Hepatocyte growth factor inhibits VEGF-forkhead-dependent gene expression in endothelial cells

FOXO1 stimulates tip cell-enriched gene expression in endothelial cells

Forkhead box O (FOXO) family proteins are expressed in various cells, and play crucial roles in cellular metabolism, apoptosis, and aging. FOXO1-null mice exhibit embryonic lethality due to impaired endothelial cell (EC) maturation and vascular remodeling. However, FOXO1-mediated genome-wide regulation in ECs remains unclear. Here, we demonstrate that VEGF dynamically regulates FOXO1 cytosol-nucleus translocation. FOXO1 re-localizes to the nucleus via PP2A phosphatase. RNA-seq combined with FOXO1 overexpression/knockdown in ECs demonstrated that FOXO1 governs the VEGF-responsive tip cell-enriched genes, and further inhibits DLL4-NOTCH signaling. Endogenous FOXO1 ChIP-seq revealed that FOXO1 binds to the EC-unique tip-enriched genes with co-enrichment of EC master regulators, and the condensed chromatin region as a pioneer factor. We identified new promoter/enhancer regions of the VEGF-responsive tip cell genes regulated by FOXO1: ESM1 and ANGPT2. This is the first study to identify cell type-specific FOXO1 functions, including VEGF-mediated tip cell definition in primary cultured ECs.

Pathogenic Mechanisms of Preeclampsia with Severe Features Implied by the Plasma Exosomal miRNA Profile

Preeclampsia is a complication of pregnancy characterized by high blood pressure and organ damage after 20 gestational weeks. It is associated with high maternal and fetal morbidity and mortality. However, at present, there is no effective prevention or treatment for this condition. Previous studies have revealed that plasma exosomal mirnas from pregnant women with preeclampsia could serve as biomarkers of pathogenic factors. However, the roles of plasma exosomal mirnas in preeclampsia with severe features (sPE), which is associated with poorer pregnancy outcomes, remain unknown. Thus, the aims of this study were to characterize plasma exosomal miRNAs in sPE and explore the related pathogenic mechanisms using bioinformatic analysis. Plasma exosomes were isolated using a mirVana RNA isolation kit. the exosomal miRNAs were detected using high-throughput sequencing and the mirnas related to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and gene ontology (GO) terms were analyzed using the clusterprofiler package of R. Fifteen miRNAs exhibited increased expression and fourteen miRNAs exhibited reduced expression in plasma exosomes from women with sPE as compared to normal pregnant women. Further, gene set enrichment analysis revealed that the differentially expressed plasma exosomal miRNAs were related to the stress response and cell junction regulation, among others. In summary, this study is the first to identify the differentially expressed plasma exosomal miRNAs in sPE. These findings highlight promising pathogenesis mechanisms underlying preeclampsia.

Growth arrest-specific 6 regulates thrombin-induced expression of vascular cell adhesion molecule-1 through forkhead box O1 in endothelial cells

BACKGROUND

Growth arrest-specific 6 (Gas6)-deficient mice are protected against venous thromboembolism (VTE), suggesting a role for Gas6 in this disorder. We previously demonstrated that Gas6 induces forkhead box O1 (FoxO-1) phosphorylation through the phosphoinositide 3-kinase-Akt pathway. FoxO-1 regulates the expression of vascular cell adhesion molecule-1 (VCAM-1), a molecule that has been implicated in VTE.

OBJECTIVES

To assess the role of FoxO-1 in Gas6-dependent VCAM-1 expression.

METHODS

Thrombin was used to stimulate endothelial cells (ECs). Wild-type (WT) and Gas6(-/-) ECs were transfected with small interfering RNA targeting Axl or FoxO-1, a luciferase-coupled plasmid containing the FoxO-1 consensus sequence, and a phosphorylation-resistant FoxO-1 mutant, or treated with an Akt inhibitor. VCAM-1 mRNA expression was measured by real time-qPCR. VCAM-1 protein expression and FoxO-1 and Akt phosphorylation were assessed by western blot analysis. FoxO-1 localization was assessed by immunofluorescence. Adhesion of bone marrow mononuclear cells (BM-MCs) on ECs was assessed by fluorescence.

RESULTS AND CONCLUSIONS

Thrombin induces both VCAM-1 expression and FoxO-1 phosphorylation and nuclear exclusion in WT ECs only. Silencing of FoxO-1 enhances VCAM-1 expression in both WT and Gas6(-/-) ECs. Inhibition of Akt or FoxO-1 phosphorylation prevents VCAM-1 expression in WT ECs. These data show that Gas6 induces FoxO-1 phosphorylation, leading to derepression of VCAM-1 expression. BM-MC-EC adhesion is increased by thrombin in WT ECs. BM-MC-EC adhesion is further increased when FoxO-1 is silenced, but decreased when FoxO-1 phosphorylation is inhibited. These results demonstrate that the Gas6-FoxO-1 signaling axis plays an important role in VCAM-1 expression in the context of VTE by promoting BM-MC-EC adhesion.

PKA turnover by the REGγ-proteasome modulates FoxO1 cellular activity and VEGF-induced angiogenesis

The REGγ-proteasome serves as a short-cut for the destruction of certain intact mammalian proteins in the absence of ubiquitin- and ATP. The biological roles of the proteasome activator REGγ are not completely understood. Here we demonstrate that REGγ controls degradation of protein kinase A catalytic subunit-α (PKAca) both in primary human umbilical vein endothelial cells (HUVECs) and mouse embryonic fibroblast cells (MEFs). Accumulation of PKAca in REGγ-deficient HUVECs or MEFs results in phosphorylation and nuclear exclusion of the transcription factor FoxO1, indicating that REGγ is involved in preserving FoxO1 transcriptional activity. Consequently, VEGF-induced expression of the FoxO1 responsive genes, VCAM-1 and E-Selectin, was tightly controlled by REGγ in a PKA dependent manner. Functionally, REGγ is crucial for the migration of HUVECs. REGγ(-/-) mice display compromised VEGF-instigated neovascularization in cornea and aortic ring models. Implanted matrigel plugs containing VEGF in REGγ(-/-) mice induced fewer capillaries than in REGγ(+/+) littermates. Taken together, our study identifies REGγ as a novel angiogenic factor that plays an important role in VEGF-induced expression of VCAM-1 and E-Selectin by antagonizing PKA signaling. Identification of the REGγ-PKA-FoxO1 pathway in endothelial cells (ECs) provides another potential target for therapeutic intervention in vascular diseases.

VEGF-A isoforms differentially regulate ATF-2-dependent VCAM-1 gene expression and endothelial-leukocyte interactions

VEGF-A isoforms differentially stimulate endothelial VCAM-1 gene expression via an ERK1/2 protein kinase and ATF-2 transcription factor–dependent mechanism. Such signal transduction enables VEGF-A isoform–specific stimulation of leukocyte binding to endothelial cells, explaining how inflammation could be differentially regulated.

Vascular endothelial growth factor A (VEGF-A) regulates many aspects of vascular physiology. VEGF-A stimulates signal transduction pathways that modulate endothelial outputs such as cell migration, proliferation, tubulogenesis, and cell–cell interactions. Multiple VEGF-A isoforms exist, but the biological significance of this is unclear. Here we analyzed VEGF-A isoform–specific stimulation of VCAM-1 gene expression, which controls endothelial–leukocyte interactions, and show that this is dependent on both ERK1/2 and activating transcription factor-2 (ATF-2). VEGF-A isoforms showed differential ERK1/2 and p38 MAPK phosphorylation kinetics. A key feature of VEGF-A isoform–specific ERK1/2 activation and nuclear translocation was increased phosphorylation of ATF-2 on threonine residue 71 (T71). Using reverse genetics, we showed ATF-2 to be functionally required for VEGF-A–stimulated endothelial VCAM-1 gene expression. ATF-2 knockdown blocked VEGF-A–stimulated VCAM-1 expression and endothelial–leukocyte interactions. ATF-2 was also required for other endothelial cell outputs, such as cell migration and tubulogenesis. In contrast, VCAM-1 was essential only for promoting endothelial–leukocyte interactions. This work presents a new paradigm for understanding how soluble growth factor isoforms program complex cellular outputs and responses by modulating signal transduction pathways.

FOXO1-mediated activation of Akt plays a critical role in vascular homeostasis

RATIONALE

Forkhead box-O transcription factors (FoxOs) transduce a wide range of extracellular signals, resulting in changes in cell survival, cell cycle progression, and several cell type-specific responses. FoxO1 is expressed in many cell types, including endothelial cells (ECs). Previous studies have shown that Foxo1 knockout in mice results in embryonic lethality at E11 because of impaired vascular development. In contrast, somatic deletion of Foxo1 is associated with hyperproliferation of ECs. Thus, the precise role of FoxO1 in the endothelium remains enigmatic.

OBJECTIVE

To determine the effect of endothelial-specific knockout and overexpression of FoxO1 on vascular homeostasis.

METHODS AND RESULTS

We show that EC-specific disruption of Foxo1 in mice phenocopies the full knockout. Although endothelial expression of FoxO1 rescued otherwise Foxo1-null animals, overexpression of constitutively active FoxO1 resulted in increased EC size, occlusion of capillaries, elevated peripheral resistance, heart failure, and death. Knockdown of FoxO1 in ECs resulted in marked inhibition of basal and vascular endothelial growth factor-induced Akt-mammalian target of rapamycin complex 1 (mTORC1) signaling.

CONCLUSIONS

Our findings suggest that in mice, endothelial expression of FoxO1 is both necessary and sufficient for embryonic development. Moreover, FoxO1-mediated feedback activation of Akt maintains growth factor responsive Akt/mTORC1 activity within a homeostatic range.

Vascular endothelial growth factor receptor-2 couples cyclo-oxygenase-2 with pro-angiogenic actions of leptin on human endothelial cells

Background

The adipocyte-derived hormone leptin influences the behaviour of a wide range of cell types and is now recognised as a pro-angiogenic and pro-inflammatory factor. In the vasculature, these effects are mediated in part through its direct leptin receptor (ObRb)-driven actions on endothelial cells (ECs) but the mechanisms responsible for these activities have not been established. In this study we sought to more fully define the molecular links between inflammatory and angiogenic responses of leptin-stimulated human ECs.

Methodology/Principal Findings

Immunoblotting studies showed that leptin increased cyclo-oxygenase-2 (COX-2) expression (but not COX-1) in cultured human umbilical vein ECs (HUVEC) through pathways that depend upon activation of both p38 mitogen-activated protein kinase (p38^MAPK) and Akt, and stimulated rapid phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2) on Tyr¹¹⁷⁵. Phosphorylation of VEGFR2, p38^MAPK and Akt, and COX-2 induction in cells challenged with leptin were blocked by a specific leptin peptide receptor antagonist. Pharmacological inhibitors of COX-2, the phosphatidylinositol 3-kinase (PI3K)/Akt pathway and p38^MAPK abrogated leptin-induced EC proliferation (assessed by quantifying 5-bromo-2′-deoxyuridine incorporation, calcein fluorescence and propidium iodide staining), slowed the increased migration rate of leptin-stimulated cells (in vitro wound healing assay) and inhibited leptin-induced capillary-like tube formation by HUVEC on Matrigel. Inhibition of VEGFR2 tyrosine kinase activity reduced leptin-stimulated p38^MAPK and Akt activation, COX-2 induction, and pro-angiogenic EC responses, and blockade of VEGFR2 or COX-2 activities abolished leptin-driven neo-angiogenesis in a chick chorioallantoic membrane vascularisation assay in vivo.

Conclusions/Significance

We conclude that a functional endothelial p38^MAPK/Akt/COX-2 signalling axis is required for leptin's pro-angiogenic actions and that this is regulated upstream by ObRb-dependent activation of VEGFR2. These studies identify a new function for VEGFR2 as a mediator of leptin-stimulated COX-2 expression and angiogenesis and have implications for understanding leptin's regulation of the vasculature in both non-obese and obese individuals.

Vascular Endothelial Growth Factor Increases Endothelial Nitric Oxide Synthase Transcription In Huvec Cells

Although it is known that VEGF increases eNOS protein, the mechanisms responsible remain unclear. To determine if VEGF alters eNOS transcription, human umbilical vein endothelial cells were transfected with reporters under the control of the eNOS promoter and stimulated with VEGF₁₆₅. VEGF significantly increased eNOS-mRNA after 2 hours exposure. VEGF significantly increased eNOS reporter activity as early as one hour (268±32%), but this increase returned to baseline after 6 hours. Using deletion constructs, the VEGF response region was initially localized to within the -722/-494 region. GMSA indicated that VEGF increased DNA binding to both a cAMP-like and AP1-like response elements. Site-specific mutations and heterologous constructs indicated that the site centered at AP1-like site was both necessary and sufficient to meditate VEGF transcriptional activation. These results indicate that VEGF rapidly activates eNOS transcription prior to a rise eNOS-mRNA, an effect mediated by a cis-trans interaction localized to an AP1-like site within the eNOS promoter.

Negative action of hepatocyte growth factor/c-Met system on angiotensin II signaling via ligand-dependent epithelial growth factor receptor degradation mechanism in vascular smooth muscle cells

RATIONALE

Neointimal hyperplasia contributes to atherosclerosis and restenosis after percutaneous coronary intervention. Vascular injury in each of these conditions results in the release of mitogenic growth factors and hormones that contribute to pathological vascular smooth muscle cell growth and inflammation. Hepatocyte growth factor (HGF) is known as an antiinflammatory growth factor, although it is downregulated in injured tissue. However, the precise mechanism how HGF reduces inflammation is unclear.

OBJECTIVE

To elucidate the mechanism how HGF and its receptor c-Met reduces angiotensin II (Ang II)-induced inflammation.

METHODS AND RESULTS

HGF reduced Ang II-induced vascular smooth muscle cell growth and inflammation by controlling translocation of SHIP2 (Src homology domain 2-containing inositol 5'-phosphatase 2), which led to Ang II-dependent degradation of epithelial growth factor receptor. Moreover, the present study also revealed a preventive effect of HGF on atherosclerotic change in an Ang II infusion and cuff HGF transgenic mouse model.

CONCLUSIONS

These data suggest that the HGF/c-Met system might regulate extrinsic factor signaling that maintains the homeostasis of organs.

Critical role for GATA3 in mediating Tie2 expression and function in large vessel endothelial cells

Endothelial phenotypes are highly regulated in space and time by both transcriptional and post-transcriptional mechanisms. There is increasing evidence that the GATA family of transcription factors function as signal transducers, coupling changes in the extracellular environment to changes in downstream target gene expression. Here we show that human primary endothelial cells derived from large blood vessels express GATA2, -3, and -6. Of these factors, GATA3 was expressed at the highest levels. In DNA microarrays of human umbilical vein endothelial cells (HUVEC), small interfering RNA-mediated knockdown of GATA3 resulted in reduced expression of genes associated with angiogenesis, including Tie2. At a functional level, GATA3 knockdown inhibited angiopoietin (Ang)-1-mediated but not vascular endothelial cell growth factor (VEGF)-mediated AKT signaling, cell migration, survival, and tube formation. In electrophoretic gel mobility shift assays and chromatin immunoprecipitation, GATA3 was shown to bind to regulatory regions within the 5'-untranslated region of the Tie2 gene. In co-immunoprecipitation and co-transfection assays, GATA3 and the Ets transcription factor, ELF1, physically interacted and synergized to transactivate the Tie2 promoter. GATA3 knockdown blocked the ability of Ang-1 to attenuate vascular endothelial cell growth factor stimulation of vascular cell adhesion molecule-1 expression and monocytic cell adhesion. Moreover, exposure of human umbilical vein endothelial cells to tumor necrosis factor-alpha resulted in marked down-regulation of GATA3 expression and reduction in Tie2 expression. Together, these findings suggest that GATA3 is indispensable for Ang-1-Tie2-mediated signaling in large vessel endothelial cells.

The FOX transcription factors regulate vascular pathology, diabetes and Tregs

A small number of upstream master genes in "higher hierarchy" controls the expression of a large number of downstream genes and integrates the signaling pathways underlying the pathogenesis of cardiovascular diseases with or without autoimmune inflammatory mechanisms. In this brief review, we organize our analysis of recent progress in characterization of forkhead (FOX) transcription factor family members in vascular pathology, diabetes and regulatory T cells into the following sections: (1) Overview of the FOX transcription factor superfamily; (2) Vascular pathology of mice deficient in FOX transcription factors; (3) Roles of FOX transcription factors in endothelial cell pathology; (4) Roles of FOX transcription factors in vascular smooth muscle cells; (5) Roles of FOX transcription factors in the pathogenesis of diabetes; and (6) Immune system phenotypes of mice deficient in FOX transcription factors. Advances in these areas suggest that the FOX transcription factor family plays important roles in vascular development and in the pathogenesis of autoimmune inflammatory cardiovascular diseases.

The forkhead transcription factors play important roles in vascular pathology and immunology

Transcription factor families are a small number of upstream master genes in "higher hierarchy" that control the expression of a large number of downstream genes. These transcription factors have been found to integrate the signaling pathways underlying the pathogenesis of cardiovascular diseases with or without autoimmune inflammatory mechanisms. In this chapter, we organize our analysis of recent progress in characterization of forkhead (Fox) transcription factor family members in vascular pathology and immune regulation into the following sections: (1) Introduction of the FOX transcription factor superfamily; (2) FOX transcription factors and endotheial cell pathology; (3) FOX transcription factors and vascular smooth muscle cells; and (4) FOX transcription factors, inflammation and immune system. Advances in these areas suggest that the FOX transcription factor family is important in regulating vascular development and the pathogenesis of autoimmune inflammatory cardiovascular diseases.