9Rgr; and Rac but not Cdc42 regulate endothelial cell permeability

Inflammatory lung injury is associated with endothelial cell mitochondrial fission and requires the nitration of RhoA and cytoskeletal remodeling

Higher levels of extracellular nicotinamide phosphoribosyltransferase (eNAMPT), a TLR4 agonist, are associated with poor clinical outcomes in sepsis-induced acute lung injury (ALI). Little is known regarding the mechanisms by which eNAMPT is involved in ALI. Our recent work has identified a crucial role for mitochondrial dysfunction in ALI. Thus, this study aimed to determine if eNAMPT-mediated inflammatory injury is associated with the loss of mitochondrial function. Our data show that eNAMPT disrupted mitochondrial bioenergetics. This was associated with cytoskeleton remodeling and the loss of endothelial barrier integrity. These changes were associated with enhanced mitochondrial fission and blocked when Rho-kinase (ROCK) was inhibited. The increases in mitochondrial fission were also associated with the nitration-mediated activation of the small GTPase activator of ROCK, RhoA. Blocking RhoA nitration decreased eNAMPT-mediated mitochondrial fission and endothelial barrier dysfunction. The increase in fission was linked to a RhoA-ROCK mediated increase in Drp1 (dynamin-related protein 1) at serine(S)616. Another TLR4 agonist, lipopolysaccharide (LPS), also increased mitochondrial fission in a Drp1 and RhoA-ROCK-dependent manner. To validate our findings in vivo, we challenged C57BL/6 mice with eNAMPT in the presence and absence of the Drp1 inhibitor, Mdivi-1. Mdivi-1 treatment protected against eNAMPT-induced lung inflammation, edema, and lung injury. These studies demonstrate that mitochondrial fission-dependent disruption of mitochondrial function is essential in TLR4-mediated inflammatory lung injury and identify a key role for RhoA-ROCK signaling. Reducing mitochondrial fission could be a potential therapeutic strategy to improve ARDS outcomes.

ARAP3 protects from excessive formylated peptide-induced microvascular leakage by acting on endothelial cells and neutrophils

Vascular permeability is temporarily heightened during inflammation, but excessive inflammation-associated microvascular leakage can be detrimental, as evidenced in the inflamed lung. Formylated peptides regulate vascular leakage indirectly via formylated peptide receptor-1 (FPR1)-mediated recruitment and activation of neutrophils. Here we identify how the GTPase-activating protein ARAP3 protects against formylated peptide-induced microvascular permeability via endothelial cells and neutrophils. In vitro, Arap3-/- endothelial monolayers were characterised by enhanced formylated peptide-induced permeability due to upregulated endothelial FPR1 and enhanced vascular endothelial cadherin internalisation. In vivo, enhanced inflammation-associated microvascular leakage was observed in Arap3-/- mice. Leakage of plasma protein into the lungs of Arap3-/- mice increased within hours of formylated peptide administration. Adoptive transfer experiments indicated this was dependent upon ARAP3 deficiency in both immune and non-immune cells. Bronchoalveolar lavages of formylated peptide-challenged Arap3-/- mice contained neutrophil extracellular traps (NETs). Pharmacological inhibition of NET formation abrogated excessive microvascular leakage, indicating a critical function of NETs in this context. The observation that Arap3-/- mice developed more severe influenza suggests these findings are pertinent to pathological situations characterised by abundant formylated peptides. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Mechanosensitive FHL2 tunes endothelial function

Endothelial tissues are essential mechanosensors in the vasculature and facilitate adaptation to various blood flow-induced mechanical cues. Defects in endothelial mechanoresponses can perturb tissue remodelling and functions leading to cardiovascular disease progression. In this context, the precise mechanisms of endothelial mechanoresponses contributing to normal and diseased tissue functioning remain elusive. Here, we sought to uncover how flow-mediated transcriptional regulation drives endothelial mechanoresponses in healthy and atherosclerotic-prone tissues. Using bulk RNA sequencing, we identify novel mechanosensitive genes in response to healthy unidirectional flow (UF) and athero-prone disturbed flow (DF). We find that the transcription as well as protein expression of Four-and-a-half LIM protein 2 (FHL2) are enriched in athero-prone DF both in vitro and in vivo. We then demonstrate that the exogenous expression of FHL2 is necessary and sufficient to drive discontinuous adherens junction morphology and increased tissue permeability. This athero-prone phenotype requires the force-sensitive binding of FHL2 to actin. In turn, the force-dependent localisation of FHL2 to stress fibres promotes microtubule dynamics to release the RhoGEF, GEF-H1, and activate the Rho-ROCK pathway. Thus, we unravelled a novel mechanochemical feedback wherein force-dependent FHL2 localisation promotes hypercontractility. This misregulated mechanoresponse creates highly permeable tissues, depicting classic hallmarks of atherosclerosis progression. Overall, we highlight crucial functions for the FHL2 force-sensitivity in tuning multi-scale endothelial mechanoresponses.

Molecular and Cellular Characterization of Primary Endothelial Cells from a Familial Cavernomatosis Patient

Cerebral cavernous malformation (CCM) or familial cavernomatosis is a rare, autosomal dominant, inherited disease characterized by the presence of vascular malformations consisting of blood vessels with an abnormal structure in the form of clusters. Based on the altered gene (CCM1/Krit1, CCM2, CCM3) and its origin (spontaneous or familial), different types of this disease can be found. In this work we have isolated and cultivated primary endothelial cells (ECs) from peripheral blood of a type 1 CCM patient. Differential functional and gene expression profiles of these cells were analyzed and compared to primary ECs from a healthy donor. The mutation of the familial index case consisted of a heterozygous point mutation in the position +1 splicing consensus between exons 15 and 16, causing failure in RNA processing and in the final protein. Furthermore, gene expression analysis by quantitative PCR revealed a decreased expression of genes involved in intercellular junction formation, angiogenesis, and vascular homeostasis. Cell biology analysis showed that CCM1 ECs were impaired in angiogenesis and cell migration. Taken together, the results obtained suggest that the alterations found in CCM1 ECs are already present in the heterozygous condition, suffering from vascular impairment and somewhat predisposed to vascular damage.

Assessment of Endothelial Barrier Functions in Extra Embryonic Vasculature of Chick Embryo as an Alternative Model

Vascular permeability, a tightly regulated process, is a direct measure of angiogenic and immune responses in the endothelium altered in several acute and chronic diseases such as sepsis, high-altitude pulmonary edema (HAPE), high-altitude cerebral edema (HACE), ischemia, and coronavirus disease 2019 (COVID-19) endotheliitis. Both endogenous and exogenous factors such as cytokines, chemokines, and hormones may affect vascular permeability. The conventional tools available for the measurement of vascular permeability in vitro and in vivo based on collagen-coated Transwell and dye-based spectrophotometric methods are indirect measures of permeability. In this chapter, we present our live in ovo protocols based on dextran-Texas red and avian chorioallantoic membrane assay developed using custom-made equipment to assess leakiness of endothelial cell barrier both in vitro and in vivo. Further, we validate this assay using different stressors such as ischemia and hypoxia known to affect endothelial barrier properties by potentiating actin stress fiber disorganization and disrupting the cell-cell junctions.

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.

cAMP: A master regulator of cadherin-mediated binding in endothelium, epithelium and myocardium

Regulation of cadherin-mediated cell adhesion is crucial not only for maintaining tissue integrity and barrier function in the endothelium and epithelium but also for electromechanical coupling within the myocardium. Therefore, loss of cadherin-mediated adhesion causes various disorders, including vascular inflammation and desmosome-related diseases such as the autoimmune blistering skin dermatosis pemphigus and arrhythmogenic cardiomyopathy. Mechanisms regulating cadherin-mediated binding contribute to the pathogenesis of diseases and may also be used as therapeutic targets. Over the last 30 years, cyclic adenosine 3',5'-monophosphate (cAMP) has emerged as one of the master regulators of cell adhesion in endothelium and, more recently, also in epithelial cells as well as in cardiomyocytes. A broad spectrum of experimental models from vascular physiology and cell biology applied by different generations of researchers provided evidence that not only cadherins of endothelial adherens junctions (AJ) but also desmosomal contacts in keratinocytes and the cardiomyocyte intercalated discs are central targets in this scenario. The molecular mechanisms involve protein kinase A- and exchange protein directly activated by cAMP-mediated regulation of Rho family GTPases and S665 phosphorylation of the AJ and desmosome adaptor protein plakoglobin. In line with this, phosphodiesterase 4 inhibitors such as apremilast have been proposed as a therapeutic strategy to stabilize cadherin-mediated adhesion in pemphigus and may also be effective to treat other disorders where cadherin-mediated binding is compromised.

β-Actin: An Emerging Biomarker in Ischemic Stroke

At present, the diagnosis of ischemic stroke mainly depends on neuroimaging technology, but it still has many limitations. Therefore, it is very important to find new biomarkers of ischemic stroke. Recently, β-actin has attracted extensive attention as a biomarker of a variety of cancers. Although several recent studies have been investigating its role in ischemic stroke and other cerebrovascular diseases, the understanding of this emerging biomarker in neurology is still limited. We examined human and preclinical studies to gain a comprehensive understanding of the literature on the subject. Most relevant literatures focus on preclinical research, and pay more attention to the role of β-actin in the process of cerebral ischemia, but some recent literatures reported that in human studies, serum β-actin increased significantly in the early stage of acute cerebral ischemia. This review will investigate the basic biology of β-actin, pay attention to the potential role of serum β-actin as an early diagnostic blood biomarker of ischemic stroke, and explore its potential mechanism in ischemic stroke and new strategies for stroke treatment in the future.

In vivo dissection of Rhoa function in vascular development using zebrafish

The small monomeric GTPase RHOA acts as a master regulator of signal transduction cascades by activating effectors of cellular signaling, including the Rho-associated protein kinases ROCK1/2. Previous in vitro cell culture studies suggest that RHOA can regulate many critical aspects of vascular endothelial cell (EC) biology, including focal adhesion, stress fiber formation, and angiogenesis. However, the specific in vivo roles of RHOA during vascular development and homeostasis are still not well understood. In this study, we examine the in vivo functions of RHOA in regulating vascular development and integrity in zebrafish. We use zebrafish RHOA-ortholog (rhoaa) mutants, transgenic embryos expressing wild type, dominant negative, or constitutively active forms of rhoaa in ECs, pharmacological inhibitors of RHOA and ROCK1/2, and Rock1 and Rock2a/b dgRNP-injected zebrafish embryos to study the in vivo consequences of RHOA gain- and loss-of-function in the vascular endothelium. Our findings document roles for RHOA in vascular integrity, developmental angiogenesis, and vascular morphogenesis in vivo, showing that either too much or too little RHOA activity leads to vascular dysfunction.

DOCK4 Regulation of Rho GTPases Mediates Pulmonary Vascular Barrier Function

BACKGROUND

The vascular endothelium maintains tissue-fluid homeostasis by controlling the passage of large molecules and fluid between the blood and interstitial space. The interaction of catenins and the actin cytoskeleton with VE-cadherin (vascular endothelial cadherin) is the primary mechanism for stabilizing AJs (adherens junctions), thereby preventing lung vascular barrier disruption. Members of the Rho (Ras homology) family of GTPases and conventional GEFs (guanine exchange factors) of these GTPases have been demonstrated to play important roles in regulating endothelial permeability. Here, we evaluated the role of DOCK4 (dedicator of cytokinesis 4)-an unconventional Rho family GTPase GEF in vascular function.

METHODS

We generated mice deficient in DOCK4' used DOCK4 silencing and reconstitution approaches in human pulmonary artery endothelial cells' used assays to evaluate protein localization, endothelial cell permeability, and small GTPase activation.

RESULTS

Our data show that DOCK4-deficient mice are viable. However, these mice have hemorrhage selectively in the lung, incomplete smooth muscle cell coverage in pulmonary vessels, increased basal microvascular permeability, and impaired response to S1P (sphingosine-1-phosphate)-induced reversal of thrombin-induced permeability. Consistent with this, DOCK4 rapidly translocates to the cell periphery and associates with the detergent-insoluble fraction following S1P treatment, and its absence prevents S1P-induced Rac-1 activation and enhancement of barrier function. Moreover, DOCK4-silenced pulmonary artery endothelial cells exhibit enhanced basal permeability in vitro that is associated with enhanced Rho GTPase activation.

CONCLUSIONS

Our findings indicate that DOCK4 maintains AJs necessary for lung vascular barrier function by establishing the normal balance between RhoA (Ras homolog family member A) and Rac-1-mediated actin cytoskeleton remodeling, a previously unappreciated function for the atypical GEF family of molecules. Our studies also identify S1P as a potential upstream regulator of DOCK4 activity.

The emerging landscape of exosomal CircRNAs in solid cancers and hematological malignancies

Circular RNAs (circRNAs) are a type of recently discovered noncoding RNA. They exert their biological functions by competitively binding to microRNAs (miRNAs) as miRNA sponges, promoting gene transcription and participating in the regulation of selective splicing, interacting with proteins and being translated into proteins. Exosomes are derived from intracavitary vesicles (ILVs), which are formed by the inward budding of multivesicular bodies (MVBs), and exosome release plays a pivotal role in intercellular communication. Accumulating evidence indicates that circRNAs in exosomes are associated with solid tumor invasion and metastasis. Additionally, emerging studies in the last 1 ~ 2 years have revealed that exosomal circRNA also have effect on hematological malignancies. In this review, we outline the properties and biological functions of circRNAs and exosomes. In particular, we summarize in detail the mechanism and roles of exosomal circRNAs and highlight their application as novel biomarkers in malignant tumors.

ArhGEF12 activates Rap1A and not RhoA in human dermal microvascular endothelial cells to reduce tumor necrosis factor-induced leak

Overwhelming inflammation in the setting of acute critical illness induces capillary leak resulting in hypovolemia, edema, tissue dysoxia, organ failure and even death. The tight junction (TJ)-dependent capillary barrier is regulated by small GTPases, but the specific regulatory molecules most active in this vascular segment under such circumstances are not well described. We set out to identify GTPase regulatory molecules specific to endothelial cells (EC) that form TJs. Transcriptional profiling of confluent monolayers of TJ-forming human dermal microvascular ECs (HDMECs) and adherens junction only forming-human umbilical vein EC (HUVECs) demonstrate ARHGEF12 is basally expressed at higher levels and is only downregulated in HDMECs by junction-disrupting tumor necrosis factor (TNF). HDMECs depleted of ArhGEF12 by siRNA demonstrate a significantly exacerbated TNF-induced decrease in trans-endothelial electrical resistance and disruption of TJ continuous staining. ArhGEF12 is established as a RhoA-GEF in HUVECs and its knock down would be expected to reduce RhoA activity and barrier disruption. Pulldown of active GEFs from HDMECs depleted of ArhGEF12 and treated with TNF show decreased GTP-bound Rap1A after four hours but increased GTP-bound RhoA after 12 h. In cell-free assays, ArhGEF12 immunoprecipitated from HDMECs is able to activate both Rap1A and RhoA, but not act on Rap2A-C, RhoB-C, or even Rap1B which shares 95% sequence identity with Rap1A. We conclude that in TJ-forming HDMECs, ArhGEF12 selectively activates Rap1A to limit capillary barrier disruption in a mechanism independent of cAMP-mediated Epac1 activation.

Endothelial Transcytosis in Acute Lung Injury: Emerging Mechanisms and Therapeutic Approaches

Acute Lung Injury (ALI) is characterized by widespread inflammation which in its severe form, Acute Respiratory Distress Syndrome (ARDS), leads to compromise in respiration causing hypoxemia and death in a substantial number of affected individuals. Loss of endothelial barrier integrity, pneumocyte necrosis, and circulating leukocyte recruitment into the injured lung are recognized mechanisms that contribute to the progression of ALI/ARDS. Additionally, damage to the pulmonary microvasculature by Gram-negative and positive bacteria or viruses (e.g., Escherichia coli, SARS-Cov-2) leads to increased protein and fluid permeability and interstitial edema, further impairing lung function. While most of the vascular leakage is attributed to loss of inter-endothelial junctional integrity, studies in animal models suggest that transendothelial transport of protein through caveolar vesicles, known as transcytosis, occurs in the early phase of ALI/ARDS. Here, we discuss the role of transcytosis in healthy and injured endothelium and highlight recent studies that have contributed to our understanding of the process during ALI/ARDS. We also cover potential approaches that utilize caveolar transport to deliver therapeutics to the lungs which may prevent further injury or improve recovery.

Blood-Brain Barrier Permeable and NO-Releasing Multifunctional Nanoparticles for Alzheimer's Disease Treatment: Targeting NO/cGMP/CREB Signaling Pathways

The development of novel therapeutic strategies for combating Alzheimer's disease (AD) is challenging but imperative. Multifunctional nanoparticles are promising tools for regulating complex pathological dysfunctions for AD treatment. Herein, we constructed multifunctional nanoparticles consisting of regadenoson (Reg), nitric oxide (NO) donor, and YC-1 in a single molecular entity that can spontaneously self-assemble into nanoparticles and load donepezil to yield Reg-nanoparticles (Reg-NPs). The Reg moiety enabled the Reg-NPs to effectively regulate tight junction-associated proteins in the blood-brain barrier, thus facilitating the permeation of donepezil through the barrier and its accumulation in the brain. Moreover, the released NO and YC-1 activated the NO/cGMP/CREB signaling pathway by stimulating soluble guanylyl cyclase and inhibiting phosphodiesterase activity, which finally reduced cytotoxicity induced by aggregated Aβ in the neurons and was beneficial for synaptic plasticity and memory formation.

The multifaceted PDCD10/CCM3 gene

The programmed cell death 10 (PDCD10) gene was originally identified as an apoptosis-related gene, although it is now usually known as CCM3, as the third causative gene of cerebral cavernous malformation (CCM). CCM is a neurovascular disease that is characterized by vascular malformations and is associated with headaches, seizures, focal neurological deficits, and cerebral hemorrhage. The PDCD10/CCM3 protein has multiple subcellular localizations and interacts with several multi-protein complexes and signaling pathways. Thus PDCD10/CCM3 governs many cellular functions, which include cell-to-cell junctions and cytoskeleton organization, cell proliferation and apoptosis, and exocytosis and angiogenesis. Given its central role in the maintenance of homeostasis of the cell, dysregulation of PDCD10/CCM3 can result in a wide range of altered cell functions. This can lead to severe diseases, including CCM, cognitive disability, and several types of cancers. Here, we review the multifaceted roles of PDCD10/CCM3 in physiology and pathology, with a focus on its functions beyond CCM.

Phosphorylated cingulin localises GEF-H1 at tight junctions to protect vascular barriers in blood endothelial cells

Dysfunction of vascular barriers is a critical step in inflammatory diseases. Endothelial tight junctions (TJs) control barrier function, and the cytoplasmic adaptor protein cingulin connects TJs to signalling pathways. However, local events at TJs during inflammation are largely unknown. In this study, we investigate the local response of TJ adaptor protein cingulin and its interaction with Rho guanine nucleotide exchange factor H1 (GEF-H1, also known as ARHGEF2) upon vascular barrier disruption to find a new approach to counteract vascular leak. Based on transendothelial-electrical-resistance (TEER) measurements, cingulin strengthened barrier integrity upon stimulation with histamine, thrombin and VEGF. Cingulin also attenuated myosin light chain 2 (MLC2; also known as MYL2) phosphorylation by localising GEF-H1 to cell junctions. By using cingulin phosphomutants, we verified that the phosphorylation of the cingulin head domain is required for its protective effect. Increased colocalisation of GEF-H1 and cingulin was observed in the vessels of vasculitis patients compared to those in healthy skin. Our findings demonstrate that cingulin can counteract vascular leak at TJs, suggesting the existence of a novel mechanism in blood endothelial cells that protects barrier function during disease.

Summary: Vascular leak in response to histamine, thrombin and VEGF can be counteracted by AMPK phosphorylating cingulin at its head domain. Consequential binding of GEF-H1 to tight junctions protects vascular barrier function.

Pazopanib ameliorates acute lung injuries via inhibition of MAP3K2 and MAP3K3

Acute lung injury (ALI) causes high mortality and lacks any pharmacological intervention. Here, we found that pazopanib ameliorated ALI manifestations and reduced mortality in mouse ALI models and reduced edema in human lung transplantation recipients. Pazopanib inhibits mitogen-activated protein kinase kinase kinase 2 (MAP3K2)- and MAP3K3-mediated phosphorylation of NADPH oxidase 2 subunit p47^phox at Ser²⁰⁸ to increase reactive oxygen species (ROS) formation in myeloid cells. Genetic inactivation of MAP3K2 and MAP3K3 in myeloid cells or hematopoietic mutation of p47^phox Ser²⁰⁸ to alanine attenuated ALI manifestations and abrogates anti-ALI effects of pazopanib. This myeloid MAP3K2/MAP3K3-p47^phox pathway acted via paracrine H₂O₂ to enhance pulmonary vasculature integrity and promote lung epithelial cell survival and proliferation, leading to increased pulmonary barrier function and resistance to ALI. Thus, pazopanib has the potential to be effective for treating ALI.

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

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

Trauma-Induced Coagulopathy: Overview of an Emerging Medical Problem from Pathophysiology to Outcomes

Coagulopathy induced by major trauma is common, affecting approximately one-third of patients after trauma. It develops independently of iatrogenic, hypothermic, and dilutive causes (such as iatrogenic cause in case of fluid administration), which instead have a pejorative aspect on coagulopathy. Notwithstanding the continuous research conducted over the past decade on Trauma-Induced Coagulopathy (TIC), it remains a life-threatening condition with a significant impact on trauma mortality. We reviewed the current evidence regarding TIC diagnosis and pathophysiological mechanisms and summarized the different iterations of optimal TIC management strategies among which product resuscitation, potential drug administrations, and hemostatis-focused approaches. We have identified areas of ongoing investigation and controversy in TIC management.

Protective effect of the sphingosine-1 phosphate receptor agonist siponimod on disrupted blood brain barrier function

Sphingosine 1 phosphate (S1P) is a bioactive sphingolipid that exerts several functions in physiological and pathological conditions. The modulation of one of its receptors, S1P1, plays an important role in the egress of lymphocytes from lymph nodes and is a useful target in multiple sclerosis (MS) treatment. A new drug, siponimod (BAF-312) has been recently approved for the treatment of secondary progressive MS and has affinity for two S1P receptors, S1P1 and S1P5. The two receptors are expressed by endothelial cells that, as components of the blood-brain barrier (BBB), prevent the access of solutes and lymphocytes into the central nervous system, function often compromised in MS. Using an in vitro BBB model exposed to inflammatory cytokines (TNFα and IFNγ, 5 UI and 10 UI respectively), we evaluated the effects of BAF-312 (100 nM) on expression and function of endothelial tight junctional proteins (Zo-1 and claudin-5), regulation of transendothelial electrical resistance (TEER) and permeability to FITC-conjugated dextran. Zo-1 expression, as well as TEER values, were promptly recovered (24 h) when both S1P1 and S1P5 were activated by BAF-312. In contrast, at this time point, activation of S1P5 with the selective agonist UC-42-WP04 (300 nM) or with BAF-312, under blockade of S1P1 with the selective antagonist NIBR-0213 (1 μM), resulted in recovery of expression and localization of claudin-5 and reduction of TNFα/INFγ-induced expression of metalloproteinase 9. Only after a prolonged BAF-312 exposure (48 h), S1P1 was involved through activation of the PI3K/Akt pathway. The PI3K inhibitor LY294002 (10 µM) prevented in fact the effects of BAF-312 on all the parameters examined. In conclusion, BAF-312, by modulating both S1P1 and S1P5, may strengthen BBB properties, thus providing additional effects in the treatment of MS.

Cytokine-induced molecular responses in airway smooth muscle cells inform genome-wide association studies of asthma

BACKGROUND

A challenge in the post-GWAS era is to assign function to disease-associated variants. However, available resources do not include all tissues or environmental exposures that are relevant to all diseases. For example, exaggerated bronchoconstriction of airway smooth muscle cells (ASMCs) defines airway hyperresponsiveness (AHR), a cardinal feature of asthma. However, the contribution of ASMC to genetic and genomic studies has largely been overlooked. Our study aimed to address the gap in data availability from a critical tissue in genomic studies of asthma.

METHODS

We developed a cell model of AHR to discover variants associated with transcriptional, epigenetic, and cellular responses to two AHR promoting cytokines, IL-13 and IL-17A, and performed a GWAS of bronchial responsiveness (BRI) in humans.

RESULTS

Our study revealed significant response differences between ASMCs from asthma cases and controls, including genes implicated in asthma susceptibility. We defined molecular quantitative trait loci (QTLs) for expression (eQTLs) and methylation (meQTLs), and cellular QTLs for contractility (coQTLs) and performed a GWAS of BRI in human subjects. Variants in asthma GWAS were significantly enriched for ASM QTLs and BRI-associated SNPs, and near genes enriched for ASM function, many with small P values that did not reach stringent thresholds of significance in GWAS.

CONCLUSIONS

Our study identified significant differences between ASMCs from asthma cases and controls, potentially reflecting trained tolerance in these cells, as well as a set of variants, overlooked in previous GWAS, which reflect the AHR component of asthma.

Fibrinogen Protects Against Barrier Dysfunction Through Maintaining Cell Surface Syndecan-1 In Vitro

BACKGROUND

We have shown that fresh frozen plasma's (FFP) protection of pulmonary endothelial barrier integrity following hemorrhagic shock is due in part to restoration of endothelial syndecan-1. In the present study, we investigated the role of fibrinogen, a major component of FFP, as an endothelial protector and hypothesize that fibrinogen stabilizes cell surface syndecan-1 to restore endothelial barrier integrity.

METHODS

Pulmonary endothelial cells were incubated in FFP, fibrinogen, or lactated Ringers (LR) then immunostained with anti-syndecan-1 or fibrinogen and barrier integrity assessed. In some experiments, cells were exposed to fibrinogen depleted plasma.

RESULTS

Cell surface syndecan-1 was increased by FFP and fibrinogen compared with LR-treated cells while barrier integrity was augmented by FFP and fibrinogen compared with LR. The physiological concentration of 2.5 mg/mL fibrinogen was sufficient to increase cell surface syndecan-1. Colocalization and co-immunoprecipitation experiments demonstrated that fibrinogen associates with syndecan-1. Fibrinogen-deficient plasma was unable to augment sydnecan-1 immunostaining and lost its endothelial protective effect on barrier integrity.

CONCLUSION

These data suggest that in vitro, fibrinogen associated with cell surface syndecan-1 and enhanced endothelial barrier integrity.

A new microfluidic model that allows monitoring of complex vascular structures and cell interactions in a 3D biological matrix

Microfluidic organ-on-a-chip designs are used to mimic human tissues, including the vasculature. Here we present a novel microfluidic device that allows the interaction of endothelial cells (ECs) with pericytes and the extracellular matrix (ECM) in full bio-matrix encased 3D vessel structures (neovessels) that can be subjected to continuous, unidirectional flow and perfusion with circulating immune cells. We designed a polydimethylsiloxane (PDMS) device with a reservoir for a 3D fibrinogen gel with pericytes. Open channels were created for ECs to form a monolayer. Controlled, continuous, and unidirectional flow was introduced via a pump system while the design facilitated 3D confocal imaging. In this vessel-on-a-chip system, ECs interact with pericytes to create a human cell derived blood vessel which maintains a perfusable lumen for up to 7 days. Dextran diffusion verified endothelial barrier function while demonstrating the beneficial role of supporting pericytes. Increased permeability after thrombin stimulation showed the capacity of the neovessels to show natural vascular response. Perfusion of neovessels with circulating THP-1 cells demonstrated this system as a valuable platform for assessing interaction between the endothelium and immune cells in response to TNFα. In conclusion: we created a novel vascular microfluidic device that facilitates the fabrication of an array of parallel soft-channel structures in ECM gel that develop into biologically functional neovessels without hard-scaffold support. This model provides a unique tool to conduct live in vitro imaging of the human vasculature during perfusion with circulating cells to mimic (disease) environments in a highly systematic but freely configurable manner.

circRNAs and Exosomes: A Mysterious Frontier for Human Cancer

Exosomes are nano-sized membrane-bound vesicles and contain active substances (DNA, noncoding RNA [ncRNA], protein), which provide a novel method of transferring effector messages between cells. Circular RNAs (circRNAs), a kind of ncRNA, have attracted increasing attention over the last decade given advances in whole-genome and transcriptome sequencing technologies. It has become increasingly clear that circRNAs regulate gene expression through various actions and play diverse roles in many fields of human cancer biology. Notably, several studies reported that circRNAs are enriched in exosomes and that exosomal circRNAs play an important role in cancer biology. Exosomal circRNAs can be taken up by neighboring or distant cells and affect many aspects of physiological and pathological conditions of the recipient cells, potentially promoting cell communication and tumor metastasis. Herein, we briefly review the molecular mechanisms of circRNAs and recent findings regarding exosomal circRNAs, and highlight the specific roles of exosomal circRNAs in human cancer.

The Presence of a High Peak Feature Within Low-Average Shear Stimuli Induces Quiescence in Venous Endothelial Cells

Wall shear stress (WSS) is an important stimulus in vascular remodelling and vascular lesion development. The current methods to assess and predict the risk associated with specific unsteady WSS consider the WSS mean values or the presence of reverse phases described by the oscillatory shear index. Recent evidence has shown that the accuracy of these methods is limited, especially with respect to the venous environment. Unsteady WSS are characterised by several features that may individually affect endothelial cells. Consequently, we assessed the effects of averaged WSS (TAWSS), temporal WSS gradient (TWSSG), maximum WSS (WSS peak) and reverse phase (OSI) by applying different WSS profiles to venous EC in-vitro, using a real-time controlled cone-and-plate cell-shearing device for 24 h. We found that TWSSG and WSS peak affect cell elongation and alignment respectively. We also found that the WSS waveforms with a peak of 1.5 Pa or higher significantly correlate with the induction of a protective phenotype. Cell phenotype induced by these high peak waveforms does not correlate to what is predicted by the hemodynamic indices currently used. The definition of reliable hemodynamic indices can be used to inform the computational models aimed at estimating the hemodynamic effects on vascular remodelling.

Ubiquitin-based modifications in endothelial cell-cell contact and inflammation

Endothelial cell-cell contacts are essential for vascular integrity and physiology, protecting tissues and organs from edema and uncontrolled invasion of inflammatory cells. The vascular endothelial barrier is dynamic, but its integrity is preserved through a tight control at different levels. Inflammatory cytokines and G-protein-coupled receptor agonists, such as histamine, reduce endothelial integrity and increase vascular leakage. This is due to elevated myosin-based contractility, in conjunction with phosphorylation of proteins at cell-cell contacts. Conversely, reducing contractility stabilizes or even increases endothelial junctional integrity. Rho GTPases are key regulators of such cytoskeletal dynamics and endothelial cell-cell contacts. In addition to signaling-induced regulation, the expression of junctional proteins, such as occludin, claudins and vascular endothelial cadherin, also controls endothelial barrier function. There is increasing evidence that, in addition to protein phosphorylation, ubiquitylation (also known as ubiquitination) is an important and dynamic post-translational modification that regulates Rho GTPases, junctional proteins and, consequently, endothelial barrier function. In this Review, we discuss the emerging role of ubiquitylation and deubiquitylation events in endothelial integrity and inflammation. The picture that emerges is one of increasing complexity, which is both fascinating and promising given the clinical relevance of vascular integrity in the control of inflammation, and of tissue and organ damage.

Exosomal circRNAs: biogenesis, effect and application in human diseases

Exosomes have emerged as critical mediators of intercellular communication, both locally and systemically, by regulating a diverse range of biological processes between cells. Circular RNA (circRNA) is a novel member of endogenous noncoding RNAs with widespread distribution and diverse cellular functions. Recently, circular RNAs have been identified for their enrichment and stability in exosomes. In this review, we outline the origin, biogenesis and function of exosomal circRNAs as well as their roles in various diseases. Although their precise roles and mechanisms of gene regulation remain largely elusive, exosomal circRNAs have potential applications as disease biomarkers and novel therapeutic targets.

Activation of SIRT1 ameliorates LPS-induced lung injury in mice via decreasing endothelial tight junction permeability

The integrity of the endothelial barrier is a determinant of the prognosis of lipopolysaccharide (LPS)-induced acute lung injury (ALI). In this study, we investigated whether and how Sirtuin 1 (SIRT1) maintained the vascular integrity during ALI. An experimental model of ALI was established in mice through intratracheal administration of LPS (10 mg/kg). LPS stimulation significantly increased the pulmonary permeability and decreased the expression of SIRT1 and tight junction proteins (TJs), including occludin, claudin-5, tight junction protein 1 and tight junction protein 2. Morphological studies showed that LPS induced obvious lung injury with inflammatory cell infiltration in the interstitial and alveolar space, hemorrhage, edema, and the thickened alveolar wall compared to the control mice. Intratracheal administration of the selective SIRT1 activator SRT1720 (6.25 mg/kg) significantly attenuated LPS-induced lung injury, lung hyper-permeability and increased TJs expression, whereas intratracheal administration of the selective SIRT1 inhibitor EX527 (6.25 mg/kg) aggravated LPS-induced ALI. Similar protective effects of SIRT1 on pulmonary cellular permeability were observed in primary human pulmonary microvascular endothelial cells treated with LPS (2 mg/mL) in vitro. We further demonstrated that the RhoA/ROCK signaling pathway was activated in SIRT1 regulation of tight junction permeability. The RhoA/ROCK inhibitor Y-27632 (10 μM) increased the expression of TJs and reversed LPS- or EX527-induced hyper-permeability. In conclusion, SIRT1 ameliorates LPS-induced lung injury via decreasing endothelial tight junction permeability, possibly via RhoA/ROCK signaling pathway. This finding may contribute to the development of new therapeutic approaches for lung injury.

A Novel Microscopic Assay Reveals Heterogeneous Regulation of Local Endothelial Barrier Function

Blood vessels are covered with endothelial cells on their inner surfaces, forming a selective and semipermeable barrier between the blood and the underlying tissue. Many pathological processes, such as inflammation or cancer metastasis, are accompanied by an increased vascular permeability. Progress in live cell imaging techniques has recently revealed that the structure of endothelial cell contacts is constantly reorganized and that endothelial junctions display high heterogeneities at a subcellular level even within one cell. Although it is assumed that this dynamic remodeling is associated with a local change in endothelial barrier function, a direct proof is missing mainly because of a lack of appropriate experimental techniques. Here, we describe a new assay to dynamically measure local endothelial barrier function with a lateral resolution of ∼15 μm and a temporal resolution of 1 min. In this setup, fluorescence-labeled molecules are added to the apical compartment of an endothelial monolayer, and the penetration of molecules from the apical to the basal compartment is recorded by total internal reflection fluorescence microscopy utilizing the generated evanescent field. With this technique, we found a remarkable heterogeneity in the local permeability for albumin within confluent endothelial cell layers. In regions with low permeability, stimulation with the proinflammatory agent histamine results in a transient increase in paracellular permeability. The effect showed a high variability along the contact of one individual cell, indicating a local regulation of endothelial barrier function. In regions with high basal permeability, histamine had no obvious effect. In contrast, the barrier-enhancing drug forskolin reduces the permeability for albumin and dextran uniformly along the cell junctions. Because this new approach can be readily combined with other live cell imaging techniques, it will contribute to a better understanding of the mechanisms underlying subcellular junctional reorganization during wound healing, inflammation, and angiogenesis.

VE-PTP stabilizes VE-cadherin junctions and the endothelial barrier via a phosphatase-independent mechanism

Juettner et al. describe a novel phosphatase-activity–independent mechanism by which the phosphatase VE-PTP restricts endothelial permeability. VE-PTP functions as a scaffold that binds and inhibits the RhoGEF GEF-H1, limiting RhoA-dependent tension across VE-cadherin junctions and decreasing VE-cadherin internalization to stabilize adherens junctions and reduce endothelial permeability.

Vascular endothelial (VE) protein tyrosine phosphatase (PTP) is an endothelial-specific phosphatase that stabilizes VE-cadherin junctions. Although studies have focused on the role of VE-PTP in dephosphorylating VE-cadherin in the activated endothelium, little is known of VE-PTP’s role in the quiescent endothelial monolayer. Here, we used the photoconvertible fluorescent protein VE-cadherin-Dendra2 to monitor VE-cadherin dynamics at adherens junctions (AJs) in confluent endothelial monolayers. We discovered that VE-PTP stabilizes VE-cadherin junctions by reducing the rate of VE-cadherin internalization independently of its phosphatase activity. VE-PTP serves as an adaptor protein that through binding and inhibiting the RhoGEF GEF-H1 modulates RhoA activity and tension across VE-cadherin junctions. Overexpression of the VE-PTP cytosolic domain mutant interacting with GEF-H1 in VE-PTP–depleted endothelial cells reduced GEF-H1 activity and restored VE-cadherin dynamics at AJs. Thus, VE-PTP stabilizes VE-cadherin junctions and restricts endothelial permeability by inhibiting GEF-H1, thereby limiting RhoA signaling at AJs and reducing the VE-cadherin internalization rate.

Quantification of adherens junction disruption and contiguous paracellular protein leak in human lung endothelial cells under septic conditions

OBJECTIVE

Sepsis is associated with dysfunction of MVEC resulting in organ edema and inflammation. VE-cadherin, a component of MVEC adherens junctions, may be disrupted in sepsis. However, the direct connection between individual MVEC VE-cadherin disruption and increased paracellular permeability is uncertain.

METHODS

Human pulmonary MVEC were cultured on a biotin matrix and treated with cytomix, as a model of sepsis, vs PBS. MVEC permeability was assessed by trans-MVEC monolayer leak of Oregon green 488-conjugated avidin, which bound subcellular biotin to localize sites of paracellular leak. Leak was correlated with individual cell-specific MVEC surface VE-cadherin continuity by fluorescence microscopy.

RESULTS

Cytomix treatment reduced total MVEC VE-cadherin density, disrupted surface VE-cadherin continuity, was associated with intercellular gap formation, and enhanced paracellular avidin leak. Cytomix-induced MVEC paracellular avidin leak was strongly correlated temporally and was highly contiguous with focal MVEC surface VE-cadherin disruption. Total cellular VE-cadherin density was less strongly correlated with MVEC paracellular avidin leak and individual cell-specific focal surface VE-cadherin discontinuity.

CONCLUSIONS

These data support a mechanistic link between septic human lung MVEC VE-cadherin disruption and contiguous paracellular protein leak, and will permit more detailed assessment of individual cell-specific mechanisms of septic MVEC barrier dysfunction.

The Functional Implications of Endothelial Gap Junctions and Cellular Mechanics in Vascular Angiogenesis

Angiogenesis—the sprouting and growth of new blood vessels from the existing vasculature—is an important contributor to tumor development, since it facilitates the supply of oxygen and nutrients to cancer cells. Endothelial cells are critically affected during the angiogenic process as their proliferation, motility, and morphology are modulated by pro-angiogenic and environmental factors associated with tumor tissues and cancer cells. Recent in vivo and in vitro studies have revealed that the gap junctions of endothelial cells also participate in the promotion of angiogenesis. Pro-angiogenic factors modulate gap junction function and connexin expression in endothelial cells, whereas endothelial connexins are involved in angiogenic tube formation and in the cell migration of endothelial cells. Several mechanisms, including gap junction function-dependent or -independent pathways, have been proposed. In particular, connexins might have the potential to regulate cell mechanics such as cell morphology, cell migration, and cellular stiffness that are dynamically changed during the angiogenic processes. Here, we review the implication for endothelial gap junctions and cellular mechanics in vascular angiogenesis.

Multiplexed, high-throughput measurements of cell contraction and endothelial barrier function

Vascular leakage, protein exudation, and edema formation are events commonly triggered by inflammation and facilitated by gaps that form between adjacent endothelial cells (ECs) of the vasculature. In such paracellular gap formation, the role of EC contraction is widely implicated, and even therapeutically targeted. However, related measurement approaches remain slow, tedious, and complex to perform. Here, we have developed a multiplexed, high-throughput screen to simultaneously quantify paracellular gaps, EC contractile forces, and to visualize F-actin stress fibers, and VE-cadherin. As proof-of-principle, we examined barrier-protective mechanisms of the Rho-associated kinase inhibitor, Y-27632, and the canonical agonist of the Tie2 receptor, Angiopoietin-1 (Angpt-1). Y-27632 reduced EC contraction and actin stress fiber formation, whereas Angpt-1 did not. Yet both agents reduced thrombin-, LPS-, and TNFα-induced paracellular gap formation. This unexpected result suggests that Angpt-1 can achieve barrier defense without reducing EC contraction, a mechanism that has not been previously described. This insight was enabled by the multiplex nature of the force-based platform. The high-throughput format we describe should accelerate both mechanistic studies and the screening of pharmacological modulators of endothelial barrier function.

Endothelial Protrusions in Junctional Integrity and Barrier Function

Endothelial cells of the microcirculation form a semi-permeable diffusion barrier between the blood and tissues. This permeability of the endothelium, particularly in the capillaries and postcapillary venules, is a normal physiological function needed for blood-tissue exchange in the microcirculation. During inflammation, microvascular permeability increases dramatically and can lead to tissue edema, which in turn can lead to dysfunction of tissues and organs. The molecular mechanisms that control the barrier function of endothelial cells have been under investigation for several decades and remain an important topic due to the potential for discovery of novel therapeutic strategies to reduce edema. This review highlights current knowledge of the cellular and molecular mechanisms that lead to endothelial hyperpermeability during inflammatory conditions associated with injury and disease. This includes a discussion of recent findings demonstrating temporal protrusions by endothelial cells that may contribute to intercellular junction integrity between endothelial cells and affect the diffusion distance for solutes via the paracellular pathway.

SHP2 protects endothelial cell barrier through suppressing VE-cadherin internalization regulated by MET-ARF1

Vascular endothelial (VE)-cadherin junctional localization is known to play a central role in vascular development, endothelial barrier integrity, and homeostasis. The sarcoma homology domain containing protein tyrosine phosphatase (SHP)2 has been shown to be involved in regulating endothelial barrier function; however, the mechanisms remain largely unknown. In this work SHP2 knockdown in an HUVEC monolayer increased VE-cadherin internalization and endothelial barrier permeability. Loss of SHP2 specifically augmented the GTPase activity of ADP-ribosylation factor (ARF)-1. ARF1 knockdown or inhibition of its guanine nucleotide exchange factors (GEFs) markedly attenuated VE-cadherin internalization and barrier hyperpermeability induced by SHP2 deficiency. SHP2 knockdown increased the total and phosphorylated levels of MET, whose activity was necessary for ARF1 activation and VE-cadherin internalization. Furthermore, constitutive endothelium-specific deletion of Shp2 in mice led to disrupted endothelial cell junctions, massive hemorrhage, and lethality in embryos. Induced and endothelium-specific deletion of Shp2 in adult mice resulted in lung hyperpermeability. Inhibitors for ARF1-GEF or MET used in pregnant mice prevented the vascular leakage in endothelial Shp2-deleted embryos. Together, our findings define a novel role of SHP2 in stabilizing junctional VE-cadherin in the resting endothelial barrier through suppressing MET and ARF1 activation.-Zhang, J., Huang, J., Qi, T., Huang, Y., Lu, Y., Zhan, T., Gong, H., Zhu, Z., Shi, Y., Zhou, J., Yu, L., Zhang, X., Cheng, H., Ke, Y. SHP2 protects endothelial cell barrier through suppressing VE-cadherin internalization regulated by MET-ARF1.

Circular RNA IARS (circ-IARS) secreted by pancreatic cancer cells and located within exosomes regulates endothelial monolayer permeability to promote tumor metastasis

BACKGROUND

Recent studies show that exosomes are involved in intercellular communication and that abundant circular RNAs (circRNAs) are present within exosomes. However, whether these exosomal circRNAs contribute to tumor invasion and metastasis remains unclear, as do their associated mechanisms.

METHODS

Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to measure the expression levels of circ-IARS in 85 pancreatic ductal adenocarcinoma (PDAC) tissues, plasma exosomes, and Hs 766 T, Hs 766 T-L2 and human microvascular vein endothelial (HUVECs) cells. RhoA, ZO-1 and RhoA-GTP levels were detected by qRT-PCR and western blotting (WB); RhoA activity analysis was also performed. Transwell assays were performed to examine changes in endothelial monolayer permeability, and immunofluorescence and WB were employed to evaluate F-actin expression and focal adhesion. Finally, an animal experiment was performed to detect the contribution of circ-IARS to cancer metastasis.

RESULTS

circ-IARS expression was up-regulated in pancreatic cancer tissues and in plasma exosomes of patients with metastatic disease. Circ-IARS was found to enter HUVECs through exosomes and promote tumor invasion and metastasis. Circ-IARS expression was positively correlated with liver metastasis, vascular invasion, and tumor-node-metastasis (TNM) stage and negatively correlated with postoperative survival time. Overexpression of circ-IARS significantly down-regulated miR-122 and ZO-1 levels, up-regulated RhoA and RhoA-GTP levels, increased F-actin expression and focal adhesion, enhanced endothelial monolayer permeability, and promoted tumor invasion and metastasis.

CONCLUSIONS

circ-IRAS accesses HUVECs via exosomes derived from pancreatic cancer cells followed by increased endothelial monolayer permeability. Furthermore, this process promotes tumor invasion and metastasis. The results of this study suggest that the presence of circRNAs in exosomes may be important indicator for early diagnosis and prognostic prediction in PDAC.

A functional siRNA screen identifies RhoGTPase-associated genes involved in thrombin-induced endothelial permeability

Thrombin and other inflammatory mediators may induce vascular permeability through the disruption of adherens junctions between adjacent endothelial cells. If uncontrolled, hyperpermeability leads to an impaired barrier, fluid leakage and edema, which can contribute to multi-organ failure and death. RhoGTPases control cytoskeletal dynamics, adhesion and migration and are known regulators of endothelial integrity. Knowledge of the precise role of each RhoGTPase, and their associated regulatory and effector genes, in endothelial integrity is incomplete. Using a combination of a RNAi screen with electrical impedance measurements, we quantified the effect of individually silencing 270 Rho-associated genes on the barrier function of thrombin-activated, primary endothelial cells. Known and novel RhoGTPase-associated regulators that modulate the response to thrombin were identified (RTKN, TIAM2, MLC1, ARPC1B, SEPT2, SLC9A3R1, RACGAP1, RAPGEF2, RHOD, PREX1, ARHGEF7, PLXNB2, ARHGAP45, SRGAP2, ARHGEF5). In conclusion, with this siRNA screen, we confirmed the roles of known regulators of endothelial integrity but also identified new, potential key players in thrombin-induced endothelial signaling.

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.

TRPV4 Blockade Preserves the Blood-Brain Barrier by Inhibiting Stress Fiber Formation in a Rat Model of Intracerebral Hemorrhage

Blood–brain barrier (BBB) disruption and subsequent brain edema play important roles in the secondary neuronal death and neurological dysfunction that are observed following intracerebral hemorrhage (ICH). In previous studies, transient receptor potential vanilloid 4 (TRPV4), a calcium-permeable mechanosensitive channel, was shown to induce cytotoxicity in many types of cells and to play a role in orchestrating barrier functions. In the present study, we explored the role of TRPV4 in ICH-induced brain injury, specifically investigating its effect on BBB disruption. Autologous arterial blood was injected into the basal ganglia of rats to mimic ICH. Adult male Sprague Dawley rats were randomly assigned to sham and experimental groups for studies on the time course of TRPV4 expression after ICH. The selective TRPV4 antagonist HC-067047 and TRPV4 siRNA were administered to evaluate the effects of TRPV4 inhibition. GSK1016790A, a TRPV4 agonist, was administered to naive rats to verify the involvement of TRPV4-induced BBB disruption. A PKC inhibitor, dihydrochloride (H7), and a selective RhoA inhibitor, C3 transferase, were administered to clarify the involvement of the PKCα/RhoA/MLC2 pathway following ICH. Post-ICH assessments including functional tests, brain edema measurements, Evans blue extravasation, western blotting and immunohistochemical assays were performed. TRPV4 inhibition remarkably ameliorated neurological symptoms, brain edema, and neuronal death, as well as BBB disruption, 24–72 h following ICH. Meanwhile, TRPV4 blockade preserved the expression of adherens and tight junction proteins, as well as BBB integrity, by inhibiting stress fiber formation, which might be correlated with the regulation of components of the PKCα/RhoA/MLC2 pathway. Furthermore, adherens and tight junction protein degradation induced by GSK1016790A treatment in naive rats was also related to PKCα/RhoA/MLC2-pathway-mediated stress fiber formation. Based on these findings, therapeutic interventions targeting TRPV4 may represent a novel approach to ameliorate secondary brain injury following ICH.

Primary angle closure glaucoma (PACG) susceptibility gene PLEKHA7 encodes a novel Rac1/Cdc42 GAP that modulates cell migration and blood-aqueous barrier function

PLEKHA7, a gene recently associated with primary angle closure glaucoma (PACG), encodes an apical junctional protein expressed in components of the blood aqueous barrier (BAB). We found that PLEKHA7 is down-regulated in lens epithelial cells and in iris tissue of PACG patients. PLEKHA7 expression also correlated with the C risk allele of the sentinel SNP rs11024102 with the risk allele carrier groups having significantly reduced PLEKHA7 levels compared to non-risk allele carriers. Silencing of PLEKHA7 in human immortalized non-pigmented ciliary epithelium (h-iNPCE) and primary trabecular meshwork cells, which are intimately linked to BAB and aqueous humor outflow respectively, affected actin cytoskeleton organization. PLEKHA7 specifically interacts with GTP-bound Rac1 and Cdc42, but not RhoA, and the activation status of the two small GTPases is linked to PLEKHA7 expression levels. PLEKHA7 stimulates Rac1 and Cdc42 GTP hydrolysis, without affecting nucleotide exchange, identifying PLEKHA7 as a novel Rac1/Cdc42 GAP. Consistent with the regulatory role of Rac1 and Cdc42 in maintaining the tight junction permeability, silencing of PLEKHA7 compromises the paracellular barrier between h-iNPCE cells. Thus, downregulation of PLEKHA7 in PACG may affect BAB integrity and aqueous humor outflow via its Rac1/Cdc42 GAP activity, thereby contributing to disease etiology.

Coagulopathy induced by traumatic brain injury: systemic manifestation of a localized injury

Traumatic brain injury (TBI)-induced coagulopathy is a common and well-recognized risk for poor clinical outcomes, but its pathogenesis remains poorly understood, and treatment options are limited and ineffective. We discuss the recent progress and knowledge gaps in understanding this lethal complication of TBI. We focus on (1) the disruption of the brain-blood barrier to disseminate brain injury systemically by releasing brain-derived molecules into the circulation and (2) TBI-induced hypercoagulable and hyperfibrinolytic states that result in persistent and delayed intracranial hemorrhage and systemic bleeding.

Vascular Endothelial Cell-Specific Connective Tissue Growth Factor (CTGF) Is Necessary for Development of Chronic Hypoxia-Induced Pulmonary Hypertension

Chronic hypoxia frequently complicates the care of patients with interstitial lung disease, contributing to the development of pulmonary hypertension (PH), and premature death. Connective tissue growth factor (CTGF), a matricellular protein of the Cyr61/CTGF/Nov (CCN) family, is known to exacerbate vascular remodeling within the lung. We have previously demonstrated that vascular endothelial-cell specific down-regulation of CTGF is associated with protection against the development of PH associated with hypoxia, though the mechanism for this effect is unknown. In this study, we generated a transgenic mouse line in which the Ctgf gene was floxed and deleted in vascular endothelial cells that expressed Cre recombinase under the control of VE-Cadherin promoter (eCTGF KO mice). Lack of vascular endothelial-derived CTGF protected against the development of PH secondary to chronic hypoxia, as well as in another model of bleomycin-induced pulmonary hypertension. Importantly, attenuation of PH was associated with a decrease in infiltrating inflammatory cells expressing CD11b or integrin α_M (ITGAM), a known adhesion receptor for CTGF, in the lungs of hypoxia-exposed eCTGF KO mice. Moreover, these pathological changes were associated with activation of—Rho GTPase family member—cell division control protein 42 homolog (Cdc42) signaling, known to be associated with alteration in endothelial barrier function. These data indicate that endothelial-specific deletion of CTGF results in protection against development of chronic-hypoxia induced PH. This protection is conferred by both a decrease in inflammatory cell recruitment to the lung, and a reduction in lung Cdc42 activity. Based on our studies, CTGF inhibitor treatment should be investigated in patients with PH associated with chronic hypoxia secondary to chronic lung disease.

Endothelial RhoB and RhoC are dispensable for leukocyte diapedesis and for maintaining vascular integrity during diapedesis

Active remodeling of the actin cytoskeleton in endothelial cells is necessary for allowing leukocytes to cross the barrier during the process of transendothelial migration (TEM). Involvement of RhoGTPases to regulate actin organization is inevitable, and we recently reported on the local function of RhoA in limiting vascular leakage during leukocyte TEM. As a follow-up we investigated here the possible involvement of two other closely-related GTPases; RhoB and RhoC, in regulating leukocyte TEM and vascular barrier maintenance. Physiological flow experiments showed no substantial involvement of either endothelial RhoB or RhoC in neutrophil adhesion and transmigration efficiency. Besides neutrophil TEM, we did not observe a role for endothelial RhoB or RhoC in limiting vascular leakage in both inflammatory conditions and during TEM. In conclusion, endothelial RhoB and RhoC are both dispensable for regulating leukocyte diapedesis and for maintaining vascular barrier function under inflammatory conditions and during leukocyte diapedesis.

Mechanistic understanding the bioeffects of ultrasound-driven microbubbles to enhance macromolecule delivery

Ultrasound-driven microbubbles can trigger reversible membrane perforation (sonoporation), open interendothelial junctions and stimulate endocytosis, thereby providing a temporary and reversible time-window for the delivery of macromolecules across biological membranes and endothelial barriers. This time-window is related not only to cavitation events, but also to biological regulatory mechanisms. Mechanistic understanding of the interaction between cavitation events and cells and tissues, as well as the subsequent cellular and molecular responses will lead to new design strategies with improved efficacy and minimized side effects. Recent important progress on the spatiotemporal characteristics of sonoporation, cavitation-induced interendothelial gap and endocytosis, and the spatiotemporal bioeffects and the preliminary biological mechanisms in cavitation-enhanced permeability, has been made. On the basis of the summary of this research progress, this Review outlines the underlying bioeffects and the related biological regulatory mechanisms involved in cavitation-enhanced permeability; provides a critical commentary on the future tasks and directions in this field, including developing a standardized methodology to reveal mechanism-based bioeffects in depth, and designing biology-based treatment strategies to improve efficacy and safety. Such mechanistic understanding the bioeffects that contribute to cavitation-enhanced delivery will accelerate the translation of this approach to the clinic.

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.

Defective Protein Catabolism in Atherosclerotic Vascular Inflammation

Vascular inflammation in atheroprone vessels propagates throughout the arterial tree in dyslipidemic patients, thereby accelerating atherosclerotic progression. To elucidate the mechanism of vascular inflammation, most previous studies have focused on inflammation-related signals that are sent in response to vasoactive stimuli. However, it is also important to understand how normal blood vessels become defective and start degenerating. Growing evidence suggests that major protein catabolism pathways, including the ubiquitin-proteasome, autophagy, and calpain systems, are disturbed in atheroprone vessels and contribute to the pathogenesis of atherosclerosis. Indeed, dysregulation of ubiquitin-proteasome pathways results in the accumulation of defective proteins in blood vessels, leading to vascular endothelial dysfunction and apoptosis in affected cells. Impaired autophagy-lysosomal degradation affects smooth muscle cell transformation and proliferation, as well as endothelial integrity and phagocytic clearance of cellular corpses. Dysregulation of the calpain system confers proatherogenic properties to endothelial cells, smooth muscle cells, and macrophages. In this review article, we will discuss the current information available on defective protein catabolism in atheroprone vessels and its potential interrelation with inflammation-related signals.

A CDC42-centered signaling unit is a dominant positive regulator of endothelial integrity

Endothelial barrier function is carefully controlled to protect tissues from edema and damage inflicted by extravasated leukocytes. RhoGTPases, in conjunction with myriad regulatory proteins, exert both positive and negative effects on the endothelial barrier integrity. Precise knowledge about the relevant mechanisms is currently fragmented and we therefore performed a comprehensive analysis of endothelial barrier regulation by RhoGTPases and their regulators. Combining RNAi with electrical impedance measurements we quantified the relevance of 270 Rho-associated genes for endothelial barrier function. Statistical analysis identified 10 targets of which six promoted- and four reduced endothelial barrier function upon downregulation. We analyzed in more detail two of these which were not previously identified as regulators of endothelial integrity. We found that the Rac1-GEF (Guanine nucleotide Exchange Factor) TIAM2 is a positive regulator and the Cdc42(Rac1)-GAP (GTPase-Activating Protein) SYDE1 is a negative regulator of the endothelial barrier function. Finally, we found that the GAP SYDE1 is part of a Cdc42-centered signaling unit, also comprising the Cdc42-GEF FARP1 and the Cdc42 effector PAK7 which controls the integrity of the endothelial barrier. In conclusion, using a siRNA-based screen, we identified new regulators of barrier function and found that Cdc42 is a dominant positive regulator of endothelial integrity.

The role and mechanism of cathepsin G in dermatomyositis

Dermatomyositis (DM) is an idiopathic inflammatory myopathy characterized by CD4+ T cells and B cells infiltration in perivascular and muscle tissue. Although the infiltration of inflammatory cells plays a key role in muscle damage, the exact mechanism is not clear. Cathepsin G (CTSG) is a member of the serine proteases family and can increase the permeability of vascular endothelial cells and the chemotaxis of inflammatory cells. In this study, we found that the expression of CTSG was increased in peripheral blood mononuclear cells and muscle tissues of DM patients. The activity of CTSG was significantly increased in DM patients and correlated with disease activity. Serum CTSG induced the expression of protease activated receptor 2 (PAR2) and altered the cytoskeleton of human dermal microvascular endothelial cells. Our studies indicate, for the first time, that CTSG may play an important role in muscle inflammatory cells infiltration by increasing the permeability of vascular endothelial cells.