PECAM-1: a multi-functional molecule in inflammation and vascular biology

Soluble platelet-endothelial cell adhesion molecule-1, a biomarker of ventilator-induced lung injury

Introduction

Endothelial cell injury is an important component of acute lung injury. Platelet-endothelial cell adhesion molecule-1 (PECAM1) is a transmembrane protein that connects endothelial cells to one another and can be detected as a soluble, truncated protein (sPECAM1) in serum. We hypothesized that injurious mechanical ventilation (MV) leads to shedding of PECAM1 from lung endothelial cells resulting in increasing sPECAM1 levels in the systemic circulation.

Methods

We studied 36 Sprague–Dawley rats in two prospective, randomized, controlled studies (healthy and septic) using established animal models of ventilator-induced lung injury. Animals (n = 6 in each group) were randomized to spontaneous breathing or two MV strategies: low tidal volume (V_T) (6 ml/kg) and high-V_T (20 ml/kg) on 2 cmH₂O of positive end-expiratory pressure (PEEP). In low-V_T septic animals, 10 cmH₂O of PEEP was applied. We performed pulmonary histological and physiological evaluation and measured lung PECAM1 protein content and serum sPECAM1 levels after four hours ventilation period.

Results

High-V_T MV caused severe lung injury in healthy and septic animals, and decreased lung PECAM1 protein content (P < 0.001). Animals on high-V_T had a four- to six-fold increase of mean sPECAM1 serum levels than the unventilated counterpart (35.4 ± 10.4 versus 5.6 ± 1.7 ng/ml in healthy rats; 156.8 ± 47.6 versus 35.6 ± 12.6 ng/ml in septic rats) (P < 0.0001). Low-V_T MV prevented these changes. Levels of sPECAM1 in healthy animals on high-V_T MV paralleled the sPECAM1 levels of non-ventilated septic animals.

Conclusions

Our findings suggest that circulating sPECAM1 may represent a promising biomarker for the detection and monitoring of ventilator-induced lung injury.

Humanized-BLT mouse model of Kaposi's sarcoma-associated herpesvirus infection

Lack of an effective small-animal model to study the Kaposi's sarcoma-associated herpesvirus (KSHV) infection in vivo has hampered studies on the pathogenesis and transmission of KSHV. The objective of our study was to determine whether the humanized BLT (bone marrow, liver, and thymus) mouse (hu-BLT) model generated from NOD/SCID/IL2rγ mice can be a useful model for studying KSHV infection. We have tested KSHV infection of hu-BLT mice via various routes of infection, including oral and intravaginal routes, to mimic natural routes of transmission, with recombinant KSHV over a 1- or 3-mo period. Infection was determined by measuring viral DNA, latent and lytic viral transcripts and antigens in various tissues by PCR, in situ hybridization, and immunohistochemical staining. KSHV DNA, as well as both latent and lytic viral transcripts and proteins, were detected in various tissues, via various routes of infection. Using double-labeled immune-fluorescence confocal microscopy, we found that KSHV can establish infection in human B cells and macrophages. Our results demonstrate that KSHV can establish a robust infection in the hu-BLT mice, via different routes of infection, including the oral mucosa which is the most common natural route of infection. This hu-BLT mouse not only will be a useful model for studying the pathogenesis of KSHV in vivo but can potentially be used to study the routes and spread of viral infection in the infected host.

Thioredoxin-interacting protein is a biomechanical regulator of Src activity: key role in endothelial cell stress fiber formation

RATIONALE

Fluid shear stress differentially regulates endothelial cell stress fiber formation with decreased stress fibers in areas of disturbed flow compared with steady flow areas. Importantly, stress fibers are critical for several endothelial cell functions including cell shape, mechano-signal transduction, and endothelial cell-cell junction integrity. A key mediator of steady flow-induced stress fiber formation is Src that regulates downstream signaling mediators such as phosphorylation of cortactin, activity of focal adhesion kinase, and small GTPases.

OBJECTIVE

Previously, we showed that thioredoxin-interacting protein (TXNIP, also VDUP1 [vitamin D upregulated protein 1] and TBP-2 [thioredoxin binding protein 2]) was regulated by fluid shear stress; TXNIP expression was increased in disturbed flow compared with steady flow areas. Although TXNIP was originally characterized for its role in redox and metabolic cellular functions, recent reports show important scaffold functions related to its α-arrestin structure. Based on these findings, we hypothesized that TXNIP acts as a biomechanical sensor that regulates Src kinase activity and stress fiber formation.

METHODS AND RESULTS

Using en face immunohistochemistry of the aorta and cultured endothelial cells, we show inverse relationship between TXNIP expression and Src activity. Specifically, steady flow increased Src activity and stress fiber formation, whereas it decreased TXNIP expression. In contrast, disturbed flow had opposite effects. We studied the role of TXNIP in regulating Src homology phosphatase-2 plasma membrane localization and vascular endothelial cadherin binding because Src homology phosphatase-2 indirectly regulates dephosphorylation of Src tyrosine 527 that inhibits Src activity. Using immunohistochemistry and immunoprecipitation, we found that TXNIP prevented Src homology phosphatase-2-vascular endothelial cadherin interaction.

CONCLUSIONS

In summary, these data characterize a fluid shear stress-mediated mechanism for stress fiber formation that involves a TXNIP-dependent vascular endothelial cadherin-Src homology phosphatase-2-Src pathway.

High proliferative potential endothelial colony-forming cells contribute to hypoxia-induced pulmonary artery vasa vasorum neovascularization

Angiogenic expansion of the vasa vasorum (VV) is an important contributor to pulmonary vascular remodeling in the pathogenesis of pulmonary hypertension (PH). High proliferative potential endothelial progenitor-like cells have been described in vascular remodeling and angiogenesis in both systemic and pulmonary circulations. However, their role in hypoxia-induced pulmonary artery (PA) VV expansion in PH is not known. We hypothesized that profound PA VV neovascularization observed in a neonatal calf model of hypoxia-induced PH is due to increased numbers of subsets of high proliferative cells within the PA adventitial VV endothelial cells (VVEC). Using a single cell clonogenic assay, we found that high proliferative potential colony-forming cells (HPP-CFC) comprise a markedly higher percentage in VVEC populations isolated from the PA of hypoxic (VVEC-Hx) compared with control (VVEC-Co) calves. VVEC-Hx populations that comprised higher numbers of HPP-CFC also demonstrated markedly higher expression levels of CD31, CD105, and c-kit than VVEC-Co. In addition, significantly higher expression of CD31, CD105, and c-kit was observed in HPP-CFC vs. the VVEC of the control but not of hypoxic animals. HPP-CFC exhibited migratory and tube formation capabilities, two important attributes of angiogenic phenotype. Furthermore, HPP-CFC-Co and some HPP-CFC-Hx exhibited elevated telomerase activity, consistent with their high replicative potential, whereas a number of HPP-CFC-Hx exhibited impaired telomerase activity, suggestive of their senescence state. In conclusion, our data suggest that hypoxia-induced VV expansion involves an emergence of HPP-CFC populations of a distinct phenotype with increased angiogenic capabilities. These cells may serve as a potential target for regulating VVEC neovascularization.

PECAM-1-dependent heme oxygenase-1 regulation via an Nrf2-mediated pathway in endothelial cells

The antioxidant enzyme heme oxygenase (HO)-1, which catalyses the first and rate-limiting step of heme degradation, has major anti-inflammatory and immunomodulatory effects via its cell-type-specific functions in the endothelium. In the current study, we investigated whether the key endothelial adhesion and signalling receptor PECAM-1 (CD31) might be involved in the regulation of HO-1 gene expression in human endothelial cells (ECs). To this end PECAM-1 expression was down-regulated in human umbilical vein ECs (HUVECs) by an adenoviral vector-based knockdown approach. PECAM-1 knockdown markedly induced HO-1, but not the constitutive HO isoform HO-2. Nuclear translocation of the transcription factor NF-E2-related factor-2 (Nrf2), which is a master regulator of the inducible antioxidant cell response, and intracellular levels of reactive oxygen species (ROS) were increased in PECAM-1-deficient HUVECs, respectively. PECAM-1-dependent HO-1 regulation was also examined in PECAM-1 over-expressing Chinese hamster ovary and murine L-cells. Endogenous HO-1 gene expression and reporter gene activity of transiently transfected luciferase HO-1 promoter constructs with Nrf2 target sequences were decreased in PECAM-1 over-expressing cells. Moreover, a regulatory role of ROS for HO-1 regulation in these cells is demonstrated by studies with the antioxidant N-acetylcysteine and exogenous hydrogenperoxide. Finally, direct interaction of PECAM-1 with a native complex of its binding partner NB1 (CD177) and serine proteinase 3 (PR3) from human neutrophils, markedly induced HO-1 expression in HUVECs. Taken together, we demonstrate a functional link between HO-1 gene expression and PECAM-1 in human ECs, which might play a critical role in the regulation of inflammation.

PECAM-1: regulator of endothelial junctional integrity

PECAM-1 (also known as CD31) is a cellular adhesion and signaling receptor comprising six extracellular immunoglobulin (Ig)-like homology domains, a short transmembrane domain and a 118 amino acid cytoplasmic domain that becomes serine and tyrosine phosphorylated upon cellular activation. PECAM-1 expression is restricted to blood and vascular cells. In circulating platelets and leukocytes, PECAM-1 functions largely as an inhibitory receptor that, via regulated sequential phosphorylation of its cytoplasmic domain, limits cellular activation responses. PECAM-1 is also highly expressed at endothelial cell intercellular junctions, where it functions as a mechanosensor, as a regulator of leukocyte trafficking and in the maintenance of endothelial cell junctional integrity. In this review, we will describe (1) the functional domains of PECAM-1 and how they contribute to its barrier-enhancing properties, (2) how the physical properties of PECAM-1 influence its subcellular localization and its ability to influence endothelial cell barrier function, (3) various stimuli that initiate PECAM-1 signaling and/or function at the endothelial junction and (4) cross-talk of PECAM-1 with other junctional molecules, which can influence endothelial cell function.

Physiological and pathological angiogenesis in the adult pulmonary circulation

Angiogenesis occurs during growth and physiological adaptation in many systemic organs, for example, exercise-induced skeletal and cardiac muscle hypertrophy, ovulation, and tissue repair. Disordered angiogenesis contributes to chronic inflammatory disease processes and to tumor growth and metastasis. Although it was previously thought that the adult pulmonary circulation was incapable of supporting new vessel growth, over that past 10 years new data have shown that angiogenesis within this circulation occurs both during physiological adaptive processes and as part of the pathogenic mechanisms of lung diseases. Here we review the expression of vascular growth factors in the adult lung, their essential role in pulmonary vascular homeostasis and the changes in their expression that occur in response to physiological challenges and in disease. We consider the evidence for adaptive neovascularization in the pulmonary circulation in response to alveolar hypoxia and during lung growth following pneumonectomy in the adult lung. In addition, we review the role of disordered angiogenesis in specific lung diseases including idiopathic pulmonary fibrosis, acute adult distress syndrome and both primary and metastatic tumors of the lung. Finally, we examine recent experimental data showing that therapeutic enhancement of pulmonary angiogenesis has the potential to treat lung diseases characterized by vessel loss.

PECAM-1 phosphorylation and tissue factor expression in HUVECs exposed to uniform and disturbed pulsatile flow and chemical stimuli

INTRODUCTION

We analyzed the relationship between platelet endothelial cell adhesion molecule-1 (PECAM-1) activation and tissue factor (TF) RNA expression in human umbilical vein endothelial cells (HUVECs) exposed to mechanical and chemical stimulation.

METHODS

Fifty percent confluent and 100% confluent HUVEC cultures were exposed to pulsatile forward flow, as a model for uniform flow, or pulsatile to-and-fro flow, as a model for disturbed flow, using a parallel-plate flow chamber system for up to 4 hours in the presence or absence of 4 U/mL thrombin. Protein lysates were immunoprecipitated for PECAM-1 and then immunoblotted with anti-phospho-tyrosine antibody. TF RNA expression was determined using quantitative reverse transcription polymerase chain reaction.

RESULTS

HUVECs exposed to disturbed flow induced higher TF expression at 4 hours than HUVECs exposed to uniform flow in sparse cultures (16.8 ± 5.8 vs 5.1 ± 1.2; P < .05). HUVECs exposed to disturbed flow and thrombin induced higher TF RNA expression at 4 hours than cultures exposed to uniform flow and thrombin in both confluent (47.0 ± 6.0 vs 30.2 ± 4.9; P < .05) and sparse (72.3 ± 10.7 vs 49.8 ± 4.7; P < .05) cultures. In confluent HUVEC cultures, PECAM-1 is minimally phosphorylated by disturbed and uniform flow, while in sparse HUVEC cultures, PECAM-1 phosphorylation at 15 minutes is greater in both disturbed and uniform flow (2.0 ± 0.2 and 2.1 ± 0.4 respectively; P < .05). Thrombin treatment of static HUVECs exhibited greater PECAM-1 phosphorylation at 15 minutes in confluent compared with sparse cultures (3.0 ± 0.5 vs 2.3 ± 0.1; P < .05). PECAM-1 phosphorylation of HUVECs exposed to both flow and thrombin is significantly higher in sparse cultures compared with either flow or thrombin stimulation alone but was suppressed in confluent cultures.

CONCLUSIONS

The significantly higher TF RNA expression induced by disturbed flow and cell confluence indicates that suppression of PECAM-1 phosphorylation may be an important contributory mechanical signal pathway that promotes TF expression when HUVECs are exposed to disturbed flow.

The effects of pneumatic tube transport on fresh and stored platelets in additive solution

BACKGROUND

Limited scientific work has been conducted on potential in vitro effects of transport on pneumatic tube systems on blood components, in particular platelets.

MATERIALS AND METHODS

To evaluate the possible effects of the Swisslog TranspoNet system on the cellular, metabolic, phenotypic and secreting properties of fresh and stored platelets, we set up a four-arm paired study comparing transported and non-transported platelets. Platelets were aliquoted, prepared with the OrbiSac system and suspended in 70% SSP+ (n=8). All in vitro parameters were monitored over a 7-day storage period.

RESULTS

Throughout storage, no differences were observed in glucose consumption, lactate production, pH, pCO2, ATP, hypotonic shock response reactivity, CD62P, PAC-1, platelet endothelial cell adhesion molecule-1 or CD42b. The release of sCD40L increased (p<0.01) in all units but without any significant differences between groups.

CONCLUSION

The storage stability of all platelets conveyed by the Swisslog TranspoNet system was not impaired throughout 7 days of storage. The Swisslog TranspoNet system does not, therefore, seem to be a risk for increased metabolic activity, activation or release reactions from the platelets. This lack of effect of the pneumatic tube transport system did not seem to be affected by the age of the platelets or repeated transport.

Interleukin-4 induces up-regulation of endothelial cell claudin-5 through activation of FoxO1: role in protection from complement-mediated injury

Injury to endothelial cells (ECs) often results in cell retraction and gap formation. When caused by antigen aggregation or complement, this injury can be prevented by pretreatment of the ECs with IL-4, suggesting that IL-4 modifies the intercellular junction. Therefore, we investigated the effects of IL-4 on expression of intercellular junction proteins and whether such effects are required for IL-4-induced resistance of ECs against complement-mediated injury. We found that IL-4 induces upregulation of the junction protein claudin-5 in porcine ECs through activation of Jak/STAT6 and phosphorylation and translocation of FoxO1 from the nucleus to the cytoplasm. Increased claudin-5 expression resulted in increased transmembrane electrical resistance of the endothelial monolayer and participated in IL-4-induced protection of the ECs from complement injury. Down-regulation of FoxO1 using siRNA by itself caused up-regulation of claudin-5 expression and partial protection from cytotoxicity. This protection was enhanced by stimulation with IL-4. We previously reported that increased phospholipid synthesis and mitochondrial protection were required for IL-4-induced resistance of ECs against complement injury and now we demonstrate a contribution of claudin-5 expression in IL-4-induced protection.

Isolation, characterization, and transplantation of cardiac endothelial cells

Isolation and ex vivo expansion of cardiac endothelial cells have been a recurrent challenge due to difficulties in isolation, cell heterogeneity, lack of specific markers to identify myocardial endothelial cells, and inadequate conditions to maintain long-term cultures. Herein, we developed a method for isolation, characterization, and expansion of cardiac endothelial cells applicable to study endothelial cell biology and clinical applications such as neoangiogenesis. First, we dissociated the cells from murine heart by mechanical disaggregation and enzymatic digestion. Then, we used flow cytometry coupled with specific markers to isolate endothelial cells from murine hearts. CD45+ cells were gated out to eliminate the hematopoietic cells. CD31+/Sca-1+ cells were isolated as endothelial cells. Cells isolated from atrium grew faster than those from ventricle. Cardiac endothelial cells maintain endothelial cell function such as vascular tube formation and acetylated-LDL uptake in vitro. Finally, cardiac endothelial cells formed microvessels in dorsal matrigel plug and engrafted in cardiac microvessels following intravenous and intra-arterial injections. In conclusion, our multicolor flow cytometry method is an effective method to analyze and purify endothelial cells from murine heart, which in turn can be ex vivo expanded to study the biology of endothelial cells or for clinical applications such as therapeutic angiogenesis.

Angiogenesis and lymphangiogenesis in the spectrum of leprosy and its reactional forms

Background

Angiogenesis and lymphangiogenesis are the processes of neovascularization that evolve from preexisting blood and lymphatic vessels. There are few studies on angiogenesis and none on lymphangiogenesis in leprosy. Thus, the role of neovascularization in the pathophysiological mechanisms of the disease was studied across the spectrum of leprosy, its reactional states and its residual lesions.

Methodology/Principal Findings

Seventy-six biopsies of leprosy skin lesions and seven healthy controls were selected. Fifty-five serum samples were used for the detection of CD105 by ELISA. Histological sections were stained with antibodies against CD31 (blood and lymphatic vessels), D2-40/podoplanin (lymphatic vessels), and CD105/endoglin (neovessels). Microvessels were counted in 100 high-power fields (400x) and the number of vessels was evaluated in relation to the extension of the inflammatory infiltrate (0-3), to the bacillary index (0-6) and to the clinical forms. Angiogenesis, as marked by CD31 and CD105, was observed across the leprosy spectrum, compared with the controls. Additionally, there was a positive correlation between these markers with extension of the infiltrate (p <0.0001). For D2/40, lymphangiogenesis was observed in the tuberculoid form (p <0.0001). There was no statistical significance for values of CD105 detected in plasma by ELISA.

Conclusions/Significance

Angiogenesis is present across the spectrum of leprosy and in its reactional forms. The increase in the number of vessels, as detected by CD31 and CD105 staining, is related to the extension of the inflammatory infiltrate. Samples from reactional lesions have a higher number of CD31+ and CD105+ stained vessels, which indicates their involvement in the pathophysiological mechanisms of the reactional states. The regression of lesions is accompanied by the regression of neovascularization. Drugs inhibiting angiogenesis may be relevant in the treatment of leprosy, in addition to multidrugtherapy, and in the prevention of the development of reactions.

Is MS an inflammatory or primary degenerative disease?

Multiple sclerosis (MS) is characterized by multiple areas of inflammation, demyelination and neurodegeneration. Multiple molecular and cellular components mediate neuroinflammation in MS. They involve: adhesion molecules, chemokines, cytokines, matalloproteases and the following cells: CD4+ T cells, CD8+ T cells, B cells, microglia and macrophages. Infiltrating Th1 CD4+ T cells secrete proinflammatory cytokines. They stimulate the release of chemokines, expression of adhesion molecules and can be factors that cause damage to the myelin sheath and axons. Chemokines stimulate integrin activation, mediate leukocyte locomotion on endothelial cells and participate in transendothelial migration. CD8+ cells can directly damage axons. B cells are involved in the production of antibodies which can participate in demyelination. B cells can also function as antigen presenting cells and contribute to T cell activation. Neuroinflammation is not only present in relapsing-remitting MS, but also in the secondary and primary progressive forms of the disease. The association between inflammation consisting of T cells, B cells, plasma cells and macrophages and axonal injury exists in MS patients including the progressive forms of the disease. The above association does not exclude the possibility that neurodegeneration can exist independently from inflammation. Very little inflammation is seen in cortical MS plaques. Anti-inflammatory therapies with different mode of action change the course of MS. Anti-inflammatory and immunomodulatory treatments are beneficial in the early relapsing stage of MS, but these treatments are ineffective in secondary progressive and primary progressive MS. In the stage of progressive MS, inflammation becomes trapped behind a closed or repaired blood-brain barrier. In such a situation current immunomodulatory, immunosuppressive or anti-inflammatory treatments might not reach this inflammatory process to exert a beneficial effect.

A glimpse of the glomerular milieu: from endothelial cell to thrombotic disease in nephrotic syndrome

Patients with nephrotic syndrome (NS) carry a high risk of venous thromboembolism (VTE) due to the abnormalities in coagulation and fibrinolysis. Although massive urine protein loss is considered to trigger the cascade of hypercoagulation, the exact nature of VTE in NS patients still remains obscure, especially in some cases when VTE occurs far before the presence of nephrotic proteinuria. Recent findings illustrate that loss of local glomerular homeostasis, like disturbance of cytokine profiles in endothelial cells or aberrant cellular crosstalks in glomerulus, is sufficient to initiate the development of thrombotic disease in glomerulonephropathy. Emerging data have highlighted the glomerular endothelial cell as a key regulator of local homeostasis, which might mediate the haemostatic derangement in the beginning of glomerular disease by expression of numerous prothrombotic factors and result in the subsequent predilection of VTE in NS. As the glomerulus-derived circulating factors are all collected and flushed into the renal vein directly, it is reasonable to suggest that increased release of glomerulus-derived thrombotic regulators, particularly from endothelial cells, may play a significant role in the highest proclivity for the renal vein as the site of thrombosis in NS. In this review, we thus discuss the current understandings of thromboembolism in NS with focus on how the glomerular endothelial cell involves in the pathogenesis of VTE, which may help to increase our understandings in the anti-thrombotic therapy for patients with NS.

The regulation of T-cell recruitment to the human liver during acute liver failure

BACKGROUND & AIMS

Acute liver failure (ALF) is a rare clinical syndrome with high mortality resulting from hepatocellular necrosis and loss of function. In seronegative hepatitis (SNH), a T-cell-rich infiltrate leads to immune-mediated hepatocyte destruction, whereas in paracetamol poisoning, toxic metabolites induce hepatocyte necrosis, followed by a macrophage-rich, lymphocytic infiltrate that is an important factor in driving repair and regeneration. The nature of the hepatic inflammatory infiltrate, key to ALF pathogenesis and outcome, is determined by the recruitment of effector cells from blood, but the molecular basis of recruitment is poorly understood. To determine the phenotype of circulating and hepatic lymphocytes in patients with ALF secondary to paracetamol overdose (POD) or SNH and investigate the molecular basis of lymphocyte recruitment.

METHODS

We used FACS, immunohistochemistry and flow-based adhesion assays to determine the regulation of lymphocyte adhesion.

RESULTS

SNH and POD intrahepatic lymphocytes were αLβ2(hi), CD69(hi) and CD38(hi) with a distinct homing phenotype being L-selectin(lo), CXCR3(hi) and CCR5(+). Expression of chemokine ligands for the receptors CCR5, CXCR3 and CXCR6 and the adhesion molecules ICAM-1, VCAM-1 and VAP-1 was markedly increased in the liver in ALF. Lymphocytes isolated from the livers of patients with SNH showed enhanced chemokine-dependent adhesion and transmigration across the human hepatic endothelium in vitro under flow and used a combination of β1 and β2 integrins to adhere to endothelium and β2 integrins, CD31 and VAP-1 to transmigrate.

CONCLUSION

Aetiology-dependent combinations of adhesion molecules and chemokines expressed within tissue during ALF recruit lymphocytes with a distinct homing phenotype.

Cardiovascular repair with bone marrow-derived cells

While bone marrow (BM)-derived cells have been comprehensively studied for their propitious pre-clinical results, clinical trials have shown controversial outcomes. Unlike previously acknowledged, more recent studies have now confirmed that humoral and paracrine effects are the key mechanisms for tissue regeneration and functional recovery, instead of transdifferentiation of BM-derived cells into cardiovascular tissues. The progression of the understanding of BM-derived cells has further led to exploring efficient methods to isolate and obtain, without mobilization, sufficient number of cell populations that would eventually have a higher therapeutic potential. As such, hematopoietic CD31⁺ cells, prevalent in both bone marrow and peripheral blood, have been discovered, in recent studies, to have angiogenic and vasculogenic activities and to show strong potential for therapeutic neovascularization in ischemic tissues. This article will discuss recent advancement on BM-derived cell therapy and the implication of newly discovered CD31⁺ cells.

A review of the current status of siRNA nanomedicines in the treatment of cancer

RNA interference currently offers new opportunities for gene therapy by the specific extinction of targeted gene(s) in cancer diseases. However, the main challenge for nucleic acid delivery still remains its efficacy through intravenous administration. Over the last decade, many delivery systems have been developed and optimized to encapsulate siRNA and to specifically promote their delivery into tumor cells and improve their pharmacokinetics for anti-cancer purposes. This review aims to sum up the potential targets in numerous pathways and the properties of recently optimized siRNA synthetic nanomedicines with their preclinical applications and efficacy. Future perspectives in cancer treatment are discussed including promising concomitant treatment with chemotherapies or other siRNA. The outcomes in human clinical trials are also presented.

Stat2 loss leads to cytokine-independent, cell-mediated lethality in LPS-induced sepsis

Deregulated Toll-like receptor (TLR)-triggered inflammatory responses that depend on NF-κB are detrimental to the host via excessive production of proinflammatory cytokines, including TNF-α. Stat2 is a critical component of type I IFN signaling, but it is not thought to participate in TLR signaling. Our study shows that LPS-induced lethality in Stat2(-/-) mice is accelerated as a result of increased cellular transmigration. Blocking intercellular adhesion molecule-1 prevents cellular egress and confers survival of Stat2(-/-) mice. The main determinant of cellular egress in Stat2(-/-) mice is the genotype of the host and not the circulating leukocyte. Surprisingly, lethality and cellular egress observed on Stat2(-/-) mice are not associated with excessive increases in classical sepsis cytokines or chemokines. Indeed, in the absence of Stat2, cytokine production in response to multiple TLR agonists is reduced. We find that Stat2 loss leads to reduced expression of NF-κB target genes by affecting nuclear translocation of NF-κB. Thus, our data reveal the existence of a different mechanism of LPS-induced lethality that is independent of NF-κB triggered cytokine storm but dependent on cellular egress.

The effects of ezetimibe/simvastatin versus simvastatin monotherapy on platelet and inflammatory biomarkers in patients with metabolic syndrome

In a randomized, double-blind, crossover study of 15 aspirin-naive patients (mean age 48.8 ± 10.2 years) with the metabolic syndrome, statin monotherapy (simvastatin 40 mg daily) was compared to combination therapy (simvastatin 40 mg and ezetimibe 10 mg daily) on biomarkers of inflammation and platelet activity. The addition of ezetimibe to simvastatin over a 4-week period was associated with reduced expression of CD141 (thrombomodulin; p = 0.02), platelet endothelial cell adhesion molecule (p < 0.0001) and CD51/61 (vitronectin receptor; p = 0.048) compared to statin monotherapy. Ezetimibe added to simvastatin improves several indices of platelet reactivity beyond statin monotherapy. However, the clinical relevance of these findings await results of the IMPROVE-IT trial (Improved Reduction of Outcomes: Vytorin Efficacy International Trial).

Circulating CD31+ leukocyte frequency is associated with cardiovascular risk factors

OBJECTIVES

CD31 identifies a heterogeneous population of cells in the blood, consisting of mature leukocytes and platelets, as well as smaller numbers of endothelial and progenitor cells. Because unfractionated CD31+ blood cells have demonstrated angiogenic properties in vivo, we hypothesized that circulating CD31+ cells would be related to the presence of cardiovascular risk factors in humans.

METHODS AND RESULTS

We studied 1487 participants, free of cardiovascular disease, from the Framingham Offspring Study. Using anti-human CD31 and CD45 antibodies, distinct CD31+/CD45+ leukocyte populations were enumerated in blood samples by FACS analysis. We used linear regression analyses to investigate the relation of each cell phenotype with cardiovascular risk factors. We identified 3 distinct leukocyte populations: CD31-, CD31 dim, and CD31 bright cells. Using forward/side scatter analyses, CD31- and CD31 dim cells mapped to lymphoid gates while CD31 bright cells were monocytoid. In multivariable analyses, higher frequency of CD31 bright cells was associated with older age, male sex, HDL cholesterol, and CRP (all P < 0.01). In contrast, CD31 dim was inversely associated with age, male sex, CRP, and smoking (all P < 0.01). Framingham Risk Score was positively associated with CD31 bright frequency (P = 0.002), and negatively associated with CD31 dim frequency (P = 0.020).

CONCLUSIONS

CD31+ staining identifies 2 major leukocyte populations, CD31 bright and CD31 dim, which demonstrated significant and opposite associations with cardiovascular risk in humans. Further research is needed to define the biological and potential therapeutic roles of CD31+ subpopulations in vascular disease.

Rapid decrease in tumor perfusion following VEGF blockade predicts long-term tumor growth inhibition in preclinical tumor models

Vascular endothelial growth factor (VEGF) is a key upstream mediator of tumor angiogenesis, and blockade of VEGF can inhibit tumor angiogenesis and decrease tumor growth. However, not all tumors respond well to anti-VEGF therapy. Despite much effort, identification of early response biomarkers that correlate with long-term efficacy of anti-VEGF therapy has been difficult. These difficulties arise in part because the functional effects of VEGF inhibition on tumor vessels are still unclear. We therefore assessed rapid molecular, morphologic and functional vascular responses following treatment with aflibercept (also known as VEGF Trap or ziv-aflibercept in the United States) in preclinical tumor models with a range of responses to anti-VEGF therapy, including Colo205 human colorectal carcinoma (highly sensitive), C6 rat glioblastoma (moderately sensitive), and HT1080 human fibrosarcoma (resistant), and correlated these changes to long-term tumor growth inhibition. We found that an overall decrease in tumor vessel perfusion, assessed by dynamic contrast-enhanced ultrasound (DCE-US), and increases in tumor hypoxia correlated well with long-term tumor growth inhibition, whereas changes in vascular gene expression and microvessel density did not. Our findings support previous clinical studies showing that decreased tumor perfusion after anti-VEGF therapy (measured by DCE-US) correlated with response. Thus, measuring tumor perfusion changes shortly after treatment with VEGF inhibitors, or possibly other anti-angiogenic therapies, may be useful to predict treatment efficacy.

The Role of Platelet-Endothelial Cell Adhesion Molecule-1 in Atheroma Formation Varies Depending on the Site-Specific Hemodynamic Environment

Objective—

Polymorphisms in the platelet-endothelial cell adhesion molecule (PECAM-1)-1 gene are linked to increased risk of coronary artery disease. Because PECAM-1 has been demonstrated to form a mechanosensory complex that can modulate inflammatory responses in murine arterial endothelial cells, we hypothesized that PECAM-1 contributes to atherogenesis in a shear-dependent and site-specific manner.

Approach and Results—

ApoE –/– mice that were wild-type, heterozygous, or deficient in PECAM-1 were placed on a high-fat diet. Detailed analysis of the aorta at sites with differing hemodynamics revealed that PECAM-1–deficient mice had reduced disease in areas of disturbed flow, whereas plaque burden was increased in areas of steady, laminar flow. In concordance with these observations, bone marrow chimera experiments revealed that hematopoietic PECAM-1 resulted in accelerated atheroma formation in areas of laminar and disturbed flow, however endothelial PECAM-1 moderated disease progression in areas of high sheer stress. Moreover, using shear stress–modifying carotid cuffs, PECAM-1 was shown to promote macrophage recruitment into lesions developing in areas of low shear stress.

Conclusions—

PECAM-1 on bone marrow cells is proatherogenic irrespective of the hemodynamic environment, however endothelial cell PECAM-1 is antiatherogenic in high shear environments. Thus, targeting this pathway therapeutically would require a cell-type and context-specific strategy.

Absence of platelet endothelial cell adhesion molecule 1, PECAM-1/CD31, in vivo increases resistance to Salmonella enterica serovar Typhimurium in mice

PECAM-1/CD31 is known to regulate inflammatory responses and exhibit pro- and anti-inflammatory functions. This study was designed to determine the functional role of PECAM-1 in susceptibility to murine primary in vivo infection with Salmonella enterica serovar Typhimurium and in in vitro inflammatory responses of peritoneal macrophages. Lectin profiling showed that cellular PECAM-1 and recombinant human PECAM-1-Ig chimera contain high levels of mannose sugars and N-acetylglucosamine. Consistent with this carbohydrate pattern, both recombinant human and murine PECAM-1-Ig chimeras were shown to bind S. Typhimurium in a dose-dependent manner in vitro. Using oral and fecal-oral transmission models of S. Typhimurium SL1344 infection, PECAM-1(-/-) mice were found to be more resistant to S. Typhimurium infection than wild-type (WT) C57BL/6 mice. While fecal shedding of S. Typhimurium was comparable in wild-type and PECAM-1(-/-) mice, the PECAM-1-deficient mice had lower bacterial loads in systemic organs such as liver, spleen, and mesenteric lymph nodes than WT mice, suggesting that extraintestinal dissemination was reduced in the absence of PECAM-1. This reduced bacterial load correlated with reduced tumor necrosis factor (TNF), interleukin-6 (IL-6), and monocyte chemoattractant protein (MCP) levels in sera of PECAM-1(-/-) mice. Following in vitro stimulation of macrophages with either whole S. Typhimurium, lipopolysaccharide (LPS) (Toll-like receptor 4 [TLR4] ligand), or poly(I·C) (TLR3 ligand), production of TNF and IL-6 by PECAM-1(-/-) macrophages was reduced. Together, these results suggest that PECAM-1 may have multiple functions in resistance to infection with S. Typhimurium, including binding to host cells, extraintestinal spread to deeper tissues, and regulation of inflammatory cytokine production by infected macrophages.

Matrigel plug assay: evaluation of the angiogenic response by reverse transcription-quantitative PCR

The subcutaneous Matrigel plug assay in mice is a method of choice for the in vivo evaluation of pro- and anti-angiogenic molecules. However, quantification of the angiogenic response in the plug remains a problematic task. Here we report a simple, rapid, unbiased and reverse transcription-quantitative PCR (RT-qPCR) method to investigate the angiogenic process occurring in the Matrigel plug in response to fibroblast growth factor-2 (FGF2). To this purpose, a fixed amount of human cells were added to harvested plugs at the end of the in vivo experimentation as an external cell tracer. Then, mRNA levels of the pan-endothelial cell markers murine CD31 and vascular endothelial-cadherin were measured by species-specific RT-qPCR analysis of the total RNA and data were normalized for human GAPDH or β-actin mRNA levels. RT-qPCR was used also to measure the levels of expression in the plug of various angiogenesis/inflammation-related genes. The procedure allows the simultaneous, quantitative evaluation of the newly-formed endothelium and of non-endothelial/inflammatory components of the cellular infiltrate in the Matrigel implant, as well as the expression of genes involved in the modulation of the angiogenesis process. Also, the method consents the quantitative assessment of the effect of local or systemic administration of anti-angiogenic compounds on the neovascular response triggered by FGF2.

Lack of the lectin-like domain of thrombomodulin worsens Shiga toxin-associated hemolytic uremic syndrome in mice

Shiga toxin (Stx)-producing Escherichia coli is a primary cause of diarrhea-associated hemolytic uremic syndrome (HUS), a disorder of thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure. The pathophysiology of renal microvascular thrombosis in Stx-HUS is still ill-defined. Based on evidence that abnormalities in thrombomodulin (TM), an anticoagulant endothelial glycoprotein that modulates complement and inflammation, predispose to atypical HUS, we assessed whether impaired TM function may adversely affect evolution of Stx-HUS. Disease was induced by coinjection of Stx2/LPS in wild-type mice (TM(wt/wt)) and mice that lack the lectin-like domain of TM (TM(LeD/LeD)), which is critical for its anti-inflammatory and cytoprotective properties. After Stx2/LPS, TM(LeD/LeD) mice exhibited more severe thrombocytopenia and renal dysfunction than TM(wt/wt) mice. Lack of lectin-like domain of TM resulted in a stronger inflammatory reaction after Stx2/LPS with more neutrophils and monocytes/macrophages infiltrating the kidney, associated with PECAM-1 and chemokine upregulation. After Stx2/LPS, intraglomerular fibrin(ogen) deposits were detected earlier in TM(LeD/LeD) than in TM(wt/wt) mice. More abundant fibrin(ogen) deposits were also found in brain and lungs. Under basal conditions, TM(LeD/LeD) mice exhibited excess glomerular C3 deposits, indicating impaired complement regulation in the kidney that could lead to local accumulation of proinflammatory products. TM(LeD/LeD) mice with HUS had a higher mortality rate than TM(wt/wt) mice. If applicable to humans, these findings raise the possibility that genetic or acquired TM defects might have an impact on the severity of microangiopathic lesions after exposure to Stx-producing E. coli infections and raise the potential for using soluble TM in the treatment of Stx-HUS.

Procurement regimens to reduce ischemia reperfusion injury of vascular grafts

BACKGROUND

Ischemia reperfusion injury is an important nonimmunological factor contributing to the development of chronic rejection. The aim of this study was to compare different cell culture media in terms of vascular lesion formation after ischemia reperfusion injury.

METHODS

BALB/c aortic grafts were incubated in different cell media (endothelial cell growth, ECG, RPMI-1640 and Waymouth/Ham's F12) for various time spans (5, 6.5 and 8.5 h) at 37°C and implanted into syngeneic BALB/c recipients. On day 30 after implantation, histology, immunofluorescence and morphometric measurements were performed.

RESULTS

A total of 36 transplants were performed for this study with an overall survival rate of 72.2%. The most frequent complication was thrombosis of the aortic graft (n = 9) and there was one late death due to other courses. All the recipients with vascular grafts incubated in the ECG medium survived and showed no signs of intimal proliferation independent of the time of ischemia. Aortic grafts incubated in the RPMI medium resulted in a reduced recipient survival rate of 66.7% and grafts incubated in the Waymouth medium showed only a 50% survival by day 30. Analysis of the vascular morphology revealed moderate amounts of intimal proliferation within two aortic grafts in this group. CD31 staining revealed superior endothelial cell integrity after incubation with the ECG medium.

CONCLUSIONS

Data from the current study suggest that under optimized conditions vascular grafts can be safely kept in tissue culture up to 8.5 h without significant ischemic damage. Differences in vascular integrity and animal survival depended mostly on the respective tissue culture medium used for the storage of the vessel.

Pulmonary artery endothelium resident endothelial colony-forming cells in pulmonary arterial hypertension

Proliferative pulmonary vascular remodeling is the pathologic hallmark of pulmonary arterial hypertension (PAH) that ultimately leads to right heart failure and death. Highly proliferative endothelial cells known as endothelial colony-forming cells (ECFC) participate in vascular homeostasis in health as well as in pathological angiogenic remodeling in disease. ECFC are distinguished by the capacity to clonally proliferate from a single cell. The presence of ECFC in the human pulmonary arteries and their role in PAH pathogenesis is largely unknown. In this study, we established a simple technique for isolating and growing ECFC from cultured pulmonary artery endothelial cells (PAEC) to test the hypothesis that ECFC reside in human pulmonary arteries and that the proliferative vasculopathy of PAH is related to greater numbers and/or more proliferative ECFC in the pulmonary vascular wall. Flow cytometric forward and side scatter properties and aggregate correction were utilized to sort unmanipulated, single PAEC to enumerate ECFC in primary PAEC cultures derived from PAH and healthy lungs. After 2 weeks, wells were assessed for ECFC formation. ECFC derived from PAH PAEC were more proliferative than control. A greater proportion of PAH ECFC formed colonies following subculturing, demonstrating the presence of more ECFC with high proliferative potential among PAH PAEC. Human androgen receptor assay showed clonality of progeny, confirming that proliferative colonies were single cell-derived. ECFC expressed CD31, von Willebrand factor, endothelial nitric oxide synthase, caveolin-1 and CD34, consistent with an endothelial cell phenotype. We established a simple flow cytometry method that allows ECFC quantification using unmanipulated cells. We conclude that ECFC reside among PAEC and that PAH PAEC contain ECFC that are more proliferative than ECFC in control cultures, which likely contributes to the proliferative angiopathic process in PAH.

Esophageal squamous cell carcinoma: assessing tumor angiogenesis using multi-slice CT perfusion imaging

OBJECTIVES

The purpose of this study was to investigate the correlation between multi-slice computed tomographic perfusion imaging (CTPI) parameters and immunohistologic markers of angiogenesis in esophageal squamous cell carcinoma (ESCC).

METHODS

Fifty patients with histologically proven esophageal squamous cell carcinoma were enrolled in this study. All subjects underwent multi-slice CT perfusion scan. The hemodynamic parameters of vascular tumor, including blood volume (BV), blood flow (BF), mean transit time (MTT) and permeability surface (PS) were generated. All the ESCC specimens were stained immunohistochemically to identify CD31 for quantification of microvessel density (MVD). CTPI parameters were correlated with MVD by using Pearson correlation analysis.

RESULTS

The value of CT perfusion parameters of ESCC were as follows: BF 116.71 ± 47.59 ml/100 g/min, BV 6.74 ± 2.70 ml/100 g, MTT 6.42 ± 2.84 s, PS 13.82 ± 6.25 ml/100 g/min. The mean MVD of all 50 tumor specimens was 34.44 ± 19.75. The PS values were significantly higher in ESCC patients with involvement of lymph node than those without involvement of lymph node (p < 0.01). Blood volume and permeability surface were positively correlated with MVD (p < 0.01), whereas no significant correlation was observed between MVD and BF or between MVD and MTT.

CONCLUSIONS

Blood volume and permeability surface were positively correlated with MVD. CTPI could reflect the angiogenesis in ESCC.

Neovascularization evaluated by CD105 correlates well with prognostic factors in breast cancers

Angiogenesis is critical for the growth, invasion and metastasis of cancers. Extensive neovascularization and tumor thrombus also correlate with a poor prognosis in breast cancer (BC). Although anti-angiogenic agents have been the therapies of choice for BC, in particular for triple-negative BCs, predictive markers for anti-angiogenic agents are lacking. Microvascular density (MVD) is commonly used to assess the neovascularization in tumors. Compared with pan-endothelial markers such as CD31, CD34 and von Willebrand factor (vWF), CD105 has a higher specificity for MVD in tumor tissues. In this study, we aimed to determine the prognostic value of CD105 in BCs. Paraffin-embedded tissue blocks from 201 BC patients were formed into tissue microarrays. Evaluation of MVD revealed that a median of 11 microvessels determined by CD105 staining correlated significantly with the pathological characteristics of BCs and also with the survival of patients. The expression of CD105 correlated inversely with hormone receptor (HR) expression but positively with Her-2 expression. Univariate analysis indicated that CD105 is a superior predictor of disease-free survival (DFS) in stage I and II diseases; multivariate analysis indicated that only hormone receptors (HRs) are suitable for predicting overall survival (OS) in stage III disease. These findings reveal for the first time that MVD measured by CD105 staining correlates positively with Her-2 expression but negatively with HR expression. The significance of MVD on OS is more apparent in early stage BCs. CD105 has the potential to be used as a predictive marker for anti-angiogenic agents; the targeting of CD105 may also be a potential anticancer strategy.

Actions of the Kunitz-type serine protease inhibitor Amblyomin-X on VEGF-A-induced angiogenesis

Amblyomin-X is a Kunitz-type serine protease inhibitor (Kunitz-type SPI) designed from the cDNA library of the Amblyomma cajennense tick, which displays in vivo anti-tumor activities. Here, the mechanisms of actions of Amblyomin-X in vascular endothelial growth factor A (VEGF-A)-induced angiogenesis were characterized. Topical application of Amblyomin-X (10 or 100 ng/10 μl; each 48 h) inhibited VEGF-A-induced (10 ng/10 μl; each 48 h) angiogenesis in the dorsal subcutaneous tissue in male Swiss mice. Moreover, similar effect was observed in the VEGF-A-induced angiogenesis in the chicken chorioallantoic membrane (CAM). Additional in vitro assays in t-End cells showed that Amblyomin-X treatment delayed the cell cycle, by maintaining them in G0/G1 phase, and inhibited cell proliferation and adhesion, tube formation and membrane expression of the adhesion molecule platelet-endothelial cell adhesion molecule-1 (PECAM-1), regardless of mRNA synthesis. Together, results herein reveal the role of Kunitz-type SPI on in vivo VEGF-A-induced angiogenesis, by exerting modulatory actions on endothelial cell proliferation and adhesion, especially on membrane expression of PECAM-1. These data provide further mechanisms of actions of Kunitz-type SPI, corroborating their relevance as scientific tools in the design of therapeutic molecules.

Endothelial progenitor cells: a new player in lupus?

Patients with systemic lupus erythematosus (SLE) have a greatly increased risk of cardiovascular disease. There is growing interest in the link between vascular damage and lupus-specific inflammatory factors. Impaired endothelial repair could account for the endothelial dysfunction in this patient group. This review describes the contribution that endothelial progenitor cells could play in the pathogenesis of premature vascular damage in this disease. The methods of isolation, detection, and characterization of endothelial progenitor cells, together with their potential role in repair of the endothelium and as a therapeutic target in SLE, are discussed.

Endothelial expression of human ABCA1 in mice increases plasma HDL cholesterol and reduces diet-induced atherosclerosis

The role of endothelial ABCA1 expression in reverse cholesterol transport (RCT) was examined in transgenic mice, using the endothelial-specific Tie2 promoter. Human ABCA1 (hABCA1) was significantly expressed in endothelial cells (EC) of most tissues except the liver. Increased expression of ABCA1 was not observed in resident peritoneal macrophages. ApoA-I-mediated cholesterol efflux from aortic EC was 2.6-fold higher (P < 0.0001) for cells from transgenic versus control mice. On normal chow diet, Tie2 hABCA1 transgenic mice had a 25% (P < 0.0001) increase in HDL-cholesterol (HDL-C) and more than a 2-fold increase of eNOS mRNA in the aorta (P < 0.04). After 6 months on a high-fat, high-cholesterol (HFHC) diet, transgenic mice compared with controls had a 40% increase in plasma HDL-C (P < 0.003) and close to 40% decrease in aortic lesions (P < 0.02). Aortas from HFHC-fed transgenic mice also showed gene expression changes consistent with decreased inflammation and apoptosis. Beneficial effects of the ABCA1 transgene on HDL-C levels or on atherosclerosis were absent when the transgene was transferred onto ApoE or Abca1 knockout mice. In summary, expression of hABCA1 in EC appears to play a role in decreasing diet-induced atherosclerosis in mice and is associated with increased plasma HDL-C levels and beneficial gene expression changes in EC.

Actions of translocator protein ligands on neutrophil adhesion and motility induced by G-protein coupled receptor signaling

The 18 kDa translocator protein (TSPO) also known as the peripheral benzodiazepine receptor (PBR), mediates the transportation of cholesterol and anions from the outer to the inner mitochondrial membrane in different cells types. Although recent evidences indicate a potential role for TSPO in the development of inflammatory processes, the mechanisms involved have not been elucidated. The present study investigated the ability of the specific TSPO ligands, the isoquinoline carboxamide PK11195 and benzodiazepine Ro5-4864, on neutrophil recruitment promoted by the N-formylmethionyl-leucyl-phenylalanine peptide (fMLP), an agonist of G-protein coupled receptor (GPCR). Pre-treatment with Ro5-4864 abrograted fMLP-induced leukocyte-endothelial interactions in mesenteric postcapillary venules in vivo. Moreover, in vitro Ro5-4864 treatment prevented fMLP-induced: (i) L-selectin shedding and overexpression of PECAM-1 on the neutrophil cell surface; (ii) neutrophil chemotaxis and (iii) enhancement of intracellular calcium cations (iCa(+2)). Intriguingly, the two latter effects were augmented by cell treatment with PK11195. An allosteric agonist/antagonist relation may be suggested, as the effects of Ro5-4864 on fMLP-stimulated neutrophils were reverted by simultaneous treatment with PK11195. Taken together, these data highlight TSPO as a modulator of pathways of neutrophil adhesion and locomotion induced by GPCR, connecting TSPO actions and the onset of an innate inflammatory response.

Decorin antagonizes the angiogenic network: concurrent inhibition of Met, hypoxia inducible factor 1α, vascular endothelial growth factor A, and induction of thrombospondin-1 and TIMP3

Decorin, a small leucine-rich proteoglycan, inhibits tumor growth by antagonizing multiple receptor tyrosine kinases including EGFR and Met. Here, we investigated decorin during normoxic angiogenic signaling. An angiogenic PCR array revealed a profound decorin-evoked transcriptional inhibition of pro-angiogenic genes, such as HIF1A. Decorin evoked a reduction of hypoxia inducible factor (HIF)-1α and vascular endothelial growth factor A (VEGFA) in MDA-231 breast carcinoma cells expressing constitutively-active HIF-1α. Suppression of Met with decorin or siRNA evoked a similar reduction of VEGFA by attenuating downstream β-catenin signaling. These data establish a noncanonical role for β-catenin in regulating VEGFA expression. We found that exogenous decorin induced expression of thrombospondin-1 and TIMP3, two powerful angiostatic agents. In contrast, decorin suppressed both the expression and enzymatic activity of matrix metalloprotease (MMP)-9 and MMP-2, two pro-angiogenic proteases. Our data establish a novel duality for decorin as a suppressor of tumor angiogenesis under normoxia by simultaneously down-regulating potent pro-angiogenic factors and inducing endogenous anti-angiogenic agents.

Knockout of the vascular endothelial glucocorticoid receptor abrogates dexamethasone-induced hypertension

BACKGROUND

Glucocorticoid-mediated hypertension is incompletely understood. Recent studies have suggested the primary mechanism of this form of hypertension may be through the effects of glucocorticoids on vascular tissues and not to excess sodium and water re-absorption as traditionally believed.

OBJECTIVE

The goal of this study was to better understand the role of the vasculature in the generation and maintenance of glucocorticoid-mediated hypertension.

METHODS

We created a mouse model with a tissue-specific knockout of the glucocorticoid receptor in the vascular endothelium.

RESULTS

We show that these mice are relatively resistant to dexamethasone-induced hypertension. After 1 week of dexamethasone treatment, control animals have a mean blood pressure (BP) increase of 13.1 mmHg, whereas knockout animals have only a 2.7 mmHg increase (P < 0.001). Interestingly, the knockout mice have slightly elevated baseline BP compared with the controls (112.2 ± 2.5 vs. 104.6 ± 1.2 mmHg, P = 0.04), a finding which is not entirely explained by our data. Furthermore, we demonstrate that the knockout resistance arterioles have a decreased contractile response to dexamethasone with only 6.6% contraction in knockout vessels compared with 13.4% contraction in control vessels (P = 0.034). Finally, we show that in contrast to control animals, the knockout animals are able to recover a significant portion of their normal circadian BP rhythm, suggesting that the vascular endothelial glucocorticoid receptor may function as a peripheral circadian clock.

CONCLUSION

Our study highlights the importance of the vascular endothelial glucocorticoid receptor in several fundamental physiologic processes, namely BP homeostasis and circadian rhythm.

CD31+ T cells, endothelial function and cardiovascular risk

Deficits in endothelial cell repair mechanisms are thought to contribute to the aetiology of endothelial dysfunction and, subsequently, cardiovascular disease (CVD). CD31(+) T cells or so-called "angiogenic T cells" are a newly defined T cell subset that exhibit favourable vascular qualities and show a strong negative relation with atherosclerotic disease severity. Despite growing evidence that CD31(+) T cells are important for vascular homeostasis, it is currently unknown if CD31(+) T cell number and function are related to endothelial function and CVD risk in healthy adults. To address this question, we studied 24 healthy adult men (ages: 21-70). Endothelial function was assessed by the forearm blood flow (FBF) response to intra-arterial infusion of acetylcholine (ACh) and CVD risk was estimated by Framingham Risk Score (FRS). CD31(+) T cell number was determined by fluorescence-activated cell sorting. Magnetic-activated cell sorting was used to isolate CD31(+) T cells for Boyden chamber migration. No relation was observed between CD31(+) T cell number and FBF response to ACh or FRS. However, CD31(+) T cell migration to stromal cell-derived factor (SDF)-1α and vascular endothelial growth factor (VEGF) was positively correlated with FBF response to ACh (r = 0.43 for SDF-1α; r = 0.38 for VEGF; both P<0.05) and inversely related to FRS (r = -0.53 for SDF-1α; r = -0.48 for VEGF; both P<0.05). These findings demonstrate that CD31(+) T cell function, but not number, is associated with in vivo endothelial function and CVD risk in healthy adult men.

Vascular endothelial growth factor (VEGF) isoform regulation of early forebrain development

This work was designed to determine the role of the vascular endothelial growth factor A (VEGF) isoforms during early neuroepithelial development in the mammalian central nervous system (CNS), specifically in the forebrain. An emerging model of interdependence between neural and vascular systems includes VEGF, with its dual roles as a potent angiogenesis factor and neural regulator. Although a number of studies have implicated VEGF in CNS development, little is known about the role that the different VEGF isoforms play in early neurogenesis. We used a mouse model of disrupted VEGF isoform expression that eliminates the predominant brain isoform, VEGF164, and expresses only the diffusible form, VEGF120. We tested the hypothesis that VEGF164 plays a key role in controlling neural precursor populations in developing cortex. We used microarray analysis to compare gene expression differences between wild type and VEGF120 mice at E9.5, the primitive stem cell stage of the neuroepithelium. We quantified changes in PHH3-positive nuclei, neural stem cell markers (Pax6 and nestin) and the Tbr2-positive intermediate progenitors at E11.5 when the neural precursor population is expanding rapidly. Absence of VEGF164 (and VEGF188) leads to reduced proliferation without an apparent effect on the number of Tbr2-positive cells. There is a corresponding reduction in the number of mitotic spindles that are oriented parallel to the ventricular surface relative to those with a vertical or oblique angle. These results support a role for the VEGF isoforms in supporting the neural precursor population of the early neuroepithelium.

Heparan sulfate proteoglycan mediates shear stress-induced endothelial gene expression in mouse embryonic stem cell-derived endothelial cells

It has been shown that shear stress plays a critical role in promoting endothelial cell (EC) differentiation from embryonic stem cell (ESC)-derived ECs. However, the underlying mechanisms mediating shear stress effects in this process have yet to be investigated. It has been reported that the glycocalyx component heparan sulfate proteoglycan (HSPG) mediates shear stress mechanotransduction in mature EC. In this study, we investigated whether cell surface HSPG plays a role in shear stress modulation of EC phenotype. ESC-derived EC were subjected to shear stress (5 dyn/cm(2)) for 8 h with or without heparinase III (Hep III) that digests heparan sulfate. Immunostaining showed that ESC-derived EC surfaces contain abundant HSPG, which could be cleaved by Hep III. We observed that shear stress significantly increased the expression of vascular EC-specific marker genes (vWF, VE-cadherin, PECAM-1). The effect of shear stress on expression of tight junction protein genes (ZO-1, OCLD, CLD5) was also evaluated. Shear stress increased the expression of ZO-1 and CLD5, while it did not alter the expression of OCLD. Shear stress increased expression of vasodilatory genes (eNOS, COX-2), while it decreased the expression of the vasoconstrictive gene ET1. After reduction of HSPG with Hep III, the shear stress-induced expression of vWF, VE-cadherin, ZO-1, eNOS, and COX-2, were abolished, suggesting that shear stress-induced expression of these genes depends on HSPG. These findings indicate for the first time that HSPG is a mechanosensor mediating shear stress-induced EC differentiation from ESC-derived EC cells.

Ginsenoside metabolite compound K differentially antagonizing tumor necrosis factor-α-induced monocyte-endothelial trafficking

Human leukocyte endothelial adhesion and transmigration occur in the early stage of the pathogenesis of atherosclerosis. Vascular endothelial cells are targeted by pro-inflammatory cytokines modulating many gene proteins responsible for cell adhesion, thrombosis and inflammatory responses. This study examined the potential of compound K to inhibit the pro-inflammatory cytokine TNF-α induction of monocyte adhesion onto TNF-α-activated human umbilical vein endothelial cells (HUVEC). HUVEC were cultured with 10ng/ml TNF-α with individual ginsenosides of Rb1, Rc, Re, Rh1 and compound K (CK). Ginsenosides at doses of ⩽50μM did not show any cytotoxicity. TNF-α induced THP-1 monocyte adhesion to HUVEC, and such induction was attenuated by Rh1 and CK. Consistently, CK suppressed TNF-α-induced expression of HUVEC adhesion molecules of VCAM-1, ICAM-1 and E-selectin, and also Rh1 showed a substantial inhibition. Rh1 and CK dampened induction of counter-receptors, α4/β1 integrin VLA-4 and αL/β2 integrin LFA-1 in TNF-α-treated THP-1 cells. Additionally, CK diminished THP-1 secretion of MMP-9 required during transmigration, inhibiting transendothelial migration of THP-1 cells. CK blunted TNF-α-promoted IL-8 secretion of HUVEC and CXCR1 expression of THP-1 monocytes. Furthermore, TNF-α-activated endothelial IκB phosphorylation and NF-κB nuclear translocation were disturbed by CK, and TNF-α induction of α4/β1 integrin was abrogated by the NF-κB inhibitor SN50. These results demonstrate that CK exerts anti-atherogenic activity with blocking leukocyte endothelial interaction and transmigration through negatively mediating NF-κB signaling.

CD31 is required on CD4+ T cells to promote T cell survival during Salmonella infection

Hematopoietic cells constitutively express CD31/PECAM1, a signaling adhesion receptor associated with controlling responses to inflammatory stimuli. Although expressed on CD4(+) T cells, its function on these cells is unclear. To address this, we have used a model of systemic Salmonella infection that induces high levels of T cell activation and depends on CD4(+) T cells for resolution. Infection of CD31-deficient (CD31KO) mice demonstrates that these mice fail to control infection effectively. During infection, CD31KO mice have diminished numbers of total CD4(+) T cells and IFN-γ-secreting Th1 cells. This is despite a higher proportion of CD31KO CD4(+) T cells exhibiting an activated phenotype and an undiminished capacity to prime normally and polarize to Th1. Reduced numbers of T cells reflected the increased propensity of naive and activated CD31KO T cells to undergo apoptosis postinfection compared with wild-type T cells. Using adoptive transfer experiments, we show that loss of CD31 on CD4(+) T cells alone is sufficient to account for the defective CD31KO T cell accumulation. These data are consistent with CD31 helping to control T cell activation, because in its absence, T cells have a greater propensity to become activated, resulting in increased susceptibility to become apoptotic. The impact of CD31 loss on T cell homeostasis becomes most pronounced during severe, inflammatory, and immunological stresses such as those caused by systemic Salmonella infection. This identifies a novel role for CD31 in regulating CD4 T cell homeostasis.

Dendritic degeneration, neurovascular defects, and inflammation precede neuronal loss in a mouse model for tau-mediated neurodegeneration

Adeno-associated virus (AAV)-mediated expression of wild-type or mutant P301L protein tau produces massive degeneration of pyramidal neurons without protein tau aggregation. We probed this novel model for genetic and structural factors and early parameters of pyramidal neurodegeneration. In yellow fluorescent protein-expressing transgenic mice, intracerebral injection of AAV-tauP301L revealed early damage to apical dendrites of CA1 pyramidal neurons, whereas their somata remained normal. Ultrastructurally, more and enlarged autophagic vacuoles were contained in degenerating dendrites and manifested as dark, discontinuous, vacuolated processes surrounded by activated astrocytes. Dendritic spines were lost in AAV-tauP301L-injected yellow fluorescent protein-expressing transgenic mice, and ultrastructurally, spines appeared dark and degenerating. In CX3CR1(EGFP/EGFP)-deficient mice, microglia were recruited early to neurons expressing human tau. The inflammatory response was accompanied by extravasation of plasma immunoglobulins. α2-Macroglobulin, but neither albumin nor transferrin, became lodged in the brain parenchyma. Large proteins, but not Evans blue, entered the brain of mice injected with AAV-tauP301L. Ultrastructurally, brain capillaries were constricted and surrounded by swollen astrocytes with extensions that contacted degenerating dendrites and axons. Together, these data corroborate the hypothesis that neuroinflammation participates essentially in tau-mediated neurodegeneration, and the model recapitulates early dendritic defects reminiscent of "dendritic amputation" in Alzheimer's disease.

Interleukin 10 deficiency exacerbates toll-like receptor 3-induced preeclampsia-like symptoms in mice

Preeclampsia may result from overactivation of the maternal immune system and is characterized by endothelial dysfunction and excessive inflammation. Given the importance of maternal immune system regulation and anti-inflammatory cytokines in normotensive pregnancies, we hypothesized that maternal immune system activation via Toll-like receptor 3 during pregnancy would cause preeclampsia-like symptoms in mice, which would be made worse by deficiency of the anti-inflammatory cytokine interleukin 10. The Toll-like receptor 3 agonist polyinosine-polycytidylic acid (poly I:C) caused hypertension, endothelial dysfunction, and proteinuria in mice only when pregnant. In the absence of poly I:C, pregnant interleukin 10 knockout mice exhibited a significant increase in systolic blood pressure, endothelial dysfunction, and serum proinflammatory cytokines, as well as aortic and placental platelet-endothelial cell adhesion molecule expression compared with pregnant wild-type mice. Deficiency of interleukin 10 further augmented these measures in poly I:C-treated pregnant mice. In addition, sera from poly I:C-treated pregnant wild-type mice significantly decreased relaxation responses and increased platelet-endothelial cell adhesion molecule expression in isolated aortas from nonpregnant wild-type mice, and these effects were augmented by sera from poly I:C-treated interleukin 10 knockout mice. Coincubation with recombinant interleukin 10 normalized relaxation responses and platelet-endothelial cell adhesion molecule expression in all of the groups. Collectively, Toll-like receptor 3 activation during pregnancy causes preeclampsia-like symptoms, which are exacerbated by the absence of interleukin 10. Exogenous interleukin 10 treatment had beneficial effects on endothelial function and may be beneficial in women with preeclampsia.

Angiopoietins-1 and -2 play opposing roles in endothelial sprouting of embryoid bodies in 3D culture and their receptor Tie-2 associates with the cell-cell adhesion molecule PECAM1

Angiopoietins 1 and 2, ligands for the receptor kinase Tie-2, have been proposed to play critical but opposing roles in vascular development. Since signaling by Tie-2 is likely affected by other endothelial cell receptors such as Flk-1, the receptor for VEGF, and cell-cell adhesion receptors PECAM1 and VE-cad, we explored their interactions in a 3D model of vasculogenesis. When murine embryoid bodies (EBs) were treated with VEGF in Matrigel in the presence or absence of Ang-1 or Ang-2 for eight days, Ang-1 abrogated vascular sprouting for treatments started at days 0 or 3. In contrast, Ang-2 greatly accelerated vascular sprouting compared to untreated EBs. These results were confirmed in a second model system where VEGF treated HUVECs were grown in Matrigel in the presence or absence of Ang-1 or Ang-2. Since vascular sprouting must be precisely controlled in the developing embryo, it is likely that cell-cell adhesion molecules play a role in sensing the density of vascular sprouts. In this respect, we have shown that PECAM1 and CEACAM1 play essential roles in vascular sprouting. We now show that PECAM1 is associated with Tie-2, becomes phosphorylated on its ITIMs, and recruits the inhibitory phosphatases SHP-1 and SHP-2. In addition, PECAM1 is associated with VE-cad and may similarly regulate its signaling via recruitment of SHP-1/2.