Endothelial cell heterogeneity

Leveraging cell type specific regulatory regions to detect SNPs associated with tissue factor pathway inhibitor plasma levels

Tissue factor pathway inhibitor (TFPI) regulates the formation of intravascular blood clots, which manifest clinically as ischemic heart disease, ischemic stroke, and venous thromboembolism (VTE). TFPI plasma levels are heritable, but the genetics underlying TFPI plasma level variability are poorly understood. Herein we report the first genome-wide association scan (GWAS) of TFPI plasma levels, conducted in 251 individuals from five extended French-Canadian Families ascertained on VTE. To improve discovery, we also applied a hypothesis-driven (HD) GWAS approach that prioritized single nucleotide polymorphisms (SNPs) in (1) hemostasis pathway genes, and (2) vascular endothelial cell (EC) regulatory regions, which are among the highest expressers of TFPI. Our GWAS identified 131 SNPs with suggestive evidence of association (P-value < 5 × 10^-8 ), but no SNPs reached the genome-wide threshold for statistical significance. Hemostasis pathway genes were not enriched for TFPI plasma level associated SNPs (global hypothesis test P-value = 0.147), but EC regulatory regions contained more TFPI plasma level associated SNPs than expected by chance (global hypothesis test P-value = 0.046). We therefore stratified our genome-wide SNPs, prioritizing those in EC regulatory regions via stratified false discovery rate (sFDR) control, and reranked the SNPs by q-value. The minimum q-value was 0.27, and the top-ranked SNPs did not show association evidence in the MARTHA replication sample of 1,033 unrelated VTE cases. Although this study did not result in new loci for TFPI, our work lays out a strategy to utilize epigenomic data in prioritization schemes for future GWAS studies.

Salvia fruticosa Induces Vasorelaxation In Rat Isolated Thoracic Aorta: Role of the PI3K/Akt/eNOS/NO/cGMP Signaling Pathway

Salvia fruticosa (SF) Mill. is traditionally used for its antihypertensive actions. However, little is known about its pharmacologic and molecular mechanisms of action. Here we determined the effects of an ethanolic extract of SF leaves on rings of isolated thoracic aorta from Sprague-Dawley rats. Our results show that SF extract increased nitric oxide production and relaxed endothelium-intact rings in a dose-dependent (0.3 µg/ml–1 mg/ml) manner, and the maximum arterial relaxation (R_max) was significantly reduced with endothelium denudation. Pretreatment of endothelium-intact rings with L-NAME (a non-selective inhibitor of nitric oxide synthase, 100 µM), or ODQ (an inhibitor of soluble guanylyl cyclase, 10 µM) significantly diminished SF-mediated vasorelaxation. Furthermore, SF induced Akt phosphorylation as well as increased cGMP levels in rings treated with increasing doses of SF. Prior exposure to PI3K inhibitors, wortmannin (0.1 µM) or LY294002 (10 µM), decreased cGMP accumulation and attenuated the SF-induced vasorelaxation by approximately 50% (R_max). SF-evoked relaxation was not affected by indomethacin, verapamil, glibenclamide, tetraethylammonium, pyrilamine or atropine. Taken together, our results indicate that SF induces endothelium-dependent vasorelaxation through the PI3K/Akt/eNOS/NO/sGC/cGMP signaling pathway. Our data illustrate the health-orientated benefits of consuming SF which may act as an antihypertensive agent to reduce the burden of cardiovascular complications.

Diet-induced obesity links to ER positive breast cancer progression via LPA/PKD-1-CD36 signaling-mediated microvascular remodeling

Obesity increases cancer risk including breast cancer (BC). However, the direct regulatory mechanisms by which obesity promotes BC progression remain largely unknown. We show that lysophosphatidic acid/protein kinase D1 (LPA/PKD-1)-CD36 signaling is a bona fide breast cancer promoter via stimulating microvascular remodeling in chronic diet-induced obesity (DIO). We observed that the growth of an estrogen receptor (ER) positive breast cancer was markedly increased when compared to the lean control, and specifically accompanied by increased microvascular remodeling in a syngeneic BC model in female DIO mice. The tumor neovessels in DIO mice demonstrated elevated levels of alpha smooth muscle actin (α-SMA), vascular endothelial growth factor receptor 2 (VEGFR 2) and endothelial differentiation gene 2/LPA receptor1 (Edg2/LPA1), enhanced PKD-1 phosphorylation, and reduced CD36 expression. Tumor associated endothelial cells (TAECs) exposed to LPA demonstrated sustained nuclear PKD-1 phosphorylation, and elevated mRNA levels of ephrin B2, and reduced mRNA expression of CD36. TAEC proliferation also increased in response to LPA/PKD-1 signaling. These studies suggest that the LPA/PKD-1-CD36 signaling axis links DIO to malignant progression of BC via stimulation of de novo tumor arteriogenesis through arteriolar remodeling of microvasculature in the tumor microenvironment. Targeting this signaling axis could provide an additional novel therapeutic strategy.

Sindbis Virus-Pseudotyped Lentiviral Vectors Carrying VEGFR2-Specific Nanobody for Potential Transductional Targeting of Tumor Vasculature

Introduction of selectivity/specificity into viral-based gene delivery systems, such as lentiviral vectors (LVs), is crucial in their systemic administration for cancer gene therapy. The pivotal role of tumor-associated endothelial cells (TAECs) in tumor angiogenesis and overexpression of vascular endothelial growth factor receptor-2 (VEGFR2 or KDR) in TAECs makes them a potent target in cancer treatment. Herein, we report the development of VEGFR2-targeted LVs pseudotyped with chimeric sindbis virus E2 glycoprotein (cSVE2s). For this purpose, either sequence of a VEGFR2-specific nanobody or its natural ligand (VEGF₁₂₁) was inserted into the binding site of sindbis virus E2 glycoprotein. In silico modeling data suggested that the inserted targeting motifs were exposed in the context of cSVE2s. Western blot analysis of LVs indicated the incorporation of cSVE2s into viral particles. Capture ELISA demonstrated the specificity/functionality of the incorporated cSVE2s. Transduction of 293/KDR (expressing VEGFR2) or 293T cells (negative control) by constructed LVs followed by fluorescent microscopy and flow cytometric analyses indicated selective transduction of 293/KDR cells (30 %) by both targeting motifs compared to 293T control cells (1-2 %). These results implied similar targeting properties of VEGFR2-specific nanobody compared to the VEGF₁₂₁ and indicated the potential for transductional targeting of tumor vasculature by the nanobody displaying LVs.

Endothelial and smooth muscle cells derived from human cardiac explants demonstrate angiogenic potential and suitable for design of cell-containing vascular grafts

Background

Endothelial and smooth muscle cells are considered promising resources for regenerative medicine and cell replacement therapy. It has been shown that both types of cells are heterogeneous depending on the type of vessels and organs in which they are located. Therefore, isolation of endothelial and smooth muscle cells from tissues relevant to the area of research is necessary for the adequate study of specific pathologies. However, sources of specialized human endothelial and smooth muscle cells are limited, and the search for new sources is still relevant. The main goal of our study is to demonstrate that functional endothelial and smooth muscle cells can be obtained from an available source—post-surgically discarded cardiac tissue from the right atrial appendage and right ventricular myocardium.

Methods

Heterogeneous primary cell cultures were enzymatically isolated from cardiac explants and then grown in specific endothelial and smooth muscle growth media on collagen IV-coated surfaces. The population of endothelial cells was further enriched by immunomagnetic sorting for CD31, and the culture thus obtained was characterized by immunocytochemistry, ultrastructural analysis and in vitro functional tests. The angiogenic potency of the cells was examined by injecting them, along with Matrigel, into immunodeficient mice. Cells were also seeded on characterized polycaprolactone/chitosan membranes with subsequent analysis of cell proliferation and function.

Results

Endothelial cells isolated from cardiac explants expressed CD31, VE-cadherin and VEGFR2 and showed typical properties, namely, cytoplasmic Weibel-Palade bodies, metabolism of acetylated low-density lipoproteins, formation of capillary-like structures in Matrigel, and production of extracellular matrix and angiogenic cytokines. Isolated smooth muscle cells expressed extracellular matrix components as well as α-actin and myosin heavy chain. Vascular cells derived from cardiac explants demonstrated the ability to stimulate angiogenesis in vivo. Endothelial cells proliferated most effectively on membranes made of polycaprolactone and chitosan blended in a 25:75 ratio, neutralized by a mixture of alkaline and ethanol. Endothelial and smooth muscle cells retained their functional properties when seeded on the blended membranes.

Conclusions

We established endothelial and smooth muscle cell cultures from human right atrial appendage and right ventricle post-operative explants. The isolated cells revealed angiogenic potential and may be a promising source of patient-specific cells for regenerative medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1156-1) contains supplementary material, which is available to authorized users.

Biomimetic, ultrathin and elastic hydrogels regulate human neutrophil extravasation across endothelial-pericyte bilayers

The vascular basement membrane-a thin, elastic layer of extracellular matrix separating and encasing vascular cells-provides biological and mechanical cues to endothelial cells, pericytes, and migrating leukocytes. In contrast, experimental scaffolds typically used to replicate basement membranes are stiff and bio-inert. Here, we present thin, porated polyethylene glycol hydrogels to replicate human vascular basement membranes. Like commercial transwells, our hydrogels are approximately 10μm thick, but like basement membranes, the hydrogels presented here are elastic (E: 50-80kPa) and contain a dense network of small pores. Moreover, the inclusion of bioactive domains introduces receptor-mediated biochemical signaling. We compare elastic hydrogels to common culture substrates (E: >2GPa) for human endothelial cell and pericyte monolayers and bilayers to replicate postcapillary venules in vitro. Our data demonstrate that substrate elasticity facilitates differences in vascular phenotype, supporting expression of vascular markers that are increasingly replicative of venules. Endothelial cells differentially express vascular markers, like EphB4, and leukocyte adhesion molecules, such as ICAM-1, with decreased mechanical stiffness. With porated PEG hydrogels we demonstrate the ability to evaluate and observe leukocyte recruitment across endothelial cell and pericyte monolayers and bilayers, reporting that basement membrane scaffolds can significantly alter the rate of vascular migration in experimental systems. Overall, this study demonstrates the creation and utility of a new and accessible method to recapture the mechanical and biological complexity of human basement membranes in vitro.

Gemcitabine kills proliferating endothelial cells exclusively via acid sphingomyelinase activation

Gemcitabine is a widely-used anti-cancer drug with a well-defined mechanism of action in normal and transformed epithelial cells. However, its effect on endothelial cells is largely unknown. Acid sphingomyelinase (ASMase) is highly expressed in endothelial cells, converting plasma membrane sphingomyelin to pro-apoptotic ceramide upon activation by diverse stresses. In the current study, we investigated gemcitabine impact in primary cultures of endothelial cells. We find baseline ASMase increases markedly in bovine aortic endothelial cells (BAEC) as they transit from a proliferative to a confluent growth-arrested state. Further, gemcitabine activates ASMase and induces release of a secretory ASMase form into the media only in proliferating endothelial cells. Additionally, proliferative, but not growth-arrested BAEC, are sensitive to gemcitabine-induced apoptotic death, an effect blocked by inhibiting ASMase with imipramine or by binding ceramide on the cell surface with an anti-ceramide Ab. Confluent growth-arrested BAEC can be re-sensitized to gemcitabine-induced apoptosis by provision of exogenous sphingomyelinase. A highly similar phenotype was observed in primary cultures of human coronary artery endothelial cells. These findings reveal a previously-unrecognized mechanism of gemcitabine cytotoxicity in endothelium that may well contribute to its clinical benefit, and suggest the potential for further improvement of its clinical efficacy via pharmacologic modulation of ASMase/ceramide signaling in proliferative tumor endothelium.

Complementary actions of dopamine D2 receptor agonist and anti-vegf therapy on tumoral vessel normalization in a transgenic mouse model

Angiogenesis contributes in multiple ways to disease progression in tumors and reduces treatment efficiency. Molecular therapies targeting Vegf signaling combined with chemotherapy or other drugs exhibit promising results to improve efficacy of treatment. Dopamine has been recently proposed to be a novel safe anti-angiogenic drug that stabilizes abnormal blood vessels and increases therapeutic efficacy. Here, we aimed to identify a treatment to normalize tumoral vessels and restore normal blood perfusion in tumor tissue with a Vegf receptor inhibitor and/or a ligand of dopamine G protein-coupled receptor D2 (D2R). Dopamine, via its action on D2R, is an endogenous effector of the pituitary gland, and we took advantage of this system to address this question. We have used a previously described Hmga2/T mouse model developing haemorrhagic prolactin-secreting adenomas. In mutant mice, blood vessels are profoundly altered in tumors, and an aberrant arterial vascularization develops leading to the loss of dopamine supply. D2R agonist treatment blocks tumor growth, induces regression of the aberrant blood supply and normalizes blood vessels. A chronic treatment is able to restore the altered balance between pro- and anti-angiogenic factors. Remarkably, an acute treatment induces an upregulation of the stabilizing factor Angiopoietin 1. An anti-Vegf therapy is also effective to restrain tumor growth and improves vascular remodeling. Importantly, only the combination treatment suppresses intratumoral hemorrhage and restores blood vessel perfusion, suggesting that it might represent an attractive therapy targeting tumor vasculature. Similar strategies targeting other ligands of GPCRs involved in angiogenesis may identify novel therapeutic opportunities for cancer.

Barcoded nanoparticles for high throughput in vivo discovery of targeted therapeutics

Nucleic acid therapeutics are limited by inefficient delivery to target tissues and cells and by an incomplete understanding of how nanoparticle structure affects biodistribution to off-target organs. Although thousands of nanoparticle formulations have been designed to deliver nucleic acids, most nanoparticles have been tested in cell culture contexts that do not recapitulate systemic in vivo delivery. To increase the number of nanoparticles that could be tested in vivo, we developed a method to simultaneously measure the biodistribution of many chemically distinct nanoparticles. We formulated nanoparticles to carry specific nucleic acid barcodes, administered the pool of particles, and quantified particle biodistribution by deep sequencing the barcodes. This method distinguished previously characterized lung- and liver- targeting nanoparticles and accurately reported relative quantities of nucleic acid delivered to tissues. Barcode sequences did not affect delivery, and no evidence of particle mixing was observed for tested particles. By measuring the biodistribution of 30 nanoparticles to eight tissues simultaneously, we identified chemical properties promoting delivery to some tissues relative to others. Finally, particles that distributed to the liver also silenced gene expression in hepatocytes when formulated with siRNA. This system can facilitate discovery of nanoparticles targeting specific tissues and cells and accelerate the study of relationships between chemical structure and delivery in vivo.

Vascular biology of hydrogen sulfide

Hydrogen sulfide (H₂S) is a ubiquitous signaling molecule with important functions in many mammalian organs and systems. Observations in the 1990s ascribed physiological actions to H₂S in the nervous system, proposing that this gasotransmitter acts as a neuromodulator. Soon after that, the vasodilating properties of H₂S were demonstrated. In the past decade, H₂S was shown to exert a multitude of physiological effects in the vessel wall. H₂S is produced by vascular cells and exhibits antioxidant, antiapoptotic, anti-inflammatory, and vasoactive properties. In this concise review, we have focused on the impact of H₂S on vascular structure and function with an emphasis on angiogenesis, vascular tone, vascular permeability and atherosclerosis. H₂S reduces arterial blood pressure, limits atheromatous plaque formation, and promotes vascularization of ischemic tissues. Although the beneficial properties of H₂S are well established, mechanistic insights into the molecular pathways implicated in disease prevention and treatment remain largely unexplored. Unraveling the targets and downstream effectors of H₂S in the vessel wall in the context of disease will aid in translation of preclinical observations. In addition, acute regulation of H₂S production is still poorly understood and additional work delineating the pathways regulating the enzymes that produce H₂S will allow pharmacological manipulation of this pathway. As the field continues to grow, we expect that H₂S-related compounds will find their way into clinical trials for diseases affecting the blood vessels.

Acidic pH reduces VEGF-mediated endothelial cell responses by downregulation of VEGFR-2; relevance for anti-angiogenic therapies

Anti-angiogenic treatments targeting the vascular endothelial growth factor or its receptors have shown clinical benefits. However, impact on long-term survival remains limited. Solid tumors display an acidic microenvironment that profoundly influences their biology. Consequences of acidity on endothelial cells and anti-angiogenic therapies remain poorly characterized and hence are the focus of this study. We found that exposing endothelial cells to acidic extracellular pH resulted in reduced cell proliferation and migration. Also, whereas VEGF increased endothelial cell proliferation and survival at pH 7.4, it had no effect at pH 6.4. Furthermore, in acidic conditions, stimulation of endothelial cells with VEGF did not result in activation of downstream signaling pathways such as AKT. At a molecular level, acidity significantly decreased the expression of VEGFR-2 by endothelial cells. Consequently, anti-angiogenic therapies that target VEGFR-2 such as sunitinib and sorafenib failed to block endothelial cell proliferation in acidic conditions. In vivo, neutralizing tumor acidity with sodium bicarbonate increased the percentage of endothelial cells expressing VEGFR-2 in tumor xenografts. Furthermore, combining sodium bicarbonate with sunitinib provided stronger anti-cancer activity than either treatment alone. Histological analysis showed that sunitinib had a stronger anti-angiogenic effect when combined with sodium bicarbonate. Overall, our results show that endothelial cells prosper independently of VEGF in acidic conditions partly as a consequence of decreased VEGFR-2 expression. They further suggest that strategies aiming to raise intratumoral pH can improve the efficacy of anti-VEGF treatments.

Blood transfusion improves renal oxygenation and renal function in sepsis-induced acute kidney injury in rats

Background

The effects of blood transfusion on renal microcirculation during sepsis are unknown. This study aimed to investigate the effect of blood transfusion on renal microvascular oxygenation and renal function during sepsis-induced acute kidney injury.

Methods

Twenty-seven Wistar albino rats were randomized into four groups: a sham group (n = 6), a lipopolysaccharide (LPS) group (n = 7), a LPS group that received fluid resuscitation (n = 7), and a LPS group that received blood transfusion (n = 7). The mean arterial blood pressure, renal blood flow, and renal microvascular oxygenation within the kidney cortex were recorded. Acute kidney injury was assessed using the serum creatinine levels, metabolic cost, and histopathological lesions. Nitrosative stress (expression of endothelial (eNOS) and inducible nitric oxide synthase (iNOS)) within the kidney was assessed by immunohistochemistry. Hemoglobin levels, pH, serum lactate levels, and liver enzymes were measured.

Results

Fluid resuscitation and blood transfusion both significantly improved the mean arterial pressure and renal blood flow after LPS infusion. Renal microvascular oxygenation, serum creatinine levels, and tubular damage significantly improved in the LPS group that received blood transfusion compared to the group that received fluids. Moreover, the renal expression of eNOS was markedly suppressed under endotoxin challenge. Blood transfusion, but not fluid resuscitation, was able to restore the renal expression of eNOS. However, there were no significant differences in lactic acidosis or liver function between the two groups.

Conclusions

Blood transfusion significantly improved renal function in endotoxemic rats. The specific beneficial effect of blood transfusion on the kidney could have been mediated in part by the improvements in renal microvascular oxygenation and sepsis-induced endothelial dysfunction via the restoration of eNOS expression within the kidney.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1581-1) contains supplementary material, which is available to authorized users.

Endothelial Response to Glucocorticoids in Inflammatory Diseases

The endothelium plays a crucial role in inflammation. A balanced control of inflammation requires the action of glucocorticoids (GCs), steroidal hormones with potent cell-specific anti-inflammatory properties. Besides the classic anti-inflammatory effects of GCs on leukocytes, recent studies confirm that endothelial cells also represent an important target for GCs. GCs regulate different aspects of endothelial physiology including expression of adhesion molecules, production of pro-inflammatory cytokines and chemokines, and maintenance of endothelial barrier integrity. However, the regulation of endothelial GC sensitivity remains incompletely understood. In this review, we specifically examine the endothelial response to GCs in various inflammatory diseases ranging from multiple sclerosis, stroke, sepsis, and vasculitis to atherosclerosis. Shedding more light on the cross talk between GCs and endothelium will help to improve existing therapeutic strategies and develop new therapies better tailored to the needs of patients.

EPHA4-FC TREATMENT REDUCES ISCHEMIA/REPERFUSION-INDUCED INTESTINAL INJURY BY INHIBITING VASCULAR PERMEABILITY

The inflammatory response is characterized by increased endothelial permeability, which permits the passage of fluid and inflammatory cells into interstitial spaces. The Eph/ephrin receptor ligand system plays a role in inflammation through a signaling cascade, which modifies Rho-GTPase activity. We hypothesized that blocking Eph/ephrin signaling using an EphA4-Fc would result in decreased inflammation and tissue injury in a model of ischemia/reperfusion (I/R) injury. Mice undergoing intestinal I/R pretreated with the EphA4-Fc had significantly reduced intestinal injury compared to mice injected with the control Fc. This reduction in I/R injury was accompanied by significantly reduced neutrophil infiltration, but did not affect intestinal inflammatory cytokine generation. Using microdialysis, we identified that intestinal I/R induced a marked increase in systemic vascular leakage, which was completely abrogated in EphA4-Fc-treated mice. Finally, we confirmed the direct role of Eph/ephrin signaling in endothelial leakage by demonstrating that EphA4-Fc inhibited tumor necrosis factor-α-induced vascular permeability in human umbilical vein endothelial cells. This study identifies that Eph/ephrin interaction induces proinflammatory signaling in vivo by inducing vascular leak and neutrophil infiltration, which results in tissue injury in intestinal I/R. Therefore, therapeutic targeting of Eph/ephrin interaction using inhibitors, such as EphA4-Fc, may be a novel method to prevent tissue injury in acute inflammation by influencing endothelial integrity and by controlling vascular leak.

In vivo uteroplacental release of placental growth factor and soluble Fms-like tyrosine kinase-1 in normal and preeclamptic pregnancies

BACKGROUND

Preeclampsia is characterized by maternal endothelial dysfunction, which underlies a highly diverse clinical presentation. The pathophysiologic condition remains to be unraveled fully, but interplay between factors that are released from the placenta and maternal vascular vulnerability is likely. An imbalance in circulating angiogenic factors is a prominent feature of preeclampsia; placental growth factor and soluble Fms-like tyrosine kinase 1 have been implemented as biomarkers of placental function and preeclampsia. Their test accuracies are limited in a clinical setting, which urges better insight into their production and removal. Current data suggest that placental growth factor and soluble Fms-like tyrosine kinase 1 are released from the placenta. Both the circulating levels and the placental expression are altered in preeclamptic pregnancies. However, in vivo placental release has not been determined in human pregnancies. Moreover, there is evidence that extra-placental tissues might contribute to the circulating levels placental growth factor and soluble Fms-like tyrosine kinase 1 in normal and preeclamptic pregnancies.

OBJECTIVES

We aimed to study the in vivo placental release of placental growth factor and soluble Fms-like tyrosine kinase 1 by determining the uteroplacental arteriovenous differences in human pregnancies. Further, we investigated whether this release was altered in early-onset preeclampsia compared with control subjects and whether there was a release of placental growth factor and soluble Fms-like tyrosine kinase 1 from maternal systemic endothelium.

STUDY DESIGN

We conducted a case-control study at Oslo University Hospital and included 23 women with preeclampsia (diagnosis <34 weeks) and 20 control subjects. During cesarean delivery, we sampled blood from 3 vessels simultaneously (uterine vein, radial artery, and antecubital vein). We determined concentrations of placental growth factor and soluble Fms-like tyrosine kinase 1 and calculated the arteriovenous differences. A possible net placental and extra-placental release was evaluated with the use of a Wilcoxon signed rank test. Differences between groups were compared by a Mann-Whitney U-test.

RESULTS

The median gestational age at delivery was 33.4 weeks (Q1, 28.3; Q3, 34.4 weeks) in the preeclamptic group and 39.3 weeks (Q1, 39.0; Q3, 39.6 weeks) in the control subjects. Women with preeclampsia had lower plasma concentrations of placental growth factor and higher concentrations of soluble Fms-like tyrosine kinase 1 compared with control subjects (P<.001). There were significant uteroplacental arteriovenous differences of soluble Fms-like tyrosine kinase 1 in preeclampsia (P<.001), but not in the control subjects. The uteroplacental arteriovenous differences of placental growth factor were significant in both groups (P<.001). Despite lower concentrations of plasma placental growth factor in women with preeclampsia, the arteriovenous differences were not significantly different from normal pregnancies (P=.53), even when we corrected for placental weight (P=.79). We found no placental growth factor or soluble Fms-like tyrosine kinase 1 concentration differences between the radial artery and the antecubital vein.

CONCLUSION

Our findings are consistent with a net release of soluble Fms-like tyrosine kinase 1 from the placenta in early-onset preeclampsia. This study demonstrated a placental release of placental growth factor to the maternal circulation but could not demonstrate that this release was impaired in the preeclamptic group. We could not find evidence of systemic endothelial release of placental growth factor and soluble Fms-like tyrosine kinase 1 by analyzing the arteriovenous differences in the forearm. This study contributes to the pathophysiologic understanding of preeclampsia by the use of the clinical setting to test current concepts in vivo and underscores that studies of in vivo degradation rates of placentally released compounds are needed.

THE ENDOTHELIUM IN SEPSIS

Sepsis affects practically all aspects of endothelial cell (EC) function and is thought to be the key factor in the progression from sepsis to organ failure. Endothelial functions affected by sepsis include vasoregulation, barrier function, inflammation, and hemostasis. These are among other mechanisms often mediated by glycocalyx shedding, such as abnormal nitric oxide metabolism, up-regulation of reactive oxygen species generation due to down-regulation of endothelial-associated antioxidant defenses, transcellular communication, proteases, exposure of adhesion molecules, and activation of tissue factor. This review covers current insight in EC-associated hemostatic responses to sepsis and the EC response to inflammation. The endothelial cell lining is highly heterogeneous between different organ systems and consequently also in its response to sepsis. In this context, we discuss the response of the endothelial cell lining to sepsis in the kidney, liver, and lung. Finally, we discuss evidence as to whether the EC response to sepsis is adaptive or maladaptive. This study is a result of an Acute Dialysis Quality Initiative XIV Sepsis Workgroup meeting held in Bogota, Columbia, between October 12 and 15, 2014.

Matricellular protein SPARCL1 regulates tumor microenvironment-dependent endothelial cell heterogeneity in colorectal carcinoma

Different tumor microenvironments (TMEs) induce stromal cell plasticity that affects tumorigenesis. The impact of TME-dependent heterogeneity of tumor endothelial cells (TECs) on tumorigenesis is unclear. Here, we isolated pure TECs from human colorectal carcinomas (CRCs) that exhibited TMEs with either improved (Th1-TME CRCs) or worse clinical prognosis (control-TME CRCs). Transcriptome analyses identified markedly different gene clusters that reflected the tumorigenic and angiogenic activities of the respective TMEs. The gene encoding the matricellular protein SPARCL1 was most strongly upregulated in Th1-TME TECs. It was also highly expressed in ECs in healthy colon tissues and Th1-TME CRCs but low in control-TME CRCs. In vitro, SPARCL1 expression was induced in confluent, quiescent ECs and functionally contributed to EC quiescence by inhibiting proliferation, migration, and sprouting, whereas siRNA-mediated knockdown increased sprouting. In human CRC tissues and mouse models, vessels with SPARCL1 expression were larger and more densely covered by mural cells. SPARCL1 secretion from quiescent ECs inhibited mural cell migration, which likely led to stabilized mural cell coverage of mature vessels. Together, these findings demonstrate TME-dependent intertumoral TEC heterogeneity in CRC. They further indicate that TEC heterogeneity is regulated by SPARCL1, which promotes the cell quiescence and vessel homeostasis contributing to the favorable prognoses associated with Th1-TME CRCs.

CRIM1 is necessary for coronary vascular endothelial cell development and homeostasis

Endothelial cells form a critical component of the coronary vasculature, yet the factors regulating their development remain poorly defined. Here we reveal a novel role for the transmembrane protein CRIM1 in mediating cardiac endothelial cell development. In the absence of Crim1 in vivo, the coronary vasculature is malformed, the number of endothelial cells reduced, and the canonical BMP pathway dysregulated. Moreover, we reveal that CRIM1 can bind IGFs, and regulate IGF signalling within endothelial cells. Finally, loss of CRIM1 from human cardiac endothelial cells results in misregulation of endothelial genes, predicted by pathway analysis to be involved in an increased inflammatory response and cytolysis, reminiscent of endothelial cell dysfunction in cardiovascular disease pathogenesis. Collectively, these findings implicate CRIM1 in endothelial cell development and homeostasis in the coronary vasculature.

Human Endothelial Cell Models in Biomaterial Research

Endothelial cell (EC) models have evolved as important tools in biomaterial research due to ubiquitously occurring interactions between implanted materials and the endothelium. However, screening the available literature has revealed a gap between material scientists and physiologists in terms of their understanding of these biomaterial-endothelium interactions and their relative importance. Consequently, EC models are often applied in nonphysiological experimental setups, or too extensive conclusions are drawn from their results. The question arises whether this might be one reason why, among the many potential biomaterials, only a few have found their way into the clinic. In this review, we provide an overview of established EC models and possible selection criteria to enable researchers to determine the most reliable and relevant EC model to use.

Talin and vinculin are downregulated in atherosclerotic plaque; Tampere Vascular Study

BACKGROUND AND AIMS

Focal adhesions (FA) play an important role in the tissue remodeling and in the maintenance of tissue integrity and homeostasis. Talin and vinculin proteins are among the major constituents of FAs contributing to cellular well-being and intercellular communication.

METHODS

Microarray analysis (MA) and qRT-PCR low-density array were implemented to analyze talin-1, talin-2, meta-vinculin and vinculin gene expression in circulating blood and arterial plaque.

RESULTS

All analyzed genes were significantly and consistently downregulated in plaques (carotid, abdominal aortic and femoral regions) compared to left internal thoracic artery (LITA) control. The use of LITA samples as controls for arterial plaque samples was validated using immunohistochemistry by comparing LITA samples with healthy arterial samples from a cadaver. Even though the differences in expression levels between stable and unstable plaques were not statistically significant, we observed further negative tendency in the expression in unstable atherosclerotic plaques. The confocal tissue imaging revealed gradient of talin-1 expression in plaque with reduction close to the vessel lumen. Similar gradient was observed for talin-2 expression in LITA controls but was not detected in plaques. This suggests that impaired tissue mechanostability affects the tissue remodeling and healing capabilities leading to development of unstable plaques.

CONCLUSIONS

The central role of talin and vinculin in cell adhesions suggests that the disintegration of the tissue in atherosclerosis could be partially driven by downregulation of these genes, leading to loosening of cell-ECM interactions and remodeling of the tissue.

BMP-SMAD signalling output is highly regionalized in cardiovascular and lymphatic endothelial networks

BACKGROUND

Bone morphogenetic protein (BMP) signalling has emerged as a fundamental pathway in endothelial cell biology and deregulation of this pathway is implicated in several vascular disorders. BMP signalling output in endothelial cells is highly context- and dose-dependent. Phosphorylation of the BMP intracellular effectors, SMAD1/5/9, is routinely used to monitor BMP signalling activity. To better understand the in vivo context-dependency of BMP-SMAD signalling, we investigated differences in BMP-SMAD transcriptional activity in different vascular beds during mouse embryonic and postnatal stages. For this, we used the BRE::gfp BMP signalling reporter mouse in which the BMP response element (BRE) from the ID1-promotor, a SMAD1/5/9 target gene, drives the expression of GFP.

RESULTS

A mosaic pattern of GFP was present in various angiogenic sprouting plexuses and in endocardium of cardiac cushions and trabeculae in the heart. High calibre veins seemed to be more BRE::gfp transcriptionally active than arteries, and ubiquitous activity was present in embryonic lymphatic vasculature. Postnatal lymphatic vessels showed however only discrete micro-domains of transcriptional activity. Dynamic shifts in transcriptional activity were also observed in the endocardium of the developing heart, with a general decrease in activity over time. Surprisingly, proliferative endothelial cells were almost never GFP-positive. Patches of transcriptional activity seemed to correlate with vasculature undergoing hemodynamic alterations.

CONCLUSION

The BRE::gfp mouse allows to investigate selective context-dependent aspects of BMP-SMAD signalling. Our data reveals the highly dynamic nature of BMP-SMAD mediated transcriptional regulation in time and space throughout the vascular tree, supporting that BMP-SMAD signalling can be a source of phenotypic diversity in some, but not all, healthy endothelium. This knowledge can provide insight in vascular bed or organ-specific diseases and phenotypic heterogeneity within an endothelial cell population.

Analysis of Body-wide Unfractionated Tissue Data to Identify a Core Human Endothelial Transcriptome

Endothelial cells line blood vessels and regulate hemostasis, inflammation, and blood pressure. Proteins critical for these specialized functions tend to be predominantly expressed in endothelial cells across vascular beds. Here, we present a systems approach to identify a panel of human endothelial-enriched genes using global, body-wide transcriptomics data from 124 tissue samples from 32 organs. We identified known and unknown endothelial-enriched gene transcripts and used antibody-based profiling to confirm expression across vascular beds. The majority of identified transcripts could be detected in cultured endothelial cells from various vascular beds, and we observed maintenance of relative expression in early passage cells. In summary, we describe a widely applicable method to determine cell-type-specific transcriptome profiles in a whole-organism context, based on differential abundance across tissues. We identify potential vascular drug targets or endothelial biomarkers and highlight candidates for functional studies to increase understanding of the endothelium in health and disease.

Oxidative stress and inflammation in cerebral cavernous malformation disease pathogenesis: Two sides of the same coin

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CCM proteins play pleiotropic roles in various redox-sensitive signaling pathways.

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CCM proteins modulate the crosstalk between redox signaling and autophagy that govern cell homeostasis and stress responses.

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Oxidative stress and inflammation are emerging as key focal determinants of CCM lesion formation, progression and severity.

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The pleiotropic functions of CCM proteins may prevent vascular dysfunctions triggered by local oxidative stress and inflammatory events.

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The distinct therapeutic compounds proposed so far for CCM disease share the ability to modulate redox signaling and autophagy.

Cerebral Cavernous Malformation (CCM) is a vascular disease of proven genetic origin, which may arise sporadically or is inherited as an autosomal dominant condition with incomplete penetrance and highly variable expressivity. CCM lesions exhibit a range of different phenotypes, including wide inter-individual differences in lesion number, size, and susceptibility to intracerebral hemorrhage (ICH). Lesions may remain asymptomatic or result in pathological conditions of various type and severity at any age, with symptoms ranging from recurrent headaches to severe neurological deficits, seizures, and stroke. To date there are no direct therapeutic approaches for CCM disease besides the surgical removal of accessible lesions. Novel pharmacological strategies are particularly needed to limit disease progression and severity and prevent de novo formation of CCM lesions in susceptible individuals.

Useful insights into innovative approaches for CCM disease prevention and treatment are emerging from a growing understanding of the biological functions of the three known CCM proteins, CCM1/KRIT1, CCM2 and CCM3/PDCD10. In particular, accumulating evidence indicates that these proteins play major roles in distinct signaling pathways, including those involved in cellular responses to oxidative stress, inflammation and angiogenesis, pointing to pathophysiological mechanisms whereby the function of CCM proteins may be relevant in preventing vascular dysfunctions triggered by these events. Indeed, emerging findings demonstrate that the pleiotropic roles of CCM proteins reflect their critical capacity to modulate the fine-tuned crosstalk between redox signaling and autophagy that govern cell homeostasis and stress responses, providing a novel mechanistic scenario that reconciles both the multiple signaling pathways linked to CCM proteins and the distinct therapeutic approaches proposed so far. In addition, recent studies in CCM patient cohorts suggest that genetic susceptibility factors related to differences in vascular sensitivity to oxidative stress and inflammation contribute to inter-individual differences in CCM disease susceptibility and severity.

This review discusses recent progress into the understanding of the molecular basis and mechanisms of CCM disease pathogenesis, with specific emphasis on the potential contribution of altered cell responses to oxidative stress and inflammatory events occurring locally in the microvascular environment, and consequent implications for the development of novel, safe, and effective preventive and therapeutic strategies.

Relative vascular permeability and vascularity across different regions of the rat nasal mucosa: implications for nasal physiology and drug delivery

Intranasal administration provides a non-invasive drug delivery route that has been proposed to target macromolecules either to the brain via direct extracellular cranial nerve-associated pathways or to the periphery via absorption into the systemic circulation. Delivering drugs to nasal regions that have lower vascular density and/or permeability may allow more drug to access the extracellular cranial nerve-associated pathways and therefore favor delivery to the brain. However, relative vascular permeabilities of the different nasal mucosal sites have not yet been reported. Here, we determined that the relative capillary permeability to hydrophilic macromolecule tracers is significantly greater in nasal respiratory regions than in olfactory regions. Mean capillary density in the nasal mucosa was also approximately 5-fold higher in nasal respiratory regions than in olfactory regions. Applying capillary pore theory and normalization to our permeability data yielded mean pore diameter estimates ranging from 13–17 nm for the nasal respiratory vasculature compared to <10 nm for the vasculature in olfactory regions. The results suggest lymphatic drainage for CNS immune responses may be favored in olfactory regions due to relatively lower clearance to the bloodstream. Lower blood clearance may also provide a reason to target the olfactory area for drug delivery to the brain.

Vascular diseases await translation of blood vessels engineered from stem cells

The discovery of human induced pluripotent stem cells (hiPSCs) might pave the way toward a long-sought solution for obtaining sufficient numbers of autologous cells for tissue engineering. Several methods exist for generating endothelial cells or perivascular cells from hiPSCs in vitro for use in the building of vascular tissue. We discuss current developments in the generation of vascular progenitor cells from hiPSCs and the assessment of their functional capacity in vivo, opportunities and challenges for the clinical translation of engineered vascular tissue, and modeling of vascular diseases using hiPSC-derived vascular progenitor cells.

Hydrogen sulfide metabolism regulates endothelial solute barrier function

Hydrogen sulfide (H₂S) is an important gaseous signaling molecule in the cardiovascular system. In addition to free H₂S, H₂S can be oxidized to polysulfide which can be biologically active. Since the impact of H₂S on endothelial solute barrier function is not known, we sought to determine whether H₂S and its various metabolites affect endothelial permeability. In vitro permeability was evaluated using albumin flux and transendothelial electrical resistance. Different H₂S donors were used to examine the effects of exogenous H₂S. To evaluate the role of endogenous H₂S, mouse aortic endothelial cells (MAECs) were isolated from wild type mice and mice lacking cystathionine γ-lyase (CSE), a predominant source of H₂S in endothelial cells. In vivo permeability was evaluated using the Miles assay. We observed that polysulfide donors induced rapid albumin flux across endothelium. Comparatively, free sulfide donors increased permeability only with higher concentrations and at later time points. Increased solute permeability was associated with disruption of endothelial junction proteins claudin 5 and VE-cadherin, along with enhanced actin stress fiber formation. Importantly, sulfide donors that increase permeability elicited a preferential increase in polysulfide levels within endothelium. Similarly, CSE deficient MAECs showed enhanced solute barrier function along with reduced endogenous bound sulfane sulfur. CSE siRNA knockdown also enhanced endothelial junction structures with increased claudin 5 protein expression. In vivo, CSE genetic deficiency significantly blunted VEGF induced hyperpermeability revealing an important role of the enzyme for barrier function. In summary, endothelial solute permeability is critically regulated via exogenous and endogenous sulfide bioavailability with a prominent role of polysulfides.

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Polysulfide from cystathionine γ-lyase (CSE) and exogenous polysulfide donors increases endothelial permeability.

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The ability of polysulfide to increase permeability is associated with junction disruption and stress fiber formation.

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CSE expression in vivo regulates VEGF induced hyper-permeability.

Senescent endothelial cells: Potential modulators of immunosenescence and ageing

Recent studies have demonstrated that the accumulation of senescent endothelial cells may be the primary cause of cardiovascular diseases. Because of their multifunctional properties, endothelial cells actively take part in stimulating the immune system and inflammation. In addition, ageing is characterized by the progressive deterioration of immune cells and a decline in the activation of the immune response. This results in a loss of the primary function of the immune system, which is eliminating damaged/senescent cells and neutralizing potential sources of harmful inflammatory reactions. In this review, we discuss cellular senescence and the senescence-associated secretory phenotype (SASP) of endothelial cells and summarize the link between endothelial cells and immunosenescence. We describe the possibility that age-related changes in Toll-like receptors (TLRs) and microRNAs can affect the phenotypes of senescent endothelial cells and immune cells via a negative feedback loop aimed at restraining the excessive pro-inflammatory response. This review also addresses the following questions: how do senescent endothelial cells influence ageing or age-related changes in the inflammatory burden; what is the connection between ECs and immunosenescence, and what are the crucial hypothetical pathways linking endothelial cells and the immune system during ageing.

Schistosoma bovis-host interplay: Proteomics for knowing and acting

Schistosoma bovis is a parasite of ruminants that causes significant economic losses to farmers throughout Africa, Southwestern Asia and the Mediterranean. Additionally, recent studies have reported its zoonotic potential through the formation of S. bovis×Schistosoma haematobium hybrids. As observed in the Schistosoma species infecting humans, it is assumed that S. bovis has also evolved host regulatory molecules that ensure its long-term survival in the bloodstream of its host. Since these molecules could be potential targets for the development of new drugs and anti-schistosome vaccines, their identification and functional characterization were undertaken. With this aim in mind, the molecular interface between S. bovis and its vertebrate host was subjected to a series of proteomic studies, which started with the analysis of the proteomes of the S. bovis moieties exposed to the host, namely, the excretory/secretory products and the tegument surface. Thus, a wealth of novel molecular information of S. bovis was obtained, which in turn allowed the identification of several parasite proteins with fibrinolytic and anticoagulant activities that could be used by S. bovis to regulate the host defensive systems. Following on, the host interface was investigated by studying the proteome of the host vascular endothelium surface at two points along the infection: in the lung vessels during the schistosomula migration and in the portal vein after the parasites have reached adulthood and sexual maturity. These studies have provided original data regarding the proteomes of the endothelial cell surface of pulmonary vasculature and portal vein in S. bovis-infected animals, and have shown significant changes in these proteomes associated with infection. This review compiles current information and the analyses of all the proteomic data from S. bovis and the S. bovis-host interface, including the molecular and functional characterization of S. bovis proteins that were found to participate in the regulation of the host coagulation and fibrinolysis systems.

Nitro-oleic acid inhibits vascular endothelial inflammatory responses and the endothelial-mesenchymal transition

BACKGROUND

Inflammatory-mediated pathological processes in the endothelium arise as a consequence of the dysregulation of vascular homeostasis. Of particular importance are mediators produced by stimulated monocytes/macrophages inducing activation of endothelial cells (ECs). This is manifested by excessive soluble pro-inflammatory mediator production and cell surface adhesion molecule expression. Nitro-fatty acids are endogenous products of metabolic and inflammatory reactions that display immuno-regulatory potential and may represent a novel therapeutic strategy to treat inflammatory diseases. The purpose of our study was to characterize the effects of nitro-oleic acid (OA-NO2) on inflammatory responses and the endothelial-mesenchymal transition (EndMT) in ECs that is a consequence of the altered healing phase of the immune response.

METHODS

The effect of OA-NO2 on inflammatory responses and EndMT was determined in murine macrophages and murine and human ECs using Western blotting, ELISA, immunostaining, and functional assays.

RESULTS

OA-NO2 limited the activation of macrophages and ECs by reducing pro-inflammatory cytokine production and adhesion molecule expression through its modulation of STAT, MAPK and NF-κB-regulated signaling. OA-NO2 also decreased transforming growth factor-β-stimulated EndMT and pro-fibrotic phenotype of ECs. These effects are related to the downregulation of Smad2/3.

CONCLUSIONS

The study shows the pleiotropic effect of OA-NO2 on regulating EC-macrophage interactions during the immune response and suggests a role for OA-NO2 in the regulation of vascular endothelial immune and fibrotic responses arising during chronic inflammation.

GENERAL SIGNIFICANCE

These findings propose the OA-NO2 may be useful as a novel therapeutic agent for treatment of cardiovascular disorders associated with dysregulation of the endothelial immune response.

Endothelial cell-cardiomyocyte crosstalk in diabetic cardiomyopathy

The incidence of diabetes is increasing globally, with cardiovascular disease accounting for a substantial number of diabetes-related deaths. Although atherosclerotic vascular disease is a primary reason for this cardiovascular dysfunction, heart failure in patients with diabetes might also be an outcome of an intrinsic heart muscle malfunction, labelled diabetic cardiomyopathy. Changes in cardiomyocyte metabolism, which encompasses a shift to exclusive fatty acid utilization, are considered a leading stimulus for this cardiomyopathy. In addition to cardiomyocytes, endothelial cells (ECs) make up a significant proportion of the heart, with the majority of ATP generation in these cells provided by glucose. In this review, we will discuss the metabolic machinery that drives energy metabolism in the cardiomyocyte and EC, its breakdown following diabetes, and the research direction necessary to assist in devising novel therapeutic strategies to prevent or delay diabetic heart disease.

Oral trehalose supplementation improves resistance artery endothelial function in healthy middle-aged and older adults

We hypothesized that supplementation with trehalose, a disaccharide that reverses arterial aging in mice, would improve vascular function in middle-aged and older (MA/O) men and women. Thirty-two healthy adults aged 50-77 years consumed 100 g/day of trehalose (n=15) or maltose (n=17, isocaloric control) for 12 weeks (randomized, double-blind). In subjects with Δbody mass less than 2.3kg (5 lb.), resistance artery endothelial function, assessed by forearm blood flow to brachial artery infusion of acetylcholine (FBFACh), increased ~30% with trehalose (13.3±1.0 vs. 10.5±1.1 AUC, P=0.02), but not maltose (P=0.40). This improvement in FBFACh was abolished when endothelial nitric oxide (NO) production was inhibited. Endothelium-independent dilation, assessed by FBF to sodium nitroprusside (FBFSNP), also increased ~30% with trehalose (155±13 vs. 116±12 AUC, P=0.03) but not maltose (P=0.92). Changes in FBFACh and FBFSNP with trehalose were not significant when subjects with Δbody mass ≥ 2.3kg were included. Trehalose supplementation had no effect on conduit artery endothelial function, large elastic artery stiffness or circulating markers of oxidative stress or inflammation (all P>0.1) independent of changes in body weight. Our findings demonstrate that oral trehalose improves resistance artery (microvascular) function, a major risk factor for cardiovascular diseases, in MA/O adults, possibly through increasing NO bioavailability and smooth muscle sensitivity to NO.

Protein Kinase D1 Signaling in Angiogenic Gene Expression and VEGF-Mediated Angiogenesis

Protein kinase D 1 (PKD-1) is a signaling kinase important in fundamental cell functions including migration, proliferation, and differentiation. PKD-1 is also a key regulator of gene expression and angiogenesis that is essential for cardiovascular development and tumor progression. Further understanding molecular aspects of PKD-1 signaling in the regulation of angiogenesis may have translational implications in obesity, cardiovascular disease, and cancer. The author will summarize and provide the insights into molecular mechanisms by which PKD-1 regulates transcriptional expression of angiogenic genes, focusing on the transcriptional regulation of CD36 by PKD-1-FoxO1 signaling axis along with the potential implications of this axis in arterial differentiation and morphogenesis. He will also discuss a new concept of dynamic balance between proangiogenic and antiangiogenic signaling in determining angiogenic switch, and stress how PKD-1 signaling regulates VEGF signaling-mediated angiogenesis.

Angiocrine functions of organ-specific endothelial cells

Endothelial cells that line capillaries are not just passive conduits for delivering blood. Tissue-specific endothelium establishes specialized vascular niches that deploy sets of growth factors, known as angiocrine factors. These cues participate actively in the induction, specification, patterning and guidance of organ regeneration, as well as in the maintainance of homeostasis and metabolism. When upregulated following injury, they orchestrate self-renewal and differentiation of tissue-specific resident stem and progenitor cells into functional organs. Uncovering the mechanisms by which organotypic endothelium distributes physiological levels of angiocrine factors both spatially and temporally will lay the foundation for clinical trials that promote organ repair without scarring.

Segregated Foxc2, NFATc1 and Connexin expression at normal developing venous valves, and Connexin-specific differences in the valve phenotypes of Cx37, Cx43, and Cx47 knockout mice

Venous valves (VVs) are critical for unidirectional blood flow from superficial and deep veins towards the heart. Congenital valve aplasia or agenesis may, in some cases, be a direct cause of vascular disease, motivating an understanding of the molecular mechanisms underlying the development and maintenance of VVs. Three gap junction proteins (Connexins), Cx37, Cx43, and Cx47, are specifically expressed at VVs in a highly polarized fashion. VVs are absent from adult mice lacking Cx37; however it is not known if Cx37 is required for the initial formation of valves. In addition, the requirement of Cx43 and Cx47 for VV development has not been studied. Here, we provide a detailed description of Cx37, Cx43, and Cx47 expression during mouse vein development and show by gene knockout that each Cx is necessary for normal valve development. The valve phenotypes in the knockout lines exhibit Cx-specific differences, however, including whether peripheral or central VVs are affected by gene inactivation. In addition, we show that a Cx47 null mutation impairs peripheral VV development but does not affect lymphatic valve formation, a finding of significance for understanding how some CX47 mutations cause inherited lymphedema in humans. Finally, we demonstrate a striking segregation of Foxc2 and NFATc1 transcription factor expression between the downstream and upstream faces, respectively, of developing VV leaflets and show that this segregation is closely associated with the highly polarized expression of Cx37, Cx43, and Cx47. The partition of Foxc2 and NFATc1 expression at VV leaflets makes it unlikely that these factors directly cooperate during the leaflet elongation stage of VV development.

Transient Receptor Potential Channel 4 Encodes a Vascular Permeability Defect and High-Frequency Ca(2+) Transients in Severe Pulmonary Arterial Hypertension

The canonical transient receptor potential channel 4 (TRPC4) comprises an endothelial store-operated Ca(2+) entry channel, and TRPC4 inactivation confers a survival benefit in pulmonary arterial hypertension (PAH). Endothelial Ca(2+) signals mediated by TRPC4 enhance vascular permeability in vitro, but the contribution of TRPC4-dependent Ca(2+) signals to the regulation of endothelial permeability in PAH is poorly understood. We tested the hypothesis that TRPC4 increases vascular permeability and alters the frequency of endothelial Ca(2+) transients in PAH. We measured permeability in isolated lungs, and found that TRPC4 exaggerated permeability responses to thapsigargin in Sugen/hypoxia-treated PAH rats. We compared endothelial Ca(2+) activity of wild-type with TRPC4-knockout rats using confocal microscopy, and evaluated how Ca(2+) signals were influenced in response to thapsigargin and sequential treatment with acetylcholine. We found that thapsigargin-stimulated Ca(2+) signals were increased in PAH, and recovered by TRPC4 inactivation. Store depletion revealed bimodal Ca(2+) responses to acetylcholine, with both short- and long-duration populations. Our results show that TRPC4 underlies an exaggerated endothelial permeability response in PAH. Furthermore, TRPC4 increased the frequency of endothelial Ca(2+) transients in severe PAH, suggesting that TRPC4 provides a Ca(2+) source associated with endothelial dysfunction in the pathophysiology of PAH. This phenomenon represents a new facet of the etiology of PAH, and may contribute to PAH vasculopathy by enabling inflammatory mediator flux across the endothelial barrier.

Evaluation of nailfold videocapillaroscopy in central serous chorioretinopathy

BACKGROUND

Nailfold videocapillaroscopy (NVC) is a diagnostic tool to evaluate micro-vasculature. The presence of choroidal vasculopathy is apparent in central serous chorioretinopathy (CSCR).

OBJECTIVES

This study was aimed at assessing capillaroscopic nailfold findings in patients with CSCR. To the best of our knowledge, there is no study assessing NVC findings in CSCR in the literature.

METHOD

Sixty-one patients with CSCR who met the inclusion criteria, and 82 age- and sex-matched healthy controls were included to the study. A videocapillaroscopy device with 200× magnification was used for capillaroscopic assessment.

RESULTS

The mean age was 48.79 ± 11.15 years in the patient group (13 female, 48 male) and 49.38 ± 9.02 years in the control group (17 female, 65 male). The age and gender were comparable in the patient and control groups (p = 0.727 and p = 0.933, respectively). The capillary count was found to be decreased in the patient group compared to control group. No significant correlation was found between capillary count and choroidal thickness (p = 0.551; r = -0.081). In the patient group, the frequencies of major capillaroscopic findings including capillary ectasia, aneurysm, micro-hemorrhage, avascular area, tortuosity, neo-formation, bizarre capillary, bushy capillary, meander capillary and extravasation were found to be increased in the patient group. However, no significant correlation was detected between capillaroscopic findings and disease type and presence of attacks.

CONCLUSIONS

This is first study in which nailfold capillary assessment was performed in patients with CSCR, and we detected major capillaroscopic changes. These findings suggest that CSCR can be a systemic microvasculopathy. Further studies are needed to clarify the diagnostic and prognostic value of capillaroscopy in CSCR.

Chronic high-magnitude cyclic stretch stimulates EC inflammatory response via VEGF receptor 2-dependent mechanism

Ventilator-induced lung injury (VILI) is associated with activated inflammatory signaling, such as cytokine production by endothelial and epithelial cells and macrophages, although the precise mechanisms of inflammatory activation induced by VILI-relevant cyclic stretch (CS) amplitude remain poorly understood. We show that exposure of human pulmonary endothelial cells (EC) to chronic CS at 18% linear distension (18% CS), but not at physiologically relevant 5% CS, induces "EC-activated phenotype," which is characterized by time-dependent increase in ICAM1 and VCAM1 expression. A preconditioning of 18% CS also increased in a time-dependent fashion the release of soluble ICAM1 (sICAM1) and IL-8. Investigation of potential signaling mechanisms of CS-induced EC inflammatory activation showed that 18% CS, but not 5% CS, induced time-dependent upregulation of VEGF receptor 2 (VEGFR2), as monitored by increased protein expression and VEGFR2 tyrosine phosphorylation. Both CS-induced VEGFR2 expression and tyrosine phosphorylation were abrogated by cotreatment with reactive oxygen species inhibitor, N-acetyl cysteine. Molecular inhibition of VEGFR2 expression by gene-specific siRNA or treatment with VEGFR2 pharmacological inhibitor SU-1498 attenuated CS-induced activation of ICAM1 and VCAM1 expression and sICAM1 release. Chronic EC preconditioning at 18% CS augmented EC inflammation and barrier-disruptive response induced by proinflammatory cytokine TNF-α. This effect of chronic 18% CS preconditioning was attenuated by siRNA-induced VEGFR2 knockdown. This study demonstrates for the first time a VEGFR2-dependent mechanism of EC inflammatory activation induced by pathological CS. We conclude that, despite the recognized role of VEGF as a prosurvival and angiogenic factor, excessive activation of VEGFR2 signaling by high-tidal-volume lung mechanical ventilation may contribute to ventilator-induced (biotrauma) lung inflammation and barrier dysfunction by augmenting cell response to VILI-associated inflammatory mediators.

Scaffold-free Tissue Formation Under Real and Simulated Microgravity Conditions

Scaffold-free tissue formation in microgravity is a new method in regenerative medicine and an important topic in Space Medicine. In this MiniReview, we focus on recent findings in the field of tissue engineering that were observed by exposing cells to real microgravity in space or to devices simulating to at least some extent microgravity conditions on Earth (ground-based facilities). Under both conditions - real and simulated microgravity - a part of the cultured cells of various populations detaches from the bottom of a culture flask. The cells form three-dimensional (3D) aggregates resembling the organs from which the cells have been derived. As spaceflights are rare and extremely expensive, cell culture under simulated microgravity allows more comprehensive and frequent studies on the scaffold-free 3D tissue formation in some aspects, as a number of publications have proven during the last two decades. In this MiniReview, we summarize data from our own studies and work from various researchers about tissue engineering of multi-cellular spheroids formed by cancer cells, tube formation by endothelial cells and cartilage formation by exposing the cells to ground-based facilities such as the 3D Random Positioning Machine (RPM), the 2D Fast-Rotating Clinostat (FRC) or the Rotating Wall Vessel (RWV). Subsequently, we investigated self-organization of 3D aggregates without scaffolds pursuing to enhance the frequency of 3D formation and to enlarge the size of the organ-like aggregates. The density of the monolayer exposed to real or simulated microgravity as well as the composition of the culture media revealed an impact on the results. Genomic and proteomic alterations were induced by simulated microgravity. Under microgravity conditions, adherent cells expressed other genes than cells grown in spheroids. In this MiniReview, the recent improvements in scaffold-free tissue formation are summarized and relationships between phenotypic and molecular appearance are highlighted.

Extracellular Matrix Stiffness Controls VEGF Signaling and Processing in Endothelial Cells

Vascular endothelial growth factor A (VEGF) drives endothelial cell maintenance and angiogenesis. Endothelial cell behavior is altered by the stiffness of the substrate the cells are attached to suggesting that VEGF activity might be influenced by the mechanical cellular environment. We hypothesized that extracellular matrix (ECM) stiffness modifies VEGF-cell-matrix tethering leading to altered VEGF processing and signaling. We analyzed VEGF binding, internalization, and signaling as a function of substrate stiffness in endothelial cells cultured on fibronectin (Fn) linked polyacrylamide gels. Cell produced extracellular matrices on the softest substrates were least capable of binding VEGF, but the cells exhibited enhanced VEGF internalization and signaling compared to cells on all other substrates. Inhibiting VEGF-matrix binding with sucrose octasulfate decreased cell-internalization of VEGF and, inversely, heparin pre-treatment to enhance Fn-matrix binding of VEGF increased cell-internalization of VEGF regardless of matrix stiffness. β1 integrins, which connect cells to Fn, modulated VEGF uptake in a stiffness dependent fashion. Cells on hard surfaces showed decreased levels of activated β1 and inhibition of β1 integrin resulted in a greater proportional decrease in VEGF internalization than in cells on softer matrices. Extracellular matrix binding is necessary for VEGF internalization. Stiffness modifies the coordinated actions of VEGF-matrix binding and β1 integrin binding/activation, which together are critical for VEGF internalization. This study provides insight into how the microenvironment may influence tissue regeneration and response to injury and disease. J. Cell. Physiol. 231: 2026-2039, 2016. © 2016 Wiley Periodicals, Inc.

Engineering tissues with a perfusable vessel-like network using endothelialized alginate hydrogel fiber and spheroid-enclosing microcapsules

Development of the technique for constructing an internal perfusable vascular network is a challenging issue in fabrication of dense three-dimensional tissues in vitro. Here, we report a method for realizing it. We assembled small tissue (about 200 μm in diameter)-enclosing hydrogel microcapsules and a single hydrogel fiber, both covered with human vascular endothelial cells in a collagen gel. The microcapsules and fiber were made from alginate and gelatin derivatives, and had cell adhesive surfaces. The endothelial cells on the hydrogel constructs sprouted and spontaneously formed a network connecting the hydrogel constructs with each other in the collagen gel. Perfusable vascular network-like structure formation after degrading the alginate-based hydrogel constructs by alginate lyase was confirmed by introducing solution containing tracer particles of about 3 μm in diameter into the lumen templated by the alginate hydrogel fiber. The introduced solution flowed into the spontaneously formed capillary branches and passed around the individual spherical tissues.

Cytotoxicity of CdTe quantum dots in human umbilical vein endothelial cells: the involvement of cellular uptake and induction of pro-apoptotic endoplasmic reticulum stress

Cadmium telluride quantum dots (CdTe QDs) have been proposed to induce oxidative stress, which plays a crucial role in CdTe QDs-mediated mitochondrial-dependent apoptosis in human umbilical vein endothelial cells (HUVECs). However, the direct interactions of CdTe QDs with HUVECs and their potential impairment of other organelles like endoplasmic reticulum (ER) in HUVECs are poorly understood. In this study, we reported that the negatively charged CdTe QDs (−21.63±0.91 mV), with good dispersity and fluorescence stability, were rapidly internalized via endocytosis by HUVECs, as the notable internalization could be inhibited up to 95.52% by energy depletion (NaN₃/deoxyglucose or low temperature). The endocytosis inhibitors (methyl-β-cyclodextrin, genistein, sucrose, chlorpromazine, and colchicine) dramatically decreased the uptake of CdTe QDs by HUVECs, suggesting that both caveolae/raft- and clathrin-mediated endocytosis were involved in the endothelial uptake of CdTe QDs. Using immunocytochemistry, a striking overlap of the internalized CdTe QDs and ER marker was observed, which indicates that QDs may be transported to ER. The CdTe QDs also caused remarkable ER stress responses in HUVECs, confirmed by significant dilatation of ER cisternae, upregulation of ER stress markers GRP78/GRP94, and activation of protein kinase RNA-like ER kinase-eIF2α-activating transcription factor 4 pathway (including phosphorylation of both protein kinase RNA-like ER kinase and eIF2α and elevated level of activating transcription factor 4). CdTe QDs further promoted an increased C/EBP homologous protein expression, phosphorylation of c-JUN NH2-terminal kinase, and cleavage of ER-resident caspase-4, while the specific inhibitor (SP600125, Z-LEVD-fmk, or salubrinal) significantly attenuated QDs-triggered apoptosis, indicating that all three ER stress-mediated apoptosis pathways were activated and the direct participation of ER in the CdTe QDs-caused apoptotic cell death in HUVECs. Our findings provide important new insights into QDs toxicity and reveal potential cardiovascular risks for the future applications of QDs.

Endothelial Cords Promote Tumor Initial Growth prior to Vascular Function through a Paracrine Mechanism

The angiogenic switch is an important oncogenic step that determines whether microtumors remain dormant or progresses further. It has been generally perceived that the primary function of this tumorgenic event is to supply oxygen and nutrients through blood circulation. Using in vivo imaging of zebrafish and mouse tumor models, we showed that endothelial cords aggressively penetrated into microtumors and remained non-circulatory for several days before undergoing vascular blood perfusion. Unexpectedly, we found that initial tumor growth in both models was significantly reduced if endothelial cords were removed by blocking VEGF-VEGFR2 signaling or using a vascular deficient zebrafish mutant. It was further shown that soluble factors including IL-8, secreted by endothelial cells (ECs) were responsible for stimulating tumor cells proliferation. These findings establish that tumor angiogenesis play a much earlier and broader role in promoting tumor growth, which is independent of vascular circulation. Understanding this novel mechanism of angiogenic tumor progression offers new entry points for cancer therapeutics.

Self-Renewal and High Proliferative Colony Forming Capacity of Late-Outgrowth Endothelial Progenitors Is Regulated by Cyclin-Dependent Kinase Inhibitors Driven by Notch Signaling

Since the discovery of endothelial colony forming cells (ECFC), there has been significant interest in their therapeutic potential to treat vascular injuries. ECFC cultures display significant heterogeneity and a hierarchy among cells able to give rise to high proliferative versus low proliferative colonies. Here we aimed to define molecularly this in vitro hierarchy. Based on flow cytometry, CD34 expression levels distinguished two populations. Only CD34 + ECFC had the capacity to reproduce high proliferative potential (HPP) colonies on replating, whereas CD34- ECFCs formed only small clusters. CD34 + ECFCs were the only ones to self-renew in stringent single-cell cultures and gave rise to both CD34 + and CD34- cells. Upon replating, CD34 + ECFCs were always found at the centre of HPP colonies and were more likely in G0/1 phase of cell cycling. Functionally, CD34 + ECFC were superior at restoring perfusion and better engrafted when injected into ischemic hind limbs. Transcriptomic analysis identified cyclin-dependent kinase (CDK) cell cycle inhibiting genes (p16, p21, and p57), the Notch signaling pathway (dll1, dll4, hes1, and hey1), and the endothelial cytokine il33 as highly expressed in CD34 + ECFC. Blocking the Notch pathway using a γ-secretase inhibitor (DAPT) led to reduced expression of cell cycle inhibitors, increased cell proliferation followed by a loss of self-renewal, and HPP colony formation capacity reflecting progenitor exhaustion. Similarly shRNA knockdown of p57 strongly affected self-renewal of ECFC colonies. ECFC hierarchy is defined by Notch signalling driving cell cycle regulators, progenitor quiescence and self-renewal potential.

Heart Development, Angiogenesis, and Blood-Brain Barrier Function Is Modulated by Adhesion GPCRs

The cardiovascular system in adult organisms forms a network of interconnected endothelial cells, supported by mural cells and displaying a high degree of hierarchy: arteries emerging from the heart ramify into arterioles and then capillaries, which return to the venous systems through venules and veins. The cardiovascular system allows blood circulation, which in turn is essential for hemostasis through gas diffusion, nutrient distribution, and cell trafficking. In this chapter, we have summarized the current knowledge on how adhesion GPCRs (aGPCRs) impact heart development, followed by their role in modulating vascular angiogenesis.

CD40-TRAF Signaling Upregulates CX3CL1 and TNF-α in Human Aortic Endothelial Cells but Not in Retinal Endothelial Cells

CD40, CX3CL1 and TNF-α promote atheroma and neointima formation. CD40 and TNF-α are also central to the development of diabetic retinopathy while CX3CL1 may play a role in the pathogenesis of this retinopathy. The purpose of this study was to examine whether CD40 ligation increases CX3CL1 and TNF-α protein expression in human endothelial cells from the aorta and retina. CD154 (CD40 ligand) upregulated membrane-bound and soluble CX3CL1 in human aortic endothelial cells. CD154 triggered TNF-α production by human aortic endothelial cells. TNF Receptor Associated Factors (TRAF) are key mediators of CD40 signaling. Compared to human aortic endothelial cells that express wt CD40, cells that express CD40 with a mutation that prevents TRAF2,3 recruitment, or CD40 with a mutation that prevents TRAF6 recruitment exhibited a profound inhibition of CD154-driven upregulation of membrane bound and soluble CX3CL1 as well as of TNF-α secretion. While both CD154 and TNF-α upregulated CX3CL1 in human aortic endothelial cells, these stimuli could act independently of each other. In contrast to human aortic endothelial cells, human retinal endothelial cells did not increase membrane bound or soluble CX3CL1 expression or secrete TNF-α in response to CD154 even though CD40 ligation upregulated ICAM-1 and CCL2 in these cells. Moreover, TNF-α did not upregulate CX3CL1 in retinal endothelial cells. In conclusion, CD40 ligation increases CX3CL1 protein levels and induces TNF-α production in endothelial cells. However, endothelial cells are heterogeneous in regards to these responses. Human aortic but not retinal endothelial cells upregulated CX3CL1 and TNF-α in response to CD40 ligation, as well as upregulated CX3CL1 in response to TNF-α. These dissimilarities may contribute to differences in regulation of inflammation in large vessels versus the retina.

Metabolic coupling in urothelial bladder cancer compartments and its correlation to tumor aggressiveness

Monocarboxylate transporters (MCTs) are vital for intracellular pH homeostasis by extruding lactate from highly glycolytic cells. These molecules are key players of the metabolic reprogramming of cancer cells, and evidence indicates a potential contribution in urothelial bladder cancer (UBC) aggressiveness and chemoresistance. However, the specific role of MCTs in the metabolic compartmentalization within bladder tumors, namely their preponderance on the tumor stroma, remains to be elucidated. Thus, we evaluated the immunoexpression of MCTs in the different compartments of UBC tissue samples (n = 111), assessing the correlations among them and with the clinical and prognostic parameters. A significant decrease in positivity for MCT1 and MCT4 occurred from normoxic toward hypoxic regions. Significant associations were found between the expression of MCT4 in hypoxic tumor cells and in the tumor stroma. MCT1 staining in normoxic tumor areas, and MCT4 staining in hypoxic regions, in the tumor stroma and in the blood vessels were significantly associated with UBC aggressiveness. MCT4 concomitant positivity in hypoxic tumor cells and in the tumor stroma, as well as positivity in each of these regions concomitant with MCT1 positivity in normoxic tumor cells, was significantly associated with an unfavourable clinicopathological profile, and predicted lower overall survival rates among patients receiving platinum-based chemotherapy. Our results point to the existence of a multi-compartment metabolic model in UBC, providing evidence of a metabolic coupling between catabolic stromal and cancer cells' compartments, and the anabolic cancer cells. It is urgent to further explore the involvement of this metabolic coupling in UBC progression and chemoresistance.