Vascular endothelial cell lineage-specific promoter in transgenic mice

Centrosomal protein FOR20 knockout mice display embryonic lethality and left-right patterning defects

Centrosomal protein FOR20 has been reported to be crucial for essential cellular processes, including ciliogenesis, cell migration, and cell cycle in vertebrates. However, the function of FOR20 during mammalian embryonic development remains unknown. To investigate the in vivo function of the For20 gene in mammals, we generated For20 homozygous knockout mice by gene targeting. Our data reveal that homozygous knockout of For20 results in significant embryonic growth arrest and lethality during gestation, while the heterozygotes show no obvious defects. The absence of For20 leads to impaired left-right patterning of embryos and reduced cilia in the embryonic node. Deletion of For20 also disrupts angiogenesis in yolk sacs and embryos. These results highlight a critical role of For20 in early mammalian embryogenesis.

Astrocytes drive cortical vasodilatory signaling by activating endothelial NMDA receptors

Astrocytes express neurotransmitter receptors that serve as sensors of synaptic activity and initiate signals leading to activity-dependent local vasodilation and increases in blood flow. We previously showed that arteriolar vasodilation produced by activation of cortical astrocytes is dependent on endothelial nitric oxide synthase (eNOS) and endogenous agonists of N-methyl-D-aspartate (NMDA) receptors. Here, we tested the hypothesis that these effects are mediated by NMDA receptors expressed by brain endothelial cells. Primary endothelial cultures expressed NMDA receptor subunits and produced nitric oxide in response to co-agonists, glutamate and D-serine. In cerebral cortex in situ, immunoelectron microscopy revealed that endothelial cells express the GluN1 NMDA receptor subunit at basolateral membrane surfaces in an orientation suitable for receiving intercellular messengers from brain cells. In cortical slices, activation of astrocytes by two-photon flash photolysis of a caged Ca²⁺ compound or application of a metabotropic glutamate receptor agonist caused endothelial NO generation and local vasodilation. These effects were mitigated by NMDA receptor antagonists and conditional gene silencing of endothelial GluN1, indicating at least partial dependence on endothelial NMDA receptors. Our observations identify a novel astrocyte-endothelial vasodilatory signaling axis that could contribute to endothelium-dependent vasodilation in brain functional hyperemia.

Rudhira/BCAS3 is essential for mouse development and cardiovascular patterning

Rudhira/Breast Carcinoma Amplified Sequence 3 (BCAS3) is a cytoskeletal protein that promotes directional cell migration and angiogenesis in vitro and is implicated in human carcinomas and coronary artery disease. To study the role of Rudhira during development in vivo, we generated the first knockout mouse for rudhira and show that Rudhira is essential for mouse development. Rudhira null embryos die at embryonic day (E) 9.5 accompanied by severe vascular patterning defects in embryonic and extra-embryonic tissues. To identify the molecular processes downstream of rudhira, we analyzed the transcriptome of intact knockout yolk sacs. Genome-wide transcriptome analysis showed that Rudhira functions in angiogenesis and its related processes such as cell adhesion, extracellular matrix organization, peptidase activity and TGFβ signaling. Since Rudhira is also expressed in endothelial cells (ECs), we further generated Tie2Cre-mediated endothelial knockout (CKO) of rudhira. CKO embryos survive to E11.5 and similar to the global knockout, display gross vascular patterning defects, showing that endothelial Rudhira is vital for development. Further, Rudhira knockdown ECs in culture fail to sprout in a spheroid-sprouting assay, strongly supporting its role in vascular patterning. Our study identifies an essential role for Rudhira in blood vessel remodeling and provides a mouse model for cardiovascular development.

Overexpression of C-type Natriuretic Peptide in Endothelial Cells Protects against Insulin Resistance and Inflammation during Diet-induced Obesity

The endogenous peptide C-type natriuretic peptide (CNP) binds its receptor, guanylyl cyclase B (GCB), and is expressed by endothelial cells in diverse tissues. Because the endothelial cells of visceral adipose tissue have recently been reported to play a role in lipid metabolism and inflammation, we investigated the effects of CNP on features of obesity by using transgenic (Tg) mice in which CNP was placed under the control of the Tie2 promoter and was thus overexpressed in endothelial cells (E-CNP). Here we show that increased brown adipose tissue thermogenesis in E-CNP Tg mice increased energy expenditure, decreased mesenteric white adipose tissue (MesWAT) fat weight and adipocyte hypertrophy, and prevented the development of fatty liver. Furthermore, CNP overexpression improved glucose tolerance, decreased insulin resistance, and inhibited macrophage infiltration in MesWAT, thus suppressing pro-inflammation during high-fat diet–induced obesity. Our findings indicate an important role for the CNP produced by the endothelial cells in the regulation of MesWAT hypertrophy, insulin resistance, and inflammation during high-fat diet–induced obesity.

miR-146a regulates glucose induced upregulation of inflammatory cytokines extracellular matrix proteins in the retina and kidney in diabetes

Hyperglycemic damage to the endothelial cells (ECs) leads to increased synthesis of inflammatory cytokines. We have previously shown miR-146a downregulation in ECs and in the tissues of diabetic mice. Here we investigated the role of miR-146a, in the production of specific inflammatory cytokines and extracellular matrix (ECM) proteins in retina and kidneys in diabetes. We generated an endothelial specific miR-146a overexpressing transgenic mice (TG). We investigated these mice and wild type (WT) controls with or without streptozotocin (STZ) induced diabetes. Retinal and renal cortical tissues from the mice were examined for mRNAs for specific inflammatory markers, (ECM) proteins and inflammation inducible transcription factor by real time RT-PCR. Corresponding proteins, where possible, were examined using immunofluorescence or ELISA. In parallel, we examined ECs following incubation with various levels of glucose with or without miR-146a mimic transfection. In the retina and kidneys of WT mice with diabetes, increased expression of inflammatory markers (IL-6, TNFα, IL1β) in association augmented expression of ECM proteins (collagen 1αIV, fibronectin) and NF κB-P65 were observed, compared to WT non-diabetic controls. These changes were prevented in diabetic miR-146a TG mice along with retinal and renal functional and structural changes. In vitro studies showed similar changes in the ECs exposed to high glucose. Such changes were corrected in the cells following miR-146a mimic transfection. Further analyses of renal cortical tissues showed diabetes induced significant upregulation of two regulators of NFκB, namely Interleukin-1 associated Kinase 1 and tumour necrosis factor receptor associated factor. Such changes were prevented in diabetic TG animals. These data indicate that augmented production of inflammatory cytokines and ECM proteins in the retina and kidneys in diabetes are regulated through endothelium derived miR-146a. Identification of such novel mechanisms may potentially lead to the development of novel therapies.

Essential role of the TFIID subunit TAF4 in murine embryogenesis and embryonic stem cell differentiation

TAF4 (TATA-binding protein-associated factor 4) and its paralogue TAF4b are components of the TFIID core module. We inactivated the murine Taf4a gene to address Taf4 function during embryogenesis. Here we show that Taf4a^−/− embryos survive until E9.5 where primary germ layers and many embryonic structures are identified showing Taf4 is dispensable for their specification. In contrast, Taf4 is required for correct patterning of the trunk and anterior structures, ventral morphogenesis and proper heart positioning. Overlapping expression of Taf4a and Taf4b during embryogenesis suggests their redundancy at early stages. In agreement with this, Taf4a^−/− embryonic stem cells (ESCs) are viable and comprise Taf4b-containing TFIID. Nevertheless, Taf4a^−/− ESCs do not complete differentiation into glutamatergic neurons and cardiomyocytes in vitro due to impaired preinitiation complex formation at the promoters of critical differentiation genes. We define an essential role of a core TFIID TAF in differentiation events during mammalian embryogenesis.

The role of TFIID core module TAFs (TATA-binding protein-associated factors) in embryogenesis is unknown. Here, the authors show that Taf4 is essential at mid-gestation and for complete neuronal differentiation of embryonic stem cells, but that Taf4a and Taf4b are redundant at early embryonic stages.

miR-200b Mediates Endothelial-to-Mesenchymal Transition in Diabetic Cardiomyopathy

Hyperglycemia-induced endothelial injury is a key pathogenetic factor in diabetic cardiomyopathy. Endothelial injury may lead to a phenotypic change (i.e., endothelial-to-mesenchymal transition [EndMT]), causing cardiac fibrosis. Epigenetic mechanisms, through specific microRNA, may regulate such a process. We investigated the mechanisms for such changes in cardiac microvascular endothelial cells and in the heart of genetically engineered mice with chemically induced diabetes. Cardiac tissues and isolated mouse heart endothelial cells (MHECs) from animals with or without endothelial-specific overexpression of miR-200b, with or without streptozotocin-induced diabetes, were examined at the mRNA and protein levels for endothelial and mesenchymal markers. Expression of miR-200b and its targets was quantified. Cardiac functions and structures were analyzed. In the hearts of wild-type diabetic mice, EndMT was observed, which was prevented in the miR-200b transgenic diabetic mice. Expression of specific markers such as vascular endothelial growth factor, zinc finger E-box-binding homeobox, transforming growth factor-β1, and p300 were increased in the hearts of diabetic mice and were prevented following miR-200b overexpression. MHECs showed similar changes. miR-200b overexpression also prevented diabetes-induced cardiac functional and structural changes. These data indicate that glucose-induced EndMT in vivo and in vitro in the hearts of diabetic mice is possibly mediated by miR-200b and p300.

The short and long of noncoding sequences in the control of vascular cell phenotypes

The two principal cell types of importance for normal vessel wall physiology are smooth muscle cells and endothelial cells. Much progress has been made over the past 20 years in the discovery and function of transcription factors that coordinate proper differentiation of these cells and the maintenance of vascular homeostasis. More recently, the converging fields of bioinformatics, genomics, and next generation sequencing have accelerated discoveries in a number of classes of noncoding sequences, including transcription factor binding sites (TFBS), microRNA genes, and long noncoding RNA genes, each of which mediates vascular cell differentiation through a variety of mechanisms. Alterations in the nucleotide sequence of key TFBS or deviations in transcription of noncoding RNA genes likely have adverse effects on normal vascular cell phenotype and function. Here, the subject of noncoding sequences that influence smooth muscle cell or endothelial cell phenotype will be summarized as will future directions to further advance our understanding of the increasingly complex molecular circuitry governing normal vascular cell differentiation and how such information might be harnessed to combat vascular diseases.

The TIE Receptor Family

The endothelial TIE1 and TIE2 receptor tyrosine kinases form a distinct subfamily characterized by their unique extracellular domains. Together with the angiopoietin growth factors (ANGPT1, ANGPT2, ANGPT4, also abbreviated as ANG), the TIE receptors form an endothelial specific signaling pathway with important functions in the regulation of lymphatic and cardiovascular development and vascular homeostasis. Angiopoietins exist in multimeric forms that activate the TIE receptors via unique mechanism. In endothelial cell–cell contacts, angiopoietins induce the formation of homomeric in trans TIE receptor complexes extending across the cell junctions, whereas matrix-bound angiopoietin-1 (ANG1) activates the TIE receptors in a cis configuration. In comparison to the vascular endothelial growth factor receptors, the TIE receptors undergo little ubiquitin-mediated degradation after activation, whereas TIE2 signaling is negatively regulated by the vascular endothelial protein tyrosine phosphatase, VE-PTP. ANG1 activation of TIE2 supports vascular stabilization, whereas angiopoietin-2 (ANG2), a context-dependent weak TIE2 agonist/antagonist, promotes pathological tumor angiogenesis, vascular permeability, and inflammation. Recently, ANG2 has been found to mediate some of its vascular destabilizing and angiogenic functions via integrin signalling. The circulating levels of ANG2 are increased in cancer, and in several human diseases associated with inflammation and vascular leak, for example, in sepsis. Blocking of ANG2 has emerged as a potential novel therapeutic strategy for these diseases. In addition, preclinical results demonstrate that genetic TIE1 deletion in mice inhibits the vascularization and growth of tumor isografts and protects from atherosclerosis, with little effect on normal vascular homeostasis in adult mice. The ability of the ANG-TIE pathway to control vessel stability and angiogenesis makes it an interesting vascular target for the treatment of the various diseases.

The NuRD chromatin-remodeling enzyme CHD4 promotes embryonic vascular integrity by transcriptionally regulating extracellular matrix proteolysis

The extracellular matrix (ECM) supports vascular integrity during embryonic development. Proteolytic degradation of ECM components is required for angiogenesis, but excessive ECM proteolysis causes blood vessel fragility and hemorrhage. Little is understood about how ECM proteolysis is transcriptionally regulated during embryonic vascular development. We now show that the NuRD ATP-dependent chromatin-remodeling complex promotes vascular integrity by preventing excessive ECM proteolysis in vivo. Mice lacking endothelial CHD4--a catalytic subunit of NuRD complexes--died at midgestation from vascular rupture. ECM components surrounding rupture-prone vessels in Chd4 mutants were significantly downregulated prior to embryonic lethality. Using qPCR arrays, we found two critical mediators of ECM stability misregulated in mutant endothelial cells: the urokinase-type plasminogen activator receptor (uPAR or Plaur) was upregulated, and thrombospondin-1 (Thbs1) was downregulated. Chromatin immunoprecipitation assays showed that CHD4-containing NuRD complexes directly bound the promoters of these genes in endothelial cells. uPAR and THBS1 respectively promote and inhibit activation of the potent ECM protease plasmin, and we detected increased plasmin activity around rupture-prone vessels in Chd4 mutants. We rescued ECM components and vascular rupture in Chd4 mutants by genetically reducing urokinase (uPA or Plau), which cooperates with uPAR to activate plasmin. Our findings provide a novel mechanism by which a chromatin-remodeling enzyme regulates ECM stability to maintain vascular integrity during embryonic development.

Angiopoietin 2 mediates microvascular and hemodynamic alterations in sepsis

Septic shock is characterized by increased vascular permeability and hypotension despite increased cardiac output. Numerous vasoactive cytokines are upregulated during sepsis, including angiopoietin 2 (ANG2), which increases vascular permeability. Here we report that mice engineered to inducibly overexpress ANG2 in the endothelium developed sepsis-like hemodynamic alterations, including systemic hypotension, increased cardiac output, and dilatory cardiomyopathy. Conversely, mice with cardiomyocyte-restricted ANG2 overexpression failed to develop hemodynamic alterations. Interestingly, the hemodynamic alterations associated with endothelial-specific overexpression of ANG2 and the loss of capillary-associated pericytes were reversed by intravenous injections of adeno-associated viruses (AAVs) transducing cDNA for angiopoietin 1, a TIE2 ligand that antagonizes ANG2, or AAVs encoding PDGFB, a chemoattractant for pericytes. To confirm the role of ANG2 in sepsis, we i.p. injected LPS into C57BL/6J mice, which rapidly developed hypotension, acute pericyte loss, and increased vascular permeability. Importantly, ANG2 antibody treatment attenuated LPS-induced hemodynamic alterations and reduced the mortality rate at 36 hours from 95% to 61%. These data indicate that ANG2-mediated microvascular disintegration contributes to septic shock and that inhibition of the ANG2/TIE2 interaction during sepsis is a potential therapeutic target.

Etv2 is expressed in the yolk sac hematopoietic and endothelial progenitors and regulates Lmo2 gene expression

During embryogenesis, the endothelial and the hematopoietic lineages first appear during gastrulation in the blood island of the yolk sac. We have previously reported that an Ets variant gene 2 (Etv2/ER71) mutant embryo lacks hematopoietic and endothelial lineages; however, the precise roles of Etv2 in yolk sac development remains unclear. In this study, we define the role of Etv2 in yolk sac blood island development using the Etv2 mutant and a novel Etv2-EYFP reporter transgenic line. Both the hematopoietic and the endothelial lineages are absent in the Etv2 mutant yolk sac. In the Etv2-EYFP transgenic mouse, the EYFP reporter is activated in the nascent mesoderm, expressed in the endothelial and blood progenitors, and in the Tie2(+), c-kit(+), and CD41(+) hematopoietic population. The hematopoietic activity in the E7.75 yolk sac was exclusively localized to the Etv2-EYFP(+) population. In the Etv2 mutant yolk sac, Tie2(+) cells are present but do not express hematopoietic or endothelial markers. In addition, these cells do not form hematopoietic colonies, indicating an essential role of Etv2 in the specification of the hematopoietic lineage. Forced overexpression of Etv2 during embryoid body differentiation induces the hematopoietic and the endothelial lineages, and transcriptional profiling in this context identifies Lmo2 as a downstream target. Using electrophoretic mobility shift assay, chromatin immunoprecipitation, transcriptional assays, and mutagenesis, we demonstrate that Etv2 binds to the Lmo2 enhancer and transactivates its expression. Collectively, our studies demonstrate that Etv2 is expressed during and required for yolk sac hematoendothelial development, and that Lmo2 is one of the downstream targets of Etv2.

Novel ROSA26 Cre-reporter knock-in C57BL/6N mice exhibiting green emission before and red emission after Cre-mediated recombination

The Cre/loxP system is a strategy for controlling temporal and/or spatial gene expression through genome alteration in mice. As successful Cre/loxP genome alteration depends on Cre-driver mice, Cre-reporter mice are essential for validation of Cre gene expression in vivo. In most Cre-reporter mouse strains, although the presence of reporter product indicates the expression of Cre recombinase, it has remained unclear whether a lack of reporter signal indicates either no Cre recombinase expression or insufficient reporter gene promoter activity. We produced a novel ROSA26 knock-in Cre-reporter C57BL/6N strain exhibiting green emission before and red after Cre-mediated recombination, designated as strain R26GRR. Ubiquitous green fluorescence and no red fluorescence were observed in R26GRR mice. To investigate the activation of tdsRed, EGFP-excised R26GRR, R26RR, mice were produced through the crossing of C57BL/6N mice with R26GRR/Ayu1-Cre F1 mice. R26RR mice showed extraordinarily strong red fluorescence in almost all tissues examined, suggesting ubiquitous activation of the second reporter in all tissues after Cre/loxP recombination. Moreover, endothelial cell lineage and pancreatic islet-specific expression of red fluorescence were detected in R26GRR/Tie2-Cre F1 mice and R26GRR /Ins1-Cre F1 mice, respectively. These results indicated that R26GRR mice are a useful novel Cre-reporter mouse strain. In addition, R26GRR mice with a pure C57BL/6N background represent a valuable source of green-to-red photoconvertible cells following Cre/loxP recombination for application in transplantation studies. The R26GRR mouse strain will be available from RIKEN BioResource Center (http://www.brc.riken.jp/lab/animal/en/).

Enhanced Angpt1/Tie2 signaling affects the differentiation and long-term repopulation ability of hematopoietic stem cells

Angiopoietin-1 (Angpt1) signaling via the Tie2 receptor regulates vascular and hematopoietic systems. To investigate the role of Angpt1-Tie2 signaling in hematopoiesis, we prepared conditionally inducible transgenic (Tg) mice expressing a genetically engineered Angpt1, cartridge oligomeric matrix protein (COMP)-Angpt1. The effects of COMP-Angpt1 overexpression in osteoblasts on hematopoiesis were then investigated by crossing COMP-Angpt1 Tg mice with Col1a1-Cre Tg mice. Interestingly, peripheral blood analyses showed that 4 week (wk)-old (but not 8 wk-old) Col1a1-Cre+/COMP-Angpt1+ mice had a lower percentage of circulating B cells and a higher percentage of myeloid cells than Col1a1-Cre-/COMP-Angpt1+ (control) mice. Although there were no significant differences in the immunophenotypic hematopoietic stem and progenitor cell (HSPC) populations between Col1a1-Cre+/COMP-Angpt1+ and control mice, lineage(-)Sca-1(+)c-Kit(+) (LSK) cells isolated from 8 wk-old Col1a1-Cre+/COMP-Angpt1+ mice showed better long-term bone marrow reconstitution ability. These data indicate that Angpt1-Tie2 signaling affects the differentiation capacity of hematopoietic lineages during development and increases the stem cell activity of HSCs.

RTEF-1 attenuates blood glucose levels by regulating insulin-like growth factor binding protein-1 in the endothelium

RATIONALE

Related transcriptional enhancer factor-1 (RTEF-1) plays an important role in endothelial cell function by regulating angiogenesis; however, the mechanism underlying the role of RTEF-1 in the endothelium in vivo is not well defined.

OBJECTIVE

We investigated the biological functions of RTEF-1 by disrupting the gene that encodes it in mice endothelium -specific RTEF-1-deficient transgenic mice (RTEF-1(-/-)).

METHODS AND RESULTS

RTEF-1(-/-) mice showed significantly increased blood glucose levels and insulin resistance, accompanied by decreased levels of insulin-like growth factor binding protein-1 (IGFBP-1) mRNA in the endothelium and decreased serum IGFBP-1 levels. Additionally, the RTEF-1(-/-) phenotype was exacerbated when the mice were fed a high-fat diet, which correlated with decreased IGFBP-1 levels. In contrast, vascular endothelial cadherin/RTEF-1-overexpressing(1) transgenic mice (VE-Cad/RTEF1) demonstrated improved glucose clearance and insulin sensitivity in response to a high-fat diet. Furthermore, we demonstrated that RTEF-1 upregulates IGFBP-1 through selective binding and promotion of transcription from the insulin response element site. Insulin prevented RTEF-1 expression and significantly inhibited IGFBP-1 transcription in endothelial cells in a dose-dependent fashion.

CONCLUSIONS

To the best of our knowledge, this is the first report demonstrating that RTEF-1 stimulates promoter activity through an insulin response element and also mediates the effects of insulin on gene expression. These results show that RTEF-1-stimulated IGFBP-1 expression may be central to the mechanism by which RTEF-1 attenuates blood glucose levels. These findings provide the basis for novel insights into the transcriptional regulation of IGFBP-1 and contribute to our understanding of the role of vascular endothelial cells in metabolism.

The Flk1-Cre-mediated deletion of ETV2 defines its narrow temporal requirement during embryonic hematopoietic development

During embryonic development, the emergence of hematopoiesis and vasculogenesis is tightly associated, with many transcription factors implicated in both developmental processes. Among those factors, ETV2 acts at the top of the hierarchy and controls the formation of both lineages. However, it is not known at which stage of mesoderm development ETV2 is acting and whether ETV2 activity is further required once mesodermal precursors have been specified to the hematopoietic and endothelial fates. In this study, we characterize the developmental window during which ETV2 expression is required for hematopoietic and endothelial development. Using cre-mediated deletion of ETV2, we demonstrate that ETV2 is acting prior to or at the time of FLK1 expression in mesodermal precursors to initiate the hematopoietic and endothelial program. Using the in vitro differentiation of embryonic stem cells as a model system, we further show that ETV2 re-expression in Etv2(-/-) Flk1-negative precursors drives hematopoiesis specification and switches on the expression of most genes known to be implicated in hematopoietic and endothelial development. Among the downstream targets of ETV2, we identify the transcription factors SCL, GATA2, and FLI1 known to operate a recursive loop controlling hematopoietic development. Surprisingly, SCL re-expression in Etv2(-/-) cells fully rescues hematopoiesis, while the re-expression of FLI1 or GATA2 promotes only a very limited rescue. Altogether, our data establish that ETV2 is required very transiently to specify mesodermal precursors to hematopoiesis and vasculogenesis and that SCL is one of the key downstream targets of ETV2 in controlling hematopoietic specification.

Pericytes support neutrophil subendothelial cell crawling and breaching of venular walls in vivo

Neutrophil transmigration through venular walls that are composed of endothelial cells (ECs), pericytes, and the venular basement membrane is a key component of innate immunity. Through direct analysis of leukocyte-pericyte interactions in inflamed tissues using confocal intravital microscopy, we show how pericytes facilitate transmigration in vivo. After EC migration, neutrophils crawl along pericyte processes to gaps between adjacent pericytes in an ICAM-1-, Mac-1-, and LFA-1-dependent manner. These gaps were enlarged in inflamed tissues through pericyte shape change and were used as exit points by neutrophils in breaching the venular wall. The findings identify previously unknown roles for pericytes in neutrophil transmigration in vivo and add additional steps to the leukocyte adhesion cascade that supports leukocyte trafficking into sites of inflammation.

Fishing for function: zebrafish BAC transgenics for functional genomics

Transgenics using bacterial artificial chromosomes (BACs) offers a great opportunity to look at gene regulation in a developing embryo. The modified BAC containing a reporter inserted just before the translational start site of the gene of interest allows for the visualization of spatio-temporal gene expression. Though this method has been used in the mouse model extensively, its utility in zebrafish studies is relatively new. This review aims to look at the utility of making BAC transgenics in zebrafish and its applications in functional genomics. We look at the various methods to modify the BAC, some limitations and what the future holds.

PAR2 absence completely rescues inflammation and ichthyosis caused by altered CAP1/Prss8 expression in mouse skin

Altered serine protease activity is associated with skin disorders in humans and in mice. The serine protease channel-activating protease-1 (CAP1; also termed protease serine S1 family member 8 (Prss8)) is important for epidermal homeostasis and is thus indispensable for postnatal survival in mice, but its roles and effectors in skin pathology are poorly defined. In this paper, we report that transgenic expression in mouse skin of either CAP1/Prss8 (K14-CAP1/Prss8) or protease-activated receptor-2 (PAR2; Grhl3^PAR2/+), one candidate downstream target, causes epidermal hyperplasia, ichthyosis and itching. K14-CAP1/Prss8 ectopic expression impairs epidermal barrier function and causes skin inflammation characterized by an increase in thymic stromal lymphopoietin levels and immune cell infiltrations. Strikingly, both gross and functional K14-CAP1/Prss8-induced phenotypes are completely negated when superimposed on a PAR2-null background, establishing PAR2 as a pivotal mediator of pathogenesis. Our data provide genetic evidence for PAR2 as a downstream effector of CAP1/Prss8 in a signalling cascade that may provide novel therapeutic targets for ichthyoses, pruritus and inflammatory skin diseases.

The activity of serine proteases, including CAP1/Prss8, is altered in some human skin disorders; however, the downstream effectors of these proteins are relatively unknown. Here, using animal models, the authors show that protease-activated receptor-2 is a critical component of the CAP1/Prss8 signalling cascade.

Vascular bed-specific regulation of the von Willebrand factor promoter in the heart and skeletal muscle

A region of the human von Willebrand factor (VWF) gene between -2812 and the end of the first intron (termed vWF2) was previously shown to direct expression in the endothelium of capillaries and a subset of larger blood vessels in the heart and skeletal muscle. Here, our goal was to delineate the DNA sequences responsible for this effect. A series of constructs containing deletions or mutations of vWF2 coupled to LacZ were targeted to the Hprt locus of mice, and the resulting animals were analyzed for reporter gene expression. The findings demonstrate that DNA sequences between -843 and -620 are necessary for expression in capillary but not large vessel endothelium in heart and skeletal muscle. Further, expression of VWF in capillaries and larger vessels of both tissues required the presence of a native or heterologous intron. In vitro assays implicated a role for ERG-binding ETS motif at -56 in mediating basal expression of VWF. In Hprt-targeted mice, mutation of the ETS consensus motif resulted in loss of LacZ expression in the endothelium of the heart and skeletal muscle. Together, these data indicate that distinct DNA modules regulate vascular bed-specific expression of VWF.

Endothelial progenitor populations in differentiating embryonic stem cells I: Identification and differentiation kinetics

Embryonic stem cells (ESCs) have enormous potential in tissue engineering and cell therapies. However, the therapeutic use of ESCs has been restricted because of the presence of undifferentiated cells or cells with undesired phenotypes. We have explored identifying and selecting endothelial cells (ECs) using green fluorescent protein (GFP) under the control of different endothelial promoters. This method can result in progenitor populations that differ based on promoter activity; however, there have not been rigorous studies comparing differentiation kinetics and selection using these promoters as well as the resulting phenotype. In this study, we examined differentiation profiles of ESCs selected using three different endothelial promoters (Flk1, PECAM, and Tie1) that correspond to endothelial proteins expressed at different time points (early, middle, and late) in ESC differentiation. All three promoters yielded cells with EC-specific protein expression and DiI-Ac-LDL uptake when sorted for GFP(+) population; however, Flk1-driven GFP(+) cells yielded both smooth muscle cells and ECs or progenitors, whereas Tie1-driven GFP(+) cells yielded mostly endothelial phenotype. Both Flk1 and PECAM promoters showed a noticeable level of GFP expression while in the undifferentiated state, making the elimination of undifferentiated cells difficult. Our findings show the differentiation kinetics of the various EC promoters and how different endothelial promoters can be used to select distinct subpopulations of ECs and endothelial precursors across a spectrum of differentiation.

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.

Transcriptional targeting of tumor endothelial cells for gene therapy

It is well known that angiogenesis plays a critical role in the pathobiology of tumors. Recent clinical trials have shown that inhibition of angiogenesis can be an effective therapeutic strategy for patients with cancer. However, one of the outstanding issues in anti-angiogenic treatment for cancer is the development of toxicities related to off-target effects of drugs. Transcriptional targeting of tumor endothelial cells involves the use of specific promoters for selective expression of therapeutic genes in the endothelial cells lining the blood vessels of tumors. Recently, several genes that are expressed specifically in tumor-associated endothelial cells have been identified and characterized. These discoveries have enhanced the prospectus of transcriptionally targeting tumor endothelial cells for cancer gene therapy. In this manuscript, we review the promoters, vectors, and therapeutic genes that have been used for transcriptional targeting of tumor endothelial cells, and discuss the prospects of such approaches for cancer gene therapy.

[Genes that make the endothelial identity]

The endothelium is a tissue with a distinct identity due to the specific expression of molecular markers by endothelial cells. Further, the endothelium displays a structural heterogeneity illustrated by the expression of specific markers in arteries and in veins. Here, we present a review of the transcriptional and epigenetic mechanisms regulating the expression of the main markers of endothelial cells in man and mouse, demonstrating that there is no common and unique mechanism of specific expression of genes in these cells.

Role of endothelial progenitors and other bone marrow-derived cells in the development of the tumor vasculature

Increasing evidence suggests the importance of bone marrow-derived cells for blood vessel formation (neovascularization) in tumors, which can occur in two mechanisms: angiogenesis and vasculogenesis. Angiogenesis results from proliferation and sprouting of existing blood vessels close to the tumor, while vasculogenesis is believed to arise from recruitment of circulating cells, largely derived from the bone marrow, and de novo clonal formation of blood vessels from these cells. Although bone marrow-derived cells are crucial for neovascularization, current evidence suggests a promotional role of these cells on the existing blood vessels rather than de novo neovascularization in tumors. This is believed to be due to the highly proangiogenic features of these cells. The bone marrow-derived cells are heterogeneous, consisting of many different cell types including endothelial progenitor cells, myeloid cells, lymphocytes, and mesenchymal cells. These cells are highly orchestrated under the influence of the specific tumor microenvironment, which varies depending on the tumor type, thereby tightly regulating neovascularization in the tumors. In this review, we highlight some of the recent findings on each of these cell types by outlining some of the essential proangiogenic cytokines that these cells secrete to promote tumor angiogenesis and vasculogenesis.

Nkx2-5 transactivates the Ets-related protein 71 gene and specifies an endothelial/endocardial fate in the developing embryo

Recent studies support the existence of a common progenitor for the cardiac and endothelial cell lineages, but the underlying transcriptional networks responsible for specification of these cell fates remain unclear. Here we demonstrated that Ets-related protein 71 (Etsrp71), a newly discovered ETS family transcription factor, was a novel downstream target of the homeodomain protein, Nkx2-5. Using genetic mouse models and molecular biological techniques, we demonstrated that Nkx2-5 binds to an evolutionarily conserved Nkx2-5 response element in the Etsrp71 promoter and induces the Etsrp71 gene expression in vitro and in vivo. Etsrp71 was transiently expressed in the endocardium/endothelium of the developing embryo (E7.75-E9.5) and was extinguished during the latter stages of development. Using a gene disruption strategy, we found that Etsrp71 mutant embryos lacked endocardial/endothelial lineages and were nonviable. Moreover, using transgenic technologies and transcriptional and chromatin immunoprecipitation (ChIP) assays, we further established that Tie2 is a direct downstream target of Etsrp71. Collectively, our results uncover a novel functional role for Nkx2-5 and define a transcriptional network that specifies an endocardial/endothelial fate in the developing heart and embryo.

An essential role for Rac1 in endothelial cell function and vascular development

Numerous cell surface receptors, including tyrosine kinase and G protein-coupled receptors, play critical roles in endothelial cell function and blood vessel development. These receptors share the ability of stimulating an intricate network of intracellular signaling pathways, including the activation of members of the Ras and Rho family of small GTPases. However, the contribution of these signaling molecules to the numerous biological activities performed by endothelial cells is still not fully understood. Here, we have used a conditional Cre/Flox approach, enabling the deletion of the Rac1 gene in endothelial cells, to examine the role of the Rho-related GTPase Rac1 in endothelial cell function and vascular development. Rac1 excision in primary endothelial cells in vitro revealed that Rac1 plays a central role in endothelial cell migration, tubulogenesis, adhesion, and permeability in response to vascular endothelial growth factor (VEGF) and sphingosine-1-phosphate (S1P), which is likely due to the inability of Rac1-deficient endothelial cells to form lamellipodial structures and focal adhesions, and to remodel their cell-cell contacts. Importantly, endothelial-specific excision of Rac1 results in embryonic lethality in midgestation (around E9.5), and defective development of major vessels and complete lack of small branched vessels was readily observed in these endothelial Rac1-deficient embryos and their yolk sacs. These findings provide direct evidence that the activity of Rac1 in endothelial cells is essential for vascular development and suggest that Rac1 and its downstream targets may represent promising therapeutic targets for the treatment of numerous human diseases that involve aberrant neovascularization.

Sequences in intron 51 of the von Willebrand factor gene target promoter activation to a subset of lung endothelial cells in transgenic mice

In vivo analyses of the VWF promoter previously demonstrated that a fragment spanning sequences -487 to +247 targets promoter activation to brain vascular endothelial cells, whereas a longer fragment including 2182 bp of the 5'-flanking sequences, the first exon, and the first intron activated expression in endothelial cells of the heart and muscles as well as the brain of transgenic mice. These results suggested that additional VWF gene sequences were required for expression in other vascular endothelial cells in vivo. We have now identified a region within intron 51 of the VWF gene that is DNase I-hypersensitive (HSS) specifically in non-endothelial cells and interacts with endothelial and non-endothelial specific complexes that contain YY1. We demonstrate that beta-actin is associated with YY1 specifically in the nucleus of non-endothelial cells and is a component of the nuclear protein complexes that interact with the DNase I-hypersensitive region. In vitro transfection analyses demonstrated that HSS sequences containing this YY1-binding site do not significantly affect VWF promoter activity. However, in vivo analyses demonstrated that addition of these sequences to the VWF promoter (-487 to +247) results in promoter activation in lung and brain vascular endothelial cells. These results demonstrate that the HSS sequences in intron 51 of the VWF gene contain cis-acting elements that are necessary for the VWF gene transcription in a subset of lung endothelial cells in vivo.

Defective vascular morphogenesis and mid-gestation embryonic death in mice lacking RA-GEF-1

A multitude of guanine nucleotide exchange factors (GEFs) regulate Rap1 small GTPases, however, their individual functions remain obscure. Here, we investigate the in vivo function of the Rap1 GEF RA-GEF-1. The expression of RA-GEF-1 in wild-type mice starts at embryonic day (E) 8.5, and continues thereafter. RA-GEF-1(-/-) mice appear normal until E7.5, but become grossly abnormal and dead by E9.5. This mid-gestation death appears to be closely associated with severe defects in yolk sac blood vessel formation. RA-GEF-1(-/-) yolk sacs form apparently normal blood islands by E8.5, but the blood islands fail to coalesce into a primary vascular plexus, indicating that vasculogenesis is impaired. Furthermore, RA-GEF-1(-/-) embryos proper show severe defects in the formation of major blood vessels. These results suggest that deficient Rap1 signaling may lead to defective vascular morphogenesis in the yolk sac and embryos proper.

Ovol2/Movo, a homologue of Drosophila ovo, is required for angiogenesis, heart formation and placental development in mice

The zinc-finger transcription factor Ovol2 (Movo, Movo2) is a mouse homologue of Drosophila ovo, which is essential for the survival and differentiation of female germ line cells. To elucidate OVOL2 function in mammals, we generated Ovol2-deficient mice by gene targeting. The Ovol2 mutants died at embryonic days 9.5-10.5 (E9.5-E10.5), as a result of defects in extraembryonic and embryonic vascularization, and in heart formation. Although the Ovol2 expression was weak, severe defects were detected in extraembryonic and embryonic vascularization, and in heart formation at E8.5-E9.5. In Ovol2(-/-) placentas, allantoic blood vessel expansion and development of the labyrinthine layer were impaired at E10.5. In an endothelial cell line, siRNAs for Ovol2 reduced the expression of Ovol2 and inhibited the capillary-like network formation on Matrigel in vitro. These results demonstrate that Ovol2 may play a critical role in vascular angiogenesis during early embryogenesis.

Estrogen-mediated endothelial progenitor cell biology and kinetics for physiological postnatal vasculogenesis

Estrogen has been demonstrated to promote therapeutic reendothelialization after vascular injury by bone marrow (BM)-derived endothelial progenitor cell (EPC) mobilization and phenotypic modulation. We investigated the primary hypothesis that estrogen regulates physiological postnatal vasculogenesis by modulating bioactivity of BM-derived EPCs through the estrogen receptor (ER), in cyclic hormonally regulated endometrial neovascularization. Cultured human EPCs from peripheral blood mononuclear cells (PB-MNCs) disclosed consistent gene expression of ER alpha as well as downregulated gene expressions of ER beta. Under the physiological concentrations of estrogen (17beta-estradiol, E2), proliferation and migration were stimulated, whereas apoptosis was inhibited on day 7 cultured EPCs. These estrogen-induced activities were blocked by the receptor antagonist, ICI182,780 (ICI). In BM transplanted (BMT) mice with ovariectomy (OVX) from transgenic mice overexpressing beta-galactosidase (lacZ) regulated by an endothelial specific Tie-2 promoter (Tie-2/lacZ/BM), the uterus demonstrated a significant increase in BM-derived EPCs (lacZ expressing cells) incorporated into neovasculatures detected by CD31 immunohistochemistry after E2 administration. The BM-derived EPCs that were incorporated into the uterus dominantly expressed ER alpha, rather than ER beta in BMT mice from BM of transgenic mice overexpressing EGFP regulated by Tie-2 promoter with OVX (Tie-2/EGFP/BMT/OVX) by ERs fluorescence immunohistochemistry. An in vitro assay for colony forming activity as well as flow cytometry for CD133, CD34, KDR, and VE-cadherin, using human PB-MNCs at 5 stages of the female menstrual-cycle (early-proliferative, pre-ovulatory, post-ovulatory, mid-luteal, late-luteal), revealed cycle-specific regulation of EPC kinetics. These findings demonstrate that physiological postnatal vasculogenesis involves cyclic, E2-regulated bioactivity of BM-derived EPCs, predominantly through the ER alpha.

Cdk8 is essential for preimplantation mouse development

The Cdk8 kinase and associated proteins form a nonessential transcriptional repressor module of the Mediator in the budding yeast Saccharomyces cerevisiae. Genetic analyses of this module have demonstrated functions ranging from environmental responses in budding yeast to organogenesis and development in worms, flies, and zebrafish. Here we have investigated the function of mammalian Cdk8 using mice harboring a gene trap insertion at the Cdk8 locus inactivating this kinase. No phenotypes were noted in heterozygote Cdk8+/- mice, but intercrossing these did not produce homozygous Cdk8-/- offspring. Developmental analysis demonstrated a requirement for Cdk8 prior to implantation at embryonic days 2.5 to 3.0. Cdk8-/- preimplantation embryos had fragmented blastomeres and did not proceed to compaction. As Cdk8 deficiency in cultured metazoan cells did not affect cell viability, the results suggest that transcriptional repression of genes critical for early-cell-fate determination underlies the requirement of Cdk8 in embryogenesis.

Filamin A (FLNA) is required for cell-cell contact in vascular development and cardiac morphogenesis

Mutations in the human Filamin A (FLNA) gene disrupt neuronal migration to the cerebral cortex and cause cardiovascular defects. Complete loss of Flna in mice results in embryonic lethality with severe cardiac structural defects involving ventricles, atria, and outflow tracts, as well as widespread aberrant vascular patterning. Despite these widespread developmental defects, migration and motility of many cell types does not appear to be affected. Instead, Flna-null embryos display abnormal epithelial and endothelial organization and aberrant adherens junctions in developing blood vessels, heart, brain, and other tissues. Essential roles for FLNA in intercellular junctions provide a mechanism for the diverse developmental defects seen in patients with FLNA mutations.

Production of endothelial nitric oxide synthase (eNOS) over-expressing piglets

Vascular function, vascular structure, and homeostasis are thought to be regulated in part by nitric oxide (NO) released by endothelial cell nitric oxide synthase (eNOS), and NO released by eNOS plays an important role in modulating metabolism of skeletal and cardiac muscle in health and disease. The pig is an optimal model for human diseases because of the large number of important similarities between the genomic, metabolic and cardiovascular systems of pigs and humans. To gain a better understanding of cardiovascular regulation by eNOS we produced pigs carrying an endogenous eNOS gene driven by a Tie-2 promoter and tagged with a V5 His tag. Nuclear transfer was conducted to create these animals and the effects of two different oocyte activation treatments and two different culture systems were examined. Donor cells were electrically fused to the recipient oocytes. Electrical fusion/activation (1 mM calcium in mannitol: Treatment 1) and electrical fusion (0.1 mM calcium in mannitol)/chemical activation (200 microM Thimerosal for 10 min followed by 8 mM DTT for 30 min: Treatment 2) were used. Embryos were surgically transferred to the oviducts of gilts that exhibited estrus on the day of fusion or the day of transfer. Two cloned transgenic piglets were born from Treatment 1 and low oxygen, and another two from Treatment 2 and normal oxygen. PCR, RT-PCR, Western blotting and immunohistochemistry confirmed that the pigs were transgenic, made message, made the fusion protein and that the fusion protein localized to the endothelial cells of placental vasculature from the conceptuses as did the endogenous eNOS. Thus both activation conditions and culture systems are compatible with development to term. These pigs will serve as the founders for a colony of miniature pigs that will help to elucidate the function of eNOS in regulating muscle metabolism and the cardiorespiratory system.

The RNA binding proteinZfp36l1is required for normal vascularisation and post-transcriptionally regulates VEGF expression

The Zfp36l1 gene encodes a zinc finger-containing mRNA binding protein implicated in the posttranscriptional control of gene expression. Mouse embryos homozygous for a targeted mutation in the Zfp36l1 locus died mid-gestation and exhibited extraembryonic and intraembryonic vascular abnormalities and heart defects. In the developing placenta, there was a failure of the extraembryonic mesoderm to invaginate the trophoblast layer. The phenotype was associated with an elevated expression of vascular endothelial growth factor (VEGF)-A in the embryos and in embryonic fibroblasts cultured under conditions of both normoxia and hypoxia. VEGF-A overproduction by embryonic fibroblasts was not a consequence of changes in Vegf-a mRNA stability; instead, we observed enhanced association with polyribosomes, suggesting Zfp36l1 influences translational regulation. These data implicate Zfp36l1as a negative regulator of Vegf-a gene activity during development.

Role of a 5′-enhancer in the transcriptional regulation of the human endothelial cell protein C receptor gene

The endothelial cell protein C receptor (EPCR) is expressed by endothelial cells of large blood vessels and by hematopoietic stem cells. DNaseI hypersensitive (DH) site mapping across 38 kb of the human EPCR gene (hEPCR) locus identified 3 potential regulatory elements. By itself, the DH region spanning the proximal promoter (PP) was unable to direct cell-specific transcription in transgenic mice. A second DH element, located upstream of PP and termed –5.5HS was hypersensitive only in endothelial cells (ECs) and immature hematopoietic cell lines. Transgenes expressing LacZ under the control of –5.5HS coupled to either PP or the SV40 promoter were able to direct β-galactosidase activity to the endothelium of large vessels during embryogenesis and adulthood. The –5.5HS exhibited enhancer activity that was conferred by the interplay of transcription factors interacting with conserved Ets and composite GATA/Tal1 motifs. The third DH element, located in intron 2, was primarily hypersensitive in EPCR-negative cells, and capable of initiating antisense transcription, suggesting a role in hEPCR silencing. This study identifies critical elements required for the tissue specificity of hEPCR and suggests a mechanism for endothelial and hematopoietic stem cell–specific transcriptional regulation that reflects the common origin of these cell types.

Heterogeneity of Tie2 expression in tumor microcirculation: influence of cancer type, implantation site, and response to therapy

To evaluate the expression of the Tie2/Tek tyrosine kinase receptor in tumor blood vessels, we examined Tie2lacZ(+)/RAG1(-) mice. There was considerable heterogeneity (Tie2-negative, Tie2-positive, or Tie2-composite blood vessels) in subcutaneous xenografts of human colorectal carcinoma (HCT116; 97.5% Tie2-positive vessels) versus human melanoma (WM115; 75.9% Tie2-positive vessels). Similar patterns of Tie2 expression occurred in abdominal metastases derived from the same cell lines. Immunostaining for endothelial markers and Tie2 revealed that endogenous protein levels corresponded with transgene activity. Endothelial cells were confirmed to be of mouse origin through triple immunofluorescence staining with mouse antiserum to human nuclei, isolectin GS-IB(4), and anti-Tie2. Similar Tie2 heterogeneity was observed in clinical specimens from a variety of human cancers, including malignant melanoma and colorectal carcinoma. We also examined the effect of Tek-Delta Fc anti-angiogenic therapy on tumor growth and Tie2 expression patterns in HCT116 and WM115 subcutaneous xenografts. Tek-Delta induced extensive tumor regression in HCT116 tumors and concomitant reductions in Tie2-expressing blood vessels. However, no significant responses were seen in Tek-Delta-treated WM115 tumors. Thus, vascular heterogeneity of Tie2 expression is cancer-type specific, suggesting that the tumor microenvironment and/or direct cancer cell interactions influence Tie2 endothelial expression.

Inflammation-induced lymphangiogenesis in the cornea arises from CD11b-positive macrophages

In the inflamed cornea, there is a parallel outgrowth of blood and lymphatic vessels into the normally avascular cornea. We tested whether adaptive and/or innate immune cells were actively involved in the genesis of new lymphatic vessels. Our results indicate that innate immune cells (CD11b+ macrophages, but not CD11c+ dendritic cells) physically contributed to lymphangiogenesis under pathological conditions and that bone marrow-derived CD11b+ macrophages expressed lymphatic endothelial markers such as LYVE-1 and Prox-1 under inflamed conditions in the corneal stromata of mice. Furthermore, blood vascular endothelial cells that expressed the Tie2 promoter did not contribute to newly formed lymphatic vessels under inflamed conditions. Our in vitro experiments demonstrated that CD11b+ macrophages alone were capable of forming tube-like structures that expressed markers of lymphatic endothelium such as LYVE-1 and podoplanin. The novel finding that CD11b+ macrophages are critical for the development of inflammation-dependent lymphangiogenesis in the eye suggests a new mechanism of lymphangiogenesis.

Conditional knockout of focal adhesion kinase in endothelial cells reveals its role in angiogenesis and vascular development in late embryogenesis

Focal adhesion kinase (FAK) is a critical mediator of signal transduction by integrins and growth factor receptors in a variety of cells including endothelial cells (ECs). Here, we describe EC-specific knockout of FAK using a Cre-loxP approach. In contrast to the total FAK knockout, deletion of FAK specifically in ECs did not affect early embryonic development including normal vasculogenesis. However, in late embryogenesis, FAK deletion in the ECs led to defective angiogenesis in the embryos, yolk sac, and placenta, impaired vasculature and associated hemorrhage, edema, and developmental delay, and late embryonic lethal phenotype. Histologically, ECs and blood vessels in the mutant embryos present a disorganized, detached, and apoptotic appearance. Consistent with these phenotypes, deletion of FAK in ECs isolated from the floxed FAK mice led to reduced tubulogenesis, cell survival, proliferation, and migration in vitro. Together, these results strongly suggest a role of FAK in angiogenesis and vascular development due to its essential function in the regulation of multiple EC activities.

Endothelial Cell Gene Regulation

Endothelial cells (ECs) display phenotypic heterogeneity. Endothelial cell heterogeneity is mediated, at least in part, by site-specific and time-dependent differences in gene transcription. The goal of this review is to provide a conceptual framework for approaching EC gene regulation in the adult vasculature. We summarize data from cell culture studies that provide insight into the transcription factors involved in mediating gene expression in ECs. Next, we review the results of in vivo studies relating to gene regulation in the intact endothelium. Finally, we draw on both the in vitro and in vivo results to propose a model of gene regulation that emphasizes the importance of the extracellular environment in controlling site- and time-specific vascular gene expression.

CRBP-III:lacZ expression pattern reveals a novel heterogeneity of vascular endothelial cells

Vascular endothelial cells are structurally and functionally heterogeneous. However, the molecular basis of this heterogeneity remains poorly defined. We used subtractive and differential screening to identify genes that exhibit heterogeneous expression patterns among vascular endothelial cells. One such gene is cellular retinol binding protein III (CRBP-III/Rbp7). Analysis of the lacZ knockin line for this gene (CRBP-III:lacZ) revealed a novel organ-specific vascular endothelial expression pattern. LacZ was expressed in vascular endothelial cells in heart, skeletal muscle, adipose tissues, thymus, and salivary gland. However, it was not detected in other tissues such as brain, liver, and lung. Furthermore, the expression within each organ was primarily restricted to small capillary endothelial cells, but could not be detected in larger vessels. This organ-specific vascular endothelial expression of CRPB:lacZ is relatively resistant to the changes of organ microenvironment. However, the level of expression can be modified by vitamin A deficiency. Therefore, our results provide novel molecular evidence for the heterogeneity of vascular endothelial cells.

Mef2c is activated directly by Ets transcription factors through an evolutionarily conserved endothelial cell-specific enhancer

Members of the Myocyte Enhancer Factor 2 (MEF2) family of transcription factors play key roles in the development and differentiation of numerous cell types during mammalian development, including the vascular endothelium. Mef2c is expressed very early in the development of the endothelium, and genetic studies in mice have demonstrated that mef2c is required for vascular development. However, the transcriptional pathways involving MEF2C during endothelial cell development have not been defined. As a first step towards identifying the transcriptional factors upstream of MEF2C in the vascular endothelium, we screened for transcriptional enhancers from the mouse mef2c gene that regulate vascular expression in vivo. In this study, we identified a transcriptional enhancer from the mouse mef2c gene sufficient to direct expression to the vascular endothelium in transgenic embryos. This enhancer is active in endothelial cells within the developing vascular system from very early stages in vasculogenesis, and the enhancer remains robustly active in the vascular endothelium during embryogenesis and in adulthood. This mef2c endothelial cell enhancer contains four perfect consensus Ets transcription factor binding sites that are efficiently bound by Ets-1 protein in vitro and are required for enhancer function in transgenic embryos. Thus, these studies identify mef2c as a direct transcriptional target of Ets factors via an evolutionarily conserved transcriptional enhancer and establish a direct link between these two early regulators of vascular gene expression during endothelial cell development in vivo.

Proteolytic inactivation of ADAMTS13 by thrombin and plasmin

The multimeric size and the function of circulating von Willebrand factor are modulated via its proteolytic cleavage by the plasma metalloproteinase, ADAMTS13. It is unclear how ADAMTS13 activity is regulated within the vascular system. In the absence of a regulatory mechanism, ADAMTS13 activity might compromise platelet adhesion at sites of vascular injury. We hypothesized that at sites of vascular injury, ADAMTS13 activity could be regulated locally by coagulation proteinases. Initiation of coagulation in human plasma resulted in the disappearance of added full-length recombinant ADAMTS13. This loss was inhibited by hirudin. Using purified proteins, we showed that ADAMTS13 is proteolyzed at several cleavage sites by thrombin in a time- and concentration-dependent manner. Furthermore, this proteolysis ablated ADAMTS13 activity against purified von Willebrand factor. Preincubation of thrombin with soluble thrombomodulin, but not heparin, inhibited the proteolysis of ADAMTS13, suggesting the involvement of thrombin exosite I (and not exosite II) in ADAMTS13 recognition. Plasmin also cleaved ADAMTS13 into similar fragments, resulting in the loss of ADAMTS13 activity. This study demonstrates the susceptibility of ADAMTS13 to proteolytic inactivation and suggests possible roles for thrombin and plasmin at sites of vascular injury.

Defective extraembryonic angiogenesis in mice lacking LBP-1a, a member of the grainyhead family of transcription factors

LBP-1a and CP2 are ubiquitously expressed members of the grainyhead transcription factor family, sharing significant sequence homology, a common DNA binding motif, and modulating a range of key regulatory and structural genes. We have reported previously that CP2-null mice are viable with no obvious abnormality. LBP-1a provides redundant function in this context. We show here that mice lacking LBP-1a expression develop intrauterine growth retardation at embryonic day 10.5, culminating in death 1 day later. No focal intraembryonic cause for this CP2-independent defect is evident. In contrast, a significant reduction in the thickness of the labyrinthine layer of the placenta is observed in LBP-1a(-/-) animals. However, expression of trophoblast differentiation markers is unperturbed in this context, and complementation studies utilizing tetraploid wild-type cells failed to rescue or ameliorate the LBP-1a(-/-) phenotype, excluding a primary trophoblast defect. An explanation for these observations is provided by the prominent angiogenic defect observed in the mutant placentas. LBP-1a(-/-) allantoic blood vessels fail to penetrate deeply and branch into the complex embryonic vasculature characteristic of the normal placenta. Interestingly, a similar defect in angiogenesis is observed in the yolk sac vasculature, primary endothelial cell-lined capillary tubes, although present, failed to connect into a characteristic intricate vascular network. Collectively, these results demonstrate that LBP-1a plays a critical role in the regulation of extraembryonic angiogenesis.

RNA-binding protein Csx1 mediates global control of gene expression in response to oxidative stress

Fission yeast Spc1 (Sty1), a stress-activated mitogen-activated protein kinase (MAPK) homologous to human p38, orchestrates global changes in gene expression in response to diverse forms of cytotoxic stress. This control is partly mediated through Atf1, a transcription factor homologous to human ATF2. How Spc1 controls Atf1, and how the cells tailor gene expression patterns to different forms of stress, are unknown. Here we describe Csx1, a novel protein crucial for survival of oxidative but not osmotic stress. Csx1 associates with and stabilizes atf1+ mRNA in response to oxidative stress. Csx1 controls expression of the majority of the genes induced by oxidative stress, including most of the genes regulated by Spc1 and Atf1. These studies reveal a novel mechanism controlling MAPK-regulated transcription factors and suggest how gene expression patterns can be customized to specific forms of stress. Csx1-like proteins in humans may perform similar tasks.