Angiopoietin-1 induces sprouting angiogenesis in vitro (original) (raw)
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Circulation Research, 1998
Angiopoietin-1 (Ang1) has been recently identified as the major physiological ligand for the tyrosine kinase receptor Tie2 and assigned responsibility for recruiting and sustaining periendothelial support cells. Angiopoietin-2 (Ang2) was found to disrupt blood vessel formation in the developing embryo by antagonizing the effects of Ang1 and Tie2 and was thus considered to represent a natural Ang1/Tie2 inhibitor. In vivo effects of either angiopoietin on postnatal neovascularization, however, have not been previously described. Accordingly, we used the cornea micropocket assay of neovascularization to investigate the impact of angiopoietins on neovascularization in vivo. Neither Ang1 nor Ang2 alone promoted neovascularization. Pellets containing vascular endothelial growth factor (VEGF) alone induced corneal neovascularity extending from the limbus across the cornea. Addition of Ang1 to VEGF (Ang1ϩVEGF) produced an increase in macroscopically evident perfusion of the corneal neovasculature without affecting macroscopic measurements of length (0.58Ϯ0.03 mm) or circumferential neovascularity (136Ϯ10°). In contrast, pellets containing Ang2ϩVEGF promoted significantly longer (0.67Ϯ0.05 mm) and more circumferential (160Ϯ15°) neovascularity than VEGF alone or Ang1ϩVEGF (PϽ0.05). Excess soluble Tie2 receptor (sTie2-Fc) precluded modulation of VEGF-induced neovascularization by both Ang2 and Ang1. Fluorescent microscopic findings demonstrated enhanced capillary density (fluorescence intensity, 2.55Ϯ0.23 e ϩ9 versus 1.23Ϯ0.17 e ϩ9 , PϽ0.01) and increased luminal diameter of the basal limbus artery (39.0Ϯ2.8 versus 27.9Ϯ1.3 m, PϽ0.01) for Ang1ϩVEGF compared with VEGF alone. In contrast to Ang1ϩVEGF, Ang2ϩVEGF produced longer vessels and, at the tip of the developing capillaries, frequent isolated sprouting cells. In the case of Ang2ϩVEGF, however, luminal diameter of the basal limbus artery was not increased (26.7Ϯ1.9 versus 27.9Ϯ1.3, PϭNS). These findings constitute what is to our knowledge the first direct demonstration of postnatal bioactivity associated with either angiopoietin. In particular, these results indicate that angiopoietins may potentiate the effects of other angiogenic cytokines. Moreover, these findings provide in vivo evidence that Ang1 promotes vascular network maturation, whereas Ang2 works to initiate neovascularization.
Proceedings of the National Academy of Sciences of the United States of America, 2002
Multiple classes of factors contribute to angiogenesis. In past years, the primary focus has been to understand the functions of individual classes of angiogenic factors. However, few studies have focused on the combinatorial roles of multiple classes of factors in angiogenesis. In this report, we have investigated the in vivo angiogenic processes regulated by two major classes of angiogenic factors, the angiopoietins and vascular endothelial growth factor (VEGF). Here we show that angiopoietin-1, a factor previously considered to be proangiogenic, can offset VEGF-induced angiogenesis in vivo. We also provide direct in vivo evidence for the synergistic effect of angiopoietin-2 and VEGF on the induction of angiogenesis. Furthermore, we show that these two classes of factors control the ratio of arterial and venous blood vessel types during angiogenesis. We believe that our study is a step toward understanding how multiple classes of factors harmonize angiogenesis and blood vessel types.
Angiopoietins in angiogenesis and beyond
Expert Opinion on Investigational Drugs, 2003
The angiopoietin (Ang) family of growth factors includes four members, all of which bind to the endothelial receptor tyrosine kinase Tie2. Two of the Angs, Ang-1 and Ang-4 activate the Tie2 receptor, whereas Ang-2 and Ang-3 inhibit Ang-1-induced Tie2 phosphorylation. While genetic models have underscored the importance of Angs in the developing cardiovascular system, other studies have demonstrated that Ang-1 promotes endothelial cell survival, sprouting and tube formation. More recently, a new aspect of the biology of this class of growth factors has emerged, namely the ability of Ang-1 to reduce inflammation. This review presents an outline of Angs and their receptors, examining their structure, expression, signalling, regulation and biological significance and comments on the role and potential usefulness of Angs in medicine.
Clinical Hemorheology and Microcirculation, 2011
Angiopoietins are important growth factors for vascular development and quiescence. They are promising targets for 12 pro-or anti-angiogenic therapies in diverse pathologies, but the mechanisms of the ANGPT/TIE2 system are complex and not 13 well understood. In the present study, the separate and combined effects of angiopoietin 1 and angiopoietin 2 were studied, using 14 a recently developed in vitro angiogenesis model that allows both a quantitative and qualitative evaluation of the angiogenic 15 cascade. This cell culture model was performed with microvascular endothelial cells (ECs) originating from different vascular 16 beds, i.e. dermal ECs and cardiac ECs. In addition, the expression of the angiopoietins and the receptors, TIE1 and TIE2 was 17 analyzed with RT-qPCR. This study revealed that the angiopoietins provoked a differential response in the two endothelial 18 cultures. Both angiopoietin 1 as well as angiopoietin 2 elicited an angiogenic cascade in the dermal ECs but not in the cardiac 19 ECs. In addition, the RT-qPCR data revealed marked differences in the endogenous expression pattern of these factors, indicating 20 that the origin of endothelial cells might have an important impact on their angiogenic potential. 21 U n c o r r e c t e d A u t h o r P r o o f 2 W. De Spiegelaere et al. / In vitro angiogenesis, angiopoietins highly complex, and a better knowledge of the molecular mechanisms of angiogenesis will aid the 30 development of future therapies that aim to enhance or inhibit angiogenesis [9]. 31 A range of growth factors has already been described to influence the process of angiogenesis. Amongst 32 these, the family of vascular endothelial growth factors (VEGFs) is the best known and best studied 33 factors. VEGFs induce capillary sprouting by stimulating endothelial migration and proliferation. Due to 34 their importance both in development and in various pathological situations, VEGF has been extensively 35 studied in the past decades [24]. The angiopoietins are another family of endothelial specific growth 36 factors, but their role during angiogenesis is still elusive. They are expressed in a range of developing 37 and adult tissues [11, 12, 17]. It is currently hypothesized that the angiopoietins play a major role during 38 maturation of the vasculature following VEGF induced angiogenesis [2, 26]. Angiopoietin 1 (ANGPT1) 39 and angiopoietin 2 (ANGPT2) are the most common and best described members of the angiopoietin 40 family. These ligands both bind the endothelial specific TIE2 (TEK) receptor [28]. ANGPT1 is described 41 as a vascular maturation factor; it induces lumen formation and vascular quiescence by activating the 42 TIE2 receptor. ANGPT2 is an antagonist of ANGPT1, as it binds the TIE2 receptor with similar affinity 43 as ANGPT1, but has a weak ability to activate TIE2 [7, 23]. In this way, ANGPT2 induces vascular 44 destabilization, which can either lead to the onset of angiogenesis or endothelial regression, depending 45
Proceedings of the National Academy of Sciences, 2002
Modulation of Tie2 receptor activity by its angiopoietin ligands is crucial for angiogenesis, blood vessel maturation, and vascular endothelium integrity. It has been proposed that angiopoietins 1 (Ang1) and 2 (Ang2) are pro-and anti-angiogenic owing to their respective agonist and antagonist signaling action through the Tie2 receptor. The function of Ang2 has remained controversial, however, with recent reports suggesting that in some circumstances, it may be pro-angiogenic. We have examined this issue using the transient ocular microvessel network called the pupillary membrane as a unique in vivo model for studying the effects of vascular regulators. We show that in vivo, in the presence of endogenous vascular endothelial growth factor (VEGF)-A, Ang2 promotes a rapid increase in capillary diameter, remodeling of the basal lamina, proliferation and migration of endothelial cells, and stimulates sprouting of new blood vessels. By contrast, Ang2 promotes endothelial cell death and vessel regression if the activity of endogenous VEGF is inhibited. These observations support a model for regulation of vascularity where VEGF can convert the consequence of Ang2 stimulation from anti-to pro-angiogenic.