress fibers and the disruption of VE–cadherin interactions between two neighboring cells in various diseases, disrupting the fiber network of intermediate filament vimentin in different ways. Intermediate filaments may be long ignored key targets in regulation of BBB permeability in health and disease.

Primaquine Diphosphate, a Known Antimalarial Drug, Blocks Vascular Leakage Acting Through Junction Stabilization

Endothelial barrier integrity is important for vascular homeostasis, and hyperpermeability participates in the progression of many pathological states, such as diabetic retinopathy, ischemic stroke, chronic bowel disease, and inflammatory disease. Here, using drug repositioning, we discovered that primaquine diphosphate (PD), previously known as an antimalarial drug, was a potential blocker of vascular leakage. PD inhibited the linear pattern of vascular endothelial growth factors (VEGF)-induced disruption at the cell boundaries, blocked the formation of VEGF-induced actin stress fibers, and stabilized the cortactin actin rings in endothelial cells. PD significantly reduced leakage in the Miles assay and mouse model of streptozotocin (STZ)-induced diabetic retinopathy. Targeted prediction programs and deubiquitinating enzyme activity assays identified a potential mechanism of action for PD and demonstrated that this operates via ubiquitin specific protease 1 (USP1). USP1 inhibition demonstrated a conserved barrier function by inhibiting VEGF-induced leakage in endothelial permeability assays. Taken together, these findings suggest that PD could be used as a novel drug for vascular leakage by maintaining endothelial integrity.