Akt-mediated transactivation of the S1P1 receptor in caveolin-enriched microdomains regulates endothelial barrier enhancement by oxidized phospholipids

Umbelliferone as an effective component of Rhodiola for protecting the cerebral microvascular endothelial barrier in cSVD

Objective

Rhodiola is a common Chinese herb in the treatment of cerebral small vessel disease (cSVD). Umbelliferone, one of the effective components of Rhodiola, can protect the endothelial barrier. But its mechanisms are still unclear. Therefore, this study is aimed to explore mechanisms of umbelliferone of an effective component of Rhodiola in protecting the cerebral microvascular endothelial barrier in cSVD.

Methods

Firstly, ETCM, SwissTargetPrediction and literatures were used to screen components and targets of Rhodiola. GeneCards was used to obtain targets of cSVD. STRING and Cytoscape were utilized for building the PPI and C-T network. Metascape was utilized to construct GO and KEGG enrichment analysis. Then, molecular docking was employed to evaluate the binding ability of the compounds for their respective target molecules. Ultimately, the endothelial cell damage caused by OGD was employed to explore the protective impact of umbelliferone, a bioactive constituent of Rhodiola, on the endothelial barrier. Endothelial cell leakage and migration assays were used to assess the permeability and migration ability of endothelial cells. IF and WB techniques were employed to ascertain the expression of endothelial tight junction protein. The major target proteins and related pathways were validated by WB.

Results

Six effective components and 106 potential targets were identified and 1885 targets of cSVD were obtained. Nine key targets were selected. GO and KEGG enrichment analysis suggested that effects of Rhodiola in cSVD were associated with PI3K-Akt, Ras, Rap1 and MAPK signal pathways. Molecular docking results showed good binding ability between 28 pairs of key proteins and compounds. Umbelliferone of an effective component of Rhodiola can protect tight junction proteins and improve the permeability and migration ability of endothelial cells damaged by OGD through MMP9, MMP2, CCND1, PTGS2 and PI3K-Akt, Ras, Rap1 signaling pathways.

Conclusion

Our study systematically clarified mechanisms of Rhodiola in treating cSVD by network pharmacology and molecular docking, characterized by its multi-component, multi-target and multi-pathway effects. This finding was validated through in vitro tests, which demonstrated that umbelliferone of an effective component in Rhodiola can protect the brain microvascular endothelial barrier. It provided valuable ideas and references for additional research.

Edema and lymphatic clearance: molecular mechanisms and ongoing challenges

Resolution of edema remains a significant clinical challenge. Conditions such as traumatic shock, sepsis, or diabetes often involve microvascular hyperpermeability, which leads to tissue and organ dysfunction. Lymphatic insufficiency due to genetic causes, surgical removal of lymph nodes, or infections, leads to varying degrees of tissue swelling that impair mobility and immune defenses. Treatment options are limited to management of edema as there are no specific therapeutics that have demonstrated significant success for ameliorating microvascular leakage or impaired lymphatic function. This review examines current knowledge about the physiological, cellular, and molecular mechanisms that control microvascular permeability and lymphatic clearance, the respective processes for interstitial fluid formation and removal. Clinical conditions featuring edema, along with potential future directions are discussed.

Non-Lethal Doses of RSL3 Impair Microvascular Endothelial Barrier through Degradation of Sphingosie-1-Phosphate Receptor 1 and Cytoskeletal Arrangement in A Ferroptosis-Independent Manner

The excess microvascular endothelial permeability is a hallmark of acute inflammatory diseases. Maintenance of microvascular integrity is critical to preventing leakage of vascular components into the surrounding tissues. Sphingosine-1-phosphate (S1P) is an active lysophospholipid that enhances the endothelial cell (EC) barrier via activation of its receptor S1PR1. Here, we delineate the effect of non-lethal doses of RSL3, an inhibitor of glutathione peroxidase 4 (GPX4), on EC barrier function. Low doses of RSL3 (50-100 nM) attenuated S1P-induced human lung microvascular barrier enhancement and the phosphorylation of AKT. To investigate the molecular mechanisms by which RSL3 attenuates S1P's effect, we examined the S1PR1 levels. RSL3 treatment reduced S1PR1 levels in 1 h, whereas the effect was attenuated by the proteasome and lysosome inhibitors as well as a lipid raft inhibitor. Immunofluorescence staining showed that RSL3 induced S1PR1 internalization from the plasma membrane into the cytoplasm. Furthermore, we found that RSL3 (100 and 200 nM) increased EC barrier permeability and cytoskeletal rearrangement without altering cell viability. Taken together, our data delineates that non-lethal doses of RSL3 impair EC barrier function via two mechanisms. RSL3 attenuates S1P1-induced EC barrier enhancement and disrupts EC barrier integrity through the generation of 4-hydroxynonena (4HNE). All these effects are independent of ferroptosis.

Mechanisms of pulmonary endothelial permeability and inflammation caused by extracellular histone subunits H3 and H4

Extracellular DNA-binding proteins such as histones are danger-associated molecular pattern released by the injured tissues in trauma and sepsis settings, which trigger host immune response and vascular dysfunction. Molecular events leading to histone-induced endothelial cell (EC) dysfunction remain poorly understood. This study performed comparative analysis of H1, H2A, H2B, H3, and H4 histone subunits effects on human pulmonary EC permeability and inflammatory response. Analysis of transendothelial electrical resistance and EC monolayer permeability for macromolecues revealed that H3 and H4, but not H1, H2A, or H2B caused dose-dependent EC permeability accompanied by disassembly of adherens junctions. At higher doses, H3 and H4 activated nuclear factor kappa B inflammatory cascade leading to upregulation EC adhesion molecules ICAM1, VCAM1, E-selectin, and release of inflammatory cytokines. Inhibitory receptor analysis showed that toll-like receptor (TLR) 4 but not TLR1/2 or receptor for advanced glycation end inhibition significantly attenuated deleterious effects of H3 and H4 histones. Inhibitor of Rho-kinase was without effect, while inhibition of Src kinase caused partial preservation of cell-cell junctions, H3/H4-induced permeability and inflammation. Deleterious effects of H3/H4 were blocked by heparin. Activation of Epac-Rap1 signaling restored EC barrier properties after histone challenge. Intravenous injection of histones in mice caused elevation of inflammatory markers and increased vascular leak. Post-treatment with pharmacological Epac/Rap1 activator suppressed injurious effects of histones in vitro and in vivo. These results identify H3 and H4 as key histone subunits exhibiting deleterious effects on pulmonary vascular endothelium via TLR4-dependent mechanism. In conclusion, elevation of circulating histones may represent a serious risk of exacerbated acute lung injury (ALI) and multiple organ injury during severe trauma and infection.

Hydrogen Sulfide Actions in the Vasculature

Hydrogen sulfide (H2 S) is a small, gaseous molecule with poor solubility in water that is generated by multiple pathways in many species including humans. It acts as a signaling molecule in many tissues with both beneficial and pathological effects. This article discusses its many actions in the vascular system and the growing evidence of its role to regulate vascular tone, angiogenesis, endothelial barrier function, redox, and inflammation. Alterations in some disease states are also discussed including potential roles in promoting tumor growth and contributions to the development of metabolic disease. © 2021 American Physiological Society. Compr Physiol 11:1-22, 2021.

Programming to S1PR1+ Endothelial Cells Promotes Restoration of Vascular Integrity

[Figure: see text].

Barrier maintenance by S1P during inflammation and sepsis

Sphingosine 1-phosphate (S1P) is a multifaceted lipid signaling molecule that activates five specific G protein-coupled S1P receptors. Despite the fact that S1P is known as one of the strongest barrier-enhancing molecules for two decades, no medical application is available yet. The reason for this lack of translation into clinical practice may be the complex regulatory network of S1P signaling, metabolism and transportation.In this review, we will provide an overview about the physiology and the network of S1P signaling with the focus on endothelial barrier maintenance in inflammation. We briefly describe the physiological role of S1P and the underlying S1P signaling in barrier maintenance, outline differences of S1P signaling and metabolism in inflammatory diseases, discuss potential targets and compounds for medical intervention, and summarize our current knowledge regarding the role of S1P in the maintenance of specialized barriers like the blood-brain barrier and the placenta.

Inhibitory effects of cudratricusxanthone O on particulate matter-induced pulmonary injury

Particulate matter 2.5 (PM_2.5), aerodynamic diameter ≤ 2.5 μm, is the primary air pollutant that plays the key role for lung injury resulted from the loss of vascular barrier integrity. Cudratricusxanthone O (CTXO) is a novel xanthone compound isolated from the root of Cudrania tricuspidata Bureau. Here, we investigated the beneficial effects of CTXO against PM-induced lung endothelial cell (EC) barrier disruption and pulmonary inflammation. Permeability, leukocyte migration, activation of proinflammatory proteins, generation of reactive oxygen species (ROS), and histology were examined in PM_2.5-treated ECs and mice. CTXO significantly scavenged PM_2.5-induced ROS and inhibited the ROS-induced activation of p38 mitogen-activated protein kinase (MAPK). Concurrently, CTXO activated Akt, which helped maintain endothelial integrity. Furthermore, CTXO reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in the bronchoalveolar lavage fluid in PM-induced lung tissues. These results indicated that CTXO may exhibit protective effects against PM-induced inflammatory lung injury and vascular hyperpermeability.

Oxidized Phospholipids in Control of Endothelial Barrier Function: Mechanisms and Implication in Lung Injury

Earlier studies investigating the pathogenesis of chronic vascular inflammation associated with atherosclerosis described pro-inflammatory and vascular barrier disruptive effects of lipid oxidation products accumulated in the sites of vascular lesion and atherosclerotic plaque. However, accumulating evidence including studies from our group suggests potent barrier protective and anti-inflammatory properties of certain oxidized phospholipids (OxPLs) in the lung vascular endothelium. Among these OxPLs, oxidized 1-palmitoyl-2-arachdonyl-sn-glycero-3-phosphocholine (OxPAPC) causes sustained enhancement of lung endothelial cell (EC) basal barrier properties and protects against vascular permeability induced by a wide variety of agonists ranging from bacterial pathogens and their cell wall components, endotoxins, thrombin, mechanical insults, and inflammatory cytokines. On the other hand, truncated OxPLs cause acute endothelial barrier disruption and potentiate inflammation. It appears that multiple signaling mechanisms triggering cytoskeletal remodeling are involved in OxPLs-mediated regulation of EC barrier. The promising vascular barrier protective and anti-inflammatory properties exhibited by OxPAPC and its particular components that have been established in the cellular and animal models of sepsis and acute lung injury has prompted consideration of OxPAPC as a prototype therapeutic molecule. In this review, we will summarize signaling and cytoskeletal mechanisms involved in OxPLs-mediated damage, rescue, and restoration of endothelial barrier in various pathophysiological settings and discuss a future potential of OxPAPC in treating lung disorders associated with endothelial barrier dysfunction.

Dooming Phagocyte Responses: Inflammatory Effects of Endogenous Oxidized Phospholipids

Endogenous oxidized phospholipids are produced during tissue stress and are responsible for sustaining inflammatory responses in immune as well as non-immune cells. Their local and systemic production and accumulation is associated with the etiology and progression of several inflammatory diseases, but the molecular mechanisms that underlie the biological activities of these oxidized phospholipids remain elusive. Increasing evidence highlights the ability of these stress mediators to modulate cellular metabolism and pro-inflammatory signaling in phagocytes, such as macrophages and dendritic cells, and to alter the activation and polarization of these cells. Because these immune cells serve a key role in maintaining tissue homeostasis and organ function, understanding how endogenous oxidized lipids reshape phagocyte biology and function is vital for designing clinical tools and interventions for preventing, slowing down, or resolving chronic inflammatory disorders that are driven by phagocyte dysfunction. Here, we discuss the metabolic and signaling processes elicited by endogenous oxidized lipids and outline new hypotheses and models to elucidate the impact of these lipids on phagocytes and inflammation.

Post-translational modifications of S1PR1 and endothelial barrier regulation

Sphingosine-1-phosphate receptor-1 (S1PR1), a G-protein coupled receptor that is expressed in endothelium and activated upon ligation by the bioactive lipid sphingosine-1-phosphate (S1P), is an important vascular-barrier protective mechanism at the level of adherens junctions (AJ). Loss of endothelial barrier function is a central factor in the pathogenesis of various inflammatory conditions characterized by protein-rich lung edema formation, such as acute respiratory distress syndrome (ARDS). While several S1PR1 agonists are available, the challenge of arresting the progression of protein-rich edema formation remains to be met. In this review, we discuss the role of S1PRs, especially S1PR1, in regulating endothelial barrier function. We review recent findings showing that replenishment of the pool of cell-surface S1PR1 may be crucial to the effectiveness of S1P in repairing the endothelial barrier. In this context, we discuss the S1P generating machinery and mechanisms that regulate S1PR1 at the cell surface and their impact on endothelial barrier function.

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.

Oxidized Phospholipids in Healthy and Diseased Lung Endothelium

Circulating and cell membrane phospholipids undergo oxidation caused by enzymatic and non-enzymatic mechanisms. As a result, a diverse group of bioactive oxidized phospholipids generated in these conditions have both beneficial and harmful effects on the human body. Increased production of oxidized phospholipid products with deleterious effects is linked to the pathogenesis of various cardiopulmonary disorders such as atherosclerosis, thrombosis, acute lung injury (ALI), and inflammation. It has been determined that the contrasting biological effects of lipid oxidation products are governed by their structural variations. For example, full-length products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine oxidation (OxPAPC) have prominent endothelial barrier protective and anti-inflammatory activities while most of the truncated oxidized phospholipids induce vascular leak and exacerbate inflammation. The extensive studies from our group and other groups have demonstrated a strong potential of OxPAPC in mitigating a wide range of agonist-induced lung injuries and inflammation in pulmonary endothelial cell culture and rodent models of ALI. Concurrently, elevated levels of truncated oxidized phospholipids are present in aged mice lungs that potentiate the inflammatory agents-induced lung injury. On the other hand, increased levels of full length OxPAPC products accelerate ALI recovery by facilitating production of anti-inflammatory lipid mediator, lipoxin A4, and other molecules with anti-inflammatory properties. These findings suggest that OxPAPC-assisted lipid program switch may be a promising therapeutic strategy for treatment of acute inflammatory syndromes. In this review, we will summarize the vascular-protective and deleterious aspects of oxidized phospholipids and discuss their therapeutic potential including engineering of stable analogs of oxidized phospholipids with improved anti-inflammatory and barrier-protective properties.

Apolipoprotein M-bound sphingosine-1-phosphate regulates blood-brain barrier paracellular permeability and transcytosis

The blood-brain barrier (BBB) is formed by the endothelial cells lining cerebral microvessels, but how blood-borne signaling molecules influence permeability is incompletely understood. We here examined how the apolipoprotein M (apoM)-bound sphingosine 1-phosphate (S1P) signaling pathway affects the BBB in different categories of cerebral microvessels using ApoM deficient mice (Apom-/-). We used two-photon microscopy to monitor BBB permeability of sodium fluorescein (376 Da), Alexa Fluor (643 Da), and fluorescent albumin (45 kDA). We show that BBB permeability to small molecules increases in Apom-/- mice. Vesicle-mediated transfer of albumin in arterioles increased 3 to 10-fold in Apom-/- mice, whereas transcytosis in capillaries and venules remained unchanged. The S1P receptor 1 agonist SEW2871 rapidly normalized paracellular BBB permeability in Apom-/- mice, and inhibited transcytosis in penetrating arterioles, but not in pial arterioles. Thus, apoM-bound S1P maintains low paracellular BBB permeability in all cerebral microvessels and low levels of vesicle-mediated transport in penetrating arterioles.

Inhibitory Effects of Black Ginseng on Particulate Matter-Induced Pulmonary Injury

Inhalation of fine particulate matter (PM2.5) is associated with elevated pulmonary injury caused by the loss of vascular barrier integrity. Black ginseng (BG), steamed and dried ginseng nine times, exhibits various pharmacological activities such as antibacterial, antihyperglycemic, anti-atopic, antibacterial, and anti-inflammatory activities. In this study, we investigated the beneficial effects of black ginseng extract (BGE) against PM-induced lung endothelial cell (EC) barrier disruption and pulmonary inflammation. Permeability, leukocyte migration, activation of proinflammatory proteins, generation of reactive oxygen species (ROS), and histology were examined in PM2.5-treated ECs and mice. BGE significantly scavenged PM2.5-induced ROS and inhibited the ROS-induced activation of p38 mitogen-activated protein kinase (MAPK). Concurrently, BGE activated Akt, which helped maintain endothelial integrity. Furthermore, BGE reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in the bronchoalveolar lavage fluid in PM-induced lung tissues. These results indicated that BGE may exhibit protective effects against PM-induced inflammatory lung injury and vascular hyperpermeability.

Inhibitory effects of collismycin C and pyrisulfoxin A on particulate matter-induced pulmonary injury

BACKGROUND

Inhalation of fine particulate matter (PM_2.5) is associated with elevated pulmonary injury caused by the loss of vascular barrier integrity. Marine microbial natural products isolated from microbial culture broths were screened for pulmonary protective effects against PM_2.5. Two 2,2'-bipyridine compounds isolated from a red alga-associated Streptomyces sp. MC025-collismycin C (2) and pyrisulfoxin A (5)-were found to inhibit PM_2.5-mediated vascular barrier disruption.

PURPOSE

To confirm the inhibitory effects of collismycin C and pyrisulfoxin A on PM_2.5-induced pulmonary injury STUDY DESIGN: In this study, we investigated the beneficial effects of collismycin C and pyrisulfoxin A on PM-induced lung endothelial cell (EC) barrier disruption and pulmonary inflammation.

METHODS

Permeability, leukocyte migration, proinflammatory protein activation, reactive oxygen species (ROS) generation, and histology were evaluated in PM_2.5-treated ECs and mice.

RESULTS

Collismycin C and pyrisulfoxin A significantly scavenged PM_2.5-induced ROS and inhibited the ROS-induced activation of p38 mitogen-activated protein kinase as well as activated Akt, which helped in maintaining endothelial integrity, in purified pulmonary endothelial cells. Furthermore, collismycin C and pyrisulfoxin A reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in the bronchoalveolar lavage fluid of PM-treated mice.

CONCLUSION

These data suggested that collismycin C and pyrisulfoxin A might exert protective effects on PM-induced inflammatory lung injury and vascular hyperpermeability.

Inhibitory effects of compounds isolated from Dioscorea batatas Decne peel on particulate matter-induced pulmonary injury in mice

Particulate matter 2.5 (PM_2.5), with an aerodynamic diameter of ≤2.5 μm, is the primary air pollutant that plays a key role associated with lung injury produced by loss of vascular barrier integrity. Dioscorea batatas Decne (Chinese yam), a perennial plant belonging to Dioscoreaceae family, is widely cultivated in tropical and subtropical regions across Asia. Both aerial parts and root of D. batatas are consumed for nutritional and medicinal purposes. The aim of this study was to (1) identify the bioactive compounds present in D. batatas peel which may be responsible for inhibition of PM_2.5-induced pulmonary inflammation in mice and (2) examine in vitro mechanisms underlying the observed effects of these compounds on mouse lung microvascular endothelial cells. The measured parameters include permeability, leukocyte migration, proinflammatory protein activation, reactive oxygen species (ROS) generation, and histology. Two phenanthrene compounds, 2,7-dihydroxy-4,6-dimethoxyphenanthrene (1) and 6,7-dihydroxy-2,4-dimethoxyphenanthrene (2) were isolated from D. batatas peels. Both these phenanthrene compounds exhibited significant scavenging activity against PM_2.5-induced ROS and inhibited ROS-induced activation of p38 mitogen-activated protein kinase. In addition, enhancement of Akt pathway, involved in the maintenance of endothelial integrity, was noted. These phenanthrene compounds also reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in the bronchoalveolar lavage fluid obtained from PM_2.5-induced lung tissues. Evidence thus indicates that phenanthrene compounds derived from D. batatas may exhibit protective effects against PM_2.5-induced inflammatory lung injury and vascular hyperpermeability in mice.

Evaluation system construction and factor impact analysis of silica-gel adsorption to extract phytosterol glycosides from soybean lecithin powder

BACKGROUND

Soybean lecithin powders are good sources of phytosterol glucosides (PGs) containing acyl-sterylglycosides (ASGs) and sterylglucosides (SGs), but PG extraction from soybean lecithin powder is difficult due to the solubilizing property of phospolipids. To comprehensively utilize soybean lecithin resources, an evaluation system construction and factor impact analysis of PG extraction by silica-gel adsorption was investigated in this article.

RESULTS

With high-performance liquid chromatography (HPLC) as the main experimental analysis method, software such as SIMICA and SPSS were applied to construct an evaluation system of PG extraction. Different from scores plot in SIMICA for distinguishing samples in chloroform from others, the loading plot and binary variant correlation analysis of all indicators in PG extraction were brought to confirm four evaluation indicators containing PG purity, ASG recovery, SG recovery and phospholipid recovery. In the factor impact analysis, four times elution from silica-gel sediment was enough to achieve a PG product with least reagent waste, while SPW in petroleum ether at 50 mg mL-1 with 1:3 silica-gel dosage (lecithin/silica-gel, w/w) was then determined as the optimum of single factors.

CONCLUSION

All studies in this article were of great significance, as they laid foundations for research of PG extraction procedure, as well as PG industrial production, facilitating the comprehensive utilization of lecithin resources. © 2019 Society of Chemical Industry.

The unconventional role of Akt1 in the advanced cancers and in diabetes-promoted carcinogenesis

Decades of research have elucidated the critical role of Akt isoforms in cancer as pro-tumorigenic and metastatic regulators through their specific effects on the cancer cells, tumor endothelial cells and the stromal cells. The pro-cancerous role of Akt isoforms through enhanced cell proliferation and suppression of apoptosis in cancer cells and the cells in the tumor microenvironment is considered a dogma. Intriguingly, studies also indicate that the Akt pathway is essential to protect the endothelial-barrier and prevent aberrant vascular permeability, which is also integral to tumor perfusion and metastasis. To complicate this further, a flurry of recent reports strongly indicates the metastasis suppressive role of Akt, Akt1 in particular in various cancer types. These reports emanated from different laboratories have elegantly demonstrated the paradoxical effect of Akt1 on cancer cell epithelial-to-mesenchymal transition, invasion, tumor endothelial-barrier disruption, and cancer metastasis. Here, we emphasize on the specific role of Akt1 in mediating tumor cell-vasculature reciprocity during the advanced stages of cancers and discuss how Akt1 differentially regulates cancer metastasis through mechanisms distinct from its pro-tumorigenic effects. Since Akt is integral for insulin signaling, endothelial function, and metabolic regulation, we also attempt to shed some light on the specific effects of diabetes in modulating Akt pathway in the promotion of tumor growth and metastasis.

Inhibitory effects of Kyung-Ok-Ko, traditional herbal prescription, on particulate matter-induced vascular barrier disruptive responses

Inhalation of fine particulate matter (PM_2.5) is associated with elevated pulmonary injury caused by the loss of vascular barrier integrity. A traditional herbal prescription, Kyung-Ok-Ko (KOK), has long been used in Oriental medicine as a tonic for age-related diseases. In this study, we investigated the beneficial effects of KOK on PM-induced lung endothelial cell (EC) barrier disruption and pulmonary inflammation. Permeability, leukocyte migration, activation of proinflammatory proteins, generation of reactive oxygen species (ROS), and histology were examined in PM_2.5-treated EC and mice. KOK significantly scavenged PM_2.5-induced ROS and inhibited the ROS-induced activation of p38 mitogen-activated protein kinase (MAPK). Concurrently, KOK activated Akt, which helped maintain endothelial integrity. Furthermore, KOK reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in bronchoalveolar lavage fluids in PM-induced lung tissues. These data suggested that KOK might exhibit protective effects in PM-induced inflammatory lung injury and vascular hyperpermeability.

Mechanosensitive Rap1 activation promotes barrier function of lung vascular endothelium under cyclic stretch

Mechanical ventilation remains an imperative treatment for the patients with acute respiratory distress syndrome, but can also exacerbate lung injury. We have previously described a key role of RhoA GTPase in high cyclic stretch (CS)-induced endothelial cell (EC) barrier dysfunction. However, cellular mechanotransduction complexes remain to be characterized. This study tested a hypothesis that recovery of a vascular EC barrier after pathologic mechanical stress may be accelerated by cell exposure to physiologic CS levels and involves Rap1-dependent rearrangement of endothelial cell junctions. Using biochemical, molecular, and imaging approaches we found that EC pre- or postconditioning at physiologically relevant low-magnitude CS promotes resealing of cell junctions disrupted by pathologic, high-magnitude CS. Cytoskeletal remodeling induced by low CS was dependent on small GTPase Rap1. Protective effects of EC preconditioning at low CS were abolished by pharmacological or molecular inhibition of Rap1 activity. In vivo, using mice exposed to mechanical ventilation, we found that the protective effect of low tidal volume ventilation against lung injury caused by lipopolysaccharides and ventilation at high tidal volume was suppressed in Rap1 knockout mice. Taken together, our results demonstrate a prominent role of Rap1-mediated signaling mechanisms activated by low CS in acceleration of lung vascular EC barrier restoration.

Inhibitory effects of protopanaxatriol type ginsenoside fraction (Rgx365) on particulate matter-induced pulmonary injury

Inhalation of fine particulate matter (PM_2.5) is associated with elevated pulmonary injury attributed to the loss of vascular barrier integrity. Black ginseng (BG), steamed 9 times and dried ginseng, and its major protopanaxatriol type ginsenosides (ginsenoside Rg4, Rg6, Rh4, Rh1, and Rg2) exhibited various biological activities including anti-septic, anti-diabetic, wound healing, immune-stimulatory, and anti-antioxidant activity. The aim of this study was to investigate the beneficial effects of Rgx365 (a protopanaxatriol type rare ginsenosides fraction) on PM-induced lung endothelial cell (EC) barrier disruption and pulmonary inflammation. Permeability, leukocyte migration, activation of proinflammatory proteins, generation of reactive oxygen species (ROS), and histology were examined in PM_2.5-treated EC and mice. Rgx365 significantly scavenged PM_2.5-induced ROS, inhibited ROS-induced activation of p38 mitogen-activated protein kinase (MAPK), activated Akt in purified pulmonary EC, which helped maintain endothelial integrity. Further, Rgx365 reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in bronchoalveolar lavage fluids in PM-induced mouse lung tissues. Data suggested that Rgx365 might exhibit protective effects in PM-induced inflammatory lung injury and vascular hyperpermeability.

Sphingolipids Signaling in Lamellipodia Formation and Enhancement of Endothelial Barrier Function

Sphingolipids, first described in the brain in 1884, are important structural components of biological membranes of all eukaryotic cells. In recent years, several lines of evidence support the critical role of sphingolipids such as sphingosine, sphingosine-1-phosphate (S1P), and ceramide as anti- or pro-inflammatory bioactive lipid mediators in a variety of human pathologies including pulmonary and vascular disorders. Among the sphingolipids, S1P is a naturally occurring agonist that exhibits potent barrier enhancing property in the endothelium by signaling via G protein-coupled S1P1 receptor. S1P, S1P analogs, and other barrier enhancing agents such as HGF, oxidized phospholipids, and statins also utilize the S1P/S1P1 signaling pathway to generate membrane protrusions or lamellipodia, which have been implicated in resealing of endothelial gaps and maintenance of barrier integrity. A better understanding of sphingolipids mediated regulation of lamellipodia formation and barrier enhancement of the endothelium will be critical for the development of sphingolipid-based therapies to alleviate pulmonary disorders such as sepsis-, radiation-, and mechanical ventilation-induced acute lung injury.

Endothelial Akt1 loss promotes prostate cancer metastasis via β-catenin-regulated tight-junction protein turnover

Background

Cancer research, in general, is focused on targeting tumour cells to limit tumour growth. These studies, however, do not account for the specific effects of chemotherapy on tumour endothelium, in turn, affecting metastasis.

Methods

We determined how endothelial deletion of Akt1 promotes prostate cancer cell invasion in vitro and metastasis to the lungs in vivo in endothelial-specific Akt1 knockdown mice.

Results

Here we show that metastatic human PC3 and DU145 prostate cancer cells invade through Akt1-deficient human lung endothelial cell (HLEC) monolayer with higher efficiency compared to control HLEC. Although the endothelial Akt1 loss in mice had no significant effect on RM1 tumour xenograft growth in vivo, it promoted metastasis to the lungs compared to the wild-type mice. Mechanistically, Akt1-deficient endothelial cells exhibited increased phosphorylation and nuclear translocation of phosphorylated β-catenin, and reduced expression of tight-junction proteins claudin-5, ZO-1 and ZO-2. Pharmacological inhibition of β-catenin nuclear translocation using compounds ICG001 and IWR-1 restored HLEC tight-junction integrity and inhibited prostate cancer cell transendothelial migration in vitro and lung metastasis in vivo.

Conclusions

Here we show for the first time that endothelial-specific loss of Akt1 promotes cancer metastasis in vivo involving β-catenin pathway.

Sphingosine-1-Phosphate Receptor-1 Agonist Sew2871 Causes Severe Cardiac Side Effects and Does Not Improve Microvascular Barrier Breakdown in Sepsis

BACKGROUND

Endothelial barrier dysfunction is a hallmark in the pathogenesis of sepsis. Sphingosine-1-phosphate (S1P) has been proposed to be critically involved in the maintenance of endothelial barrier function predominately by activating S1P receptor-1 (S1P1). Previous studies have shown that the specific S1P1 agonist SEW2871 improves endothelial barrier function under inflammatory conditions. However, the effectiveness of SEW2871 and potential side effects remained largely unexplored in a clinically relevant model of sepsis. Therefore, this study aimed to evaluate the effects of SEW2871 in the Colon ascendens stent peritonitis (CASP) model.

METHODS

Polymicrobial sepsis was induced in Sprague-Dawley rats using CASP model that enabled the monitoring of macro-hemodynamic parameters. Twelve hours after surgery, animals received either SEW2871 or sodium chloride. Mesenteric endothelial barrier function was evaluated 24 h after sepsis induction by intravital microscopy. Organ pathology was assessed in lungs. S1P levels, blood gas analyses, and blood values were measured at different time points. In parallel the effect of SEW2871 was evaluated in human dermal microvascular endothelial cells.

RESULT

In vitro SEW2871 partially stabilized TNF-α-induced endothelial barrier breakdown. However, in vivo SEW2871 caused severe cardiac side effects in septic animals leading to an increased lethality. Sepsis-induced endothelial barrier dysfunction was not attenuated by SEW2871 as revealed by increased FITC-albumin extra-vasation, requirement of intravasal fluid replacement, and pulmonary edema. Interestingly, Sham-operated animals did not present any side effects after SEW2871 treatment.

CONCLUSION

Our study demonstrates that the application of SEW2871 causes severe cardiac side effects and cannot attenuate the inflammation-induced endothelial barrier breakdown in a clinically relevant sepsis model, suggesting that the time point of administration and the pro-inflammatory milieu play a pivotal role in the therapeutic benefit of SEW2871.

Injured lung endothelium: mechanisms of self-repair and agonist-assisted recovery (2017 Grover Conference Series)

The lung endothelium is vulnerable to both exogenous and endogenous insults, so a properly coordinated efficient repair system is essential for the timely recovery of the lung after injury. The agents that cause endothelial injury and dysfunction fall into a broad range from mechanical forces such as pathological cyclic stretch and shear stress to bacterial pathogens and their virulent components, vasoactive agonists including thrombin and histamine, metabolic causes including high glucose and oxidized low-density lipoprotein (OxLDL), circulating microparticles, and inflammatory cytokines. The repair mechanisms employed by endothelial cells (EC) can be broadly categorized into three groups: (1) intrinsic mechanism of recovery regulated by the cross-talk between small GTPases as exemplified by Rap1-mediated EC barrier recovery from Rho-mediated thrombin-induced EC hyperpermeability; (2) agonist-assisted recovery facilitated by the activation of Rac and Rap1 with subsequent inhibition of Rho signaling as observed with many barrier protective agonists including oxidized phospholipids, sphingosine 1-phosphate, prostacyclins, and hepatocyte growth factor; and (3) self-recovery of EC by the secretion of growth factors and other pro-survival bioactive compounds including anti-inflammatory molecules such as lipoxins during the resolution of inflammation. In this review, we will discuss the molecular and cellular mechanisms of pulmonary endothelium repair that is critical for the recovery from various forms of lung injuries.

Lipid mediators in the regulation of endothelial barriers

Lipid mediators play a critical role in the development and resolution of vascular endothelial barrier dysfunction caused by various pathologic interventions. The accumulation of excess lipids directly impairs endothelial cell (EC) barrier function that is known to contribute to the development of atherosclerosis and metabolic disorders such as obesity and diabetes as well as chronic inflammation in the vascular endothelium. Certain products of phospholipid oxidation (OxPL) such as fragmented phospholipids generated during oxidative and nitrosative stress show pro-inflammatory potential and cause endothelial barrier dysfunction. In turn, other OxPL products enhance basal EC barrier and exhibit potent barrier-protective effects in pathologic settings of acute vascular leak caused by pro-inflammatory mediators, barrier disruptive agonists and pathologic mechanical stimulation. These beneficial effects were further confirmed in rodent models of lung injury and inflammation. The bioactive oxidized lipid molecules may serve as important therapeutic prototype molecules for future treatment of acute lung injury syndromes associated with endothelial barrier dysfunction and inflammation. This review will summarize recent studies of biological effects exhibited by various groups of lipid mediators with a focus on the role of oxidized phospholipids in control of vascular endothelial barrier, agonist induced EC permeability, inflammation, and barrier recovery related to clinical settings of acute lung injury and inflammatory vascular leak.

Pleiotropic effects of oxidized phospholipids

Oxidized phospholipids (OxPLs) are increasingly recognized to play a role in a variety of normal and pathological states. OxPLs were implicated in regulation of inflammation, thrombosis, angiogenesis, endothelial barrier function, immune tolerance and other important processes. Rapidly accumulating evidence suggests that OxPLs are biomarkers of atherosclerosis and other pathologies. In addition, successful application of experimental drugs based on structural scaffold of OxPLs in animal models of inflammation was recently reported. This review briefly summarizes current knowledge on generation, methods of quantification and biological activities of OxPLs. Furthermore, receptor and cellular mechanisms of these effects are discussed. The goal of the review is to give a broad overview of this class of lipid mediators inducing pleiotropic biological effects.

The effect of oxidized phospholipids on phenotypic polarization and function of macrophages

Oxidized phospholipids are products of lipid oxidation that are found on oxidized low-density lipoproteins and apoptotic cell membranes. These biologically active lipids were shown to affect a variety of cell types and attributed pro-as well as anti-inflammatory effects. In particular, macrophages exposed to oxidized phospholipids drastically change their gene expression pattern and function. These 'Mox,'macrophages were identified in atherosclerotic lesions, however, it remains unclear how lipid oxidation products are sensed by macrophages and how they influence their biological function. Here, we review recent developments in the field that provide insight into the structure, recognition, and downstream signaling of oxidized phospholipids in macrophages.

Sphingosine 1-phosphate (S1P) signalling: Role in bone biology and potential therapeutic target for bone repair

The lipid mediator sphingosine 1-phosphate (S1P) affects cellular functions in most systems. Interest in its therapeutic potential has increased following the discovery of its G protein-coupled receptors and the recent availability of agents that can be safely administered in humans. Although the role of S1P in bone biology has been the focus of much less research than its role in the nervous, cardiovascular and immune systems, it is becoming clear that this lipid influences many of the functions, pathways and cell types that play a key role in bone maintenance and repair. Indeed, S1P is implicated in many osteogenesis-related processes including stem cell recruitment and subsequent differentiation, differentiation and survival of osteoblasts, and coupling of the latter cell type with osteoclasts. In addition, S1P's role in promoting angiogenesis is well-established. The pleiotropic effects of S1P on bone and blood vessels have significant potential therapeutic implications, as current therapeutic approaches for critical bone defects show significant limitations. Because of the complex effects of S1P on bone, the pharmacology of S1P-like agents and their physico-chemical properties, it is likely that therapeutic delivery of S1P agents will offer significant advantages compared to larger molecular weight factors. Hence, it is important to explore novel methods of utilizing S1P agents therapeutically, and improve our understanding of how S1P and its receptors modulate bone physiology and repair.

Endothelial cell-cell adhesion and signaling

Endothelial cells line blood vessels and provide a dynamic interface between the blood and tissues. They remodel to allow leukocytes, fluid and small molecules to enter tissues during inflammation and infections. Here we compare the signaling networks that contribute to endothelial permeability and leukocyte transendothelial migration, focusing particularly on signals mediated by small GTPases that regulate cell adhesion and the actin cytoskeleton. Rho and Rap GTPase signaling is important for both processes, but they differ in that signals are activated locally under leukocytes, whereas endothelial permeability is a wider event that affects the whole cell. Some molecules play a unique role in one of the two processes, and could therefore be targeted to selectively alter either endothelial permeability or leukocyte transendothelial migration.

Prostaglandin E receptor-4 receptor mediates endothelial barrier-enhancing and anti-inflammatory effects of oxidized phospholipids

Unlike other agonists that cause transient endothelial cell (EC) response, the products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC) oxidation that contain cyclopenthenone groups, which recapitulate prostaglandin-like structure, cause sustained enhancement of the pulmonary EC barrier. The mechanisms that drive the sustained effects by oxidized PAPC (OxPAPC) remain unexplored. On the basis of the structural similarity of isoprostanoid moieties that are present in full-length oxygenated PAPC species, we used an inhibitory approach to perform the screening of prostanoid receptors as potential candidates that mediate OxPAPC effects. Results show that only prostaglandin E receptor-4 (EP4) was involved and mediated the sustained phase of the barrier-enhancing effects of OxPAPC that are associated with the activation of Rac GTPase and its cytoskeletal targets. EC incubation with OxPAPC also induced EP4 mRNA expression in pulmonary ECs and lung tissue. EP4 knockdown using gene-specific small interfering RNA did not affect the rapid phase of OxPAPC-induced EC barrier enhancement or the protective effects against thrombin-induced EC permeability, but abolished the advanced barrier enhancement phase and suppressed the protective effects of OxPAPC against more sustained EC barrier dysfunction and cell inflammatory response caused by TNF-α. Endothelial-specific knockout of the EP4 receptor in mice attenuated the protective effect of intravenous OxPAPC administration in the model of acute lung injury caused by intratracheal injection of LPS. Taken together, these results demonstrate a novel role for prostaglandin receptor EP4 in the mediation of barrier-enhancing and anti-inflammatory effects caused by oxidized phospholipids.-Oskolkova, O., Gawlak, G., Tian, Y., Ke, Y., Sarich, N., Son, S., Andreasson, K., Bochkov, V. N., Birukova, A. A., Birukov, K. G. Prostaglandin E receptor-4 receptor mediates endothelial barrier-enhancing and anti-inflammatory effects of oxidized phospholipids.

Anti-Inflammatory Effects of OxPAPC Involve Endothelial Cell-Mediated Generation of LXA4

RATIONALE

Oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC) generates a group of bioactive oxidized phospholipid products with a broad range of biological activities. Barrier-enhancing and anti-inflammatory effects of OxPAPC on pulmonary endothelial cells are critical for prevention of acute lung injury caused by bacterial pathogens or excessive mechanical ventilation. Anti-inflammatory properties of OxPAPC are associated with its antagonistic effects on Toll-like receptors and suppression of RhoA GTPase signaling.

OBJECTIVE

Because OxPAPC exhibits long-lasting anti-inflammatory and lung-protective effects even after single administration in vivo, we tested the hypothesis that these effects may be mediated by additional mechanisms, such as OxPAPC-dependent production of anti-inflammatory and proresolving lipid mediator, lipoxin A4 (LXA4).

METHODS AND RESULTS

Mass spectrometry and ELISA assays detected significant accumulation of LXA4 in the lungs of OxPAPC-treated mice and in conditioned medium of OxPAPC-exposed pulmonary endothelial cells. Administration of LXA4 reproduced anti-inflammatory effect of OxPAPC against tumor necrosis factor-α in vitro and in the animal model of lipopolysaccharide-induced lung injury. The potent barrier-protective and anti-inflammatory effects of OxPAPC against tumor necrosis factor-α and lipopolysaccharide challenge were suppressed in human pulmonary endothelial cells with small interfering RNA-induced knockdown of LXA4 formyl peptide receptor-2 (FPR2/ALX) and in mFPR2^-/- (mouse formyl peptide receptor 2) mice lacking the mouse homolog of human FPR2/ALX.

CONCLUSIONS

This is the first demonstration that inflammation- and injury-associated phospholipid oxidation triggers production of anti-inflammatory and proresolution molecules, such as LXA4. This lipid mediator switch represents a novel mechanism of OxPAPC-assisted recovery of inflamed lung endothelium.

Simvastatin-induced sphingosine 1-phosphate receptor 1 expression is KLF2-dependent in human lung endothelial cells

We have demonstrated that simvastatin and sphingosine 1−phosphate (S1P) both attenuate increased vascular permeability in preclinical models of acute respiratory distress syndrome. However, the underlying mechanisms remain unclear. As Krüppel-like factor 2 (KLF2) serves as a critical regulator for cellular stress response in endothelial cells (EC), we hypothesized that simvastatin enhances endothelial barrier function via increasing expression of the barrier-promoting S1P receptor, S1PR1, via a KLF2-dependent mechanism. S1PR1 luciferase reporter promoter activity in human lung artery EC (HPAEC) was tested after simvastatin (5 μM), and S1PR1 and KLF2 protein expression detected by immunoblotting. In vivo, transcription and expression of S1PR1 and KLF2 in mice lungs were detected by microarray profiling and immunoblotting after exposure to simvastatin (10 mg/kg). Endothelial barrier function was measured by trans-endothelial electrical resistance with the S1PR1 agonist FTY720-(S)-phosphonate. Both S1PR1 and KLF2 gene expression (mRNA, protein) were significantly increased by simvastatin in vitro and in vivo. S1PR1 promoter activity was significantly increased by simvastatin (P < 0.05), which was significantly attenuated by KLF2 silencing (siRNA). Simvastatin induced KLF2 recruitment to the S1PR1 promoter, and consequently, significantly augmented the effects of the S1PR1 agonist on EC barrier enhancement (P < 0.05), which was significantly attenuated by KLF2 silencing (P < 0.05). These results suggest that simvastatin upregulates S1PR1 transcription and expression via the transcription factor KLF2, and consequently augments the effects of S1PR1 agonists on preserving vascular barrier integrity. These results may lead to novel combinatorial therapeutic strategies for lung inflammatory syndromes.

Extracellular α-synuclein induces sphingosine 1-phosphate receptor subtype 1 uncoupled from inhibitory G-protein leaving β-arrestin signal intact

Parkinson’s disease (PD) is the second most common neurodegenerative disorder. The presence of α-synuclein (α-Syn)-positive intracytoplasmic inclusions, known as Lewy bodies, is the cytopathological hallmark of PD. Increasing bodies of evidence suggest that cell-to-cell transmission of α-Syn plays a role in the progression of PD. Although extracellular α-Syn is known to cause abnormal cell motility, the precise mechanism remains elusive. Here we show that impairment of platelet-derived growth factor-induced cell motility caused by extracellular α-Syn is mainly attributed to selective inhibition of sphingosine 1-phosphate (S1P) signalling. Treatment of human neuroblastoma cells with recombinant α-Syn caused S1P type 1 (S1P₁) receptor-selective uncoupling from inhibitory G-protein (Gi) as determined by both functional and fluorescence resonance energy transfer (FRET)-based structural analyses. By contrast, α-Syn caused little or no effect on S1P₂ receptor-mediated signalling. Both wild-type and α-Syn(A53T), a mutant found in familiar PD, caused uncoupling of S1P₁ receptor, although α-Syn(A53T) showed stronger potency in uncoupling. Moreover, S1P₁ receptor-mediated β-arrestin signal was unaltered by α-Syn(A53T). These results suggest that exogenous α-Syn modulates S1P₁ receptor-mediated signalling from both Gi and β-arrestin signals into β-arrestin-biased signal. These findings uncovered a novel function of exogenous α-Syn in the cells.

Selective Role of Vinculin in Contractile Mechanisms of Endothelial Permeability

Increased vascular endothelial cell (EC) permeability is a result of intercellular gap formation that may be induced by contraction-dependent and contraction-independent mechanisms. This study investigated a role of the adaptor protein vinculin in EC permeability induced by contractile (thrombin) and noncontractile (IL-6) agonists. Although thrombin and IL-6 caused a similar permeability increase in human pulmonary ECs and disrupted the association between vinculin and vascular endothelial-cadherin, they induced different patterns of focal adhesion (FA) arrangement. Thrombin, but not IL-6, caused formation of large, vinculin-positive FAs, phosphorylation of FA proteins, FA kinase and Crk-associated substrate, and increased vinculin-talin association. Thrombin-induced formation of talin-positive FA and intercellular gaps were suppressed in ECs with small interfering RNA-induced vinculin knockdown. Vinculin knockdown and inhibitors of Rho kinase and myosin-II motor activity also attenuated thrombin-induced EC permeability. Importantly, ectopic expression of the vinculin mutant lacking the F-actin-binding domain decreased thrombin-induced Rho pathway activation and EC permeability. In contrast, IL-6-induced EC permeability did not involve RhoA- or myosin-dependent mechanisms but engaged Janus kinase/signal transducer and activator of transcription-mediated phosphorylation and internalization of vascular endothelial-cadherin. This process was vinculin independent but Janus kinase/tyrosine kinase Src-dependent. These data suggest that vinculin participates in a contractile-dependent mechanism of permeability by integrating FA with stress fibers, leading to maximal RhoA activation and EC permeability response. Vinculin inhibition does not affect contractile-independent mechanisms of EC barrier failure. This study provides, for the first time, a comparative analysis of two alternative mechanisms of vascular endothelial barrier dysfunction and defines a specific role for vinculin in the contractile type of permeability response.

Akt1 promotes stimuli-induced endothelial-barrier protection through FoxO-mediated tight-junction protein turnover

Vascular permeability regulated by the vascular endothelial growth factor (VEGF) through endothelial-barrier junctions is essential for inflammation. Mechanisms regulating vascular permeability remain elusive. Although 'Akt' and 'Src' have been implicated in the endothelial-barrier regulation, it is puzzling how both agents that protect and disrupt the endothelial-barrier activate these kinases to reciprocally regulate vascular permeability. To delineate the role of Akt1 in endothelial-barrier regulation, we created endothelial-specific, tamoxifen-inducible Akt1 knockout mice and stable ShRNA-mediated Akt1 knockdown in human microvascular endothelial cells. Akt1 loss leads to decreased basal and angiopoietin1-induced endothelial-barrier resistance, and enhanced VEGF-induced endothelial-barrier breakdown. Endothelial Akt1 deficiency resulted in enhanced VEGF-induced vascular leakage in mice ears, which was rescued upon re-expression with Adeno-myrAkt1. Furthermore, co-treatment with angiopoietin1 reversed VEGF-induced vascular leakage in an Akt1-dependent manner. Mechanistically, our study revealed that while VEGF-induced short-term vascular permeability is independent of Akt1, its recovery is reliant on Akt1 and FoxO-mediated claudin expression. Pharmacological inhibition of FoxO transcription factors rescued the defective endothelial barrier due to Akt1 deficiency. Here we provide novel insights on the endothelial-barrier protective role of VEGF in the long term and the importance of Akt1-FoxO signaling on tight-junction stabilization and prevention of vascular leakage through claudin expression.

Role of End Binding Protein-1 in endothelial permeability response to barrier-disruptive and barrier-enhancing agonists

Rapid changes in microtubule (MT) polymerization dynamics affect regional activity of small GTPases RhoA and Rac1, which play a key role in the regulation of actin cytoskeleton and endothelial cell (EC) permeability. This study tested the role of End Binding Protein-1 (EB1) in the mechanisms of increased and decreased EC permeability caused by thrombin and hepatocyte growth factor (HGF) and mediated by RhoA and Rac1 GTPases, respectively. Stimulation of human lung EC with thrombin inhibited peripheral MT growth, which was monitored by morphological and biochemical evaluation of peripheral MT and the levels of stabilized MT. In contrast, stimulation of EC with HGF promoted peripheral MT growth and protrusion of EB1-positive MT plus ends to the EC peripheral submembrane area. EB1 knockdown by small interfering RNA did not affect partial MT depolymerization, activation of Rho signaling, and permeability response to thrombin, but suppressed the HGF-induced endothelial barrier enhancement. EB1 knockdown suppressed HGF-induced activation of Rac1 and Rac1 cytoskeletal effectors cortactin and PAK1, impaired HGF-induced assembly of cortical cytoskeleton regulatory complex (WAVE-p21Arc-IQGAP1), and blocked HGF-induced enhancement of peripheral actin cytoskeleton and VE-cadherin-positive adherens junctions. Altogether, these data demonstrate a role for EB1 in coordination of MT-dependent barrier enhancement response to HGF, but show no involvement of EB1 in acute increase of EC permeability caused by the barrier disruptive agonist. The results suggest that increased peripheral EB1 distribution is a critical component of the Rac1-mediated pathway and peripheral cytoskeletal remodeling essential for agonist-induced EC barrier enhancement.

A Stromal Cell-Derived Factor 1α Analogue Improves Endothelial Cell Function in Lipopolysaccharide-Induced Acute Respiratory Distress Syndrome

Endothelial cell (EC) dysfunction is a critical mediator of the acute respiratory distress syndrome (ARDS). Recent studies have demonstrated that stromal cell-derived factor 1α (SDF-1α) promotes EC barrier integrity. Our previous studies used a SDF-1α analogue CTCE-0214 (CTCE) in experimental sepsis and demonstrated that it attenuated vascular leak and modulated microRNA (miR) levels. We examined the hypothesis that CTCE improves EC function in lipopolysaccharide (LPS)-induced ARDS through increasing miR-126 expression. Human microvascular endothelial cells (HMVECs) were treated with thrombin to disrupt the EC integrity followed by incubation with CTCE or SDF-1α. Barrier function was determined by trans-endothelial electrical resistance assay. CTCE-induced alterations in miRNA expression and signaling pathways involved in barrier function were determined. Thrombin-induced vascular leak was abrogated by both CTCE and SDF-1α. CTCE also prevented thrombin-induced decreases of vascular endothelial (VE)-cadherin cell surface expression and expansion of the intercellular space. CTCE increased miR-126 levels and induced activation of AKT/Rac 1 signaling. Cotreatment with a miR-126 inhibitor blocked the protective effects of CTCE on AKT activation and endothelial permeability. In subsequent in vivo studies, ARDS was induced by intratracheal instillation of LPS. Intravenous injection of CTCE diminished the injury severity as evidenced by significant reductions in protein, immune cells, inflammatory cytokines and chemokines in the bronchoalveolar lavage fluid, increased miR-126 expression and decreased pulmonary vascular leak and alveolar edema. Taken together, our data show that CTCE improves endothelial barrier integrity through increased expression of miR-126 and activation of Rac 1 signaling and represents an important potential therapeutic strategy in ARDS.

Chronic high-magnitude cyclic stretch stimulates EC inflammatory response via VEGF receptor 2-dependent mechanism

Ventilator-induced lung injury (VILI) is associated with activated inflammatory signaling, such as cytokine production by endothelial and epithelial cells and macrophages, although the precise mechanisms of inflammatory activation induced by VILI-relevant cyclic stretch (CS) amplitude remain poorly understood. We show that exposure of human pulmonary endothelial cells (EC) to chronic CS at 18% linear distension (18% CS), but not at physiologically relevant 5% CS, induces "EC-activated phenotype," which is characterized by time-dependent increase in ICAM1 and VCAM1 expression. A preconditioning of 18% CS also increased in a time-dependent fashion the release of soluble ICAM1 (sICAM1) and IL-8. Investigation of potential signaling mechanisms of CS-induced EC inflammatory activation showed that 18% CS, but not 5% CS, induced time-dependent upregulation of VEGF receptor 2 (VEGFR2), as monitored by increased protein expression and VEGFR2 tyrosine phosphorylation. Both CS-induced VEGFR2 expression and tyrosine phosphorylation were abrogated by cotreatment with reactive oxygen species inhibitor, N-acetyl cysteine. Molecular inhibition of VEGFR2 expression by gene-specific siRNA or treatment with VEGFR2 pharmacological inhibitor SU-1498 attenuated CS-induced activation of ICAM1 and VCAM1 expression and sICAM1 release. Chronic EC preconditioning at 18% CS augmented EC inflammation and barrier-disruptive response induced by proinflammatory cytokine TNF-α. This effect of chronic 18% CS preconditioning was attenuated by siRNA-induced VEGFR2 knockdown. This study demonstrates for the first time a VEGFR2-dependent mechanism of EC inflammatory activation induced by pathological CS. We conclude that, despite the recognized role of VEGF as a prosurvival and angiogenic factor, excessive activation of VEGFR2 signaling by high-tidal-volume lung mechanical ventilation may contribute to ventilator-induced (biotrauma) lung inflammation and barrier dysfunction by augmenting cell response to VILI-associated inflammatory mediators.

Dual role of vinculin in barrier-disruptive and barrier-enhancing endothelial cell responses

Endothelial cell (EC) barrier disruption induced by edemagenic agonists such as thrombin is a result of increased actomyosin contraction and enforcement of focal adhesions (FA) anchoring contracting stress fibers, which leads to cell retraction and force-induced disruption of cell junctions. In turn, EC barrier enhancement by oxidized phospholipids (OxPAPC) and other agonists is a result of increased tethering forces due to enforcement of the peripheral actin rim and enhancement of cell-cell adherens junction (AJ) complexes promoting EC barrier integrity. This study tested participation of the mechanosensitive adaptor, vinculin, which couples FA and AJ to actin cytoskeleton, in control of the EC permeability response to barrier disruptive (thrombin) and barrier enhancing (OxPAPC) stimulation. OxPAPC and thrombin induced different patterns of FA remodeling. Knockdown of vinculin attenuated both, OxPAPC-induced decrease and thrombin-induced increase in EC permeability. Thrombin stimulated the vinculin association with FA protein talin and suppressed the interaction with AJ protein, VE-cadherin. In contrast, OxPAPC stimulated the vinculin association with VE-cadherin. Thrombin and OxPAPC induced different levels of myosin light chain (MLC) phosphorylation and caused different patterns of intracellular phospho-MLC distribution. Thrombin-induced talin-vinculin and OxPAPC-induced VE-cadherin-vinculin association were abolished by myosin inhibitor blebbistatin. Expression of the vinculin mutant unable to interact with actin attenuated EC permeability changes and MLC phosphorylation caused by both, thrombin and OxPAPC. These data suggest that the specific vinculin interaction with FA or AJ in different contexts of agonist stimulation is defined by development of regional actyomyosin-based tension and participates in both, the barrier-disruptive and barrier-enhancing endothelial responses.

Extracellular Vesicles from Caveolin-Enriched Microdomains Regulate Hyaluronan-Mediated Sustained Vascular Integrity

Defects in vascular integrity are an initiating factor in several disease processes. We have previously reported that high molecular weight hyaluronan (HMW-HA), a major glycosaminoglycan in the body, promotes rapid signal transduction in human pulmonary microvascular endothelial cells (HPMVEC) leading to barrier enhancement. In contrast, low molecular weight hyaluronan (LMW-HA), produced in disease states by hyaluronidases and reactive oxygen species (ROS), induces HPMVEC barrier disruption. However, the mechanism(s) of sustained barrier regulation by HA are poorly defined. Our results indicate that long-term (6–24 hours) exposure of HMW-HA induced release of a novel type of extracellular vesicle from HLMVEC called enlargeosomes (characterized by AHNAK expression) while LMW-HA long-term exposure promoted release of exosomes (characterized by CD9, CD63, and CD81 expression). These effects were blocked by inhibiting caveolin-enriched microdomain (CEM) formation. Further, inhibiting enlargeosome release by annexin II siRNA attenuated the sustained barrier enhancing effects of HMW-HA. Finally, exposure of isolated enlargeosomes to HPMVEC monolayers generated barrier enhancement while exosomes led to barrier disruption. Taken together, these results suggest that differential release of extracellular vesicles from CEM modulate the sustained HPMVEC barrier regulation by HMW-HA and LMW-HA. HMW-HA-induced specialized enlargeosomes can be a potential therapeutic strategy for diseases involving impaired vascular integrity.

Lipopolysaccharide-induced caveolin-1 phosphorylation-dependent increase in transcellular permeability precedes the increase in paracellular permeability

Background

Lipopolysaccharide (LPS) was shown to induce an increase in caveolin-1 (Cav-1) expression in endothelial cells; however, the mechanisms regarding this response and the consequences on caveolae-mediated transcellular transport have not been completely investigated. This study aims to investigate the role of LPS-induced Cav-1 phosphorylation in pulmonary microvascular permeability in pulmonary microvascular endothelial cells (PMVECs).

Methods

Rat PMVECs were isolated, cultured, and identified. Endocytosis experiments were employed to stain the nuclei by DAPI, and images were obtained with a fluorescence microscope. Permeability of endothelial cultures was measured to analyze the barrier function of endothelial monolayer. Western blot assay was used to examine the expression of Cav-1, pCav-1, triton-insoluble Cav-1, and triton-soluble Cav-1 protein.

Results

The LPS treatment induced phosphorylation of Cav-1, but did not alter the total Cav-1 level till 60 min in both rat and human PMVECs. LPS treatment also increased the triton-insoluble Cav-1 level, which peaked 15 min after LPS treatment in both rat and human PMVECs. LPS treatment increases the intercellular cell adhesion molecule-1 expression. Src inhibitors, including PP2, PP1, Saracatinib, and Quercetin, partially inhibited LPS-induced phosphorylation of Cav-1. In addition, both PP2 and caveolae disruptor MβCD inhibited LPS-induced increase of triton-insoluble Cav-1. LPS induces permeability by activating interleukin-8 and vascular endothelial growth factor and targeting other adhesion markers, such as ZO-1 and occludin. LPS treatment also significantly increased the endocytosis of albumin, which could be blocked by PP2 or MβCD. Furthermore, LPS treatment for 15 min significantly elevated Evans Blue-labeled BSA transport in advance of a decrease in transendothelial electrical resistance of PMVEC monolayer at this time point. After LPS treatment for 30 min, transendothelial electrical resistance decreased significantly. Moreover, PP2 and MβCD blocked LPS-induced increase in Evans Blue-labeled BSA level.

Conclusion

Our study demonstrates that LPS-induced Cav-1 phosphorylation may lead to the increase of transcellular permeability prior to the increase of paracellular permeability in a Src-dependent manner. Thus, LPS-induced Cav-1 phosphorylation may be a therapeutic target for the treatment of inflammatory lung disease associated with elevated microvascular permeability.

Hyaluronan regulation of endothelial barrier function in cancer

Vascular integrity or the maintenance of blood vessel continuity is a fundamental process regulated by endothelial cell-cell junctions. Defects in endothelial barrier function are an initiating factor in several disease processes including tumor angiogenesis and metastasis. The glycosaminoglycan, hyaluronan (HA), maintains vascular integrity through specific mechanisms including HA-binding protein signaling in caveolin-enriched microdomains, a subset of lipid rafts. Certain disease states, including cancer, increase enzymatic hyaluronidase activity and reactive oxygen species generation, which break down high molecular weight HA (HMW-HA) to low molecular weight fragments (LMW-HA). LMW-HA can activate specific HA-binding proteins during tumor progression to promote disruption of endothelial cell-cell contacts. In contrast, exogenous administration of HMW-HA promotes enhancement of vascular integrity. This review focuses on the roles of HA in regulating angiogenic and metastatic processes based on its size and the HA-binding proteins present. Further, potential therapeutic applications of HMW-HA in treating cancer are discussed.

Prostacyclin post-treatment improves LPS-induced acute lung injury and endothelial barrier recovery via Rap1

Protective effects of prostacyclin (PC) or its stable analog beraprost against agonist-induced lung vascular inflammation have been associated with elevation of intracellular cAMP and Rac GTPase signaling which inhibited the RhoA GTPase-dependent pathway of endothelial barrier dysfunction. This study investigated a distinct mechanism of PC-stimulated lung vascular endothelial (EC) barrier recovery and resolution of LPS-induced inflammation mediated by small GTPase Rap1. Efficient barrier recovery was observed in LPS-challenged pulmonary EC after prostacyclin administration even after 15 h of initial inflammatory insult and was accompanied by the significant attenuation of p38 MAP kinase and NFκB signaling and decreased production of IL-8 and soluble ICAM1. These effects were reproduced in cells post-treated with 8CPT, a small molecule activator of Rap1-specific nucleotide exchange factor Epac. By contrast, pharmacologic Epac inhibitor, Rap1 knockdown, or knockdown of cell junction-associated Rap1 effector afadin attenuated EC recovery caused by PC or 8CPT post-treatment. The key role of Rap1 in lung barrier restoration was further confirmed in the murine model of LPS-induced acute lung injury. Lung injury was monitored by measurements of bronchoalveolar lavage protein content, cell count, and Evans blue extravasation and live imaging of vascular leak over 6 days using a fluorescent tracer. The data showed significant acceleration of lung recovery by PC and 8CPT post-treatment, which was abrogated in Rap1a(-/-) mice. These results suggest that post-treatment with PC triggers the Epac/Rap1/afadin-dependent mechanism of endothelial barrier restoration and downregulation of p38MAPK and NFκB inflammatory cascades, altogether leading to accelerated lung recovery.

Asef mediates HGF protective effects against LPS-induced lung injury and endothelial barrier dysfunction

Increased vascular endothelial permeability and inflammation are major pathological mechanisms of pulmonary edema and its life-threatening complication, the acute respiratory distress syndrome (ARDS). We have previously described potent protective effects of hepatocyte growth factor (HGF) against thrombin-induced hyperpermeability and identified the Rac pathway as a key mechanism of HGF-mediated endothelial barrier protection. However, anti-inflammatory effects of HGF are less understood. This study examined effects of HGF on the pulmonary endothelial cell (EC) inflammatory activation and barrier dysfunction caused by the gram-negative bacterial pathogen lipopolysaccharide (LPS). We tested involvement of the novel Rac-specific guanine nucleotide exchange factor Asef in the HGF anti-inflammatory effects. HGF protected the pulmonary EC monolayer against LPS-induced hyperpermeability, disruption of monolayer integrity, activation of NF-kB signaling, expression of adhesion molecules intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, and production of IL-8. These effects were critically dependent on Asef. Small-interfering RNA-induced downregulation of Asef attenuated HGF protective effects against LPS-induced EC barrier failure. Protective effects of HGF against LPS-induced lung inflammation and vascular leak were also diminished in Asef knockout mice. Taken together, these results demonstrate potent anti-inflammatory effects by HGF and delineate a key role of Asef in the mediation of the HGF barrier protective and anti-inflammatory effects. Modulation of Asef activity may have important implications in therapeutic strategies aimed at the treatment of sepsis and acute lung injury/ARDS-induced gram-negative bacterial pathogens.