Activated protein C mediates novel lung endothelial barrier enhancement: role of sphingosine 1-phosphate receptor transactivation

THE NEUROENDOTHELIAL AXIS IN TRAUMATIC BRAIN INJURY: MECHANISMS OF MULTIORGAN DYSFUNCTION, NOVEL THERAPIES, AND FUTURE DIRECTIONS

ABSTRACT

Severe traumatic brain injury (TBI) often initiates a systemic inflammatory response syndrome, which can potentially culminate into multiorgan dysfunction. A central player in this cascade is endotheliopathy, caused by perturbations in homeostatic mechanisms governed by endothelial cells due to injury-induced coagulopathy, heightened sympathoadrenal response, complement activation, and proinflammatory cytokine release. Unique to TBI is the potential disruption of the blood-brain barrier, which may expose neuronal antigens to the peripheral immune system and permit neuroinflammatory mediators to enter systemic circulation, propagating endotheliopathy systemically. This review aims to provide comprehensive insights into the "neuroendothelial axis" underlying endothelial dysfunction after TBI, identify potential diagnostic and prognostic biomarkers, and explore therapeutic strategies targeting these interactions, with the ultimate goal of improving patient outcomes after severe TBI.

Thrombomodulin Switches Signaling and Protease-Activated Receptor 1 Cleavage Specificity of Thrombin

BACKGROUND

Cleavage of the extracellular domain of PAR1 (protease-activated receptor 1) by thrombin at Arg41 and by APC (activated protein C) at Arg46 initiates paradoxical cytopathic and cytoprotective signaling in endothelial cells. In the latter case, the ligand-dependent coreceptor signaling by EPCR (endothelial protein C receptor) is required for the protective PAR1 signaling by APC. Here, we investigated the role of thrombomodulin in determining the specificity of PAR1 signaling by thrombin.

METHODS

We prepared a PAR1 knockout (PAR1-/-) EA.hy926 endothelial cell line by CRISPR/Cas9 and transduced PAR1-/- cells with lentivirus vectors expressing PAR1 mutants in which either Arg41 or Arg46 was replaced with an Ala. Furthermore, human embryonic kidney 293 cells were transfected with wild-type or mutant PAR1 cleavage reporter constructs carrying N-terminal Nluc (NanoLuc luciferase) and C-terminal enhanced yellow fluorescent protein tags.

RESULTS

Characterization of transfected cells in signaling and receptor cleavage assays revealed that, upon interaction with thrombomodulin, thrombin cleaves Arg46 to elicit cytoprotective effects by a β-arrestin-2 biased signaling mechanism. Analysis of functional data and cleavage rates indicated that thrombin-thrombomodulin cleaves Arg46>10-fold faster than APC. Upon interaction with thrombin, the cytoplasmic domain of thrombomodulin recruited both β-arrestin-1 and -2 to the plasma membrane. Thus, the thrombin cleavage of Arg41 was also cytoprotective in thrombomodulin-expressing cells by β-arrestin-1-biased signaling. APC in the absence of EPCR cleaved Arg41 to initiate disruptive signaling responses like thrombin.

CONCLUSIONS

These results suggest that coreceptor signaling by thrombomodulin and EPCR determines the PAR1 cleavage and signaling specificity of thrombin and APC, respectively.

Designer high-density lipoprotein particles enhance endothelial barrier function and suppress inflammation

High-density lipoprotein (HDL) nanoparticles promote endothelial cell (EC) function and suppress inflammation, but their utility in treating EC dysfunction has not been fully explored. Here, we describe a fusion protein named ApoA1-ApoM (A1M) consisting of apolipoprotein A1 (ApoA1), the principal structural protein of HDL that forms lipid nanoparticles, and ApoM, a chaperone for the bioactive lipid sphingosine 1-phosphate (S1P). A1M forms HDL-like particles, binds to S1P, and is signaling competent. Molecular dynamics simulations showed that the S1P-bound ApoM moiety in A1M efficiently activated EC surface receptors. Treatment of human umbilical vein ECs with A1M-S1P stimulated barrier function either alone or cooperatively with other barrier-enhancing molecules, including the stable prostacyclin analog iloprost, and suppressed cytokine-induced inflammation. A1M-S1P injection into mice during sterile inflammation suppressed neutrophil influx and inflammatory mediator secretion. Moreover, systemic A1M administration led to a sustained increase in circulating HDL-bound S1P and suppressed inflammation in a murine model of LPS-induced endotoxemia. We propose that A1M administration may enhance vascular endothelial barrier function, suppress cytokine storm, and promote resilience of the vascular endothelium.

Factor VIIa releases phosphatidylserine-enriched extracellular vesicles from endothelial cells by activating acid sphingomyelinase

BACKGROUND

Our recent studies showed that activated factor (F) VII (FVIIa) releases extracellular vesicles (EVs) from the endothelium. FVIIa-released EVs were found to be enriched with phosphatidylserine (PS) and contribute to the hemostatic effect of FVIIa in thrombocytopenia and hemophilia.

OBJECTIVE

To investigate mechanisms by which FVIIa induces EV biogenesis and enriches EVs with PS.

METHODS

FVIIa activation of acid sphingomyelinase (aSMase) was evaluated by its translocation to the cell surface. The role of aSMase in the biogenesis of FVIIa-induced EVs and their enrichment with PS was investigated using specific siRNAs and inhibitors of aSMase and its downstream metabolites. Wild-type and aSMase-/- mice were injected with a control vehicle or FVIIa. EVs released into circulation were quantified by nanoparticle tracking analysis. EVs hemostatic potential was assessed in a murine thrombocytopenia model.

RESULTS

FVIIa activation of aSMase is responsible for both the externalization of PS and the release of EVs in endothelial cells. FVIIa-induced aSMase activation led to ceramide generation and de novo expression of transmembrane protein 16F. Inhibitors of ceramidases, sphingosine kinase, or sphingosine-1-phosphate receptor modulator blocked FVIIa-induced expression of transmembrane protein 16F and PS externalization without interfering with FVIIa release of EVs. In vivo, FVIIa release of EVs was markedly impaired in aSMase-/- mice compared with wild-type mice. Administration of a low dose of FVIIa, sufficient to induce EVs release, corrected bleeding associated with thrombocytopenia in wild-type mice but not in aSMase-/- mice.

CONCLUSION

Our study identifies a novel mechanism by which FVIIa induces PS externalization and releases PS-enriched EVs.

Severe Trauma-Induced Coagulopathy: Molecular Mechanisms Underlying Critical Illness

Trauma remains one of the leading causes of death in adults despite the implementation of preventive measures and innovations in trauma systems. The etiology of coagulopathy in trauma patients is multifactorial and related to the kind of injury and nature of resuscitation. Trauma-induced coagulopathy (TIC) is a biochemical response involving dysregulated coagulation, altered fibrinolysis, systemic endothelial dysfunction, platelet dysfunction, and inflammatory responses due to trauma. The aim of this review is to report the pathophysiology, early diagnosis and treatment of TIC. A literature search was performed using different databases to identify relevant studies in indexed scientific journals. We reviewed the main pathophysiological mechanisms involved in the early development of TIC. Diagnostic methods have also been reported which allow early targeted therapy with pharmaceutical hemostatic agents such as TEG-based goal-directed resuscitation and fibrinolysis management. TIC is a result of a complex interaction between different pathophysiological processes. New evidence in the field of trauma immunology can, in part, help explain the intricacy of the processes that occur after trauma. However, although our knowledge of TIC has grown, improving outcomes for trauma patients, many questions still need to be answered by ongoing studies.

SHOCK INDUCES ENDOTHELIAL PERMEABILITY AFTER TRAUMA THROUGH INCREASED ACTIVATION OF RHOA GTPASE

ABSTRACT

Introduction: Severely injured patients develop a dysregulated inflammatory state characterized by vascular endothelial permeability, which contributes to multiple organ failure. To date, however, the mediators of and mechanisms for this permeability are not well established. Endothelial permeability in other inflammatory states such as sepsis is driven primarily by overactivation of the RhoA GTPase. We hypothesized that tissue injury and shock drive endothelial permeability after trauma by increased RhoA activation leading to break down of endothelial tight and adherens junctions. Methods: Human umbilical vein endothelial cells (HUVECs) were grown to confluence, whereas continuous resistance was measured using electrical cell-substrate impedance sensing (ECIS) Z-Theta technology, 10% ex vivo plasma from severely injured trauma patients was added, and resistance measurements continued for 2 hours. Areas under the curve (AUCs) were calculated from resistance curves. For GTPase activity analysis, HUVECs were grown to confluence and incubated with 10% trauma plasma for 5 minutes before harvesting of cell lysates. Rho and Rac activity were determined using a G-LISA assay. Significance was determined using Mann-Whitney tests or Kruskal-Wallis test, and Spearman ρ was calculated for correlations. Results: Plasma from severely injured patients induces endothelial permeability with plasma from patients with both severe injury and shock contributing most to this increased permeability. Surprisingly, Injury Severity Score (ISS) does not correlate with in vitro trauma-induced permeability (-0.05, P > 0.05), whereas base excess (BE) does correlate with permeability (-0.47, P = 0.0001). The combined impact of shock and injury resulted in a significantly smaller AUC in the injury + shock group (ISS > 15, BE < -9) compared with the injury only (ISS > 15, BE > -9; P = 0.04) or minimally injured (ISS < 15, BE > -9; P = 0.005) groups. In addition, incubation with injury + shock plasma resulted in higher RhoA activation ( P = 0.002) and a trend toward decreased Rac1 activation ( P = 0.07) compared with minimally injured control. Conclusions: Over the past decade, improved early survival in patients with severe trauma and hemorrhagic shock has led to a renewed focus on the endotheliopathy of trauma. This study presents the largest study to date measuring endothelial permeability in vitro using plasma collected from patients after traumatic injury. Here, we demonstrate that plasma from patients who develop shock after severe traumatic injury induces endothelial permeability and increased RhoA activation in vitro . Our ECIS model of trauma-induced permeability using ex vivo plasma has potential as a high throughput screening tool to phenotype endothelial dysfunction, study mediators of trauma-induced permeability, and screen potential interventions.

Procr functions as a signaling receptor and is essential for the maintenance and self-renewal of mammary stem cells

The protein C receptor (Procr) has been implicated as a stem cell surface marker in several tissues. It is unknown whether Procr acts as a functional signaling receptor in stem cells. Here, by conditional knockout in mammary stem cells (MaSCs), we demonstrate that Procr is essential for mammary gland development and homeostasis. Through proteomics profiling, we identify that, upon stimulation by the ligand protein C, Procr interacts with heat shock protein 90 (HSP90AA1) via its short cytoplasmic tail, recruiting Src and IGF1R to the complex at the plasma membrane. We show that Procr acts as a signaling receptor of protein C in regulation of MaSCs through HSP90, Src, and IGF1R in vitro. In vivo, IGF1R deletion in MaSCs displays similar phenotypes to Procr deletion. These findings illustrate the essential role of Procr signaling in MaSC maintenance, shedding light onto the molecular regulation by Procr in tissue stem cells.

aPC/PAR1 confers endothelial anti-apoptotic activity via a discrete, β-arrestin-2-mediated SphK1-S1PR1-Akt signaling axis

Endothelial dysfunction is associated with vascular disease and results in disruption of endothelial barrier function and increased sensitivity to apoptosis. Currently, there are limited treatments for improving endothelial dysfunction. Activated protein C (aPC), a promising therapeutic, signals via protease-activated receptor-1 (PAR1) and mediates several cytoprotective responses, including endothelial barrier stabilization and anti-apoptotic responses. We showed that aPC-activated PAR1 signals preferentially via β-arrestin-2 (β-arr2) and dishevelled-2 (Dvl2) scaffolds rather than G proteins to promote Rac1 activation and barrier protection. However, the signaling pathways utilized by aPC/PAR1 to mediate anti-apoptotic activities are not known. aPC/PAR1 cytoprotective responses also require coreceptors; however, it is not clear how coreceptors impact different aPC/PAR1 signaling pathways to drive distinct cytoprotective responses. Here, we define a β-arr2-mediated sphingosine kinase-1 (SphK1)-sphingosine-1-phosphate receptor-1 (S1PR1)-Akt signaling axis that confers aPC/PAR1-mediated protection against cell death. Using human cultured endothelial cells, we found that endogenous PAR1 and S1PR1 coexist in caveolin-1 (Cav1)-rich microdomains and that S1PR1 coassociation with Cav1 is increased by aPC activation of PAR1. Our study further shows that aPC stimulates β-arr2-dependent SphK1 activation independent of Dvl2 and is required for transactivation of S1PR1-Akt signaling and protection against cell death. While aPC/PAR1-induced, extracellular signal-regulated kinase 1/2 (ERK1/2) activation is also dependent on β-arr2, neither SphK1 nor S1PR1 are integrated into the ERK1/2 pathway. Finally, aPC activation of PAR1-β-arr2-mediated protection against apoptosis is dependent on Cav1, the principal structural protein of endothelial caveolae. These studies reveal that different aPC/PAR1 cytoprotective responses are mediated by discrete, β-arr2-driven signaling pathways in caveolae.

Signaling pathways and intervention therapies in sepsis

Sepsis is defined as life-threatening organ dysfunction caused by dysregulated host systemic inflammatory and immune response to infection. Over decades, advanced understanding of host-microorganism interaction has gradually unmasked the genuine nature of sepsis, guiding toward new definition and novel therapeutic approaches. Diverse clinical manifestations and outcomes among infectious patients have suggested the heterogeneity of immunopathology, while systemic inflammatory responses and deteriorating organ function observed in critically ill patients imply the extensively hyperactivated cascades by the host defense system. From focusing on microorganism pathogenicity, research interests have turned toward the molecular basis of host responses. Though progress has been made regarding recognition and management of clinical sepsis, incidence and mortality rate remain high. Furthermore, clinical trials of therapeutics have failed to obtain promising results. As far as we know, there was no systematic review addressing sepsis-related molecular signaling pathways and intervention therapy in literature. Increasing studies have succeeded to confirm novel functions of involved signaling pathways and comment on efficacy of intervention therapies amid sepsis. However, few of these studies attempt to elucidate the underlining mechanism in progression of sepsis, while other failed to integrate preliminary findings and describe in a broader view. This review focuses on the important signaling pathways, potential molecular mechanism, and pathway-associated therapy in sepsis. Host-derived molecules interacting with activated cells possess pivotal role for sepsis pathogenesis by dynamic regulation of signaling pathways. Cross-talk and functions of these molecules are also discussed in detail. Lastly, potential novel therapeutic strategies precisely targeting on signaling pathways and molecules are mentioned.

Ectodomain shedding by ADAM proteases as a central regulator in kidney physiology and disease

Besides its involvement in blood and bone physiology, the kidney's main function is to filter substances and thereby regulate the electrolyte composition of body fluids, acid-base balance and toxin removal. Depending on underlying conditions, the nephron must undergo remodeling and cellular adaptations. The proteolytic removal of cell surface proteins via ectodomain shedding by A Disintegrin and Metalloproteases (ADAMs) is of importance for the regulation of cell-cell and cell-matrix adhesion of renal cells. ADAM10 controls glomerular and tubule development in a Notch1 signaling-dependent manner and regulates brush border composition. ADAM17 regulates the renin angiotensin system and is together with ADAM10 involved in calcium phosphate homeostasis. In kidney disease ADAMs, especially ADAM17 contribute to inflammation through their involvement in IL-6 trans-signaling, Notch-, epithelial growth factor receptor-, and tumor necrosis factor α signaling. ADAMs are interesting drug targets to reduce the inflammatory burden, defective cell adhesion and impaired signaling pathways in kidney diseases.

Comparison of polynomial fitting versus single time point analysis of ECIS data for barrier assessment

Electrical cell-substrate impedance sensing (ECIS) is an in vitro methodology for measuring the barrier integrity of a variety of cell types, including pulmonary endothelial cells. These experiments are frequently used for in vitro assessment of lung injury. The data derived from ECIS experiments consists of repeated measures of resistance across an endothelial monolayer. As such, these data reflect the dynamic changes in electrical resistance that occur over time. Currently methodologies for assessing ECIS data rely on single point assessments of barrier function, such as the maximal drop in trans-endothelial electrical resistance (TERMax ). However, this approach ignores the myriad of changes in resistance that occur before and after the TERMax data point. Herein, we utilize polynomial curve fitting on experimentally generated ECIS data, thus allowing for comparing ECIS experiments by examining the mean polynomial coefficients between groups. We show that polynomial curves accurately fit a variety of ECIS data, and that concordance between TERMax and coefficient analysis varies by type of stimulus, suggesting that TERMax differences may not always correlate with a significant difference in the overall shape of the ECIS profile. Lastly, we identify factors that impact coefficient values obtained in our analyses, including the length of time devoted to baseline measurements before addition of stimuli. Polynomial coefficient analysis is another tool that can be used for more comprehensive interrogation of ECIS data to better understand the biological underpinnings that lead to changes in barrier dysfunction in vitro.

Apolipoprotein A-I enhances activated protein C cytoprotective activity

High-density lipoprotein and apolipoprotein A-I enhance activated protein C cytoprotective activity. High-density lipoprotein and apolipoprotein A-I significantly increase the rate at which activated protein C degrades cytotoxic extracellular histones.

Long-term outcomes of intravitreal activated protein C injection for ischemic central retinal vein occlusion: an extension trial

Purpose

Our previous 1-year pilot study evaluated the efficacy of intravitreally injected activated protein C (APC) in 10 eyes with ischemic central retinal vein occlusion (CRVO). The reperfusion of the areas of retinal nonperfusion (RNP) exceeded 50% of the baseline in five (50%) eyes 1 year after the APC injection. The current study evaluated the long-term efficacy and safety of intravitreal APC.

Methods

The 10 eyes in the pilot study were included in this study. Other treatments were administered at the physicians’ discretion after the pilot study. We evaluated visual acuity (VA), central retinal thickness (CRT) and perfusion status, and adverse events and severity over the long term.

Results

The median follow-up was 60 months (range, 48–68 months). Compared with baseline, the post-treatment VA improved significantly (P < 0.001) from 1.39 to 1.06 logarithm of the minimum angle of resolution. The CRT improved significantly (P < 0.001) from 1090 to 195 μm at the last visit. The RNP areas decreased from an average 29.7 disc areas (DAs) at baseline to an average 16.5 DAs at the last examination (mean, 40 ± 6.5 months after the first APC treatment). No adverse events were related to intravitreal APC.

Conclusion

No complications were associated with intravitreal APC, the clinical course improved, and improved RNP was maintained for the long term, suggesting that intravitreal APC may be an alternative treatment for CRVO.

Immunohistochemical study of dissociation and association of adherens junctions in splenic sinus endothelial cells

It is not yet clear whether cellular junctions between splenic sinus endothelial cells are open or closed. In order to clarify this, immunolocalization of thrombomodulin (TM), endothelial protein C receptor (EPCR), protease-activated receptor 1 (PAR1), sphingosine 1-phosphate receptor 1 (S1P₁), β-catenin phosphorylated at Try142 (β-catenin Y142) and β-catenin phosphorylated at Try654 (β-catenin Y654), which are related proteins that regulate dissociation and association of the adherens junctions of endothelial cells, are examined in rats using laser microscopy and electron microscopy. TM, EPCR, PAR1 and S1P₁ were colocalized in the entire circumference of the endothelial cells, as well as in the caveolar membranes and junctional membranes of adjacent endothelial cells. These molecules may protect the adherens junctions of the endothelial cells. On the other hand, β-catenin Y142 and β-catenin Y 654 colocalized with α-catenin and β-catenin, respectively and in addition, β-catenin Y142 and β-catenin Y 654 were localized in the vicinity of the adherens junctions of the endothelial cells from immunogold electron microcopy. The adherens junctions are considered to be partially dissociated at the site where β-catenin Y142 and β-catenin Y 654 are localized. Thus, the system that protects the adherens junctions and the system that dissociates them may concurrently coexist in the endothelial cells and dissociation and association of the adherens junctions may be constantly repeated at the cell boundary of the endothelial cells.

Stroke Treatment With PAR-1 Agents to Decrease Hemorrhagic Transformation

Ischemic stroke is the most widespread cause of disability and a leading cause of death in developed countries. To date, the most potent approved treatment for acute stroke is recanalization therapy with thrombolytic drugs such as tissue plasminogen activator (rt-PA or tPA) or endovascular mechanical thrombectomy. Although tPA and thrombectomy are widely available in the United States, it is currently estimated that only 10-20% of stroke patients get tPA treatment, in part due to restrictive selection criteria. Recently, however, tPA and thrombectomy selection criteria have loosened, potentially allowing more patients to qualify. The relatively low rate of treatment may also reflect the perceived risk of brain hemorrhage following treatment with tPA. In translational research and a single patient study, protease activated receptor 1 (PAR-1) targeted therapies given along with thrombolysis and thrombectomy appear to reduce hemorrhagic transformation after recanalization. Such adjuncts may likely enhance the availability of recanalization and encourage more physicians to use the recently expanded selection criteria for applying recanalization therapies. This narrative review discusses stroke therapies, the role of hemorrhagic transformation in producing poor outcomes, and presents the data suggesting that PAR-1 acting agents show promise for decreasing hemorrhagic transformation and improving outcomes.

Targeting Endothelial Dysfunction in Acute Critical Illness to Reduce Organ Failure

During hyperinflammatory conditions that can occur in acute critical illness, such as shock or hypoperfusion, inflammatory mediators activate the endothelium, fueling a proinflammatory host-response as well as procoagulant processes. These changes result in shedding of the glycocalyx, endothelial hyperpermeability, edema formation, and lead to disturbed microcirculatory perfusion and organ failure. Different fluid strategies that are used in shock may have differential effects on endothelial integrity. Collectively, low protein content fluids seem to have negative effects on the endothelial glycocalyx, aggravating endothelial hyperpermeability, whereas fluids containing albumin or plasma proteins may be superior to normal saline in protecting the glycocalyx and endothelial barrier function. Targeting the endothelium may be a therapeutic strategy to limit organ failure, which hitherto has not received much attention. Treatment targets aimed at restoring the endothelium should focus on maintaining glycocalyx function and/or targeting coagulation pathways or specific endothelial receptors. Potential treatments could be supplementing glycocalyx constituents or inhibiting glycocalyx breakdown. In this review, we summarize mechanisms of endothelial dysfunction during acute critical illness, such as the systemic inflammatory response, shedding of the glycocalyx, endothelial activation, and activation of coagulation. In addition, this review focuses on the effects of different fluid strategies on endothelial permeability. Also, potential mechanisms for treatment options to reduce endothelial hyperpermeability with ensuing organ failure are evaluated. Future research is needed to elucidate these pathways and to translate these data to the first human safety and feasibility trials.

The acute respiratory distress syndrome biomarker pipeline: crippling gaps between discovery and clinical utility

Recent innovations in translational research have ushered an exponential increase in the discovery of novel biomarkers, thereby elevating the hope for deeper insights into "personalized" medicine approaches to disease phenotyping and care. However, a critical gap exists between the fast pace of biomarker discovery and the successful translation to clinical use. This gap underscores the fundamental biomarker conundrum across various acute and chronic disorders: how does a biomarker address a specific unmet need? Additionally, the gap highlights the need to shift the paradigm from a focus on biomarker discovery to greater translational impact and the need for a more streamlined drug approval process. The unmet need for biomarkers in acute respiratory distress syndrome (ARDS) is for reliable and validated biomarkers that minimize heterogeneity and allow for stratification of subject selection for enrollment in clinical trials of tailored therapies. This unmet need is particularly highlighted by the ongoing SARS-CoV-2/COVID-19 pandemic. The unprecedented numbers of COVID-19-induced ARDS cases has strained health care systems across the world and exposed the need for biomarkers that would accelerate drug development and the successful phenotyping of COVID-19-infected patients at risk for development of ARDS and ARDS mortality. Accordingly, this review discusses the current state of ARDS biomarkers in the context of the drug development pipeline and highlight gaps between biomarker discovery and clinical implementation while proposing potential paths forward. We discuss potential ARDS biomarkers by category and by context of use, highlighting progress in the development continuum. We conclude by discussing challenges to successful translation of biomarker candidates to clinical impact and proposing possible novel strategies.

Platelet-derived calpain cleaves the endothelial protease-activated receptor 1 to induce vascular inflammation in diabetes

Diabetes mellitus is a major risk factor for cardiovascular disease. Platelets from diabetic patients are hyperreactive and release microparticles that carry activated cysteine proteases or calpains. Whether platelet-derived calpains contribute to the development of vascular complications in diabetes is unknown. Here we report that platelet-derived calpain1 (CAPN1) cleaves the protease-activated receptor 1 (PAR-1) on the surface of endothelial cells, which then initiates a signaling cascade that includes the activation of the tumor necrosis factor (TNF)-α converting enzyme (TACE). The latter elicits the shedding of the endothelial protein C receptor and the generation of TNF-α, which in turn, induces intracellular adhesion molecule (ICAM)-1 expression to promote monocyte adhesion. All of the effects of CAPN1 were mimicked by platelet-derived microparticles from diabetic patients or from wild-type mice but not from CAPN1^−/− mice, and were not observed in PAR-1-deficient endothelial cells. Importantly, aortae from diabetic mice expressed less PAR-1 but more ICAM-1 than non-diabetic mice, effects that were prevented by treating diabetic mice with a calpain inhibitor as well as by the platelet specific deletion of CAPN1. Thus, platelet-derived CAPN1 contributes to the initiation of the sterile vascular inflammation associated with diabetes via the cleavage of PAR-1 and the release of TNF-α from the endothelial cell surface.

Stabilizing Cellular Barriers: Raising the Shields Against COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its clinical manifestation (COVID-19; coronavirus disease 2019) have caused a worldwide health crisis. Disruption of epithelial and endothelial barriers is a key clinical turning point that differentiates patients who are likely to develop severe COVID-19 outcomes: it marks a significant escalation in respiratory symptoms, loss of viral containment and a progression toward multi-organ dysfunction. These barrier mechanisms are independently compromised by known COVID-19 risk factors, including diabetes, obesity and aging: thus, a synergism between these underlying conditions and SARS-CoV-2 mechanisms may explain why these risk factors correlate with more severe outcomes. This review examines the key cellular mechanisms that SARS-CoV-2 and its underlying risk factors utilize to disrupt barrier function. As an outlook, we propose that glucagon-like peptide 1 (GLP-1) may be a therapeutic intervention that can slow COVID-19 progression and improve clinical outcome following SARS-CoV-2 infection. GLP-1 signaling activates barrier-promoting processes that directly oppose the pro-inflammatory mechanisms commandeered by SARS-CoV-2 and its underlying risk factors.

New PAR1 Agonist Peptide Demonstrates Protective Action in a Mouse Model of Photothrombosis-Induced Brain Ischemia

Protease-activated receptors (PARs) are involved not only in hemostasis but also in the development of ischemic brain injury. In the present work, we examined in vivo effects of a new peptide (AP9) composing Asn⁴⁷-Phen⁵⁵ of PAR1 “tethered ligand” generated by activated protein C. We chose a mouse model of photothrombosis (PT)-induced ischemia to assess AP9 effects in vivo. To reveal the molecular mechanism of AP9 action, mice lacking β-arrestin-2 were used. AP9 was injected intravenously once 10 min before PT at doses of 0.2, 2, or 20 mg/kg, or twice, that is, 10 min before and 1 h after PT at a dose of 20 mg/kg. Lesion volume was measured by magnetic resonance imaging and staining of brain sections with tetrazolium salt. Neurologic deficit was estimated using the cylinder and the grid-walk tests. Blood–brain barrier (BBB) disruption was assessed by Evans blue dye extraction. Eosin-hematoxylin staining and immunohistochemical staining were applied to evaluate the number of undamaged neurons and activated glial cells in the penumbra. A single administration of AP9 (20 mg/kg), as well as its two injections (20 mg/kg), decreased brain lesion volume. A double administration of AP9 also reduced BBB disruption and neurological deficit in mice. We did not observe the protective effect of AP9 in mice lacking β-arrestin-2 after PT. Thus, we demonstrated for the first time protective properties of a PAR1 agonist peptide, AP9, in vivo. β-Arrestin-2 was required for the protective action of AP9 in PT-induced brain ischemia.

Activated Protein C Attenuates Experimental Autoimmune Encephalomyelitis Progression by Enhancing Vascular Integrity and Suppressing Microglial Activation

Background

Activated protein C (APC), a serine protease with antithrombotic effects, protects in animal models of ischemic stroke by suppressing inflammation and enhancing vascular integrity, angiogenesis, neurogenesis and neuroprotection. A small number of animal studies suggest it might also have therapeutic potential in multiple sclerosis (MS), though results have been mixed. Based on these conflicting data, the goals of this study were to clarify the therapeutic potential of APC in the experimental autoimmune encephalomyelitis (EAE) model of MS and to determine mechanistically how APC mediates this protective effect.

Methods

The protective potential of APC was examined in a chronic progressive model of EAE. Vascular breakdown, tight junction protein expression and vascular expression of fibronectin and α5β1 integrin as well as vascularity and glial activation were analyzed using immunofluorescence (IF) of spinal cord sections taken from mice with established EAE. The direct influence of APC on microglial activation was evaluated in vitro by a combination of morphology and MMP-9 expression.

Results

APC attenuated the progression of EAE, and this was strongly associated at the histopathological level with reduced levels of leukocyte infiltration and concomitant demyelination. Further analysis revealed that APC reduced vascular breakdown which was associated with maintained endothelial expression of the tight junction protein zonula occludens-1 (ZO-1). In addition, APC suppressed microglial activation in this EAE model and in vitro studies revealed that APC strongly inhibited microglial activation at both the morphological level and by the expression of the pro-inflammatory protease MMP-9.

Conclusion

These findings build on the work of others in demonstrating strong therapeutic potential for APC in the treatment of inflammatory demyelinating disease and suggest that enhancement of vascular integrity and suppression of microglial activation may be important mediators of this protection.

Significance of sphingosine-1-phosphate in cardiovascular physiology and pathology

Sphingosine-1-phosphate (S1P) is a signaling lipid, synthetized by sphingosine kinases (SPHK1 and SPHK2), that affects cardiovascular function in various ways. S1P signaling is complex, particularly since its molecular action is reliant on the differential expression of its receptors (S1PR1, S1PR2, S1PR3, S1PR4, S1PR5) within various tissues. Significance of this sphingolipid is manifested early in vertebrate development as certain defects in S1P signaling result in embryonic lethality due to defective vasculo- or cardiogenesis. Similar in the mature organism, S1P orchestrates both physiological and pathological processes occurring in the heart and vasculature of higher eukaryotes. S1P regulates cell fate, vascular tone, endothelial function and integrity as well as lymphocyte trafficking, thus disbalance in its production and signaling has been linked with development of such pathologies as arterial hypertension, atherosclerosis, endothelial dysfunction and aberrant angiogenesis. Number of signaling mechanisms are critical - from endothelial nitric oxide synthase through STAT3, MAPK and Akt pathways to HDL particles involved in redox and inflammatory balance. Moreover, S1P controls both acute cardiac responses (cardiac inotropy and chronotropy), as well as chronic processes (such as apoptosis and hypertrophy), hence numerous studies demonstrate significance of S1P in the pathogenesis of hypertrophic/fibrotic heart disease, myocardial infarction and heart failure. This review presents current knowledge concerning the role of S1P in the cardiovascular system, as well as potential therapeutic approaches to target S1P signaling in cardiovascular diseases.

Phosphoproteomic analysis of protease-activated receptor-1 biased signaling reveals unique modulators of endothelial barrier function

Thrombin, a procoagulant protease, cleaves and activates protease-activated receptor-1 (PAR1) to promote inflammatory responses and endothelial dysfunction. In contrast, activated protein C (APC), an anticoagulant protease, activates PAR1 through a distinct cleavage site and promotes anti-inflammatory responses, prosurvival, and endothelial barrier stabilization. The distinct tethered ligands formed through cleavage of PAR1 by thrombin versus APC result in unique active receptor conformations that bias PAR1 signaling. Despite progress in understanding PAR1 biased signaling, the proteins and pathways utilized by thrombin versus APC signaling to induce opposing cellular functions are largely unknown. Here, we report the global phosphoproteome induced by thrombin and APC signaling in endothelial cells with the quantification of 11,266 unique phosphopeptides using multiplexed quantitative mass spectrometry. Our results reveal unique dynamic phosphoproteome profiles of thrombin and APC signaling, an enrichment of associated biological functions, including key modulators of endothelial barrier function, regulators of gene transcription, and specific kinases predicted to mediate PAR1 biased signaling. Using small interfering RNA to deplete a subset of phosphorylated proteins not previously linked to thrombin or APC signaling, a function for afadin and adducin-1 actin binding proteins in thrombin-induced endothelial barrier disruption is unveiled. Afadin depletion resulted in enhanced thrombin-promoted barrier permeability, whereas adducin-1 depletion completely ablated thrombin-induced barrier disruption without compromising p38 signaling. However, loss of adducin-1 blocked APC-induced Akt signaling. These studies define distinct thrombin and APC dynamic signaling profiles and a rich array of proteins and biological pathways that engender PAR1 biased signaling in endothelial cells.

Cell biology of activated protein C

PURPOSE OF REVIEW

The serine protease activated protein C (aPC) was initially characterized as an endogenous anticoagulant, but in addition conveys anti-inflammatory, barrier-protective, and pro cell-survival functions. Its endogenous anticoagulant function hampered the successful and continuous implantation of aPC as a therapeutic agent in septic patients. However, it became increasingly apparent that aPC controls cellular function largely independent of its anticoagulant effects through cell-specific and context-specific receptor complexes and intracellular signaling pathways. The purpose of this review is to outline the mechanisms of aPC-dependent cell signaling and its intracellular molecular targets.

RECENT FINDINGS

With the advent of new therapeutic agents either modulating directly and specifically the activity of coagulation proteases or interfering with protease-activated receptor signaling a better understanding not only of the receptor mechanisms but also of the intracellular signaling mechanisms controlled by aPC in a disease-specific and context-specific fashion, is required to tailor new therapeutic approaches based on aPC's anti-inflammatory, barrier-protective, and pro cell-survival functions.

SUMMARY

This review summarizes recent insights into the intracellular signaling pathways controlled by aPC in a cell-specific and context-specific fashion. We focus on aPC-mediated barrier protection, inhibition of inflammation, and cytoprotecting within this review.

Down-regulation of endothelial protein C receptor promotes preeclampsia by affecting actin polymerization

Preeclampsia is a severe pregnancy-related disease that is found in 3%-5% of pregnancies worldwide and is primarily related to the decreased proliferation and invasion of trophoblast cells and abnormal uterine spiral artery remodelling. However, studies on the pathogenesis of placental trophoblasts are insufficient, and the aetiology of PE remains unclear. Here, we report that endothelial protein C receptor (EPCR), a transmembrane glycoprotein, was down-regulated in placentas from preeclamptic patients. Moreover, lack of EPCR significantly reduced the trophoblast cell proliferation, invasion and tube formation capabilities. Microscale thermophoresis analysis showed that EPCR directly bound to protease-activated receptor 1 (PAR-1), a G protein-coupled receptor. This change resulted in a substantial reduction in active Rac1 and caused excessive actin rearrangement. Our findings reveal a previously unidentified role of EPCR in the regulation of trophoblast proliferation, invasion and tube formation through promotion of actin polymerization, which is required for normal placental development.

Sphingosine-1-phosphate receptor-independent lung endothelial cell barrier disruption induced by FTY720 regioisomers

RATIONALE

Vascular permeability is a hallmark of acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury pathobiology; however, the mechanisms underlying this vascular dysregulation remain unclear, thereby impairing the development of desperately needed effective therapeutics. We have shown that sphingosine-1-phosphate (S1P) and 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol (FTY720) analogues are useful tools for exploring vascular barrier regulation mechanisms.

OBJECTIVE

To experimentally define the effects of FTY720 regioisomers on lung endothelial cell barrier regulation.

METHODS

Specific barrier-regulatory receptor and kinase inhibitors were utilized to probe signaling mechanisms involved in FTY720 regioisomer-mediated human lung endothelial cell barrier responses (trans-endothelial electrical resistance, TER). Docking simulations with the S1P1 receptor were performed to further evaluate FTY720 regioisomer signaling.

RESULTS

FTY720 regioisomers produced potent endothelial cell barrier disruption reflected by declines in TER alterations. Pharmacologic inhibition of Gi-coupled S1P receptors (S1P1, S1P2, S1P3) failed to alter FTY720 regioisomer-mediated barrier disruption; findings that were corroborated by docking simulations demonstrating FTY720 regiosomers were repelled from S1P1 docking, in contrast to strong S1P1 binding elicited by S1P. Inhibition of either the barrier-disrupting PAR-1 receptor, the VEGF receptor, Rho-kinase, MAPK, NFkB, or PI3K failed to alter FTY720 regioisomer-induced endothelial cell barrier disruption. While FTY720 regioisomers significantly increased protein phosphatase 2 (PP2A) activity, PP2A inhibitors failed to alter FTY720 regioisomer-induced endothelial cell barrier disruption.

CONCLUSIONS

Together, these results imply a vexing model of pulmonary vascular barrier dysregulation in response to FTY720-related compounds and highlight the need for further insights into mechanisms of vascular integrity required to promote the development of novel therapeutic tools to prevent or reverse the pulmonary vascular leak central to ARDS outcomes.

Molecular basis of protease-activated receptor 1 signaling diversity

Protease-activated receptors (PARs) are a family of highly conserved G protein-coupled receptors (GPCRs) that respond to extracellular proteases via a unique proteolysis-dependent activation mechanism. Protease-activated receptor 1 (PAR1) was the first identified member of the receptor family and plays important roles in hemostasis, inflammation and malignancy. The biology underlying PAR1 signaling by its canonical agonist thrombin is well characterized; however, definition of the mechanistic basis of PAR1 signaling by other proteases, including matrix metalloproteases, activated protein C, plasmin, and activated factors VII and X, remains incompletely understood. In this review, we discuss emerging insights into the molecular bases for "biased" PAR1 signaling, including atypical PAR1 proteolysis, PAR1 heterodimer and coreceptor interactions, PAR1 translocation on the membrane surface, and interactions with different G-proteins and β-arrestins upon receptor activation. Moreover, we consider how these new insights into PAR1 signaling have acted to spur development of novel PAR1-targeted therapeutics that act to inhibit, redirect, or fine-tune PAR1 signaling output to treat cardiovascular and inflammatory disease. Finally, we discuss some of the key unanswered questions relating to PAR1 biology, in particular how differences in PAR1 proteolysis, signaling intermediate coupling, and engagement with coreceptors and GPCRs combine to mediate the diversity of identified PAR1 signaling outputs.

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

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

Antiapoptotic Effect by PAR-1 Antagonist Protects Mouse Liver Against Ischemia-Reperfusion Injury

BACKGROUND

Coagulation disturbances in several liver diseases lead to thrombin generation, which triggers intracellular injury via activation of protease-activated receptor-1 (PAR-1). Little is known about the thrombin/PAR-1 pathway in hepatic ischemia-reperfusion injury (IRI). The present study aimed to clarify whether a newly selective PAR-1 antagonist, vorapaxar, can attenuate liver damage caused by hepatic IRI, with a focus on apoptosis and the survival-signaling pathway.

METHODS

A 60-min hepatic partial-warm IRI model was used to evaluate PAR-1 expression in vivo. Subsequently, IRI mice were treated with or without vorapaxar (with vehicle). In addition, hepatic sinusoidal endothelial cells (SECs) pretreated with or without vorapaxar (with vehicle) were incubated during hypoxia-reoxygenation in vitro.

RESULTS

In naïve livers, PAR-1 was confirmed by immunohistochemistry and immunofluorescence analysis to be located on hepatic SECs, and IRI strongly enhanced PAR-1 expression. In IRI mice models, vorapaxar treatment significantly decreased serum transaminase levels, improved liver histological damage, reduced the number of apoptotic cells as evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling staining (median: 135 versus 25, P = 0.004), and induced extracellular signal-regulated kinase 1/2 (ERK 1/2) cell survival signaling (phospho-ERK/total ERK 1/2: 0.96 versus 5.34, P = 0.004). Pretreatment of SECs with vorapaxar significantly attenuated apoptosis and induced phosphorylation of ERK 1/2 in vitro (phospho-ERK/total ERK 1/2: 0.66 versus 3.04, P = 0.009). These changes were abolished by the addition of PD98059, the ERK 1/2 pathway inhibitor, before treatment with vorapaxar.

CONCLUSIONS

The results of the present study revealed that hepatic IRI induces significant enhancement of PAR-1 expression on SECs, which may be associated with suppression of survival signaling pathways such as ERK 1/2, resulting in severe apoptosis-induced hepatic damage. Thus, the selective PAR-1 antagonist attenuates hepatic IRI through an antiapoptotic effect by the activation of survival-signaling pathways.

Role of ADAM17 in kidney disease

It is known that the renin-angiotensin system plays a major role in the pathophysiology of cardiovascular disease and renal injury. Within the renin-angiotensin system, angiotensin-converting enzyme 2 (ACE2) cleaves ANG II to generate ANG(1–7) peptide, which counteracts the adverse effects of ANG II accumulation. ACE2 can undergo cleavage or shedding to release the catalytically active ectodomain into the circulation by a disintegrin and metalloprotease (ADAM)17, also known as TNF-α-converting enzyme. ADAM17 is involved in many pathological processes such as cancer, inflammatory diseases, neurological diseases, cardiovascular diseases, atherosclerosis, diabetes, and hypertension. Clinical and experimental studies have shown that ADAM17 is involved in chronic kidney disease (CKD) with a proinflammatory and profibrotic role, suggesting that it could be an important mediator of CKD progression. ADAM17 inhibition attenuates fibrosis and inflammation, suggesting that its inhibition may be a possible new valuable therapeutic tool in fibrotic kidney disease treatment. In addition, in renal disease, some experimental studies have demonstrated that ADAM17 is differently expressed in the kidney. Thus, ADAM17 is highly expressed in distal renal tubules and increased in the whole kidney in diabetic models. In this article, we will review the role of ADAM17 under physiological and pathological conditions. We will mainly focus on the importance of ADAM17 in the context of CKD.

A nonapoptotic endothelial barrier-protective role for caspase-3

Noncanonical roles for caspase-3 are emerging in the fields of cancer and developmental biology. However, little is known of nonapoptotic functions of caspase-3 in most cell types. We have recently demonstrated a disassociation between caspase-3 activation and execution of apoptosis with accompanying cytoplasmic caspase-3 sequestration and preserved endothelial barrier function. Therefore, we tested the hypothesis that nonapoptotic caspase-3 activation promotes endothelial barrier integrity. Human lung microvascular endothelial cells were exposed to thrombin, a nonapoptotic stimulus, and endothelial barrier function was assessed using electric cell-substrate impedance sensing. Actin cytoskeletal rearrangement and paracellular gap formation were assessed using phalloidin staining. Cell stiffness was evaluated using magnetic twisting cytometry. In addition, cell lysates were harvested for protein analyses. Caspase-3 was inhibited pharmacologically with pan-caspase and a caspase-3-specific inhibitor. Molecular inhibition of caspase-3 was achieved using RNA interference. Cells exposed to thrombin exhibited a cytoplasmic activation of caspase-3 with transient and nonapoptotic decrease in endothelial barrier function as measured by a drop in electrical resistance followed by a rapid recovery. Inhibition of caspases led to a more pronounced and rapid drop in thrombin-induced endothelial barrier function, accompanied by increased endothelial cell stiffness and paracellular gaps. Caspase-3-specific inhibition and caspase-3 knockdown both resulted in more pronounced thrombin-induced endothelial barrier disruption. Taken together, our results suggest cytoplasmic caspase-3 has nonapoptotic functions in human endothelium and can promote endothelial barrier integrity.

Protease-activated receptors (PARs): mechanisms of action and potential therapeutic modulators in PAR-driven inflammatory diseases

Inflammatory diseases have become increasingly prevalent with industrialization. To address this, numerous anti-inflammatory agents and molecular targets have been considered in clinical trials. Among molecular targets, protease-activated receptors (PARs) are abundantly recognized for their roles in the development of chronic inflammatory diseases. In particular, several inflammatory effects are directly mediated by the sensing of proteolytic activity by PARs.

PARs belong to the seven transmembrane domain G protein-coupled receptor family, but are unique in their lack of physiologically soluble ligands. In contrast with classical receptors, PARs are activated by N-terminal proteolytic cleavage. Upon removal of specific N-terminal peptides, the resulting N-termini serve as tethered activation ligands that interact with the extracellular loop 2 domain and initiate receptor signaling. In the classical pathway, activated receptors mediate signaling by recruiting G proteins. However, activation of PARs alternatively lead to the transactivation of and signaling through receptors such as co-localized PARs, ion channels, and toll-like receptors.

In this review we consider PARs and their modulators as potential therapeutic agents, and summarize the current understanding of PAR functions from clinical and in vitro studies of PAR-related inflammation.

Endothelial Protein C Receptor (EPCR), Protease Activated Receptor-1 (PAR-1) and Their Interplay in Cancer Growth and Metastatic Dissemination

Endothelial protein C receptor (EPCR) and protease activated receptor 1 (PAR-1) by themselves play important role in cancer growth and dissemination. Moreover, interactions between the two receptors are essential for tumor progression. EPCR is a cell surface transmembrane glycoprotein localized predominantly on endothelial cells (ECs). It is a vital component of the activated protein C (APC)—mediated anticoagulant and cytoprotective signaling cascade. PAR-1, which belongs to a family of G protein–coupled cell surface receptors, is also widely distributed on endothelial and blood cells, where it plays a critical role in hemostasis. Both EPCR and PAR-1, generally considered coagulation-related receptors, are implicated in carcinogenesis and dissemination of diverse tumor types, and their expression correlates with clinical outcome of cancer patients. Existing data explain some mechanisms by which EPCR/PAR-1 affects cancer growth and metastasis; however, the exact molecular basis of cancer invasion associated with the signaling is still obscure. Here, we discuss the role of EPCR and PAR-1 reciprocal interactions in cancer progression as well as potential therapeutic options targeted specifically to interact with EPCR/PAR-1-induced signaling in cancer patients.

Changes in Neuronal Signaling and Cell Stress Response Pathways are Associated with a Multigenic Response of Drosophila melanogaster to DDT Selection

The adaptation of insect populations to insecticidal control is a continual threat to human health and sustainable agricultural practices, but many complex genomic mechanisms involved in this adaption remain poorly understood. This study applied a systems approach to investigate the interconnections between structural and functional variance in response to dichlorodiphenyltrichloroethane (DDT) within the Drosophila melanogaster strain 91-R. Directional selection in 6 selective sweeps coincided with constitutive gene expression differences in DDT resistant flies, including the most highly upregulated transcript, Unc-115 b, which plays a central role in axon guidance, and the most highly downregulated transcript, the angiopoietin-like CG31832, which is involved in directing vascular branching and dendrite outgrowth but likely may be under trans-regulatory control. Direct functions and protein–protein interactions mediated by differentially expressed transcripts control changes in cell migration, signal transduction, and gene regulatory cascades that impact the nervous system. Although changes to cellular stress response pathways involve 8 different cytochrome P450s, stress response, and apoptosis is controlled by a multifacetted regulatory mechanism. These data demonstrate that DDT selection in 91-R may have resulted in genome-wide adaptations that impacts genetic and signal transduction pathways that converge to modify stress response, cell survival, and neurological functions. This study implicates the involvement of a multigenic mechanism in the adaptation to a chemical insecticide, which impact interconnected regulatory cascades. We propose that DDT selection within 91-R might act systemically, wherein pathway interactions function to reinforce the epistatic effects of individual adaptive changes on an additive or nonadditive basis.

Pathophysiology of Septic Shock

Fundamental features of septic shock are vasodilation, increased permeability, hypovolemia, and ventricular dysfunction. Vasodilation owing to increased nitric oxide and prostaglandins is treated with vasopressors (norepinephrine first). Increased permeability relates to several pathways (Slit/Robo4, vascular endothelial growth factor, angiopoietin 1 and 2/Tie2 pathway, sphingosine-1-phosphate, and heparin-binding protein), some of which are targets for therapies. Hypovolemia is common and crystalloid is recommended for fluid resuscitation. Cardiomyocyte-inflammatory interactions decrease contractility and dobutamine is recommended to increase cardiac output. There is benefit in decreasing heart rate in selected patients with esmolol. Ivabradine is a novel agent for heart rate reduction without decreasing contractility.

An ADAM-10 dependent EPCR shedding links meningococcal interaction with endothelial cells to purpura fulminans

Purpura fulminans is a deadly complication of Neisseria meningitidis infections due to extensive thrombosis of microvessels. Although a Disseminated Intra-vascular Coagulation syndrome (DIC) is frequently observed during Gram negative sepsis, it is rarely associated with extensive thrombosis like those observed during meningococcemia, suggesting that the meningococcus induces a specific dysregulation of coagulation. Another specific feature of N. meningitidis pathogenesis is its ability to colonize microvessels endothelial cells via type IV pili. Importantly, endothelial cells are key in controlling the coagulation cascade through the activation of the potent anticoagulant Protein C (PC) thanks to two endothelial cell receptors among which the Endothelial Protein C Receptor (EPCR). Considering that congenital or acquired deficiencies of PC are associated with purpura fulminans, we hypothesized that a defect in the activation of PC following meningococcal adhesion to microvessels is responsible for the thrombotic events observed during meningococcemia. Here we showed that the adhesion of N. meningitidis on endothelial cells results in a rapid and intense decrease of EPCR expression by inducing its cleavage in a process know as shedding. Using siRNA experiments and CRISPR/Cas9 genome edition we identified ADAM10 (A Disintegrin And Metalloproteinase-10) as the protease responsible for this shedding. Surprisingly, ADAM17, the only EPCR sheddase described so far, was not involved in this process. Finally, we showed that this ADAM10-mediated shedding of EPCR induced by the meningococcal interaction with endothelial cells was responsible for an impaired activation of Protein C. This work unveils for the first time a direct link between meningococcal adhesion to endothelial cells and a severe dysregulation of coagulation, and potentially identifies new therapeutic targets for meningococcal purpura fulminans.

Neisseria meningitidis (meningococcus) is responsible for a severe syndrome called purpura fulminans in which the coagulation system is totally dysregulated, leading to an extensive occlusion of blood microvessels. The pathogenesis of this syndrome is still not understood. Here we show that the meningococcus, when adhering on the apical surface of endothelial cells, induces the activation of membranous protease named ADAM-10, which in turn hydrolyses a cellular receptor called EPCR. The latter is key for the activation of a circulating potent anticoagulant, the Protein C (PC). PC activation is then impaired following meningococcal adhesion on endothelial cells. This work unveils for the first time a specific dysregulation of coagulation induced by the meningococcus and potentially identifies new therapeutic targets for meningococcal purpura fulminans.

Relationship between G proteins coupled receptors and tight junctions

Tight junctions (TJs) are sites of cell-cell adhesion, constituted by a cytoplasmic plaque of molecules linked to integral proteins that form a network of strands around epithelial and endothelial cells at the uppermost portion of the lateral membrane. TJs maintain plasma membrane polarity and form channels and barriers that regulate the transit of ions and molecules through the paracellular pathway. This structure that regulates traffic between the external milieu and the organism is affected in numerous pathological conditions and constitutes an important target for therapeutic intervention. Here, we describe how a wide array of G protein-coupled receptors that are activated by diverse stimuli including light, ions, hormones, peptides, lipids, nucleotides and proteases, signal through heterotrimeric G proteins, arrestins and kinases to regulate TJs present in the blood-brain barrier, the blood-retinal barrier, renal tubular cells, keratinocytes, lung and colon, and the slit diaphragm of the glomerulus.

Coagulopathy in Severe Sepsis: Interconnectivity of Coagulation and the Immune System

BACKGROUND

Disseminated intravascular coagulation (DIC) remains a challenging complication of infection with inadequate treatment and significant morbidity and mortality rates.

METHODS

Review of the English-language literature.

RESULTS

Disseminated intravascular coagulation arises from the immune system's response to microbial invasion, as well as the byproducts of cell death that result from severe sepsis. This response triggers the coagulation system through an interconnected network of cellular and molecular signals, which developed originally as an evolutionary mechanism intended to isolate micro-organisms via fibrin mesh formation. However, this response has untoward consequences, including hemorrhage and thrombosis caused by dysregulation of the coagulation cascade and fibrinolysis system. Ultimately, diagnosis relies on clinical findings and laboratory studies that recognize excessive activation of the coagulation system, and treatment focuses on supportive measures and correction of coagulation abnormalities. Clinically, DIC secondary to sepsis in the surgical population presents a challenge both in diagnosis and in treatment. Biologically, however, DIC epitomizes the crosstalk between signaling pathways that is essential to normal physiology, while demonstrating the devastating consequences when failure of local control results in systemic derangements.

CONCLUSIONS

This paper discusses the pathophysiology of coagulopathy and fibrinolysis secondary to sepsis, the diagnostic tools available to identify the abnormalities, and the available treatments.

Protein C receptor stimulates multiple signaling pathways in breast cancer cells

The protein C receptor (PROCR) has emerged as a stem cell marker in several normal tissues and has also been implicated in tumor progression. However, the functional role of PROCR and the signaling mechanisms downstream of PROCR remain poorly understood. Here, we dissected the PROCR signaling pathways in breast cancer cells. Combining protein array, knockdown, and overexpression methods, we found that PROCR concomitantly activates multiple pathways. We also noted that PROCR-dependent ERK and PI3k-Akt-mTOR signaling pathways proceed through Src kinase and transactivation of insulin-like growth factor 1 receptor (IGF-1R). These pathway activities led to the accumulation of c-Myc and cyclin D1. On the other hand, PROCR-dependent RhoA-ROCK-p38 signaling relied on coagulation factor II thrombin receptor (F2R). We confirmed these findings in primary cells isolated from triple-negative breast cancer-derived xenografts (PDX) that have high expression of PROCR. To the best our knowledge, this is the first comprehensive study of PROCR signaling in breast cancer cells, and its findings also shed light on the molecular mechanisms of PROCR in stem cells in normal tissue.

Effect of moesin phosphorylation on high‑dose sphingosine‑1‑phosphate‑induced endothelial responses

It was previously reported that low‑dose sphingosine‑1‑phosphate (S1P) enhanced endothelial barrier integrity, whereas high‑dose S1P induced endothelial monolayer hyperpermeability responses. A number of studies have revealed the underlying molecular mechanisms of the physiological‑dose of S1P on barrier‑protective effect. However, little work has been performed to determine the effect of S1P‑induced endothelial barrier responses. In the present study, the role of moesin phosphorylation in excessive S1P‑induced endothelial hyperpermeability was investigated by western blotting, fluorescence staining and transendothelial electrical resistance detection. It was revealed that S1P induced moesin phosphorylation in a time‑ and concentration‑dependent manner. In addition, it was confirmed that high‑dose S1P‑induced moesin phosphorylation occurred via S1P receptor 2 (S1PR2). Moesin phosphorylation was required for S1P‑induced F‑actin rearrangement and endothelial barrier disruption. The results suggested that the S1PR2‑moesin axis is involved in high‑dose S1P‑induced endothelial barrier responses. The results of the present study may provide novel therapeutic targets for endothelial injury‑associated vascular disorders.

EPCR expression marks UM171-expanded CD34+ cord blood stem cells

Publisher's Note: There is an Inside Blood Commentary on this article in this issue.

Uncoupling of the profibrotic and hemostatic effects of thrombin in lung fibrosis

Fibrotic lung disease, most notably idiopathic pulmonary fibrosis (IPF), is thought to result from aberrant wound-healing responses to repetitive lung injury. Increased vascular permeability is a cardinal response to tissue injury, but whether it is mechanistically linked to lung fibrosis is unknown. We previously described a model in which exaggeration of vascular leak after lung injury shifts the outcome of wound-healing responses from normal repair to pathological fibrosis. Here we report that the fibrosis produced in this model is highly dependent on thrombin activity and its downstream signaling pathways. Direct thrombin inhibition with dabigatran significantly inhibited protease-activated receptor-1 (PAR1) activation, integrin αvβ6 induction, TGF-β activation, and the development of pulmonary fibrosis in this vascular leak-dependent model. We used a potentially novel imaging method - ultashort echo time (UTE) lung magnetic resonance imaging (MRI) with the gadolinium-based, fibrin-specific probe EP-2104R - to directly visualize fibrin accumulation in injured mouse lungs, and to correlate the antifibrotic effects of dabigatran with attenuation of fibrin deposition. We found that inhibition of the profibrotic effects of thrombin can be uncoupled from inhibition of hemostasis, as therapeutic anticoagulation with warfarin failed to downregulate the PAR1/αvβ6/TGF-β axis or significantly protect against fibrosis. These findings have direct and important clinical implications, given recent findings that warfarin treatment is not beneficial in IPF, and the clinical availability of direct thrombin inhibitors that our data suggest could benefit these patients.

Activated protein C binds directly to Tie2: possible beneficial effects on endothelial barrier function

Activated protein C (APC) is a natural anticoagulant with strong anti-inflammatory, anti-apoptotic, and barrier stabilizing properties. These cytoprotective properties of APC are thought to be exerted through its pathway involving the binding of APC to endothelial protein C receptor and cleavage of protease-activated receptors. In this study, we found that APC enhanced endothelial barrier integrity via a novel pathway, by binding directly to and activating Tie2, a transmembrane endothelial tyrosine kinase receptor. Binding assays demonstrated that APC competed with the only known ligands of Tie2, the angiopoietins (Angs). APC bound directly to Tie2 (Kd ~3 nM), with markedly stronger binding affinity than Ang2. After binding, APC rapidly activated Tie2 to enhance endothelial barrier function as shown by Evan's blue dye transfer across confluent cell monolayers and in vivo studies. Blocking Tie2 restricted endothelial barrier integrity. This study highlights a novel mechanism by which APC binds directly to Tie2 to enhance endothelial barrier integrity, which helps to explain APC's protective effects in vascular leakage-related pathologies.

G-protein coupled receptor 15 mediates angiogenesis and cytoprotective function of thrombomodulin

Thrombomodulin (TM) stimulates angiogenesis and protects vascular endothelial cells (ECs) via its fifth epidermal growth factor-like region (TME5); however, the cell surface receptor that mediates the pro-survival signaling activated by TM has remained unknown. We applied pull-down assay followed by MALDI-TOF MS and western blot analysis, and identified G-protein coupled receptor 15 (GPR15) as a binding partner of TME5. TME5 rescued growth inhibition and apoptosis caused by calcineurin inhibitor FK506 in vascular ECs isolated from wild type (WT) C57BL/6 mice. On the other hand, TME5 failed to protect ECs isolated from GPR15 knockout (GPR15 KO) mice from FK506-caused vascular injury. TME5 induced activation of extracellular signal-regulated kinase (ERK) and increased level of anti-apoptotic proteins in a GPR15 dependent manner. In addition, in vivo Matrigel plug angiogenesis assay found that TME5 stimulated angiogenesis in mice. TME5 promoted endothelial migration in vitro. Furthermore, TME5 increased production of NO in association with activated endothelial NO synthase (eNOS) in ECs. All these pro-angiogenesis functions of TME5 were abolished by knockout of GPR15. Our findings suggest that GPR15 plays an important role in mediating cytoprotective function as well as angiogenesis of TM.

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

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

Sphingosine-1-Phosphate Signaling in Endothelial Disorders

Numerous preclinical studies indicate that sustained endothelial activation significantly contributes to tissue edema, perpetuates the inflammatory response, and exacerbates tissue injury ultimately resulting in organ failure. However, no specific therapies aimed at restoring endothelial function are available as yet. Sphingosine-1-phosphate (S1P) is emerging as a potent modulator of endothelial function and endothelial responses to injury. Recent studies indicate that S1PR are attractive targets to treat not only disorders of the arterial endothelium but also microvascular dysfunction caused by ischemic or inflammatory injury. In this article, we will review the current knowledge of the role of S1P and its receptors in endothelial function in health and disease, and we will discuss the therapeutic potential of targeting S1PR not only for disorders of the arterial endothelium but also the microvasculature. The therapeutic targeting of S1PR in the endothelium could help to bridge the gap between biomedical research in vascular biology and clinical practice.

2016 Scientific Sessions Sol Sherry Distinguished Lecturer in Thrombosis: Thrombotic Stroke: Neuroprotective Therapy by Recombinant-Activated Protein C

APC (activated protein C), derived from the plasma protease zymogen, is antithrombotic and anti-inflammatory. In preclinical injury models, recombinant APC provides neuroprotection for multiple injuries, including ischemic stroke. APC acts directly on brain endothelial cells and neurons by initiating cell signaling that requires multiple receptors. Two or more major APC receptors mediate APC's neuroprotective cell signaling. When bound to endothelial cell protein C receptor, APC can cleave protease-activated receptor 1, causing biased cytoprotective signaling that reduces ischemia-induced injury. Pharmacological APC alleviates bleeding induced by tissue-type plasminogen activator in murine ischemic stroke studies. Remarkably, APC's signaling promotes neurogenesis. The signaling-selective recombinant variant of APC, 3K3A-APC, was engineered to lack most of the APC's anticoagulant activity but retain APC's cell signaling actions. Recombinant 3K3A-APC is in ongoing National Institutes of Health (NIH)-funded clinical trials for ischemic stroke.

Breaking down brain barrier breaches in cerebral malaria

Recent findings have linked brain swelling to death in cerebral malaria (CM). These observations have prompted a number of investigations into the mechanisms of this pathology with the goal of identifying potential therapeutic targets. In this issue of the JCI, Gallego-Delgado and colleagues present evidence that implicates angiotensin receptors and the relocation of β-catenin to the endothelial cell nucleus in CM. This study provides a renewed focus on infected erythrocyte debris as the cause of endothelial damage and challenges previous work implicating direct effects of infected erythrocyte sequestration in the brain as the major driver of disease. While this work provides potential therapeutic avenues for CM, it leaves a number of questions unanswered.