Activation of an endothelial Notch1-Jagged1 circuit induces VCAM1 expression, an effect amplified by interleukin-1β

Endothelial Notch1 signaling in white adipose tissue promotes cancer cachexia

Cachexia is a major cause of morbidity and mortality in individuals with cancer and is characterized by weight loss due to adipose and muscle tissue wasting. Hallmarks of white adipose tissue (WAT) remodeling, which often precedes weight loss, are impaired lipid storage, inflammation and eventually fibrosis. Tissue wasting occurs in response to tumor-secreted factors. Considering that the continuous endothelium in WAT is the first line of contact with circulating factors, we postulated whether the endothelium itself may orchestrate tissue remodeling. Here, we show using human and mouse cancer models that during precachexia, tumors overactivate Notch1 signaling in distant WAT endothelium. Sustained endothelial Notch1 signaling induces a WAT wasting phenotype in male mice through excessive retinoic acid production. Pharmacological blockade of retinoic acid signaling was sufficient to inhibit WAT wasting in a mouse cancer cachexia model. This demonstrates that cancer manipulates the endothelium at distant sites to mediate WAT wasting by altering angiocrine signals.

Notch Signaling in the Vasculature: Angiogenesis and Angiocrine Functions

Formation of a functional blood vessel network is a complex process tightly controlled by pro- and antiangiogenic signals released within the local microenvironment or delivered through the bloodstream. Endothelial cells precisely integrate such temporal and spatial changes in extracellular signals and generate an orchestrated response by modulating signaling transduction, gene expression, and metabolism. A key regulator in vessel formation is Notch signaling, which controls endothelial cell specification, proliferation, migration, adhesion, and arteriovenous differentiation. This review summarizes the molecular biology of endothelial Notch signaling and how it controls angiogenesis and maintenance of the established, quiescent vasculature. In addition, recent progress in the understanding of Notch signaling in endothelial cells for controlling organ homeostasis by transcriptional regulation of angiocrine factors and its relevance to disease will be discussed.

Endothelial RBPJ Is Essential for the Education of Tumor-Associated Macrophages

Epithelial ovarian cancer (EOC) is one of the most lethal gynecologic cancers worldwide. EOC cells educate tumor-associated macrophages (TAM) through CD44-mediated cholesterol depletion to generate an immunosuppressive tumor microenvironment (TME). In addition, tumor cells frequently activate Notch1 receptors on endothelial cells (EC) to facilitate metastasis. However, further work is required to establish whether the endothelium also influences the education of recruited monocytes. Here, we report that canonical Notch signaling through RBPJ in ECs is an important player in the education of TAMs and EOC progression. Deletion of Rbpj in the endothelium of adult mice reduced infiltration of monocyte-derived macrophages into the TME of EOC and prevented the acquisition of a typical TAM gene signature; this was associated with stronger cytotoxic activity of T cells and decreased tumor burden. Mechanistically, CXCL2 was identified as a novel Notch/RBPJ target gene that regulated the expression of CD44 on monocytes and subsequent cholesterol depletion of TAMs. Bioinformatic analysis of ovarian cancer patient data showed that increased CXCL2 expression is accompanied by higher expression of CD44 and TAM education. Together, these findings indicate that EOC cells induce the tumor endothelium to secrete CXCL2 to establish an immunosuppressive microenvironment.

SIGNIFICANCE

Endothelial Notch signaling favors immunosuppression by increasing CXCL2 secretion to stimulate CD44 expression in macrophages, facilitating their education by tumor cells.

EGF repeats of epidermal growth factor‑like domain 7 promote endothelial cell activation and tumor escape from the immune system

The tumor blood vessel endothelium forms a barrier that must be crossed by circulating immune cells in order for them to reach and kill cancer cells. Epidermal growth factor‑like domain 7 (Egfl7) represses this immune infiltration by lowering the expression levels of leukocyte adhesion receptors on the surface of endothelial cells. However, the protein domains involved in these properties are not completely understood. Egfl7 is structurally composed of the predicted EMI‑, EGF‑ and C‑terminal domains. The present study aimed to investigate the roles of these different domains in tumor development by designing retroviruses coding for deletion mutants and then infecting 4T1 breast cancer cell populations, which consequently overexpressed the variants. By performing in vitro soft‑agar assays, it was found that Egfl7 and its deletion variants did not affect cell proliferation or anchorage‑independent growth. When 4T1 cells expressing either the wild‑type Egfl7 protein or Egfl7 domain variants were implanted in mice, Egfl7 expression markedly promoted tumor development and deletion of the EGF repeats decreased the tumor growth rate. By contrast, deleting any other domain displayed no significant effect on tumor development. The overexpression of Egfl7 also decreased T cell and natural killer cell infiltration in tumors, as determined by immunofluorescence staining of tumor sections, whereas deletion of the EGF repeats inhibited this effect. Reverse transcription‑quantitative PCR analysis of the mechanisms involved revealed that deleting the EGF repeats partially restored the expression levels of vascular cell adhesion molecule 1 and E‑selectin, which were suppressed by overexpression of Egfl7 in endothelial cells in vitro. This resulted in a higher number of lymphocytes bound to HUVEC expressing Egfl7‑ΔEGF compared with HUVEC expressing wild‑type Egfl7, as assessed by fluorescent‑THP‑1 adhesion assays onto endothelial cells. Overall, the present study demonstrated that the EGF repeats may participate in the protumoral and anti‑inflammatory effects of Egfl7.

Adding a "Notch" to Cardiovascular Disease Therapeutics: A MicroRNA-Based Approach

Dysregulation of the Notch pathway is implicated in the pathophysiology of cardiovascular diseases (CVDs), but, as of today, therapies based on the re-establishing the physiological levels of Notch in the heart and vessels are not available. A possible reason is the context-dependent role of Notch in the cardiovascular system, which would require a finely tuned, cell-specific approach. MicroRNAs (miRNAs) are short functional endogenous, non-coding RNA sequences able to regulate gene expression at post-transcriptional levels influencing most, if not all, biological processes. Dysregulation of miRNAs expression is implicated in the molecular mechanisms underlying many CVDs. Notch is regulated and regulates a large number of miRNAs expressed in the cardiovascular system and, thus, targeting these miRNAs could represent an avenue to be explored to target Notch for CVDs. In this Review, we provide an overview of both established and potential, based on evidence in other pathologies, crosstalks between miRNAs and Notch in cellular processes underlying atherosclerosis, myocardial ischemia, heart failure, calcification of aortic valve, and arrhythmias. We also discuss the potential advantages, as well as the challenges, of using miRNAs for a Notch-based approach for the diagnosis and treatment of the most common CVDs.

The Notch pathway: a novel therapeutic target for cardiovascular diseases?

Introduction: The Notch pathway is involved in determining cell fate during development and postnatally in continuously renewing tissues, such as the endothelium, the epithelium, and in the stem cells pool. The dysregulation of the Notch pathway is one of the causes of limited response, or resistance, to available cancer treatments and novel therapeutic strategies based on Notch inhibition are being investigated in preclinical and clinical studies in oncology. A large body of evidence now shows that the dysregulation of the Notch pathway is also involved in the pathophysiology of cardiovascular diseases (CVDs). Areas covered: This review discusses the molecular mechanisms involving Notch which underlie heart failure, aortic valve calcification, and aortic aneurysm. Expert opinion: Despite the existence of preventive, pharmacological and surgical interventions approaches, CVDs are the first causes of mortality worldwide. The Notch pathway is becoming increasingly recognized as being involved in heart failure, aortic aneurysm and aortic valve calcification, which are among the most common global causes of mortality due to CVDs. As already shown in cancer, the dissection of the biological processes and molecular mechanisms involving Notch should pave the way for new strategies to prevent and cure these diseases.

The Use of Nutraceuticals to Counteract Atherosclerosis: The Role of the Notch Pathway

Despite the currently available pharmacotherapies, today, thirty percent of worldwide deaths are due to cardiovascular diseases (CVDs), whose primary cause is atherosclerosis, an inflammatory disorder characterized by the buildup of lipid deposits on the inside of arteries. Multiple cellular signaling pathways have been shown to be involved in the processes underlying atherosclerosis, and evidence has been accumulating for the crucial role of Notch receptors in regulating the functions of the diverse cell types involved in atherosclerosis onset and progression. Several classes of nutraceuticals have potential benefits for the prevention and treatment of atherosclerosis and CVDs, some of which could in part be due to their ability to modulate the Notch pathway. In this review, we summarize the current state of knowledge on the role of Notch in vascular health and its modulation by nutraceuticals for the prevention of atherosclerosis and/or treatment of related CVDs.

Estrogen-mediated protection against coronary heart disease: The role of the Notch pathway

Estrogen regulates a plethora of biological processes, under physiological and pathological conditions, by affecting key pathways involved in the regulation of cell proliferation, fate, survival and metabolism. The Notch receptors are mediators of communication between adjacent cells and are key determinants of cell fate during development and in postnatal life. Crosstalk between estrogen and the Notch pathway intervenes in many processes underlying the development and maintenance of the cardiovascular system. The identification of molecular mechanisms underlying the interaction between these types of endocrine and juxtacrine signaling are leading to a deeper understanding of physiological conditions regulated by these steroid hormones and, potentially, to novel therapeutic approaches to prevent pathologies linked to reduced levels of estrogen, such as coronary heart disease, and cardiotoxicity caused by hormone therapy for estrogen-receptor-positive breast cancer.

Sox7 is involved in antibody-dependent endothelial cell activation and renal allograft injury via the Jagged1-Notch1 pathway

BACKGROUND

Antibody-mediated rejection (AMR) can cause graft loss and reduces long-term graft survival after kidney transplantation. Human leukocyte antigen (HLA) and/or non-HLA antibodies play a key role in the pathogenesis of AMR by targeting the allograft epithelium via complement activation and complement-independent mechanisms. However, the precise mechanisms of AMR remain unclear and treatment is still limited.

METHODS

In this study, we investigated the role of the endothelial-associated transcription factor Sox7 in AMR, using the anti-HLA antibody W6/32, shRNA-mediated Sox7 knockdown, and by manipulating the Notch pathway. We used an in vitro human kidney glomerular endothelial cells (HKGECs) model and an in vivo MHC-mismatched kidney transplantation model.

RESULTS

Sox7 expression was upregulated and the Jagged1-Notch1 pathway was activated in HKGECs after W6/32 activation. W6/32 antibodies increased the expression of adhesion molecules (VCAM-1, ICAM-1), inflammatory cytokines (IL-6, TNF-α), and chemokines (CXCL8, CXCL10), and Sox7 knockdown and inhibition of the Notch pathway by DAPT significantly reduced these effects. Jagged1 overexpression rescued the inhibitory effects of Sox7 knockdown. In addition, Sox7 knockdown attenuated acute allograft kidney injury in mice and reduced the expression of adhesion molecules and Jagged1-Notch1 signaling after transplantation.

CONCLUSIONS

Our findings suggest that Sox7 plays an important role in mediating HLA I antibody-dependent endothelial cell activation and acute kidney allograft rejection via the Jagged1-Notch1 pathway. Manipulating Sox7 in donor organs may represent a useful treatment for AMR in solid organ transplantation.

Arecoline N-oxide regulates oral squamous cell carcinoma development through NOTCH1 and FAT1 expressions

Areca nut has been evaluated as a group I carcinogen to humans. However, the exact compounds of areca nut causing oral cancer remain unproven. Previous findings from our lab revealed that arecoline N-oxide (ANO), a metabolite of arecoline, exhibits an oral fibrotic effect in immune-deficient NOD/SCID mice. The aim of this study is to investigate the oral potentially malignant disorders (OPMD) inductive activity between areca-alkaloid arecoline and its metabolite ANO in C57BL/6 mice. Our findings show that ANO showed higher activity in inducing hyperplasia with leukoplakia and collagen deposition in C57BL/6 mice compared with the arecoline treated groups. Importantly, immunohistochemical studies showed significant upregulation of NOTCH1, HES1, FAT1, PCNA, and Ki67 expressions in the pathological hyperplastic part. In addition, in vitro studies showed that upregulation of NOTCH1 and FAT1 expressions in ANO treated HGF-1 and DOK cell models. We found that NOTCH1 regulates TP53 expression from NOTCH1 knockdown oral cancer cells. The DNA damage was significantly increased after arecoline and ANO treatment. Further, we found that arecoline-induced H2AX expression was regulated by FMO3. Altogether, our findings show that ANO exhibited higher toxicity in OPMD activity and play a significant role in the induction of areca nut mediated oral tumorigenesis.

NLRP3 inflammasome promotes diabetes-induced endothelial inflammation and atherosclerosis

BACKGROUND

NLRP3 inflammasome can be activated by high glucose and links inflammation and metabolic disease. This study aimed to investigate the role of NLRP3 inflammasome in hyperglycemia-induced endothelial inflammation and diabetic atherosclerosis.

METHODS

NLRP3 levels in peripheral blood mononuclear cell (PBMC) and plasma IL-1β level were measured in diabetes patients. The activation of NLPR3 was detected in diabetic ApoE-/- mice and human umbilical vein endothelial cells (HUVECs).

RESULTS

Compared with healthy controls, NLRP3 expression levels in PBMC and plasma IL-1β level were significantly higher in diabetes patients but considerably decreased after lifestyle interventions and medicine. Moreover, carotid atherosclerosis was significantly related to plasma IL-1β level in diabetes patients. In diabetic atherosclerosis mouse model, NLRP3 knockdown suppressed NLRP3 inflammasome activation, inhibited the expression of adhesion molecules ICAM-1 and VCAM-1 in intima, reduced atherosclerosis and stabilized atherosclerotic plaque. In vitro, the expression of NLRP3 inflammasome components and the secretion of IL-1β were augmented by high glucose in HUVECs. Moreover, either high glucose or IL-1β promoted the expression of adhesion molecules, which were suppressed by NLRP3 knockdown or IL-1β receptor antagonist.

CONCLUSION

These findings provide novel insights into pathological mechanisms of diabetic atherosclerosis and have potential therapeutic implications for cardiovascular complications in diabetes.

Molecular mechanism of Notch signaling with special emphasis on microRNAs: Implications for glioma

Glioma is the most aggressive primary brain tumor and is notorious for resistance to chemoradiotherapy. Although its associated mechanisms are still not completely understood, Notch signaling, an evolutionarily conserved pathway, appears to be the key processes involved. Nevertheless, its mechanisms are sophisticated, due to a variety of targets and signal pathways, especially microRNA. MicroRNAs, which are small noncoding regulatory RNA molecules, have been proposed as one of the key mechanisms in glioma pathogenesis. Among the known glioma associated microRNA, microRNA-129, microRNA-34 family, and microRNA-326 have been shown to influence the progress of glioma through Notch signaling. Evidence also indicates that recurrence is due to development or persistence of the glioma stem-like cells and active angiogenesis, which are tightly regulated by a variety of factors, including Notch signaling. In this review, we summarize the recent progress regarding the functional roles of Notch signaling in glioma, including Notch ligand, microRNA, intracellular crosstalk, glioma stem-like cells and active angiogenesis and explore their clinical implications as diagnostic or prognostic biomarkers and molecular therapeutic targets for glioma.

Notch Signaling in Macrophages in the Context of Cancer Immunity

Macrophages play both tumor-suppressing and tumor-promoting roles depending on the microenvironment. Tumor-associated macrophages (TAMs) are often associated with poor prognosis in most, but not all cancer. Understanding how macrophages become TAMs and how TAMs interact with tumor cells and shape the outcome of cancer is one of the key areas of interest in cancer therapy research. Notch signaling is involved in macrophage activation and its effector functions. Notch signaling has been indicated to play roles in the regulation of macrophage activation in pro-inflammatory and wound-healing processes. Recent evidence points to the involvement of canonical Notch signaling in the differentiation of TAMs in a breast cancer model. On the other hand, hyperactivation of Notch signaling specifically in macrophages in tumors mass has been shown to suppress tumor growth in an animal model of cancer. Investigations into how Notch signaling is regulated in TAMs and translates into pro- or anti-tumor functions are still largely in their infancy. Therefore, in this review, we summarize the current understanding of the conflicting roles of Notch signaling in regulating the effector function of macrophages and the involvement of Notch signaling in TAM differentiation and function. Furthermore, how Notch signaling in TAMs affects the tumor microenvironment is reviewed. Finally, the direct or indirect cross-talk among TAMs, tumor cells and other cells in the tumor microenvironment via Notch signaling is discussed along with the possibility of its clinical application. Investigations into Notch signaling in macrophages may lead to a more effective way for immune intervention in the treatment of cancer in the future.

Inhibition of Endothelial NOTCH1 Signaling Attenuates Inflammation by Reducing Cytokine-Mediated Histone Acetylation at Inflammatory Enhancers

OBJECTIVE

Endothelial upregulation of adhesion molecules serves to recruit leukocytes to inflammatory sites and appears to be promoted by NOTCH1; however, current models based on interactions between active NOTCH1 and NF-κB components cannot explain the transcriptional selectivity exerted by NOTCH1 in this context.

APPROACH AND RESULTS

Observing that Cre/Lox-induced conditional mutations of endothelial Notch modulated inflammation in murine contact hypersensitivity, we found that IL (interleukin)-1β stimulation induced rapid recruitment of RELA (v-rel avian reticuloendotheliosis viral oncogene homolog A) to genomic sites occupied by NOTCH1-RBPJ (recombination signal-binding protein for immunoglobulin kappa J region) and that NOTCH1 knockdown reduced histone H3K27 acetylation at a subset of NF-κB-directed inflammatory enhancers.

CONCLUSIONS

Our findings reveal that NOTCH1 signaling supports the expression of a subset of inflammatory genes at the enhancer level and demonstrate how key signaling pathways converge on chromatin to coordinate the transition to an infla mmatory endothelial phenotype.

Control of Blood Vessel Formation by Notch Signaling

Blood vessels span throughout the body to nourish tissue cells and to provide gateways for immune surveillance. Endothelial cells that line capillaries have the remarkable capacity to be quiescent for years but to switch rapidly into the activated state once new blood vessels need to be formed. In addition, endothelial cells generate niches for progenitor and tumor cells and provide organ-specific paracrine (angiocrine) factors that control organ development and regeneration, maintenance of homeostasis and tumor progression. Recent data indicate a pivotal role for blood vessels in responding to metabolic changes and that endothelial cell metabolism is a novel regulator of angiogenesis. The Notch pathway is the central signaling mode that cooperates with VEGF, WNT, BMP, TGF-β, angiopoietin signaling and cell metabolism to orchestrate angiogenesis, tip/stalk cell selection and arteriovenous specification. Here, we summarize the current knowledge and implications regarding the complex roles of Notch signaling during physiological and tumor angiogenesis, the dynamic nature of tip/stalk cell selection in the nascent vessel sprout and arteriovenous differentiation. Furthermore, we shed light on recent work on endothelial cell metabolism, perfusion-independent angiocrine functions of endothelial cells in organ-specific vascular beds and how manipulation of Notch signaling may be used to target the tumor vasculature.

Persistent Expression of VCAM1 in Radial Glial Cells Is Required for the Embryonic Origin of Postnatal Neural Stem Cells

During development, neural stem cells (NSCs) undergo transitions from neuroepithelial cells to radial glial cells (RGCs), and later, a subpopulation of slowly dividing RGCs gives rise to the quiescent adult NSCs that populate the ventricular-subventricular zone (V-SVZ). Here we show that VCAM1, a transmembrane protein previously found in quiescent adult NSCs, is expressed by a subpopulation of embryonic RGCs, in a temporal and region-specific manner. Loss of VCAM1 reduced the number of active embryonic RGCs by stimulating their premature neuronal differentiation while preventing quiescence in the slowly dividing RGCs. This in turn diminished the embryonic origin of postnatal NSCs, resulting in loss of adult NSCs and defective V-SVZ regeneration. VCAM1 affects the NSC fate by signaling through its intracellular domain to regulate β-catenin signaling in a context-dependent manner. Our findings provide new insight on how stem cells in the embryo are preserved to meet the need for growth and regeneration.

Context-dependent function of ROS in the vascular endothelium: The role of the Notch pathway and shear stress

Reactive oxygen species (ROS) act as signal molecules in several biological processes whereas excessive, unregulated, ROS production contributes to the development of pathological conditions including endothelial dysfunction and atherosclerosis. The maintenance of a healthy endothelium depends on many factors and on their reciprocal interactions; in this framework, the Notch pathway and shear stress (SS) play two lead roles. Recently, evidence of a crosstalk between ROS, Notch, and SS, is emerging. The aim of this review is to describe the way ROS interact with the Notch pathway and SS protecting from-or promoting-the development of endothelial dysfunction. © 2017 BioFactors, 43(4):475-485, 2017.

Effects of Notch signalling pathway on the relationship between vascular endothelial dysfunction and endothelial stromal transformation in atherosclerosis

At present, with the improvement of living standards and population aging, the incidence of cardiovascular and cerebrovascular disease is on the rise and has been a serious threat to human health. Statistics show that the current death caused by cardiovascular and cerebrovascular disease has become the first cause of death has been increasing year by year. Therefore, studies on coronary heart disease and atherosclerosis (AS) have become a hot topic in clinical and basic research. In this study, the question of the effect of Notch signalling pathway on the relationship between endothelial dysfunction and endothelial stromal transformation in AS was studied in depth. Based on our results, we drew conclusions as follows. First, the Notch signalling pathway was activated in the atherosclerotic model; secondly, the Notch signalling pathway was demonstrated to enhance AS by promoting vascular endothelial dysfunction; thirdly, it was demonstrated that the Notch signalling pathway was mediated by promoting endothelial and to enhance AS; finally, we confirmed the endothelial function through the Notch signalling pathway to affect the transformation of endothelial stroma to achieve synergistic AS effect. The results of this study have a good guiding significance for the important role of Notch signalling in AS and indicate the ability to influence endothelial function and endothelial stromal transformation by intervening Notch signalling pathway and can affect the relationship between them, and thus eventually achieve the treatment of AS.

Determination of Genes Related to Uveitis by Utilization of the Random Walk with Restart Algorithm on a Protein-Protein Interaction Network

Uveitis, defined as inflammation of the uveal tract, may cause blindness in both young and middle-aged people. Approximately 10–15% of blindness in the West is caused by uveitis. Therefore, a comprehensive investigation to determine the disease pathogenesis is urgent, as it will thus be possible to design effective treatments. Identification of the disease genes that cause uveitis is an important requirement to achieve this goal. To begin to answer this question, in this study, a computational method was proposed to identify novel uveitis-related genes. This method was executed on a large protein–protein interaction network and employed a popular ranking algorithm, the Random Walk with Restart (RWR) algorithm. To improve the utility of the method, a permutation test and a procedure for selecting core genes were added, which helped to exclude false discoveries and select the most important candidate genes. The five-fold cross-validation was adopted to evaluate the method, yielding the average F1-measure of 0.189. In addition, we compared our method with a classic GBA-based method to further indicate its utility. Based on our method, 56 putative genes were chosen for further assessment. We have determined that several of these genes (e.g., CCL4, Jun, and MMP9) are likely to be important for the pathogenesis of uveitis.

Notch signaling facilitates crossing of endothelial barriers by tumor cells

Blood vessels supply tumor cells with oxygen and nutrients and provide the basis for metastatic dissemination. In addition, endothelial cells can provide factors that orchestrate the behavior of tumor cells. Here, we expand upon our previous findings that link activation of Notch signaling in the endothelium to cellular senescence, weakening of cell junctions, and expression of adhesion molecules, which facilitates tumor and immune cell migration across the vessel wall and homing at distant sites.

Endothelial Cell Activation Is Regulated by Epidermal Growth Factor-like Domain 7 (Egfl7) during Inflammation

Activation of the blood vessel endothelium is a critical step during inflammation. Endothelial cells stimulated by pro-inflammatory cytokines play an essential part in the adhesion and extravasation of circulating leukocytes into inflamed tissues. The endothelial egfl7 gene (VE-statin) represses endothelial cell activation in tumors, and prior observations suggested that it could also participate in the regulation of endothelial cell activation during inflammation. We show here that Egfl7 expression is strongly repressed in mouse lung endothelial cells during LPS- and TNFα-induced inflammation in vivo LPS have a limited effect on Egfl7 expression by endothelial cells in vitro, whereas the pro-inflammatory cytokine TNFα strongly represses Egfl7 expression in endothelial cells. TNFα regulates the egfl7 gene promoter through regions located between -7585 and -5550 bp ahead of the main transcription start site and via an NF-κB-dependent mechanism. Conversely, Egfl7 regulates the response of endothelial cells to TNFα by restraining the induced expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin, resulting in a decreased adhesion of leukocytes onto endothelial cells stimulated by TNFα. Egfl7 regulates the expression of these adhesion molecules through the NF-κB and MEK/Erk pathways, in particular by preventing the proteasome-mediated degradation of IkBα both in non-activated endothelial cells and during activation. Egfl7 is thus an endogenous and constitutive repressor of blood vessel endothelial cell activation in normal and inflammatory conditions and participates in a loop of regulation of activation of these cells by pro-inflammatory cytokines.