Changes in cytosolic Ca2+ associated with von Willebrand factor release in human endothelial cells exposed to histamine. Study of microcarrier cell monolayers using the fluorescent probe indo-1

Global trends in research on endothelial cells and sepsis between 2002 and 2022: A systematic bibliometric analysis

Sepsis is a systemic syndrome involving physiological, pathological, and biochemical abnormalities precipitated by infection and is a major global public health problem. Endothelial cells (ECs) dysfunction is a major contributor to sepsis-induced multiple organ failure. This bibliometric analysis aimed to identify and characterize the status, evolution of the field, and new research trends of ECs and sepsis over the past 20 years. For this analysis, the Web of Science Core Collection database was searched to identify relevant publications on ECs in sepsis published between January 1, 2002, and December 31, 2022. Microsoft Excel 2021, VOSviewer software, CiteSpace software, and the online analysis platform of literature metrology (http://bibliometric.com) were used to visualize the trends of publications' countries/regions, institutions, authors, journals, and keywords. In total, 4200 articles were identified and screened, primarily originating from 86 countries/regions and 3489 institutions. The USA was the leading contributor to this research field, providing 1501 articles (35.74 %). Harvard University's scientists were the most prolific, with 129 articles. Overall, 21,944 authors were identified, among whom Bae Jong Sup was the most prolific, contributing 129 publications. Additionally, Levi Marcel was the most frequently co-cited author, appearing 538 times. The journals that published the most articles were SHOCK, CRITICAL CARE MEDICINE, and PLOS ONE, accounting for 10.79 % of the total. The current emerging hotspots are concentrated on "endothelial glycocalyx," "NLRP3 inflammasome," "extracellular vesicle," "biomarkers," and "COVID-19," among others. In conclusion, this study provides a comprehensive overview of the scientific productivity and emerging research trends in the field of ECs in sepsis. The evidence supporting the significant role of ECs in both physiological and pathological responses to sepsis is continuously growing. More in-depth studies of the molecular mechanisms underlying sepsis-induced endothelial dysfunction and EC-targeted therapies are warranted in the future.

Influence of nanoparticles on the haemostatic balance: between thrombosis and haemorrhage

Maintenance of a delicate haemostatic balance or a balance between clotting and bleeding is critical to human health. Irrespective of administration route, nanoparticles can reach the bloodstream and might interrupt the haemostatic balance by interfering with one or more components of the coagulation, anticoagulation, and fibrinolytic systems, which potentially lead to thrombosis or haemorrhage. However, inadequate understanding of their effects on the haemostatic balance, along with the fact that most studies mainly focus on the functionality of nanoparticles while forgetting or leaving behind their risk to the body's haemostatic balance, is a major concern. Hence, our review aims to provide a comprehensive depiction of nanoparticle-haemostatic balance interactions, which has not yet been covered. The synergistic roles of cells and plasma factors participating in haemostatic balance are presented. Possible interactions and interference of each type of nanoparticle with the haemostatic balance are comprehensively discussed, particularly focusing on the underlying mechanisms. Interactions of nanoparticles with innate immunity potentially linked to haemostasis are mentioned. Various physicochemical characteristics that influence the nanoparticle-haemostatic balance are detailed. Challenges and future directions are also proposed. This insight would be valuable for the establishment of nanoparticles that can either avoid unintended interference with the haemostatic balance or purposely downregulate/upregulate its key components in a controlled manner.

The Manifold Cellular Functions of von Willebrand Factor

The plasma glycoprotein von Willebrand factor (VWF) is exclusively synthesized in endothelial cells (ECs) and megakaryocytes, the precursor cells of platelets. Its primary function lies in hemostasis. However, VWF is much more than just a "fishing hook" for platelets and a transporter for coagulation factor VIII. VWF is a true multitasker when it comes to its many roles in cellular processes. In ECs, VWF coordinates the formation of Weibel-Palade bodies and guides several cargo proteins to these storage organelles, which control the release of hemostatic, inflammatory and angiogenic factors. Leukocytes employ VWF to assist their rolling on, adhesion to and passage through the endothelium. Vascular smooth muscle cell proliferation is supported by VWF, and it regulates angiogenesis. The life cycle of platelets is accompanied by VWF from their budding from megakaryocytes to adhesion, activation and aggregation until the end in apoptosis. Some tumor cells acquire the ability to produce VWF to promote metastasis and hide in a shell of VWF and platelets, and even the maturation of osteoclasts is regulated by VWF. This review summarizes the current knowledge on VWF's versatile cellular functions and the resulting pathophysiological consequences of their dysregulation.

Lysophosphatidylcholine in phospholipase A2-modified LDL triggers secretion of angiopoietin 2

BACKGROUND AND AIMS

Secretory phospholipase A₂ (PLA₂) hydrolyzes LDL phospholipids generating modified LDL particles (PLA₂-LDL) with increased atherogenic properties. Exocytosis of Weibel-Palade bodies (WPB) releases angiopoietin 2 (Ang2) and externalizes P-selectin, which both play important roles in vascular inflammation. Here, we investigated the effects of PLA₂-LDL on exocytosis of WPBs.

METHODS

Human coronary artery endothelial cells (HCAECs) were stimulated with PLA₂- LDL, and its uptake and effect on Ang2 release, leukocyte adhesion, and intracellular calcium levels were measured. The effects of PLA₂-LDL on Ang2 release and WPB exocytosis were measured in and ex vivo in mice.

RESULTS

Exposure of HCAECs to PLA₂-LDL triggered Ang2 secretion and promoted leukocyte-HCAEC interaction. Lysophosphatidylcholine was identified as a critical component of PLA₂-LDL regulating the WPB exocytosis, which was mediated by cell-surface proteoglycans, phospholipase C, intracellular calcium, and cytoskeletal remodeling. PLA₂-LDL also induced murine endothelial WPB exocytosis in blood vessels in and ex vivo, as evidenced by secretion of Ang2 in vivo, P-selectin translocation to plasma membrane in intact endothelial cells in thoracic artery and tracheal vessels, and reduced Ang2 staining in tracheal endothelial cells. Finally, in contrast to normal human coronary arteries, in which Ang2 was present only in the endothelial layer, at sites of advanced atherosclerotic lesions, Ang2 was detected also in the intima, media, and adventitia.

CONCLUSIONS

Our studies reveal PLA₂-LDL as a potent agonist of endothelial WPB exocytosis, resulting in increased secretion of Ang2 and translocation of P-selectin. The results provide mechanistic insight into PLA₂-LDL-dependent promotion of vascular inflammation and atherosclerosis.

Angiopoietin-2 is released during anaphylactic hypotension in anesthetized and unanesthetized rats

Angiopoietin (Angpt)-2, a permeability-increasing growth factor, is involved in vascular leakage of sepsis and acute lung injury, and could be released from endothelium in response to anaphylaxis-related secretagogues such as histamine and leukotrienes, or cytokines. However, roles of Angpt-2 in the hyperpermeability during systemic anaphylaxis are not known. Thus, we determined plasma levels of Angpt-2 and cytokines and vascular permeability during anaphylactic hypotension in unanesthetized rats. Anaphylaxis was induced by an intravenous injection of ovalbumin antigen. Mean arterial blood pressure (MBP) was measured, and hematocrit (Hct) and plasma levels of Angpt-2 and cytokines were assessed for 24 h after antigen injection. Separately, vascular permeability was measured in various organs using the Evans blue dye method, and Angpt-2 mRNA expression in liver was measured. After antigen injection, MBP decreased to the nadir at 6 min, and returned to baseline at 45 min, and Hct peaked at 20 min and thereafter progressively declined, suggesting that vascular leak and hypotension occurred within 20 min. Plasma Angpt-2 levels began to increase significantly at 1 h after antigen, reaching the peak 2.7-fold baseline at 6 h with a return to baseline at 24 h. Detected cytokines of IL-1α, IL-1β, IL-6, IL-10, and TNF-α peaked 1 or 2 h after antigen. Angpt-2 mRNA increased at 2 h and showed an increasing tendency at 6 h. Vascular permeability in bronchus, trachea, intestines, mesentery and skeletal muscle was increased at 10 min but not at 6 h after antigen. In addition, we confirmed using anesthetized rat anaphylaxis models that plasma Angpt-2 levels increased at 1 h after antigen. In conclusion, plasma Angpt-2 is elevated presumably due to increased cytokines and enhanced gene transcription during anaphylaxis in anesthetized and unanesthetized rats.

A sticky proposition: The endothelial glycocalyx and von Willebrand factor

Von Willebrand factor (VWF) is a critical component of the hemostatic system. Basal secretion of VWF from endothelial cells is the principal determinant of an individual's baseline plasma VWF levels, while endothelial VWF release can also be induced by several biochemical agonists and biomechanical forces such as increased shear stress. However, the mechanotransduction machinery responsible for this latter response is unclear. Here we propose that the endothelial glycocalyx (EGC), a dynamic layer of proteins and carbohydrates that covers the surface of the vascular endothelium, may play a key role in mediating this response. The EGC has previously been implicated in mediating the mechanotransduction of shear stress in other shear-responsive endothelial processes, such as nitric oxide production and stem cell differentiation. Here, we hypothesize that a similar mechanism may be responsible for the basal secretion of endothelial VWF, whereby the EGC mediates the mechanotransduction of physiological shear stress generated by flowing blood, that in turn contributes to the maintenance of physiological plasma VWF levels.

Synaptotagmin 5 regulates Ca2+-dependent Weibel-Palade body exocytosis in human endothelial cells

Elevations of intracellular free Ca²⁺ concentration ([Ca²⁺]_i) are a potent trigger for Weibel-Palade body (WPB) exocytosis and secretion of von Willebrand factor (VWF) from endothelial cells; however, the identity of WPB-associated Ca²⁺-sensors involved in transducing acute increases in [Ca²⁺]_i into granule exocytosis remains unknown. Here, we show that synaptotagmin 5 (SYT5) is expressed in human umbilical vein endothelial cells (HUVECs) and is recruited to WPBs to regulate Ca²⁺-driven WPB exocytosis. Western blot analysis of HUVECs identified SYT5 protein, and exogenously expressed SYT5-mEGFP localised almost exclusively to WPBs. shRNA-mediated knockdown of endogenous SYT5 (shSYT5) reduced the rate and extent of histamine-evoked WPB exocytosis and reduced secretion of the WPB cargo VWF-propeptide (VWFpp). The shSYT5-mediated reduction in histamine-evoked WPB exocytosis was prevented by expression of shRNA-resistant SYT5-mCherry. Overexpression of SYT5-EGFP increased the rate and extent of histamine-evoked WPB exocytosis, and increased secretion of VWFpp. Expression of a Ca²⁺-binding defective SYT5 mutant (SYT5-Asp197Ser-EGFP) mimicked depletion of endogenous SYT5. We identify SYT5 as a WPB-associated Ca²⁺ sensor regulating Ca²⁺-dependent secretion of stored mediators from vascular endothelial cells.

Histamine and diabetic nephropathy: an up-to-date overview

The classification of diabetic nephropathy (DN) as a vascular complication of diabetes makes the possible involvement of histamine, an endogenous amine that is well known for its vasoactive properties, an interesting topic for study. The aim of the present review is to provide an extensive overview of the possible involvement of histamine in the onset and progression of DN. The evidence collected on the role of histamine in kidney function together with its well-known pleiotropic action suggest that this amine may act simultaneously on glomerular hyperfiltration, tubular inflammation, fibrosis development and tubular hypertrophy.

Inflammation in sickle cell disease

The primary β-globin gene mutation that causes sickle cell disease (SCD) has significant pathophysiological consequences that result in hemolytic events and the induction of the inflammatory processes that ultimately lead to vaso-occlusion. In addition to their role in the initiation of the acute painful vaso-occlusive episodes that are characteristic of SCD, inflammatory processes are also key components of many of the complications of the disease including autosplenectomy, acute chest syndrome, pulmonary hypertension, leg ulcers, nephropathy and stroke. We, herein, discuss the events that trigger inflammation in the disease, as well as the mechanisms, inflammatory molecules and cells that propagate these inflammatory processes. Given the central role that inflammation plays in SCD pathophysiology, many of the therapeutic approaches currently under pre-clinical and clinical development for the treatment of SCD endeavor to counter aspects or specific molecules of these inflammatory processes and it is possible that, in the future, we will see anti-inflammatory drugs being used either together with, or in place of, hydroxyurea in those SCD patients for whom hematopoietic stem cell transplants and evolving gene therapies are not a viable option.

Ecto-protein kinase CK2, the neglected form of CK2

Ecto-protein kinases, including protein kinase CK2 (former name, casein kinase 2), have been the focus of research for more than 30 years. At the beginning of the ecto-kinase research their identification was performed with substrates and inhibitors whose specificity under the current knowledge was rather limited. Since all currently known ecto-kinases, including ecto-CK2, have intracellular counterparts, one has to exclude that an ecto-localization originates from intracellular counterparts after cell damage. Protein kinase CK2 is involved in cellular key processes such as cell cycle progression, inhibition of apoptosis, DNA damage repair, differentiation and many other processes. CK2 is composed of two catalytic CK2α or CK2α' subunits and two non-catalytic CK2β subunits. Progress in the ecto-kinase and in particular ecto-CK2 studies was made with the use of transfected tagged CK2 subunits, which allowed to follow their individual transport and localization on the cell surface after transfection. Furthermore, immunofluorescence studies with antibodies against CK2 subunits as well as affinity chromatography with a binding partner of CK2 subunits have improved ecto-kinase research. The use of new and more specific inhibitors as well as of substrates, which do not cross the plasma membrane, have further improved the specificity for ecto-CK2. From the various substrates of ecto-CK2, it can be concluded that ecto-CK2 plays a role in Alzheimer disease, cell adhesion, platelet aggregation, immune response and cellular signalling. New tools and techniques, to study ecto-CK2 activity, are required to identify new substrates and thereby new functional implications for ecto-CK2.

Weibel-Palade bodies at a glance

The vascular environment can rapidly alter, and the speed with which responses to both physiological and pathological changes are required necessitates the existence of a highly responsive system. The endothelium can quickly deliver bioactive molecules by regulated exocytosis of its secretory granules, the Weibel-Palade bodies (WPBs). WPBs include proteins that initiate both haemostasis and inflammation, as well those that modulate blood pressure and angiogenesis. WPB formation is driven by von Willebrand factor, their most abundant protein, which controls both shape and size of WPBs. WPB are generated in a range of sizes, with the largest granules over ten times the size of the smallest. In this Cell Science at a Glance and the accompanying poster, we discuss the emerging mechanisms by which WPB size is controlled and how this affects the ability of this organelle to modulate haemostasis. We will also outline the different modes of exocytosis and their polarity that are currently being explored, and illustrate that these large secretory organelles provide a model for how elements of secretory granule biogenesis and exocytosis cooperate to support a complex and diverse set of functions.

Mast Cells Granular Contents Are Crucial for Deep Vein Thrombosis in Mice

RATIONALE

Deep vein thrombosis (DVT) and its complication pulmonary embolism have high morbidity reducing quality of life and leading to death. Cellular mechanisms of DVT initiation remain poorly understood.

OBJECTIVE

We sought to determine the role of mast cells (MCs) in DVT initiation and validate MCs as a potential target for DVT prevention.

METHODS AND RESULTS

In a mouse model, DVT was induced by partial ligation (stenosis) of the inferior vena cava. We demonstrated that 2 strains of mice deficient for MCs were completely protected from DVT. Adoptive transfer of in vitro differentiated MCs restored thrombosis. MCs were present in the venous wall, and the number of granule-containing MCs decreased with thrombosis. Pharmacological depletion of MCs granules or prevention of MC degranulation also reduced DVT. Basal plasma levels of von Willebrand factor and recruitment of platelets to the inferior vena cava wall after DVT induction were reduced in MC-deficient mice. Stenosis application increased plasma levels of soluble P-selectin in wild-type but not in MC-deficient mice. MC releasate elevated ICAM-1 (intercellular adhesion molecule-1) expression on HUVEC (human umbilical vein endothelial cells) in vitro. Topical application of compound 48/80, an MC secretagogue, or histamine, a Weibel-Palade body secretagogue from MCs, potentiated DVT in wild-type mice, and histamine restored thrombosis in MC-deficient animals.

CONCLUSIONS

MCs exacerbate DVT likely through endothelial activation and Weibel-Palade body release, which is, at least in part, mediated by histamine. Because MCs do not directly contribute to normal hemostasis, they can be considered potential targets for prevention of DVT in humans.

Platelet-independent adhesion of calcium-loaded erythrocytes to von Willebrand factor

Adhesion of erythrocytes to endothelial cells lining the vascular wall can cause vaso-occlusive events that impair blood flow which in turn may result in ischemia and tissue damage. Adhesion of erythrocytes to vascular endothelial cells has been described in multiple hemolytic disorders, especially in sickle cell disease, but the adhesion of normal erythrocytes to endothelial cells has hardly been described. It was shown that calcium-loaded erythrocytes can adhere to endothelial cells. Because sickle erythrocyte adhesion to ECs can be enhanced by ultra-large von Willebrand factor multimers, we investigated whether calcium loading of erythrocytes could promote binding to endothelial cells via ultra-large von Willebrand factor multimers. We used (immunofluorescent) live-cell imaging of washed erythrocytes perfused over primary endothelial cells at venular flow rate. Using this approach, we show that calcium-loaded erythrocytes strongly adhere to histamine-stimulated primary human endothelial cells. This adhesion is mediated by ultra-large von Willebrand factor multimers. Von Willebrand factor knockdown or ADAMTS13 cleavage abolished the binding of erythrocytes to activated endothelial cells under flow. Platelet depletion did not interfere with erythrocyte binding to von Willebrand factor. Our results reveal platelet-independent adhesion of calcium-loaded erythrocytes to endothelium-derived von Willebrand factor. Erythrocyte adhesion to von Willebrand factor may be particularly relevant for venous thrombosis, which is characterized by the formation of erythrocyte-rich thrombi.

The role of leukocytes in thrombosis

In recent years, the traditional view of the hemostatic system as being regulated by a coagulation factor cascade coupled with platelet activation has been increasingly challenged by new evidence that activation of the immune system strongly influences blood coagulation and pathological thrombus formation. Leukocytes can be induced to express tissue factor and release proinflammatory and procoagulant molecules such as granular enzymes, cytokines, and damage-associated molecular patterns. These mediators can influence all aspects of thrombus formation, including platelet activation and adhesion, and activation of the intrinsic and extrinsic coagulation pathways. Leukocyte-released procoagulant mediators increase systemic thrombogenicity, and leukocytes are actively recruited to the site of thrombus formation through interactions with platelets and endothelial cell adhesion molecules. Additionally, phagocytic leukocytes are involved in fibrinolysis and thrombus resolution, and can regulate clearance of platelets and coagulation factors. Dysregulated activation of leukocyte innate immune functions thus plays a role in pathological thrombus formation. Modulation of the interactions between leukocytes or leukocyte-derived procoagulant materials and the traditional hemostatic system is an attractive target for the development of novel antithrombotic strategies.

Proteomic study of acute respiratory distress syndrome: current knowledge and implications for drug development

The acute respiratory distress syndrome (ARDS) is a common cause of acute respiratory failure, and is associated with substantial mortality and morbidity. Dozens of clinical trials targeting ARDS have failed, with no drug specifically targeting lung injury in widespread clinical use. Thus, the need for drug development in ARDS is great. Targeted proteomic studies in ARDS have identified many key pathways in the disease, including inflammation, epithelial injury, endothelial injury or activation, and disordered coagulation and repair. Recent studies reveal the potential for proteomic changes to identify novel subphenotypes of ARDS patients who may be most likely to respond to therapy and could thus be targeted for enrollment in clinical trials. Nontargeted studies of proteomics in ARDS are just beginning and have the potential to identify novel drug targets and key pathways in the disease. Proteomics will play an important role in phenotyping of patients and developing novel therapies for ARDS in the future.

Regulatory components of the alternative complement pathway in endothelial cell cytoplasm, factor H and factor I, are not packaged in Weibel-Palade bodies

It was recently reported that factor H, a regulatory component of the alternative complement pathway, is stored with von Willebrand factor (VWF) in the Weibel-Palade bodies of endothelial cells. If this were to be the case, it would have therapeutic importance for patients with the atypical hemolytic-uremic syndrome that can be caused either by a heterozygous defect in the factor H gene or by the presence of an autoantibody against factor H. The in vivo Weibel-Palade body secretagogue, des-amino-D-arginine vasopressin (DDAVP), would be expected to increase transiently the circulating factor H levels, in addition to increasing the circulating levels of VWF. We describe experiments demonstrating that factor H is released from endothelial cell cytoplasm without a secondary storage site. These experiments showed that factor H is not stored with VWF in endothelial cell Weibel-Palade bodies, and is not secreted in response in vitro in response to the Weibel-Palade body secretagogue, histamine. Furthermore, the in vivo Weibel-Palade body secretagogue, DDAVP does not increase the circulating factor H levels concomitantly with DDAVP-induced increased VWF. Factor I, a regulatory component of the alternative complement pathway that is functionally related to factor H, is also located in endothelial cell cytoplasm, and is also not present in endothelial cell Weibel-Palade bodies. Our data demonstrate that the factor H and factor I regulatory proteins of the alternative complement pathway are not stored in Weibel-Palade bodies. DDAVP induces the secretion into human plasma of VWF--but not factor H.

VWF excess and ADAMTS13 deficiency: a unifying pathomechanism linking inflammation to thrombosis in DIC, malaria, and TTP

Absent or severely diminished activity of ADAMTS13 (A Disintegrin And Metalloprotease with a ThromboSpondin type 1 motif, member 13) resulting in the intravascular persistence and accumulation of highly thrombogenic ultra large von Willebrand factor (UL-VWF) multimers is the pathophysiological mechanism underlying thrombotic thrombocytopenic purpura. Reduced VWF-cleaving protease levels, however, are not uniquely restricted to primary thrombotic microangiopathy (TMA), e. g. thrombotic thrombocytopenic purpura, but also occur in other life-threatening thrombocytopenic conditions: severely decreased ADAMTS13 activity is seen in severe sepsis, disseminated intravascular coagulation (DIC) and complicated malarial infection. The clinical relevance of these secondary thrombotic microangiopathies is increasingly recognised, but its therapeutic implications have not yet been determined. The presence of a secondary TMA in certain diseases may define patient groups which possibly could benefit from ADAMTS13 replacement or a VWF-targeting therapy. This short-review focuses on the role of UL-VWF multimers in secondary TMA and discusses the potential of investigational therapies as candidates for the treatment of TTP. In conclusion, prospective clinical trials on the effectiveness of protease replacementin vivo seem reasonable. Carefully selected patients with secondary TMA may benefit from therapies primarily intended for the use in patients with TTP.

The role of hemostasis in infective endocarditis

Infective endocarditis (IE) is a thromboinflammatory disease of the endocardium, with pathophysiology mostly the result of the interplay between microorganisms and modifiers of the hemostasis system. In this setting, the evidence gathered so far warrants a more systematic appraisal. In this review article, experimental and clinical data on the role of hemostasis in IE are summarized. Starting from the current pathogenetic model of IE, we discuss the dual role of platelets in this condition, the microbial interaction with the hemostasis system, also describing nonspecific hemostasis changes during sepsis. We finally propose our hypothesis of thrombophilia as a possible trigger of IE, highlighting the challenges that the study of hemostasis in IE presents. The role of hemostasis in IE appears to be an exciting field of research. The activity of the hemostasis system is highly relevant in terms of susceptibility, progression, and treatment of IE. Pharmacologic modulation of hemostasis before and after IE onset is possible and represents still a largely unexplored area of study.

Histamine-induced vasodilatation in the human forearm vasculature

AIM

To investigate the mechanism of action of intra-arterial histamine in the human forearm vasculature.

METHODS

Three studies were conducted to assess changes in forearm blood flow (FBF) using venous occlusion plethysmography in response to intra-brachial histamine. First, the dose-response was investigated by assessing FBF throughout a dose-escalating histamine infusion. Next, histamine was infused at a constant dose to assess acute tolerance. Finally, a four way, double-blind, randomized, placebo-controlled crossover study was conducted to assess FBF response to histamine in the presence of H1 - and H2 -receptor antagonists. Flare and itch were assessed in all studies.

RESULTS

Histamine caused a dose-dependent increase in FBF, greatest with the highest dose (30 nmol min(-1) ) infused [mean (SEM) infused arm vs. control: 26.8 (5.3) vs. 2.6 ml min(-1)  100 ml(-1) ; P < 0.0001]. Dose-dependent flare and itch were demonstrated. Acute tolerance was not observed, with an increased FBF persisting throughout the infusion period. H2 -receptor antagonism significantly reduced FBF (mean (95% CI) difference from placebo at 30 nmol min(-1) histamine: -11.9 ml min(-1)  100 ml(-1) (-4.0, -19.8), P < 0.0001) and flare (mean (95% CI) difference from placebo: -403.7 cm(2) (-231.4, 576.0), P < 0.0001). No reduction in FBF or flare was observed in response to the H1 -receptor antagonist. Itch was unaffected by the treatments. Histamine did not stimulate vascular release of tissue plasminogen activator or von Willebrand factor.

CONCLUSION

Histamine causes dose-dependent vasodilatation, flare and itch in the human forearm. H2 -receptors are important in this process. Our results support further exploration of combined H1 - and H2 -receptor antagonist therapy in acute allergic syndromes.

Update on von Willebrand factor multimers: focus on high-molecular-weight multimers and their role in hemostasis

Normal hemostasis requires von Willebrand factor (VWF) to support platelet adhesion and aggregation at sites of vascular injury. VWF is a multimeric glycoprotein built from identical subunits that contain binding sites for both platelet glycoprotein receptors and collagen. The adhesive activity of VWF depends on the size of its multimers, which range from 500 to over 10 000 kDa. There is good evidence that the high-molecular-weight multimers (HMWM), which are 5000-10 000 kDa, are the most effective in supporting interaction with collagen and platelet receptors and in facilitating wound healing under conditions of shear stress. Thus, these HMWM of VWF are of particular clinical interest. The unusually large multimers of VWF are, under normal conditions, cleaved by the plasma metalloproteinase ADAMTS13 to smaller, less adhesive multimers. A reduction or lack of HMWM, owing to a multimerization defect of VWF or to an increased susceptibility of VWF for ADAMTS13, leads to a functionally impaired VWF and the particular type 2A of von Willebrand disease. This review considers the biology and function of VWF multimers with a particular focus on the characterization of HMWM - their production, storage, release, degradation, and role in normal physiology. Evidence from basic research and the study of clinical diseases and their management highlight a pivotal role for the HMWM of VWF in hemostasis.

Regulation of cellular communication by signaling microdomains in the blood vessel wall

It has become increasingly clear that the accumulation of proteins in specific regions of the plasma membrane can facilitate cellular communication. These regions, termed signaling microdomains, are found throughout the blood vessel wall where cellular communication, both within and between cell types, must be tightly regulated to maintain proper vascular function. We will define a cellular signaling microdomain and apply this definition to the plethora of means by which cellular communication has been hypothesized to occur in the blood vessel wall. To that end, we make a case for three broad areas of cellular communication where signaling microdomains could play an important role: 1) paracrine release of free radicals and gaseous molecules such as nitric oxide and reactive oxygen species; 2) role of ion channels including gap junctions and potassium channels, especially those associated with the endothelium-derived hyperpolarization mediated signaling, and lastly, 3) mechanism of exocytosis that has considerable oversight by signaling microdomains, especially those associated with the release of von Willebrand factor. When summed, we believe that it is clear that the organization and regulation of signaling microdomains is an essential component to vessel wall function.

G protein-coupled receptor kinase 2 moderates recruitment of THP-1 cells to the endothelium by limiting histamine-invoked Weibel-Palade body exocytosis

BACKGROUND

G protein-coupled receptors (GPCRs) are a major family of signaling molecules, central to the regulation of inflammatory responses. Their activation upon agonist binding is attenuated by GPCR kinases (GRKs), which desensitize the receptors through phosphorylation. G protein-coupled receptor kinase 2(GRK2) down-regulation in leukocytes has been closely linked to the progression of chronic inflammatory disorders such as rheumatoid arthritis and multiple sclerosis. Because leukocytes must interact with the endothelium to infiltrate inflamed tissues, we hypothesized that GRK2 down-regulation in endothelial cells would also be pro-inflammatory.

OBJECTIVES

To determine whether GRK2 down-regulation in endothelial cells is pro-inflammatory.

METHODS

siRNA-mediated ablation of GRK2 in human umbilical vein endothelial cells (HUVECs) was used in analyses of the role of this kinase. Microscopic and biochemical analyses of Weibel-Palade body (WPB) formation and functioning, live cell imaging of calcium concentrations and video analyses of adhesion of monocyte-like THP-1 cells provide clear evidence of GRK2 function in histamine activation of endothelial cells.

RESULTS

G protein-coupled receptor kinase 2 depletion in HUVECs increases WPB exocytosis and P-selectin-dependent adhesion of THP-1 cells to the endothelial surface upon histamine stimulation, relative to controls. Further, live imaging of intracellular calcium concentrations reveals amplified histamine receptor signaling in GRK2-depleted cells, suggesting GRK2 moderates WPB exocytosis through receptor desensitization.

CONCLUSIONS

G protein-coupled receptor kinase 2 deficiency in endothelial cells results in increased pro-inflammatory signaling and enhanced leukocyte recruitment to activated endothelial cells. The ability of GRK2 to modulate initiation of inflammatory responses in endothelial cells as well as leukocytes now places GRK2 at the apex of control of this finely balanced process.

cAMP-induced secretion of endothelial von Willebrand factor is regulated by a phosphorylation/dephosphorylation switch in annexin A2

The large multimeric glyocoprotein von Willebrand factor (VWF) is a crucial component of both primary and secondary hemostasis. It is stored in secretory granules of vascular endothelial cells, the Weibel-Palade bodies (WPBs), and is released following stimulation by agonists that raise intracellular Ca(2+) or cyclic adenosine monophosphate (cAMP) levels. cAMP-induced exocytosis of WPBs requires protein kinase A activity, but downstream factors that are regulated by phosphorylation/dephosphorylation are not known. Here we identify the complex consisting of the lipid-binding protein annexin A2 (AnxA2) and S100A10 as such a factor. Knockdown and specific rescue approaches reveal that a functional AnxA2-S100A10 complex is required for the forskolin-induced, cAMP-dependent release of VWF. Forskolin triggers dephosphorylation of AnxA2 that is mediated by a calcineurin-like phosphatase and stabilizes the AnxA2-S100A10 complex, thereby promoting VWF release. Serine 11 of AnxA2 was identified as the target residue of this phosphorylation switch because a phosphomimicking mutation at this site prevents complex formation with S100A10 and, in contrast to wild-type or S11A-AnxA2, is unable to restore cAMP-dependent VWF secretion in AnxA2-depleted cells. Thus, complex formation of AnxA2 with S100A10 is a central regulatory mechanism in the acute release of VWF in response to cAMP-elevating agonists.

Histamine: an undercover agent in multiple rare diseases?

Histamine is a biogenic amine performing pleiotropic effects in humans, involving tasks within the immune and neuroendocrine systems, neurotransmission, gastric secretion, cell life and death, and development. It is the product of the histidine decarboxylase activity, and its effects are mainly mediated through four different G-protein coupled receptors. Thus, histamine-related effects are the results of highly interconnected and tissue-specific signalling networks. Consequently, alterations in histamine-related factors could be an important part in the cause of multiple rare/orphan diseases. Bearing this hypothesis in mind, more than 25 rare diseases related to histamine physiopathology have been identified using a computationally assisted text mining approach. These newly integrated data will provide insight to elucidate the molecular causes of these rare diseases. The data can also help in devising new intervention strategies for personalized medicine for multiple rare diseases.

Clinical and prognostic implications of low or high level of von Willebrand factor in patients with Waldenstrom macroglobulinemia

Acquired von Willebrand syndrome is described in patients with Waldenström macroglobulinemia (WM). Assessment of ristocetin cofactor activity (VWF:RCo) and von Willebrand factor (VWF) antigen (VWF:Ag) in 72 consecutive patients with WM showed a negative relation between VWF levels < 130 U/dL and both monoclonal immunoglobulin M concentration (mIgMC) and viscosity. Ten patients with VWF:RCo < 50 U/dL (< 40 for patients with blood group O) fulfilled the acquired von Willebrand syndrome criteria. They had higher mIgMC and viscosity. Reduction in mIgMC was associated with increase in VWF levels. The low VWF:RCo/VWF:Ag ratio suggested that high viscosity might be associated with increased shear force and cleavage of multimers. Surprisingly, 43 patients (59%) presented with high VWF:Ag (> 110 U/dL). They had higher bone marrow microvessel density and vascular endothelial growth factor expression on bone marrow mast cells. Five-year survival rates of patients with VWF:Ag < 110, between 110 and 250, and more than 250 U/dL were 96%, 71%, and 44%, respectively (P < .0001). High VWF:Ag was also a significant adverse prognostic factor for survival after first-line therapy (P < .0001), independently of the international scoring system. These results support systematic assessment of VWF in patients with WM. The adverse prognostic value of high VWF levels raises issues on interactions between lymphoplasmacytic cells, mast cells, and endothelial cells in WM.

Thrombin-induced ATP release from human umbilical vein endothelial cells

ATP and its degradation products play an important role as signaling molecules in the vascular system, and endothelial cells are considered to be an important source of nucleotide release. To investigate the mechanism and physiological significance of endothelial ATP release, we compared different pharmacological stimuli for their ability to evoke ATP release from first passage cultivated human umbilical vein endothelial cells (HUVECs). Agonists known to increase intracellular Ca(2+) levels (A23187, histamine, thrombin) induced a stable, non-lytic ATP release. Since thrombin proved to be the most robust and reproducible stimulus, the molecular mechanism of thrombin-mediated ATP release from HUVECs was further investigated. ATP rapidly increased with thrombin (1 U/ml) and reached a steady-state level after 4 min. Loading the cells with BAPTA-AM to capture intracellular calcium suppressed ATP release. The thrombin-specific, protease-activated receptor 1 (PAR-1)-specific agonist peptide TFLLRN (10 μM) fully mimicked thrombin action on ATP release. To identify the nature of the ATP-permeable pathway, we tested various inhibitors of potential ATP channels for their ability to inhibit the thrombin response. Carbenoxolone, an inhibitor of connexin hemichannels and pannexin channels, as well as Gd(3+) were highly effective in blocking the thrombin-mediated ATP release. Specifically targeting connexin43 (Cx43) and pannexin1 (Panx1) revealed that reducing Panx1 expression significantly reduced ATP release, while downregulating Cx43 was ineffective. Our study demonstrates that thrombin at physiological concentrations is a potent stimulus of endothelial ATP release involving PAR-1 receptor activation and intracellular calcium mobilization. ATP is released by a carbenoxolone- and Gd(3+)- sensitive pathway, most likely involving Panx1 channels.

Regulation of Weibel-Palade body exocytosis by alpha-synuclein in endothelial cells

alpha-Synuclein is a small presynaptic protein implicated in the pathogenesis of Parkinson disease. Nevertheless, its physiological roles and mechanisms remain incompletely understood. alpha-Synuclein is not only expressed in neurons but also in the vascular endothelium, which contains intracellular granules called Weibel-Palade bodies (WPBs) that contain a number of chemokines, adhesive molecules, and inflammatory cytokines. This study explored whether the exocytosis of WPB is regulated by alpha-synuclein. Phorbol 12-myristate 13-acetate-, thrombin-, or forskolin-induced von Willebrand factor release or translocation of P-selectin from endothelial cells were inhibited by alpha- and beta-synuclein but not gamma-synuclein. Three point mutants (A30P, A53T, and E46K) found in familial Parkinson disease also inhibited WPB exocytosis similar to that of wild-type alpha-synuclein. Furthermore, the negative regulation of WPB exocytosis required the N terminus or the nonamyloid beta-component of Alzheimer disease amyloid region of alpha-synuclein, but not the C-terminal acidic tail, and alpha-synuclein affected WPB exocytosis through interference with RalA activation by enhancing the interaction of RalGDS-beta-arrestin complexes. Immuno-EM analysis revealed that alpha-synuclein was localized close to WPBs. These findings imply that alpha-synuclein plays as a negative regulator in WPB exocytosis in endothelial cells.

Alpha1G T-type calcium channel selectively regulates P-selectin surface expression in pulmonary capillary endothelium

Regulated P-selectin surface expression provides a rapid measure for endothelial transition to a proinflammatory phenotype. In general, P-selectin surface expression results from Weibel-Palade body (WPb) exocytosis. Yet, it is unclear whether pulmonary capillary endothelium possesses WPbs or regulated P-selectin surface expression and, if so, how inflammatory stimuli initiate exocytosis. We used immunohistochemistry, immunofluorescence labeling, ultrastructural assessment, and an isolated perfused lung model to demonstrate that capillary endothelium lacks WPbs but possesses P-selectin. Thrombin stimulated P-selectin surface expression in both extra-alveolar vessel and alveolar capillary endothelium. Only in capillaries was the thrombin-stimulated P-selectin surface expression considerably mitigated by pharmacologic blockade of the T-type channel or genetic knockout of the T-type channel alpha(1G)-subunit. Depolarization of endothelial plasma membrane via high K(+) perfusion capable of eliciting cytosolic Ca(2+) transients also provoked P-selectin surface expression in alveolar capillaries that was abolished by T-type channel blockade or alpha(1G) knockout. Our findings reveal an intracellular WPb-independent P-selectin pool in pulmonary capillary endothelium, where the regulated P-selectin surface expression is triggered by Ca(2+) transients evoked through activation of the alpha(1G) T-type channel.

The pathogenetic and prognostic value of biologic markers in acute lung injury

Over the past 2 decades, measurement of biomarkers in both the airspaces and plasma early in the course of acute lung injury has provided new insights into the mechanisms of lung injury. In addition, biologic markers of cell-specific injury, acute inflammation, and altered coagulation correlate with mortality from acute lung injury in several single center studies as well as in multicenter clinical trials. To date, biomarkers have been measured largely for research purposes. However, with improved understanding of their role in the pathogenesis of acute lung injury, biomarkers may play an important role in early detection of lung injury, risk stratification for clinical trials, and, ultimately, tailoring specific therapies to individual patients. This article provides a review of biologic markers in acute lung injury, with an emphasis on recent analysis of results from multicenter clinical trials.

New insights into leukocyte recruitment by intravital microscopy

Leukocyte recruitment to sites of inflammation requires adhesion to and transmigration through the blood vessel wall. Recent progress in optical equipment and new genetic and molecular tools have revealed additional steps in the leukocyte adhesion cascade beyond rolling, adhesion, and transmigration. In vivo studies using intravital microscopy (IVM) were essential for the discovery of slow rolling, postadhesion strengthening, intraluminal crawling, and different routes of transmigration. IVM revealed unique features of leukocyte recruitment in different organs. This review focuses on insights into the leukocyte adhesion cascade gained by IVM.

Protein kinase C-delta mediates von Willebrand factor secretion from endothelial cells in response to vascular endothelial growth factor (VEGF) but not histamine

BACKGROUND

Vascular endothelial growth factor (VEGF) and histamine induce von Willebrand factor (VWF) release from vascular endothelial cells. Protein kinase C (PKC) is involved in the control of exocytosis in many secretory cell types.

OBJECTIVES

We investigated the role of PKC and the interactions between PKC and Ca2+ signaling in both VEGF-induced and histamine-induced VWF secretion from human umbilical vein endothelial cells (HUVECs).

RESULTS

Several PKC inhibitors (staurosporine, Ro31-8220, myristoylated PKC peptide inhibitor and Go6983) block VEGF-induced but not histamine-induced VWF secretion. PKC-alpha and novel PKCs (PKC-delta, PKC-epsilon, and PKC-eta), but not PKC-beta, are expressed in HUVECs. Both VEGF and histamine activate PKC-delta. However, gene inactivation experiments using small interfering RNA indicate that PKC-delta (but not PKC-alpha) is involved in the regulation of VEGF-induced but not histamine-induced secretion. Both VEGF and histamine induce a rise in cytosolic free Ca2+ ([Ca2+]c), but the response to VEGF is weaker and even absent in a significant subset of cells. Furthermore, VEGF-induced secretion is largely preserved when the rise in [Ca2+]c is prevented by BAPTA-AM.

CONCLUSIONS

Our study identifies striking agonist specificities in signal-secretion coupling. Histamine-induced secretion is dependent on [Ca2+]c but not PKC, whereas VEGF-induced secretion is largely dependent on PKC-delta and significantly less on [Ca2+]c. Our data firmly establish the key role of PKC-delta in VEGF-induced VWF release, but suggest that a third, VEGF-specific, signaling intermediate is required as a PKC-delta coactivator.

Integrin alpha(v)beta(3) on human endothelial cells binds von Willebrand factor strings under fluid shear stress

Acutely secreted von Willebrand factor (VWF) multimers adhere to endothelial cells, support platelet adhesion, and may induce microvascular thrombosis. Immunofluorescence microscopy of live human umbilical vein endothelial cells showed that VWF multimers rapidly formed strings several hundred micrometers long on the cell surface after stimulation with histamine. Unexpectedly, only a subset of VWF strings supported platelet binding, which depended on platelet glycoprotein Ib. Electron microscopy showed that VWF strings often consisted of bundles and networks of VWF multimers, and each string was tethered to the cell surface by a limited number of sites. Several approaches implicated P-selectin and integrin alpha(v)beta(3) in anchoring VWF strings. An RGDS peptide or a function-blocking antibody to integrin alpha(v)beta(3) reduced the number of VWF strings formed. In addition, integrin alpha(v) decorated the VWF strings by immunofluorescence microscopy. Furthermore, lentiviral transduction of shRNA against the alpha(v) subunit reduced the expression of cell-surface integrin alpha(v)beta(3) and impaired the ability of endothelial cells to retain VWF strings. Soluble P-selectin reduced the number of platelet-decorated VWF strings in the absence of Ca(2+) and Mg(2+) but had no effect in the presence of these cations. These results indicate that VWF strings bind specifically to integrin alpha(v)beta(3) on human endothelial cells.

The vessel wall and its interactions

Blood cell interactions with the vessel wall were first documented almost 170 years ago. Modern advances have revealed that leukocyte and platelet interactions with the endothelium are at the nexus of complex, dynamic cellular and molecular networks that, when dysregulated, may lead to pathological inflammation and thrombosis, which are major sources of morbidity and mortality in the Western world. In this review, we relate the history of blood cell interactions with the vasculature, discuss recent progress, and raise some unresolved questions awaiting the field.

Inflammation, endothelium, and coagulation in sepsis

Sepsis is a systemic response to infection, and symptoms are produced by host defense systems rather than by the invading pathogens. Amongst the most prominent features of sepsis, contributing significantly to its outcome, is activation of coagulation with concurrent down-regulation of anticoagulant systems and fibrinolysis. Inflammation-induced coagulation on its turn contributes to inflammation. Another important feature of sepsis, associated with key symptoms such as hypovolemia and hypotension, is endothelial dysfunction. Under normal conditions, the endothelium provides for an anticoagulant surface, a property that is lost in sepsis. In this review, data about the interplay between inflammation and coagulation in sepsis are summarized with a special focus on the influence of the endothelium on inflammation-induced coagulation and vice versa. Possible procoagulant properties of the endothelium are described, such as expression of tissue factor (TF) and von Willebrand factor and interaction with platelets. Possible procoagulant roles of microparticles, circulating endothelial cells and endothelial apoptosis, are also discussed. Moreover, the important roles of the endothelium in down-regulating the anticoagulants TF pathway inhibitor, antithrombin, and the protein C (PC) system and inhibition of fibrinolysis are discussed. The influence of coagulation on its turn on inflammation and the endothelium is described with a special focus on protease-activated receptors (PARs). We conclude that the relationship between endothelium and coagulation in sepsis is tight and that further research is needed, for example, to better understand the role of activated PC signaling via PAR-1, the role of the endothelial PC receptor herein, and the role of the glycocalyx.

Angiotensin II directly triggers endothelial exocytosis via protein kinase C-dependent protein kinase D2 activation

Angiotensin II (AII) has been reported to induce leukocyte adhesion to endothelium through up-regulation of P-selectin surface expression. However, the underlying molecular and cellular mechanisms remain unknown. P-selectin is stored in Weibel-Palade bodies (WPBs), large secretory granules, in endothelial cells. In this study, we examined the role of protein kinase D (PKD), a newly identified regulator of protein transport, in AII-induced WPB exocytosis and the resultant P-selectin surface expression. We demonstrated that PKD2 was rapidly activated by AII in endothelial cells through phosphorylation of the activation loop at Ser744/748. AII-induced PKD2 activation correlated with increased P-selectin surface expression. Furthermore, AII-regulated PKD2 activation is protein kinase C (PKC) alpha-dependent. Importantly, knock-down of either PKD2 or PKCalpha expression inhibited AII-mediated P-selectin surface expression and monocyte adhesion. Our findings provide the first evidence that stimulation of P-selectin surface expression via PKCalpha-dependent PKD2 activation could be an important mechanism in the early onset of AII-initiated endothelial adhesiveness.

Trauma-associated lung injury differs clinically and biologically from acute lung injury due to other clinical disorders

OBJECTIVE

Patients with trauma-associated acute lung injury have better outcomes than patients with other clinical risks for lung injury, but the mechanisms behind these improved outcomes are unclear. We sought to compare the clinical and biological features of patients with trauma-associated lung injury with those of patients with other risks for lung injury and to determine whether the improved outcomes of trauma patients reflect their baseline health status or less severe lung injury, or both.

DESIGN, SETTING, AND PATIENTS

Analysis of clinical and biological data from 1,451 patients enrolled in two large randomized, controlled trials of ventilator management in acute lung injury.

MEASUREMENTS AND MAIN RESULTS

Compared with patients with other clinical risks for lung injury, trauma patients were younger and generally less acutely and chronically ill. Even after adjusting for these baseline differences, trauma patients had significantly lower plasma levels of intercellular adhesion molecule-1, von Willebrand factor antigen, surfactant protein-D, and soluble tumor necrosis factor receptor-1, which are biomarkers of lung epithelial and endothelial injury previously found to be prognostic in acute lung injury. In contrast, markers of acute inflammation, except for interleukin-6, and disordered coagulation were similar in trauma and nontrauma patients. Trauma-associated lung injury patients had a significantly lower odds of death at 90 days, even after adjusting for baseline clinical factors including age, gender, ethnicity, comorbidities, and severity of illness (odds ratio, 0.44; 95% confidence interval, 0.24-0.82; p = .01).

CONCLUSIONS

Patients with trauma-associated lung injury are less acutely and chronically ill than other lung injury patients; however, these baseline clinical differences do not adequately explain their improved outcomes. Instead, the better outcomes of the trauma population may be explained, in part, by less severe lung epithelial and endothelial injury.

Rate, extent and concentration dependence of histamine-evoked Weibel-Palade body exocytosis determined from individual fusion events in human endothelial cells

The rate, concentration dependence and extent of histamine-evoked Weibel-Palade body (WPB) exocytosis were investigated with time-resolved fluorescence microscopy in cultured human umbilical vein endothelial cells expressing WPB-targeted chimeras of enhanced green fluorescent protein (EGFP). Exocytosis of single WPBs was characterized by an increase in EGFP fluorescence, morphological changes and release of WPB contents. The fluorescence increase was due to a rise of intra-WPB pH from resting levels, estimated as pH 5.45+/-0.26 (s.d., n=144), to pH 7.40. It coincided with uptake of extracellular Alexa-647, indicating the formation of a fusion pore, prior to loss of fluorescent contents. Delays between the increase in intracellular free calcium ion concentration evoked by histamine and the first fusion event were 10.0+/-4.42 s (n=9 cells) at 0.3 microM histamine and 1.57+/-0.21 s (n=15 cells) at 100 microM histamine, indicating the existence of a slow process or processes in histamine-evoked WPB exocytosis. The maximum rates of exocytosis were 1.20+/-0.16 WPB s(-1) (n=9) at 0.3 microM and 3.66+/-0.45 WPB s(-1) at 100 microM histamine (n=15). These occurred 2-5 s after histamine addition and declined to lower rates with continued stimulation. The initial delays and maximal rate of exocytosis were unaffected by removal of external Ca2+ indicating that the initial burst of secretion is driven by Ca2+ release from internal stores, but sustained exocytosis required external Ca2+. Data were compared to exocytosis evoked by a maximal concentration of the strong secretagogue ionomycin (1 microM), for which there was a delay between calcium elevation and secretion of 1.67+/-0.24 s (n=6), and a peak fusion rate of approximately 10 WPB s(-1).

Delay of acute intracellular pH recovery after acidosis decreases endothelial cell activation

Reperfusion after ischemic conditions induces massive endothelial cell (EC) activation, an initial step of reperfusion injury. Reperfusion is characterized by reoxygenation, realkalinization and a localized increase of inflammatory stimuli. In this study, we focused on the influence of extracellular realkalinization on human umbilical vein endothelial cell (HUVEC) activation. We examined intracellular pH (pH(in)) and intracellular free calcium concentration ([Ca(2+)](in)), a second messenger known to mediate von Willebrand factor (VWF) exocytosis in endothelium, upon realkalinization. Furthermore, we measured the agonist-stimulated exocytosis of VWF, Interleukin-8 and soluble P-selectin (sP-Selectin) as markers of EC activation. To verify a morphological correlate of EC activation, we finally observed platelet-endothelial adherence during realkalinization using shear flow. Realkalinization of HUVEC was simulated by switching from bicarbonate buffered Ringer solution of an acidotic pH(ex) of 6.4 to a physiologic pH(ex) of 7.4. Extracellular realkalinization was accompanied by pH(in) recovery from 6.5 to 7.2 within 10 min. Application of cariporide, an inhibitor of the Na(+)/H(+) exchanger subtype 1 (NHE), during extracellular realkalinization significantly delayed the early kinetics of intracellular realkalinization. Histamine stimulated [Ca(2+)](in) was significantly increased upon realkalinization compared to control cells. Also agonist-stimulated release of VWF, Interleukin-8 and sP-Selectin was massively enhanced during pH(in) recovery in comparison to control. Furthermore, we observed an increased platelet binding to endothelium. Interestingly, each of these realkalinization-induced effects were significantly reduced by early application of cariporide. Therefore, delay of acute NHE-dependent pH(in) recovery may represent a promising mechanism for inhibition of EC activation upon reperfusion.

Cav3.1 (alpha1G) controls von Willebrand factor secretion in rat pulmonary microvascular endothelial cells

The T-type Ca2+ channel Cav3.1 subunit is present in pulmonary microvascular endothelial cells (PMVECs), but not in pulmonary artery endothelial cells (PAECs). The present study sought to assess the role of Cav3.1 in thrombin-induced Weibel-Palade body exocytosis and consequent von Willebrand factor (VWF) release. In PMVECs and PAECs transduced with a green fluorescent protein (GFP)-tagged VWF chimera, we examined the real-time dynamics and secretory process of VWF-GFP-containing vesicles in response to thrombin and the cAMP-elevating agent isoproterenol. Whereas thrombin stimulated a progressive decrease in the number of VWF-GFP-containing vesicles in both cell types, isoproterenol only decreased the number of VWF-GFP-containing vesicles in PAECs. In PMVECs, thrombin-induced decrease in the number of VWF-GFP-containing vesicles was nearly abolished by the T-type Ca2+ channel blocker mibefradil as well as by Cav3.1 gene silencing with small hairpin RNA. Expression of recombinant Cav3.1 subunit in PAECs resulted in pronounced increase in thrombin-stimulated Ca2+ entry, which is sensitive to mibefradil. Together, these data indicate that VWF secretion from lung endothelial cells is regulated by two distinct pathways involving Ca2+ or cAMP, and support the hypothesis that activation of Cav3.1 T-type Ca2+ channels in PMVECs provides a unique cytosolic Ca2+ source important for Gq-linked agonist-induced VWF release.

Early elevation of plasma von Willebrand factor antigen in pediatric acute lung injury is associated with an increased risk of death and prolonged mechanical ventilation

OBJECTIVE

Von Willebrand factor antigen (vWF-Ag) is a marker of pulmonary and systemic endothelial activation and injury. Adult studies indicate that patients with plasma vWF-Ag levels > or = 450% of control early in the course of acute lung injury (ALI) have an increased risk of death. The objective of this study was to evaluate whether vWF-Ag is elevated in the early phase of ALI in children and whether the magnitude of the increase was predictive of two important outcomes: mortality or duration of mechanical ventilation.

DESIGN

Two-center, prospective observational study.

SETTING

Two pediatric intensive care units: one in an academic university setting and one in a major community children's hospital.

PATIENTS

After appropriate consent, plasma was collected from 48 pediatric patients on day 1 of ALI, 45 patients on day 2 of ALI, and four intubated controls.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Mean PaO2/FiO2 at the onset of ALI was 140 +/- 70, and mortality rate was 17%. vWF-Ag levels on day 1 of ALI were higher in patients compared with controls (287 +/- 183 vs. 87 +/- 84% of control [mean +/- SD], p < .05). Patients with vWF-Ag levels > or = 450% of control on day 1 of ALI had a markedly greater risk of death (odds ratio, 7.0; confidence interval, 1.31, 37.30; p < .05). Multivariate analysis revealed that elevated vWF-Ag level and either presence of multiple organ system failure or Pediatric Risk of Mortality III score independently predict increased risk of death. vWF-Ag levels on day 2 of ALI were significantly higher in patients who required prolonged mechanical ventilation (316 +/- 173 vs. 191 +/- 89% of control, p < .05).

CONCLUSIONS

Early injury to the systemic and pulmonary endothelium, as measured by plasma vWF-Ag levels, is associated with an increased risk of death and prolonged mechanical ventilation in pediatric patients with ALI.

Tumor-derived matrix metalloproteinase-1 targets endothelial proteinase-activated receptor 1 promoting endothelial cell activation

In the vascular system, circulating tumor cells interact with endothelial cells. Tumor-endothelial cross-talk transforms the intravascular milieu to a prothrombotic, proinflammatory, and cell-adhesive state called endothelial cell activation (ECA). In the present study, we analyze the potential of metastatic tumor-derived soluble factors to transform the vascular endothelium into a prothrombotic and proinflammatory activated state. Supernatant from cultured melanoma and colon cancer cells (A375, WM9, A7, and HT-29) induced an acute activation of macrovascular and microvascular endothelial cells (human umbilical vein endothelial cells and human dermal microvascular endothelial cells) as shown by intracellular calcium flux and secretion of von Willebrand factor and interleukin-8, all markers of acute ECA. This process was inhibited using specific proteinase-activated receptor 1 (PAR1) inhibitors (RWJ-58259 and SCH-79797), indicating a mediating role for endothelial thrombin receptors. Immunofluorescence, Western blot analysis, and collagenase activity assay of tumor cells and culture supernatant revealed the presence of matrix metalloproteinase-1 (MMP-1), a recently described activator of PAR1. Inhibition of MMP-1 in supernatant from cultured tumor cells significantly attenuated ECA. Additional studies using isolated human MMP-1 (5 nmol/L) proved the presence of a functional MMP-1/PAR1 axis in tumor-endothelial communication. These findings show a new pathway of tumor-endothelial cross-talk via an intravascular MMP1/PAR1 axis in microvascular and macrovascular endothelium. Inhibition of this cross-talk may be a powerful means to prevent tumor-induced ECA and thus thrombotic and inflammatory cell adhesion.

Dopamine modulates von Willebrand factor secretion in endothelial cells via D2-D4 receptors

OBJECTIVE

von Willebrand factor (VWF) is acutely released from endothelial cells in response to numerous calcium-raising agents (e.g. thrombin, histamine) and cAMP-raising agents (e.g. epinephrine, adenosine, vasopressin). In contrast, very few inhibitors of endothelial VWF secretion have been described. The neurotransmitter dopamine is a modulator of exocytosis in several endocrine cells, and is possibly involved in the regulation of several endothelial cell functions. We therefore investigated the effect of dopamine on endothelial VWF secretion.

RESULTS

Dopamine, D2/D3- and D4-specific agonists inhibited histamine- but not thrombin-induced VWF secretion. Expression of dopamine D2, D3 and D4 receptors was demonstrated by reverse transcription polymerase chain reaction (RT-PCR) in both human aortic (HAEC) and umbilical vein (HUVEC) endothelial cells. D2-D4 agonists did not inhibit histamine-induced rise in [Ca(2+)](i): they inhibited histamine-induced secretion even in the absence of extracellular calcium. Thus, the dopamine effects are not mediated by [Ca(2+)](i)-dependent signalling. D2/D3- and D4-specific agonists inhibited neither the rise in cAMP nor VWF secretion in response to epinephrine and adenosine, arguing against an effect on cAMP-mediated signalling. D1 and D5 receptors were not detected in HAEC or HUVEC by RT-PCR, and the D1/D5-specific agonist SKF 38 393 failed to modulate VWF secretion, arguing against a role for these receptors in endothelial exocytosis.

CONCLUSIONS

Dopamine inhibits histamine-induced endothelial exocytosis by activating D2-D4 receptor, via a mechanism distinct from [Ca(2+)](i)-or cAMP-mediated signaling. In contrast, D1 and D5 receptors are not functionally expressed in cultured endothelial cells. Dopamine agonists may be useful as inhibitors of endothelial activation in inflammation and cardiovascular disease.

von Willebrand factor, endothelial dysfunction, and cardiovascular disease

von Willebrand factor (VWF), a glycoprotein involved in arterial thrombus formation, is released into the circulation by secretion from endothelial cells. Plasma VWF levels are determined by genetic factors including ABO blood groups and VWF mutations, and by non-genetic factors including aging, impaired nitric oxide production, inflammation, free radical production and diabetes. Plasma VWF levels have been proposed as a risk factor for cardiovascular events. Although they are only weakly associated with the risk of coronary heart disease (CHD) in the general population, they are a more promising CHD risk factor in high-risk populations with previous cardiovascular events, diabetes or old age. However, is it still unclear whether VWF levels directly determine the rate and severity of arterial thrombus formation or whether they merely reflect alteration in other endothelial functions. The future status of VWF levels as a cardiovascular risk factor depends on additional studies on the genetic determinants of both VWF levels and cardiovascular outcomes. Further studies on VWF levels as a predictor of the risk of stroke (rather than CHD) in elderly or other high-risk population are also promising. Such studies could lead to the clinical use of plasma VWF levels to refine the estimation of the cardiovascular risk and of the expected benefit of antithrombotic agents.

Systemic antithrombotic effects of ADAMTS13

The metalloprotease ADAMTS13 (a disintegrin-like and metalloprotease with thrombospondin type I repeats 13) cleaves highly adhesive large von Willebrand factor (VWF) multimers after their release from the endothelium. ADAMTS13 deficiency is linked to a life-threatening disorder, thrombotic thrombocytopenic purpura (TTP), characterized by platelet-rich thrombi in the microvasculature. Here, we show spontaneous thrombus formation in activated microvenules of Adamts13^−/− mice by intravital microscopy. Strikingly, we found that ADAMTS13 down-regulates both platelet adhesion to exposed subendothelium and thrombus formation in injured arterioles. An inhibitory antibody to ADAMTS13 infused in wild-type mice prolonged adhesion of platelets to endothelium and induced thrombi formation with embolization in the activated microvenules. Absence of ADAMTS13 did not promote thrombi formation in αIIbβ3 integrin-inhibited blood. Recombinant ADAMTS13 reduced platelet adhesion and aggregation in histamine-activated venules and promoted thrombus dissolution in injured arterioles. Our findings reveal that ADAMTS13 has a powerful natural antithrombotic activity and recombinant ADAMTS13 could be used as an antithrombotic agent.

Dynamics and plasticity of Weibel-Palade bodies in endothelial cells

Agonist-induced release of endothelial cell specific storage granules, designated Weibel-Palade bodies (WPBs), provides the endothelium with the ability to rapidly respond to changes in its micro-environment. Originally being defined as an intracellular storage pool for von Willebrand factor (VWF), it has recently been shown that an increasing number of other components, including P-selectin, interleukin (IL)-8, eotaxin-3, endothelin-1, and angiopoietin-2, is present within this subcellular organelle, implicating a role for WPB exocytosis in inflammation, hemostasis, regulation of vascular tone and angiogenesis. Recent studies emphasize that WPBs provide a dynamic storage compartment whose contents can be regulated depending on the presence of inflammatory mediators in the vascular micro-environment. Additionally, release of WPBs is tightly regulated and feedback mechanisms have been identified that prevent excessive release of bioactive components from this subcellular organelle. The ability to regulate both contents and exocytosis of WPBs endows these endothelial cell specific organelles with a remarkable plasticity. This is most likely needed to allow for controlled delivery of bioactive components into the circulation on vascular perturbation.

Dynein-dynactin complex mediates protein kinase A-dependent clustering of Weibel-Palade bodies in endothelial cells

OBJECTIVE

Perinuclear clustering is observed for several different organelles and illustrates dynamic regulation of the secretory pathway and organelle distribution. Previously, we observed that a subset of Weibel-Palade bodies (WPBs), endothelial cell-specific storage organelles, undergo centralization when endothelial cells are stimulated with cAMP-raising agonists of von Willebrand factor (vWF) secretion. In this study, we investigated this phenomenon of WPB clustering in more detail.

METHODS AND RESULTS

Our results demonstrate that the clustered WPBs are localized at the microtubule organizing center and that cluster formation depends on an intact microtubule network. Disruption of the microtubules by nocodazole completely abolished clustering, whereas treatment with the actin depolymerizing compound cytochalasin B had no effect on WPB clustering. Interfering with the dynein-dynactin interaction by overexpression of the p50 dynamitin subunit or the CC1 domain of the p150glued subunit of the dynactin complex completely inhibited perinuclear clustering of WPBs, suggesting that dynein activity mediates this process. Furthermore, we found that inhibition of dephosphorylation resulted in an increase in clustering, whereas inhibition of protein kinase A (PKA) markedly reduced WPB clustering.

CONCLUSIONS

These results suggest that perinuclear clustering of WPBs involves PKA-dependent regulation of the dynein-dynactin complex. Endothelial cell stimulation with epinephrine results in retrograde movement of a subset of WPBs to the microtubule organizing center. This minus-end directed transport requires an intact microtubular network and is mediated by the motor protein dynein. Together, our results suggest that epinephrine-induced clustering of WPBs involves PKA-dependent regulation of the dynein-dynactin complex.

Characterization of a Novel Chemokine-Containing Storage Granule in Endothelial Cells: Evidence for Preferential Exocytosis Mediated by Protein Kinase A and Diacylglycerol

We have recently shown that several proinflammatory chemokines can be stored in secretory granules of endothelial cells (ECs). Subsequent regulated exocytosis of such chemokines may then enable rapid recruitment of leukocytes to inflammatory sites. Although IL-8/CXCL8 and eotaxin-3/CCL26 are sorted to the rod-shaped Weibel-Palade body (WPB), we found that GROalpha/CXCL1 and MCP-1/CCL2 reside in small granules that, similarly to the WPB, respond to secretagogue stimuli. In the present study, we report that GROalpha and MCP-1 colocalized in 50- to 100-nm granules, which occur throughout the cytoplasm and at the cell cortex. Immunofluorescence confocal microscopy revealed no colocalization with multimerin or tissue plasminogen activator, i.e., proteins that are released from small granules of ECs by regulated exocytosis. Moreover, the GROalpha/MCP-1-containing granules were Rab27-negative, contrasting the Rab27-positive, WPB. The secretagogues PMA, histamine, and forskolin triggered distinct dose and time-dependent responses of GROalpha release. Furthermore, GROalpha release was more sensitive than IL-8 release to inhibitors and activators of PKA and PKC but not to an activator of Epac, a cAMP-regulated GTPase exchange factor, indicating that GROalpha release is regulated by molecular adaptors different from those regulating exocytosis of the WPB. On the basis of these findings, we designated the GROalpha/MCP-1-containing compartment the type 2 granule of regulated secretion in ECs, considering the WPB the type 1 compartment. In conclusion, we propose that the GROalpha/MCP-1-containing type 2 granule shows preferential responsiveness to important mediators of EC activation, pointing to the existence of selective agonists that would allow differential release of selected chemokines.

Neuropeptide Y expression, localization and cellular transducing effects in HUVEC

BACKGROUND INFORMATION

NPY (neuropeptide Y) may have an effect on the properties of vascular endothelial cells such as pro-angiogenic effects and potentiation of noradrenaline-induced vasoconstriction. In HUVEC (human umbilical-vein endothelial cells), immunoreactive neuropeptide Y has been detected, but NPY synthesis, storage and secretion have not been studied. The aim of the present study was to establish NPY expression, storage and cellular transducing effects in HUVEC.

RESULTS

HUVEC contain 0.19 fmol of NPY/microg of protein and 0.46 fmol of pro-NPY/microg of protein, as measured by ELISA. RT (reverse transcriptase)-PCR confirmed the expression of NPY in HUVEC. Immunofluorescence revealed the presence of NPY in small punctate structures, with a fluorescence pattern different from that observed for von Willebrand factor, indicating distinct storage compartments. Double labelling for NPY and Rab3A demonstrated similar granular patterns, with at least partial co-localization. Electron microscopy showed NPY immunoreactivity in vesicle-like cytoplasmic structures, of a fine fibrillar texture, as well as in mitochondria and in the nucleus. A similar general distribution pattern was also obtained for Rab3A. Y1 and Y2 receptors were expressed in HUVEC as assessed by RT-PCR, and they were functional since NPY induced a 42 nM intracellular calcium increase within 100 s, representing 22% of the histamine-induced response. In contrast with histamine, NPY did not induce acute von Willebrand factor secretion.

CONCLUSIONS

HUVEC produce, store and respond to NPY, suggesting an autocrine regulatory role for NPY in the endothelium.

Serum biomarkers in acute respiratory distress syndrome an ailing prognosticator

The use of biomarkers in medicine lies in their ability to detect disease and support diagnostic and therapeutic decisions. New research and novel understanding of the molecular basis of the disease reveals an abundance of exciting new biomarkers who present a promise for use in the everyday clinical practice. The past fifteen years have seen the emergence of numerous clinical applications of several new molecules as biologic markers in the research field relevant to acute respiratory distress syndrome (translational research). The scope of this review is to summarize the current state of knowledge about serum biomarkers in acute lung injury and acute respiratory distress syndrome and their potential value as prognostic tools and present some of the future perspectives and challenges.