Journal articles on the topic 'Tie2'
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Leppänen, Veli-Matti, Pipsa Saharinen, and Kari Alitalo. "Structural basis of Tie2 activation and Tie2/Tie1 heterodimerization." Proceedings of the National Academy of Sciences 114, no. 17 (April 10, 2017): 4376–81. http://dx.doi.org/10.1073/pnas.1616166114.
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The endothelial cell (EC)-specific receptor tyrosine kinases Tie1 and Tie2 are necessary for the remodeling and maturation of blood and lymphatic vessels. Angiopoietin-1 (Ang1) growth factor is a Tie2 agonist, whereas Ang2 functions as a context-dependent agonist/antagonist. The orphan receptor Tie1 modulates Tie2 activation, which is induced by association of angiopoietins with Tie2 in cis and across EC–EC junctions in trans. Except for the binding of the C-terminal angiopoietin domains to the Tie2 ligand-binding domain, the mechanisms for Tie2 activation are poorly understood. We report here the structural basis of Ang1-induced Tie2 dimerization in cis and provide mechanistic insights on Ang2 antagonism, Tie1/Tie2 heterodimerization, and Tie2 clustering. We find that Ang1-induced Tie2 dimerization and activation occurs via the formation of an intermolecular β-sheet between the membrane-proximal (third) Fibronectin type III domains (Fn3) of Tie2. The structures of Tie2 and Tie1 Fn3 domains are similar and compatible with Tie2/Tie1 heterodimerization by the same mechanism. Mutagenesis of the key interaction residues of Tie2 and Tie1 Fn3 domains decreased Ang1-induced Tie2 phosphorylation and increased the basal phosphorylation of Tie1, respectively. Furthermore, the Tie2 structures revealed additional interactions between the Fn 2 (Fn2) domains that coincide with a mutation of Tie2 in primary congenital glaucoma that leads to defective Tie2 clustering and junctional localization. Mutagenesis of the Fn2–Fn2 interface increased the basal phosphorylation of Tie2, suggesting that the Fn2 interactions are essential in preformed Tie2 oligomerization. The interactions of the membrane-proximal domains could provide new targets for modulation of Tie receptor activity.
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Saharinen, Pipsa, Katja Kerkelä, Niklas Ekman, Marie Marron, Nicholas Brindle, Gyun Min Lee, Hellmut Augustin, Gou Young Koh, and Kari Alitalo. "Multiple angiopoietin recombinant proteins activate the Tie1 receptor tyrosine kinase and promote its interaction with Tie2." Journal of Cell Biology 169, no. 2 (April 25, 2005): 239–43. http://dx.doi.org/10.1083/jcb.200411105.
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The Tie1 receptor tyrosine kinase was isolated over a decade ago, but so far no ligand has been found to activate this receptor. Here, we have examined the potential of angiopoietins, ligands for the related Tie2 receptor, to mediate Tie1 activation. We show that a soluble Ang1 chimeric protein, COMP-Ang1, stimulates Tie1 phosphorylation in endothelial cells with similar kinetics and angiopoietin dose dependence when compared with Tie2. The phosphorylation of overexpressed Tie1 was weakly induced by COMP-Ang1 also in transfected cells that do not express Tie2. When cotransfected, Tie2 formed heteromeric complexes with Tie1, enhanced Tie1 activation, and induced phosphorylation of a kinase-inactive Tie1 in a ligand-dependent manner. Tie1 phosphorylation was also induced by native Ang1 and Ang4, although less efficiently than with COMP-Ang1. In conclusion, we show that Tie1 phosphorylation is induced by multiple angiopoietin proteins and that the activation is amplified via Tie2. These results should be important in dissecting the signal transduction pathways and biological functions of Tie1.
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Moore, Jason O., Mark A. Lemmon, and Kathryn M. Ferguson. "Dimerization of Tie2 mediated by its membrane-proximal FNIII domains." Proceedings of the National Academy of Sciences 114, no. 17 (April 10, 2017): 4382–87. http://dx.doi.org/10.1073/pnas.1617800114.
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Tie1 and Tie2, members of the tyrosine kinase family with immunoglobulin and EGF homology domains, are receptor tyrosine kinases found primarily in endothelial cells with key roles in development and maintenance of the vasculature and in angiogenesis. They are attractive targets for therapeutic intervention in tumor angiogenesis, inflammation, and sepsis. Tie2 is regulated directly by the multimeric angiopoietin (Ang) ligands, with Ang1 being its primary activator. Structural studies have shown how Angs bind to the Tie2 ligand-binding region, but do not explain Tie2 activation and suggest a passive role for the Tie2 extracellular region (ECR) in ligand-induced receptor dimerization. Here we show that the Tie2 ECR forms strong dimers even in the absence of bound ligand. Dimerization is mediated by membrane-proximal fibronectin type III (FNIII) domains that were omitted in previous structural studies. We describe a 2.5-Å resolution X-ray crystal structure of the membrane-proximal three Tie2 FNIII domains, Tie2(FNIIIa–c), revealing two possible dimerization modes that primarily involve the third FNIII domain, FNIIIc. Mutating these dimer interfaces implicates one of them (dimer 1) in soluble Tie2 (sTie2) dimerization in solution but suggests that both could play a role in Ang1-induced Tie2 activation, possibly modulated by Tie1. Through small-angle X-ray scattering studies of sTie2 dimers in solution and modeling based on crystal structures, we suggest that Ang1 binding may cross-link Tie2 dimers into higher-order oligomers, potentially explaining how Tie2 is differentially clustered following ligand engagement in different cellular contexts. Our results also firmly implicate FNIII domain-mediated interactions in Tie2 activation, identifying a potential Achilles’ heel for therapeutic inhibition.
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Singh, Harprit, Tariq A. Tahir, Deborah O. A. Alawo, Eyad Issa, and Nicholas P. J. Brindle. "Molecular control of angiopoietin signalling." Biochemical Society Transactions 39, no. 6 (November 21, 2011): 1592–96. http://dx.doi.org/10.1042/bst20110699.
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The angiopoietins act through the endothelial receptor tyrosine kinase Tie2 to regulate vessel maturation in angiogenesis and control quiescence and stability of established vessels. The activating ligand, Ang1 (angiopoietin-1), is constitutively expressed by perivascular cells, and the ability of endothelial cells to respond to the ligand is controlled at the level of the Ang1 receptor. This receptor interacts with the related protein Tie1 on the cell surface, and Tie1 inhibits Ang1 signalling through Tie2. The responsiveness of endothelium to Ang1 is determined by the relative levels of Tie2 and the inhibitory co-receptor Tie1 in the cells. Tie1 undergoes regulated ectodomain cleavage which is stimulated by a range of factors including VEGF (vascular endothelial growth factor), inflammatory cytokines and changes in shear stress. Ectodomain cleavage of Tie1 relieves inhibition of Tie2 and enhances Ang1 signalling. This mechanism regulates Ang1 signalling without requiring changes in the level of the ligand and allows Ang1 signalling to be co-ordinated with other signals in the cellular environment. Regulation of signalling at the level of receptor responsiveness may be an important adaptation in systems in which an activating ligand is normally present in excess or where the ligand provides a constitutive maintenance signal.
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SHYU, Kou-Gi, Chih-Chuan CHANG, Bao-Wei WANG, Peiliang KUAN, and Hang CHANG. "Increased expression of angiopoietin-2 and Tie2 receptor in a rat model of myocardial ischaemia/reperfusion." Clinical Science 105, no. 3 (September 1, 2003): 287–94. http://dx.doi.org/10.1042/cs20030025.
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The angiopoietins and Tie receptors are involved in blood vessel formation. The role of the angiopoietin/Tie receptor system in myocardial ischaemia/reperfusion is not well known. To investigate the participation of angiopoietins and Tie receptors in myocardial ischaemia/reperfusion, adult Wistar rats were studied in which the left coronary artery was ligated for 30 min, followed by reperfusion. Angiopoietin-1 (Ang1), angiopoietin-2 (Ang2), Tie1 and Tie2 were measured immediately after relief of occlusion, and 1, 6, 24 and 72 h after reperfusion, by Northern blot, Western blot and immunohistochemical staining. Ang2 mRNA was increased significantly at 24 h and 48 h after reperfusion, and returned to baseline levels at 72 h, in the jeopardized myocardium. Tie2 mRNA increased 3.4-fold immediately after the relief of occlusion, reached a maximum 8-fold increase at 24 h after reperfusion and remained elevated up to 72 h. Ang2 protein levels also increased after reperfusion, reaching a maximum 2.2-fold increase at 48 h after reperfusion. Tie2 protein increased immediately after relief of ischaemia, and showed a significant increase from 6 h to 72 h after reperfusion as compared with the sham control. Ang1 and Tie1 mRNA and protein did not show significant changes after ischaemia/reperfusion. Immunohistochemical studies also showed increased immunoreactivity of Ang2 and Tie2 in the jeopardized myocardium after ischaemia/reperfusion. In conclusion, expression of both Ang2 and Tie2 increased after ischaemia/reperfusion in the rat ventricular myocardium, while the expression of Ang1 and Tie1 did not.
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Winski, Shannon L., LouAnn Cable, Grant Hogeland, Suzy Brown, Dan Weaver, Jenn Garrus, Susan Rhodes, et al. "Role of p38 MAPK and Tie2 in the Pathogenesis of MDS and Their Inhibition by Dual Inhibitor ARRY-614." Blood 120, no. 21 (November 16, 2012): 2825. http://dx.doi.org/10.1182/blood.v120.21.2825.2825.
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Abstract Abstract 2825 Myelodysplastic syndromes (MDS) are a heterogeneous collection of disorders characterized by dysfunctional bone marrow progenitors leading to peripheral cytopenias. The molecular mechanisms underlying MDS pathophysiology are unclear, but emerging data support a role for both p38 MAPK (p38) and TEK (Tie2). Over-activation of the p38 pathway and increased apoptosis have been reported in the bone marrow of MDS patients, and dysregulation of Tie2 signaling, a potential regulator of hematopoiesis via maintenance of normal hematopoietic stems cell (HSC) quiescence, is associated with worse outcome. To better understand the role of Tie2 in hematopoiesis, CD34+ cells from human cord blood were separated by multi-parameter flow cytometry and cell sorted into HSCs (i.e., CD34+, CD38−) or the more differentiated common myeloid progenitors (CMPs; i.e., CD38+, IL-3Rαlo, CD45RA−), myeloid erythroid progenitors (MEPs; i.e., CD38+, IL-3Rα−, CD45RA−), and granulocyte myeloid progenitors (GMPs; i.e., CD38+, IL-3Rαlo, CD45RA+). Expression of Tie2, Tie1, Ang-1 (Tie2 agonist) and Ang-2 (Tie2 antagonist) was determined by qPCR. The data showed that Tie2, Tie1, and Ang-1 were expressed in CD34+ cells and appeared to be regulated during differentiation, with reduced Tie2 expression observed in the GMP population. To further understand the roles of p38 and Tie2 in MDS, bone marrow and plasma samples were analyzed from a Phase 1 clinical study conducted with ARRY-614, a p38/Tie2 inhibitor, in patients with IPSS Low/Int-1 Risk MDS. At baseline, 65% (13/20) of the MDS patients showed aberrant p38 activation (≥5% phospho-p38 positive cells). Following treatment with ARRY-614, the median percent of cells positive for phospho-p38 was decreased by 85% through up to 4 cycles of treatment (∼112 days). Apoptosis in patient bone marrow samples was reduced as well (monitored by cleaved caspase-3). In cell-based assays, ARRY-614 inhibits both p38-mediated HSP27 phosphorylation (IC50 = 1 nM) and Tie2-dependent AKT phosphorylation (IC50 = 13 nM). Cellular IC50 values, corrected for plasma protein binding, and preliminary pharmacokinetic parameters were used to predict inhibition of these targets in patients. Analysis of the highest administered dose (1200 mg QD) of ARRY-614 as a powder-in-capsule (PiC) formulation in the Phase 1 clinical study predicted robust suppression of phospho-p38 (≥ 50% for 24 hours), consistent with bone marrow and plasma biomarker findings. However, partial inhibition of Tie2 (≥ 50% for 17.1 hours) was predicted. In a second Phase 1 clinical study, an optimized ARRY-614 formulation has demonstrated decreased intra- and inter-patient variability and increased peak plasma concentrations. With this new formulation, peak plasma concentrations of the 400 mg QD cohort were ∼50% higher than those of the 1200 mg QD PiC formulation cohort, possibly affording more extensive Tie2 inhibition. In summary, these observations suggest that inhibition of both p38 and Tie2 may be important for the effects of ARRY-614 in MDS patients. The ongoing Phase 1 dose escalation trial of the optimized ARRY-614 formulation may further our understanding of the contributions of these targets to the pathogenesis of MDS. Disclosures: Winski: Array Biopharma Inc.: Employment. Cable:Array Biopharma Inc.: Employment. Hogeland:Array Biopharma Inc.: Employment. Brown:Array Biopharma Inc.: Employment. Weaver:Array Biopharma Inc.: Employment. Garrus:Array Biopharma Inc.: Employment. Rhodes:Array Biopharma Inc.: Employment. Maloney:Array Biopharma Inc.: Employment. Ptaszynski:Array BioPharma: Consultancy. Chantry:Array Biopharma Inc.: Employment.
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Fonseca, J. A., I. Tomada, N. Tomada, H. Almeida, and D. Neves. "Immunofluorescent detection of Tie1 in the endothelium of the Rat and Human corpus cavernosum during aging." Microscopy and Microanalysis 19, S4 (August 2013): 39–40. http://dx.doi.org/10.1017/s1431927613000810.
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Vasculogenic erectile dysfunction (ED) is an age-related disease partially dependent on vascular growth factors availability and their specific endothelium receptors activation. Among these, angiopoietins-tyrosine kinase with immunoglobulin and EGF homology domain-2 (Tie2) system seems to be particularly dependent on aging, both in rat and in human corpus cavernosum (CC). Angiopoietins (Ang)1 and 2 are produced by pericytes and endothelial cells respectively, and bind with the same affinity to Tie2 receptor. Ang1 was shown to act as an obligatory agonist inducing Tie2 phosphorylation, which promotes cell-cell and cell-extracellular matrix interactions. On the other hand, Ang2 acts in a context-dependent fashion in the increment or, otherwise, destabilization of pre-existent vasculature.Interestingly, it has been demonstrated that activation of Tie2 receptor could also be modulated by Tie1, an additional member of the Tie family of receptor tyrosine kinases, and that co-expression of Tie2 is required for Tie1 activation. Indeed, Tie1 similarly to Tie2 is involved in the maintenance of the vascular integrity. Nevertheless, its role in Angiopoietins-Tie system regulation remains poorly understood, and the identification of a true ligand has remained elusive. In the present study, we aim to demonstrate the expression of Tie1 in the endothelium of aged CC in the Rat and Human species.Twenty-five male Wistar rats were divided in five groups (n=5) and sacrificed by decapitation when they reached the ages of study (6, 12, 18, 24 and 36 months). The penises were excised and immediately fixed in formalin solution. Human CC fragments were obtained from organ donors without known risk factors for ED and divided in two groups: young (16–35 years) and aged (59–74 years). Paraffin embedded sections were deparaffinized, rehydrated and submitted to epitope retrieval with heated Tris-EDTA pH 9.0 buffer before dual-immunolabeling of Tie1 (rabbit anti-Tie1 antibody -abcam) and specific markers of endothelium and smooth muscle cell (goat- anti-PECAM-1 and mouse anti-m-actin antibodies, Santa Cruz Biotechnology Inc. and Millipore, respectively). Appropriate secondary antibodies were employed (anti-rabbit labelled with Alexa 488 with anti-mouse, or, anti –goat labelled with Alexa 568). Nuclei counterstaining was achieved with 4´-6-diamino-2-phenylindole. Images were observed in an Apotome microscope (Carl Zeiss System, Göttingen, Germany) using the filter sets, 01 to DAPI, 09 to Alexa 488 and 31 to Alexa 568, and acquired with Axio Vision 3.0 program (Carl Zeiss System).Tie1 was detected in the endothelium in the CC of Rat, co-localizing with PECAM-1 (Figure 1a) but not with w-actin (Figure 1b). The intensity of Tie1 immunolabeling was higher in the older animals (24 and 36 months). Tie1 was also detected in Human CC endothelium, suggesting an up-regulation in samples obtained from older individuals (Figure 2a and 2b).The present results demonstrate for the first time the expression of Tie1 in the endothelium of CC in Rat and Human, which appears to exhibit an age-dependent up-regulation. Ongoing research employing molecular studies will clarify this aspect.
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Leppänen, Veli-Matti, Pascal Brouillard, Emilia A. Korhonen, Tuomas Sipilä, Sawan Kumar Jha, Nicole Revencu, Veerle Labarque, et al. "Characterization of ANGPT2 mutations associated with primary lymphedema." Science Translational Medicine 12, no. 560 (September 9, 2020): eaax8013. http://dx.doi.org/10.1126/scitranslmed.aax8013.
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Primary lymphedema is caused by developmental and functional defects of the lymphatic vascular system that result in accumulation of protein-rich fluid in tissues, resulting in edema. The 28 currently known genes causing primary lymphedema can explain <30% of cases. Angiopoietin 1 (ANGPT1) and ANGPT2 function via the TIE1-TIE2 (tyrosine kinase with immunoglobulin-like and epidermal growth factor–like domains 1 and 2) receptor complex and α5β1 integrin to form an endothelial cell signaling pathway that is critical for blood and lymphatic vessel formation and remodeling during embryonic development, as well as for homeostasis of the mature vasculature. By screening a cohort of 543 individuals affected by primary lymphedema, we identified one heterozygous de novo ANGPT2 whole-gene deletion and four heterozygous ANGPT2 missense mutations. Functional analyses revealed three missense mutations that resulted in decreased ANGPT2 secretion and inhibited the secretion of wild-type (WT)–ANGPT2, suggesting that they have a dominant-negative effect on ANGPT2 signaling. WT-ANGPT2 and soluble mutants T299M and N304K activated TIE1 and TIE2 in an autocrine assay in human lymphatic endothelial cells. Molecular modeling and biophysical studies showed that amino-terminally truncated ANGPT subunits formed asymmetrical homodimers that bound TIE2 in a 2:1 ratio. The T299M mutant, located in the dimerization interphase, showed reduced integrin α5 binding, and its expression in mouse skin promoted hyperplasia and dilation of cutaneous lymphatic vessels. These results demonstrate that primary lymphedema can be associated with ANGPT2 mutations and provide insights into TIE1 and TIE2 activation mechanisms.
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CHANG, Hang, Bao-Wei WANG, Peiliang KUAN, and Kou-Gi SHYU. "Cyclical mechanical stretch enhances angiopoietin-2 and Tie2 receptor expression in cultured human umbilical vein endothelial cells." Clinical Science 104, no. 4 (March 20, 2003): 421–28. http://dx.doi.org/10.1042/cs1040421.
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Endothelial cells are essential for neovascularization. Angiopoietins and Tie receptors are required for a normal vasculature. How cyclical mechanical stretch affects the expression of components of the angiopoietin system is not known. In this study, we investigated the regulation of angiopoietins and Tie receptors by cyclical mechanical stretch in cultured human umbilical vein endothelial cells (HUVECs). HUVECs grown on a flexible membrane base were stretched by vacuum to 20% elongation, at 60cycles/min. The levels of angiopoietin-2 protein began to increase as early as 2h after stretch was initially applied, reached a maximum of 2.7-fold over the control value by 6h. The Tie2 receptor protein showed the same pattern as Ang-2. These increases in angiopoietin-2 and Tie2 receptor proteins at 6h were blocked by the addition (30min before stretch) of the protein kinase C inhibitor Gö6976 (16nM) or the tyrosine kinase inhibitor herbimycin A (24µM). Similar to protein expression, the levels of angiopoietin-2 and Tie2 receptor mRNAs in HUVECs increased 3.1-fold and 2.5-fold respectively after stretch for 6h. These increases were also blocked by Gö6976 or herbimycin A. Cyclical mechanical stretch increased (and Gö6976 or herbimycin A abrogated these increases) the immunohistochemical labelling of angiopoietin-2 and Tie2 receptor after a 6h stretch. The levels of angiopoietin-1 and Tie1 receptor proteins, mRNAs and immunohistochemical staining were unaffected by cyclical mechanical stretch. Thus cyclical mechanical stretch activates the expression of angiopoietin-2 and the Tie2 receptor, but not angiopoietin-1 or the Tie1 receptor, in cultured HUVECs. This mechanical effect is probably mediated by the tyrosine kinase and protein kinase C pathways.
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Wuitschick, Jeffrey D., Paul R. Lindstrom, Alison E. Meyer, and Kathleen M. Karrer. "Homing Endonucleases Encoded by Germ Line-Limited Genes in Tetrahymena thermophila Have APETELA2 DNA Binding Domains." Eukaryotic Cell 3, no. 3 (June 2004): 685–94. http://dx.doi.org/10.1128/ec.3.3.685-694.2004.
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ABSTRACT Three insertion elements were previously found in a family of germ line-limited mobile elements, the Tlr elements, in the ciliate Tetrahymena. Each of the insertions contains an open reading frame (ORF). Sequence analysis of the deduced proteins encoded by the elements suggests that they are homing endonucleases. The genes are designated TIE1-1, TIE2-1, and TIE3-1 for Tetrahymena insertion-homing endonuclease. The endonuclease motif occupies the amino terminal half of each TIE protein. The C-terminal regions of the proteins are similar to the APETELA2 DNA binding domain of plant transcription factors. The TIE1 and TIE3 elements belong to families of repeated sequences in the germ line micronuclear genome. Comparison of the genes and the deduced proteins they encode suggests that there are at least two distinct families of homing endonuclease genes, each of which appears to be preferentially associated with a specific region of the Tlr elements. The TIE1 and TIE3 elements and their cognates undergo programmed elimination from the developing somatic macronucleus of Tetrahymena. The possible role of homing endonuclease-like genes in the DNA breakage step in developmentally programmed DNA elimination in Tetrahymena is discussed.
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Hamaguchi, Isao, Toru Morisada, Masaki Azuma, Kyoko Murakami, Yuichi Oike, and Toshio Suda. "Tie2 Is Essential for the Development of Lymphangiogenic Endothelial Cell during ES Cell Differentiation." Blood 104, no. 11 (November 16, 2004): 844. http://dx.doi.org/10.1182/blood.v104.11.844.844.
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Abstract Tie2 is a receptor type tyrosine kinase, and is expressed in the hematopoietic stem cells and endothelial cells. We have recently shown that Tie2 and its ligand Angiopoietin-1 (Ang1) signal play a crucial role for maintenance of long-term repopulating hematopoietic stem cells in adult bone marrow (Cell, Vol 118, 149, 2004). Although Tie2 deficient mice showed defect of endothelial cell development, it is not clear whether Tie2 is critical for the development of hematopoietic and lymphangiogenic endothelial cells. In order to clarify the function of Tie2 during the developmental stage, we have developed the cell culture system of ES cell differentiation. After removing LIF, ES cells were cultured on collagen type IV coated plates to promote the differentiation to mesodermal lineage for two days, and the cells were cultured on OP9 stromal cells. Using our system hematopoietic and endothelial progenitors were differentiated efficiently on OP9 cells from the different ES cell straines, E14, TT2, and R1. Expression study showed that ES cell derived cells expressed Tie2 and Flk1 at day 5 of culture on OP9 cells. When we compared the cell fraction sorted by Tie2 and Flk1 mAb regarding differentiation potential, Tie2+Flk1+ fraction was revealed to be an enriched fraction of progenitors for hematopoietic cells and PECAM-1+ endothelial cells. To detect the lymphangiogenic endothelial cells derived from ES cells, we prepared the monoclonal antibody against LYVE-1, which is the receptor for extracellular matrix, glycosaminoglycan. And we confirmed that LYVE-1 was expressed in the embryonic lymphatic endothelium. By using LYVE-1 mAb, we sorted out LYVE-1+ cells from differentiated ES cells and carried out RT-PCR assay. LYVE-1+ cells expressed lymphangiogenic endothelial cell-specific genes, VEGFR-3, Podoplanin, and Prox-1, moreover LYVE-1+ cells took up the DiI-Ac-LDL. These findings indicate that LYVE-1+ cells derived from ES cells have a character of lymphangiogenic endothelial cells. When we compared the cell fraction sorted by Tie2 and Flk1 mAb, LYVE-1+ cells were differentiated from Tie2+Flk1+ fraction dominantly, but not from the other fractions, Tie2-Flk1+, Tie2+Flk1−, and Tie2-Flk1− fraction. These findings suggest that Tie2 is crucial for development of lymphangiogenic endothelial cells as well as hematopoietic cells and endothelial cells. In order to analyze the function of Tie2 during the developmental stage, we differentiated Tie2−/− ES cells using our system. The LYVE-1+ and PECAM-1+ cells derived from Tie2−/− ES cells dramatically decreased as culturing days went by, and at day6 of culture the LYVE-1+ and PECAM-1+ cells derived from Tie2−/− ES cells were one sixth and one third of Tie2+/− cells respectively. When we added 100μM of caspase inhibitor in the culture media, the number of both LYVE-1+ cells and PECAM-1+ cells were recovered. These findings suggest that developmental defect of lymphangiogenic endothelial and endothelial cells are caused by apoptosis because of the blockage of Tie2 signaling. However we could not detect abnormal development of hematopoietic cells from Tie2−/− ES cells. In conclusion, Tie2+Flk1+ fraction derived from ES cells is an enriched fraction of progenitors for lymphangiogenic endothelial cells, and Tie2 signaling is dispensable for lymphangiogenic endothelial cell development as well as endothelial cell development as an anti-apoptotic signaling during ES cell differentiation, but Tie2 is not essential for hematopoietic development.
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Hamaguchi, Isao, Tohru Morisada, Masaki Azuma, Kyoko Murakami, Madoka Kuramitsu, Takuo Mizukami, Kazuyuki Ohbo, et al. "Loss of Tie2 receptor compromises embryonic stem cell–derived endothelial but not hematopoietic cell survival." Blood 107, no. 3 (February 1, 2006): 1207–13. http://dx.doi.org/10.1182/blood-2005-05-1823.
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AbstractTie2 is a receptor-type tyrosine kinase expressed on hematopoietic stem cells and endothelial cells. We used cultured embryonic stem (ES) cells to determine the function of Tie2 during early vascular development and hematopoiesis. Upon differentiation, the ES cell–derived Tie2+Flk1+ fraction was enriched for hematopoietic and endothelial progenitor cells. To investigate lymphatic differentiation, we used a monoclonal antibody against LYVE-1 and found that LYVE-1+ cells derived from Tie2+Flk1+ cells possessed various characteristics of lymphatic endothelial cells. To determine whether Tie2 played a role in this process, we analyzed differentiation of Tie2-/- ES cells. Although the initial numbers of LYVE-1+ and PECAM-1+ cells derived from Tie2-/- cells did not vary significantly, the number of both decreased dramatically upon extended culturing. Such decreases were rescued by treatment with a caspase inhibitor, suggesting that reductions were due to apoptosis as a consequence of a lack of Tie2 signaling. Interestingly, Tie2-/- ES cells did not show measurable defects in development of the hematopoietic system, suggesting that Tie2 is not essential for hematopoietic cell development.
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Khan, Aafaque Ahmad, Varot K. Sandhya, Priyata Singh, Deepak Parthasarathy, Awinav Kumar, Jayshree Advani, Rudrappa Gattu, et al. "Signaling Network Map of Endothelial TEK Tyrosine Kinase." Journal of Signal Transduction 2014 (October 13, 2014): 1–6. http://dx.doi.org/10.1155/2014/173026.
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TEK tyrosine kinase is primarily expressed on endothelial cells and is most commonly referred to as TIE2. TIE2 is a receptor tyrosine kinase modulated by its ligands, angiopoietins, to regulate the development and remodeling of vascular system. It is also one of the critical pathways associated with tumor angiogenesis and familial venous malformations. Apart from the vascular system, TIE2 signaling is also associated with postnatal hematopoiesis. Despite the involvement of TIE2-angiopoietin system in several diseases, the downstream molecular events of TIE2-angiopoietin signaling are not reported in any pathway repository. Therefore, carrying out a detailed review of published literature, we have documented molecular signaling events mediated by TIE2 in response to angiopoietins and developed a network map of TIE2 signaling. The pathway information is freely available to the scientific community through NetPath, a manually curated resource of signaling pathways. We hope that this pathway resource will provide an in-depth view of TIE2-angiopoietin signaling and will lead to identification of potential therapeutic targets for TIE2-angiopoietin associated disorders.
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Souma, Tomokazu, Benjamin R. Thomson, Stefan Heinen, Isabel Anna Carota, Shinji Yamaguchi, Tuncer Onay, Pan Liu, et al. "Context-dependent functions of angiopoietin 2 are determined by the endothelial phosphatase VEPTP." Proceedings of the National Academy of Sciences 115, no. 6 (January 22, 2018): 1298–303. http://dx.doi.org/10.1073/pnas.1714446115.
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The angiopoietin (ANGPT)–TIE2/TEK signaling pathway is essential for blood and lymphatic vascular homeostasis. ANGPT1 is a potent TIE2 activator, whereas ANGPT2 functions as a context-dependent agonist/antagonist. In disease, ANGPT2-mediated inhibition of TIE2 in blood vessels is linked to vascular leak, inflammation, and metastasis. Using conditional knockout studies in mice, we show TIE2 is predominantly activated by ANGPT1 in the cardiovascular system and by ANGPT2 in the lymphatic vasculature. Mechanisms underlying opposing actions of ANGPT2 in blood vs. lymphatic endothelium are poorly understood. Here we show the endothelial-specific phosphatase VEPTP (vascular endothelial protein tyrosine phosphatase) determines TIE2 response to ANGPT2. VEPTP is absent from lymphatic endothelium in mouse in vivo, permitting ANGPT2/TIE2-mediated lymphangiogenesis. Inhibition of VEPTP converts ANGPT2 into a potent TIE2 activator in blood endothelium. Our data support a model whereby VEPTP functions as a rheostat to modulate ANGPT2 ligand effect on TIE2.
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Wehrle, Christina, Paul Van Slyke, and Daniel J. Dumont. "Angiopoietin-1-induced ubiquitylation of Tie2 by c-Cbl is required for internalization and degradation." Biochemical Journal 423, no. 3 (October 12, 2009): 375–80. http://dx.doi.org/10.1042/bj20091010.
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Tie2 [where ‘Tie’ is an acronym from tyrosine kinase with Ig and EGF (epidermal growth factor) homology domains] is a receptor tyrosine kinase expressed predominantly on the surface of endothelial cells. Activated by its ligands, the angiopoietins, Tie2 initiates signalling pathways that modulate vascular stability and angiogenesis. Deletion of either the Tie2 or Ang1 (angiopoietin-1) gene in mice results in lethal vascular defects, signifying their importance in vascular development. The mechanism employed by the Tie2 signalling machinery to attenuate or cause receptor trafficking is not well defined. Stimulation of Tie2-expressing cells with Ang1 results in its ubiquitylation, suggesting that this may provide the necessary signal for receptor turnover. Using a candidate molecule approach, we demonstrate that Tie2 co-immunoprecipitates with c-Cbl in an Ang1-dependent manner and its ubiquitylation can be inhibited by the dominant-interfering molecule v-Cbl (a viral form of c-Cbl that contains only the tyrosine kinase-binding domain region). Inhibition of the Tie2–Cbl interaction by overexpression of v-Cbl blocks ligand-induced Tie2 internalization and degradation. In summary, our results illustrate that c-Cbl interacts with the Tie2 signalling complex in a stimulation-dependent manner, and that this interaction is required for Tie2 ubiquitylation, internalization and degradation.
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Chatterjee, Anupriya, Rachana Eshwaran, Hongpeng Huang, Di Zhao, Martina Schmidt, Thomas Wieland, and Yuxi Feng. "Role of the Ang2–Tie2 Axis in Vascular Damage Driven by High Glucose or Nucleoside Diphosphate Kinase B Deficiency." International Journal of Molecular Sciences 21, no. 10 (May 25, 2020): 3713. http://dx.doi.org/10.3390/ijms21103713.
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Ablation of nucleoside diphosphate kinase B (NDPK-B) in mice causes a breakdown of the neurovascular unit in the retina, mimicking diabetic retinopathy. The NDPK-B deficiency-induced vascular damage is mediated by excessive angiopoietin 2 (Ang2). Herein, the potential involvement of its receptor, Tie2, was investigated. NDPK-B-deficient mouse retinas showed an upregulation of Tie2, specifically in the deep capillary layer. A similar upregulation of Tie2 was observed in cultured endothelial cells (ECs) from different origins upon NDPK-B depletion, whereas high glucose (HG) treatment did not alter Tie2 expression. Immunofluorescence staining and subcellular fractionation showed that the majority of Tie2 upregulation occurred at the plasma membrane. Similar to HG, however, NDPK-B depletion reduced Tie2 tyrosine phosphorylation. Compared to HG, a stronger increase of Ang2 was observed in NDPK-B depleted ECs. Treatment of ECs with soluble Tie2 or siRNA-mediated Tie2 knockdown attenuated NDPK-B depletion- but not HG-induced Ang2 upregulation. Like NDPK-B depletion, overexpression of recombinant Ang2 in ECs enhanced Ang2 secretion and concomitantly promoted the upregulation of Tie2. Thus, we identified a new mechanism showing that after reaching a threshold level of secretion, Ang2 sustains its own expression and secretion by a Tie2-dependent positive feedback loop.
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Sako, Kosuke, Daisuke Sakai, Yoshihiko Nakamura, Jordy Schol, Erika Matsushita, Takayuki Warita, Natsumi Horikita, Masato Sato, and Masahiko Watanabe. "Effect of Whole Tissue Culture and Basic Fibroblast Growth Factor on Maintenance of Tie2 Molecule Expression in Human Nucleus Pulposus Cells." International Journal of Molecular Sciences 22, no. 9 (April 29, 2021): 4723. http://dx.doi.org/10.3390/ijms22094723.
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Previous work showed a link between Tie2+ nucleus pulposus progenitor cells (NPPC) and disc degeneration. However, NPPC remain difficult to maintain in culture. Here, we report whole tissue culture (WTC) combined with fibroblast growth factor 2 (FGF2) and chimeric FGF (cFGF) supplementation to support and enhance NPPC and Tie2 expression. We also examined the role of PI3K/Akt and MEK/ERK pathways in FGF2 and cFGF-induced Tie2 expression. Young herniating nucleus pulposus tissue was used. We compared WTC and standard primary cell culture, with or without 10 ng/mL FGF2. PI3K/Akt and MEK/ERK signaling pathways were examined through western blotting. Using WTC and primary cell culture, Tie2 positivity rates were 7.0 ± 2.6% and 1.9 ± 0.3% (p = 0.004), respectively. Addition of FGF2 in WTC increased Tie2 positivity rates to 14.2 ± 5.4% (p = 0.01). FGF2-stimulated expression of Tie2 was reduced 3-fold with the addition of the MEK inhibitor PD98059 (p = 0.01). However, the addition of 1 μM Akt inhibitor, 124015-1MGCN, only reduced small Tie2 expression (p = 0.42). cFGF similarly increased the Tie2 expression, but did not result in significant phosphorylation in both the MEK/ERK and PI3K/Akt pathways. WTC with FGF2 addition significantly increased Tie2 maintenance of human NPPC. Moreover, FGF2 supports Tie2 expression via MEK/ERK and PI3K/Akt signals. These findings offer promising tools and insights for the development of NPPC-based therapeutics.
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Kugathasan, Lakshmi, Julie Basu Ray, Yupu Deng, Effat Rezaei, Daniel J. Dumont, and Duncan J. Stewart. "The angiopietin-1–Tie2 pathway prevents rather than promotes pulmonary arterial hypertension in transgenic mice." Journal of Experimental Medicine 206, no. 10 (September 8, 2009): 2221–34. http://dx.doi.org/10.1084/jem.20090389.
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The role of the angiopoietin-1 (Ang1)–Tie2 pathway in the pathogenesis of pulmonary arterial hypertension (PAH) is controversial. Although Ang1 is well known to prevent endothelial activation and injury in systemic vascular beds, this pathway has been suggested to mediate pulmonary vascular remodeling in PAH. Therefore, we used transgenic models to determine the effect of increased or decreased Tie2 activity on the development of PAH. We now report modest spontaneous elevation in right ventricular systolic pressure in Tie2-deficient mice (Tie2+/−) compared with wild-type (WT) littermate controls, which was exacerbated upon chronic exposure to the clinically relevant PAH triggers, serotonin (5-HT) or interleukin-6 (IL-6). Moreover, overexpression of Ang1 in transgenic mice had no deleterious effect on pulmonary hemodynamics and, if anything, blunted the response to 5-HT. Exposure to 5-HT or IL-6 also decreased lung Ang1 expression, further reducing Tie2 activity and inducing pulmonary apoptosis in the Tie2+/− group only. Similarly, cultured pulmonary artery endothelial cells subjected to Tie2 silencing demonstrated increased susceptibility to apoptosis after 5-HT treatment. Finally, treatment of Tie2-deficient mice with Z-VAD, a pan-caspase inhibitor, prevented the pulmonary hypertensive response to 5-HT. Thus, these findings firmly establish that endothelial survival signaling via the Ang1–Tie2 pathway is protective in PAH.
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Darrow, April L., J. Gregory Maresh, and Ralph V. Shohet. "Mouse Models and Techniques for the Isolation of the Diabetic Endothelium." ISRN Endocrinology 2013 (June 11, 2013): 1–12. http://dx.doi.org/10.1155/2013/165397.
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Understanding the molecular mechanisms underlying diabetic endothelial dysfunction is necessary in order to improve the cardiovascular health of diabetic patients. Previously, we described an in vivo, murine model of insulin resistance induced by feeding a high-fat diet (HFD) whereby the endothelium may be isolated by fluorescence-activated cell sorting (FACS) based on Tie2-GFP expression and cell-surface staining. Here, we apply this model to two new strains of mice, ScN/Tie2-GFP and ApoE(−/−)/Tie2-GFP, and describe their metabolic responses and endothelial isolation. ScN/Tie2-GFP mice, which lack a functional toll-like receptor 4 (TLR4), display lower fasting glucose and insulin levels and improved glucose tolerance compared to Tie2-GFP mice, suggesting that TLR4 deficiency decreases susceptibility to the development of insulin resistance. ApoE(−/−)/Tie2-GFP mice display elevated glucose and cholesterol levels versus Tie2-GFP mice. Endothelial isolation by FACS achieves a pure population of endothelial cells that retain GFP fluorescence and endothelial functions. Transcriptional analysis of the aortic and muscle endothelium isolated from ApoE(−/−)/Tie2-GFP mice reveals a reduced endothelial response to HFD compared to Tie2-GFP mice, perhaps resulting from preexisting endothelial dysfunction in the hypercholesterolemic state. These mouse models and endothelial isolation techniques are valuable for assessing diabetic endothelial dysfunction and vascular responses in vivo.
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Yuan, Hai Tao, Eliyahu V. Khankin, S. Ananth Karumanchi, and Samir M. Parikh. "Angiopoietin 2 Is a Partial Agonist/Antagonist of Tie2 Signaling in the Endothelium." Molecular and Cellular Biology 29, no. 8 (February 17, 2009): 2011–22. http://dx.doi.org/10.1128/mcb.01472-08.
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ABSTRACT Angiopoietin 2 (Ang2) was originally shown to be a competitive antagonist for Ang1 of the receptor tyrosine kinase Tie2 in endothelial cells (ECs). Since then, reports have conflicted on whether Ang2 is an agonist or antagonist of Tie2. Here we show that Ang2 functions as an agonist when Ang1 is absent but as a dose-dependent antagonist when Ang1 is present. Exogenous Ang2 activates Tie2 and the promigratory, prosurvival PI3K/Akt pathway in ECs but with less potency and lower affinity than exogenous Ang1. ECs produce Ang2 but not Ang1. This endogenous Ang2 maintains Tie2, phosphatidylinositol 3-kinase, and Akt activities, and it promotes EC survival, migration, and tube formation. However, when ECs are stimulated with Ang1 and Ang2, Ang2 dose-dependently inhibits Ang1-induced Tie2 phosphorylation, Akt activation, and EC survival. We conclude that Ang2 is both an agonist and an antagonist of Tie2. Although Ang2 is a weaker agonist than Ang1, endogenous Ang2 maintains a level of Tie2 activation that is critical to a spectrum of EC functions. These findings may reconcile disparate reports of Ang2's effect on Tie2, impact our understanding of endogenous receptor tyrosine kinase signal transduction mechanisms, and affect how Ang2 and Tie2 are targeted under conditions such as sepsis and cancer.
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Jones, Nina, Stephen H. Chen, Celina Sturk, Zubin Master, Jennifer Tran, Robert S. Kerbel, and Daniel J. Dumont. "A Unique Autophosphorylation Site on Tie2/Tek Mediates Dok-R Phosphotyrosine Binding Domain Binding and Function." Molecular and Cellular Biology 23, no. 8 (April 15, 2003): 2658–68. http://dx.doi.org/10.1128/mcb.23.8.2658-2668.2003.
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ABSTRACT Tie2/Tek is an endothelial cell receptor tyrosine kinase that induces signal transduction pathways involved in cell migration upon angiopoietin-1 (Ang1) stimulation. To address the importance of the various tyrosine residues of Tie2 in signal transduction, we generated a series of Tie2 mutants and examined their signaling properties. Using this approach in conjunction with a phosphorylation state-specific antibody, we identified tyrosine residue 1106 on Tie2 as an Ang1-dependent autophosphorylation site that mediates binding and phosphorylation of the downstream-of-kinase-related (Dok-R) docking protein. This tyrosine residue is contained within a unique interaction motif for the phosphotyrosine binding domain of Dok-R, and the pleckstrin homology domain of Dok-R further contributes to Tie2 binding in a phosphatidylinositol 3′-kinase-dependent manner. Introduction of a Tie2 mutant lacking tyrosine residue 1106 into endothelial cells interferes with Dok-R phosphorylation in response to Ang1. Furthermore, this mutant is unable to restore the migration potential of endothelial cells derived from mice lacking Tie2. Together, these findings demonstrate that tyrosine residue 1106 on Tie2 is critical for coupling downstream cell migration signal transduction pathways with Ang1 stimulation in endothelial cells.
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Drescher, Florian, Patricia Juárez, Danna L. Arellano, Nicolás Serafín-Higuera, Felipe Olvera-Rodriguez, Samanta Jiménez, Alexei F. Licea-Navarro, and Pierrick G. J. Fournier. "TIE2 Induces Breast Cancer Cell Dormancy and Inhibits the Development of Osteolytic Bone Metastases." Cancers 12, no. 4 (April 3, 2020): 868. http://dx.doi.org/10.3390/cancers12040868.
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Breast cancer (BCa) cells disseminating to the bone can remain dormant and resistant to treatments for many years until relapsing as bone metastases. The tyrosine kinase receptor TIE2 induces the dormancy of hematopoietic stem cells, and could also induce the dormancy of BCa cells. However, TIE2 is also a target for anti-angiogenic treatments in ongoing clinical trials, and its inhibition could then restart the proliferation of dormant BCa cells in bone. In this study, we used a combination of patient data, in vitro, and in vivo models to investigate the effect of TIE2 in the dormancy of bone metastases. In BCa patients, we found that a higher TIE2 expression is associated with an increased time to metastases and survival. In vitro, TIE2 decreased cell proliferation as it increased the expression of cyclin-dependent kinase inhibitors CDKN1A and CDKN1B and arrested cells in the G0/G1 phase. Expression of TIE2 also increased the resistance to the chemotherapeutic 5-Fluorouracil. In mice, TIE2 expression reduced tumor growth and the formation of osteolytic bone metastasis. Together, these results show that TIE2 is sufficient to induce dormancy in vitro and in vivo, and could be a useful prognostic marker for patients. Our data also suggest being cautious when using TIE2 inhibitors in the clinic, as they could awaken dormant disseminated tumor cells.
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Chen, Stephen H., Yael Babichev, Natalie Rodrigues, Daniel Voskas, Ling Ling, Vicky P. K. H. Nguyen, and Daniel J. Dumont. "Gene expression analysis of Tek/Tie2 signaling." Physiological Genomics 22, no. 2 (July 14, 2005): 257–67. http://dx.doi.org/10.1152/physiolgenomics.00063.2005.
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The elaboration of the vasculature during embryonic development involves restructuring of the early vessels into a more complex vascular network. Of particular importance to this vascular remodeling process is the requirement of the Tek/Tie2 receptor tyrosine kinase. Mouse gene-targeting studies have shown that the Tie2-deficient embryos succumb to embryonic death at midgestation due to insufficient sprouting and remodeling of the primary capillary plexus. To identify the underlying genetic mechanisms regulating the process of vascular remodeling, transcriptomes modulated by Tie2 signaling were analyzed utilizing serial analysis of gene expression (SAGE). Two libraries were constructed and sequenced using embryonic day 8.5 yolk sac tissues from Tie2 wild-type and the Tie2-null littermates. After tag extraction, 45,689 and 45,275 SAGE tags were obtained for the Tie2 wild-type and Tie2-null libraries, respectively, yielding a total of 21,376 distinct tags. Close to 62% of the tags were uniquely annotated, whereas 10% of the total tags were unknown. Using semiquantitative PCR, the differential expression of eight genes was confirmed that included Elk3, an important angiogenic switch gene which was upregulated in the absence of Tie2 signaling. The results of this study provide valuable insight into the potential association between Tie2 signaling and other known angiogenic pathways as well as genes that might have novel functions in vascular remodeling.
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Ghosh, Chandra C., Sascha David, Ruyang Zhang, Anthony Berghelli, Katelyn Milam, Sarah J. Higgins, Jon Hunter, et al. "Gene control of tyrosine kinase TIE2 and vascular manifestations of infections." Proceedings of the National Academy of Sciences 113, no. 9 (February 16, 2016): 2472–77. http://dx.doi.org/10.1073/pnas.1519467113.
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Ligands of the endothelial-enriched tunica interna endothelial cell kinase 2 (Tie2) are markedly imbalanced in severe infections associated with vascular leakage, yet regulation of the receptor itself has been understudied in this context. Here, we show that TIE2 gene expression may constitute a novel vascular barrier control mechanism in diverse infections. Tie2 expression declined rapidly in wide-ranging models of leak-associated infections, including anthrax, influenza, malaria, and sepsis. Forced Tie2 suppression sufficed to attenuate barrier function and sensitize endothelium to permeability mediators. Rapid reduction of pulmonary Tie2 in otherwise healthy animals attenuated downstream kinase signaling to the barrier effector vascular endothelial (VE)-cadherin and induced vascular leakage. Compared with wild-type littermates, mice possessing one allele of Tie2 suffered more severe vascular leakage and higher mortality in two different sepsis models. Common genetic variants that influence TIE2 expression were then sought in the HapMap3 cohort. Remarkably, each of the three strongest predicted cis-acting SNPs in HapMap3 was also associated with the risk of acute respiratory distress syndrome (ARDS) in an intensive care unit cohort of 1,614 subjects. The haplotype associated with the highest TIE2 expression conferred a 28% reduction in the risk of ARDS independent of other major clinical variables, including disease severity. In contrast, the most common haplotype was associated with both the lowest TIE2 expression and 31% higher ARDS risk. Together, the results implicate common genetic variation at the TIE2 locus as a determinant of vascular leak-related clinical outcomes from common infections, suggesting new tools to identify individuals at unusual risk for deleterious complications of infection.
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Chen, Haiming, Richard A. Campbell, Melinda S. Gordon, Steven J. Manyak, Cathy Wang, Mingjie Li, Hee Jin Lee, et al. "Circulating Tie2-Expressing Cells Are Increased in Multiple Myeloma Patients, Correlate with Serum Pleiotrophin Levels and May Develop from This Myeloma Angiogenic and Growth Factor." Blood 106, no. 11 (November 16, 2005): 2494. http://dx.doi.org/10.1182/blood.v106.11.2494.2494.
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Abstract Tie2, an endothelial cell-specific receptor kinase, plays an important role in tumor angiogenesis. This protein is essential to the development of embryonic vasculature as well as vascular growth and maintenance in adult tissues. Because of the increasing importance that angiogenesis has been shown to play in multiple myeloma (MM), we determined the number of Tie2-expressing cells in the peripheral blood (PB) of MM patients and its relationship to the serum levels and gene expression of a recently identified angiogenic factor, pleiotrophin (PTN). We have recently demonstrated that PTN is expressed and secreted by MM tumor cells, and serum levels of this protein are highly elevated in MM patients. We quantified the number of Tie2-positive cells in MM patients (n=15) and age-matched control subjects (n=10) using an immunohistochemical technique. Tie2-expressing cells were significantly elevated in the PB mononuclear cells (MCs) from MM patients compared to the normal controls (p<0.05). We also analyzed gene expression for Tie2 in these same samples using RT-PCR. The results showed that Tie2 mRNA was strongly expressed in the PBMCs from MM patients whereas control samples showed no or low expression of this gene. Serum levels of PTN were tested with ELISA, and PTN mRNA concentrations were quantified by RT-PCR in PBMCs from these same patients and control subjects. The results showed that serum levels of PTN correlated with the number of Tie2-expressing PBMCs in MM patients (R2=0.5778). PTN mRNA levels also correlated with Tie2 gene expression in PBMC samples. We further examined whether monocyte colony stimulating factor (mCSF), PTN and vascular endothelial growth factor (VEGF) may be capable of inducing Tie2 expression in highly purified human monocytes that lack Tie2 expression. Normal PB monocytes were purified using density centrifugation followed by anti-CD14 micro-bead affinity column selection. Although none of these three proteins alone or the combinations of either VEGF and mCSF or VEGF and PTN induced Tie2 gene expression in the monocytes following one week of incubation, the combination of PTN (100 nM) and mCSF (20 nM) led to expression of Tie2 in these cells. We quantified the proportion of cells expressing Tie2 in these samples with RT-PCR using serial dilutional analysis with B or T cells that lack Tie2 expression, and showed that approximately 0.1–1.0% of the monocytes expressed this gene following incubation with PTN and mCSF. Moreover, the addition of VEGF (20 ng/ml) to PTN and mCSF increased the proportion of cells expressing Tie2 (to >10%). Anti-PTN antibody blocked the induction of Tie2 gene expression in these monocytes by this cytokine combination. These results show that Tie2-expressing cells are elevated in the peripheral blood of MM patients, and correlate with PTN serum and PTN mRNA expression. PTN in combination with VEGF and mCSF induces Tie2 gene expression in a large proportion of circulating human monocytes. These results suggest that MM patients show increased numbers of vasculogenic progenitors in their circulation that may result from the presence of elevated levels of circulating angiogenic factors including PTN and VEGF.
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van Meurs, Matijs, Neng F. Kurniati, Francis M. Wulfert, Sigridur A. Asgeirsdottir, Inge A. de Graaf, Simon C. Satchell, Peter W. Mathieson, et al. "Shock-induced stress induces loss of microvascular endothelial Tie2 in the kidney which is not associated with reduced glomerular barrier function." American Journal of Physiology-Renal Physiology 297, no. 2 (August 2009): F272—F281. http://dx.doi.org/10.1152/ajprenal.00137.2009.
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Both hemorrhagic shock and endotoxemia induce a pronounced vascular activation in the kidney which coincides with albuminuria and glomerular barrier dysfunction. We hypothesized that changes in Tie2, a vascular restricted receptor tyrosine kinase shown to control microvascular integrity and endothelial inflammation, underlie this loss of glomerular barrier function. In healthy murine and human kidney, Tie2 is heterogeneously expressed in all microvascular beds, although to different extents. In mice subjected to hemorrhagic and septic shock, Tie2 mRNA and protein were rapidly, and temporarily, lost from the renal microvasculature, and normalized within 24 h after initiation of the shock insult. The loss of Tie2 protein could not be attributed to shedding as both in mice and healthy volunteers subjected to endotoxemia, sTie2 levels in the systemic circulation did not change. In an attempt to identify the molecular control of Tie2, we activated glomerular endothelial cell cultures and human kidney slices in vitro with LPS or TNF-α, but did not observe a change in Tie2 mRNA levels. In parallel to the loss of Tie2 in vivo, an overt influx of neutrophils in the glomerular compartment, which coincided with proteinuria, was seen. As neutrophil-endothelial cell interactions may play a role in endothelial adaptation to shock, and these effects cannot be mimicked in vitro, we depleted neutrophils before shock induction. While this neutrophil depletion abolished proteinuria, Tie2 was not rescued, implying that Tie2 may not be a major factor controlling maintenance of the glomerular filtration barrier in this model.
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Cordeiro, Ana Lúcia, António Figueiredo, Inês Tomada, Henrique de Almeida, and Delminda Neves. "Characterization of the Expression of Ang1, Ang2, and Tie2 in the Corpus Cavernosum of the Rat during Aging." Microscopy and Microanalysis 16, no. 6 (October 25, 2010): 699–709. http://dx.doi.org/10.1017/s1431927610094006.
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AbstractAging is the single most significant risk factor for erectile dysfunction (ED), leading to structural modification of cavernous tissue and altering expression of vascular growth factors. The angiopoietin/Tie2 system has been recently considered as a potential target for therapy of vascular disorders, including ED. Hence, the aim of this study was to analyze expression of angiopoietin1 (Ang1), angiopoietin2 (Ang2), and their receptor Tie2 in corpus cavernosum (CC) of rat during aging (6, 12, 18, and 24 months). The expression of Ang1, Ang2, and Tie2 was studied by immunohistochemistry and immunofluorescence, followed by semiquantification after Western blotting. Both Ang1 and Ang2 were localized mainly in perivascular smooth muscle and endothelial cells, while Tie2 was strictly detected at the vascular endothelium. A significant decrease in Ang2's expression was observed at 12 months when compared with 6-month-old rats, a tendency that reverses in older animals. No significant differences were demonstrated for Ang1 or Tie2, which is consistent with their constitutive expression in CC. The ratios Ang1/Tie2 and Ang2/Tie2 were also calculated and both decrease during aging, while no marked variation was observed for Ang1/Ang2. Our results suggest that the angiopoietin/Tie2 system participate in the vascular maintenance and remodeling of the CC during aging.
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Kontos, Christopher D., Thomas P. Stauffer, Wen-Pin Yang, John D. York, Liwen Huang, Michael A. Blanar, Tobias Meyer, and Kevin G. Peters. "Tyrosine 1101 of Tie2 Is the Major Site of Association of p85 and Is Required for Activation of Phosphatidylinositol 3-Kinase and Akt." Molecular and Cellular Biology 18, no. 7 (July 1, 1998): 4131–40. http://dx.doi.org/10.1128/mcb.18.7.4131.
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ABSTRACT Tie2 is an endothelium-specific receptor tyrosine kinase that is required for both normal embryonic vascular development and tumor angiogenesis and is thought to play a role in vascular maintenance. However, the signaling pathways responsible for the function of Tie2 remain unknown. In this report, we demonstrate that the p85 subunit of phosphatidylinositol 3-kinase (PI3-kinase) associates with Tie2 and that this association confers functional lipid kinase activity. Mutation of tyrosine 1101 of Tie2 abrogated p85 association both in vitro and in vivo in yeast. Tie2 was found to activate PI3-kinase in vivo as demonstrated by direct measurement of increases in cellular phosphatidylinositol 3-phosphate and phosphatidylinositol 3,4-bisphosphate, by plasma membrane translocation of a green fluorescent protein-Akt pleckstrin homology domain fusion protein, and by downstream activation of the Akt kinase. Activation of PI3-kinase was abrogated in these assays by mutation of Y1101 to phenylalanine, consistent with a requirement for this residue for p85 association with Tie2. These results suggest that activation of PI3-kinase and Akt may in part account for Tie2’s role in both embryonic vascular development and pathologic angiogenesis, and they are consistent with a role for Tie2 in endothelial cell survival.
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Sivina, Mariela, Takeshi Yamada, Natalie Dang, and H. Daniel Lacorazza. "Hemangiogenic Role of ELF4 in Bone Marrow Post Myeloablation." Blood 108, no. 11 (November 16, 2006): 1783. http://dx.doi.org/10.1182/blood.v108.11.1783.1783.
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Abstract Bone marrow suppression is an important cause of death in patients exposed to radiation or in cancer patients treated with conventional chemotherapeutic agents. Myeloablative treatments (i.e. 5-fluorouracil administration) lead to apoptosis of blood forming cells and to regression of blood vessels in bone marrow. It is well known that hematological recovery post-bone marrow insult depends on the capacity of hematopoietic stem cells to regenerate the entire hematopoietic system, however, the transcriptional machinery involved in the regeneration of sinusoidal blood vessels in bone marrow from endothelial progenitor cells is largely unknown. Endothelial cells express the Tie2 receptor tyrosine kinase (a.k.a. Tek), which is involved in the angiogenic remodeling and vessel stabilization. Gene targeting of Tie2 showed that it is not required for differentiation and proliferation of definitive hematopoietic lineages in the embryo although Tie2 is needed during postnatal bone marrow hematopoiesis. ELF is a subgroup of the ETS family of transcription factors composed by ELF1, ELF2 (a.k.a. NERF), ELF3, ELF4 (a.k.a. MEF) and ELF5. ELF1 and ELF2 have been shown to regulate Tie2 expression in vitro. Recently we showed that ELF4 modulates the exit of hematopoietic stem cells (HSC) from quiescence (Lacorazza et al., Cancer Cell2006, 9:175–187). Given the high homology between ELF1 and ELF4 and the same origin of HSC and endothelial progenitor cells, we hypothesize that ELF4 regulates proliferation and Tie2 expression of endothelial cells. We used a luciferase gene reporter system in COS-7 and HEK cells to examine the capacity of ELF proteins to activate Tie2. ELF4 is the strongest activator of Tie2 expression following the hierarchy ELF4>ELF1>ELF2 variant 1>ELF2 variant 2. Site directed mutagenesis of each of the five ETS-binding sites (EBS) present in the Tie2 promoter shows that ELF4 binds preferentially to EBS 1, 3 and 5. Binding of ELF4 to the Tie2 promoter was confirmed by chromatin immunoprecipitation and EMSA. Although Elf1 gene expression is essentially normal in Elf4−/− bone marrow cells collected after 5-FU treatment, we detected diminished Tie2 expression compared to Elf4+/+ bone marrow cells. The association of this effect to human endothelial cells derived from umbilical cord (HUVEC cells) was investigated. All-trans retinoic acid (ATRA) and vascular-endothelial growth factor (VEGF) induced ELF4 expression in HUVEC cells in a dose and time dependent manner which was followed by increased Tie2 expression, suggesting that expression of ELF4 is modulated by angiogenic signals. Moreover, endothelial cells treated with ATRA showed rapid wound colonization in a wound assay. Expression of the pan-endothelial marker MECA-32 was determined by immunohistochemistry to correlate Tie2 with the regeneration of blood vessels: myeloablated Elf4−/− femurs exhibited a reduction of MECA-32 positive arterioles. Finally, temporal and spatial expression of Tie2 during hematological recovery post ablation was measured in bone marrow using transgenic Tie2-LacZ mice crossed to Elf4−/− mice. Collectively, our data suggests that ELF4 regulates Tie2 expression in endothelial cells but most importantly their proliferative capacity in response to angiogenic signals.
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Kopp, Hans-Georg, Scott T. Avecilla, Rafael Tejada, Ronald G. Crystal, Neil R. Hackett, and Shahin Rafii. "Tie-2 Activation Is Required for Regeneration of Marrow Vasculature, Supporting Hematopoietic Reconstitution." Blood 104, no. 11 (November 16, 2004): 1297. http://dx.doi.org/10.1182/blood.v104.11.1297.1297.
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Abstract Accumulating evidence from our lab (Nature Med.2004; 10(1): 64–71) and others have shown that myelosuppression not only results in apoptosis of the hematopoietic cells but also in regression of bone marrow (BM) sinusoidal vessels. Remarkably, we have shown that restoration of hematopoiesis is dependent on the regeneration of BM sinusoidal neo-vessels. However, the mechanism whereby vascular reconstitution is regulated is unknown. Because Tie2/Angiopoietins are critical in the remodeling of neo-vessels, we hypothesized that activation of Tie2 plays a role in regeneration of sinusoidal neo-vessels and restoration of hematopoiesis. To this end, we took advantage of transgenic mice where the Tie2 promoter drives the expression of beta-galactosidase (LacZ) in order to follow the expression of Tie2 in hematopoietic progenitor cells after myelosuppression. Under steady-state conditions, only few LacZ/Tie-2+ cells were localized in the endosteal/osteoblastic region, without any expression within the BM sinusoidal neo-vessels. However, after a myelosuppressive dose of 5-Fluorouracil (5-FU) there was a robust expression of Tie2 expression in the regenerating BM sinusoidal neo-vessels. The expression of Tie2 on the regenerating neo-vasculature reached a maximum at day 10 and reverted back to steady-state by day 20 post 5-FU, the time in which the majority of the neo-vessels were functionally assembled. Blocking angiopoietin/Tie2 signaling with the soluble decoy-receptor, Tie2Fc, after 5-FU inhibited platelet recovery as well as vascular reconstitution. There was a paradoxical accumulation of megakaryocytes in the bone-marrow during the prolonged thrombocytopenic phase, which we have previously shown to be due to vascular niche disruption and inability of megakaryocytes to release platelets. To examine the possibility that Tie2+ progenitors can reconstitute BM sinusoids in the recipient mice, lethally irradiated wildtype mice were transplanted with the BM of Tie2-lacZ knock-in mice. After full recovery, the chimeric mice were challenged with a myelosuppressive dose of 5-FU and Tie2+ neo-vessels were detected histologically on day 5, 10, and 14 by LacZ staining. Remarkably, the reconstituted bone marrow showed the presence of Tie2+ vessels, which unambiguously demonstrates the contribution of donor-derived endothelial progenitors to the reconstitution of the regressed vasculature. Together, our data support the hypothesis that Tie2/angiopoietin signaling is essential for functional regeneration of BM sinusoidal neo-vessels and contributes to the reconstitution of hematopoiesis, specifically to thrombopoiesis. In addition, the use of Tie2-LacZ mice provides an invaluable model to quantify the number of regenerating BM neo-vessels. Angiopoietins may be used in clinical setting in conjunction with other lineage specific cytokines to enhance hematopoiesis after myelosuppression.
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Kopp, Hans-Georg, Scott T. Avecilla, Andrea T. Hooper, Sergey V. Shmelkov, Carlos A. Ramos, Fan Zhang, and Shahin Rafii. "Tie2 activation contributes to hemangiogenic regeneration after myelosuppression." Blood 106, no. 2 (July 15, 2005): 505–13. http://dx.doi.org/10.1182/blood-2004-11-4269.
Full textAbstract:
Abstract Chemotherapy- or radiation-induced myelosuppression results in apoptosis of cycling hematopoietic cells and induces regression of bone marrow (BM) sinusoidal vessels. Moreover, timely regeneration of BM neovessels is essential for reconstitution of hematopoiesis. However, the identity of angiogenic factors that support reconstitution of BM's vasculature is unknown. Here, we demonstrate that angiopoietin/tyrosine kinase with immunoglobulin and epidermal growth factor homology domains-2 (Tie2) signaling contributes to the assembly and remodeling of BM neovessels after myelosuppression. Using transgenic mice where the Tie2 promoter drives the reporter LacZ gene (Tie2-LacZ), we demonstrate that at steady state, there was minimal expression of Tie2 in the BM vasculature. However, after 5-fluorouracil (5-FU) treatment, there was a rapid increase in plasma vascular endothelial growth factor A (VEGF-A) levels and expansion of Tie2-positive neovessels. Inhibition of Tie2 resulted in impaired neoangiogenesis, leading to a delay in hematopoietic recovery. Conversely, angiopoietin-1 (Ang-1) stimulated hematopoiesis both in wild-type and thrombopoietin-deficient mice. In addition, Ang-1 shortened the duration of chemotherapy-induced neutropenia in wild-type mice. Exogenous VEGF-A and Ang-1 stimulated Tie2 expression in the BM vasculature. These data suggest that VEGF-A–induced up-regulation of Tie2 expression on the regenerating vasculature after BM suppression supports the assembly of sinusoidal endothelial cells, thereby promoting reconstitution of hematopoiesis. Angiopoietins may be clinically useful to accelerate hemangiogenic recovery after myelosuppression.
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Kim, Chungho, Hyo Seon Lee, Deokjae Lee, Sang Don Lee, Eun-Gyung Cho, Soo Jung Yang, Sang Bum Kim, Dongeun Park, and Moon Gyo Kim. "Epithin/PRSS14 proteolytically regulates angiopoietin receptor Tie2 during transendothelial migration." Blood 117, no. 4 (January 27, 2011): 1415–24. http://dx.doi.org/10.1182/blood-2010-03-275289.
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Abstract Epithin/PRSS14, a type II transmembrane serine protease, is involved in normal epithelial development and tumor progression. Here we report, as an interacting substrate of epithin, a receptor tyrosine kinase Tie2 that is well known for important roles in the vessel stability. Epithin interacts with and degrades the Tie2 extracellular portion that contains the ligand-binding domain. Epithin is located in the neighbor of Tie2-expressing vessels in normal tissue. Furthermore, epithin can cleave and degrade Tie2 not only in the same cell but also from neighboring cells nearby, resulting in the degradation of the Tie2 ectodomain. The remaining Tie2 fragment was highly phosphorylated and was able to recruit a downstream effector, phosphatidylinositol 3-kinase. Knocking down epithin expression using short hairpin RNA in thymoma cell severely impaired the migration through endothelial cells that show the actin rearrangement during the process. The diminution of epithin protein expression in 4T1 breast cancer cells caused the significant decrease in the number of transendothelial migrating cells in vitro as well as in those of metastasizing tumor nodules in vivo, Therefore, we propose that epithin, which regulates endothelial Tie2 functions, plays a critical role in the fine tuning of transendothelial migration for normal and cancer cells.
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Akwii, Racheal G., Md S. Sajib, Fatema T. Zahra, and Constantinos M. Mikelis. "Role of Angiopoietin-2 in Vascular Physiology and Pathophysiology." Cells 8, no. 5 (May 17, 2019): 471. http://dx.doi.org/10.3390/cells8050471.
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Angiopoietins 1–4 (Ang1–4) represent an important family of growth factors, whose activities are mediated through the tyrosine kinase receptors, Tie1 and Tie2. The best characterized are angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2). Ang1 is a potent angiogenic growth factor signaling through Tie2, whereas Ang2 was initially identified as a vascular disruptive agent with antagonistic activity through the same receptor. Recent data demonstrates that Ang2 has context-dependent agonist activities. Ang2 plays important roles in physiological processes and the deregulation of its expression is characteristic of several diseases. In this review, we summarize the activity of Ang2 on blood and lymphatic endothelial cells, its significance in human physiology and disease, and provide a current view of the molecular signaling pathways regulated by Ang2 in endothelial cells.
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Cascone, Ilaria, Lucia Napione, Fabrizio Maniero, Guido Serini, and Federico Bussolino. "Stable interaction between α5β1 integrin and Tie2 tyrosine kinase receptor regulates endothelial cell response to Ang-1." Journal of Cell Biology 170, no. 6 (September 12, 2005): 993–1004. http://dx.doi.org/10.1083/jcb.200507082.
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During angiogenic remodeling, Ang-1, the ligand of Tie2 tyrosine kinase, is involved in vessel sprouting and stabilization through unclear effects on nascent capillaries and mural cells. In our study, we hypothesized that the Ang-1/Tie2 system could cross-talk with integrins, and be influenced by the dynamic interactions between extracellular matrix and endothelial cells (ECs). Here, we show that α5β1 specifically sensitizes and modulates Tie2 receptor activation and signaling, allowing EC survival at low concentrations of Ang-1 and inducing persistent EC motility. Tie2 and α5β1 interact constitutively; α5β1 binding to fibronectin increases this association, whereas Ang-1 stimulation recruits p85 and FAK to this complex. Furthermore, we demonstrate that Ang-1 is able to mediate selectively α5β1 outside-in FAK phosphorylation. Thus, Ang-1 triggers signaling pathways through Tie2 and α5β1 receptors that could cross-talk when Tie2/α5β1 interaction occurs in ECs plated on fibronectin. By using blocking antibodies, we consistently found that α5β1, but not αvβ3 activation, is essential to Ang-1–dependent angiogenesis in vivo.
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Tachibana, Kazunobu, Nina Jones, Daniel J. Dumont, Mira C. Puri, and Alan Bernstein. "Selective Role of a Distinct Tyrosine Residue on Tie2 in Heart Development and Early Hematopoiesis." Molecular and Cellular Biology 25, no. 11 (June 1, 2005): 4693–702. http://dx.doi.org/10.1128/mcb.25.11.4693-4702.2005.
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ABSTRACT The development of the cardiovascular system and the development of the early hematopoietic systems are closely related, and both require signaling through the Tie2 receptor tyrosine kinase. Although endothelial cells and hematopoietic cells as well as their precursors share common gene expression patterns during development, it remains completely unknown how Tie2 signaling coordinately regulates cardiovascular development and early hematopoiesis in vivo. We show here that mice with a targeted mutation in tyrosine residue 1100 in the carboxyl-terminal tail of Tie2 display defective cardiac development and impaired hematopoietic and endothelial cell development in the paraaortic splanchnopleural mesoderm similar to that seen in Tie2-null mutant mice. Surprisingly, however, unlike Tie2-null mutant mice, mice deficient in signaling through this tyrosine residue show a normal association of perivascular cells with nascent blood vessels. These studies are the first to demonstrate the physiological importance of a single tyrosine residue in Tie2, and they suggest that multiple tyrosine residues in the receptor may coordinate cardiovascular development and early hematopoietic development.
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Hitchcock, Ian S., Michelle E. Roh, Veena Sangkhae, Leah Etheridge, Rose Chen, Norma E. Fox, and Kenneth Kaushansky. "Lineage Restricted JAK2V617F Expression and Its Role in Thrombosis and Hemostasis; The Potential Involvement of Endothelial JAK2V617F in Clotting Abnormalities." Blood 118, no. 21 (November 18, 2011): 1737. http://dx.doi.org/10.1182/blood.v118.21.1737.1737.
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Abstract Abstract 1737 Myeloproliferative disorders (MPDs) are a heterogeneous group of bone marrow disorders characterized by increases in one or more blood cell lineages. A single, somatic mutation in JAK2 (V617F) is responsible for many of the features of Philadelphia chromosome-negative MPDs (Polycythemia Vera, Essential Thrombocythemia and Primary Myelofibrosis). Clinically, the most common cause of death in these patients is arterial thrombosis; however some patients display a bleeding diathesis. Although the incidence and potential causes of dysfunctional hemostasis in patients with MPDs has been studied extensively, the critical regulating factors are unclear and therefore it has been difficult to develop an effective therapeutic regimen for these complications. As the formation of stable thrombi requires interactions between endothelial cells, platelets and leukocytes, we have recently generated mice that express human JAK2V617F in each of these cell lineages by crossing a JAK2V617F/Flip-Flop (FF1) mouse with mice expressing lineage-specific Cre recombinases. These crosses have generated the following mice; 1) Tie2-Cre/FF1, where JAK2V617F is expressed in all hematopoietic and endothelial cells, 2) Pf4-Cre/FF1, where JAK2V617F expression is limited to platelets, and 3) LysM-Cre/FF1, where JAK2V617F expression is limited to leukocytes. Expression of human JAK2V617F was confirmed in megakaryocytes, platelets, leukocytes and endothelial cells (Tie2-Cre/FF1), megakaryocytes and platelets (Pf4-Cre/FF1) and leukocytes (LysM-Cre/FF1) by conventional and real-time PCR. Of the 3 mouse strains, only Tie2-Cre/FF1 exhibited a MPD phenotype. Platelet counts were significantly increased compared to Tie2-Cre controls (at 3 months, Tie2-Cre: 779 (±61)/ml;Tie2-Cre/FF1: 2943 (± 217)/ml) without significant increases in any other cells types. Tie2-Cre/FF1 mice also exhibit greatly increased number of CFU-MKs and bone marrow derived megakaryocytes. Therefore, Tie2-Cre/FF1 mouse exhibits an ET-like phenotype. Although circulating platelet counts did not increase in Pf4-Cre/FF1 mice, we did observe an increase in the number of CFU-MKs in colony assays. Next we determined the roles of the lineage-restricted JAK2V617F expression on hemostasis in vitro and in vivo. Aggregometry on washed platelets showed no significant difference between any group and their controls in response to PAR4 (100–400mM), ADP (2–20mM) or collagen (1–10mg/ml). Additionally, we were unable to show a significant difference in GPIIbIIIa activation or surface expression of P-selectin in response to the same agonists. Despite no clear platelet abnormalities in any of the 3 mouse lineages, we identified significant hemostatic abnormalities in vivo in Tie2-Cre/FF1 mice. Tail bleeding time was significantly increased in Tie2-Cre/FF1 mice compared to Tie2-Cre controls (Tie2-Cre average, 2min 47secs; Tie2-Cre/FF1, 6mins 37secs) while Tie2-Cre/FF1 mice also exhibited an increased occurrence of re-bleeding compared to Tie2-Cre controls. Additionally, we performed FeCl3 carotid artery occlusion assays to better determine in vivo thrombosis. We found that at 10% FeCl3, Tie2-Cre control mice exhibited complete artery occlusion in approximate 6 min. In contrast, Tie2-Cre/FF1 mice failed to show any sign of arterial occlusion throughout the duration of the experiment (30 min). Given the significant increase in platelet numbers in Tie2-Cre/FF1 mice, we next determined if acquired von Willibrand Disease (VWD) could account for prolonged bleeding and reduced clotting; plasma vW Factor levels by ELISA were normal. In contrast to Tie2-Cre/FF1 mice, neither the PF4-Cre/FF1 or LysM-Cre/FF1 mice exhibit dysfunctional thrombosis. These data provide compelling evidence that expression of JAK2V617F in cells other than just platelets or just leukocytes is necessary to generate the hemostatic abnormalities seen in patients with MPDs. Recent findings show that some patients express endothelial JAK2V617F and patients with ET exhibit increased numbers of circulating endothelial progenitors. Thus, our data is consistent with the hypothesis that expression of JAK2V617F in endothelial cells, in addition to hematopoietic cells results in the bleeding diathesis seen in patients with MPDs. Disclosures: No relevant conflicts of interest to declare.
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Zacharek, Alex, Jieli Chen, Ang Li, Xu Cui, Yi Li, Cynthia Roberts, Yifan Feng, Qi Gao, and Michael Chopp. "Angiopoietin1/TIE2 and VEGF/FLK1 Induced by MSC Treatment Amplifies Angiogenesis and Vascular Stabilization after Stroke." Journal of Cerebral Blood Flow & Metabolism 27, no. 10 (March 14, 2007): 1684–91. http://dx.doi.org/10.1038/sj.jcbfm.9600475.
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Bone marrow stromal cells (MSCs) increase vascular endothelial growth factor (VEGF) expression and promote angiogenesis after stroke. Angiopoietin-1 (Ang1) and its receptor Tie2 mediate vascular integrity and angiogenesis as does VEGF and its receptors. In this study, we tested whether MSC treatment of stroke increases Ang1/Tie2 expression, and whether Ang1/Tie2 with VEGF / vascular endothelial growth factor receptor 2 (VEGFR2) (Flk1), in combination, induced by MSCs enhances angiogenesis and vascular integrity. Male Wistar rats were subjected to middle cerebral artery occlusion (MCAo) and treated with or without MSCs. Marrow stromal cell treatment significantly decreased blood—brain barrier (BBB) leakage and increased Ang1, Tie2, and occludin (a tight junction protein) expression in the ischemic border compared with MCAo control. To further test the mechanisms of MSC-induced angiogenesis and vascular stabilization, cocultures of MSCs with mouse brain endothelial cells (MBECs) or astrocytes were performed. Supernatant derived from MSCs cocultured with MBECs significantly increased MBEC expression of Ang1/Tie2 and Flk1 compared with MBEC alone. Marrow stromal cells cocultured with astrocytes also significantly increased astrocyte VEGF and Ang1/Tie2 expression compared with astrocyte culture alone. Conditioned media from MSCs alone, and media from cocultures of MSCs with astrocytes or MBECs, all significantly increased capillary tube-like formation of MBEC compared with control Dulbecco's modified Eagle's medium media. Inhibition of Flk1 and/or Ang1 significantly decreased MSC-induced MBEC tube formation. Knockdown of Tie2 expression in MBECs significantly inhibited MSC-induced tube formation. Our data indicate MSC treatment of stroke promotes angiogenesis and vascular stabilization, which is at least partially mediated by VEGF/Flk1 and Ang1/Tie2.
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Lelievre, Etienne, Pierre-Marie Bourbon, Li-Juan Duan, Robert L. Nussbaum, and Guo-Hua Fong. "Deficiency in the p110α subunit of PI3K results in diminished Tie2 expression and Tie2-/-–like vascular defects in mice." Blood 105, no. 10 (May 15, 2005): 3935–38. http://dx.doi.org/10.1182/blood-2004-10-3955.
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AbstractPhosphoinositide 3-kinase (PI3K) is activated by transmembrane tyrosine kinases such as vascular endothelial growth factor (VEGF) receptors and Tie2 (tunica intima endothelial kinase 2), both of which are key regulators of vascular development. However, the in vivo role of PI3K during developmental vascularization remains to be defined. Here we demonstrate that mice deficient in the p110α catalytic subunit of PI3K display multiple vascular defects, including dilated vessels in the head, reduced branching morphogenesis in the endocardium, lack of hierarchical order of large and small branches in the yolk sac, and impaired development of anterior cardinal veins. These vascular defects are strikingly similar to those in mice defective in the Tie2 signaling pathway. Indeed, Tie2 protein levels were significantly lower in p110α-deficient mice. Furthermore, RNA interference of p110α in cultured endothelial cells significantly reduced Tie2 protein levels. These findings raise the possibility that PI3K may function as an upstream regulator of Tie2 expression during mouse development.
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Momose, Haruka, Kazuya Takizawa, Madoka Kuramitsu, Takuo Mizukami, Atsuko Masumi, Kazunari Yamaguchi, and Isao Hamaguchi. "Ang1 Functions as An Autocrine Activating Factor of Tie2 Signaling In Hematopoietic Stem Cells." Blood 116, no. 21 (November 19, 2010): 1548. http://dx.doi.org/10.1182/blood.v116.21.1548.1548.
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Abstract Abstract 1548 Hematopoietic stem cells (HSCs) are clonogenic cells that possess the self-renewal capacity to produce more HSCs, as well as the multilineage potential that gives rise to a defined set of mature differentiated progeny for maintenance or repair of the whole blood system. HSCs lie in the hematopoietic niches located along the inner surface of the bone or the sinusoidal endothelium, and are in contact with niche cells. The cell-cell interactions with niche cells are believed to be an important prerequisite to trigger signaling events in HSCs, thereby controlling the balance between HSC self-renewal and differentiation. However, the precise molecular mechanisms regulating niche cell-HSC interactions are not well understood. One of the key molecules for those interactions is Angiopoietin-1 (Ang1). Ang1 is expressed by the niche cells and has been identified as an activating ligand for Tie2 (tyrosine kinase with Ig-like loops and epidermal growth factor homology domains 2). The expression of Tie2 is dominant in HSCs, and Tie2 in HSCs is supposed to be stimulated by Ang1 derived from niche cells. However, Ang1 is also expressed in HSCs. Detailed analysis has shown that Ang1 expression was found to be restricted in long-term HSCs (CD34-lineage-Sca-1+c-Kit+), indicating that Ang1 derived from HSCs plays a role in regulating HSCs. We attempted to elucidate a novel regulating system for HSCs through Ang1-Tie2 signaling by utilizing a hematopoietic cell line in which Tie2 was stably expressed (Ba/F3-Tie2). In Ba/F3-Tie2 cells, Tie2 was found to be phosphorylated on tyrosine residues, even without exogenous addition of Ang1. In the same cells, the expression level of endogenous Ang1 was increased four-fold. When Ang1 expression was down-regulated by transduction with a lentiviral vector expressing short hairpin RNA (shRNA) for Ang1 (shAng1), the phosphorylation of Tie2 was suppressed, suggesting that Tie2 expressed in Ba/F3-Tie2 cells could be stimulated by endogenous Ang1. To mimic the physiological circumstances of the bone marrow, Ba/F3-Tie2 cells were cultured on OP9 stromal cells. Under these culture conditions, the effect of endogenous Ang1 was investigated. Down-regulation of Ang1 by shAng1 demonstrated an approximate 50% reduction in the proliferation of Ba/F3-Tie2 cells on the OP9 cell layer. A HSC-rich population of cells prepared from bone marrow (lineage-Sca-1+c-Kit+; LSK) was also analyzed on OP9 cell layers. Similar to the results obtained from the analysis of Ba/F3-Tie2 cells, down-regulation of Ang1 by shAng1 resulted in an approximately 70% decrease in the proliferation of LSK cells cultured on OP9 monolayers. We confirmed that the suppressive effect on HSC proliferation was due to the lack of Ang1 from HSCs by culturing on Ang1-defective OP9 cells. Finally, we performed in vivo analysis to confirm the importance of endogenous Ang1 to HSCs. Ly5.2 LSK cells transduced with the shAng1 expressing vector were transplanted along with Ly5.1xLy5.2 bone marrow cells into lethally irradiated Ly5.1 mice. The Ly5.2 donor-derived cells in the recipient's peripheral blood were monitored every 2 weeks. As expected, shAng1-introduced donor cells were at decreased ratios at week four (mean ratios, 31.5% for control vs. 17.5% for shAng1), and were reduced to an even lower level at week 12 (mean ratios, 27.1% for control vs. 6.79% for shAng1). This phenomenon was also confirmed by histochemical results, where statistically fewer HSCs existed in the bone marrow of recipient mice in which shAng1-introduced HSCs were transplanted, as compared to the control. Altogether, our data suggested that Tie2 in HSCs could be stimulated by the Ang1 produced by the surrounding HSCs, and this possible autocrine regulation might control the functions of HSCs. Disclosures: No relevant conflicts of interest to declare.
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Satchell, Simon C., Steve J. Harper, John E. Tooke, Dontscho Kerjaschki, Moin A. Saleem, and Peter W. Mathieson. "Human Podocytes Express Angiopoietin 1, a Potential Regulator of Glomerular Vascular Endothelial Growth Factor." Journal of the American Society of Nephrology 13, no. 2 (February 2002): 544–50. http://dx.doi.org/10.1681/asn.v132544.
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ABSTRACT. Vascular endothelial growth factor (VEGF) is abundantly expressed by podocytes, but its role in glomeruli is unknown. Angiopoietins are endothelial cell growth factors that function in concert with VEGF but have not previously been observed in human glomeruli. Angiopoietin 1 (Ang1) acts via the endothelial receptor Tie2 to promote maturation and stabilization of blood vessels, resisting angiogenesis and opposing some actions of VEGF. Ang1, Ang2, Tie2, and VEGF expression in normal human renal cortex was examined with immunofluorescence and immunohistochemical analyses. High-power, multiple-color, immunofluorescence analyses and additional antibodies (specific for particular components of the glomerular filtration barrier) were used to determine the exact locations of Ang1 and Tie2 in the glomerular capillary wall. Immuno-electron-microscopic analysis of rat glomeruli was used to further localize endothelial Tie2 expression. RNA and protein extracted from human glomeruli, cultured human podocytes, and cultured human endothelial cells were analyzed for Ang1, Ang2, and Tie2 by using reverse transcription-PCR and Western blotting. Ang1 was detected in podocytes in normal glomeruli and, with VEGF, was concentrated in podocyte foot processes. Tie2 was demonstrated on glomerular capillary endothelial cells, particularly on the abluminal surface. Reverse transcription-PCR and Western blotting analyses confirmed the expression of Ang1 and Tie2 in glomeruli and of Ang1 in cultured podocytes. These findings suggest a role for Ang1 in the maintenance of the glomerular endothelium and make it a good candidate to be a regulator of the actions of VEGF on glomerular permeability, resisting angiogenesis while allowing the induction of high permeability to water and small solutes.
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Carota, Isabel A., Yael Kenig-Kozlovsky, Tuncer Onay, Rizaldy Scott, Benjamin R. Thomson, Tomokazu Souma, Christina S. Bartlett, et al. "Targeting VE-PTP phosphatase protects the kidney from diabetic injury." Journal of Experimental Medicine 216, no. 4 (March 18, 2019): 936–49. http://dx.doi.org/10.1084/jem.20180009.
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Diabetic nephropathy is a leading cause of end-stage kidney failure. Reduced angiopoietin-TIE2 receptor tyrosine kinase signaling in the vasculature leads to increased vascular permeability, inflammation, and endothelial cell loss and is associated with the development of diabetic complications. Here, we identified a mechanism to explain how TIE2 signaling is attenuated in diabetic animals. Expression of vascular endothelial protein tyrosine phosphatase VE-PTP (also known as PTPRB), which dephosphorylates TIE2, is robustly up-regulated in the renal microvasculature of diabetic rodents, thereby reducing TIE2 activity. Increased VE-PTP expression was dependent on hypoxia-inducible factor transcriptional activity in vivo. Genetic deletion of VE-PTP restored TIE2 activity independent of ligand availability and protected kidney structure and function in a mouse model of severe diabetic nephropathy. Mechanistically, inhibition of VE-PTP activated endothelial nitric oxide synthase and led to nuclear exclusion of the FOXO1 transcription factor, reducing expression of pro-inflammatory and pro-fibrotic gene targets. In sum, we identify inhibition of VE-PTP as a promising therapeutic target to protect the kidney from diabetic injury.
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Zhang, Xueyang, Yanyi Liu, Yuan Su, Xiaohui Fan, and Fei Hu. "A study of the effects of hydroxyapatite bioceramic extract on Ang/Tie2 system of umbilical vein endothelial cells." Technology and Health Care 29 (March 25, 2021): 531–38. http://dx.doi.org/10.3233/thc-218050.
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OBJECTIVE: We aimed to investigate the effects of hydroxyapatite bioceramic extract on Ang/Tie2 system and cell proliferation of umbilical vein endothelial cells. METHODS: Human umbilical vein endothelial cells (HUVECs) were used in this research. There are two induvial groups, control group and hydroxyapatite bioceramics extract treatment group. Cell Counting Kit-8 (CCK-8) was used to evaluate cell proliferation. Western blot and real time quantitative PCR (Q-PCR) were used to evaluate the protein and mRNA expression levels of Ang1, Ang2 and Tie2 in Ang/Tie2 system, respectively. All the results were statistically analyzed by Spss19.0. All data were presented as mean ± standard error of mean (SEM). Student’s t-test was performed to determine the differences among grouped data. RESULTS: Hydroxyapatite bioceramics extract showed no effect on the cell morphology and cell proliferation of HUVECs. Interestingly, we found that both Ang2 and Tie2 protein and mRNA level were markedly increased by hydroxyapatite bioceramics extract. CONCLUSIONS: Hydroxyapatite bioceramic extract showed no cytotoxicity to HUVECs, and might regulate vascular remodeling by mediating Ang/Tie2 system.
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Zhang, Xingshuo, Julien Guerrero, Andreas S. Croft, Christoph E. Albers, Sonja Häckel, and Benjamin Gantenbein. "Spheroid-Like Cultures for Expanding Angiopoietin Receptor-1 (aka. Tie2) Positive Cells from the Human Intervertebral Disc." International Journal of Molecular Sciences 21, no. 24 (December 10, 2020): 9423. http://dx.doi.org/10.3390/ijms21249423.
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Lower back pain is a leading cause of disability worldwide. The recovery of nucleus pulposus (NP) progenitor cells (NPPCs) from the intervertebral disc (IVD) holds high promise for future cell therapy. NPPCs are positive for the angiopoietin-1 receptor (Tie2) and possess stemness capacity. However, the limited Tie2+ NPC yield has been a challenge for their use in cell-based therapy for regenerative medicine. In this study, we attempted to expand NPPCs from the whole NP cell population by spheroid-formation assay. Flow cytometry was used to quantify the percentage of NPPCs with Tie2-antibody in human primary NP cells (NPCs). Cell proliferation was assessed using the population doublings level (PDL) measurement. Synthesis and presence of extracellular matrix (ECM) from NPC spheroids were confirmed by quantitative Polymerase Chain Reaction (qPCR), immunostaining, and microscopy. Compared with monolayer, the spheroid-formation assay enriched the percentage of Tie2+ in NPCs’ population from ~10% to ~36%. Moreover, the spheroid-formation assay also inhibited the proliferation of the Tie2- NPCs with nearly no PDL. After one additional passage (P) using the spheroid-formation assay, NPC spheroids presented a Tie2+ percentage even further by ~10% in the NPC population. Our study concludes that the use of a spheroid culture system could be successfully applied to the culture and expansion of tissue-specific progenitors.
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Mori, Yusaku, Marel Gonzalez Medina, Zhiwei Liu, June Guo, Luke S. Dingwell, Simon Chiang, Carl Ronald Kahn, Mansoor Husain, and Adria Giacca. "Roles of vascular endothelial and smooth muscle cells in the vasculoprotective effect of insulin in a mouse model of restenosis." Diabetes and Vascular Disease Research 18, no. 3 (May 2021): 147916412110273. http://dx.doi.org/10.1177/14791641211027324.
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Background: Insulin exerts vasculoprotective effects on endothelial cells (ECs) and growth-promoting effects on vascular smooth muscle cells (SMCs) in vitro, and suppresses neointimal growth in vivo. Here we determined the role of ECs and SMCs in the effect of insulin on neointimal growth. Methods: Mice with transgene CreERT2 under the control of EC-specific Tie2 (Tie2-Cre) or SMC-specific smooth muscle myosin heavy chain promoter/enhancer (SMMHC-Cre) or littermate controls were crossbred with mice carrying a loxP-flanked insulin receptor (IR) gene. After CreERT2-loxP-mediated recombination was induced by tamoxifen injection, mice received insulin pellet or sham (control) implantation, and underwent femoral artery wire injury. Femoral arteries were collected for morphological analysis 28 days after wire injury. Results: Tamoxifen-treated Tie2-Cre+ mice showed lower IR expression in ECs, but not in SMCs, than Tie2-Cre− mice. Insulin treatment reduced neointimal area after arterial injury in Tie2-Cre− mice, but had no effect in Tie2-Cre+ mice. Tamoxifen-treated SMMHC-Cre+ mice showed lower IR expression in SMCs, but not in ECs, than SMMHC-Cre− mice. Insulin treatment reduced neointimal area in SMMHC-Cre− mice, whereas unexpectedly, it failed to inhibit neointima formation in SMMHC-Cre+ mice. Conclusion: Insulin action in both ECs and SMCs is required for the “anti-restenotic” effect of insulin in vivo.
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Seegar, Tom C. M., Becca Eller, Dorothea Tzvetkova-Robev, Momchil V. Kolev, Scott C. Henderson, Dimitar B. Nikolov, and William A. Barton. "Tie1-Tie2 Interactions Mediate Functional Differences between Angiopoietin Ligands." Molecular Cell 37, no. 5 (March 2010): 643–55. http://dx.doi.org/10.1016/j.molcel.2010.02.007.
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De Ceunynck, Karen E. P., Sarah J. Higgins, Sharjeel A. Chaudhry, Samir Parikh, and Robert C. Flaumenhaft. "Dysfunctional Endothelium Drives a Pre-DIC State in Endotoxemia." Blood 128, no. 22 (December 2, 2016): 3725. http://dx.doi.org/10.1182/blood.v128.22.3725.3725.
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Abstract Uncontrolled pro-coagulant responses in sepsis can lead to disseminated intravascular coagulation (DIC), a complication associated with markedly increased mortality. Abnormalities of coagulation, fibrinolysis, and platelet function can lead to both microvascular thrombosis contributing to multi-organ dysfunction syndrome or hemorrhagic complications. To understand the inciting causes of DIC in sepsis, we first evaluated the time course of platelet function, coagulation parameters and markers of endothelial activation following LPS exposure. These studies demonstrated that endothelial dysfunction preceded derangement of platelet function or coagulation parameters. To evaluate the thrombotic response of the endothelium early in endotoxemia, we injured the microvascular endothelium of cremaster arterioles of mice using a laser 1-3 hours following LPS exposure. Platelet and fibrin formation at sites of injury were significantly increased following LPS exposure to respectively 190% (p=0.026) and 195% (p<0.001) of control values. No significant differences were observed in platelet counts, platelet function (aggregation and activation) or coagulation parameters (PT) in mice treated with LPS for 3 hours compared to vehicle controls. Plasma levels of the endothelial markers VWF, soluble VCAM and E-selectin, however, were significantly increased following LPS exposure, demonstrating early endothelial activation. Furthermore, even when platelet accumulation was inhibited using the anti-platelet drug eptifibatide, fibrin generation at sites of laser injury was still significantly (p<0.01) increased in LPS-treated mice. Together, these data show that endothelial activation precedes disruption of platelets and coagulation in endotoxemia. Endothelial dysfunction is associated with perturbation of the endothelial Ang1/Tie2 pathway, characterized by significantly reduced Tie2 function and Ang1 levels. Therefore, we assessed thrombus formation in Tie2+/- mice in the absence of LPS. Fibrin generation at sites of laser injury was significantly increased in Tie2+/- mice to 192% of littermate (Tie2+/+) controls (p<0.01). As loss of Tie2 mimics the LPS-induced phenotype, we next determined whether activation of the Tie2 pathway could reduce fibrin clot formation. Ang1 stimulates phosphorylation of Tie2, promoting protective signaling in endothelium. To determine whether the pro-thrombotic consequences of endotoxemia on Tie2 signaling could be reversed using Ang1, mice were injected with adenovirus expressing Ang1 or control adenovirus prior to LPS exposure. Dephoshorylation of Tie2 associated due to LPS exposure was reduced with Ang1-treatment. In our in vivo thrombosis model, Ang1 inhibited the increased fibrin accumulation at sites of laser injury in endotoxemic mice to baseline levels. Tail snip assays showed that even though elevated Ang1 levels normalized LPS-induced augmentation of thrombus formation, increased Ang1 did not affect bleeding times. These data indicate that Ang1 stimulation of Tie2 signaling can regulate pathologic clot formation in the setting of inflammation without bleeding risk. Together, our studies show that endothelial dysfunction drives a pre-DIC state in endotoxemia. Targeting these early endothelial responses might represent an novel approach for reducing thrombosis in sepsis without enhancing bleeding risks. Future studies will evaluate the mechanism involved. Disclosures No relevant conflicts of interest to declare.
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Che, Jishan, Mitsuhiko Okigaki, Tomosaburo Takahashi, Asako Katsume, Yasushi Adachi, Shinichiro Yamaguchi, Shinsaku Matsunaga, et al. "Endothelial FGF receptor signaling accelerates atherosclerosis." American Journal of Physiology-Heart and Circulatory Physiology 300, no. 1 (January 2011): H154—H161. http://dx.doi.org/10.1152/ajpheart.00075.2010.
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Members of the fibroblast growth factor (FGF) family have been clinically applied to the treatment of ischemic diseases because of their strong angiogenic actions. Although tissue ischemia is predominantly caused by atherosclerosis, the roles of endothelial FGF receptors (FGF-Rs) in atherosclerosis remain obscure. We generated endothelial cell (EC)-targeted constitutively active FGF-R2-overexpressing mice, using the Tie2 promoter (Tie2-FGF-R2-Tg), and crossed them with apolipoprotein E (ApoE)-deficient mice (ApoE-KO) to generate Tie2-FGF-R2-Tg/ApoE-deficient mice (Tie2-FGF-R2-Tg/ApoE-KO). After being fed a Western diet for 8 wk, the Tie2-FGF-R2-Tg/ApoE-KO demonstrated 2.0-fold greater atherosclerotic lesion area on the luminal surfaces of the aortas than the ApoE-KO ( P < 0.01). The level of p21Cip1 protein, a cell cycle inhibitor, in the FGF-R2-overexpressing EC was 2.5-fold greater than that in the wild-type (WT) EC at the baseline ( P < 0.01). FGF-R2 overexpression in the EC resulted in increased expression of VCAM-1 and ICAM-1, acceleration of apoptosis, and decreased proliferative activity, all of which were normalized by small interfering RNA (siRNA)-mediated knockdown of p21Cip1 (75% reduction in protein level, P < 0.01). Furthermore, the expression of PDGF-B and Egr-1, a PDGF/p21Cip1-inducible transcription factor, in the aortic endothelium of Tie2-FGF-R2-Tg/ApoE-KO was significantly greater than that in ApoE-KO. The proliferation of vascular smooth muscle cells in the aortic media of Tie2-FGF-R2-Tg/ApoE-KO was 2.0-fold higher than that in ApoE-KO ( P < 0.01). Thus our study reveals that endothelial FGF-R2 signaling aggravates atherosclerosis by promoting p21Cip1-mediated EC dysfunction and cautions against the use of FGF for therapeutic angiogenesis in the setting of atherosclerosis.
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Guignabert, C., C. M. Alvira, T. P. Alastalo, H. Sawada, G. Hansmann, M. Zhao, L. Wang, N. El-Bizri, and M. Rabinovitch. "Tie2-mediated loss of peroxisome proliferator-activated receptor-γ in mice causes PDGF receptor-β-dependent pulmonary arterial muscularization." American Journal of Physiology-Lung Cellular and Molecular Physiology 297, no. 6 (December 2009): L1082—L1090. http://dx.doi.org/10.1152/ajplung.00199.2009.
Full textAbstract:
Peroxisome proliferator-activated receptor (PPAR)-γ is reduced in pulmonary arteries (PAs) of patients with PA hypertension (PAH), and we reported that deletion of PPARγ in smooth muscle cells (SMCs) of transgenic mice results in PAH. However, the sequelae of loss of PPARγ in PA endothelial cells (ECs) are unknown. Therefore, we bred Tie2-Cre mice with PPARγflox/flox mice to induce EC loss of PPARγ (Tie2 PPARγ−/−), and we assessed PAH by right ventricular systolic pressure (RVSP), RV hypertrophy (RVH), and muscularized distal PAs in room air (RA), after chronic hypoxia (CH), and after 4 wk of recovery in RA (Rec-RA). The Tie2 PPARγ−/− mice developed spontaneous PAH in RA with increased RVSP, RVH, and muscularized PAs vs. wild type (WT); both genotypes exhibited a similar degree of PAH following chronic hypoxia, but Tie2 PPARγ−/− mice had more residual PAH compared with WT mice after Rec-RA. The Tie2 PPARγ−/− vs. WT mice in RA had increased platelet-derived growth factor receptor-β (PDGF-Rβ) expression and signaling, despite an elevation in the PPARγ target apolipoprotein E, an inhibitor of PDGF signaling. Inhibition of PDGF-Rβ signaling with imatinib, however, was sufficient to reverse the PAH observed in the Tie2 PPARγ−/− mice. Thus the disruption of PPARγ signaling in EC is sufficient to cause mild PAH and to impair recovery from CH-induced PAH. Inhibition of heightened PDGF-Rβ signaling is sufficient to reverse PAH in this genetic model.
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House, Stacey L., Angela M. Castro, Traian S. Lupu, Carla Weinheimer, Craig Smith, Attila Kovacs, and David M. Ornitz. "Endothelial fibroblast growth factor receptor signaling is required for vascular remodeling following cardiac ischemia-reperfusion injury." American Journal of Physiology-Heart and Circulatory Physiology 310, no. 5 (March 1, 2016): H559—H571. http://dx.doi.org/10.1152/ajpheart.00758.2015.
Full textAbstract:
Fibroblast growth factor (FGF) signaling is cardioprotective in various models of myocardial infarction. FGF receptors (FGFRs) are expressed in multiple cell types in the adult heart, but the cell type-specific FGFR signaling that mediates different cardioprotective endpoints is not known. To determine the requirement for FGFR signaling in endothelium in cardiac ischemia-reperfusion injury, we conditionally inactivated the Fgfr1 and Fgfr2 genes in endothelial cells with Tie2-Cre ( Tie2-Cre, Fgfr1f/f, Fgfr2f/fDCKO mice). Tie2-Cre, Fgfr1f/f, Fgfr2f/fDCKO mice had normal baseline cardiac morphometry, function, and vessel density. When subjected to closed-chest, regional cardiac ischemia-reperfusion injury, Tie2-Cre, Fgfr1f/f, Fgfr2f/fDCKO mice showed a significantly increased hypokinetic area at 7 days, but not 1 day, after reperfusion. Tie2-Cre, Fgfr1f/f, Fgfr2f/fDCKO mice also showed significantly worsened cardiac function compared with controls at 7 days but not 1 day after reperfusion. Pathophysiological analysis showed significantly decreased vessel density, increased endothelial cell apoptosis, and worsened tissue hypoxia in the peri-infarct area at 7 days following reperfusion. Notably, Tie2-Cre, Fgfr1f/f, Fgfr2f/fDCKO mice showed no impairment in the cardiac hypertrophic response. These data demonstrate an essential role for FGFR1 and FGFR2 in endothelial cells for cardiac functional recovery and vascular remodeling following in vivo cardiac ischemia-reperfusion injury, without affecting the cardiac hypertrophic response. This study suggests the potential for therapeutic benefit from activation of endothelial FGFR pathways following ischemic injury to the heart.
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Hossain, Mohammad B., Rehnuma Shifat, David G. Johnson, Mark T. Bedford, Konrad R. Gabrusiewicz, Nahir Cortes-Santiago, Xuemei Luo, et al. "TIE2-mediated tyrosine phosphorylation of H4 regulates DNA damage response by recruiting ABL1." Science Advances 2, no. 4 (April 2016): e1501290. http://dx.doi.org/10.1126/sciadv.1501290.
Full textAbstract:
DNA repair pathways enable cancer cells to survive DNA damage induced after genotoxic therapies. Tyrosine kinase receptors (TKRs) have been reported as regulators of the DNA repair machinery. TIE2 is a TKR overexpressed in human gliomas at levels that correlate with the degree of increasing malignancy. Following ionizing radiation, TIE2 translocates to the nucleus, conferring cells with an enhanced nonhomologous end-joining mechanism of DNA repair that results in a radioresistant phenotype. Nuclear TIE2 binds to key components of DNA repair and phosphorylates H4 at tyrosine 51, which, in turn, is recognized by the proto-oncogene ABL1, indicating a role for nuclear TIE2 as a sensor for genotoxic stress by action as a histone modifier. H4Y51 constitutes the first tyrosine phosphorylation of core histones recognized by ABL1, defining this histone modification as a direct signal to couple genotoxic stress with the DNA repair machinery.