The C-terminus region of β-arrestin1 modulates VE-cadherin expression and endothelial cell permeability

Endothelial cell sphingosine 1-phosphate receptor 1 restrains VE-cadherin cleavage and attenuates experimental inflammatory arthritis

In rheumatoid arthritis, inflammatory mediators extravasate from blood into joints via gaps between endothelial cells (ECs), but the contribution of ECs is not known. Sphingosine 1-phosphate receptor 1 (S1PR1), widely expressed on ECs, maintains the vascular barrier. Here, we assessed the contribution of vascular integrity and EC S1PR1 signaling to joint damage in mice exposed to serum-induced arthritis (SIA). EC-specific deletion of S1PR1 or pharmacological blockade of S1PR1 promoted vascular leak and amplified SIA, whereas overexpression of EC S1PR1 or treatment with an S1PR1 agonist delayed SIA. Blockade of EC S1PR1 induced membrane metalloproteinase-dependent cleavage of vascular endothelial cadherin (VE-cadherin), a principal adhesion molecule that maintains EC junctional integrity. We identified a disintegrin and a metalloproteinase domain 10 (ADAM10) as the principal VE-cadherin "sheddase." Mice expressing a stabilized VE-cadherin construct had decreased extravascular VE-cadherin and vascular leakage in response to S1PR1 blockade, and they were protected from SIA. Importantly, patients with active rheumatoid arthritis had decreased circulating S1P and microvascular expression of S1PR1, suggesting a dysregulated S1P/S1PR1 axis favoring vascular permeability and vulnerability. We present a model in which EC S1PR1 signaling maintains homeostatic vascular barrier function by limiting VE-cadherin shedding mediated by ADAM10 and suggest this signaling axis as a therapeutic target in inflammatory arthritis.

Alveolar-capillary endocytosis and trafficking in acute lung injury and acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is associated with high morbidity and mortality but lacks specific therapeutic options. Diverse endocytic processes play a key role in all phases of acute lung injury (ALI), including the initial insult, development of respiratory failure due to alveolar flooding, as a consequence of altered alveolar-capillary barrier function, as well as in the resolution or deleterious remodeling after injury. In particular, clathrin-, caveolae-, endophilin- and glycosylphosphatidyl inositol-anchored protein-mediated endocytosis, as well as, macropinocytosis and phagocytosis have been implicated in the setting of acute lung damage. This manuscript reviews our current understanding of these endocytic pathways and subsequent intracellular trafficking in various phases of ALI, and also aims to identify potential therapeutic targets for patients with ARDS.

Breaking barriers: exploring mechanisms behind opening the blood-brain barrier

The blood-brain barrier (BBB) is a selectively permeable membrane that separates the bloodstream from the brain. While useful for protecting neural tissue from harmful substances, brain-related diseases are difficult to treat due to this barrier, as it also limits the efficacy of drug delivery. To address this, promising new approaches for enhancing drug delivery are based on disrupting the BBB using physical means, including optical/photothermal therapy, electrical stimulation, and acoustic/mechanical stimulation. These physical mechanisms can temporarily and locally open the BBB, allowing drugs and other substances to enter. Focused ultrasound is particularly promising, with the ability to focus energies to targeted, deep-brain regions. In this review, we examine recent advances in physical approaches for temporary BBB disruption, describing their underlying mechanisms as well as evaluating the utility of these physical approaches with regard to their potential risks and limitations. While these methods have demonstrated efficacy in disrupting the BBB, their safety, comparative efficacy, and practicality for clinical use remain an ongoing topic of research.

Low-Level Laser Treatment Induces the Blood-Brain Barrier Opening and the Brain Drainage System Activation: Delivery of Liposomes into Mouse Glioblastoma

The progress in brain diseases treatment is limited by the blood-brain barrier (BBB), which prevents delivery of the vast majority of drugs from the blood into the brain. In this study, we discover unknown phenomenon of opening of the BBBB (BBBO) by low-level laser treatment (LLLT, 1268 nm) in the mouse cortex. LLLT-BBBO is accompanied by activation of the brain drainage system contributing effective delivery of liposomes into glioblastoma (GBM). The LLLT induces the generation of singlet oxygen without photosensitizers (PSs) in the blood endothelial cells and astrocytes, which can be a trigger mechanism of BBBO. LLLT-BBBO causes activation of the ABC-transport system with a temporal decrease in the expression of tight junction proteins. The BBB recovery is accompanied by activation of neuronal metabolic activity and stabilization of the BBB permeability. LLLT-BBBO can be used as a new opportunity of interstitial PS-free photodynamic therapy (PDT) for modulation of brain tumor immunity and improvement of immuno-therapy for GBM in infants in whom PDT with PSs, radio- and chemotherapy are strongly limited, as well as in adults with a high allergic reaction to PSs.

Brain blood vessel autoantibodies in patients with NMDA and GABAA receptor encephalitis: identification of unconventional Myosin-X as target antigen

Introduction: The antibody repertoire from CSF-derived antibody-secreting cells and memory B-cells in patients with encephalitis contains a considerable number of antibodies that do not target the disease-defining autoantigen such as the GABA or NMDA receptors. This study focuses on the functional relevance of autoantibodies to brain blood vessels in patients with GABA_A and NMDA receptor encephalitis. Methods: We tested 149 human monoclonal IgG antibodies from the cerebrospinal fluid of six patients with different forms of autoimmune encephalitis on murine brain sections for reactivity to blood vessels using immunohistochemistry. Positive candidates were tested for reactivity with purified brain blood vessels, effects on transendothelial electrical resistance (TEER), and expression of tight junction proteins as well as gene regulation using human brain microvascular endothelial hCMEC/D3 cells as in vitro blood-brain barrier model. One blood-vessel reactive antibody was infused intrathecally by pump injection in mice to study in vivo binding and effects on tight junction proteins such as Occludin. Target protein identification was addressed using transfected HEK293 cells. Results: Six antibodies reacted with brain blood vessels, three were from the same patient with GABA_AR encephalitis, and the other three were from different patients with NMDAR encephalitis. One antibody from an NMDAR encephalitis patient, mAb 011-138, also reacted with cerebellar Purkinje cells. In this case, treatment of hCMEC/D3 cells resulted in decreased TEER, reduced Occludin expression, and mRNA levels. Functional relevance in vivo was confirmed as Occludin downregulation was observed in mAb 011-138-infused animals. Unconventional Myosin-X was identified as a novel autoimmune target for this antibody. Discussion: We conclude that autoantibodies to blood vessels occur in autoimmune encephalitis patients and might contribute to a disruption of the blood-brain barrier thereby suggesting a potential pathophysiological relevance of these antibodies.

Photodynamic Opening of the Blood-Brain Barrier and the Meningeal Lymphatic System: The New Niche in Immunotherapy for Brain Tumors

Photodynamic therapy (PDT) is a promising add-on therapy to the current standard of care for patients with glioblastoma (GBM). The traditional explanation of the anti-cancer PDT effects involves the PDT-induced generation of a singlet oxygen in the GBM cells, which causes tumor cell death and microvasculature collapse. Recently, new vascular mechanisms of PDT associated with opening of the blood-brain barrier (OBBB) and the activation of functions of the meningeal lymphatic vessels have been discovered. In this review, we highlight the emerging trends and future promises of immunotherapy for brain tumors and discuss PDT-OBBB as a new niche and an important informative platform for the development of innovative pharmacological strategies for the modulation of brain tumor immunity and the improvement of immunotherapy for GBM.

Neutrophil Elastase Increases Vascular Permeability and Leukocyte Transmigration in Cultured Endothelial Cells and Obese Mice

Neutrophil elastase (NE) plays a pivotal role in inflammation. However, the mechanism underlying NE-mediated inflammation in obesity remains unclear. Here, we report that NE activates protease-activated receptor-2 (PAR2), stimulates actin filament (F-actin) formation, decreases intercellular junction molecule VE-cadherin expression, and increases the permeability of human arterial endothelial cells (hECs). NE also prompts degradation of VE-cadherin and its binding proteins p120- and β-catenins via MG132-sensitive proteasomes. NE stimulates phosphorylation of myosin light-chain (MLC) and its regulator myosin phosphatase target subunit-1 (MYPT1), a target of Rho kinase (ROCK). Inhibitors of PAR2 and ROCK prohibit NE-induced F-actin formation, MLC phosphorylation, and VE-cadherin reduction in hECs, and impede monocyte transmigration through hEC monolayer pretreated with either neutrophils or NE. Further, administration of an NE inhibitor GW311616A significantly attenuates vascular leakage, leukocyte infiltration, and the expression of proinflammatory cytokines in the white adipose tissue from high-fat diet (HFD)-induced obese mice. Likewise, NE-deficient mice are resistant to HFD-induced vascular leakage in the heart. Together, NE regulates actomyosin cytoskeleton activity and VE-cadherin expression by activating PAR2 signaling in the endothelial cells, leading to increased vascular permeability and leukocyte extravasation. Hence, inhibition of NE is a potential approach to mitigate vascular injury and leukocyte infiltration in obesity-related systemic inflammation.

Endothelial cell infection and dysfunction, immune activation in severe COVID-19

Rationale: Pulmonary vascular endotheliitis, perivascular inflammation, and immune activation are observed in COVID-19 patients. While the initial SARS-CoV-2 infection mainly infects lung epithelial cells, whether it also infects endothelial cells (ECs) and to what extent SARS-CoV-2-mediated pulmonary vascular endotheliitis is associated with immune activation remain to be determined. Methods: To address these questions, we studied SARS-CoV-2-infected K18-hACE2 (K18) mice, a severe COVID-19 mouse model, as well as lung samples from SARS-CoV-2-infected nonhuman primates (NHP) and patient deceased from COVID-19. We used immunostaining, RNAscope, and electron microscopy to analyze the organs collected from animals and patient. We conducted bulk and single cell (sc) RNA-seq analyses, and cytokine profiling of lungs or serum of the severe COVID-19 mice. Results: We show that SARS-CoV-2-infected K18 mice develop severe COVID-19, including progressive body weight loss and fatality at 7 days, severe lung interstitial inflammation, edema, hemorrhage, perivascular inflammation, systemic lymphocytopenia, and eosinopenia. Body weight loss in K18 mice correlated with the severity of pneumonia, but not with brain infection. We also observed endothelial activation and dysfunction in pulmonary vessels evidenced by the up-regulation of VCAM1 and ICAM1 and the downregulation of VE-cadherin. We detected SARS-CoV-2 in capillary ECs, activation and adhesion of platelets and immune cells to the vascular wall of the alveolar septa, and increased complement deposition in the lungs, in both COVID-19-murine and NHP models. We also revealed that pathways of coagulation, complement, K-ras signaling, and genes of ICAM1 and VCAM1 related to EC dysfunction and injury were upregulated, and were associated with massive immune activation in the lung and circulation. Conclusion: Together, our results indicate that SARS-CoV-2 causes endotheliitis via both infection and infection-mediated immune activation, which may contribute to the pathogenesis of severe COVID-19 disease.

Phenomenon of music-induced opening of the blood-brain barrier in healthy mice

Music plays a more important role in our life than just being an entertainment. For example, it can be used as an anti-anxiety therapy of human and animals. However, the unsafe listening of loud music triggers hearing loss in millions of young people and professional musicians (rock, jazz and symphony orchestra) owing to exposure to damaging sound levels using personal audio devices or at noisy entertainment venues including nightclubs, discotheques, bars and concerts. Therefore, it is important to understand how loud music affects us. In this pioneering study on healthy mice, we discover that loud rock music below the safety threshold causes opening of the blood-brain barrier (OBBB), which plays a vital role in protecting the brain from viruses, bacteria and toxins. We clearly demonstrate that listening to loud music during 2 h in an intermittent adaptive regime is accompanied by delayed (1 h after music exposure) and short-lasting to (during 1-4 h) OBBB to low and high molecular weight compounds without cochlear and brain impairments. We present the systemic and molecular mechanisms responsible for music-induced OBBB. Finally, a revision of our traditional knowledge about the BBB nature and the novel strategies in optimizing of sound-mediated methods for brain drug delivery are discussed.

Epigenetic regulation of TLR2-mediated periapical inflammation

AIM

To determine the methylation pattern of TLR2 gene promoter and its association with the transcriptional regulation of periapical inflammatory and angiogenic responses in symptomatic and asymptomatic forms of apical periodontitis.

METHODOLOGY

In this cross-sectional study, apical lesions were obtained from volunteers with asymptomatic apical periodontitis (AAP) (n = 17) and symptomatic apical periodontitis (SAP) (n = 17) scheduled for tooth extraction, and both total RNA and DNA were extracted. DNA was bisulfite-treated, a region of CpG island within the TLR2 gene was amplified by qPCR and the products were sequenced. Additionally, the mRNA expression of TLR2, TLR4, IL-6, IL-12, TNFalpha, IL-23, IL-10, TGFbeta, VEGFA and CDH5 was analysed by qPCR. The data were analysed with chi-square tests, Mann-Whitney or unpaired t-tests, and Spearman´s correlation; variable adjustments were performed using multiple linear regression (P < 0.05).

RESULTS

TLR2 depicted a hypomethylated DNA profile at the CpG island in SAP when compared with AAP, along with upregulated expression of TLR2, with pro-inflammatory cytokines IL-6 and IL-23, and the angiogenesis marker CDH5 (P < 0.05). TLR2 methylation percentage negatively correlated with mRNA levels of IL-23 and CDH5 in apical periodontitis. Lower methylation frequencies of single CpG dinucleotides -8 and -10 localized in close proximity to nuclear factor κB (NFκB) binding within the TLR2 promoter were identified in SAP versus AAP (P < 0.05). Finally, unmethylated -10 and -8 single sites demonstrated up-regulation of IL-23, IL-10 and CDH5 transcripts compared to their methylated counterparts (P < 0.05).

CONCLUSIONS

TLR2 gene promoter hypomethylation was linked to transcriptional activity of pro-inflammatory cytokines and angiogenic markers in exacerbated periapical inflammation. Moreover, unmethylated single sites in close proximity to NFκB binding were involved in active transcription of IL-23, IL-10 and CDH5.

Human Umbilical Vein Endothelial Cells (HUVECs) Co-Culture with Osteogenic Cells: From Molecular Communication to Engineering Prevascularised Bone Grafts

The repair of bone defects caused by trauma, infection or tumor resection is a major clinical orthopedic challenge. The application of bone grafts in orthopedic procedures is associated with a problem of inadequate vascularization in the initial phase after implantation. Meanwhile, the survival of cells within the implanted graft and its integration with the host tissue is strongly dependent on nutrient and gaseous exchange, as well as waste product removal, which are effectuated by blood microcirculation. In the bone tissue, the vasculature also delivers the calcium and phosphate indispensable for the mineralization process. The critical role of vascularization for bone healing and function, led the researchers to the idea of generating a capillary-like network within the bone graft in vitro, which could allow increasing the cell survival and graft integration with a host tissue. New strategies for engineering pre-vascularized bone grafts, that apply the co-culture of endothelial and bone-forming cells, have recently gained interest. However, engineering of metabolically active graft, containing two types of cells requires deep understanding of the underlying mechanisms of interaction between these cells. The present review focuses on the best-characterized endothelial cells-human umbilical vein endothelial cells (HUVECs)-attempting to estimate whether the co-culture approach, using these cells, could bring us closer to development and possible clinical application of prevascularized bone grafts.

The anti-hyperglycemia effects of Rhizoma Coptidis alkaloids: A systematic review of modern pharmacological studies of the traditional herbal medicine

Hyperglycemia is a common endocrine system disease, which seriously affects people's health with a increasing morbidity in recent years. Rhizoma Coptidis (RC), one of the most commonly used traditional Chinese medicines, has been applied to treat diabetes in clinic for thousands of years. Since scientists demonstrated that alkaloids from RC owned the amazing anti-hyperglycemia activities 30 years ago, these compounds have been widely used for the treatment of diabetes and hyperglycemia with unconspicuous toxicities and side effects. With the help of molecular biology, immunology and other techniques, the mechanisms about anti-hyperglycemia effect of RC alkaloids have been extensively discussed. Numerous studies showed that RC alkaloids balanced the glucose homeostasis not only by widely recognizing insulin resistance pathways, but also by promoting insulin secretion, regulating intestinal hormones, ameliorating gut microbiota structures and many other ways. In this review, we combine the latest advances and systematically summarize the mechanisms of RC alkaloids in treating hyperglycemia and diabetic nephropathy to provide a deeper understanding of these natural alkaloids. In addition, the important role of gut microbiota associated with the glucose metabolism is also reviewed.

Photodynamic opening of the blood-brain barrier to high weight molecules and liposomes through an optical clearing skull window

The photodynamic (PD) effect has been reported to be efficient for the opening of the blood-brain barrier (BBB), which provides a new informative platform for developing perspective strategies towards brain disease therapy and drug delivery. However, this method is usually performed via craniotomy due to high scattering of the turbid skull. In this work, we employed a newly-developed optical clearing skull window for investigating non-invasive PD-induced BBB opening to high weight molecules and 100-nm fluid-phase liposomes containing ganglioside GM1. The results demonstrated that the BBB permeability to the Evans blue albumin complex is related to laser doses. By in vivo two-photon imaging and ex vivo confocal imaging with specific markers of the BBB, we noticed PD-related extravasation of rhodamine-dextran and liposomes from the vessels into the brain parenchyma. The PD induced an increase in oxidative stress associated with mild hypoxia and changes in the expression of tight junction (CLND-5 and ZO-1) and adherens junction (VE-cadherin) proteins, which might be one of the mechanisms underlying the PD-related BBB opening for liposomes. Our experiments indicate that optical clearing skull window will be a promising tool for non-invasive PD-related BBB opening for high weight molecules and liposomes that provides a novel useful tool for brain drug delivery and treatment of brain diseases.

Honokiol protects pulmonary microvascular endothelial barrier against lipopolysaccharide-induced ARDS partially via the Sirt3/AMPK signaling axis

AIMS

Acute respiratory distress syndrome (ARDS) is characterized by acute hypoxemia with diffuse alveolar damage and increased pulmonary microvascular permeability. Honokiol (HKL), the principal active ingredient of Chinese herb magnolia officinalis, protected the lung of experimental ARDS models via attenuation of inflammation and oxidative stress. However, whether HKL has protective effects against the dysfunction of pulmonary microvascular endothelial barrier and the potential mechanisms remain unclear.

MAIN METHODS

In the present study, we examined the levels of plasma Angiopoietin-2 (Ang-2) in ARDS patients, explored the effects of HKL on the vascular endothelial barrier at the ARDS animal and cell levels.

KEY FINDINGS

Our data showed that compared with the healthy controls, circulating Ang-2 level was higher in the patients with ARDS, and were usually supposed to be positively related to the severity of ARDS. Moreover, HKL effectively inhibited lung inflammatory injury and microvascular leakage, and improved ARDS mice survival. HKL also inhibited the expression of Ang-2, ICAM-1 and VCAM-1, and restored the expression of Sirt3, β-Catenin and VE-Cadherin. Furthermore, HKL improved ECs survival and inhibited the apoptosis of ECs. The inhibition of Ang-2 expression in vitro by HKL is accompanied by the upregulation of Sirt3 and AMPK phosphorylation.

SIGNIFICANCE

Our data demonstrated that HKL protected pulmonary microvascular endothelial barrier against LPS-induced ARDS at least in part through activating the Sirt3/AMPK signaling and inhibiting the Ang-2 expression. Thus, our findings show that the activation of Sirt3 signaling is a potential mechanism for the protective effects of HKL on vascular barrier.

Endothelial monolayer permeability under controlled oxygen tension

Endothelial permeability has been extensively investigated in the context of pathologies such as cancer and also in studies of drug delivery from the circulation. Hypoxia is a critical regulator of endothelial cell (EC) behavior and affects the barrier function of endothelial linings, yet its role has been little studied. This paper reveals the effect of hypoxia on the permeability of an EC monolayer by cellular experiments using a microfluidic device and a conventional cell culture dish. Human umbilical vein endothelial cells (HUVECs) were seeded into one microfluidic channel, creating an EC monolayer on each vertical surface of a collagen gel confined to a central chamber. Oxygen tension was regulated to produce normoxic (21% O₂) or hypoxic (3% O₂) conditions by the supply of gas mixtures of oxygen, carbon dioxide, and nitrogen at predefined ratios into channels fabricated into the device. Permeability of the EC monolayer quantified by analyzing diffusion of fluorescence-labelled dextrans into the collagen gel increases with barrier function loss by 6 hour hypoxic exposure, showing 11-fold and 4-fold increases for 70 kDa and 10 kDa dextrans, respectively, on average. Consistent with this, subsequent immunofluorescent staining and separate western blot analysis of HUVECs on a culture dish demonstrate loose cell-cell adhesion resulting from internalization of VE-cadherin under hypoxia. Thus, hypoxic stress increases endothelial permeability by altering cell-cell junction integrity.

Identification of Phosphorylation Codes for Arrestin Recruitment by G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) mediate diverse signaling in part through interaction with arrestins, whose binding promotes receptor internalization and signaling through G protein-independent pathways. High-affinity arrestin binding requires receptor phosphorylation, often at the receptor's C-terminal tail. Here, we report an X-ray free electron laser (XFEL) crystal structure of the rhodopsin-arrestin complex, in which the phosphorylated C terminus of rhodopsin forms an extended intermolecular β sheet with the N-terminal β strands of arrestin. Phosphorylation was detected at rhodopsin C-terminal tail residues T336 and S338. These two phospho-residues, together with E341, form an extensive network of electrostatic interactions with three positively charged pockets in arrestin in a mode that resembles binding of the phosphorylated vasopressin-2 receptor tail to β-arrestin-1. Based on these observations, we derived and validated a set of phosphorylation codes that serve as a common mechanism for phosphorylation-dependent recruitment of arrestins by GPCRs.

Exposure to Concentrated Ambient Fine Particulate Matter Induces Vascular Endothelial Dysfunction via miR-21

Vascular endothelial permeability transition does not cause significant lesions, but enhanced permeability may contribute to the development of vascular and other diseases, including atherosclerosis, hypertension, heart failure and cancer. Therefore, elucidating the effect of Particulate Matter 2.5 (PM_2.5) on vascular endothelial permeability could help prevent disease that might be caused by PM_2.5. Our previous study and the present one revealed that PM_2.5 significantly increased the permeability of vascular endothelial cells and disrupted the barrier function of the vascular endothelium in Sprague Dawley (SD) rats. We found that the effect occurred mainly through induction of signal transducer and activator of transcription 3 (STAT3) phosphorylation, further transcriptional regulation of microRNA21 (miR-21) and promotion of miR-21 expression. These changes post-transcriptionally repress tissue inhibitor of metalloproteinases 3 (TIMP3) and promote matrix metalloproteinases 9 (MMP9) expression. This work provides evidence that PM_2.5 exerts direct inhibitory action on vascular endothelial barrier function and might give rise to a number of vascular diseases.

p120-catenin regulates VE-cadherin endocytosis and degradation induced by the Kaposi sarcoma-associated ubiquitin ligase K5

Endocytosis of VE-cadherin in response to the Kaposi sarcoma E3 ubiquitin ligase K5 is dependent on two membrane-proximal lysine residues but independent of a constitutive endocytosis motif. p120-catenin blocks endocytosis mediated by both motifs, demonstrating that p120 is a master regulator of multiple context-dependent endocytic signals.

Vascular endothelial (VE)-cadherin undergoes constitutive internalization driven by a unique endocytic motif that also serves as a p120-catenin (p120) binding site. p120 binding masks the motif, stabilizing the cadherin at cell junctions. This mechanism allows constitutive VE-cadherin endocytosis and recycling to contribute to adherens junction dynamics without resulting in junction disassembly. Here we identify an additional motif that drives VE-cadherin endocytosis and pathological junction disassembly associated with the endothelial-derived tumor Kaposi sarcoma. Human herpesvirus 8, which causes Kaposi sarcoma, expresses the MARCH family ubiquitin ligase K5. We report that K5 targets two membrane-proximal VE-cadherin lysine residues for ubiquitination, driving endocytosis and down-regulation of the cadherin. K5-induced VE-cadherin endocytosis does not require the constitutive endocytic motif. However, K5-induced VE-cadherin endocytosis is associated with displacement of p120 from the cadherin, and p120 protects VE-cadherin from K5. Thus multiple context-dependent signals drive VE-cadherin endocytosis, but p120 binding to the cadherin juxtamembrane domain acts as a master regulator guarding cadherin stability.

Renoprotective effects of berberine and its potential effect on the expression of β-arrestins and intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in streptozocin-diabetic nephropathy rats

BACKGROUND

Berberine has been shown to exert protective effects against diabetic nephropathy (DN), but the mechanisms involved have not been fully characterized. The aim of the present study was to explore the effects of berberine on the expression of β-arrestins, intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in DN rat kidneys and investigate the underlying molecular mechanisms.

METHODS

To create the DN model, rats fed a high-fat and high-glucose diet were injected with a single dose of streptozotocin (35 mg/kg, i.p.). Then, DN rats were either treated or not with berberine (50, 100, 200 mg/kg per day, i.g., 8 weeks). Periodic acid-Schiff staining was used to evaluate renal histopathological changes. Renal tissue levels of β-arrestin 1 and β-arrestin 2 were determined by Western blot analysis, whereas immunohistochemistry was used to determine renal ICAM-1 and VCAM-1 levels.

RESULTS

Berberine (100, 200 mg/kg) ameliorated the histopathological changes in the diabetic kidney. Western blot analysis revealed significant increases in ICAM-1 and VCAM-1 levels in the kidneys of DN rats, which were reversed by treatment with 100 and 200 mg/kg berberine. In addition, berberine treatment (50, 100, 200 mg/kg) increased diabetic-induced decreases in β-arrestin 1 and β-arrestin 2.

CONCLUSIONS

Berberine exhibited renoprotective effects in DN rats. The underlying molecular mechanisms may be associated with changes in the levels and regulation of β-arrestin expression, as well as ICAM-1 and VCAM-1 levels in the rat kidney.

Disorders of Vascular Permeability

The endothelial barrier maintains vascular and tissue homeostasis and modulates many physiological processes, such as angiogenesis. Vascular barrier integrity can be disrupted by a variety of soluble permeability factors, and changes in barrier function can exacerbate tissue damage during disease progression. Understanding endothelial barrier function is critical for vascular homeostasis. Many of the signaling pathways promoting vascular permeability can also be triggered during disease, resulting in prolonged or uncontrolled vascular leak. It is believed that recovery of the normal vasculature requires diminishing this hyperpermeable state. Although the molecular mechanisms governing vascular leak have been studied over the last few decades, recent advances have identified new therapeutic targets that have begun to show preclinical and clinical promise. These approaches have been successfully applied to an increasing number of disease conditions. New perspectives regarding how vascular leak impacts the progression of various diseases are highlighted in this review.

Catalpol downregulates vascular endothelial‑cadherin expression and induces vascular hyperpermeability

Catalpol, an iridiod glucoside isolated from Rehmannia glutinosa, has been reported to possess anti‑inflammatory properties. However, the molecular mechanisms underlying this effect have not been fully elucidated. This study aimed to investigate the effects of catalpol on vascular permeability. Using Transwell permeability assays and measurements of trans‑endothelial electrical resistance (TEER), it was demonstrated that 1 mM catalpol induces a significant increase in the permeability of the monolayers of human umbilical vein endothelial cells (HUVECs). Western blotting and immunofluorescence demonstrated that catalpol inhibits the expression of vascular endothelial (VE)‑cadherin, the key component of adherens junctions, but not occludin, the major constituent of tight junctions. In addition, catalpol inhibits the ETS transcription factor ERG, a positive regulator of VE‑cadherin. Knockdown of ERG expression compromised the catalpol‑induced reduction of TEER in HUVECs. The present study revealed a novel effect of catalpol on vascular permeability and gave insight into the multifaceted roles of catalpol in inflammation.

Endothelial permeability and VE-cadherin: a wacky comradeship

The endothelium forms a selective semi-permeable barrier controlling bidirectional transfer between blood vessel and irrigated tissues. This crucial function relies on the dynamic architecture of endothelial cell–cell junctions, and in particular, VE -cadherin-mediated contacts. VE -cadherin indeed chiefly organizes the opening and closing of the endothelial barrier, and is central in permeability changes. In this review, the way VE -cadherin-based contacts are formed and maintained is first presented, including molecular traits of its expression, partners, and signaling. In a second part, the mechanisms by which VE -cadherin adhesion can be disrupted, leading to cell–cell junction weakening and endothelial permeability increase, are described. Overall, the molecular basis for VE -cadherin control of the endothelial barrier function is of high interest for biomedical research, as vascular leakage is observed in many pathological conditions and human diseases.

Control of CXCR2 activity through its ubiquitination on K327 residue

Background

The interleukin-8 chemokine (IL-8) G-protein coupled receptor CXCR2 governs pro-inflammatory and pro-angiogenic responses in leukocytes and endothelial cells. At a molecular standpoint, CXCR2 is widely reported to operate through calcium flux, phosphoinoisitide 3 kinase (PI3K) and mitogen-activated protein kinase (MAPK). While CXCR2 trafficking is suspected to be intertwined with its signaling, the exact mechanism is not fully elucidated.

Results

Here, we identified the lysine 327 within the CXCR2 C-terminal tail as a key residue for ubiquitination, internalization, and signaling. First, the substitution to an arginine of K327 mutation was associated with a reduction in CXCR2 poly-ubiquitination. While WT CXCR2 was rapidly internalized following IL-8 administration, K327R mutant remained at the plasma membrane. Finally, K327R mutant failed to promote the recruitment of β-arrestin2, as estimated by imagery and bioluminescence resonance transfer. As a consequence, the activation of intracellular signaling, including both early events such as ERK phosphorylation and the increase in calcium flux, and the latter activation of the AP1 and NF-κB transcription factors, was blunted.

Conclusions

Overall, our results demonstrate that CXCR2 ubiquitination on K327 residue modulates agonist-activated CXCR2 cell sorting and intracellular signaling. Thus, the inhibition of K327 ubiquitination might emerge as an effective mean to curb exacerbated CXCR2 signaling in several pathological conditions, such as inflammatory diseases and cancer.

Penehyclidine hydrochloride decreases pulmonary microvascular permeability by upregulating beta arrestins in a murine cecal ligation and puncture model

BACKGROUND

Penehyclidine hydrochloride (PHC) is a new anticholinergic drug, which has been shown to have a good curative effect for sepsis. Beta arrestins have been demonstrated to play important roles in sepsis. This study is to investigate the effects of PHC on pulmonary microvascular permeability and on expressions of beta arrestins in lung injury induced by the cecal ligation and puncture (CLP) procedure.

MATERIALS AND METHODS

Thirty healthy female mice were randomly divided into three groups (n = 10 each): sham operation group (control group), CLP group (CLP group), and PHC 0.45 mg/kg group (PHC group). In the PHC group, mice were given an intraperitoneal injection of PHC 0.45 mg/kg 1 h before surgery. Mice in the other two groups received an intraperitoneal injection of the same volume of normal saline. At 12 h after surgery, serum and bronchoalveolar lavage fluid were collected to examine lung permeability index. The lung tissue samples were collected to examine expressions of myosin light chain kinase (MLCK), vascular endothelial-cadherin (VE-cadherin), vascular cell adhesion molecule 1 (VCAM-1), myeloperoxidase (MPO), NF-κB, and beta arrestins.

RESULTS

Compared with the control group, pulmonary microvascular permeability, MPO activity, NF-κB, VCAM-1, and MLCK expressions were significantly increased, whereas VE-cadherin and beta-arrestin protein expressions were obviously decreased in CLP group. Furthermore, compared with the CLP group, PHC group markedly decreased pulmonary microvascular permeability, MPO activity, NF-κB, VCAM-1, and MLCK expressions, and increased expressions of VE-cadherin and beta arrestins.

CONCLUSIONS

This study suggests that in the CLP-induced lung injury model, PHC could reduce pulmonary microvascular permeability by upregulating expressions of beta arrestins.

The P2Y2 Receptor Interacts with VE-Cadherin and VEGF Receptor-2 to Regulate Rac1 Activity in Endothelial Cells

Vascular endothelial cadherin (VE-cadherin) mediates homophylic adhesion between endothelial cells and is an important regulator of angiogenesis, blood vessel permeability and leukocyte trafficking. Rac1, a member of the Rho family of GTPases, controls VE-cadherin adhesion by acting downstream of several growth factors, including angiopoietin-1 and vascular endothelial growth factor (VEGF). Here we show that UTP-induced activation of the G_q protein-coupled P2Y₂ nucleotide receptor (P2Y₂R) in human coronary artery endothelial cells (HCAECs) activated Rac1 and caused a transient complex to form between P2Y₂R, VE-cadherin and VEGF receptor-2 (VEGFR-2). Knockdown of VE-cadherin expression with siRNA did not affect UTP-induced activation of extracellular signal-regulated kinases 1/2 (ERK1/2) but led to a loss of UTP-induced Rac1 activation and tyrosine phosphorylation of p120 catenin, a cytoplasmic protein known to interact with VE-cadherin. Activation of the P2Y₂R by UTP also caused a prolonged interaction between p120 catenin and vav2 (a guanine nucleotide exchange factor for Rac) that correlated with the kinetics of UTP-induced tyrosine phosphorylation of p120 catenin and VE-cadherin. Inhibitors of VEGFR-2 (SU1498) or Src (PP2) significantly diminished UTP-induced Rac1 activation, tyrosine phosphorylation of p120 catenin and VE-cadherin, and association of the P2Y₂R with VE-cadherin and p120 catenin with vav2. These findings suggest that the P2Y₂R uses Src and VEGFR-2 to mediate association of the P2Y₂R with VE-cadherin complexes in endothelial adherens junctions to activate Rac1.

VE-cadherin and endothelial adherens junctions: active guardians of vascular integrity

VE-cadherin is a component of endothelial cell-to-cell adherens junctions, and it has a key role in the maintenance of vascular integrity. During embryo development, VE-cadherin is required for the organization of a stable vascular system, and in the adult it controls vascular permeability and inhibits unrestrained vascular growth. The mechanisms of action of VE-cadherin are complex and include reshaping and organization of the endothelial cell cytoskeleton and modulation of gene transcription. Here we review some of the most important pathways through which VE-cadherin modulates vascular homeostasis and discuss the emerging concepts in the overall biological role of this protein.

Endothelial permeability and VE-cadherin: a wacky comradeship

The endothelium forms a selective semi-permeable barrier controlling bidirectional transfer between blood vessel and irrigated tissues. This crucial function relies on the dynamic architecture of endothelial cell-cell junctions, and in particular, VE-cadherin-mediated contacts. VE-cadherin indeed chiefly organizes the opening and closing of the endothelial barrier, and is central in permeability changes. In this review, the way VE-cadherin-based contacts are formed and maintained is first presented, including molecular traits of its expression, partners, and signaling. In a second part, the mechanisms by which VE-cadherin adhesion can be disrupted, leading to cell-cell junction weakening and endothelial permeability increase, are described. Overall, the molecular basis for VE-cadherin control of the endothelial barrier function is of high interest for biomedical research, as vascular leakage is observed in many pathological conditions and human diseases.

Vascular endothelial growth factor (VEGF), mast cells and inflammation

Vascular endothelial growth factor (VEGF) is one of the most important inducers of angiogenesis, therefore blocking angiogenesis has led to great promise in the treatment of various cancers and inflammatory diseases. VEGF, expressed in response to soluble mediators such as cytokines and growth factors, is important in the physiological development of blood vessels as well as development of vessels in tumors. In cancer patients VEGF levels are increased, and the expression of VEGF is associated with poor prognosis in diseases. VEGF is a mediator of angiogenesis and inflammation which are closely integrated processes in a number of physiological and pathological conditions including obesity, psoriasis, autoimmune diseases and tumor. Mast cells can be activated by anti-IgE to release potent mediators of inflammation and can also respond to bacterial or viral antigens, cytokines, growth factors and hormones, leading to differential release of distinct mediators without degranulation. Substance P strongly induces VEGF in mast cells, and IL-33 contributes to the stimulation and release of VEGF in human mast cells in a dose-dependent manner and acts synergistically in combination with Substance P. Here we report a strong link between VEGF and mast cells and we depict their role in inflammation and immunity.

Vascular permeability and drug delivery in cancers

The endothelial barrier strictly maintains vascular and tissue homeostasis, and therefore modulates many physiological processes such as angiogenesis, immune responses, and dynamic exchanges throughout organs. Consequently, alteration of this finely tuned function may have devastating consequences for the organism. This is particularly obvious in cancers, where a disorganized and leaky blood vessel network irrigates solid tumors. In this context, vascular permeability drives tumor-induced angiogenesis, blood flow disturbances, inflammatory cell infiltration, and tumor cell extravasation. This can directly restrain the efficacy of conventional therapies by limiting intravenous drug delivery. Indeed, for more effective anti-angiogenic therapies, it is now accepted that not only should excessive angiogenesis be alleviated, but also that the tumor vasculature needs to be normalized. Recovery of normal state vasculature requires diminishing hyperpermeability, increasing pericyte coverage, and restoring the basement membrane, to subsequently reduce hypoxia, and interstitial fluid pressure. In this review, we will introduce how vascular permeability accompanies tumor progression and, as a collateral damage, impacts on efficient drug delivery. The molecular mechanisms involved in tumor-driven vascular permeability will next be detailed, with a particular focus on the main factors produced by tumor cells, especially the emblematic vascular endothelial growth factor. Finally, new perspectives in cancer therapy will be presented, centered on the use of anti-permeability factors and normalization agents.