Regulation of endothelial junctional permeability

Circulating Extracellular Vesicles Carry Immune Regulatory miRNAs and Regulate Vaccine Efficacy and Local Inflammatory Response After Vaccination

Vaccination is the best prophylaxis for the prevention of infectious diseases, including coronavirus disease 2019. However, the efficacy of vaccines and onset of adverse reactions vary among individuals. Circulating extracellular vesicles (EVs) regulate the immune responses after vaccination by delivering microRNAs (miRNAs) to myeloid and lymphoid cells. Among these, miR-192 levels in serum EVs increase with aging, in an IL-6-dependent manner, reducing excessive IL-6 expression in aged mice, creating a negative feedback loop. Excessive IL-6 expression reduces vaccination efficacy in aged mice, while EV miR-192 improves efficacy in these aged mice as well, making this miRNA an interesting focus of study. miR-21 levels in serum EVs also increase with aging, and regulates the expression of IL-12 required for Th1 responses; therefore, EV miR-21 is expected to regulate vaccine efficacy. miR-451a, another important miRNA, is abundant in serum EVs and controls the expression of cytokines, such as type I interferon and IL-6. However, levels differ among individuals and correlate with local inflammatory symptoms experienced after a seasonal flu vaccination. These findings suggest the importance of EV miRNAs as a tool to improve vaccine efficacy and also as biomarkers to predict the immune response and adverse reactions after vaccinations.

PEA prevented early BBB disruption after cerebral ischaemic/reperfusion (I/R) injury through regulation of ROCK/MLC signaling

Palmitoylethanolamide (PEA) offers a strong protection against BBB disruption and neurological deficits after cerebral ischaemic/reperfusion (I/R) injury. To date, these BBB protective effects of PEA are mainly attributed to PPARα-mediated actions. However, whether PEA protects against BBB disruption through direct regulation of cytoskeletal microfilaments remains unknown. Here, we identified PEA as a Rho-associated protein kinase (ROCK2) inhibitor (IC₅₀ = 38.4 ± 4.8 μM). In vitro data suggested that PEA reduced the activation of ROCK/MLC signaling and stress fiber formation within microvascular endothelial cells (ECs) after oxygen-glucose deprivation (OGD), and consequently attenuated early (0-4 h) EC barrier disruption. These actions of PEA could not be blocked by the PPARα antagonist GW6471. In summary, the present study described a previously unexplored role of PEA as a ROCK2 inhibitor, and propose a PPARα-independent mechanism for pharmacological effects of PEA.

Flavonoids and cellular stress: a complex interplay affecting human health

Flavonoid consumption has beneficial effects on human health, however, clinical evidence remains often inconclusive due to high interindividual variability. Although this high interindividual variability has been consistently observed in flavonoid research, the potential underlying reasons are still poorly studied. Especially the knowledge on the impact of health status on flavonoid responsiveness is limited and merits more investigation. Here, we aim to highlight the bidirectional interplay between flavonoids and cellular stress. First, the state-of-the-art concerning inflammatory stress and mitochondrial dysfunction is reviewed and a comprehensive overview of recent in vitro studies investigating the impact of flavonoids on cellular stress, induced by tumor necrosis factor α, lipopolysaccharide and mitochondrial stressors, is given. Second, we critically discuss the influence of cellular stress on flavonoid uptake, accumulation, metabolism and cell responses, which has, to our knowledge, never been extensively reviewed before. Next, we advocate the innovative insight that stratification of the general population based on health status can reveal subpopulations that benefit more from flavonoid consumption. Finally, suggestions are given for the development of future cell models that simulate the physiological micro-environment, including interindividual variability, since more mechanistic research is needed to establish scientific-based personalized food recommendations for specific subpopulations.

Role of Junctional Adhesion Molecule-C in the Regulation of Inner Endothelial Blood-Retinal Barrier Function

Although JAM-C is abundantly expressed in the retinae and upregulated in choroidal neovascularization (CNV), it remains thus far poorly understood whether it plays a role in the blood-retinal barrier, which is critical to maintain the normal functions of the eye. Here, we report that JAM-C is highly expressed in retinal capillary endothelial cells (RCECs), and VEGF or PDGF-C treatment induced JAM-C translocation from the cytoplasm to the cytomembrane. Moreover, JAM-C knockdown in RCECs inhibited the adhesion and transmigration of macrophages from wet age-related macular degeneration (wAMD) patients to and through RCECs, whereas JAM-C overexpression in RCECs increased the adhesion and transmigration of macrophages from both wAMD patients and healthy controls. Importantly, the JAM-C overexpression-induced transmigration of macrophages from wAMD patients was abolished by the administration of the protein kinase C (PKC) inhibitor GF109203X. Of note, we found that the serum levels of soluble JAM-C were more than twofold higher in wAMD patients than in healthy controls. Mechanistically, we show that JAM-C overexpression or knockdown in RCECs decreased or increased cytosolic Ca²⁺ concentrations, respectively. Our findings suggest that the dynamic translocation of JAM-C induced by vasoactive molecules might be one of the mechanisms underlying inner endothelial BRB malfunction, and inhibition of JAM-C or PKC in RCECs may help maintain the normal function of the inner BRB. In addition, increased serum soluble JAM-C levels might serve as a molecular marker for wAMD, and modulating JAM-C activity may have potential therapeutic value for the treatment of BRB malfunction-related ocular diseases.

Tumor microenvironment remodeling-based penetration strategies to amplify nanodrug accessibility to tumor parenchyma

Remarkable advances in nano delivery systems have provided new hope for tumor prevention, diagnosis and treatment. However, only limited clinical therapeutic effects against solid tumors were achieved. One of the main reasons is the presence of abundant physiological and pathological barriers in vivo that impair tumoral penetration and distribution of the nanodrugs. These barriers are related to the components of tumor microenvironment (TME) including abnormal tumor vasculature, rich composition of the extracellular matrix (ECM), and abundant stroma cells. Herein, we review the advanced strategies of TME remodeling to overcome these biological obstacles against nanodrug delivery. This review aims to offer a perspective guideline for the implementation of promising approaches to facilitate intratumoral permeation of nanodrugs through alleviation of biological barriers. At the same time, we analyze the advantages and disadvantages of the corresponding methods and put forward possible directions for the future researches.

Single-cell metabolic imaging reveals a SLC2A3-dependent glycolytic burst in motile endothelial cells

Single-cell motility is spatially heterogeneous and driven by metabolic energy. Directly linking cell motility to cell metabolism is technically challenging but biologically important. Here, we use single-cell metabolic imaging to measure glycolysis in individual endothelial cells with genetically encoded biosensors capable of deciphering metabolic heterogeneity at subcellular resolution. We show that cellular glycolysis fuels endothelial activation, migration and contraction and that sites of high lactate production colocalize with active cytoskeletal remodelling within an endothelial cell. Mechanistically, RhoA induces endothelial glycolysis for the phosphorylation of cofilin and myosin light chain in order to reorganize the cytoskeleton and thus control cell motility; RhoA activation triggers a glycolytic burst through the translocation of the glucose transporter SLC2A3/GLUT3 to fuel the cellular contractile machinery, as demonstrated across multiple endothelial cell types. Our data indicate that Rho-GTPase signalling coordinates energy metabolism with cytoskeleton remodelling to regulate endothelial cell motility.

Depletion of Arg/Abl2 improves endothelial cell adhesion and prevents vascular leak during inflammation

Endothelial barrier disruption and vascular leak importantly contribute to organ dysfunction and mortality during inflammatory conditions like sepsis and acute respiratory distress syndrome. We identified the kinase Arg/Abl2 as a mediator of endothelial barrier disruption, but the role of Arg in endothelial monolayer regulation and its relevance in vivo remain poorly understood. Here we show that depletion of Arg in endothelial cells results in the activation of both RhoA and Rac1, increased cell spreading and elongation, redistribution of integrin-dependent cell-matrix adhesions to the cell periphery, and improved adhesion to the extracellular matrix. We further show that Arg is activated in the endothelium during inflammation, both in murine lungs exposed to barrier-disruptive agents, and in pulmonary microvessels of septic patients. Importantly, Arg-depleted endothelial cells were less sensitive to barrier-disruptive agents. Despite the formation of F-actin stress fibers and myosin light chain phosphorylation, Arg depletion diminished adherens junction disruption and intercellular gap formation, by reducing the disassembly of cell-matrix adhesions and cell retraction. In vivo, genetic deletion of Arg diminished vascular leak in the skin and lungs, in the presence of a normal immune response. Together, our data indicate that Arg is a central and non-redundant regulator of endothelial barrier integrity, which contributes to cell retraction and gap formation by increasing the dynamics of adherens junctions and cell-matrix adhesions in a Rho GTPase-dependent fashion. Therapeutic inhibition of Arg may provide a suitable strategy for the treatment of a variety of clinical conditions characterized by vascular leak.

[Role of prostacyclin and thromboxane A2 in pulmonary hyper-permeability induced by mechanical ventilation in rabbits]

OBJECTIVE

To explore the role of prostacyclin (PGI2) and thromboxane A2 (TXA2) in lung hyper-permeability induced by mechanical ventilation (MV) in rabbits.

OBJECTIVE

Forty-eight healthy Japanese white rabbits were randomly allocated to vehicle treatment group (group V), tranylcypromine (a PGI2 synthase inhibitor) treatment group (group T), dazoxiben (a TXA2 synthase inhibitor) treatment group (group D), vehicle-treated MV group (group VM), tranylcyprominetreated MV group (group TM) and dazoxiben-treated MV group (group DM). The contents of PGI2 and TXA2 in the lung tissues and TNF-α level in BALF and lung tissues were measured by ELISA. The lung wet/dry weight (W/D) ratio, lung permeability index and pulmonary expressions of myosin light chain kinase (MLCK) protein and mRNA were detected to evaluate the pulmonary permeability. The severities of lung injury were assessed by lung histological scores.

OBJECTIVE

The measured parameters did not differ significantly among the rabbits receiving different treatments without MV. In rabbits in group VM, the contents of PGI2 and TXA2 in the lungs, TNF-α in BALF and lung tissues, PGI2/TXA2 ratio, lung W/D ratio, lung permeability index, pulmonary expressions of MLCK protein and mRNA and histological scores of the lungs all increased significantly (P < 0.05) as compared with those in group V, group T and group D. In rabbits undergoing MV, inhibition of PGI2 production by tranylcypromine significantly decreased the PGI2/TXA2 ratio (P < 0.05), further enhanced the production of TNF-α in the BALF and lung tissue (P < 0.05), and worsened lung hyper-permeability and lung injury (P < 0.05), while treatment with dazoxiben significantly reduced TXA2 production in the lung tissue (P < 0.05), increased the PGI2/TXA2 ratio (P < 0.05) and decreased TNF-α production in the BALF and lung tissue (P < 0.05), thus resulting in alleviated lung hyperpermeability and lung injury (P < 0.05).

OBJECTIVE

PGI2 plays a protective role against MV-induced lung hyper-permeability and lung injury by downregulating TNF-α/MLCK signaling pathway, while TXA2 can exacerbate MV-induced lung hyperpermeability in rabbits by up-regulating TNF-α/ MLCK signaling pathway.

Fractalkine Is Linked to the Necrosome Pathway in Acute Pulmonary Inflammation

Acute pulmonary inflammation affects over 10% of intensive care unit (ICU) patients and is associated with high mortality. Fractalkine (CX₃CL1) and its receptor, CX₃CR1, have been shown to affect pulmonary inflammation, but previous studies have focused on macrophages. In a murine model of acute pulmonary inflammation, we identified inflammatory hallmarks in C57BL/6J and CX₃CR1^−/− mice. Pulmonary inflammation was significantly enhanced in the CX₃CR1^−/− animals compared to the C57BL/6J animals, as assessed by microvascular permeability, polymorphonuclear neutrophil (PMN) migration into lung tissue and alveolar space. The CX₃CR1^−/− mice showed increased levels of apoptotic PMNs in the lungs, and further investigations revealed an increased activation of necrosome-related receptor-interacting serine/threonine-protein kinases 1 (RIPK1), 3 (RIPK3), and mixed-lineage kinase domain-like pseudokinase (MLKL). Phosphorylated MLKL leads to membrane rupture and damage-associated molecular pattern (DAMP) release, which further enhance inflammation. The release of DAMPs was significantly higher in the CX₃CR1^−/− mice and led to the activation of various cascades, explaining the increased inflammation. RIPK3 and MLKL inhibition improved the inflammatory response in human PMNs in vitro and confirmed our in vivo findings. In conclusion, we linked CX₃CL1 to the necrosome complex in pulmonary inflammation and demonstrated a pivotal role of the necrosome complex in human PMNs.

Regulatory T Cells Prevent Neutrophilic Infiltration of Skin during Contact Hypersensitivity Reactions by Strengthening the Endothelial Barrier

The healing phase of contact hypersensitivity reactions is critically dependent on regulatory T cells (Tregs), but even the early inflammatory phase, that is, 6-24 hours after induction of a contact hypersensitivity reaction, is susceptible to Treg-mediated suppression. To investigate the underlying mechanisms, we injected Tregs before the challenge and analyzed the skin-infiltrating cells as early as 6 hours later. Early on, we found mainly neutrophils in the challenged skin, but only a few T cells. This influx of neutrophils was blocked by the injection of Tregs, indicating that they were able to prevent the first wave of leukocytes, which are responsible for starting an immune reaction. As an underlying mechanism, we identified that Tregs can tighten endothelial junctions by inducing intracellular cAMP, leading to protein kinase A-RhoA‒dependent signaling. This eventually reorganizes endothelial junction proteins, such as Notch3, Nectin 2, Filamin B, and VE-cadherin, all of which contribute to the tightening of the endothelial barrier. In summary, Tregs prevent the leakage of proinflammatory cells from and into the tissue, which establishes a mechanism to downregulate immune reactions.

Naringenin prevents TNF-α-induced gut-vascular barrier disruption associated with inhibiting the NF-κB-mediated MLCK/p-MLC and NLRP3 pathways

The microvasculature endothelium accurately regulates the passage of molecules across the gut-vascular barrier (GVB), which plays an essential role in intestinal immunity. Naringenin is reported to have therapeutic potential against several intestinal disorders. However, the effect of naringenin on GVB disruption has been rarely studied. This study aims to investigate the effect of naringenin on GVB function and the potential mechanism. In the present study, the in vitro GVB disruption of rat intestinal microvascular endothelial cells (RIMVEC) was induced by 50 ng mL^-1 of tumor necrosis factor-α (TNF-α). The integrity of the in vitro GVB was determined by Evans blue (EB)-albumin efflux assay and trans-endothelial electrical resistance (TER). Meanwhile, the expression of tight junction proteins and the related NF-κB, MLCK/p-MLC and NLRP3 pathways were determined using enzyme-linked immunosorbent assay (ELISA), real-time quantitative polymerase chain reaction (RT-qPCR), western blot analysis and immunofluorescence. The results show that naringenin (100 μM) inhibits TNF-α-induced interleukin (IL)-6 hypersecretion, alleviates GVB disruption and mitigates the change in the tight junction protein expression pattern. Naringenin inhibits the GVB-disruption-associated activation of the MLCK/p-MLC system and TLR4/NF-κB/NLRP3 pathways. Furthermore, naringenin shows a similar effect to that of NF-κB inhibitor Bay 11-7082 in reducing the TNF-α-induced activation of NLRP3, p-MLC and secondary GVB disruption. The results suggest that naringenin evidently alleviates TNF-α-induced in vitro GVB disruption via the maintenance of a tight junction protein pattern, partly with the inhibition of the NF-κB-mediated MLCK/p-MLC and NLRP3 pathway activation.

Post-treatment with yiqifumai injection and its main ingredients attenuates lipopolysaccharide-induced microvascular disturbance in mesentery and ileum

OBJECTIVE

To investigate the effect of Yiqifumai injection (YQFM), a compound Chinese medicine, and its main active ingredients on lipopolysaccharide (LPS)-induced microvascular disturbance in mesentery and ileum.

METHODS

Rats were infused with LPS (5 mg/kg/h) for 90 min. Thirty minutes after initiation of LPS administration, YQFM (160 mg/kg/h), Rb1 (5 mg/kg/h), Sch (2.5 mg/kg/h), or Rb1+Sch (5 mg/kg/h + 2.5 mg/kg/h) was infused until 90 min. Human umbilical vein endothelial cells (HUVECs) were incubated with LPS (100 ng/ml) for 90 min. YQFM (1 mg/ml), Rb1 (100 µM), Sch (100 µM), or Rb1+Sch (200 µM) was added 30 min after initiation of LPS stimulation.

RESULTS

Yiqifumai injection and Rb1+Sch inhibited mesenteric venule hyperpermeability, suppressed microvillar erosion and submucosal edema, and protected claudin-5 from downregulation and interleukin-1β from upregulation in ileal tissues after LPS. Study in HUVECs confirmed the effect of YQFM and Rb1+Sch on JAM-1 after LPS and revealed a similar effect on other junction proteins. Moreover, YQFM and Rb1+Sch attenuated the dysfunctional energy metabolism and the activation of TLR-4/Src/NF-κB signaling with Rb1 and Sch being partially effective.

CONCLUSION

These results demonstrated the beneficial effect of post-treatment with YQFM, which is attributable to its main ingredient Rb1 and Sch, and likely mediated by targeting TLR-4/Src/NF-κB signaling pathway.

Molecular Mechanisms of Vascular Damage During Lung Injury

A variety of pulmonary and systemic insults promote an inflammatory response causing increased vascular permeability, leading to the development of acute lung injury (ALI), a condition necessitating hospitalization and intensive care, or the more severe acute respiratory distress syndrome (ARDS), a disease with a high mortality rate. Further, COVID-19 pandemic-associated ARDS is now a major cause of mortality worldwide. The pathogenesis of ALI is explained by injury to both the vascular endothelium and the alveolar epithelium. The disruption of the lung endothelial and epithelial barriers occurs in response to both systemic and local production of pro-inflammatory cytokines. Studies that evaluate the association of genetic polymorphisms with disease risk did not yield many potential therapeutic targets to treat and revert lung injury. This failure is probably due in part to the phenotypic complexity of ALI/ARDS, and genetic predisposition may be obscured by the multiple environmental and behavioral risk factors. In the last decade, new research has uncovered novel epigenetic mechanisms that control ALI/ARDS pathogenesis, including histone modifications and DNA methylation. Enzyme inhibitors such as DNMTi and HDACi may offer new alternative strategies to prevent or reverse the vascular damage that occurs during lung injury. This review will focus on the latest findings on the molecular mechanisms of vascular damage in ALI/ARDS, the genetic factors that might contribute to the susceptibility for developing this disease, and the epigenetic changes observed in humans, as well as in experimental models of ALI/ADRS.

Echovirus-30 Infection Alters Host Proteins in Lipid Rafts at the Cerebrospinal Fluid Barrier In Vitro

Echovirus-30 (E-30) is a non-polio enterovirus responsible for meningitis outbreaks in children worldwide. To gain access to the central nervous system (CNS), E-30 first has to cross the blood-brain barrier (BBB) or the blood-cerebrospinal fluid barrier (BCSFB). E-30 may use lipid rafts of the host cells to interact with and to invade the BCSFB. To study enteroviral infection of the BCSFB, an established in vitro model based on human immortalized brain choroid plexus papilloma (HIBCPP) cells has been used. Here, we investigated the impact of E-30 infection on the protein content of the lipid rafts at the BCSFB in vitro. Mass spectrometry analysis following E-30 infection versus uninfected conditions revealed differential abundancy in proteins implicated in cellular adhesion, cytoskeleton remodeling, and endocytosis/vesicle budding. Further, we evaluated the blocking of endocytosis via clathrin/dynamin blocking and its consequences for E-30 induced barrier disruption. Interestingly, blocking of endocytosis had no impact on the capacity of E-30 to induce loss of barrier properties in HIBCPP cells. Altogether, these data highlight the impact of E-30 on HIBCPP cells microdomain as an important factor for host cell alteration.

The Role of MSC Therapy in Attenuating the Damaging Effects of the Cytokine Storm Induced by COVID-19 on the Heart and Cardiovascular System

The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) has led to 47 m infected cases and 1. 2 m (2.6%) deaths. A hallmark of more severe cases of SARS-CoV-2 in patients with acute respiratory distress syndrome (ARDS) appears to be a virally-induced over-activation or unregulated response of the immune system, termed a "cytokine storm," featuring elevated levels of pro-inflammatory cytokines such as IL-2, IL-6, IL-7, IL-22, CXCL10, and TNFα. Whilst the lungs are the primary site of infection for SARS-CoV-2, in more severe cases its effects can be detected in multiple organ systems. Indeed, many COVID-19 positive patients develop cardiovascular complications, such as myocardial injury, myocarditis, cardiac arrhythmia, and thromboembolism, which are associated with higher mortality. Drug and cell therapies targeting immunosuppression have been suggested to help combat the cytokine storm. In particular, mesenchymal stromal cells (MSCs), owing to their powerful immunomodulatory ability, have shown promise in early clinical studies to avoid, prevent or attenuate the cytokine storm. In this review, we will discuss the mechanistic underpinnings of the cytokine storm on the cardiovascular system, and how MSCs potentially attenuate the damage caused by the cytokine storm induced by COVID-19. We will also address how MSC transplantation could alleviate the long-term complications seen in some COVID-19 patients, such as improving tissue repair and regeneration.

Endothelial Damage in Acute Respiratory Distress Syndrome

The pulmonary endothelium is a metabolically active continuous monolayer of squamous endothelial cells that internally lines blood vessels and mediates key processes involved in lung homoeostasis. Many of these processes are disrupted in acute respiratory distress syndrome (ARDS), which is marked among others by diffuse endothelial injury, intense activation of the coagulation system and increased capillary permeability. Most commonly occurring in the setting of sepsis, ARDS is a devastating illness, associated with increased morbidity and mortality and no effective pharmacological treatment. Endothelial cell damage has an important role in the pathogenesis of ARDS and several biomarkers of endothelial damage have been tested in determining prognosis. By further understanding the endothelial pathobiology, development of endothelial-specific therapeutics might arise. In this review, we will discuss the underlying pathology of endothelial dysfunction leading to ARDS and emerging therapies. Furthermore, we will present a brief overview demonstrating that endotheliopathy is an important feature of hospitalised patients with coronavirus disease-19 (COVID-19).

PBN inhibits a detrimental effect of methamphetamine on brain endothelial cells by alleviating the generation of reactive oxygen species

Methamphetamine (METH) is a powerful psychostimulant that is causing serious health problems worldwide owing to imprudent abuses. Recent studies have suggested that METH has deleterious effects on the blood-brain barrier (BBB). A few studies have also been conducted on the mechanisms whereby METH-induced oxidative stress causes BBB dysfunction. We investigated whether N-tert-butyl-α-phenylnitrone (PBN) has protective effects on BBB function against METH exposure in primary human brain microvascular endothelial cells (HBMECs). We found that METH significantly increased reactive oxygen species (ROS) generation in HBMECs. Pretreatment with PBN decreased METH-induced ROS production. With regard to BBB functional integrity, METH exposure elevated the paracellular permeability and reduced the monolayer integrity; PBN treatment reversed these effects. An analysis of the BBB structural properties, by immunostaining junction proteins and cytoskeleton in HBMECs, indicated that METH treatment changed the cellular localization of the tight (ZO-1) and adherens junctions (VE-cadherin) from the membrane to cytoplasm. Furthermore, METH induced cytoskeletal reorganization via the formation of robust stress fibers. METH-induced junctional protein redistribution and cytoskeletal reorganization were attenuated by PBN treatment. Our results suggest that PBN can act as a therapeutic reagent for METH-induced BBB dysfunction by inhibiting excess ROS generation.

[Prostanoids regulate vascular permeability]

In normal condition, vasculature transports only small molecules such as nutrients across vascular wall. When inflammation occurs, inflammatory stimuli increase the permeability of vessel, which induces the extravasation of molecules larger than 40 kDa including plasma proteins. These extravasated molecules cause further inflammation by promoting the infiltration of inflammatory cells and the production of inflammatory mediators. Although it is known that vascular hyper-permeability plays an important role in inflammation, the detailed mechanism of vascular permeability regulation is still unclear. It is known that vascular permeability is controlled by two types of cells: endothelial cells and vascular mural cells. Endothelial cells cover the luminal side of vascular wall in a single layer and form endothelial barrier. Vascular mural cells regulate the blood flow volume of the downstream tissue by contracting or relaxing vascular wall. Endothelial barrier enhancement and vasocontraction suppress the vascular permeability, while endothelial barrier disruption and vasorelaxation promote it. Vascular permeability is regulated by the balance between the response of endothelial cells and vascular mural cells. Prostanoids are cell membrane-derived lipid mediators which bind to each specific G protein-coupled receptor (GPCR), prostanoid receptors. Recently, several studies showed that prostanoids regulate vascular permeability by acting on endothelial cells and/or vascular mural cells. In this review, we would like to describe the role of each prostanoid in vascular permeability by focusing on the characteristics of each specific receptor.

Activation of Piezo1 by ultrasonic stimulation and its effect on the permeability of human umbilical vein endothelial cells

The acoustic radiation forces produced by ultrasonic stimulation induce shear stress on objects in the acoustic field. Piezo1, a mechanosensitive ion channel protein that is expressed on the plasma membranes of vertebrate cells, can sense shear stress and transduce it into downstream signaling. In this study, we examined the sensitivity of Piezo1 to ultrasonic stimulation and assessed its downstream biological functions in human umbilical vein endothelial cells (HUVECs). Ultrasonic stimulation using a stimulation power of 0.2 W and a frequency of 1 MHz for 10 s did not induce cell damage. However, ultrasonic stimulation induced an influx of calcium ions, which increased with an increase in the stimulation duration. Knockdown of Piezo1 protein decreased the influx of calcium ions during ultrasonic stimulation, which demonstrated that Piezo1 may be activated by the shear stress produced by ultrasonic stimulation. The influx of calcium ions in response to ultrasonic stimulation could be modulated by the Piezo1 protein level. Additionally, ultrasonic stimulation reduced the levels of downstream factors such as MLCK and ATP, which are involved in the Ca²⁺/CaM/MLCK pathway, by suppressing Piezo1. As the Ca²⁺/CaM/MLCK pathway influences the permeability of the cell membrane, the internalization of FITC-Dextran into cells under ultrasonic stimulation was validated. Ultrasonic stimulation was demonstrated to promote the increase in cell permeability, and the suppression of Piezo1 was shown to induce the decrease in cell permeability. Therefore, this study shows that ultrasonic stimulation may modulate the permeability of the membrane of HUVECs by modulating the expression of Piezo1 protein.

Mechanisms of endothelial stiffening in dyslipidemia and aging: Oxidized lipids and shear stress

Vascular stiffening of the arterial walls is well-known as a key factor in aging and the development of cardiovascular disease; however, the role of endothelial stiffness in vascular dysfunction is still an emerging topic. In this review, the authors discuss the impact of dyslipidemia, oxidized lipids, substrate stiffness, age and pro-atherogenic disturbed flow have on endothelial stiffness. Furthermore, we investigate several mechanistic pathways that are key contributors in endothelial stiffness and discuss their physiological effects in the onset of atherogenesis in the disturbed flow regions of the aortic vasculature. The findings in this chapter describe a novel paradigm of synergistic interaction of plasma dyslipidemia/oxidized lipids and pro-atherogenic disturbed shear stress, as well as aging has on endothelial stiffness and vascular dysfunction.

Cell chirality in cardiovascular development and disease

The cardiovascular system demonstrates left-right (LR) asymmetry: most notably, the LR asymmetric looping of the bilaterally symmetric linear heart tube. Similarly, the orientation of the aortic arch is asymmetric as well. Perturbations to the asymmetry have been associated with several congenital heart malformations and vascular disorders. The source of the asymmetry, however, is not clear. Cell chirality, a recently discovered and intrinsic LR asymmetric cellular morphological property, has been implicated in the heart looping and vascular barrier function. In this paper, we summarize recent advances in the field of cell chirality and describe various approaches developed for studying cell chirality at multi- and single-cell levels. We also examine research progress in asymmetric cardiovascular development and associated malformations. Finally, we review evidence connecting cell chirality to cardiac looping and vascular permeability and provide thoughts on future research directions for cell chirality in the context of cardiovascular development and disease.

ERG-Associated lncRNA (ERGAL) Promotes the Stability and Integrity of Vascular Endothelial Barrier During Dengue Viral Infection via Interaction With miR-183-5p

Dengue virus (DENV) continues to be a major public health problem. DENV infection will cause mild dengue and severe dengue. Severe dengue is clinically manifested as serious complications, including dengue hemorrhagic fever and/or dengue shock syndrome (DHF/DSS), which is mainly characterized by vascular leakage. Currently, the pathogenesis of severe dengue is not elucidated thoroughly, and there are no known therapeutic targets for controlling the disease effectively. This study aimed to further reveal the potential molecular mechanism of severe dengue. In this study, the long non-coding RNA, ERG-associated lncRNA (lncRNA-ERGAL), was activated and significantly up-regulated in DENV-infected vascular endothelial cells. After knockdown of lncRNA-ERGAL, the expression of ERG, VE-cadherin, and claudin-5 was repressed; besides, cell apoptosis was enhanced, and cytoskeletal remodeling was disordered, leading to instability and increased permeability of vascular endothelial barrier during DENV infection. Fluorescence in situ hybridization (FISH) assay showed lncRNA-ERGAL to be mainly expressed in the cytoplasm. Moreover, the expression of miR-183-5p was found to increase during DENV infection and revealed to regulate ERG, junction-associated proteins, and the cytoskeletal structure after overexpression and knockdown. Then, ERGAL was confirmed to interact with miR-183-5p by luciferase reporter assay. Collectively, ERGAL acted as a miRNA sponge that can promote stability and integrity of vascular endothelial barrier during DENV infection via binding to miR-183-5p, thus revealing the potential molecular mechanism of severe dengue and providing a foundation for a promising clinical target in the future.

A Review of the Impact of Smoking on Inhaled Insulin: Would You Stop Smoking if Insulin Can Be Inhaled?

High prevalence of diabetes and the need for tight glycemic control have been well established. With the invention of inhaled insulin, an alternate route has been explored and shows great promise. Inhaled insulin shows a similar physiologic response to subcutaneous insulin, with a faster onset of action, making it suitable for post-prandial hyperglycemia. This comes as a great relief, especially to those who are hesitant to use multiple injections in a day. Many factors affect insulin absorption, including device, particle size, airway patency. Another essential factor is smoking, which is prevalent among people with diabetes, as is in the non-diabetic population. Smoking increases the absorption of inhaled insulin, but it is not a straight fact, since acute smoking, passive smoking, chronic smoking - all have different effects on inhaled insulin. Furthermore, inhaled insulin is also affected by lung diseases. Most studies that have been conducted have included limited populations, thus questioning their generalisability. The studies from inception till 2020 have shown increased permeability of epithelial with acute smoking, change of epithelial layer back to normal after few weeks of smoking cessation, and reverting to chronic smoker levels with just one to two days of start in smoking. Data also suggests that smoking causes a reduction in insulin sensitivity, which could compensate for its increased absorption. Nicotine causes a decrease in the absorption of subcutaneous insulin, but its effect has not been seen on inhaled insulin. More studies, including diabetic smoker patients, need to be performed to give a specific set of variables. This would also add another reason to encourage smokers to quit smoking.

Exercise hormone irisin mitigates endothelial barrier dysfunction and microvascular leakage-related diseases

Increased microvascular leakage is a cardinal feature of many critical diseases. Regular exercise is associated with improved endothelial function and reduced risk of cardiovascular disease. Irisin, secreted during exercise, contributes to many health benefits of exercise. However, the effects of irisin on endothelial function and microvascular leakage remain unknown. In this study, we found that irisin remarkably strengthened endothelial junctions and barrier function via binding to integrin αVβ5 receptor in LPS-treated endothelial cells. The beneficial effect of irisin was associated with suppression of the Src-MLCK-β-catenin pathway, activation of the AMPK-Cdc42/Rac1 pathway, and improvement of mitochondrial function. In preclinical models of microvascular leakage, exogenous irisin improved pulmonary function, decreased lung edema and injury, suppressed inflammation, and increased survival. In ARDS patients, serum irisin levels were decreased and inversely correlated with disease severity and mortality. In conclusion, irisin enhances endothelial barrier function and mitigates microvascular leakage-related diseases.

Myosin light chain kinase inhibitor ML7 improves vascular endothelial dysfunction and permeability via the mitogen-activated protein kinase pathway in a rabbit model of atherosclerosis

Endothelial dysfunction (ED) and hyperpermeability are considered as the initiating steps in early atherosclerosis. Phosphorylation of myosin light chain (MLC) is key to cause vascular hyperpermeability via endothelial cell contraction. However, it is unclear whether MLC phosphorylation can also regulate the balance between contraction and relaxation of endothelial cells, thereby affecting endothelium-dependent diastolic function and leading to ED. The present study investigated relationships between ED and MLC phosphorylation and underlying mechanisms. Twenty-four male New Zealand white rabbits were randomly divided into three groups: control, AS, and ML7 (MLCK inhibitor) groups, and fed with normal diet, high-fat diet (HFD), and HFD plus oral ML7 (1 mg/kg daily) respectively. HFD-fed rabbits showed typical atheromatous lesions and endothelial hyperpermeability, and these lesions could be partly reversed following ML7 therapy. Western blotting revealed significant increased expression of myosin light chain kinase (MLCK) and phosphorylation of MLC, JNK, and ERK in the arterial wall of rabbits in the AS group compared with those of the control group (p < 0.05), whereas the ML7 group showed markedly decreased levels of these proteins compared with the AS group (p <  0.05). The endothelium-dependent relaxation rate was significantly reduced both in vitro and in vivo in AS group, and was improved using ML7 therapy. Taken together, these results indicate that MLCK expression and subsequent MLC phosphorylation increase vascular endothelial permeability and endothelium-dependent diastolic dysfunction by promoting endothelial cell contraction, which may be initiated by the activation of the MAP/ERK (MEK) and MAP/JNK (MEK) pathways.

Reciprocal integrin/integrin antagonism through kindlin-2 and Rho GTPases regulates cell cohesion and collective migration

Collective cell behaviour during embryogenesis and tissue repair requires the coordination of intercellular junctions, cytoskeleton-dependent shape changes controlled by Rho GTPases, and integrin-dependent cell-matrix adhesion. Many different integrins are simultaneously expressed during wound healing, embryonic development, and sprouting angiogenesis, suggesting that there is extensive integrin/integrin cross-talk to regulate cell behaviour. Here, we show that fibronectin-binding β1 and β3 integrins do not act synergistically, but rather antagonize each other during collective cell processes in neuro-epithelial cells, placental trophoblasts, and endothelial cells. Reciprocal β1/β3 antagonism controls RhoA activity in a kindlin-2-dependent manner, balancing cell spreading, contractility, and intercellular adhesion. In this way, reciprocal β1/β3 antagonism controls cell cohesion and cellular plasticity to switch between extreme and opposing states, including epithelial versus mesenchymal-like phenotypes and collective versus individual cell migration. We propose that integrin/integrin antagonism is a universal mechanism to effectuate social cellular interactions, important for tissue morphogenesis, endothelial barrier function, trophoblast invasion, and sprouting angiogenesis.

Extracellular adenosine enhances pulmonary artery vasa vasorum endothelial cell barrier function via Gi/ELMO1/Rac1/PKA-dependent signaling mechanisms

The vasa vasorum (VV), the microvascular network around large vessels, has been recognized as an important contributor to the pathological vascular remodeling in cardiovascular diseases. In bovine and rat models of hypoxic pulmonary hypertension (PH), we have previously shown that chronic hypoxia profoundly increased pulmonary artery (PA) VV permeability, associated with infiltration of inflammatory and progenitor cells in the arterial wall, perivascular inflammation, and structural vascular remodeling. Extracellular adenosine was shown to exhibit a barrier-protective effect on VV endothelial cells (VVEC) via cAMP-independent mechanisms, which involved adenosine A1 receptor-mediated activation of Gi-phosphoinositide 3-kinase-Akt pathway and actin cytoskeleton remodeling. Using VVEC isolated from the adventitia of calf PA, in this study we investigated in more detail the mechanisms linking Gi activation to downstream barrier protection pathways. Using a small-interference RNA (siRNA) technique and transendothelial electrical resistance assay, we found that the adaptor protein, engulfment and cell motility 1 (ELMO1), the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-2, and atypical Gi- and Rac1-mediated protein kinase A activation are implicated in VVEC barrier enhancement. In contrast, the actin-interacting GTP-binding protein, girdin, and the p21-activated kinase 1 downstream target, LIM kinase, are not involved in this response. In addition, adenosine-dependent cytoskeletal rearrangement involves activation of cofilin and inactivation of ezrin-radixin-moesin regulatory cytoskeletal proteins, consistent with a barrier-protective mechanism. Collectively, our data indicate that targeting adenosine receptors and downstream barrier-protective pathways in VVEC may have a potential translational significance in developing pharmacological approach for the VV barrier protection in PH.

Phospholipase D2 restores endothelial barrier function by promoting PTPN14-mediated VE-cadherin dephosphorylation

Increased permeability of vascular lung tissues is a hallmark of acute lung injury and is often caused by edemagenic insults resulting in inflammation. Vascular endothelial (VE)-cadherin undergoes internalization in response to inflammatory stimuli and is recycled at cell adhesion junctions during endothelial barrier re-establishment. Here, we hypothesized that phospholipase D (PLD)-generated phosphatidic acid (PA) signaling regulates VE-cadherin recycling and promotes endothelial barrier recovery by dephosphorylating VE-cadherin. Genetic deletion of PLD2 impaired recovery from protease-activated receptor-1-activating peptide (PAR-1-AP)-induced lung vascular permeability and potentiated inflammation in vivo In human lung microvascular endothelial cells (HLMVECs), inhibition or deletion of PLD2, but not of PLD1, delayed endothelial barrier recovery after thrombin stimulation. Thrombin stimulation of HLMVECs increased co-localization of PLD2-generated PA and VE-cadherin at cell-cell adhesion junctions. Inhibition of PLD2 activity resulted in prolonged phosphorylation of Tyr-658 in VE-cadherin during the recovery phase 3 h post-thrombin challenge. Immunoprecipitation experiments revealed that after HLMVECs are thrombin stimulated, PLD2, VE-cadherin, and protein-tyrosine phosphatase nonreceptor type 14 (PTPN14), a PLD2-dependent protein-tyrosine phosphatase, strongly associate with each other. PTPN14 depletion delayed VE-cadherin dephosphorylation, reannealing of adherens junctions, and barrier function recovery. PLD2 inhibition attenuated PTPN14 activity and reversed PTPN14-dependent VE-cadherin dephosphorylation after thrombin stimulation. Our findings indicate that PLD2 promotes PTPN14-mediated dephosphorylation of VE-cadherin and that redistribution of VE-cadherin at adherens junctions is essential for recovery of endothelial barrier function after an edemagenic insult.

miR-144-mediated Inhibition of ROCK1 Protects against LPS-induced Lung Endothelial Hyperpermeability

Dysfunctional endothelial cell (EC) barrier and increased lung vascular permeability is a cardinal feature of acute lung injury and sepsis that may result in a pathophysiological condition characterized by alveolar flooding, pulmonary edema, and subsequent hypoxemia. In lung ECs, activation of Rho-associated kinase-1 (ROCK1) phosphorylates myosin light chain (MLC)-associated phosphatase at its inhibitory site, which favors phosphorylation of MLC, stress fiber formation, and hyperpermeability during acute lung injury. The role of microRNA-144 (miR-144) has been well investigated in many human diseases, including cardiac ischemia/reperfusion-induced injury, lung cancer, and lung viral infection; however, its role in pulmonary EC barrier regulation remains obscure. Here, we investigated the miR-144-mediated mechanism in the protection of endothelial barrier function in an LPS-induced lung injury model. By using transendothelial electrical resistance and transwell permeability assay to examine in vitro permeability and immunofluorescence microscopy to determine barrier integrity, we showed that ectopic expression of miR-144 effectively blocked lung EC barrier disruption and hyperpermeability in response to proinflammatory agents. Furthermore, using a gain-and-loss-of-function strategy, overexpression of miR-144 significantly decreased ROCK1 expression. Concomitantly, miR-144 inhibits ROCK1-mediated phosphorylation of MLC phosphatase^Thr853 and thus phosphorylation of MLC^Thr18/Ser19 to counteract stress fiber formation in LPS-activated EC. Finally, in LPS-challenged mice, intranasal delivery of miR-144 mimic via liposomes attenuated endotoxemia-induced increases in lung wet/dry ratio, vascular permeability, and inflammation. In conclusion, these data suggest that miR-144-attenuated activation of inflammatory ROCK1/MLC pathway in vascular ECs is a promising therapeutic strategy to counter inflammatory lung injury.

Lung Endothelial Transcytosis

Transcytosis of macromolecules through lung endothelial cells is the primary route of transport from the vascular compartment into the interstitial space. Endothelial transcytosis is mostly a caveolae-dependent process that combines receptor-mediated endocytosis, vesicle trafficking via actin-cytoskeletal remodeling, and SNARE protein directed vesicle fusion and exocytosis. Herein, we review the current literature on caveolae-mediated endocytosis, the role of actin cytoskeleton in caveolae stabilization at the plasma membrane, actin remodeling during vesicle trafficking, and exocytosis of caveolar vesicles. Next, we provide a concise summary of experimental methods employed to assess transcytosis. Finally, we review evidence that transcytosis contributes to the pathogenesis of acute lung injury. © 2020 American Physiological Society. Compr Physiol 10:491-508, 2020.

Downregulation of S1P Lyase Improves Barrier Function in Human Cerebral Microvascular Endothelial Cells Following an Inflammatory Challenge

Sphingosine 1-phosphate (S1P) is a key bioactive lipid that regulates a myriad of physiological and pathophysiological processes, including endothelial barrier function, vascular tone, vascular inflammation, and angiogenesis. Various S1P receptor subtypes have been suggested to be involved in the regulation of these processes, whereas the contribution of intracellular S1P (iS1P) through intracellular targets is little explored. In this study, we used the human cerebral microvascular endothelial cell line HCMEC/D3 to stably downregulate the S1P lyase (SPL-kd) and evaluate the consequences on endothelial barrier function and on the molecular factors that regulate barrier tightness under normal and inflammatory conditions. The results show that in SPL-kd cells, transendothelial electrical resistance, as a measure of barrier integrity, was regulated in a dual manner. SPL-kd cells had a delayed barrier build up, a shorter interval of a stable barrier, and, thereafter, a continuous breakdown. Contrariwise, a protection was seen from the rapid proinflammatory cytokine-mediated barrier breakdown. On the molecular level, SPL-kd caused an increased basal protein expression of the adherens junction molecules PECAM-1, VE-cadherin, and β-catenin, increased activity of the signaling kinases protein kinase C, AMP-dependent kinase, and p38-MAPK, but reduced protein expression of the transcription factor c-Jun. However, the only factors that were significantly reduced in TNFα/SPL-kd compared to TNFα/control cells, which could explain the observed protection, were VCAM-1, IL-6, MCP-1, and c-Jun. Furthermore, lipid profiling revealed that dihydro-S1P and S1P were strongly enhanced in TNFα-treated SPL-kd cells. In summary, our data suggest that SPL inhibition is a valid approach to dampenan inflammatory response and augmente barrier integrity during an inflammatory challenge.

Endovascular procedures cause transient endothelial injury but do not disrupt mature neointima in Drug Eluting Stents

Extensive application of coronary intravascular procedures has led to the increased need of understanding the injury inflicted to the coronary arterial wall. We aimed to investigate acute and prolonged coronary endothelial injury as a result of guidewire use, repeated intravascular imaging and stenting. These interventions were performed in swine (N = 37) and injury was assessed per coronary segment (n = 81) using an Evans Blue dye-exclusion-test. Scanning electron microscopy and light microscopy were then used to visualize the extent and nature of acute (<4 hours) and prolonged (5 days) endothelial injury. Guidewire and imaging injury was mainly associated with denudation and returned to control levels at 5 days. IVUS and OCT combined (Evans Blue staining 28 ± 16%) did not lead to more acute injury than IVUS alone (33 ± 15%). Stent placement caused most injury (85 ± 4%) and despite early stent re-endothelialization at 5 days, the endothelium proved highly permeable (97 ± 4% at 5 days; p < 0.001 vs acute). Imaging of in-stent neointima at 28 days after stent placement did not lead to neointimal rupture. Guidewire, IVUS and OCT induce acute endothelial cell damage, which does not increase during repeated imaging, and heals within 5 days. Interestingly, endothelial permeability increases 5 days post stenting despite near complete re-endothelialization.

Shengui Sansheng Pulvis maintains blood-brain barrier integrity by vasoactive intestinal peptide after ischemic stroke

Background Shengui Sansheng Pulvis (SSP) has about 300 years history used for stroke treatment, and evidences suggest it has beneficial effects on neuro-angiogenesis and cerebral energy metabolic amelioration post-stroke. However, its protective action and mechanisms on blood-brain barrier (BBB) is still unknown. Purpose Based on multiple neuroprotective properties of vasoactive intestinal peptide (VIP) in neurological disorders, we investigate if SSP maintaining BBB integrity is associated with VIP pathway in rat permanent middle cerebral artery occlusion (MCAo) model. Methods Three doses of SSP extraction were administered orally. Evaluations of motor and balance abilities and detection of brain edema were performed, and BBB permeability were assessed by Evans blue (EB) staining. Primary brain microvascular endothelial cells (BMECs) were subjected to oxygen-glucose deprivation, and incubated with high dose SSP drug-containing serum and VIP-antagonist respectively. Transendothelial electrical resistance (TEER) assay and Tetramethylrhodamine isothiocyanate (TRITC)-dextran (4.4 kDa) and fluorescein isothiocyanate (FITC)-dextran (70 kDa) were used to evaluate the features of paracellular junction. Western blot detected the expressions of Claudin-5, ZO-1, Occludin and VE-cadherin, matrix metalloproteinase (MMP) 2/9 and VIP receptors 1/2, and immunofluorescence staining tested VIP and Claudin-5 expressions. Results Our results show that SSP significantly reduces EB infiltration in dose-dependent manner in vivo and attenuates TRITC- dextran and FITC-dextran diffusion in vitro, and strengthens endothelial junctional complexes as represented by decreasing Claudin-5, ZO-1, Occludin and VE-cadherin degradations and MMP 2/9 expression, as well as promoting TEER in BMECs after ischemia. Moreover, it suggests that SSP notably enhances VIP and its receptors 1/2 expressions. VIP-antagonist exacerbates paracellular barrier of BMECs, while the result is reversed after incubation with high dose SSP drug-containing serum. Additionally, SSP also improve brain edema and motor and balance abilities after ischemic stroke. Conclusions we firstly demonstrate that the ameliorated efficacy of SSP on BBB permeability is related to the enhancements of VIP and its receptors, suggesting SSP might be an effective therapeutic agent on maintaining BBB integrity post-stroke.

On the Mechanisms of Action of the Low Molecular Weight Fraction of Commercial Human Serum Albumin in Osteoarthritis

The low molecular weight fraction of commercial human serum albumin (LMWF5A) has been shown to successfully relieve pain and inflammation in severe osteoarthritis of the knee (OAK). LMWF5A contains at least three active components that could account for these antiinflammatory and analgesic effects. We summarize in vitro experiments in bone marrow-derived mesenchymal stem cells, monocytic cell lines, chondrocytes, peripheral blood mononuclear cells, fibroblast-like synoviocytes, and endothelial cells on the biochemistry of anti-inflammatory changes induced by LMWF5A. We then look at four of the major pathways that cut across cell-type considerations to examine which biochemical reactions are affected by mTOR, COX-2, CD36, and AhR pathways. All three components show anti-inflammatory activities in at least some of the cell types. The in vitro experiments show that the effects of LMWF5A in chondrocytes and bone marrow- derived stem cells in particular, coupled with recent data from previous clinical trials of single and multiple injections of LMWF5A into OAK patients demonstrated improvements in pain, function, and Patient Global Assessment (PGA), as well as high responder rates that could be attributed to the multiple mechanism of action (MOA) pathways are summarized here. In vitro and in vivo data are highly suggestive of LMWF5A being a disease-modifying drug for OAK.

P-Cresylsulfate, the Protein-Bound Uremic Toxin, Increased Endothelial Permeability Partly Mediated by Src-Induced Phosphorylation of VE-Cadherin

The goal of our study was to investigate the impact of p-cresylsulfate (PCS) on the barrier integrity in human umbilical vein endothelial cell (HUVEC) monolayers and the renal artery of chronic kidney disease (CKD) patients. We measured changes in the transendothelial electrical resistance (TEER) of HUVEC monolayers treated with PCS (0.1–0.2 mM) similar to serum levels of CKD patients. A PCS dose (0.2 mM) significantly decreased TEER over a 48-h period. Both PCS doses (0.1 and 0.2 mM) significantly decreased TEER over a 72-h period. Inter-endothelial gaps were observed in HUVECs following 48 h of PCS treatment by immunofluorescence microscopy. We also determined whether PCS induced the phosphorylation of VE-cadherin at tyrosine 658 (Y658) mediated by the phosphorylation of Src. Phosphorylated VE-cadherin (Y658) and phosphorylated Src levels were significantly higher when the cells were treated with 0.1 and 0.2 mM PCS, respectively, compared to the controls. The endothelial barrier dysfunction in the arterial intima in CKD patients was evaluated by endothelial leakage of immunoglobulin G (IgG). Increased endothelial leakage of IgG was related to the declining kidney function in CKD patients. Increased endothelial permeability induced by uremic toxins, including PCS, suggests that uremic toxins induce endothelial barrier dysfunction in CKD patients and Src-mediated phosphorylation of VE-cadherin is involved in increased endothelial permeability induced by PCS exposure.

Protective Effect of Naringin on In Vitro Gut-Vascular Barrier Disruption of Intestinal Microvascular Endothelial Cells Induced by TNF-α

Naringin is a polymethoxylated flavonoid commonly found in citrus species and has therapeutic potential in intestinal disorders. However, the effect and mechanism of naringin on gut-vascular barrier disruption has not yet been reported. This study aimed to investigate the distinguishing and selectively protective effects of naringin on tumor necrosis factor (TNF)-α-induced gut-vascular barrier disruption and elucidate the potential mechanism. In the present study, an in vitro gut-vascular barrier model composed of rat intestinal microvascular endothelial cells (RIMVECs) was studied. Evans blue-albumin efflux assay showed that naringin (50 μM) evidently protected the integrity of RIMVEC monolayer barriers against TNF-α-induced disruption. Naringin maintained the expression and distribution of tight junction proteins including zona occludin-1, occludin, claudin-1, and claudin-2. Additionally, naringin protected RIMVECs from TNF-α-induced apoptosis and cell migration suppression (41.1 ± 2.2 vs 51.1 ± 3.5%; 61.0 ± 5.1 vs 72.2 ± 6.2%). Our results indicate that naringin effectively ameliorates gut-vascular barrier disruption.

Contrasting effects of stored allogeneic red blood cells and their supernatants on permeability and inflammatory responses in human pulmonary endothelial cells

Transfusion of red blood cells (RBCs) is a common life-saving clinical practice in severely anemic or hemorrhagic patients; however, it may result in serious pathological complications such as transfusion-related acute lung injury. The factors mediating the deleterious effects of RBC transfusion remain unclear. In this study, we tested the effects of washed long-term (RBC-O; >28 days) versus short-term (RBC-F; <14 days) stored RBCs and their supernatants on lung endothelial (EC) permeability under control and inflammatory conditions. RBCs enhanced basal EC barrier function as evidenced by an increase in transendothelial electrical resistance and decrease in permeability for macromolecules. RBCs also attenuated EC hyperpermeability and suppressed secretion of EC adhesion molecule ICAM-1 and proinflammatory cytokine IL-8 in response to LPS or TNF-α. In both settings, RBC-F had slightly higher barrier protective effects as compared with RBC-O. In contrast, supernatants from both RBC-F and RBC-O disrupted the EC barrier. The early phase of EC permeability response caused by RBC supernatants was partially suppressed by antioxidant N-acetyl cysteine and inhibitor of Src kinase family PP2, while addition of heme blocker and inhibition of NOD-like receptor family pyrin domain containing protein 3 (NLRP3), stress MAP kinases, receptor for advanced glycation end-products (RAGE), or Toll-like receptor-4 (TLR4) signaling were without effect. Morphological analysis revealed that RBC supernatants increased LPS- and TNF-α-induced breakdown of intercellular junctions and formation of paracellular gaps. RBC supernatants augmented LPS- and TNF-α-induced EC inflammation reflected by increased production of IL-6, IL-8, and soluble ICAM-1. These findings demonstrate the deleterious effects of RBC supernatants on EC function, which may have a major impact in pathological consequences associated with RBC transfusion.

Differential Regulation of LPS-Mediated VE-Cadherin Disruption in Human Endothelial Cells and the Underlying Signaling Pathways: A Mini Review

Endothelial cells lining the inner vascular wall form a monolayer that contributes to the selective permeability of endothelial barrier. This selective permeability is mainly regulated by an endothelium-specific adherens junctional protein, known as vascular endothelial-cadherin (VE-cadherin). In endothelial cells, the adherens junction comprises of VE-cadherin and its associated adhesion molecules such as p120, α-catenin, and β-catenin, in which α-catenin links cytoplasmic tails of VE-cadherin to actin cytoskeleton through β-catenin. Proinflammatory stimuli such as lipopolysaccharide (LPS) are capable of attenuating vascular integrity through the disruption of VE-cadherin adhesion in endothelial cells. To date, numerous studies demonstrated the disruption of adherens junction as a result of phosphorylation-mediated VE-cadherin disruption. However, the outcomes from these studies were inconsistent and non-conclusive as different cell fractions were used to examine the effect of LPS on the disruption of VE-cadherin. By using Western Blot, some studies utilized total protein lysate and reported decreased protein expression while some studies reported unchanged expression. Other studies which used membrane and cytosolic fractions of protein extract demonstrated decreased and increased VE-cadherin expression, respectively. Despite the irregularities, the results of immunofluorescence staining are consistent with the formation of intercellular gap. Besides that, the overall underlying disruptive mechanisms of VE-cadherin remain largely unknown. Therefore, this mini review will focus on different experiment approaches in terms of cell fractions used in different human endothelial cell studies, and relate these differences to the results obtained in Western blot and immunofluorescence staining in order to give some insights into the overall differential regulatory mechanisms of LPS-mediated VE-cadherin disruption and address the discrepancy in VE-cadherin expression.

Simvastatin improves lysosome function via enhancing lysosome biogenesis in endothelial cells

Nlrp3 inflammasomes were shown to play a critical role in triggering obesity-associated early onsets of cardiovascular complications such as endothelial barrier dysfunction with endothelial hyperpermeability. Statins prevent endothelial dysfunction and decrease cardiovascular risk in patients with obesity and diabetes. However, it remains unclear whether statin treatment for obesity-induced endothelial barrier dysfunction is in part due to the blockade of Nlrp3 inflammasome signaling axis. The results showed that simvastatin, a clinically and widely used statin, prevented free fatty acid-induced endothelial hyperpermeability and disruption of ZO-1 and VE-cadherin junctions in mouse microvascular endothelial cells (MVECs). This protective effect of simvastatin was largely due to improved lysosome function that attenuated lysosome injury-mediated Nlrp3 inflammasome activation and subsequent release of high mobility group box protein-1 (HMGB1). Mechanistically, simvastatin induces autophagy that promotes removal of damaged lysosomes and also promotes lysosome regeneration that preserves lysosome function. Collectively, simvastatin treatment improves lysosome function via enhancing lysosome biogenesis and its autophagic turnover, which may be an important mechanism to suppress Nlrp3 inflammasome activation and prevents endothelial hyperpermeability in obesity.

MicroRNA-34a Promotes Endothelial Dysfunction and Mitochondrial-mediated Apoptosis in Murine Models of Acute Lung Injury

Recent evidence has shown that microRNAs (miRs) are involved in endothelial dysfunction and vascular injury in lung-related diseases. However, the potential role of miR-34a in the regulation of pulmonary endothelial dysfunction, vascular injury, and endothelial cells (ECs) apoptosis in acute lung injury (ALI)/acute lung respiratory distress syndrome is largely unknown. Here, we show that miR-34a-5p was upregulated in whole lungs, isolated ECs from lungs, and ECs stimulated with various insults (LPS and hyperoxia). Overexpression of miR-34a-5p in ECs exacerbated endothelial dysfunction, inflammation, and vascular injury, whereas the suppression of miR-34a-5p expression in ECs and miR-34a-null mutant mice showed protection against LPS- and hyperoxia-induced ALI. Furthermore, we observed that miR-34a-mediated endothelial dysfunction is associated with decreased miR-34a direct-target protein, sirtuin-1, and increased p53 expression in whole lungs and ECs. Mechanistically, we show that miR-34a leads to translocation of p53 and Bax to the mitochondrial compartment with disruption of mitochondrial membrane potential to release cytochrome C into the cytosol, initiating a cascade of mitochondrial-mediated apoptosis in lungs. Collectively, these data show that downregulating miR-34a expression or modulating its target proteins may improve endothelial dysfunction and attenuate ALI.

Contribution of cathepsin B-dependent Nlrp3 inflammasome activation to nicotine-induced endothelial barrier dysfunction

Recent studies indicate that endothelial Nlrp3 inflammasome is critically involved in the development of cardiovascular complications. However, it remains unknown whether endothelial inflammasome is involved in endothelial barrier dysfunction associated with smoking. This study aims to investigate the role of endothelial Nlrp3 inflammasome in nicotine-induced disruption of inter-endothelial tight junctions and consequent endothelial barrier dysfunction. The confocal microscopic analysis demonstrated that mice treated with nicotine exhibited disrupted inter-endothelial tight junctions as shown by decreased ZO-1 and ZO-2 expression in the coronary arterial endothelium, whereas the decreases in ZO-1/2 were prevented by Nlrp3 gene deficiency. In cultured endothelial cells, nicotine caused Nlrp3 inflammasome complex formation and enhances the inflammasome activity as shown by increased cleavage of pro-caspase-1, and interleukin-1β (IL-1β) production. Further, nicotine disrupted tight junction and increased permeability in an endothelial cell monolayer, and this nicotine-induced effect was prevented by silencing of Nlrp3 gene, inhibition of caspase-1, or blockade of high mobility group box 1 (HMGB1). Nicotine increased endothelial cell lysosomal membrane permeability and triggered the lysosomal release of cathepsin B, whereas these events were prevented by pretreating cells with a lysosome stabilizing agent, dexamethasone. Collectively, our data suggest that nicotine enhances cathepsin B-dependent Nlrp3 inflammasome activation and the consequent production of a novel permeability factor HMGB1, which causes disruption of inter-endothelial tight junctions leading to endothelial hyperpermeability. Instigation of endothelial inflammasomes may serve as an important pathogenic mechanism contributing to the early onset of vasculopathy associated with smoking.

Low molecular weight heparin (nadroparin) improves placental permeability in rats with gestational diabetes mellitus via reduction of tight junction factors

Placental structural abnormalities and dysfunction in those with gestational diabetes mellitus (GDM) can lead to increased placental permeability, which is in turn related to a poorer maternal and fetal prognosis. The present study sought to assess whether increased placental permeability in rats with GDM was accompanied by alterations in tight junction (TJ) factors and to evaluate the impact of low molecular weight heparin (LMWH) on these factors. The present study was conducted using pregnant female rats that were randomized into control, GDM and GDM + LMWH groups. Diabetes was induced via intraperitoneal administration of streptozotocin to rats in the GDM and GDM + LMWH groups, whereas rats in the GDM + LMWH group received daily subcutaneous LMWH starting on day 5 of pregnancy. On gestational day 16, all rats were sacrificed and Evans Blue (EB) assay was used to gauge vascular permeability based on EB dye leakage. Transmission electron microscopy was further used to assess TJ structures, and the TJ proteins zonular occludens-1 (ZO-1) and occludin (OCLN) were assessed using immunohistochemistry and western blotting. Blood samples were obtained from the abdominal aorta for ELISA measurements of advanced glycation end products (AGEs) concentrations, and placental receptor for AGEs (RAGE) and vascular endothelial growth factor (VEGF) expression was assessed using reverse transcription-quantitative PCR. In addition, western blotting was used to measure placental NF-κB. Compared with in the control group, EB leakage was markedly increased in GDM group rats; this was associated with reduced ZO-1 and OCLN expression. Conversely, LMWH attenuated this increase in placental permeability in rats with GDM and also mediated a partial recovery of ZO-1 and OCLN expression. Blood glucose and serum AGEs concentrations did not differ between the GDM and GDM + LMWH groups. Furthermore, LMWH treatment resulted in decreases in RAGE and VEGF mRNA expression levels, which were upregulated in the GDM group, whereas it had the opposite effect on the expression of NF-κB. In conclusion, GDM was associated with increased placental permeability and this may be linked with changes in TJs. LMWH intervention mediated protection against this GDM-associated shift in placental permeability via the RAGE/NF-κB pathway.

Dynamic trafficking and turnover of JAM-C is essential for endothelial cell migration

Junctional complexes between endothelial cells form a dynamic barrier that hinders passive diffusion of blood constituents into interstitial tissues. Remodelling of junctions is an essential process during leukocyte trafficking, vascular permeability, and angiogenesis. However, for many junctional proteins, the mechanisms of junctional remodelling have yet to be determined. Here, we used receptor mutagenesis, horseradish peroxidase (HRP), and ascorbate peroxidase 2 (APEX-2) proximity labelling, alongside light and electron microscopy (EM), to map the intracellular trafficking routes of junctional adhesion molecule-C (JAM-C). We found that JAM-C cotraffics with receptors associated with changes in permeability such as vascular endothelial cadherin (VE-Cadherin) and neuropilin (NRP)-1 and 2, but not with junctional proteins associated with the transmigration of leukocytes. Dynamic JAM-C trafficking and degradation are necessary for junctional remodelling during cell migration and angiogenesis. By identifying new potential trafficking machinery, we show that a key point of regulation is the ubiquitylation of JAM-C by the E3 ligase Casitas B-lineage lymphoma (CBL), which controls the rate of trafficking versus lysosomal degradation.

An isogenic hiPSC-derived BBB-on-a-chip

The blood-brain barrier (BBB) is composed of brain microvascular endothelial cells (BMECs) that regulate brain homeostasis, and astrocytes within the brain are involved in the maintenance of the BBB or modulation of its integrity in disease states via secreted factors. A major challenge in modeling the normal or diseased BBB is that conventional in vitro models lack either the physiological complexity of the BBB or key functional features such as formation of a sufficiently tight barrier. In this study, we utilized human induced pluripotent stem cell (hiPSC)-derived BMECs in a BBB-on-a-chip device that supports flow and coculture with an astrocyte-laden 3D hydrogel. The BMECs are separated from the hydrogel by a porous membrane with either 0.4 or 8.0 μm pore size, making the device suitable for studying the transport of molecules or cells, respectively, across the BBB. In addition, all cells seeded in the device are differentiated from the same hiPSC line, which could enable genetic and rare disease modeling. Formation of a confluent BMEC barrier was confirmed by immunocytochemistry of tight junction proteins and measurement of fluorescein permeability. Integrity of the barrier was further assessed by performing impedance spectroscopy in the device. Finally, the ability of this device to recapitulate a disease model of BBB disruption was demonstrated, with apical addition of TGF-β1 leading to transendothelial electrical resistance reduction and indicators of astrocyte activation. These results demonstrate the utility of the fabricated device for a broad range of applications such as drug screening and mechanistic studies of BBB disruption.

Biomechanical Forces and Oxidative Stress: Implications for Pulmonary Vascular Disease

Significance: Oxidative stress in the cell is characterized by excessive generation of reactive oxygen species (ROS). Superoxide (O₂^-) and hydrogen peroxide (H₂O₂) are the main ROS involved in the regulation of cellular metabolism. As our fundamental understanding of the underlying causes of lung disease has increased it has become evident that oxidative stress plays a critical role. Recent Advances: A number of cells in the lung both produce, and respond to, ROS. These include vascular endothelial and smooth muscle cells, fibroblasts, and epithelial cells as well as the cells involved in the inflammatory response, including macrophages, neutrophils, eosinophils. The redox system is involved in multiple aspects of cell metabolism and cell homeostasis. Critical Issues: Dysregulation of the cellular redox system has consequential effects on cell signaling pathways that are intimately involved in disease progression. The lung is exposed to biomechanical forces (fluid shear stress, cyclic stretch, and pressure) due to the passage of blood through the pulmonary vessels and the distension of the lungs during the breathing cycle. Cells within the lung respond to these forces by activating signal transduction pathways that alter their redox state with both physiologic and pathologic consequences. Future Directions: Here, we will discuss the intimate relationship between biomechanical forces and redox signaling and its role in the development of pulmonary disease. An understanding of the molecular mechanisms induced by biomechanical forces in the pulmonary vasculature is necessary for the development of new therapeutic strategies.

Calcium signals that determine vascular resistance

Small arteries in the body control vascular resistance, and therefore, blood pressure and blood flow. Endothelial and smooth muscle cells in the arterial walls respond to various stimuli by altering the vascular resistance on a moment to moment basis. Smooth muscle cells can directly influence arterial diameter by contracting or relaxing, whereas endothelial cells that line the inner walls of the arteries modulate the contractile state of surrounding smooth muscle cells. Cytosolic calcium is a key driver of endothelial and smooth muscle cell functions. Cytosolic calcium can be increased either by calcium release from intracellular stores through IP3 or ryanodine receptors, or the influx of extracellular calcium through ion channels at the cell membrane. Depending on the cell type, spatial localization, source of a calcium signal, and the calcium-sensitive target activated, a particular calcium signal can dilate or constrict the arteries. Calcium signals in the vasculature can be classified into several types based on their source, kinetics, and spatial and temporal properties. The calcium signaling mechanisms in smooth muscle and endothelial cells have been extensively studied in the native or freshly isolated cells, therefore, this review is limited to the discussions of studies in native or freshly isolated cells. This article is categorized under: Biological Mechanisms > Cell Signaling Laboratory Methods and Technologies > Imaging Models of Systems Properties and Processes > Mechanistic Models.

Angiopoietin 1 attenuates interleukin-6-induced endothelial cell permeability through SHP-1

The regulation of endothelial cell (EC) permeability is critical for the physiological homeostasis of blood vessels and tissues. The elevation of pro-inflammatory cytokines is highly associated with lesions, such as the increased vascular permeability of diabetic retinas. We have previously reported that interleukin-6 (IL-6) increases EC permeability through the downregulation of tight junction protein expression. Angiopoietin 1 (Ang1) has an anti-permeability function, but the effect of Ang1 on vascular permeability induced by inflammatory cytokines is unclear. In the present study, we investigated the effect of Ang1 on IL-6-induced EC permeability and its underlying molecular mechanisms. We demonstrated that Ang1 inhibited the IL-6-induced increase in EC permeability by inhibiting the reductions in the levels of tight junction protein ZO-1 and occludin, which was related to the decrease in vascular endothelial growth factor (VEGF) secretion through the inhibition of STAT3 activation by Ang1. Mechanistically, Ang1 induced the dissociation of the tyrosine phosphatase SHP-1 from the Tie2 receptor and increased the binding of SHP-1 to JAK1, JAK2, and STAT3, which are IL-6 downstream signaling proteins. We conclude that SHP-1 plays an important role in the Ang1-induced inhibition of JAK/STAT3 signaling. These results provide evidence for a potential beneficial role of Ang1 in suppressing the vascular permeability induced by the pro-inflammatory cytokine IL-6 in diabetic retinopathy.

Cysteine Glutathionylation Acts as a Redox Switch in Endothelial Cells

Oxidative post-translational modifications (oxPTM) of receptors, enzymes, ion channels and transcription factors play an important role in cell signaling. oxPTMs are a key way in which oxidative stress can influence cell behavior during diverse pathological settings such as cardiovascular diseases (CVD), cancer, neurodegeneration and inflammatory response. In addition, changes in oxPTM are likely to be ways in which low level reactive oxygen and nitrogen species (RONS) may contribute to redox signaling, exerting changes in physiological responses including angiogenesis, cardiac remodeling and embryogenesis. Among oxPTM, S-glutathionylation of reactive cysteines emerges as an important regulator of vascular homeostasis by modulating endothelial cell (EC) responses to their local redox environment. This review summarizes the latest findings of S-glutathionylated proteins in major EC pathways, and the functional consequences on vascular pathophysiology. This review highlights the diversity of molecules affected by S-glutathionylation, and the complex consequences on EC function, thereby demonstrating an intricate dual role of RONS-induced S-glutathionylation in maintaining vascular homeostasis and participating in various pathological processes.

TIMAP inhibits endothelial myosin light chain phosphatase by competing with MYPT1 for the catalytic protein phosphatase 1 subunit PP1cβ

Transforming growth factor-β membrane associated protein (TIMAP) is an endothelial cell (EC)-predominant PP1 regulatory subunit and a member of the myosin phosphatase target (MYPT) protein family. The MYPTs preferentially bind the catalytic protein phosphatase 1 subunit PP1cβ, forming myosin phosphatase holoenzymes. We investigated whether TIMAP/PP1cβ could also function as a myosin phosphatase. Endogenous PP1cβ, myosin light chain 2 (MLC2), and myosin IIA heavy chain coimmunoprecipitated from EC lysates with endogenous TIMAP, and endogenous MLC2 colocalized with TIMAP in EC projections. Purified recombinant GST-TIMAP interacted directly with purified recombinant His-MLC2. However, TIMAP overexpression in EC enhanced MLC2 phosphorylation, an effect not observed with a TIMAP mutant that does not bind PP1cβ. Conversely, MLC2 phosphorylation was reduced in lung lysates from TIMAP-deficient mice and upon silencing of endogenous TIMAP expression in ECs. Ectopically expressed TIMAP slowed the rate of MLC2 dephosphorylation, an effect requiring TIMAP-PP1cβ interaction. The association of MYPT1 with PP1cβ was profoundly reduced in the presence of excess TIMAP, leading to proteasomal MYPT1 degradation. In the absence of TIMAP, MYPT1-associated PP1cβ readily bound immobilized microcystin-LR, an active-site inhibitor of PP1c. By contrast, TIMAP-associated PP1cβ did not interact with microcystin-LR, indicating that the active site of PP1cβ is blocked when it is bound to TIMAP. Thus, TIMAP inhibits myosin phosphatase activity in ECs by competing with MYPT1 for PP1cβ and blocking the PP1cβ active site.